Post on 21-Jan-2021
AWD COMPONENT ANALYSIS Project Report, May 31, 2016
Gunter Niederbacher Pilot Systems International
Contract T8080-150132
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Contents
1 Abstract.................................................................................................................................... 6
2 Executive Summary ................................................................................................................. 7
3 Introduction ........................................................................................................................... 10
3.1 Background ..................................................................................................................... 10
3.2 Purpose........................................................................................................................... 11
3.3 Data Sources ................................................................................................................... 11
1 AWD/4WD Systems and Components .................................................................................. 12
1.1 AWD Systems Classification ........................................................................................... 12
1.1.1 Definitions ............................................................................................................... 12
1.1.2 AWD Component Nomenclature ............................................................................ 15
1.1.3 AWD Systems Classification .................................................................................... 15
1.2 Current and Future AWD Systems ................................................................................. 17
1.2.1 System Architecture ................................................................................................ 17
1.2.2 Components / Function .......................................................................................... 22
1.2.3 System Function & Operating Modes ..................................................................... 37
1.3 Comparative Assessment of Positives and Negatives .................................................... 40
1.3.1 Vehicle Architecture ............................................................................................... 40
1.3.2 Disconnect Systems ................................................................................................ 40
1.3.3 Secondary Driveline Torque Limitation & Duty Cycle Management ...................... 41
1.3.4 Full Time vs. On-Demand Systems .......................................................................... 41
1.3.5 Rear Axle Architecture ............................................................................................ 42
2 AWD Vehicles by Make & Model ........................................................................................... 43
2.1 The North American AWD Vehicle Market - Overview .................................................. 43
2.1.1 Fuel Consumption and Vehicle Mass Data ............................................................. 43
2.2 AWD Vehicles by Make & Model ................................................................................... 47
2.2.1 Audi ......................................................................................................................... 48
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2.2.2 BMW ....................................................................................................................... 52
2.2.3 Daimler Benz ........................................................................................................... 58
2.2.4 Fiat Chrysler (FCA) ................................................................................................... 64
2.2.5 Ford ......................................................................................................................... 74
2.2.6 General Motors (GM) .............................................................................................. 76
2.2.7 Honda ...................................................................................................................... 80
2.2.8 Hyundai (Kia) ........................................................................................................... 82
2.2.9 Jaguar Land Rover (JLR - Tata) ................................................................................ 85
2.2.10 Mazda ...................................................................................................................... 88
2.2.11 Mitsubishi ................................................................................................................ 89
2.2.12 Nissan (Infiniti) ........................................................................................................ 92
2.2.13 Subaru ..................................................................................................................... 94
2.2.14 Tesla ........................................................................................................................ 97
2.2.15 Toyota .................................................................................................................... 98
2.2.16 Volkswagen ........................................................................................................ 101
2.2.17 Volvo ................................................................................................................... 103
3 AWD Efficiency Improvement Potentials ............................................................................ 106
3.1 Definitions .................................................................................................................... 106
3.2 System Level ................................................................................................................. 106
3.2.1 Architecture .......................................................................................................... 106
3.2.2 Disconnect System ................................................................................................ 107
3.2.3 Downsizing ............................................................................................................ 107
3.2.4 Electric Rear Axle Drive (eRAD) ............................................................................. 108
3.3 Component Level ......................................................................................................... 109
3.3.1 Fuel Efficient (FE) Bearings ................................................................................... 109
3.3.2 Low Drag Seals ...................................................................................................... 111
3.3.3 Lubrication Strategies ........................................................................................... 111
3.3.4 Advanced CV Joints ............................................................................................... 113
3.3.5 Dry Clutch Systems ............................................................................................... 113
3.4 Design ........................................................................................................................... 113
3.4.1 Hypoid Offset Optimization .................................................................................. 113
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3.4.2 Non Serviceable Components ............................................................................... 114
3.4.3 Bearing Preload Optimization ............................................................................... 114
3.4.4 Single Shaft Power Transfer Units ........................................................................ 115
3.4.5 Propshaft Gear Ratio ............................................................................................. 115
3.5 Materials ...................................................................................................................... 116
3.5.1 Magnesium Housings ............................................................................................ 116
3.5.2 High Efficiency Lubricants ..................................................................................... 117
3.6 Manufacturing Process ................................................................................................ 117
3.6.1 Vacuum Die Casting .............................................................................................. 117
3.6.2 Hypoid Manufacturing .......................................................................................... 118
3.7 Advanced Engineering / Development Process ........................................................... 119
3.7.1 AWD Duty Cycle Management ............................................................................. 119
3.7.2 Performance Adaptation to Vehicle Variants ....................................................... 119
3.8 Advanced Operating and Control Strategies................................................................ 119
3.8.1 Disconnect strategies ............................................................................................ 119
3.9 Summary of Efficiency Improvement Potentials ......................................................... 120
4 Trend Analysis ...................................................................................................................... 122
4.1 The Baseline ................................................................................................................. 122
4.1.1 Global Vehicle Production .................................................................................... 122
4.1.2 Fuel Consumption ................................................................................................. 123
4.2 Technical Trend Analysis in AWD Research and Development ................................... 126
1.1.1 Technical Trend Analysis in AWD Research and Development ............................. 126
4.3 AWD Market Trend Analysis ........................................................................................ 127
5 AWD System Teardown Analysis ......................................................................................... 130
5.1 Ford Fusion ................................................................................................................... 133
5.1.1 AWD Technology ................................................................................................... 133
5.1.2 Power Transfer Unit .............................................................................................. 136
5.1.3 Propshaft, Axles .................................................................................................... 141
5.1.4 Rear Drive Module ................................................................................................ 142
5.1.5 Mass & Rotational inertia Analysis ....................................................................... 152
5.1.6 Design Analysis ...................................................................................................... 154
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5.2 Jeep Cherokee .............................................................................................................. 158
5.2.1 AWD Technology ................................................................................................... 158
5.2.2 Power Transfer Unit (PTU) .................................................................................... 161
5.2.3 Propshaft & Axles .................................................................................................. 167
5.2.4 Rear Drive Module (RDM) ..................................................................................... 168
5.2.5 Mass & Rotational inertia Analysis ....................................................................... 179
5.2.6 Design Analysis ...................................................................................................... 181
5.3 Volkswagen Tiguan ....................................................................................................... 185
5.3.1 AWD Technology ................................................................................................... 185
5.3.2 Power Transfer Unit (PTU) .................................................................................... 187
5.3.3 Propshaft & Axles .................................................................................................. 191
5.3.4 Rear Drive Module (RDM) ..................................................................................... 192
5.3.5 Mass & Rotational inertia Analysis ....................................................................... 201
5.3.6 Design Analysis ...................................................................................................... 203
6 Disconnect System Cost Analysis......................................................................................... 207
6.1 Jeep Cherokee .............................................................................................................. 208
6.1.1 Power Transfer Unit (PTU) .................................................................................... 209
6.1.2 Rear Drive Module (RDM) ..................................................................................... 210
6.2 Alternative Disconnect Systems ................................................................................... 212
6.2.1 Side Shaft Disconnect ........................................................................................... 212
6.2.2 Front Axle Center Disconnect ............................................................................... 213
6.2.3 Others ................................................................................................................... 214
7 Summary and Conclusions .................................................................................................. 215
7.1 AWD/4WD Systems and Components ......................................................................... 215
7.1.1 Current and Future AWD Systems ........................................................................ 215
7.1.2 Component and System Function ......................................................................... 217
1.1.2 Comparative Assessment of Positives and Negatives ........................................... 219
7.2 AWD Vehicles by Make & Model ................................................................................. 221
7.2.1 The North American AWD Vehicle Market – Overview ........................................ 221
7.2.2 Fuel Consumption and Vehicle Mass Data ........................................................... 223
7.3 AWD Efficiency Improvement Potentials ..................................................................... 224
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7.3.1 System Level ......................................................................................................... 224
7.3.2 Component Level and Design ............................................................................... 225
7.3.3 Materials ............................................................................................................... 226
7.3.4 Manufacturing Process ......................................................................................... 226
7.3.5 Summary of Efficiency Improvement Potentials .................................................. 227
7.4 Trend Analysis .............................................................................................................. 228
7.4.1 Technical Trend Analysis in AWD Research and Development ............................ 228
7.4.2 AWD Market Trend Analysis ................................................................................. 228
7.5 AWD System Teardown Analysis.................................................................................. 230
7.5.1 Component Data Comparison .............................................................................. 231
7.5.2 Mass & Rotational Inertias.................................................................................... 233
7.6 AWD Disconnect System Cost Assessment .................................................................. 235
8 Appendix A: List of Tables and Figures ................................................................................ 236
9 Appendix B: Major North American AWD System Suppliers .............................................. 244
10 Appendix C: Vehicle Data .................................................................................................... 249
11 Appendix D: Equivalent Mass Definition ............................................................................. 250
11.1 Equivalent Mass ........................................................................................................... 250
11.2 Relative Effects of Rotational inertia on Vehicle Dynamics ......................................... 251
12 Appendix E: Evaluation of Rotational Inertia and Equivalent Mass .................................... 253
13 Appendix F: List of Terms and Acronyms ............................................................................ 255
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1 Abstract
All Wheel Drive (AWD) vehicles have become increasingly popular in North America.
Canada and the northern regions of the USA are seeing increasing demand for vehicles
with AWD.
This report addresses various aspects of AWD in conjunction with mass reduction and
fuel efficiency.
In the first section AWD systems and components currently on the market are
categorized. Vehicle architecture, design aspects and component function are
explained. Operating modes and AWD controls are explained and individual systems
advantages and disadvantages are discussed. Specific enablers for efficiency
improvements (e.g. AWD disconnect systems) are listed and their direct and indirect
effects are discussed.
The second section contains a list of vehicles currently on the market by make and
model broken down into vehicle platforms and AWD system architecture. Basic vehicle
data is given and design specifics on component level are discussed. Special emphasis is
put on added mass and fuel consumption for a selected list of vehicles.
In the third section AWD efficiency improvement potentials are discussed on a
qualitative level. The section is broken down into system, component and parts level
and includes design, materials and manufacturing process aspects.
A general trend analysis for AWD technology is included in the fourth section Market
data and historic trends are discussed.
Section five covers the teardown of three popular AWD vehicles: Ford Fusion, Jeep
Cherokee and Volkswagen Tiguan. Driveline components were completely
disassembled. Mass and rotational inertia data is listed for each individual part. A photo
documentation of the assemblies and major parts and a presentation of special design
features is included.
In section six a high level cost analysis for AWD disconnect systems is documented.
Section seven finalizes the report with a summary and the conclusions from the above
analyses.
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2 Executive Summary
Transport Canada (TC) contracted Pilot Systems International to perform a study
concerning the North American passenger car and light duty truck All Wheel Drive
(AWD) market at its current status and future trends.
In a first section current and future AWD systems are analyzed and AWD technology is
explained. The second section contains an overview of the AWD vehicles currently on
the market. An efficiency improvement potential analysis was performed in the third
section, followed by a general trend analysis in section four. Section five contains a
teardown analysis of the main AWD components of three selected vehicles. A high level
cost analysis of AWD disconnect systems was performed in section six. The study
concludes with a summary and conclusions in the seventh section.
AWD systems are classified in SAE Standard J1952 into
Part Time Systems
Full Time Systems
On-Demand Systems
In a part time system driver intervention is required to rigidly engage AWD. Part time
systems have been traditionally mechanical systems with no electronic controls. Driver
activated AWD systems with an electronically controlled clutch, as currently used in light
trucks, are considered on-demand systems.
Full time AWD systems feature a center differential to distribute torque between the
front and rear axle permanently with a preset torque bias. An active or passive locking
device may be added to improve the traction potential of the system. Full time systems
take advantage of sophisticated Brake Traction Control (BTC) systems. BTC offers a very
cost effective way of maintaining traction in adverse conditions by using the brake
system and specific control logics to keep wheel slip within dynamic limits.
On-demand systems are by far the most prevalent AWD systems on the market today.
The core of the system is a Torque Transfer Device (TTD), typically contained in a Rear
Drive Module (RDM). Most vehicles have active systems which electronically control
torque distribution between the front and rear axle.
With the addition of a mechanical driveline disconnect device part of an on-demand
AWD driveline can be brought to a complete standstill while the vehicle is in motion.
Driveline parts that are not rotating do not generate parasitic losses.
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AWD systems add mass to a vehicle and generate additional driveline losses with the
result of increased fuel consumption.
Figure A: Fuel Consumption Increase (L/100km) over Added Mass in AWD Vehicles – City and Highway Cycles (Red dots indicate vehicles with AWD disconnect systems)
Figure A shows the increase of fuel consumption over added mass for a selected list of
AWD vehicles. Data is based on fuel efficiency estimates published annually by the US
Environmental Protection Agency (EPA).
Several areas of potential improvement have been identified:
A highly integrated vehicle architecture allows AWD components to be as compact and
lightweight as possible. A single shaft Power Transfer Unit (PTU) can save up to 10kg in
component mass compared to a more complex two shaft unit.
AWD disconnect systems have the ability to lower fuel consumption between 2 and 7%
compared to a non-disconnect AWD system.
Downsizing the AWD drivelines is a very effective way of taking mass out of AWD
components. For passenger cars and small SUVs the axle torque level required to
provide sufficient traction in adverse conditions is relatively small and can be
transferred in a smaller package.
Magnesium has been used for a long time to reduce transfer case and axle housing
mass. The 30% mass reduction compared to aluminum can take as much as 8% out of
the total mass of an RDM.
Small improvements on driveline parts (e.g. bearings, seals etc.) and refined
manufacturing processes (e.g. ground hypoid gears) add up to considerable gains in
efficiency.
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On the high end, hybrid and electric systems can provide a breakthrough in overall
system efficiency. Vehicle pricing has so far proven prohibitive and widespread use of
this type of vehicles is dependent on cost reductions and changes in the economic
environment.
Three main technological trends have been identified:
Actively controlled Multi-Plate Clutches, (MPC)
Active Disconnect Systems, (ADS)
Electric Rear Axle Drives, (eRAD)
Controlled MPC in on-demand systems are the dominating technology in AWD
drivetrains. ADS are a more recent trend to reduce real world fuel consumption in AWD
vehicles. eRAD is the latest emerging technology to dramatically improve fuel economy.
Volvo was the most recent entry into the market with the XC90 Hybrid SUV.
The popularity of CUV/SUV in North America is driving an increase in the adaption of
AWD/4WD systems. About one third of all vehicles sold in North America in 2015 were
AWD. The AWD take rate varies dramatically between vehicle segments and equipment
levels. Sedans throughout the segments are the least likely to be sold with an AWD
system. In the SUV and pick-up segments AWD outnumber 2WD drivelines, with the
luxury vehicles having the highest take rate in their respective segments.
Regional differences in the USA are also very distinctive, with northern and rural states
having the largest percentage of AWD vehicles. This fact suggests similar Canadian
trends.
In a teardown analysis, three PTUs and
RDMs were disassembled and analyzed
with respect to mass, rotational inertias
and design features. Figure B shows the
contribution of individual AWD driveline
components to the added mass.
Rotational inertias add very little
equivalent mass and have therefore been
found negligible with respect to fuel
consumption. Figure B: AWD Component Mass Comparison
A high level cost analysis of AWD disconnect devices shows the system incremental
price to be in the range of $90 – $100 US, including the mechanical disconnect device
and modifications necessary to the TTD. Jeep Cherokee is an exception since the system
was designed to accommodate a planetary low gear, which adds mass and cost not
related to AWD disconnect.
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3 Introduction1
Transport Canada’s (TC) ecoTECHNOLOGY for Vehicles Program (eTV)
Transport Canada’s ecoTECHNOLOGY for Vehicles Program (eTV) www.tc.gc.ca/eTV is a
horizontal initiative of the Clean Air Agenda, which forms part of the Government of
Canada’s broader efforts to address the challenges of climate change and air pollution.
eTV’s mandate is to carry out proactive work to assess the safety and environmental
performance of emerging advanced on-road vehicle technologies. The program tests,
evaluates and provides expert technical information on light-duty vehicle (LDV) and
heavy-duty vehicle (HDV) technologies that are expected to enter the Canadian market
over the next 10-15 years.
Environment Canada
EC’s mandate is to protect the environment, conserve the country's natural heritage,
and provide weather and meteorological information to keep Canadians informed and
safe. Environment Canada is building on its accomplishments with the environment
through credible science, effective regulations and legislation, successful partnerships,
and high-quality service delivery to Canadians.
U.S. Environmental Protection Agency (EPA) Assessment and Standards Division,
National Vehicle and Fuel Emissions Laboratory, Office of Transportation and Air
Quality
The U.S. Environmental Protection Agency’s (EPA) Assessment and Standards Division
identifies and develops future emission control strategies (such as new vehicle, engine,
and fuel quality standards) and national policy on mobile source emission control. The
division develops regulations and policies, determines the contribution of mobile
sources to pollutant emission inventories, and assesses the feasibility, cost, and in-use
effectiveness of emission control technologies.
3.1 Background
In the U.S. North East, Upper Midwest and in Canada, All Wheel Drive (AWD) can
represent up to 70% of sales volume depending on vehicle model. The additional mass
associated with AWD systems is typically about 90 kg, or roughly 4% to 10% of total
vehicle mass. Because of this increased system mass, as well as added drivetrain
parasitic losses, AWD typically increases fuel consumption and CO2 emissions by
between 2% and 8%. As GHG emissions regulations become more stringent
1 Request for Proposal T8080-150132- All Wheel Drive Component Analysis, Transport Canada
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manufacturers continue to seek opportunities to reduce the added mass, friction, and
drag associated with All Wheel Drive (AWD) systems, using a variety of methods and
technologies.
3.2 Purpose
AWD vehicles are increasingly popular in Canada, due in part to their performance in
challenging winter driving conditions. However, the inclusion of AWD systems can result
in reductions in overall vehicle fuel efficiency and increases in GHG emissions due to
added vehicle mass and drivetrain parasitic losses.
3.3 Data Sources
The following data sources were used to compile this report, in dropping order of
magnitude:
Pilot Systems International team non-confidential experience/knowledge
OEM, Tier 1&2 and dealer websites
Publications in technical papers, brochures
OEM and supplier publications
OEM and supplier interviews
Research groups
Academia
Customer advocate groups (e.g. Consumers Report)
Sources are referenced in footnotes. Non-referenced tables, figures and
diagrams have been developed by Pilot Systems and associates for non-
exclusive use in this report. Vehicle images in section 2 are for illustration
purposes only and have been downloaded from OEM and dealer websites.
All trademarks, logos and company or product names used in this report are
property of the individual vehicle or parts manufacturer.
This project will characterize how current and future advances in AWD
systems can potentially reduce these losses, in addition to comparing existing
2WD and AWD vehicles, in terms of GHG emission and fuel consumption
performance.
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1 AWD/4WD Systems and Components
1.1 AWD Systems Classification
This chapter follows the SAE J19522 standard in its October 2013 revision. System
descriptions, nomenclature and classification have been edited to reflect latest
developments in the area of AWD system development.
1.1.1 Definitions
A conventional All Wheel Drive (AWD) system consists of a means to distribute torque
to all wheels of a vehicle. The term ‘AWD’ stands for all systems that drive all wheels of
a vehicle regardless of the number of axles or the mechanics or controls involved. Based
on desired performance, traction and handling characteristics, there are different types
of systems to achieve these ends. These AWD systems include 4X43 and other
configurations. There are three basic types of systems and a combination of those
defined below:
Part-Time
Full-Time
On-Demand
Combinations of the above
AWD systems may have an additional, selectable reduction gear to provide two speeds -
one for normal driving (High-range) and one for improved ground speed control and
increased tractive force (Low-range).
PART-TIME AWD (4WD) SYSTEM
In a part-time AWD system (sometimes also simply called 4WD system) driver
intervention is required to rigidly couple and decouple primary and secondary axles.
When a part-time system is engaged the primary and secondary axles become rigidly
connected through the torque distribution device (i.e., Power Transfer Unit (PTU),
transfer case). The primary axle is normally connected unless in neutral mode. The
secondary axle(s) is/are engaged in AWD and disengaged in two-wheel drive. The torque
distribution device is commonly referred to as a transfer case (or T-case) in primary rear
2 SAE J1952 All Wheel Drive Systems Classification (Oct 2013) 3 Indicates the total number of wheels (4) and the number of wheels driven (4) – not part of the official nomenclature, although OEMs are using this term for marketing (decals, etc.)
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wheel drive based AWD vehicles. In a primary front wheel drive based vehicle the
torque distribution functions are typically managed in the PTU, transaxle, or secondary
axle(s).
This basic type of system requires the driver to select between two-wheel drive and
AWD commonly using either a switch or lever. Part-time systems may allow the driver to
shift between two-wheel drive and AWD while the vehicle is in motion.
Although part-time AWD achieves maximum traction under certain conditions it should
be limited to off-pavement usage or on-pavement usage in low traction scenarios.
Torque "wind up" is experienced during on-road dry pavement usage when making
moderate to tight low speed turns. This "wind up" (also referred to as crow hop or
binding) is due to the fact the front and rear axles are rigidly connected (no center
differential) and rotating at the same speed but traveling different distances.
FULL-TIME AWD SYSTEM
In a full-time AWD system front and rear axles are driven at all times through a center
differential.
Unlike a part-time system, the full-time system employs a center (inter-axle) differential
that allows the front and rear axles to turn at different speeds on any surface.
Depending upon the design of the differential, the input torque can be nominally split to
the front and rear axles in a fixed ratio. As an example, a 35:65 split means that 35% of
the torque is directed to the front axle and 65% to the rear axle.
For maintaining traction in adverse conditions torque through the center differential
must be modulated to distribute power to the axles with the greatest traction. Torque
modulation can be done passively, actively, with a torque biasing device, or with brake
based traction control systems.
This type of system can be used on any surface at any speed.
ON-DEMAND AWD SYSTEM
In an on-demand all-wheel drive system, the secondary drive axle may be driven by an
active or passive coupling device, or by an independently powered drive system. A
secondary drive axle, which is driven by an independently powered drive system, may
also provide the primary vehicle propulsion.
In a typical on-demand AWD system, the vehicle operates in 2WD (either front or rear
depending upon the basic vehicle architecture) until AWD is required, such as during
primary axle slip, yaw correction, or by other control strategies. In the case of secondary
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axles driven by an active or passive coupling device, torque transfer from the primary to
the secondary axle(s) can be modulated, dependent on driving conditions. Most systems
are typically relative speed control devices and activate when there is a speed difference
between the primary and secondary axle(s) due to slippage; however, pre-emptive slip
or other control strategies are common.
On-demand systems may have a disconnect device that allows the vehicle to be driven
in the more fuel efficient 2WD mode under normal driving conditions. The engagement
of AWD can be driver controlled or automatic, with sophisticated engagement
algorithms in place.
This type of system can be used on any surface at any speed.
COMBINATION SYSTEMS
Some of the AWD systems currently on the market offer selectable features that would
place them in the Part-time, Full-time or On-demand category, depending on what
mode the driver has selected. These vehicles are typically rear wheel drive based SUVs
or trucks, with a highly flexible transfer case providing multiple driving modes. Most
systems offer a combination of Part-time and On-demand systems, many times paired
with a selectable low gear to provide enhanced speed control and tractive force in off-
road conditions.
For classification purposes, the highest level mode (Part-time -> Full time -> On-demand
low to high) will be used as the main category for the vehicle. However, part-time or
full-time capabilities need to be noted to assure the full spectrum of vehicle
performance is understood.
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1.1.2 AWD Component Nomenclature
Figure 1-1: AWD Nomenclature
1.1.3 AWD Systems Classification4
This high level classification concentrates on functional attributes and does not include
architecture, vehicle class or information about the type of controls.
An attempt has been made to include hybrid drives but the large variety of driveline
architectures and component combinations would make it difficult to keep up with the
fast pace of development in the field of hybridization and electrification.
4 SAE J1952 All Wheel Drive Systems Classification (Oct 2013)
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Table 1-1: AWD Systems Classification
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Synchronisation capable: capable of synchronizing front and rear axle during AWD engagement while vehicle is in motion;
Synchronizer clutch or AWD coupler are the classic components to provide that capability
Longitudinal speed differentiation: front and rear axle can be at different speed (e.g. cornering) w/o torque wind-up
Typically enabled by either a center differential or an AWD coupler
Longitudinal torque distribution mode: type of torque transfer between front and rear
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
Passive: non controlled torque transfer determined by external feedback (typically wheel speed difference)
Torque modulation: torque transfer device type
Fixed: torque bias fixed by design (e.g. open diff)
Variable: torque bias variable by design (e.g. passive/active torque transfer device or active locking diff etc.;
hybrids with independently driven electric rear axle fall also into this category)
Indeterminate: torque bias determined by input torque, wheel speed and tractive conditions
Typical for part time systems
Active: electronically controlled torque transfer
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1.2 Current and Future AWD Systems
1.2.1 System Architecture
1.2.1.1 Front wheel drive (FWD) based system architecture
Upgrading FWD vehicles to AWD is relatively simple. Most AWD systems are so called
hang-on systems with passive or active on-demand torque transfer devices (AWD
couplers). Very few vehicle manufacturers offer permanent AWD via center differential,
which requires additional measures to assure traction is maintained if one wheel loses
grip entirely (see also next chapter: ‘RWD based system architecture’).
Added components
Power Transfer Unit Rear axle shafts
Propshaft Electronic control unit
Rear Drive Module Rear axle subframe and suspension modifications
Figure 1-2: FWD Based AWD System Architecture
The base FWD driveline architecture offers a line of advantages over RWD:
Underbody packaging becomes easier
Overall driveline mass is reduced
No NVH (Noise, Vibration & Harshness) problems with a propshaft at high
speed
Driveline efficiency is better because of the lack of hypoid gear sets
Traction is typically better because of more mass on the drive axle
Vehicle dynamics are more docile, understeer is more manageable for the
average driver
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Reduced cost
Sales of FWD vehicles have outnumbered RWD vehicles for many years and continue to
gain market share. However, some of the obvious advantages of FWD need to be
sacrificed when converting to AWD for improved traction and vehicle dynamics in
adverse conditions.
1.2.1.2 Rear wheel drive (RWD) based system architecture
RWD vehicles are typically sold in the upper and luxury segments, in the light truck and
SUV segment and as a niche product or sports cars. The base RWD architecture offers
some advantages over FWD:
Front end packaging allows for larger engines and transmissions with better
performance
RWD drivelines typically can manage higher torque output
Sports car drivers typically prefer moderate oversteer characteristics
Most framed vehicles (e.g. light trucks) have simple rear axle layouts for
heavy loads
Added components
Transfer case Rear propshaft (modified)
Front propshaft Electronic control unit
Front axle Figure 1-3: RWD Based AWD System Architecture
The centerpiece of the RWD based AWD architecture is the transfer case (T-case) which
splits up torque between the axles. Many T-cases in today’s vehicles incorporate an
AWD coupler and have on-demand characteristics. However, the center differential (CD)
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can still be found in many upper class vehicles. Torque bias between front and rear axle
is typically between 50/50 and 40/60.
Open CD equipped vehicles need some means of torque management to overcome the
disadvantage of losing traction if only one wheel loses grip (note: now you have four
wheels hunting for that slick spot so an open CD can be worse than 2WD). Mechanical
locking devices, torque sensing limited slip differentials or active/passive couplers are
some of the ways to improve traction in adverse conditions. An elegant and very
popular way is to use the brake system to slow down a slipping wheel. So called ‘Brake
Traction Control’ is known from 2WD vehicles and works very well for AWD vehicles.
A special version of this architecture is the ‘Symmetrical AWD’ from Subaru. This
purpose built AWD architecture tries to minimize the number of gears involved in
transferring torque from the transmission to the wheels. Audi is using a similar layout in
some of their quattro™ systems. The main difference from conventional T-case layouts
is that the front propshaft is integrated in the transmission. In this case, the
transmission becomes dedicated to AWD rather than a modular component that can be
used for RWD and AWD with minimal modifications. Applications are therefore limited
to vehicle lines purpose built for AWD.
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1.2.1.3 Front wheel drive based hybrid AWD architecture
Added components
Rear axle electric drive Control unit
Battery Optional: engine/transmission driven generator Power electronics
Figure 1-4: FWD Based ‘Through the Road’ Hybrid AWD
One way of dramatically improving Fuel Efficiency (FE) and simultaneously providing
AWD to a FWD based vehicle is adding an electric drive axle to the rear. This type of
architecture is typically used as a Plug in Hybrid Electric Vehicle (PHEV) with battery
sizes that allow driving some distance in pure electric mode.
The FE penalty associated with the added mass of approximately 250 - 350 kg5
(depending on the battery size) in pure gasoline powered mode can be compensated by
the ability to recuperate brake energy and the use of electric power assistance or pure
electric drive for short distance driving. The results are highly dependent on the mission
profile and the size of the battery.
An optional generator driven by the primary powertrain adds flexibility to this concept.
