The paper presents a brief review of developments in understanding of gear tooth contact lubrication in relation to problems of surface durability and distress. Gear tooth contacts tend to operate under conditions where the lubricating oil film is thin compared with surface roughness. This feature is shown to have a significant effect on scuffing capacity and friction and is also thought to be a factor in micropitting. Recent developments in thin-film micro-elastohydrodynamic lubrication theory are described and these should lead to a better understanding of the behaviour and modes of surface distress in gears. The paper also describes the application of elastohydrodynamic analysis to other transmission components such as high-conformity gears and thrust cones.
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