A continuously variable
gear transmission has a hemispherical drive gear providing an axially varying
pitch diameter and an axially varying effective circular
pitch, and a driven gear with a constant
pitch diameter having teeth tapering axially in an opposite sense to the axially varying effective circular pitch of the drive gear. A
pitch control drum guides teeth of the driven gear relatively around the shaft axis to continuously vary their effective circular pitch to match a circular pitch of the teeth of the drive gear for ensuring meshing engagement throughout the varying axial positions, whereby the
velocity ratio of the transmission is varied continuously. The control drum has a guiding surface extending therearound with an axially tapering, conical guiding portion providing an arcuate guiding surface portion of constant transverse and continuously axially varying
radius. An interconnected rod
assembly links the adjacent movable teeth together for movement as a ring around the guiding surface of the drum so that the effective circular pitch of the teeth engaging the drive gear is determined by the
radius of the guiding portion and so that a tooth engaging the drive gear has a
constant angular velocity throughout such engagement, The shaft of the driven gear comprises a plurality of coaxial sub-shafts carrying respective individual teeth mounted coaxially with the drum. A mechanism continuously and simultaneously varies both an angle of intersection of the drive and driven gear shafts, bringing different circumferential locations of the drive gear having different pitch diameters into engagement with the driven gear, and a relative axial position of engagement of the gears, changing a circular pitch of the driven gear to match a circular pitch of the drive gear. A differential connects the selected teeth of the driven gear gear to a
power output only when the teeth are at the
constant angular velocity.