Patent ID: 7556584

Claim:
A variable speed drive for a continuously variable transmission, said variable speed drive comprising a first transmission element that is rotatable around a first axis of rotation and having a convexly-curved transmission surface that is rotationally symmetrical around the first axis of rotation, a second transmission element that is rotatable around a second axis of rotation and having a concavely-curved transmission surface that is rotationally symmetrical around the second axis of rotation, wherein the concavely-curved transmission surface of the second transmission element is a toroidal surface, a rigid transmission ring positioned between and in contact with each of the curved transmission surfaces and movable within a displacement range relative to the transmission surfaces, which ring transmits a torque between the first and the second transmission surfaces, wherein lines of intersection of the transmission surfaces with a plane that extends through the axes of rotation are parallel, at least within the displacement range of the transmission ring, and wherein the spherically-curved surface and a generating circle of the toroidal surface have the same center of curvature, and for a radius r 2 of the toroidal surface, r 2 =d+r 1 , where d is the smallest distance between the toroidal surface and the spherically-curved surface and r 1 is the radius of the spherically-curved surface.