5 Compare to 50 – 150 kg of added mass for a mechanical AWD system, see Figure 2-3
21
1.2.1.4 Electric Drive
Figure 1-5: Electric AWD
Added components
Front & rear axle electric drive Control unit
Battery
Power electronics
Deleted Components
Internal combustion engine
Transmission & driveline components
Gasoline fuel system
22
1.2.2 Components / Function
1.2.2.1 Power Transfer Unit (PTU)
The PTU is an integral part of a typical FWD based AWD driveline. It is directly bolted to
the transmission and picks up torque from the front differential located in the final drive
section of the transmission (Figure 1-6).
Figure 1-6: Power Transfer Unit6
The main function of a PTU, besides picking up torque from the front axle, is to provide
a 90° angular drive (typically a hypoid drive) to transfer torque to the rear axle via the
propshaft.
The PTU may contain a disconnect device, usually a shift sleeve or a dog clutch, to
improve fuel efficiency by disconnecting the rear driveline (see chapter 1.2.2.4).
6 http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
23
There are various types of PTUs: the simplest version is a single shaft PTU as shown in
Figure 1-6. The single stage PTU is the most cost effective and most efficient solution.
However, packaging constraints may require a two shaft or even a three shaft (with an
idler gear, see Figure 1-7) PTU to enable repositioning the output shaft in the usually
very complicated underbody environment. This adds cost, mass and creates additional
losses in the drivetrain. Newer vehicle designs try to incorporate AWD options from the
beginning and provide necessary space for the best solution.
Figure 1-7: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right)
24
Figure 1-8: Power Flow in a PTU (2015 VW Tiguan)7
The power flow in a single shaft PTU is shown in Figure 1-8. The final drive and the
differential are part of the transmission. The hollow shaft connects to the differential
cage via spline and picks up power directly from the final drive. The ring and pinion
(hypoid set) redirect power by 90°, with the pinion driving the propshaft to the rear.
1.2.2.2 Rear Drive Module (RDM)
The RDM is driven by the propshaft and provides a 90° angle to drive the rear wheels via
drive shafts. It also houses the rear axle differential.
In FWD based AWD systems the RDM typically contains an integrated Torque Transfer
Device (TTD) that actively or passively controls torque delivered to the rear axle. Current
AWD systems typically rely on the active TTD to improve tractive force and vehicle
dynamics with a minimum of compromise.
The TTD is the corresponding part in a modern ‘disconnect system’, besides the PTU
disconnect clutch.
There are various options for the location of the TTD within the RDM. The conventional
solution was in-line, directly at the input, as shown in Figure 1-9. More sophisticated
RDMs with disconnect function require a more complex solution as described in the
next chapter.
7 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf
25
Figure 1-9: RDM with integrated Torque Transfer Device 8
1.2.2.3 Torque Transfer Device (TTD)
The TTD, or more commonly called the ‘AWD coupler’, modulates drive torque to the
rear axle either passively (e.g. viscous couplers, progressive hydraulic units etc.) or
actively. The main components are the Multi Plate Clutch pack (MPC, see Figure 1-10)
and a subsystem to compress the clutch pack to transfer torque from the input shaft to
the output. Today’s AWD systems are predominantly active type systems to provide
flexible torque control with integrated Electronic Control Units (ECU).
Active units can be of 4 different types with similar functionality:
hydraulic
electro-hydraulic
electro-mechanic
electro-magnetic
Hydraulic types generate pressure with a pump that acts on speed difference between
input and output shaft. The electro-hydraulic type uses an electric motor driven pump
independently from coupler speed and provides better response. Most hydraulic
8 http://www.kfztech.de/kfztechnik/triebwerk/allrad/haldex.htm
26
systems fall into this category. The system architecture is highly flexible and is preferred
for high end systems.
Electro-mechanic actuators use gear or cam driven ball ramps to pressurize the clutch
pack. Performance is equal to the electro-hydraulic systems. However, packaging
constraints may prove challenging.
Electro-magnetic actuators (Figure 1-10) use a magnetic field to pressurize a small pilot
clutch. The pressure generated by the magnetic field results in a small torque in the pilot
clutch which is augmented in the main clutch pack via ball ramp mechanism.
Active couplers are controlled by an Electronic Control Unit (ECU) and are capable of
adjusting torque based on various sensor inputs and therefore can respond to varying
driving conditions within milliseconds. Vehicle dynamics, safety and performance can be
significantly enhanced. Control algorithms interact with other vehicle control systems
such as ABS or vehicle stability control to optimize vehicle performance.
The core of the TTD is typically a wet clutch pack compressed by a piston to modulate
torque. (Figure 1-10) The clutch pack needs to be designed to carry the required
maximum torque without slipping or overheating. Electronic protection algorithms are
typically utilized.
Figure 1-10: Electro-magnetically actuated AWD coupler 9
The TTD is also a key element in AWD disconnect systems. If properly designed it
provides minimal drag in the open position to allow the AWD drivetrain to come to a
complete standstill while driving the vehicle at any speed. This is usually accomplished
by establishing a large gap between the clutch plates, sometimes supported by wave
springs to establish even separation throughout the clutch pack. If AWD is required
9 Source: www.borgwarner.com
27
either by driver intervention or by vehicle dynamic controls the TTD synchronizes the
standing drivetrain to allow the front dog clutch to engage. The process takes longer
than the typical AWD drive response time, approximately 200 – 400 milliseconds vs. 100
ms, to allow the piston to travel the increased distance due to the gaps. It should be
without any negative feedback to the driver. Once engaged the coupler response is back
to less than 100 ms for torque modulation.
The location of the AWD coupler within the RDM is critical to its function. Figure 1-11
shows four different arrangements for the AWD coupler:
• In-line represents the conventional layout for FWD based AWD systems. The
coupler is directly driven by the propshaft and runs at the lower propshaft
torque and higher speed.
• The parallel arrangement is required if the AWD coupler needs to act as the rear
disconnect and synchronization device. This way the hypoid set, which is a main
contributor to parasitic losses, comes to a standstill when disconnected
• Half shaft disconnect is an alternative to parallel. However, the differential gears
are spinning inside the differential housing and can create additional losses.
Torque is modulated by the coupler and balanced across the differential.
• The dual clutch system provides a way of eliminating the axle differential
entirely. Two individually controlled couplers are required. The advantages are
the functionality of a limited slip differential and, within limitations, the
possibility of torque vectoring.
Figure 1-11: Rear Drive Module Architecture Variants
28
AWD couplers are using a specially formulated lubricant to provide optimum friction
behavior in terms of noise, vibration and harshness, thermal stability, lowest possible
viscosity to support responsiveness of the hydraulic system and low drag characteristics
in open mode. Hypoid sets on the other hand are requiring higher viscosity fluids to
maintain lubrication in the sliding contact areas of hypoid gears up to maximum
operating temperature. RDMs therefore have separated lubrication systems for the
AWD coupler and the gear sets.
1.2.2.4 Torque Vectoring
Torque vectoring is a feature that allows the drivetrain to transfer more torque to the
outside wheels during cornering, thus making even a heavy vehicle more ‘nimble’.
Figure 1-12 illustrates that effect, with significantly higher tractive force on the outside
wheels, shown in green, than on the inside wheels, shown in red. This can be achieved
by two completely different methods:
1. Brake Traction Control induced torque vectoring
2. Clutch controlled torque vectoring
1) Braking the inside wheels slightly during cornering induces positive yaw10 which
helps the vehicle to turn faster. This method does not require any mechanical
devices and simply uses the brake system, with special algorithms included in the
electronic control unit to address vehicle dynamics inputs and driver request
through the steering wheel. It also works during acceleration and braking. The
system could be considered an extension of Vehicle Dynamic Control since it uses
the same mechanical components.
The downside of this method is that the brake force used to generate positive yaw is
converted into heat and therefore lost. It can also be a challenge to the brake
system.
10 Yaw is the movement of a vehicle about its vertical axis. Positive yaw is the movement towards the inside of the path (oversteer), negative yaw is the movement towards the outside of the path (understeer)
29
______ Figure 1-12: Torque Vectoring11
2) Clutch controlled torque vectoring (Figure 1-13) requires an array of mechanical
components to allow the generation of positive yaw: The rear drive module has two
wet clutches and a pair of overdrive gears as opposed to only one AWD coupler in
conventional systems.
Since the outside wheels during cornering travel a longer path, they are turning
faster, with the differential balancing torque and speed. However, torque can only
be transferred from a faster turning part to a slower turning part. In order to direct
drive torque to the faster turning (outside) wheel, torque vectoring systems feature
a pair of overdrive gear sets that rise the ring gear speed to a higher level. The clutch
picks up that higher speed and can now actively control torque flow to the
respective wheel.
This method does not waste any driveline torque but rather transfers the available
tractive force to the outside wheel to generate positive yaw. Cost, complexity and
mass penalties are on the negative side.
11 https://www.audiusa.com/technology/performance/quattro
30
______ Figure 1-13: Audi Sport Differential12
1.2.2.5 Disconnect Systems
Most OEMs have disconnect systems on the market or are developing them for their
next generation AWD vehicles. Light trucks and SUVs were leading the way more than a
decade ago not only for fuel efficiency improvements but also for better Noise,
Vibration and Harshness (NVH) performance.
Today, the development focuses on FWD based AWD systems where additional cost and
complexity are accepted in order to improve fuel efficiency. The improvement potential
lies somewhere in the range of 2 – 4 % depending on the test cycles used for
comparison13. These numbers are valid only for comparison between 2WD and AWD
modes and will be reduced in real life conditions where engagement algorithms
determine the actual time driven in the more efficient 2WD mode. (see also 3.2). The
goal is to eliminate parasitic losses and rotational inertias in the secondary driveline
12 http://www.audiworld.com/articles/the-audi-s4-quattro-drive-and-sport-differential/ 13 SAE 2015-01-1099 ‘Beyond Driveline Disconnect’
31
when traction is sufficient for safe driving. The additional mass of an AWD system
remains in place.
The FWD based disconnect system consists of three main components:
The front end disconnect, typically a dog clutch
The rear end disconnect, typically provided by a specially designed and located
AWD coupler
A control system that, preferably without driver intervention,
activates/deactivates AWD based on driving conditions.
Figure 1-14 shows the front end of an AWD drivetrain for a vehicle with FWD based
architecture. A shift sleeve or dog clutch (shown in two positions) engages/disengages
the front ring gear, typically actuated by an electric linear actuator.
Figure 1-14: Front Axle Disconnect System, Integrated in the PTU
32
Figure 1-15 shows the counterpart on the rear axle. The AWD coupler has been moved
from the input shaft downstream between the rear ring gear and the differential.
Special care needs to be taken in the design of the coupler: In a conventional open
clutch the residual oil film causes drag that can be large enough to cause significant
losses. The coupler therefore allows for larger spacing of the clutch plates to overcome
that negative effect although at the expense of increased reaction time for engagement.
Figure 1-15: Rear axle disconnect via AWD coupler
Figure 1-16 shows a comparison between active AWD and 2WD mode. In the right hand
schematic the AWD system is disengaged. The green parts of the driveline are at a
complete standstill although the vehicle is driving at normal speed. The components not
rotating include the hypoid sets which are a main contributing factor for parasitic losses.
Rotational motion is in the front between the hollow shaft carrying the ring gear and the
PTU input shaft. In the rear speed difference is between the clutch plates in the AWD
coupler.
33
Figure 1-16: AWD System Status Before (left) and after (right) Disconnect – FWD based vehicles
Engagements and disengagements require precise sequencing: During disengagement
the AWD coupler needs to unload the secondary driveline first to allow the front dog
clutch to freely disengage subsequently. On reconnect, the AWD coupler needs to
synchronize the secondary driveline first. The dog clutch in the front connects the two
parts then at (or close to) the same speed.
While variations of disconnect systems in the market or under development do exist, their
functionality does not vary dramatically. What may vary is the location of the disconnect
device.
Besides the system described above front end disconnects can be located at the front
wheel hubs, thus stopping even the front differential and drive shafts, or in one of the
drive shafts, stopping only the hypoid set but allowing the differential gears and the
drive shafts to spin. A balance of cost, complexity and efficiency gains must be found.
The rear end disconnect couplers may also be located on one or, in so called ‘Twin
Systems’, in both outputs of the axle, with the same effect as described above.
RWD based disconnect systems for on-demand and 4WD drivetrains are actually
somewhat simpler and therefore cheaper to implement. The transfer case architecture
need not be changed since either a mechanical clutch (4WD) or an AWD coupler will already
exist. Originally this type of system was used on trucks and SUVs with a driver actuated
system. New developments (Chrysler 300) show fully automated systems as well.
34
Figure 1-17: AWD System Status Before and After Disconnect – RWD based vehicles
The front axle disconnect is typically a shift sleeve or a dog clutch, very similar to the
components used in FWD based disconnect systems.
Figure 1-17 shows the system status before and after disconnect. In a typical application
(Chevrolet Silverado, Ram 1500, Chrysler LX), the chain drive in the transfer case and the
front hypoid set are at a standstill, while the front differential is spinning. The main
contributors to driveline losses are here non-rotating.
Figure 1-18: Front Wheel Hub Disconnect
Further improvements can be achieved by disconnecting the front driveline directly at
the wheel hubs, as shown in Figure 1-18. The complete front axle including the
35
differential and drive shafts, are non-rotating when disconnected. However, this comes
with significantly increased complexity and associated cost, with relatively minor gains
in efficiency.
1.2.2.6 Transfer case
Transfer cases (also known as T-cases) are typically found in light trucks and SUVs with
RWD base architecture. The transfer case is commonly bolted directly to the rear end of
the longitudinal transmission and splits torque between the front and the rear axle.
There are several types of T-cases available today:
4WD manually activated or electrically shifted – creates a positive lock between
front and rear axles and is typically used for rugged off-road driving
Center differential AWD – typically comes with an active or passive locking
device for the CD to provide traction in difficult terrain
Active transfer cases – an electronically controlled torque transfer device
typically directs torque to the front axle when needed. This type of transfer case
is often combined with a front axle disconnect device that improves fuel
efficiency. Multiple modes of activation are provided, ranging from full lock (off-
road) to full control. A driver interface allows different modes to be selected.
Figure 1-19 shows an active 2-speed transfer case as used in light trucks and SUVs. The
driver selectable low gear option allows for greater speed control when driven in
challenging off-road situations, and provides extra torque for the tough jobs.
Most transfer cases are single-offset in which the front propshaft is driven by a gear set
or a chain drive off center, whereas the rear output which drives the rear propshaft is in
line with the input.
Double-offset T-cases have front and rear output in line, offset from the input. They are
mostly used in heavy trucks and equipment.
The so-called symmetrical AWD (Subaru) architecture is a minimal offset version, where
the input and rear output are in line and the front propshaft is integrated in the
transmission.
36
______ Figure 1-19: Active 2-speed transfer case14
Figure 1-20: Torque Flow in an On-demand Transfer case
14 http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
37
Figure 1-20 shows the torque flow in an active on-demand T-case. The rear axle is
directly driven by the engine and transmission, the front axle is connected via active
coupler and the front axle torque is modulated by the AWD coupler.
As an alternative to chain drive as shown above, a conventional gear drive has been
used. This design is not as cost efficient as the chain drive and is not the first choice for
light duty vehicles, but in the underbody environment of sedans and SUVs it might help
with packaging issues.
Gear drive becomes a necessity when torque requirements exceed the capacity of chain
drives. Gear drives are used in medium to heavy truck applications and in very few truck
based and off-road oriented SUVs (e.g. Mercedes G-Wagon).
1.2.3 System Function & Operating Modes
AWD disconnect system control
To maximize fuel efficiency, AWD vehicles equipped with automatic AWD disconnect
devices should be driven in the more efficient 2WD status as much as possible, with
AWD mode employed only when required. Sophisticated engagement/disengagement
algorithms are put in place to make sure the driver has the best possible experience
under all circumstances. Figure 1-21 shows a high level approach to maximize efficiency
and make good use of the AWD system when required.
38
______ Figure 1-21: High Level AWD System Disconnect Algorithm15
The shift logics use an array of sensors, many of them already available in the vehicle
(e.g. ambient temperature, windshield wipers, wheel speed sensors, accelerometers,
etc.) to decide on a strategy to react to any environmental changes as required.
At low vehicle speed (1st, sometimes 2nd gear) the AWD system is very often engaged to
avoid wheel spin at high torque. At this speed, adverse effects on efficiency are
negligible. However, this may significantly increase the disconnect shift frequency and
may be a challenge regarding durability and driving comfort.
In automatic mode the driver has no direct control over the disconnect system. Based on
sensor input algorithms determine when to engage or disengage the AWD system.
However, many systems provide an override option for the driver to have AWD
permanently engaged. This obviously eliminates the system advantages.
15 U.S. Patent 8,164,767
39
Secondary driveline torque limitation (‘Downsizing’)
The amount of additional torque needed to propel the vehicle through adverse
conditions is relatively small and usually does not have to exceed a level that exploits
the tractive potential of the secondary axle to the maximum. That opens up the
possibility to limit torque in the secondary driveline, with downsized components saving
cost, mass and fuel. In most driving conditions, the effect of torque limitation is hardly
noticeable to the driver and does not negatively affect performance.
Duty cycle management
An advanced method to allow for downsizing the AWD driveline is active duty cycle
management. In addition to torque limitation, control algorithms minimize the work the
AWD system has to go through, thus enhancing component durability and allowing for
downsized parts in the system.
40
1.3 Comparative Assessment of Positives and Negatives
This chapter provides a snapshot of positive and negative effects of vehicle architecture
and features added to the AWD system to improve efficiency and performance.
The facts & features are color coded for positive or negative effects as follows;
Quantitative effects are typically system related and cannot be given in a simplified way.
Vehicle simulation with accurate driveline component models would allow an in depth
analysis of quantitative and qualitative effects on fuel efficiency. Additional information
and an attempt to quantify gains and losses can be found in chapter 3.9.
1.3.1 Vehicle Architecture
FWD based AWD
RWD based AWD
Very efficient base architecture due to lack of hypoid gears
Not as efficient base architecture as FWD
Secondary drivetrain is very inefficient due to two hypoid sets, high use of AWD drives total efficiency down significantly
Front drivetrain has nearly the same efficiency as rear, permanent use has little negative effect on efficiency
Packaging allows for hybridization by adding an independent electric rear axle
Typically offers more torque capacity
Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline
Table 1-2: FWD/RWD Architecture Positives and Negatives
1.3.2 Disconnect Systems
FWD based AWD
RWD based AWD
Significant efficiency improvements, more so for FWD based systems, if in 2WD mode most of the time
Added complexity and cost
Compromise between AWD availability for vehicle dynamics events and efficiency improvements
AWD coupler needs to move from in-line to parallel arrangement with added complexity
AWD coupler in the transfer case is already located ideally
Table 1-3: Disconnect Systems Positives and Negatives
41
1.3.3 Secondary Driveline Torque Limitation & Duty Cycle Management
Significant mass and some rotational inertia savings possible
Extreme off-road performance compromised
Compromise between AWD availability for vehicle dynamics events and mass savings
Table 1-4: Torque Limitation Positives and Negatives
1.3.4 Full Time vs. On-Demand Systems
Full Time
On-Demand
Superior vehicle handling potential Handling compromise at low speed if RWD based (torque oversteer)
No torque management devices necessary if used with Brake Traction Control (BTC)
AWD coupler (passive or active) required to manage torque transfer
Proven mechanical torque biasing devices work well with BTC
Electronic Limited Slip Differentials (eLSD) provide additional flexibility
Always transfers torque across at least one less efficient hypoid set
Primary driveline is highly efficient (FWD based vehicles)
Always transfers torque across a less efficient hypoid set (RWD based vehicle)
No downsizing because of permanent torque transfer; driveline sizing needs to account for biasing devices
Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline Driveline sizing based on torque split if
used with BTC only
2WD vehicle dynamics characteristics can be preserved (understeer for FWD, oversteer for RWD)
Table 1-5: Full Time vs. On-Demand AWD Positives and Negatives
42
1.3.5 Rear Axle Architecture
This table illustrates Positives and Negatives for rear drive module (RDM) architecture
variants per Figure 1-11 in FWD based AWD vehicles.
In-Line Parallel Half-shaft Dual clutch
Torque level required + o o o
Rotational inertia - o o o
Packaging + - + -
Disconnect compatibility no yes yes yes
Complexity + - + -
Cost + - o - Table 1-6: RDM Architecture Positives and Negatives
43
2 AWD Vehicles by Make & Model
In the past years almost every OEM in the North American automobile market
developed and offered AWD versions of part of their vehicle lineup. Originally a
stronghold of off-road vehicles and trucks, AWD technology advanced significantly and
found its way into virtually all vehicle segments typically used in every day, on-road
driving. This has led to a vast array of AWD systems on the market. Many of them are
similar or identical in architecture, component design and mode of operation. Rather
than repeating design details on every make and model, identical systems are cross-
referenced in this chapter. Unique details relevant to fuel efficiency will be outlined for
every model.
This chapter covers the most popular vehicles on the market. It also tries to cover the
most influential or promising AWD systems in terms of mass reduction, component
efficiency improvements and control strategies aimed at enhancing fuel efficiency
regardless of their sales numbers. Exotic systems with low annual sales or AWD
technology from older vehicles (4WD systems) not relevant to fuel efficiency
improvements are not covered.
System classification follows SAE standards as described in 1.1.3. For standard size
trucks and SUVs with multiple operating modes the highest level mode was used for
classification.
2.1 The North American AWD Vehicle Market - Overview
The following chapters show some more detailed information about some of the most
popular or, from a system standpoint, most interesting AWD vehicles on the North
American market. The number of platforms listed for the larger OEMs gives an
impression of the variety of systems on the market. However, many of these platforms
share the same system architecture and functional features with only design variations
for packaging reasons and torque level.
A comparison will be given between 2WD and AWD versions to understand mass and
fuel efficiency penalties that come with added components and complexity. Numerical
values can be found in Appendix C.
2.1.1 Fuel Consumption and Vehicle Mass Data
The following charts show the difference in fuel consumption between 2WD and AWD
for selected vehicles (Figure 2-1 and Figure 2-2). The numbers reflect EPA estimates.
Fuel consumption increase for AWD vehicles is typically in the range of 5 – 10%. Added
mass and driveline losses contribute to this effect.
44
Mass data is shown in Figure 5-3. Vehicles with the largest mass increase include the Jeep
Cherokee (135 kg increase partially due to the disconnect system) and the Acura MDX
(‘Super Handling AWD’ mostly due to complexity).
______ Figure 2-1: Fuel Consumption Comparison between 2WD and AWD, MY 201516
16 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites, data tables see chapter 10
(No 2WD versions)
AWD Disconnect
AWD Disconnect
45
______ Figure 2-2: Fuel Consumption Comparison between 2WD and AWD, MY 2015 (continued)17
17 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites, data tables see chapter10
(No 2WD versions)
AWD Disconnect
AWD Disconnect
46
______ Figure 2-3: Vehicle Mass Comparison between 2WD and AWD versions, MY 201518
18 Source: Dealer websites, data tables see chapter10
(No 2WD versions)
AWD Disconnect
AWD Disconnect
47
2.2 AWD Vehicles by Make & Model
The following table is used to explain the AWD architecture of individual vehicle
platforms with color coding providing a quick overview of a manufacturer’s vehicle line
up with respect to AWD systems. A more detailed description can be found in section
1.1.3.
Table 2-1: AWD System Classification (SAE J1952, Oct 2013)
Synchronization capable: capable of synchronizing front and rear axle during AWD engagement while
vehicle is in motion; Synchronizer clutch or AWD coupler are the classic components to provide that
capability"
Longitudinal speed differentiation: front and rear axle can be at different speed (e.g. cornering) w/o
torque wind-up; typically enabled by either a center differential or an AWD coupler"
Longitudinal torque distribution mode: type of torque transfer between front and rear
Fixed: torque bias fixed by design (e.g. open differential)
Variable: torque bias variable by design (e.g. passive/active torque transfer device or active
locking differential etc. Hybrids with independently driven electric rear axle fall also into this
category)"
Indeterminate: torque bias determined by input torque, wheel speed and tractive conditions.
Typical for part time systems
Torque modulation: torque transfer device type
Active: electronically controlled torque transfer
Passive: non controlled torque transfer determined by external feedback (typically wheel speed
difference)
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
48
2.2.1 Audi
Table 2-2: Audi Platforms and Models
SAE AWD Classification
Table 2-3: Audi AWD Classification
Audi is selling their AWD system under the quattro™ brand. The systems have evolved
from the original Audi quattro™ to currently three different systems. The entry level
models A3, Q3 and TT are based on the Volkswagen MQB platform and use the Haldex
on-demand system similar to VW.
The larger sedans have permanent AWD with a Torsen™ center differential in
combination with automatic transmissions (NA market), and a ‘crown gear’ differential
with rear axle bias with their dual clutch transmission (not sold in NA).
The large SUVs use a transfer case with Torsen ™ center differential.
19 Phased out in 2016
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
Audi
Platform Nameplate
MLB B/C A4/A5/A6/A7/Q5
MLB D A8/Q7
MQB A/B A3/TT
PQ35 Q3
PL71-7219 Q7
49
Audi has just announced their latest development in AWD technology: the ‘Audi
quattro™ with ultra technology’ features an electro-mechanically actuated AWD coupler
in place of the Torsen™ center differential and a mechanical rear axle disconnect
device20. That makes the driveline an on-demand system with disconnect capability. This
system will ultimately replace the permanent system in the larger sedans.
20 http://jalopnik.com/audis-high-tech-new-quattro-is-about-to-piss-off-its-bi-1760502139
50
A6
Table 2-4: Audi A6 Basic Information
The A6 driveline is based on a longitudinal FWD architecture and features full-time AWD
with a Torsen® center differential (CD). The Torsen® CD provides a mechanical torque
sensing locking effect, the overall system performance is enhanced by brake traction
control. For classification purposes, this defines the A6 as a full-time variable torque
passive system. Figure 2-4 shows the 8-speed automatic transmission with Torsen®
center differential.
Powertrain
Engine Longitudinal 4, 6 or 8 cyl
Transmission 8-speed longitudinal automatic
Driveline
Architecture FWD based
T-case Type Integrated Torsen® center differential
Source ZF Mass n/a
Features none
RDM Type Open rear differential
Actuation n/a Source n/a
Mass n/a Torque transfer n/a
Features Optional dual clutch torque vectoring
AWD Controls
Passive AWD torque modulation
Brake traction control assist
Brake assisted torque vectoring
Optional: Active torque vectoring
51
The engine is entirely located in front of the front axle with the front axle differential
nested between the engine and the transmission and driven by an integrated front
propshaft. Subaru is using a similar architecture.
______ Figure 2-4: Audi 8-Speed Automatic Transmission with Integrated Torsen Differential21
21 http://www.audi-technology-portal.de/en/drivetrain/transmission-technologies/tiptronic_en
52
2.2.2 BMW
Table 2-5: BMW Platforms and Models
SAE AWD Classification
Table 2-6: BMW AWD Classification
BMW is marketing their AWD vehicles under the ‘x-Drive’ name and is well known for
their RWD platforms. All vehicles starting with the 2-series sedan and the X1 series SUV
up have a RWD based architecture, with a transfer case with an active coupler driving
the front axle. Smaller vehicles like the Minis and the Active Tourer are based on the
new UKL FWD platform. Some others will follow. All systems are active on-demand.
BMW
Platform Nameplate
L2 X1
L3 Mini
L7 X3, X4, 2/3/4-Series
L4 X5, X6
LG X7
L6 5/6-Series
LG 7-Series
UKL X1, 2-series Active Tourer, Countryman, Paceman
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
53
BMW Active Tourer
Table 2-7: BMW Active Tourer Basic Information
Powertrain
Engine Transversal 4-cyl
Transmission 9-speed automatic
Driveline
Architecture FWD based
PTU Type 2- shaft
Source GKN Mass n/a
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic Source BorgWarner
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
54
BMW 3/4/5/6/7 Series with xDrive
Table 2-8: BMW 3/4/5/6/7 Series Basic Information
Powertrain
Engine Longitudinal 4, 6 or 8-cyl
Transmission 8-speed longitudinal automatic
Driveline
Architecture RWD based
RDM Type Open differential
Source n/a Mass n/a
Features none
T-Case
Type Single speed, active on demand Geared drive, LH drop
Actuation Electro-mechanical Source Magna Powertrain
Mass n/a Torque transfer AWD coupler to front axle
AWD Controls
Active AWD torque control
Brake traction control assist
55
Figure 2-5: BMW 3/4/5/6/7 Series Transfer Case with Geared Drive22
XDrive for BMW sedans features a geared transfer case, as shown in Figure 2-5). The
reason for using geared drive in this type of vehicle is underbody packaging. It carries
some cost and mass penalties over the more prevalent chain drive, with no efficiency or
performance advantages (see also section 1.2.2.6).
The function of the active torque control is identical to chain drive T-cases used in the
cross over models (X3 – X6, see Figure 2-6).
