Improvements in Dynamo Electric Machines.
Year: 1892

page_text: Date of Application, 1st Mar., 1892-Accepted, 9th Apr., 1892
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machines.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings in the
County of Middlesex, Patent Agent, do hereby declare the nature of this invention,
a communication to me from Robert Lundell of the City, County and State of
New York, United States of America, Inventor, and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
The present invention relates to the construction and arrangement of several
parts of dynamos or electric motors and especially to the construction of the field
magnets, and the arrangement of the magnetizing coils for said field magnets.
In the accompanying drawing:
Figure 1. is a central section of the improved machine;
Figure 2. is a side view of one section of the field magnet looking at the faces of
the pole-pieces;
Figure 3. is a side view of one of the yokes of the field magnet; and
Figures 4 and 5 show a modification.
In the machine illustrated, the armature 1. is an ordinary disc armature,
preferably having radial grooves 2 at regular intervals, in which grooves the
armature coils are wound; for the sake of simplicity in illustration the coils are
omitted. The commutator 3 is also of any suitable construction, and is preferably
mounted on the armature shaft + inside of the bracket 5, so that the wires leading
from the armature coils to the commutator segments may pass directly to the
commutator without the necessity of leading them through a hollow shaft or
bushing, as is usual. At the opposite end of the armature shaft is an ordinary
pulley 6. At a suitable point on the shaft is placed a hard metal sleeve 7, on
which are rings 8, 9, holding between them series of steel balls 10, which are
confined by an encircling ring 11. On the armature shaft is also a collar 12
resting directly against one face of the hub from which the armature is supported.
It will be seen that this arrangement provides a ball or anti-friction bearing for
receiving the thrust whenever the armature shaft tends to move toward the right or
toward the left as sometimes occurs, when, for example, the magnetic pull of the
field magnet on the armature on one side is stronger than on the other. 12' is a
spider resting on the yoke of the field magnet and forming a bearing for the
armature shaft. Each section of the double field magnet of the machine comprises
a frame or yoke 13, and several detachable pole-pieces 14, 15 at or near the edges
or sides and a magnetizing coil 16. The general outline of the yoke is shown in
Figure 3, it being of ring-shape with supporting feet 17, and having a series of
recesses 18 at regular intervals on its inner edge, and a series of recesses 19, alternating
with recesses 18, on its outer edge.
While 18 and 19 are referred to as recesses, it is evidently not essential that the
fourth side of the recess should be open as illustrated; in other words, instead of
being notches in the yoke they may be holes through the yoke into which the pole-
pieces can be set. The yoke is also provided with perforated lugs 20 for the
reception of bolts for mechanically joining the two yokes of a machine. In Figure 3
the yoke is shown with three inner and three outer recesses, but this number is not
essential. The pole-pieces are preferably laminated, being made up of several
plates of sheet iron of substantially the shape shown at 14, Figure 1, the plates
being piled together and secured by rivets 21. These pole-pieces may be described
as shaped, and it will be found that the nearer to this shape, they are made, the
better they will serve the purpose, still it is possible to vary their shape to some
extent, as by rounding or curving one or more of the sides, without destroying their
2

