Variable steering ratio characteristics for steerbywire vehicle
                                                                        LI Wenqi，WU Xiaodong
                       (School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)

Abstract: Aiming at improving handling performance of steerbywire vehicle, method for variable steering ratio characteristics was studied. Based on an objective vehicle handling performance index with multiobjective evaluation functions, combined with analysis on simulation results of doublelanechange tests conducted on a closedloop “drivervehicleroad” system, optimal steering ratio characteristics varied with vehicle speed was obtained. On this basis, the adverse effect of the nonlinear vehicle yaw rate gain properties on driver steering, was considered steering ratio characteristics varied with steering wheel angle was designed. Comparison experiments for steerbywire vehicles with fixed steering ratio system and variable steering ratio system were simulated. The results of lemniscate curve and double lanechange tests indicate that, compared with fixed steering ratio system, the proposed variable steering ratio system can not only improve vehicle maneuverability at low speed and path following performance at medium and high speed, but also reduce driver’s steering workload in controlling the vehicle.

Key words: steerbywire（SBW）; variable steering ratio; handling performance; simulation analysis