Implicit regulation for automotive variators

Abstract

A well-known practice uses mechanical variators to realize the so-called continuously variable transmissions (CVTs) for automotive application. A remarkable problem for one of the most used CVTs is given by the hydraulic control of the axial thrust on the half-pulleys that is necessary for torque transmission. It involves a heavy decrease in transmission efficiency. In the present paper, the possible production of the required axial thrust by a simple spring to eliminate hydraulic losses is analysed. It is shown that the power capacity of such a regulated variator is near to the maximum possible, and the belt torque loss is always considerably lower than the sum of the belt and pump losses of a standard controlled CVT. Moreover, it is not much greater than a slip limit controlled CVT for medium-low vehicle speeds, and slightly lower for higher speeds. Finally, the power capacity by the spring thrust is evaluated when the variator is used in split power transmissions, considering several configurations and steady ideal operation.