Design of an Electromechanical Ratio and Clamping Force Actuator for a Metal V-belt Type CVT 2004-40-0008

Apart from enabling continuous ratio change under load, the Continuously Variable Transmission (CVT) offers, between limits, the ability to choose engine rotational speed independently of vehicle speed. Here lies a potential efficiency benefit, because the engine can operate more fuel efficiently. There are unfortunately considerable power losses within the CVT itself, causing many CVT equipped cars to be less fuel-efficient than cars with a manual transmission. The internal losses are caused for a substantial part by the CVT’s hydraulic actuation.

An electromechanical CVT pulley actuation system was designed to overcome the hydraulic power loss and hence improve CVT efficiency. Spindles are driven from the fixed world through epicyclic gearings by electric motors that are placed outside the transmission housing in a cool environment. A mechanical link between the adjustment mechanisms on the two shafts provides energy exchange, thus lowering shifting power demand and actuator size. Because of this, only one electric motor actuates pulley movement on both shafts for ratio change. A second actuator keeps the belt tensioned and controls belt clamping force. A high degree of independency between ratio- and clamping force actuation can be established.

A prototype was designed as a modification on a commercially available belt type CVT, which is currently in the realization phase. After trials on a test rig, the transmission will be built in to a vehicle to further evaluate the new concept.