22 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
56
BMW X3/X4/X5/X6 with xDrive
Table 2-9: BMW X3/4/5/6 Basic Information
Powertrain
Engine Longitudinal 4, 6 or 8-cyl
Transmission 8-speed longitudinal automatic
Driveline
Architecture RWD based
T-Case
Type Single – speed, active on-demand, Chain drive, LH drop
Actuation Electro-mechanical Source Magna Powertrain
Mass n/a Torque transfer AWD coupler
Front Axle Type Open differential
RDM Type Open differential
AWD Controls
Active AWD torque control
Brake traction control assist
57
Figure 2-6: BMW X3 / X4 / X5 / X6 Single Speed Active On-demand Transfer Case with Chain Drive23
23 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
58
2.2.3 Daimler Benz
Table 2-10: Daimler Benz Platforms and Models
SAE AWD Classification
Table 2-11: Daimler Benz AWD Classification
Mercedes uses the 4MATIC™ designation for their lineup of AWD vehicles. Entry level
vehicles are built on the FWD based MFA platform and have an electro-hydraulically
actuated AWD coupler in the RDM, which classifies them as on-demand AWD systems.
All upper level vehicles are RWD based and have a transfer case with center differential.
On sedans traction is enhanced by brake traction control only. SUVs have optional
passive limited slip devices.
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Daimler Benz
Platform Nameplate
MFA A-Class, B-Class, CLA, GLA
MRA MID-SIZE C-Class, GLC
W212 CLS, E-Class
W204 GLK, C-Class Coupe
W164 GL-Class/GLS, R-Class, ML-Class/GLE
W222 S-Class
W461 G-Wagen
59
The G-Wagen is an extreme off-road capable vehicle and has a unique drivetrain. It has a
frame mounted geared 2-speed transfer case with center differential. All three
differentials have driver activated mechanical full locks.
60
Mercedes Benz CLA/GLA 4-Matic
Table 2-12: Mercedes CLA/GLA Basic Information
Powertrain
Engine Transversal 4 or 6-cyl
Transmission 7-speed DCT
Driveline
Architecture FWD based
PTU Type Single shaft
Source GKN Mass 8.5 kg
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic Source Magna Powertrain
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
61
Figure 2-7: Mercedes CLA/GLA 4-Matic Power Transfer Unit24
The GLA has a very highly integrated PTU as shown in Figure 2-7. The input shaft picks
up torque right from the transmission final drive, which from a design and cost
standpoint is about as efficient as it can possibly be. From a gear efficiency standpoint it
is equivalent to a two shaft PTU.
Figure 2-8: Mercedes CLA/GLA Rear Drive Module25
24 25 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems http://www.automobilismo.it/tecnica-la-trazione-integrale-4matic-mercedes-per-classe-a-classe-b-e-cla-auto-20265
62
Mercedes Benz C, E & S-class 4-Matic
Table 2-13: Mercedes C, E and S-Class Basic Information
Powertrain
Engine Longitudinal 4, 6 or 8-cyl
Transmission 7-speed longitudinal automatic
Driveline
Architecture RWD based
T-Case
Type
Integrated open center differential, 50/50 torque split Single stage beveled gear drive, RH drop
Actuation n/a Source Mercedes Benz
Mass n/a Torque transfer n/a
Front Axle Type open
RDM Type open
AWD Controls
Brake traction control assist
63
______ Figure 2-9: Mercedes C, E and S-Class 4-Matic Powertrain
The longitudinal 4-Matic drivetrain used by Mercedes in the C, E and S-Class vehicles has
a planetary center differential with a 50/50 torque split between front and rear axles.
One notable feature (similar to Porsche’s Panamera and the MLB platform from Audi) is
a slightly beveled gear set to drive the front axle. Packaging reasons were the main
driver behind this technology. The T-case does not have an idler gear or a chain drive
and packages much closer to the main driveline. Taking one gear set out of the driveline
also increases efficiency.
The AWD system is assisted by Brake Traction Control, a feature common in AWD and
2WD vehicles.
64
2.2.4 Fiat Chrysler (FCA)
Table 2-14: FCA Platforms and Models
SAE AWD Classification
Table 2-15: FCA AWD Classification
Fiat Chrysler
Platform Nameplate
C-EVO/CUSW 200, Cherokee
LX 300, Charger
WK Grand Cherokee, Durango
WK Grand Cherokee, Durango
JK Wrangler
MK Compass, Patriot
BU (Small Wide) Renegade
DS/DJ 1500 Pickup
DS/DJ 1500 Pickup
C/D Journey
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
65
Jeep is marketing their AWD systems under a variety of names. Basic on-demand
systems on FWD based vehicle platforms start with an AWD coupler in the RDM, options
include locking devices on both axles depending on model.
Cherokee and Renegade are equipped with an AWD disconnect system with a low gear
option in their Trailhawk versions.
RWD based models (Grand Cherokee, Dodge Durango) may have full time AWD in their
base version, and on-demand transfer cases in the premium versions, with optional axle
locking devices.
A complete lineup of Jeep AWD systems and nomenclature can be found on the Jeep
website under http://www.jeep.com/en/4x4/#FreedomDrive2.
66
Jeep Cherokee
Table 2-16: Jeep Cherokee Basic Information
Powertrain
Engine Transversal 4 or 6-cyl
Transmission 9-speed automatic
Driveline
Architecture FWD based
PTU Type 2- shaft with integrated disconnect
Source AAM Mass 22.6 kg
Features none
RDM Type Parallel AWD coupler; active on-demand
Actuation Electro – hydraulic Source AAM
Mass 33.1 kg Torque transfer Multi plate clutch
Features AWD coupler acts as rear disconnect
AWD Controls
Active AWD torque control
Brake traction control assist
Secondary axle disconnect
67
Versions
Trailhawk
Trail Rated® version of the Jeep Cherokee
Table 2-17: Jeep Cherokee Trailhawk Basic Information
AWD Systems:
ACTIVE DRIVE I: Base system with active coupler on the rear and brake traction control;
selectable driving mode for Auto / Snow / Sport / Sand and Mud.
ACTIVE DRIVE II: Low gear with 56:1 crawl ratio is added to the base system
ACTIVE DRIVE LOCK: Mechanical rear axle lock is added
Technical information and AWD component breakdown for the standard version of Jeep
Cherokee is provided in section 5.2.
Driveline
PTU Features 2-speed PTU, planetary low gear
RDM
Features 2-speed Mechanical differential locker
Vehicle
More ground clearance with 1” suspension lift and larger tires
Better break-over and approach/departure angles
68
Jeep Grand Cherokee
Table 2-18: Jeep Grand Cherokee Basic Information
Powertrain
Engine Longitudinal 6 and 8-cyl
Transmission 8-speed longitudinal automatic
Driveline
Architecture RWD based
T-Case
Type
Chain drive, LH drop Base version: Single speed, Permanent AWD, Center differential with 50/50 split Premium(P): 2-speed electric shift
Actuation (P): electro-mechanical Source Magna Powertrain
Mass n/a Torque transfer AWD coupler
Front Axle Type open
RDM Type open
AWD Controls
Active AWD torque control
Brake traction control assist
69
Figure 2-10: Jeep Grand Cherokee Single Speed (left) and 2-speed (right) Transfer Cases26
Jeep Grand Cherokee offers a base version with an open center differential and 50/50
torque split in single speed and with a 2-speed option, and a premium version with a 2-
speed electric shift and active on-demand AWD coupler. Figure 2-10 shows the
difference in complexity between the two versions.
AWD systems:
QUADRA-TRAC I®: Full Time AWD with single speed transfer case and 50/50 center
differential
QUADRA-TRAC II®: 2-speed active on-demand transfer case
QUADRA-DRIVE® II: eLSD added to the rear axle
QUADRA-TRAC® SRT®: Single speed on-demand Transfer case and rear axle eLSD,
upgraded in strength for SRT®
Jeep Grand Cherokee is sharing its QUADRA-TRAC® I and II AWD systems with Dodge
Durango.
26 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
70
Jeep Wrangler
Table 2-19: Jeep Wrangler Basic Information
Powertrain
Engine Longitudinal V6
Transmission 6-speed manual, optional 5-speed automatic
Driveline
Architecture RWD based
T-Case
Type Chain drive, LH drop 2-speed, part time
Actuation Electric shift, driver actuated Source Magna Powertrain
Mass n/a
Front Axle Type Open differential
Rear Axle
Type Open differential, optional limited slip (‘Trac Loc™)
AWD Controls
Brake traction control assist
71
Versions
Rubicon
Extreme off-road version of the Wrangler
Table 2-20: Jeep Wrangler Rubicon Basic Information
AWD Systems:
COMMAND-TRAC®: 2-speed part time transfer case (2.72:1) with open axle differentials
ROCK-TRAC®: 2-speed part time transfer case with 4:1 low gear, electric axle locks front
and rear, electronic front sway bar disconnect
Driveline
Transfer Case Features 2-speed part time, 4:1 low ratio
Axles Features Mechanical 100% differential locks, driver actuated
Vehicle
More ground clearance with larger tires
Electric sway bar disconnect
72
Chrysler 300
Table 2-21: Chrysler 300 Basic Information
Powertrain
Engine Longitudinal 6 or 8-cyl
Transmission 8-speed longitudinal automatic
Driveline
Architecture RWD based
T-Case
Type Single speed active on—demand Chain drive, RH drop
Actuation Electro-magnetic Source BorgWarner
Mass n/a Torque transfer AWD Coupler
Front Axle Type open
Source Magna Powertrain (axle) and Warn Industries (Disconnect)
Mass n/a
Features AWD disconnect, electro-mechanically actuated
RDM Type open
AWD Controls
Active AWD torque control
Brake traction control assist
Front axle automatic disconnect
73
Figure 2-11: Chrysler 300 Axle Disconnect Unit (left) and Front Axle (right)27
The Chrysler 300 front axle is directly bolted to the right hand side of the structural
engine oil pan, with the cross shaft shown in Figure 2-11 going right through the oil pan.
The disconnect system is bolted to the opposite side and provides an electro-
mechanically activated disconnect to the front left half shaft.
The transfer case is a conventional chain driven unit with integrated, electro-
magnetically actuated AWD coupler.
27 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems and Warn Industries
74
2.2.5 Ford
Table 2-22: Ford Platforms and Models
SAE AWD Classification
Table 2-23: Ford AWD Classification
Ford is offering AWD on their based platforms with an electro-magnetically activated
AWD coupler in the rear axle.
The full size SUVs and F150 trucks feature on-demand transfer cases. Some basic
versions of F150 have a part time transfer case.
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Full Time
(FT)n/a Yes
variable
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Ford
Platform Nameplate
CD4 Edge, Fusion, S-Max, MKX/MKZ
C1 Escape, Focus, MKC
PN96/T1 Expedition, Navigator
D3/D4 Explorer, Flex, Taurus, MKS/MKT
T3 F150
F150
75
Ford Fusion
Table 2-24: Ford Fusion Basic Information
Technical information and AWD component breakdown is provided in section 5.1.
Powertrain
Engine Transversal 4-cyl
Transmission 6-speed automatic
Driveline
Architecture FWD based
PTU Type Single shaft
Source GKN Mass 12.2 kg
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – magnetic Source Sterling Axle (Ford)
Mass 26.1 kg Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
76
2.2.6 General Motors (GM)
Table 2-25: General Motors Platforms and Models
SAE AWD Classification
Table 2-26: General Motors AWD Classification
GM FWD platforms feature on-demand AWD systems with an active coupler in the
RDM.
Full size trucks and SUVs are equipped with 2-speed transfer cases with an active
coupler driving the front axle. The systems have front axle disconnect devices that are
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
On-Demand
(OD)
yes yes variable
General Motors
Platform Nameplate
31XX Canyon/Colorado
ALPHA ATS/CTS
EPSILON XTS, Regal/LaCrosse
GAMMA Trax/Encore/Mokka
LAMBDA Acadia/Traverse
THETA ANTARA/Captiva/Equinox/SRX/Terrain
K2XX Silverado/Escalade/Sierra/Suburban/Tahoe/Yukon
K2XX Silverado, Sierra
77
driver activated. Small trucks and entry level full size trucks (work trucks) have a part
time transfer case.
Chevrolet Equinox
Table 2-27: Chevrolet Equinox Basic Information
Powertrain
Engine Transversal 4 or 6-cyl
Transmission Transversal 6-speed
Driveline
Architecture FWD based
PTU Type 2- shaft
Source GKN Mass 22.5 kg
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation n/a Source n/a
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
78
Chevrolet Silverado / GMC Sierra
Table 2-28: Chevrolet Silverado / GMC Sierra Basic Information
Powertrain
Engine Longitudinal 6 and 8-cyl
Transmission 6-speed longitudinal automatic
Driveline
Architecture RWD based
T-Case Base Model
Type 2 Speed Manual Shift Chain drive, LH-Drop
Actuation Manual-Mechanical or optional electric shift Source Magna Powertrain
Mass n/a Torque transfer Cone Synchronizer w Dog Clutch
T-case Premium
Type
2-speed electric shift Active on-demand Multi plate Clutch
Source Magna Powertrain
Front Axle
Type Frame mounted, open diff
Source AAM
Mass n/a
Features Center disconnect , electro-mechanically actuated shift sleeve
Rear Axle
Type Open,
Source AAM
Mass n/a
Features optional mechanical locker (G80)
AWD Controls
Active AWD torque control (premium only)
Brake traction control assist
79
Figure 2-12: Chevrolet Silverado / GMC Sierra Transfer Cases: 4WD Base Model (left) and AWD Premium Model (right)28
The Chevrolet/GMC line-up of full size trucks is a typical example of an AWD
architecture developed for full frame vehicles. The transfer case comes in 3 different
types: The base model is 2-speed part time 4WD with the option of manual or electrical
shift, and is mostly used for work trucks. Figure 2-12 shows the difference in complexity.
The premium model with 2 speeds has four driver selected modes:
2Hi is the most fuel efficient mode and provides torque to the rear wheels only.
The front axle is disconnected and not rotating.
AUTO is the preferred AWD mode when driving in inclement weather or
moderate off-road. An electromechanically controlled multi plate clutch
modulates torque as required.
4Hi has the AWD coupler locked at full torque capacity and provides extra
traction in off-road conditions
4Lo engages the reduction planetary gear set to provide better speed control
and higher tractive force in harsh off-road conditions.
The front axle disconnect system is driver controlled and does not have an automatic
mode.
28 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
80
2.2.7 Honda
Table 2-29: Honda Platforms and Models
SAE AWD Classification
Table 2-30: Honda AWD Classification
Honda AWD vehicles are active on-demand. The top-of-the-line vehicles offer ‘Super
Handling AWD’ (SH-AWD), which is the Honda version of torque vectoring (compare to
Audi, BMW and Mitsubishi)
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Honda
Platform Nameplate
2SL/2SF Pilot/MDX
C-5 CR-V, RDX
D-5 RLX, Odyssey, Crosstour, TLX
GSP(2) HRV/Fit
81
CR-V
Table 2-31: Honda CR-V Basic Information
Powertrain
Engine Transversal 4-cyl
Transmission CVT with sport mode
Driveline
Architecture FWD based
PTU Type Single shaft
Source Honda Mass 8.9 kg
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic Source Honda – Tochigi
Mass 18.9 kg Torque transfer Multi plate clutch
Features none
AWD Controls
Active AWD torque control
Brake traction control assist
82
2.2.8 Hyundai (Kia)
Table 2-32: Hyundai Platforms and Models
SAE AWD Classification
Table 2-33: Hyundai AWD Classification
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Hyundai / Kia
Platform Nameplate
HD Ix35, Sportage, Tucson
NF/CM Santa Fe, Sorento, Maxcruz, Veracruz
83
SantaFe
Table 2-34: Hyundai SantaFe Basic Information
Powertrain
Engine Transversal 6-cyl
Transmission 6-speed automatic
Driveline
Architecture FWD based
PTU Type Single shaft
Source Hyundai-Wia Mass n/a
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic Source Magna Powertrain (Axle from Hyundai-Wia)
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
84
Figure 2-13: Magna Dynamax AWD Coupler29
Figure 2-13 shows one of the most compact AWD couplers on the market. The unit consists of an electro-hydraulic actuator and a multi plate clutch. The coupler bolts directly to the rear axle in an in-line configuration and is optimized in terms of torque level and AWD control system response.
29 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems
85
2.2.9 Jaguar Land Rover (JLR - Tata)
Table 2-35: Jaguar Land Rover Platforms and Models
SAE AWD Classification
Table 2-36: Jaguar Land Rover AWD Classification
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
Jaguar Land Rover
Platform Nameplate
PLA-D6a F-Type, XJ
PLA-D7a XE, XF,
D8 Discovery, Evoque
DEFENDER Defender
PLA-D7u Range Rover
86
Range Rover Evoque
Table 2-37: Range Rover Evoque Basic Information
Powertrain
Engine Transversal 4-cyl
Transmission 9-speed automatic
Driveline
Architecture FWD based
PTU Type Single shaft
Source GKN Mass n/a
Features Electro-mechanically actuated disconnect
RDM Type Dual clutch AWD coupler; active on-demand
Actuation Electro – hydraulic Source GKN
Mass n/a Torque transfer Multi plate clutch
Features disconnect
AWD Controls
Active AWD torque control
Brake traction control assist
Automatic disconnect
87
Figure 2-14: Evoque Rear Drive Module and RDM Architecture (insert)30
The Evoque RDM features a unique twin coupler (or dual clutch) system which
eliminates the need for a differential (Figure 2-14, see also Figure 1-11). The rear axle
system has limited slip characteristics and, within limitations, torque vectoring
capabilities. The RDM also acts as a disconnect device in conjunction with the PTU.
30 http://www.automobilrevue.ch/artikel/a/auf-die-sparsame-tour.html
88
2.2.10 Mazda
Table 2-38: Mazda Platforms and Models
SAE AWD Classification
Table 2-39: Mazda AWD Classification
Mazda AWD vehicles use an electro-magnetic AWD coupler similar to the Ford Fusion.
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Mitsubishi
Platform Nameplate
SKYACTIV B CX-3
SKYACTIV C CX-5
SKYACTIV D CX-9
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2.2.11 Mitsubishi
Table 2-40: Mitsubishi Platforms and Models
SAE AWD Classification
Table 2-41: Mitsubishi AWD Classification
Mitsubishi AWD Technology
Mitsubishi offers two different AWD systems under the name ‘Super All Wheel Control’.
The Outlander features the baseline system with an electro-magnetically actuated AWD
coupler very similar to the Ford Fusion (see also section 1.2.2.4). In addition to the in-
line AWD coupler Outlander also features an Active Front axle Differential (AFD) which
controls wheel slip across the front axle by means of an electronically controlled coupler
(a.k.a. eLSD or electronically controlled Limited Slip Differential). Figure 2-15 shows a
schematic of the Outlander system. Traction is further enhanced by Brake Traction
control.
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Mitsubishi
Platform Nameplate
GS Outlander, Lancer
90
Figure 2-15: Mitsubishi S-AWC (‘Super – All Wheel Control’)31
The top-of-the-line system is Mitsubishi’s Active Yaw Control (AYC) system. It is available
in the GSR version of the Lancer. The system was the first in the North American market
to provide full torque vectoring capabilities (see also section 1.2.2.4). Audi, BMW and
Honda followed much later with similar systems. However, cost, complexity and mass
penalties have kept torque vectoring systems in a market niche.
31 http://www.mitsubishi-motors.com/en/spirit/technology/library/s-awc.html
91
Figure 2-16: Lancer Evolution Rear Drive Module with Active Yaw Control (AYC) 32
32 http://www.mitsubishi-motors.com/en/spirit/technology/library/s-awc.html
92
2.2.12 Nissan (Infiniti)
Table 2-42: Nissan Platforms and Models
SAE AWD Classification
Table 2-43: Nissan AWD Classification
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
Nissan
Platform Nameplate
B Juke
B0 Terrano
D Murano, Pathfinder, QX60
X61B Frontier, Titan, Armada, Xterra, QX80
CMF-C/D Rogue
FR-L Q50, Q60, Q70, QX50, QX70,
93
Nissan Rogue
Table 2-44: Nissan Rogue Basic Information
Powertrain
Engine Transversal 4-cyl
Transmission CVT
Driveline
Architecture FWD based
PTU Type Single shaft
Source Univance Mass n/a
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – magnetic Source Nissan / GKN
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
94
2.2.13 Subaru
Table 2-45: Subaru Platforms and Models
SAE AWD Classification
Table 2-46: Subaru AWD Classification
Entry models sold in North America feature manual transmissions and permanent AWD
with a rear axle biased center differential – the original ‘Symmetric All Wheel Drive’.
Premium models are equipped with the Lineartronic™ CVT with an on-demand AWD
system (Figure 2-17).
The Subaru Lineartronic ™ is a Continuously Variable Transmission (CVT). The transfer
case, front axle drive and rear axle drive are completely integrated. The transmission is
purpose built for AWD and Subaru does not offer a 2WD version. Torque transfer to the
rear axle is managed in the transmission via AWD coupler33.
33 http://www.subaru-global.com/tec_awd.html
Subaru
Platform Nameplate
SI(2) Legacy, Impreza, Forester, WRX, Outback, Crosstrek
SI(2) Impreza, Forester, WRX, Crosstrek
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
On-Demand
(OD)
yes yes variable
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
95
Figure 2-17: Subaru AWD CVT Transmission34
34 http://www.subaruforester.org/vbulletin/f155/subaru-lineartronic-cvt-cutaway-102264/
96
Outback
Table 2-47: Subaru Outback Basic Information
Powertrain
Engine Transversal 4 or 6-cyl
Transmission Lineartronic ™ CVT
Driveline
Architecture AWD dedicated
Transfer Case Type Integrated AWD with coupler driving rear axle
Source n/a Mass n/a
Features none
Axles Type open
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
97
2.2.14 Tesla
Model S
Table 2-48: Tesla Model S Basic Information
Powertrain
Engine 2 electric
Transmission Single speed e-drive
Driveline
Architecture Permanent AWD
AWD Controls
Electric motor control units
98
2.2.15 Toyota
Table 2-49: Toyota Platforms and Models
SAE AWD Classification
Table 2-50: Toyota AWD Classification
Toyota (Lexus)
Platform Nameplate
F1 Land Cruiser 200, LX, Sequoia, Tundra
F2 Tacoma
GS GS, IS
LS LS
MC-M RAV-4, Highlander, Sienna, Venza
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Rav4
Table 2-51: Toyota Rav4 Basic Information
Powertrain
Engine Transversal 4-cyl
Transmission 6-speed automatic
Driveline
Architecture FWD based
PTU Type Single shaft
Source Toyota Mass 11.7 kg
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – magnetic Source Toyota
Mass 17 kg Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
100
Highlander
Table 2-52: Toyota Highlander Basic Information
The Highlander is based on the same platform as RAV4 and the AWD system
architecture is identical.
Highlander offers a full hybrid version with electric rear axle drive (eRAD). This AWD
system is not a classic eRAD system as described in section 1.2.1.3 but a full hybrid with
an additional electric rear axle drive. It does not have plug-in capabilities (PHEV).
Powertrain
Engine Transversal 4/6-cyl
Transmission 6-speed automatic
Driveline
Architecture FWD based
PTU Type n/a
Source Toyota Mass n/a
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – magnetic Source Toyota
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
101
2.2.16 Volkswagen
Table 2-53: Volkswagen Platforms and Models
SAE AWD Classification
Table 2-54: Volkswagen AWD Classification
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque activeSAE J1952 (Oct 2013)
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
Volkswagen
Platform Nameplate
MQB A/B Passat, Golf,
PL71-72 Touareg
PQ35 Tiguan
102
Tiguan
Table 2-55: Volkswagen Tiguan Basic Information
Technical information and AWD component breakdown is provided in section 5.3.
Powertrain
Engine Transversal 4 or 6-cyl
Transmission 7-speed DCT
Driveline
Architecture FWD based
PTU Type Single shaft
Source Magna Powertrain Mass 17.2
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic
Source Magna powertrain, AWD coupler BorgWarner Haldex Gen IV
Mass 35.3 Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
103
2.2.17 Volvo
Table 2-56: Volvo Platforms and Models
SAE AWD Classification
Table 2-57: Volvo AWD Classification
Volvo AWD systems are based on the Haldex AWD coupler and are exclusively on-
demand. All systems are Haldex Gen V, except for XC90 which kept Gen IV35.
Volvo also offers a hybrid version of the XC90, with a ‘through the road’ AWD
architecture. The vehicle is not yet available on the North American market, and critical
data have not yet been officially released.
35 The Haldex system is explained in detail in section 5.3.1 (VW Tiguan)
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
Part Time
(PT)
Full Time
(FT)n/a Yes
variable
On-Demand
(OD)
yes yes variable
Volvo
Platform Nameplate
C1 V40
CD-EU S60, S80, V60, V70, XC70, XC60,
SPA XC90
104
XC90
Table 2-58: Volvo XC 90 Basic Information
Powertrain
Engine Transversal 4 cyl supercharged
Transmission 8-speed Automatic (Aisin)
Driveline
Architecture FWD based
PTU Type n/a
Source n/a Mass n/a
Features none
RDM Type In-line AWD coupler; active on-demand
Actuation Electro – hydraulic Source Haldex
Mass n/a Torque transfer Multi plate clutch
Features None
AWD Controls
Active AWD torque control
Brake traction control assist
105
XC90 T8 PHEV
Table 2-59: Volvo XC90 T8 PHEV Basic Information
Powertrain
Engine Transversal 4 cyl supercharged Electric Motor (eRAD)
Transmission 8-speed Automatic (Aisin)
Driveline
Architecture FWD based, AWD only, eRAD
Front Axle Drive
Internal Combustion Engine, with Starter Generator
Rear Axle Drive Electric Rear Axle Drive (eRAD)
AWD Controls
Brake traction control assist
106
3 AWD Efficiency Improvement Potentials
The following section explains design features, materials and processes that may offer
improvements to driveline efficiency or component mass reductions. The numbers
referenced are mostly from supplier publications and may reflect special circumstances
on a particular component. These numbers cannot be applied to other similar
components. Actual improvements in fuel economy need to be evaluated, preferably by
method of vehicle simulation.
3.1 Definitions
There are two basic types of losses in a drivetrain:
Torque transfer losses
Parasitic losses
Torque transfer losses are generated whenever the driveline transfers any level of
torque. They include gear friction losses, bearing losses due to reaction forces and losses
in driveline joints.
Parasitic losses occur in any component that moves relative to another contacting
surface or medium independently from the actual torque transferred. They include seal
drag, bearing preload losses, churning losses from gears submerged in the lubricant,
pumping losses from bearings or idling lubricant pumps and drag in a multi plate clutch.
Both types of losses are dependent on the operating temperature of the driveline
component. As the temperature rises to a typical operating temperature of 70 to 120°C
the losses drop significantly. However, driving statistics indicate that short distance
driving during which operating temperatures do not stabilize is the most frequent mode
of operation in urban environments. Special care needs to be taken therefore to
optimize component efficiency in all temperature ranges.
3.2 System Level
3.2.1 Architecture
AWD systems have traditionally been seen as add-ons to existing platforms. Many times
the original design did not possess provisions to easily accommodate the AWD
components. As an example, power transfer units (PTUs) in FWD based vehicles have
107
been difficult to package in the tight space between the engine, transmission and body
structure.
More recent vehicles have been designed with the AWD option in mind from the
beginning, and take advantage of simpler, light mass and more efficient components like
a single shaft PTU (see also 3.4.4)
The rear drive module in AWD vehicles is typically mounted in a subframe to isolate
reaction forces and noise paths. Optimized structures can save mass within the rear
suspension module.
3.2.2 Disconnect System
Axle disconnect systems are available for FWD and RWD based vehicle architectures
(see also chapter 1.2.2.4). They are most effective on FWD architectures because they
take out two hypoid sets that are main contributors to parasitic losses. The secondary
driveline also has a dramatically lower overall torque transfer efficiency, again, because
the hypoid sets typically run with 3 – 5% losses each under load. This is addressed by
optimizing AWD engagement strategies and torque levels.
In addition, disconnecting the secondary driveline also eliminates the rotational inertia
effects since the driveline components do not have to be accelerated/decelerated with
the varying vehicle speed. The effects can be described by calculating the ‘Equivalent
Mass’ (see Appendix D). The translational kinetic energy is still there, but the rotational
kinetic energy becomes zero. The vehicle performs as if the equivalent mass would have
been taken out.
Disconnect systems can save up to 4% - 7% in fuel consumption36 /37, depending on
vehicle application and driving conditions. Some lower percentages were given at the
2015 SAE World Congress: 2.4 – 3.3 %38 depending on driving conditions. However, a
sophisticated, fully automated disconnect strategy is required to balance fuel efficiency
with vehicle dynamics, traction and safety requirements in real-life driving. Driver
override options (‘Sport’, Off-road, etc.) can further reduce the actual effectiveness of
disconnect systems.
3.2.3 Downsizing
The torque capacity of secondary drivetrains in FWD based AWD vehicles is a major
factor for increased mass and decreased efficiency. The relative amount of torque
required to drive on snowy surfaces is far lower than that typically provided by the AWD
36 http://articles.sae.org/13610/ 37 http://articles.sae.org/13615/ 38 http://papers.sae.org/2015-01-1099/
108
system. Downsizing therefore provides a high potential for improvements with minimal
impact on overall vehicle performance. Downsizing also reduces cost of the drivetrain
and, with proper algorithms to manage the duty cycle of the secondary drivetrain, has
no negative effect on strength and durability.
