Improvements in Electric Motors.
Year: 1890

page_text: COMPLETE STEIFICATIVA.
Improvements in Electric Motors.
We LOUIS DUNCAN, of Johns Hopkins University in the City of Baltimore, in the
State of Maryland, United States of America, Professor, and HIRAM HENRY
CARPENTER of 22 Old Broad Street, in the City of London, Electrician, 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 electric motors and has for its object a construction, which
shall be relatively of small weight and great efficiency, wherein the revoluble parts
shall move at a low rate of speed thereby dispensing with intermediate gearing, or
belting, which is necessary, where slowly moving machinery is driven by ordinary
motors and also wherein the resultants of the moving forces are evenly distributed
throughout the revoluble parts.
Referring to the accompanying drawings, wherein the same indicating letters and
numerals, refer to the same parts on each figure,
Figure 1, represents a part sectional side view of the motor proper, a portion being
broken away to show the internal arrangement of the parts.
Figure 2, is a cross-section on the line -x of Figure 1, showing also a section of
the polar projections on one side of the motor only.
Figure 8, is a view in perspective of a portion of the armature, showing the method
of winding the same.
Figaro 4, is a similar view showing the method of winding the field, also showing
in cross-section two opposite and adjacent polar projections on each side of the
motor.
Figure 5, is a view showing the armature partly in perspective, with only four, (4)
coils of the 30 thirty, coils shown in Figure 2, the remaining twenty-six (26) coils
being omitted as they are not necessary to a proper understanding of this figure.
This also shows a plan view of a portion of the commutator, with four (4) groups of
the segments thereon, the remaining segments, numbering three hundred and sixty
(360) being equally distributed around the face of the commutator, and are omitted
in the drawings as they are not necessary for a proper understanding of this figure.
This figure shows a form of commutator, differing from that shown in Figure 1,
and which may be used with the peculiar field magnet and armature of this motor.
A, represents the shaft of the motor; B, the field magnet, which consists of the
part a, extending from side to side of the motor and the parts b, b', which I herein
denominate "polar projections" those upon the one side being further marked N,
those on the other being marked S; and the insulated wire c, comprising the winding
of the field. C, represents the armature, d, d', the windings of the same, said
armature is centered on the field, through spokes and sleeve. D, shows one form of
the commutator and e, e', e, ell, represent the intermeshing gear wheels, by
which the brushes f, ", are rotated upon it, the rings g, g, upon which the
brushes bear are connected with the opposite poles of the source of electrical
energy.
In the form shown, the field magnet is made of metal composed of the cylindrical
portion a, shrunken upon the shaft A, and of the polar projections, b, b₁, fastened
securely to the part a, bent at the upper part so that their inner surfaces form right
angles, enclosing the armature C, and so arranged that the ends of the projections on
the one side are midway between the projections on the other side. In the drawings,
a motor having twenty-eight (28) polar projections, fourteen (14) on each side is
shown. The field windings are divided into two (2) coils for convenience and are so
connected as to magnetize the field magnets in the same direction. They may be

page_text: energized by the current flowing through the armature, or they may be connectedl
in shunt relation to the armature, or otherwise in accordance with methods in
common .
I do not confine myself to this particular form of field and win ling, for under some
circumstances, it might be better that the section of the armature having the greatest
length should perpendicular to the motor shaft, instead of parallel as shown, and in
this ease the polar projections need not be returnet over the armature, but could be
straight and still present considerable surfe to the armature.
·
The essential feature of the field magnet, which forms a part of my invention, is
that the polar projections of one electrical polarity on the one side, shall be opposite
the speres between those of opposite polarity on the other side, and that they be
Tower by some even number than the coils on the armature, for a purpose hereinafter
fully describe l.
In the form of motor delineated in the drawings, the field is revoluide and attached
to the motor shaft, A, which it drives, while the armature, C, is stationary, being held
fast by the lugs, L. 12, as shown in Figure 1. but the field may be held stationary
ani the armature revoluble and attached to the shaft, A. and the motor would still
combine the essential features of my invention, which is applicable spally to either
method of driving the motor shaft A. It is necessary to state that in the latt r
mlification, it would convenient to after the forms of the field magnet and
armature.
