Study On The Structure Optimization Of Wet Clutch And Shift Quality In HMCVT

HMCVT as a new type of hydraulic and mechanical transmission device can automatically change gears according to tha change of load to improve transmission efficiency of gearbox.HMCVT is the research direction of the transmission system of heavy tractor.When tractors working in the field,the gearbox needs to change sections frequently to adapt to the changeable working conditions.The impact of tractor section change will affect the life of wet clutch and transmission system.In order to reduce shift impact and improve driving comfort,this research combined simulation analysis and bench test,and the following research is carried out from four aspects:optimization of structural parameters with the goal of reducing the sliding friction of wet clutch,simulation test on factors affecting the quality of shift impact,construction of test bench and bench test analysis of shift quality.(1)According to the required transmission torque in each section of HMCVT transmission scheme,then select the type and specification of friction plates,calculate the number of friction pair and piston storke,and determine the amount of oil required for lubrication and cooling.And design the seal position and seal way of wet clutch.(2)The paper combined I-PSO algorithm with Matlab/Simulink and a new method of optimal design is proposed to optimize the friction plate parameters of wet clutch.First,based on the dynamic analysis of the wet clutch,the simulation model of power transfer was built in Matlab/Simulink.The improved particle swarm optimization algorithm is improved again according to the simulated annealing algorithm,and the improved effect is verified based on a test function.Finally,the sliding friction work and volume of the clutch are selected as the optimization target,and the wet clutch simulation model established in Matlab/Simulink is combined with the improved particle swarm optimization algorithm to carry out the multi-objective optimization design of the wet clutch.The results show that the total objective function of the optimized wet clutch is reduced by 40.12%and the silding friction work is reduced by 61.8%,indicating that the optimization effect is obvious.(3)In order to improve switching quality of heavy tractors equipped with hydro-mechanical continuously variable transmission(HMCVT),model of power shift process was established by SimulationX software.Firstly,the simulation model is established according to the transmission principle of the gearbox,and the accuracy of the simulation model is verified indirectly.Then,three kinds of factors:structural design factor,environmental factor and adjustable factor were determined to affect the quality of the shift quality.And the five-factors and four-level orthogonal test was carri ed out in the simulation model.Stepwise regression analysis and range analysis were used to process the data of the orthogonal test results,and the influence degree of each factor on the shift quality was obtained.The mothod of determining the variance weight was proposed to match the parameters of two indicators with opposite correlation to obtain the mathematical model the total quality of the total shift quality.Finally,a single factor test is carried out on the structural design factors to determine the exact relationship between eaah factor and the index of section change.The results shows that during wet clutch engagement,the main factors affecting the speed drop are oil pressure、flow rate and load pressure,the main factors affecting the dynamic load are oil pressure and load pressure.Among the structural design factors,the number of friction plates plays a significant part in the quality of shift process,and the ratio of inner and outer diameters of friction plates has little connection with quality of shift process.The method of variance weight determination is combined with stepwise regression analysis to provide a high precision modeling method for the quality study of segment change.(4)The HMCVT test bench was built and the shift quality test was carried out to obtain the influence of oil pressure and engine speed on shift quality.Firstly,the structure design of HMCVT frame,drive module,load module and various sensors were selected and the hydraulic control system of wet clutch was designed.Then,the oil filling test of wet clutch and the test of the influence of oil pressure and engine speed on the quality of the change section were carried out on the bench.The result shows that the wet clutch can the wet clutch can fill oil correctly and effectively,and it lays a foundation for the test of changing section.The influence of engine speed on speed drop is similar to that of dynamic load.The influence of oil pressure on speed drop is more significant than that of dynamic load.