3.2.4 Electric Rear Axle Drive (eRAD)
Hybrids are generally known to substantially improve vehicle efficiency, sometimes
doubling the mpg compared to their conventional base vehicles. The eRAD architecture
is actually a simple FWD based vehicle with an added electric drive on the rear axle. It is
perfectly suited for hybridization of vehicles with a FWD architecture, since the electric
part of the drivetrain is independent from the conventional drive in the front (see also
section 1.2.1.3).
Besides providing additional power to overcome added mass, the eRAD is capable of
recuperating brake energy to feed back into the battery and such improve efficiency.
Figure 3-1: Volvo XC90 T8 Hybrid39
39 http://www.volvocars.com/us/cars/new-models/xc90-t8-twin-engine
109
3.3 Component Level
3.3.1 Fuel Efficient (FE) Bearings
Tapered roller bearings (TRB) used in axle drives to support hypoid gear sets are
typically assembled with substantial preload to cope with driveline forces and thermal
expansion. This inevitably leads to significant parasitic losses. Bearing suppliers have
recently addressed this problem by developing technology that greatly improves rolling
resistance and therefore bearing efficiency. One way is to use ball bearings instead of
tapered rollers, in particular angular contact double row ball bearings with different
diameters and ball sizes between the rows to create the tapered effect (Figure 3-2).
Figure 3-2: Angular Contact Double Row Ball Bearing (left) as a Replacement for Tapered Roller Bearings40, Power Loss Comparison (Under Lab Conditions, right)41
The manufacturer claims an improvement of up to 50% in internal friction and up to
1.5% savings in fuel consumption42 when combined with other axle improvements. This
technology comes at a price and has not been implemented throughout the vehicle
lines.
Other bearing manufacturers were able to improve conventional tapered roller bearings
to a point close to the above mentioned, with less cost penalty.
40 http://articles.sae.org/11380/ 41 http://www.schaeffler.com/remotemedien/media/_shared_media/08_media_library/01_publications/schaeffler_2/symposia_1/downloads_11/Schaeffler_Kolloquium_2010_28_en.pdf 42 Schaeffler Group, http://articles.sae.org/11380/
110
Figure 3-3: Substitution of Tapered Roller Bearings (red) with Angular Contact Ball Bearings (blue)43
Figure 3-3 shows an example for the application of FE bearings in a rear axle. Ring &
pinion bearing design calls for pairs of bearings capable of taking high axial and radial
forces in all directions. Significant axial preload needs to be established to keep the
axle’s performance within specifications. In the above illustration pinion bearings show
the innovative tandem design (blue) that can take the high reaction loads, whereas the
ring gear bearings can be angular contact ball bearings (blue) with lower load capacity.
The red bearings show the conventional solution. The required sizes between TRBs and
FE bearings are very similar so the upgrades do not create significant design challenges.
Figure 3-4: Power Loss Distribution between Gears, Bearings and Oil Splash in a Single Stage Axle under Load44
43 http://www.powertransmission.com/issues/0810/pte0810.pdf 44
111
3.3.2 Low Drag Seals
Shaft seals are subject to friction forces between surfaces rotating at different speeds
(or rotating/non rotating surfaces). The ‘tightness’ of a seal is required to provide
sufficient performance through the vehicle life. By optimizing the seal specifications
parasitic losses can be minimized.
Figure 3-5: Low Drag Seal45; Conventional Seal with Garter Spring on the Right Hand Side for Comparison46
Manufacturers may use different design options to design efficient seals. Figure 3-5 shows
a radial shaft seal ring with no garter spring to increase radial seal forces. A 70%
reduction (35W vs. 110W) is claimed in a specific application47 with the same durability
and functionality. For comparison, a conventional seal with garter spring is shown on
the right hand side.
Another way of improving friction performance is to coat the seal lips with a low friction
compound.
3.3.3 Lubrication Strategies
Axles with hypoid sets require special lubricant formulations to provide constant
performance over the lifetime of a vehicle. Axles are typically filled for life48 and do not
require oil changes for a long time.
The viscosity of axle fluids is typically higher than transmission fluids and creates
therefore more parasitic losses. The lubricant level and distribution within the axle is
one specific area where improvements can be made. Lubricant additives to enhance
performance are being developed.
45 http://articles.sae.org/7639/ 46 http://supersprings.biz/garter-springs 47 Freudenberg-NOK; http://articles.sae.org/7639/ 48 ‘Life’ is typically considered to be up to 150,000 miles
112
Recent developments in lubrication strategies have included dry sump systems to
minimize shear losses from driveline parts rotating partially submerged in the oil sump.
A dedicated scavenger pump moves oil from the sump to a separate reservoir and
provides on-demand lubrication for driveline components engaged during AWD
operation.
Figure 3-6 shows a comparison of a standard AWD system and a disconnect system with
a controlled dry sump lubrication system. Significant power savings can be achieved at
vehicle speeds above 40 mph (64 kph).
Figure 3-6: Spin Loss Comparison between Standard and Disconnect AWD Systems49
Chassis dynamometer tests conducted with a baseline AWD driveline and a disconnect
system showed a 3.3% improvement in fuel efficiency in the FTP75 cycle and 2.4% in the
highway cycle due to improvements in windage losses.49
49 SAE 2015-01-1099 ‘Beyond Driveline Disconnect’
113
3.3.4 Advanced CV Joints
Constant Velocity (CV) joints as shown in Figure 3-7 are used in propshafts and half
shafts. CV joints have increased torque losses at the extreme angles experienced during
suspension articulation or, as front axle joints, due to steering. New joint geometry has
been shown to improve the overall performance of the drive shafts. Significantly
improved efficiency comes also with increased strength or reduced packaging size and
mass.
Figure 3-7: Advanced Driveshaft Joint for Reduced Friction and Mass50
3.3.5 Dry Clutch Systems
Dry clutches do not have any drag losses while in the open position, and have been used
in transmissions in many applications. There are no known AWD system applications as
of today.
3.4 Design
3.4.1 Hypoid Offset Optimization
Hypoid gears are designed with an offset between input shaft and output shaft to
balance strength and durability between pinion and ring gear. This offset creates
additional sliding motion between the engaged gear tooth surfaces and thus increased
system friction. Hypoid gear losses under torque can be in the range of 3 – 5% and are
one of the biggest contributing factors to overall driveline efficiency.
50 http://media-centre.gkndriveline.com/drivelinecms/opencms/en/media-centre/news/gkn-news/article_0132.html
114
Figure 3-8: Hypoid Offset
By reducing this offset a compromise needs to be found between efficiency and
strength. Bevel gears with no offset (spiral gears) offer the best efficiency but are not as
strong as hypoids and need to be sized accordingly, giving up some of the advantages by
increasing mass. The need for an offset is reduced as gear ratios get lower (see also
3.4.5).
3.4.2 Non Serviceable Components
Axles and power transfer units are relatively simple and reliable components. This fact
allows for design solutions that eliminate access/assembly covers and bolts by simply
welding the housing parts. The unit becomes non-serviceable, but mass reductions and
a fully automated assembly/welding process justify the move to this technology. One of
the methods used is fully automated friction stir welding.
3.4.3 Bearing Preload Optimization
Tapered bearing preload is a necessity for hypoid assemblies and contributes
significantly to parasitic losses. By carefully designing the components to minimize this
preload in axles and PTUs some efficiency improvements can be achieved. Special care
needs to be given to assemblies with different materials since the thermal expansion
coefficients may be different, such as aluminum housings and steel shafts. The overall
performance of a component becomes highly temperature dependent.
115
3.4.4 Single Shaft Power Transfer Units
Figure 3-9: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right)
The PTU is typically located in an area that does not provide much extra space. Older
AWD vehicles were mostly converted from FWD base vehicles and required
complicated, multi-shaft PTUs to find a way from the front axle to the rear.
As AWD vehicles become more popular, the AWD option has been designed into the
base vehicle already, allowing for a more direct way to transfer torque to the rear axle
via single shaft PTU (Figure 3-9 center). Eliminating additional gears in a PTU saves cost,
mass and improves efficiency.
3.4.5 Propshaft Gear Ratio
Decreasing the propshaft gear ratio allows for better balanced hypoid sets with less
offset and therefore improves efficiency. However, the increased propshaft torque level
requires a heavier propshaft.
Typical axle ratios are between 2.5 and 3 to reduce propshaft torque and mass.
Applications are known to go as low as 1.05 (non-matching numbers of teeth to
minimize noise problems)
116
3.5 Materials
3.5.1 Magnesium Housings
The material of choice for AWD component housings today is aluminum. As an
alternative, magnesium alloys have been proven to provide significant mass savings on
housings when properly designed.51
Magnesium is approximately 30% lighter than aluminum with similar material
properties. The magnesium casting process allows for very thin walled parts in areas
where stresses are low, which opens up design opportunities to save additional mass
and cost without compromising structural integrity.
The surface quality of magnesium parts is superior to aluminum die cast which enables
the use of net formed parts with minimal machining in some applications.
Higher material prices and a more complicated manufacturing process52 have so far
slowed down the more widespread use of magnesium. However, under pressure from
fuel efficiency regulations, several initiatives are under way to promote the use of
magnesium in structural driveline component applications.
A current application for magnesium is housings for transfer cases currently being equipped on
light trucks. The location of the transfer case provides sufficient cooling for operating
temperatures well within the material specifications of magnesium. PTUs and RDMs are typically
designed with very small oil volume and high power density. The consequential elevated
operating temperatures and limited cooling make it difficult to use magnesium in these
applications
51 The old Volkswagen Beetle from the 50’s era had an engine block and a transmission housing made from magnesium 52 Magnesium and especially Mg chips are flammable and need special precautions during machining
117
3.5.2 High Efficiency Lubricants
Small improvements to the efficiency of gear trains can be made by changing the
chemistry of the lubricants with additives aimed at specific problem areas. Better heat
resistance allows for lower base viscosity lubricants.
Figure 3-10: Influence of Lubricants and Temperature on Driveline Torque Losses53
Figure 3-10 shows Torque losses for different lubricants at various temperatures and the
corresponding viscosity. Note that differences in lubricants become very small at the
typical operating temperature of 90˚C and above.
3.6 Manufacturing Process
3.6.1 Vacuum Die Casting
AWD component housing design addresses the need for strength and durability.
However, some areas of a housing are not under stress and do not require increased
wall thickness.
53 http://www.geartechnology.com/issues/0912x/gt0912.pdf
118
Vacuum high pressure die casting processes require a minimum wall thickness to make
sure the dies can be filled properly. New technology in the casting process allows to
reduce the minimum wall thickness and eliminates redundant housing material54.
3.6.2 Hypoid Manufacturing
The gear manufacturing process defines some characteristics of the finished gears. The
typical process used today is hobbing/lapping. The gears are cut and in a finishing
process ‘broken in’ with abrasive lapping paste providing the final surface quality. The
final step is heat treating. Hobbing and lapping is the mainstream manufacturing
process in North America today.
As a newer alternative, gears can be cut, then heat treated and finally precision ground.
This method provides better control over the final surface geometry and can improve
efficiency and NVH performance. European OEMs seem to be more likely to use this
process.
Figure 3-11: Influence of Micro Finishing and Coating on the Friction Coefficient in Gears55
Micro finishing or coating gear sets has been introduced recently as a further
improvement to surface quality and performance, as shown in Figure 3-11. The
coefficient of friction can be lowered significantly with both methods. Differences may
show over the lifetime of the gears as gear surfaces ‘wear in’ and coatings can ‘wear off’
over time.
54 http://articles.sae.org/13615/ 55 http://www.geartechnology.com/issues/0912x/gt0912.pdf
119
3.7 Advanced Engineering / Development Process
3.7.1 AWD Duty Cycle Management
Many AWD systems used in current on-road vehicles are typically dormant until a
traction event or a vehicle dynamic situation requires them to jump into action. The
secondary drivetrain therefore does not have the same requirements in terms of
strength and durability as the main drive does.
AWD control algorithms are capable of limiting the maximum torque and the time of
exposure to the minimum required for proper function and performance. This allows for
light mass secondary drive lines without sacrificing base performance.
3.7.2 Performance Adaptation to Vehicle Variants
AWD systems can be easily designed and tuned to different torque and performance
levels, even within the same family of vehicles. By carefully adapting the system to
vehicle requirements mass and cost savings can be achieved.
3.8 Advanced Operating and Control Strategies
3.8.1 Disconnect strategies
Disconnect strategies contribute significantly to efficiency gains in FWD based AWD
vehicles. More details are given in chapter 1.2.3.
120
3.9 Summary of Efficiency Improvement Potentials
Table 3-1 and Table 3-2 show a summary of the above listed potentials for fuel
efficiency improvements with their direct effects in different areas. The tables are an
estimate generated in peer discussions and should be used to gain an understanding of
the direction each measure is aiming and a rough quantity of gains, losses and
compromises. Fuel efficiency and mass savings were the decisive factors for the
do/don’t columns.
It seems evident that the most effective area of improvements is on the systems level.
Some of the most promising measures are also coming at significant cost and will have
to be looked at from an amortization standpoint as well as efficiency.
Table 3-1: Summary of Efficiency Improvement Potentials
Cost [$] > 100 10 - 100 < 10 < 10 10 - 100 >100
Weight [kg] >2.5 .5 - 2.5 < .5 < .5 .5 - 2.5 >2.5
Fuel Consumption [%] > 2 .5 - 2 < .5 < .5 .5 - 2 >2
Performance [%] > 10 1 - 10 < 1 < 1 1 - 10 > 10
Packaging difficult improved
cost / deterioration savings / improvements
easy
Co
st
We
igh
t
Fue
l Efi
cie
ncy
Pe
rfo
rman
ce
Pac
kagi
ng
Do
it
~ Do
n’t
Disconnect system FWD
Disconnect system RWD
downsizing
eRAD (Hybrid)
FE bearings
Low drag seals
Actuator technology
Lubrication strategies
Advanced CV-joints
Dry clutch systems
Component Level
System Level
121
Many of the listed items contribute only marginally to fuel efficiency. However, if looked
at from a cost per gain perspective, they all add up to some considerable improvements.
OEMs constantly assess the effectiveness of new technology but tend to implement it only
on a step by step basis.
Table 3-2: Summary of Efficiency Improvement Potentials (continued)56
56 * Magnesium housings recommended for transfer cases, more difficult for PTUs and RDMs
Co
st
We
igh
t
Fue
l Efi
cie
ncy
Pe
rfo
rman
ce
Pac
kagi
ng
Do
it
~ Do
n’t
Hypoid offset reduction
Lube level
Friction welded housings
Bearing preload optimization
single shaft PTU
Propshaft gear ratio
Subframe / integrated mount system
MaterialsMagnesium housings *
High efficiency lube
Thin Wall Vacuum Die Casting
Microfinished hypoid gear sets
AWD duty cycle management
Performance adaptation to vehicle variants
Disconnect strategy
Advanced Engineering / Development Process
Advanced Operating and Control Strategies
Design
Manufacturing Process
122
4 Trend Analysis
4.1 The Baseline
4.1.1 Global Vehicle Production
Vehicle production numbers have been in a steady growth in the past years. IHS data
suggests that this trend will last past 2021 in an almost linear fashion, as shown in Figure
4-1. The largest markets, China, Europe and North America are showing solid growth
rates, with China clearly in the lead (Figure 4-2). The most aggressive growth rates can be
found in the South Asia and Africa regions but these regions comprise much smaller
volumes.
Figure 4-1: Global Light Vehicle Production Forecast by Region, total numbers57
57 Source: IHS Data, 2015
123
Figure 4-2: Global Light Vehicle Production Growth between 2014 and 202158
4.1.2 Fuel Consumption
After a long period of stagnation, fuel efficiency as defined by CAFE rules has been
improving dramatically in the last ten years (Figure 4-3). This is true for passenger cars
as well as light trucks. This trend can be expected to keep its momentum, with the
automotive industry successfully taking on the challenge to improve even further.
Figure 4-4 shows the adjusted fuel efficiency for the period between 1975 and 2015.
Adjusted fuel efficiency reflects real world driving and is not comparable to automaker
CAFE standards compliance testing. It is typically about 20% lower than standard values
(‘Window sticker’). However, the same tendency as shown in Figure 4-3 can be seen
here.
AWD vehicles are typically rated about 3 – 7% below the average of all vehicles due to
increased mass and driveline losses, depending on base vehicle architecture and
technology level.
58 Source: IHS Data, 2015
124
Figure 4-3: Average Fuel Efficiency of U.S. Light Duty Vehicles (CAFE)59
Figure 4-4: Adjusted CO2 Emissions (left) and Adjusted Fuel Economy (right) for MY 1975-201560
59 U.S. Department of Transportation, National Highway Traffic Safety Administration, Summary of Fuel Economy Performance (Washington, DC: Annual Issues), available at http://www.nhtsa.gov/fuel-economy as of Mar. 12, 2014. 60 http://www3.epa.gov/otaq/fetrends.htm
mpg
125
One interesting trend is shown in Figure 4-5: Although vehicle mass and horsepower have increased substantially between 1980 and 2015, the adjusted fuel economy has, after a light setback up to 2005, actually got much better in the last decade. This indicates that the automotive industry has been able to overcompensate the generally negative effects of mass and horsepower increase on fuel economy. The turning points came in the mid-eighties when horsepower became decoupled from fuel efficiency, and around 2005 when the prospect of stricter CAFE regulations put in place by legislation (and technology that became available in the last decade) helped increase fuel efficiency without sacrificing performance and driving comfort.
Figure 4-5: Fuel Economy, Horsepower and Mass Changes between 1975 and 201561
AWD technology is following this trend by applying new technology (e.g. driveline
disconnect devices), optimizing components (e.g. bearing technology, mass reduction,
mass optimization) and applying sophisticated control algorithms (e.g. torque limitation,
duty cycle management, aggressive disconnect algorithms).
61 http://www3.epa.gov/otaq/fetrends.htm
126
4.2 Technical Trend Analysis in AWD Research and Development
1.1.1 Technical Trend Analysis in AWD Research and Development
Three major technology trends can be identified:
Actively controlled Multi-Plate Clutches, (MPC)
Active Disconnect Systems, (ADS)
Electric Rear Axle Drives, (eRAD)
Actively controlled MPC are the dominant technology in AWD driveline systems. Every OEM in
the North American market offers at least one vehicle platform equipped with this technology.
This type of AWD offers great flexibility in terms of torque bias, vehicle dynamics, peak and duty
cycle torque management, vehicle integration (packaging, electronic control system etc.) and
cost control. The system is flexible enough to use a single system design across multiple vehicles
or platforms. It also provides driver selectable automatic modes for different road or
environmental conditions (e.g. sand, rock, snow, etc.) or driving dynamics (e.g. economy, sport,
etc.) within the same software package.
Active AWD disconnect systems are a more recent trend in AWD systems. Driver activated
center axle disconnect devices have been in use in pick-up trucks and full size SUVs for a long
time, preceded by manual locking hubs and similar devices. The current trend favors fully
automated, electronically controlled devices. Their main operating mode is without driver
intervention, although an override option usually exists. The majority of disconnect systems
uses an actively controlled MPC to synchronize the driveline components during engagement
while the vehicle is in motion.
Electric Rear Axle Drives are the latest emerging technology to dramatically improve fuel
economy. This technology is focused on the FWD based vehicle architecture with a transverse
powertrain. Volvo was the most recent entry into the market with the XC90 Hybrid SUV. The
electric rear axle is completely independent from the conventionally powered front axle
(‘through the road hybrid’), and adds additional power and the ability to recuperate energy
during braking. A front end starter/generator enhances front axle drive efficiency. System cost is
currently limiting this application to luxury vehicles and first adopters as customers.
In addition to the three main trends driveline component manufacturers around the
world are honing the performance of their product by applying the latest technologies
to reduce mass and internal friction. Although savings on the individual parts (e.g.
bearings, seals etc.) may seem very small, they all add up to considerable improvements
in fuel efficiency. These items may be considered ‘low hanging fruit’ since they are not
very cost intensive and can in many cases be ‘dropped in’ to existing designs.
127
4.3 AWD Market Trend Analysis
The popularity of CUV/SUV in North America is driving an increase in the adaption of
AWD/4WD systems. Recent data reported by WardsAuto showed a 55.4% of all light
trucks, CUV and SUV were built with AWD or 4WD in 2014, an increase of 8.2% from
2009. As North America is the largest Market for AWD/4WD now and into the future,
forecasts by IHS Automotive predicts a 21% increase in AWD/4WD by 2020, a CAGR of
6.3% from 2014 to 2021.
Figure 4-6: MY 2015 Driveline Architecture Distribution in NA, All Segments62
However, demand is impacted by other regional and economic factors which are shown
in the following charts. As seen in the charts in Figure 4-7 AWD/4WD demand rate are
highest in the Luxury and Utility (Pickup) market segments. Non-CUV and passenger
vehicles have the lowest usage.
62 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data
128
Figure 4-7: AWD Take Rate by Vehicle Segment in MY 201563
Northern and agricultural US regions tend to have the largest adaption rates per capita. The five states with the greatest market share of four-wheel-drive vehicles are also the five with the lowest population densities:
FOUR-WHEEL-DRIVE SALES (%)/POPULATION-DENSITY RANKING:
Alaska: 78/50
Wyoming: 76/49
North Dakota: 76/47
Montana: 72/48
South Dakota: 67/46
63 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data
129
Figure 4-8: AWD Take Rate [%] by US State, Sorted by Regions, MY 201564
Figure 4-9: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD Content64
64 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data
130
5 AWD System Teardown Analysis
Three vehicles were selected for AWD component teardown analysis:
Ford Fusion
Jeep Cherokee
Volkswagen Tiguan
All three vehicles have a FWD based AWD system architecture with the AWD coupler
incorporated in the rear drive module as shown in Figure 5-1. One of the vehicles, Jeep
Cherokee, includes an AWD disconnect system.
Figure 5-1: AWD System Architecture
The scope of work in this section is to provide the total mass of AWD components,
subsystems and parts and an estimate for the associated rotational inertias for rotating
parts. Total component masses are shown relative to the total vehicle mass. Rotational
inertias are broken down into an equivalent mass to demonstrate the effects of
rotational inertia on vehicle dynamics. Rotational inertias for parts less than 50 grams
are not reported.
Technical aspects of the AWD systems are discussed. In the design analysis section
special enablers for fuel efficiency improvements, mass reductions, packaging
advantages and cost reductions applied in the components are outlined.
Power Transfer Units (PTU) and Rear drive Modules (RDM) were purchased and
disassembled to a level that did not require destructive methods. As a result, some
parts were not separated (e.g. pressed in bearing cups and shims from housings or
131
shafts, vent tubes, etc.). Although the Bill of Materials (BoM) may list these parts they
have no mass associated since it is included in the main part they are attached to.
Actuators and some coupler parts were not completely disassembled and are listed with
their subsystem mass and rotational inertia. Total mass and rotational inertia values are
not compromised by this method.
Lubricants were drained and measured at room temperature. However, not all of the
lubricant can be expected to drain in a teardown operation. The draining process was
considered complete when dripping stopped.
Mass are shown as measured. Small discrepancies between parts mass and the initial
total mass of the AWD components as delivered due to residual lubricant in the coupler
sections, main component sections and measurement rounding errors have been
corrected based on service manual information and estimates.
Unless specifically denoted
Displacements were measured using hand tools (electronic vernier caliper, ruler
etc.) to an accuracy of 0.1 mm
Masses up to 5.7 kg were measured with a Dymo M25-US scale to an accuracy of
+- 5.7 grams (all individual parts after disassembly); Components as received
were measured with a Rubbermaid Model 4010 with an accuracy of +- 1%
Volumes were measured with domestic, kitchen style measuring jugs to an
accuracy of 0.01 L
Rotational inertias are calculated based on measurements made with the
accuracies above
and estimates for complex structures; they are accurate to +- 5%
Equivalent masses are calculated based on measurements made with the
accuracies above
All measurements in SI units unless otherwise indicated
Total incremental mass between 2WD and AWD as listed in the vehicle data also
includes modifications to the vehicle body or subframe, which can be significantly
different from the 2WD version. An example is shown in Figure 5-2. The difference
between the measured AWD components and listed vehicle mass is categorized as
‘Others’ in the mass analysis sections.
132
Figure 5-2: Chassis Integration of an RDM (Ford Fusion)65
The following information is provided:
AWD technology overview
Components o Power Transfer Unit o Propshaft66 o Rear Drive Module o Axle shaftsError!
ookmark not defined.
General component data o Technical data o Rotational inertia o Equivalent mass of
rotating parts
Bill of Materials (BoM) including
o Component o Materials67 o Mass o Rotational inertias
Main parts picture documentation
Design review o Masses & rotational
inertias o Notable design
features
65 Source: Ford Motor Company / Dealerships 66 Propshafts and axle shafts: general data only 67 High level material specs, no detailed analysis performed, only non-ferrous components indicated
133
5.1 Ford Fusion
5.1.1 AWD Technology
The Ford Fusion AWD system is a front wheel drive based on-demand system with an
active in-line AWD coupler in the Rear Drive Module (RDM). The coupler is electro-
magnetically activated and controlled via remote AWD Electronic Control Unit (ECU). It
does not have a driveline disconnect system.
5.1.1.1 AWD Coupler
The internals of the AWD coupler are shown in Figure 5-3. There are six main
components:
Electro-magnetic coil
Electro-magnetic control clutch
Cam mechanism to augment the control torque
Main clutch transferring the rear drive torque
Input case connecting to the propshaft
Output shaft connecting to the rear differential
Figure 5-3: Ford Fusion AWD Coupler68/69
68 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf 69 Not an exact cross section of the Ford fusion AWD coupler, balloons refer to coupler BoM in Table 5-6
134
The electro-magnetic coil is stationary; the other five components rotate at propshaft
speed.
Figure 5-4 shows the operating principle of the clutch. In the left image the current is off
and the clutch plates are separated, not transferring torque. In the right image coil
current creates magnetic flux which pulls the armature and compresses the control clutch.
The torque generated in the control clutch activates the cam mechanism and creates
the compression force for the main clutch. The drive torque to the rear wheels is
transferred through the main clutch. The amount of torque is determined by the current
in the magnetic coil and can be controlled between zero (open clutch) and maximum
torque per AWD algorithms in the ECU.
Figure 5-4: Electro-magnetic Clutch - Operating Principle70
5.1.1.2 AWD Control Logic
A high level look at the control logic is given in Figure 5-5. The basic control module
consists of six main parts:
Road surface condition judgment is based on wheel speed sensors, accelerometer
inputs and yaw sensors. This is the main module that controls slip between front
and rear wheels.
Drivetrain system input torque control translates the torque request from the
control module into the corresponding electric current in the coil.
70 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf
135
Driveline vibration / noise reduction provides a compromise between vehicle
dynamics, traction and noise/vibration in the driveline by selecting optimal
operating points in the system
Highly accurate control is required to have quick system response and accurate
torque bias between front and rear wheels according to the driving situation.
Driving mode judgment decides whether to run in automatic mode or respond to
the driver selected override mode.
Coordinate with other electronically controlled devices: ABS and vehicle dynamic
control are higher in the vehicle control system hierarchy. The AWD control
system needs to work with the boundary conditions given by those systems and
create an integrated torque transfer strategy.
Overheat protection (detail): AWD couplers have limited heat capacity. If worked
hard the temperature limits may be reached. First line of defense is to go to
maximum torque, if driving situation allows, to limit heat generation in the
slipping clutch. If that does not work or is not applicable due to vehicle driving
situations the system reverts into 2WD mode. A cool-off period is required before
going back into full AWD mode.
This high level description of an AWD control logic is valid for most on-demand AWD
systems controls and, with some variations, has been adopted by most OEMs.
