US2607815A - Method and means for dividing, generating, and transforming direct current voltages - Google Patents

Description

Aug. 19, 1952 L. L. DAVIS METHOD AN EANS FOR DIVIDING, GENERATING AND Filed Jan. 2, 1951 TRANS RMING DIRECT CURRENT VOLTAGES 5 Sheets-Sheet l INVENTOR: r Le/md flaws BY Z1) ATTORNEK 19, 1952 L. L. DAVIS METHOD AND MEANS FOR DIVIDING, GENERATING AND TRANSFORMING DIRECT CURRENT VOLTAGES Filed Jan. 2, 1951 a b c d 3 Sheets-Sheet 2 INVENTOR.

19, 1952 L. L. DAVIS METHOD A MEANS FOR DIVIDING, GENERATING AND TRA ORMING DIRECT CURRENT VOLTAGES Filed Jan. 2, 1951 5 Sheets-Sheet 3 Patented Aug. 19, 1952 METHOD AND MEANS FOR DIVIDING, GEN- ERATING, AND TRANSFORMING DIRECT CURRENT VOLTAGES Leland L. Davis, Stilwell, Kans.

Application January 2, 1951, Serial No. 203,983

- 6 Claims. 1

This invention relates to electrical devices and particularly to a combination dynamo and motor having a novel arrangement of parts for transferring electrical current to and/or from the armature thereof whereby to permit a large number of uses of the device including dividing of line voltage, increasing or decreasing voltage and obtaining of differing voltages or currents, each adapted for application to a separate load as desired.

As will hereinafter appear, the electrical apparatus hereof is adaptable for a large number of uses, but one of its most advantageous applications and for which it has been initially developed, is in the field of electrical vehicles such as trolley busses, street cars, elevated lines, subways and thelike. As is well known, direct current car operation is in universal use. The car control embodies a controller or rotary switch or contactor group that is operated by the motorman to actuate the impelling motor or motors. The first advance of the control unit connects the motor or motors in series with a starting resistance. As the control is further advanced, the starting resistance is gradually cut out to accelerate the car. Finally, the controller reaches a position connecting the motor or motors directly across the supply line, eliminating the resistance. Only when the motors are connected directly across the supply line (trolley and rail in the case of rail cars, or positive and negative wire in the case of trolley busses) is waste power reduced to'a point of rendering such operation relatively economical. Because of accompanying heat that is generated in such systems, a considerable amount of electric energy is wasted in the starting resistors.

One of the primary objects of the present invention therefore, is to provide electrical apparatus for replacing the resistance starting control now used in electrical vehicle systems, the apparatus having means for receiving the line voltage, dividing the same, and operating the vehicle motors through a number of external circuits that may be selectively placed in use by the motormanaccording to the degree of vehicle acceleration desired.

It is an important object of this invention to provide an electrical device which may or may not have all of the appearances of a conventional dynamo or electrical motor, but differing in winding of the armature thereof, relative arrangement of the commutator segments and brushes, and coupling of external circuits to adapt the same to a large number of uses not heretofore made possible by use of similar devices.

Another object of this invention is to provide apparatus taking the form of a combination dynamo and transformer, capable of use either as a conventional dynamo, utilizing the principle of magnetic induction for converting mechanical energy into electrical energy; to provide a plurality of differing voltages as desired in separate external circuits; or for use similar to that of an A. C. autotransformer to either step-up or step-down the voltage.

A further object of this invention is to provide an armature using truly open coil windings in an advantageous and fully novel manner to produce the results above enumerated, together with the production of high mutual inductance between adjacent coils whereby to effect a sharp reduction or cut-off of conduction as the coils emerge from beneath the brushes.

A still further object of this invention is to make possible through novel construction and arrangement of armature coil windings, the provision of an unlimited number of external circuits which may of themselves be adapted for use independently or be used together through one or more conventional couplings to either supply various loads with needed power or to receive electromotive forces and thereupon divide or multiply the same for such use as may be desired.

Other objects of the present invention include the provision of electrical apparatus capable of dividing an impressed voltage into'a number of voltages of lower values totaling the impressed voltage; optionally usable to increase an impressed voltage to one or more higher values; op-

i erable to commutate voltage and current irrespective of electrical positioning of brushes and magnetic poles; and fully adaptable to change either an alternating current voltage to direct current voltages of differing values or to change a direct current voltage to an alternating current voltage as desired.

