scope:

Heat generation due to friction at the gear contact interface is a parasitic energy loss and may require designers to include active cooling systems further decreasing the net usable energy. It is known that changing the surface roughness of the mating gear flanks influences friction in the contact. Mixed lubrication conditions are common in gear contact where both direct asperity interaction and lubricant properties contribute to the resulting power loss. Presenting different surface finishes to the contact directly influences the amount of asperity interaction. Gear designers and manufacturers must carefully balance costs associated with surface finishing processes while achieving target goals for transmission design. This study utilizes a closed form model combining a gear load distribution model, a statistical microcontact model, and a lubricant rheological model to predict friction in mixed lubrication contact conditions as well as gear mechanical power loss. Profilometer roughness measurements from a wide variety of manufacturing processes are collected and input into the model to predict friction coefficient and mechanical power loss under a wide variety of surface finish pairings for several operating conditions consistent with automotive applications. Relative magnitudes of reductions in power loss and friction are compared for the various surface finish types and pairings.