A lubrication–heat transfer coupling method for analyzing frictional heat flux of spur gears in mixed lubrication

This study proposes a more rational and efficient lubrication–heat transfer coupling method for analyzing the lubrication characteristics and frictional heat flux of spur gears with a rough tooth surface under mixed lubrication conditions. This method integrates the unified Reynolds equation, roughness-inclusive oil film thickness equation, lubricant rheology equation, fluid energy equation, flash temperature solving equation, and the thermal network model. The viscous shearing in the hydrodynamic area and solid friction in the asperity contact area serve as thermal intensity inputs for the flash temperature solution and the thermal network model. Meanwhile, the solutions for flash temperature and bulk temperature are coupled with the energy equation through boundary conditions. The efficacy of the thermal network model facilitates multiple iterations of bulk temperature to ensure the stability of the temperature field. The effectiveness and universality of this method have been validated by previous bulk temperature experiments. The results indicate that the full-film lubrication mode cannot accurately predict bulk temperature under mixed lubrication status. Asperity contacts bear contact loads exceeding their own area ratio and generate a much greater heat flux. The effect of film thickness ratio on heat flux characteristics is investigated, and the frictional heat can be significantly reduced by modulating the film thickness ratio with appropriate surface roughness. This research can be used for the analysis of gear contact lubrication characteristics and meshing efficiency improvement techniques.