Thermal-fluid Coupling Simulation And Analysis Of Cooling Oil Circuit Of Wet Clutch

As an important mechanical device of automatic transmissions,wet clutches are widely used due to their soft and smooth shifting,stable torque transmission performance,good cooling performance.During engagement process,the friction plate and the steel plate slide against each other due to the difference in speed and generate great amount of sliding heat,which is absorbed by the friction pair.And the surface temperature of friction pair rises rapidly,which causes the deterioration of the surface material of the friction pair and the surface ablation of the steel plate.The clutch has thermal failure due to high temperature,which greatly reduces the service life of the clutch.Therefore,the good heat dissipation performance of the cooling oil way is of great significance for improving the working quality of the wet clutch.The wet clutch with radial grooves is taken as research object in this paper,and the oil circuit characteristics of wet clutch under sliding conditions are simulated and analyzed,which includes the heat transfer characteristics、flow field characteristics and oil-gas two-phase distribution characteristics.The work content of this paper is expanded as follows.Firstly,the flow characteristics and the heat transfer characteristics of the cooling oil way of wet clutch are analyzed theoretically based on fluid dynamics and heat transfer theory.The heat exchange form of each wall in the oil circuit model is classified and the relevant convective heat transfer coefficient is calculated,which lays the theoretical foundation for the subsequent analysis.Secondly,a wet clutch oil circuit model with radial grooves was built by CATIA software.The steady-state heat flow coupling simulation model of the cooling oil circuit of the wet clutch was built by STAR-CCM+ software on the basis of considering the viscosity-temperature characteristics of the oil and the two-phase mixing effect of oil and gas.The flow field characteristics 、 the temperature field characteristics and the oil-gas two-phase distribution characteristics of the wet clutch oil way under different relative speed、different inlet flow and different friction pair clearance are simulated and analyzed.Then,the variation of heat dissipation performance of oil circuit with structural parameters is discussed by changing the structural parameters of radial grooves.The study found that as the relative speed increases,the oil percentage of friction pair shows a downward trend,the circumferential unevenness of the oil-gas two-phase distribution increases,and the wall heat transfer value decreases rapidly,but the radial temperature distribution of the oil film tends to be uniform.The heat transfer value of the sliding surface of friction pair goes up with the increase of inlet flow,but the radial temperature difference of oil film increases accordingly.The increase of the gap value mainly improves the heat transfer effect of the groove surface,and the uniformity of the friction fluid oil pressure distribution is improved accordingly.With the increase of the depth and the external diameter of radial grooves,the heat transfer performance of the friction pair wall surface is improved,which provides ideals for advancing the performance of cooling oil circuit for wet clutch.Finally,the wet clutch test bench was built by using a constant torque-variable speed scheme,and the variation curve of the temperature of the steel plate surface and the oil outlet with the joining time under the given inlet flow was obtained.The simulation results is compared with testing results,which verifies that the simulation model is reasonable.