Spiral Bevel Gears with Optimised Tooth-end Geometry

Abstract

Industrially-manufactured, spiral bevel gears with complementary tooth-end surfaces as a rule have reduced tooth thickness and subsequently reduced strength at the tooth ends. The weakened tooth ends of octoid gearing are generally produced by machining, inevitably resulting in a certain lengthwise dimensional discrepancy and slight profile difference. This in turn very often leads to systematic breakage of teeth. Serious, systematic damage occurs irrespective of the transmission tightness of the outer or inner tooth ends.Gear manufacturers currently use several solutions to avoid such breakages, including artificial inclination near to the teeth or deliberately reducing the back or outer cone angle and increasing the front or root cone angle.This paper outlines an improved design of gear blanks, with optimised tooth ends. Our research concluded that it is possible to optimise rectangular-generated, spiral bevel pinion/gear pairs with constant tooth height and a common pitch cone apex. We can successfully achieve this through recalculation of the gear blanks, without any changes in the flank geometry or tooth-cutting process. Thus the gear pair with optimised tooth ends can be cut without interference to the customary tooth-cutting process. To prove the concept, an example of the recalculation is provided. These improvements result in increased tooth strength, simplification of the gear blank geometry and more suitable geometry for modern machining, as well as a smaller outer diameter of the gear.