Figure 5-5: Ford Fusion AWD Basic Control Logic71
71 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf
136
5.1.2 Power Transfer Unit
Mass72 [kg] 12.2
BoM mass summation (% difference) [kg] 12.1 (1%)
Lubricant73 [L] 0.450
Gear tooth count (ring/pinion) 31/11
Gear ratio 2.818
Gear manufacturing process Hobbed/lapped
Mass of rotating parts [kg] 7.287
Total rotational inertia input shaft [kg.m2] 9.041e-03
Total rotational inertia output shaft [kg.m2] 3.48e-03
Dynamic tire radius [m] 0.334
Equivalent mass of rotational inertias [kg] 0.329
Equivalent mass factor74 1.027 Table 5-1: Ford Fusion Power Transfer Unit – Technical Data
72 As received, Includes lubricant 73 Nominal, per service information 74 See section 11 Appendix D
137
Figure 5-6: Ford Fusion Power Transfer Unit75
Ford Fusion Power Transfer Unit - Bill of Materials
Name Material76 Qty Mass Rotational inertia
[kg] [kg.m2]
1 Output flange nut 1 0.064 25e-05
2 Output flange 1 0.852 1.38e-03
3 Deflector Syn 1 0.010
4 Transfer case rear seal Syn/Mix 1 0.044
5 Outer output shaft tapered roller bearing 1 0.233 2.59e-04
6 Outer output shaft shim 1 0.006
7 Input Shaft Seal LH Syn/Mix 1 0.020
8 Transfer case vent77 1
9 PTU housing Al 1 3.240
10 Input shaft 1 3.632 8.30e-03
11 Input shaft bushing Syn 1 0.006
12 Input shaft outer bearing 1 0.198 3.22e-03
13 Input shaft outer bearing shim 1
14 O-ring cover seal Syn 1 0.006
15 PTU cover Al 1 0.882
16 PTU cover bolts (.010 ea) 9 0.090
17 Intermediate shaft seal Syn/Mix 1 0.056
18 PTU fill plug 1 0.018
19 Input shaft seal RH Syn/Mix 1 0.030
20 Output shaft 1 1.735 1.16e-03
21 Inner output shaft tapered roller bearingError! Bookmark not defined. bearingError! Bookmark not defined.
1 0.397 6.53e-04
22 Inner output shaft shim 1
23 PTU drain plug 1 0.028
24 Face seal Syn/Mix 1 0.004
25 Input shaft inner bearing 1 0.176 4.19e-04
26 Input shaft inner bearing shim 1
27 Lubricant (415 ml) Lub. 0.354
Table 5-2: Ford Fusion Power Transfer Unit, Bill of Material rotating parts [input]/[output]
75 Source: Ford Motor Company / Dealerships 76 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub. – lubricant, no indication - steel 77 Unspecified masses included in housings
138
Figure 5-7: Ford Fusion Power Transfer Unit - Parts
139
Figure 5-8: Ford Fusion PTU, Top View
Figure 5-9: Ford Fusion PTU Input Shaft Figure 5-10: Ford Fusion PTU Output Shaft
140
Figure 5-11: Ford Fusion PTU, Output Shaft with Pinion in Main Housing
141
5.1.3 Propshaft, Axles78
Propshaft
Mass [kg] 9.5
Total rotational inertia [kg.m2] 7.556e-03
Equivalent mass [kg] 0.537
Equivalent mass factor 1.057
Left Axle Shaft
Mass [kg] 6.0
Total rotational inertia [kg.m2] 5.177e-03
Equivalent mass [kg] 0.046
Equivalent mass factor 1.008
Right Axle Shaft
Mass [kg] 6.0
Total rotational inertia [kg.m2] 5.181e-03
Equivalent mass [kg] 0.046
Equivalent mass factor 1.008 Table 5-3: Ford Fusion Propshaft/Axle Technical Data79
78 Inertias and equivalent mass are estimates based on mass and design features 79 Masses are from similar Escape AWD system
142
5.1.4 Rear Drive Module
Mass80 [kg] 26.1
BoM mass summation (% difference) [kg] 25.8 (1.2%)
Lubricant main81 [L] 1.15
Lubricant Coupler [L] 0.28
Gear tooth count (ring/pinion) 31/11
Gear ratio 2.818
Gear manufacturing process Hobbed/lapped
Mass of rotating parts [kg] 16.002
Total rotational inertia input shaft [kg.m2] 1.30e-02
Total rotational inertia output shaft [kg.m2] 1.34e-02
Dynamic tire radius [m] 0.334
Equivalent mass of rotational inertias [kg] 1.046
Equivalent mass factor 1.040 Table 5-4: Ford Fusion Rear Drive Module – Technical Data
Figure 5-12: Ford Fusion Rear Drive Module82
80 As received, Includes lubricant 81 Nominal, per service information 82 Source: Ford Motor Company / Dealerships
143
Ford Fusion Rear Drive Module - Bill of Materials
ID Part Name Mat’l83 Qty Mass Rotational
inertia
kg Kg.m2
1 RDM housing Al 4.096
2 drain plug 0.018
3 fill plug 0.016
4 companion flange bolt 0.034
5 companion flange 1.180 1.26E-03
6 companion flange washer 0.082 3.28E-05
7 rock shield Syn 0.012
8 seal, AWD coupler cover Syn 0.040
9 retaining clip, AWD coupler cover 0.014
10 outer bearing, AWD coupler cover 0.280 1.12E-04
11 shim, outer bearing AWD coupler cover 0.004
12 button screw, torx for AWD coupler cover (0.018 ea.) 4 0.072
13 AWD coupler cover Al 1.064
14 AWD coupler stub shaft 0.980 1.01E-03
15 oval head countersunk screw, torx for stub shaft (0.02 ea.) 4 0.080
16 AWD coupler assembly Steel/Mix 5.014 9.77E-03
17 race bearing, AWD coupler output 0.094 6.19E-05
18 AWD coupler coil Syn/Mix 0.272
19 AWD coupler yoke 0.392
20 AWD coupler snap ring 0.004
21 button screw, torx for AWD coupler yoke (0.004 ea.) 3 0.012
22 pinion gear 1.656 6.28E-04
23 seal, for pinion gear Syn 0.072
24 nut, for pinion gear 0.050
25 inner ball bearing for pinion gear 0.204 5.18E-05
26 outer ball bearing for pinion gear 0.234 5.94E-05
27 crush sleeve 0.046 1.50E-05
28 cover, for differential housing Al 1.888
29 Large hexagon flange screw for cover (0.074 ea.) 4 0.296
30 small hexagon flange screw for cover (0.002 ea.) 5 0.100
31 drain plug for cover 0.026
32 ring gear 1.840 6.79E-03
33 hexagon flange screw, for ring gear (0.022 ea.) 10 0.220 9.50E-04
34 differential case 3.134 5.05E-03
35 tapered bearing v2 side of differential case 0.230 1.06E-04
83 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub. – lubricant, no indication - steel
144
36 tapered bearing v4 side of differential case 0.230 1.06E-04
37 shim side gear V2 side 0.012
38 side gear 0.228 8.57E-05
39 shim side gear V4 side 0.012
40 side gear 0.228 8.57E-05
41 shim pinion gear V1 side 0.004
42 pinion gear 0.114 6.57E-05
43 shim pinion gear V3 side 0.004
44 pinion gear 0.114 6.57E-05
45 differential pinion gear cross shaft 0.140 1.03E-04
46 Half shaft seal, V2 side 0.094
47 inner half shaft race cup V2 side 0.126
48 shim for inner half shaft race cup V2 side 0.078
49 Half shaft seal, V4 side 0.096
50 inner half shaft race cup V4 side 0.126
51 shim for inner half shaft race cup V4 side 0.074
52 Lubricant, main case (440 ml) Lub. 0.366 Table 5-5: Ford Fusion Rear Drive Module, Bill of Material rotating parts [input]/[output]
145
Figure 5-13: Ford Fusion Rear Drive Module - Parts
146
Figure 5-14: Ford Fusion Rear Drive Module
Figure 5-15: Ford Fusion Rear Axle Differential Assembly
147
Figure 5-16: Ford Fusion Rear Axle Assembly: Pinion in the Center Part [1] of the 3-piece Housing
Figure 5-17: Ford Fusion AWD Coupler Assembly
148
5.1.4.1 Ford Fusion AWD Coupler
Ford Fusion AWD Coupler – Bill of Materials
ID Part Name Material84 Qty Mass
kg
1 Input case Al 0.978
2 Rear housing 1.410
3 O-ring cover Syn 0.002
4 retainer clip for inside parts 0.010
5 output shaft 0.670
6 retainer clip for race bearing bottom 0.002
7 race bearing for bottom of shaft 0.106
8 shim for top race bearing 0.008
9 race bearing for top 0.016
10 control cam 0.074
11 cam balls (0.002 ea.) 6 0.012
12 control clutch reaction plates (0.026 ea.) 2 0.052
13 control clutch friction plate 0.022
14 Armature 0.160
15 Main cam 0.282
16 Friction plates (0.038 ea.) 12 0.456
17 Reaction plates (0.046 ea.) 12 0.552
18 Lubricant, coupler (170 ml) Lub. 0.124 Table 5-6: Ford Fusion AWD Coupler, Bill of Materials85 rotating parts [input]/[output]
84 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 85 Inertias included in RDM BoM
149
Figure 5-18: Ford Fusion AWD Coupler, Control Clutch and Ball Ramp Mechanism
Figure 5-19: Ford Fusion AWD Coupler, Input Case
150
Figure 5-20: Ford Fusion AWD Coupler Control Clutch Plates
Figure 5-21: Ford Fusion Main Clutch Plates
151
Figure 5-22: Ford Fusion AWD Coupler - Parts
152
5.1.5 Mass & Rotational inertia Analysis
Figure 5-23: Ford Fusion AWD Mass Analysis86/87
Ford Fusion AWD adds 72 kg or 4.5% to the 2WD base vehicle. Figure 5-23 on the right
hand side indicates contribution of the added parts. Equivalent mass based on
rotational inertias and gear ratios is shown in Figure 5-24 below.
Figure 5-24: Ford Fusion Equivalent Mass Analysis
86 Source: Vehicle mass: Dealer website, AWD components measured 87 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements etc.)
153
Table 5-7: Ford Fusion Mass Distribution Analysis
The front axle carries 12.55 kg more mass on top of the added AWD components
(category ‘other’), most likely due to variations in driveline components (Transmission
and front drive shafts).
Most of the AWD rear axle mass increase over FWD is due to the added AWD
components
88 Reported mass of TC FWD/AWD model variants 89 AWD components measurements 90 Split 50/50 between front and rear 91 The category ‘other’ represents the difference in mass between the FWD model plus added AWD parts and the AWD model
Mass [kg]
Total front rear
FWD88 1612 956 656
AW
D
add
ed
par
ts8
9 PTU 12.2 12.2
Propshaft90 8.5 4.25 4.25
RDM 26.1 26.1
Halfshafts 12.0 12.0
Other91 13.2 12.55 0.65
AWD110 1684 985 699
154
5.1.6 Design Analysis
5.1.6.1 Power Transfer Unit (PTU)
The vehicle has a very compact and lightweight single shaft PTU. The ring gear on the
input shaft is laser welded as shown in the pictures below. This design feature saves
more than 1 kg in structural mass compared to a bolt-on solution.
Figure 5-25: Ford Fusion PTU Laser Welded Ring Gear
155
5.1.6.2 Rear Drive Module (RDM)
The RDM has a three piece housing with a rarely seen axial split line as shown in Figure
5-26.
The picture also shows the ring gear that is bolted to the differential case. This design is
heavier than laser welded solutions and requires a more complex assembly process. The
unit shown below carries the same torque as the one in Figure 5-25. More material is
required on the back side of the ring gear to provide sufficient thread depth for the ring
gear bolts.
The differential bearings are conventional tapered roller bearings.
Figure 5-26: Ford Fusion Rear Axle Differential
156
Figure 5-27 shows the rear axle pinion. The pinion bearings are a pair of high efficiency
tandem ball bearings (only one shown here). Preload is determined by the size of the
crush sleeve between the bearings, which is a more cost efficient and robust design
compared to shimming.
Figure 5-27: Ford Fusion Rear Axle Pinion with High Efficiency Tandem Ball Bearings
5.1.6.3 AWD Coupler
The Ford Fusion AWD coupler is a cost effective, completely sealed unit with very little
lubricant content and limited external cooling. The advantage of compact size may be
offset by making thermal management difficult because of lack of heat sink capacity and
cooling circuit.
The unit input case that holds the outer multi plate clutch elements (Figure 5-28 is made
from aluminum for mass saving, with a steel flange bolted to it on the input side to
provide the necessary torque capacity. The rear housing is threaded and permanently
secured by pins. The advantage of the electro-magnetic actuator is that there is no active
mechanical element outside the coupler housing.
157
Figure 5-28: Ford Fusion AWD coupler - Input Case Detail
158
5.2 Jeep Cherokee
5.2.1 AWD Technology
The Jeep Cherokee AWD system is a front wheel drive based on-demand system with an
active parallel AWD coupler in the Rear Drive Module (RDM). The coupler is electro-
hydraulically activated and controlled via remote AWD Electronic Control Unit (ECU). It
also features a driveline disconnect system.
5.2.1.1 AWD Coupler
Figure 5-29 shows the hydraulic system schematics: An electro-hydraulic actuator
(basically a hydraulic pump driven by an electric motor) pressurizes the high pressure
circuit and activates the piston in the hydraulic module.
Figure 5-29: Jeep Cherokee AWD Hydraulic System
159
The Cherokee coupler is completely integrated in the RDM as a result of the unique
architecture. Lubrication circuits are separated by a sealed hydraulic system body and
cover on the right hand side of the RDM (see Figure 5-30). The parallel arrangement
requires the AWD coupler to carry full axle torque, which subsequently increases the
size of the multi plate clutch.
The AWD coupler acts also as the rear disconnect device and is responsible for
synchronizing the driveline during the AWD reengagement process.
Torque is transferred through the transfer shaft into the differential cage and is split
between left and right in the differential.
Figure 5-30: Jeep Cherokee AWD Coupler92
92 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013
160
5.2.1.2 Disconnect System
The system consists of the electro-mechanically activated PTU disconnect (see also
Figure 5-35) and the electro-hydraulically activated AWD coupler in the RDM. In 2WD
mode the entire rear driveline between the two hypoid sets, including the hypoids, is at
standstill.
Engagement/disengagement is controlled by the electronic control unit (ECU). ECU
algorithms are networking with vehicle sensors and controls (e.g. ABS, brake traction
control or vehicle dynamic controls).
At low speeds AWD is always engaged to be ready for high acceleration in 1st gear. The
disengagement sequence proceeds as follows:
1) Disengage AWD coupler to relieve driveline torque
2) Disengage shift sleeve in the PTU
3) AWD coupler goes into low drag mode to allow the driveline to come to a
complete standstill
In case the control system senses the need to reengage, the order of actions is reversed:
1) The AWD coupler engages very dynamically to synchronize the driveline to
match speed on both sides of the shift clutch in the PTU
2) As soon as synchronization speed is established the shift sleeve is activated
and connects the input shaft with the primary shaft (Figure 5-31). Small
speed differences at the shift sleeve can be tolerated without creating noise
or structural problems. The reconnect process takes normally about 300
milliseconds.
Figure 5-31: Jeep Cherokee PTU Disconnect Cross-section, Shift Fork Actuator Module on the Right
161
The added mass for the Jeep Cherokee disconnect system is 0.6 kg in the PTU and 8.6
kg93 for the RDM. However, the RDM includes mass to accommodate a potential low
gear option. Disconnect without that option could be achieved at much lower mass.
Basic AWD torque control follows the example shown in section 5.1.1 for the Ford
system.
5.2.2 Power Transfer Unit (PTU)
Mass94 [kg] 22.6
BoM mass summation (% difference) [kg] 22.4 (0.9%)
Lubricant main95 [L] 0.7
Gear tooth count (helical1/helical2, ring/pinion) 38/33 29/13
Gear ratio (helical1/helical2, ring/pinion, total) 1.152 / 2.231 /2.570
Gear manufacturing process Hobbed/lapped
Mass of rotating parts [kg] 11.008
Total rotational inertia input shaft [kg.m2] 4.36e-03
Total rotational inertia secondary shaft [kg.m2] 6.42e-03
Total rotational inertia output shaft [kg.m2] 7.16e-04
Dynamic tire radius [m] 0.362
Equivalent mass of rotational inertias [kg] 0.134
Equivalent mass factor 1.006 Table 5-8: Jeep Cherokee Power Transfer Unit – Technical Data
93 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013 94 As received, includes lubricant 95 Nominal, per service information
162
Figure 5-32: Jeep Cherokee Power Transfer Unit96
Figure 5-32 shows a cross section of the single speed PTU for the standard version,
viewed from the front. The input from the transmission is via the hollow input shaft that
carries the front axle disconnect shift sleeve. A helical gear set drives the secondary
shaft that carries the hypoid ring gear. The hypoid pinion gear drives the propshaft to
the rear axle.
Note: The front axle intermediate shaft connects the front differential side gear (not
shown) to the right hand front wheel and is not part of the AWD system.
Jeep Cherokee Power Transfer Unit – Bill of Materials
ID Part Name Mat'l97 Qty Mass Rotational
inertia
kg Kg.m2
1 PTU Body; with inner & outer race cups for output Al 4.890
2 screw, short 6 point with shoulder 0.004
2 screw, long 6 point with shoulder (0.008 ea.) 3 0.024
3 shift module Steel/Mix 0.930
4 c-clip, output pinion V3 side 0.002
5 deflector , output V3 0.092 0.00E+00
96 AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013 97 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel
163
5 seal, output V3 Syn/Mix 0.054
6 O-ring, output V3 0.000
7 cover, V4 side Al 2.348
8 fill plug 0.044
9 flat ring seal Syn/Mix 0.010
10 seal, in cover Syn/Mix 0.014
11 screw, 6 point flange & washer for cover (0.016 ea.) 12 0.192
12 pinion gear with portion of tapered race bearing 1.736 5.35E-04
13 inner tapered race bearing pieces for pinion98 0.142 7.04E-05
14 outer race bearing for pinion 0.230 8.54E-05
15 sleeve shim for pinion 0.032
16 nut to pinion 0.640 2.51E-05
17 intermediate shaft99 1.714 2.50E-04
18 retaining clip V2 side drive 0.002
19 1st retaining clip v4 side drive 0.016
20 2nd retaining clip v4 side drive 0.004
21 Intermediate shaft output bearing (sealed)99 0.180 9.87E-05
22 ring gear assembly with pinion intermediate gear 3.778 6.18E-03
23 shim v2 side ring gear 0.006
24 race cup v2 side ring gear 0.064
25 tapered race bearing v2 side ring gear 0.128 7.20E-05
26 shim v4 side ring gear 0.008
27 race cup v4 side ring gear 0.108
28 tapered race bearing v4 side ring gear 0.260 1.66E-04
29 Primary shaft 2.698 3.28E-03
30 race cup v2 side shift intermediate gear 0.112
31 tapered race bearing v2 side shift intermediate gear 0.190 1.69E-04
32 shim for cup v4 side shift intermediate gear 0.010
33 race cup v4 side shift intermediate gear 0.108
34 tapered race bearing v4 side shift intermediate gear 0.262 1.66E-04
35 shift gear 0.624 3.56E-04
36 shift gear sleeve 0.240 3.45E-04
37 shift gear race bearing 0.080 4.00E-05
38 shift gear seal Syn/Mix 0.018
39 Lubricant (540 ml) Lub. 0.430 Table 5-9: Jeep Cherokee Power Transfer Unit, Bill of Material rotating parts [input]/intermediate/[output]
98 All tapered roller bearings w/o cup 99 Not part of AWD driveline
164
Figure 5-33: Jeep Cherokee Power Transfer Unit - Parts
165
Figure 5-34: Jeep Cherokee PTU Assembly, Shift Actuator (black)
Figure 5-35: Jeep Cherokee PTU, View of Input Shaft and Primary Shaft (w/ Shift Sleeve, Actuator Removed)
166
Figure 5-36: Jeep Cherokee PTU, View of Helical Gear Stage, Primary Shaft (large) and Secondary Shaft (small)
Figure 5-37: Jeep Cherokee PTU, Primary Shaft (left) and Secondary Shaft (right)
167
Figure 5-38: Jeep Cherokee PTU, Pinion
5.2.3 Propshaft & Axles100
Propshaft
Mass [kg] 13.1
Total rotational inertia [kg.m2] 1.043e-02
Equivalent mass [kg] 0.595
Equivalent mass factor 1.045
Left Axle Shaft
Mass [kg] 8.3
Total rotational inertia [kg.m2] 7.184e-03
Equivalent mass [kg] 0.055
Equivalent mass factor 1.007
Right Axle Shaft
Mass [kg] 8.5
Total rotational inertia [kg.m2] 7.167e-03
Equivalent mass [kg] .055
Equivalent mass factor 1.007 Table 5-10: Jeep Cherokee Propshaft/Axle Technical Data
100 Inertias and equivalent mass are estimates based on mass and design features
168
5.2.4 Rear Drive Module (RDM)
Mass101 [kg] 33.1
BoM mass summation (% difference) [kg] 32.9 (0.7%)
Lubricant, main case102 [L] 0.8
Lubricant, AWD coupler [L] 0.4
Gear tooth count (ring/pinion) 41/15
Gear ratio 2.733
Gear manufacturing process Hobbed/lapped
Mass of rotating parts [kg] 19.2
Total rotational inertia input shaft [kg.m2] 2.07e-03
Total rotational inertia output shaft [kg.m2] 3.59e-02
Dynamic tire radius [m] 0.362
Equivalent mass of rotational inertias [kg] 0.392
Equivalent mass factor 1.012 Table 5-11: Jeep Cherokee Rear Drive Module – Technical Data
Figure 5-39: Jeep Cherokee Rear Drive Module
101 As received, Includes lubricant 102 Nominal, per service information
169
Figure 5-39 shows a cross section of the single speed RDM. The pinion drives the hypoid
ring gear, and via a spline connection the inner friction plate carrier of the TTD. The
actuator provides hydraulic pressure to modulate torque transfer in the TTD. The outer
friction plate carrier is driving the rear axle differential via hollow shaft.
The TTD acts as the rear axle disconnect. By opening the gaps between the friction
plates wide enough it reduces drag in the clutch pack and allows the secondary driveline
to come to a complete standstill while the vehicle is driving at speed.
Jeep Cherokee Rear Drive Module – Bill of Materials
ID Part Name Mat'l103 Qty Mass
Rotational inertia
kg Kg.m2
1 RDM housing Al 5.270
2 housing fill plug 0.046
3 input flange 1.028 1.18E-03
4 input coupler nut 0.052 1.70E-05
5 input coupler washer 0.018 0.00E+00
5 input flinger 0.090 1.08E-04
6 seal, input coupler Syn/Mix 0.042
7 cap screw, Allen for oil reservoir cover (0.003 ea.) 4 0.012
8 oil reservoir cover Syn/Mix 0.202
9 oil reservoir gasket Syn 0.020
10 cap screw, Allen for pump assembly 0.018
11 actuator assembly Steel/Mix 1.200
12 pinion 1.420 4.28E-04
13 shim for inner bearing pinion gear 0.004
14 Inner tapered roller bearing for pinion104 0.232 7.31E-05
15 Outer tapered roller bearing for pinion 0.208 6.55E-05
16 crush sleeve 0.092 3.12E-05
17 clutch cover Al 1.522
18 hexagon flange screw for cover (0.005 ea.) 9 0.450
19 hexagon flange screw for cover (o.032 ea.) 2 0.640
20 output flinger 0.060 1.08E-04
21 seal V4 output Syn/Mix 0.040
103 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 104 All tapered roller bearings w/o cup
170
22 V4 output O-ring Syn 0.000
23 V4 output shaft c-clip 0.002
24 Hydraulic system body Al 2.970
25 oil pressure sensor 0.020
26 oil pressure port plug, torx #30 0.004
27 drain plug under pump 0.014
28 drain plug above pump 0.014
29 shim, for clutch body race cup 0.010
330 race cup, for clutch body 0.112
31 Tapered roller bearing, for ring gear 0.190 1.75E-04
32 hexagon flange screw, for clutch body (0.032 ea.) 4 0.128
33 seal , flat ring ; between housing and clutch housing Syn/Mix 0.012
34 output shaft, V4 1.940 2.43E-04
35 transfer shaft 1.222 4.82E-04
36 ball bearing, for transfer shaft 0.248 1.09E-04
37 clutch thrust bearing 0.172 6.91E-04
38 clutch thrust bearing 0.172 6.91E-04
39 clutch assembly
39.1 Clutch Cage 1.708 8.10E-03
39.2 Clutch plates 1.610 8.18E-03
39.3 Hub 0.760 1.56E-03
39.4 Retaining ring105 0.00E00
39.5 Springs106 3 0.00E00
40 ring gear 4.128 1.18E-02
41 V4 output shaft c-clip, inside 0.002
42 inside c-clip, v2 shaft 0.002
43 outside c-clip, v2 shaft 0.002
44 O-ring V2 side Syn 0.000
45 v2 output shaft 0.850 1.26E-04
46 Housing insert Al 0.312
47 shim, inside plate 0.008
48 race cup, inside plate 0.112
49 tapered roller bearing, ring gear 0.188 1.75E-04
50 retainer clip output V2 side 0.002
51 seal, output V2 side 0.040
52 output flinger 0.060 1.08E-04
53 retainer clip for differential bearing V2 side 0.004
54 race bearing for differential V2 side 0.106 3.00E-05
105 Included in clutch pack 106 Included in cage
171
55 differential case 1.812 2.10E-03
56 shim side gear V2 side 0.006 0.00E+00
57 side gear 0.220 1.23E-04
58 shim side gear V4 side 0.006 0.00E+00
59 side gear 0.218 1.23E-04
60 shim pinion gear V1 side 0.004 0.00E+00
61 differential pinion 0.106 5.07E-04
62 shim pinion gear V3 side 0.004 0.00E+00
63 differential pinion 0.106 5.07E-04
64 differential small gear pin & c-clip 0.162 1.28E-04
65 Lubricant, main case (400 ml) Lub. 0.314
66 Lubricant, AWD coupler (140 ml) Lub. 0.102
Table 5-12: Jeep Cherokee Rear Drive Module, Bill of Materials rotating parts [input]/[output]
172
Figure 5-40: Jeep Cherokee Rear Drive Module - Parts
173
Figure 5-41: Jeep Cherokee RDM, Top View with Actuator and Oil Reservoir Cover
Figure 5-42: Jeep Cherokee RDM, Hydraulic System Body with Ring Gear and Clutch Pack
174
Figure 5-43: Jeep Cherokee RDM, Pinion with inner TRB and Crush Sleeve
Figure 5-44: Jeep Cherokee RDM, Ring Gear
175
Figure 5-45: Transfer Shaft with Ball Bearing
Figure 5-46: Jeep Cherokee RDM, Differential
176
5.2.4.1 Jeep Cherokee AWD Coupler
Figure 5-47: Jeep Cherokee AWD Coupler107 - Parts
107 Parts list included in main BoM
177
Figure 5-48: Jeep Cherokee Clutch Assembly, Hydraulic System Body, and Transfer Shaft Ball Bearing
Figure 5-49: Jeep Cherokee AWD Coupler, Outer (left) and Inner (right) Plate, Reaction Side
178
Figure 5-50: Jeep Cherokee RDM, Outer (left) and Inner (right) Plate, Friction Side
179
5.2.5 Mass & Rotational inertia Analysis
Figure 5-51: Jeep Cherokee Mass Analysis108/109
Jeep Cherokee AWD adds 135 kg or 8.1% to the 2WD base vehicle. Figure 5-51 on the right hand side indicates the contribution of the added parts. Equivalent mass based on rotational inertias and gear ratios is shown in Figure 5-52.
Figure 5-52: Jeep Cherokee Equivalent Mass Analysis
108 Source: Vehicle mass: Dealer website, AWD components measured 109 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements, etc.)
180
Table 5-13: Jeep Cherokee Mass Distribution Analysis
Table 5-13 shows a comparison of FWD and AWD vehicle mass distribution between
front and rear.
The negative value in the category ‘other’ for the front axle load represents FWD parts
taken off and replaced by AWD parts (transmission cover, intermediate shaft etc.) and
minor design changes to the front structure.
The AWD rear axle carries 56.6 kg more structural mass than FWD (category ‘other’),
representing rear axle subframe and suspension changes and structural reinforcements
to the body.
110 Reported mass of TC FWD/AWD model variants 111 AWD components measurements 112 Split 50/50 between front and rear 113 The category ‘other’ represents the difference in mass between the FWD model plus added AWD parts and the AWD model
Mass [kg]
Total front rear
FWD110 1677 998 679
AW
D
add
ed
par
ts1
11 PTU 22.6 22.6
Propshaft112 13.1 6.55 6.55
RDM 33.1 33.1
Halfshafts 16.8 16.8
Other113 49.4 -7.15 56.55
AWD110 1812 1020 792
181
5.2.6 Design Analysis
5.2.6.1 Power Transfer Unit
The PTU is a two shaft design, most likely driven by packaging constraints, that adds
mass to the overall drivetrain.
The ring gear on the secondary shaft is laser welded, as shown in Figure 5-53.
Figure 5-53: Jeep Cherokee PTU, Laser Welded Ring Gear
182
5.2.6.2 Rear drive Module
The RDM features a laser welded ring gear with the weld seam very close to the outside
diameter of the ring gear, which is beneficial from a structural perspective (Figure 5-54).
Figure 5-54: Jeep Cherokee RDM Ring Gear Laser Weld
The hydraulic system body has a built-in strainer that eliminates the need for an
external oil filter, as shown in Figure 5-55.
Figure 5-55: Jeep Cherokee Hydraulic System Body with Integrated Strainer
183
5.2.6.3 AWD Coupler
The AWD coupler is very efficiently designed as a module, with a pre-assembled multi
plate clutch assembly that plugs right into the hydraulic body (Figure 5-56).
Figure 5-56: Jeep Cherokee AWD Clutch Assembly
The Jeep Cherokee coupler features a unique clutch plate design with every plate
carrying friction material on one side and acting as a smooth reaction plate on the other
side, as shown in Figure 5-57. This design may improve the performance of the multi
plate clutch pack as a heat sink and help with peak temperature management.
The clutch plates also have an approximately 50% larger diameter, compared to Ford
Fusion and VW Tiguan, to carry the design axle torque and allow for geometrical
integration.
