Project Title: Traction Electric Motor Drive                                                               
Research Team: Dr. Sabri Cetinkunt                                                                                       
Sponsor: MRC

Project Description:

Environmental protection and fuel efficiency concerns have been driving research and development efforts in alternative fuel vehicles over the gasoline fuel based vehicles. The electric motors will play a fundamental role as the electrical to mechanical power conversion devices in the future vehicles. While the fuel cell based vehicles are likely to take many more years to mature, electric motor based energy conversion has the promise of improving the power conversion efficiency, hence improve the fuel efficiency of gasoline based vehicles.

The power train in a traditional vehicle includes the engine as power source, a mechanical transmission (adjustable ratio gear box) to transmit the engine motion to the wheels through axles. The power is transmitted from the engine to the wheels via the transmission and large axle shafts. The electric motor based traction concept eliminates the transmission and axles. The power from engine is transmitted to the wheel by an electric motor. An electric generator is connected to the engine and provides a bus power to the electric motors connected to each wheel. Hence, the power is transmitted from engine to the wheels via electrical power cables instead of large rotating shafts. Hence, the energy to overcome the friction in axle bearings and transmission is saved. In addition, the acceleration/deceleration capability of the vehicle using the same level of engine power is improved since the transmission and axle inertia is eliminated. Furthermore, with electric motor based power delivery, it is possible to recover the regenerative energy during deceleration phases of motion (i.e. recharge batteries, reduce fuel consumption in the engine) instead of dumping out as the brake friction heat.

Traction electric motor concept includes an electric motor (i.e. induction motor, switched reluctance motor) with a planetary gear reducer directly designed into the wheel of a tire. The stator and rotor assembly is liquid cooled in order to increase the power density of the motor per unit size.

There is also fail-safe friction disk brakes at each wheel similar to the traditional vehicles. Power electronics can be packaged right into the wheel or can be housed in the vehicle cab. Each wheel has a local controller (slave) which controls the wheel in either open loop torque, closed loop velocity or position control mode. The commands are received over a CAN-bus from a higher level controller (master) which generates the appropriate commands for each wheel taking into effect traction control, vehicle stability, and ABS requirements.

The challenges in this project are as follows:
1. Design of a compact mechanical electric motor, gear reducer, brakes, and cooling system package for large power density and reliability,
2. Reliable coordinated control of each wheel by the master-slave controller hierarchy including traction control, vehicle stability, and ABS requirements,
3. Reliable and efficient use of regenerative energy to save fuel,
4. Cost effective in terms of manufacturing, operation, and maintenance.