Research On Shifting Of Compound Hydro-Mechanical Transmission(CHMT) Based On Power Internal Shunt

Hydro-Mechanical Transmission(HMT)is composed of a flow dividing device,a hydraulic system,a confluence device and a stepped shifting system.According to the structure characteristics of the flow dividing device and confluence device,the HMT system can be divided into internal shunt and external shunt(sink).The internal shunt HMT eliminates the corresponding transmission components such as the differential,which reduces the mechanical loss of the system and has a compact structure.It also can realize the clutch function by cutting off the power transmission.So,the system has great potential in engineering application.Combined Hydro-Mechanical Transmission(CHMT),which draws on the transmission principle of Dual Clutch Transmission(DCT)and makes use of the HMT system's "clutch" function,is compounded by two internal shunt type HMT systems.It not only retains the characteristics of DCT shifting process without power interruption,but also integrates the advantages of HMT system transmission.Therfore,it has broad application prospects.This paper replaces the power shifting part of a tractor gearbox with CHMT system,studies the transmission characteristics and shift control process of CHMT system,and provides theoretical reference for CHMT engineering application.The main contents of the work are as follows:(1)The working characteristics of the internal and external split HMT system is compared and the internal shunt HMT structure scheme is proposed.Then,its transmission characteristics and function realization are studied.On this basis,the structural scheme of the CHMT system is proposed and the relationship between system output,throttle opening and displacement ratio is discussed.(2)The shift control scheme of CHMT system is studied.Two different upshift schemes based on low-gear pure machinery and low-gear HMT conditions are proposed.On this basis,the upshift characteristics of low-haul HMT conditions are emphasized.And considering the influence of hydraulic efficiency change,the output change of shift scheme is analyzed by Simulink simulation.(3)In response to the system output oscillation caused by the sudden change of motor flow during the upshift process,the CHMT system shifting process is optimized by introducing hydraulic motor volumn control and replacing the original program oil circuit check valve with the speed control valve.And the effectiveness of the optimization scheme is verified by simulation.(4)Three different downshift control schemes of CHMT system are analyzed,namely high gear pure machinery-low gear pure machinery,high gear pure machinery-low gear HMT and high gear HMT-low gear HMT.The transmission characteristics of three control schemes are studied.On the basis,the mathematical model of downshift was established and the feasibility of the scheme was verified by simulation.(5)By integrating the CHMT shifting scheme,it is proposed that the system has three shifting modes: single pure mechanical switching,single HMT switching and hybrid shifting mode.Besides,combining with the mathematical model of engine,the optimal dynamic shift law of CHMT system is discussed according to different shifting modes.(6)The experimental device was designed and the content of the experiment was established.