US403630A - willson - Google Patents

Description

(No Mam.) 5 Sheets-Sheet 1.

T. L. WILLSON.

DYNAMO ELECTRIC MACHINE.

No. 403,630. Patented May 21, 1889.

"w. Wn'unglon, o. c.

(No Model.) 5 SheetsSheet 2.

.T. L. WILLSON. DYNAMO ELECTRIC MACHINE;

No. 403,630. Patented May 21, 1889.

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INVENTOR:

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By M; Aflorneys;

N. PETERS. Hmo-Lnho u her. wasnm mn, D. C.

(No Model.) 5 SheetsSheet 3.

T. L. WILLSON. DYNAMO ELECTRIC MACHINE.

- No. 403,630. Patented May 21, 1889.

INVENTOR:

WITNESS SI' By 1125 Attorneys, 4 W- W m AMM q (No Model.) T L WILLSON 5 Sheets-Sheet 4.

DYNAMO ELECTRIC MACHINE.

No. 403,630. Patented May 21, 1889.

I N VE N TO R By his Attarneys,

willarn WTNESS s;

N. warms, nun-um W 0, c.

(No Modem 5 Sheets-Sheet 5.

T. L. WILLSON.

DYNAMO ELECTRIC MACHINE.

No. 408,630. Patented May 21, 1889.

INVENTOR: WITNESSE 61 1mm Will/ 011, M By his Attorneys,

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biATES UNITED tATENT OFFICE.

THOMAS L. \VILLSON, OF BROOKLYN, NElV YORK, ASSIGNOR 'lO JOHN C. MCGUIRE, OF SAME PLACE.

DYNAMO-ELECTRIC MACHINE.

SPECIFICATION forming part of Letters Patent No. 403,630, dated May 21, 1889.

Application filed December 10, 1888. Serial No. 293,133. (No model.)

To aZZ whom it may concern.-

3e it known that l, Tnonas L. WILLsoN, a citizen of the United States, residing in Brooklyn, Kings county, State of New York, have invented certain new and useful Improvements in. Dynamo-Electric Machines, of which the following is a specification.

This invention relates to dynamos of the general class known as open-coil machines, or those in which the armature-conductors are cut out of the external circuit as soon as they pass out of the eiii'ective magnetic field of force and are leftwith open terminals during their period of inactivity. More specifically, it pertains to the special type of such dynamos characterized by the employment of a drum-shaped armature, the winding of which consists of asingle layer of longitudi nal conducting-bars insulated from each other, (each constituting, essentially, a separate coil,) having com mutating-brushes bearing upon them at one or both ends in line with the fields of force to conduct the current to and from each bar during its passage through the magnetic field. A machine of this type is exemplified in the socalled Mouse Mill Dynamo of Sir \Villiam Thomson. Heretofore dynamos of this type have had merely a theoretical existence, the only embodiments of them thathave been actually made amounting to nothing more than laboratory experiments or philosophical curiosities, and being quite devoid of practicability. The impracticability of these machines has been due in part to their extremely low eilicieney, resulting from the fact that the conducting armature-bars are necessarily idle during much the greater part of the time, and also in part to the current generated by them being of such slight volume as to be practically useless. These machines have also in the constructions heretofore proposed been subject to mechanical defects, which alon 0 would have been su liicient to render them impracticable. My invention provides an improved and commercially-practicable dynamo of this type. It aims to improve upon the construction heretofore proposed both in mechanical and electrical features in order to render the machine el'licient, economical of energy, and capablcot yielding a large volume of current under sulticient electro-niotive force to render it suitable for such purposes as incandescent electric lighting, electroplating, electric smelting, electric welding, fee.

The improvements introduced by my invention relate, chiefly, to the armatllre and to the commutating-brushes and their connections. They relate, also, in. part to the fieldmagnet and the brush-holders and the means for adjusting the brushes.