184
Figure 5-57: Jeep Cherokee AWD Inner and Outer Clutch Plates, Friction Side on the left, Reaction side on the right
185
5.3 Volkswagen Tiguan
5.3.1 AWD Technology
The Volkswagen Tiguan AWD system is a front wheel drive based on-demand system
with an active in-line AWD coupler in the Rear Drive Module (RDM). The coupler is
electro-hydraulically activated and controlled via integrated AWD Electronic Control
Unit (ECU). It does not have a driveline disconnect system.
Figure 5-58: Volkswagen Tiguan / Haldex Gen IV Hydraulic System
Figure 5-58 shows the hydraulic system schematics: An electrically driven axial piston
pump draws oil from a reservoir and delivers it into the high pressure system. An
accumulator stores energy and a check valve prevents high pressure from bleeding back
into the reservoir when the pump is not running.
A solenoid controlled by the AWD ECU is proportioning the pressure delivered to the
multi plate clutch according to the torque level requested by the control algorithms.
186
The systems described above are combined into an add-on module to the RDM. Tight
packaging is shown in Figure 5-59.
Figure 5-59: Volkswagen Tiguan AWD Coupler – Haldex Gen IV114
The AWD coupler module is produced by BorgWarner under the Haldex brand (Haldex
Gen IV). For model year 2017 Tiguan Volkswagen is moving to a Gen V system, which
basically eliminates the accumulator and the solenoid but has the same functionality. In
Gen V the clutch pressure is controlled via a patented combination of an axial piston
pump and a unique ‘centrifugal pressure control valve’.115 Cost and mass savings have
been achieved with the transition to the Gen V system.
Basic AWD torque control follows the example shown in section 5.1.1 for the Ford
system.
114 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf 115 https://www.youtube.com/watch?v=CDRVTjMPK9Q
187
5.3.2 Power Transfer Unit (PTU)
Mass116 [kg] 17.5
BoM mass summation (% difference) [kg] 17.1 (2.1%)
Lubricant117 [L] 0.9
Gear tooth count (ring/pinion) 27/17
Gear ratio 1.588
Gear manufacturing process Face milled/ground
Mass of rotating parts [kg] 9.966
Total rotational inertia input shaft [kg.m2] 9.20e-03
Total rotational inertia output shaft [kg.m2] 3.40e-03
Dynamic tire radius [m] 0.343
Equivalent mass of rotational inertias [kg] 0.151
Equivalent mass factor 1.009
Table 5-14: Volkswagen Tiguan Power Transfer Unit – Technical Data
Figure 5-60: Volkswagen Tiguan Power Transfer Unit118
116 Includes lubricant 117 Nominal, per service information 118 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf
188
Table 5-15: Volkswagen Tiguan Power Transfer Unit, Bill of Material rotating parts [input]/[output]
119 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 120 Not part of the AWD drivetrain 121 Mass included in PTU housing
Volkswagen Tiguan Power Transfer Unit – Bill of Materials
ID Part Name Mat'l119 Qty Mass Rotational
inertia
kg Kg.m2
1 PTU housing Al 3.920
2 Bolt, hex hd with shoulder (0.009 ea.) 4 0.036
3 seal Syn/Mix 0.050
4 seal bolt (combination) (0.004 ea.) 2 0.008
5 double collared stud 0.046
6 cap for transmission breather Syn
7 sealing cap Syn
8 seal G Syn/Mix 0.014
9 seal Syn/Mix 0.038
10 O-ring Syn 0.000
11 cover Al 0.586
12 Screw, hex. Hd. (0.003 ea.) 6 0.018
13 seal Syn/Mix 0.022
14 flange 0.798 9.54E-04
15 hex nut 0.066 1.70E-05
16 Intermediate shaft120 1.702
17 lock ring 0.000
18 O-ring Syn 0.000
19 needle sleeve 0.026
20 needle sleeve 0.026
21 circlip 0.000
22 lock ring 0.000
23 V4 side cover Al 1.636
24 O-ring for V4 side cover Syn 0.000
25 65 mm hex nut 0.144 1.20E-04
26 outer shim V4 side 0.030
27 outer bearing V4 0.254 1.60E-04
28 inner bearing V4 0.254 1.60E-04
29 Hollow shaft with ring gear 4.044 8.76E-03
30 output pinion gear 2.344 2.27E-03
31 outer shim for pinion 0.016
32 pinion tail bearing 0.200 1.10E-04
33 pinion head bearing 0.160 5.18E-05
34 Pinion nose bearing121 3.00E-05
35 Lubricant (850 ml) Lub. 0.704
189
Figure 5-61: Volkswagen Tiguan Power Transfer Unit - Parts
190
Figure 5-62: VW Tiguan PTU, Top View
Figure 5-63: VW Tiguan Ring Gear (left) and Pinion (right)
191
5.3.3 Propshaft & Axles122
Propshaft
Mass [kg] 11.4
Total rotational inertia [kg.m2] 9.083e-03
Equivalent mass [kg] 0.195
Equivalent mass factor 1.017
Left Axle Shaft
Mass [kg] 6.2
Total rotational inertia [kg.m2] 5.358e-03
Equivalent mass [kg] 0.046
Equivalent mass factor 1.007
Right Axle Shaft
Mass [kg] 6.4
Total rotational inertia [kg.m2] 5.501e-03
Equivalent mass [kg] 0.047
Equivalent mass factor 1.007
Table 5-16: Volkswagen Tiguan Propshaft/Axle Technical Data
122 Inertias and equivalent mass are estimates based on mass and design features
192
5.3.4 Rear Drive Module (RDM)
Mass123 [kg] 35.6
BoM mass summation (% difference) [kg] 35.3 (0.9%)
Lubricant main124 [L] 0.9
Lubricant coupler [L] 0.7
Gear tooth count (ring/pinion) 27/17
Gear ratio 1.588
Gear manufacturing process Face milled/ground
Mass of rotating parts [kg] 19.946
Total rotational inertia input shaft [kg.m2] 7.77e-03
Total rotational inertia output shaft [kg.m2] 1.36e-02
Dynamic tire radius [m] 0.343
Equivalent mass of rotational inertias [kg] 0.282
Equivalent mass factor 1.008 Table 5-17: Volkswagen Tiguan Rear Drive Module – Technical Data
Figure 5-64: Volkswagen Tiguan Rear drive Module125
123 Includes lubricant 124 Nominal, per service information 125 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf
193
Table 5-18: Volkswagen Tiguan Rear Drive Module, Bill of Materials rotating parts [input]/[output]
126 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel
Volkswagen Tiguan Rear Drive Module – Bill of Materials
ID Part Name Mat'l126 Qty Mass Rotational
inertia
kg Kg.m2
1 RDM housing Al 8.308
2 housing drain screw 0.026
3 input flange 0.560 6.52E-04
4 input flange nut 0.040 0.00E+00
5 input flinger Syn 0.020 0.00E+00
6 hex flange bolt for module (0.008 ea.) 2 0.016
7 AWD control module Syn/Mix 0.204
8 Actuator Steel/Mix 1.000
9 hex flange bolt for pump 0.008
9 hex flange bolt for pump 0.008
10 clutch assembly 4.832 4.58E-03
11 hexagon flange screw (0.044 ea.) 4 0.176
12 retain clip for outer bearing pinion gear 0.008
13 shim for outer bearing pinion gear 0.030
14 Outer tapered roller bearing for pinion127 0.164 6.12E-05
15 Inner tapered roller bearing for pinion 0.388 2.21E-04
16 pinion gear 3.408 2.26E-03
17 RDM cover Al 3.524
18 drain plug for cover (0.008 ea.) 3 0.024
19 Screw, hex. hd. for cover (0.036 ea.) 12 0.432
20 output flange V2 side with c-clip 1.218 1.12E-03
21 seal V2 side Syn/Mix 0.030
22 outer tapered bearing V2 side 0.286 2.18E-04
23 output flange V4 side with c-clip 1.888 1.58E-03
24 seal V4 side Syn/Mix 0.030
25 outer tapered bearing V4 side 0.198 1.08E-04
26 differential case w ring gear 5.578 9.66E-03
27 differential inner gear shim 0.018
28 side gear 0.418 2.19E-04
29 side gear 0.418 2.19E-04
30 differential pinion 0.156 1.00E-04
31 differential pinion 0.156 1.00E-04
32 differential cross shaft 0.218 2.33E-04
33 shear pin for differential small gear pin 0.000
34 Lubricant main case (840 ml) Lub. 0.698
35 Lubricant AWD Coupler (1000 ml) Lub. 0.792
194
Figure 5-65: Volkswagen Tiguan Rear Drive Module - Parts
127 All tapered roller bearings w/o cup
195
Figure 5-66: VW Tiguan RDM, Top View
Figure 5-67: VW Tiguan Ring Gear (left) and Pinion (right)
Parting line
196
Figure 5-68: VW Tiguan RDM, AWD Coupler Module with Multi Plate Clutch Assembly and Actuator
5.3.4.1 AWD Coupler
Volkswagen Tiguan AWD Coupler – Bill of Materials
ID Part Name Qty Mass
kg
1 housing 1.330
2 seal 0.018
3 retainer clip 0.008
4 thrust bearing housing side 0.094
5 thrust bearing plate holder side 0.094
6 Hub 1.030
7 ball bearing gear shaft 0.110
8 cage 0.886
9 Thrust plate128 0.152
10 friction plate (0.05 ea.) 13 0.650
11 reaction plate (0.034 ea.) 12 0.408 Table 5-19: Volkswagen Tiguan AWD Coupler rotating parts [input]/[output]
128 End side thrust plate same size as reaction plates
197
Figure 5-69: Volkswagen Tiguan AWD Coupler129/130
129 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf 130 Piston and spring plate are part of the housing and are not listed in the coupler BoM
198
Figure 5-70: Volkswagen Tiguan AWD Coupler - Parts
Figure 5-71: VW Tiguan AWD Coupler Assembly
199
Figure 5-72: VW Tiguan AWD Coupler, Cage (left), Multi Plate Clutch and Hub (right)
200
Figure 5-73: VW Tiguan AWD Coupler, Outer (left) and Inner (right) Plate
201
5.3.5 Mass & Rotational inertia Analysis
Figure 5-74: Volkswagen Tiguan Mass Analysis131/132
VW Tiguan AWD adds 78 kg or 5.0% to the 2WD base vehicle. The right hand image in
Figure 5-74 details mass contributions. Equivalent mass based on rotational inertias and
gear ratios is shown in Figure 5-75 below.
Figure 5-75: Volkswagen Tiguan Equivalent Mass Analysis
131 Source: Vehicle mass: Dealer website, AWD components measured 132 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements, etc.)
202
Table 5-20: Volkswagen Tiguan Mass Distribution Analysis
Except for 0.9 kg all of the added mass is due to AWD driveline components
133 Reported mass of TC FWD/AWD model variants 134 AWD components measurements 135 Split 50/50 between front and rear 136 The category ‘other’ represents the difference in mass between the FWD model plus added AWD parts and the AWD model
Mass [kg]
Total front rear
FWD133 1550 910 640
AW
D
add
ed
par
ts1
34 PTU 17.5 17.5
Propshaft135 11.4 5.7 5.7
RDM 35.6 35.6
Halfshafts 12.6 12.6
Other136 0.9 -1.2 2.1
AWD110 1628 932 696
203
5.3.6 Design Analysis
5.3.6.1 Power Transfer Unit
The VW Tiguan PTU is a single stage unit with a laser welded ring gear, as shown in
Figure 5-76.
Figure 5-76: VW Tiguan PTU – Laser Welded ring Gear
204
5.3.6.2 Rear drive Unit
The Tiguan RDM features a laser welded ring gear.
Figure 5-77: VW Tiguan RDM, Ring Gear/Differential Case Laser Welding
Figure 5-78: VW Tiguan RDM Pinion
The pinion appears to have a unique bearing arrangement. The inner tapered roller bearing is leaning against a thrust bearing on the back side of the pinion to take up axial load. This might aid in reducing parasitic losses due to bearing preload in the pinion setup.
205
5.3.6.3 AWD Coupler
Figure 5-79: VW Tiguan AWD Coupler, Friction and Reaction Plates
The MY 2015 Tiguan has a Haldex Gen IV AWD coupler. Friction plates, as shown in
Figure 5-79, have dual sided sinter metal coated friction plates and smooth reaction
plates.
Figure 5-80: VW Tiguan AWD Coupler Hub
The coupler hub features lubrication paths to aid oil flow through the multi plate clutch
and support thermal management of the AWD system (Figure 5-80).
206
Figure 5-81: VW Tiguan AWD Coupler Cage
The Tiguan AWD coupler cage is a very cost and mass effective net formed steel part
with minimal machining.
207
6 Disconnect System Cost Analysis
Cost analysis in this section is based on Pilot System’s expert knowledge and peer
discussions and is considered directional. No purchasing activities or forensic cost
analyses have been performed.
Production volumes, technology content and market conditions may vary significantly
and lead to different cost structures.
Cost as indicated in this section is considered to be a mix of Direct Manufacturing Cost
(DMC) for parts made in-house by a tier 1 supplier and, where applicable, purchasing
cost for parts and subsystems from a tier 1 supplier perspective. These costs do not
include engineering recovery, initial tooling cost, investment for capital equipment and
tier 1 profit and SG&A. Depending on the percentage of vertical integration for a tier 1
supplier the additional margin can range from 25 – 40 % up to the final selling price to
an OEM. For comparison purpose In the tables below the incremental cost to the OEM
was calculated with 25% cost added to the tier 1 cost.
All costing has been done on an incremental basis compared to an actual or conceptual
non-disconnect system.
208
6.1 Jeep Cherokee
The Jeep Cherokee AWD system has been designed with the intent of adding a low gear
option for the Trailhawk™ version. Due to the FWD based drivetrain the PTU and RDM
architectures had to be capable of supporting the standard version and the addition of a
planetary gear reduction for Trailhawk™.
Figure 6-1: Jeep Cherokee AWD Configuration
Although the PTU cost is not significantly increased, the RDM should be seen as a
compromise between cost and the flexibility of including a low gear option.
Considerable complexity has been added by adopting a parallel RDM architecture rather
than a half-shaft disconnect (see also section 1.3.5). Figure 6-1 shows the driveline
architecture of the Jeep Cherokee Sport (standard version).
There is no non-disconnect version of this drivetrain available, so cost estimates are
based on design assumptions rather than direct comparisons.
Total AWD Disconnect system cost of $150.00 US includes PTU and RDM adaptations. A
cost breakdown is given in the following sections. Although midsize crossover vehicles
are among the best selling vehicles in today’s market, because of the specific
requirements for the low gear option this should not be considered a mainstream
example of an AWD disconnect system.
209
6.1.1 Power Transfer Unit (PTU)
Major changes to the PTU include splitting the primary shaft (into primary and input
shaft) to provide for a disconnect point and adding the shift mechanics/mechatronics
(shift sleeve and smart linear actuator). The case had to be designed to house the
additional elements and allow access for the actuator, as shown in Figure 6-2.
Figure 6-2: Jeep Cherokee PTU, Bottom Front View137
Incremental cost estimates total $86.00 US, with a breakdown shown in Table 6-1. The major cost additions are the shift actuator and mechanism. Additional
mechanical changes and assembly procedure adjustments are minor.
137 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013
210
Jeep Cherokee PTU Component Add/change Cost
Actuator assembly Add smart actuator $ 60
Input shaft / Primary shaft Split up primary shaft, add shift tooth profile & bearing
$ 17
Shift sleeve Add $ 5
Housing Added volume to house disconnect mechanism $ 1
Assembly Added complexity $ 3
Total $ 86
Total cost to OEM $ 107 Table 6-1: Jeep Cherokee AWD Disconnect Incremental Cost estimate – PTU
6.1.2 Rear Drive Module (RDM)
The RDM is designed to accommodate a planetary gear set offering a low gear option. A
parallel coupler arrangement (see also section 1.3.5) has therefore been chosen. In this
RDM architecture the AWD coupler has to carry the entire axle torque (as opposed to
in-line, which carries axle torque divided by the axle ratio, or a half shaft disconnect that
carries only half the axle torque due to balancing across the differential). This requires
significantly increased coupler torque capacity and consequently size.
Additional complexity is added with the ring gear and transfer shafts, as shown in Figure
6-3, and resized ball bearings to accommodate larger shaft diameters and increased
reaction forces.
Estimated incremental cost totals $64.00 US, with a breakdown shown in Table 6-2. Major contributors are the shafts and the increased AWD coupler capacity.
The AWD coupler’s actuation subsystem does not require significant modifications and
therefore contributes only marginally to the cost of the disconnect system.
211
Figure 6-3: Jeep Cherokee RDM138
Jeep Cherokee RDM Component Add/Change Cost
Ring gear shaft Add $ 15
Increased size of AWD coupler
Change, needs full axle torque capacity $ 12
Larger housing for hydraulic system
Change $ 1
Transfer shaft Add, 2 splines, 2 bearing journals, length $ 18
Increase complexity of output shaft
Asymmetrical design $ 8
2 Ball bearings for differential and transfer shaft
Added size compared to in-line design $ 4
Complex assembly process $ 6
Total $ 64
Total cost to OEM $ 80 Table 6-2: Jeep Cherokee AWD Disconnect Incremental Cost estimate - RDM
138 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013
212
6.2 Alternative Disconnect Systems
6.2.1 Side Shaft Disconnect
One very cost efficient RDM option to provide full AWD disconnect capabilities is the
rear half-shaft disconnect as shown in Figure 6-4. The AWD coupler still needs to be
upgraded to half the axle torque (as opposed to an inline coupler that carries only axle
torque divided by the axle ratio). With this solution the differential side gears will spin in
opposite directions, but the ring and pinion as the main contributors to parasitic losses
would be at standstill while the vehicle is in motion and the system is in disconnect
mode.
Total incremental system cost (assuming the use of a Cherokee type PTU disconnect
system) would be $93.00 US.
Figure 6-4: Side Shaft Disconnect, Parallel System in the Background for Comparison
Side Shaft Disconnect Component Add/Change Cost
PTU Disconnect Add 86
Increased size of AWD coupler
Change, needs half axle torque capacity $ 7
Total $ 93
Total cost to OEM $ 116 Table 6-3: AWD Disconnect Incremental Cost Estimate – Side Shaft Disconnect
213
6.2.2 Front Axle Center Disconnect
Front axle center disconnect is used for RWD based vehicles. Frontrunners were the
light duty trucks, with passenger cars following recently. Figure 6-5 shows the system
used in the Chrysler 300 (see also section 1.2.2.5). It basically splits up the left hand half-
shaft between the cross-shaft, as shown in the figure, and the actual half-shaft driving
the LH wheel. A simple shift sleeve solution was chosen, since the AWD coupler in the
transfer case is providing synchronization of the front drivetrain in order to enable
reconnect without driveline clunk or damage to the clutch components. The cross shaft
reaches through the structural engine oil pan to connect with the front axle located on
the RH side of the engine and is part of the original AWD system.
Figure 6-5: Front End Center Disconnect (Chrysler 300)139
The system is very cost effective since the only parts added are the front end disconnect unit and minimal modifications to the transfer case to allow for ‘wide open’ mode to reduce drag in the multi plate clutch. The fact that Chrysler 300 moved from a mechanical center differential transfer case to an on-demand unit was not considered part of the incremental cost since this follows a trend away from permanent AWD to on-demand independently from the increased use of disconnect systems.
139 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems and Warn Industries
214
The cost breakdown is shown in Table 6-4 below. The AWD coupler in the transfer case needs to be adjusted to allow for ‘wide – open’ mode. No significant cost should be expected with that modification.
Front Axle Center Disconnect Component Add/Change Cost
Actuator Add $ 60
Housing Add $ 15
Shaft modifications, shift sleeve, bearing, assembly etc.
Add/modify $ 20
Transfer case modify $ 1
Total $ 97
Total cost to OEM $ 121 Table 6-4: Front End Center Incremental Disconnect Cost Estimate
6.2.3 Others
The dual clutch RDM architecture (as shown in the Range Rover Evoque in section 1.3.5)
has not been included in this cost assessment. The system basically eliminates a
mechanical differential and adds a second clutch, with all cost associated with an active
coupler system. Increased cost compared to a more basic disconnect system may be
offset by added functionality since the pair of clutches provides limited slip capabilities
across the rear axle and some limited torque vectoring. These features are provided in
most vehicles by brake traction control to a comparable level.
215
7 Summary and Conclusions
7.1 AWD/4WD Systems and Components
7.1.1 Current and Future AWD Systems
AWD systems have been classified by SAE in Standard J1952, most recently updated in October 2013. There are three basic types of systems as shown in Table 7-1. Some vehicles also have combinations of the below listed types that are driver
selectable. Trucks and SUVs for example can have a 2WD normal operating mode (2Hi), an on-
demand AWD mode (4AUTO) and with a fully locked transfer case a non-synchro 4WD mode
(4Hi).
Figure 7-1: AWD System Classification per SAE J1952 (Oct 2013) Standard
AWD system architecture is not included in the SAE classification. Figure 7-2 shows a lineup of
characteristic AWD system architectures:
The FWD based systems are by far the most prevalent, mainly because of the dominance of
FWD base vehicles. Added components are the Power Transfer Unit (PTU), the Rear Drive
Module (RDM), propshafts and halfshafts, an Electronic Control Unit (ECU) and modifications to
the rear suspension and subframe.
The RWD based systems are typically found in large and luxury cars and in light trucks and full
size SUVs. Added components are a transfer case, a front axle, the front propshaft, a modified
rear propshaft and an ECU.
Recently some OEMs have introduced a front wheel drive based hybrid AWD system using an
electrical Rear Axle Drive (eRAD). One example is the Volvo XC90, introduced in early 2016. This
Type Synchronization
capable
Longitudinal
speed
differentiation
capable
Longitudinal
torque
distribution
mode
Torque
modulation
System Designation
No No indeterminate n/a PT non-synchro
Yes No indeterminate n/a PT synchro
fixed n/a FT fixed torque
passive FT variable torque passive
active FT variable torque active
passive OD synchro variable torque passive
active OD synchro variable torque active
n/a yes indeterminate activeOD independently powered
variable torque active
Part Time
(PT)
Full Time
(FT)
On-Demand
(OD)
n/a Yesvariable
yes yes variable
216
architecture is currently only a niche product since the added component cost make the vehicle
expensive. Enablers for a more widespread use of hybrid technology would be cost reductions in
components due to higher volumes and advances in battery and power electronics technology,
or a dramatically changed economic environment.
Electric AWD, as introduced by Tesla in their Model S, should be considered exotic at this time.
Further development in the battery sector might pave the way for purely electric propulsion.
Figure 7-2: AWD System Architecture: (1) FWD based; (2) RWD based; (3) FWD based, through the Road PHEV; (4) Electric
1 2 3 4
217
7.1.2 Component and System Function
On-Demand Systems – The Torque Transfer Device (TTD)
The core element in an on-demand driveline is the TTD, also known as AWD coupler. Passive
systems (e.g. viscous couplers, gerotor couplers et.) have been replaced in the past decade with
active systems capable of electronically controlling torque flow between the front and rear axle.
Active units can be of 4 different types with similar functionality:
hydraulic
electro-hydraulic
electro-mechanic
electro-magnetic
The electro-magnetic system is contained in a completely sealed unit and is controlled via a
stationary electric coil. Torque is generated in a control clutch by magnetic flux. A ball cam
mechanism augments the control torque and pressurizes the multi plate clutch to transfer
driveline torque to the axles.
Figure 7-3: Active AWD Coupler Systems: Electro-magnetic (left), Electro-hydraulic (right)140
Due to its modular design and the lack of an active hydraulic system this type of AWD coupler is
very cost effective. However, the small lubricant volume and limited heat exchange make it
challenging to manage the unit’s temperature under demanding driving conditions. The system
reverts to 2WD mode if temperature limits are reached. That makes this type of AWD coupler
more attractive to smaller vehicles without off-road capability.
140 Source: www.borgwarner.com
218
Electro-hydraulic AWD couplers are used in all vehicle segments. They can be sized to handle
high torque and extended use by increasing the lubricant volume and provide extra cooling by
designing oil reservoirs with cooling fins.
Electro-mechanic actuators use a mechanical cam or gear mechanism to apply axial pressure to
a multi plate clutch. Due to packaging constraints this type of actuator is mainly found in
transfer cases. It is very robust and can handle driveline torque levels typically found in light
trucks and SUVs.
Full Time Systems
Full time AWD systems feature a center differential to distribute torque between the front and
rear axle permanently with a preset torque bias. An active or passive locking device may be
added to improve the traction potential of the system.
Full time systems are taking advantage of sophisticated Brake Traction Control (BTC) systems.
BTC offers a very cost effective way of maintaining traction in adverse conditions by using the
brake system and with specific control logics to keep wheel slip within dynamic limits.
AWD Disconnect Systems
Disconnect systems (shown in Figure 7-4 for a FWD based AWD system) have two main
components: the front axle disconnect and an AWD coupler that acts as an axle disconnect
device and also as a synchronizer to allow reengagement while the vehicle is in motion.
Figure 7-4: AWD Disconnect System Schematic
219
The engagement/disengagement sequences are controlled via Electronic Control Unit (ECU) and
in most applications do not require driver intervention (trucks and SUVs are an exception). The
driver can override the controls and dial in continuous on-demand operation. Automatic control
draws information from the vehicle sensors and reacts on vehicle dynamic status and
environmental conditions (e.g. ambient temperature, etc.).
1.1.2 Comparative Assessment of Positives and Negatives
This chapter provides a snapshot of positive and negative effects of vehicle architecture and
AWD system characteristic with respect to efficiency and performance.
The facts & features are color coded for positive or negative effects as follows;
FWD based AWD
RWD based AWD
Very efficient base architecture due to lack of hypoid gears
Not as efficient base architecture as FWD
Secondary drivetrain is very inefficient due to two hypoid sets, high use of AWD drives total efficiency down significantly
Front drivetrain has nearly the same efficiency as rear, permanent use has little negative effect on efficiency
Packaging allows for hybridization by adding an independent electric rear axle
Typically offers more torque capacity
Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline
Table 7-1: FWD/RWD Architecture Positives and Negatives
220
Full Time
On-Demand
Superior vehicle handling potential Handling compromise at low speed if RWD based (torque oversteer)
No torque management devices necessary if used with Brake Traction Control (BTC)
AWD coupler (passive or active) required to manage torque transfer
Proven mechanical torque biasing devices work well with BTC
Electronic Limited Slip Differentials (eLSD) provide additional flexibility
Always transfers torque across at least one less efficient hypoid set
Primary driveline is highly efficient (FWD based vehicles)
Always transfers torque across a less efficient hypoid set (RWD based vehicle)
No downsizing because of permanent torque transfer; driveline sizing needs to account for biasing devices
Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline Driveline sizing based on torque split if
used with BTC only
2WD vehicle dynamics characteristics can be preserved (understeer for FWD, oversteer for RWD)
Table 7-2: Full Time vs. On-Demand AWD Positives and Negatives
221
7.2 AWD Vehicles by Make & Model
7.2.1 The North American AWD Vehicle Market – Overview
In this report all major vehicle manufacturers that offer AWD vehicles in the North
American Market are captured.
Table 7-1 lists the OEMs with their platform structure and number of nameplates.
Table 7-3: AWD Market Overview; AWD Systems per OEM and Number of Platforms/Nameplates141/142
The most prevalent AWD system is the on-demand system with offerings from all OEMs. This
includes FWD and RWD based vehicle architectures, with most of the systems being active
electronic control AWD systems. This type of AWD offers great flexibility in terms of torque bias,
vehicle dynamics, peak and duty cycle torque management, vehicle integration (packaging,
electronic control system etc.) and cost control.
141 Niche vehicles and models with small sales volumes not included 142 (FCA) – Fiat Chrysler Automobili; (GM) – General Motors; (JLR) – Jaguar – Land Rover; (VW) - Volkswagen
Platforms Nameplates Platforms Nameplates Platforms Nameplates
Total 5 9 15 27 57 140
Audi 3 8 2 3
BMW 8 17
Daimler 6 13 1 4
FCA 1 2 1 1 7 11
Ford 1 1 4 16
GM 1 1 8 23
Honda 4 10
Hyundai 2 7
JLR 2 2 3 6
Mazda 3 3
Mitsubishi 1 2
Nissan 6 16
Subaru 1 6
Tesla 1 1
Toyota 2 5 2 2 1 4
VW 1 1 2 3
Volvo 3 8
Part Time Full Time On-Demand
222
The field of full time systems is dominated by Audi and Daimler Benz, both of which rely heavily
on this type. Daimler Benz vehicles are predominantly RWD based, whereas Audi builds on a
longitudinal FWD platform. While Daimler Benz relies solely on BTC, Audi offers a torque
sensitive center differential with asymmetric torque bias to further enhance the tractive
potential and vehicle dynamics.
Audi has just introduced an on-demand system as a replacement for their full time systems. The
extent of this change is not known as of today.
Part time systems, also known as 4WD systems, are mainly found in dedicated off-road vehicles,
like Jeep Wrangler, or work trucks as an entry model. Part time systems require driver
intervention to select the appropriate driving mode. Although they provide great traction they
are not supposed to be driven in 4WD mode on surfaces with high friction coefficients (e.g. dry
pavement).
