Improvements in Dynamo-Electric Machines and Electro-Motors.
Year: 1887

page_text: Date of Application, 18th Nov., 1887"
Specification Accepted, 27th Jan., 1888
Improvements in Dynamo-Electric Machines and Electro-Motors.
I, WILLIAM MAIN, of number 857 Marcy Avenue, in the City of Brooklyn, in the
County of Kings in the State of New York, United States of America, Electrical
Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement:-
This invention relates to dynamo-electric or magneto electric machines for generating
alternating or continuous currents, and to electro-motors. Its objects are to combine
the utmost efficiency with the least weight and the greatest compactness that are
practically possible in such machines.
To this end I have introduced by this invention some radically new principles and
features applicable to machinery of this class. Before proceeding to describe the
mechanical constructions which I have devised for the operative machines built
according to my invention, 1 will endeavour to make clear the new general principles
which it involves.
In a dynamo or motor the magnetic circuit consists of two parts, one comprised in
the field-magnet and the other in the armature. Throughout this circuit there exists a
condition of strain known as magnetism, and which develops itself along certain lines
known as "lines of force". When a magnetic circuit is closed, and is of nearly equal
magnetic conductivity throughout, these lines of force are confined entirely within the
circuit and give no external manifestations; but on any break being made in the
magnetic connection the lines of force are compelled to stretch themselves through air,
or other non-magnetic body, which opposes an extreme resistance, and proportionally
reduces the strength of the magnetic excitation. In a dynamo it is necessary for
mechanical reasons to leave a gap or air-space at two places in the magnetic circuit to
divide the moving from the stationary part thereof. In the accompanying drawings
Fig. 1 shows the magnetic circuit of an ordinary type, of dynamo, A being the
armature and F the field-magnet. The dotted lines show approximately the direction
and distribution of the lines of force.
.
The magnetic strain is necessarily equal at all parts of a magnetic circuit, so that,
as in an electric circuit, conditions that increase resistance and lessen flow or magnetic
strain at one point will also equally reduce the magnetism at all other points. Thus

page_text: magnetic lines at that point, and, if the excitation is sufficient, will result in saturation,
thereby forcing some of the lines of force to pass through the air, and by the
resistance thus created reducing proportionally the magnetism on the entire circuit.
In the construction of a dynamo or motor the following conditions are most
desirable -
1st. Least length of the iron circuit and least possible break in it.
2nd. Greatest cross-section for the iron circuit.
3rd. Greatest length of the electric conductor.
4th. Least distance of the iron from the electric conductor.
The first two of these conditions relate to the resistance of the magnetic circuit,
which should be kept as low as possible, to avoid saturation. The last two relate to
the reaction between the iron and the conducting wire, the object being to ensure the
conversion of the greatest number of lines of force that is possible without waste.
For example, experience proves that a greater total magnetization may be realized from
a given length of wire by winding it in a shallow coil around a large iron drum than
by winding it in a thicker coil around a core of less diameter.
Bearing in mind these general principles, I will now proceed to indicate the generic
feature of my present invention.
Let us assume as an example an annular armature of the character of a Gramme
ring. On passing a current through its coils it develops magnetic poles at diametrically
opposite sides. In the absence of a field-magnet the lines of force would be closed
through the air. In the ordinary constructions of dynamos a field-magnet is arranged
exterior to the ring, which closes the magnetic circuit by gathering together all the
external lines of force and passing them in a compact bundle through the U-shaped
iron of the field-magnet. This is shown graphically in Fig. 1. It is thus far the
almost universal construction in dynamos, being varied only in arrangement and
mechanical construction, but not in principle. Its defect lies in the necessity for
considerable length of field-magnet cores, thus creating unnecessary magnetic resist-
ance, and also involving, in most constructions, some magnetic short-circuiting, or
leaking of the lines of force across between the field cores instead of passing them all
through the armature. It also involves a great disproportion in weight and bulk
between the armature and the field magnet, whereas theoretically the stationary and
moving parts of the magnetic circuit should be of equal mass, although in practice it
is found desirable in dynamos to give the field magnet considerable preponderance of
weight. This disproportion is essential in self-exciting dynamos, as otherwise the
counter-current on starting them would neutralize the direct current, and there would
be no excitation of the field.
