The new estimation formula of coefficient of friction in rolling-sliding contact surface under mixed lubrication condition for the power loss reduction of power transmission gears

This paper proposes new formulae for estimating the coefficient of friction at rolling-sliding contact surfaces under a mixed lubrication condition. The lubrication condition is expressed as a function of the ratio of the maximum height of surface roughness to the minimum oil film thickness under elasto-hydrodynamic lubrication. Empirical results are presented to verify the new formulae. Two-disc tests and gear tests were conducted. The measured values agreed well with the estimated values, confirming the usefulness of the proposed formulae. A program for evaluating mesh power loss by applying the new formulae is also explained using examples of several gear pair tests conducted on helical gears and conical involute gears.