Clutch system and method of operating an accessory shaft

A clutch system, comprising:

• a rotary input member that defines an axis;
• a rotary output member that is rotatable relative to the rotary input member, about the axis, wherein the rotary output member is movable from a stationary position through a first range of motion;
• an armature that is movable axially between an armature engagement position and an armature disengagement position, wherein, in the armature engagement position, the armature is frictionally rotationally engaged with the rotary input member, and in the armature disengagement position the armature is frictionally rotationally disengaged from the rotary input member;
• and
• a wrap spring clutch having a first helical end, a second helical end, and a plurality of coils therebetween, wherein the first helical end is operatively engaged with the rotary output member, wherein the plurality of coils have a coil engagement surface that is one of a radially outer surface of the plurality of coils and a radially inner surface of the plurality of coils, wherein the second helical end is rotationally connected to the armature,
• wherein the wrap spring clutch is movable between a coil engagement position and a coil disengagement position, wherein, in the coil engagement position, the coil engagement surface is engaged with the rotary input member, and wherein in the coil disengagement position, the coil engagement surface is disengaged from the rotary input member,
• wherein, when the armature is in the armature disengagement position, the wrap spring clutch is in the coil disengagement position,
• wherein, when the armature is in the armature engagement position torque is transferred initially from the rotary input member into the second helical end of the wrap spring clutch, helically through the wrap spring clutch from the second helical end of the wrap spring clutch to the first helical end of the wrap spring clutch, and from the first helical end of the wrap spring clutch into the rotary output member to drive the rotary output member through the first range of motion without moving the wrap spring clutch to the coil engagement position,
• and wherein beyond the first range of motion while the armature is in the armature engagement position, the wrap spring clutch is moved to the coil engagement position, such that torque is transferred at least in part from the rotary input member into the wrap spring clutch through the coil engagement surface, at least in part from the coil engagement surface through the wrap spring clutch to the first helical end of the wrap spring clutch, and from the first helical end of the wrap spring clutch into the rotary output member to drive the rotary output member.

A method of driving an accessory shaft of an accessory, comprising:

• a) providing a clutch system that includes a rotary input member, a rotary output member that is operatively connected to the accessory shaft, and a wrap spring clutch having a first helical end, a second helical end, and a plurality of coils therebetween, wherein the first helical end is operatively engaged with the rotary output member, wherein the plurality of coils have a coil engagement surface that is one of a radially outer surface of the plurality of coils and a radially inner surface of the plurality of coils, wherein the second helical end is rotationally connected to the armature;
• b) moving the armature to engage the rotary input member so as to drive the armature rotationally;
• c) transmitting a first torque from the rotary input member to the armature, from the armature to the second helical end of the wrap spring clutch, from the second helical end of the wrap spring clutch to the first helical end of the wrap spring clutch and from the first helical end of the wrap spring clutch into the rotary output member to drive the rotary output member through a first range of motion, without moving the wrap spring clutch to a coil engagement position, thereby initiating rotation of the rotary output member from a stationary position without engagement of the coil engagement surface of the wrap spring clutch with the rotary input member;
• d) after step c), transmitting a coil engagement torque that is higher than the first torque, thereby driving the coil engagement surface of the wrap spring clutch to engage the rotary input member;
• and
• e) after step d), transmitting a second torque that is higher than the coil engagement torque to drive the accessory shaft to carry out an operation of the accessory.