An Investigation Into the Thermal Behavior of Planetary Gear Systems Under Mixed Lubrication

Abstract The planetary gear system typically operates under mixed lubrication, where elevated temperatures can accelerate lubricant film breakdown and lead to thermal deformation and scuffing. This article proposes a finite element method (FEM)-based model that combines a mixed elastohydrodynamic lubrication (EHL) model with a structural thermal analysis model to investigate the thermal behavior of planetary gears. The lubrication of rough surfaces is simulated using a mixed EHL submodel that incorporates measured surface topographies into the film thickness calculation, whereby the friction coefficients are obtained and utilized for the calculation of frictional heat flux. The structural thermal analysis submodel incorporates thermal boundary conditions based on convective heat transfer coefficients to simulate the temperature field, and the effects of speed and torque on the temperature distribution are examined. The thermal deformation and stress of gears are calculated, and their distribution and underlying formation mechanisms are investigated. Finally, the scuffing safety factor is determined using the contact temperature and critical scuffing temperature to evaluate the scuffing risk within the planetary gear system. The conclusions may offer valuable insights for the design of planetary gear systems with enhanced resistance to thermal deformation and scuffing failure.