Determination of the accelerated RCF operating condition of the sun-planet contact of a tractor final drive using a computational method

This study proposes a computational approach to determine the operating condition, under which the rolling contact fatigue (RCF) crack nucleation of the sun-planet mesh of a tractor final drive is accelerated. Although the experimental RCF time period can be reduced by increasing the rotational velocity, the resultant increase in the film thickness promotes the lubrication condition and thus lengthens the fatigue life. To counteract this fatigue performance variation, it is proposed to increase the lubricant temperature at the same time. In the process, the lubricant viscosity decreases and offsets lubrication film thickness increase introduced by the rotational velocity increase. A physics-based gear contact fatigue model that includes the descriptions of the mixed elastohydrodynamic lubrication, the multi-axial stresses and the multi-axial fatigue is used to quantify the impacts of the lubricant temperature and the rotational velocity on the crack formation, allowing the fine tune of the temperature and velocity parameters.