Wheel Motors were developed for the Autonomy fuel cell concept vehicle project. Enables the low profile “skateboard” chassis by placing the traction motors in the wheels. Allows more chassis space for Fuel Cell components.

1. 1
Wheel Hub Motors for
Automotive Applications
EVS-21
April 5, 2005
James Nagashima
General Motors
Advanced Technology Center

2. 2
Concept Development
• Wheel Motors were
developed for the
Autonomy fuel cell
concept vehicle project.
• Enables the low profile
“skateboard” chassis by
placing the traction
motors in the wheels.
• Allows more chassis
space for Fuel Cell
components.

3. 3
What is a
Wheel Hub Motor ?
• High torque, permanent magnet
electric motor
• Completely contained within the
wheel
• Low Speed, 1,200 RPM
• Direct drive, no gears
• Integrated with wheel bearing
and hub

4. 4
Advantages of
Wheel Motors
• Eliminates drivetrain losses, harmonics and gear
backlash
• No gears – extremely quiet
• Electric motor can compensate for gear-shift torque
disturbances from ICE to enhance driver comfort
• Provides lots of low-end torque
• Enables higher level of vehicle control flexibility
– Natural tie-in to AWD and stability control
– Capability to control torque at each wheel independently and
selectively
• More even mass distribution for better handling and
driver comfort
• Universally applicable to anything with wheels

5. 5
Motor Operating
Principle
• Surface PM Axial Flux machine
• 2 outer Rotors with NdFeB
magnets and 1 central Stator.
• Magnetic flux crosses stator air-
gap parallel to axis of rotation.
• Current flows radially in stator
coils wound around laminated
core.
• Lorenz force is created as
cross product of current & flux,
creating torque around axis of
rotation.
Current
Torque
Flux
Stator
Rotor 1 Rotor 2
Magnets

6. 6
Magnetic Core vs.
Coreless Designs
Coreless design
• Stator windings fixed in epoxy with
non-magnetic coolant tube in center
• Lower overall mass due to epoxy core
• Large air-gap = Large magnet mass
• Low inductance = Small flux
weakening range
Slotted core design
• Stator wires wound around laminated
magnetic core.
• Higher overall mass due to iron core.
• Small air-gap = Low magnet mass.
• High inductance = Large flux
weakening range

7. 7
Wheel Motor
Requirements
Max. Speed (Operating) 1200 rpm
Max. Mechanical Speed (Non-Operating) 1500 rpm
Base speed 750 rpm
Peak torque, 30 sec. 500 Nm
Peak power, 30 sec. 25 kW
Continuous torque 200 Nm
Continuous power 16 kW
Max. overall diameter 390 mm
Max. overall length 95 mm
Max. mass 30 kg
• Two wheel motors are mounted on the rear axle to
supplement the front traction system. They provide 60%
additional torque to the existing S-10 electric truck.

8. 8
Motor Design
Parameters
• Motor designed to fit
within 17” wheel
• Used modified wheel
bearing and hub from
Buick Rendezvous
• Electrical parameters to
match existing GM power
inverter.
• Liquid cooling using
separate pump and
radiator
Number of phases 3
Number of poles 24
Peak torque 500 Nm
Stator o.d. 340 mm
Max. axial length 75 mm
Peak machine power 25 kW
Nominal bus voltage 280V
Peak machine current 150 Arms
Max. machine speed 1200 rpm

9. 9
Machine Fabrication
and Tests
• Motor was jointly designed
between University of Rome and
GMATC Torrance.
• All motors built at Lucchi
Elettromeccanica, Italy.
• Initial testing in Rome
– Generator operation, back EMF,
thermal, low power.
• Dynamometer testing at ATC
– Controls development
– Thermal, full torque, power,
efficiency, spin loss, etc.
Power Leads
Coolant Connections
Resolver Leads
Hub
Finished Wheel Motor on the bench
Wheel Motor in Assembly at Lucchi

10. 10
Torque, Measured
vs. Predicted
-600
-400
-200
0
200
400
600
0 200 400 600 800 1000 1200 1400
Speed (rpm)
Torque
(N-m)
250V Motor Measured 250V Motor Simulated 350V Motor Measured
350V Motor Simulated 250V Regen Measured 250V Regen Simulated
350V Regen Measured 350V Regen Simulated Specification
• 500 Nm torque range exceeded specification.
• At 350 VDC full torque to top speed.

