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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.

As some of today's bus industry is moving toward electrically powered, low-emission buses, very compact drivetrain package, the driveline design which links electrical motor to spiral bevel or hypoid gears can become a significant challenge especially under severe environment and certain design constraints. The drive axle layout under consideration is depicted in the Figure 1. A design that have an integral shaft extended from cone apex (narrow end) of the pinion to connect to electrical motor is considered. In this design the undercut situation of the shaft by cutter tip during gear tooth generation becomes very critical. The purpose of this paper is to study the effect of cutter radius to provide a solution which is able to avoid or alleviate the interference condition and/or to determine undercut-free shaft diameter and location.

As modern vehicular applications demand higher power density gears, accurate analytical tools to predict gear stress are required. The finite element method has been successfully applied to the analysis and design of components and structures of a vehicle. However, it is still difficult to apply to gears due to very complicated geometry, especially in the root fillet area. Since a good knowledge of the gear root geometry is required to calculate bending stress, the purpose of this paper is to present the root fillet geometry of spur, helical, spiral bevel, and hypoid gears. The gear root fillet equations are derived based on the simulation of cutting tool motion on the gear blank during the manufacturing process. For spur and helical gears, the root fillet geometry cut by a rack with and without cutter tip radius is discussed. The phenomenon of undercut is discussed as well.