Research On Nonlinear Control Of Four-wheel Steering System

With the development of modern automobile technology,more and more attention has been paid to active safety technology.Four-wheel steering vehicle can effectively reduce turning radius and improve maneuverability when driving at low speed;while driving at high speed,it can reduce the sideslip angle of the center of mass of the vehicle and effectively improve the driving stability and active safety of the vehicle.Therefore,four-wheel steering technology has become one of the important directions of automobile development.Traditional research on four-wheel steering technology was mostly based on Two-Degree-of-Freedom(2-DOF)linear model,but when the car was turning at high speed,the body roll was large,neglecting the roll will easily lead to larger errors.Based on this,considering the roll factor,a 3-DOF linear model was established,and a 3-DOF non-linear model was built for the tire roll characteristics.The steering characteristics and handling stability of the 3-DOF 4WS model were analyzed.The formulas of angular velocity gain and stability factor of steady yaw are deduced.The control stability of the 2-DOF linear model and the 3-DOF non-linear model were compared and analyzed.The analysis results show that the steering characteristics of the two models are basically the same,but the 3-DOF non-linear model can more truly reflect the steering characteristics of 4WS vehicles.Based on the 3-DOF 4WS nonlinear model and the zero sideslip angle of the center of mass,the proportional feed-forward and fuzzy PID integrated controller and the optimal controller were studied,and the step-by-step simulation analysis was carried out.In order to further verify the control effect of the controller,a 4WS vehicle multi-body dynamic model was built in ADAMS/Car,and the typical test conditions are selected for the co-simulation analysis of ADAMS-MATLAB.The results show that the four-wheel steering controller can effectively reduce the sideslip angle of the center of mass and improve the stability and safety of the vehicle.Among them,the optimal controller has the best control effect,which improves the vehicle's low-speed maneuverability and high-speed stability.