Brush holder and brush

July 18, 1950

2,515,768

P. C. GARDINER ET AL

BRUSH HOLDER AND BRUSH

Filed Feb. 6, 1948

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Inventors : Char-les W. Frick, Paul C. Gar-diner·,

Their AttorneLj.

Patented July 18, 1950

2,515,768

UNITED STATES PATENT OFFICE

2,515,768

BRUSH HOLDER AND BRUSH

Paul Cooke Gardiner, Scotia, and Charles W. Frick, Schenectady, N. Y., assignors to General Electric Company, a corporation of New Yort

Application February 8,1948, Serial No. 6,736

Claims. (CL 171—823)

This invention relates to brushes and brush holders for dynamoelectric machines. Heretofore, brush holders for electric contact brushes used for contacting a collector such as a commutator of a dynamoelectric machine have had 5 certain disadvantages in that they do not force the brushes down on the collector with true evenness of contact. Where the collector is a commutator, this causes the brush to “tumble” from bar to bar causing excessive wear, poor &gt; operating characteristics and other disadvantages such as the creation of radio interference.

Observation of radio noise generation, as by means of an oscilloscope, serves to indicate that the mere application of properly directed hand &gt; pressure to a conventional brush will result in better commutation with relatively radio-noisefree operation. Such an experiment demonstrates that quiet operation is dependent on good contact between brush and collector especially 20 at the trailing edge of the brush. Yet with conventional brushes and brush holders an initial good contact does not remain as the brush surfaces become worn.

With conventional brushes, the spring action 25 is generally radial with respect to the commutator surface. This establishes a vulnerability to tilting. With a brush having a cross-section of one inch square a tilt of only one tenth of one degree may be sufficient to cause the toe of 30 the brush to lift approximately 1 mil. Even a much smaller lift will cause arcing, bad commutation and high radio noise.

In addition, the performance of the typical “prior art” brush is bad insofar as it “tumbles” 35 from bar to bar with highly varying contact resistance. This is one of the main causes of poor commutation and consequent radio noise.

It is an object of the present invention to provide means for overcoming the above-mentioned difficulties.

It is a further object of the present invention to provide a brush holder and brush adapted to make' a good and even contact with a collector surface. 45

It is a still further object of the present invention to minimize radio noise caused by arcing contact of electric contact brushes with commutator-type collectors.

Broadly the means employed in the embodiments herein illustrated and described comprises a brush holder and brush designed to allow for change of brush contact area with wear. This is done by tilting the brush with respect to the flat (i. e., axially extending) surface of the collector and allowing parts of the brush to turn to follow irregularities of the collector. With a brush and brush holder of our improved design, commutation will be improved and radio noise generation reduced.

Other objects and advantages will become apparent and our invention will be better understood from consideration of the following description taken in connection with the accompanying drawing in which Fig. 1 is a perspective view of a dynamoelectric machine commutator together with a brush holder and segmented brush illustrating one embodiment of our invention; Fig. 2 is an end view, pig. 3 a crosssectional view and Fig. 4 is a transverse view (along the line 4—4 of Fig. 3) of another embodiment of our invention; and Fig. 5 is a perspective view of a commutator together with a brush and brush holder illustrating a third embodiment of our invention.

Referring now to Fig. 1, 10 represents a portion of the stationary frame of a dynamoelectric machine having a commutator It. At each brush position (of which only one is shown) the commutator is contacted by a plurality of “hugging” brush leaves 12 of carbonaceous material. These leaves are separated from each other by an air space except at the top of the leaves where they are all fastened in a conducting brush holder 13, being held in place in said brush holder by a plurality of bolts 14. The entire brush, made up of the leaves 12, has its leading and trailing faces substantially parallel to a plane through the axis of rotation of the commutator and has its front and back faces disposed at a 45 degree angle to a line over the axially extending surface of the commutator periphery to give, through the action of the flexible brush leaves 12 and flat spring member 15, the “hugging” effect desired. Spring member 15 provides the necessary feed to replace the brush with wear. While the mounting shown holds the brush substantially parallel to a plane through the axis of rotation, deviation from this position may be made and the hugging action still retained so long as the brush forms an acute angle in the opposite plane of preferably from 40 to 70 degrees with the surface of the commutator.

It is most important to prevent arcing at the trailing edges of the brush. With operation of a brush on a commutator connected to a rotor coil, the coil inductance tends to maintain the flow of current to an individual commutator bar even though it slips from the edge of the com“ mutating brush. Hence, the voltage of the bar will rise and cause arcing just as it leaves the brush unless this inductive kick of very short duration is by-passed, one means of accomplishing this by-passing is shown in Fig. 1 where, W for the direction of commutator rotation indicated by arrow 16, we have provided a trailing leaf 17. since the trailing leaf 17, even if it is identical with the other leaves, will have a resistance which is greater than the resistance of all •® of the other leaves considered in parallel, this

2,616,768 trailing leaf 17 is adapted to reduce Such an inductive kick before final separation and reduce arcing.

