Improvements in Electro Motors.
Year: 1889

page_text: Date of Application, 6th July, 1889
Complete Specification Left. 15th Mar., 1890-Accepted, 19th Apr., 1890
PROVISIONAL SPECIFICATION.
Improvements in Electro Motors.
We MICHAEL VON DOLIVO-DOBROWOLSKY and the ALLGEMEINE ELECTRICITATS-
GESELLSCHAFT both of 26 Schlegelstrasse at Berlin N. German Empire do hereby
declare the nature of this Invention to be follows:-
The present Invention relates to secondary electric machines in which rotary
movement is produced by alternate electric currents in such manner that two or more
groups of bobbins or coils standing at a certain angle are so connected that on the
one hand they are traversed by alternate currents of different phases as for instance
produced by an alternate current dynamo with alternating armature coils) and on
the other hand the resulting line of the magnetic field of these coils travels in a
determined direction of rotation and that a conducting body is placed in this rotating
field. In consequence of the reaction between the magnetic field and the Foucault
currents induced in the conducting body the latter is caused to rotate.
When the body in question is composed of copper the intensity of the magnetic
field is small and when it is composed of iron it is not a sufficiently good conductor
for the Foucault currents. No high degree of useful effect is obtained with the
electro-motor in either case.
In order to obviate the above-mentioned disadvantages and obtain an electro motor
of the class herein before referred to possessing a high degree of working capacity
our invention consists in imparting to the aforesaid conducting body bereinafter
referred to as the armature such properties that it increases the strength of the
magnetic field and at the same time forms a good conductor for the Foucault
currents as hereinafter explained.
With this object we form the armature mainly of iron and introduce into its mass
conductors or veins of copper of suitable form (bars, rods, wires, bands and the like
and provide a good electrical connection between the ends of these conductors or
veins.
When an armature of this description is brought within the rotating magnetic field
the mass of iron increases the strength of the field and at the same time the copper
conductors or veins allow strong Foucault currents to circulate which increase the
magnetic inertia of the armature and thereby increase the power with which it is
impelled in the circular path by the action of the rotating magnetic field.
The armature may be very advantageously composed of an iron cylinder, and the
upper conductors or veins of copper bars passing through the mass of iron in a
direction parallel with the axis and being electrically connected together at both of
their ends by means of copper discs rings or plates or other suitable connections. It
is however not necessary for the copper rods to be entirely imbedded in the mass of
iron and they may be simply laid in longitudinal grooves or recesses in the circum-
ference or surface of the cylinder the extremities being connected together by good
electrical conductors. The iron cylinder or body may according to another arrange-
ment be wholly or partially covered with an electrically connected covering or layer
of copper.
The armature may be of any suitable form and it is not essential to insulate the
iron from the copper.
The invention is perfectly independent of the general arrangement or construction.
of the electro motor which may be constructed with two or more poles and with the
armature within or without the magnetic system and with either rotating armature.
or rotating field.
Dated this 6th day of July 1889.
J. H. JOHNSON & CO.,
47, Lincoln's Inn Fields, London, W.C.

page_text: Improvements in Electro Motors.
We, MICHAEL ΤΟΝ Dolivo-DobrowOLSKY, Engineer and the Company
"ALLGEMEINE ELEKTRICITÄTS-GESELLSCHAFT," both of 20 Schlegel Strasse,
Berlin, N., German Empire, 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 present invention relates to secondary electric machines in which rotary move-
'ment is produced by alternating electric currents after the method proposed by
Professor Ferraris in Turin. According to this method two or more magnetizing-
'coils or groups of coils placed at angle to each other, are so connected that on
'one hand, they are traversed by alternating currents of different phases, (such as are
obtained by an alternating current dynamo in which the armature-coils are shifted in
respect to each other), and that on the other hand, the resulting magnetic field of the
said magnetizing-coils travels in a determined direction of rotation, while a con-
ducting body capable of rotating is placed in this rotating field. In consequence of
the reaction between the magnetic field and the Foucault currents induced in the
conducting body, the latter is caused to rotate.
If the body in question is composed of copper the intensity of the magnetic
field is, however, but small, and if it is composed of iron, it is not a sufficiently
good conductor for the Foucault currents, no high degree of useful effect being
obtained with the electro motor in either case.
In order to obviate these disadvantages and to obtain an electro-motor of the class
herein before referred to, possessing a high degree of working capacity, we impart to
the aforesaid conducting body, hereinafter referred to as the armature, such properties
that it increases the strength of the magnetic field and at the same time forins a good
conductor for the Foucault currents.
With this object we form the armature mainly of iron and introduce into its mass
conductors or veins of copper of suitable form (bars, rods, wires, bands and the like)
and provide a good electrical connection between the ends thereof. The said con-
ductors or veins are arranged in such position as to be transverse to the direction of
motion of the rotating part of the motor (which may be the armature or the
magnetizing-coils) and also transverse to the lines of force of the magnetic field.
When an armature of this description is brought within the rotating magnetic field,
the mass of iron increases the strength of the field and at the same time the copper
conductors or veins allow strong Foucault currents to circulate, which increase the
magnetic inertia of the armature and thereby increase the power with which it is
impelled in the circular path by the action of the rotating magnetic field.
The armature, which requires to be carried out in form of a body of rotation, may
for instance consist of a solid or hollow iron cylinder, and the copper conductors or
veins of copper bars passing through the mass of iron in a direction parallel with the
axis, and being electrically connected together at both of their ends by means of
copper discs, rings, or plates, or other snitable connections. It is, however, not
necessary for the copper rods to be entirely imbedded in the mass of iron and they
may be simply laid in longitudinal grooves or recesses in the circumference or surface
of the cylinder, the extremities being connected together by good electrical conductors.
The armature may also consist in an iron ring traversed by the copper conductors
in a direction either parallel to its axis or at a right angle thereto, according as the
lines of force of the magnetic field are directed.
The iron instead of forming one solid body, may, in certain cases, be composed with
advantage of a plurality of plates or pieces of other form, and these may be insulated
from each other or not. The copper does not require to be insulated from the iron,
because the object of the improvement is only to present to the Foucault currents in
addition to the iron, a path which is more conductive than the latter, and thereby to
increase the magnetic inertia of the armature.

page_text: The invention is perfectly independent of the general arrangement or construction
of the electro motor which may be constructed with two or more poles and with the
armature within or without the magnetic system and, as already stated, with either
rotating armature or rotating magnetizing-coils.
In the annexed drawings are shown in end-views and in longitudinal sections
different arrangements of armatures carried out according to our invention.
According to figs. 1 and 2 the armature consists in an iron cylinder a, fixed on
a shaft d and provided with three rows of perforations parallel to its axis; into the
said perforations the copper bars c are inserted, and these bars are conductively
connected together at both ends by the copper disks b.
If an armature of this description is placed in the rotating magnetic field, such as
may be produced by the poles P P¹, it will be perceived that the bars c are trans-
verse to their direction of motion and also transverse to the line 1-2 representing
the direction of the lines of force of the said field in a given moment.
The armature shown by figs. 3 and 4 differs from the foregoing only in this that
there is but one row of bars c connected together by flat rings b.
Figs. 5 and 6 represent an armature in which the copper bars c are imbedded in
grooves cut into the periphery of the cylinder a; the conductors whereby the bars
are connected together at their ends having, in this arrangement also, the form of
flat rings.
Figs. 7 and 8 are sectional views of a ring-armature a³, arranged to rotate between
poles P and P¹, which are opposite to the sides or end-surfaces of the ring. The
bars c are in this case placed radially, on account of the magnetic lines of force 3-4
being parallel to the shaft d, and they are connected together by the copper rings b¹ 6²,
being respectively outside and inside of the armature-ring.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :
In a secondary electric machine, the combination, with a magnetic field, of an
armature composed of an iron body of rotation, bars, strips or wires of copper
arranged transversely to the direction of rotation of the machine and also transversely
to the lines of force of the magnetic field, and copper conductors whereby the said
bars, strips, or wires are connected together at both ends, substantially as described.
Dated this 15th day of March 1890.