Electromagnetic clutch and method of closing and opening an electromagnetic clutch

An electromagnetic clutch, comprising:

• a shifting sleeve which has a first toothing, is arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state,
• a first clutch body, which has a second toothing and which is aligned coaxially to the first shaft,
• a stator, which includes a first coil, which serves for the direct or indirect displacement of the shifting sleeve linearly along the first shaft,
• wherein the first and/or the second toothing has/have undercuts in the direction of the engaged state, which are configured such that a torque transmission between the first shaft and the first clutch body generates a force on the shifting sleeve in the direction of the engaged state, and
• wherein, in the engaged state, there is a positive fit due to the first and the second toothing between the shifting sleeve and the first clutch body,
• wherein an armature is provided which is coupled to the shifting sleeve, and wherein the armature is adapted to be displaced along the first shaft by energizing the first coil, the armature and the shifting sleeve being coupled so as to be displaceable relative to each other in the axial direction,
• wherein the armature and the shifting sleeve are coupled via at least a first spring unit which is elastic in the axial direction and which deflects when the shifting sleeve and the armature are displaced axially relative to each other, and
• wherein at least one spring unit is arranged such that, when the shifting sleeve is not yet coupled to the first clutch body, this spring unit is preloaded to exert a spring force on the shifting sleeve in the direction of the engaged state.

A method of closing and opening an electromagnetic clutch, including an armature and a shifting sleeve coupled thereto, which has a first toothing, is arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state, a first clutch body having a second toothing, which is aligned coaxially to the first shaft, a first coil, which serves to displace the shifting sleeve linearly along the first shaft into the engaged state, and a second coil, which serves to displace the shifting sleeve linearly along the first shaft against the engaged state, the method comprising:

• a) applying voltage to the first coil and generating a magnetic force acting on the armature towards the first clutch body;
• b) displacing the armature and entraining the shifting sleeve by the armature from a disengaged state in the direction of the engaged state with the interposition of a spring unit between the armature and the shifting sleeve;
• c) moving the shifting sleeve into the engaged state of the shifting sleeve and forming a positive fit between the shifting sleeve and the first clutch body by the first and the second toothing, the first and the second toothing having a first axial overlap with respect to each other;
• d) transmitting a torque between the first clutch body and the first shaft and displacing the shifting sleeve relative to the armature towards the first clutch body, the first and the second toothing having a second axial overlap with respect to each other, which exceeds the amount of the first one;
• e) canceling or reducing the transmitted torque between the first clutch body and the first shaft and displacing the shifting sleeve relative to the armature away from the first clutch body, the first and the second toothing having the first axial overlap with respect to each other;
• f) canceling or reducing the magnetic force acting on the armature by the first coil;
• g) applying voltage to the second coil and generating a magnetic force acting on the armature;
• and
• h) displacing the armature and entraining the shifting sleeve by means of the armature from an engaged state to the disengaged state.