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A valve assembly for a viscous clutch includes an orifice plate defining a bore to allow the passage of a fluid through the orifice plate, a reed valve secured relative to the orifice plate, an armature comprising a magnetic flux-conducting material, an anchor spring secured to the armature, and a s

A valve assembly for a viscous clutch includes an orifice plate defining a bore to allow the passage of a fluid through the orifice plate, a reed valve secured relative to the orifice plate, an armature comprising a magnetic flux-conducting material, an anchor spring secured to the armature, and a stiffening plate. The reed valve includes a tongue configured to selectively cover the bore of the orifice plate, and a first pivot location along the tongue. A second pivot location is defined along the anchor spring at an edge of the stiffening plate. The first and second pivot locations are spaced from each other. The armature is configured to selectively apply a force to the reed valve to pivot at least a portion of the tongue about the first pivot location.

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1. A viscous clutch comprising: an input member to accept input torque;a rotor secured to the input member to rotate therewith;an output member located adjacent to the rotor;a working chamber defined between the rotor and the output member;a reservoir configured to hold a shear fluid;a return path d

1. A viscous clutch comprising: an input member to accept input torque;a rotor secured to the input member to rotate therewith;an output member located adjacent to the rotor;a working chamber defined between the rotor and the output member;a reservoir configured to hold a shear fluid;a return path defined between the working chamber and the reservoir;an electromagnetic coil for selectively generating a magnetic field; anda valve assembly configured to selectively control shear fluid flow between the reservoir and the working chamber, the valve assembly comprising: an orifice plate defining a bore to allow the passage of the shear fluid through the orifice plate;a reed valve secured relative to the orifice plate, the reed valve including: a tongue portion configured to selectively cover the bore of the orifice plate; anda first pivot location along the tongue portion about which a distal end of the tongue portion can pivot;an armature comprising a magnetic flux-conducting material, the armature configured to selectively apply a force to the reed valve as a function of the magnetic field generated by the electromagnetic coil to pivot at least the distal end of the tongue portion about the first pivot location;an anchor spring secured to the armature; anda stiffening plate, wherein a second pivot location is defined along the anchor spring at an edge of the stiffening plate, and wherein the first and second pivot locations are spaced from each other. 2. The viscous clutch of claim 1, wherein the anchor spring and the orifice plate are secured to the rotor, such that the valve assembly can rotate with the rotor. 3. The viscous clutch of claim 1 and further comprising: a stop secured to the rotor and spaced from the orifice plate, wherein the stop is configured to limit travel of the armature toward the electromagnetic coil. 4. The viscous clutch of claim 1, wherein the armature comprises: a body portion; andan extension from the body portion, wherein the extension is configured to contact the tongue of the reed valve when actuated, and wherein the body portion and the extension are arranged to be substantially co-planar. 5. The viscous clutch of claim 4, where the armature further comprises: a tab extending from the body portion approximately 90° from the extension. 6. The viscous clutch of claim 1, the valve assembly further comprising: a back plate secured to the anchor spring and extending along the anchor spring from an edge of the armature toward the second pivot location, wherein the back plate is arranged on an opposite side of the anchor spring from the stiffening plate. 7. The viscous clutch of claim 6, wherein the back plate at least partially overlaps the stiffening plate. 8. The viscous clutch of claim 1, wherein the stiffening plate is radially spaced from the armature along the anchor spring by a gap L. 9. The viscous clutch of claim 1 and further comprising: a stationary shaft, wherein the output member and the input member are each rotatably supported by the stationary shaft. 10. The viscous clutch of claim 9, wherein the reservoir is secured to the rotor such that the reservoir can rotate with the rotor, and wherein the electromagnetic coil is positioned within the reservoir. 11. A method for operating a viscous clutch, the method comprising: generating a magnetic field;pivoting an armature about a first pivot location using the magnetic field;applying force to a reed valve with the armature while the magnetic field is being generated, wherein the armature presses against the reed valve while force is applied;pivoting at least a portion of the reed valve about a second pivot location spaced from the first pivot location as a function of the applied force; andcovering a bore with the reed valve to limit fluid flow therethrough, wherein in order to cover the bore the reed valve is pivoted toward the bore when force is applied by the armature, and wherein the bore is located in a plate, and wherein a portion of the reed valve at or near the second pivot location enters a depression in the plate when the bore is covered with the reed valve. 12. A method for operating a viscous clutch, the method comprising: generating a magnetic field;pivoting an armature about a first pivot location using the magnetic field;applying force to a reed valve with the armature while the magnetic field is being generated, wherein the armature presses against the reed valve while force is applied;pivoting at least a portion of the reed valve about a second pivot location spaced from the first pivot location as a function of the applied force;covering a bore with the reed valve to limit fluid flow there through, wherein in order to cover the bore the reed valve is pivoted toward the bore when force is applied by the armature;pivoting a back plate about the first pivot location along with the armature; andlimiting flexure of an anchor spring attached to the armature with the back plate, wherein the first pivot location is defined by the anchor spring. 13. The method of claim 12 and further comprising: defining a location of the first pivot location along an anchor spring that is attached to the armature using an edge of a stiffening plate positioned in contact with the anchor spring, wherein the edge of the stiffening plate is spaced from the armature. 