For speed matching and torque between prime mover and driven machine, power transmission units are required. At changing operating conditions, in particular of the machine, the use of variable speed drives would optimize the combined operation 01 the prime mover and the machine.

The essential elements of the PIV mechanical variable speed drives A are two pairs of conical wheels which are movable on their shafts in an axial direction and connected by a special chain.

An opposite axial movement 01 the conical wheels will change the pitch circle of the chain and thereby the speed of the output shaft.