A Study of the Lubrication under Impact Loading - Experimental and Analytical Application to Push Belt CVTs

Abstract

This study investigated oil film in contact portions formed by the dynamic loading of a push belt and pulley sheaves for automobile CVTs. Technical difficulties of direct oil film measurement came from the structure and movement of components in variator. We therefore employed an estimation method, which included the measurements of duochromatic interference of actual CVT belt elements, and thin film pressure sensors formed on a pulley sheave. Interferometry measurements showed that the film thickness, calculated by the formulae derived from the similarities between stable and transient Reynolds equations, indicated an accuracy of about 88%. This estimation approach was applied to an actual CVT variator under a typical operation mode. Crucial parameters regarding impulse contact were measured by the thin film sensor and sensor pressure showed peaks just after and immediately before contacts. Film thickness, which was estimated by the loading time and maximum pressure, indicated that the lubrication film had a thickness lower than the surface roughness of the components. That means the lubrication regime was in mixed or boundary, and the fact supports previous estimations by unit testing and chemical analysis of tribofilms.

Keywords

• impact loading
• elastohydrodynamic lubrication
• cvt
• optical interferometry
• thin film sensor
• pressure measurement