Instantaneous Efficiency and Coefficient of Friction of an Involute Gear Drive

In this work the authors, using a testing machine designed for this investigation, determined experimentally the variation in the friction losses in gearing during an individual tooth engagement period. Based upon the obtained data “instantaneous efficiency” of various gear drives and the variation of “apparent coefficient of friction” during the engagement period were evaluated. This “apparent” or “effective” coefficient of friction is a coefficient which represents the effect of the friction due to rolling or a combination of rolling and sliding motion between the engaged teeth in the gear drives. The instantaneous coefficients of friction in the gearing during the engagement cycle were obtained for a large number of different operational conditions. The following factors were used as variable parameters: the torque transmitted by the gears, the speed of gear rotation, the diametral pitch, and the contact ratio of the gearing.