page_text: general shape, and the term L-shaped is intended to include these slight variations
in form. The pole-pieces are preferably provided with grooves 22 of width equal
to the thickness of the yoke. The pole-pieces, constructed as described, are placed
in the recesses 18, 19, the grooves 22 fitting over the yoke. The pole-pieces are
so placed in the recesses 18 that the foot 23 of each pole-piece points from the
centre of the yoke, while the pole-pieces in the recesses 19 are so placed that the
feet 23 point toward the centre. This is most clearly indicated in Figure 1, in
which the upper pole-pieces are mounted in inner recesses while the lower pole-
pieces are mounted in outer recesses. The pole-pieces are secured to the yokes by
suitable bolts 24.
The single field magnet coil for each section is made by taking
a former of suitable shape, and made of some rigid insulating material, such as
prepared asbestos, and winding the coil in the former. In Figure 1. the former is
indicated by the heavy black lines 25 surrounding the coil 16 on three sides. In
building up the machine it is preferred to first secure the lower pole-picce 14 in
place, and rest the former with its enclosed coil 16 on this pole-piece in the position
indicated in Figure 2. and then to secure in place the two pole-pieces 14¹ 14";
this securely binds the coil in position and the other pole-pieces may be inserted
at will. No fastening devices for the coil are needed in addition to the pole-
pieces.
By arranging the several parts as already described, a multipolar machine is
provided adapted for use with a disc armature and having several extended pole-
pieces, the faces of which will lie close to, and parallel with, the sides, as distinguished
from the inner and outer peripheries of the armature, and the pole-pieces on each
side of the armature are all energized by a single coil, the coil passing between-the
north and south poles, and not being wrapped around them; this arrangement is
just as efficient as though the coils were wrapped around the pole-pieces and
provides an exceedingly simple and cheap construction. The disc armature will be
very strongly magnetized by the magnets on its opposite sides, the magnets having
their like poles opposite each other.
When the pole-picces are formed as described the ends or faces thereof will be
rectangular, as shown in Figure 2, and the edges of the poles will not be radial,
but will be in lines parallel with a diameter passing through their centres.
Since the coils on the armature are arranged in radial grooves, as the armature
rotates in the field the armature coils will pass in front of, and away from, the poles
gradually, that is, the armature coils will first pass over one of the lower corners of
cach pole-piece, and then will gradually pass on so that it stands directly over the
pole-piece, and will then pass over one of the upper corners of the pole-piece, and
finally will leave the pole-piece entirely. This causes a gradual rise and fall in
the magnetic changes in the machine and obviates or largely reduces sparking at
the commutator brushes.
As already indicated, the number and shape of the poles of the field magnet may
be varied without departing from the invention. The construction of the field
magnet coils may also be varied, the only essential being that the coils should pass
between and not around the pole-pieces, as described. The same construction of
field magnet is applicable to alternating current machines.
In the form of machine shown in Figures 4 and 5, which form is especially
designed for large machines, the two field-magnets are made in a different manner
from that shown in the other figures. On central sleeves 26 are placed a series of
radiating north poles 27 secured to the hubs by suitable bolts and at their outer
ends are extended to form bearings for the cross rods 23, which secure the two
field-magnets together and hold them in proper relation to the armature 29. The
rods 28 are extended and carry insulating spools 30, which hold the conducting
rings 31, 32 in place. One of these rings carries all of the positive commutator
brushes, and the other carries all of the negative brushes, and said brushes are
arranged to bear on the periphery of the armature, which is bared of insulation for
this purpose. On the same hubs 26 are mounted a series of south poles 33. These
alternate with the north poles as shown, their faces adjacent to the armature being

page_text: in the same or substantially the same plane as the faces of the north poles. The
magnetizing coil 34 for each field-magnet is, especially in large machines, divided
into sections separated from each other, by air spaces 35 to allow circulation of
air.
It will be understood that the three sections shown constitute in effect a single
coil, and in building the machine these coils would be put in place before the south
poles. In this machine the pole-pieces are not shown laminated as in the other
figures. Such lamination is only necessary in connection with Pacinotti armatures
having wide teeth which move close to the field-magnet poles.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed declare that what I
claim is:-
1. The combination of an armature, and a double field-magnet having a set of
positive and negative poles on each side of the armature, each set of pole-pieces
being magnetized by a single magnetizing coil, substantially as described.
2. The combination, in a dynamo-electric machine, of an armature, two field-
magnets one on one side and one on the opposite side of the armature, each magnet
having alternate positive and negative poles having faces in the same plane and
substantially parallel with the sides of the armature, substantially as set forth.
3. A yoke for the field-magnet of dynamo-electric machines consisting of a ring-
shaped frame or plate having recesses arranged at intervals around it alternately
on the inner and outer edges, in combination with L shaped pole-pieces placed in
said recesses and secured to said frame or plate, the pole-pieces in the inner and
outer recesses respectively being extended in opposite directions, substantially as
described.
4. The combination, in a dynamo-electric machine, of a disc armature, a field-
magnet consisting of a yoke with pole-pieces mounted alternately at or near its
inner and outer edges, the pole-pieces at one edge being positive and those at the
other edge being negative, and all of the pole-pieces having faces in the same
plane and substantially parallel with the sides of the disc armature, as set forth.
Dated March 1st 1892.
TALCHARLICI 150 TONE
B. J. B. MILLS,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.