Field assemblies having pole pieces with axial lengths less than an axial length of a back iron portion and methods of making same

• US 20050189840A1
• Filed: 02/18/2005
• Published: 09/01/2005
• Est. Priority Date: 09/05/2003
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Du, Hung T., Verbrugge, Brandon L., McCormick, Garrett P., Ortt, Earl M.
• Granted Patent: US 7,211,920 B2
• Time in Patent Office: Days
• US Class Current: 310/216.1
• CPC Class Codes: H02K 1/148 Sectional cores H02K1/141 takes precedence
• CPC Class Codes: H02K 1/18 Means for mounting or fastening magnetic stationary parts on to, or to, the stator structures
• CPC Class Codes: H02K 15/0435 Wound windings
• CPC Class Codes: H02K 15/10 Applying solid insulation to windings, stators or rotors
• CPC Class Codes: H02K 15/12 Impregnating, heating or drying of windings, stators, rotors or machines
• CPC Class Codes: H02K 3/325 for windings on salient poles, such as claw-shaped poles
• CPC Class Codes: H02K 3/522 for generally annular cores with salient poles

Abstract

An electric motor, power tool using the electric motor, and method of making the electric motor includes making a stator that includes pole portions that have axial lengths less than an axial length of a back iron portion. Alternatively, or in addition, the pole portions have axially opposed ends that decrease in width. Alternatively, or in addition, the pole portions have dovetail features that are received in corresponding recesses of the back iron portion.

Claims

1. An electric motor, comprising:

a. a stator having a back iron portion and at least two pole portions on which field coils are disposed, the pole portions having an axial length less than an axial length of back iron portion; and

b. an armature disposed in the stator.

2. The electric motor of claim 1 wherein the field coils are formed so that ends don'"'"'t extend beyond axial ends of the back iron portion.

3. The electric motor of claim 1 wherein each pole portion has opposed ends that gradually decrease in width.

4. The electric motor of claim 1 wherein the back iron portion comprises at least two return path pieces and each pole portion includes a pole piece, the return path pieces and pole pieces being separately formed and mated together.

5. The electric motor of claim 4 wherein the field coils are preformed and placed on the pole pieces before the pole pieces are mated to the return path pieces.

6. The electric motor of claim 4 wherein the field coils are wound on the pole pieces after the pole pieces have been mated to the return path pieces.

7. The electric motor of claim 5 wherein each pole piece has opposed ends that gradually decrease in width.

8. The electric motor of claim 1 wherein the pole portions, back iron portion and field coils are separately formed, each pole portion having a neck with a radial outer end having a dovetail feature, the dovetail feature of each pole piece received in a corresponding recess of the back iron portion after one of the field coils has been placed over the neck of that pole piece.

9. The electric motor of claim 8 wherein each pole piece has opposed ends that gradually decrease in width.

10. A power tool, comprising:

a. a housing;

b. a motor disposed in the housing, the motor including;

i. a stator having a back iron portion and at least two pole portions on which field coils are disposed, the pole pieces having an axial length less than an axial length of back iron portion; and

ii. an armature disposed in the stator.

11. The power tool of claim 10 wherein the field coils are formed so that ends don'"'"'t extend beyond axial ends of the return path pieces.

12. The power tool of claim 10 wherein each pole portion has opposed ends that gradually decrease in width.

13. The power tool of claim 10 wherein the back iron portion comprises at least two return path pieces and each pole portion includes a pole piece, the return path pieces and pole pieces being separately formed and mated together.

14. The power tool of claim 13 wherein the field coils are preformed and placed on the pole pieces before the pole pieces are mated to the return path pieces.

15. The power tool of claim 13 wherein the field coils are wound on the pole pieces after the pole pieces have been mated to the return path pieces.

16. The power tool of claim 13 wherein each pole piece has opposed ends that gradually decrease in width.

17. The power tool of claim 10 wherein the pole portions, back iron portion and field coils are separately formed, each pole portion having a neck with a radial outer end having a dovetail feature, the dovetail feature of each pole piece received in a corresponding recess of the back iron portion after one of the field coils has been placed over the neck of that pole piece.

18. The power tool of claim 17 wherein each pole piece has opposed ends that gradually decrease in width.

19. A method of making an electric motor, comprising:

a. forming a stator with a back iron portion and at least two pole portions so that the pole portions have an axial length less than the back iron portion;

b. disposing field coils on the pole portions; and

c. disposing an armature in the stator.

20. The method of claim 19 including forming the field coils so that when they are disposed on the pole portions, ends of the field coils don'"'"'t extend beyond axial ends of the back iron portion.

21. The method of claim 19 including forming the pole portions to have opposed axial ends that gradually decrease in width.

22. The method of claim 19 including forming the back iron portion and pole portions by separately forming return path pieces and pole pieces and mating them together.

23. The method of claim 19 including forming the field coils and placing them on the pole pieces prior to mating the pole pieces and return path pieces together.

24. The method of claim 19 including winding the field coils on the pole pieces after the pole pieces and return path pieces have been mated together.

25. The method of claim 19 including separately forming the pole portions, back iron portion and field coils, wherein forming each pole portion includes forming it to have a dovetail feature at a radial outer end of a neck, forming the back iron portion includes forming it to have recesses for receiving the dovetail features of the pole portions, and inserting the dovetail feature of each pole piece in one of the recesses in the back iron portion after one of the field coils has been disposed on the neck of that pole piece and securing that pole piece to the back iron portion.

26. The method of claim 25 including forming the pole portions to have opposed axial ends that gradually decrease in width.