The Study Of Vehicle Attitude Control Based On Active Hydro-pneumatic Suspension

With nonlinear stiffness characteristics of the hydro-pneumatic suspension is mainlyused in special vehicles and large vehicles. And another advantage of it could realize thecharging or discharging fluid control as long as add the additional necessary componentsincluding valve group, pipeline, oil pump, oil tank and so on, can realize the vehicleattitude adjustment and active suspension function by the computer control.This paper based on the theory of the sliding mode control and the backsteppingcontrol in order to implement the attitude control of static vehicle. The research process wasadopted by the gradually progressive approach. Firstly, control the height of the singlewheel which could research and analysis the basic mechanism of the vehicle height control.Secondly, control the attitude of the half car to ensure that the vehicle can accomplish thevertical and the pitch motion. Finally, research on the vehicle attitude control based on theabove theoretical.Established the nonlinear model of the single wheel and the half car, adopteda doubleclosed-loop control strategy. The outer loop utilized backstepping algorithm to achieve thevehicle body attitude control and analyzed the zero dynamics. The inner loop used thesliding mode control algorithm to compensate the nonlinear term caused by the stiffness ofhydraulic actuator and servo valve, to make the actuator pressure tracking the desiredpressure that computed by the outer loop. Due to the chattering problems existed in thesliding mode control are analyzed and corrected in this paper. Ultimately, simulation andanalysis the control strategies used by the single wheel and the half car model to verify theeffectiveness of the control strategy.Establish the nonlinear model of the full car and designed the oil system that couldrealize the vehicle attitude adjustment. Considered the complexity of the full car model, itcould be divided into two main steps. Firstly, the ideal actuator control force of vehicleattitude control is conducted by PID algorithm for the linear suspension model whichignore the dynamics of the actuator. Secondly, the nonlinear model of the full car includingthe actuator dynamics is established with considering the oil compressibility, the nonlinearcharacteristic of the servo valve group and the friction between the piston and cylinder. Thenonlinear sliding mode control algorithm is applied to make the actuator pressure track thedesired control pressure. Through simulation and analysis to verify the designed controller could control the vehicle body attitude with rapidly and accurately.In summary，the attitude control for single wheel，half car and full car is studied bycombining the theoretical analysis and simulation calculation and the corresponding controlstrategies is presented.