11. 11
Power, Measured
vs. Predicted
-80
-60
-40
-20
0
20
40
60
80
0 200 400 600 800 1000 1200 1400
Speed (rpm)
Power
(kw)
250V Motor Measured 250V Motor Simulated 350V Motor Measured
350V Motor Simulated 250V Regen Measured 250V Regen Simulated
350V Regen Measured 350V Regen Simulated Specification
• Peak power (30 sec rating) exceeded spec.

12. 12
Magnetic Wedges
Reduce Losses
0
500
1000
1500
2000
2500
3000
0 200 400 600 800 1000 1200 1400
Speed (rpm)
Power
(W)
Machine with Magnetic Wedge Machine without Magnetic Wedge
• Soft magnetic composite wedges were inserted into slot
openings which greatly reduced slot harmonic losses.

13. 13
System Efficiency
(Inverter + Motor)
• Overall system efficiency in the mid-80% range in both
motoring and regeneration.
Motoring @ 350VDC Regeneration @ 350VDC

14. 14
Test Vehicle
Construction
• Started with existing
electric S-10 Truck with
100 kW front electric motor
and 320 V battery pack.
• Two 25 kW , 500 Nm
wheel hub motors added
to rear axle.
• Vehicle modifications were
done at Quantum
Technologies facilities.

15. 15
Chassis
Modifications
• Two 70 kW inverters and
radiators are mounted
underneath the vehicle
behind the rear axle.
• Coolant fill and reservoir for
rear traction system
mounted on side of bed.
Identical systems on left
and right hand sides.

16. 16
Suspension
Modifications
• Axle length shortened to
maintain correct rear track
• Wheel Motors bolted to
modified flange on solid
axle.

17. 17
Interior
Modifications
• Added controls mounted
between the driver and
passenger. PC laptop
mounting provided here.
Operator can choose
front/rear/both traction
systems.
• Data Acquisition System
installed to monitor key
parameters.

18. 18
Media Event
• Event held at Irwindale
Raceway August 2003
• Press briefing by Dr.
Lawrence Burns, GM R&D.
• Drag racing against 4 & 6
cylinder S-10 trucks.
• Wheel motors provided
60% more torque.
• Wheel motors outperformed
competitors in ¼ mile drag.

19. 19
GM Tech Tours
• Showcase of GM
automotive technology
• Los Angeles, San
Francisco, Tokyo, Beijing
• Test drives for Press,
Government Officials,
Celebrities, and Public
• >1,000 drivers, extreme
weather. No motor
problems
• Everyone loved the brisk
acceleration.

20. 20
Potential Applications
• Applies to ICE, Electric,
and Fuel Cell vehicles.
• 2WD or 4WD applications
• Easily added to FWD or
RWD platforms
• Creates on-demand AWD
Hybrid
• Enhanced vehicle stability
controls not possible with
mechanical traction.

21. 21
More Applications
• Advanced 4 wheel
steering. Mechanical
steering or torque
steering.
• Could enhance lane
keeping, collision
avoidance, and advanced
stability controls
• Permits zero turning
radius in 4WD. Gets out
of tight parking spaces.
Auto-Park controls.

22. 22
Next Generation
• Next Generation of Wheel Hub Motors are
featured on “Sequel” FC Concept Vehicle.

23. 23
Conclusions
• Presented design and development of an axial
flux PM, direct drive wheel hub motor.
• Measured performance exceeded requirements.
• Demonstration vehicle shown to public at media
event and GM Tech Tours in 2003
• Next Generation motor shown on Sequel FC
vehicle in 2005.
• Unique features make them desirable for future
applications.

24. 24
• Dr. Khwaja Rahman, GM Powertrain
• Professor Fabio Crescimbini, University Roma Tre
• Professor Federico Caricchi, University of Rome “La Sapienza”
• Dr. Giorgio Lucchi, Lucchi Elettromeccanica
• Quantum Technologies, Irvine CA
• GM Advanced Technology Center Team
Acknowledgments