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Transcript of Automotive motors: Recent accomplishments and challenges · PDF fileAutomotive motors: Recent...
![Page 1: Automotive motors: Recent accomplishments and challenges · PDF fileAutomotive motors: Recent accomplishments and challenges ahead Electric power steering Source: ... • Future development](https://reader031.fdocuments.us/reader031/viewer/2022022423/5a9e5ef57f8b9aee4a8da642/html5/thumbnails/1.jpg)
October 2016, Slide 1
Bruno Lequesne -
Consultant, E-Motors Consulting, LLC
www.emotorseng.com
Automotive motors: Recent
accomplishments and challenges ahead
Electric power steering
Source: Nexteer
Electric supercharger
Source: Valeo
Hairpin windingSource: Borg-Warner
Efficiency optimizationSource: Burwell, et. al, Tokyo 2013
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October 2016, Slide 2
Introduction
• Hybrids and EVs get a lot of press – Well deserved, these are
tremendous technical achievements
• There is however a much deeper groundswell of electrification
throughout the automobile
• Going to the origin of the automobile
• Pushing technology forward
Source: Conrad, AIEE, 1913
Magneto (ignition)
Light
Gear for
starter motor
![Page 3: Automotive motors: Recent accomplishments and challenges · PDF fileAutomotive motors: Recent accomplishments and challenges ahead Electric power steering Source: ... • Future development](https://reader031.fdocuments.us/reader031/viewer/2022022423/5a9e5ef57f8b9aee4a8da642/html5/thumbnails/3.jpg)
October 2016, Slide 3
Automotive companies: At the forefront of motor technology?
• Example: Is integration of power electronics and motors cutting edge?
Lundell motor1950s
Source: Bosch
Enabling Technologies Thrust
Center for Power Electronics Systems /
U. of Wisconsin, 2016
Source: cpes.vtu.edu
Integrated rectifier /
Diode bridge
Source: intechopen.com
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October 2016, Slide 4
Presentation outline
• Power steering
• Accessory motors and concentrated windings
• High-speed motors
• Generators, starter-generators, and hybrid motors
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October 2016, Slide 5
Steering
• Best (recent) success story in automotive electrification
• Electric power steering becoming standard
• Provides power on demand: Significant fuel economy benefit (4%)
• Issues:
• Torque ripple
• Fault tolerance
• Cost
Source: Nexteer
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October 2016, Slide 6
Steering: Torque ripple
• Torque ripple felt by the driver on the steering wheel
• Marketing issue (more than technical issue)
• Solution involved all aspects of motor and controller design and
manufacturing:
• Initial approach based on sinusoidal waveforms, current and flux
• Motor:
• Matching of magnet back-emf with current
excitation (magnet shape, etc)
• Magnet skewing, pole/slot design, etc
Source: Islam, et. al., IEEE T. IA, 2005
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October 2016, Slide 7
Torque ripple; Effect of saturation
• Saturation increases harmonic content
• Can be evaluated with finite elements
Source: Islam, et. al., IEEE T. IA, 2005
No saturation
With saturation
To
rqu
e (
Nm
)
3.1
2.8
3.1
2.8
To
rqu
e (
Nm
)
Position (deg)
Position (deg)
Saturation
Cogging
Harmonics
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October 2016, Slide 8
Torque ripple: Manufacturing issues
• Importance of Six Sigma methods to understand impact of build
variations on performance
• Motor: Magnet misplacement, etc
• Controller:
• Sensor positioning and accuracy
• Switching frequency, delays
Source: Islam, et. al., IEEE T. IA, 2004 Source: Chen, et. al., IEEE T. IA, 2002
Encoder resolution (el. degree/count)To
rqu
e r
ipp
le, p
k-t
o-p
k (
%) Phase angle
10
5
0
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October 2016, Slide 9
Steering: Fault tolerance
• Mechanical link to wheels kept, just in case
• Last resort option
• Hardware solutions:
