| Suspension, as a main assembly in modern vehicles, influences vehicle performances profoundly. Therefore, it is important to properly design the suspension and optimize the suspension structure based on the whole car performance.Conventional suspension includes elastic components and shock absorbers. Due to its simple structure and high reliability, this kind of suspension has been widely used. However, this kind of suspension do have some disadvantages, e.g., when the loads change, the height and the frequency of car body change greatly with them. These shortcomings could be successfully overcame by Hydro-pneumatic suspension. Such suspension can have a stabilize frequency during the loads changed because of its nonlinearly stiffness. Besides, the hydro-pneumatic suspension can adjust the height of the vehicle by pumping the oil.The design process o f hydro-pneumatic suspension system mainly includes following steps: parameter design, manufacture, assembling, and test. With a reasonable theoretical performance and design parameters of the hydro-pneumatic suspension, we can save a lot of cost in engineering design and test period. The theoretical design stage only needs a relatively low cost because the main work of this stage is to carry out the related calculation, analysis, optimization, and simulation. The setting parameters and simulation conditions are easy to be modified and can be more efficient debugging and determine the technical scheme. Therefore, it is very important to study the design method of the theoretical design process, improve the design skill and reduce the time cost, which is very important for the design of the hydro-pneumatic suspension.Based on my experience of the hydro-pneumatic suspension system design, parameters matching and optimization, simulation and structure design in a project of hydro-pneumatic suspension, the main work of this thesis is to determine the property parameters, structure design of hydro-pneumatic suspension, and the leveling system design based on hydro pneumatic suspension.Hydro-pneumatic spring is an essential component of a hydro-pneumatic suspensio n, which plays not only as an elastic element but also provides the damping for the suspension. Firstly, this dissertation started with the determination of suitable damping characteristics and elastic characteristics, using Fourier transform method to calculate the time domain signals of three kinds of random road surfaces according to the frequency domain parameters of three kinds of pavement. Simplified model of vehicle vibration and the 1/4 suspension damping has been developed in Matlab/Simulink. By us ing genetic algorithm to optimize suspension damping coefficient of different road surfaces, we got three group of suitable suspension restoration and compression damping coefficient.Secondly, the matching relationship of hydro-pneumatic suspension structure parameters and vehicle performance is studied, and the structure parameter design and optimization method is discussed. The structure and working principle of the hydro-pneumatic suspension is introduced, and also deduced the calculation formula of partial frequency. Then the influence of hydro pneumatic suspension structure parameters on vehicle performance is analyzed according to the suspension frequency at empty and full load.Thirdly, a novel hydro-pneumatic suspension structure is designed. The d issertation introduced a hydro-pneumatic suspension damper control valve system using electromagnetic proportional valve. Through the assembly debugging realization damping coefficients obtained from simulations and analysis requirements. Then the system is validated in a real vehicle, the results shows that the ride comfort has been greatly improved.Finally, based on the principle of three point leveling principle, a leveling system based on hydro-pneumatic suspension and its control logic are introduced. Then the factors of this system are analyzed and the control system is validated in real vehicle tests. The test results show that this leveling system can meet the precision requirement and reduce the requirement of sensors, and provide a practical leveling method and the control logic for off-road vehicles. |
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