US2813208A

US2813208A - Electrical contact brush

Info

Publication number: US2813208A
Application number: US424433A
Authority: US
Inventors: George D Ritter
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-04-20
Filing date: 1954-04-20
Publication date: 1957-11-12
Anticipated expiration: 1974-11-12

Description

2 Sheets-Sheet INVHV & K

TOR. GEORGE D. RITTER ATTORNEY Nov. 12, 1957 s. D. RITTER ELECTRICAL CONTACT BRUSH M v I 3 m, 94% 5 7 Filed April 20. 1954 Nov. 12, 1957 G. D. RITTER 2,313,203

- ELECTRICAL CONTACT BRUSH Filed April 20. 1954 2 Sheets-Sheet 2 FIG. 8

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- INVENTO GEORGE o. m R

ATTORREY United States Patent ELECTRICAL CONTACT BRUSH George D. Ritter, Uniontown, Ohio Application April 20, 1954, Serial No. 424,433

8 Claims. (Cl. 310-247) This invention relates to an electrical contact brush of the type used to provide sliding electrical contact in electrical machines.

The invention has particular application in small commutator-type electric motors having a pair of springpressed contact brushes, usually of carbon or graphite, which apply a voltage to the armature by making sliding contact with a rotating commutator. These brushes are subjected to substantial frictional Wear, and also to a certain degree electrical arcing, such that the commutatorcontacting ends of the brushes are slowly consumed or reduced until they become too short to operate properly and consequently must be replaced. If replacement is not made promptly, when a brush does become too short to operate properly, the usual metal spring which urges the brush against the commutator either feeds against a part of the brush holder and leaves the brush without tension or else continues to follow the brush until it touches the commutator; In either event, the commutator is subjected to serious damage from excessive wear and arcing.

It is the chief object of this invention to prevent the occurrence of such damage by providing an improved brush unit for a motor, for example, which will automatically urge the spring-pressed contact brush away from contact with the motor commutator, when a prede-.

termined portion of the contact end of the brush has been consumed by natural wear, thus breaking the usual armature circuit and stopping the motor.

Further objects of the invention are to provide various embodiments which are simple in construction, inexpensive to manufacture and dependable in operation. All embodiments, however, make use of a spring-loaded plunger located in the upper portion of the contact brush and so arranged as to be the sole contact with the commutator upon being released by the wearing away of the brush material normally restraining said plunger. When released electrically the end of the plunger which pushes against the commutator is insulated from the contacting portion of the brush assembly, whereby upon contact of the plunger with the commutator the motor is stopped.

These and other objects of the invention will be manifest from the following brief description and the accompanying drawings.

Of the accompanying drawings:

Figure 1 is a fragmentary cross-sectional view of an electric motor, having therein a contact brush unit embodying the features of the invention in inoperative condition.

Figure 2 is a vertically transverse cross-section, on a larger scale, taken substantially on the line 2-2 of Figure 1.

Figure 3 is a cross-section which is the same as Figure 2, except that it illustrates a worn condition of the contact brush in which the motor is rendered inoperative.

Figures 4 and 5 are vertical cross-sections illustrating modified forms of brush bodies.

Figure 6 illustrates a vertical cross-section of a modified form of safety plunger utilized with the brush unit of Figures 1 to 3.

Figures 7 and 8 are cross-sections corresponding to Figures 2 and 3, respectively, but illustrating a modified form of brush unit.

Referring particularly to Figures 1 and 2 of the drawings, a brush holder unit 10 is shown mounted in a housing 11 of an electric motor 12, in association with the usual motor commutator 13, and in conjunction with an oppositely disposed like brush holder unit (not shown). Brush holder unit 10 may include a contact brush or member 14, embodying the features of the invention, axially slidably received in an electro-conductive metal sleeve 15 which is in turn secured within an insulating sleeve 16 secured in an opening 16a through the wall of motor casing 11, the inner or contact end of brush 14 normally being yieldingly pressed against the commutator 13 by a compression spring 17 connected between the outer end of the contact brush and a cap 18 removably threaded in the outer end of metal sleeve 15. The cap 18 is removable for ready installation or replacement of the contact brush 14 and associated parts. The improved contact brush 14 may be of the usual round or rectangular cross-section, and made of suitable electro-conductive material, such as carbon or graphite.

