Modeling And Simulation Analysis Of Hydro-pneumatic Coupled Suspension System

Four-wheel vehicle suspension generates four vertical forces positioning the body. In the premise of ensuring the freedom of the car plane, three force will be enough from the positioning request, and the forth one comes into being excessive. When the road roughness is close to or greater than static deflection, the disadvantage of the excessive force will become more prominent. Although the cancellation of a wheel can be viable, the performance of handling stability and ride of three-wheeled vehicle is not ideal when compared with the four-wheeled vehicles. Such shortcomings, in the automotive design process, usually based on increasing the static deflection of the suspension, but the static deflection increase causes various difficulties.The existence of excessive constraint will inevitably lead to the uneven load on each wheel. The longevity of other auto parts will be affected when the body is excessive deformation by the impact and torsion on rough road. Accidented road can even lead to phenomenon of early damage like cracks.Based on the problem and the Value Controlled Coupled Equalizing Suspension System revealed by Prof. Konghui Guo, this thesis studies and analyses coupled equalizing suspension system. Hydro-pneumatic coupled equalizing suspension system can eliminate accessional torsion and bending load by coupling the hydro-pneumatic of each wheel. In the premise of not harming the performance of longitudinal and lateral stability, this can improve the ride performance and even load of each wheel. Also this can make full use of the adhesive force on accidented road, and it means improvement of traffic ability and vehicle speed on accidented road.This thesis introduces the principle, classification, character and study development about hydro-pneumatic spring and coupled hydro-pneumatic suspension. Hydro-pneumatic coupled equalizing suspension system is more streamlined structure and lower cost than previous mechanical coupled suspension and torsion-free cylinder suspension.Then this thesis analyses the work principle of the single chamber and hydro-pneumatic separate spring which is suitable to coupled suspension. Based on the structure principle of hydro-pneumatic spring, the virtual model of hydro-pneumatic spring has been built with AMESim/Hydraulic and analyzed the single action cylinder, gas accumulator, orifices and the influence on stiffness and damping of hydro-pneumatic spring.After that the thesis analyses spring force and damping force of hydro-pneumatic spring, and sums up the dynamic model of hydro-pneumatic spring by studying gas accumulator, orifices and check valve. The model is built by Simulink, and compares with the hydro-pneumatic spring model build by AMESim, for the purpose of verifying the correctness of Simlink model.Derived through the hydro-pneumatic model, the thesis derives and analyses the dynamic stiffness and static stiffness, and analyses the related parameter, provided the principle of spring selection and design. At the same time, the thesis analyses the check valve by a method of logistic modeling instead of model derivation. Then the model will be less difficult.Based on these models, the simulation experiment of hydro-pneumatic suspension goes to run. The thesis research the response of hydro-pneumatic suspension to different drive condition and different road.At last, the thesis derives the stiffness of the hydro-pneumatic suspension, and finds inner rule of the coupling stiffness, then builds the stiffness model for full-vehicle analysis. By simulation of ride and handling stability, the thesis studies the influence on full-vehicle performance by hydro-pneumatic suspension.The main work of this thesis analyses the influence of the four vertical restrictions by the accidented on body posture, then illustrates the action principle of the hydro-pneumatic coupled suspension and makes a standard formula of the stiffness of the coupled suspension system. And based on hydro-pneumatic spring model in AMESim, the thesis accomplishes test simulation of hydro-pneumatic coupled suspension on different drive condition. The thesis designs different road to test the effect on coupled suspension system. The tests contain single-frequency road excitation, parallel round jump excitation and so on, and it analyses the influence of the diameter of the valve on hydro-pneumatic suspension. Through an easy and effective test method and numerical method, The thesis execute curve fitting and parameter identification to obtain the stiffness of hydro-pneumatic suspension. The fluid mechanics equation of hydro-pneumatic suspension is very complex. But this quasi-static test method is easy and effective and it avoids complicated model derivation on coupled hydraulic system. At the same time, the test provides references on study of damping characteristic. The results of simulation improve that: added the hydro-pneumatic system, the effect of the ability of adhesion to the ground and decreasing the torsion in body is evident, the anticipative object is good for the next work including real car simulation and test.