| Tractor has a long time driving in the poor condition road,the vibration is particularly acute.So the study of tractor vibration isolation system is very important.Due to the level of economic development,the manufacture cost and sales price factors,most of the domestic tractors adopt the no suspension structure of rigid connection,the vibration strength is much higher than road vehicles.In Europe developed countries,due to the integrated use of the driver’s seat suspension,cab suspension and front axle suspension vibration reduction technology,the vibration of the tractor intensity is much lower than our country.Hydro-pneumatic suspension was studied a lot overseas,and it has been widely used in off-road vehicles.But hydro-pneumatic suspension still in the research and development stage in the domestic,and it has no practical applications.Studies of tractor front axle hydro-pneumatic suspensions are rarely reported.Taking the CF700 tractor as the research object,vibration characteristics of no suspension tractor was studied theoretically.Vibration acceleration of no suspension tractor driving in different road conditions was tested.Using MATLAB as the research platform,the front axle suspension stiffness and damping parameters are optimized by genetic algorithm,and the influence of tractor front axle suspension stiffness and damping parameters on tractor vibration characteristics was researched by simulation.Hydro-pneumatic suspension with controllable stiffness and damping was designed and the stiffness and damping nonlinear mathematical model of hydro-pneumatic suspension was established.The influence of structure parameters on hydro-pneumatic suspension characteristics was studied by simulation,and the static and dynamic characteristics and vibration response characteristic of the hydro-pneumatic spring was researched by experiment.The main work and research conclusions were generalized as follows:No suspension tractor 2-DOF planar vibration model was built up.The main parameters of tractor system were obtained by measuring,testing and calculation method.The tractor vibration test system was built,vibration acceleration of tractor driving in GB/T 10910-2004 100m standard smooth test road and four kinds of typical rural road including the rice straw field、the wheat straw field、Paddy field and the farm track was tested,and the random elevation of the rice straw field and the wheat straw field was obtained with the tire rolling method.Front axle suspension tractor 3-DOF planar vibration model was built up and the frequency response function was obtained.The calculation formula of tractor seat installation position vibration acceleration RMS value,front and rear wheel dynamic load RMS values,and front axle suspension dynamic deflection RMS value,etc were derived theoretically.Determine the front axle suspension stiffness and damping parameters scope according to the requirements of the tractor system parameters.The front axle suspension stiffness and damping parameters were optimized using the genetic algorithm toolbox in MATLAB.The optimized suspension stiffness kfas and damping cfas values are:142.8kN·m-1、9.5kN·s·m-1.It is shown that the RMS of seat position vertical vibration acceleration,the RMS of seat position pitch angle vibration acceleration,the front and rear tire dynamic load of tractor with front axle suspension are respectively reduced by 5.3%、43.7%、76.0%and 9.5%.The influence of front axle suspension parameters to the vibration characteristics of tractor including mass center vertical acceleration,mass center pitch angle acceleration,seat vertical acceleration,suspension dynamic deflection,front and rear tire dynamic load coefficient,etc was simulated and researched.Hydro-pneumatic suspension with controllable stiffness and damping was designed,and introduces the working principle and level control device of hydro-pneumatic spring.Using fluid mechanics theory,the stiffness and damping mathematical model of hydro-pneumatic suspension under various work condition was established and the structural parameters was calculated.Stiffness and damping parameters of hydro-pneumatic suspension was linearized,and get the stiffness and damping coefficient of hydro-pneumatic system in the equilibrium position.According to the dynamic analysis and parameter requirements select and assemble the parts of the hydro-pneumatic spring element,and the main parameters of hydro-pneumatic spring were determined.The simulation model of hydro-pneumatic spring is established by MATLAB/Simulink software.Characteristics of the dynamic stiffness,damping force and output force under various work condition of hydro-pneumatic suspension and the influence of the structural parameters on suspension output force were simulation studied,including initialization nitrogen volume,initialization nitrogen pressure,piston cylinder diameter,piston rod diameter,proportional valves orifice diameter and throttle valves 6 and 8 orifice diameter,etc.The designed hydro-pneumatic spring can realize suspension stiffness and damping of the "soft" and "hard" state switch,and the stiffness and damping were available to be controlled at a certain range.The static and dynamic characteristics of the hydro-pneumatic spring with controllable stiffness and damping were researched by experiment.Nonlinear stiffness characteristic of hydro-pneumatic spring was studied and the static stiffness of hydro-pneumatic spring in equilibrium position is 72.6kN·m-1.The influence of proportional valve current size,the opening of the throttle valve size and excitation frequency to output force of hydro-pneumatic spring were studied by dynamic experiment.Simulating the actual working load of the tractor front axle suspension,a quarter vehicle tests have been carried out for the designed hydro-pneumatic spring,the suspension displacement transmissibility,the sprung mass vibration acceleration and tire dynamic load response were studied by experiment. |
