| The vibration of non-suspension off-road vehicles, such as agricultural vehicles, forestry vehicles, tractors and some engineering vehicles, is more poignant than cars, buses and trucks. With the increasing of running speed, this problem is increasingly outstanding. More attention will be paid to the comfort of vehicle with the development direction aimed to large-scale, highspeed and comfort. Some investigations indicated that one of the effective methods to change present situation is to fix suitable front axle suspension, based on the structural characteristics of non-suspension off-road vehicle and the present economy and technology level. To deeply study the design theory and vibration characteristics of front axle hydro-pneumatic suspension system has important significance to the research and development of front axle hydro-pneumatic suspension vehicle.Taken CF200tractor made in Changfa Groupe of Jiangsu province as prototype, based on the parameters of mass properties of vehicle system and vibrational characteristics of tires obtained by test, the vibrational mathematical models of non-suspension and front axle suspension vehicle system were put forward in this paper. At the same time, the natural frequencies of system were analysized and the research of vibrational characteristics of vehicle system and parameter matching of front axle suspension system were made using MATLAB/Simulink. Taken the structural and parameter characteristics of model vehicle into account, damping-adjustable front axle hydro-pneumatic suspension suitable for model vehicle was designed and machined. The simulation investigation of static stiffness and damping characteristics and output force characteristics and the experiment investigation of output force characteristics of hydro-pneumatic suspension system were made, and the experimental dynamic characteristic research of front axle hydro-pneumatic suspension vehicle system was made by test. The finished work and achieved results are generalized as following:1. Referring to relevant national standard, the mass parameters, such as quality, centroid position and pitching rotational inertia etal, and stiffness and damping coefficients of front and rear tires were determined.2. The natural frequencies of vertical vibration and pitching angle vibration were calculated, based on the analysis of vibrational differential equation and natural frequencies of non-suspension vehicle system. Taken integral white noise random road of grade D as excitation, the displacement and acceleration of vertical vibration and pitching angle vibration were studied using MATLAB/Simulink. The comparison of displacement and acceleration of vertical vibration was made in this paper, the result showed that the amplitude of vertical vibration displacement of front axle was nearly equal to that of rear axle, but the vertical vibration acceleration of front axle was greater than that of rear axle obviously.3. Taken the influence of driver’s mass on centroid position and pitching rotational inertia of off-road vehicle into account, the vibrational mathematical model of front axle suspension vehicle system suitable to structural parameters was put forward. Changing parameters of front suspension, the simulation of vibrational characteristics of front axle suspension and parameter matching problem of damping and stiffness of suspension system were studied using MATLAB/Simulink.4. Based on related theories of fluid mechanics and gas state equation, the mathematical model of damping-adjustable hydro-pneumatic suspension was established, and the static stiffness characteristics of hydro-pneumatic suspension was analyzed. Non-linear characteristics of damping, dynamic output force and pressure of every cavity of hydro-pneumatic suspension were simulated using MATLAB/Simulink by changing initial working pressure and volume of Nitrogen, frequency and amplitude of sine excitation, the diameter of piston damping, check valve and adjustable damping valve.5. The test-bed of vibrational characteristics was constructed, and the measurement and control system of test-bed was developed based on Lab VIEW, through which the characteristics experiment of hydro-pneumatic such as static stiffness and dynamic output can be completed. The experiment of dynamic parameters such as dynamic amplification factor and vertical vibration acceleration of hydro-pneumatic suspension, dynamic deflection and dynamic load of suspension system, dynamic pressure of every cavity etal also can be completed on this test-bed.6. The whole structure of hydro-pneumatic suspension with adjustable damping and the parameters of main parts were determined. The static characteristic experiment of hydro-pneumatic under various initial working pressures and volume of Nitrogen was carried out. The experiment of dynamic parameters was carried out by changing initial working pressure and volume of Nitrogen, frequency and amplitude of sine excitation, the diameter of piston damping, check valve and adjustable damping valve etal.7. Based on the construction and analysis of mathematical model for front axle half suspension system of vehicle, the experiment of front axle hydro-pneumatic suspension system was carried out using a test set. Effect of various parameters of suspension system on the dynamic amplification factor and root mean square value of acceleration of sprung mass and dynamic load of wheel were studied, and these parameters include the initial working volume of Nitrogen, amplitude of sine excitation, the diameter of check valve and adjustable valve of damper.This work provides theoretical basis and technical support for the research of off-road vehcile with front axle hydro-pneumatic suspension system. |
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