Dynamic Study On Vehicle Hydro-Pneumatic Suspension System

Hydro-pneumatic spring is a kind of gas spring which uses inert gas (usually nitrogen) as spring medium and hydraulic oil as damping medium. Due to the nonlinear stiffness characteristics and nonlinear damping characteristics, vehicle hydro-pneumatic suspension system which takes hydro-pneumatic spring as the elastic element can meet the engineering requirements of vehicle ride comfort to the best. It becomes the focus of vehicle suspension study in recent years.Based on the analysis of hydro-pneumatic spring principles, a nonlinear mathematical model of hydro-pneumatic spring system is established with the system mechanical modeling in engineering. Specific equations of output force of hydro-pneumatic spring piston rod are given. At the same time, the relationship between output force and displacement, velocity of hydro-pneumatic spring system piston arc analyzed and studied by numerical simulation.According to the nonlinear mathematical model, damping and stiffness characteristics of hydro-pneumatic spring system and various factors which impact them are studied. The stiffness and damping linearization formula of vehicle hydro-pneumatic spring is given which provides a reasonable stiffness and damping parameters for system dynamics modeling. Two degrees of freedom dynamic model of vehicle hydro-pneumatic spring system is established. The hydro-pneumatic spring suspension system response is numerically simulated by Simulink software with different level road displacement excitation. The frequency characteristics of the system is also been analyzed.The PID controller structure on the active hydro-pneumatic suspension system is designed on the basis of established hydro-pneumatic spring suspension system dynamic model. The parameters of suspension acceleration, suspension deflections and tire load weight are simulated to both active and passive suspension systems under different road conditions. Eventually, a mechanical model of the system is established by ADAMS dynamic simulation software. The union simulation model of ADAMS and MATLAB of hydro-pneumatic spring suspension system is also been established which provides a new method for dynamic simulation of ydro-pneumatic spring suspension system. The study results show that by using active suspension system, the acceleration RMS value of the vehicle body can be reduced by one-third, the suspension dynamic travel RMS value is reduced six percentage points and the vehicle dynamic load RMS value is reduced one-third which means active suspension system can significantly improve vehicle riding comfort.Hydro-pneumatic spring and vehicle hydro-pneumatic spring suspension system dynamics model are established in this paper. Dynamics equations of hydro-pneumatic spring and vehicle hydro-pneumatic spring suspension system are also been derived. Those models and equations can be used to sovle dynamics questions in engineering of hydro-pneumatic spring suspension system. The research method of this paper has theoretical significance and engineering applications. The results of this study also has reference value in theory analysis and design of hydro-pneumatic spring.