US2683829A - Brush holder for electric motors - Google Patents

Description

July 13, 1954 c, GERBER 2,683,829

BRUSH HOLDER FOR ELECTRIC MOTORS Filed Jan. 19, 1950 2 Sheets-Sheet l IN VEN TOR. Dale 6. Genb er BY ATTOHNE Y.

July 13, 1954 D. c. GERBER BRUSH HOLDER FOR ELECTRIC MOTORS 2 Sheets-Sheet 2 Filed Jan. 19, 1950 Patented July 13, 1954 BRUSH HOLDER EOE, ELECTRIC MOTORS Dale G. Gerber, North Canton, Ohio, assignor to The Hoover Company, North Canton, Ohio, a corporation of Ohio Application January 19, 1950, Serial No. 139,463

9 Claims. (01. 310246) This invention relates to electric motors and more particularly to a cartridge type commutator brush holder therefor.

It is usual practice to provide a longitudinally coiled compression spring for holding commutator brushes against the commutator. Such constructions require that the upper end of the cartridge casing be closed to form an abutment for the upper end of the spring which must be removed and replaced each time the brushes are replaced.

In addition, the use of coiled compression springs have a tendency to permit the brush to move sidewise in the cartridge casing and thus produce brush chatter and a consequent rapid wearing of the brush. It is essential that the pressure between the brush and commutator does not go below a minimum. As a result compression springs are designed to give the necessary minimum pressure when the brush is at its minimum length and needs replacement. Thus, when the brush is new the pressure between the brush and commutator is greater than is necessary which results in further excessive wear of the brush.

According to one feature of the present invention, a tension spring is provided which does not require the upper end of the cartridge casing to be closed. Specifically, a flat spring is prestressed so as to naturally wind into a free tight Numerous attempts have been made to prevent brush chatter by holding the entire length of the brush against the trailing edge of the cartridge casing. According to the present invention that result can be readily accomplished by merely positioning the circumference of the free coil against a wedge shaped end of the brush.

According to another object of this invention the hat spring is prestressed in such a manner that it takes a cross sectional camber as it unwinds from the tight volute and the camber is used to press the brush tightly against the brush holder and thus prevent the brush from chattering and the resulting excessive wearing away of the brush.

According to another feature of this invention the spring is prestressed in such a manner that as the diameter of the tight volute increases as the brush wears away to permit more of the spring to wind itself onto the volute the force tending to rewind the spring onto the coil will remain constant.

Other objects and advantages of this invention will become apparent as the description proceeds when taken in connection with the accompanying drawings in which:

Figure 1 is a plan view of a commutator with a pair of cartridge brush holders associated therewith showing how this invention is applied;

Figure 2 is a view of the invention of Fig. l

volute. lhe one end of the spring is then attaken at right angles to Fig. 1; tachecl to the inside of the cartridge casing at its Figure 3 is a view similar to Fig. 2 showing how commutator end and the free coil positioned over the invention is applied to prevent brush chatter; the outer end of the brush so that the natural Figure 4 is a view of the invention of Fig. 3 tendency for the spring to rewind itself onto the taken at right angles to Fig. 3; and coil presses the brush against the commutator. Figure 5 is a cross-sectional view of a modified Another disadvantage in the use of compresform of the invention. sion springs is that the pressure applied to the Referring to Figs. 1 and 2, the commutator is brush decreases as the brush wears away. The represented by the reference numeral ID, the ideal situation is to apply constant pressure to cartridge brush casing by H, the carbon brushes the brushes at all times and complicated linkage 40 by 52, and the pigtail connections by 13. mechanisms have been suggested for that pur- Flat elongated narrow springs [4 are prepose. According to the present invention, such stressed along their length so as to naturally ascomplicated linkage mechanisms are unnecessume a free, tight or solid volute coil l5 of a disary. As long as the unwound portion of the ameter approximately the width of the brushes spring is held. in a straight position, the forces 45 E2. The ends of the springs M are secured to tending to rewind it onto the coil have a negligithe interior of the cartridge casing H at their ble effect. the force applied to the brush commutator ends by rivets It so as to lie between is only that applied by the free portion of the the brushes i2 and the interior of the cartridge spring between the coil and the end of the brush casing l l. which is substantially constant, 50 The free coils 25 are positioned within the cartridge casing H with their edges extending through a slot in the casing and pressing against the outer ends of the brushes l2.

The straight portions of the springs lie between the brushes l2 and the walls of easing ii and therefore there is no tendency for that portion of the spring to exert a force tending to wind itself onto the coils 55. Thus, the only force pressing upon the brush ends is the force exerted by that portion or" bhE spring between the brush end and the periphery of the coil 55. It can thus be seen that the inward force exerted on the ends of the brushes is substantially constant regardless of the length of the brushes.

if the spring is stressed uniformly along its length the inner loop of the coil will assume a circle on its natural radius. As more loops are wound about the inner loop, the radius of the coil will increase and part of the pro-stressed forces will be locked out of action by the tendency to compress the inner loops. Ihus, the coil diameter increases as the brush is shortened from wear and the force pressing inwardly on the brushes will decrease slightly as the diameter of the coil increases. To offset that tendency the spring may be prestressed so as to tend to form a free are or decreasing radius starting from the free end and extending to the end which is attached to the commutator end of the cartridge casing. In other words, the spring is prestressed from end to end in such manner tin t the attached end of the spring will tend to as sume an arc of smaller radius than the radius of the arc its free end tends to assume.

