Motor armature having distributed windings for reducing arcing

Abstract

An armature for a brush commutated electric motor having a distributed coil winding arrangement for reducing brush arcing and electromagnetic interference (EMI). The winding pattern involves segmenting each coil into first and second subcoil portions with differing pluralities of turns. Each subcoil portion is wound around separate pairs of spaced apart slots of a lamination stack. Adjacent coils are wound such that one subcoil portion of each is wound in a common slot to therefore form an overlapping arrangement of each pair of adjacently coils. The winding pattern serves to “shift” the resultant magnetic axes of each coil in such a manner so as to significantly reduce brush arcing and the EMI resulting therefrom. The reduction in EMI is sufficient to eliminate the need for EMI reducing components, such as chokes, which have typically been required to maintain EMI to acceptably low levels. Commutation efficiency is also improved by the distributed winding pattern described above because of the reduction in the unevenness of the magnetic coupling between adjacent coils.

Description

TECHNICAL FIELD

[0002] This invention relates to electric motors, and more particularly to a winding pattern for winding the coils on an armature in a manner to reduce electromagnetic interference and arcing at the brushes in contact with the commutator of the armature.

BACKGROUND OF THE INVENTION

[0003] Present day brush commutated electric motors include an armature having a plurality of coils wound in slots formed in the lamination stack of the armature. With traditional motor designs, the lamination stack of the armature forms a plurality of circumferentially arranged slots extending between adjacent pairs of lamination posts. Typically, two coils per slot are used when winding the armature coils on the lamination stack. Among the two coils of the same slot, the one which commutates first is referred to as the first coil and the one which commutates second as the second coil. The second coil has inherently poorer magnetic commutation than the first coil because the second coil passes beyond the magnetic neutral zone within the stator before it finishes commutation. This is illustrated in simplified fashion in FIG. 1, wherein the commutation zone of the first coil is designated by Z1 and the commutator zone of the second coil is designated by Z2. A Rotor “R” is shown positioned at the mid-point of the first coil commutation zone. As a result, the second coil commutation can generate significant brush arcing, and becomes the dominant source of the total brush arcing of the motor. This can also cause electromagnetic interference (EMI) to be generated which exceeds acceptable levels set by various government regulatory agencies. This brush arcing can also lead to accelerated brush wear.

[0004] Accordingly, it is a principal object of the present invention to provide an armature for a brush commutated electric motor having a plurality of coils wound thereon in a unique sequence which serves to significantly reduce brush arcing and improve the commutation efficiency of the motor.

[0005] It is a further object of the present invention to provide an armature for a brush commutated electric motor which incorporates a unique winding pattern for the coils wound on the armature in a manner which does not otherwise require modification of any component of the armature or the need for additional components.

[0006] It is still a further object of the present invention to provide a winding pattern for the armature coils of an armature which allows EMI components usually required to sufficiently attenuate the EMI generated by brush arcing to be eliminated, thus allowing the motor to be constructed less expensively and with fewer components.

SUMMARY OF THE INVENTION

[0007] The above and other objects are provided by an armature for a brush commutated electric motor incorporating a unique, distributed winding pattern for the coils thereof, in accordance with a preferred embodiment of the present invention. The winding pattern involves segmenting each coil into first and second subcoil portions. With a first coil, the first subcoil portion is wound around two spaced apart slots for a first plurality of turns and the second subcoil portion is wound around a second pair of spaced apart slots which are shifted circumferentially from the first pair of slots. The second subcoil portion is also formed by a different plurality of winding turns than the first subcoil portion. The two subcoil portions are wound in series with one end coupled to a first commutator segment of the armature and the other end coupled to a second commutator segment.

[0008] A second coil is also divided into first and second subcoil portions, with the first subcoil portion being wound with the same number of turns as the second subcoil portion of the first coil, and in the second pair of spaced apart slots. The second subcoil portion of the second coil, however, is laterally shifted such that it is wound in a third pair of spaced apart slots shifted laterally by one slot from the second pair of slots. The second subcoil portion of the second coil is also wound a plurality of turns in accordance with that of the first portion of the first coil. One end of the first subcoil portion of the second coil is coupled to commutator segment number two while the end of subcoil portion two of coil two is coupled to commutator segment number three.