In the drawings:

Figure 1 is a star wiring diagram illustrating the armature winding of apparatus for dividing,

generating and transforming electrical voltages made pursuant to my present invention.

Fig. 2 is a plane wiring diagram of the armature winding illustrating one possible externa; circuit arrangement.

Figs. 3, 4 and 5 are views similar to Fig. 2 showing other external circuit arrangements.

Fig. 6 is a view similar to Fig. 2, showing progressively different relative positions of brushes and commutator segments.

Fig. 7 is a graph showing the relationship of current in an external circuit with that of the armature coils of a uniformly loaded apparatus, and with the armature mechanically driven.

Fig. 8 is a schematic view corresponding to Fig. 2 showing the manner of loading to produce the relationship of Fig. 7.

Fig. 9 is a graph showing the relationship of current in various armature coils with load connected to one armature coil and with armature operating as a motor taking current from a supply line.

Fig. 10 is a schematic view corresponding to Fig. 9 showing the mannerof: loading to produce the results of Fig. 9.

Fig. 11 is a fragmentary view showing a modified form of commutator-brush arrangement;

and

Fig. 12 is a fragmentary view showing another form of commutator-brush arrangement.

As above indicated, the apparatus hereof may be quite conventional from the standpoint of appearance and mechanical construction. As in any generator or motor, there is provided a field frame mounted on a suitable base and carrying the field coils and their shoes therewithin; end

frames each provided with a bearing for rotatably supporting an armature shaft; a commutator on the shaft and coupled with the windings of the armature; brush holders carried by one of the end frames for holding the. brushes in engagement with the commutator; external circuits, and brush connections; and such other auxiliary fixtures as is quite common in this field. The mechanical construction. of such parts forms no part of this invention however, and has not been shown.

In the drawings there is shown a pair of poles 2i and 22 of opposite polarity, to produce a. magnetic field, preferably using electromagnets as is customary. The legs of the magnets, the ends ofwhich form poles and 22, are so disposed that an armature, broadly designated by the numeral 2t, revolves between them and within the lines of flux forming the magnetic field.

While a bipolar arrangement is illustrated, this invention contemplates use of as many electromagnets as is desired since it may well be advantageous to include the features hereof in multipolar design, particularly in larger machines.

The method of field excitation may also be chosen as desired, i-. e., either self-excited or separately excited. In the latter, current that is caused to flow into the field magnet coils is impelled by an outside source separate from the device itself. In self-excitation, current may be impelled by armature 24 through. any one of a number of common field winding arrangements, including series, shunt, 01' compound windings.

The armature 24 is provided with. a core upon which are mounted a plurality of truly open, preferably drum wound separate coils 26 for generating an E. M. F. as armature 24. is rotated within the magnetic field so that the lines of flux thereof are cut by inductors 36 forming. a part of the open coil windings 26. Each coil 26 may include as many turns as desired depending upon the number of cutting conductors required, but in each case the inductors 3 5 are disposed or spaced approximately 180 electrical degrees apart as illustrated.

For reasons hereinafter to be made more clear, armature 24 differs also from conventional direct current machines having commutators in that the mutual coupling between coils 26 should be as high or close as possible to produce high mutual inductance therebetween.

There are shown in the drawing for purposes of illustration only, ten identical open coils 2t,

5 designated 26a and 267 inclusive, and each having a pair of segment connections.

Commutation or rectification is produced by means of a commutator broadly designated by the numeral 32, provided to change the alternating E. M. F. or current output of armature 24 to direct E. M. F. or current as is customary in devices of this character. Twenty metallic segments or bars, separated by suitable insulation form the commutator 32, there being a segment' for each of the connections 34 respectively. The segments are designated by the letters a to t inclusive and are mounted for rotation with armature 24. Segments a--t of commutator 32 are joined directly to the corresponding ends of inductors 36 by connectionsii l.

It is seen therefore, that coils 26a267 do not as a whole forma closed. circuit upon themselves with the commutator segments, to which they are connected and. that each coil does not always forma. part. of a closed circuit. Each coil instead is. in circuit only when the commutator bars thereof contact a pair of brushes-38. The ten. brushes shown are designated a to Stylinclusive in the drawings.

