Coupling Analysis Of Dynamic Performance And Tehl State Of Aeroengine Main Shaft Bearing

The main shaft bearigs are the key components of aero-engine,which can keep the aircrafts working steadily and reliably,and high-speed,heavy-load and high-temperature are the typical running conditions.With the higher requirement of thrust-weight ratio in the aero-engines,the running conditions of the main shaft bearings also become worse,which bring the rise of the failure rates.However,with the development of bearing materials,the main failure types from fatigue and fracture become relatively fewer,and the failures caused by sliding,friction or wear related with lubrication are in the majority.So the research of the lubrication property and mechanism of aero-engine main shaft bearings under typical running conditions will be very meaningful.In this paper,we take the main shaft rolling bearing in aero-engine as an research object and the typical running conditions as the calculation cases,the coupling analysis of bearing quasi-dynamics and thermal elastohydrodynamic lubrication(TEHL)is built,further,considering roughness,non-Newtonian,transient effect and multi-lubrication states in the coupling analysis,a complete bearing analysis system from quasi-dynamics to TEHL,then contact state analysis is built,which can obtain the rolling bearing dynamic properties,lubrication states and properties,and contact stress distributions accurately.The main research contents are as follows:The coupling analysis of rolling bearing quasi-dynamics and TEHL under demanding and complicated working conditions is built.Quasi-dynamic analysis can provide mechanical and kinematic parameters in micro-contact region for TEHL analysis,and the TEHL analysis also can feedback lubrication properties to quasi-dynamic analysis,so the coupling analysis is implemented by looping and iteration.The tested minimum film thickness is compared with that obtained by the fitting equations and current method,which claim the results by our new coupling method agree better with the tested data.Comparing the bearing dynamic properties with the traditional quasi-dynamic analysis,the minimum film thickness and friction coefficient have changed considering thermal effect,film thickness decreases,the contact deformation and contact load increase,the stiffness gets larger,the micro-contact region changes and the relative sliding becomes higher,and the friction coefficient affects the friction force,so the loading and motion states of the whole rolling bearing change.With the increased load,the contact angle of the ball bearing becomes smaller,the spinning motion is restrained and spin-roll ratio decreases;the loading roller number of roller bearing increases,and the cage sliding ratio gets smaller.Based on the coupling analysis method,the parametric study of rolling bearing TEHL properties is carried on.With the increase of inner race coefficient of ball bearing,the contact load becomes larger,the film thickness gets thinner,which is bad for lubrication;with the increase of initial contact angle and the number of balls,the contact stress decreases,the film thickness increases and the lubrication is improved;the TEHL properties become asymmetry with the spinning motion caused by high speed,the minimum film thickness becomes thinner and the maximum film temperature gets higher,which also bring a bad lubrication.In addition,with the increasing radial clearance of roller bearing,the loading roller n umber decreases,the cage sliding ratio, (product of contact stress and relative sliding)value increase and the film thickness becomes thinner,the film temperature gets higher,which is bad for lubrication;with the increase of inner race ellipticity,the loading roller number increases,the cage sliding ratio, value get decreased,the film thickness becomes thicker and the film temperature gets lower,the lubrication properties are improved.On the basis of quasi-dynamic results,taking the the non-Newtonian fluid and three-dimensional random roughness effect as consideration,the non-Newtonian micro-TEHL analysis model of main shaft ball bearing is built.The TEHL properties with Gaussian,sine and sooth surface roughness are compared,and the root mean square(RMS)and working conditions effects on lubrication properties and states of main shaft ball bearing are discussed.The non-Gaussian roughness parameters including skewness,curtosis,transverse texture and longitudinal texture effects on the lubrication properties and surface stress distributions of main shaft ball bearing are studied.Combining the finite element method(FEM),the subsurface stress is calculated,and the maximum equivalent stress is verified.Further,the non-Gaussian surface roughness parameters effects on the relative fatigue life of main shaft ball bearing are investigated.Considering the transient effect and multi-lubrication states in changing speed states of the aero-engine main shaft ball bearing,coupling the bearing quasi-dynamics,the transient mixed TEHL analysis model is built.In order to validate the reliability of the method,the changing speed and heavy-load conditions are taken as the cases,and the optical interference test data are compared with that by transient mixed TEHL analysis.The change of lubrication states and properties of main shaft ball bearing from BL to full EHL between a single ball and inner race during start-up are investigated,and the lubrication properties and states between balls and inner race at different azimuth angles are given,which are compared with that in shut-down,results show the lubrication state in shut-down is better,the BL(boundary lubrication)time is shoter and the ball number in BL region is less.The rotation velocity increasement effect on lubrication properties of main shaft ball bearing is dicussed,with its increase,the film thickness increases and friction coefficient reduces quickly,which can short the bad lubrication time.The working conditions,stuctural parameters and lubricant prameters effects on transient mixed TEHL properties of main shaft ball bearing during shut-down are discussed,results show the increase of radial and axial loads,inner race coefficient and inlet film temperature can make the main shaft ball bearing go into unsafe mixed lubrication ahead and the BL time become longer,the film thickness gets thinner,which is bad for lubrication.But as the lubricant viscocity and the number of ball increase,the main shaft ball bearing goes into unsafe mixed lubrication late,and the BL time get s shorter,the film thickness increase and the temperature decrease,the lubrication is improved.The coupling analysis model of aero-engine main shaft bearing quasi-dynamics and TEHL can provide theoretical bases for getting accurate bearing dynamic and lubrication properties,resonable judgement of lubrication state and effective prediction of lubrication failure,and lay the groundwork for optimizing bearing structure design and prolonging fatigue life,which has important theoretical significance and engineering application value.