Analysis Of Thermal Mixed Lubrication Of Angular Contact Ball Bearing In High-speed Railway Gearboxs

Angular contact ball bearing is one of key bearings in gearboxs of high-speed train,and its lubricating performance determines the safety and life of the train.In this paper,the mixed lubrication problem of angular contact ball bearing in gearboxs of high-speed train is mainly studied theoretically and experimentally.Four parts are included: Quasi-static modelling and analysis of angular contact ball bearing;Thermal mixed lubrication performance based on quasi-static analysis;The influence of oil supply conditions on the thermal mixed lubrication performance of angular contact ball bearings;Experimental study on film forming performance of ceramic ball contact pair and steel ball contact pair.Firstly,considering the effects of axial force,radial force,centrifugal force and gyroscopic moments comprehensively,a quasi-static model of angular contact ball bearing was established,and the effects of rolling element material,initial contact angle,rotating velocity and pitch diameter on the contact load,contact angle and velocity of inner and outer rings were analyzed.The results show that the contact condition of hybrid ceramic ball bearing is better than that of steel ball bearing and is more suitable for working at high speed.With the increase of rotating velocity,contact load of roller and inner ring,contact angle between the ball and the outer ring,and velocity of inner and outer ring increase,whereas contact load between the roller and the outer ring,and contact angle of inner ring decrease.The pitch diameter has less influence on the contact load and greater influence on entrainment velocity.Secondly,a quasi-static thermal mixed lubrication model was established to reveal the lubrication status of multiple rollers and to discuss the influence of initial contact angle and ambient viscosity on the mixed lubrication performance of angular contact ball bearings.The results show that when thermal effects are considered,the oil film thickness and average friction coefficient are smaller,but the asperity contact load is larger than those under isothermal condition.The ball bearings have the best mixed lubrication performance when the initial contact angle is 15 degrees.The higher the ambient viscosity of lubricating oil,the smaller the average friction coefficient,the lubrication state transits from boundary lubrication to mixed lubrication,and the mixed lubrication performance is improved.Compared with steel ball bearings,hybrid ceramic ball bearings can reduce the friction coefficient,but increase asperity contact load.Thirdly,considering the condition of oil supply,a thermal starved mixed lubrication model for angular contact ball bearings was established to estimate the lubrication status of rolling elements,and to study the effects of oil supply,rolling element materials,rotating velocity and ambient viscosity on the lubrication performance.The results show that,with the increase of oil supply quantity,the film thickness ratio and the maximum film temperature increase,the asperity contact load ratio and the average friction coefficient decrease,but finally tend to be stable,and reach a quasi fully flooded condition.Under the starved condition,the film thickness ratio and average friction coefficient of steel ball bearings are larger than those of hybrid ceramic ball bearings,and the asperity contact load ratio and maximum oil film temperature are smaller.With the increase of rotating velocity or ambient viscosity,the film thickness ratio and temperature increase,the asperity contact load ratio and the average friction coefficient decrease.Different from fully flooded condition,the mixed lubrication performance is poor under the starved condition.Finally,film-forming tests of silicon nitride ceramic/steel ball-glass disc contact pair were carried out on interference elastohydrodynamic lubrication test rig.The effects of velocity,loads,contact materials and lubricant viscosity on the shape and thickness of oil film were studied.The results show that the influence of load on film thickness is relatively greater at high speed than that at low speed,and the lubrication performance is the best at high speed and light load.When viscosity of lubricating oil is low,the film thickness of steel ball and ceramic ball is similar.With the increase of the viscosity of lubricating oil,the film thickness difference between steel ball and ceramic ball gradually increases.