It is noted that brushes 38 are arranged in pairs. spaced 180 electrical. degrees, 1. ve. brush 38a is opposed to brush. 38f, brush 38b is opposed to brush 339, etc. Accordingly, when any one brush 33 is in full contact. with a segment of commutator 32, its opposed. brushis in full. contact with the opposite commutator segment of the same coil 26.. r

For instance, asshown in Figs. 1- and 2, when.

brush 380 is in full contact with-segment f of coil 26d,.the opposed brush 38h is in full contact with segment-p of coil 26d. However, when the commutator 32 of. armaturev 24. is positioned relative to brushes 38 as shown in Figsl and 2, only one-half. of the coils 2B are contacted by brushes 38, the other half of the coils being fully inactive and out of circuit. In other words, since. all of the coils. 2B. are separately insulated and all of the commutator segments separated by insulation, no current will flow in the inactive coils though. voltage is induced thereinto. Thus, for example, segments 6 and o of. coil 260 have no brush contact, and this coil, together with coils 2611, 26c, 26g and 262', are all out of circuit. Coils 261), 2661, 26f; 26h and 26.7 are all in circuit by such direct contact between their commutator segments and corresponding brushes 38 In Figs. 1 and 2, each brush 38 of each of the five. pairs thereof is series-coupled with one of the brushes 38 of another pairby a conductor forterminals 52 and 54, the series connection of five of the coils 25 may be traced in Figs. 2 and 8 as follows:

From terminal 52 through conductor 40, brush Assuming D. C. line current to be coupled with 380., segment b, coil 25b, segment Z, brush 38i,

conductor 48, brush 38e, segment 7, coil 26f, segment t, brush 389, conductor 42, brush 38b, segment d, coil 26h, segment 12, brush 38g, conductor 46, brush 38d, segment 71., coil 267', segment r, brush 382', conductor 44, brush 38c, segment coil 26d, segment p, brush 38h, and conductor 40 to terminal 54.

Obviously, when the commutator 32 moves from the position shown in Figs. 1 and 2 to a point where the remaining segments thereof are in full contact with the ten brushes, the five coils just above mentioned will become inactive and the remainin five coils will be placed in a series circuit with the line current coupled with terminals 52 and 54 and will carry current equal to the line current, but at different relative voltages.

Consequently, current will flow intoany load orcombination of loads connected between any pair or combination of pairs of lines 56, 58, 60, 62 or terminals 5254.

As soon as the commutator 32 moves to a position where each adjacent pair of segments thereof engages a brush, all of the coils 26 become active and carry current, there being two groups of five coils 26 each, joined in parallel and series coupled within the respective group. Again, by virtue of insulation separating the commutator segments, each pair of coils carries a different relative voltage. In Fig. 6, the brushes 38 are shown each making half contact with a pair of adjacent segments of commutator 32 and each coil 26 therefore, carries current equal to approximately one-half of the line current directed to conductors 40,

The relationship of current in the main line coupled with conductors 40 (see Fig, 8) and the adjacent coil groups 26 is shown in Fig. 7, one complete armature revolution being indicated alon the abscissa of the graph. Lines 64 and 66 represent no current flow and maximum line current respectively. Full lines 68'l0 refer to current flow in one group of live coils 26 while dash lines 1214 refer to current flow through the remaining five coils 26.

It is seen that as the ten commutator segments of five of the coils 26 commence to engage the ten brushes 38, the current flow thereof rapdily rises as indicated by lines 68 from zero line 64, reaching maximum current flow as indicated by line 66 when the ten segments are in full contact with the brushes.

At the same time the remaining segments are leaving the brushes with a drop in current flow in the coils thereof as shown by lines 14. Thus, the output of all external circuits remains substantially constant, the sum of the currents represented by lines 68 and 14 being equal to the current indicated by line 66 and induced into the system through conductors 40. Curve 16 of Fig. 7, indicates magnetization of fieldpoles 20 and 22.

In Fig. of the drawings the induced voltage is shown across brushes 38h and conductor 48 and a large load is coupled with brush 38h and line 58. No current flows through brush 38a and the current through the coil having a segment engaged by such brush 38a is zero. Through such external tapping the instrument operates similarly to an autotransformer with the current in the load across brushes 381' and 33h approximately three times that of the supplied current. The current in the coil that is connected through its commutator segments with brushes 38h and 38c, is approximately double that of the other active coils.

