Passive magnetorheological clutch

A passive magnetorheological clutch comprising:

• an input member that is driven at a selected speed and includes a first end and a second end;
• an output member journaled on the input member between the first and second ends by a bearing assembly so as to be supported thereon in a substantially nonrotating state and to be concentrically rotatable substantially in concert therewith;
• a cavity presented between the input and output members containing a quantity of magnetorheological fluid and an engagement mechanism including a permanent magnet generating a magnetic field and carried on the input member near the second end by a rotor, and a ferromagnetic ring positioned near the permanent magnet and carried by the output member with an operative gap between the permanent magnet and the ferromagnetic ring, wherein the operative gap's dimension is variable to effect changes in the magnetic field passing between the permanent magnet and the ferromagnetic ring;
• and
• an actuator with a spindle providing a motive force to move the rotor axially to vary the relative position between the permanent magnet and the ferromagnetic ring, wherein when the actuator effects a reduction in the distance between the permanent magnet and the ferromagnetic ring, the amount of magnetic field increases in density adjacent the ferromagnetic ring and a resultant torque transfer from the input member to the output member is effected across the operative gap and through the magnetorheological fluid so that as the operative gap is reduced, the input and output members are engaged in a progressive and gradual manner.

A passive magnetorheological clutch for variably engaging rotation of an engine cooling fan comprising:

• an input member that is driven at a selected speed and includes a first end and a second end with an intermediate segment between the first and second ends and a reduced diameter segment adjacent the second end;
• an output member journaled on the input member at the intermediate segment by a pair of bearing assemblies so as to be supported on the input member in a substantially nonrotating state and to be concentrically rotatable substantially in concert with the input member;
• a sealed cavity presented between the input and output members containing a quantity of magnetorheological fluid and an engagement mechanism including a permanent magnet generating a magnetic field and carried on the reduced diameter segment of input member near the second end by a rotor in an axially slidable manner, and a ferromagnetic ring positioned near the permanent magnet and carried by the output member with an operative gap between the permanent magnet and the ferromagnetic ring, wherein the operative gap's dimension is variable to effect changes in the magnetic field passing between the permanent magnet and the ferromagnetic ring;
• a thermal actuator with a spindle providing a motive force to move the rotor axially to vary the relative position between the permanent magnet and the ferromagnetic ring;
• and
• a spring biasing the rotor toward the thermal actuator, wherein when the thermal actuator compresses the spring effecting a reduction in the distance between the permanent magnet and the ferromagnetic ring, the amount of magnetic field increases in density adjacent the ferromagnetic ring and a resultant torque transfer from the input member to the output member is effected across the operative gap and through the magnetorheological fluid so that as the operative gap is reduced, the input and output members are engaged in a progressive and gradual manner.