Magnetoelastic torque transducer
First Claim
1. A magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, said member having a ferromagnetic and magnetostrictive region formed of a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute, said transducer comprising:
- a pair of axially spaced-apart annular bands defined within said region, said bands having respectively symmetrical right and left hand helically directed residual stress created magnetic anisotropy of sufficiently large magnitude compared with the random magnetic anisotropy in said member that the contribution to total magnetic anisotropy of any random anisotropy is negligible, each said band having at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length;
means for applying a cyclically time varying magnetic field to said bands;
means for sensing the change in permeability of said bands caused by said applied torque; and
,means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member.
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Accused Products
Abstract
A magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, the member including ferromagnetic, magnetostrictive means affixed to, associated with or forming a part of the surface of the torqued member for altering in magnetic permeability in response to the application of torque to the member. The ferromagnetic, magnetostrictive means is advantageously formed of a thermally hardened or iron-nickel martensite hardenable steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of one or more elements selected from Ni, Cr, Co, Ti, Al, Mn, Mo, Cu and B to raise the alloy magnetostriction to at least 5 ppm absolute. Preferably, the ferromagnetic, magnetostrictive means is formed of nickel maraging steel. The transducer comprises a pair of axially spaced-apart annular bands defined within a region of the ferromagnetic, magnetostrictive means, the bands being endowed with residual stress created, respectively symmetrical right and left hand helically directed magnetic anisotropy of sufficiently large magnitude that the contribution to total magnetic anisotropy of any random anisotropy in the member is negligible. In one aspect of the invention, each said band has at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length. In another aspect of the invention, the alloy is thermally hardened before the bands are endowed with the residual stress-created magnetic anisotropy.
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Citations
50 Claims
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1. A magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, said member having a ferromagnetic and magnetostrictive region formed of a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute, said transducer comprising:
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a pair of axially spaced-apart annular bands defined within said region, said bands having respectively symmetrical right and left hand helically directed residual stress created magnetic anisotropy of sufficiently large magnitude compared with the random magnetic anisotropy in said member that the contribution to total magnetic anisotropy of any random anisotropy is negligible, each said band having at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length; means for applying a cyclically time varying magnetic field to said bands; means for sensing the change in permeability of said bands caused by said applied torque; and
,means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 43, 44, 45, 46, 47, 48, 49, 50)
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11. A magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member, said member having a ferromagnetic and magnetostrictive region, said transducer comprising:
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a pair of axially spaced-apart annular bands defined within a thermally hardened portion of said region, said bands having respectively symmetrical right and left hand helically directed residual stress created magnetic anisotropy instilled therein subsequent to thermal hardening of sufficiently large magnitude compared with the random magnetic anisotropy in said member that the contribution to total magnetic anisotropy of any random anisotropy is negligible, each said band having at least one circumferential region which is free of residually unstressed areas over at least 50% of its circumferential length; means for applying a cyclically time varying magnetic field to said bands; means for sensing the change in permeability of said bands caused by said applied torque; and means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member. - View Dependent Claims (12)
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- 13. In a magnetoelastic torque transducer for providing an electrical signal indicative of the torque applied to a member including ferromagnetic, magnetostrictive means associated with said member for altering in magnetic permeability in response to the application of torque to said member, means for applying a magnetic field to said ferromagnetic magnetostrictive means, means for sensing the change in permeability caused by said applied torque, and means for converting said sensed change in permeability to an electrical signal indicative of the magnitude of the torque applied to said member, the improvement comprising forming said ferromagnetic, magnetostrictive means from a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute.
- 29. In a method of sensing the torque applied to a member having ferromagnetic, magnetostrictive means associated therewith which includes the steps of applying a magnetic field to said ferromagnetic, magnetostrictive means, sensing the change in permeability caused by said applied torque and converting said sensed change in permeability to an electrical signal indicative of the magnitude of the applied torque, the improvement comprising forming said ferromagnetic, magnetostrictive means of a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute.
- 34. In a method of sensing the torque applied to a member having a ferromagnetic and magnetostrictive region including the steps of endowing at least a portion of said region with helically directed residual stress-created magnetic anisotropy, applying a cyclically time varying magnetic field to said portion and to an area of said member not so endowed, and sensing the permeability difference between said portion and said area resulting from the application of torque to said member, the difference being indicative of the magnitude of the applied torque, the improvement comprising forming said region of a thermally hardened steel alloy characterized by a substantially isotropic magnetostriction having an absolute value of at least 5 ppm and including from 0.05 to 0.75 percent by weight carbon and sufficient of an element selected from the group consisting of nickel, chromium, cobalt, titanium, aluminum, manganese, molybdenum, copper, boron, and combinations thereof to raise said alloy magnetostriction value to said at least 5 ppm absolute.
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37. In a method of sensing the torque applied to a member having a ferromagnetic and magnetostrictive region, including the steps of endowing a pair of axially spaced-apart annular bands within said region with respectively symmetrical right and left hand helically directed magnetic anisotropy, applying a cyclically time varying magnetic field to said bands, and sensing the permeability difference between said bands resulting from the application of torque to said member, the difference being indicative of the magnitude of the applied torque, the improvement comprising:
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thermally hardening said member, at least within said region, for imparting desirable mechanical properties to the material from which said region is formed; defining said bands at the surface of said thermally hardened member; and
,endowing said bands with magnetic anisotropy by instilling a residual stress distribution in each band which is sufficiently extensive that at least one circumferential region within each band is free of residually unstressed areas over at least 50% of its circumferential length. - View Dependent Claims (38, 39, 40, 41, 42)
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Specification