223
7.2.2 Fuel Consumption and Vehicle Mass Data
Added mass and increased torque and parasitic losses result in an increase of fuel consumption
for AWD vehicles. The following charts are based on EPA’s annually published fuel efficiency
estimates for city, highway and combined cycles. The left hand column shows the increase of
fuel consumption over the added mass from the AWD components. The fact that the data points
are scattered over a broad band indicates that mass is not the only factor for the increase of fuel
consumption, although the trend lines follow a common pattern.
The right hand side shows fuel consumption over total vehicle mass. The trend lines are
comparable with the AWD-only data.
Figure 7-5: Increase of Fuel Consumption over AWD Mass Increase (LH Column of Charts) Compared to the Total Fuel
Consumption over Vehicle Mass for a Selection of AWD Vehicles [the Red Dot Indicates Vehicles with AWD Disconnect]143
143 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites
224
It is interesting to note that vehicles with AWD disconnect (red dotted in the left hand
charts) do not show any improvements over conventional drivetrains. EPA test
procedures capture spin losses in an AWD drivetrain during coastdown; however,
torque related losses in the secondary driveline are not measured. Testing of
electronically controlled AWD systems on a chassis dyno in fully active mode would be
complicated.
7.3 AWD Efficiency Improvement Potentials
The documentation of efficiency improvement potentials was broken down into
System level
Component level
Design
Materials
Manufacturing Process
Advanced engineering/development process
Advanced operating and control strategies The following sections cover the more influential measures to improve driveline efficiency and
performance.
7.3.1 System Level
Architecture
AWD systems have traditionally been seen as add-ons to existing platforms which required
compromises in design and packaging of components. More recent vehicles have been designed
with the AWD option in mind from the beginning and take advantage of simpler, light mass and
more efficient components like a single shaft PTU (see also 3.4.4). The difference between a
single shaft PTU and a 2-shaft PTU can be shown by comparing Ford Fusion and Jeep Cherokee
PTUs:
Jeep Cherokee (2-shaft): 22.6 kg
Discount for disconnect system: 144 -0.6 kg
Ford Fusion (single shaft): 12.20 kg
Net Difference: 9.8 kg
Savings can also be achieved with the integration of the Rear Drive Module (RDM) into the rear
axle subframe.
144 Jeep Cherokee has an AWD disconnect system, which adds 0.6 kg to the base mass of the PTU
225
Disconnect System
The AWD disconnect systems can reduce total fuel consumption by 2.4 – 7%145 depending on
driving conditions. However, a sophisticated, fully automated disconnect strategy is required to
balance fuel efficiency with vehicle dynamics, traction and safety requirements in real-life
driving. Driver override options (‘Sport’, ‘Off-road’, etc.) can further reduce the actual
effectiveness of disconnect systems.
Downsizing
The torque capacity of secondary drivetrains in FWD based AWD vehicles is a major
factor for increased mass and decreased efficiency. The relative amount of torque
required to drive on snowy surfaces is far lower than what is typically provided by the
AWD system. Downsizing therefore provides a high potential for improvements with
minimal impact on overall vehicle performance. Downsizing also reduces drivetrain cost
and, with proper algorithms to manage the duty cycle of the secondary drivetrain, has
no negative effect on strength and durability.
Electric Rear Axle Drive (eRAD)
The eRAD carries probably the biggest potential for reducing overall fuel consumption.
The effectiveness largely depends on the size of the battery in a plug-in hybrid
configuration and the individual mission profile. The system would be most effective in
urban driving with frequent recharging stops.
Sales volumes of the several systems on the market have been disappointing partly
explained by the high price for this type of system.
7.3.2 Component Level and Design
On the component level many small improvements in bearing technology, seals, shaft joints and
lubrication strategies add up to measurable savings in fuel consumption.
Design optimizations on hypoid offset and bearing preload have the potential to further improve
efficiency.
145 http://articles.sae.org/13610/; http://articles.sae.org/13615/; http://papers.sae.org/2015-01-1099/
226
7.3.3 Materials
The material of choice for AWD component housings today is aluminum (Al). As an alternative,
magnesium (Mg) alloys have been proven to provide significant mass savings on housings when
properly designed.146
In the AWD drivetrain transfer cases would be prime candidates and Rear Drive Modules (RDMs)
could be potential candidates for the application of magnesium alloys147. The following example
assumes an average mass savings of 30% compared to an aluminum housing:
Table 7-4: Mass Comparison between Aluminum and Magnesium on an RDM148
Under the above assumptions a mass savings of 2kg, which is 8.1% of the total RDM mass or
0.12% of the total vehicle mass, could be achieved.
Another area of potential improvements is the formulation of lubricants. Friction enhancing
additives can significantly improve parasitic losses, especially at temperatures below the normal
operating range of 90 - 120° C.
7.3.4 Manufacturing Process
Two areas in manufacturing appear to offer a good potential for mass savings and efficiency
improvements:
Aluminum die cast processes have been refined such that very thin walled sections can be cast
in areas with low stress. Vacuum high pressure die casting is an example.
Certain applications allow for squeeze casting, where partially molten aluminum is forced into a
die. The result is a high strength aluminum part with minimal porosity.
On the component side, hypoid manufacturing has been improved: ground (vs. hobbed &
lapped) gears promise advantages in efficiency and noise performance. Coatings and micro
finished surfaces can improve friction parameters and result in highly efficient gear sets.
146 The old Volkswagen Beetle from the 50’s era had an engine block and a transmission housing made from magnesium 147 PTUs have a very high power density and limited external cooling due to the proximity to transmission, engine block and the exhaust system and should not be considered ideal for a conversion to magnesium 148 Estimate only; for accurate results design changes need to be considered
Ford Fusion RDM Component Al Mass [kg] Mg Mass [kg] Savings [kg]
RDM housing 4.096 2.867 1.229
AWD coupler cover 1.064 0.745 0.319
Differential cover 1.888 1.322 0.566
Total 7.048 4.934 2.114
227
7.3.5 Summary of Efficiency Improvement Potentials
The biggest gains in efficiency and mass loss can be achieved on system level:
Highly integrated components (e.g. single shaft PTUs) can reduce system mass
significantly and, as an added benefit, reduce cost and improve driveline
efficiency.
Disconnect systems eliminate AWD driveline parasitic losses during times when
AWD is not needed. Real world efficiency depends highly on the engagement
algorithms and driving conditions.
On the high end, hybrid and electric systems can provide a breakthrough in overall
system efficiency. Vehicle pricing has so far proven prohibitive and widespread
use of this type of vehicles remains dependent on cost reductions and changes in
the economic environment.
228
7.4 Trend Analysis
7.4.1 Technical Trend Analysis in AWD Research and Development
Three major technology trends can be identified:
Actively controlled Multi-Plate Clutches, (MPC)
Active Disconnect Systems, (ADS)
Electric Rear Axle Drives, (eRAD) Actively controlled MPC are the dominant technology in AWD driveline systems. Every OEM in
the North American market offers at least one vehicle platform equipped with this technology.
This type of AWD offers great flexibility in terms of torque bias, vehicle dynamics, peak and duty
cycle torque management, vehicle integration (packaging, electronic control system etc.) and
cost control.
Active AWD disconnect systems are a more recent trend in AWD systems. Driver activated
center axle disconnect devices have been in use in pick-up trucks and full size SUVs for a long
time, preceded by manual locking hubs and similar devices. The current trend favors fully
automated, electronically controlled devices. Their main operating mode is without driver
intervention, although an override option usually exists.
Electric Rear Axle Drives are the latest emerging technology to dramatically improve fuel
economy. Volvo was the most recent entry into the market with the XC90 Hybrid SUV. The
electric rear axle is completely independent from the conventionally powered front axle, and
adds additional power and the ability to recuperate energy during braking. A front end
starter/generator enhances front axle drive efficiency. System cost is currently limiting this
application to luxury vehicles and first adopters as customers.
7.4.2 AWD Market Trend Analysis
Figure 7-6: MY 2015 Driveline Architecture Distribution in NA, All Segments149
149 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data
229
The popularity of CUV/SUV in North America is driving an increase in the adaption of AWD/4WD
systems. About one third of all vehicles sold in North America in 2015 were AWD. The AWD take
rate varies extremely between vehicle segments and equipment levels. Sedans throughout the
segments are the least likely to be sold with an AWD system. In the SUV and pick-up segments
AWD outnumber 2WD drivelines, with the luxury vehicles having the highest take rate in their
respective segments.
Regional differences in the USA are also very distinctive, with northern and rural states having
the largest percentage of AWD vehicles (Figure 7-7). This fact suggests similar Canadian trends.
Figure 7-7: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD150
150 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data
230
7.5 AWD System Teardown Analysis
Three vehicles were selected for AWD component teardown analysis:
Ford Fusion
Jeep Cherokee
Volkswagen Tiguan
All three vehicles have a FWD based AWD system architecture with the AWD coupler
incorporated in the rear drive module as shown in Figure 5-1. One of the vehicles, Jeep
Cherokee, includes an AWD disconnect system.
Figure 7-8: AWD System Architecture
Power Transfer Units (PTU) and Rear drive Modules (RDM) were purchased and disassembled to
a level that did not require destructive methods. The following tables and charts compare
component data and analysis results.
231
7.5.1 Component Data Comparison
151 As received, Includes lubricant 152 Nominal, per service handbook
PTU Ford Jeep VW
Mass151 [kg] 12.2 22.6 17.5
Lubricant152 [L] 0.450 0.700 0.900
Gear tooth count 31/11 38/33 29/13 27/17
Gear ratio 2.818 1.152 + 2.231 /2.735
1.588
Gear cutting process Hobbed / lapped
Hobbed / lapped
Milled / ground
Mass of rotating parts [kg] 7.287 11.008 9.966
Total rotational inertia input shaft
[kg.m2] 9.041e-03 4.36e-03 9.20e-03
Total rotational inertia secondary shaft
6.42e-03
Total rotational inertia output shaft
[kg.m2] 3.48e-03 7.16e-04 3.59e-03
Dynamic tire radius [m] 0.334 0.362 0.343
Equivalent mass of rotational inertias
[kg] 0.329 0.111 0.152
Equivalent mass factor 1.027 1.005 1.009
RDM
Mass151 [kg] 26.1 33.1 35.6
Lubricant main152 [L] 1.15 0.800 0.900
Lubricant Coupler152 [L] 0.28 0.400 0.700
Gear tooth count (ring/pinion)
31/11 41/15 27/17
Gear ratio 2.818 2.733 1.588
Gear cutting process Hobbed / lapped
Hobbed / lapped
Milled / ground
Mass of rotating parts [kg] 16.002 19.2 19.946
Total rotational inertia input shaft
[kg.m2] 1.30e-02 2.07e-03 7.77e-03
Total rotational inertia output shaft
[kg.m2] 1.34e-02 3.56e-02 1.36e-02
Equivalent mass of rotational inertias
[kg] 1.046 0.389 0.282
Equivalent mass factor 1.040 1.012 1.008
232
Table 7-5: Component Data Comparison (notable differences highlighted)
Propshafts Ford Jeep VW
Mass [kg] 9.5 13.1 11.4
Rotational Inertia [kg.m2] 7.556e-03 1.043e-02 9.083e-03
Equivalent mass of rotational inertias
[kg] 0.537 0.595 0.195
Equivalent mass factor 1.057 1.045 1.017
Halfshafts
left
Mass [kg] 6.0 8.3 6.2
Rotational Inertia [kg.m2] 5.177e-03 7.184e-03 5.358e-03
Equivalent mass of rotational inertias
[kg] 0.046 0.055 0.046
Equivalent mass factor 1.008 1.007 1.007
right
Mass [kg] 6.0 8.5 6.4
Rotational Inertia [kg.m2] 5.181e-03 7.167e-03 5.501e-03
Equivalent mass of rotational inertias
[kg] 0.046 .055 0.047
Equivalent mass factor 1.008 1.007 1.007
233
7.5.2 Mass & Rotational Inertias
Figure 7-9 illustrates significant differences in component masses:
Ford Fusion (midsize car) has a very efficiently designed PTU with a mass probably near the
optimum. The RDM also has the lowest mass although some design features indicate further
potential for improvement (bolted vs. welded ring gear). Together with a magnesium housing
the RDM could save approximately 3kg without compromising structural integrity or function.
Jeep Cherokee (small SUV) has the heaviest PTU since it is the only one in this comparison with
a two shaft design for packaging reasons. The RDM adds considerable mass because it was
designed to accommodate a low gear planetary set for the Trailhawk™ version. Mass was added
to the shafts to provide torque capacity for off-roading. A significant amount of incremental
mass is not accounted for in the analysis and most likely was used to adapt chassis parts.
VW Tiguan (small SUV) has a very complex RDM which adds mass to the system. The rear axle
torque rating is higher than with Ford Fusion.
Figure 7-9: AWD Component Mass Comparison
For this comparison vehicles with matching powertrains and trim levels have been selected. The
category ‘other’ includes any parts not directly related to driveline components (e.g. driveline
variations, body structure reinforcements, suspension subframes etc.)
234
Figure 7-10: AWD Component Rotational inertia Equivalent Mass
Ford Fusion has the highest equivalent mass due to the fact that a 5 kg AWD coupler with
considerable diameter is rotating at propshaft speed. Although that is the case for VW Tiguan as
well, Tiguan has a much lower axle gear ratio (1.588 vs. 2.818) and therefore a much smaller
rotational inertia effect.
For comparison, a wheel with a total mass (tire + rim) of 26kg and a dynamic tire radius of 0.334
m would have an rotational inertia equivalent mass of approximately 13.5 kg, which for the
wheel subsystem equals to 54 kg compared to 0.7 – 2 kg for the entire AWD system in the above
chart.
Rotational inertia effects in the AWD driveline are therefore negligible with respect to fuel
efficiency. However, rotational inertias play a major role in disconnect systems since the
synchronizing unit (i.e. the AWD coupler) must accelerate the non-moving part of the driveline
to the equivalent of vehicle speed within a very short period of time (approximately 200 - 400
ms).
235
7.6 AWD Disconnect System Cost Assessment
The following tables show a summary of the cost associated with upgrading a conventional AWD
system to accommodate fuel efficient disconnect capability. Cost is incremental to the base
system without disconnect.
The total cost includes the actual mechanical disconnect system including a smart actuator plus
any changes to the AWD coupler necessary to minimize parasitic losses (i.e. architecture, AWD
coupler clutch plate separation etc.).
The total system cost associated with disconnect devices is in the range of $90.00 to $100.00
US. The Jeep Cherokee system may be an exception since design perspectives included the
option of a low gear which adds unrelated cost to the system.
Pricing is from a tier 1 cost perspective. Sales price for a basic system to an OEM would be in the
range of $110.00 to $130.00 US with the addition of engineering, capital investment, SG&A,
profits and volume considerations.
Jeep Cherokee Sport Component Cost
PTU $ 86
RDM $ 64
Total $ 150 Table 7-6: Jeep Cherokee AWD Disconnect Cost Summary
Side Shaft Disconnect Component Cost
PTU $ 86
RDM $ 7
Total $ 93 Table 7-7: Generic Side Shaft Disconnect Cost Summary
Front Axle Center Disconnect (Chrysler 300) Component Cost
Front axle center disconnect $ 96
T-case $ 1
Total $ 97 Table 7-8: Chrysler 300 Front Axle Center Disconnect Cost Summary
236
8 Appendix A: List of Tables and Figures
Table 1-1: AWD Systems Classification ....................................................................................... 16
Table 1-2: FWD/RWD Architecture Positives and Negatives ..................................................... 40
Table 1-3: Disconnect Systems Positives and Negatives ............................................................ 40
Table 1-4: Torque Limitation Positives and Negatives ............................................................... 41
Table 1-5: Full Time vs. On-Demand AWD Positives and Negatives .......................................... 41
Table 1-6: RDM Architecture Positives and Negatives ............................................................... 42
Table 2-1: AWD System Classification (SAE J1952, Oct 2013) .................................................... 47
Table 2-2: Audi Platforms and Models ........................................................................................ 48
Table 2-3: Audi AWD Classification ............................................................................................. 48
Table 2-4: Audi A6 Basic Information .......................................................................................... 50
Table 2-5: BMW Platforms and Models ...................................................................................... 52
Table 2-6: BMW AWD Classification ............................................................................................ 52
Table 2-7: BMW Active Tourer Basic Information ...................................................................... 53
Table 2-8: BMW 3/4/5/6/7 Series Basic Information ................................................................. 54
Table 2-9: BMW X3/4/5/6 Basic Information ............................................................................. 56
Table 2-10: Daimler Benz Platforms and Models ........................................................................ 58
Table 2-11: Daimler Benz AWD Classification ............................................................................. 58
Table 2-12: Mercedes CLA/GLA Basic Information ..................................................................... 60
Table 2-13: Mercedes C, E and S-Class Basic Information .......................................................... 62
Table 2-14: FCA Platforms and Models ....................................................................................... 64
Table 2-15: FCA AWD Classification ............................................................................................. 64
Table 2-16: Jeep Cherokee Basic Information ............................................................................. 66
Table 2-17: Jeep Cherokee Trailhawk Basic Information............................................................ 67
Table 2-18: Jeep Grand Cherokee Basic Information .................................................................. 68
Table 2-19: Jeep Wrangler Basic Information ............................................................................. 70
Table 2-20: Jeep Wrangler Rubicon Basic Information ............................................................... 71
Table 2-21: Chrysler 300 Basic Information ................................................................................ 72
Table 2-22: Ford Platforms and Models ...................................................................................... 74
Table 2-23: Ford AWD Classification ........................................................................................... 74
Table 2-24: Ford Fusion Basic Information .................................................................................. 75
Table 2-25: General Motors Platforms and Models ................................................................... 76
Table 2-26: General Motors AWD Classification ......................................................................... 76
Table 2-27: Chevrolet Equinox Basic Information ....................................................................... 77
Table 2-28: Chevrolet Silverado / GMC Sierra Basic Information .............................................. 78
Table 2-29: Honda Platforms and Models ................................................................................... 80
Table 2-30: Honda AWD Classification ........................................................................................ 80
Table 2-31: Honda CR-V Basic Information ................................................................................. 81
237
Table 2-32: Hyundai Platforms and Models ................................................................................ 82
Table 2-33: Hyundai AWD Classification ..................................................................................... 82
Table 2-34: Hyundai SantaFe Basic Information ......................................................................... 83
Table 2-35: Jaguar Land Rover Platforms and Models ............................................................... 85
Table 2-36: Jaguar Land Rover AWD Classification ..................................................................... 85
Table 2-37: Range Rover Evoque Basic Information ................................................................... 86
Table 2-38: Mazda Platforms and Models .................................................................................. 88
Table 2-39: Mazda AWD Classification ........................................................................................ 88
Table 2-40: Mitsubishi Platforms and Models ............................................................................ 89
Table 2-41: Mitsubishi AWD Classification.................................................................................. 89
Table 2-42: Nissan Platforms and Models ................................................................................... 92
Table 2-43: Nissan AWD Classification ........................................................................................ 92
Table 2-44: Nissan Rogue Basic Information ............................................................................... 93
Table 2-45: Subaru Platforms and Models .................................................................................. 94
Table 2-46: Subaru AWD Classification ....................................................................................... 94
Table 2-47: Subaru Outback Basic Information .......................................................................... 96
Table 2-48: Tesla Model S Basic Information .............................................................................. 97
Table 2-49: Toyota Platforms and Models .................................................................................. 98
Table 2-50: Toyota AWD Classification ....................................................................................... 98
Table 2-51: Toyota Rav4 Basic Information ................................................................................ 99
Table 2-52: Toyota Highlander Basic Information .................................................................... 100
Table 2-53: Volkswagen Platforms and Models ........................................................................ 101
Table 2-54: Volkswagen AWD Classification ............................................................................. 101
Table 2-55: Volkswagen Tiguan Basic Information ................................................................... 102
Table 2-56: Volvo Platforms and Models .................................................................................. 103
Table 2-57: Volvo AWD Classification ....................................................................................... 103
Table 2-58: Volvo XC 90 Basic Information ............................................................................... 104
Table 2-59: Volvo XC90 T8 PHEV Basic Information ................................................................. 105
Table 3-1: Summary of Efficiency Improvement Potentials ..................................................... 120
Table 3-2: Summary of Efficiency Improvement Potentials (continued) ................................. 121
Table 5-1: Ford Fusion Power Transfer Unit – Technical Data ................................................. 136
Table 5-2: Ford Fusion Power Transfer Unit, Bill of Material rotating parts
[input]/[output] ......................................................................................................................... 137
Table 5-3: Ford Fusion Propshaft/Axle Technical Data ............................................................. 141
Table 5-4: Ford Fusion Rear Drive Module – Technical Data .................................................... 142
Table 5-5: Ford Fusion Rear Drive Module, Bill of Material rotating
parts [input]/[output] ................................................................................................................ 144
Table 5-6: Ford Fusion AWD Coupler, Bill of Materials rotating parts
[input]/[output] ......................................................................................................................... 148
Table 5-7: Ford Fusion Mass Distribution Analysis ................................................................... 153
Table 5-8: Jeep Cherokee Power Transfer Unit – Technical Data ............................................. 161
238
Table 5-9: Jeep Cherokee Power Transfer Unit, Bill of Material rotating parts
[input]/intermediate/[output] .................................................................................................. 163
Table 5-10: Jeep Cherokee Propshaft/Axle Technical Data ...................................................... 167
Table 5-11: Jeep Cherokee Rear Drive Module – Technical Data ............................................. 168
Table 5-12: Jeep Cherokee Rear Drive Module, Bill of Materials rotating
parts [input]/[output] 171
Table 5-13: Jeep Cherokee Mass Distribution Analysis ............................................................ 180
Table 5-14: Volkswagen Tiguan Power Transfer Unit – Technical Data ................................... 187
Table 5-15: Volkswagen Tiguan Power Transfer Unit, Bill of Material rotating
parts [input]/[output] ................................................................................................................ 188
Table 5-16: Volkswagen Tiguan Propshaft/Axle Technical Data .............................................. 191
Table 5-17: Volkswagen Tiguan Rear Drive Module – Technical Data ..................................... 192
Table 5-18: Volkswagen Tiguan Rear Drive Module, Bill of Materials rotating parts
[input]/[output] 193
Table 5-19: Volkswagen Tiguan AWD Coupler rotating parts [input]/[output] .............. 196
Table 5-20: Volkswagen Tiguan Mass Distribution Analysis .................................................... 202
Table 6-1: Jeep Cherokee AWD Disconnect Incremental Cost estimate – PTU ....................... 210
Table 6-2: Jeep Cherokee AWD Disconnect Incremental Cost estimate - RDM ...................... 211
Table 6-3: AWD Disconnect Incremental Cost Estimate – Side Shaft Disconnect ................... 212
Table 6-4: Front End Center Incremental Disconnect Cost Estimate ....................................... 214
Table 7-1: FWD/RWD Architecture Positives and Negatives ................................................... 219
Table 7-2: Full Time vs. On-Demand AWD Positives and Negatives ........................................ 220
Table 7-3: AWD Market Overview; AWD Systems per OEM and Number of
Platforms/Nameplates/ ............................................................................................................. 221
Table 7-4: Mass Comparison between Aluminum and Magnesium on an RDM ..................... 226
Table 7-5: Component Data Comparison (notable differences highlighted) ........................... 232
Table 7-6: Jeep Cherokee AWD Disconnect Cost Summary ...................................................... 235
Table 7-7: Generic Side Shaft Disconnect Cost Summary ......................................................... 235
Table 7-8: Chrysler 300 Front Axle Center Disconnect Cost Summary ..................................... 235
Table 10-1: Vehicle Data ............................................................................................................ 249
Figure 1-1: AWD Nomenclature ................................................................................................... 15
Figure 1-2: FWD Based AWD System Architecture ..................................................................... 17
Figure 1-3: RWD Based AWD System Architecture ..................................................................... 18
Figure 1-4: FWD Based ‘Through the Road’ Hybrid AWD ........................................................... 20
Figure 1-5: Electric AWD .............................................................................................................. 21
Figure 1-6: Power Transfer Unit ................................................................................................... 22
Figure 1-7: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right) .. 23
Figure 1-8: Power Flow in a PTU (2015 VW Tiguan).................................................................... 24
239
Figure 1-9: RDM with integrated Torque Transfer Device ......................................................... 25
Figure 1-10: Electro-magnetically actuated AWD coupler ......................................................... 26
Figure 1-11: Rear Drive Module Architecture Variants .............................................................. 27
Figure 1-12: Torque Vectoring ..................................................................................................... 29
Figure 1-13: Audi Sport Differential............................................................................................. 30
Figure 1-14: Front Axle Disconnect System, Integrated in the PTU ........................................... 31
Figure 1-15: Rear axle disconnect via AWD coupler ................................................................... 32
Figure 1-16: AWD System Status Before (left) and after (right) Disconnect – FWD based
vehicles ......................................................................................................................................... 33
Figure 1-17: AWD System Status Before and After Disconnect – RWD based vehicles ............ 34
Figure 1-18: Front Wheel Hub Disconnect .................................................................................. 34
Figure 1-19: Active 2-speed transfer case ................................................................................... 36
Figure 1-20: Torque Flow in an On-demand Transfer case ......................................................... 36
Figure 1-21: High Level AWD System Disconnect Algorithm ...................................................... 38
Figure 2-1: Fuel Consumption Comparison between 2WD and AWD, MY 2015 ....................... 44
Figure 2-2: Fuel Consumption Comparison between 2WD and AWD, MY 2015 (continued) ... 45
Figure 2-3: Vehicle Mass Comparison between 2WD and AWD versions, MY 2015 ................. 46
Figure 2-4: Audi 8-Speed Automatic Transmission with Integrated Torsen Differential .......... 51
Figure 2-5: BMW 3/4/5/6/7 Series Transfer Case with Geared Drive ....................................... 55
Figure 2-6: BMW X3 / X4 / X5 / X6 Single Speed Active On-demand Transfer Case with Chain
Drive .............................................................................................................................................. 57
Figure 2-7: Mercedes CLA/GLA 4-Matic Power Transfer Unit .................................................... 61
Figure 2-8: Mercedes CLA/GLA Rear Drive Module .................................................................... 61
Figure 2-9: Mercedes C, E and S-Class 4-Matic Powertrain ........................................................ 63
Figure 2-10: Jeep Grand Cherokee Single Speed (left) and 2-speed (right) Transfer Cases ...... 69
Figure 2-11: Chrysler 300 Axle Disconnect Unit (left) and Front Axle (right) ............................. 73
Figure 2-12: Chevrolet Silverado / GMC Sierra Transfer Cases: 4WD Base Model (left) and
AWD Premium Model (right) ....................................................................................................... 79
Figure 2-13: Magna Dynamax AWD Coupler ............................................................................... 84
Figure 2-14: Evoque Rear Drive Module and RDM Architecture (insert) ................................... 87
Figure 2-15: Mitsubishi S-AWC (‘Super – All Wheel Control’) .................................................... 90
Figure 2-16: Lancer Evolution Rear Drive Module with Active Yaw Control (AYC) .................. 91
Figure 2-17: Subaru AWD CVT Transmission ............................................................................... 95
Figure 3-1: Volvo XC90 T8 Hybrid .............................................................................................. 108
Figure 3-2: Angular Contact Double Row Ball Bearing (left) as a Replacement for Tapered
Roller Bearings, Power Loss Comparison (Under Lab Conditions, right) ................................. 109
Figure 3-3: Substitution of Tapered Roller Bearings (red) with Angular Contact Ball Bearings
(blue) ........................................................................................................................................... 110
Figure 3-4: Power Loss Distribution between Gears, Bearings and Oil Splash in a Single Stage
