Dynamic Driving/Braking Force Distribution in Electric Vehicle with Independently Driven Four Wheels

Abstract

Novel algorithm of the dynamic driving/braking force distribution is proposed for electric vehicle (EV) with four in-wheel motors. In such EV, the vehicle lateral motion can be controlled by yaw moment, generated with torque difference between wheels. This method is known as DYC (Direct Yaw moment Control) in normal engine vehicle engineering, however, the torque difference can be generated more directly with in-wheel motors. One problem of DYC is its instability on the slippery road, such as wet or snowy asphalt. To achieve high stability, the loads of wheels are preferable to be equal. The load of each wheel can be evaluated with root sum square of driving/braking force and side force. Therefore, the driving/braking forces, or motor torques, should be distributed depending on the side forces of wheels, to minimize the load imbalance between the wheels. The proposed algorithm can solve this optimization problem approximately with a few calculation cost, thus this method can be applied for real-time calculation within a control period. The approximate solutions with proposed method are evaluated by comparison with numerical solutions that require long calculation time. Difference between these solutions is negligible one, and this indicates the effectiveness of proposed method. © 2000, The Institute of Electrical Engineers of Japan. All rights reserved.