Research On Chassis Integrated Fault-Tolerant Control Based On Driving And Partial Steering

With the increasing environmental pollution brought about by the popularization of traditional automobiles,electric vehicles have attracted more and more attention.With the development of automotive electronics technology,X-by-wire technology will be widely utilized in automobiles.However,although the X-by-wire technology of electric vehicles has been greatly developed,its active safety and reliability are still the focus of research.This paper focuses on the problem of the left front wheel failure of the steering system for electric vehicles.The main tasks include the following sections:(1)Based on the CarSim and Simulink software and under the premise of certain assumptions and simplifications,the sub-modules of electric vehicles with steer-by-wire technology and four-wheel driving independently were established respectively.(2)On the basis of the optimal preview lateral acceleration driver model,a non-linear neural network PID driver model with the neural network combined with the traditional PID algorithm was established.Then,these subsystems are integrated into the "human-vehicle" closed-loop simulation model for electric vehicle with four-wheel driving independently and steer-br-wire technology.(3)The estimation method of the side slip angle was proposed.With the characteristics that the side slip angle is not directly measurable,a non-linear two-degree-of-freedom vehicle dynamics model is established under the premise of considering the side slip angle,the yaw rate and the front wheel rotation angle.At the same time,based on the recursive least squares algorithm,a side slip angle estimator which utilized the lateral velocity as the intermediate variable is proposed.Furthermore,based on RLS,an adaptive adjustment rule of weighting coefficient based on phase trajectory is introduced to establish a side slip angle estimator.Under the open-loop and closed-loop operating conditions respectively,the simulation algorithm was verified and analyzed.Corresponding simulation results show that the side slip angle estimation method established in this paper has good estimation accuracy.(4)Aiming at the left front wheel failure problem of the steering system studied in this paper,a fault-tolerant control strategy based on the over-actuated system is proposed.The whole control system adopts a hierarchical integrated control architecture,which is composed of an upper-level motion controller and a lower-level control distributor.The upper-level motion controller designs a corresponding sliding mode controller to obtain the yaw moment compensation expected by the vehicle in this driving state,according to the vehicle's desired yaw rate and theside slip angle as the control target;the lower-level control distributor introduces a weighted pseudo-inverse control distribution method and regards the longitudinal force and lateral force of the wheels as the control goal.The goal is optimized to meet the yaw moment required for the vehicle.Meanwhile,with the constraint of the tire adhesion and motor drive peaks,the tire longitudinal force and lateral force are properly allocated to achieve optimal control.(5)For the steering fault-tolerant integrated control strategy established in this paper,simulation verification was carried out under the open-loop and closed-loop tests respectively.The vehicle's motion state with the integrated fault-tolerant control strategy is compared and analyzed when the vehicle has no failure in the steering system,left front wheel steering failure.The important state parameters of the vehicles are obtained,such as the side slip angle and the yaw rate error.The simulation results show that the maximum relative error utilizing the integrated fault-tolerant control strategy for the side slip angle and the yaw rate error relative to the reference value respectively is only 8.47% and 19.3%,respectively.Hence,it was proved that the integrated fault-tolerant control strategy based on the active steering system and the driving/braking system can ensure the Safety and stability of the electric vehicles.