Design And Control Of Range Shifting System For Tractor Hydro-mechanical Continuously Variable Transmission

As the most important agricultural power machinery,the output speed and load torque of tractor need to be adjusted in real time to adapt to the complex working conditions.HMCVT（Hydro-mechanical continuously variable transmission）not only can realize a wide range of transmission ratio adjustment,but also has a larger load driving power and higher transmission efficiency.It is an ideal tractor transmission form.The research of tractor HMCVT continuously variable transmission started late in China,and its industrial application has not been realized so far.Based on the analysis of domestic and foreign HMCVT continuously variable transmission technology,this paper puts forward a transmission scheme of HMCVT continuously variable transmission which is suitable for tractors,and then completes the design and prototype trial production of the section changing system including mechanical system,hydraulic system and control system,and analyzes the section changing quality of the working section switching of the transmission.（1）Design of mechanical system for changing section.In this paper,the scheme of HMCVT continuously variable transmission of continuously variable tractor is proposed firstly,then the transmission parameters（matching engine,rear axle parameters,transmission ratio,etc.）and structural parameters（shaft parameters,gear parameters,etc.）of the gearbox are determined.Finally,the prototype of the gearbox is designed and manufactured.The prototype provides an important research platform for the design,test and analysis of HMCVT transmission section changing system.（2）Design of hydraulic system for changing section.The hydraulic system is an important part of the section changing system of the gearbox.The hydraulic components involved include four wet clutches,one brake and one integrated pump controlled hydraulic motor.For this reason,the hydraulic system designed in this paper includes four proportional reducing valves and four electromagnetic directional valves to form the clutch control oil circuit,one electromagnetic directional valve to form the brake control oil circuit,as well as the lubricating oil circuit,cooling oil circuit,pump control hydraulic motor oil supply circuit and pump station,and finally completed the prototype trial production and related valve group"step"test and calibration work.（3）The design of section changing control system.According to the expected functional requirements of the HMCVT continuously variable transmission section changing system,a transmission remote control system composed of upper computer（industrial control computer）and lower computer（PLC）is designed.Firstly,the communication protocol between the upper computer and the lower computer is established;secondly,the control system is developed based on Lab VIEW and PLC,and the selection,installation and debugging of the data acquisition card are completed;finally,the test of the control system is completed through the pressure tracking test of the wet clutch on the preset curve.（4）The construction of dynamic model of tractor changing section and the analysis of changing section quality.Firstly,the dynamic model of the whole tractor is constructed,including the proportional reducing valve,wet clutch,pump controlled hydraulic motor,gear,transmission shaft and so on.Secondly,based on the speed regulation characteristics and efficiency characteristics of the continuously variable transmission tractor,the optimal section changing point of the transmission is determined.Thirdly,a new section changing method of HMCVT transmission based on the section bridging strategy is proposed,that is,when the requirements are met under the condition of constant speed shifting,C₂ and C₄ clutches are switched to make the gearbox switch from HM1 to transition section,and then C₁ and C₃clutches are switched to make the gearbox switch from transition section to HM2 section.Finally,the quality problem of tractor shifting under this strategy is analyzed and optimized based on orthogonal method.（5）The strategy analysis of gear box segment selection based on efficiency.Firstly,the efficiency model of the gearbox is improved;secondly,the efficiency characteristic field and fuel economy characteristic field of the"engine gearbox"system are constructed;finally,based on the above field model,the macro stage selection strategy of the gearbox is proposed.