Improvements in and relating to Electric Motors or Dynamo Electric Machines.
Year: 1891

page_text: Date of Application, 5th May, 1891-Accepted, 11th July, 1891
COMPLETE SPECIFICATION.
[Communicated from abroad by THE CROCKER WHEELER ELECTRIC MOTOR
COMPANY, of 430 to 432, West 14th Street, New York, United States of
America.]
Improvements in and relating to Electric Motors or Dynamo Electric
Machines.
I, HENRY HARRIS LAKE, of the firm of Haseltine Lake & Co. Patent Agents,
45 Southampton Buildings in the County of Middlesex, 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 :-
The first part of this invention comprises improvements in armatures for electric
motors or dynamo electric machines.
Heretofore, armatures for electric motors and dynamo electric machines have
been constructed with the iron armature cores projecting from the faces of the pole
pieces the copper conductors or winding being sunk in slots of greater or less depth
in the surface of the cores. The advantages of constructing an armature on this
principle are, First, that it increases the specific strength of the magnetism in the
armature, owing to the fact that the gaps in the magnetic circuit are largely
reduced, and it also increases the amount of conductor or winding that can be put
upon the armature, since the slots can be made of considerable depth, and Second
that it reduces the amount of copper on the field magnet necessary to bring it up to
strength and the copper winding being sunk in the iron core, is entirely protected
by it from mechanical injury.
This part of the invention consists in certain improvements in this kind of an
armature, especially applicable to the Gramme ring form, the object being to increase,
as much as possible, the amount of conductor or winding and to present as large a
tooth surface as possible to the field; to have the openings of the slots so narrow
compared with the iron portions or teeth lying between them that the pole pieces
can be brought close to the armature core without the production of eddy or Foucault
currents in the pole pieces, and to provide a better means of mechanically mounting
the armature upon its shaft.
In the accompanying drawings,
Figure 1 shows an end view of the improved armature core with a part of the
armature coils in place.
Figures 2 and 3, are side and end views respectively.
Figure 4, is a perspective view of the improved core.
Figure 5, represents one portion of a field magnet, comprising the pole piece and
core proper; a frame in which it is clamped in a certain fixed position, and a tool
for shaping the end of the core according to my invention.
Figure 6 shows the completed field magnet with the parts shown partly in
elevation and partly in section
Figure 7 illustrates in side elevation, a milling tool in position for milling or
dressing the end of a field magnet core held in alignment with the axis of the
core.
Figure 8, is an end or plan view of said tool.
Figure 9 is a sectional view taken through Figure 5 and
Figure 10 shows a frame or jig for boring or shaping the base of the field magnet
so as to receive the cores.
It may
A is the iron armature core which is preferably made in two halves.
conveniently be wound separately and afterwards united together by dove-tail joints
and pins, or bolts B B passing through the joints, though, of course, it can be made
in a solid ring.

page_text: The slots or spaces a a a in which the windings are placed are made in trapezoidal
or tapering form as shown in the drawings, that is, so that they are quite
narrow at the top and comparatively wide at the bottom with inclined sides. The
shape of these slots, that is their depth and their comparative width at the top
and bottom, as well as their average width, is determined by the size of the ring and
the number of coils or sections there are to be in the winding. In the armature
shown in Figure 1, for example, there are twelve coils or armature sections, and the
shape of each coil is preferably made such, that they will form trapezoidal coils by
lying close to each other and completely filling the polygonal space on the inside of
the ring. This trapezoidal shape of the inside portion of the coils determines the
shape of the slots a a a which receive the outer portion of the coils as clearly shown.
To secure the greatest theoretical amount of winding for a given sized slot, it is
evident that the shape of the coils should be strictly trapezoidal, the slot having
straight sides; but this, of course, is not essential to this part of the invention, as
the slots and coils might be made of a generally trapezoidal shape, that is so as to
be wider at the bottom than at the top, without materially affecting the value of the
construction.
By constructing the slots and coils in this way, a number of very important
advantages are secured viz.:-1st: The ring holds the greatest possible amount of
copper conductor or winding since the inner space of the ring which determines the
amount of winding, is completely or nearly filled with wire, the adjacent coils lying
in contact and being trapezoidal or approximately trapezoidal, practically occupy
the full armature space so that the output of the armature is as great as possible
from that cause. 2nd Each coil is symmetrical outside and inside the ring, so
that the windings may be easily and neatly laid in place and none of the wires cross
each other. 3rd: By making the slots a a a very narrow at their openings, the area
of the tooth surface or iron portion of the core presented to the field is increased to
a maximum, which increases the specific strength of the magnetic field and enables the
field to be saturated with less winding. 4th: The openings of the slots or gaps in
the iron core being very small compared with the whole surface of the core, the
pole pieces can be brought close to the teeth, without the production of eddy or
Foucault currents. 5th When the winding is once packed in the slot the tapering
shape thereof prevents it from flying out by centrifugal force.
In order to prevent the insulated conductors from touching the iron core, a sheet
or strip of insulating material C, such as canvas is folded in to fit the slots and
may be conveniently glued in place before the conductors are wound in place. At
each end of the ring a plate of hard insulating material D, D, such as fibre, is
secured. It is cut in the shape of the iron core of the same size or a trifle larger so
that its edges slightly overhang the edges of the slot, as shown, and so that when
the wire is wound in place, it will bear on the corners upon the fibre plate, instead
of upon the edges or corners of the iron, thus making leaks in the armature from
this cause practically impossible.
In this form of armature, with the iron core reaching out to the pole pieces, the
magnetism is found to be so intense that with an unsymmetrical field, such as the
ordinary horse-shoe form, as shown in the drawing, there is a strong tendency of
the field to draw the armature toward the yoke or the centre of the field magnet.
To overcome this tendency as far as possible, the toes or outer ends T T of the pole
pieces are curved further around the armature than the corresponding points t t of
the poles on the other side of the armature, and in this way the magnetism is
uniformly distributed with reference to the centre line of the armature.
The second part of this invention is directed to a novel method of, and means for
bringing about the most accurate union or connection between the field magnets and
the yoke which unites them; and the means for accomplishing this are fully
illustrated in Figures 5, 6, 7, 8, 9 and 10 of the drawings.
It is preferred to construct the field magnet of two cores C¹ C₁ formed with pole
pieces P', attached and fitted in the yoke or base B' as clearly shown in Figure 6.
These cores and pole pieces are preferably constructed in the form of wrought iron

