Research On Control Strategy Of Four Wheel Steering Vehicle's Rear Wheel Steering

Four-wheel steering is one of the ways to improve active safety of vehicle.At the low speed,the front and rear wheels have different rotation,reduce the turning radius,greatly improve the low-speed vehicle steering servo and parking agility operation;At the high speed,the vehicle is driven by the same rotation of the front and rear wheels,reduce the probability of occurrence of the slip accident and improve the stability and safety of high-speed vehicles.Based on this,this paper takes a suv as the prototype,according to the nonlinear characteristics of vehicle,design a nonlinear controller of rear wheel angle,expecting to improve vehicle performance.First of all,aiming at the error that is caused by lateral properties of tires and rolling of sprung when two degrees of freedom vehicle model is used to describe the steering process of vehicle,introduce the tire of magic formula,and set up a three-degree-of-freedom 4WS nonlinear vehicle model.The two degrees of freedom linear and three degrees of freedom nonlinear models are simulated and compared respectively,the results show that the steering characteristics of the three-degree-of-freedom nonlinear model are basically the same as those of the current two-degree-of-freedom model,and the real steering characteristics of the vehicle can be reflected in more detail,lay a foundation for the design of the rear wheel steering controller.Secondly,the stability factor formulas of yaw rate gain and steering characteristics of three degree of freedom 4WS vehicle are derived.And the influence of structural parameters on steering characteristics of four wheel steering vehicle is analyzed,which provides reference for the design of the rear wheel steering controller.Finally,based on the nonlinear characteristics of the vehicle,the design of fuzzy PID controller and sliding mode controller is studied emphatically.Meanwhile,based on the three degree of freedom nonlinear model,a simulation is carried out.The results show that two kinds of controller have good control effect,but the sliding mode controller has more advantages.Then,based on the ADAMS/Car software,eatablish the virtual dynamic model of four wheel steering vehicle,select the typical experimental conditions,carry out a co-simulation of ADAMS/Simulink.The effectiveness of the sliding mode controller has been proved again.