• Minimize impact of fault (e.g., short circuit current)
• Redundancy: Enough to be effective, not too much
(FMEA)
• Software solutions:
• Many faults have signatures in the current waveform
• But, motor is always in dynamic situation
• Alternatives to Fourier analysis needed
• Wavelet, Wagnerville, windowed-Fourier…
Source: Rajagopalan, et. al., IEEE T. IA, 2006
Frequency (Hz)
Ma
gn
itu
de
Fundamental
Harmonics and fault signature
Eccentricity
Gear
fault
Eccentricity
Curr
en
t
Time
Time
Fre
qu
en
cy Fault signature
Dynamics and fault frequencies
Max
Min
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October 2016, Slide 10
Accessory motors: Emergence of concentrated windings
Fuel pump
Gerotor pump
mechanism
Rotor with
permanent magnetsConcentrated
stator windings
Source: Continental Source: MMT
Speed gauge actuator
Source: wikipedia
Crankshaft starter-generator
Mounted on flywheel (Honda 1999) • Developed first for 1) low
cost and 2) short packages
• Performance on par with
distributed windings
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October 2016, Slide 11
Concentrated windings used on power steering
• Power steering, with the most stringent torque ripple spec, is going with
concentrated windings!
• Proper combination of slot/poles, and shaping of magnets and slots critical
1st generation
• Distributed windings
• Ring magnet
2nd generation
• Concentrated windings
• Ring magnet
3rd generation
• Concentrated windings
• Segmented, shaped
magnets
Source: Nidec
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October 2016, Slide 12
High-speed motors for supercharging
• Basic concept: Pressurize intake air to expand engine output
• Turbocharger: Uses exhaust pressure to run a turbine
• Uses waste energy, but suffers from lag
• Supercharger: Direct actuation of pressurizing turbine
• Mechanical (belt driven): Cheaper, simple, but limited speed not ideal for turbine
• Electrical
Air intake
High-speed
motor
InverterDC bus Turbine
ExhaustPressurized air
Combustion
chamber
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October 2016, Slide 13
Electric super-chargers
• Can go to very high speed (70 to 150 krpm for 1-2 kW)
• Good for turbine
• Can be done with motors, but a first for automotive
• Issues of cost, controls, motor design from 12V
• First production-ready system (Valeo) uses switched reluctance motor
• 70 krpm
Source: Valeo
Compressor
Compressed air
Inverter
Control
board
Switched
reluctance
motor
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October 2016, Slide 14
Generator: Steady improvements
Lundell motor
Magnet
Source: Radomski (GM), US 4,959,577
Source: Bosch
• Lundell (claw pole) AC generator replaced DC generator in 50s
• Low cost, hard to beat! But, low efficiency (50%)
• Improved with:
• Magnets between claws
• Water cooled
• Active rectifier
• Lower losses (resistive drop better than
diode voltage drop)
• Control of phase angle
Source: Liang, Miller, Xu (Ford), T. IA, 1999 Speed (rpm)O
utp
ut cu
rre
nt (p
u)
1.5k 2.k 3.k 4k 5k 6k
Diode bridge
Active bridgeActive bridge
Alternator
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October 2016, Slide 15
Starter-generator
• Starter motors are used for 30 seconds then “dead weight” during regular driving
• Starting needs high torque at low speed (0 to 200 engine rpm), generation power
over a wide engine speed range (800 to 6,000 rpm)
• Combination starting to occur (finally) due to:
• More and more power demand (specs merging)
• Idle-off (stop-start) feature (4% fuel economy benefit)
• Belt-driven system offer good packaging
• PM: Research level
• Induction: GM eAssist (no magnet, wide speed range)
• Lundell: Toyota Lexus 2003, GM Saturn Vue 2005 (lowest cost solution)
GM induction
generator
Source: automobilemag.com
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October 2016, Slide 16
Hybrid/EV motors: New technologies
• Drive cycle optimization
• Winding
• Need for higher fill factors
• Magnet supply issue
• Higher speeds
• Materials and losses
