CA1169463A - Capacitive brush construction for a dc machine - Google Patents
Capacitive brush construction for a dc machineInfo
- Publication number
- CA1169463A CA1169463A CA000375649A CA375649A CA1169463A CA 1169463 A CA1169463 A CA 1169463A CA 000375649 A CA000375649 A CA 000375649A CA 375649 A CA375649 A CA 375649A CA 1169463 A CA1169463 A CA 1169463A
- Authority
- CA
- Canada
- Prior art keywords
- brush
- main
- auxiliary
- brush portion
- commutator
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R39/00—Rotary current collectors, distributors or interrupters
- H01R39/02—Details for dynamo electric machines
- H01R39/46—Auxiliary means for improving current transfer, or for reducing or preventing sparking or arcing
Landscapes
- Motor Or Generator Current Collectors (AREA)
- Dc Machiner (AREA)
Abstract
Case 2595 CAPACITIVE BRUSH CONSTRUCTION FOR A DC MACHINE
ABSTRACT OF THE DISCLOSURE
A brush arrangement for use in a DC dynamo-electric machine to reduce the sparking which can occur at the trailing edge of a brush as it leaves a commutator segment. The main brush portion has affixed to the trailing side an auxiliary brush portion which is insulated from the main brush portion and from the brush holder.
The auxiliary brush portion is normally much thinner than the main brush portion. A capacitor connects the main and auxiliary brush portions.
ABSTRACT OF THE DISCLOSURE
A brush arrangement for use in a DC dynamo-electric machine to reduce the sparking which can occur at the trailing edge of a brush as it leaves a commutator segment. The main brush portion has affixed to the trailing side an auxiliary brush portion which is insulated from the main brush portion and from the brush holder.
The auxiliary brush portion is normally much thinner than the main brush portion. A capacitor connects the main and auxiliary brush portions.
Description
i3 - 1 - Case 2595 CAPACITIVE BRUSH CONSTRUCTION FOR A DC MACHINE
This invention relates to a brush construction for brushes used in DC dynamoelectric machines.
In DC dynamoelectric machines having a commutator and electrical brushes contacting segments of the commutator, there is a tendency for sparking to occur at the edge of a brush as a commutator segment is leaving -the brush face. In such a dynamoelectric machine there is a coil or winding connecting each commutator segment to another to form a curr~nt path from a first brush, through the commutator segment under the brush face, through the winding connected between that commutator segment to another segment underneath a second brush, and out from that second brush. The winding has inductance and, as a commutator segment connected to the winding leaves a brush face and interrupts the current through the inductive winding, there is a tendency for sparking. The sparking is undesirable.
It is a feature of the present invention to provide a brush construction which reduces or eliminates sparking when a commutator segment Ieaves a brush face.
It is another feature of the invention to provide an auxiliary brush-adjacent the trailing edge of the main brush and having a capacitive connection with the main brush to reduce spar~ing.
- ' ' ,' .
.
Case 2595 The present invention thus proposes an auxiliary brush, which for convenience and strength may be secured to the main brush by an insulating means and interconnected with the main brush by a capacitor. For example, the auxiliary brush may be cemented to the trailing side of the main brush using an insulating cement. The auxiliary brush must, of course, be insulated from the brush holder.
While it is not usual, it is possible that sparking may occur at the leading edge of a brush as a commutator segment moves under the brush. This might occur in a machine with a high flux density and there-fore a high voltage gradient at the brush. If there is a sparking problem at the leading edge of a brush, then an auxiliary brush could be provided closely adjacent the leading edge and connected to the main brush by a capacitor.
Therefore, in accordance with one form of the present invention there is provided a brush construction for a DC dynamoelectric machine, comprising a main brush portion having opposite main surfaces, and an auxiliary brush portion mounted adjacent one of said surfaces and insulated therefrom.
In accordance with another form of the invention there is provided in combination with a brush holder for a DC dynamoelectric machine having a commutator, a brush construction for reducing sparking comprising, a main brush portion having a width for extending across said commutator and a thickness for extending in the direction of rotation of said commutator, the said thickness being defined by a leading side and a trailing side with respect to said direction of rotation, a layer of insulating material on said trailing side, an auxiliary brush portion mounted adjacent said layer of insulating .
