Performance Study And Simulation Of Hydro-pneumatic Suspension System For High Speed Backhoe-loader

Hydro-pneumatic suspension (HPS) appeared in 1970s. With oil as forcetranslation and inert gases (such as N2) as spring medium, it is a new typesuspension system that integrates the spring unit and shock absorber. With itsadvanced non-linear characteristics and excellent shock-absorption performance, itcan meet the demands on ride comfort and handling stability of engineeringvehicles at maximum level. Today, hydragas suspension has been wildly used oncar, dump track, cross-country truck, military vehicle and special vehicle.Based on a great deal of study of literature and comprehensive investigation,the actuality of the characteristic, development and application were gotten.Hydro-pneumatic suspension system with isolated single gas-accumulator for highspeed backhoe-loader is taken as the object for analysis and research in the paper.On the base of analyzing fore-researchers' investigation work at home and abroad,the physical and mathematic model of HPS system , simulating, analysis andsimulating for vehicle dynamics are finished with the application of hydraulictransmission theory, the vehicle dynamics theory and computer simulationtechnology.This paper mainly includes the following contents:1. The fix structure on the vehicle of HPS system with isolated singlegas-accumulator is introduced .Not only its working principles but also four statesof elastic suspension state, rigid suspension state etc. by controlling valves for needare analyzed.2. On the basis of analysis of its structural form and working principles, thephysical model of HPS system is established through properly simplifying thepractical structure according to its working elements. Depending on equation of gas,hydrodynamics and etc., the non-linear mathematical model of HPS system withisolated single gas-accumulator is set up. Making use of the simulative programwith the software of MATLAB, it is carried out that groups of contrast simulationswith same frequency, different amplitude and those with same amplitude ,differentfrequency. It is gotten from simulation that results described by the displacementcharacteristic and velocity characteristic of HPS, which respectively represents therelationship between the displacement of input signal and the output, and thevelocity of input signal and the output force of HPS.3. The thesis deduces the mathematical model presented by a series ofequations between damping force and elastic force of HPS from the HPS physicalmodel and mathematical model , which intuitionally supports that HPS has non-linear by means of the computer simulation. Analysis on the affection disciplines ofparameters such as excitation parameters, structural parameters and workingparameters on rigidity characteristic and damping characteristic of HPS system isperformed in detail by the simulative program. Frequency characteristic of HPS isprovided in theory.4. Referring to the international standards about road classitication, a time-domain model of road surface based on power spectrum density of road surface isbuilt up. According to non-linear characteristics of HPS, the thesis sets up thetwo-freedom non-linear dynamics model(the quarter vehicle dynamics model) forthe HPS system excited by the random road surfaces. By the use of the specialsimulation software programmed in MATLAB/Simulink, the simulation of thedynamics model of HPS system is performed to obtain acceleration of suspensionmass , acceleration of non-suspension mass, dynamic displacement of suspension,dynamic relative load of wheel and other time-domain signals. The indexes such asroot-mean-square values of acceleration of suspension mass, dynamic displacementof suspension, dynamic relative load of wheel are put forward to value thehydro-pneumatic vehicle in the paper. The results of simulation indicate that ridecomfort and handling stability of vehicle with HPS become well. The influences ofthe initial pressure of gas in the gas-accumulator, the diameter of the damper andthe diameter of the cylinder on ride comfort of the vehicle were analyzed by meansof theoretical simulation, which can be treated as the theoretical base to select theproper parameters of the HPS .