14. The method of claim 13 and further comprising: varying a width of the stiffening plate to adjust a spring rate of the anchor spring. 15. A valve assembly for a viscous clutch, the assembly comprising: an orifice plate defining a bore to allow the passage of a fluid through the orifice plate;a reed valve secured relative to the orifice plate, the reed valve including: a tongue configured to selectively cover the bore of the orifice plate; anda first pivot location along the tongue;an armature comprising a magnetic flux-conducting material, the armature configured to selectively apply a force to the reed valve to pivot at least a portion of the tongue about the first pivot location, wherein the armature comprises: a body portion;an extension from the body portion, wherein the extension is configured to contact the tongue of the reed valve when actuated, and wherein the body portion and the extension are arranged to be substantially co-planar; anda tab extending from the body portion approximately 90° from the extension;an anchor spring secured to the armature and configured to allow selective pivotal movement of the armature in order to selectively apply the force to the reed valve; anda stiffening plate located adjacent to the anchor spring, wherein a second pivot location is defined along the anchor spring at an edge of the stiffening plate, and wherein the first and second pivot locations are spaced from each other. 16. The assembly of claim 15 and further comprising: a back plate secured to the anchor spring and extending along the anchor spring from an edge of the armature toward the second pivot location, wherein the back plate is arranged on an opposite side of the anchor spring from the stiffening plate. 17. The assembly of claim 16, wherein the back plate at least partially overlaps the stiffening plate. 18. A valve assembly for a viscous clutch, the assembly comprising: an orifice plate defining a bore to allow the passage of a fluid through the orifice plate;a reed valve secured relative to the orifice plate, the reed valve including: a tongue configured to selectively cover the bore of the orifice plate; anda first pivot location along the tongue;an armature comprising a magnetic flux-conducting material, the armature configured to selectively apply a force to the reed valve to pivot at least a portion of the tongue about the first pivot location;an anchor spring secured to the armature and configured to allow selective pivotal movement of the armature in order to selectively apply the force to the reed valve; anda stiffening plate located adjacent to the anchor spring, wherein a second pivot location is defined along the anchor spring at an edge of the stiffening plate, and wherein the first and second pivot locations are spaced from each other, wherein the stiffening plate is radially spaced from the armature along the anchor spring by a gap L. 19. The assembly of claim 15, wherein the orifice plate includes a depression facing the reed valve, and wherein the first pivot location is aligned with the depression. 20. A viscous clutch comprising: an electromagnetic coil for selectively generating a magnetic field; anda valve assembly configured to selectively control shear fluid flow between a reservoir and a working chamber through a bore as a function of the magnetic field generated by the electromagnetic coil, the valve assembly comprising: a first valve subassembly comprising: an armature, wherein the armature is configured to pivot about a first pivot location towards the electromagnetic coil when the magnetic field is generated by the electromagnetic coil;an anchor spring secured to the armature; anda stiffening plate, wherein the first pivot location is defined along the anchor spring at an edge of the stiffening plate; anda second valve subassembly comprising a reed valve, wherein at least a portion of the reed valve is configured to pivot about a second pivot location spaced from the first pivot location, the first valve subassembly configured to selectively apply a force to the second valve subassembly when the magnetic field is generated by the electromagnetic coil such that the reed valve can selectively cover the bore. 21. The viscous clutch of claim 20 and further comprising: a rotor, wherein the valve assembly is carried by the rotor. 22. The viscous clutch of claim 20 and further comprising: a rotor, wherein the working chamber is located adjacent to the rotor, and wherein the valve assembly is positioned generally between the electromagnetic coil and the rotor. 23. The method of claim 11 and further comprising: spring biasing the reed valve to an open position by default, in which the bore is uncovered. 24. The method of claim 23 and further comprising: spring biasing the armature away from the reed valve by default. 25. The viscous clutch of claim 1 and further comprising: a stop configured to limit travel of the armature relative to the orifice plate, wherein the stop is offset from the orifice plate by an axial gap. 26. The viscous clutch of claim 1 and further comprising: a groove in the rotor, wherein the orifice plate is located adjacent to the groove, and wherein at least a portion of the reed valve is positioned between the orifice plate and the rotor within the groove. 27. The viscous clutch of claim 26, wherein the groove is open to the reservoir away from the bore in the orifice plate, in order for at least a portion of the armature to enter the groove. 28. A valve assembly for a viscous clutch, the assembly comprising: an orifice plate defining a bore to allow the passage of a fluid through the orifice plate;a reed valve secured relative to the orifice plate, the reed valve including: a tongue configured to selectively cover the bore of the orifice plate; anda first pivot location along the tongue;an armature comprising a magnetic flux-conducting material, the armature configured to selectively apply a force to the reed valve to pivot at least a portion of the tongue about the first pivot location;an anchor spring secured to the armature and configured to allow selective pivotal movement of the armature in order to selectively apply the force to the reed valve, wherein the armature is located to one side of the orifice plate in all pivotal positions; anda stiffening plate located adjacent to the anchor spring, wherein a second pivot location is defined along the anchor spring at an edge of the stiffening plate, and wherein the first and second pivot locations are spaced from each other.