In a dynamo the current induced by the rotation of the armature opposes the
stationary lines of force and tends to drive them back into the field-magnet poles. In
a motor on the contrary there is no such effect, since it is necessarily operated by au
independent and overmastering current, and the stationary and moving magnetic lines
created thereby oppose each other in one tangential direction and reinforce each other
in the other. Hence the theoretical equal division of the armature and field magnet
should be for a motor the best condition.
Figs. 2 and 3 illustrate a method of closing the magnetic circuit that has been used
with motors. The armature A is here made of large diameter, and the field magnet F
is arranged within it, crossing diametrically from one side to the other (see Fig. 2) in
the plane of the armature (see Fig. 3). The dotted lines show the direction of the
lines of force. This disposition of field magnet has the disadvantage that the field
magnet is too small and its polar are is too large proportionally to the armature, so
that on the one hand the field magnet has insufficient magnetic force to effect a
thorough reaction with the armature, and on the other hand the wide poles magnetic-
ally short-circuit and render useless a large proportion of the armature. In motors
made according to this plan the field magnet has only 25 per cent. while the armature
has 75 per cent. of the weight.
Thus heretofore the magnetic circuit between the opposite poles of an armature has

page_text: been closed in two different ways:-by means of (1) a field-magnet entirely outside
of the armature; and (2) a field-magnet entirely inside of the armature. In both
cases the number of poles has been multiplied, using 4, 6, 8 or more poles instead of 2.
In either case either the armature or field-magnet may rotate ;-for mechanical reasons
the lighter member is best made the rotative one, so that in machines of the 1st class
the armature has been made rotative, and in those of the 2nd class the field-magnet
has been made to rotate. By the armature I mean the part in the coils of which the
alternations of current occur, and by the field-magnet I mean the part in the coils of
which the current is continuous.
My present invention relates, not to those generators or motors whose armature is
of the "Gramme type," but to those in which the magnetic "lines of force" are
always substantially perpendicular to the plane of the armature coils, and in which
the action is due to a transition either from a dense to a feeble magnetic "field of
force," or from a field of force of one polarity to that of the opposite polarity. Most
alternate-current dynamos are of this class. The armature which I employ is of ring-
form, consisting of coils arranged with their axes approximately parallel to one another
and parallel to and equally distant from the axis of rotation.
Figs. 4, and 6 are diagrammatic views illustrating the principle of my invention
as embodied in a dynamo of the simplest construction. Fig. 4 is a vertical mid-section,
cut in the plane of the axis; Fig. 5 is a front elevation of the armature and the field-
exciting coil, (the field-magnet being removed); and Fig. 6 is a front view of the
field-magnet alone, in mid-section cut transversely of the axis.
A is the ring-shaped armature, having an open centre, and F is the field-magnet.
The magnetic circuit of the armature is closed by the field-magnet passing through
the open centre of the armature, from one side thereof to the other, thereby crossing
the plane of the armature. Thus the field-magnet is arranged neither entirely outside
of the armature, as in Fig. 1, nor entirely inside the armature, as in Figs. 2 and 3 ;
but it is partly outside of and partly inside the armature. The middle portion of the
field-magnet passes through the centre of the armature, being preferably parallel with
the axis of rotation, xx, and each end of the field-magnet extends thence radially and
terminates in poles a a, which come close to the armature, adjacent to the respective
poles therein. Thus the contrary poles of the field-magnet are on opposites sides of
the plane of the armature.
