Research On Control Strategy Of Vehicle Steer-by-Wire System Based On CarSim

Compared with the traditional steering system,the steer-by-wire system eliminates the mechanical connection between the steering wheel and the steering gear,and is completely replaced by an electronic control system,so that the steering transmission ratio can be freely designed,and is convenient for the vehicle steering system to integrate with other active safety control systems,which is beneficial to improve the steering stability of the vehicle,and is of great significance for the research of driving comfort and active safety of the vehicle.However,there is no uniform standard for the design of the steer-by wire steering ratio at home and abroad.The vehicle stability control strategy is also constantly optimized.In view of this situation,the paper mainly studied the ideal variable steering ratio of the steer-by-wire system and the active steering control strategy of vehicle driving stability.The main research contents are as follows:1.The structure and working principle of the steer-by-wire system were analyzed in detail,and the dynamic differential equation of the steer-by-wire system was established.The dynamic simulation model of the steer-by-wire system was built by MATLAB/Simulink software,and embedded in the CarSim vehicle model that removes the mechanical steering system,thus completing the establishment of the steer-by-wire vehicle model.And the correctness of the model was verified by typical simulation conditions.2.Study and analyze the steering characteristics of traditional steering systems and steer-by-wire systems.According to the advantage that the steering transmission ratio of the steer-by-wire system is not limited by mechanical components,based on the two-degree-of-freedom vehicle model,the fixed steering sensitivity method was used to realize the variable steering ratio control of the steer-by-wire system.The simulation results show that,compared with the traditional fixed angle transmission ratio,the variable steering transmission ratio of steer-by-wire system designed by this method can improve the steering stability of the vehicle at medium-low speeds and medium-high speeds,but it is not conducive to the stability of the vehicle at high speed.Therefore the variable steering ratio of steer-by-wire system needs to the further optimized design.3.In order to design a more ideal steering ratio of steer-by-wire system and comprehensively improve the steering stability of the vehicle,based on the CarSim real vehicle model,the vehicle characterization simulation analysis was carried out,and the calculation formula of the actual yaw rate gain of the front wheel angle to the vehicle response was derived.Based on this,the variable steering transmission ratio designed with multiple schemes.Through the simulation and verification,it is determined that the variable steering transmission ratio designing by the segmentation idea and considering the steering sensitivity and the lateral acceleration gain is the ideal variable steering transmission ratio,which can make the vehicle have better steering stability at different speeds.4.Based on the control of variable steering ratio,the active steering control strategy of vehicle with the yaw rate as the feedback control target was studied.For the nonlinearity and time-varying characteristics of the steering system,paper selects the sliding mode control algorithm based on radial basis neural network to adjust the switching gain for active front steering control of steer-by-system system.The simulation results show that it not only has strong robustness,but also effectively weakens the chattering phenomenon in the simple sliding mode control,and achieves accurate tracking of the target front wheel angle.So that the vehicle can achieve stable steering according to the driver's input operation at different speeds and complicated road conditions.And the steering performance of the vehicle is improved.