:
11~;9~3 Case 2595 material and having substantially the same width as said width of said main brush portion and having a thickness smaller than the thickness of said main brush portion, means for insulating said auxiliary brush portion from said brush holder, and a capacitor connecting said main brush portion and said au~iliary brush portion.
The present invention will be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic cross-sectional view of a brush and a portion of commutator, Figure 2 is a schematic cross-sectional view, similar to Figure 1, showing in addition an auxiliary brush portion, and Figure 3 is an isometric view of the brush according to an embodiment of the invention.
Referring now to Figure 1, there is shown schematically a brush 10 resting on a surface 11 of a commutator 12. The brush is mounted in a brush holder which is not shown and does not form part of the invention. The commutator ]2 has a plurality of commutator segments 14 separated from one another by insulation 13. The commutator segments 14 are joined by coils or windings 15 which, as is well known, carry the current from one brush to another.
Only one brush is shown in Figure 1. The commutator 12 is, of course, mounted on the rotor of a DC dynamo-electric machine (not shown~ in a manner well known in the art. The direction of rotation of the commutator is indicated by arrow 16. The brush 10 has opposite main surfaces 18a and 18b facing the direction of rotation and the opposite direction.
Sparking occurs at area 17, i.e., on the side of the brush facing the direction of rotation and referred .,....... . " . . . . . .
'~' '' ' : ' .
s9l~3 Case 2595 to as the trailing side, when a commutator segment, shown as segment 14a in Figure 1, moves away from the brush. This is due to the inductance of the coils.
Figure 2 shows a similar arrangement, however the brush lOa now has an auxiliary brush 20 which is conveniently mounted to the trailing side of brush lOa using an insulating adhesive 21.
The brush 20 must be insulated from the brush holder in which it is mounted. The auxiliary brush 20 may, of course, be mounted by other means such as an insulating tape encircling brush lOa and auxiliary brush 20 with an insulating material 21 sandwiched between them. Again the auxiliary brush should be insulated from the brush holder when a common brush holder is used. The auxiliary brush 20 could be mounted in a separate brush holder, if desired, provided the separate brush holder could be mounted closely adjacent so the brush 20 engaged the 2Q commutator closely adjacent brush 10. The auxiliary brush 20 may be relatively thin as it carries only small amounts of current as compared to main brush lOa.
The brush lOa and brush 20 are connected by a capacitor 22 which is conveniently connected at the brush pigtails 23. The capacitance value of~capacitor 22 is not critical. In fact, there is frequently a reduction of sparking when no external capacitor is used and the auxiliary brush 20 is not connected to anything, i.e., the brush 20 engages the commutator but is insulated from brush lOa and from the brush holder and no external capacitor used. Presu~ably the sma]l amount of inherent capacitance bet~een the brushes lOa and 20 is sufficient to cause some reduction in sparking. However, the use of an external capacitor is preferred.
, ~ ' ' , :
, Case 2595 Capacitors having values between 50 micro-farads and 0.1 microfarads were tested on a 100 HP
motor under various loads. All the values tested, including 0.1 microfarad capacitors, eliminated the sparking for all practical purposes. The size of the capacitor probably has a relationship to the amount of inductance in the windings and the level of current.
However, the value is not critical and a suitable value can readily be found by trial.
It was previously mentioned that sparking could also occur at the leading edge of a brush in a machine with a very high flux density. If there is sparking at the leading edge, a similar auxiliary brush and connecting capacitor can be used to eliminate it.
Figure 3 is an isometric view of one form of brush according to the invention. The brush lOa in Figure 3 i5 of a normal carbon composition and has auxiliary brush 20 of the same material mounted to the trailing side. A capacitor 22 extends to connect the brush 20 to pigtails 23 of brush lOa.
It is believed that the brush has been adequately described and variations in form and structure suitable for different installations will be apparent.
,, - .
' ' " . ' : ~
.
. ', .
This invention relates to a brush construction for brushes used in DC dynamoelectric machines.
