Research On Active Fault Tolerant Control Of Steer-by-Wire System For Multi-Sensor Failure

The steer-by-wire(SBW)system eliminates the mechanical connection between the steering wheel and the front wheels,and uses bus technology to replace the traditional mechanical steering system to transmit signals.The electrical control unit(ECU)determines the target steering wheel angle based on the transmission ratio and the compensation angle obtained from the vehicle state feedback,and drives the steering motor to run through the relevant control algorithm,so that the steering wheel angle is finally equal to the target angle,so as to realize the car steering.The sensors are required to obtain vehicle state and steering wheel angle,while these sensors in the SBW system are more susceptible to the external environment and cause various types of failures.This kind of the sensors failure will affect steering control strategy and degrade steering performance that even cause system instability.Up to now,it is still a topic to makes the current SBW system fully satisfying the requirements of functional safety level.Therefore,in view of the presence of multiple sensors faults in the SBW system,this study focuses on the fault diagnosis and fault-tolerant control to suppress the impact of sensors faults on the SBW system.The main research work can be included as following parts.Firstly,the various components of the SBW system and the working principle of steering are introduced,and the dynamics model of steering module and vehicle dynamics model are established.In view of the SBW system with parameter perturbation and sensors failure,the dynamics model of steer-by-wire vehicle for simulation is established.Secondly,the steering control strategy in SBW system is introduced.Adopt ideal transmission ratio control and linear quadratic regulator control,the front wheel active steering control is designed with yaw rate feedback.The simulation results indicate that the SBW system with ideal transmission ratio has better driving portability and steering sensitivity than the mechanical steering system with fixed transmission ratio,and the SBW system with yaw rate feedback control has better handling stability than the SBW system without yaw rate feedback control.In order to illustrate the influence of sensors faults on the front wheel active steering control,the steering angle sensor and yaw rate sensor have sudden failures.The simulation results indicate that the sensors faults will seriously damage the attitude of the vehicle,therefore affecting the handling stability and safety of the vehicle,which illustrates the necessity of sensor fault tolerant control.Thirdly,this paper proposes a multi-objective constrained fault estimator for multiple sensors faults in SBW systems to estimate sensor faults in SBW systems.On this basis,an active fault-tolerant control framework is further proposed with integrating fault detector,fault estimator and fault compensator.Among them,the fault detector is used to detect whether the system has a fault.The fault estimator uses the residual obtained from the fault detector to estimate the fault size and time-varying characteristics of the faulty sensor.The fault compensator uses the fault estimation value and the fault output of SBW to control the faulty sensor.Finally,in order to verify the effectiveness of the SBW active fault-tolerant control strategy proposed in this paper,a simulation analysis is carried out under the dual line-shifting test conditions.The simulation results show that the fault-tolerant control strategy proposed in this paper can ensure that the SBW system with fault still has the steering characteristics close to that of the fault-free SBW system under the condition of sensors failure,so as to ensure the vehicle’s handling stability and driving safety.