page_text: forgings and may be most readily and cheaply made of the required accurarcy in
strips by drop forging them in dies in the well known way. The great advantage of
the wrought iron cores and pole pieces is that they can be made in one piece, and
the core can be as small as possible in section and still have the necessary magnetic
capacity and by drop forging them they can be brought to shape with sufficient
accuracy to enable them to be manufactured by this method of turning and fitting
the parts together.
The field cores C¹ C' as they come from the drop-forging are clamped upon a
block or jig K, mounted upon the slide or table of a suitable milling machine so that
the core can be fed along endwise into a milling tool or cutter made in the form of
a "hollow mill" which revolves in the machine. The field core C is placed so that
the concave side of its pole piece fits upon a cylindrical block J forming part of the
jig K and set in such a position as to bring the axis of the hollow milling tool W,
provided with an adjustable retaining collar located around the outer circumference
of its teeth and being concentric with the axis of the cylindrical part of the core C¹.
The straight part of the core C₁is held in truc position by a support S and a clamp s
which secures it in place. The position sidewise of the core is determined by the
support S which is made in the form of a V or crotch, and the pin against which
the side of the pole piece is forced; the position of the field core being thus
determined with reference to three things; the round part of the core C; the
concave face of the pole piece; and the side or edge of the pole piece, all of which
are practically true and accurate in the drop forgings.
"
The field core as thus clamped in position is gradually fed into the hollow milling
ool W, and the end of the core thus reduced to a uniform size and a perfectly
true cylindrical shape the end of the core being shaped entirely and accurately
with reference to the concave face of the pole piece. The movement of the core
is continued until the milling tool W strikes the stop T₁, thus determining the
length of core milled off in this way and leaving a shoulder at a uniform point
which determines the depth to which the cores sink when slipped into the yoke or
bed plate B' which unites them together. The bed plate of the machine itself may
preferably be employed to form the yoke and at the same time the support or
mounting of the field cores, and as this may be made large, it may as well be made
of cast iron. In order to fit the cores into this bed plate B in their true position
so that the faces of the pole pieces form a true cylindrical space for the armature
(which is especially important where a form of armature is employed in which the
iron core fills the armature space and reaches out to the faces of the pole pieces),
the base is clamped in a boring frame or jig K having a hinged cover or portion N
provided with drill bushing L L placed so that their axes are exactly the same
distance apart as are the axes of the field cores C¹ C' when they are in their true
positions. This is easily found by measurement or by experiment, and when they
are once set, all that is necessary is to place the jig K in a suitable drill press, and
drill the holes in the bed plate as clearly shown.
By this simple method of centering and milling the ends of the field magnet cores.
held
upon a fixed former J adapted to accurately fit into the curvilinear portion of
the field pole, one is enabled to construct each field core so that it is the exact
counterpart of its fellow, and by the accurate method of centering and drilling, the
yoke B', when held in a jig or form K, as shown in Figure 10, one is enabled to
construct yokes for dynamos or electric motors which shall receive the milled ends
of the field cores, said cores being always in exact alignment, and at equal distances
from each other, thus assuring an absolutely cylindrical opening between the free
ends of the field cores for the reception of the armature. In other words, all field
cores made by the improved method are so exactly similar that they may be
interchanged at all times without the fear of in any way disturbing the mechanica
symmetry of the entire machine.
It will thus be seen that this method of construction prepares a field magnet.
which, when put together, is absolutely symmetrical, a feature which is of great
importance in the construction of electric motors or dynamio electric machines, it