[0009] Coil number three is segmented into first and second subcoil portions with the first subcoil portion being wound a number of turns in accordance with the second subcoil portion of the second coil, and wound around the second pair of spaced apart slots. The second subcoil portion of the third coil is wound around the third pair of spaced apart slots but with a number of turns in accordance with the first subcoil portion of the second coil. The end of the first subcoil portion of the third coil is coupled to commutator segment number three while the end of the second subcoil portion of coil three is coupled to commutator segment number four.

[0010] The above winding pattern continues in alternating fashion such that an overlapping of the coils occurs around the lamination stack. In effect, all of the first subcoil portions shift their magnetic axes forward with respect to rotation of the armature, and all of the second coil portions shift their magnetic axes backward relative to the direction of armature rotation. With a desired turns ratio between the two subcoil portions of each coil, which ratio may vary considerably but is preferably about 3:1, the above described winding pattern smoothes out the “unevenness” in the magnetic coupling between adjacent armature coils, thus improving commutation efficiency. This also improves the commutation efficiency for the second subcoil portion of each coil, thus reducing brush arcing. This in turn serves to significantly reduce EMI. The reduction of EMI eliminates the need for expensive EMI suppression components that have previously been required for use with the motor brushes to ensure that EMI levels remain below regulated limits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The various advantages of the present invention will become apparent to one skilled in the art by reading the following specification and subjoined claims and by referencing the following drawings in which:

[0012] FIG. 1 is a simplified diagrammatic end view of an armature having a traditional coil winding pattern employed, and illustrating how the commutation zone of the second coil of a two-coil-per-slot winding arrangement causes the commutation zone of the second coil to lag behind the commutation zone of the first coil, thus leading to brush arcing;

[0013] FIG. 2 is a side elevational view of an exemplary armature constructed in accordance with the teachings of the present invention;

[0014] FIG. 3 is a simplified cross sectional end view of the armature of FIG. 2 illustrating a lamination stack for an armature having a plurality of twelve slots around which the coils of the armature are to be wound;

[0015] FIG. 4 illustrates in simplified fashion a coil winding pattern in accordance with the present invention; and

[0016] FIG. 5 is a simplified end view of the armature illustrating how the winding pattern produces commutation zones for the first and second coil with subcoil portions which are radially aligned with one another to improve commutation efficiency and reduce brush arcing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring to FIG. 2, there is shown an armature 10 for a brush commutated electric motor 11 having a plurality of coils wound in accordance with the teachings of the present invention. The armature 10 includes a commutator 12 which, merely by way of example, includes 24 independent commutator segments 121-1224. A lamination stack 14 is used to support a plurality of 24 coils 251-2524 wound thereon. An armature shaft 22 extends through the lamination stack 14 and is fixedly coupled to a gear reduction assembly 20 and also to a fan 18. It will be appreciated, though, that the fan 18 and the gear reduction assembly 20 are optional and not essential to the armature 10 of the present invention, and shown merely because they are components that are often used in connection with an armature for an electric motor.

[0018] Referring to FIG. 3, the lamination stack 14 is illustrated without any coils wound thereon. The lamination stack 14 includes a plurality of radially projecting lamination posts or “teeth” 24. Twelve slots S1-S12 are formed between the posts 24. It will be appreciated immediately, however, that while twelve such slots are illustrated, that a greater or lesser plurality could be employed. The overall number of slots depends on the number of commutator segments and will always be one-half the number of commutator segments used.

[0019] Referring now to FIG. 4, the winding pattern of the present invention will be described. Coil number 1 (251) has a first subcoil portion 1A and a second subcoil portion 1B formed in series with subcoil portion 1A. Subcoil portion 1A has one end thereof coupled to commutator segment number 121 and the end of second subcoil portion 1B is coupled to commutator segment number 122. Subcoil portion 1A of coil 251 includes a first plurality of turns, for example seven turns, which are wound around slots S12 and S5 of the lamination stack 14. Subcoil portion 1 B of coil 251 is then wound for a larger plurality of turns, in this example 17 turns, in slots S1 and S6 of the lamination stack 14. It will be appreciated that the precise number of windings of each subcoil portion can vary considerably, but in the preferred embodiment the number of turns between the subcoil portion 1B and portion 1A of coil 251 is such that one has preferably about three times as many winding turns as the other. The number of turns also alternates between the subcoils, as will be described further, such that adjacent coils will always have the two first subcoil portions with differing numbers of winding turns, and the two second subcoil portions with differing numbers of winding turns.

