Theoretical And Experimental Research On Drag Torque Of Wet Clutch

As a significant part of vehicle power transmission,wet clutch is widely used in vehicle transmission system because of its advantages such as smooth joint,fast shifting and good heat dissipation performance.However,the viscous shearing of oil within disengaged wet clutches will produce drag torque which results in a substantial amount of power loss.The paper focuses on theoretical and experimental research of drag torque in wet clutch.Main contents are as follows.(1)Based on N-S equation and continuity equation,the mathematical model of the oil film flow field between friction pairs is established,the analytical solution of oil film flow field velocity,pressure and theoretical demand flow is obtained respectively.By establishing the 3D VOF model of oil film,the effects of factors such as rotational speed difference,oil film thickness and supply flow on the flow field and oil film distribution of oil film were derived respectively by simulation.The results show that when the velocity difference of friction disk or oil film thickness increases to a certain extent,or the supply flow decreases to a certain extent,it is hard to maintain a complete oil film between friction pair which shows different shapes of shrinkage,roughly serrated distribution.(2)Based on surface tension of oil film,the calculation model of drag torque is established and the variation law drag torque with rotation speed difference is theoretically studied and simulated under different oil film thickness and supply flow.That is,when the oil film thickness increases or the supply flow decreases,the drag torque first increases and then gradually decreases with the increase of the rotation speed difference,but the peak torque and its corresponding rotational speed difference decrease..(3)Oil groove structure with single throat pipe and double throat pipe is designed.The influence of oil groove structure on oil film shrinkage and drag torque is simulated.The research shows that compared with traditional radial oil groove,the oil groove with single throat pipe and double throat pipe enhance the oil film shrinkage and reduce the drag torque,and the peak of drag torque reduces by about 24.59% in oil groove with single throat pipe,more obviously,the peak of drag torque reduces by 47.27% in oil groove with double throat pipe.(4)The wet clutch test bench was built,so the effects of rotation speed difference and oil groove structure on the drag torque are studied experimentally.The experiment shows that the experimental results are consistent with the theoretical results,which verifies the correctness of the theoretical model.However,due to the influence of mechanical friction during the experiment,the results are about 7% lower than the simulation results.The peak of drag torque in oil groove with double throat pipe is 21.29% lower than that in oil groove with single throat pipe,however,the manufacturing error in oil groove makes the experimental reduction rate 1.39% lower than in simulation.The average temperature rise of oil film in oil groove with double throat pipe is 4 °C lower than when in oil groove with single throat pipe,which indicates that the oil groove with double throat pipe has good heat dissipation performance.