Referring to Fig. 9; andiollowin'g the current flow to a segment-as the same passes'from brush to brush, it is obvious that such current-flow is zero whenever the segment is in engagement with brush 38a. The coil current rises to a maximum value as indicated by line lgfwhe'n the segment is in engagement with brush'38b; reverses and rises to double the. supplied current value under brush 380 as indicated at 19; reversesagain and rises to supplied current value 18 under both brushes 38d and 38e; falls to zero whenengaging brush 381 because of the disconnectionof brush 38a; rises to line currentvalue 18 under brush.

38 reverses and rises to'approximately double the value of the supplied current when engaging brush 38h; and reverses again and rises to.the value of the supplied current under both brushes 382 and 387. Curve 8| indicates current flowing in the load circuit 54-58 in Fig..l0.v 7

It is seen that upon rotation of the armature 24, supplying current to a load, each coil 26 of the armature 24 supplies an impulse current to the load as it passes under a brush 38. The following coil 26 thereupon picks upthe impulse as it passes under the brush. As each coil 26 passes under a pole 20-22 of given polarity, the current flow therethrough is, composed of a series of pulses in a given direction. .As soon as thecoil leaves such pole and passes under a pole of reversed polarity, the current pulses reversesdirection but so long as a coil is under the influence of either pole, it maintainsa voltage across its respective commutator segments 32in a definite direction. The rise and .fall of currentin the coils is continuously repeatedv but in alternately, reversed directions as ,polarity reverses. Accordingly, the current flowing in the external circuits is continuous and made up of current pulses. .7

It is clear from the foregoing that the device of Figs. 1 and 2 may be used either as a dynamo, as an electric motor or as a transformer. When used to operate from a D. C. line appropriate terminals 52, 54, 56, 58, 60 or 62 are connected to the supply line as above indicated. Line voltage is thereupon impressed upon a portion or all of the commutator 32 depending upon the coupling with the supply line. The armature 24 will thereupon act as a motor revolving and taking energy from the D. C. supply line. Divided voltages will appear across the remaining terminals and the loads connected-thereacross will receive energy from the D. C. supplied line but at differing voltages. In this respect thereforathe device is operable as an autotransformer on a D. C. supplied line to reduce or increasethe supply voltage as desired. V

It is seen that one onmorevoltages higher than the impressed supplyvoltage may be, produced; one or more voltages each of a lower value than the impressed voltage may be connected to various loads and that through propercoupling of the supply line voltage to the, external circuits of the apparatus, the samemay be used both as a voltage increase and a. voltage decrease device simultaneously.

Obviously, the-device maybe driven mechanically in the samemanner asa conventional generator through rotation of the armature 24 by means of an auxiliary prime mover connected with the shaft of the'arm'ature 24. In this case the instrument will develop a-plurality of voltages across its brush terminals. Similarly, when operating as a ge'neratorthr'ough driving of armature 24, auxiliary line voltag maybe impressed 'ri ngs](not shown) may be added to the shaft of armature 24 andconnected tothe coils 26 in the conventional manner. for feeding into the machine, alternating E. M. F. for motor operation or taking; from. the machine alternating E, for use in anexternal circuit. By using a pair of slip, rings for each. phase, any number of phases, may be impressed, on the machine up to the. limit of. the number of coils 26 on the armature 2.4. The same phase relationship would, of course, have to be maintained in connecting the armature coils 2,6 as that of the A. C. supply line. For example, two-phase operation would require 90 electrical degree connection to armature coilsj 2,6. and similarly, 6, phase diametrical connectipn would require a 60 electrical degre relationship.

In conventional, direct current machines, it is desirable to holdmutual, inductance between the armature coils to a minimum in order to minimizesparking and. burning or brushes as the armature coils undergo. commutation. The cona verse is desired in the. present machine in order to inducethe reverse action in the adjacent coils 2B,. As current builds, up in a particular coil 25 when its segments move into engagement with pairs of brushes,38,.ind .tive action reduces the voltage. in adjacent. coils 26 emerging from under such brushes, producing therefore, .better commutation.

