Study On Lubrication Performance Of Ball-type Tripod Universal Joint Considering Surface Defects

The ball-type tripod universal joint is a new type of joint,which has the advantages of good cushioning and damping,good synchronization performance,and large bearing capacity.Material defects,improper heat treatment,lubricating oil pollution,and other factors will cause defects of different shapes on the surface of the joint friction pair.These surface defects will inevitably affect the lubrication performance of the joint.Therefore this paper studied the influence of surface scratches and elliptical dents on the lubrication performance of the ball-type tripod universal joint and carried out elastohydrodynamic lubrication(EHL)experiments to verify the numerical calculation results under isothermal conditions.The main research contents are as follows:(1)The elastohydrodynamic lubrication model of the ball-type tripod universal joint considering surface defects under isothermal conditions was established.The numerical algorithm was programmed by Matlab language,and the numerical solutions of lubricating oil film pressure and film thickness distribution were obtained.The impact of surface scratch and dent size parameters on the lubrication performance of the joint was investigated.The results show that there are obvious peak oil film pressures at the edges of scratches and dent defects in the contact area,the oil film pressure inside the defect decreases sharply,and the film thickness at the edge of the defect entrance decreases.Scratch has a great influence on the minimum film thickness in the contact area,and the dent has little effect on the minimum film thickness in the contact area.Scratches and dents at any position in the contact area will have a serious impact on the lubrication performance of the joint,and the closer to the center of the contact area,the greater the impact.Compared with the scratch width,increasing the depth and number of the dent will lead to a sharp increase in the maximum oil film pressure and a sharp decrease in the minimum oil film thickness.Compared with the aspect ratio of the dent,the depth and direction angle of the dents have a greater influence on the oil film pressure in the contact area.(2)Based on the lubrication model established in the second chapter,the energy equation and the temperature conditions boundary of the upper and lower interfaces were added to consider the influence of the thermal effect on the lubrication performance of the joint.The effects of the surface dent defect size,coupling structure parameters and working condition parameters on the oil film temperature rise,pressure,and film thickness in the contact area were analyzed and discussed.The results show that compared with the case of smooth surface,.the oil film pressure and temperature rise at the edge of the dent increase sharply,and the fluctuation of the film thickness is relatively small.With the length-width ratio and depth of surface dents,the peak oil film pressure and temperature rise in the contact area gradually increase,and the lubrication performance of the joint gradually deteriorates.When the long axis of the dent is parallel to the direction of entrainment velocity,the oil film pressure and temperature rise at the edge of the dent fluctuate most seriously,and the peak oil film pressure and temperature rise in the contact area increase sharply,which has the most serious influence on the lubrication performance of the joint.Appropriately reducing the joint input torque,input frequency and comprehensive elastic modulus of the contact pair is beneficial to reduce the peak oil film pressure and temperature rise in the contact area between the ball and the slider groove.Increasing the radius of the ball,the peak oil film pressure and temperature rise in the contact area gradually decrease,and the film thickness gradually increases,which is beneficial to improve the lubrication performance of the joint.(3)The isothermal lubrication model was modified to synthetically investigate the effects of surface dent defects and Gaussian random rough surfaces on the elastohydrodynamic lubrication performance of the joint.The finite element solution model of subsurface stress was established by ANSYS software,and the subsurface stress was solved by reading the pressure field in the lubrication zone to study the influence of Gaussian random rough surface parameters and surface dent defect parameters on oil film pressure,film thickness,and subsurface von mises stress distribution.The results show that as the root mean square of the Gaussian random rough surface increases,the oil film pressure and film thickness in the contact fluctuate obviously,and the high-stress area of the subsurface gradually moves upward to the surface layer.Compared with the transverse texture direction,the longitudinal texture direction has a greater influence on the lubrication performance of the joint.With the increase of surface dent depth,minor axis radius and length-width ratio,the maximum von Mises stress and oil film pressure in the contact area gradually increase,and serious stress concentration occurs at the edge of the dent.(4)The experimental study of smooth steel balls and steel balls with surface dents under variable speed and variable load conditions was carried out by using the elastohydrodynamic lubrication oil film measuring instrument,and the correctness of the elastohydrodynamic lubrication model under isothermal conditions was verified.The experimental results are in good agreement with the numerical simulation results.The typical characteristics of EHL film thickness are more obvious when the speed and load are higher.When the dent was in the center of the contact area,the film thickness decreases locally on the rear side of the dent,and a film thickness increase area is formed on the rear side of the dent.When the dent was at the entrance,the film thickness increase area affected the film thickness fluctuation of the whole contact area.When the dent was at the outlet of the contact area,the area where the film thickness increases behind the dent disappeared.When the dent was on both sides of the earlobe,the earlobe area was affected by the dent and moves to the middle of the contact area.