My invention thus introduces a radical departure in the arrangement of the field-
magnet, by which the average length of the magnetic circuit is reduced, and its
aggregate cross-section is proportionally increased. Thereby, for electro-motors, the
enlargement of the armature to equal mass with the field-magnet (whereby the highest
efficiency attained) is rendered possible, without necessitating the abnormally long
field-magnet needed for external closure of the magnetic circuit (Fig. 1); while at
the same time the abnormally small field-magnets unavoidable with the system of
internal closure (Figs. 2 and 3) are avoided. My system admits of the convenient
division of large armatures into the consecutive magnetic sections which experience
proves to add so greatly to their efficiency, without thereby multiplying the field-
magnet coils.
In addition, my invention introduces a feature of mechanical advantage which is
practically very important, namely, the ability to dispense with all moving wire, since
both the armature and field coils may be made stationary. Thus the revolving part is
relieved of carrying a load of wire with it, and the electrical connections are
simplified.
I will now describe Figs. 4, 5 and 6 in detail. The machine that they illustrate is
a dynamo for generating alternating currents. The armature A consists of twelve
coils c c arranged equi-distantly in a circle with parallel axes. Within each coil is a
short iron core j. The coils c c are connected together serially in alternate order so
that a continuous current traversing them would impart to their cores alternately-
opposite polarities.
The field-magnet F has a large central core b at each end of which are six radial
pole-pieces a a which extend in the manner shown in Figs. 4 and 6 and terminate

page_text: close to the ends of the cores jj, so that when one of these cores is in line with two
opposite pole-pieces the magnetic circuit is closed in the manner indicated by the dotted
lines of force in Fig. 4. The opposite pole-pieces a a are arranged directly opposite
each other.
The field-exciting coil E is arranged within the ring-armature, and it encloses the
core 6 of the field-magnet, a clearance space being left between them, to admit of the
free rotation of the field-magnet. The pole-pieces a a extend radially past the opposite
ends of this coil.
Either the armature or field-magnet may be stationary. These figures show the
armature stationary and the field-magnet rotative. The coil E is fastened in the
armature, and is stationary.
The "lines of force" generated in the field-magnet by an electric current in the
coil E stream through the core bin a short bundle or column and are distributed
radially by the pole-pieces, the magnetic circuit being completed through the
cores ff.
The action is substantially the same as in previous alternating machines. As each
pair of field-poles advance one-twelfth of a revolution, from the position coincident
with one core j, to that coincident with the next one, a current in one direction is
generated in the armature coils, and as the poles advance the next twelfth of a
revolution, to coincidence with the next successive core j, a current in the opposite
direction is generated. Thus with twelve coils c c and six pole-pieces a a the direction
of the current is reversed twelve times to each revolution."
For an alternating current dynamo there may be any number of pairs of contrary
pole-pieces a a, and there should be twice as many coils c c as there are pairs of
pole-pieces.
If it is desired to generate rectified or pulsatory currents, a simple rectifying
commutator will be added, as any practical electrician will understand.
If the machine is to generate continuous currents of uniform potential, the number
of pairs of poles a a must be either greater or less than half the number of armature
coils, and a suitable commutator must be provided to reverse the current in each coil
whenever a pair of poles comes into line with its axis, and to again reverse it when
the next following pair of poles has approached to a point where it and the receding
pair are equally distant from the coil. I will describe such a commutator.
For an electro-motor to be driven by a continuous current this last construction
should be used. The armature coils will then attract all the poles a a in the same
direction, causing the field-magnet to rotate.
I will now describe a complete, practical electro-motor, embodying my entire
invention.
Fig. 7 is a front elevation of this improved electro-motor.
Fig. 8 is a side elevation thereof, the enclosing case being partly broken away.
Fig. 9 is a vertical longitudinal mid-section looking in the same direction as
Fig. 8.
Fig. 10 is a front view in vertical transverse section cut on the line 10-10 in
Figs. 8 and 9.
Fig. 11 is a front view showing the armature and field-coils partially dissected in
planes denoted by the three dotted lines 11-11 in Figs. 8 and 9.