It is now also seen that the device hereof is particularly adaptable for use-in transit systems, powered by D. Q. motors to replace starting resistors now. commonly used. and thereby reduce electricalenergy waste in the form of heat. While the machine may have many other applications, wherever millt D, C. voltages or divided D. C. voltages are required, its application toproyide a number of progressively increased voltage levels. for starting D. C, motors in streetcars and other electrically powered vehicles or machines. of all. kinds, is perhaps one of its most important uses. Such heavy duty motors are commonly employed intheoperation of elevators,

propulsion. of ships, driving of electric trucks, rolling mills and many other electrical devices. Desired D. C. voltage either of greater value or of lesser value than that of the line supply may be applied through use of the machine hereof to various contrivances including lamps, .motors, projectors, radios and the like. Intermediate grounding of all). C, voltage, such as may be required by a three-wire, Edison, system or other related circuits, presents another advantageous use of the machine. above described.

The machine, presents a method of dividing impressed D. C. voltages into sub-voltages of lower values, the sum of which equal thev impressed voltage; a method of increasing the impressed D. C. voltage to a higher value or values; the method of generating D.- C. voltages of several independent values by mechanically rotating the armature 24.; and a method of changing A. C. voltage to multi-value D. C. voltages; or conversely for changing- D'; C. voltage to, A. C.

voltage. 7. 4 r

While the above, deSQription contemplates an illu trated device wherein th b u 38 are se a a d y a ins e e e t a o r i utator 32, one. modification that is possibleis illus.

trated in Fig. ll of the drawing whereina pair of commutator segments I00 separate brushes I02 whenever the latter are in full engagement with one segment I00. Similarly, in Fig. 12, another modification is illustrated wherein eachbrush I04 is capable of full engagement With two. commutator segments I06 at the same time while brushes I04 are separated by two or more of the.

segments I06.

The modifications thus far considered havebeen limited to series connected brushes in ex ternal circuits, but it is obvious that the novel. armature constructions hereof permits of infinite other coupling arrangements. v

In Figs. 3 to 5 inclusive, commutator 32 and brushes 33 are shown, using the same designations as in Figs. 1 and 2; and the coils 2 6 join the segments of commutator 32 in the same. manneras above described.

Independent external circuits are shown in Fig. 3, there being shown in this particular ar-. rangement external circuits equal in number tov one-half the number of open coils 26. The first independent circuit is composed of lines. 200 and 202 connected with brushes. 38a and 38f respectively. Lines 20.4, and 206 join brushes 38c and 38h respectively, forming a second circuit. lhe third external circuit joins brushes 38c and 389' by lines 208 and 2I0 respectively. Lines 2I2 and 2 I4 connect with brushes 3% and 30g and lines 2L6 and 2I8 couple with brushes 38d and 38 2' to form the fourth and fifth circuits.

It is noted that when the device is as shown in Fig. 3, one circuit may be traced from line 200. through brush 33a, commutator segment 32b, the corresponding coil 26, segment 32L, and brush 38 to line 202. The remaining four circuits are traceable similarly. When segment 32a moves under brush 38a and segment 32k moves under brush 38 the coil between segments. 32 and 3272 becomes active with respect to the circuit 200-202.

Thus, the coils are alternately active and inactive as in the form of Figs. 1 and 2. With rotation of the armature, each of the coils. 26 will successively become active and then inactive with respect to each of the successive brushes 38a to. 387, and each external circuit is continually energized with pulsating D. C. energy by the coils 26 moving successively into series with the respective brushes 38 thereof.

A parallel arrangement of external circuits is 1shown by Fig. 4, one of which is traceable as. fol-.

ows:

From a lead line 220 to line 224, brush 38f, segment 32L, a coil 26, segment 32?), brush 30a and line 222 to lead line 226, and:

From line 220 to line 228, brush 38g, segment 3212, a coil 26, segment 32d, brush 38b and line 23.0 to line 226.

Another arrangement shown in Fig. 4 is traced as follows:

From lead line 232, through line 234, brush 383', segment 32t, a coil 20, segment 32], brush 38c, and line 236, to lead line 233, and:

From line 232, line 240 and 242, brush 33 2, segment 327', a coil 26, segment 32h, brush 30d and lines 244 and 246 to line 238, and:

From line 232, to. lines 240.. and 248, brush 38h, segment 32p, a coil 26, segment 32 brush 38.0, and lines 250 and 206v to lead line 238'.

