scope:

Gear reliability is a key requirement of any automotive transmission. Two common failure modes of gears are pitting and bending fatigue. Bending stress of gear teeth is significantly affected by the root fillet geometry, which is commonly generated by a hob cutter. Generally, hob rack parameters are defined from the initial gear geometry, based on which hobs are manufactured by hob suppliers. Differences in the actual hob cutter compared to the one specified on the gear drawing may change root fillet geometry causing deviations of bending stress from the predicted bending stress during the design stage. This paper presents a comparison of root fillet shape generated by the design hob rack to actual measured root fillet shape of manufactured gears and determines the impact of root fillet shape deviations on tooth bending stress. Bending stress was calculated based on design hob rack and compared to bending stresses of measured root fillets using a finite element-based module of WindowsLDP gear program. The parameters that caused deviations in bending stress were identified and discussed. The results of this paper emphasize the importance of robust engineering specification and inspection control plan of root fillet shape for attaining high gear reliability