In the accompanying drawings, Figure 1 is a side elevation of my improved dynamoelcctric machine in its preferred form, the right-hand portion being in vertical mid-section. Fig. 2 is an end elevation looking in the direction of the arrow in Fig. 1. Fig. is a vertical transverse section in the plane of the line 3 3 in Figs. 1 and i. Fig. 4: is a horizontal transverse section in the planes indicated by the line i l in Fig. 3. Fig. 5 is a diagrammatic view, the armature-conducting bars or winding being developed in a plane, the field-magnet poles shown over them in section, and the field-magnet winding being indicated by white spaces inclosing the poles, and the commutator-brushes being turned sidewise. Fig. 6 is a fragmentary transverse section of the armature on an enlarged scale. Figs. 7 and 8 show the lnush-holders, Fig. '7 being a section on the line 7 7 in Fig. 8, and Fig. 8 being a rear elevation. Fig. i) shows one of the conunutatordnush conductors or coupling-sections detached. Fig. 1o is a diagram sin'iilar to Fig. 5, but showing a modified method of coupling the commutator. Fig. 11 is a similar diagram of a inodilied construction of dynamo, showing a still. further modification in the method. of conunutatorcoupling. Fig. 12 is a sectional view out in the plane denoted by the line 12 12 in Fi l, and showing the arrangement of the brushes and the connections between them for the machine indicated in F1 11. Figs. 13 to 15 show a modified machine. Fig. 13 is a transverse section cut on the line 123 .3 in Fig. ll. Fig. l-l: is a plan partly in horizontal mid-section. 15 is an end elevation, partly in vertical section, on the line l5 15 in Fig. 1i.

I will first describe the construction shown in Figs. '1 to E inclusive.

Let F d esignatc the iicldanagnet as a whole,

and A the armature as a whole. B B are the commutator-brushes. O is the armature-shaft. D D are the supporting-frames in which the shaft has its bearings, and E is the base-plate or support on which the machine is mounted.

The field-magnet F consists of a greater or less alllllnbGl of radial poles or pole-pieces S N S N, of alternately contrary polarities, c011- verging toward the axis of rotation, and all in the construction shown connected together by a neutral portion, f, inthe shape of a hollow cylinder. The radial pole-pieces are provided with field-exciting coils c 0, formed on spools, which are slipped onto the pole-pieces and fastened thereon in any suitable manner. Preferably the pole-pieces and neutral portion f are all cast in one piece. This construction of field-magnet is not in itself new,

bein em loved with some forms of alternat-.

in g-current dynamos.

The armature A is mounted on the axial shaft 0 and rotates within the field-magnet. It is of barrel form, being cylindrical, or approximately so, and its ends project beyond the field-magnet. The armature is constructed with a cylindriealcore, a, of soft iron, and an exterior winding, consisting of a single layer of longitudin al conducting-bars b b, surroundin g the core fastened thereto. The soft-iron core may be made in any way-in which armature-cores have heretofore been made, being preferably laminated, at least in large machines, in order to prevent eddy-currents. I prefer to build it up of disks or washers of thin sheet-iron interleaved with sheets of tissue-paper, the iron washers being formed with inner notches to constitute a keyway,.

and placed over the shaft (1, which has a key fitting this keyway The shaft is provided with a collar, cl, fixed on it and coming against one end of the core, and with a loose collar, or disk, 61', coming against the other end of the core, as shown in Fig. 4, the core being tightly compacted by means of nuts 0 e, screwed on a threaded portion of the shaft against the collard. The length of the core thus formed is preferably equal to the length of the field-magnet, including its excitingcoils, as seen in Fig. 4. I

The conducting-bars b b are preferably of copper, their sides being tapered to form radii from the axis of rotation; or, in other words,

the bars are prisms the cross-section of which is a truncated sector. The bars are placed edgewise against the exterior of the armaturecore a, a layer, g, of insulating material being interposed in order to insulate them from the core, as shown in Fig. 6. Between the bars are placed thin sheets of insulating material 1 t, Fig. (3, preferably of mica. The bars are held against the core by exterior bands, h h,

of fine wire wound around the armature after the manner of the hoops on a barrel, an-insulating layer being interposed between the exterior of the bars and these hoops or hands. I11 order to provide a driving-connection between the winding of bars I) b and the arma-v armature-windin g and core will in most cases be'sufficient.

The armature thus built up consists, electrically, of a winding of a great number of longitudinal copper bars, each bar constituting, essentially, a separate coil open at both ends and entirely disconnected from the other bars. This winding is superposed upon a softiron core,which forms a means for closing the magnetic circuit betweeen the field-poles, the lines of magnetic force flowing as indicated with reference to two of the poles by dotted lines in Fig. 3. As the armature is revolved, the conducting-bars b b are whirled through a succession of concentrated magnetic fields of altern ately-reversed polarities, and thereby have potentials induced in them during the instant of their passage through these fields of electric currents by the application of commutator-brushes to the opposite ends of the which are passing through the respective fields of, force.

