Design of new variable steering ratio for mechanical active steering system

For active steering vehicle, a proper steering ratio is important to the driver´s handling stability. This paper focuses on variable steering ratio. Based on the structure of double planet gear set, the relationship of steering wheel angle and motor angle is described, and the kinematic model of front wheel´s additional angle is established. In order to overcome the large steering workload in low speed and large lateral acceleration in high speed, a new variable steering ratio control law is proposed. The simulation results show the steering performance of vehicle is improved by using the designed variable steering ratio.