In DC dynamoelectric machines having a commutator and electrical brushes contacting segments of the commutator, there is a tendency for sparking to occur at the edge of a brush as a commutator segment is leaving -the brush face. In such a dynamoelectric machine there is a coil or winding connecting each commutator segment to another to form a curr~nt path from a first brush, through the commutator segment under the brush face, through the winding connected between that commutator segment to another segment underneath a second brush, and out from that second brush. The winding has inductance and, as a commutator segment connected to the winding leaves a brush face and interrupts the current through the inductive winding, there is a tendency for sparking. The sparking is undesirable.
It is a feature of the present invention to provide a brush construction which reduces or eliminates sparking when a commutator segment Ieaves a brush face.
It is another feature of the invention to provide an auxiliary brush-adjacent the trailing edge of the main brush and having a capacitive connection with the main brush to reduce spar~ing.
- ' ' ,' .
.
Case 2595 The present invention thus proposes an auxiliary brush, which for convenience and strength may be secured to the main brush by an insulating means and interconnected with the main brush by a capacitor. For example, the auxiliary brush may be cemented to the trailing side of the main brush using an insulating cement. The auxiliary brush must, of course, be insulated from the brush holder.
While it is not usual, it is possible that sparking may occur at the leading edge of a brush as a commutator segment moves under the brush. This might occur in a machine with a high flux density and there-fore a high voltage gradient at the brush. If there is a sparking problem at the leading edge of a brush, then an auxiliary brush could be provided closely adjacent the leading edge and connected to the main brush by a capacitor.
Therefore, in accordance with one form of the present invention there is provided a brush construction for a DC dynamoelectric machine, comprising a main brush portion having opposite main surfaces, and an auxiliary brush portion mounted adjacent one of said surfaces and insulated therefrom.
In accordance with another form of the invention there is provided in combination with a brush holder for a DC dynamoelectric machine having a commutator, a brush construction for reducing sparking comprising, a main brush portion having a width for extending across said commutator and a thickness for extending in the direction of rotation of said commutator, the said thickness being defined by a leading side and a trailing side with respect to said direction of rotation, a layer of insulating material on said trailing side, an auxiliary brush portion mounted adjacent said layer of insulating .
:
11~;9~3 Case 2595 material and having substantially the same width as said width of said main brush portion and having a thickness smaller than the thickness of said main brush portion, means for insulating said auxiliary brush portion from said brush holder, and a capacitor connecting said main brush portion and said au~iliary brush portion.
The present invention will be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic cross-sectional view of a brush and a portion of commutator, Figure 2 is a schematic cross-sectional view, similar to Figure 1, showing in addition an auxiliary brush portion, and Figure 3 is an isometric view of the brush according to an embodiment of the invention.
Referring now to Figure 1, there is shown schematically a brush 10 resting on a surface 11 of a commutator 12. The brush is mounted in a brush holder which is not shown and does not form part of the invention. The commutator ]2 has a plurality of commutator segments 14 separated from one another by insulation 13. The commutator segments 14 are joined by coils or windings 15 which, as is well known, carry the current from one brush to another.
Only one brush is shown in Figure 1. The commutator 12 is, of course, mounted on the rotor of a DC dynamo-electric machine (not shown~ in a manner well known in the art. The direction of rotation of the commutator is indicated by arrow 16. The brush 10 has opposite main surfaces 18a and 18b facing the direction of rotation and the opposite direction.
Sparking occurs at area 17, i.e., on the side of the brush facing the direction of rotation and referred .,....... . " . . . . . .
'~' '' ' : ' .
s9l~3 Case 2595 to as the trailing side, when a commutator segment, shown as segment 14a in Figure 1, moves away from the brush. This is due to the inductance of the coils.
Figure 2 shows a similar arrangement, however the brush lOa now has an auxiliary brush 20 which is conveniently mounted to the trailing side of brush lOa using an insulating adhesive 21.
