IMPROVEMENTS IN DYNAMO- ELECTRIC MACHINES AND ELECTRIC MOTORS
Year: 1884

page_text: I, GEORGE HOOKHAM of 7 & 8 New Bartholomew St. Birmingham Manufacturer
do hereby declare the nature of my invention for IMPROVEMENTS IN DYNAMO-
ELECTRIC MACHINES AND ELECTRIC MOTORS to be as follows:-
An armature is used having grooves in the Iron in which the coils of the
conductor lie. The iron of the armature passes very near to the pole pieces of the
field magnets and consequently the magnetic circuit is almost unbroken. The
improvement consists in inserting a second armature in the magnetic circuit.
Or the magnets may be arranged so as to allow of three or more armatures being
so inserted. A comparatively slight increase in the total length of the magnets is
sufficient to maintain the original strength of field.
In a second arrangement two armatures are placed in line on one spindle, and
the field magnets bent so as to produce magnetically the same effect as in the first
case.
When an armature, whether of the Siemens (or drum) type, or of the Pacinotti
(or ring) type, is so formed for the reception of the conductor that that part of the
conductor which extends over the portions of the armature which pass nearest to
the magnet poles lies in grooves formed in the iron core, it is possible so to arrange
the armature and the magnet poles that the magnetic circuit is almost unbroken..
The faces of the iron ribs or flanges of the armature between which the conductor
is wound may pass very closely to the faces of the magnet poles, and the sum of
such ribs or flanges at one time opposite to a magnet pole may possess a total
magnetic section equal or nearly equal to the magnetic section of the armaturo
taken through its axis: or at least they may have a magnetic section not appreciably
different from that of the rest of the armature in its capacity for conveying the
lines of force passing through the system. Thus, with the exception of the thin
layers of air or other non-magnetic substance between the faces of the ribs and the
magnet-poles, the magnetic circuit is composed entirely of iron.
If, now, the magnets and armature are so arranged that the armature rotates
between pole-pieces placed at the ends of two straight electro-magnets parallel to
each other and having their other ends joined by an iron yoke, (as in the smaller
Edison machines), this iron yoke may be replaced by pole-pieces and an armature
similar to those at the other end; and, if the armatures are of the kind above

page_text: "
described, the lines of force passing through each armature will be nearly equal to
those passing through the original single armature, and approximately double the
effect will be obtained from the same magnets; or actually double the effect may
be obtained from magnets slightly longer (other dimensions and the magnetizing
current remaining the same) than were required to produce a given effect with the
single armature.
Any number of such armatures may be used in the same magnetic circuit,
e. g. three magnets of suitable proportions may be placed as a triangle having
pole-pieces and an armature at each angle; or, similarly, four may be placed as a
square; or figures of many sides may be used: or any number of armatures may
be placed at proper intervals between magnets forming a circle, or any other
convenient figure. In all cases there is great economy in the materials and energy
required to produce the magnetic fields.
In some cases for the sake of simplicity of construction I mount two armatures
on the same spindle at a distance apart equal to about half their diameter, and
wind the conductor round the two treating them as a single armature, and attach
the conductor to a single commutator. I use two pairs of similar pole-pieces, one
pair being applied to each armature in the usual way: all four lying in the same
plane. I connect these alternately by electro-magnets which are preferably of a
circular section and bent to a semicircular or nearly semicircular curve, one curved
magnet passing on one side and the other on the other side of the spindle and its
armatures. For instance, supposing the pole-pieces to be placed horizontally with
regard to the armatures and an observer to be viewing them in side elevation, then
the one curved magnet might pass from the pole-piece on the observer's left on the
nearer side, over the armatures to the pole-piece on the observer's right on the
further side; the other would then pass from the pole-piece on the near right
under the armatures to the left pole-piece on the further side. The two poles on
one side of the armatures are similar. In the case instanced the two poles on the
nearer side of the armatures might both be north poles in which case the poles on
the further side would both be south, or vice versa.
This arrangement is electrically equivalent to that first described in which two
armatures on separate spindles are used with straight magnets, (the one armature
replacing the iron yoke,) provided that the length of the curved magnets is
magnetically equal to the length of the straight magnets, and the armatures and
pole-pieces are similar; the magnetic circuit being completed in the same way,
viz. through the magnets and through the two armatures; but the machine is
simplified by having both armatures on a common spindle and with a common
commutator.
The space between the armatures may be greater or less than half their diameter,
or they may form one continuous armature.
The above descriptions apply to electro-magnets, but these may be replaced by
permanent magnets.

page_text: COMPLETE SPECIFICATION.
I, GEORGE HOOкHAм of 7 and 8 New Bartholomew Street Birmingham,
Manufacturer, do hereby declare the nature of said invention for "IMPROVEMENTS
IN DYNAMO ELECTRIC MACHINES AND ELECTRIC MOTORS" and in what manner
the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
In dynamo-electric armatures whether of the Siemens (or drum) type, or of the
Pacinotti (or ring) type in which the conductor is wound in grooves in the iron
core, it is possible to arrange the armature and the magnet poles in such a way
that the magnetic circuit is almost unbroken. The faces of the iron ribs of the
armature between which the conductor is wound may pass very closely to the faces
of the magnet poles, and the number of them at one time opposite each pole may
present a total magnetic section equal or nearly equal to the magnetic section of
the armature. Thus with the exception of the thin layers of air (or other non-
magnetic material) between the pole pieces and the ribs or flanges of the armature,
the magnetic circuit consists entirely of iron. If now the magnets are formed like
those known as the Edison type, in which a Siemens or drum armature rotates
between pole-pieces at the lower ends of vertical magnets, the upper ends being
joined by a heavy iron yoke, this yoke may be re-placed by pole-pieces and an
armature similar to those at the lower end; and with armatures of the kind above
described the magnetic field through each armature will be nearly equal to that
through the original single armature, and approximately double the effect will be
obtained from the same magnets; or double the effect may be obtained from
slightly longer magnets than were necessary to produce a given effect with the
single armature.
Any number of such armatures may be used in the same magnetic circuit,
e.g, three magnets of suitable proportions may be placed as a triangle and pole-
pieces and an armature placed at each angle; or, in like manner, four may be
placed as a square; or figures of any number of sides may be used; or any number
of such armatures may be placed at proper intervals between magnets forming a
circle, or any other convenient figure-In all cases there is great economy in the
materials and energy required to produce the magnetic fields,
I will now proceed to describe my invention with reference to the accompanying
Drawings Figure 1 is a section of an armature core A, constructed according to
my invention, placed in position between the poles B. C, of an electro-magnet―
a. a. a. a, represent the ribs or ridges of the armature above described-b. b. b. b,
are the grooves in which is wound the conductor (not shown) _ In the centre is
shown the circular aperture through which the spindle of the machine passes -All,
or nearly all the lines of force passing from one pole of the electro-magnet to the
other traverse those of the ribs or ridges of the armature-core as are at the time
opposite and in close proximity to the pole-pieces and pass through the solid part
of the armature core-The breadth of this solid part is equal to twice the
distance from the bottom of any groove to the point of the circular aperture

page_text: lying immediately opposite to it and on the same side of the centre; and the
ribs a, a, a, are made of such a width measured along the periphery of the
armature-core, that the sum of the magnetic sections of those at one time imme-
diately under one of the pole-pieces is equal to the magnetic section of what I have
termed the solid part: e.g, if the solid part should measure in all, (i,e, adding
together the two parts on the two sides of the central aperture) two inches along
the dotted line c. d, and if in the figure, there are about eight ribs at one time
under each pole-piece then each of these ribs should measure about inch in the
t
direction indicated-It is clear that the magnetic circuit consists entirely of iron
with the exception of the small clearance between the faces of the ribs a, a, a, and
the faces of the pole-pieces.
Figure 2 represents the arrangement for two armatures, the total length of the
magnets must be greater for an armature of the same dimensions than in Figure 1,
but less than twice the length, the ampère-turns per inch run remaining the
нате.
In Figure 3 is shown the arrangements for four armatures-Here again the total
length of the magnets added together must be greater than the length in Figure 2,
but may be less than twice that length, other conditions remaining the same And
a similar rule applies to the use of three or a greater number of armatures.
It will be observed that in the figures the ribs are shewn of parallel section and
the slots with inclined sides-The sides of the slots may have a less incline or may
be parallel The ribs will then have inclined sides-In this case it is sufficient that
the sum of the average magnetic sections of the ribs should be equal to the
magnetic section of the solid part of the armature.
In using the expression solid part of the armature I do not mean to preclude the
splitting up of the armature into lamina at right angles to the axis by the use of
insulated plates or discs, in the usual method.-But each plate may be spoken of as
having a solid ring bounded by the periphery of the central aperture, and a circle
touching the bottoms of the grooves.
I do not confine myself to the use of any special form of electro-magnets, and
I may use a Gramme or Pacinotti ring armature instead of a Siemens or drum
armature.
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
First The use of a ribbed and slotted armature so proportioned that the sum
of the magnetic sections of the ribs or ridges shall equal or nearly equal the
magnetic section of the solid part of the armature as hereinbefore described and
illustrated.
Secondly The use of such armatures with two or more electro-magnets as
hereinbefore described and illustrated.