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A magnetorheological fluid brake utilizing a positive displacement fluid pump adapted to pump a magnetorheological fluid through a viscosity regulator. The viscosity regulator is adapted to controllably vary the viscosity of the magnetorheological fluid, altering the pumping restriction against the

A magnetorheological fluid brake utilizing a positive displacement fluid pump adapted to pump a magnetorheological fluid through a viscosity regulator. The viscosity regulator is adapted to controllably vary the viscosity of the magnetorheological fluid, altering the pumping restriction against the fluid pump, resulting in variable resistance to pump shaft rotation relative to the pump housing. An electronic steering system for a work vehicle utilizing the illustrated magnetorheological brake as a resistance device to provide tactile feedback as a function of steering shaft rotational position.

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1. A brake comprising:a positive displacement fluid pump having a rotating pump shaft, a pump housing, a first port, and a second port, the pump adapted to pump a magnetorheological fluid from one of the first and the second ports to the other of the first and the second ports when the pump shaft is

1. A brake comprising:a positive displacement fluid pump having a rotating pump shaft, a pump housing, a first port, and a second port, the pump adapted to pump a magnetorheological fluid from one of the first and the second ports to the other of the first and the second ports when the pump shaft is rotated relative to the pump housing; a viscosity regulator fluidly connected between the first port and second port, though which flows the magnetorheological fluid is pumped from the fluid pump, the viscosity regulator adapted to controllably vary the viscosity of the magnetorheological fluid passing there through, thereby varying pumping restriction against the fluid pump, resulting in variable resistance to pump shaft rotation relative to the pump housing. 2. The brake as defined in claim 1 wherein the viscosity regulator comprises a flow orifice though which flows the magnetorheological fluid pumped from the fluid pump, and an electromagnet adjacent to the flow orifice, the electromagnet adapted to controllably impart a magnetic field upon the magnetorheological fluid flowing through the flow orifice, thereby varying the viscosity of the magnetorheological fluid.3. The brake as defined in claim 2 further comprising a controller in communication with the viscosity regulator, the controller adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing there through.4. The brake as defined in claim 3 wherein the fluid pump is a gear-type pump.5. The brake as defined in claim 2 wherein the electromagnet comprises a coil assembly surrounding the flow control orifice though which an electrical current controllably flows, the coil assembly adapted to variably impart the magnetic field upon the magnetorheological fluid flowing through the flow orifice in proportion to the magnitude of the electrical current.6. The brake as defined in claim 5 further comprising a controller in communication with the viscosity regulator, the controller adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing there through.7. The brake as defined in claim 6 wherein the fluid pump is a gear-type pump.8. A brake comprising:a positive displacement fluid pump having a rotating pump shaft, a pump housing, a first port, and a second port, the pump adapted to pump a magnetorheological fluid from one of the first and the second ports to the other of the first and the second ports when the pump shaft is rotated relative to the pump housing; a viscosity regulator fluidly connected between the first port and second port, the viscosity regulator comprising a flow orifice though which flows the magnetorheological fluid pumped from the fluid pump, and an electromagnet adjacent to the flow orifice, the electromagnet adapted to controllably impart a magnetic field upon the magnetorheological fluid flowing through the flow orifice, thereby varying the viscosity of the magnetorheological fluid, and thus varying the pumping restriction-against the fluid pump, resulting in variable resistance to pump shaft rotation relative to the pump housing. 9. The brake as defined in claim 8 further comprising a controller in communication with the viscosity regulator, the controller adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing there through.10. The brake as defined in claim 9 wherein the fluid pump is a gear-type pump.11. The brake as defined in claim 8 wherein the electromagnet comprising a coil assembly surrounding the flow control orifice though which an electrical current controllably flows, the coil assembly adapted to variably impart the magnetic field upon the magnetorheological fluid flowing through the flow orifice in proportion to the magnitude of the electrical current.12. The brake as defined in claim 11 further comprising a controller in communication with the viscosity regulator, the controller adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing there through.13. The brake as defined in claim 12 wherein the fluid pump is a gear-type pump.14. A steering mechanism for a vehicle having a frame, wheels, and an actuator to controllably vary vehicle steering angle, the mechanism comprising:a steering wheel adapted for rotation relative to the vehicle frame by a vehicle operator corresponding to a desired vehicle steering angle; a steering shaft operatively coupled to the steering wheel; an sensor operatively coupled to the steering shaft adapted sense rotational position of the steering shaft; a brake comprising a positive displacement fluid pump having a pump shaft, a pump housing, a first port, and a second port, the pump adapted to pump a magnetorheological fluid from one of the first and the second ports to the other of the first and the second ports when the pump shaft is rotated relative to the pump housing, the brake further comprising a viscosity regulator fluidly connected between the first port and second port, the viscosity regulator comprising a flow orifice though which flows the magnetorheological fluid pumped from the fluid pump, and an electromagnet adjacent to the flow orifice, the electromagnet adapted to controllably impart a magnetic field upon the magnetorheological fluid flowing through the flow orifice, thereby varying the viscosity of the magnetorheological fluid, and thus varying the pumping restriction against the fluid pump, resulting in variable resistance to pump shaft rotation, and thus variable resistance to steering shaft rotation; a controller in communication with the actuator, the sensor, and the viscosity regulator, the controller adapted command the actuator to controllably vary vehicle steering angle in response to rotational position of the steering shaft sensed by the sensor, and the controller further adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing through, resulting in variable resistance to steering shaft rotation as a function of steering shaft rotational position sensed by the sensor. 