Influence of the addendum modification on spur gear efficiency

Nowadays, in the field of transmissions, one of the most important objectives is to realize gears with high efficiency so as to reduce power losses, operating temperatures, noise and wear. The target of this work is to analyze spur gear efficiency through two different approaches for friction coefficient calculation along the line of action in order to evaluate the possible differences. The first method analyzed considers a mean friction coefficient that follows Niemann's equation, the second method considers a local value for the friction coefficient following Hai Xu studies. For this purpose the efficiency variation versus the addendum modification of the pinion is taken into consideration for each of the following: operating conditions, transmission ratio and sum of addendum modification coefficient variations. Moreover, using the results of the first part of the paper, some of the more used methods for gear teeth optimization, in terms of the apportion of the addendum modification coefficient, are investigated in depth and compared in terms of efficiency so as to find out the best behaviour about: load capacity, safety against wear, noise and vibration.