Research On Characteristics And Starting Control Of Hydro-mechanical Continuously Variable Transmission

With the development of modern engineering and agriculture,the vehicles need to be updated to adapt the growing conditions,while more gearshifts of the vehicle transmission are required to adapt to the different load and running speed.The ideal vehicle transmission mode is continuously variable transmission.The hydro-mechanical continuously variable transmission(HMCVT)which is composed of planet gear mechanism and hydraulic system is a new stepless transmission.The transmission mechanism with the advantages of mechanical and hydraulic transmission is obtaining research and development worldwide.Supported by Ministry of Agriculture "948" project,Jiangsu Science&Technology Support Plan(BE2014134)and Jiangsu Union Innovation Fund(BY2014128-04),the transmission principle,characteristics,performance and starting control of the hydro-mechanical continuously variable transmission are researched.The main research work and conclusions are as follows:(1)Transmission principle and characteristics of the HMCVT are analyzed theoretically.Speed and torque characteristics and distribution ratio are researched by combining with distributary and converge of gear mechanism and transmission principle.Influencing regularity about efficiency of volume timing system is researched by combining with efficiency characteristics of hydraulic pump,motor and transmission test bench.Influencing factors follow the order:variable pump displacement ratio,pump speed,main oil pressure difference.Results:the greater the variable displacement pump is,the greater the distribution ratio is.Efficiency of the hydraulic system is affected obviously by the hydraulic pump displacement ratio.With increasing displacement ratio,efficiency of the hydraulic system is increased gradually.Influences of efficiency of the hydraulic system about the variable pump speed and main oil pressure difference is relatively small.(2)The dynamic characteristics of the hydraulic system are researched.The transfer function of the transmission ratio and variable pump excitation current is obtained by combining with the hydraulic system of kinematics equations,force balance equations and variable displacement pump adjustment mechanism.The dynamic model of hydraulic transmission system which is about input variable pump excitation current and output speed ratio of the transmission system identification is obtained by step response tests in conjunction with the System Identification Toolbox Matlab.(3)Theoretical analysis and experimental study is used on the research of the starting quality of HMCVT.On the research of the initial boundary conditions of transmission,the maximum transmission ratio of the starting time is obtained and maximum gradient is checked.Based on test bench,the starting evaluations of qualities and factors are made.the experiment of starting process of HMCVT for tractor is made.Results:the variable pump displacement ratio changes from 0.113 to 1.000 are determined.The starting evaluation indexes of qualities are starting pressure,degree of jerk,response time and speed drop.Influencing factors about the starting quality follow the order:load,hydraulic pump displacement,engine speed.(4)Starting control strategy is developed by combining with the characteristics of the transmission and the actual needs of control.Fuzzy controller of identification of the driver's driving intention and variable pump displacement ratio change rate is designed.Fuzzy inference form of identification of the driver's driving intention and variable pump displacement ratio change rate fuzzy controller is obtained by using tools vector test generation method.It lays the foundation for the subsequent PLC fuzzy control.The simulation model of the vehicle starting phase is set up,and the simulation results are analyzed.The results show that the control strategy of the vehicle starting meets the needs of the vehicle starting control.(5)The Siemens S7-200(CPU224)micro PLC is chosen as the controller,and the STEP 7-Micro/WIN is chosen as the control programming software.The control element&a variable allocation of transmission starting control is described.According to the flowchart of starting control and fuzzy inference form of identification of the driver's intention and variable pump displacement ratio change rate fuzzy controller,transmission start fuzzy control PLC program is written.Experimental research is carried out,the results show that control strategy of vehicle starting meets the needs of the vehicle starting control.