Development of traction drive CVT for automobiles

Many improvements have been made to make the conventional automatic transmission more efficient, and multi-stage designs have been introduced in recent years. However, in order to be able to operate the engine at a proper level while the load is constantly changing, it is necessary to devise a continuously variable transmission (CVT) as the ultimate solution. Although many ideas have been tried, the metal belt type is the first CVT to be put to a practical use. As the higher output engine is becoming more popular these days, the CVT is required to have a higher load capacity. As a CVT intended for a large power transmission, the traction drive type CVT seems to be more promising, so that many designs have been proposed in that category since the early days of this century but none has been successful so far. Since 1978, the authors have been developing a half-toroidal traction drive type CVT, an automatic transmission intended for the use on automobiles of various sizes; the purpose of the article is to present its history and current status. (from Authors)