page_text: being absolutely essential for the most perfect maintenance of the magnetic circuit in
such machines that there be a minimuni amount of air space resistance, and this is
accomplished by the construction of and adaptation of these parts in the manner
above set forth.
Tools have heretofore been devised for dressing the ends of cylindrical bodies of
metal, so as to adapt them to be fitted into cylindrical openings, and no claim is
hereinafter made broad enough to include the use of such tools, the claims to this
feature of the invention being directed to the novel methods of the construction of
field magnets for electric motors, whereby the most perfect symmetry of organization
may be had and a minimum amount of magnetic reluctance offered to the passage of
the magnetic lines of force.
Having now particularly described and ascertained the nature of this inven
Gion and in what manner the same is to be performed as communicated to me by my
foreign correspondent, I declare that what I claim is :-
First. The ring armature formed with slots or openings in its periphery of
greater width at the bottom than at the top and shaped so as to form flat or
substantially flat surfaces at the bottom of the slot, so that the armature coils can be
wound regularly and form coils substantially flat in the inside and symmetrical with
respect to both the inside and outside of the ring, substantially as described.
Second. An armature core formed with trapezoidal slots or openings in its
periphery or greater width at the bottom than at the top, the windings or conductors
being contained in the slots, substantially as described.
Third. The ring armature core formed with trapezoidal slots or openings in its
periphery, and coils or windings laid in the slots and passing through the inside of
the ring the windings on the inside of the ring forming trapezoidal shaped coils or
sections which fit against one another and fill the interior of the ring, and the slots
being of the same shape and cross section so that the coils are symmetrical with
respect to the outside and inside of the ring, substantially as described.
Fourth. An electric motor or dynamo electric machine having an unsymmetrically
fed field magnet as in the horse-shoe type, the armature and field being so
constructed on the side opposite the origin of the field magnetism as to cause an
increased amount of magnetism to pass through the half of the armature and thereby
more or less neutralize the tendency of the field magnet to draw the armature away
from its axis of revolution resulting from the unsymmetry of the field, substantially
as described.
Fifth. An electric motor or dynamo electric machine having an unsymmetrically
fed field magnet, as in the horse-shoe type, the pole pieces being formed so as to
embrace the armature on the side opposite the origin of the field magnetism to a
greater extent than on the other side so that the tendency of the field magnet to
draw the armature away from its axis of revolution resulting from the unsymmetrical
field magnet is more or less neutralized, substantially as described.
Sixth. The method of forming field magnets of electric motors or dynamo electric
machines, which consists in boring the yoke or base and trimming the end of the
field forgings with reference to the centre of its concave part, so that when
assembled, the parts form a true cylindrical space for the armature, substantially as
described.
Seventh. The method herein described of constructing the field magnets of
electric motors and dynamo electric machines, consisting in forming each core and
pole piece in one portion hollow milling the end of the core with reference to the
concave face of the pole piece, and boring suitable holes in a bed plate or yoke at a
fixed distance so that when the cores are slipped into the bed plate their pole pieces
form a true cylindrical space to receive the armature, substantially as described.
Eighth. The method herein described of constructing the field magnets of electric
motors and dynamo electric machines consisting in forming each core and pole piece
in one portion fixing the core and pole piece in a milling machine table in such a
position that the axis of the core coincides with the axis of a hollow milling tool,

page_text: and then hollow milling the end of the core to a definite point, and fitting the
cores thus milled into a bed-plate or yoke suitably bored to receive them and
support them so that their faces will form a true cylindrical space to receive the
armature, substantially as described.
Ninth. The described method of forming the field magnets of an electric motor
or dynamo electric machine consisting in maintaining the cores in a fixed position
against a cylindrical block having the same diameter as the armature, and in
trimming the ends of the core while thus held; then boring the yoke, while held in
a fixed position, and finally assembling the parts, substantially as described.
Tenth. The described apparatus for preparing field magnet cores, preparatory
to attaching said cores to their yokes, consisting of a cylindrical block having the
same contour as the free end of the field magnet core in combination with a support
and clamp adapted to hold the core in a fixed position preparatory to milling the
end which is to be fixed to the yoke, substantially as described.
Eleventh. The described apparatus for boring the yoke of an electric motor or
dynamo electric machine, consisting of a boring frame having drill bushings secured
to a removable portion thereof, in combination with adjustable means for securing
the yoke in position in the frame beneath the drill bushings, substantially as
described.
1001
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.