Study On Friction Torque And Vibration Characteristics Of The Friction Pairs During Wet Clutch Engagement

With the development of heavy-duty vehicles towards high speed and high energy density,the performance requirements of its transmission components are also increasing.Wet clutch is a key component of vehicle transmission system.Clutch engagement stability directly affects the comfort and safety of vehicle driving.Taking the wet clutch carried by large heavy-duty vehicles as the research object,starting from the surface microstructure of the clutch friction pair,combined with theoretical modeling,simulation analysis and experimental research,this paper studies the sliding friction vibration characteristics of the clutch,enriches the clutch design database and improves the clutch design system,which has important theoretical significance.The work done in this paper includes:(1)Based on Hertz contact theory and the rough surface contact model proposed by Greenwood and Williamson,the side-contact and viscoelastic force produced by the asperities of the friction pair of wet clutch in the process of sliding and friction were considered.Combined with the methods of parameter normalization and statistics,the relationship between the micro parameters of the friction pair surface and the macro contact force of the friction pair was established.The calculation formulas of normal contact force and tangential contact moment between friction pairs of rotating sliding friction were deduced.(2)Based on the contact force model of friction pair,the influence of the change of axial dimensionless distance on the friction torque of clutch friction pair during sliding friction was considered and the axial dynamic model of clutch friction pair during sliding friction was established.In addition,the micro mechanism of friction torque speed negative slope at low speed was obtained,and the effects of dimensionless curvature radius of asperities and axial pressure on the dynamic characteristics of negative slope were analyzed.The results show that when the axial pressure and dimensionless radius of curvature decrease,the minimum value of change rate(d T_f/dn)will increase,the change of friction torque will decrease,and the friction torque velocity curve tends to be flat.At the same time,through the bench test,the action relationship between the negative slope characteristic and relevant parameters is reproduced,and the key parameters of friction torque change under different axial pressure are obtained.Through the comparison between the theoretical and the test results,the accuracy of the theoretical model is 87%,which shows the accuracy of the simulation results.(3)Using the finite element method,modal analysis and transient dynamic analysis were carried out on the structural characteristics of the friction pair and the dynamic response under circumferential impact,respectively.Considering the nonlinear change characteristics of friction torque during the engagement process,the dynamic response of the pair of steel plates when the friction plates are combined with different axial pressures and initial speeds.The results show that the first-order natural frequency of the dual steel sheet is 55.29 Hz;during the combination process,the circumferential vibration acceleration response characteristic presents the characteristics of"three-stage",and the duality will be lost at the moment of high-speed engagement and the low-speed range when the combination is about to be completed.The steel sheet produces a large circumferential impact,and increasing the axial pressure and the initial speed will increase the vibration intensity of the engagement process.(4)Aiming at the characteristics of high linear velocity slippage of the friction pair when the wet clutch is engaged,the whole-process vibration test of the clutch engagement is carried out,and the circumferential vibration acceleration under multiple sets of working conditions is tested.The results show that although the effective value of the vibration acceleration of the friction pair in the whole process of engagement increases with the increase of the speed,when the frequency of the external excitation is close to the natural frequency of the dual steel sheet near 3200rmp,it will increase the amplitude of vibration acceleration at the moment of engagement.and affect the stability of the system.