The Effect of Oil Viscosity on the Power-Transmitting Capacity of Spur Gears

Abstract

Abstract In tests made on spur gears with mineral oils of various viscosities, it was observed that a relationship exists between the maximum horsepower which the gears can transmit without scoring, and the product of gear speed and lubricant viscosity. An analysis of the factors entering into this relation indicates that these are the same that occur in Lewis’ equation used in gear design, except that the latter does not contain the lubricant viscosity. If this viscosity is introduced into the Lewis equation, the latter represents the experimental points for horsepower transmitted at the onset of scoring very well over a wide range of speeds and lubricant viscosity. This modified Lewis equation appears to apply to spur gears, in general, and indicates that the influence of lubricant viscosity on the power-transmitting capacity of gears is much too great to be neglected in the design of gears.