Research On Matching And Control Of Tractor Hydrostatic Transmission System

Hydrostatic transmission has the advantages of wide speed range,good stability at low speed,small shift impact.The application of hydrostatic transmission to small and medium sized tractors can make the tractors adapt to the needs of different operating conditions and operating environment,then improve the working quality.It can also reduce the labor intensity of drivers,then improve the driver's work efficiency.It is full of important research value to study the matching and control of tractor hydrostatic transmission system and improve the working performance and economic performance of the hydrostatic drive tractor.The paper theoretically analyzed the transmission characteristics of hydrostatic transmission,including speed ratio characteristic and torque ratio characteristic,power ratio characteristic and efficiency characteristic,based on the transmission principle of hydrostatic transmission.According to the experience formula of mechanical efficiency and volume efficiency of variable pump and quantitative motor in the hydrostatic transmission,the influence of input speed,displacement ratio and system pressure on the efficiency of hydrostatic transmission was analyzed in detail.The dynamic models of all parts of the tractor hydrostatic transmission system were established according to the transmission characteristics and structural characteristics of the tractor hydrostatic transmission system,including the engine model,hydrostatic transmission model,main drive model,walking mechanism model and load model.The simulation model of the whole machine was built by using SIMSCAPE toolbox in MATLAB/SIMULINK software.Then the dynamic characteristics of the tractor under the ploughing condition were simulated and analyzed.The evaluation index of optimal economic matching of tractor hydrostatic transmission system was put forward,and the influencing factors of tractor economic matching were analyzed.The objective function and constraint conditions of optimal economy were established,and the optimal throttle opening and the optimal displacement ratio of hydrostatic transmission were obtained when the fuel consumption rate of the tractor was the lowest under the operating conditions of arbitrary speed and traction load based on particle swarm optimization(PSO)algorithm.The matching implementation scheme of binary cooperative control between the engine throttle opening and the displacement ratio of hydrostatic transmission was put forward,which lays a foundation for the study of the optimal economic control strategy of the tractor.Based on the control strategy proposed in this paper,a fuzzy PID controller was designed to control the engine throttle opening and the displacement ratio of hydrostatic transmission under the optimal economic condition of the tractor.The optimal economy of the tractor was guaranteed by the coordinated control of the engine throttle and the displacement ratio of the hydrostatic transmission.MATLAB/SIMULINK simulation platform was used to verify the feasibility of the control strategy.The simulation results showed that the tractor can operate in the best economic working state according to the target speed set by the driver.The control strategy proposed in this paper has good control effect.