Automotive Traction Drive CVTs - An Overview

This paper is based on a prepared discussion which was presented at the CVT Panel (Session #1PC26) during the 1985 SAE International Congress and Exposition. The paper reviews the background of this rather intriguing class of variable-ratio mechanical drives and briefly summarizes the past worldwide research which led to the development of several automotive traction drive CVTs. The “toric” CVT, which was a subject of extensive research and development effort at General Motors and elsewhere, is used as an example for illustrating typical traction drive characteristics. Further, discussion is presented of the desirable attributes of traction drives, as well as of the various technical concerns arising from the power transfer through traction forces of a rolling contact under conditions unique to automotive transmission applications. The current state-of-the-art traction drive technology and several new developments in the area of automotive traction drive CVTs, reported in recent literature, are also discussed.