The Influence of Pressure Angle of Spur Gears on Bending Stress Considering the Effect of Root Fillet Radius

Abstract

AbstractTooth breakage from excessive bending stress and surface pitting from excessive contact stress are the two primary fatigue failure modes for gears. Tooth breakage will end the gear life, so gear bending stress has to be accurately calculated for reliable operation. Many efforts have been made to increase gear bending strength including improving gear material property. With increasing demand for high power density gear applications, the need to optimize gears for minimum stress becomes increasingly important. It is imperative to understand the effect of gear parameters on bending stress in the initial stage of designing gears. Gear pressure angle is an important parameter affecting tooth bending stress. Because the critical section occurs in the gear root fillet, the root fillet radius largely affected by tool (hob) tip radius also has a great significance for improving the bending strength. The maximum tool tip radius will vary with the pressure angle changing due to the geometrical relationship of basic rack. This paper investigates the influence of pressure angle of spur gears on bending stress considering the variation of root fillet radius, and provides a recommendation on how to optimize the pressure angle for high bending strength gears. For analysis and validation of results, three methods of predicting bending stress– ISO standard, 3D-TCA (tooth contact analysis) method and Finite Element Analysis are applied and discussed.KeywordsGear bending stressGear pressure angleRoot fillet radiusGear material property