Thermal-fluid Coupling Analysis Of Cooling System For Wet Dual Clutch

As the main energy transmission component of the vehicle transmission system,the wet clutch has good working performance,which can ensure the smooth starting and shifting of the vehicle,and improve the ride performance.Then,the appearance of wet double clutch can effectively improve the transmission shift hysteresis and reduce the engine power loss.In the working process,the wet clutch transmits power through torque transmission.At this point,the friction plate and the steel plate rotate at different speeds and gradually join,resulting in a large amount of friction heat.When the friction heat exists in the clutch for a long time,the surface temperature of the friction elements will rise sharply,resulting in the loss or erosion of the surface materials,which directly reduces the service life of the friction elements,and even cause the accidents caused by the shift failure of the vehicle.Therefore,a good cooling system is of great significance to improve the performance of the wet double clutch.Based on the theoretical basis of heat transfer and computational fluid dynamics,this paper studies the heat transfer characteristics and performance optimization of the oil circuit of the cooling system with the wet double clutch as the research object.The main contents are as follows:Firstly,the fluid flow characteristics,heat generation mechanism and heat transfer characteristics in the process of wet double clutch sliding and grinding were analyzed.Also,the types of turbulent motion,the forms of heat exchange and the coupling analysis theory of multi physical fields were described.The convective heat transfer coefficient of each wall of the oil pipeline was calculated to determine the thermal boundary conditions,as the theoretical basis for the subsequent simulation study.Secondly,considering the viscosity temperature characteristics of oil and the mixing effect of gas and liquid,the numerical simulation of the heat dissipation characteristics of the oil way in the dynamic engagement process of the wet internal clutch with radial groove was carried out by using the finite element method.The dynamic path of air and the distribution of gas-liquid mixture were obtained by simulation,so as to study the influence of gas-liquid mixture on the heat transfer characteristics of oil-liquid.The working condition parameters and structural parameters of the clutch were taken as the influencing factors,and the heat transfer on the wall,the distribution of oil and gas and the distribution of temperature were taken as the evaluation indexes.After that,through the orthogonal analysis method,the multi factor orthogonal simulation scheme was established,and the primary and secondary order of each influencing factor and the best factor level combination were calculated.Then,based on radial groove,the direction and size of groove Angle were optimized.The results show that the heat transfer performance of the friction plate with negative groove Angle is better,and the optimum groove Angle size should be determined according to the operating speed range of the clutch.Thirdly,based on the internal clutch oil way model,a radial nested double clutch model was built.The heat transfer of internal and external clutches under two sliding conditions was studied with the inlet flow as the influencing factor.It is found that the highest value of oil temperature appears at the outer diameter of the moving friction plate;while the change of flow rate can effectively reduce the temperature difference and oil outlet temperature of the friction pair under the internal clutch sliding wear condition,but the improvement of cooling performance under the external clutch sliding wear condition has little effect.The research conclusion and model structure can provide some reference for future cooling flow matching scheme of wet double clutch.Finally,the test bench for the thermal fluid characteristics of wet clutch was built.Taking the constant torque as the test heat generation condition,the relationship between inlet flow rate,relative speed,number of oil entrance holes and oil temperature was studied.The simulation results coincided with the test results,which ensures the correctness and rationality of the simulation model.