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Wheel Hub Motors forWheel Hub Motors for Automotive Applications Automotive Applications

EVS-21April 5, 2005

James NagashimaGeneral Motors

Advanced Technology Center

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Concept DevelopmentConcept 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.

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What is aWhat is a Wheel Hub Motor ? 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

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Advantages ofAdvantages of Wheel Motors 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

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Motor OperatingMotor Operating Principle 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

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Magnetic Core vs.Magnetic Core vs. Coreless Designs 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

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Wheel Motor Wheel Motor RequirementsRequirements

Max. Speed (Operating) 1200 rpmMax. Mechanical Speed (Non-Operating) 1500 rpmBase speed 750 rpmPeak torque, 30 sec. 500 NmPeak power, 30 sec. 25 kWContinuous torque 200 NmContinuous power 16 kWMax. overall diameter 390 mmMax. 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.

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Motor DesignMotor Design Parameters 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

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Machine Fabrication Machine Fabrication and Testsand 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

HubFinished Wheel Motor on the bench

Wheel Motor in Assembly at Lucchi

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Torque, MeasuredTorque, Measured vs. Predicted vs. Predicted

-600

-400

-200

0

200

400

600

0 200 400 600 800 1000 1200 1400

Speed (rpm)

Torq

ue (N

-m)

250V Motor Measured 250V Motor Simulated 350V Motor Measured350V Motor Simulated 250V Regen Measured 250V Regen Simulated350V Regen Measured 350V Regen Simulated Specification

• 500 Nm torque range exceeded specification. • At 350 VDC full torque to top speed.

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Power, MeasuredPower, Measured vs. Predicted vs. Predicted

-80

-60

-40

-20

0

20

40

60

80

0 200 400 600 800 1000 1200 1400

Speed (rpm)

Po

wer

(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.

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Magnetic WedgesMagnetic Wedges Reduce Losses Reduce Losses

0

500

1000

1500

2000

2500

3000

0 200 400 600 800 1000 1200 1400

Speed (rpm)P

ower

(W)

Machine with Magnetic Wedge Machine without Magnetic Wedge

• Soft magnetic composite wedges were inserted into slot openings which greatly reduced slot harmonic losses.

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System Efficiency System Efficiency (Inverter + Motor)(Inverter + Motor)

• Overall system efficiency in the mid-80% range in both motoring and regeneration.

Motoring @ 350VDC Regeneration @ 350VDC

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Test Vehicle Test Vehicle ConstructionConstruction

• 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.

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ChassisChassis Modifications 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.

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SuspensionSuspension Modifications Modifications

• Axle length shortened to maintain correct rear track

• Wheel Motors bolted to modified flange on solid axle.

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InteriorInteriorModificationsModifications

• 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.

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Media EventMedia 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.

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GM Tech ToursGM 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.

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Potential ApplicationsPotential 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.

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More ApplicationsMore 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.

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Next GenerationNext Generation

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

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ConclusionsConclusions

• 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.

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• 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

AcknowledgmentsAcknowledgments