The commutator-brushes B B are arranged at the opposite ends of 'the field-magnet and bear upon the portions of the armature-bars which project beyond the field-magnet, these projecting portions forming, essentially, commutator-segments The number of pairs of this number being six in the construction shown. The two brushes of each pair are arranged at the opposite ends of the corresponding field-pole and bear upon the segmental bars for an angular distance equal to the width of the concentrated-field of force emanating from the pole. In practice the brushes will have a slight lead in consequence of the deflection of the lines of force by the rotation of the armature.

Fig. 5 clearly shows the circuit arrangement when the commutator-brushes are coupled in series. The current passes from the negative binding-post P into the first brush holder through the brush thereof into the armaturebars, and through the latter from right to left past the N pole of the field-magnet, thence the bars from the brush holder thereof, through a coupling pieceor section, G, into the next brush in advance at that end, back brushes is equal to the number of radial poles,

from left to right through the bars passing. through the S, field of force, out through the of force, which may be taken off in .the form IOO bars, in such position as to bear upon the bars ,out through the brush'at the opposite end of connniiitator-brush at the right-hand end of the machine, through a coupling-bar, G, to the next brush in advance, and so on back and forth, until finally the current passes out at the positive binding-post P, its entire course being indicated by the tailless arrows in Fig. 5. The feathered arrow in this figure shows the direction of movement of the armaturebars by the rotation of the armature. As each bar enters the magnetic field of force its opposite ends pass into contact with the respective brushes, so that the potential induced by its movement through the field of force causes a current to flow through it from one brush to the other. Upon its passage out of the eoncentrated field of force, or into a feebler portion thereof, its ends pass out of contact with the brushes, so that during its movement into the next field of force it remains open-circuited. \Vhen the bar passes into the next field, which is of opposite polarity, the current generated in it is in the opposite direction.

The c0mmutator-brushes I B are built up of a great number of sheets or leaves of copper in order to afford not only an extended t'aee sutlicient to bear upon all of the bars that are passing through one field of force, but also to constitute a conductor of extremely low resistance for carrying away the large volume of current generated in the ar mature. This is a practical requisite of great importance, since all of the parallel armaturebars I) l) which are traversing one of the fields of force are in eitect one bar, since they are connected at both ends in multiple by reason of the brushes at both ends bearing upon the bars for the entire width of the field of force. Hence a current of very great volume is generated by reason of the large cross-section of the combined conductors in each field of force, and to carry off this current a conductingbrush of at least equal conductivity is required. In practice I give the brushes a conductivity considerablyin excess of that of the bars upon which they bear in order to provide against the heating of the brushes. For the same reason it is requisite to construct the brush-holders in such way that the current in iiowing from the brushes through the holders shall be insured a path of extremely low resistance. To meet these requirements, I have devised the construction of duplex brushes and brush-hohlers, which I will now describe.

In order to give the requisite area of contact between the brushes and the armatureconductors, the brushes are made broad, so as to bear upon a considerable length of the projecting portion of the armature. The total width of the brush is subdivided into two sections, which may be regarded as distinct brushes. These twin brushes are inclosed within a stationary holder-frame, II, Figs. 7 and S, which is formed with a standard or stud,I. The holder-frame His an open rectangular l:rame,through which the twin brushes are thrust. Each of the two brushesis clamped between two plates or gibs, 7;, above and 7 beneath, these plates being forced together by screws in. order to compress the copper leaves or laminae together. The plates 7; and Z are of only the same width as the lamina upon which they bear, so that those of one of the twin brushes are movable independently of the other. The lower plate, Z, is constructed to rock on a pivot, '11, and is provided with an adj ustingscrcw, m, by which in connection with this pivot its angle relatively to the holder II may be varied, and thereby the angle at which the brush bears upon the armature may be adjusted. The upper plate, 7., is provided with two screws, 1) p, by which to adjust it, whereby it is capable of assuming any angle to which the plate Zhas beenset. Thus the twin brushes may be adjusted to different angles, as shown in. Fig. 7, where one is given a slight lead over the other. This capability is practically useful in order to vary at will the width of contact of the brushes with the armature-conductors in originally adjusting the machine. \Vhcn once adjusted, the screw on need not subsequently be touched, the adjustment of the brushes forward to take up wear being effected by loosening the screws p.

