An experimental parametric mechanical efficiency study of parallel-axis gear pairs lubricated with modern automotive fluids

Abstract

Geared transmission systems are highly advanced products which combine several types of machine elements to transmit power efficiently. Detailed knowledge of power loss sources is critical for component and system optimization. Gearbox efficiency is a primary goal for engineers facing the challenges of environmental sustainability and increased energy costs. Load-dependent losses in gear contacts develop in the contact zone where either sheared lubricant separates the meshing surfaces or asperity interactions occur. Engineered surface textures and specialized lubricants containing specifically designed additive packages and chemical composition influence the local contact conditions and ultimately alter the mechanical efficiency. As such, the focus of this study was to experimentally investigate gear mechanical efficiency targeting modern automotive transmission applications. A parametric study of high-fidelity gear experiments was performed on a four-square power circulator for multiple automotive transmission fluids and gear surface textures. Traditional operating and mechanical loading procedures were not consistent enough to fairly assess efficiency results, so a new methodology was implemented, and internal torque was monitored by a strain gauge. Gear mechanical efficiency was isolated by removing the influence of bearings through simple model predictions. Decreasing surface roughness resulted in the largest gain in mechanical efficiency of 0.18 ± 0.08%. Using a low viscosity lubricant negatively impacted mechanical efficiency regardless of surface texture amplitude by 0.05 ± 0.06%. The spur and helical gears designed for this study did not have any significant influence on gear mechanical efficiency, but high torque tests showed a 0.19 ± 0.17% improvement in gearbox efficiency for the spur gear arrangement.