[0020] Coil number 2 (252) also has a first subcoil portion 2A and a second subcoil 2B in series with one another. Subcoil portion 2A is wound in slots S1 and S6 with seventeen turns. Subcoil portion 2B is wound in series with portion 2A but around slots 52 and 57 of the lamination stack 14, and with seven winding turns. The end of subcoil portion 2A is coupled to commutator segment 122 while the end of subcoil portion 2B is coupled to commutator segment 123. The first subcoil portion 2A of coil 252 overlaps the second subcoil portion 1B of coil 251.

[0021] Coil number 3 (253) includes a first subcoil portion 3A and a second subcoil portion in series with one another 3B. Subcoil portion 3A is attached to commutator segment number 123 and includes seven winding turns wound around slots S1 and S6. Subcoil portion 3B is formed in series with subcoil portion 3A and includes seventeen turns wound in slots S2 and S7, with the end thereof being coupled to commutator segment 124.

[0022] Coil 4 (254) also includes a first subcoil portion 4A and a second subcoil portion 4B in series with subcoil portion 4A. Subcoil portion 4A has its end coupled to commutator segment 124 and includes seventeen turns wound around slots S2 and S7. Subcoil portion 4B includes seven turns wound around slots S3 and S8, with the end thereof being coupled to commutator segment 125. It will be noted that coil 254 partially overlaps coil 253. In effect, one of the subcoil portions of each adjacent pair of coils 25 overlap with each other.

[0023] The above-described pattern for coils 251-254 is repeated until all of the coils (in this example 12 coils) are wound onto the lamination stack 14. Each of the ends of the coils 251-2512 are further secured to immediately adjacent pairs of commutator segments 121-1224. For example, coil 255 has its ends secured to commutator segments 125 and 126, coil 256 to segments 126 and 127, and so forth.

[0024] The above-described winding pattern significantly improves the commutation performance of all of the second coil portions of the coils 25. Splitting each coil 25 into first and second subcoil portions allows each first subcoil portion to shift its magnetic axis away (i.e., laterally), from the position it would have otherwise had in a traditional two-coil-per-slot approach. This is illustrated in FIG. 5. All of the first subcoil portions shift their magnetic axes forward to produce a first coil commutation zone, as indicated by line 30, and all of the second subcoil portions shift their magnetic axes backward to produce a second coil commutation zone, as indicated by line 32, in reference to the armature's 10 rotational direction. Both of these commutation zones are now in a magnetic neutral zone between field coils 34. With a turns ratio between the two subcoils of about 3:1, this winding pattern smoothes out the magnetic “unevenness” between adjacent coils, which is a drawback with traditional two-coil-per-slot winding patterns. This, in connection with the shifting of the resultant magnetic axes of each coil, serves to significantly improve the commutation efficiency of the motor and to reduce the overall brush arcing.

[0025] The winding pattern employed on the armature 10 of the present invention also serves to significantly reduce the cost of constructing the armature by eliminating components that would otherwise be needed to sufficiently attenuate the EMI that results from traditional two-coil-per-slot winding patterns. Typically, inductive components are required to form a choke circuit associated with each armature brush. These additional components increase the overall cost of manufacturing a motor, as well as increase the complexity of the task of replacing the brushes during repair procedures.

[0026] The apparatus and method of the present invention thus allows an armature to be formed which significantly reduces brush arcing, and therefore the EMI that is present with traditional two-coil-per-slot armature constructions for all brush commutated electric motors. The apparatus and method of the present invention further does not increase the complexity of the manufacturing process or require additional component parts that would otherwise increase the overall cost of construction of an armature.

[0027] Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.

Claims

1. An electric motor having an armature, the electric motor comprising: a lamination stack forming the armature, and having a plurality of radially extending, spaced apart posts, said posts forming a plurality of slots therebetween; a first coil having first and second subcoil portions, said first subcoil portion being wound in a first pair of said slots, and said second subcoil portion being wound in a second pair of said slots that are offset from said first pair of slots; a second coil having a first subcoil portion wound in said second pair of said slots, and a second subcoil portion wound in a third pair of said slots offset from said second pair of slots; a third coil having first and second subcoil portions wound in the same slots as said subcoil portions of said second coil; and a plurality of additional coils wound in said slots such that a winding pattern defined by said subcoil portions of said first, second and third coils is repeated.

2. The electric motor of claim 1, wherein said first and second subcoil portions of said first coil comprise different pluralities of windings.

