US2515768A - Brush holder and brush - Google Patents

Description

July 18, 1950 P. c. GARDINER EIAL BRUSH HOLDER AND BRUSH Filed Feb. 6, 1948 Inventors: Charles W. Prick, Paul C. Gar-diner,

Their- Attorney.

Patented July 18, 1950 BRUSH HOLDER AND BRUSH Paul Cooke Gardiner, Scotia, and Charles W. Frick, Schenectady, N. Y., assignon to General Electric Company, a corporation of New York Application February 6, 1948, Serial No. 6,736

evenness of contact. Where the collector is a commutator, this causes the brush to tumble" from bar to bar causing excessive wear, poor operating characteristics and other disadvantage 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 pressure to a conventional brush will result in better commutation with relatively radio-noise-,

free operation. Such an experiment demonstrates that quiet operation is dependent on good contact between brush and collector especially 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 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 suflicient to cause the toe of 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 from bar to bar with highly varying contact resistance. This is one of the main causes of poor commutationand consequent radio noise.

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

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.

. 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 col lector 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 eneration reduced.

(CL rib-323) 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, Fig. 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, l0 represents a portion of the stationary frame of a dynamoelectric machine having a commutator I I. At each brush position (of which only one is shown) the commutator ls-contacted by a plurality of hugging brush leaves I! 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 I3, being held in place in said brush holder by a plurality of bolts II. The entire brush, made up of the leaves I2, 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 degree angle to a line over the axially extending surface of the commutator periphery to give, through the action of the flexible brush leaves l2 and fiat spring member IS, the hugging effect desired. spring member I5 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 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 commutating 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, for the direction of commutator rotation indicated by arrow it, we have provided a trailing leaf ll. Since the trailing leaf ll, 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 the dynamoelectric machine stationary frame member 24 by means of a bolt 25. The individual brush leaves 2| 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 21 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 efl'ectively 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. 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. we have shown a third embodiment of our invention in which a commutator 40 is provided with a solid brush 4| held by a brush holder 42 in a plane throughthe 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 isprovided 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 A plurality of 4 commutator and achieve the desired hug ing 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 tofurther 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 im-- provement, 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 contac 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 l. A dynamoelectric machine having a stationary frame, a rotatable collector member, a brush holder attached to said frame, a separate electrical contact brush element disposed in said brush holder with the longitudinal axis of said brush element approximately in a plane through the axis of rotation of said collector and forming an acute angle with the surface of said collector such that the surface of said brush element in contact with said collector will have a heel portion and a toe portion at right angles to the trailing edge and the leading edge thereof, and means for causing said brush element to feed to said collector surface, and means including a dimensioning of said brush element to provide a substantially greater length from leading edge to trailing edge than from heel to toe thereof for causing said brush element to hug said collector surface.

2. A dynamoelectric machine having a stationary frame, a commutator, a brush holder attached to said frame, an electrical contact brush disposed in said brush holder with the long axis of said brush approximately in a plane through the axis of rotation of said commutator and forming an acute angle of from 40 to '10 degrees with the surface of said commutator, said brush having its shortest axis approximately in a plane through the-axis of rotation of said commutator, and having its third axis extending substantially parallel to the surface of said commutator in the direction of rotation thereof, spring means for causing said brush to feed to said commutator surface, and spring means for causing said brush to hug said commutator surface.

8. In combination a dynamoelectric machine commutator comprising a plurality of metallic commutator bars insulated from each other, a brush holder fastened to the frame of said dynamoelectric machine, a plurality of spaced apart brush leaves adapted to be held by said brush holder with one end of each leaf against the surface of said commutator with the longitudinal axis of said leaves substantially in a plane through the axis of rotation of said commutator and forming an acute angle with the axially extending commutator bars and with said end extending a greater distance along'the direction of rotation of said commutator than transverse thereto to allow each leaf to turn to follow any irregularities of said commutator, and spring means to cause said turning and assure good contact between said commutator and at least the trailing edge of each of said leaves.

.4. In combination a dynamoelectric machine commutator, a brush holder, and a plurality of brush segments partially insulated from each other, the longitudinal axes of said segments forming an acute angle with the longitudinal axes of the commutator bars which said segments contact at their other ends, with at least one of said segments arranged on said commutator so that for a certain direction of commutator rotation it trails the rest of the segments located in the same brush holder to provide a higher resistance at the trailing edge of said assembly, and spring means to cause turning of said segments to assure good contact between said commutator and said segments.

5. A dynamoelectric machine commutator, an electric contact brush comprising a plurality of brush segments, a brush holder adapted to hold said segments apart from each other and against the surface of said commutator at an acute angle with a line parallel to the axis of rotation of said commutator, means including at last one spring interposed between said segments and a portion of said brush holder for feeding said segments inwardly toward said commutator. and additional spring means acting on the outer inclined faces of said segments at each side of the longitudinal center of each segment for causing said segments to turn so as to hug the surface of said commu-- tator'.

6. A dynamoelectric machine commutator, an

electric contact brush comprising a plurality of commutator, means including springs interposed between said segments and a portion of said brush holder for feeding said segments inwardly' toward said commutator, and additional spring means acting on the outer inclined faces of said. segments at each side of the longitudinal center thereof for causing said segments to turn so as to hug the surface of said commutator with each of said segments comprising a pluralitysof mutually insulated laminations with at least one centrally located lamination of each segment of lower resistivity than the lamination at at least one edge of the same segments, and means for conducting current from all of said laminations of all of said segments.

7. A dynamoelectric machine commutator, an electric contact brush comprising a plurality of brush segments, a brush holder adapted to hold said segments apart from each other and against the surface of said commutator at an acute angle with a line parallel to the axis of rotation of said commutator, spring means interposed between said segments and a portion of said brush holder for feeding said segments inwardly toward said commutator, and additional spring means acting on the outer inclined faces of said segments at each side of the longitudinal center thereof for causing said segments to hug the surface of said commutator, each of said segments comprising a plurality of mutually insulated laminations with the lamination at at least one edge of each segment of greater hardness than more centrally located laminations of the same segment, and means for conducting current from all of said laminations of all of said segments.

8. In combination with a dynamoelectric machine having a stationary frame, a commutator, a brush holder attached to said frame, an electric contact brush disposed in said brush holder and forming an acute angle with the surface of said commutator, means including a coil spring for feeding said brush toward said commutator, and means including fingers of spring material attachedto said brush holder and bearing on opposite sides of an inclined face of said brush for causing said brush to hug said commutator surface.

PAUL COOKE GARDINER. CHARLES W. FRICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 289,200 Weston Nov. 27, 1883 407,225 Loomis July 16. 1888 490,449 Lundell Jan. 24, 1893 599,781 Gutmann Mar. 1. 1898 1,743,682 Oswald Jan. 14, 1930

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