| At present,the demand for large and medium-sized tractors in China is becoming increasingly saturated,and there is an urgent need to improve their working performance and fuel economy.The traditional tractor gearbox has many gears,which requires frequent operation by the driver under complex working conditions.The strong shift impact greatly reduces the driver’s working comfort.The Hydro-mechanical CVT has the advantages of convenient gear shifting and automatic speed regulation according to working conditions,and it has been widely used.As a key transmission part in the gearbox,wet clutch directly determines the overall performance of the gearbox,which also affects tractor performance and fuel economy.At present,the research foundation for the dynamic engagement performance of the wet clutch in the whole gearbox is weak,the corresponding model is not accurate enough,and there is a lack of comprehensive optimization methods for clutch performance.Therefore,it is of great significance to carry out the dynamic engagement performance simulation and comprehensive performance optimization of wet clutch in the whole machine to promote the industrialization of the tractor.Therefore,this paper took "Research and Development of Key Technologies for Intelligent Heavy-Duty Tractor CVT"(Project Number:2016YFD0701103)funded by the National Key Research and Development Plan as the research background,and carried out the whole machine simulation and test based on the wet clutch in the selfdeveloped Hydro-mechanical CVT,aiming to reveal the change law of the influencing factors on its sliding characteristics and the change of temperature field,so as to provide a scientific basis for its comprehensive optimization.First,according to the performance index and design requirements of the wet clutch,the design and calculation of clutch’s key components were completed,and the three-dimensional assembly model and physical model were given.Secondly,the friction coefficient function was fitted by the test data,and the exclusive friction coefficient model of this paper was obtained.Considering the influence of other parts in the transmission system such as engine and load on the wet clutch,models of Hydro-mechanical CVT and wet clutch were established based on SimulationX software.The influence of clutch axial force and friction coefficient on engagement torque and sliding power were discussed.Then,the ANSYS/WORKBENCH simulation software was used to perform transient thermal analysis on the slipping process of the wet clutch,and the radial and axial temperature fields of the friction pairs were obtained.The results show that the friction pairs reach a peak temperature of 166.47℃ in about 3s after engagement.Each measuring point temperature in the radial direction of the friction disc shows a trend that increasing first and then decreasing.The heat in the axial direction of the friction disc is transferred from the surface to the inside.Finally,considering the thermal stability and light weight of the wet clutch,the orthogonal evaluation and AHP method were used to obtain the comprehensive evaluation index W,and the clutch optimization was based on the PSO algorithm.The optimal solution for the oil pressure is 3.441 MPa,the optimal outer diameter is 182.481mm,and the optimal number of friction pairs is 8.028.Comparing the radial temperature between optimized solution condition and the optimal condition of the orthogonal test,the results show that the optimized performance of the friction disc is the best under the optimized solution condition,which lay the foundation for design optimization of wet clutch.In conclusion,the paper designed a wet clutch that matches the Hydro-mechanical CVT which was designed by the research group.The dynamic engagement performance and thermal performance were studied,and the paper carried out the comprehensively optimize of the wet clutch,which provides a theoretical basis for the optimization design of the wet clutch and reduce noise and vibration of the gearbox. |
