Study On The Characteristic Of Automatic Wet Clutch Engagement Process

Automatic transmission system is one of the most important developing aspects of automobile technology. Automatic wet clutch is the important component of automobile automatic transmission system. Thorough research of the control of engagement and its dynamic characteristic has great significance of improving the design level of automobile key components and promotion of automatic transmission industry. From the present status of domestic research and the need of the theoretical research and practical project, some key problems were studied to improve engagement quality and its life-span. From the point of the optimal control method and improvement of design parameters, the main work of this dissertation include the dynamic model of clutch engagement, optimal control of engagement process, judder and stability of engagement process ,thermal load of engagement process and so on.In chapter 1, the background of the research work and important significance of the dissertation were discussed. Some crucial techniques involved with the research project, such as automobile automatic clutch control, clutch judder of engagement process, thermal load of engagement process, clutch test bench and etc., were analyzed. Finally, detailed research contents and chapters arrangement were given.In chapter 2, the dynamic model of multi-plate wet clutch engagement was studied in detail.Having introduced structure and principle of wet clutch and model of automobile automatic transmission system, this dissertation has established the dynamic model of vehicle transmission system through the analysis of wet clutch engagement process. The parameters of model were also analyzed to establish mechanical model and control model of hydraulic executive machine in automatic wet clutch.In chapter 3, the optimal control trajectory of automatic clutch and tracking control method were studied. Having investigated the engagement quality of clutch, this dissertation has pointed out that engagement quality of clutch has much to do with the change of friction torque in clutch engagement process. In accordance with the dynamic model of engagement process, this dissertation has established the state-space equation which takes change speed of friction torque as its control variable. The jerk and the dissipated energy were regarded as quadratic performance index, weight coefficient was used to adjust control tactic, friction torque optimal contrail was achieved under disturbing matrix through the usage of optimal control theory. Having aimed at unobservable friction torque and nonlinear hydraulic executive machine, this dissertation has designed the sliding mode controller with the usage of sliding mode control theory. Optimal contrail track of clutch engagement was realized to increase control precision and robustness of control system. Finally, the jerk and the dissipated energy were regarded as fitness function.And the parameter optimization method based on genetic algorithm for present control method in dual-clutch engagement was studied. In chapter 4, the mechanism of clutch judder and engagement stability of clutch engagement process were investigated. Having studied the friction torque and its simulation model, this dissertation has established 4-DOF torsional vibration model of transmission system. The mechanism of clutch engagement judder was analyzed from the perspective of self-induced vibration. The stability of clutch engagement process was discussed through linearization of friction coefficient. In order to improve the friction characteristic of clutch and provide reference for design of transmission system, this dissertation also analyzed the effect through simulation on the clutch judder influenced by friction coefficient gradient, static coefficient of friction, transmission system damping, stiffness, fluctuation of engagement pressure.In chapter 5, friction thermal load of clutch engagement process was studied. Having analyzed produce of thermal flux in clutch engagement process, this dissertation has established axisymmetric heat transfer model and thermoelastic model with certain boundary and initial condition. Coupling solving was operated with FEM method on temperature field and stress field. The calculation result of certain engagement condition was analyzed on the basis of the dynamic model of clutch engagement. This dissertation has also discussed the effect on thermal load influenced by pressure control, velocity load, friction structure, material parameter. Finally, some important conclusions were drawn to provide useful reference for design of clutch friction.In chapter 6, the design of a bench to test clutch engagement dynamic characteristic was introduced. Having analyzed the design requirement of test bench, this dissertation has presented the structure and principle of LHZ clutch test bench. This dissertation mainly studied some crucial technology of test bench such as electricity-feedback, electrical-inertia simulation and friction surface temperature measurement etc. Finally, the software of test bench was presented.In chapter 7, main results and conclusions of this dissertation were systematical summarized, the prospects and study emphases of the future research work were discussed and forecast.