Influence of tooth asymmetry and mating gear material on the tooth deflection characteristics of polymer gears

Abstract

Transmission error (TE) in polymer gears is significantly affected by the elastic deflection of meshing teeth. The present work describes the deflection characteristics of the asymmetric Nylon 66 spur gears under similar and dissimilar engagements. The load sharing and deflection behavior were estimated numerically using a linear viscoelastic material model. Experimental determination of mesh deflection was carried out through static load tests. The peak mesh deflection in a cycle for the 20°/34° configuration was found to be 8% and 12% smaller as compared to 34°/20° and 20°/20° configurations, respectively. The peak tooth deflection was found to be highest for the 34°/20° configuration and lowest for the 20°/34° configuration, with the deviation between their peak deflections being 15% in metal-polymer pairs and 17% in polymer-polymer pairs. In the 34°/20° configuration, the higher drive side pressure angle increased the single tooth contact period, causing greater peak-to-valley amplitude in a cycle. The negligible tooth compliance of steel gear caused unsymmetrical load sharing in the double tooth contact zones of metal-polymer engagements. The greater compliance of driver gear in polymer-polymer engagements increased the mesh deflections of 20°/20° and 20°/34° configurations by 45% and that of 34°/20° configuration by 37%. Also, gear pairs with similar material stiffness balanced the load sharing in the addendum and dedendum double tooth contact zones. The large tooth deflection extended the contact duration of all configurations for both the similar as well as for the dissimilar engagements, respectively. This was signified by the contact path extension at the peripheries of the mesh cycle.