Search Results

Engineering specifications, i.e. test bogeys, are criterion for determining the success or failure of durability designs in the product development process. Considerations in the development of the specifications for vehicle structural components, such as axle housings and suspension torque rods, have been presented in a previous SAE paper [1]. This paper has been prepared because the factors on the same subject for vehicle drive train components, such as gears and bearings, are quite different. The center of this study is on “how to define equivalent duty cycles for lab test”. Several issues distinguish this task for drive train components: High cycle fatigue, high accelerated tests, competitive failures and failure modes, empirical component load-life data, loading, field correlation, and system level tests.

Premature parts breakdown in the final drive of heavy vehicle powertrains in vehicles equipped with high power retarders leads one to believe that the coasting mode gear forces may be higher than anticipated. There is limited experimental data that supports this hypothesis in the observation of high bearing load and gear bending stress in coast mode. However, without an in-depth analysis, it is unclear exactly how the high load is generated. There are several suggested causes: friction, gear geometry, and system compliance. The present study focuses on the effects of hypoid gear friction on the powertrain. Analytical expressions of the gear friction vector as a function of gear pressure, pitch and spiral angles, spiral hand and directions of rotation and applied torque were derived and examined. Attempts were made to correlate test-measured quantities and results from analytical models with and without the consideration of gear friction.