The Use of Nonstandard Tooth Proportions and Center Distance to Improve the Performance of Gear Trains

摘要

During the design of a gear train, there may exist geometric constraints leading to the use of a nonstandard center distance and a profile shift in the gears. That is the case with countershafts, or gears with small numbers of teeth where undercut is to be avoided. Besides these special cases, the use of nonstandard proportions in the teeth of the gears may be used to improve the performance of the transmission in aspects like contact ratio, specific sliding, bending strength, balance in life, scoring capability, efficiency, etc. With the right selection of nonstandard center distance and tool shifting, it may be possible to use standard tools to improve the gear set capacity with a considerable reduction in cost when compared to the use of special tools. This paper presents an analysis of the effects in the performance of gears due to a deviation from the standard proportions and proposes an optimization procedure for the selection of the best geometry of the gears assuming generation with a standard rack or hob.