Study On Several Working Characteristics Of Wet Clutch

Wet clutch has been widely used for the vehicle automatic transmission, and its working characteristics have an important influence on the operational performance of automatic transmission. Thorough research of wet clutch working characteristics has great significance to improving the research and design level of domestic automatic transmission and promoting domestic automatic transmission industry. Therefore, aiming at the development status of domestic wet clutch technology and the needs of the theoretical study and practical project, this dissertation makes deep and systematic research on the working characteristics of wet clutch to decrease drag losses, improve engagement characteristics and enhance friction wear characteristics.Chapter 1, the structure features of wet clutch and the development history of wet friction material were introduced, and the background and significance of the research work were discussed. And then the previous research work at home and abroad were summarized, emphasizing on a review of the research status and existing problems of wet clutch drag losses characteristics, engagement characteristics, running-in wear characteristics and clutch test rig. Finally, the main research contents and chapters arrangement were introduced.Chapter 2, the formation mechanism of drag torque of wet clutch was studied. According to the motion equation and the continuity equation based on laminar flow of viscosity hydrodynamics and considering the centrifugal effect to cooling and lubricating oil, radial velocity model of the oil film in clearance was established. The equivalent outer radius was introduced to describe the effect of the centrifugal force on the oil film, and the new model of drag torque was derived by combining the effect of surface tension of oil film with the Newton inner friction law, and the effects of parameters in the model on drag torque was studied by numerical calculation. Finally, theoretical analysis conclusions were verified by test data from clutch test rig.Chapter 3, the average pressure model of oil film and the asperity contact pressure model was established on the basis of hydrodynamic lubrication theory and asperity contact model of two surfaces in wet clutch engagement process. And then according to bearing capacity model and friction torque model, the oil film thickness rate, the relative angular velocity rate and torque calculation model of engagement process were deduced, and the effects of parameters in the model on engagement characteristics were analyzed by numerical calculation. Finally, analytical results were validated by test data from clutch test rig.Chapter 4, the wear mechanism in wear-in process of wet clutch friction pairs was investigated through the wear-in test and surface analysis technology. And then according to its wear mechanism and the advantage of fractal parameters which can describe asperity surface profiles with scale independence, the fractal prediction model of running-in wear of wet clutch friction pairs was established, and the effects of fractal dimension and other parameters of wear rate were discussed. Finally, in order to study the prediction of the wear-in state in wet clutch test, some methods based on box dimension, correlation dimension and multifractal spectrum of friction-torque signal of pressing stage in engagement were proposed to predict and evaluate the wear-in state.Chapter 5, the design of clutch comprehensive performances test rig and the functions of some test modules were introduced. And the test criterion for thermal failure of friction pairs of wet clutch was studied on the clutch test rig. Finally, some key technologies of the test rig were studied such as the temperature measurement of friction disk surface, the automatic measurement of wear rate and anti-interference methods of signals on test rig etc.Chapter 6, the main results and conclusions of the dissertation were systematically summarized, and the prospects of further research work were discussed.