3. The electric motor of claim 1, wherein one of said first and second subcoil portions of said first coil has approximately three times as many winding turns as the other.

4. The electric motor of claim 1, wherein said third pair of slots is offset from said second pair of slots by one slot position.

5. The electric motor of claim 1, wherein said second pair of slots is offset by one slot position from said first pair of slots.

6. An electric motor having an armature, the electric motor comprising: a lamination stack forming the armature, the lamination stack having a plurality of radially extending, spaced apart posts, said posts forming a plurality of winding slots therebetween; a first coil having first and second subcoil portions, said first subcoil portion being wound in a first pair of said slots and said second subcoil portion being wound in a second pair of said slots that are offset from said first pair of said slots; a second coil having first and second subcoil portions with said first subcoil portion thereof being wound in a third pair of slots that are offset from said first pair of slots, and said second subcoil portion of said second coil being wound in a fourth pair of slots; a third coil having first and second subcoil portions that are wound in the same pair of said slots as said subcoil portions of said second coil; and an additional plurality of coils wound such that a winding pattern defined by said first, second and third coils is repeated.

7. The electric motor of claim 6, wherein said fourth pair of slots is offset by one slot position from said second pair of slots.

8. The electric motor of claim 6, wherein said third pair of said slots and said second pair of said slots comprise the same pair of said slots.

9. The electric motor of claim 6, wherein said first and second subcoil portions of said first coil have different pluralities of winding turns.

10. The electric motor of claim 6, wherein said first subcoil portion of said second coil has a different plurality of winding turns than said second subcoil portion of said first coil.

11. The electric motor of claim 10, wherein said second subcoil portion of said first coil is wound in the same pair of said slots as said first subcoil portion of said second coil.

12. The electric motor of claim 6, wherein said second pair of slots is offset by one slot position from said first pair of slots.

13. The electric motor of claim 6, wherein said first and second subcoil portions of said first coil have pluralities of winding turns that differ such that one has approximately three times a number of winding turns as the other.

14. An electric motor comprising: an armature having a plurality of spaced-apart posts defining a plurality of winding slots therebetween; a stator disposed coaxially with the armature, said stator having a plurality of spaced apart field coils defining a magnetic neutral zone between each adjacent pair of said field coils; a coil having a first subcoil portion and a second subcoil portion; said first subcoil portion having a first plurality of winding turns and being wound in a first pair of spaced apart ones of said slots that are advanced, relative to a given one of said field coils, during rotation of said armature; said second subcoil portion having a second plurality of winding turns and being wound in a second pair of spaced apart ones of said slots that are offset from said first pair of spaced apart slots, and retarded, relative to said given field coil, during rotation of said armature; a second coil having first and second subcoil portions would in third and fourth pairs, respectively, of spaced apart ones of said slots; wherein a magnetic axis of said first coil is advanced, relative to said given field coil, when said first coil is excited; wherein a magnetic axis of said second coil is retarded, relative to said given field coil, when said second coil is excited; and wherein both of said coils at least substantially complete commutation within a spaced apart pair of said magnetic neutral zones when said coils are excited.

15. The electric motor of claim 14, wherein said first plurality of winding turns differs from said second plurality of winding turns in number.

16. The electric motor of claim 14, wherein one of said first and second pluralities of winding turns has approximately three times a number of winding turns as the other.

17. A two coil-per-slot electric motor comprising: an armature having a plurality of spaced-apart posts defining a plurality of winding slots therebetween; a commutator having a plurality of commutator bars that number twice that of said winding slots; a stator disposed coaxially with the armature, said stator having a plurality of spaced apart field coils defining a magnetic neutral zone between each adjacent pair of said field coils; a first coil having a first subcoil portion and a second subcoil portion; said first subcoil portion being wound in a first pair of spaced apart ones of said slots; said second subcoil portion being wound in a second pair of spaced apart ones of said slots that are offset from said first pair of spaced apart slots; a second coil having a first subcoil portion and a second subcoil portion; said first subcoil portion of said second coil being wound in said second pair of spaced apart slots so as to overlap said second subcoil portion of said first coil; said second subcoil portion of said second coil being wound in a third pair of spaced apart ones of said slots offset from said second pair of spaced apart slots; wherein a magnetic axis of said first coil is advanced, relative to a given said field coil, when said first coil is excited; wherein a magnetic axis of said second coil is retarded, relative to said given field coil, when said second coil is excited; wherein both of said coils at least substantially complete commutation when each said coil is excited within a spaced apart pair of said magnetic neutral zones such that substantially no commutation of either of said coils occurs outside of any of said magnetic neutral zones.

