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Product Development & Global Technology

An Introduction to Hydro-

mechanical Transmissions

Mike Cronin

28 Nov 2012(Previously titled: Cost Savings With Hydro-mechanical Transmissions)

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Introduction

Topics Covered: Speaker Background

Simple Hydro-mechanical Transmission Schematic Current Industry Examples Important Design Characteristics

How Fuel Is Saved Other Beneficial Characteristics

Caveats: Not A Design Guide Limited To Off-road Perspective

Hydro-mechanical transmission architectures are growing in popularity as acost effective means to provide continuously variable transmission (CVT)

functionality in the heavy-duty off-road market segment. This presentation willintroduce the audience to the basics of operation and commonly used terms.

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Mike Cronins CV J oined Caterpillar upon graduation from Michigan State University with a

BSME in 1973

Entire career working on off-road drivetrain performance and design: Hydro-mechanical transmissions for a broad range of applications Electric drive for TTT

TTT & Belted machine steering systems and components Assorted lower powertrain projects

Assorted powershift transmission concepts

Drivetrain related patents 23 Granted

10 Pending 9 Notifications

Retired in 2010

Rejoined Caterpillars Drivetrain Research Dept on a part time basis tocontinue work on hydro-mechanical drivetrains.

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EngineGear

System

Gear

System

Variator

Transfer Gear

And/or Axle

Reductions

Wheel

Or

Sprocket

Transmission

General Parallel Path Transmission Schematic

a.k.a. Split Torque, Power Split, Hydro-mechanical, Electro-mechanical etc.

A variator is a device that can vary the speed or torque ratioacross its two shafts in a continuous manner.

Several types are available: hydraulic, electric, traction etc.

In addition to gears these systems may contain clutches,brakes or other familiar transmission componentsconnected in various ways.

A very large number of combinations are possible.

There must be at leastone planetary

PlanetaryGear

System

Hydraulic Power Path

Mechanical Power Path

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Speed 1

Speed 2

General Planetary

Gear System

Planetaries Are Splitters and Adders

Output speed is the sumof the input speeds.

Output Speed =

A*Speed1+

B*Speed2

Speed

Adder

TorqueSplitter

Output Torque1 = A*Torque

Output Torque2 = B*Torque

Torque

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Engine FinalDrive

Wheelsor

Tracks

Pump Motor

Hydro-Mechanical CVT

EngineSpeed

General PlanetaryGear System

Variable

Speed

Output Speed =

A*Engine Speed+

B*Variable Speed

Even if engine speed isconstant, if the other speedis variable then the output

speed is still variable.

Hydrostatic Variator Shown

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Why choose hydro-mechanical?

Scaling Variators are only available in a limited number of sizes. A given size variator matches to a larger machine when used in a hydro-

mechanical configuration.

Larger machines now have access to CVT behavior.

Efficiency The power path carries a fraction of engine power Less hydraulic power means fewer losses.

Less fuel More power to ground

Cost Most cost effective CVT technology for 200-400 hp wheel loaders.

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Hydro-mechanical Transmission Examples

AG

IVTEccom/IVT/S-maticVario

IVT CVT

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Hydro-mechanical Transmission Examples

Wheel Loader

Cat

CVT

Dana/Rexroth

HVT

ZF

cPower

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Important Design Differentiators

Variator Type Discussed Above

Coupling Type Input Output Compound Split

Number of Ranges or Modes One

Two Three Four

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Variable Pump

Fixed Motor

Integrated, Inline Package

Used in ZF Designed cPower Shown @ 2010 Bauma

Variable Pump

Variable Motor

Pump and Motor Displacements Linked

Motor Displacement Decreases while PumpDisplacement Increases

Integrated, U Package

Variator Examples

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Input Coupled/ Output Split

In Out

PlanetaryGear

System

Double Coupled/ Unsplit

In Out

PlanetaryGear

System

Output Coupled/ Input Split

In Out

PlanetaryGear

System

Uncoupled/ Compound Split

In Out

PlanetaryGear

System

Explaining the term Coupled

The Variator is Coupled to theOutputThe Variator is Coupled to the Input

Cat CVT

JD 6000, 7000 IVT

S-Matic

Graziano

Fiat/Ag

ZF Eccom

Rexroth HVT 2nd,3rd

914

ST125 1st

Rexroth HVT 1st

D6E

D7E

795AC

Vario

8000 IVT 1st,3rd

ZF CP

Prius

Dual Mode/AHSII/EP40 1st

8000 IVT 2nd,4th

ZF CP 2nd,3rd

Dual Mode/AHSII/EP40 2nd

Hydraulic

Variators

Electric

Variators

Volt

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Engine Speed vs Ground Speed

w Discrete Step Transmission

600

800

1000

1200

1400

1600

1800

2000

2200

0 5 10 15 20 25

Ground Speed mph

EngineSpeedrpm

Discrete Ratio Powertrain Schematic

Engine Transmission

Aux Loads

Discrete Ratio Transmission

Several selectable gear ratios

Slipping clutch for launch

Transfer Gear

And /or Axle

Reductions

Wheel

Or

Sprocket

Ground Speed 2

One Engine Speed

Possible atGround Speed 2

Ground Speed 1

Two Engine Speeds

Possible at Ground

Speed 1

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1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

Engine Speed rpm

EngineGrossPo

werkW

Hypothetical Engine Fuel Rate Contours

g/min

800-900

700-800

600-700

500-600

400-500

300-400

200-300

100-200

0-100

Approximate Minimum

Fuel Consumption

Ground Speed 1 Ground Speed 2

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Continuously Variable Ratio Powertrain Schematic

Engine Transmission

Aux Loads

Continuously Variable Transmission

Ratio co ntinuously managed forperformance and launch

Transfer Gear

And /or Axle

Reductions

Wheel

Or

Sprocket

Engine Speed vs Ground Speed

600

800

1000

1200

1400

1600

1800

2000

2200

0 5 10 15 20 25

Ground Speed mph

EngineSpeed

rpm

Functional Defin ition of CVT:

Engine speed can be placed and maint ained at the

desired level regardless of grou nd speed.

Any Engine Speed

Possible at Any

Ground Speed

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END

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