Study On Gearing Mixed Elastohydrodynamic Lubrication Based On Surface Roughness Profiles

At present, the contact fatigue strength design of gear transmission is based on Hertz theory which only applies to the smooth surface of dry contact. However, most of the gear transmission mesh in the mixed lubrication state, that is, the lubricant film and the direct collision of the rough peak exist between two contact tooth surfaces, there is an obvious difference with the Hertz theory. Therefore, the study of mixed elastohydrodynamic lubrication is necessary and has a strong theoretical significance of gear transmission.In exploring the mixed elastohydrodynamic lubrication of gear transmission, researchers often assume one or more rough peak or use sine (cosine) function for characterizing the distribution of tooth face roughness; it is undoubtedly that there is a wide gap with the true rough texture of the tooth surface. Using W-M fractal function simulate the rough texture of tooth face, and add it to the film thickness equation, after that, using multiple grid method to solve pressure distribution, using multiple grid integration method to solve oil film thickness distribution, using the sequential column sweeping scheme to solve the temperature distribution, then, taking a mine heavy-load gear transmission as example, numerical calculating the pressure distribution、oil film thickness distribution and subsurface stress distribution along five special meshing point. In addition, through discussing the influence of tooth surface roughness and lubricant viscosity on subsurface contact stress distribution and film thickness, then giving the regression equation through the result of regression analysis. The main conclusions are as follows:(1) There are obvious differences of pressure distribution and subsurface stress distribution with Hertz distribution after using rough surface. So, the contact fatigue strength design of gear transmission which based on Hertz theory need to improve.(2) The approach point is the danger point on meshing line, because the minimum oil film thickness and the maximum contact stress at this point. Therefore, the contact fatigue strength design of gear transmission which based on the node parameters is debatable.(3) The average film thickness increases monotonically as the tooth surface roughness rises, whereas the subsurface maximum principal shear stress increases after decreasing, there is a parabolic relation between τmax and σ. Therefore, when the tooth surface finish reaches a certain value, blindly improve the processing quality of the tooth surface can not achieve the purpose of extending the fatigue life of gear transmission. (4) Tooth face roughness can make the film thickness and the pressure distribution occur saw tooth wave shape change, the lower the lubricant viscosity and the more violent fluctuations. When other parameters is fixed, the gear drive lubrication state from boundary lubrication after mixed lubrication gradual transition to full-film lubrication as lubricant viscosity rises. Therefore, in certain industrial conditions, improve the lubricant viscosity can effectively reduce the tooth surface contact stress, thereby increasing the contact fatigue life of gear transmission.