Numerical simulation of transient mixed elastohydrodynamic lubrication for spiral bevel gears

In spiral bevel gears, the entraining velocity, contact load and radii of curvature along tooth surface are always changed dramatically, which results in remarkable transient squeezing effect on lubricating performance, especially it operates in high-speed and heavy-load conditions. Available elastohydrodynamic lubrication (EHL) and mixed EHL studies for spiral bevel gears are mainly performed under quasi-static (steady-state) assumptions which ignores these transient influences. Therefore, in this paper, a transient mixed EHL model for spiral bevel gears is presented, in which takes into account most variable parameters along meshing surface including contact load, contact radii of curvature, entraining and sliding velocity vectors. Note that all these transient parameters of spiral bevel gears are employed from the results of loaded tooth contact analysis (LTCA). In order to improve the computational efficiency and convergent accuracy with a relatively dense grids, the progressive mesh densification (PMD) method for this transient mixed EHL model is also introduced. A comparison between the present transient mixed EHL model and those data from literature is executed to verify the correctness of the newly developed model. After that, systematically investigations of transient squeezing impact are carried out for spiral bevel gears and compared with the corresponding steady-state EHL results with and without real machined surface roughness. The obtained results reveal that the transient squeezing action can significantly affect the film thickness distribution in each contact zone and along the meshing track line in spiral bevel gears, and lead to dramatic growth in asperity contact area as well. Besides, the steady-state EHL appears to be greatly overestimated the lubricating characteristics for spiral bevel gears.