Effect of Short Teeth on Contact Fatigue in Planetary Gears under Mixed Lubrication

Planetary drives with small teeth number (PDSTD) are designed with short tooth depth in order to avoid the interference of addendum, which results in shorter contact width than Hertzian contact width and cause the reduction of contact strength. In order to analyse the effect on contact fatigue of short teeth in PDSTD, the uniform equation of mixed EHL for short teeth in PDSTD was established with factors of contact width, wedge clearance, finite line contact and surface roughness. Then pressure distribution and friction were calculated, as well as the subsurface von Mises stress. According to Zaretsky’s model, contact fatigue life of meshing tooth in different operating conditions and engaged positions was predicted. The results indicate that contact width cannot be ignored in the prediction of fatigue life in PDSTD, and fatigue life in meshing-in and meshing-out was different due to the wedge clearance.