US714811A - Brush-holder. - Google Patents

Description

I BEST AVNLABLE @om No.7|4-,an. Patented Dec. 2., |902. 1 f i w.v n. x.lTcHFlsLn.

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eEsT Amr/ABLE- com .,U-NrrE-nl STATES PATENT OFFICE.

WALTER D. LITCHFIELD, or scnizsno'rnnr, New 1'onn, Ass1cNOR 'To GENERAL'ELECTRIC COMPANY, A CORPORATION or New YORK.

"BRUSH-HOLDER.

, fsPCIYFiccrIoN forming vpm ef Letters patent No. 714,811, atea December 2, 190e.

Be it known that I,WALTERD. LITCH FIELD, a citizen of the United States, residing at.

" Schenectady, county of Schenectady, State of New York, have inve'n-*ed certain new and useful Improvements in Brush-Holders, (Case No. 2,159,) of which the following a specifica- This invention relatesto improvements in brush-holders for.electric machines; and it .g consists ina novel means for preventing the overheating and consequent decrease of resiliency of the Springsgvhich are combined with the brush-holders to 'force'pthe' brush against the commutator or collector ring of the machine.

It .is well known thatthe temper or re siliency of metal is impaired or totally deetroyed by'heatinv. It is essential that a spring be employed in brush-holders for the purpose ofmaintaining the brush in good electrical contact with the commutator or col- A lector, and thesesprings are almost always in electrical connection with the bruslnand consequently take current. A good spring has considerableresistance, and consequentlybecomes very hot, so that its resiliency is impaired. One of the most serious problems with which constructors of electrical inachines have had to deal is that of preventing this decrease of resiliency. In some classes of work an adequate remedy has been provided in the form of flexible braided-wirev leads or cables, which are secured to the carbon brushes generally employed and to some condu'cting portion of the brush holder.

' These iiexiblc leadsvare familiar-ly known in the art as pigtails'.A In certain other classes of worl, however-such as railway-motors,

in connection withwhich this invention was lmadethe brushes becoxneso hotthat the cou- Y sppiicatiantieuprn30,1901. anni 110.521.153. hameau vention which is incompatible .with its use in connection with au auxiliary cable, and, in fact, the drawings herein disclose an application of the invention in combination with a cable of the type which is securedto an auxiliary contact-piece which bears on the vtop ofthe brush. .In such cases the invention serves as an additional means for the `preservation of the life of the spring; but iu' cases where the flexible cable is not employed at all the invention maybe so utilized as to shunt practically all the current from the spring.

The invention comprises a piece of good conducting metal, such as copper, which is combined with a brush-holder spring in such manner that the current which would otherwise flow through the spring to heat it and destroy its spring 'qualities will be shunted through the piece of copper.

The'leads or cables which have hitherto been employed for the purpose of shunting current from the springs have, as described above, been made flexible in order to permit free movement of the spring, so that' the latter could follow the downward movement of the brush toward the commutator when the brush wore away. rllhe same movement of the spring should be permitted in all cases, and hence the piece which is combined with the spring iu accordance with this invention should be of ductile metal, and for this purpose I prefer to employ copper, which is atv once the most ductile and highly conductive. of metals. A

inasmuch as the object of the invention is to prevent the brush-l1older spring from be-A coming veryhot, it is desirable that the auxiliary metal piece should be a good conductor of heat in order to abstract the heat from the spring. Again, l prefer copper for this purpose, because in addition to its properties oi' d uctilit-y and electric conductivity it is also a very good conductor of heat..

'lhe drawings herein disclose a spring' which comprises a flat strip wound into a spiralicoil, which is th'c best embodiment of my invention known to. me, but the invention in its broader aspect may be employed in practice in combination with any other form of spring, as the stri p need not be coiled,

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but may be a'ilat spring, and the Aspring itself might be of any' other cross-'sectional out- 1iue,or resili'entmaterial of any desirableoutline whatsoever might be coiled helically' instead 'of spirally-.1

Of the drawings, litigare)A ispan' elevation of a,hrush-holder embodyiu" the invention,

and Eig.: 2 is a perspective view of the spring" shown in Fig. 1 and constructed in one of.

lo the numerous ways .which the invention will frame of the machine by means of the partssuggest to thos'e skilled iny the art.

Thelbrush-holder H is suitably mounted 'on and insulated from the portion X of the x5 D, E, F, and G and has an insulatorl interposed between itself and said parts in accordance with the'commonly-employed method disclosed vin the patent to Priest, No. 648,052.

