No abstract

In this study, the impact of misalignments on root stresses of hypoid gear sets is investigated experimentally and theoretically. An experimental set-up designed to allow operation of a hypoid gear pair under loaded quasi-static conditions with various types of tightly controlled misalignments is introduced. These misalignments include the position errors (V and H) of the pinion along the vertical and horizontal directions, the position error (G) of the gear along its axis, and the angle error (γ) between the two gear axes. For example, face-hobbed hypoid gear pair from an automotive axle application is instrumented via a set of strain gauges positioned at the roots along the faces of multiple teeth to measure root strains within a range of input torque. These root strain measurements at different V, H, G, and γ values are presented. A computational model is also proposed to predict the root stresses of face-milled and face-hobbed hypoid gear pairs under various loading and misalignment conditions. The model employs an automated finite elements mesh generator based on a predefined template for a general and computationally efficient treatment of the problem. Model predictions are compared to measurements at the end to assess the accuracy of the model and describe the measured sensitivities.

In this study, the results of an experimental parametric study of the combined influence of shaft misalignments and gear lead modifications on the load distribution and tooth bending stresses of helical gear pairs are presented. A set of helical gear pairs having various amounts of total lead crown was operated under loaded, low-speed conditions with varying amounts of tightly controlled shaft misalignments. Gear teeth were instrumented through strips of strain gages along the face width of gears at the tooth fillet region at a roll angle that is near the start of the active profile. Variations of root strains along the face width were quantified for different levels of shaft misalignments and gear lead crown. The results presented demonstrate the direct link between the lead crown and gear misalignments as well as the effectiveness of the lead crown in preventing edge loading conditions due to misalignment. The results presented here form a database that should be available for a validation of gear contact models in terms of their ability to simulate misalignments.

In this study, a crack initiation life prediction methodology for the tooth bending fatigue of hypoid gears is proposed. This methodology employs a previously developed finite-element based hypoid gear root stress model (Hotait et al. 2011, “An Investigation of Root Stresses of Hypoid Gears with Misalignments,” ASME J. Mech. Des., 133, p. 071006) of face-milled and face-hobbed hypoid gears to establish the multiaxial stress time histories within the root fillet regions. These stress time histories are combined with a multiaxial crack initiation fatigue criterion to predict life distributions along roots of the pinion and the gear. The predictions of the multiaxial fatigue model are compared to those from a conventional uniaxial fatigue model to establish the necessity for a multiaxial approach. The model is exercised with an example face-milled hypoid gear set from an automotive application to demonstrate the impact of various misalignments well as the key cutting tool parameters on the resultant tooth bending lives.

In this study, combined influence of shaft misalignments and gear lead crown on the load distribution and tooth bending stresses is investigated experimentally. A set of helical gear pairs having various amounts of lead crown was tested under loaded, low-speed conditions with varying amounts of tightly-controlled shaft misalignments. Gear teeth were instrumented through strips of strain gauges along the face width of gears at the tooth fillet region near the start of active profile. Variations of root strains along the face width were recorded for different levels of shaft misalignments and gear lead crown. At the end, the experimental results were correlated to the predictions of a gear load distribution model and recommendations were made on how much lead crown is optimal for a given misalignment condition.