Development of Toroidal Traction Drive CVTF for Automobile 2002-01-1696

Toroidal traction drive continuously variable transmissions (CVTs) for automobiles have adopted the latest automatic transmission technology, including torque converters, wet clutch systems and hydraulic systems. Therefore CVT fluids must function as conventional automatic transmission fluids as well as traction fluids. The performance of an automatic transmission fluid is mainly dependent upon the additive technology, while the traction performance and low-temperature viscosity are strongly dependent on the base fluid. Thus, the optimal traction fluid for automotive applications is a high-traction base fluid containing additives appropriate for conventional automatic transmission fluid. However, a higher traction tends to result in a higher low-temperature viscosity.

In order to resolve this contradiction, several new traction base fluids with either two naphthene rings or a polycyclic structure hydrocarbon were synthesized. The carbon numbers of these base fluids are 14 to 18. A four-roller machine was used to measure the traction coefficient of the base fluids, and a Brookfield viscometer was used to measure their low-temperature viscosity. As a result, new traction base fluids that have a low low-temperature viscosity and high traction coefficient were developed.

The performance of automotive traction fluids made with these base fluids is described in this paper. The traction coefficient, viscosity characteristics, antiwear and antiseizure properties, influence on rolling fatigue, shear stability, oxidative stability, wet clutch properties and material compatibility were compared with conventional automatic transmission fluids and traction fluids for automobiles. It was found that the new automotive traction fluid shows excellent performance.