Simplified Calculation Method for the Efficiency of Involute Spur Gears

The traditional methods for computation of the efficiency of cylindrical gear transmissions are based on the hypotheses of constant friction coefficient and uniform load distribution along the line of contact. However, the changing rigidity of the pair of teeth along the path of contact produces a non–uniform load distribution, which has significant influence on the friction losses, due to the different relative sliding at any point of the line of contact. In previous works, the authors obtained a non-uniform model of load distribution based on the minimum elastic potential criterion. This load distribution was applied to compute the efficiency of spur and helical gears, resulting in slightly greater values of the efficiency than those obtained if the load distribution along the line of contact is assumed to be uniform. In this work, this non-uniform model of load distribution is applied to study the efficiency of involute spur gears with transverse contact ratio between 1 and 2 (i.e., the load is shared among one or two pairs of teeth), assuming the friction coefficient to be constant along the path of contact. Analytical expressions for the power losses due to friction, for the transmitted power and for the efficiency are presented. A study of the influence of some transmission parameters (as gear ratio, pressure angle, etc.) on the efficiency is also presented.