Development of Fluids for Chain Type CVTs

Abstract

In the area of transmissions, continuously variable transmissions (CVTs) have been adopted for cars with various engine displacements mainly in Japan and North America because of their better fuel economy and smooth shift feeling. Continuously variable transmission fluids (CVTFs) with lower viscosity and optimal friction property for chain and pulley will be effective for improving fuel saving performance in CVT. In this study, compared with a market chain CVTF, the developed oil had a lower viscosity, a higher metal friction coefficient, and higher clutch transmission capacity, while its anti-seizure property was better than a market chain CVTF. As to higher metal friction coefficient, small islands were observed on friction surface by atomic force microscopy (AFM) .It is supposed that those islands promote a shift to the boundary lubrication regime, contributing to a higher friction coefficient. The developed oil containing some additives demonstrated 10% higher variator torque capacity compared with a commercial CVTF.