Power transmission system

Abstract

A torque transmission system has driving and driven pulley units around which an endless V-belt extends. Each pulley unit has a stationary pulley part rotatable with a shaft and a movable pulley part disposed to define with the stationary pulley part a circumferentially continuous groove for receiving the V-belt. The movable pulley parts of the pulley units are axially resiliently biased so that the radii of the circle along which the V-belt engages the driving and driven pulley units are varied to change the speed-change ratio of the transmission system. The movable pulley part of the driven pulley unit is axially shifted by the action of fly weights held between a stationary plate fixed to the shaft and a holder fixed to the movable pulley part. A cover is provided to cover the outer end of the movable pulley part, the stationary plate and an adjacent end of the shaft and cooperates with the stationary plate to define therebetween a first space which is communicated through a port in the stationary plate with a second space defined between the stationary plate and the holder. The first space is also communicated with the atmosphere through an axial bore extending axially through the shaft. A third space defined between the stationary and movable pulley parts is communicated with the axial bore through a second communication port formed radially in the shaft, whereby the three spaces are maintained substantially at the atmospheric pressure regardless of changes of the volumes of the spaces due to axial movements of the axially movable members, so that the torque transmission system can be free from any adverse effect which would otherwise be caused by the compression of air in the mentioned spaces.