Improvements in or in connection with Dynamo-electric Machinery.
Year: 1892

page_text: Date of Application, 21st Dec., 1892
Complete Specification Left, 26th Aug., 1893-Accepted, 28th Oct., 1893
PROVISIONAL SPECIFICATION.
Improvements in or in connection with Dynamo-electric Machinery.
We, WILFRID L. SPENCE, Civil Engineer, and D. STEWART AND CO. LTD.,
Mechanical Engineers, of The London Road Iron Works, Glasgow, do hereby
declare the nature of this invention to be as follows:-
Our improvements relate more particularly to the disc or short ring types of
dynamo electric machines but they are in part applicable also to other classes.
Field magnets: In order to minimise as far as possible the effect of cross
magnetization by the armature we adopt an iron-clad form of field in which the
exciting coils are radial and which are partially wound over and thus directly
magnetize the armature.
Radial pole pieces project inwardly and surround the armature on the two end
faces and on the periphery. The yoke completing the magnetic circuit has an
approximately rectangular box section, it encloses the whole of the machine and
supports the bearings at each end.
This form, which we do not claim as new, lends itself particularly to the
In the faces of the
neutralization of cross induction by the following means.
poles we form slots and through the adjacent portions of the yoke holes to
correspond, and in them we place a coil or coils of wire to carry the whole or a
certain proportion of the armature current. These coils which, on a radial section,
enclose the poles are in planes parallel to those through the coils on the armature.
Axially they are therefore perpendicular to the direction of the flux in the pole
pieces. The direction of the current in them is such as to neutralize the effect of
cross magnetization. Such coils in combination with the afore-mentioned field-
magnets obstruct the main flux but very little while they increase the reluctance
of the cross magnetized circuit considerably.
Armature and commutator: In bar armature machines which give comparatively
low electromotive forces it has been proposed to let the brushes rub directly on the
armature conductors thus doing away with the necessity for a separate commutator.
This method is inapplicable to machines which in comparison with their size work
We overcome the difficulty as
at high pressures because they are wire wound.
follows:
A short-ring armature is adopted by preference and the coils are wound in slots,
Pacinotti-wise, so as not to cover the whole of the periphery. The iron ribbon
of which the core is formed grooved or corrugated to give stiffness and to hold
in place insulating distance pieces which are let in on the periphery between
adjacent coils.
These blocks are secured longitudinally by the corrugation and radially by wire
bands in the usual way. Comparatively thin copper segments insulated with mica
are then laid outside this rim and secured in a similar or other suitable manner.
By the foregoing construction a completely enclosed machine is obtained, with the
minimum of weight and occupying the least possible space. The bearings may be
brought within a few inches of one another and, being carried by the end portions
of the yoke, do not occupy floor space. The bearing shells we do not cast integral
with the frame but let them detachably into a seat which is cast hollow and forms
an oil well below the bearing. The machine frame is divided horizontally on the
centre line and at each side we provide a hand hole covered by a hinged or
removeable door opposite the place where the brushes make contact with the
armature. These doors are best made of iron but they may have glass windows if
desired.

page_text: Brushes and holders: We prefer carbon brushes in the form of short lengths of
rod of suitable diameter. The carrier is preferably about six inches long and is
composed of one, two, three or more strips of springy metal; sheet brass about
027 inch thick is very suitable. At the end remote from the commutator these
strips are soldered together and at the other end they may be loose or not and are
slit into separate prongs, say one-half inch wide. These each carry a clip to hold
the carbon rod end-on to the commutator. This clip we make of a 'short length of
sheet brass, say three-eighths inch wide, doubled into a U form and having a saw
cut at the bent portion by which it is let over the end of the prong aforementioned.
It is then soldered or otherwise secured in place, and after insertion the carbon is
fastened by the two free ends being drawn together. A saw-cut or file mark in
the carbon fits over the end of the prong which thus acts as a key to prevent the
block being shaken loose.
Dated this 20th day of December 1892.