The prestressing of the spring is such that it tends to assume an outwardly bowed camber as it unwinds from the volute. That will cause the spring to hold the brushes in the cartridge casings against sideward movement and thus prevent chatter and the consequent excessive Wear on the brushes.

The modification of Figs. 3 and l is especially designed to prevent chatter of the brushes applying a force tending to hold the entire length of the brush against the cartridge casing on the trailing side. In this modification axes of the coils 55 are rotated 96 from the position of Figs. 1 and 2 so that they are parallel to the axis of the commutator and the slots ll are on the trailing side of the cartridge casing. The tops of the brushes !2 are wedge shaped and slope downwardly toward the leading side thereof. Thus, the pressure exerted by the coil 55 will hold the outer ends of the brushes l2 against the trailing side of the cartridge casing and the rotation of the commutator will hold their inner ends against it.

That will prevent the brushes from moving sideward in the cartridge casing to prevent chatter of the brushes and the consequent excessive wear.

Referring to Fig. 5 the brush holder 26 has a channel 2? to receive the spring i5. The channel 26 does not extend the entire width of the holder 29 so that shoulders 22 are formed. shoulders 22 form close fitting guides for tl e brush 12 while the channel 21 is of such depth to receive springs having the maximum camber. in manufacturing springs it is difdcult to make them all with the same camber and according to this modification the tolerances of the springs need not be held so closely as in the other modifications.

It is to be noted that in this modification the camber of the spring does not hold the brush against the side of the holder. In order to vent brush chatter some expedient such shown in Figs 3 and l may be resorted to.

From the foregoing, it can be seen that this invention provides an arrangement in which the commutator brushes are given a substantially constant pressure regardless of the length thereof and are prevented from chattering. in each modification it only necessary to pull the coils outwardly of the cartridge casing in order to replace brushes.

While I have shown but two modifications of my invention, it is to be understood that these modifications are to be taken as illustr and not in a limiting sense. I do not wish to be limited to the particular structure shown and described, but to include all equivalent variations thereof except as limited by the scope or" the claims.

I claim:

1. A. commutator brush holder comprising, an elongated brush casing, and a elongated spring in said casing and or a w n to fit edge- Wise in said casing having a straight portion at one end secured to the commutator end of and within said casing and its other coi. into prethat spring extends into said casing heter thereof and a brush positioned ther y the tendency of the straight portion of spring to rewind itself is locked out of action.

3. A commutator brush holder according to claim 2 in which said spring is prestressed 1g its length in such manner that the free end forms a solid coil whereby the entire length of said spring tends to rewind itself about coil.

4. A commutator brush holder according to claim 3 in which said spring is prcstressed in such manner as to form an outward camber as it is unwound from said coil whereby camber Will press against the brush in said casing to hold it from chattering yet permit it to move freely through said casing.

5. A cartridge type commutator brush comprising, an elongated brush holder in the form of a casing, a carbon brush in said and a flat elongated spring inside said casing ha ng a fiat portion at one end secured to the interior of said casing at the commutator end thereof and extending outwardly along the side of s d brush and having its free end coiled a seirewinding volute resting against the outer end of said brush.

6. A commutator brush according to claim 5 in which said spring is prestressed along its entire length so as to tend to wind itself tightly about said volute.

7. A commutator brush according to claim 6 in which the outer end of said brush wedgeshaped having its long edge at the trailing le of said casing whereby said spr ng tends to hold the outer end of said brush against the trailing side of said casing.

8. A commutator brush according to claim 5 in which the prestressing of said spring varies along its length in such manner hat the commutator end of said spring tends to form an arc of smaller radius than that of its free end.

9. A commutator brush according to claim 5 in which said holder is provided with a channel 5 6 for receiving said, spring and said spring is pre- Number Name Date stressed so as to form an outwardly bowed 1,964,280 Witchger June 26, 193}; camber as it is unwound from said volute. 1,977,546 Fornelius Oct. 16, 1934 2,273,644 Hope Feb. 17, 1942 References Cited in the file of this patent 5 2,280,735 Weissinger Apr. 21, 1942 UNITED STATES PATENTS 2,647,743 (300k u 1953 Number Name Date FOREIGN PATENTS 2,288 Smith DEC. 26, 1871 Number Country Date 65 Van D p le F 2 1890 10 603,159 Germany Sept. 25, 1934 gofig l l J I- g 658,776 Germany Apr. 11, 1938 un e u y 697,432 Bassett Apr. 15, 1992 OTHER REFERENCES 728,273 Mix May 19, 1903 Publication Product Engineering, July 1.949, 1,488,575 Wagner Apr. 1, 1924 F pages 136 to 140. 1,495,203 Robel'g May 27, 1924

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