Electric motor having a low loss magnetic flux return path

• US 5,243,248 A
• Filed: 03/30/1992
• Issued: 09/07/1993
• Est. Priority Date: 12/20/1989
• Status: Expired due to Fees

• Current Assignee: Charles J. Hire
• Original Assignee: Daniel J. Shramo, Deceased, Susan M. Benford
• Inventors: Benford, deceased, Susan M., Shramo, executor, by Daniel J.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): BARRERA, RAMON M
• Application Number:
  US07/859,589
• Time in Patent Office: 526 Days
• Field of Search: 310/42, 310/216, 310/217, 310/218, 310/254, 310/256, 310/259, 310/258, 336/177, 336/234, 336/213, 29/605, 29/606
• US Class Current: 310/256
• CPC Class Codes: H01F 3/06 made from wires
• CPC Class Codes: H02K 1/12 Stationary parts of the magnetic circuit
• CPC Class Codes: H02K 2201/06 Magnetic cores, or permanent magnets characterised by their skew

Abstract

The invention is directed to an electric motor construction having a magnetic flux return path which exhibits very low losses due to eddy currents or hysteresis, and simplifies construction thereof. In the motor construction, the magnetic flux return path is constructed from discrete magnetic material wire which is wrapped or otherwise formed in the desired return path configuration. The magnetic material wire is wound in a direction which generally crosses the flow of magnetic flux and yet is substantially tolerant of cross-winding fields. In this way, the flux return path provides easy construction in that coil winding techniques may be used, and the winding direction is less critical as it can cross the flow of flux therein. The flux return path greatly reduces eddy current losses as the cross section of the path to eddy current flow is the cross section of discrete wires, and because the discrete wires are formed with high packing fraction which will minimize skin effects especially at high frequencies.

Claims

1. An electric motor having a low loss magnetic flux return path comprising,

a permanent magnet rotor including an output shaft rotatably supported on bearing means,

a stator including field windings positioned around said rotor, wherein an electric current is introduced into said field windings to selectively energize said field windings and generate magnetic fields acting on said permanent magnet rotor to induce rotation of said output shaft,

a return yoke member associated with said rotor and constructed of a soft magnetic material to provide a fixed flux path for the magnetic flux generated by said permanent magnet rotor, and

a flux return path positioned around said field windings and having a cross-section characterized as a plurality of discrete high permeability magnetic wires, said magnetic wires being wound in a direction generally crossing the flow of magnetic flux generated by said permanent magnet rotor, said plurality of discrete wires being packed with high packing fraction sufficient to result in said flux return path being tolerant to cross-layer and cross-winding magnetic fields generated at the location of the crossing magnetic flux, said flux return path forming a body of high permeability magnetic material surrounding said field windings and extending approximately the length of the magnetic field generated by the rotating permanent magnets associated with said rotor, with the thickness of said body of high permeability magnetic material dimensioned to fully accommodate the generated magnetic fields,

wherein said discrete windings forming said flux return path minimize losses due to eddy currents and hysteresis and the thickness of said flux return path will minimize losses due to magnetic saturation.

2. The electric motor of claim 1, wherein,

the dimensions of said magnetic material wire provide a small cross-sectional area which enables said plurality of windings to be positioned in a very close packed configuration such that the penetration depth of the magnetic flux is limited to within said plurality of windings.

3. The electric motor of claim 1, wherein,

eddy currents generated and circulating within said magnetic flux return path are carried by each of said discrete windings of magnetic material wire to minimize losses due to eddy currents.

4. The electric motor of claim 1, wherein,

said magnetic material wire is formed of a high magnetic permeability material.

5. The electric motor of claim 1, wherein,

said return path is constructed of a plurality of layers formed from said plurality of windings in a closely packed configuration and the thickness of said plurality of layers is chosen to minimize skin effects and to limit the flux density of the generated alternating magnetic fields from said rotating permanent magnet rotor to below the magnetic saturation level of said magnetic material.

6. The electric motor of claim 1, wherein,

said magnetic material wire has a cross sectional geometry which allows a high packing fraction to be obtained in said at least one layer of said discrete windings.

7. The electric motor of claim 1, wherein,

the cross section to eddy current circulation within said magnetic flux return path is the cross section of each of said discrete windings of magnetic material wire.

8. The electric motor of claim 1, wherein

said plurality of discrete windings are formed from low carbon iron.

9. The electric motor of claim 1, wherein,

said plurality of discrete windings of magnetic material wire have a circular cross-sectional configuration, wherein each of said discrete windings of magnetic material wire are positioned in closely adjacent relationship to one another.

10. The electric motor of claim 1, wherein,

said plurality of discrete windings of magnetic material wire have a non-circular geometric cross-sectional configuration which allows said plurality of windings to be packed in said high packing fraction.

11. The electric motor of claim 10, wherein

said non-circular geometric cross-sectional configuration of said magnetic material wire comprises a rectilinear geometric cross-sectional configuration wherein each of said discrete windings may be positioned such that sides of the rectilinear configuration will lie directly adjacent to a side of an adjacent winding of magnetic material wire to obtain said high packing fraction.

12. The electric motor of claim 11, wherein

said rectilinear cross-sectional configuration is formed as a flat ribbon of magnetic material wire.

13. The electric motor of claim 10, wherein,

said non-circular geometric cross-sectional configuration of said magnetic material wire comprises a triangular geometric cross-sectional configuration wherein at least two sides of each of said triangular magnetic material wires are positioned directly adjacent to another side of an adjacent winding of magnetic material wire to obtain said high packing fraction.

14. The electric motor of claim 10, wherein,

said non-circular geometric cross-sectional configuration of said magnetic material wire comprises an oval cross-sectional configuration, wherein each of said discrete windings of magnetic material wire are positioned directly adjacent to another winding of magnetic material wire to obtain said high packing fraction.

15. The electric motor of claim 1, wherein,

said motor generates alternating magnetic fields at high frequencies and said cross-sectional configuration of discrete windings each provide a small cross-section of wire to eddy currents and said high packing fraction minimizes skin effects associate with said high frequency alternating magnetic fields.

16. The electric motor of claim 1, wherein,

said plurality of discrete windings formed into one or more layers of high permeability are designed to have a width and thickness so as to have core magnetic permeability flux density below the level of magnetic saturation of said magnetic material forming said windings.

17. The electric motor of claim 1, wherein,

said plurality of discrete windings formed into one or more layers of high permeability magnetic material are formed by standard coil winding techniques, whereby the geometric cross-sectional configuration of said windings allows said windings to be packed with said high packing fraction using said coil winding techniques.