Safety Threshold of the Oil Film Stiffness of a CVT Pulley–Sheet Friction Pair Based on Mixed Lubrication Theory

Abstract

The instability of oil film stiffness in mixed elastohydrodynamic lubrication (EHL) is a prominent cause of the fretting wear of continuously variable transmission pulley–metal sheet friction pairs. In severe cases, it can induce dynamic system failure. In this study, an oil film normal stiffness model equivalent to a massless spring element is established using linear contact mixed EHL theory. The effects of microscopic parameters (roughness amplitude) and macroscopic operating parameters (torque ratio) on the oil film stiffness in the pulley–sheet contact area are studied. The film stiffness increases initially and then decreases with an increase in roughness amplitude. In addition, it increases continuously and then stabilizes with an increase in torque ratio. The effects of macro- and microparameters are considered and a safety threshold model of oil film stiffness is established. Results show that oil film stiffness exhibits the highest safety stability when the roughness amplitude is 0.10 μm and the torque ratio is 0.8. The influence of roughness amplitude on the safety threshold of oil film stiffness is greater than that of torque ratio.