A Robust Control Invariant Set Approach to Yaw Stability of Four-Wheel Drive Electric Vehicle

In this paper, a novel yaw stability control strategy for four-wheel drive electric vehicle under critical driving situations is presented. The motivation of this research is that oversteer occurs or yaw response performance is reduced when an inappropriate desired yaw rate is designed during the yaw rate tracking control. Although the bounded desired yaw rate is widely utilized to prevent oversteer in literatures, it is difficult to put forward the desired yaw rate which takes both yaw response and stability performance into account in practice. Considering that oversteer is caused by lateral forces saturation of rear wheels, this paper proposes a control strategy to constrain the lateral forces of rear wheels directly instead of bounding the desired yaw rate. The key of this work is that the state space consisting of yaw rate and side slip angle is firstly divided into two parts: saturated and unsaturated space of lateral forces of rear wheels. In the unsaturated space, the yaw rate tracking control is applied to enhance the yaw response performance. And in the saturated space, a robust invariant set yaw rate control is proposed to keep the tire slip angle of rear axle in a robust invariant set to constrain lateral forces of rear wheels. In this paper, the design approach of the robust invariant set control for yaw stability is discussed in detail. Simulation results show the effectiveness of the proposed method for enhancing yaw rate response performance and preventing lateral forces saturation of rear wheels.