A compact clutch for a drive unit has an element (18) whose properties are changed by applying an electric current and which alters its state/shape to provide an axial thrust for a control clutch (3) which connects the drive. The element is contained in a chamber closed on one side by a movable wall and with connections into the chamber e.g. ribs.- DETAILED DESCRIPTION - One type of element has a variable viscosity when an electric current is applied, another type has a variable volume. The active element only requires electrical connections and has no mechanical components
