A continuously variable transmission of the type employing a flat belt extending between driving and driven pulley assemblies, each having a circumferential array of radially adjustable belt engaging elements, is disclosed in conjunction with a self-energized control system for establishing the instantaneous radial position of the belt engaging elements. The radial positions of the belt engaging elements of each pulley assembly depend upon the angular relationship between inner and outer guideway disk structures carrying logarithmic spiral guideways oriented in the opposite sense, the resulting intersections of the spiral guideways supporting bearing regions at the ends of the belt engaging elements. Each pulley assembly includes a power consuming element, which is coupled through differential gearing, such as a harmonic drive, to the inner and outer guideway disks and to the power consuming element. |