Research And Simulation On The Algorithm Of Height Control Used For Hydro-pneumatic Suspension

With features of regulating the gap of the chassis to the ground and controlling pitch and roll angles of vehicle body, the vehicle height control can increase the vehicle speed and improve the trafficability of the vehicle on rough roads. In this paper, the nonlinear characteristic of the vehicle height regulating system based on hydro-pneumatic suspension was studied both theoretically and experimentally and the vehicle height regulating model based on hydro-pneumatic suspension was built; With the whole vehicle model, the vehicle height control strategy based on hydro-pneumatic was researched, which served as theoretical support for the application of vehicle height control technology to vehicles equipped with hydro-pneumatic suspension. The main research with conclusions is as follows:(1) Taking the nonlinear characteristics in the charging and discharging processes of the hydro-pneumatic suspension system into consideration, the pressure gradient equation of oil in the cylinder and the pressure and volume gradient equations of gas in the accumulator were built, the mathematical description of the nonlinear characteristics in the charging and discharging processes of the hydro-pneumatic suspension was realized. With the modelling of the proportional solenoid valve model, the 1/4 vehicle model of vehicle height control system based on hydro-pneumatic suspension was further completed. The state variables’ responses of the AMESim model and the mathematical model were compared and the coincidence of the two hydro-pneumatic suspension models was verified. The validity of the mathematical model of the hydro-pneumatic spring was validated through bench test, which laid the foundation for the following hydro-pneumatic suspension control strategy.(2) Based on the mathematical model of 1/4 vehicle with vehicle height control system, the on-off controller was built, the existence of “overshoot” was verified, and the influence of the parameters of the cylinder and the accumulator, the characteristics and parameters of the electromagnetic valve and the oil pressure to the vehicle height regulating process was analyzed.(3) Based on the mathematical model of 1/4 vehicle with vehicle height control system, the PID controller, sliding-mode controller and model predictive controller were built. It is shown in the simulation results that, PID controller, sliding mode controller and model predictive controller all can solve the problem of “overshoot” in the vehicle height regulating process rapidly and stably improve the quality and accuracy of vehicle height control, while the response of vehicle height under the function of model predictive controller is the fastest.(4) The 7 – DOF mathematical model of the whole vehicle height regulating system based on hydro-pneumatic suspension and the road surface model were built. The nonlinear model of the whole vehicle height based on hydro-pneumatic suspension was linearized on the basis of linearization theories such as the states feedback linearization, with which the sliding mode control algorithm and model predictive control algorithm of the whole vehicle were designed. It is shown in the simulation results that, in both parking and driving conditions, the sliding mode controller and the model predictive controller designed can make the vehicle height reach the goal position rapidly and accurately and solve the problem of “overshoot” in the whole vehicle height regulating process. Compared with the model predictive control, the sliding mode control, with stronger robustness, has better performance in controlling of pitch and roll angle of the vehicle body, makes the vehicle height regulating process more stable and improves the quality and accuracy of vehicle height control significantly.