Safety means is provided to prevent damage to the motor upon the brush 14 becoming substantially worn, as described above. Accordingly, extending axially to be a substantial depth from the outer end of the brush may be a cylindrical bore 19 (see Figure 2) within which is press-fitted or otherwise attached a hollow metal retainer sleeve 20, which protrudes beyond the outer end of the brush. Also, a plunger element 22 is axially shiftably mounted within retainer sleeve 20 to be yieldingly pressed against the normally solid inner end of said bore 19, said element being of electrical insulating material, such as bakelite, ceramic, hard rubber or fiber. For urging said plunger into said yielding contact with the inner end of bore 19, the plunger 22 is shown provided with a reduced stem portion 23 defining an annular shoulder 24, between which shoulder and a backing wall 25, provided at the outer end of the retainer sleeve 20, may extend a compression spring 26. In order to accomplish most efiiicient operation of the plunger in use, as will be described later, the inner end of bore 19 may terminate in an annular groove 27 defining an axially outwardly convex protuberance which is normally yieldingly engaged by an oppositely convex inner face portion 28 of the plunger.

In addition to provision of a press-fit between sleeve 20 and brush 14, the contacting surfaces of these two parts may also be bonded with suitable cement to insure against loosening of the parts during the life of the brush assembly.

A section of shunt wire 29 may be soldered or otherwise connected between the top of metal retainer sleeve 2%) and a metal disc 30 backed against removable cap 18, thereby providing an electrical conductor to the brush through said retainer. Thus, the complete brush assembly may include the encased plunger 22 and spring 26, shunt wire 29, cap or disc 30, and spring 17. For this purpose the outer end of spring 17 is shown engaging disc 30 to hold it backed against threaded cap 18.

The arrangement of parts described above completes a conductive path between leads 32 of two such brush units 10 through which an electric current can pass. Included in this path are two brushes 14 and their respective brush holders 15, shunts 29, caps 30, etc., the bars of commutator l3 normally constantly contacted by said brushes, and the usual winding in armature 33 of the motor. As longas both brushes ldof. the motor are in electrical contact with cornmutatorlS the motor may beoperated; On the otherhand, the armatur will not rotate, as a motor, unless current passing. through its winding and as a flow of current depends on both brushes making contact with the commutator 13, it'follows that if either brush were pushed away from the commutator a sufficient distance to breal contact the motor would stop operating, This s ould be kept in mind in connection with subsequent explanation-of the operationof the improved brush assembly embodying the above-described specific features of the invention.

In use of the invention in connection with an electric motor 12 as described, the safety feature of the improved brush assembly does not come into play until at least one brush has become worn to a point where the commutator-bearing surface thereof extends across the innermost end of the respective brush bore 19, Whereby, as shown in Figure 3, the dielectric plunger 22 will be urged outwardly of the bore and into contact with the commutator 13, the spring 26 at the same time being sufiiciently strong to overcome whatever predeterminate compressive strength remains in compression spring 17 and urge the brush out of effective electrical contact with commutator 13, and otherwise preventing damage to themotor by cutting off current to the armature 33. The motor can be operated again only after replacement of the worn brush assembly.

Figures 4 and show modified forms of brush members corresponding to brush member 14, as best shown in Figure 2, but having different shapes of inner end walls 34 which simplify manufacture by certain methods.

Figure 6 shows a modified form of plunger corresponding to plunger 23 in Figure 2, but being a metal pin 35 having an enlarged head or plunger part 36 covered with a layer of dielectric material.

Figure 7 corresponding to Figure 2, shows a brush holder unit 37, which includes in operative condition a modified form of brush assembly 38, incorporated in substantially the same brush-mounting or brush-holding means as before, like numerals being given to the same parts, unless otherwise noted.