The several brush-holders II II are mounted and supported by their studs I I being projected through holes in a disk-shaped yoke, J, as shown at the right hand in Fig. 1. The disks .I are mounted rotatively on the bearing-frames I) I), being fastened thereto byset-screws q q, so that if required they can by loosening these screws be slightly turned to alter the lead of the brushes and again fixed in position by tightening the screws. The positive and negative terminal brush-holders have binding-posts I I clamped on them for the attachment of the line-conductors, as shown in Figs. 1, 2, and The connection between the brushes through the couplingsections G G in Fig. 5 is not shown. in Figs. 1 to 4, these connectors being omitted for the sake of clearness. One of the connectors is shown detached in Fig. i). It consists of a subdivided sectional bar the parts of which are drawn together by screws so as to embrace betwcen them the studs I I of the two brush-hohlers which it is desired to couple together.

It will be seen from an examination of Fig 4. that the projectin end portions of the armat-ure-winding which constitute the comm utators extend beyond the core a as well as beyond the tiel .l.-magnet. This construction aifords a recess at each end of the armature, in which recess collars d r? and nuts (3 c are inclosed.

In view of the fact that in thismachine the electroanotive force varies in direct proportion to the length of the bars 71 1), it is desirable in order to secure a suitable electro-- motive force to make the armature and fieldmagnet both as long practicable. I hence use by preference a Iield-magn et considerably IIO ' buted field of force.

sired.

into sections, as clearly shown in Figs. 4: and

5,where each pole-piece S and each pole-piece N is divided longitudinally into two sections, each of which is provided with a separate exciting-coil, o. By this subdivision I secure in addition to mechanical advantages in construction a stronger and more equally distri- Preferably the exterior cylindrical neutral portion f is not longitudinally subdivided, although it may be, if de- In machines having still longer fieldmagnets the pole-pieces may be subdivided into three or even four or more sections instead of two. In the diagram shown in Fig. 11 the pole-pieces are not subdivided.

The field-exciting coils c a may be wound in any manner known in'the art, and may be coupled or connected together in series multiple are or multiple series, as maybe preferred, to adapt the machine to any desired service. It is one of the advantages of my invention that I produce a dynamo the'armature resistance of which is reduced almost to zero, being so slight as to be practically inappreciable. This renders it possible to make the machine self-regulating by the employment of a simple shunt-winding for the field-magnet coils, a result which has been reached theoretically, but has never heretofore been realized in practice so far as I am aware.

I have shown. in Figs. 5, 10, and 11 three dilferent'methods of coupling up the commutator-brushes. In Fig. 5 they are coupled in series, as already described, so that the electromotix e force of the currentfrom the machine becomes the product of that'generated in one bar in passing through a field of force at a certain speed multiplied by the number of fields of force through which the armaturebars are simultaneously passing. \Vhen thus coupled, the quantity of current that the machine is capable of developing is proportional to the combined conductivities of the bars in contact with one pair of brushes.

. In Fig. 10 the brushes are coupled together in multiple, so that the electro-motive force of the generated current is equal only to that generated in one armature-bar in passing through one field of force at a certain speed,

or with six pole-pieces the electro-motive force will be one-sixth of that developed with the series coupling shown in Fig. 5, and the total current developed 'is proportional to the combined conductivities of all the armaturebars that are touched by thebrushes, or with the number of field-poles shown the volume will be six times that resulting from a machine coupled as in Fig. 5'. The couplingconnections in this figure are shown in thagram only as being wires or rods 1" 1", leading the remaining brushes to the positive terminal P. It will be understood that the connections represented by these slender wires or rods will in practice be heavy couplingconnections of great conductivity. The direction of the current is denoted by arrows, the circuit being divided into as many branches as there are fields of force.

In Fig. 11 a multiple-series coupling is shown, the circuit being divided into as many branches as half the number of fields-of force, and each branch traversing two fields of force. The terminal connections are made with the brushes at one end of the machineonly, a conductor represented by the wire or rod r leading from the negative terminal P to every alternate brush, and another conductor represented by the wire or rod 7", leading from the intervening brushes to the positive terminal P. At the other end of the machine the' brushes are joined inpairs by conductors or coupling-sections r, so that the current flowing toward the right through one field of force is permitted to pass back toward the left through the next field of force. Obviously all the brushes at the right might be connected together, since, it is immaterial through which of the fields of force the current flows back. They might all be thusconnected by connect-ing their brush-holder studs I I electrically with the disk-shaped yoke J at that end of the machine instead of insulating these studs from the yoke; or all the brushes from this end of the machine might be removed and all the armature-conducting bars I) b be connected together at this end, as in Sir William Thomsons ,Mouse Mill Dynamo, before referred to. I prefer, howey er, the employment of brushes at this end and their connection together either in pairs, as shown in Fig. 11, or by connecting all the brush es together.