In this electro-motor the armature A has 12 coils c c, and is stationary; while the
field-magnet F has 5 pole-pieces a a and is rotative.
On the base B are fastened two upright frames D D, (Figs. 7 and 8) which form
bearings for the axial shaft C. The field-magnet consists of a thick tubular cylindrical
core b which is fastened on the shaft C, and of two end pieces or heads a¹ a¹ (Figs. 9
and 10 which are fastened against the opposite ends of the core b and are formed
with five equi-distant arms or pole-pieces a a. To each of these projecting arms is
fastened a block a", which blocks constitute the extreme pole-pieces or poles of the
field-magnet, and approach each other in pairs on the opposite sides of the armature,
(see Fig. 8).
The armature A consists of twelve short iron cores jj on which are wound the

page_text: coils c c, and of two iron rings R R which rest against the ends of the respective
cores on opposite sides of the armature.
The rings R R make a magnetic connection between the successive cores, thereby
forming a succession of closed magnetic circuits, as will be understood on reference
to the diagram Fig. 12, which is a development of the iron portion of the armature
in a flat plane. The dotted lines illustrate the lines of force, and show how they pass
from each core through the rings R R in both directions to the next core j and
back. The rings R R thus avoid the waste of magnetic energy due to the projection
through the air of the lines of magnetic force generated in the armature.
For preventing Foucault currents it preferable to slit the cores jj along one
side (Fig. 11) and to laminate the rings R R. Each ring R is made by winding a
soft-iron ribbon spirally upon itself, with a strip of paper or other insulating material
to separate its convolutions, (Figs. 9 and 11). Twelve plates kk (also slitted to
avoid Foucault currents) are sunk flush into notches cut in the outer side of each
ring R (Fig. 11) and the screws by which the rings R R are fastened to the cores
are passed through these plates (Fig. 9).
The coils ce may be of round insulated wire, as shown in Figs. 4 and 5, but I
prefer to make them of overlapping coils of copper ribbon, as shown in Figs. 9
and 11. The copper ribbon is wound spirally with a thickness of paper, silk or other
insulating material between its convolutions, and disks of insulating material are
placed against the opposite sides of the spiral coils. Each coil covers only half the
length of the core j and overlaps the adjoining coils on both sides. As the current
flows in opposite directions in the successive coils, it necessarily flows in the same
general direction (i.e. toward or from the axis of rotation) in the overlapping portions
of the coils, so that the current in one coil co-operates with and reinforces that in the
next coil.
The field-coil E is wound within the circle of armature coils and extends outwardly
on both sides thereof, (Fig. 9) nearly to the rings RR. Two rings are slipped
over the coil E and fit inside of the rings R R. The field-coil E is thus united firmly
to the armature. The armature is fastened to the fixed frames D D through the
medium of two cylindrical hoops mm (Figs. 8 and 9) each of which fits into a
concentric rabbet on the inner side of one of the frames D, and is itself formed with
a rabbet which engages the outer corner of the ring R. The frames D D are drawn
together by means of screws or bolts n n to tightly clamp the parts. The rings m m,
in connection with the frames D D serve as a casing for partially enclosing the
rotating field-magnet, in order to protect the pole-pieces from contact with
obstructions.
I will now describe the commutator. It has stationary segments e e connected to
the stationary armature coils c c, and rotating brushes ff1 carried by the shaft C.
Two positive and two negative brushes are shown, but one is sufficient. The two
positive brushes ff are mounted on arms g g which project from one hub h, against
the end of which is pressed a copper strip or take-off brush i, all as shown in Fig. 9.
