Electric vehicle system independently driving front and rear wheels

A new type electric vehicle suitable for city cars is proposed which can easily cope with traffic situations such as traffic jams, frequently starting and stopping operations, and the failure of the motor drive system occurring while running on the city routes. The proposed electric vehicle drive system is mainly composed of a permanent magnet type synchronous motor (SM) for the front wheel drive and an induction motor (IM) for the rear wheel drive. Each motor is directly connected via the differential gear (ratio of 5:1) and have the ability to independently drive the front and rear wheels. The torque reference generated from the accelerator is mainly distributed to the SM for driving the front wheels. The torque of the IM for the rear drive is normally controlled so as to accord with the speed of the SM in order to prevent the IM from operating as the load of the SM. The torque reference generated from the accelerator is distributed to the IM when it is judged that the torque generated from the SM is insufficient to drive the EV. The torque control to accord with the speed of the front wheels is immediately stopped when the speed of the rear wheel is increased up to excess speeds by slips of front wheels. The proposed drive system has also fail-safe functions to keep on running, even if either the front or rear wheel drive system has failed. These functions with the proposed EV system were verified through simulations.