Patent ID: 7841456

Claim:
An adjustable hysteresis driver comprising: a rotor component ( 5 ), being drivable and rotatably supported by a shaft ( 4 ), and a stator component ( 7 ′); an armature component ( 8 ) being fixed to the shaft ( 4 ); a hysteresis component ( 9 ) being connected to the armature component ( 8 ); the stator component ( 7 ′) comprises an electromagnet ( 7 a ) which induces magnetic flux in the rotor component ( 5 ) and in the stator component ( 7 ′) such that the rotor component ( 5 ) electromagnetically couples the armature component ( 8 ) to transmit torque therebetween, the torque transmitted between the rotor component ( 5 ) and the armature component ( 8 ) being electromagnetically adjustable; a hysteresis clutch for implementing “fail-safe” operation, if electrical current to the electromagnet ( 7 a ) fails, to ensure that torque is transferred between the rotor component ( 5 ) of the hysteresis clutch and the armature component ( 8 ), the hysteresis clutch comprising a first mechanical clutch element ( 12 ) that is rotationally fixed to the rotor component ( 5 ) and axially movable, such that during “fail safe” operation when supply of the electrical current to the electromagnet ( 7 a ) fails, the first mechanical clutch element ( 12 ) engages a second mechanical clutch element ( 13 ) which is fixed to the armature component ( 8 ); the first mechanical clutch element ( 12 ) is biased towards the second mechanical clutch element ( 13 ) by a spring force during “fail safe” operation and is fixed by magnetic force on the rotor component ( 5 ) of the hysteresis clutch by the electromagnet ( 7 a ) during normal operation; and the spring force providing overload protection which at least reduces engagement between the first and the second mechanical clutch elements ( 12 , 13 ).