15. The steering mechanism as defined in claim 14 wherein the pump shaft is operative coupled to the steering shaft, and the pump housing is attached to the frame.16. The steering mechanism as defined in claim 15 wherein the viscosity regulator of the brake comprises a flow orifice though which flows the magnetorheological fluid pumped from the fluid pump, and an electromagnet adjacent to the flow orifice, the electromagnet adapted to controllably impart a magnetic field upon the magnetorheological fluid flowing through the flow orifice, thereby varying the viscosity of the magnetorheological fluid.17. The steering mechanism as defined in claim 16 wherein the electromagnet of the viscosity regulator comprises a coil assembly surrounding the flow control orifice though which an electrical current controllably flows, the coil assembly adapted to variably impart the magnetic field upon the magnetorheological fluid flowing through the flow orifice in proportion to the magnitude of the electrical current.18. The steering mechanism as defined in claim 17 wherein the fluid pump of the brake is a gear-type pump.19. The steering mechanism as defined in claim 18 further comprising a flexible coupling extending from the pump shaft to the steering shaft, adapted to operatively couple the steering shaft to the pump shaft.20. The steering mechanism as defined in claim 15 further comprising a mechanical brake having a rotating portion operatively coupled to the steering shaft, and a stationary portion attached to the vehicle frame, wherein the controller is adapted to inhibit steering shaft rotation relative to the frame as a function of steering shaft rotational position sensed by the sensor.21. The steering mechanism as defined in claim 20 further comprising a flexible coupling extending from the rotating portion of the mechanical brake to the steering shaft, adapted to operatively couple the steering shaft to the rotating portion of the mechanical brake.22. A steering mechanism for a vehicle having a frame, wheels, and an actuator to controllably vary vehicle steering angle, the mechanism comprising:a steering wheel adapted for rotation relative to the vehicle frame by a vehicle operator corresponding to a desired vehicle steering angle; a steering shaft operatively coupled to the steering wheel; an sensor operatively coupled to the steering shaft adapted sense rotational position of the steering shaft; a brake comprising a positive displacement fluid pump having a pump shaft, a pump housing, a first port, and a second port, the pump adapted to pump a magnetorheological fluid from one of the first and the second ports to the other of the first and the second ports when the pump shaft is rotated relative to the pump housing, the brake further comprising a viscosity regulator fluidly connected between the first port and second port, the viscosity regulator comprising a flow orifice though which flows the magnetorheological fluid pumped from the fluid pump, and an electromagnet adjacent to the flow orifice, the electromagnet adapted to controllably impart a magnetic field upon the magnetorheological fluid flowing through the flow orifice, thereby varying the viscosity of the magnetorheological fluid, and thus varying the pumping restriction against the fluid pump, resulting in variable resistance to pump shaft rotation relative to the pump housing; a controller in communication with the actuator, the sensor, and the viscosity regulator, the controller adapted command the actuator to controllably vary vehicle steering angle in response to rotational position of the steering shaft sensed by the sensor, and the controller further adapted to command the viscosity regulator to controllably vary the viscosity of the magnetorheological fluid passing through, resulting in variable resistance to steering shaft rotation as a function of steering shaft rotational position sensed by the sensor. 23. The steering mechanism as defined in claim 22 wherein the pump shaft is operative coupled to the steering shaft, and the pump housing is attached to the frame.24. The steering mechanism as defined in claim 23 wherein the electromagnet of the viscosity regulator comprising a coil assembly surrounding the flow control orifice though which an electrical current controllably flows, the coil assembly adapted to variably impart the magnetic field upon the magnetorheological fluid flowing through the flow orifice in proportion to the magnitude of the electrical current.25. The steering mechanism as defined in claim 24 wherein the fluid pump of the brake is a gear-type pump.26. The steering mechanism as defined in claim 25 further comprising a flexible coupling extending from the pump shaft to the steering shaft, adapted to operatively couple the steering shaft to the pump shaft.27. The steering mechanism as defined in claim 23 further comprising a mechanical brake having a rotating portion operatively coupled to the steering shaft, and a stationary portion attached to the vehicle frame, wherein the controller is adapted to inhibit steering shaft rotation relative to the frame as a function of steering shaft rotational position sensed by the sensor.28. A steering mechanism as defined in claim 27 further comprising a flexible coupling extending from the rotating portion of the mechanical brake to the steering shaft, adapted to operatively couple the steering shaft to the rotating portion of the mechanical brake.