The machine represented by the diagrams, Figs. 11 and 12, has eight fields of force instead of six. Obviously. my invention may be applied with any number of fields of force from two up; but the greatest efiiciency is derived from the multiplication of the fields of 'force, so that each armature-bar passes as quickly as possible from one field of force into another, so that the least practicable portion of the time is wasted in idleness.

Fig. 12 showsthe preferable way of making the connections at the left-hand end of the machine in a multiple-series coupling such as shown in Fig. 11, the connections being made by arc-shaped coupling-sections G G, communicating-with the negative bindingpost P, curving inwardly to avoid the intervening brush-holders, and by coupling-sections G, communicating with the positive binding-post P and, curving outwardlyto avoid the negative brush-holders.

My invention is susceptible of considerable modification in respect both of its mechanical construction and of its electrical proportioning,- and I therefore wish it. to be un- Lil derstood that I do not limit myself to any of the details of construction or to any of the proportions hereinbefore stated, except such as are recited in the claims as being essential. I have ilhistrated an example of one such modification in Figs. 13, 14:, and 15. The machine shown in these figures has a fieldmagnet with only two poles, arranged dia metrically opposite, the pole-pieces embracing the armature between them and covering extended ares thereof after the manner of dynamos of the Gramme ring or Siemens drum type. The armature-winding is laid directly upon the exterior of the shaft, the interposed laminated core shown in the previous construction being omitted. The shaft (,1 becomes thus in eiiect the core of the armature. This construction of armature is suitable for small machines wherein but little difliculty is occasioned by eddycurrents. The commutator-brushes make contact with the armature-conductors in line with the fields of force, as before; but since the fields of force extend over a greater are of the arma ture-surface it is necessary to employ two or more brushes for each field of force at each end of the machine. Two such brushes are shown in Fig. 15. Being necessarily set at different angles, they are required to be mounted in separate ln'ush-holders; but both the brush-holders are electrically and mechanically connected through the medium of a bar or link, 1 and the two diametrically-opposite links are mounted on a yoke, J, in the ordinary manner, or otherwise supported. In the construction here shown the field-magnet has its cores or pole-pieces N S made in separate pieces from the neutral portion j", which latter forms on the lower side the base-plate of themachine.

It will be understood that my invention may be applied as an electromotor to be driven by the passage of a current through it upon suitably altering the lead. of the brushes, as is well known to electricians.

The armature of my dynamo is clearly distinguished from those of dynamos wherein armature-scgments insulated from one another are revolved in an annular space between two contrary magnetic poles, so that they cut the radial lines of force traversing such space, by reason of the fact that in such. dynamos the armature-bars are connected at their opposite ends to collector-rin gs, by means of which the current is continually conducted. to and from them by means of brushes, so that the bars are continually in closed circuit, whereas in the case of my armature the bars are independent of each other and electrically disconnected at one or both ends, so that the bars are normally open-circuited and are made a part of the circuit only during the time when they are actually passing beneath the brushes.

I claim as my invention the improvements in dynamo-electrie machines and electrometors substantially as hereinbefore specified, viz:

1. A dynaim-armature consisting of an iron core mounted to rotate on an axis, with a layer of independent and normally open-circuited conducting-bars insulated from each other extending longitudinallyover the core and fast ened thereto, so as to rotate therewith.

2. A dynamo-armature consisting of a cylindrical iron core mounted on a revolving shaft, and a layer of independent and normally open-circuited eonductingbars insulated from each other extending longitudinally over the cylindrical core and fastened thereto, so as to rotate therewith.

3. A d yn amo-armature consisting of an iron core mounted to rotate on an axis, with a single layer of independent and normally opencircuited segmental comlucting-bars applied over said core and fastened thereto, extending longitudinally thereof, insulated therefrom by an interposed insulating-envelopc, and insulated from each other by being alternated with insulating-leaves.

it. A dynamo-armature consisting of a cylindrical iron core mounted on a revolving shaft, and a layer of independent and normally open-circuited conducting bars insulated from each other applied around the exterior of the cylindrical core, fastened thereto to rotate therewith, extending loi'igitudinally thereof, and projecting at the end beyond the end of the core.