18. The electric motor of claim 17, wherein said first and second subcoil portions of said first coil have differing pluralities of winding turns.

19. The electric motor of claim 17, wherein one of said first and second subcoil portions of said first coil has approximately three times a number of winding turns as the other.

20. The electric motor of claim 17, further comprising a third coil having first and second subcoil portions that are wound in the same said slots as said subcoil portions of said second coil.

21. An electric motor comprising: an armature having a plurality of spaced apart posts defining a plurality of spaced apart winding slots therebetween; a first coil having first and second subcoil portions coupled in series; a second coil having first and second subcoil portions coupled in series; a third coil having first and second subcoil portions coupled in series; said subcoil portions of said first coil being wound in first and second spaced apart pairs of said slots; said subcoil portions of said second coil being wound in a third and fourth spaced apart pairs of said slots, wherein said third pair of spaced apart slots is offset by at least one slot position from said first pair of spaced apart slots; said subcoil portions of said third coil being wound in said third and fourth slots so as to overlap said first and second subcoil portions of said second coil; and an additional plurality of coils wound on said armature, with each one of said additional plurality of coils being segmented into first and second subcoil portions, and further wound such that a winding pattern defined by windings of said first, second and third coils is repeated.

22. The electric motor of claim 21, further comprising a commutator having a plurality of commutator segments that is twice that in number of said plurality of winding slots.

23. An electric motor having an armature, the electric motor comprising: a lamination stack having a plurality of radially extending posts, said posts forming a plurality of slots therebetween, said slots being arranged in a circumferential pattern; a plurality of coils wound around said slots, said coils being arranged in pairs about said lamination stack; each said coil being divided into first and second subcoil portions, with said first subcoil portion having a first plurality of winding turns and said second subcoil portion having a second plurality of winding turns, and wherein said first and second subcoil portions are wound in different, circumferentially offset pairs of said slots and coupled to designated pairs of commutator segments of a commutator; wherein a first pair of said coils are wound in an overlapping fashion such that the first subcoil portion of a second one of said first pair of coils is wound in the same slots as said second subcoil portion of a first one of said first pair of coils, and said second subcoil portion of said second one of said first pair of coils is wound in a pair of slots offset by one slot position from said slots that said second subcoil portion of said first one of said first pair of coils is wound in; and wherein a second pair of coils circumferentially offset from said first pair of coils is further wound such that a first subcoil portion of a first one of said second pair of coils is wound in the same slots as said first subcoil portion of said second coil of said first pair of coils, and said second subcoil portion of said first one of said second one of second pair of coils is wound in the same slots as said second subcoil portion of said second coil of said first pair of coils.

24. The electric motor of claim 23, wherein one of said first and second subcoil portions of each said coil has a greater number of winding turns that the other of said subcoil portions.

25. The electric motor of claim 23, wherein one of said first and second subcoil portions of each said coil has approximately three times the number of winding turns as the other of said subcoil portions.

26. An electric, rotating machine comprising: a stator having a plurality of field coils, wherein said field coils are spaced apart to form gaps therebetween, said gaps representing magnetic neutral zones; an armature having a plurality of coils wound thereon; and wherein said coils are wound such that each said coil begins, and at least substantially completes, commutation while said coil passes through one of said magnetic neutral zones.

27. The machine of claim 26, wherein said coils are wound such that each said coil begins and completes commutation within one of said magnetic neutral zones, such that no commutation of any of said coils occurs outside of said magnetic neutral zones.

28. The machine of claim 26, wherein each said coil is segmented into two subcoil portions coupled in series.

29. The machine of claim 28, wherein said subcoil portions of first and second ones of said coils are wound such that said subcoil portions of each partially overlap.

30. An electric motor, comprising: a stator having a plurality of field windings spaced apart around said stator, and defining magnetic neutral zones therebetween; an armature having a plurality of coils wound thereon in accordance with a winding pattern defining a greater than one coil per slot construction; wherein first ones of said coils are wound so as to have their magnetic axes advanced, relative to given ones of said field coils, during rotation of said armature; wherein second ones of said coils are wound so as to have their magnetic axes retarded, relative to given ones of said field coils, during rotation of said armture; and wherein said coils are further arranged so as to begin and at least substantially complete commutation within said magnetic neutral zones.