Thermal Elastohydrodynamic Lubrication Analysis of Grease in Tripod Sliding Universal Couplings

The tripod sliding universal coupling (TSUC) is a novel type of coupling developed through independent research. This study theoretically investigates the effects of the grease flow index and initial viscosity on thermal elastohydrodynamic lubrication (TEHL) properties. Three common grease formulations were evaluated for TSUC lubrication. The numerical results yielded the following insights: a larger flow index increases film thickness and elevates the secondary pressure peak. A higher initial viscosity enhances film thickness yet significantly elevates the temperature distribution due to quadratic growth in viscous dissipation. It also intensifies the secondary pressure peak, which may exceed the central Hertzian pressure under heavy loads, thereby accelerating surface fatigue. The lubrication performance varies significantly across grease types. When pressure–viscosity coefficients and densities are similar, the initial viscosity becomes the dominant factor. These findings provide a theoretical basis for optimizing grease selection in TSUC systems to improve the efficiency and durability of lubrication.