The armature C, is a ring similar in form to the well known Paccinote, or Gramme
ring, but differing essentially as to the method of winding. A- I construct it, in a
motor having twenty-eight (28) polar projections, it has thirty (30) coils, d. d'.
surrounding it, the adjacent coils feing wound in opposite directions, instead of all
being in the same direction as in the Gramine ring. This is clearly shown in Figure 3,
there being a wire from the junction of the a tjacent coils, d, d', to one bar of a thirty
part commutator, as in the ordinary Gramme armature.
The commutator may be stationary as shown in Figure 1,-D-or revoluble as
shown in Figure 5,-1-In the Stationary form shown in Figure 1, the two
1 rn-hes, any connected with the positive and negative poles respectively of the
source of electrical energy, through the stationary rings, g², upon which they bear.
The brush o ir duble, its motion being imparted from the rotating magnet
through the train of geurs, e,,,, which is so proportioned that the brushes
me fourteen (14 revolutions for every revolution of the magnets and in opposite
direction, for the purpose hereinafter explained. In the form of commutator shown
in Figure 5, the commutator is revoluble and his four hundred and twenty (420)
segments forming the commutator Lars, divided into twenty-ight (28) group of
fifteen (15) segments each. It will be observed that there are riff as many segments
on the commutator D. us results from the multiplication at the number of polar
projections by the number of coils on the armature. The brush', are connected
with the positive and negative poles respectively of the source of electrical energy.
The turning of the commutator" D, coincides with that of the motor shaft. A. As
before stated, but four, (4) of the groups of commutator sogments are shown in the
figure, and but four (4) of the coils upon the armature; the path of the current is as
follows, it enters the commutator by the brush, passes from thence to the segment of
the commutator immediately beneath it, thence in the direction of the arrow, along
the connecting wire to the divided connection between the coils, d, d', of the
armaturo, thenee dividing the current passes through the coils d, d', shown at tho
upper part of the figure, and thence simultaneously through the other coils on each
side of the armature, around to the coils d, d', on the lower part of the figuro, thence
coming togather at the divided connection between the last mentioned coils, it follows
the direction of the arrows, back to the bar of the commutator immediately under the
brush, through which it returns to the source of energy. When the brushes are
upon these segments, all the teeth of the armaturo are energized excepting those
between the coils d, d, shown on both sides of the armature, thuse portions, by reason
of the direction of the current and the windings of the coils aro consequent poles and

page_text: therefore not energized. The connection of the brushes are so arranged that when
the current enters the coils d, d', the teeth between those coils are exactly opposite the
polar projections of the field magnet. When the commutator moves a four hundred
and twentieth of a revolution, the teeth between the succeeding coils will be exactly
opposite the succeeding polar projections, and as at the same instant the brushes pass
upon the succeeding segments of the commutator, and as these segments are divided
into groups of fifteen each, and as it is provided that all the segments of each group
shall send the current in the same direction, and also that each succeeding group of
segments shall change the direction of the current it is evident that there will be
twenty-eight (28) changes in the direction of the current at each revolution of the
commutator, a number corresponding to the number of polar projections in the field
magnet.
The operation of the motor may now be clearly understood, by referring to figure 2;
here a section of the armature is shown, together with a cross-section of one set of the
polar projections, which are marked N, these being all of the same polarity. As there
are two less of the polar projections than of the coils, d, d, of tho armature C, then if
one of these polar projections, (to which indicating numerals are added in this figure)
No. 1, is directly opposite one of the armature teeth, (which teeth are also numerically
distinguished in this figure, Nos. 1', to 30' inclusive), No. 1', then polar projection No. 15
will be opposite the armature tooth No. 16. The portion of the armature between the
coils d, d, I herein denominate "teeth."
In the position above described, when projection No. 1 is opposite tooth No. 1, and
projection No. 15 is opposite tooth No. 161, one of the brushes should be on that
seginent of the commutator connected with the coils on either side of tooth No. 1',
and the other brush should be on that segment of the commutator connected on either
side of tooth No. 16¹.
