Influence of Micro-Geometry on Gear Scuffing 2015-26-0187

Scuffing is an instantaneous failure which occurs when the meshed gear flanks undergo adhesive wear under extreme operating temperatures at medium- or high-speed conditions. It is one of the common failures in transmission gears, which tend to operate under long-duty cycle hours. The tip and the root regions often experience higher contact pressures because of the loading and surface curvature. These higher pressures, coupled with higher sliding velocities and heat generation, make the tip and root regions in the gear susceptible to scuffing.

Gear geometry, material composition and lubricant properties influence scuffing. A balanced gear tooth design with lower sliding velocities is often chosen as an approach to avoid scuffing. However, in the current scenarios of transmissions with high power density requirements, achieving a balanced gear tooth design is rare. Lubricants with higher viscosity avoid scuffing, but have adverse effects on the transmission efficiency. As per ISO 6336, there are no sufficient methods or techniques available to measure and prevent scuffing failures on gears. AGMA 925-A03 provides a method for determining the scuffing risk based on lubricant and gear macro-geometry properties through quantifying critical scuffing temperature. Higher quality gear materials, better manufacturing process and scuffing additives in lubricants avoid scuffing but involve significant costs.

In this study, we have used a statistical-based model to highlight the influence of gear mesh micro-geometries on the contact pressure and temperature distribution for an indication of scuffing risk in an automotive transmission. There is a discussion of the sensitivity of modifications on scuffing temperature and an optimal solution for a particular gear-mesh loading.