Modeling And Influencing Factor Analysis Of Start Judder Of Automotive Transmission System

The gas disturbance moment caused by the pressure change in the engine cylinder and the excitation of the inertia moment caused by the inertia load of the engine rotating parts and reciprocating parts to the engine crankshaft system will cause many NVH problems of the whole vehicle system,among which the vehicle starting judder problem is one of the most common ones.This paper analyses and solves the problem of vehicle starting judder from two aspects of simulation modeling and test.The mechanism of engine torsional vibration is briefly analyzed.The starting judder is caused by the self-excited vibration caused by the friction characteristics of clutch and the fluctuation of pressure caused by the installation deviation of clutch.A Four-Degree-of-Freedom dynamic model of the transmission system of a vehicle with starting judder problem is established.The model includes engine,clutch and vehicle.The model mainly considers the moment transfer process during clutch engagement.The system state equation is obtained and solved by Runge-Kutta method.At the same time,the characteristics of cushion spring are taken into account in the Four-Degree-of-Freedom dynamic model.Through the clutch module of the dynamics simulation software,the system response of the model can be obtained by directly inputting the cushion spring characteristic curve.The research of cushion spring characteristic on the starting judder problem is more efficient.The dynamic response of the calculation model is compared with the actual vehicle test results,which verifies the correctness of the dynamic model.Using the established dynamic model,the effects of clutch torsional stiffness and cushion spring axial stiffness on clutch start judder are analyzed.The results show that reducing the torsional stiffness of clutch and the axial stiffness of waveform can reduce the starting judder of automobile.Aiming at the problem of pressure fluctuation caused by clutch installation deviation,a dynamic model of pressure plate-driven disk system is established.The influence of pressure plate parameters on the stability of the system is qualitatively analyzed.The results show that reducing the thickness of pressure plate,friction coefficient and increasing the stiffness of pressure plate are beneficial to the stability of the system.The axial force-displacement of the cushion spring has a strong non-linear characteristic,which is useful for automobile start-up.Clutch has influence on the transmission of engine output torque and the NVH performance of transmission system.Rigidity of cushion spring is an important index of force-displacement characteristics.A method for calculating the characteristic curve of cushion spring is proposed,and the method is improved on the basis of this method,which makes the results more consistent with the test results.The effectiveness of the method is verified by the test.It is found that the shape parameters of the cushion spring have a great influence on the start judder and the adjustment of the shape parameters of the cushion spring is realized.Therefore,the influence of the shape parameters of the cushion spring on the force-displacement characteristic curve was studied.The factors affecting the characteristics of cushion spring were studied by orthogonal experiment,taking the thickness of waveform,forming height,radius of waveform fillet,bending width and bending inclination as design variables.The results show that the main factors affecting the stiffness of cushion spring are the thickness and bending width of waveform.Increasing the thickness and decreasing bending width of the cushion spring will increase the overall stiffness of the cushion spring.The subjective and objective evaluation criteria of judder are established.Finally,the parameters of the clutch are optimized with the longitudinal acceleration of the body as the optimization objective.According to the optimization results,the vehicle test is carried out.The longitudinal acceleration values of the body before and after the optimization start and reverse start were tested and compared.The test results show that the starting judder problem of the vehicle model has been greatly improved after the optimization of clutch parameters.It is verified that the model construction and test method in this paper have certain guiding significance for the analysis of vehicle starting judder.