Abstract: A new system of modifications for power train gearing, called "differential crowning," has both advantages and disadvantages over the previous system of modifications based on tip and/or root relief. The advantages of differential crowning are three-fold: (1) it affords substantially constant stiffness, so that it is equally effective at all loads; (2) it is adapted to minimize both first and second harmonic excitations, whereas conventional modifications can mitigate only the first harmonic excitation, and that only at one "design load;" and (3), it is as insensitive to manufacturing inaccuracies as conventional gearing is sensitive to them. Differential crowning, however, has two disadvantages in its previously disclosed forms: (1) it is difficult to optimize; and (2), it is more expensive than conventional modifications unless the production runs are very large.

Abstract: Spectrum analyses of gear noise show that the predominant frequencies are the tooth contact frequency (1.times.TCF) and twice the tooth contact frequency (2.times.TCF). The reason for this is that at two positions in the tooth engagement cycle, the effective mesh stiffness of conventional gearing differs substantially from the ideal mesh stiffness that eliminates the dynamic increment of load. One of these two positions occurs once per tooth engagement cycle and the other one twice, giving rise to the 1.times.TCF and 2.times.TCF excitations respectively. These periodic fluctuations in the effective mesh stiffness, which are in proportion to what is called "static transmission error," produce inertia forces between engaged teeth that increase with both speed and proximity to the critical (resonance) speed of the gear pair. In conventional gearing the dynamic increment of load generated by these inertia forces can be as large as or even larger than the useful transmitted load.

Abstract: The usual expedient employed by gear designers seeking to reduce gear noise at all loads has been to specify finer teeth, which in effect trades away torgue capacity for quietness. The present disclosure describes a tooth form that substantially eliminates gear noise while at the same time significantly increasing torque capacity. This tooth form involves (a) the synchronization of the loading and unloading phases of tooth engagement with the inverse phases (i.e., unloading and loading phases, respectively) of another tooth pair, combined with (b) the introduction of particular patterns of topographic tooth surface crowning that transform the elastic tooth pair stiffness curve into a curve that not only maintains this synchronization at loads greater or smaller than the design load but also eliminates transmission error to any extent desired.