Thermal Elastohydrodynamic Lubrication And Fatigue Analysis Of Centrifugal Detached Overrunning Clutch

Centrifugal detached overrunning clutch is mainly used in auxiliary power unit,which belongs to sprag overrunning clutch.With the development of aviation industry in China,the overrunning clutch,as an important transmission part,directly affects the overall performance of the power system.In order to improve the working performance of the overrunning clutch,based on the thermal elastohydrodynamic lubrication theory,the research on the lubrication performance and fatigue life of overrunning clutch was carried out,it has important theoretical and engineering significance for reducing friction and wear and increasing fatigue life of overrunning clutch.Based on the working conditions of centrifugal detached overrunning clutch,considering the influence of rough surface,in this paper,a thermal elastohydrodynamic lubrication(TEHL)analysis model is established to predict the fatigue life of centrifugal detached overrunning clutch,the lubrication performance and fatigue life of overrunning clutch are analyzed.The main contents are as follows:Based on the structure parameters of overrunning clutch,the calculation formulas of stress and radial deformation of main components of overrunning clutch in APU starting condition are derived,and the structure parameters are checked,the contact stress of APU starting condition is verified by finite element method.At the same time,on the basis of centrifugal force and spring force,the force on the wedge block under the wind-driven rotation condition is analyzed.On the basis of the force analysis of the wind-driven rotation condition,the TEHL analysis model of the overrunning clutch is established considering the effect of roughness,the influence of windmill speed and ambient temperature on the lubrication performance of overrunning clutch was studied.The fatigue life prediction model and the method of subsurface stress analysis are proposed to study the influence of windmill speed on subsurface stress distribution and relative fatigue life of overrunning clutch,the influence of ambient temperature on fatigue life and subsurface stress and the influence of sampling interval on the results of subsurface stress distribution are analyzed.A test was designed to verify the accuracy of the temperature rise results of TEHL,the maximum error is 23.5% and the minimum error is17.4%,and the cause of the test error was analyzed.Based on the TEHL theory and the fatigue life prediction method,the influence of the windmill speed,the ambient temperature and the sampling distance is analyzed in this paper,increasing the oil film pressure,film thickness and temperature rise,increasing the subsurface stress,reducing the overrunning clutch relative fatigue life;The increase of ambient temperature will reduce the oil film pressure,film thickness and temperature rise,and reduce the subsurface stress,the increase of ambient temperature has a positive effect on the contact performance of the overrunning clutch,and the sampling distance has a certain effect on the TEHL and fatigue life analysis,especially,the influence on the results of temperature rise analysis can not be ignored.This study provides a theoretical basis and reference value for the research on the reduction of friction and wear and the improvement of fatigue life of overrunning clutch.