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Little information is available concerning the bending fatigue behavior of helical gears with tall thin teeth and high contact ratios, particularly for planetary pinions which are subjected to fully reversed loading. The most common methods to acquire gear bending fatigue data are either through a four-square recirculating power arrangement or unidirectional single tooth bending experiments on standardized spur gears. There are some advantages to these test methods, but they generally do not represent actual operating conditions of a planetary gear environment. The purpose of this study was to develop a bending fatigue test for planetary pinions in automatic transmissions which would better represent actual operating conditions. The new testing procedure was used to evaluate the bending fatigue behavior of three gear steel/processing combinations. The results from the planetary gear testing is compared with laboratory four-point bending experiments.

Designing highly loaded spur and helical gears for truck transmissions that are both strong and quiet requires an analysis method that can easily be implemented and also provides information on bending stress, load distribution, and transmission error. The finite element method is capable of providing this information, but the time needed to create such a model is very great. In order to reduce the modeling time, a preprocessor program that creates the geometry needed for a finite element analysis has been developed. While requiring a minimum of user input, the program generates a three-dimensional model of contacting spur or helical gears using eight node brick elements. Gap elements are used to model the contact that normally occurs between meshing gear teeth as well as the contact that may occur off the line of action due to the teeth deflecting under load.