The brush 20 must be insulated from the brush holder in which it is mounted. The auxiliary brush 20 may, of course, be mounted by other means such as an insulating tape encircling brush lOa and auxiliary brush 20 with an insulating material 21 sandwiched between them. Again the auxiliary brush should be insulated from the brush holder when a common brush holder is used. The auxiliary brush 20 could be mounted in a separate brush holder, if desired, provided the separate brush holder could be mounted closely adjacent so the brush 20 engaged the 2Q commutator closely adjacent brush 10. The auxiliary brush 20 may be relatively thin as it carries only small amounts of current as compared to main brush lOa.
The brush lOa and brush 20 are connected by a capacitor 22 which is conveniently connected at the brush pigtails 23. The capacitance value of~capacitor 22 is not critical. In fact, there is frequently a reduction of sparking when no external capacitor is used and the auxiliary brush 20 is not connected to anything, i.e., the brush 20 engages the commutator but is insulated from brush lOa and from the brush holder and no external capacitor used. Presu~ably the sma]l amount of inherent capacitance bet~een the brushes lOa and 20 is sufficient to cause some reduction in sparking. However, the use of an external capacitor is preferred.
, ~ ' ' , :
, Case 2595 Capacitors having values between 50 micro-farads and 0.1 microfarads were tested on a 100 HP
motor under various loads. All the values tested, including 0.1 microfarad capacitors, eliminated the sparking for all practical purposes. The size of the capacitor probably has a relationship to the amount of inductance in the windings and the level of current.
However, the value is not critical and a suitable value can readily be found by trial.
It was previously mentioned that sparking could also occur at the leading edge of a brush in a machine with a very high flux density. If there is sparking at the leading edge, a similar auxiliary brush and connecting capacitor can be used to eliminate it.
Figure 3 is an isometric view of one form of brush according to the invention. The brush lOa in Figure 3 i5 of a normal carbon composition and has auxiliary brush 20 of the same material mounted to the trailing side. A capacitor 22 extends to connect the brush 20 to pigtails 23 of brush lOa.
It is believed that the brush has been adequately described and variations in form and structure suitable for different installations will be apparent.
,, - .
' ' " . ' : ~
.
. ', .
Claims (3)
1. In combination with a brush holder for a DC dynamoelectric machine having a commutator a brush construction for reducing sparking comprising, a main brush portion having a width for extending across said commutator and a thickness for extending in the direction of rotation of said commutator, the said thickness being defined by a leading side and a trailing side with respect to said direction of rotation, a layer of insulating material on said trailing side, an auxiliary brush portion mounted adjacent said layer of insulating material and having substantially the same width as said width of said main bursh portion and having a thickness smaller than the thickness of said main brush portion, means for insulating said auxiliary brush portion from said brush holder, and a capacitor connecting said main brush portion and said auxiliary brush portion.
2. The combination as defined in claim 1 in which said means for insulating said auxiliary brush portion from said brush holder comprises a layer of insulating material applied to said auxiliary brush portion.
3. The combination as defined in claims 1 and 2 in which said capacitor has a capacitance value of at least 0.1 microfarad.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000375649A CA1169463A (en) | 1981-04-16 | 1981-04-16 | Capacitive brush construction for a dc machine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000375649A CA1169463A (en) | 1981-04-16 | 1981-04-16 | Capacitive brush construction for a dc machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169463A true CA1169463A (en) | 1984-06-19 |
Family
ID=4119753
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375649A Expired CA1169463A (en) | 1981-04-16 | 1981-04-16 | Capacitive brush construction for a dc machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1169463A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0239230A2 (en) * | 1986-02-21 | 1987-09-30 | Hitachi, Ltd. | Current-collecting brush apparatus |
| US20130264906A1 (en) * | 2012-04-09 | 2013-10-10 | Johnson Electric S.A. | Multi-Layer Brush |
-
1981
- 1981-04-16 CA CA000375649A patent/CA1169463A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0239230A2 (en) * | 1986-02-21 | 1987-09-30 | Hitachi, Ltd. | Current-collecting brush apparatus |
| EP0239230A3 (en) * | 1986-02-21 | 1988-03-30 | Hitachi, Ltd. | Current-collecting brush apparatus |
| US20130264906A1 (en) * | 2012-04-09 | 2013-10-10 | Johnson Electric S.A. | Multi-Layer Brush |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |