Cogging reduction in permanent magnet machines

• US 20070273234A1
• Filed: 05/23/2006
• Published: 11/29/2007
• 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
• Granted Patent: US 7,385,328 B2
• Time in Patent Office: Days
• US Class Current: 310/156.530
• 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 plurality of permanent magnets defining a plurality of poles, 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, and 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 the permanent magnets are internally mounted in the rotor.

3. The permanent magnet motor of claim 1, wherein each pole is defined by two permanent magnets that are mounted in a V-shaped arrangement.

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

5. The permanent magnet motor of claim 1, wherein the permanent magnets are externally mounted on the rotor.

6. The permanent magnet motor of claim 1, wherein the number of poles is 4.

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

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

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

10. An electric motor, comprising:

a rotor having a plurality of poles defined by permanent magnets, each of the poles having a flux field with a first flux edge and a second flux 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 flux edge does not generally align with a tooth at the same time that another flux edge generally aligns with a tooth.

11. The electric motor of claim 10, wherein the permanent magnets are internally mounted in the rotor.

12. The electric motor of claim 10, wherein the permanent magnets are mounted in a V-shape.

13. The electric motor of claim 12, wherein the permanent magnets are internally mounted at approximately a 119 degree angle.

14. The electric motor of claim 10, wherein the number of poles is four.

15. The electric motor of claim 10, wherein the number of teeth is 48.

16. An electric motor comprising:

a rotor having a plurality of permanent magnets defining a plurality of poles, each pole having a leading edge and a trailing edge, wherein the rotor is configured to rotate about a rotor axis of rotation; and

a stator having a plurality of teeth that are generally parallel to the rotor axis of rotation, wherein the number of teeth is an integer multiple of the number of poles, and wherein adjacent teeth are angularly spaced from one another by a predetermined pitch, and wherein the leading edge and the trailing edge of each pole are radially spaced from one another by an angle that is not an integer multiple of the pitch of the teeth.

17. The electric motor of claim 16, wherein the number of poles is 4.

18. The electric motor of claim 16, comprising a discontinuity in a rotor core that further defines the poles.

19. The electric motor of claim 16, wherein the predetermined pitch is 7.5 degrees and the number of teeth is 48.

20. The electric motor of claim 16, wherein two permanent magnets are reflectively symmetrically mounted about a centerline of each pole.

21. A permanent magnet motor comprising:

a rotor having a plurality of permanent magnets defining a plurality of poles, 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, and wherein the leading and trailing edges of each pole are angularly disposed with respect to the stator teeth to reduce cogging torque.

22. A method, comprising:

providing a stator having a plurality of teeth separated by winding slots, wherein each tooth and an adjacent winding slot defines one tooth pitch; and

providing a rotor having a plurality of poles extending generally parallel to the teeth, each pole having a pole width, wherein the smallest difference in size between at least one pole width and an integer multiple of the tooth pitch is greater than 10% of the tooth pitch.

23. The method of claim 22, wherein the smallest difference in size between each pole width and an integer multiple of the tooth pitch is greater than 20% of the tooth pitch

24. The method of claim 22, wherein the smallest difference in size between at least one pole width and an integer multiple of the tooth pitch is greater than 40% of the tooth pitch.

25. The method of claim 22, comprising windings configured for 3 phases of electrical power.