It is noted that in the parallel circuit first traced, two coils 26 are coupled in parallel through the brushes 38 to either feed the external circuit including lines 220 and 226 or receive energy therefrom. 'Hereagain half of the coils are inactive when the'commutator-32 is positioned' as shown in Fig. '4 and half are active. The current capacity of this circuit is therefore, increased by the parallel coupling.

' In the last-mentionedcircuit; three coils are coupled in parallel and the current capacity of theexternal circuit including lines-232 and 238 is increased accordingly.

Fig. shows how the open coil structure permits use of both series and parallel external circuits coupled for possible advantageous uses.

' First there is shown in Fig. 5 a parallel, external coupling identical with that of Fig. 4 wherein three coils 26-are joined in parallel. Thus, the same designating numerals are used in- ' cluding lead lines 232 and 238.

Additionally, there is provided a pair of seriesconnected coils 26 joined in series with such 3- coil parallel arrangement, traceable as follows:

From lead line 238 to line 252, brush 38 segment 32L, a-coil 26, segment 32b, brush 38a, line '25 4,brush 38g, segment 3211., a coil 26, segment connections have been illustrated and described.

All of the forms contemplated hereby have the open-coil arrangement in common with each coil provided with a pair of commutator segments connected to the ends thereof. Thus, there must always be an even number of segments 32. The number of coils and the number of turns for each may however, vary. And the number of pairs of field poles may be selected as desired.

Also, the brushes 38 must be even in number but not necessarily half as many brushes 38 as segments 32. Each brush may be capable of spanning a full segment as in Fig. 2, two or more segments as in Fig. 12, or only part of a segment. Further, one brush of the series thereof may be capable of full contact with but one segment while other brushes in the same device may be of such size as to span the distance between two or more commutator segments.

It is preferable however, that the relationship between each brush and proximal segments at any given point in the cycle of operation be the same as the relationship between other brushes and their proximal segments.

Thus, for example in Fig. 2, when a given brush is in full contact with one segment all of the remaining brushes should likewise be in full contact with one brush. By way of further example in a modification where at least some of the brushes are capable of covering two commutator segments, under such condition all of the remaining brushes should cover or full contact at least one segment at any given instant in the cycle of operation.

Also, while in virtually all of the systems above outlined, one-half of the coils are active and the other half inactive during a given condition of operation, such may also be modified. One exampie is shown in Fig. 11 where two coils are inactive while adjacent coils are conducting.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

1. In an electrical device, field structure including at least one pair of field magnets having poles of opposite polarity for producing a magnetic field; an armature having a number of open-coil, electrical windings mounted thereon, said armature and said field magnets being relatively rotatable and said windings being disposed to cut lines of magnetic flux produced by said field as the armature and the magnets rotate relatively; a commutator connected to said armature and provided with a plurality of conductible segments having insulating meansseparating the same, there-being a segment joined to each end respectively of each of said windings presentin a number of pairs of segments, the segments of each pair thereof being spaced approximately electrical degrees; a number of pairs of separate, conductible brushes, the brushes of each pair thereof being spaced approximately 180 electrical degrees, said brushes and the commutator being relatively rotatable, said brushes being disposed for successive engagement with the commutator segments of the windings; and means adapting the brushes for connection with external circuits, each brush being always in engagement with at least one segment.

2. In an electrical device, field structure including at least one pair of field magnets having poles of opposite polarity for producing a magnetic field; an armature having a number of open-coil, electrical windings mounted thereon, said armature and said field magnets being relatively rotatable and said windings being disposed to cut lines of magnetic'fiux produced by said field the armature and the-magnets rotate relatively; a commutator connected to said armature and provided with a plurality of conductible segments having insulating means separating the same, there being a segment joined to each end respectively of each of said windings presenting a number of pairs of segments, the segments of each pair thereof being spaced approximatel 180 electrical degrees; a number of pairs of separate, conductible brushes, the brushes of each pair thereof being spaced approximately 180 electrical degrees, said brushes and the commutator bein relatively rotatable, sai d brushes being disposed for successive engagement with the commutator segments of the windings; and means adapting the brushes for connection with external circuits, each brush being always in engagement with at least one segment, all remaining brushes being simultaneously in full contact with at least one segment during full engagement of any one brush with at least one segment.

