Study On Pneumatic And Hydraulic Control System Of Vehicle With Active Hydro-pneumatic Suspension

Hydro-pneumatic suspension, as one of the new suspensions, not only has the functions of the traditional passive suspension, but also can develop into the active suspension by using hydraulic transmission and control technology, which have a perfect performance. Hydro-pneumatic spring is an executive component of Hydro-pneumatic suspension, which has a good nonlinear stiffness and damping characteristics. These excellent properties ensure that the vehicle can get a better ride comfort and handling. Therefore Hydro-pneumatic suspension has high research value in the automotive suspension domains.On the basis of analysis the non-linear characteristics of Hydro-pneumatic spring, this paper study on two different types of active hydro-pneumatic suspension using appropriate control methods. Through theoretical analysis and simulation, the paper gives the detailed types of active hydro-pneumatic suspension and its efficacy. The main works of this paper contents the following parts:(1)According to the traditional two DOF passive suspensions and the seven DOF of the whole vehicle, this paper established the suspension vibration models and the corresponding mathematical models including the equations of active suspensions. We give the ride evaluation methods of the car, as the suspension system output indicators. Theoretical analysis and simulate the impact and random road respectively, both of which will be used as road disturbance input suspension system, in order to analyze the different road conditions.(2) By splitting the main components of the gas springs and damping orifice valve systems, etc., the paper analyses the major structures and working principles of Hydro-pneumatic spring. Analyze and simplify the two main components of Hydro-pneumatic spring and establish a nonlinear mathematical model for MATLAB/Simulink simulation. We also establish the physical model directly in the advanced modeling software AMESim, comparing the results of the mathematical model and AMESim model to verify the correctness of the mathematical model. The nonlinear Hydro-pneumatic spring linearization and study the frequency characteristics.(3) Export the relationship between the capacitance of sphere(or suspension stiffness) and the multiple accumulators in the active suspension switching stiffness mode. For the active hydro-pneumatic suspension which has two different types, we use the servo-valve as the control element. By using two layer cascaded control method, we study on these two versions of hydro-pneumatic suspension. Analyze vibration suppression of two versions in random roads by using co-simulation with AMESim and MATLAB/Simulink. Contrast active and passive Hydro-pneumatic suspension to road excitation of amplitude-frequency characteristics.(4) Considering the major impact of the external environment on the vehicle vibration, we derived the braking model and the turn model and establish the pneumatic and hydraulic control system of Hydro-pneumatic suspension. Using co-simulation with AMESim and MATLAB/Simulink, we build the model of pneumatic and hydraulic control system and discuss each of them. Under the conditions of road excitation, breaking and turning, we compare the control effects of different pneumatic and hydraulic control systems. At last we make a brief summary of different pneumatic and hydraulic control systems about how to use the systems.