Effect of surface finish on gear tooth friction

A special four-gear rig has been used to determine gear tooth frictional losses at loads and speeds representative of engineering practice using a gas-turbine engine oil. The effect of surface finish has been investigated by comparing the frictional losses of conventionally ground teeth (with roughness average, Ra, of approximately 0.4 mu m) with those of teeth which were superfinished to approximately 0.05 mu m Ra. It was found that superfinishing resulted in a reduction of friction of typically 30 percent with correspondingly lower tooth surface temperatures under the same conditions of load and speed. Film generation and frictional traction in the experiments were simulated theoretically using a thin film non-Newtonian micro-elastohydrodynamic lubrication solver, and encouraging agreement between friction measurements and theoretical predictions was obtained.