Fail safe electric cone clutch

An electromagnetic friction device for transmitting torque comprising:

• an input shaft;
• output means coaxially disposed with said input shaft and free to rotate thereon, said output means adapted to translate torque;
• an inner body member coaxially disposed with said input shaft for rotation therewith;
• said inner body member having an inside diameter adapted to mount to said input shaft, an outside diameter having means for translating torque and a plurality of pole faces between said inside and outside diameters;
• a friction ring member coaxially disposed with said inner body member, said friction ring member having one end portion and an opposite end portion;
• said one end portion having means for engaging said inner body member, said engagement means adapted to cooperate with said translating means of said inner body diameter, said opposite end portion having means for frictional engagement adapted to engage said output means;
• clutch actuating means mounted adjacent to said output means, said actuating means including:
• an electromagnetic winding;
• an armature coaxially disposed with said input shaft opposite said pole faces of said inner body member, said armature being movable axially toward and away from said pole faces of said inner body member in response to said clutch actuating means, said armature further having an outer helical threaded surface and a serrated face portion normal to said outer helical threaded surface;
• means for biasing said friction ring member into engagement with said output means, said biasing means maintaining the electromagnetic friction device into engagement when said electromagnetic winding is de-energized and
• an annular retarder member disposed coaxially with said armature, said retarder member having second means for biasing said armature, said second biasing means allowing rotational movement of said armature in one direction and preventing rotational movement of said armature in another opposite direction, whereby said clutch actuating means produces a circuitous flux path when energized, said flux path passing through said pole faces and said armature moving said armature into engagement with said pole faces, said armature being threadably engaged with said friction ring member such that upon engagement of said armature with said pole faces of said inner body member, said armature moves rotatably on said helical thread towards said inner body member to compensate for the wear occurring at the frictional clutch surfaces, said retarder maintaining the relative position established between the armature and inner body member when said clutch actuating means is de-energized and said biasing means engage said output means;

In combination with an electromagnetic clutch of the type wherein torque is transmitted from an input means to an output means upon de-energizing of an electromagnetic coil means and wherein an armature is disposed coaxial with said clutch axis adjacent magnetic pole faces on the input means, said armature having an outer helical threaded surface, the improvement comprising:

• an annular friction ring member having one end portion and another end portion, said one end portion having a torque transmitting means for imparting rotational motion to said annular friction ring member;
• said other end portion having an inner helical threaded surface adapted to engage the helical threaded surface of said armature and a plurality of angularly spaced axial grooves to provide axial movement of said friction ring member with respect to said armature;
• means for biasing said friction ring member in a direction away from said pole face of said input means, said means adapted to engage the annular friction ring member with the output means upon de-energizing the electromagnetic coil;
• and
• an annular retarder member disposed coaxially with said armature, said retarder having means for biasing said armature whereby said biasing means allows rotational movement of said armature in one direction and prevents rotational movement of said armature below a predetermined level in another opposite direction;
• whereby upon de-energizing said electromagnetic coil means said friction ring member engages said output means and the relative position between said armature and said friction ring member is maintained by said retarder member until the electromagnetic coil means again becomes energized.