Abstract: A phase change device of the type wherein a phase change is effected between an input member and an output member in response to the axial movement of an advancing element interconnecting the input member and the output member, and wherein such axial movement is effected by retarding the rotation of a drum member engaged with the advancing element. A grooved thread is formed in the drum member, and a plurality of balls carried in slots formed in the output member are received in the thread and in helical grooves formed in the input member to effect the relative rotation between the input and output members as the balls advance axially along the thread in response to retardation of the drum member.

Abstract: An actuator for a phase change device of the type wherein a phase change is effected between an input member and output member in response to the axial movement of an advancing member interconnecting the input member and the output member, and wherein such axial movement is effected by retarding the rotation of a drum member engaged with the advancing member. The retarding force is provided by an electromagnetic wet brake mounted in juxtaposition with a brake disk surface formed on the drum in a fixed angular position but capable of limited axial movement relative to the brake disk surface.