• Torque ripple and noise
• Integration of magnetic and thermal
models
PM motor
Toyota hybrid (Camry 2007)
Induction motor
Tesla electric
Source: ORNL
Source: insideevs.com
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October 2016, Slide 17
Cycle optimization
• Importance of efficiency over actual cycles came to the fore in the early
stages of hybrid and EV development
• Top torque and speed are needed for emergency, passing, etc, but rarely used
• Some softwares now allow automatic calculations of desired/standard
operating points
Source: Burwell, et. al, Tokyo 2013 (Int. Copper Association)
Efficiency maps
Dots indicate actual operating points
based on standard drive cycles
Motoring
Generating
City driving (UDDS) Highway driving (HWFET)
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October 2016, Slide 18
Bar winding
• Introduced on GM 2006 Tahoe (motor by then Remy)
• Advantage of bars:
• Higher fill factor (60%)
• Shorter end turns
• Easier cooling
• Easier manufacturing
• If inserted from end (hairpin), small slot opening
• Advantage of round wires:
• Can have more turns/slot (more flexibility in design)
• Lower high frequency/speed losses
Source: Rahman, et. al, IEEE TIA 2014Source: Borg-Warner
Hairpin winding
Source: Jurkovic, et. al, IEEE TIA 2015
End bundle
Minimal space
between bars
Bar winding
Stranded
winding
Time
Tem
pera
ture
ris
e
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October 2016, Slide 19
Bar winding: High speed
• Proximity losses in bar windings need careful consideration
• AC resistance can be 10 times the DC resistance!
• Zhang and Jahns, IEMDC 2015
Source: Zhang and Jahns, IEMDC 2015
Traction motor, 4-bar winding
Current density versus position within slot
900 Hz 12,000 Hz
Resistance versus frequency
Base: DC
1
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October 2016, Slide 20
Magnet supply issue
• Rare-earth prices shot up sky high some 5 years ago
• Speculation over, but demand still growing
• Issue especially with “heavy rare earth” such as Dysprosium
• Research in new materials
• Strong argument for induction motors
• Dysprosium critical to prevent demagnetization under load at high temperature
• Or is it? New grades with “boundary diffusion process” can circumvent problem
$/kg
3,000
Dysprosium
Neodymium
Copper
$480/kg
$80/kg
$7/kg2001 2005 2008 2011 2013
2,000
1,000
Source: world.honda.com, July 2016
Honda Freed first hybrid vehicle
with magnet free of heavy rare earth
(Honda news, July 2016)
Source: metal-pages.com
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October 2016, Slide 21
Torque ripple and noise
• Electric machine #1 noise/vibration producer under the hood in EVs
• Even for hybrids, engines are quieter, and motors have annoying higher-frequency pitch
• Solutions:
• Magnet slot shape
• Asymmetric North and South poles
• Uneven rotor surface to cancel specific harmonics
GM Cadillac CT6 Plug-in hybrid
Rotor magnets
2 Vs
Indentations on rotor surface
(not to scale)
Additional pockets
Source: Jurkovic, et. al., IEEE ECCE 2016
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October 2016, Slide 22
Conclusions
• Automotive applications have driven many innovations, will continue to do so
• Challenging environment (temperature, cost) with a variety of applications
• Each with own needs (low torque ripple, efficiency, etc)
• Future development in:
• Higher speed, from hybrid motor reaching upward of 15,000 rpm to superchargers at
70,000 rpm
• Loss reduction at high speed, particularly in bar windings
• Reduced use of heavy rare-earth
• Integration of magnetic and thermal models for robust optimization
• Noise reduction
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October 2016, Slide 23
Bruno Lequesne -
Consultant, E-Motors Consulting, LLC
www.emotorseng.com
Thank you!
Electric power steering
Source: Nexteer
Electric supercharger
Source: Valeo
Hairpin windingSource: Borg-Warner
Efficiency optimizationSource: Burwell, et. al, Tokyo 2013