The two negative brushes f₁fare mounted on two arms g₁ g¹ which project from
a disk h, from the centre of which a pin h projects axially and on it is screwed
a nut ¹, against the face of which is pressed a copper strip or take-off brush 2
shown in Figs. 7 and 9. The take-off strips i and i¹ are pressed into good electrical
contact with the surfaces of the hub h and nut by means of a screw n¹ of
insulating material which presses them apart. The respective strips are clamped
to separate binding frames or posts o and o¹, to which the respective circuit wires are
connected. Thus the terminals of the circuit are carried into the respective commutator
brushes ff and f¹ƒ³.
as
The stationary parts of the commutator are carried by a cup G which is fastened
to the front frame D. There are 60 commutator segments e e (being the product of
the 12 armature coils multiplied by the pairs of pole pieces). Each segment e is
notched on its front and rear sides, so that when the 60 segments are fitted together
their notches coincide and form concentric grooves, into which are fitted rings 99,
with intervening insulations, as shown in Fig. 9. The segments are held in position

page_text: by screwing a nange p onto the cup, thereby clamping them against a uxed
flange p.
On the outside of the cup G, behind the flange p, are twelve rings rr of metal,
with intervening insulations. Each ring has five equi-distant arms a projecting
from it, as shown in the perspective view, Fig. 13. Between each two of the armature
coils a wire or conductor d is connected and the 12 wires d d are connected to the
12 rings respectively. The five arms of each ring rare bent forward and
attached each to a separate one of the commutator segments e, as shown in Figs. 8
and 9. Thus the 60 segments e e are divided into 5 groups of 12 segments in each
group, the first segment being connected to the first coil c, the second segment to
the second coil, and so on through the entire 12 segments of each group.
The two positive brushes ff should be so adjusted that when one of them is in
contact with one of the five commutator segments that are in connection with one
ring and one coil c the other brush will be in contact with any other one of these
five segments, so that the current entering by these two brushes will reunite in the
one plater and be thence conducted by the one conductor d to one pair of coils.
The negative brushes f₁ f' are likewise arranged to make contact both with the
segments of one set of five.
The brush-arms g g¹ are fixed to a hub H of insulating material, which is slipped
onto the front end of the shaft C, (within the cup G) and, when adjusted to the
correct position, is fastened thereto as shown in Fig. 14. A screw
may be turned
by a screw-driver from the front, and on screwing it in, a cone formed on it engages
eccentrically with a hole in a sliding key s, thus forcing this key against the shaft C,
and thereby binding the hub firmly thereto, so that the brushes cannot become
displaced.
The general method of commutation here employed is not new in itself. I will
briefly describe its action.
As the brushes revolve forward successive reversals of current occur in the armature
coils in a backward direction. An imaginary diametrical line crossing the armature
from the point where the current enters and divides to the point where the current
reunites and leaves the armature, and which may be called the "neutral line," rotates
backward one entire revolution, while the field-magnet moves forward one-fifth of a
revolution. The current in each coil is thus reversed ten times to each revolution of
the field, so that there are one hundred and twenty reversals to each complete revolu-
tion. In each coil the current flows in one direction during one-tenth of a
revolution, while it is attracting a pole of the field, and it is then reversed for the
ensuing one-tenth of a revolution during which it acts to repel this pole. At each
one-sixtieth of a revolution two diametrically opposite coils are reversed.
The reactions of the field-magnet poles against the armature may be understood
from Fig. 12. The lines of force stream across from the north poles on one side to
the south poles on the other, following almost entirely the iron of the armature. It
will be observed that these lines of force are all deflected in one direction. This is
due to the reaction of the lines of force generated in the armature by the coils c c
thereof The well known tendency of the lines of force to shorten themselves results
in pulling forward the field-magnet poles, in the direction of the arrow.
My invention may be modified in many ways without departing from its essential
features. Figs. 15 and 16 illustrate an example of one such modification. These
figures illustrate a machine designed as a dynamo for generating continuous
currents.
Fig. 15 is a vertical longitudinal section of the machine in the plane of the axis of
rotation; and
Fig. 16 is a front view thereof partly in section cut on the line 16-16 in Fig. 15.
The field-magnet F is of greater mass than in the previous construction, and has a
larger exciting coil. The core b, consists of a large open tube, around which is
wound the exciting coil E. This tube b is confined between the polar disks a¹ a¹,
which are formed with eight radiating arms or pole-pieces a a, which approach each
other, leaving only room between them for the armature.

