Study On Fault-tolerant Control For X-by-wire Four-wheel Independent Driving Electric Vehicles With Steering Failure

Under the dual pressures of energy crisis and environment pollution,the electric vehicle,as the effective way to solve the problems above,has attracted more and more attention.The electric vehicle with four-wheel driving independently and steer-by-wire technology has become the key point in vehicle dynamic research and vehicle technology development worldwide for the each wheel could be controlled independently,easier to implement complex movement control and provides more space to boost the whole vehicle performance.Although electric vehicle technology matures gradually,its safety and reliability are still the focus of attention.Based on the fault-tolerant control of steering failure problem for electric vehicle with four-wheel driving independently,a series of research has been carried out in this paper.The main works are listed as follows:First of all,the simulation model of electric vehicle with four-wheel driving independently has been established.Considering vehicle longitudinal,lateral and horizontal yaw movement and four wheel rotation,the vehicle model with seven degrees of freedom is established.With magic tire model,use MATLAB/Simulink to build simulation model of the vehicle.Analyze the simulation results of two kinds of conditions,and contrast with the Carsim software simulation results,the accuracy of vehicle dynamic model is verified.Secondly,the key state parameters estimation of vehicle has been studied.Based on extended kalman filter method and considering the tire cornering characteristics,the vehicle key state parameters have been estimated.Using virtual simulation software,some certain simulation conditions are selected to verify the accuracy of the estimation algorithm.Then,the fault-tolerant control strategy for steering system failure has been researched.According to redundancy control,establish the fault-tolerant control architecture,including the driver model,upper motion controller and the lower control distributor.Based on preview optimal lateral acceleration driver model,combining with the characteristics of fuzzy control and traditional PID control,the fuzzy-PID driver model is established for expect motion state;design the motion controller based on sliding mode control theory to get the overall virtual control;aim to reducing tire utilization and improving the tire adhesion margin,lower control distributor distribute the expected yaw moment to the driving motors at each four wheels through the collaborative work between the optimal and axial load ratio distribution modes.Considering the transfer of vertical load,the weight coefficients are adjusted according to the lateral shift rate of the center of gravity in the process of optimal allocation mode.Finally,in order to verify the validity of the fault-tolerant control strategy proposed in this paper,the simulation has carried on based on high adhesion step and low adhesion double line conditions.Simulation results show that the proposed fault tolerant control strategy for steering failure could ensure the vehicle realize the expected response and improve the driving safety after the fault.