Ideal steering characteristics have important significance to the improvement of handling and stability of vehicle. In this paper,a novel variable transmission-ratio control strategy for rear-wheel active steering is proposed based on LQR optimal control theory. Firstly with concurrent considerations of low-speed handling responsiveness and high-speed driving stability,the ideal steering characteristics of a 4WIS electric vehicle are established. Then,the expected yaw rate is designed according to variable transmission-ratio curve,and by applying LQR optimal control theory,an active rear-wheel steering control strategy is proposed,so as to trace the expected values of yaw rate. Finally,a simulation on human-vehicle-road closed loop control under typical double lane change condition is conducted. The results show that with the control strategy proposed,the ideal steering characteristics can be well implemented.
variable transmission ratio
closed loop control simulation