Research On Model-based Fault Diagnosis And Fault-tolerant Control For Actuators Of ECAS System

Electronically controlled air suspension(ECAS)system has been widely applied to commercial vehicles and advanced passenger cars because of its excellent performances.One of main features for ECAS is that its body height can be effectively adjusted in real time.However,the actuators,namely the air spring solenoid valves for ECAS system are very easy to fail because of the complexity of the road conditions and the bad working environment.Failures of actuator can lead to poor control effect of ECAS system,which will deteriorate the performance of vehicle height adjustment and attitude control.Thus,in order to ensure the performance of height adjustment and attitude control of ECAS system,actuator fault diagnosis and fault-tolerant control are studied in this paper.Firstly,the basic structure and functions of ECAS system are introduced,including the sensors and air spring solenoid valves.By using the failure modes and effects analysis method,failures,failure effects and causes of sensors and air spring solenoid valves in ECAS system are analyzed.Risk priority numbers are used to evaluate the risk levels of different failures.Through using the fault tree analysis technique,the logical relation between components faults and system failures are presented figuratively and visually.Secondly,the height agjustment mathematical model for ECAS system of whole vehicle is built on the basis of vehicle dynamics and aerothermodynamics theory.The models of faulty actuators are also constructed based on the relation of duty cycle and mass flow in the air spring solenoid valve and common fault types.In order to verify the performance of fault diagnosis and fault-tolerant control method,the physical model of controlled object for ECAS system of whole vehicle is built based on AMESim.Aiming at the problem of actuator failures,faulty solenoid valves are added in the model.Therefore,fault occurrence can be simulated by switching between normal and faulty solenoid valves.The physical model provides the basic simulation platform for the research of actuator fault diagnosis and fault-tolerant control for ECAS system.Thirdly,height adjustment and attitude controllers of the ECAS system are designed by using PID/PWM strategy and fuzzy control algorithm.Aiming at the actuator fault diagnosis,filter bank designed by extended kalman algorithm is established to estimate state information.Residuals are obtained with measurement outputs and fault detection indexs are also achieved.At the same time,self-adaptive thresholds are designed to improve the accuracy of fault diagnosis.Then,the residual feature description is formed to realize the fault detection and isolation.Further more,aiming at fault-tolerant control problem,fault parameter is estimated based on analytical model of air spring solenoid valve.Failure types are judged according to fault estimates.For the failure fault,vehicle adjustment will be cancled.For constant gain fault,controller parameters will be changed on line.Co-simulation results show that the proposed algorithm of fault diagnosis and active fault-tolerant control can detect and isolate actuator faults rapidly and accurately,and improve the performance of vehicle adjustment and attitude control under faults efficiently.Finally,in order to check the fault diagnosis and fault-tolerant control algorithm performance in the actual controller,the hardware-in-the-loop test platform for fault-tolerant control of ECAS system is constructed by building the model of controlled object,developing the rapid control prototype of algorithm software and creating system project files and user interface.The Hi L test results show that the actual controller with the designed algorithm of fault diagnosis and fault-tolerant control can work normally and can effectively realize the fault diagnosis and fault-tolerant control for actuators of ECAS system.