The path of the current is from the battery or dynamio to one of the rings, 9,
(see figure 1) through the brush to the segment of the commutator if the same is of
the kind shown in Figure 1. If a commutator is used, such as is shown in figure 5,
then the path of the current is through the segment of the commutator from the
brush, by the wire connection to said tooth No. 1, and in both forms of commutator,
then dividing, one-half goes through the coils to the right of that tooth and the other
half through these coils to its left, the two halves uniting after flowing through the
coils adjacent to tooth No. 16', thence passing on to the other brush, to the ring g',
and to the source of electrical energy, where the commutator is stationary as shown
in figure 1, but where the commutator is revoluble as shown in figure 5, the current
passes from tooth No. 16' to a segment of the commutator then immediately in
contact with the brush f1, and thence back to the source of energy. Under these
circumstances, the tooth No. 1' will be a consequent pole, Nos. 2 and 30', being of
opposite polarity and the same will be true of No. 16. The location of teeth Nos. 1¹
and 16 are indicated upon figure 2, by the inwardly pointing arrows.
The distribution of polarity among the remaining teeth will be as indicated thereon,
by the letters N, S, in figure 2. If the polar projections are of positive polarity, the
direction will be opposite to that of the hands of a watch.
When the motor has passed through a portion of a revolution equal to one twenty-
eighth of a revolution less one thirtieth of a revolution, that is to say through one
four hundred and twentieth part of a revolution, the polar projection No. 28,-
(between the teeth No. 1' and 27)-will come opposite the tooth No. 30, and pro-
jection No. 14 will be opposite tooth No. 15. The condition of affairs will now be
precisely as before, for in either form of commutator the brushes are on the segment
of the commutator corresponding with and connected to teeth No. 15¹ and No. 30',
they having gone through one thirtieth of a revolution, in the form of commutator
shown in figure 1; and the commutator having moved through one four hundred and
twentieth of a revolution in the form shown in figure 5, and the next succeeding
segment has been brought under the brushes.
It is evident that in the case of a stationary commutator with revoluble brushes,
such as is shown in figure 1, that the brushes move through one thirtieth of a

page_text: revolution while the field magnet moves through one four hundred and twentieth of a
resolution, for the brushes move fourteen times faster than the magnet, this multiple
of the rate of speed being effected by means of the gear wheel, e, el, el, e, sucli a
commutator wont have thirty segments, or if as shown in Ggure 5, the commutator is
revoluble and the brushes stationary, the current is brought into the coils on the
armature at the instant of apposition of the coils and polar projection, by providing
such commnitor with twenty-eight groups of segments with 15 segments in each
group and revolving the commutator at a rate of speed coincident with the motor
slift A.
I do not confine myself to any particular form of commutator, only requiring the
essential feature that the brushes Shall be on the commutator segments corresponding
to the teeth which are at that instant exactly opposite the polar projections.
Having now particularly described and ascertained the nature of our suid inven-
tion and in what inanner” the same is to be performed we declare that what we
claim is :-
1. In an electric motor, the field magnet B. having polar projections, b, b', on
opposite sides those upon the one side being of one magnetic polarity, and those upon
the opposite being of opposite polarity, arranged so that those upon the one side shall
he opposite the spaces upon the opposite side, in combination with the armature (',
having a number of coils wound thereon, each adjacent coil being wound in an
opposite direction, and the number of said coils greater by some even number than
the number of said polar projections, as and for the purpose intended, substantially as
described.
2. In an electric motor, the combination of the field magnet B, having polar
projections, b, b', of opposite magnetic polarity, armature C, having a number of coils
wound thereon, each adjacent coil being wound in an opposite direction, and the
number of said coils leing greater by some even number than the number of said polar
projections and the revolvable commutator 1, composed of the following parts, to-wit,
the brushes, connected with the source of electrical energy, , and hearing upon the
face of the commutator, the segments of the revoluble part, of a number equal to that
number which results from the multiplication of the number of the polar projections
by the number of coils upon the armature, divided by the difference between the
number of such coils and the number of such polar projections, the succeeding
segments bring connected with the succeeding coils upon the armature, as and for the
purpose intended, substantially as described.
3. In an electric motor, the combination of the herein described field magnet B,
with the opposite polar projections, h, the herein described armature (, and its
adjacent oppositely wound coils, d, d', and the herein described commutating device,
so arranged and connected with said coils that the brushes, will always be upon
those segments of the commutator, which are connected with those coils upon the
armature enclosing the teeth, which are at that instant directly opposite the polar
projections of the said field magnet, as and for the purpose intended, substantially as
described.
.1
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