An Improvement in Toothed Armature Plates.
Year: 1899

page_text: Date of Application, 11th Aug., 1899-Accepted, 16th Sept., 1899
COMPLETE SPECIFICATION.
An Improvement in Toothed Armature Plates.
I, JAMES BURKE, of Oudenarderstrasse 24/25 Berlin, in, the Empire of Ger-
many, 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 :-
It is a well known practice in the construction of electromagnetic machines, to
built up the armature core of a number of thin iron or steel discs, around the
periphery of which radial slots or notches are cut, the armature core being thus
provided with deep longitudinal grooves for the reception of the armature wind-
ing.
As it is most convenient that the notches, forming these grooves, should be of
equal width throughout their entire length, it is a natural consequence, that the
teeth left standing between the notches are contracted toward the centre of the
disc. For this reason a limit is given to the radial depth of the notches, as their
width decreases in proportion to their radial depth. This decrease of the iron
body left standing between the notches, must naturally detract from the magnetic
influence acting in the armature.
My invention relates to a new method of making armature discs, by which a
more ample space for the armature winding is gained without increasing the
radial depth of the notches and without decreasing the minimum mass of iron left
between them.
For this purpose, I make each notch in the form of a curve in such a way, that
the notches remain of approximately equal sectional width throughout their whole
length and the width of the teeth between the notches is not diminished to any
sensible degree.
It is evident that it is possible to make curved notches in armature discs in a
number of different ways, as for instance that the inner part of the notch starts
out radially and then extends toward the periphery in a curve, or that the notch
is formed by a succession of straight lines, tangential to a curve.
Fig. 1 shews one way of making the armature disc p, on which the notches
follow the lines of an involute curve and I consider this curve as the one that
affords the best results. It has the advantage of preserving to the notches n, n,
and the teeth z, z, an equal width throughout their entire length, while the
capacity for receiving armature windings is materially increased. As will be
seen in Fig. 1 and 2, small gaps c are cut into the end of the teeth z, which form
a groove on each side of the armature slots, when the whole armature core is
put together. After the winding of the armature is completed, wooden strips or
wedges are pushed into these grooves to secure the armature winding in its
position.
Fig. 2 shews an armature disc of the usual form and the same letters represent
similar parts as in Fig. 1.
It is obvious that with the same radial depth of the notches made in this way,
considerably less space is afforded for the reception of the armature winding than
is the case with curved notches.

page_text: By thus increasing the capacity of the armature notches, the capacity of the
armature for electric current is correspondingly increased.
By a comparison of Figs. 3 and 4, it may be observed that a considerable
technical advantage is secured, when the windings or coils to be placed into the
notches, are previously prepared on a suitable forming machine.
When the armature slots are curved, as shewn in Fig. 1, the coils readily
describe the arc necessary to place them in position as shewn in Fig. 3.
When however, the armature core is provided with radial slots as shewn in
Figs. 2 and 4, it is evident, that the distance between two given slots n at the
periphery is much greater than at their inner ends, and it is for this reason that
previously formed armature coils can be introduced only by bending them out
of shape to bring them over edge k, as illustrated in Fig. 4 by the dotted lines.
Reference has previously been made to small gaps c being cut into the ends
of teeth ; as will be readily seen from Fig. 2, these gaps must necessarily reduce
the cross-section of the teeth at that particular point, and consequently magnetic
induction must in some degree be diminished.
In Fig. 1 these gaps are in a similar way cut into the end of the teeth, but
owing to the curved form of the notch, they are transposed toward each other in
such a way that the cross-section of the tooth is only reduced by one notch.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what I claim is:-
The herein described method of preparing the plates, which, when put together,
constitute an armature by cutting these plates with curved notches to receive the
armature windings, substantially as described with reference to the drawings.
Dated this 11th day of August 1899.
ABEL & IMRAY,
Agents for the Applicant.