Patent ID: 9726234
Date: 2017-08-08
CPC Classifications: B60K,F16D

Claim:
1. A clutch assembly, comprising: a first, input, clutch member that is rotatable about an axis; a second, output, clutch member that is rotatable about the axis; a wrap spring having a first end, a second end and a plurality of helical coils between the first end and the second end, wherein one of the first and second clutch members is rotationally operatively connected with the first end of the wrap spring; an armature that is rotationally operatively connected to the second end of the wrap spring; an actuator, wherein the actuator is rotationally operatively connected to the second end of the wrap spring and the armature is rotationally operatively connected to the actuator, but is slidable axially relative to the actuator; and an electromagnetic unit including an electromagnet, wherein energization of the electromagnet generates a magnetic flux that flows through the other of the first and second clutch members rotationally operatively connected with the wrap spring first end, through the armature and back into the electromagnetic unit, wherein, when the first clutch member is rotating and the second clutch member is stationary, the magnetic flux draws the armature axially into engagement with the other of the first and second clutch members rotationally operatively connected with the wrap spring first end with sufficient force to frictionally cause rotation of the armature and the second end of the wrap spring relative to the first end of the wrap spring so as to radially expand the wrap spring into engagement with the other of the first and second clutch members rotationally operatively connected with the wrap spring first end thereby operatively connecting the first clutch member to the second clutch member; wherein the armature has an axial length and a radial thickness, the axial length being greater than the radial thickness and the radial thickness being selected to permit the armature to become magnetically saturated at a selected voltage and at a selected temperature such that the magnetic force exerted between the other of the first and second clutch members and the armature is substantially constant over a selected range of operating temperatures and voltages.