| Aiming at the problem that the lubrication mechanism and fretting wear mechanism in the sliding friction transmission process of the existing metal belt continuously variable transmission(CVT)affect the safety and efficiency of the metal belt transmission.The research object uses the self-developed domestic CVT to analyze the lubrication characteristics between the CVT pulley friction pairs and the wear characteristics between the steel ring friction pairs,and adopts the method of combining theory and experiment to clarify the lubrication characteristics and wear characteristics in the variable temperature environment.changing trend.Through the global sensitivity analysis method,the proportion of the corresponding variable factors affecting the lubrication characteristics and wear characteristics is obtained,the failure mechanism of the transmission system under complex working conditions is revealed,and the safety domain boundary of the CVT system instability is analyzed and solved,and the corresponding safety margin is obtained.The optimal torque under the obtained safety margin is quantitatively analyzed,and the corresponding bench test is carried out to verify the effectiveness of CVT transmission efficiency improvement.The main research contents of this paper are as follows:(1)The structural composition and transmission principle of the metal belt continuously variable transmission are expounded.According to the variable operating conditions of the transmission,the pulley friction pair and the steel ring are established based on the theory of point contact thermal elastohydrodynamic lubrication and the theory of fretting dissipation.Numerical model of friction pair,vector iterative calculation of lubrication and wear characteristics using multigrid method and FORTRAN coding.(2)The variation law of oil film pressure,oil film thickness and oil film temperature rise between the pulley friction pairs was studied by numerical simulation,and the lubrication characteristics of the oil film between the two friction pairs were analyzed.Using the same numerical calculation method,the variation law of the oil film characteristics of the steel ring friction pair with the roughness amplitude is studied.The influence law of the wear depth of the ring friction pair is analyzed,and the wear characteristics of the steel ring friction pair are analyzed,and the SEM electron microscope experiment is carried out to compare the simulation results and the observation results,which lays the foundation for the research on the transmission efficiency of the CVT.(3)A corresponding failure function is established according to the failure characteristics of the CVT transmission system,and whether the shear stress of the lubricating oil film is greater than its ultimate maximum shear stress is used as the criterion for the reliability failure of the CVT transmission.Since the CVT system is a complex coupled system with transient working conditions under the influence of multiple factors,when the output results are predicted,the magnitude of the influence of each parameter variable on the output results is unknown.The degree analysis model is used to calculate the influence ratio of each parameter variable to the output result,find the key factors from a variety of variable factors,and carry out the interpolation calculation of the corresponding parameter variables according to the obtained results,and obtain the safety margin result of the reliable operation of the CVT.(4)Use Matlab/Simulink simulation software to build a corresponding simulation model for the required solution variables,including torque module,engine module,and speed ratio module.Through the optimal transmission torque result in the required safety domain,the obtained torque in the safety domain is obtained.The torque result is used as the upper limit of the input parameter,and the CVT transmission efficiency is solved.It is found that when the input torque reaches 134.8 N·m,the transmission efficiency at this time reaches its peak value.When the transmission efficiency exceeds this value,the transmission efficiency of the CVT will gradually decrease,and Reliability can also be out of balance.Based on the numerical simulation results,the corresponding CVT transmission bench test verification is carried out,and three test conditions are set.The actual transmission torque of the CVT should be kept at 80%～90% of the maximum torque that it can transmit,that is,the torque ratio is.The optimal torque in the safety domain obtained above is in line with the optimal torque range of transmission efficiency obtained by the bench test.It can be seen that the obtained optimal torque value is reliable and accurate. |
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