Variable Steering Ratio Design for Vehicle Steer-by-wire with Joystick Based on Variable Yaw Rate Gain

A joystick is utilized to substitute the conventional steering wheel with typical vehicle steer-by-wire(SBW) system and studied the variable steering ratio design method in this novel control structure.A 2-DOF dynamic reference model of vehicle is established and focused on the vehicle steering performance of drivers control joystick.The drawbacks are analyzed that traditional ideal steering ratio of constant yaw rate gain of SBW system with steering wheel is applied to joystick.The velocity factor and angle factor are presented to design variable steering ratio that keep the vehicle yaw rate gain linear variation.In addition,the vehicle model and steering ratio design method are computed and analyzed by using the software of Matlab/Simulink.A fixed driving simulator is used to verify variable steering ratio design method.The test results show that the proposed method can improve vehicle handling stability and comfort,which can effectively carry out steering intention of drivers that the joystick is better than the steering wheel in the lane tracking performance.