| Today,with the rapid development of high-speed trains,their safety issues have increasingly attracted attention.As a key component of the running gear of high-speed trains,the performance of axle box bearings directly affects the safe and stable operation of trains.Cylindrical roller bearings are one of the most common types of axle box bearings in high-speed trains.They are often in a mixed lubrication state during train operation,and carry certain moment loads due to installation errors and other factors,therefore,the roller will be tilted,and lead to lubrication failure of the bearings.Based on cylindrical roller bearing of the axle box,the overall mechanical characteristics have been combined with the bearing lubrication model considering roller tilting effects,and lubricating performance has been investigated from both theory and experiment,so that,a theoretical basis will be provided for the improvement of the axle box bearing of the train.The main research content includes four parts:Establishing a quasi-static model of cylindrical roller bearings considering the roller tilting effect;Analysis of the isothermal elastohydrodynamic lubrication performance of tilting roller bearings coupled with a quasi-static model;Discussion of thermal mixed lubrication performance of tilting roller bearings;Experimentally study on the lubrication performance of tilting roller pairs under different working conditions.Firstly,a quasi-static model of cylindrical roller bearing under action of the moment load was established,and the mechanical characteristics of the bearing were investigated.Some research on the cage slip rate was also conducted.The results show that radial load,moment load,number and length of rollers all affect the mechanical properties of bearings.The heavier the moment load,the greater the roller tilting angle;When the number and length of rollers decrease appropriately,and ceramic（Si3N4）materials are used as rollers and races,the slip rate will reduce significantly for tilted roller bearings.Secondly,the quasi-static model of bearings has been coupled with the isothermal finite line contact elastohydrodynamic lubrication model,and effects of mechanical properties on the isothermal elastohydrodynamic lubrication performance of bearings was studied.The results show that under the moment loading,the pressure and thickness of the oil film exhibit an asymmetric phenomenon;The greater the radial load and inner ring rotation speed,the smaller the asymmetry of oil film pressure deflection,and the greater the moment load,the more obvious the asymmetric effect of oil film pressure and film thickness,so lubrication performance of the bearing will be easily deteriorated;Reducing the length of rollers and increasing the number of rollers can reduce oil film pressure and improve the lubrication performance of bearings.Thirdly,coupled with the quasi-static model of the bearing,a non Newtonian finite line contact thermal mixed lubrication model was established based on the average flow rate model,and the effects of operating conditions and structural parameters on the thermal mixed lubrication performance of the bearing were investigated.The results show that after considering the moment load,asymmetry appears for the mid-layer film temperature with the higher temperature at the load bearing end and the lower temperature at the non-load bearing end;As the radial load increases,the load bearing end is always in a mixed lubrication state,and the difference of the film temperature gradually increases at both ends of the roller;When the rotation speed of the inner ring increases,the full film lubrication state is achieved at both ends of the roller,and the average friction coefficient and load ratio decrease;The greater the moment load,the smaller the oil film thickness,the higher the oil film temperature,and the roller is in a mixed lubrication state at the load bearing end of the roller.However,as the moment load increases,the oil film thickness increases,the temperature decreases,and a full film lubrication state is implemented at the non-load bearing end.Increasing the number of rollers and reducing the roller length can reduce the oil film temperature at both ends of the roller and improve the lubrication state.Finally,the viscosities of three types of lubricating oils,PAO10,PAO4,and PAG,were measured on a rheometer EC-Twist 502.On an optical interference test rig of oil film measurement for roller pairs,the oil film thickness distribution under different roller tilting angles,entrainment speeds,loads,and lubricating oil viscosity was studied,and corresponding analysis was conducted to verify the theoretical results.The results show that when the roller is tilted,the shape of the oil film in the Hertzian contact area will appear as one end is large and the other is small,and the positions 1and 2 are always in a mixed lubrication state;The higher the entrainment speed,the greater the overall film thickness,and the lubrication state at position 2 changes from mixed lubrication to full film lubrication;The influence of load on the shape of the oil film in the contact area is relatively obvious,but the influence on the film thickness is relatively small.Increasing the viscosity of the lubricating oil can reduce the tilt effect of the rollers,and this is coincident with the theory. |
