MOTOR ARMATURE HAVING DISTRIBUTED WINDINGS FOR REDUCING ARCING
An armature for a brush commutated electric motor having a distributed coil winding arrangement for reducing brush arcing and electro-magnetic interference (EMI). The winding pattern involves winding a first coil into a first pair of slots of the armature. A second coil having a first subcoil portion is then wound into the same slots as the first coil, while a second subcoil portion of the second coil is wound into a pair of slots that is offset by one slot position from the first pair of slots. The two subcoil portions have the same number of turns, and the total turns of the two subcoil portions equals the number of turns of the first coil. A third coil is then wound in the same slots as the second subcoil portion of the second coil. The third coil has the same number of turns as the first coil. This pattern is repeated around the armature. In a two coil per slot armature, this pattern enables the magnetic axis of each coil to be maintained at a constant angular position relative to the commutator bars to which it is coupled without the need for using uneven numbers of turns for the two subcoil portions of each segmented coil.
This application is a divisional of U.S. Ser. No. 10/936,003, which is a continuation-in-part of U.S. Ser. No. 10/404,857, filed Apr. 1, 2003, which is a divisional of U.S. Ser. No. 09/594,357, filed Jun. 14, 2000, and presently issued as U.S. Pat. No. 6,566,782 on May 20, 2003.
FIELD OF THE INVENTION1. Technical Field
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.
2. Background of the Invention
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
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.
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.
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 INVENTIONThe 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.
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.
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.
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.
In an alternative preferred embodiment of the present invention a motor is disclosed having an armature that incorporates a plurality of coils wound in an overlapping fashion. Alternating ones of the coils are segmented into serially coupled subcoils that overlap with non-segmented coils. This pattern permits the same number of winding turns to be used for the two subcoil portions, while still obtaining the benefits of reduced brush arcing and improved commutation efficiency in a two coil per slot electric motor. In this embodiment slots 1 and 6 of the armature include a plurality of winding turns from a first coil. Slots 1 and 6 of the armature also include a plurality of winding turns from a first subcoil portion of a second coil. The second subcoil portion of the second coil is wound in slots 2 and 7, and thus is offset by one slot position from the first subcoil portion. Each of the two subcoil portions has the same number of turns. The total turns of the two subcoil portions preferably add up to the same number of turns as employed with the first coil. A third coil is then wound in slots 2 and 7 with the same number of winding turns used for coil one. A fourth coil has first and second subcoil portions, with the first subcoil portion being wound in slots 2 and 7 and the second subcoil portion being wound in slots 3 and 8. Thus, the first subcoil portion of the fourth coil overlaps completely the windings of the third coil. This arrangement also helps to smooth out the unevenness in the magnetic coupling between adjacent coils while providing a close coupling between the coils wound in adjacent pairs of winding slots of the armature. This construction further has the advantage of reducing winding costs by reducing the number of winding machine indexes that must be employed, and thus simplifying the motor construction process.
BRIEF DESCRIPTION OF THE DRAWINGSThe 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:
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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 S2 and S7 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.
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.
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.
The above-described pattern for coils 251-254 is repeated until all of the coils (in this example 24 coils) are wound onto the lamination stack 14. Each of the ends of the coils 251-2524 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.
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
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.
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.
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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. A method for forming a power tool, comprising:
- forming a stator having at least a pair of field coils separated by a gap, said gap defining a commutation zone;
- locating the stator within a tool housing;
- locating an armature coaxially relative to the stator, and within the housing;
- forming the armature with a plurality of circumferentially arranged winding slots;
- winding a first coil into a first pair of said winding slots;
- forming a second coil with first and second serially coupled subcoil portions, and winding said first subcoil portion into said first pair of slots, and winding said second subcoil portion into a second pair of slots that are offset by one slot position from said first pair of slots;
- winding a third coil in said second pair of slots; and
- forming a fourth coil with first and second subcoil portions, and winding said first subcoil portion of said fourth coil in said second pair of slots, and winding said second subcoil portion of said fourth coil in a third pair of slots that are offset by one slot position from said second pair of slots; and
- wherein each of said coils at least substantially completes commutation within said commutation zone.
2. The method of claim 1, further comprising winding each of said subcoil portions with approximately half the number of winding turns as said first coil.
3. The method of claim 1, further comprising winding each of said subcoil portions with the same number of winding turns.
4. The method of claim 1, further comprising winding each of said first and third coils with an identical number of winding turns.
5. The method of claim 1, further comprising winding each of said first and third coils with identical numbers of winding turns; and
- winding each of said subcoil portions with identical numbers of winding turns.
6. A method for forming an electric motor, comprising:
- forming a stator having a pair of field coils defining a gap therebetween, the gap defining a commutation zone;
- forming an armature and locating the armature coaxially relative to said stator;
- forming said armature with a plurality of parallel, circumferentially arranged slots;
- winding a first coil in a first pair of said slots;
- forming a second coil in first and second subcoil portions connected serially with one another;
- winding said second coil such that said first subcoil portion is wound in said first pair of slots, and said second subcoil portion is wound in a second pair of slots offset by one slot position from said first pair of slots;
- winding a third coil in said second pair of slots;
- forming a fourth coil having first and second subcoil portions serially connected with one another, and winding said first subcoil portion of said fourth coil in said second pair of slots, and winding said second subcoil portion of said fourth coil in a third pair of slots offset by one slot position from said second pair of slots; and
- wherein each of said coils substantially complete commutation while a magnetic axis of each said coil passes through said commutation zone.
7. The method of claim 6, wherein said electric motor forms an electric motor with twice the number of commutator bars as armature slots.