5. The combination, with a lield magnet formed with converging poles of alternatelycontrary polarities facing a central axis, of an armature consisting of a cylindrical iron core mounted to rotate on said axis, and a single layer of longitudinal conducting-bars insulated from each other fastened to said core, and extending at one, end (or both) beyond the ends of the poles to form a commutatingsurface, and a series of co1nmutator-brushes equal in number to the field-poles arranged to bear on said comimitating-surface in positions coincident with the respective fields of force.

6. The combination, with a field-magnet formed with converging poles of alternatelycontrary polarities facing a central axis, of an armature consistingof a cylindrical iron core mounted to rotate on. said axis, and a single layer of longitudinal conducting-bars insulated from each other, fastened to said core, and extending at both ends beyond the ends of the poles to form cominutating-surfaces, and two series of commutator-brushes, one series arranged at each end to bear on said commutating-surfaee, and each series equal in number to the field-poles and arranged coincidently with the successive fields of force.

7. The combination of a field-magnet having converging poles of alternately-contrary polarities, an armature consisting of a cylindrical layer of longitudinal conducting-bars mounted to revolve within the field-poles, two

IIO

series of collecting brushes, each equal in number to the field-magnet poles, arranged to bear against said bars in coincidence with the fields of force, and electrical connections with the respective brushes, whereby they are all coupled together between the positive and negative terminals of the machine.

8. The combination of a field-magnet havin g converging poles of alternately-contrary polarities, an armature consisting of a cylindrieal layer of longitudinal conducting-bars mounted to revolve within the field-poles, two series of colleetin g -brushes, each equal in number to the field-magnet poles, arranged to bear against-said bars in coincidence with the fields of force, and electrical connections between alternately-successive pairs of brushes in each series, the connected pairs in one series alternating with those of the other series, whereby the generated current is caused to flow back and forth through the armature and to traverse the several brushes serially.

9. The combination of a field-magnet having converging poles of alternately-contrary polarities, an armature consistingof a cylindrical layer of longitudinal conducting-bars mounted to revolve within the field-poles, a series of collecting-brushes, equal in number to the field-poles, arranged to bear against the said bars in coincidence with the fields of force, holders for the respective brushes, and segmental coupling-bars constructed for engagement at their opposite ends with the respective holders and adapted to form electrical connections between them.

10. The combination of a field-magnet having converging poles of alternately-contrary polarities, an armature consisting of a cylindrical layer of longitudinal conducting-bars mounted to revolve within the field of force, a series of collectin g-b rushes arranged to bear against said bars in coincidence with the respective fields of force, holders for the respective brushes, and a yoke or disk mounted on a rotative bearing carrying said brushholdeysand adjustable on its bearing to vary the lead of the brushes.

11. In a dynamo of the described type, the

combination, with the armature having its end projecting to form a commutating-surface, of collecting-brushes bearing on said surface, a holder for each of said brushes formed with aprojecting stud, and a segmental coupling-bar adapted to electrically connect two of said holders, and constructed at its ends to be clamped upon the studs thereof. 1

12. In a dynamo, the combination, with a brush-holder consisting of a rigid open frame, of a commutator-brush passing freely through said frame, two clamping-plates within said frame embracing the brush between them, and adjusting-screws reacting against the frame for pressing said plates against the brush and adjusting their inclination relatively to the holder. v

13. In a dynamo, the combination, with a brush-holder consisting of an open frame formed with a rocker-bearing within it, of a commutator-brush passing freely through said frame, two clamping-plates within said frame embracing the brush between them, and one of said plates rocking on said rocker-bearing, a screw engaging said latter plate for adj usting it on said bearing to diiferent inclinations relatively to the holder, and a screw for pressing the opposite plate toward the rocking plate to clamp the brush between them.

let. A dynamo-armature consisting of an iron core mounted to rotate on an axis and formed with longitudinal grooves, with a layer of independent and normally open-circuited conducting-bars insulated from each other extending longitudinally over the core, and with certain of the bars at intervals made wider than the others and projecting into said grooves in the core, with an insulating-layer interposed between the core and said bars.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

THOMAS L. WILLSON.

Witnesses:

ARTHUR C. FRASER, J NO. E. GAVIN.

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