Sheave drive type automatic transmission device

Claim 1

A sheave drive type automatic transmission device for the output shaft of an engine comprising a conical sheave member fixed on the output shaft of an engine to be rotatable therewith; a movable conical sheave member defining with the stationary conical sheave member a drive transmission belt-receiving space which is progressively broadened toward the outside in the radial direction, said movable conical sheave member being mounted on the shaft for axial sliding movement; spring means for normally biassing the movable conical sheave member away from the stationary sheave member; a weight pivoted to a support fixed on the output shaft and, when the engine is put into operation, rotatable about a fulcrum due to a centrifugal force acting thereon, the weight having a pawl portion engaging the movable conical sheave member, thereby urging said movable conical sheave member toward the stationary conical sheave member; and a contact surface forming the surface of engagement between said pawl and the movable conical sheave member, which is shaped to have a curvature in the direction in which the pawl portion of the weight slides along said contact plane upon rotation of the weight due to centrifugal force caused by shaft rotation, said contact surface when cut by a plane passing through the central axis of the shaft, being defined by a curvature consisting of an outer convex curve and a substantially straight line extending inwardly towards the shaft center from said outer convex curve.