A study of churning losses in dip-lubricated spur gears

Abstract

Churning losses contribute significantly, both to overall inefficiency and to oil heating, in many dip-lubricated transmission systems, notably in automotive applications. For this reason, a reasonably accurate estimate of churning loss is often desirable at the design stage. However, the published literature contains several empirical calculation methods that give widely different results, even within the claimed range of accuracy. For example, a single 72-tooth, 3 mm module spur gear rotating at 4500 r/min immersed in 20W50 motor oil to a depth of 54 mm would be predicted to exert a churning torque of 75 N m by the method of Boness but less than 5 N m by the method of Terekhov. In order to resolve the discrepancy, churning torques have been measured on a range of meshed and single spur gears with different speeds, lubricants and temperatures. Results are compared with the predictions from various literature sources.