Tip-Fillet Interference in Cylindrical Gears

The occurrence of severe tip-fillet interference which could not be explained by existing formulas, and the tendency of modern design rules to go up to the geometrical limits, were reasons to develop three new views. The old geometrical condition proved to be incorrect. It required the usable flank to exceed the active flank, which guarantied only a correct mating on the line of action. However, while the involute flanks are mating regularly in an arbitrary position, then outside the line of action the tip of the pinion may penetrate the fillet of the mating gear. The possible tip-fillet interference is not restricted to one single position, but takes up a certain part of the path of action. The deduction of a completely new geometrical condition was based on a positive free distance between tip and fillet in each position. Secondly, a condition based exclusively on nominal dimensions did not suffice. The neglect of inaccuracies and deformations was as irresponsible as neglecting functional backlash in any conventional gear pair. Emphatically, the geometrical condition has to answer the same influences. Therefore, a new algorithm includes a relation with maximal backlash. Thirdly, by introducing a quality dependent backlash function in a geometrical condition, there will be more necessity to standardize a clear backlash-related tolerance system than in the past was required for the minimal functional backlash.