Magnetorheological brake with high torque and fast response

1. A magnetorheological (MR) brake comprising:

a rotor constructed at least partially of a ferromagnetic material;

a housing that supports the rotor such that the rotor and the housing are rotatable relative to each other about an axis, wherein the housing and rotor are configured such that a fluid gap is defined between the housing and an upper surface of the rotor, between the housing and a lower surface of the rotor, and between the housing and an annular edge surface of the rotor, and wherein portions of the housing adjacent the rotor are constructed at least partially of a ferromagnetic material;

a magnetorheological (MR) fluid disposed in the fluid gap;

a current-carrying coil excitable to generate a magnetic field that is concentrated in the ferromagnetic portions of the rotor and the housing and acts on the MR fluid; and

at least one element constructed of a material having low magnetic permeability configured to route the lines of magnetic flux through surrounding higher permeability material on opposite sides of the fluid gap to route the lines of magnetic flux to transition across the fluid gap multiple times and act on the MR fluid disposed in the fluid gap, wherein the at least one element comprises a first element embedded in the upper surface of the rotor, a second element embedded in the lower surface of the rotor, and a third element embedded in the edge surface of the rotor.

2. The MR brake recited in claim 1 , wherein the at least one element constructed of a material having low magnetic permeability is configured to cause the magnetic flux to transition across the gap adjacent the upper surface of the rotor, the lower surface of the rotor, and the edge surface of the rotor.

3. The MR brake recited in claim 1 , wherein the material having low magnetic permeability comprises aluminum.

4. The MR brake recited in claim 1 , wherein the first, second, and third elements are ring-shaped.

5. The MR brake recited in claim 1 , wherein the current-carrying coil is housed in the rotor, the rotor being configured in use to be mounted stationary, the housing being rotatable relative to the rotor about the axis.

6. The MR brake recited in claim 1 , wherein the rotor comprises a ferromagnetic disk and a shaft for supporting the rotor in the housing, and wherein the current-carrying coil is toroidal and housed in the disk.

7. The MR brake recited in claim 6 , wherein each of the first, second, and third elements comprises a ring-shaped element that is embedded in the disk and extends from a surface of the disk to adjacent the current-carrying coil.

8. The MR brake recited in claim 7 , wherein each of the ring-shaped elements are configured to extend along the surface of the current-carrying coil.

9. The MR brake recited in claim 6 , wherein the material having low magnetic permeability comprises aluminum.

10. The MR brake recited in claim 6 , wherein:

the first element extends from the upper surface of the disk to adjacent the current-carrying coil;

the second element extends from the lower surface of the disk to adjacent the current-carrying coil; and

the third element extends from the edge surface of the disk to adjacent the current-carrying coil.

11. The MR brake recited in claim 6 , wherein the housing comprises an upper end cap comprising a disk-shaped upper plate and a bushing for receiving the rotor shaft, a lower end cap comprising a disk-shaped lower plate and a bushing for receiving the rotor shaft, and a shell comprising a cylindrical sidewall that extends from the upper plate to the lower plate.

12. The MR brake recited in claim 10 , wherein the fluid gap is defined between the upper rotor surface and the upper plate, between the lower rotor surface and the lower plate, and between the rotor edge surface and the shell.

13. The MR brake recited in claim 1 , wherein the first element comprises a ring embedded in the upper surface of the rotor, the second element comprises a ring embedded in the lower surface of the rotor, and the third element comprises a ring embedded in the edge surface of the rotor.

14. The MR brake recited in claim 1 , wherein the first element comprises a ring embedded flush with the upper surface of the rotor, the second element comprises a ring embedded flush with the lower surface of the rotor, and the third element comprises a ring embedded flush with the edge surface of the rotor.

15. A magnetorheological (MR) brake comprising:

a rotor constructed at least partially of a ferromagnetic material;

a housing that supports the rotor such that the rotor and the housing are rotatable relative to each other about an axis, wherein the housing and rotor are configured such that a fluid gap is defined between the housing and the rotor, and wherein portions of the housing adjacent the rotor are constructed at least partially of a ferromagnetic material;

a magnetorheological (MR) fluid disposed in the fluid gap;

a current-carrying coil excitable to generate a magnetic field that is concentrated in the ferromagnetic portions of the rotor and the housing and acts on the MR fluid; and

at least one element embedded in at least two of an upper surface, lower surface, and edge surface of the rotor and positioned adjacent the fluid gap, the at least one element being constructed of a material having low magnetic permeability configured to route the lines of magnetic flux through surrounding higher permeability material on opposite sides of the fluid gap to route the lines of magnetic flux to transition across the fluid gap multiple times and act on the MR fluid disposed in the fluid gap.

16. The MR brake recited in claim 15 , wherein each of the at least one elements comprises an aluminum ring.

17. The MR brake recited in claim 15 , wherein the rotor comprises a ferromagnetic disk and a shaft for supporting the rotor in the housing, and wherein the current-carrying coil is toroidal and housed in the disk.

18. The MR brake recited in claim 15 , wherein each of the at least one elements comprises a ring-shaped element that is embedded in the disk and extends from the fluid gap to adjacent the current-carrying coil.

19. The MR brake recited in claim 15 , wherein the at least one element comprises:

a first ring-shaped element that is embedded in the disk and extends from the upper surface of the disk to adjacent the current-carrying coil;

a second ring-shaped element that is embedded in the disk and extends from the lower surface of the disk to adjacent the current-carrying coil;

a third ring-shaped element that is embedded in the disk and extends from the edge surface of the disk to adjacent the current-carrying coil.

20. A magnetorheological (MR) brake comprising:

a rotor constructed at least partially of a ferromagnetic material;

a housing that supports the rotor such that the rotor and the housing are rotatable relative to each other about an axis, wherein the housing and rotor are configured such that a fluid gap is defined between the housing and the rotor, and wherein portions of the housing adjacent the rotor are constructed at least partially of a ferromagnetic material;

a magnetorheological (MR) fluid disposed in the fluid gap;

a current-carrying coil excitable to generate a magnetic field that is concentrated in the ferromagnetic portions of the rotor and the housing and acts on the MR fluid; and

at least one element constructed of a material having low magnetic permeability configured to route the lines of magnetic flux through surrounding higher permeability material on opposite sides of the fluid gap to route the lines of magnetic flux to transition across the fluid gap multiple times and act on the MR fluid disposed in the fluid gap, wherein the rotor comprises a ferromagnetic disk and a shaft for supporting the rotor in the housing, and wherein the current-carrying coil is toroidal and housed in the disk, and wherein the at least one element constructed of a material having low magnetic permeability comprises:

a first ring-shaped element that is embedded in the disk and extends from an upper surface of the disk to adjacent the current-carrying coil;

a second ring-shaped element that is embedded in the disk and extends from a lower surface of the disk to adjacent the current-carrying coil; and

a third ring-shaped element that is embedded in the disk and extends from an edge surface of the disk to adjacent the current-carrying coil.