page_text: The field-magnet and its coil E are stationary, being fastened on the central
shaft C which is itself clamped fast to the bearing frames D D. The armature A is
made rotative, being mounted in a shell or casing P which serves also as a pulley for
carrying a belt in order to drive the armature. The armature is fastened to the
casing P by being clamped between a fixed flange m, and a ring m' which are drawn
together by means of screws or bolts n n.
With the proportions shown the armature has 16 coils, while the field-magnet has
9 pole-pieces. I have shown that when the number of pairs of pole-pieces is less than
half the number of coils c c the "neutral line" in the armature, if the latter be
stationary, rotates backward. Conversely, when the number of pairs of pole-pieces is
greater than half, the "neutral line" rotates forward. In this case if the armature
were stationary and the pole-pieces revolving, the neutral line would revolve forward
with nine times the rapidity of the poles. But since in this machine the armature
revolves forward while the field-magnet is stationary, the "neutral line" actually
revolves backward (i.e. in the opposite direction to the armature) with a velocity, as
compared with the armature, of 9 to 1, but as compared with a stationary part it
revolves backward 8 times while the armature is revolving forward once. This may
be accomplished by means of stationary commutator brushes and a commutator of
nine successive series of sixteen segments in each (i.e. of 144 segments in all), but
the method shown in the drawings accomplishes this purpose by different means,
namely, by rotating the commutator brushes backward at a speed of eight revolutions
while the armature and commutator segments are revolving forward one revolution.
The commutator segments e e are carried on the hub of one of the disks P' of the
casing P. Attached to this disk is an internal gear I, which gears with a pinion J,
fastened on a short shaft J', on which is fastened a gear K₁ which meshes with a
pinion K that turns freely on the stationary shaft C. The proportions of the several
gears I J J K and K are such that a rotation of I in one direction causes a rotation
of K at eight times the velocity in the opposite direction. Attached to the pinion J
are the brush arms 9 9' carrying the brushes ff, and which are
respectively with two insulated rings h h which are swept by take-off brushes i
and . The respective movements of the commutator segments and brushes result
in 288 reversals of current in the armature coils to each revolution of the armature.
My invention is adapted to magneto-electric machines as well as to dynamo electric
machines. For such it is only necessary to employ permanent magnets for the
field-magnet F and to omit the exciting coil E.
connected
The iron armature rings R R are not essential to my invention, and may be
omitted. They are chiefly desirable in an electro-motor. The armature cores jj
may be omitted if desired, in which case the coils c c should be made flat and thin,
to bring the opposite poles a a as close together as possible, and shorten the gap or
"field of force.'
My improved disposition of field-magnet may be applied with any kind of armature
which is ring-shaped and has an open centre through which the field-magnet may
extend. But I make no claim in this application for patent to its employment with
armatures of the Gramme type, since that is intended to be claimed by me in another
application for patent for "Improvements in Electro-Motors and Dynamo Electric
Machines."
It is characteristic of my present invention and essential to it, that the armature
shall be so wound as to develop alternate north and south poles presented to the
poles of the field-magnet as the armature is traversed circumferentially; and there
may be any suitable number of magnetic poles in the armature. But as before stated
my present application for patent excludes armatures of the "Gramme type."
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed, I declare that what I claim is
In a dynamo (or magneto) electric machine, or an electro-motor, the following-
defined features:―
1. A ring armature consisting of coils so wound as to develop alternating poles

page_text: (but excepting armatures of the Gramme type) in combination with a field-magnet
extending through the open centre of the armature, and having its contrary poles
disposed adjacent to the armature on opposite sides thereof.
2. A ring armature consisting of coils so wound as to develop alternating poles
around its circumference, (but excepting armatures of the Gramme type) and a
commutator adapted to alternately reverse the current in each coil, and to effect
successive reversals in the successive coils, in combination with a field-magnet
extending through the open centre of the armature and having its contrary poles
disposed adjacent to the armature on opposite sides thereof.