WILFRID L. SPENCE.
.D. STEWART & CO., LTD.,
ARTHUR J. DAVEY, Director.
COMPLETE SPECIFICATION.
Improvements in or in connection with Dynamo-electric Machinery.
We, WILFRID L. SPENCE, Civil Engineer and D. STEWART & Co. LTD.,
Mechanical Engineers of The London Road Iron Works, Glasgow 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 :-
Our improvements relate more particularly to the disc or short ring types of
dynamo electric machines, but they are in part applicable also to other classes.
Field magnets: In order to minimise as far as possible the effect of cross
magnetization by the armature we adopt an ironclad form of field in which the
exciting coils are radial and which are partially wound over and thus directly
magnetize the armature.
Radial pole pieces project inwardly and surround the armature on the two end
faces and on the periphery. The yoke completing the magnetic circuit has an
approximately rectangular box section, it encloses the whole of the machine and
supports the bearings at each end. This form which we do not claim as new lends
itself particularly to the neutralization of cross induction by the following means.
In the faces of the poles we form slots and through the adjacent portions of the
yoke holes to correspond, and in them we place a coil or coils of wire to carry the
whole or a certain proportion of the armature current. These coils which, on a
radial section, enclose the poles are in planes parallel to those through the coils on
the armature. Axially they are therefore perpendicular to the direction of the flux
in the pole pieces. The direction of the current in them is such as to neutralize the
effect of cross magnetization. Such coils in combination with the aforementioned
field magnets obstruct the main flux but very little while they increase the reluctance
of the cross magnetized circuit considerably.
Armature and commutator: In bar armature machines which give comparatively
low electro-motive forces it has been proposed to let the brushes rub directly on
the armature conductors thus doing away with the necessity for a separate com-
mutator. This method is inapplicable to machines which in comparison with their
size work at high pressures because they are wire wound. We overcome the
difficulty as follows: A short ring armature is adopted by preference and the coils
are wound in slots on the end faces, Pacinotti-wise, so as not to cover the whole of
the periphery. The iron ribbon of which the core is formed is grooved or
corrugated to give stiffness and to hold in place insulating distance pieces which

page_text: are let in on the periphery between adjacent coils. These blocks are secured
longitudinally by the corrugation and radially by wire bands in the usual way.
Comparatively thin copper segments insulated with mica are then laid outside this
rim and secured in a similar or other suitable manner. By the foregoing construction
a completely enclosed machine is obtained with the minimum of weight and
occupying the least possible space. The bearings may be brought within a few
inches of one another and being carried by the end portions of the yoke do not
occupy floor space. The machine frame is divided horizontally on the centre line
and at each side we provide a hand hole covered by a hinged or removeable door
opposite the place where the brushes make contact with the armature.
We will now describe our invention more particularly with reference to the
drawings.
The essential features of our improved field magnet and armature are shown by
Figures 1 and 2. In their entirety they are applicable only to machines in which
the direction of the flux is into the end faces parallel to the shaft and not radial
into the periphery.
The method which we adopt to obtain sparkless commutation at an invariable
point is to surround the pole piece by one or more coils which are in series with the
armature, carrying the whole or a certain proportion of the current, and which
create a secondary field in such a sense as to neutralize the magnetization due to
the armature current so far as it affects the line of cominutation. As in inost
existing dynamos such a coil at the centre of the pole would seriously interfere
with the flow of lines we adopt the form shown which lends itself readily to this
method.
It will be observed that the axis of the neutralizing coil, N, is perpendicular to
the direction of the flow which is but little interfered with while the path of
the cross magnetized circuit, which in any case has a section relatively small
compared with that through the armature, may be brought to any desired degree of
reluctance.
