Abstract
In the past, some steering structures and control methods to stabilize vehicle motion have been studied. Active front steering (AFS) system controls the front axle wheel angle automatically to stabilize vehicle dynamics with variable gear ratio by planetary gear or harmonic gear or steer-by-wire system. The driver receives reaction torque from road surface via steering wheel. The driver needs the torque for steering operation. In case of the steering system with variable gear ratio, the reaction torque control is difficult because of causing steering interference between steering torque and road reaction torque during AFS operation. On the other hand, steer-by-wire can decouple the interference. However, the driver can not receive road information due to separation between steering wheel and the front axle wheel. This paper proposes to control vehicle motion characteristics dynamically without variable gear ratio structure or steer-by-wire. It consists of electric power assist steering and differential torque with In-Wheel-Motors on electric vehicle. In addition, we propose two degree of freedom of variable assist torque control. Our proposed method combined with these techniques can control both vehicle dynamics and road reaction torque. And it will provide driver-friendly man-machine interface to reduce driver operation errors and traffic accidents.
Keywords: Electric vehicle, In-wheel-motor, Steering control, Human interface, Vehicle dynamics control