Motor design for reducing cogging torque and torque ripple while maintaining efficiency

• US 9,502,928 B2
• Filed: 03/24/2011
• Issued: 11/22/2016
• Est. Priority Date: 03/25/2010
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Inventors: Li, Hu, Yoshikawa, Yuichi, Murakami, Hiroshi, Kado, Haruhiko, Kawamura, Kiyomi
• Primary Examiner(s): Kenerly, Terrance
• Assistant Examiner(s): Singh, Alexander
• Application Number:
  US13/636,303
• Publication Number:
  US 20130076195A1
• Time in Patent Office: 2,070 Days
• Field of Search: 310216001-216137
• US Class Current: 1/1
• CPC Class Codes: H02K 1/146 consisting of a generally annular yoke with salient poles
• CPC Class Codes: H02K 1/16 Stator cores with slots for windings
• CPC Class Codes: H02K 1/165 Shape, form or location of the slots
• CPC Class Codes: H02K 1/2733 Annular magnets
• CPC Class Codes: H02K 21/16 having annular armature cores with salient poles with homopolar co-operation H02K21/20
• CPC Class Codes: H02K 2213/03 Machines characterised by numerical values, ranges, mathematical expressions or similar information
• CPC Class Codes: H02K 29/03 with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems
• CPC Class Codes: H02K 3/18 Windings for salient poles

Abstract

A motor of this invention comprises a rotor having a permanent magnet, the number of which magnet poles is P, and a stator including M pcs of teeth, the teeth arranged in a circumferential direction in a manner to face the permanent magnet through a spatial gap, wherein the stator includes stator core having the number M of the teeth, and a winding wire wound about each of the tooth, wherein the number P of the magnet poles and the number M of the teeth have a relation defined by formulae (2/3)M<P<(4/3)M, and M≠P, and wherein ratio (t1/Ds) of teeth tip width t1 to stator inside diameter Ds is given by a formula 0.18<(t1/Ds)<0.25.

Claims

1. A motor being an inner rotor type brushless motor in which a rotor is rotatably positioned inside an internal circumference of a stator, the motor comprising;

the rotor having a rotor core connected to a rotational axis, and a permanent magnet on which ten (10) magnetic poles are magnetized as a single and cylindrical ring type magnet, the permanent magnet being held on an outer peripheral side of the rotor core; and

the stator including a stator core having a ring-shape yoke and twelve (12) teeth that extrude from an internal circumference of the ring-shape yoke, and a winding wire wound about each of the teeth, the teeth being arranged in a circumferential direction in a manner to face the permanent magnet through a spatial gap,

wherein the stator core is configured by the yoke and the twelve (12) teeth which are integrated monolithically with the ring-shape yoke, and

wherein an interval of adjacent teeth tips is set to be larger than a diameter of the winding wire and ratio (t1/Ds) of teeth tip width t1 to stator inside diameter Ds of the monolithically integrated stator core is set in a range given by a formula 0.18<

(t1/Ds)<

0.25 so that cogging torque is reduced below about 2 mNm and reduction in motor efficiency is within 0.2% from a highest point, and

wherein the teeth tip width t1 is the width of a teeth tip which is wider than the rest of the teeth and the stator inside diameter Ds is larger than an inner diameter of the rotor.

2. The motor as listed in claim 1, wherein the stator core is structured by laminating a plurality of magnetic thin plates in a direction of thickness thereof.

3. An electric apparatus equipped with the motor listed in claim 2.

4. The motor as listed in claim 1, wherein the winding wire wound about the teeth has a space factor of at least 60%.

5. An electric apparatus equipped with the motor listed in claim 4.

6. The motor as listed in claim 1, wherein the stator is molded with a resin.

7. An electric apparatus equipped with the motor listed in claim 6.

8. The motor as listed in claim 1, wherein the teeth tip width t1 is the width of a teeth tip which is wider than the rest of the teeth within a range that does not exceed twice the rest of the teeth.

9. An electric apparatus equipped with the motor listed in claim 8.

10. The motor as listed in claim 1, wherein the permanent magnet is a bonded rare earth magnet.

11. An electric apparatus equipped with the motor listed in claim 10.

12. The motor as listed in claim 1, wherein the permanent magnet is magnetized to have a surface magnetic flux of substantially a rectangular waveform in the circumferential direction.

13. An electric apparatus equipped with the motor listed in claim 12.

14. An electric apparatus equipped with the motor listed in claim 1.

15. The motor as listed in claim 1, wherein the motor efficiency depends from integrated loss which are balanced between iron loss that increase in accordance with teeth tip width t1 and copper loss that decrease in accordance with teeth tip width t1.