| The steering and suspension system are two key subsystems of vehicle chassis,whichaffect vehicle handling stability,safety and comfort.The steering assist systems based on EPS are used in modern vehicles to assist the driver in steering task,which make driving easily.Electronic suspensions are used to improve vehicle ride comfort and handling statility under steering condition.However,considering driver manipulate failure and components fault in electronic control systems,which cause traffic accidents and performance decline of vehicle,road safety and the performance of electronic control systems cannot be guaranteed.Applying fault-tolerant control theory to vehicle steering and suspension control is an effective way to improve road safety and the reliability of vehicle.This dissertation mainly focuses on electric power steering(EPS)based human-machine cooperative steering system and semi-active suspension system(SASS),the fault-tolerant control strategy of which is studied through theoretical simulation and test.The main work completed and the innovation is summarized as follows:1)The working principle and discriminating method of EPS working mode in assist steering or assist driving is analyzed.For the assist mode of EPS,considering the simultaneous fault of the sensor and actuator of the EPS system and perturbation of the model parameters,robust unknown input observer is designed to simultaneously estimate the fault of sensor and actuator,the parameter perturbation is effectively suppressed to the performance of fault estimation.Active fault-tolerant control methods for sensor and actuator fault are designed respectively.Based on simulation and experiments,it is verified that the proposed active fault-tolerant control method of EPS can reduce the impact of the fault on EPS assist performance,the assisted torque under each fault mode can be restored to the original assisted torque by the percentage of 80 at least.2)Aiming at the assistance driving mode of EPS,Considering lane departure causedby driver manipulate failure,an EPS-based assistance driving system and driver cooperative fault-tolerant control method is proposed.Vehicle-road model with longitudinal vehicle speed as time-varying parameters is established,and lane keeping asssit system(LKAS)controller is designed based on model predictive control.Time to line crossing is used as a decision indicator for lane departure,which reflected driver manipulate failure.According to the state of driver,vehicle,the relative position of the vehicle and road,the cooperative control factor of driver and LKAS controller is determined in real time,and the system assist torque is determined by the cooperative control factor and the output torque of LKAS controller.Simulation and test verified that the lane departure assistance system based on man-machine coordinated fault-tolerant control can effectively avoid lane departure and reduce human-machine conflict.3)LQG and H_?controller for SASS is designed,and further,the robustness ofparametric perturbation and actuator fault of the two controller is compared.For actuator fault such as gain,deviation,jamming and signal interruption,in order to reduce the impact of fault on the performance of suspension system,adaptive observer is designed to estimate the values of fault,active fault-tolerant control based on fault compensation of SASS is proposed.Simulation and test verified that the proposed method can restore the performance of the fault suspension system to a level close to that of the normal one.4)Considering the coupling between the steering and the suspension system,human-machine cooperative steering and suspension integrated control based on hierarchical structure is built.The upper optimization layer establishes the integrated optimization objective functions of the EPS-based human-machine steering system and suspension system,in intermediate control layer,genetic algorithm is used to optimize the controller parameters of each subsystem respectively,the lower layer executes the control instructions of the intermediate layer and generates response through the vehicle dynamics system,corresponding signals of which is feed back to the upper layer.Further,the integrated coordination fault-tolerant control strategy for actuators with different fault severity is designed based on the genetic algorithm and hierarchical architecture,which reduces the impact of faults on the performance of vehicle.5)Test bench is established to verify the proposed fault-tolerant control algorithm.Firstly,an EPS hardware in-loop test bench based on LabVIEW PXI is built,and the effectiveness of the EPS active fault-tolerant control algorithm is verified.Secondly,hardware-in-the-loop test platform based on CarSim/LabVIEW RT is built to verify the effectiveness of the lane departure human-machine cooperative fault-tolerant control.Again,force-velocity characteristic test of the shock absorber is performed on single-channel electro-hydraulic servo suspension dynamic performance test bench,effectiveness of semi-active suspension fault-tolerant control test is conducted on a four-channel road simulation shaker further.Finally,SASS and LKAS integrated control is carried out based on the vehicle model in CarSim,the complete failure of SASS influence on LKAS and vehicle performance is analyzed on human-manchine cooperative lane departure assistance system test bench. |
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