Cogging reduction in permanent magnet machines

• US 7,385,328 B2
• Filed: 05/23/2006
• Issued: 06/10/2008
• Est. Priority Date: 05/23/2006
• Status: Active Grant

• Current Assignee: Baldor Electric Company (ABB Limited)
• Original Assignee: Reliance Electric Technologies LLC (ABB Limited)
• Inventors: Melfi, Michael J.
• Primary Examiner(s): Le; Dang D
• Application Number:
  US11/438,753
• Publication Number:
  US 20070273234A1
• Time in Patent Office: 749 Days
• Field of Search: 310/156.38, 310/156.45, 310/156, 310/156.56, 310/156.41, 310/156.53
• US Class Current: 310/156.45
• CPC Class Codes: H02K 1/2766 having a flux concentration effect
• CPC Class Codes: H02K 1/278 Surface mounted magnets; Inset magnets
• CPC Class Codes: H02K 21/14 with magnets rotating within the armatures
• CPC Class Codes: H02K 29/03 with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems

Abstract

A permanent magnet motor having a rotor and a stator and configured such that when the leading edge of each pole of the rotor aligns with a stator tooth the trailing edge of that pole is generally not aligned with a stator tooth.

Claims

1. A permanent magnet motor comprising:

a rotor having a shaft and a contiguous rotor core extending along the shaft, the rotor having a plurality of permanent magnets defining a plurality of poles, wherein each pole is defined by permanent magnets that are mounted in a V-shaped arrangement, the V-shaped arrangement for each pole being formed with the same obtuse angle and each pole being equiangularly spaced about a center axis of the rotor, each pole having a leading edge and a trailing edge; and

a stator having a plurality of teeth that are generally parallel to the permanent magnets, wherein the number of teeth is an integer multiple of the number of poles, wherein when the leading edge of each pole aligns with a stator tooth the trailing edge of that pole is generally not aligned with a stator tooth.

2. The permanent magnet motor of claim 1, wherein each permanent magnet is defined by two permanent magnetic elements that are mounted in the V-shaped arrangement.

3. The permanent magnet motor of claim 2, wherein the number of poles is four, the number of teeth is 48, and the two permanent magnetic elements defining each pole are mounted at a 119 degree angle.

4. The permanent magnet motor of claim 1, wherein the number of poles is an even number integer no less than 2.

5. The permanent magnet motor of claim 1, wherein the teeth are generally parallel to an axis of rotation of the permanent magnet motor.

6. The permanent magnet motor of claim 1, wherein the poles are rotationally symmetric.

7. The permanent magnet motor of claim 1, comprising windings disposed between the teeth and configured to accept three phases of electrical power.

8. The permanent magnet motor of claim 1, wherein the contiguous rotor core is formed from a plurality of laminations with like geometry mounted on the shaft uniformly along an axis of the shaft.

9. The permanent magnet motor of claim 1, wherein the leading edge and the trailing edge of each pole correspond to locations with a distinct change in air gap flux density.

10. An electric motor, comprising:

a rotor having a shaft and a contiguous rotor core extending along the shaft with a plurality of permanent magnets embedded therein, each of the magnets having a V-shaped cross-section with an obtuse angle therebetween, the obtuse angle being the same for each magnet, and each magnet being equiangularly spaced about a center the rotor, the V-shaped cross-section being defined by an inner V-surface and an outer V-surface, each of the magnets being magnetized to cause the inner V-surface and the outer V-surface to have a different polarity, each magnet defining a pole with a first edge and a second edge; and

a stator having winding slots separated by respective teeth, the number of teeth being an integer multiple of the number of poles, wherein at least one pole edge does not generally align with a tooth at the same time that another pole edge generally aligns with a tooth.

11. The electric motor of claim 10, wherein each of the magnets comprises a pair of magnetic elements separated by a gap.

12. The electric motor of claim 11, wherein the gap is disposed between two spaces, the two spaces housing the pair of magnet elements and extending through the contiguous rotor core.

13. The electric motor of claim 10, wherein the number of poles is four, the number of teeth is 48, and the angle between the inner V-Shaped cross section is 119 degrees.

14. The electric motor of claim 10, wherein the number of poles is an even number integer no less than 2.

15. The electric motor of claim 10, wherein the obtuse angle is between 109 and 129 degrees.

16. The electric motor of claim 10, wherein the number of poles is four, the number of teeth is 48, and the angle between the outer V-Shaped cross section is 119 degrees.

17. The electric motor of claim 10, wherein the contiguous rotor core is formed from a plurality of laminations with like geometry mounted on the shaft uniformly along an axis of the shaft.

18. The electric motor of claim 10, wherein the pole first and second edges correspond to locations with a distinct change in air gap flux density.