Design And Control Strategy Research Of Horticultural Tractor Steer By Wire Hydraulic Steering System

With the burgeon of horticultural equipment in China,horticultural tractor has become a very important power machinery in modern agriculture.The performance of steering system in horticultural tractor will directly affect the driving experience and working efficiency of the operator.This thesis selects the steering system of horticultural tractor with the maximum steering angle of 57° as the research target,and the wire control transformation is carried out on the basis of the existing full hydraulic steering system.For the sake of further improving the steering characteristics of horticultural tractor,the tractor’s steering control system is studied.Aiming at solving the problems existing in the control system,the radial basis neural network composite synovium control algorithm is introduced to optimize it.The detailed study content is as listed below:First of all,combined with the steering by wire technology to transform the hydraulic steering system,the framework and steering explanation of the optimized steering system are introduced in detail.The hydraulic steering system and the mechanical steering system of the steering executive model of the horticultural tractor are designed respectively.The mathematical relevance between the steering cylinder stroke and the front wheel angle of the vehicle is deduced,and the main working parameters of the system are calculated.Secondly,the structure and composition of the steering-by-wire hydraulic steering control system of the horticultural tractor are analyzed,on the basis of the theory of transfer function means,the simplified mathematical form of steering control system is deduced,a simplified mathematical formula of the steering control system is building-up,and the state space expression of the system is building-up by selecting the displacement,velocity and acceleration of the steering cylinder as the state variables of the system.The open-loop Bode diagram of the steering control system is drawn by using Matlab software,and the Simulink mathematical model is established.The results show that the system meets the stability requirements.Thirdly,the physical simulation model of the steering-by-wire hydraulic steering control system of horticultural tractor is established by using Amesim software,and the actual working situation of the vehicle steering system is simulated.The control characteristics of the steering system is studied and analyzed.The outcomes express that the system has a certain steering control performance,but the steering following error is large.Combined with the practical application environment of horticultural tractor steer by wire control system,the effects of different system oil supply pressure,different electro-hydraulic proportional directional valve dead zone,different steering cylinder piston diameter,different steering cylinder leakage coefficient and different electronic amplifier gain on the dynamic characteristics of the system were discussed.The validity of Amesim physical simulation model is verified by bench test.Finally,in order to solve the problem of large errors in the steering and following of horticultural tractors,the RBF composite synovium control algorithm suitable for horticultural tractors is established in Matlab/Simulink.Through Matlab/Simulink and Amesim co-simulation,the simulation results show that the control effect of RBF composite synovial control is better than that of conventional synovial control,and contrasted with routine synovial control,RBF composite synovial control can effectively reduce chattering in synovial control system.The system can reduce the risk of component damage caused by input chattering.