Fatigue failure mechanism of planetary gear train for wind turbine gearbox

According to the statistics, failure of gearbox often leads to the longest downtime and maximum economic loss for wind turbine. Operational experience reveals that damage morphology often occurs on planetary gear trains. Based on real cases, the hypothesis that failure developing process of planetary gear is divided into two stages including fretting wear and fatigue source generation has been proposed. For the fretting wear stage, the research work focuses on testing the hardness difference between gear inner surface and bearing outer ring, analyzing the influence of interference fit tolerance on fretting slip distance, and exploring the influence of gear hub thickness on fretting slip distance. The relevant technical improvement measures are proposed and following experimental data have shown these measures are quite effective. At the stage of fatigue source generation, the roundness error of gear inner surface and the profile error of tooth surface can affect the radial clearance of the meshing gear pair. As a result, uneven load region on gear inner surface appears. Following quantitative analysis of comprehensive stress on the uneven load region reveals the formation mechanism of symmetrical fatigue source, which has been verified by the real failure case eventually.