Three-dimensional mixed lubrication analysis of spur gears with machined roughness

The timing gears of the ship internal combustion engine usually undergo dynamic loading conditions, and often work in a mixed lubrication state. In this study, by considering the three-dimensional (3D) machined roughness, an integrated model with the analysis of mixed lubrication state and dynamic-meshing performance for the spur gear is developed. The model is verified by comparing its results with the predictions using the typical line-contact EHL formulas. The machined roughness apparently affects the local 3D distributions of the film pressure and thickness. The shaved surfaces have the minimum film thickness ratio and the worst lubrication state, while the polished surfaces can improve the lubrication performance of the timing gear pairs greatly. Under the conditions of heavy-load and low-speed, almost all of the Hertzian contact zone appears to be in contact with 0 film thickness, and the local maximum pressure may lead to serious stress concentration, film breakdown, and excessive wear, etc. By optimizing the gear module and pressure angle, the loading capacity of the timing gear is promoted and the contact area gets reduced, the lubrication state improves significantly from mixed lubrication to full film lubrication.