Elastohydrodynamic lubricants for CVTs

In metal-to-metal continuously variable transmissions, EHLs momentarily become part of the machinery, allowing for a much higher traction coefficient than is possible with hydrodynamic fluids.

For decades, the continuously variable transmission (CVT) was mostly mythical-an idea that automotive manufacturers sometimes talked about but rarely acted on. Today that scenario is changing very rapidly, with most automakers investigating or having production plans for CVTs.

There are two basic types of CVTs. The most popular in automotive applications, the belt-and-pulley type, is already used in snowmobiles, ATVs, and a few passenger vehicles. The other type (and the subject of this article) transfers power by smooth, curved metal surfaces, with some designs including toroidal (doughnut-shaped) elements. Some industry forecasters believe that, over the next several years, metal-to-metal CVTs will become common in passenger cars, light trucks, and even heavy trucks.