Research On Lateral And Longitudinal Coordination And Steering Failure Fault Tolerance Control Of Intelligent Vehicles

Intelligent vehicles,as an integrated systems of environment perception,planning and decision-making,and execution control,which has significant advantages in improving road utilization and traffic safety,and has become a research hotspot in the current automotive field and a new direction for the future development of the automotive industry.Among them,efficient and stable trajectory tracking control is one of the necessary conditions for realizing intelligent and practical vehicles.However,current research mostly focus on lateral motion and does not consider the influence of longitudinal speed changes on trajectory tracking control.At the same time,the steering control capability of the intelligent vehicle is closely related to the trajectory tracking control,and when the steering system fails during the driving process of the car,it will affect the trajectory tracking effect of the intelligent car and even lead to instability.Therefore,this thesis designs a lateral and longitudinal integrated control system and a fault-tolerant control strategy based on differential steering for a fourwheel independent drive intelligent vehicles,ensuring that intelligent vehicles can maintain good trajectory tracking effect and driving stability during operation.Firstly,MATLAB/Simulink is used to establish the vehicle dynamics model,which mainly includes the vehicle lateral and longitudinal dynamic model,wheel model and tire model..Under the same working conditions,the established vehicle model is compared with the CarSim vehicle model through simulation,and the results show that the vehicle model established in this thesis can effectively reflect the vehicle motion and provide a model basis for subsequent controller design.Secondly,based on the Model Predictive Control(MPC)theory,an intelligent vehicle lateral path tracking controller was designed,and the process of applying the MPC theory in path tracking control was analyzed.Meanwhile,considering that the prediction horizon in the MPC controller would affect the path tracking performance,an adaptive prediction horizon control strategy was designed to optimize the prediction horizon.The lateral path tracking controller was simulated using a double-line road as the reference trajectory,and the results showed that the controller can achieve tracking of the vehicle’s reference trajectory,and has good robustness to vehicle speed and tire-road friction coefficient.Then,based on the longitudinal dynamic model,a MPC-based longitudinal speed controller and a PID longitudinal speed controller were designed,and the performance of the two speed controllers was compared through simulation analysis.A comprehensive control system for both lateral and longitudinal motion was designed with longitudinal speed as the coupling point.The expected speed sequence was generated by a preview speed decision-making model,and both lateral and longitudinal motion of the vehicle were controlled.The effectiveness of the control strategy was verified in a joint simulation environment using CarSim and Simulink.Finally,considering the problem of steering failure during trajectory tracking of intelligent vehicles,a fault-tolerant control strategy based on differential steering principle was designed.The upper layer calculated the differential torque required for tracking front wheel steering angle using sliding mode variable structure control.The lower layer established a torque optimization allocation controller to allocate the driving torque and differential torque with the control objective of minimizing tire comprehensive adhesion utilization.Through simulation analysis of the fault-tolerant control strategy,the results show that the designed strategy can enable the vehicle to track the reference trajectory even when the steering system fails.