3. In an electrical device, field structure including at least one pair of field magnets having poles of opposite polarity for producing a magnetic field; an armature having a number of open-coil, electrical windings mounted thereon, said armature and said field magnets being relatively rotatable and said windings being disposed to cut lines of magnetic fiux produced by said field as the armature and the magnets rotate relatively; a commutator connected to said armature and provided with a plurality of conductible segments having insulating means separating the same, there being a segment joined to each end respectively of each of said windings presenting a number of pairs of segments, the segments of each pair thereof being spaced approximately 180 electrical degrees; a number of pairs of separate,

genesis conductible brushes, the brushes or each pair thereof being spaced approximately 180 electrical degrees, said brushes and the commutator being relatively rotatable, said brushes being disposed for successive engagement with the commutator segments of the windings and an external circuit for each pair oi brushes respectively, said circuits and the brushes thereof being arranged relative to the segments forsuccessive connection of the windings in series wtih the circuits.

a. In an electrical device, fieldstructure having means for producing a magnetic field; an armaturehaving a number of open-coil, electrical windings mounted thereon, said armature and said field structure being relatively rotatable and said windings being disposed to cut lines of magnetic flux produced by said field as the armature andthe field structure rotate relatively; a commutator connected to said armature and provided with a plurality of conductible segments having insulating means separating the same, there being a segment joined to each end respectively of each of said windings presentinga number of pairs of segments; a number of pairs of separate, conductible brushesfsaid'brushes and the commutator beingrelatively rotatable, said brushes being disposed for successive engagement with the commutator segments of the windings; and means adapting the brushes for connection with external circuits, each brush being always in engagement with at least one segment. a 7

5. Inan electrical device, field structure including at leas'tone pairof field magnets having poles of opposite polarity for producing a magnetic field; an armature having a number of open-coil, electrical windings mounted thereon, said armature and said field magnets being relatively rotatable and said windings being disposed to cut lines of magnetic flux produced by said I field as the armature and the magnets rotate relatively; a commutator connected to said armature and provided with a plurality of conductible segments having insulating means separating the same, therebeing a segment joined to each end respectively of each of said windings presenting a number of pairs of segments, the segments of each pair thereof being spaced approximately 180 electrical degrees; a number of pairs of separate, conductible brushes, the brushes of each pair thereof being spaced approximately 180 electrical degrees, and being disposed for engagement with the commutator segments, said brushes and the commutator being relatively rotatable; and an external circuit including electrical conautism taming brie brush "tiffc'fi'e J e fif in parallel withjonelbrus'hbf atl'eastbrie'other pair thereof, said circuit and the brushesthereof being arranged relative to the segmerits for "Successive connection df-s'aid windings in parallel With the conductors. Y

6. In an electrical dfi'egfield structure including at least one 'pairjof fiem mag'nets having poles of opposite polarityio'riproduciiig a magnetic field; an 'armatiire having a "iiiifiiiber of openc911, electrical windings 'in'oiintfdfthereon, said armature amend. fild'inag nets' beirigrelatively rotatable and said windings being disposed to cut lines of magnets: "'fi'ux l foduced by said field "as the armature and the magnets rotate relatively a cornmu'tatcr'cbnnectedto said armature and provided with a'pliirality' of'conduc'tible segments having insulating means" separating the same, there being assailan joindto'ach end respectively of eachp f sa id a um i.s a s9 feemen s. g each pair thereof being spacedapp'ro ately electrical degrees a nmnberbfsangarsepara e, conductible brushes, the brushes of "each pair thereof beingspacedapproximately180"elctrical degrees, and beingdispose d for' engagemiit"with the commutator segmle fits jsaid tissues "his the commutator being relatively rotatableQa-first'external circuit including electri ial cdriducto rsi oining one brush of one-pair thereof 'inpa'fallel'with one brush of at leastone othe rlpailr ftherof. said i a e ri b s the ciksies ga relative to the segments for successive "connection of saidwindings in par allel withthecom ductors of said circuit; and electri'cal conductdrs joined with a third aggard bruslisto'prsent a second external circuit, 'said second circuit being arranged relative to the' sginents'for successive connection'of windingsin serisfsaid first external circuit and said second enema circuit and their respectiveibrushe's "being 'arranged relative to the segments for succ ssive connection in series-parallel oi -said "wind-mas throughout operation oftlie device. LELAND L. DAVIS.

'Spon,-New York, New York, 1888, 'Chapter'X,

Open-Coil Dynamos, pp. 221 -249.

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