Research On Sensor Fault Diagnosis And Fault-tolerant Control Of Intelligent Vehicle Steer-by-wire System

Without any mechanical connections between the steering wheel and the front wheel,steerby-wire(SBW)system gives the steering system great advantages in steering performance,structural arrangement and ride comfort,and gradually attracts attention in the field of intelligent vehicles.However,the current SBW system cannot fully meet the functional safety requirements due to the reduction of vehicle controllability in the case of system failure,which is the focus and difficulty of the research of SBW systems.In this paper,according to the actual needs of the scientific research project,the sensor's fault diagnosis and fault-tolerant control of SBW system for intelligent vehicles are studied from the perspective of functional safety.Firstly,according to ISO26262-3,the scenarios and risk events of the SBW system are comprehensively analyzed.The ASIL evaluation of the system is completed,and the corresponding safety objectives of the system risk events are determined.Through the determination of the main safety mechanisms and measures,it is pointed out that the current functional safety research of SBW technology focuses on the fault detection and fault-tolerant compensation of sensors,motors and ECUs.Combined with the scientific research project,the fault diagnosis and fault-tolerant compensation algorithm of the angle sensor is selected as the research focus.According to the structural similarity between the electric power steering system and the SBW system,the prototype structure of the SBW system is determined,and a dynamic model is built.Considering the nonlinearity of vehicle dynamics model and tire model,a complete steeringtire-vehicle dynamics model is built.Secondly,based on the dynamic model,the Unscented Kalman Filter(UKF)algorithm with better filtering effect for the non-linear system is selected to design the vehicle front wheel angle estimator,and the accuracy of the algorithm for the vehicle front wheel angle estimation is validate.At the same time,the self-diagnosis strategy of the estimator is designed to ensure the validity of the front wheel angle estimation.For sensor fault diagnosis,by modeling and analysis of typical failure modes of sensors,the sensor stuck fault diagnosis algorithm based on the statistical characteristics of the sensor's own measurement sequence and the sensor noise and offset fault diagnosis algorithm based on the statistical characteristics of the sensor residual sequence are proposed.In the third chapter,the correctness of the fault diagnosis algorithm is discussed.For fault-tolerant compensation,an Adaptive Kalman Filter(AKF)is designed for noise faults in the correctable domain,and the compensation output sequence is more accurate than the estimation sequence.For the other fault types,fault tolerant compensation output is the estimation sequence.To avoid a sudden change of the angle value,the switching weight function is designed to smooth the process of outputting the estimation sequence and avoid the large disturbance to the control system.Finally,the intelligent vehicle path tracking control is selected as the upper control function to validate the fault-tolerant control performance of proposed algorithms.According to the optimal control theory of linear quadratic regulator,the state feedback control of path tracking control is designed.Feedforward control is added to decrease the steady-state tracking error of the system and to achieve zero position error control under the ideal control of the system.A path tracking control system based on fault diagnosis and fault-tolerant compensation algorithm is built by CarSim-MATLAB/Simulink simulation platform,and the effect of sensor fault-tolerant control is analyzed.Based on the NI PXIe8135 real-time controller,the hardware-in-the-loop(HIL)experimental platform of the angle sensor is built,and the fault injection of the angle sensor is carried out to validate the real-time performance and effectiveness of the fault diagnosis and fault-tolerant compensation algorithm.In the field tests,by designing and modifying the real vehicle SBW system,the active angle control of the test vehicle is completed by using NI Compact RIO as the prototype of controller.Vehicle test is carried out by using dSPACE MicroAutoBox II as the realtime computation platform of the algorithm,and the feasibility and effectiveness of the algorithm in vehicle application are validated.