Research On Control Strategy Of Off-road Vehicle's Hydro-electric Active Suspension System

To maintain a good stability of off-road vehicle which is running when the road bumps. So we hope that the suspension of off-road vehicle not only can lower and make automobile possess good handing stability and ride comfort when it runs along straight line, speed up, brakes and turns, but also can improve the pass ability. And it should have an additional function that adjusts the height, to adapt to the need of transportation and battle.The suspension system is one of the most important devices of automobile. It links the vehicle body and wheel flexibly, in order to achieve the goal that make the vehicle running normally ,the suspension transfers the force and the moment between vehicle body and wheel, and mitigate the body vibrancy that is brought by impact force. It has been proved that the choice of suspension structure not only determine the pass ability, but also is subjected to the stability of steering. So the significance of designing excellent suspension system is very important. Now the researches into active suspension focus on two fields, one is the control theory and the other is the actuator, adopt different math models and control theories, to attain a good controlled effect.This dissertation mainly combined the Jilin University 985 automobile innovation project "The research on large working space of active and semi-active suspension ", It mainly made research into the active suspension control theory of off-road vehicle.Below are the main jobs of this dissertation:1 .This dissertation advances that using the technology of active-suspension on the off-road vehicle, and take the cylinders controlled by the electro-hydraulic servo valve as the actuator, And the active-suspension hydraulic servo system is designed according to the traits of suspension system of off-road vehicle and the variety of road, and fix on the primary parameters of hydraulic servo system and choose the primary elements with correlative technical parameters according to the structure coefficient of a kind of heavy off-road vehicle.2. The mathematical model for active suspension system of off-road vehicle is established, and then compute the transferable functions based on the parameter that acquired in chapter three, and establish the road surface model with filter white noise as the input.3. Do some research on the influence of factor change with time to the active suspension system. The factor includes road surface,speed,load and so on. Through analyzing the performance index curve through simulation, though factor change with time influence the system a little, all are controlled under the perfect range, this also show that the validity of using active control to the suspension.4.Generally considering characteristics of researching system and all kinds of strategies, mainly do some researches on optimal control and part preview control base on optimal theory, determine the controllable and observable facet of system, and systemic performance index is expressed with secondary model, calculate the matries Q,R,N with the motorial equation, figured out the suspension model based on full states feedback, build the performance function under the primary abilities, and get the control function U = -KX , At the same time respectively do some research on two ways of control which are wheelbase preview control and axial middle preview control, ratiocinate the state equations of different control ways.5.Use Maflab/Simulink to establish the simulation model of passive suspension and optimal active suspension based on the half of vehicle, and attain the active suspension simulation model of wheelbase preview control and axial middle preview control through do a little modification on the latter. Analyzing the performance index curve through simulation, we can know that use of optimal control hydro-electric active suspension in off-road vehicle brings a perfect result. the body acceleration,suspension working space,dynamic tyre displacement are all improved, able to ensure the need of stability of steering and pass ability of the vehicle. And wheelbase preview control and axial middle preview control improve the performance of latter part more efficiently.6.Do some experiments about cylinders controlled by the electro-hydraulic servo valve on the multifunctional hydraulic test bench, mainly research on flux without load and dynamic response of displacement of cylinder, the results of them indicate that cylinders controlled by the electro-hydraulic servo valve this dissertation used can satisfy the need of active suspension actuator of this project.