Optimisation and validation of pin profiling for sliding planet gear bearings

The helical gearing generates a complex combination of force and moment loads for the planet bearing. This unfavourable load situation and the deformation of the very flexible components, especially in a planetary gearbox for wind power, require a precise bearing design. A decisive factor is the crowning or profiling of the bearing, which is responsible for a uniform load on the bearing across the entire width. This article describes a novel analytical approach to optimize a bearing profiling that maximizes the load carrying capacity for a certain operating point. The method is validated with tests on a planetary bearing test rig that reproduces the kinematic as well as mechanical deformations of a planetary gearbox. A special design feature of the novel test rig is the rotatable pin, in which several pressure sensors are installed across the bearing width. Consequently, the hydrodynamic pressure distribution can be measured not only at several locations but in the entire load zone and is used for comparison with the calculated results. In addition to the hydrodynamic pressure, the bearing temperatures are also used for validation. Surface roughness and profiling are measured before and after the test proving that no hard mixed friction occurred during the experimental investigation. The research results indicate that the optimization approach for profiling leads to a contour that provides the highest load carrying capacity at nominal load case while ensuring sufficiently high film thickness at other load conditions. Therefore, robustness and reliability can be improved, and safe bearing operation is ensured as mixed friction conditions are minimized.