Research On Control Strategy Of Electronically Controlled Air Suspension For Tractor

Electronically controlled air suspension(ECAS)for tractor use distance senor and solenoid valve,instead of traditional height control valve,to realize adjusting the stiffness of air spring and the height of the vehicle body automatically according to the change of vehicle driving state and external excitation,reducing the road impact and vibration.Compared with traditional spring suspension and mechanical air suspension,it has better riding comfort and handing stability.In addition,the ECAS system for 6×2 tractor can control the lifting axle according to the load of the drive axle,which can improve the fuel economy of the vehicle,enhance the vehicle trafficability on the smooth pavement and climbing ability.Electronically controlled air suspension has become the main trend of suspension system because of its superior performance.However,at present,the domestic independent development capability of ECAS is relatively weak,and it needs to rely on the introduction of advanced ECAS products and services abroad.Therefore,the research on the key technology of electronically controlled air suspension is of great significance to improve the independent research and development ability.This paper analyzes the research status of domestic and foreign commercial vehicle ECAS system.Aiming at the widely used 6×2 tractor,research on control strategy of ECAS system for tractor through software simulation,and build the hardware-in-the-loop test bench to test and verify the designed ECAS system function and the fault detection function.The main research contents include the following parts.(1)The composition and principle of ECAS system are introduced.The basic function and special lifting axle control function for 6×2 tractor ECAS system are introduced.Aiming at the parameters of target tractor,this paper matches the ECAS system function.Based on permanently optimised traction control mode,calculating load distribution c on each axle.(2)According to the parameters of the target tractor and matching requirements,the selection of air spring is done.The mathematical model of the air spring is built by applying thermodynamics,hydromechanics and Newtonian mechanics.According to the research needs,this paper combine the above established air spring model with the vehicle model of TruckSim to establish the integrated simulation model,which provides simulation basis for the design and development of control strategy.The B Level Pavement model is established to carry out the simulation experiment of riding comfort.(3)Based on the established air spring discharge model,a single set of air spring target height tracking model is established by using the sliding membrane variable structure control method,and design the sliding mode variable structure controller.The attitude balance control strategy of the whole vehicle is designed to solve the problem of unstable attitude of the front and rear axle charging and releasing speed caused by uneven load.A vehicle height switching and height stability control strategy is designed,and corresponding control strategy is designed for matching the lifting axle control function.Simulation experiments verify the effectiveness of the control strategy mentioned above.(4)Based on Microprogrammed Control Unit(XC2365),the hardware circuit and software program are designed,realize the functions including the basic function and the controller's fault detection.The hardware-in-the-loop test bench for ECAS controller is built based on Matlab/dSPACE technology.The effectiveness of the designed controller is verified by the hardware-in-the-loop test bench,mainly including fault diagnosis test,the static height of up / down regulation experiment,body height switching regulation experiment at low speed,auto body height automatic recovery regulation experiment,auto body height stability adjustment during load changing process.