Retaining Hypoid Gear Performance Characteristics With Differential Housing and Shafts Deflections

Hypoid gears are widely used in rear drive and 4WD vehicle axles. Investigation of their sensitivity to misalignments is one of the most important aspects of their design and optimization procedures. Because of unavoidable mounting deflections under working load, the values for mounting distances and angle deviate from the designed (desired) values (due to elastic deformation of differential housing and gear shafts). As a result the performance characteristics will be changed. This study provides a calculation procedure to design "optimized vehicle differential housing side elastic coefficients" that maintains primary performance characteristics during load variations (caused by both the road and engines). The calculation is based on third order contact surface parameters for combined mismatched tooth surfaces. Calculations will be done in four separate groups to maintain four primary groups of performance characteristics, including: i) the amount of transmission error ii) contact pattern shape (by controlling bias angle) iii) backlash and iv) contact pattern size; in all mentioned cases theoretical contact pattern position during differential housing deflections is kept unchanged. Moreover, an experimental analysis was performed on a hypoid gear pair, the results of which were in close relation to theoretical results of sensitivity of contact pattern location. The method used in this study gives insight to effects of differential housing and gear shaft deflections (as misalignments) on hypoid gear performance. Considering this information in differential housing and gear shaft design will provide more correlations between hypoid gear pair and their housing and shafts in order to optimize performance characteristics under actual load.