Axle under Load .......................................................................................................................... 110
240
Figure 3-5: Low Drag Seal; Conventional Seal with Garter Spring on the Right Hand Side for
Comparison ................................................................................................................................. 111
Figure 3-6: Spin Loss Comparison between Standard and Disconnect AWD Systems ............ 112
Figure 3-7: Advanced Driveshaft Joint for Reduced Friction and Mass ................................... 113
Figure 3-8: Hypoid Offset ........................................................................................................... 114
Figure 3-9: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right) 115
Figure 3-10: Influence of Lubricants and Temperature on Driveline Torque Losses ............... 117
Figure 3-11: Influence of Micro Finishing and Coating on the Friction Coefficient in Gears ... 118
Figure 4-1: Global Light Vehicle Production Forecast by Region, total numbers .................... 122
Figure 4-2: Global Light Vehicle Production Growth between 2014 and 2021 ........................ 123
Figure 4-3: Average Fuel Efficiency of U.S. Light Duty Vehicles (CAFE) .................................... 124
Figure 4-4: Adjusted CO2 Emissions (left) and Adjusted Fuel Economy (right) for MY 1975-2015
..................................................................................................................................................... 124
Figure 4-5: Fuel Economy, Horsepower and Mass Changes between 1975 and 2015 ............ 125
Figure 4-6: MY 2015 Driveline Architecture Distribution in NA, All Segments ........................ 127
Figure 4-7: AWD Take Rate by Vehicle Segment in MY 2015 ................................................... 128
Figure 4-8: AWD Take Rate [%] by US State, Sorted by Regions, MY 2015 ............................. 129
Figure 4-9: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD Content64 ... 129
Figure 5-1: AWD System Architecture ....................................................................................... 130
Figure 5-2: Chassis Integration of an RDM (Ford Fusion) ......................................................... 132
Figure 5-3: Ford Fusion AWD Coupler/ ...................................................................................... 133
Figure 5-4: Electro-magnetic Clutch - Operating Principle ....................................................... 134
Figure 5-5: Ford Fusion AWD Basic Control Logic ..................................................................... 135
Figure 5-6: Ford Fusion Power Transfer Unit ............................................................................ 137
Figure 5-7: Ford Fusion Power Transfer Unit - Parts ................................................................. 138
Figure 5-8: Ford Fusion PTU, Top View ...................................................................................... 139
Figure 5-9: Ford Fusion PTU Input Shaft Figure 5-10: Ford Fusion PTU Output
Shaft 139
Figure 5-11: Ford Fusion PTU, Output Shaft with Pinion in Main Housing .............................. 140
Figure 5-12: Ford Fusion Rear Drive Module ............................................................................. 142
Figure 5-13: Ford Fusion Rear Drive Module - Parts ................................................................. 145
Figure 5-14: Ford Fusion Rear Drive Module ............................................................................. 146
Figure 5-15: Ford Fusion Rear Axle Differential Assembly ....................................................... 146
Figure 5-16: Ford Fusion Rear Axle Assembly: Pinion in the Center Part [1] of the 3-piece
Housing ....................................................................................................................................... 147
Figure 5-17: Ford Fusion AWD Coupler Assembly..................................................................... 147
Figure 5-18: Ford Fusion AWD Coupler, Control Clutch and Ball Ramp Mechanism ............... 149
Figure 5-19: Ford Fusion AWD Coupler, Input Case .................................................................. 149
Figure 5-20: Ford Fusion AWD Coupler Control Clutch Plates .................................................. 150
Figure 5-21: Ford Fusion Main Clutch Plates ............................................................................. 150
Figure 5-22: Ford Fusion AWD Coupler - Parts .......................................................................... 151
241
Figure 5-23: Ford Fusion AWD Mass Analysis/ ......................................................................... 152
Figure 5-24: Ford Fusion ............................................................................................................. 152
Figure 5-25: Ford Fusion PTU Laser Welded Ring Gear ............................................................. 154
Figure 5-26: Ford Fusion Rear Axle Differential ........................................................................ 155
Figure 5-27: Ford Fusion Rear Axle Pinion with High Efficiency Tandem Ball Bearings .......... 156
Figure 5-28: Ford Fusion AWD coupler - Input Case Detail .......................... 157
Figure 5-29: Jeep Cherokee AWD Hydraulic System ................................................................. 158
Figure 5-30: Jeep Cherokee AWD Coupler ................................................................................ 159
Figure 5-31: Jeep Cherokee PTU Disconnect Cross-section, Shift Fork Actuator Module on the
Right ............................................................................................................................................ 160
Figure 5-32: Jeep Cherokee Power Transfer Unit ..................................................................... 162
Figure 5-33: ................................................................................................................................. 164
Figure 5-34: Jeep Cherokee PTU Assembly, Shift Actuator (black) .......................................... 165
Figure 5-35: Jeep Cherokee PTU, View of Input Shaft and Primary Shaft (w/ Shift Sleeve,
Actuator Removed) .................................................................................................................... 165
Figure 5-36: Jeep Cherokee PTU, View of Helical Gear Stage, Primary Shaft (large) and
Secondary Shaft (small) ............................................................................................................. 166
Figure 5-37: Jeep Cherokee PTU, Primary Shaft (left) and Secondary Shaft (right) ................ 166
Figure 5-38: Jeep Cherokee PTU, Pinion .................................................................................... 167
Figure 5-39: Jeep Cherokee Rear Drive Module ........................................................................ 168
Figure 5-40: ................................................................................................................................. 172
Figure 5-41: Jeep Cherokee RDM, Top View with Actuator and Oil Reservoir Cover ............. 173
Figure 5-42: Jeep Cherokee RDM, Hydraulic System Body with Ring Gear and Clutch Pack .. 173
Figure 5-43: Jeep Cherokee RDM, Pinion with inner TRB and Crush Sleeve ............................ 174
Figure 5-44: Jeep Cherokee RDM, Ring Gear ............................................................................. 174
Figure 5-45: Transfer Shaft with Ball Bearing ............................................................................ 175
Figure 5-46: Jeep Cherokee RDM, Differential .......................................................................... 175
Figure 5-47: Jeep Cherokee AWD Coupler - Parts ..................................................................... 176
Figure 5-48: Jeep Cherokee Clutch Assembly, Hydraulic System Body, and Transfer Shaft Ball
Bearing ........................................................................................................................................ 177
Figure 5-49: Jeep Cherokee AWD Coupler, Outer (left) and Inner (right) Plate, Reaction Side
..................................................................................................................................................... 177
Figure 5-50: Jeep Cherokee RDM, Outer (left) and Inner (right) Plate, Friction Side .............. 178
Figure 5-51: Jeep Cherokee Mass Analysis/ .............................................................................. 179
Figure 5-52: Jeep Cherokee ........................................................................................................ 179
Figure 5-53: Jeep Cherokee PTU, Laser Welded Ring Gear ....................................................... 181
Figure 5-54: Jeep Cherokee RDM Ring Gear Laser Weld .......................................................... 182
Figure 5-55: Jeep Cherokee Hydraulic System Body with Integrated Strainer ........................ 182
Figure 5-56: Jeep Cherokee AWD Clutch Assembly .................................................................. 183
242
Figure 5-57:
Jeep Cherokee AWD Inner and Outer Clutch Plates, Friction Side on the left, Reaction side on
the right ...................................................................................................................................... 184
Figure 5-58: Volkswagen Tiguan / Haldex Gen IV Hydraulic System ....................................... 185
Figure 5-59: Volkswagen Tiguan AWD Coupler – Haldex Gen IV ............................................. 186
Figure 5-60: Volkswagen Tiguan Power Transfer Unit .............................................................. 187
Figure 5-61: Volkswagen Tiguan Power Transfer Unit - Parts .................................................. 189
Figure 5-62: VW Tiguan PTU, Top View ..................................................................................... 190
Figure 5-63: VW Tiguan Ring Gear (left) and Pinion (right) ...................................................... 190
Figure 5-64: Volkswagen Tiguan Rear drive Module ................................................................ 192
Figure 5-65: Volkswagen Tiguan Rear Drive Module - Parts .................................................... 194
Figure 5-66: ................................................................................................................................. 195
Figure 5-67: VW Tiguan Ring Gear (left) and Pinion (right) ...................................................... 195
Figure 5-68: VW Tiguan RDM, .................................................................................................... 196
Figure 5-69: Volkswagen Tiguan AWD Coupler/ ....................................................................... 197
Figure 5-70: Volkswagen Tiguan AWD Coupler - Parts ............................................................. 198
Figure 5-71: VW Tiguan AWD Coupler Assembly ...................................................................... 198
Figure 5-72: VW Tiguan AWD Coupler, Cage (left), Multi Plate Clutch and Hub (right) .......... 199
Figure 5-73: VW Tiguan AWD Coupler, Outer (left) and Inner (right) Plate ............................ 200
Figure 5-74: Volkswagen Tiguan Mass Analysis/ ...................................................................... 201
Figure 5-75: Volkswagen Tiguan Equivalent Mass Analysis.................................................... 201
Figure 5-76: VW Tiguan PTU – Laser Welded ring Gear ............................................................ 203
Figure 5-77: VW Tiguan RDM, Ring Gear/Differential Case Laser Welding ............................. 204
Figure 5-78: VW Tiguan RDM Pinion ......................................................................................... 204
Figure 5-79: VW Tiguan AWD Coupler, Friction and Reaction Plates ................................. 205
Figure 5-80: VW Tiguan AWD Coupler Hub ............................................................................... 205
Figure 5-81: VW Tiguan AWD Coupler Cage .............................................................................. 206
Figure 6-1: Jeep Cherokee AWD Configuration ......................................................................... 208
Figure 6-2: Jeep Cherokee PTU, Bottom Front View ................................................................. 209
Figure 6-3: Jeep Cherokee RDM ................................................................................................. 211
Figure 6-4: Side Shaft Disconnect, Parallel System in the Background for Comparison ......... 212
Figure 6-5: Front End Center Disconnect (Chrysler 300) ........................................................... 213
Figure 7-1: AWD System Classification per SAE J1952 (Oct 2013) Standard ............................ 215
Figure 7-2: AWD System Architecture: (1) FWD based; (2) RWD based; (3) FWD based, through
the Road PHEV; (4) Electric ........................................................................................................ 216
Figure 7-3: Active AWD Coupler Systems: Electro-magnetic (left), Electro-hydraulic (right) .. 217
Figure 7-4: AWD Disconnect System Schematic ........................................................................ 218
Figure 7-5: Increase of Fuel Consumption over AWD Mass Increase (LH Column of Charts)
Compared to the Total Fuel Consumption over Vehicle Mass for a Selection of AWD Vehicles
[the Red Dot Indicates Vehicles with AWD Disconnect] .......................................................... 223
Figure 7-6: MY 2015 Driveline Architecture Distribution in NA, All Segments ........................ 228
243
Figure 7-7: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD .................... 229
Figure 7-8: AWD System Architecture ....................................................................................... 230
Figure 7-9: AWD Component Mass Comparison ....................................................................... 233
Figure 7-10: AWD Component Rotational inertia Equivalent Mass ......................................... 234
Figure 9-1: AWD couplers - Power transfer units - Transfer cases - Integrated rear drive
modules (left to right) ................................................................................................................ 244
Figure 9-2: Transfer cases - AWD couplers - Electric rear drive modules (left to right) .......... 245
Figure 9-3: Power Transfer Units - AWD couplers - Electric drive modules (left to right) ...... 246
Figure 9-4: Light trucks / SUVs - FWD based passenger cars - RWD based passenger cars (left
to right) ....................................................................................................................................... 247
Figure 9-5: Hybrid drives - Power Transfer Units - Rear drive modules - Engineered gears (left
to right) ....................................................................................................................................... 248
Figure 11-1: Relative Rotational inertia Effects on Vehicle Dynamics ..................................... 251
Figure 12-1: Evaluation of Rotational inertia ............................................................................ 253
Figure 12-2: Spreadsheet to Support Evaluation of Rotational inertia .................................... 254
244
9 Appendix B: Major North American AWD System
Suppliers
________________________________________________________________________
Magna Powertrain (Source: Magna website)
Magna, one of the largest and most diversified Tier 1 suppliers worldwide, develops and
manufactures a full line of AWD products, from cost effective solutions up to top of the
line systems. Magna has a large market share in transfer cases for SUVs, mainly in North
America, and FWD based AWD systems, mainly in Europe and increasingly in Asia.
Magna has joined the group of hybrid and electric drive developers and has AWD
technology available in the hybrid field.
Figure 9-1: AWD couplers - Power transfer units - Transfer cases - Integrated rear drive modules (left to right)
‘Magna Powertrain is a premier supplier for the global automotive
industry with full capabilities in powertrain design, development, testing
and manufacturing. Offering complete system integration sets us apart
from our competitors’
Magna Website
245
________________________________________________________________________
Borg Warner (Source: BorgWarner website)
The Borg Warner TorqTransfer group delivers a complete line of products for FWD and
RWD based AWD vehicles. The group offers cost effective systems as well as top of the
line AWD systems with electronic limited slip functions. With their recent acquisition of
Haldex they have top technology in their portfolio.
Electric drives capable of converting a FWD based vehicle into a through the road AWD
hybrid are also in the lineup, as well as transmission systems for purely electric vehicles.
Figure 9-2: Transfer cases - AWD couplers - Electric rear drive modules (left to right)
‘BorgWarner is a global product leader in powertrain solutions. We focus
on developing leading powertrain technologies that improve fuel
economy, emissions and performance. Our facilities are located across
the globe to provide local support for our diverse customer base’
Borg Warner Website
246
________________________________________________________________________
GKN Automotive (Source: GKN website)
GKN’s Driveline group concentrates on FWD based AWD vehicles with power transfer
units, AWD couplers, axles and e-drives. Advanced disconnect devices have been
developed. No transfer cases are in the product lineup.
GKN is also a major supplier of propshafts and CV joints.
Figure 9-3: Power Transfer Units - AWD couplers - Electric drive modules (left to right)
‘The global leader in efficient all-wheel drive systems, GKN Driveline
continues to deliver driveline systems and solutions to the world’s
premier automotive manufacturers.
With an enviable world class reputation since the emergence of the motor
car, GKN Driveline is committed to the unique development and
manufacture of full AWD systems.
GKN Driveline is a solutions provider, with advanced technology centred
on continuous improvement, innovation and a depth of understanding in
systems integration to optimise the very best components’
GKN Website
247
________________________________________________________________________
American Axle Manufacturing (Source: AAM website)
AAM is developing and manufacturing a full line of driveline products for light trucks /
SUVs (Front axles, rear beam axles, transfer cases with various functional levels), FWD
based passenger cars (power transfer units, rear axles including torque transfer devices,
propshafts) and RWD passenger cars (rear axles, transfer cases).
Most notably, AAM is the manufacturer of the Jeep Cherokee AWD system, with state of
the art disconnect system for fuel efficiency and a unique low gear option for enhanced
off-road capabilities.
Figure 9-4: Light trucks / SUVs - FWD based passenger cars - RWD based passenger cars (left to right)
‘AAM is a leading, global Tier-One automotive supplier of driveline and
drivetrain systems and related components for light trucks, SUVs,
passenger cars, crossover vehicles and commercial vehicles with a
regionally cost competitive and operationally flexible global
manufacturing, engineering and sourcing footprint. Through highly-
engineered, advanced technology products, processes and systems and
industry leading operating performance, the AAM team provides a
competitive advantage to our customers’
AAM Website
248
________________________________________________________________________
Linamar (Source: Linamar website)
Linamar has an impressive array of manufacturing plants for powertrain and driveline
parts, mainly acting as a Tier 2 supplier. A large gear manufacturing operation is capable
of supplying quality gears for in-house products and Tier 1 customers.
As a Tier 1 they are supplying power transfer units and a highly integrated rear drive
module with a sophisticated electronic limited slip differential.
Linamar has recently developed an electric rear drive module that can be used to
convert a FWD based vehicle into an AWD hybrid. The RDM has two electric motors,
each driving one wheel, and is capable of providing torque vectoring.
Driveline product groups
Figure 9-5: Hybrid drives - Power Transfer Units - Rear drive modules - Engineered gears (left to right)
‘As a leading edge Tier 1 supplier to the automotive markets, Linamar
provides core engine components including cylinder blocks & heads,
camshafts and connecting rods. For transmission, Linamar builds
differential assemblies, gear sets, shaft & shell assemblies, as well as
clutch modules. For the vehicle's driveline, Linamar is a full service
supplier of gears and gear driven systems such as PTUs and RDUs for use
in all-wheel drive systems. From single machine components to complex
assemblies, Linamar is the supplier of choice for OEM customers’
Linamar Website
10 Appendix C: Vehicle Data153
Table 10-1: Vehicle Data
153 Source: mass & price: dealer websites, EPA data: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf, converted from original mpg into L/100 km
Base vehicle
architecture Model Price Curb Weight city hwy combined Price Curb Weight city hwy combined
USD kg l/100 l/100 l/100 USD kg l/100 l/100 l/100
Audi A4 FWD 2.0L 35,900$ 1567 9.9 7.4 8.8 1632 10.8 7.7 9.5
X3 RWD 2.0L 38,950$ 1814 11.3 8.5 9.9 40,500$ 1868 11.3 8.5 9.9
X5 RWD 53,900$ 2106 12.5 8.8 10.8 56,200$ 2156 13.2 8.8 11.3
C-Class RWD C350 38,950$ 1538 9.5 7.0 8.5 40,950$ 1617 9.9 7.7 8.8
E-Class RWD E350 53,100$ 1721 11.9 8.2 10.3 55,600$ 1791 11.9 8.5 10.3
Cherokee FWD 2.4L 23,395$ 1645 10.8 7.7 9.5 25,395$ 1779 11.3 8.5 9.9
Grand Cherokee RWD Laredo 29,995$ 2045 14.0 9.5 11.9 31,995$ 2105 14.0 9.9 12.5
300 RWD 3.6L 32,015$ 1813 12.5 7.7 10.3 34,515$ 1890 13.2 8.8 11.3
Fusion FWD SE 2.0L 23,680$ 1598 10.8 7.2 9.1 1670 10.8 7.7 9.5
Escape FWD 1.6L 25,300$ 1576 10.3 7.4 9.1 27,050$ 1640 10.8 8.2 9.5
F150 RWD XL 28,610$ 1989 14.0 9.9 11.9 33,255$ 2089 14.0 10.3 12.5
ATS RWD 2.oL Turbo 35,215$ 1518 11.3 7.9 9.9 37,245$ 1594 11.9 8.5 10.3
Acadia FWD 3.6L 34,175$ 2095 14.0 9.9 12.5 36,175$ 2183 14.8 10.3 12.5
Equinox FWD 2.4L 25,210$ 1705 10.8 7.4 9.1 26,960$ 1767 11.9 8.2 10.3
MDX FWD 43,015$ 1782 11.9 8.5 10.3 45,015$ 1888 13.2 8.8 11.3
CR-V FWD LX 23,595$ 1524 8.8 7.0 8.2 24,895$ 1575 9.1 7.2 8.5
Hyundai SantaFe FWD Sport 2.0L 24,950$ 1557 12.5 8.8 10.8 26,700$ 1627 13.2 9.9 11.3
Mazda CX-5 FWD Sport automatic 21,795$ 1545 9.1 7.4 8.2 24,445$ 1615 9.5 7.7 8.5
Rogue FWD S 23,290$ 1534 9.1 7.2 8.5 24,640$ 1596 9.5 7.4 8.5
QX60 FWD 42,400$ 1973 11.3 8.8 10.3 43,800$ 2036 12.5 9.1 10.8
Subaru Outback RWD 2.5L n/a n/a n/a n/a n/a 31,245$ 1635 9.5 7.2 8.5
Toyota Rav4 FWD 23,680$ 1546 10.3 7.9 9.1 25,080$ 1598 10.8 8.2 9.5
Highlander FWD 3.5L LE 23,681$ 1910 12.5 9.5 11.3 25,081$ 1979 13.2 9.9 11.9
VW Tiguan FWD S 24,890$ 1532 11.3 9.1 10.3 26,865$ 1616 11.9 9.1 10.3
AWD
EPA L/100 km EPA L/100 km
2WD
GM
Honda
Nissan
BMW
Daimler
FCA
Ford
250
11 Appendix D: Equivalent Mass Definition
11.1 Equivalent Mass
A driveline component’s moment of rotational inertia directly affects vehicle dynamics
and subsequently system efficiency. One easy way to show this effect is to convert
rotational inertia into an equivalent mass. This gives us an understanding of the
magnitude of influence on the vehicles dynamic capabilities, expressed relative to the
actual vehicle mass.
Equation [1] represents the total energy 𝑬 stored in a driveline component at the speed
𝒗 as a combination of translational and rotational kinetic energy. The introduction of the
equivalent mass 𝒎𝒆𝒒 in equation [2] allows us to describe the rotational energy
equivalent in a system with no rotating parts.
𝐸 = 𝑚𝑣2
2 +
𝐼𝜔2
2 [1]
𝑚𝑒𝑞𝑣2
2=
𝐼𝜔2
2 [2]
𝑣 = 1
𝑖𝜔𝑅𝑑𝑦𝑛 [3]
𝑚𝑒𝑞 = 𝐼 (𝑖
𝑅𝑑𝑦𝑛)
2
[4]
𝑚𝑡𝑜𝑡𝑎𝑙 = 𝑚 + 𝑚𝑒𝑞 [5]
𝑚𝑓 = 𝑚𝑡𝑜𝑡𝑎𝑙 / 𝑚 [6]
Equation [3] describes the ratio between a vehicle’s speed 𝒗 and the rotational speed 𝝎
of an individual driveline component. The gear ratio 𝒊 represents the speed ratio
between the wheels and the actual location of the component within the driveline (e.g.
an axle or transmission ratio or a combination of all driveline components).
Combining equations [2] and [3] allows us to isolate 𝒎𝒆𝒒 and express the rotational
inertia equivalent mass based on the value of the rotational inertia. The results are
cumulative, with every component being calculated using its moment of rotational
inertia and the actual gear ratio.
E Total system energy 𝑚 Static component mass 𝑣 Vehicle speed I Rotational inertia ω Rotational speed
𝑚𝑒𝑞 Equivalent mass
𝑖 Gear ratio 𝑅𝑑𝑦𝑛 Dynamic tire radius
𝑚𝑡𝑜𝑡𝑎𝑙 Total equivalent mass 𝑚𝑓 Equivalent mass factor
251
Total [equivalent] mass 𝒎𝒕𝒐𝒕𝒂𝒍 is the sum of actual mass and 𝒎𝒆𝒒 from rotational inertia
calculation (equations [4] and [5]). The Equivalent Mass Factor is defined per equation
[6].
11.2 Relative Effects of Rotational inertia on Vehicle Dynamics
Figure 11-1 shows the effects of rotational inertia on vehicle dynamics relative to the
location of a component in the drivetrain. Since equivalent mass grows by the square of
the gear ratio (per equation [4] in section 11.1), the rotational inertia I of propshaft
elements (medium) may have an influence up to 10+ times as much as wheel speed
level components (low), based on the axle ratio (here shown as 3.0, which would give a
factor of 9).
Figure 11-1: Relative Rotational inertia Effects on Vehicle Dynamics
Transmission ratios are typically in a range of 0.8 to 3.5. Any component upstream of
the transmission (high) would have again an equivalent mass growing with the square of
the total gear ratio, including transmission gear stage. This is obviously variable,
depending on the actual gear selected. The effects are highest in low gears and would
give a maximum factor of (3 * 3.5)2 = 110 in the above example. That means a flywheel
or a torque converter (high level) for instance would have 110 times the equivalent
mass of a component with the same rotational inertia at wheel speed level (low) in 1st
gear.
AWD components fall into the medium or low categories and have very limited
influence on fuel consumption based on their rotational inertia.
252
However, disconnect systems for example have to quickly accelerate driveline
components in order to synchronize them with the wheel speeds when engaging the
AWD systems. Rotational inertias have to be taken into consideration to ensure smooth
transition from 2WD to AWD. In other driveline components, e.g. transmissions, even
small reductions in rotational inertia can improve performance significantly.
AWD disconnect systems do not eliminate all effects of rotational inertia since there are
still some added components spinning, depending on architecture (e.g. half shafts
unless there is a wheel hub disconnect. However, effects are minimal and eliminating
them would not justify added complexity.
253
12 Appendix E: Evaluation of Rotational Inertia and
Equivalent Mass
Rotational inertia have been evaluated for all rotating parts in the RDMs and PTUs of all
three vehicles listed in the teardown part of this report. Measurements have been done
with simple lab methods, i.e. electronic calipers and high definition scales.
The evaluation was executed in the following steps:
1. All parts, components and subsystems were weighed (0.002 kg accuracy)
2. Component measurement: All rotating components were broken down into
cylindrical segments as shown in Figure 12-1. Segments with non-cylindrical
shapes (e.g. gears, differential cases etc.) were estimated.
3. From the measurements the mass was calculated. The results were compared to
the actual mass measured in step 1, and a correction factor was applied to
correlate dimensional values with measured masses.
4. A second correction factor was estimated for complex geometries to reflect mass
offset in the calculation of rotational inertias (e.g. voids in clutch plates,
differential cases, bearings etc.)
5. Rotational inertias were calculated for every segment by the formulas listed in
Figure 12-2. The rotational inertias were finally multiplied by the estimated
factor from step 4
6. The actual rotational inertia for each component is the sum of all segments and
is listed in the BoM for each individual part in section 5 of this report.
Figure 12-1: Evaluation of Rotational inertia
254
Figure 12-2: Spreadsheet to Support Evaluation of Rotational inertia
This process makes the listed rotational inertias estimates rather than exact
measurements. However, the method should be considered accurate enough to
produce values very close to the actual numbers.
The equivalent mass was calculated with the formulas listed in Appendix D. The actual
gear ratio was determined for all parts to account for the exact location in the driveline.
That means RDMs and PTUs have two groups of rotational inertias, one on wheel speed
level and one upstream of the hypoid set with the axle ratio taken into account.
Mass Inertia
ffactor … form factor to compensate for non-uniformity 7850 steel density [kg/m3] [kg] [kg m2]
Ifactor … orm actor or partially rotating parts (bearings) 3.14159 Pi Total: 1.655 6.279E-04C
[kg] [kg m2]
Dinner Douter L Offset ffactor Ifactor m I
1 0 25.2 35.7 1 1 0.140 1.110E-05
1 0 27.1 51.8 1 1 0.235 2.153E-05
1 0 30.2 29.2 1 1 0.164 1.872E-05
1 0 31.8 19.1 1 1 0.119 1.505E-05
1 0 33.4 24.6 1 1 0.169 2.359E-05
1 0 72.1 31.5 0.82 1 0.828 5.379E-04
1 0 1 1 0.000 0.000E+00
1 0 1 1 0.000 0.000E+00
1 0 1 1 0.000 0.000E+00
1 1 0.000 0.000E+00
Total 1.654646 6.279E-04
[kg] [kg m2]
L d Offset ffactor m I
1 1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
Total 0 0.000E+00
[kg] [mm] [kg] [kg m2]
m Offset ffactor m I
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
1 0.000 0.000E+00
Total 0 0.000E+00
Point Mass(Parallel Axis Theorem)
Qty
Cylinder TubeQty
[mm]
RodQty [mm]
255
13 Appendix F: List of Terms and Acronyms
2WD Two Wheel Drive
4WD Four Wheel Drive, used per SAE definition for part time systems
4x4 Four by Four – general term, equivalent to AWD for 4-wheeled vehicles
ABS Anti-lock Braking System
ADS Active Disconnect System, a driveline setup that allows one or more sections of the driveline to be disconnected from the torque flow and brought to a standstill while the vehicle is in motion
AWD All Wheel Drive, general term for vehicles where all wheels (4X4, 6X6 etc.) receive torque
BoM Bill of Materials
BTC Brake Traction Control, a set of algorithms that allows the use of selective braking of individual wheels to enhance traction and vehicle dynamics
CAFE Corporate Average Fuel Economy
CD Center Differential
CUV Cross-over Utility Vehicle
CV Joint Constant Velocity Joint, a driveline joint type that minimizes rotational speed oscillations in a multi piece shaft at an angle
CVT Continuously Variable Transmission, a transmission type that does not have individual gear ratios or steps across a predefined range
DCT Dual Clutch Transmission, a mechanical transmission type using two clutches that allows automatic shifts between gears without interrupting torque flow
DMC Direct Manufacturing Cost, the cost to manufacture a component from base materials, including direct labor cost
EC Environment Canada
ECU Electronic Control Unit, an electronic device containing a set of algorithms to control torque flow in a driveline
eLSD electronic Limited Slip Differential, a device that allows the controlled redistribution of torque across a differential in a ratio different from the mechanically predefined torque bias
EPA U.S. Environmental Protection Agency
Equivalent Mass Factor
The Equivalent Mass Factor is defined as [(component or vehicle mass) + equivalent mass of rotational inertias] divided by (component or vehicle mass)
eRAD electric Rear Axle Drive, an electric drive unit to drive the rear axle independently (with no mechanical connection) from the front axle drive
256
eTV Transport Canada’s ecoTECHNOLOGY for Vehicles Program
EV Electric Vehicle
FE Fuel Efficiency
FWD Front Wheel Drive
GHG Green House Gases
HDV Heavy Duty Vehicle, typically heavy trucks and SUVs up to class 8 tractor/trailers
LDV Light Duty Vehicle, typically passenger cars and light trucks and SUVs
LH Left Hand
LSD Limited Slip Differential, a device that redistributes torque across a differential based on predefined design features and vehicle status with no external controls
MPC Multi Plate Clutch, a stack of multiple pairs of friction plates and reaction plates, alternately connected to the hub and the housing of a clutch; integral part of an AWD coupler
NVH Noise Vibration & Harshness
OEM Original Equipment Manufacturer – the vehicle manufacturers
PHEV Plug In Hybrid Electric Vehicle, an electric hybrid vehicle with a battery pack large enough to provide a significant amount of electric propulsion in addition to the internal combustion engine
PTU Power Transfer Unit, a mechanical device that picks up torque from the front axle and provides a mechanical connection to the rear axle
RDM Rear Drive Module, a mechanical device to drive the rear axle of a vehicle, typically contains a torque transfer device to control the amount of torque delivered
RH Right Hand
RWD Rear Wheel Drive
SG&A Sales, General and Administrative, part of the component cost structure
SUV Sport Utility Vehicle
TC Transport Canada
T-Case Transfer Case, a mechanical device typically found in RWD based AWD vehicles; splits torque between the front and rear axles in a fixed or controlled way
Tier 1 A Tier 1 Supplier sells parts and components directly to the car companies, also called the OEMs.
TRB Tapered Roller Bearing, roller bearings that can take substantial axial and radial loads, typically found in axles and PTUs
TTD Torque Transfer Device, also known as AWD coupler; a mechanical device that actively or passively controls the amount of torque passing through