Electromagnetic torque sensor for a rotary shaft

• US 4,724,710 A
• Filed: 12/22/1986
• Issued: 02/16/1988
• Est. Priority Date: 12/22/1986
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Murty, Balarama V.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US06/944,865
• Time in Patent Office: 421 Days
• Field of Search: 73/862.33, 324/208
• US Class Current: 73/862.23
• CPC Class Codes: G01L 3/104 involving permanent magnets

Abstract

An electromagnetic sensor for measuring the twist of a rotary shaft in response to the transmission of torque therethrough. Rotary magnetic sleeve means coupled to longitudinally displaced points on the shaft rotate relative to each other in proportion to the shaft deformation. Permanent magnets provide a source of magnetic flux, and a magnetic flux path is defined by a combination of the rotary sleeve means and a segmented stationary sleeve means. Relative rotation of the rotary sleeve means with deformation of the shaft progressively alters the density of the magnetic flux in the segmented stationary sleeve means, and a magnetic flux transducer positioned in an air gap between the stationary sleeve means segments detects the flux density therein to provide an indication of the amount of torque transmitted through the shaft.

Claims

1. A sensor mechanism for sensing the magnitude and direction of torque transmitted through a rotary shaft, comprising:

rotor means rigidly secured to the shaft for rotation therewith, including inner, intermediate, and outer radially displaced rotary sleeve means disposed about said shaft in substantial longitudinal alignment, the inner and outer sleeve means comprising magnetic flux sources and magnetic flux conducting elements defining a plurality of radially extending magnetic flux paths magnetically linked at said inner sleeve means and extending radially through the intermediate sleeve means, and the intermediate sleeve means comprising magnetic flux conducting elements adapted to variably bridge the sources and flux conducting elements of said inner and outer sleeve means, the intermediate sleeve means being secured to said shaft at a point longitudinally displaced from that of said inner and outer sleeve means so that deformation of said shaft due to transmission of torque therethrough produces rotation of said intermediate sleeve means relative to said inner and outer sleeve means and a corresponding variation in the bridging of the sources and flux conducting elements of the inner and outer sleeve means;

stator means supported so as to remain stationary with respect to said shaft, including a pair of stationary magnetic flux conducting sleeve means adjacently disposed to define an air gap therebetween, and radially disposed about said outer rotary sleeve means in substantial longitudinal alignment therewith for providing a magnetic flux path for coupling the magnetically linked radially extending flux paths, thereby completing a magnetic flux circuit through said inner, intermediate and outer rotary sleeve means; and

magnetic flux density transducer means mounted in the air gap between said pair of stationary magnetic flux conducting sleeve means for generating an electrical output signal in accordance with the density of the magnetic flux passing therethrough, thereby to provide an indication of the magnitude and direction of torque transmitted through said shaft.

2. A sensor mechanism as set forth in claim 1, wherein the shaft comprises a two rigid sections joined by a twistable torsion bar, the inner and outer sleeve means are secured to the rigid shaft section on one end of the torsion bar, and the intermediate sleeve is secured to the rigid shaft section on the other end of the torsion bar.

3. A sensor mechanism as set forth in claim 2, including a lost motion mechanical coupling between the two rigid shaft sections which limits twist of the torsion bar.

4. A sensor mechanism as set forth in claim 1, wherein the inner sleeve means comprises an annular magnetic flux conducting member, and a plurality of radially magnetized permanent magnets of alternately north and south polarity disposed about the outer circumference thereof.

5. A sensor mechanism for sensing the magnitude and direction of torque transmitted through a rotary shaft, comprising:

inner and outer radially displaced sleeve means disposed about the shaft in substantial longitudinal alignment and mutually secured to the shaft for rotation therewith, the inner sleeve means comprising a plurality of radially magnetized permanent magnets of alternately north and south polarity disposed on and magnetically linked by an annular magnetic flux conducting member, and the outer sleeve means comprising a north rotary flux ring adapted to collect magnetic flux associated with the north polarity permanent magnets of the inner sleeve means, and a south rotary flux ring longitudinally displaced from said north flux means and adapted to collect magnetic flux associated with the south polarity permanent magnets of the inner sleeve means;

intermediate sleeve means disposed between the inner and outer sleeve means in substantial longitudinal alignment therewith, comprising north flux conducting elements adapted to variably bridge individual north polarity permanent magnets of the inner sleeve means with the north rotary flux ring of the outer sleeve means, and south flux conducting elements adapted to variably bridge individual south polarity permanent magnets of the inner sleeve means with the south rotary flux ring of the outer sleeve means, the intermediate sleeve means being secured to said shaft at a point longitudinally displaced from that of said inner and outer sleeve means so that deformation of said shaft due to transmission of torque therethrough produces rotation of said intermediate sleeve means relative to said inner and outer sleeve means and a corresponding variation in the bridging of the permanent magnets with the respective north and south rotary flux rings;

stationary sleeve means supported so as to remain stationary with respect to said shaft, and radially disposed about said outer rotary sleeve means, comprising north and south stationary flux rings disposed in substantially longitudinal alignment with said north and south rotary flux rings, and adjacently disposed to define an air gap therebetween, thereby completing a magnetic flux circuit through said inner, intermediate and outer rotary sleeve means; and

magnetic flux density transducer means mounted in the air gap between said north and south stationary flux rings for generating an electrical output signal in accordance with the magnetic flux density therein, thereby to provide an indication of the magnitude and direction of torque transmitted through said shaft.

6. A sensor mechanism as set forth in claim 5, wherein the shaft comprises a two rigid sections joined by a twistable torsion bar, the inner and outer sleeve means are secured to the rigid shaft section on one end of the torsion bar, and the intermediate sleeve is secured to the rigid shaft section on the other end of the torsion bar.

7. A sensor mechanism as set forth in claim 6, including a lost motion mechanical coupling between the two rigid shaft sections which limits the twist of the torsion bar.

8. A sensor mechanism as set forth in claim 5, wherein the outer sleeve means comprises a plurality of longitudinally extending north salient poles emanating from the north rotary flux ring in radial alignment with the north permanent magnets of the inner sleeve means, and a plurality of longitudinally extending south salient poles emanating from the south rotary flux ring in radial alignment with the south permanent magnets of the inner sleeve means.