A brush member 39, of the same suitable shape and material as brush 14, however, may have a cylindrical recess or bore 40 extending axially inwardly from the outer end thereof to somewhat less than half the original length of the brush, and a cylindrical pin or plunger 42 of hard insulating material axially slidably received in said bore is spring-pressed toward stop engagement of the inner end of the pin with the corresponding end of the bore. For this purpose, the outer end of the pin 42 has a slot 43 therein retaining a cross-piece d4 of a double-acting spring 45, to have a compression spring part 46 compressively extended between the and a disc 47 backedagainst screw cap 13 threaded in the outer end of brush holder sleeve i5. Thus, the spring part 46 by pressing the pin inwardly against the inner endof the bore 49, also serves to urge brush member 39 into electrical contact with commutator An integral'tension spring part 48 of spring extends inwardly of cross-piece 44 and has its inner end firmly anchored to a reduced neck portion oi 1e outer end of brush 39, the arrangement being such 48 is maintained under tension, but is r tiveto urge the pin relative to the brush. 7

In use of the brush unit of Figure 7 the brush 39 will, by continued spring-pressed contact with rotating cornmutator as before, eventually become shortened by wear to a point at which 'bore 4% will be opened at its inner end, as shown in Figure 8. At this point spring part 46 will urge the pin 42 to break through'the inner end of the brush into direct contact. withcommutator "13, and at the same time the normally extended tension spring part 48 will be allowed to contract and thereby draw the brush out of electrical contact with the commutator (see Figure 8). In this way, as in the case of the brush unit shown in Figures 1 to 3, predetermined maximum wear on thebrush-prevents damage to the motor by cutting ofi current to the armature 33.

Other modifications of the invention. may be resorted to without departing from the spirit thereof or the scope of the appended claims.

What is claimed is: V

l. A contact brush adapted to fit in the usual brush holder unit of an'electrical machine for providing electrical contact with a movable part of said machine, comprising a contact member axially shiftable in said unit, said contact member having an inner contact end and an opposite end, spring means connected to said opposite end pf said member adaptedin use to yieldingly urge the member into contact of said contact end thereof with said moving part, said member having a recess in said opposite end extending. to substantial depth axially of the member, a dielectric element received in said member recess, and resilient means between the member and element yieldingly tending to urge said element inwardly of the member, whereby upon said member being worn in use to point of opening said inner end of said member recess said. element is urged by said resilient means toward sole contact with said movable part, said element having a portion protruding axially outwardly from said recess of the member, said spring means including a compression spring compressively extended axially outward from said protruding portion of said element and a tension spring tensionally connected between the protruding portion of the element andthe member. 7

2. A contact'brush adapted to fit in the usual brush holder unit of an electrical machine for providing electrical contact with a'movable part of said machine, comprising a contact member axially shiftable in said unit, said contact member having aninner contact end and an opposite end, spring means connected to said opposite end of said member adapted in use to yieldingly urge the member into contact of said contact end thereof with said moving part, said member having a recess in said oppoiste end extending to substantial depth axially ward from said protruding portion of said element and a a tension spring tensionally connected bet veen the protruding portion of the element and the member, said tension spring being an integral extension of said compression spring and connected thereto by a cross-piece, said' protruding portion of said element having a recess in the end'thereof receiving said cross-piece.

3. A contact brush adapted to fit in the usual brush holder unit of an electrical machine for providing electrical contact with a movable part of said machine, comprising a contact member axially shiftable in said unit, said contact member having an inner contact end and an opposite end, a cylindrical recess in said opposite end extending to substantial depth axially of the member, a dielectric element received in said recess with a sliding fit, said element having a length greater than the depth of the recess and thus leaving a protruding end, a com pression spring connected to the protruding end of said element and extending outwardly therefrom adapted in use to 'yielding'ly maintain contact between said contact end of the member and said movable part, and a tension spring tensionally connected between the protruding end of said element and said opposite end of the member, whereby upon said member being worn down in use to point of opening the inner end of said recess said member is retracted leaving said dielectric element in sole contact with said movable part, said tension spring being an integral extension of said compression spring and connected thereto by a cross-piece, said protruding end of said element having a recess receiving said crosspiece.

