Root Stresses and Bending Fatigue Breakage of Planet Gear

Abstract

A root stress analysis by means of the two-dimensional finite element method (FEM) and a bending fatigue test for planet and idle gears were carried out. The effects of rim thickness and internal pressure due to a press-fitted bush on the root stresses and the position of the fatigue crack initiation were investigated. In thin-rimed planet and idle gears considerably large stresses occur near the bottom of every unloaded tooth as well as two loaded teeth. The root stresses increase at the tensile side and decrease at the compressive side with a decreasing rim thickness. The fatigue crack of a planet or an idle gear with a press-fitted bush may occur near the tooth bottom due to the effect of residual tensile stress produced by press-fitting.