, The brush B is free to move up and down 2o through the brush-holder and is adapted to 'engage thesegmeuts of the commutator M. `Currentistaken from the brush-holder by the lead Y, secured by the bolt Z. The coustruction described up to this point is already well known' in the art.

. The spring S is arranged to force the brush 'through the holder `against the comm ut-ator l and is iu electrical connection with the' brush, \s'o that `it takes current'. In the example 3o shown the spring is a flat strip, a'portiou of which is coiled into a spiral, the end U of the sp ring in the center of the coil being straight and adapted to be secured in a slot in the stud 4o conductor.

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that my invention .may be most usefully em# ployed in connection with a spring of this A fiat strip A, preferably of copper,is placed upon the phosphor-bronze spring,

so that it lies in contact therewit.li,'aml in the particular type disclosed herein the copper strip is wound -with the spring and riveted v thereto. I n testing the invention I employed 5o asprug of Scoville bronze iive-eighths of au inch wideand one-sixteentlrof an inch thick.

The popper strip was also 'live-eighths of Van inch wide and vthree one-hundredths of an inch thick, and when wound in parallel with the bronze spring the copper strip had five times the conductivity of the spring, and hence it is obvious that most of the current was shunted from theI spring, with the result that it did not become oven-heated. The cop- 6o per strip being such a good comluetor may be sovery thin that it will interfere in no way with the free movement of the spring S, especially alsoas copper is most ductile, so that the spring cau move freely to keep the brush in engagement with thc segments ol' the com mutator.

As shown in thc drawings," the copper strip extends on both sides of the spring for a considerable portion of the length of the latter, and as the copper strip is a goed conductor .of heat and has alarge extent of surface cx- 4posed tothe air it is evident that in this arrangement the little heat rhich may be developed in .the spring by the passage therethrough of a small current will be absorbed by the copper strip and dissipated therefrom by radiation and convection. A'The spring thus may be used in cases Where a'pigtail is secured to the brush-holder for the purpose of coperatingwith the pigtailinshuntingcurrentfrom the spring and to serve as a safeguard in case the brush should become so hot that the connection of the pigtail with it might be destroyed. The invention may also be used, as shown in the drawings, in cases where it is not desired to have the free end of the spring engage directly with the top of the brush in order to prevent the poor contact which sometimes results between the spring and the brush. In such cases a separate contact-piece C bears o`n the top of the brush and the spring presses on this contactpiece. Thus a uniformly good contact is provided between the top of the brush and the contact-piece; but in order to provide a better path for the current than that betu'eenthe contact-pieceand the spring a flexible lead P, consisting of a braided-Wire cable is secured to the portion J of the coutact-piece C, as shown in Fig. '2. Since the spring is, in accordance withthis invention, provided with the copper strip A, the cable P may be attached to the' strip A by means of the clip L and the rivets R. The reinforced spring is lient atits free end, and the bent portion is adapted to rest ou the contact-piece C and to be held thereto by means 4ot a pin N, which passes through the holes O and the portion J of the contact-piece C. Thus two paths for the current are provided from the contact-piece C, but they join at the copper strip A, so that all the current flows through the reinforced spring, which it may safely do owing to the copper strip.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

l. The combination with a brushlholder, of a contact-piece arranged to bear on the top of the brush, a spring arranged to bear on the contact-piece to force the brush against the commutator, a piece of good conducting metal provided with an auxiliary conductingstrip IOO' arranged in contact with the spring to shunt current therefrom, and a ilexible connection between the contact-piece and said piece of conducting metal. l

2. The combination with a brush-holder, of a slotted stud, and a spring coiled about said stud having one end bent to engage in said slot-and the other cud adapted to force the brush against the comniutator, said spring Acomprising.; a flat strip of resilient metal, and

a strip ol'good conduct-ing xnetai arranged in contact with the resilient strip to shunt lurrcut therefrom.

714,8@EST VALABLE CPX 4.. The combination with a brush-holder, of

xo a contactfpiece arranged to bear against the bmah, a spring arrangedlobear onthe contact-piece, a piece of good conducting metal to shunt current around the spring, and a fiexible connection between the contact-piece and said piece of conducting metal.

In Witness whereof I have hereunto set my hand this 29th day of April, 1901.

WALTER D. LITCHFIELD.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WooLLEY.'

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