4. A contact brush adapted to fit in the usual brush holder unit of an electrical machine for providing electrical contact with a movable part of said machine, comprising a contact member axially shiftable in said unit, said contact member having an inner contact end and an opposite end, said member having a recess in said opposite end extending to substantial depth axially of the member, a dielectric element sfidably received in said recess, compression spring means extending between the end of said element outwardly of said recess and a fixed part of the holder unit adapted in use yieldingly to maintain contact between said contact end of the member and said movable part, and a tension spring tensionally connected between the said element and said opposite end of the member and operable upon said member being worn down in use to point of opening the inner end of said recess to retract said member, and thereby leaving said dielectric element in sole contact with said movable part, said tension spring being an integral extension of said compression spring and having a cross-piece connected to the end of said element outwardly of said member recess.

5. A contact brush adapted to fit in the usual brush holder unit of an electrical machine for providing electrical contact with a movable part of said machine, comprising a contact member axially shiftable in said unit, said contact member having an inner contact and and an opposite end, said member having a recess in said opposite end extending to substantial depth axially of the member, a dielectric element slidably received in said recess, compression spring means extending between the end of said element outwardly of said recess and a fixed part of the holder unit adapted in use yieldingly to maintain contact between said contact end of the member and said movable part, and a tension spring tensionally connected between the said element and said opposite end of the member and operable upon said member being worn down in use to point of opening the inner end of said recess to retract said member, and thereby leaving said dielectric element in sole contact with said movable part.

6. In a contact brush adapted to fit in the usual brush holder of an electrical machine for providing electrical contact with a movable part of said machine, a contact member adapted to be axially shiftable in a said brush holder, said contact member having-a contact end and an opposite end, said member having a cylindrical bore extending axially inwardly from said opposite end to within a predetermined distance of said contact end, an insulated pushing element slidably received in said bore, pressure means adapted in normal use yieldingly to urge said element against the inner end of said bore and thereby through said element to maintain contact between said contact end of the member and said movable part, and spring means connected between said element and said member and operable independently of said pressure means upon said contact end being worn away a said predetermined distance to urge said contact member away from said movable part, and thereby leaving said in sulated pushing element in sole contact with the said movable part.

7. In a contact brush adapted to fit in the usual brush holder of an electrical machine for providing electrical contact with a movable part of said machine, a contact member adapted to be axially shiftable in a said brush holder, said contact member having a contact end and an opposite end, said member having a cylindrical bore extending axially inwardly from said opposite end to within a predetermined distance of said contact end, an insulated pushing element slidably received in said bore, pressure means adapted in normal use yieldingly to urge said element against the inner end of said bore and thereby through said element to maintain contact between said contact end of the member and said movable part, and spring means connected between said element and said member and operable independently of said pressure means upon said contact end being worn away a said predetermined distance to urge said contact member away from said movable part, and thereby leaving said insulated pushing element in sole contact with the said movable part, the inner end of said bore terminating in a peripheral groove defining a central protuberance adapted to separate from said member substantially as soon as the wear on said member reaches the innermost depth of said groove. 7

8, In a contact brush adapted to fit the usual brush holder of an electrical machine for providing electrical contact with a movable part of said machine, a contact member of electro-conductive material adapted to be axially shiftable when in use with said brush holder, said contact member having a contact end and an opposite end, said member having a recess extending in a substantially axial direction inwardly from said opposite end to within a predetermined distance of said contact end, an insulated pushing element received in said recess, pressure means adapted in normal use yieldingly to urge said element against the inner end of said recess and thereby through said element to maintain contact between said contact end of the member and said movable part, and spring means connected between said element and said member and operable independently of said pressure means upon said contact end being worn away a said predetermined distance to urge said contact member away from said movable part, and thereby leaving said insulated pushing element in sole contact with the said movable part.

References Cited in the file of this patent FOREIGN PATENTS 577,400 Great Britain May 16, 1946 614,404 Germany June 7, 1935 847,307 Germany Aug. 21, 1952