The construction is clearly indicated. On the polar face the coil lies in a
channel of suitable dimensions while on the back it passes through a corresponding
hole in the yoke. Although but one coil is shown two or more may be used
extending on either side towards the edges of the poles, and instead of enclosing
the pole piece only the portion of the coil remote from the armature may be
extended backwards so as to surround a section of the magnetizing coil, M, and
the portion of the yoke covering it. It will be understood that our invention
in this particular is essentially different from the small subsidiary coils which
have at various times been proposed for use on the polar tips with a view to
furnishing a reversing fringe.
Hitherto it has been customary in dynamo electric machines with iron clad
fields to have the bearing seats cast half with the upper and half with the lower
portion of the frame. (Vide Figure 22 Specification 12828, 1891.) We find it
more convenient to cast the seat wholly with the lower portion of the frame
and to have a separately removable cap to the bearing. The seat is cast hollow
and it is made deep enough to form a substantial oil well into which a chain or
other continuous lubricator dips.
The armature core, A, is formed of a thin iron ribbon which is grooved or
corrugated to give stiffness and to hold in place the insulating distance pieces, W,
hich may be of bard wood or other suitable material. These blocks are secured
radially by wire bands in the well known manner. They serve to support the
commutator bars, B, which are laid outside them and which are themselves secured
by pins or screws entering the insulating blocks and by wire bands insulated with
mica or otherwise. As the path of the magnetic lines into the armature is through
the end faces and not into the periphery these bars will not be subject to injurious
heating by eddy currents. As an additional precaution they may be slit from each
end longitudinally towards the centre and the slits filled with a light insulation.
The brushes will ordinarily make contact with the armature on the borizontal

page_text: diameter and they may therefore be completely enclosed within the machine frame.
In multipolar machines we arrange that both brushes shall make contact on the
upper portion of the armature through open spaces like that shown, thus bringing
the lines of commutation well within view. This is effected by carrying the
connections along the core through the requisite angular distance before joining up
to the commutator bars.
Brushes and holders: The drawings Figures 3 to 8 Sheet 2 show clearly the
features of our invention. A short length of carbon rod is cut and after the ends
have been trimmed a file mark, K, is made on one side at the middle of its length.
The carrier plate is of thin sheet metal, P, and it may be composed of any desired
number of layers. It is preferably slit up at one end into separate prongs, say,
one-half inch wide (or about equal in width to the diameter of the carbon rod).
These each carry a clip, H, also of thin sheet metal which is doubled into a U form,
Figures 4 and 7, and let over the end of the prong. A slit, S, Figure 8, is shown
for this purpose.
Grooves, G, same figure, may be formed with a view to stiffening
the clip. The attachment to the plate carrier may either be by soldering or
brazing as Figure 6 or where there is liability to heat by rivetting as Figures 3,
4, 5, and 7.
After the insertion of the carbon rod the free ends of the holder are
drawn together either by the natural springiness of the material or by external
Whatever the
means such as the ring, R, Figure 3 or a spring clip, C, Figure 7.
means adopted the effect is to force the carbon down on to the key, K, and so
prevent it from being shaken loose. The limbs of the holder, H, may if desired
be slightly recessed into the body of the carbon block by a groove either longitudinal
as, G, Figures 3 and 4 or transverse. In the former case no top lugs are necessary
and in the latter the key, K, becomes superfluous.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :
1. In disc or short ring armature dynamo electric machines the combination with
"iron-clad " fields and pole pieces which present a relatively small section to the
cross magnetized circuit of the hereindescribed method of neutralizing the effect of
the magnetism due to the armature current substantially as described, and illustrated
with reference to Figures 1 and 2.
2. In wire-wound disc or short ring armature dynamo electric machines in which
the periphery of the core is not entirely covered by the winding and in which the
direction of the flux is into the end faces, placing the commutator circumferentially
outside the same.
3. In machines of the class mentioned in the preceding claim the construction of
the commutator substantially as described and illustrated with reference to
Figures 1 and 2.
4. The brush holder for carbon or other rubbing blocks substantially as described
and illustrated.
Dated this 25th day of August 1893.
WILFRID L. SPENCE,
Agent for Applicants.