Design of a variable steering ratio for steer-by-wire vehicle with a joystick:

Steer-by-wire system has replaced the conventional mechanical linkages with electronic actuators. In this article, a joystick is utilized to substitute the conventional steering wheel and study the variable steering ratio design methods in this new human-machine interface. With this structure of steer-by-wire system, the steering angle and torque ratio can be designed flexibly. A dynamic model of joystick of steer-by-wire system is built based on bilateral control scheme. Through comparing the vehicle steering performance of joystick with steering wheel, three conventional steering ratio design methods are studied that are speed-dependent, speed- and angle-dependent and constant yaw rate gain. The drawbacks are analysed by three kinds of conventional steering ratio, and a novel variable yaw rate gain steering ratio design method is investigated. A driving simulator is used to verify and compare these steering ratio design methods. The computer simulation and experimental test results demonstrate that the variable yaw rate gain steering ratio design method can effectively guarantee vehicle steering performance.