8. A method for reducing brush arcing in an electric motor, comprising:
- forming a stator having at least a pair of field coils separated by a gap, the gap defining a commutation zone;
- forming an armature with a plurality of circumferentially arranged slots, a second plurality of commutator bars, and locating the armature coaxially adjacent said stator;
- winding a first coil in a first pair of said slots;
- segmenting a second coil into first and second subcoil portions and winding said first subcoil portion in said first pair of slots, and said second subcoil portion in a second pair of slots offset by one slot position from said first pair of slots;
- winding a third coil in said second pair of slots;
- segmenting a fourth coil into first and second subcoil portions, and winding said first subcoil portion of said fourth coil into said second pair of slots and winding said second subcoil portion of said fourth coil into a third pair of slots that are offset by one slot position from said second pair of slots; and
- further arranging said first and second subcoil portions of each of said second and fourth coils such that a magnetic axis of said first subcoil portions are advanced, relative to a pair of commutator bars with which it is associated, and that said second subcoil portions each have a magnetic axis that is retarded, relative to its associated pair of commutator bars; and
- wherein each of said coils substantially completes commutation with said commutation zone.
9. The method of claim 8, wherein said subcoil portions of said third coil each have a magnetic axis, with one of said magnetic axes being retarded, relative to a pair of commutator bars to which said third coil is coupled, and the other of said subcoil portions being advanced, relative to said commutator bars.
10. A method for controlling commutation in an electric motor to reduce brush arcing, the method comprising:
- winding a plurality of slots of an armature with a plurality of first coils and a plurality of second coils;
- forming each of said second coils with first and second subcoil portions;
- winding each of said first coils about a single pair of slots;
- winding said second coils about two spaced apart pairs of slots, and further such that said first subcoil portion thereof is wound in a common pair of slots with one of said first coils, and the second subcoil portion is wound in a pair of slots that is spaced apart, by one slot position, from the first subcoil portion; and
- further winding said subcoil portions such that one of said portions is advanced, relative to a pair of commutator bars with which it is coupled, while the other one of the pair is retarded relative to the same pair of commutator bars.
11. The method of claim 10, further comprising winding each of said subcoil portions with the same number of winding turns.
12. The method of claim 10, further comprising winding each subcoil portion with a lesser number of turns that each said first coil.
13. A method of controlling commutation of an electric motor, comprising:
- forming an armature with a plurality of circumferentially arranged winding slots;
- forming the armature with a circumferentially arranged plurality of commutator bars;
- winding a first coil around a first pair of said slots and coupling said coil to a first pair of adjacent ones of said commutator bars such that a magnetic axis of said first coil is centered over the first pair of commutator bars;
- forming a second coil into first and second subcoil portions, winding said first subcoil portion in the same pair of slots as the first coil and winding said second subcoil portion in a pair of winding slots that is offset by one slot position from said slots in which said first coil is wound in, and coupling ends of said second coil to a second pair of commutator bars that is offset by one said commutator bar from said first pair of commutator bars,
- winding each of said first and subcoil portions with a number of turns such that said a magnetic axis of said first subcoil portion is advanced, relative to said second pair of commutator bars, and a magnetic axis of said second subcoil portion is retarded, relative to said second pair of commutator bars, and further such that a resultant magnetic axis of said second coil is centered over said second pair of commutator bars; and
- each of said first and second coils at least substantially completing commutation with a predetermined, fixed commutation zone.
14. The method of claim 13, further comprising alternating winding said first and second coils around said slots such that one of said subcoil portions is wound in an overlapping pair of slots with one of said first coils.
15. A method for forming an electrically powered power tool, comprising:
- providing a tool housing;
- forming a motor having a stator and an armature disposed coaxially within said stator, and locating the motor within the tool housing;
- forming said stator to have at least a pair of field coils separated by a gap, said gap defining a commutation zone;
- forming the armature with a plurality of circumferentially arranged winding slots;
- forming a first plurality of coils and a second plurality of coils, with each of said second plurality of coils being comprised of first and second serially connected subcoil portions;
- alternately winding ones of said first plurality of coils and ones of said second plurality of coils in slots around said armature such that said first subcoil portion of each coil of said second plurality of coils fully overlaps a previously wound one of said first plurality of coils, while said second one of said subcoils is wound in a pair of slots that is offset from by one slot pitch from said previously wound coil of said first plurality of coils; and
- wherein each one of said first and second pluralities of coils is aligned relative to said gap such that each one of said first and second pluralities of coils substantially completes commutation within said commutation zone.
16. A method for forming an electrically powered power tool, comprising:
- providing a tool housing;
- forming a two-coil-per-slot motor having a stator and an armature disposed coaxially within said stator, and locating the motor within the tool housing;
- forming said stator to have at least a pair of field coils separated by a gap, said gap defining a commutation zone;
- forming the armature with a plurality of circumferentially arranged winding slots;
- forming a first plurality of coils and a second plurality of coils, with each of said second plurality of coils being comprised of first and second serially connected subcoil portions;
- alternately winding ones of said first plurality of coils and ones of said second plurality of coils in said slots around said armature;
- further winding said first and second pluralities of coils such that each one of said second coils has one of its subcoil portions overlapping a previously wound one of said coils of said first plurality of coils; and
- wherein each one of said first and second pluralities of coils is aligned relative to said gap such that each one of said first and second pluralities of coils substantially completes commutation within said commutation zone as said armature rotates.
Type: Application
Filed: Jul 30, 2007
Publication Date: Jan 24, 2008
Inventors: Richard Walter (Baltimore, MD), Ren Wang (Timonium, MD)
Application Number: 11/830,423
International Classification: H02K 15/00 (20060101); H01R 43/10 (20060101);