Study On Hydro-mechanical Continuously Variable Transmission Of Amphibious High-power Tractors

Tractor working condition is complex,not only engaged in rotary tillage,plowing,planting and transportation,but also engaged in paddy field operations.In order to meet the requirements of the complex working condition of tractor,transmission of domestic high-power tractors was set up a lot of gear.Overmuch gear of transmission makes its structure complicated,its operation tedious and its fuel economy difficult guarantee.To solve this problem,a hydro-mechanical continuously variable transmission(HMCVT)scheme of high-power wheeled tractors used in southern China was designed reference to technique of the hydro-mechanical CVT adopted by the world's advanced tractors and the hydro-mechanical CVT studied under the financial support of "948" project from Ministry of Agriculture(fund No.2010-Z18).The main research work and results are as follows:(1)The DF1004 wheeled tractor,used in paddy field and dry field,was selected to as research object.Empty running test and rotary tillage test about DF1004 wheeled tractor were conducted in paddy field and dry field.The result showed that the mechanical transmission of high-power tractors was complex and error-prone,and its fuel economy was poor.(2)A hydro-mechanical CVT design scheme suitable to tractors was put forward based on analysis of transmission principle,the basic types and transmission characteristics of hydro-mechanical CVT.Than its working principle was analyzed.(3)The design scheme of the hydro-mechanical CVT used to amphibious high-power tractors was confirmed.According to the design scheme of hydro-mechanical CVT,the theory model was established and the structure parameters their values were confirmed.Hydraulic system components,variable pump and quantitative motor,for the hydro-mechanical CVT were selected.(4)Dynamic Characteristics of the hydro-mechanical CVT system was researched.The variable speed features,the torque features,the power flow,the cycle power and efficiency of the hydro-mechanical CVT were analyzed.Then the Linear relationship between displacement ratio and the transmission ratio,the output speed,cycle power,transmission efficiency of hydro-mechanical CVT was analyzed by MATLAB software.The results showed that the hydro-mechanical CVT designed above could meet the requirements of amphibious high-power tractor working in various conditions.(5)The whole transmission system model of hydro-mechanical CVT was created in the AMESim software for simulation and research.Before simulation,the engine experimental model,pump-motor transmission system model,planetary gear model,load model,the wet clutch model and synchronization model need to be created to build the whole transmission model.The test results showed that stepless characteristics and cycle power characteristics of hydro-mechanical CVT were in conformity with the theoretical analysis.Then the dynamic characteristics of the pump and motor as well as output speed were verified by adding step load excitation.The research showed that the amphibious high-power tractor with hydro-mechanical CVT designed above could meet the requirements of domestic agricultural production at the present stage in theory,and laid the theoretical foundation for the practical application of hydro-mechanical CVT in the amphibious tractor.