Research On Active Steering Control Strategy Of Front Wheel Steer-by-wire System

In essence,the steer-by-wire system controls the operation of the motor by means of electrical signal transmission to realize vehicle steering.It can interact with other electronic control systems in real time through bus technology,cooperate to control the transverse and longitudinal movement of the vehicle,which improves the handling stability of the vehicle.The research on steer-by-wire system is conducive to the integrated development of chassis by wire and promote the development of automobile intelligence.In this paper,the active steering control strategy is chosen as the starting point,and the research on steer-by-wire system is carried out around the variable angle ratio and vehicle stability control.The main contents are as follows:The first step is to complete the modeling work,which is prepared for follow-up research.The simulation model of steer-by-wire system and Car Sim vehicle model without steering mechanism are built respectively.The steer-by-wire vehicle model is constructed by defining a co-simulation interface and the reliability of the model is verified.In addition,a two-degree-of-freedom linear model is also built to obtain the ideal state parameters when the car is turning.Secondly,the variable steering gear ratio is designed.By exploring the difference of steering performance of traditional vehicles at different speeds,the design principles that should be followed for variable steering gear ratio are analyzed.The effect of designing variable steering gear ratio by different constant steady-state steering gain is studied,including the yaw rate gain and lateral acceleration gain.After simulation and comparison,the former is selected as the design scheme.The optimal value of steadystate yaw rate gain is searched by the method of genetic algorithm optimization.The improved S-function fitting method is selected to solve the problem that the upper and lower limits of the curve of variable steering gear ratio are not smooth,and after that the curve of variable steering gear ratio is finally obtained.The last step is to design the vehicle stability controller.Aiming at the transient process with large fluctuation range when the steer-by-wire vehicle turns,a feedback control strategy is proposed to continuously adjust the state parameters of the vehicle at every moment,and the vehicle stability controller is designed based on the theory of sliding mode control.According to the yaw rate of the steer-by-wire vehicle model,the ideal yaw rate of the linear reference model and the deviation between them,the controller determines the additional angle of the front wheel as compensation,so as to continuously adjust the motion state of the steer-by-wire vehicle and make it track the ideal response of the reference model.The simulation results proves that the control of variable steering gear ratio can improve the steady-state response of the vehicle and ensure that the steering characteristics of the vehicle tend to be consistent at different speeds.It also proves that the vehicle stability control can optimize the transient process of the vehicle.Under the joint control,the handling stability of steer-by-wire vehicle has been effectively improved when it turns actively.