Another embodiment of our invention is shown in Figs. 2, 3 and 4 in which a plurality of brush leaves 21, each comprising a plurality of insulated laminations 22, are positioned in a fabricated brush holder 23 which may conveniently be made of brass and which is adapted to be fastened to the dynamoelectric machine stationary frame member 24 by means of a bolt 25. The individual brush leaves 21 are inclined with respect to the commutator surface the same as the brush leaves in Fig. 1. In the embodiment in Figs. 2, 3 and 4 individual feed springs 26 are provided for each leaf. Feed springs 26 are disassociated from hugging spring members comprising the projecting fingers 27 of fiat plates 28 of metallic spring material, such as steel, arranged above each brush leaf and held in place by slots 29 in the inner faces of the brush holder. The metallic flat plates 28 and the holder 23 serve to contact all of the laminations (which then are effectively insulated from each other only at their ends adjacent the commutator) so that any connection (not shown) to the metallic brush holder 23 will collect current from all of the laminations of all of the brush leaves within the holder. A plurality of screws 30 in slotted recesses 31 of a top angle member 32 may conveniently be used to adjustably vary the pressure exerted by the feed springs

26. The brush holder assembly is conveniently made of two pieces 23a and 23b which are held together by a screw 33. With the direction of commutator rotation indicated by the arrow 34 in Fig. 2, the brush trailing edge is at 35 and the brush leading edge is at 36. It is desirable to have the laminations 22 at 35 of a high resistance to prevent arcing at the trailing edge. With the other laminations, especially those at the center of the brush, of low resistance the rapid reversal of current during commutation will be aided and sparking reduced. A further improvement is effected if the trailing edge material is harder than the material of the more centrally located segments. Such provision allows a higher unit pressure to be automatically maintained at the very important trailing edge of the brush to reduce contact resistance at this point.

In Fig. 5 we have shown a third embodiment of our invention in which a commutator 40 is provided with a solid brush 41 held by a brush holder 42 in a plane through the axis of rotation of the commutator and at an angle of substantially 45 degrees to the axially extending surface of the commutator periphery. The brush holder is attached to the stationary frame 43 of the dynamoelectric machine by means of bolts 44 and the holder is provided with a feed spring 45 and a plurality of hugging springs 46 which cause the brush to turn to follow any irregularities of the commutator and to insure that the leading and trailing edges of the brush are independently held down on the commutator by their respective springs. The hugging springs 46 comprise fingers of spring-like material, such as steel, which are attached to the brush holder and bear on a surface or surfaces of the brush. As shown in Fig. 5, it is desirable to have at least two fingers exerting pressure on the outer inclined surface of the brush, with the two fingers exerting pressure on this surface at opposite sides of the longitudinal center. In this way, with an assumed sloppy fit of the brush in the brush holder, the brush is forced to turn to follow any irregularities in the commutator and achieve the desired hugging action. If desired the solid brush of Fig. 5 may be modified to keep the trailing edge current low with respect to the load current of the brush as by providing a single high resistance lamination at this edge. In each of the three embodiments as illustrated, however, provision is made to assure a good contact at both leading and trailing edge so that there will be only a small contact drop at these points.

It has already been explained how the trailing leaf of Fig. 1 provides means for absorbing the energy of the trailing edge transient. If desired, this trailing edge leaf may be made of a harder material than the other leaves to further insure good contact at the trailing edge as explained in connection with the laminations of Fig. 2.

In the embodiments of Figs. 1-4 it should be noted that each individual leaf is separately sprung and separated from any other leaf by an air space so that it is adapted to individually hug the rounded collector surface, when, as shown, each separate leaf has a collector contacting cross-sectional area having a length (considered in the direction of commutator movement) greater than its width (considered axially across the commutator surface). A similar requirement obtains for a solid brush such as that shown in Fig. 5 which cannot readily be made to hug unless its leading to trailing edge length is greater than its toe to heel width.

With the construction shown in Figs. 2,3, and 4 the main mass of the brush is driven slowly toward the commutator for feed, but is not much involved in vibration periods encountered. Each leaf of the brush is somewhat flexible and follows the commutator irregularities or vibration individually thereby allowing better contact between brush and commutator. With such means, i. e. thin slanting leaves separately sprung, the improvement, in terms of radio noise meter readings, has been found to be about ten to one.

With any of the three embodiments described above, the brush, or individual leaf, is free to “twist” thereby taking advantage of the low moment of inertia around its long axis. This action allows both leading and trailing edges to be simultaneously held on the collector surface.

We thereby accomplish good contact at the various parts of a commutator brush by (1) avoiding the usual tumbling brush design and (2) incorporating individual light weight low resistivity elements or leaves with “good contact” maintained throughout the entire action of the brush.

If desired, a hugging brush of any of the types described may be used as a trailing brush in combination with one or more conventional brushes.

While we have illustrated and described particular embodiments of our invention, it will be understood that numerous variations and modifications may be made without departing from our invention, and we intend in the appended claims to cover any such variations and modifications as fall within the true spirit and scope of our invention.