Development And Verification Of Active Control Strategy For Electro-hydraulic Coupling Steering System

As the main transport equipment for long distance passenger and cargo transportation,in recent years,the safety and comfort of commercial vehicles have aroused wide attention from manufacturers and consumers.Because the steering system is a manipulating system that directly interacts with the driver,so how to reduce the fatigue of the driver and improve the safety of the vehicle is an important problem facing the design of power-steering system nowadays.The Electric Power Steering(EPS)system equipped with passenger cars has good handling characteristics and is able to carry out active compensation control under external disturbances.Combined with the National Natural Science Foundation of China," Control Mechanism and Evaluation Method of New Type of Steering System Based on Driver Characteristics "(No.51575223),and based on the commercial vehicle Electro-hydraulic Coupling Steering(EHCS)system,the active control strategy is developed in this paper,so that the steering characteristic of commercial vehicles will be similar to passenger cars.EHCS system is a new type of commercial vehicle steering auxiliary system.On the basis of the traditional Hydraulic Power Steering(HPS)system,a assist motor is added.The advanced functions such as anti crosswind,anti impact and active steering are realized by active control of the motor.After studying the related results of the EHCS system at home and abroad,an active control strategy including assist control,return control,anti crosswind control and anti road impact control is established in this paper.Then,a software simulation platform based on Matlab/Simulink,AMESim and TruckSim is established to verify the effectiveness of the control strategy.Finally,the EHCS test bed is set up,and the control strategy is further verified.The main contents are as follows:(1)In order to analyze the influence of crosswind and road impact on commercial vehicle at high speed,a simplified three degree of freedom vehicle dynamics model under crosswind influence and EHCS system model under road impact influence are established.Based on the three degree of freedom simplified model,the response characteristics of the yaw rate,the side slip angle and the roll angle of the vehicle under crosswind influence are analyzed.Based on the EHCS model,the response characteristics of the angle and torque at the steering wheel under road impact are analyzed.Finally,through the simulation analysis,the adverse effects of the crosswind and the road impact on the moving vehicle are shown intuitively.(2)In order to solve the contradiction between the portability and stability of the traditional commercial vehicle steering system,on the basis of the original control method of the research group,the assist control strategy and the active return control strategy are optimized in this paper.Based on the ideal hand torque and the EHCS test bed,the assist characteristic curve is designed.An incremental PID current closed loop method is used to control the assist motor so as to track the target moment.In the design of the active return control strategy,the flexible PID return control method based on the corner closed loop is adopted.PI control is used to improve the returning insufficiency at the low speed and PD control is used to suppress the returning overshoot at the high speed.(3)In the design of the active anti crosswind control strategy,the different control methods are designed.If the driver clenched the steering wheel,an adaptive compensation control was adopted to reduce the driver’s holding torque,and conversely switched to the compensation state(hold).Two control strategies are designed for the compensation state,the reverse assist and the synovium control,to reduce the yaw rate and side slip angle of the vehicle.The design of the anti impact control strategy is based on the impact torque estimation and the reverse assist compensation.By establishing the dynamic equation from the steering wheel to the circular ball steering gear of the EHCS system,the impact moment of the steering column is estimated,and then the impact compensation current is obtained,which is input to the assist motor,so as to reduce the impact of the road.In order to verify the effectiveness of the control strategy,a software simulation platform based on Matlab/Simulink,AMESim and TruckSim is built.(4)In order to further verify the designed control strategy,a test bed of the EHCS system is established.In the test process,aiming at the problem of time delay,large following deviation and inability to simulate small torque input conditions in the resistance simulation system,the combined control method of torque-speed control,torque closed loop control and compensation control are applied to improve the system performance.Finally,referring to the relevant standards of steering system test,the corresponding test conditions are designed according to the EHCS functions.By adjusting the active control parameters in the interface of the control platform,the control strategy is verified in the hardware environment.