3. A ring armature having its coils so wound as to develop alternating poles (but
excepting armatures of the Gramme type) and a field-magnet having its middle
portion or core extending through the open centre of the armature, from one side to
the other thereof, in combination with a field-exciting coil wound to enclose the core
of the field-magnet.
4. A stationary ring armature (but excepting armatures of the Gramme type) and
a rotative field-magnet having its middle portion or core extending through the open
centre of the armature from one side to the other thereof, in combination with a
stationary field-exciting coil enclosing the rotative core of the field-magnet, whereby
all moving wire may be avoided.
5. The combination with a ring armature of a field-magnet having its middle
portion extending through the open centre of the armature, and having pairs of poles
of contrary polarity arranged closely adjacent to the armature on opposite sides
thereof and the two poles of each pair arranged directly opposite each other.
6. A ring armature consisting of a succession of oppositely-wound coils arranged
in a circle with their axes substantially parallel to the axis of rotation, in combination
with a field-magnet extending through the open centre of the armature and having
pairs of poles of contrary polarity disposed oppositely to one another and adjacent to
the opposite sides of the armature, the poles of one polarity being on one side of the
armature and those of the contrary polarity on the opposite side thereof.
7. A ring armature consisting of a succession of oppositely-wound coils arranged
in a circle with their axes parallel to the axis of rotation, in combination with a field-
magnet extending through the open centre of the armature and having radial pole-
pieces extending to equidistant points around the circumference of the armature, with
the poles of contrary polarities arranged in pairs opposite to each other and on opposite
sides of the armature, the said pairs of poles being greater or less in number than half
the number of coils in the arinature, and with a commutator adapted to reverse the
current in each coil of the armature whenever any pair of poles reaches a position
opposite to such coil, and to again reverse the current in such coil whenever any two
successive pairs of poles reach positions equally distant therefrom.
8. A ring armature consisting of a circular series of cores wound with coils and
arranged with their axes parallel to the axis of rotation, and two iron rings fastened
against opposite ends of said cores, whereby said rings serve to form closed magnetic
circuits between the successive cores, in combination with a field-magnet having pairs
of poles of contrary polarity arranged face to face on opposite sides of the armature
and closely adjacent to said iron rings.
9. The construction of the iron rings R R of spiral laminae having their convolutions
insulated from one another, to prevent Foucault currents.
10. The construction of the ring armature with flat alternated coils c c overlapping
one another.
11. The construction by means of which the ring armature is held in place, and the
rotating field-magnet is enclosed and protected, consisting of the cylindrical hoops m m
embracing the arinature between them, and clamped between the frames D D.
12. A ring armature consisting of a circular series of cores wound with coils and
arranged with their axes parallel to the axis of rotation, in combination with a field-
exciting coil wound within and fixed to said armature, and a field-magnet consisting
of a central core arranged to revolve within said exciting coil, and radial pole-pieces
fastened to opposite ends of said core, extending beyond said exciting coil at both

page_text: ends thereof and terminating in poles closely adjacent to the armature on opposite
sides of the latter.
13. A stationary ring armature having its successive coils wound in opposite
directions, and a revolving field-magnet, in combination with a commutator consisting
of as many stationary segments as the product of the number of armature coils
multiplied by the number of pairs of field-magnet poles, electrical connections between
each coil and as many segments, equidistantly disposed, as there are pairs of field-
magnet poles, and the commutator brushes revolving with the field-magnet.
14. The combination with the armature coils and commutator segments of the con-
struction of electrical connections for grouping the segments consisting of the rings rr
having arms connected to the respective segments as described.
15. The construction of fastening for uniting the commutator brushes to the shaft,
consisting of a hub fastened to the shaft by a radial key, moved by an eccentric coned
screw, substantially as shown in Fig. 14.