Improvements in Dynamo Electric Machines.
Year: 1896

page_text: Date of Application, 30th Nov., 1896
Complete Specification Left, 29th Sept., 1897-Accepted, 27th Nov., 1897
PROVISIONAL SPECIFICATION.
Improvements in Dynamo Electric Machines.
We, WILLIAM BROOKS SAYERS, of Glenwood, Bearsden near Glasgow in the
County of Dumbarton, Electrical Engineer, and HENRY ALEXANDER MAVOR,
WILLIAM ARTHUR COULSON and SAMUEL MAVOR all of 57 West Nile Street,
Glasgow aforesaid, Engineers and Electricians, do hereby declare the nature of
this invention to be as follows:-
This invention of improvements in dynamo electric machines has reference
more particularly to machines of the kind constructed according to the specifica-
tions of former Letters Patents No. 16572 of 1891 and No. 10298 of 1893 and it
has for object to secure fixity of position of the brushes with varying load and
whether the machines be running in one direction as generators or in the opposite
direction as motors.
In a machine for this purpose, according to this invention, frames of iron, each
of sufficient cross-section to carry the requisite induction, are fixed around or at
opposite sides of the armature so as to be kept clear of the field magnet, or
magnets as far as practicable, the necessary support being provided by brackets
or other suitable devices of non-magnetic material such as brass or gun-metal.
Each frame is preferably kept in the region of one pole only of the field magnet
or magnets, so as to minimise magnetic leakage. Two opposite sides of each
frame have formed upon them polar projections which are arranged longitudinally
with relation to the cylindrical surface of the armature but are separated there-
from by a suitable distance. The arrangement is such that when a current is
flowing in the armature, there will be generated through the circuit formed by
the armature core and the frames, a magnetic flux which will be proportional
to the armature current throughout a considerable range. The frames with their
polar projections, are so relatively adjusted that the distance between the two
polar projections belonging to opposite frames, and measured over the surface of
the armature or tangential thereto, is rather greater than the distance between
two sides of a commutator coil such as described in one of the said former specifica-
tions riz. No. 10298 of 1893. By this means the magnetic flux generated will
be of the proper direction to bring about the reversal of the current in the armature
sections at the required times, in whichever direction the machine may be running
and whether as a generator or as a motor.
In one construction of machine the field magnet is of approximately rectangular
shape as seen in end view with the exciting coils on its vertical portions, and the
iron frames each consist of two semi-circular shaped bars of iron arranged parallel
to each other and connected at their ends by flat iron bars which form the polar
projections above referred to, the polar projections on one frame facing those on
the other.
1900

page_text: Improvements in Dynamo Electric Machines.
We, WILLIAM BROOKS SAYERS, of Glenwood, Bearsden near Glasgow in the
County of Dumbarton, Electrical Engineer, and HENRY ALEXANDER MAVOR,
WILLIAM ARTHUR COULSON and SAMUEL MAVOR all late of 57 West Nile Street,
now of 47 King Street, Mile End, Glasgow aforesaid, Engineers and Electricians,
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:
This invention of improvements in dynamo electric machines has reference
more particularly to machines of the kind constructed according to the specifica-
tions of former Letters Patents No. 16572 of 1891 and No. 10298 of 1893 and it
has for object to secure fixity of position of the brushes with varying load in
whichever direction the machine be run and whether as a generator or as a motor.
In a machine for this purpose, according to this invention, frames of iron, each
of sufficient cross-section to carry the requisite induction, are fixed around or at
opposite sides of the armature so as to be kept clear of the field magnet or
magnets as far as practicable, the necessary support being provided by brackets
or other suitable devices of non-magnetic material such as brass or gun-metal.
Each frame is preferably kept in the region of one pole only of the field magnet
or magnets, so as to minimise magnetic leakage. Two opposite sides of each
frame have formed upon them polar projections which are arranged longitudinally
with relation to the cylindrical surface of the armature but are separated there-
from by a suitable distance. The arrangement is such that when a current is
flowing in the armature, there will be generated through the circuit formed by
the armature core and the frames, a magnetic flux which will be proportional
to the armature current throughout a considerable range. The frames with their
polar projections, are so relatively adjusted that the distance between the two
polar projections belonging to opposite frames, and measured over the surface of
the armature or tangential thereto, is rather greater than the distance between
two sides of a commutator coil such as described in one of the said former specifica-
tions viz. No. 10298 of 1893. By this means the magnetic flux generated will
be in the proper direction to bring about the reversal of the current in the armature
sections at the required times in whichever direction the machine may be running
and whether as a generator or as a motor.
Figs. 1, 2 and 3 of the accompanying illustrative drawings show respectively
in end, side and plan view so much of a two pole dynamo electric machine of the
kind referred to as is necessary to illustrate the application thereto of reversing
means according to the present invention. Fig. 3* is a diagram, to a larger scale than
Figs. 1 to 3 inclusive, showing part of an armature winding with commutator
coils arranged according to the said former specification No. 10298 of 1893 and
reversing means according to the present invention. Fig. 4 is a part sectional
end elevation and Fig. 5 a sectional plan on the line A B of Fig. 4, showing the
application of the invention to a multipolar dynamo electric machine of the kind
referred to. In each arrangement A is an armature provided with a winding
and commutator coils arranged according to the said former specification
No. 10298 of 1893, and C is the commutator the strips of which are connected to
the armature winding through the said coils.
In the construction of two pole machine shown in Figs. 1, 2 and 3, the field
magnet M is of approximately rectangular shape as seen in end view, the exciting
coils being placed on its vertical portions, and the iron frames each consist of

page_text: two nearly semi-circular shaped bars or yoke pieces y of iron arranged parallel
to each other, fixed to the ends of the field magnet by brackets or blocks y of
non-magnetic material and bolts, and connected at their ends by flat iron bars p
which form the polar projections or reversing poles above referred to, the polar
projections on one frame facing those on the other and being separated from each
other by a distance greater than the distance between the two sides B1 B2 of
each commutator coil (Fig. 3).
In the construction of four pole machine shown in Figs. 4 and 5, each of the
iron frames comprises a practically U-shaped yoke piece y secured by brackets y
of non-magnetic material to the yokes M of the machine so as to partly surround
the corresponding pole M and provided with flat iron bars ? that are arranged
parallel to each other and to the axis of the armature and serve as the polar
projections of the iron frames.
In each case the cross section of the reversing pole pieces p and also of the
yokes y, or the sum of the cross sections of the pole pieces and of the yokes if
the circuit is completed in more than one path, as is the case in the two pole
machine shown in Figs. 1, 2 and 3 should be approximately equal to or greater
than the cross section of the armature teeth a (Fig. 1) upon which each reversing
pole piece p is desired to act, the section being measured in each case in a direction
at right angles to the magnetic flow. The number of armature teeth a upon
which each reversing pole piece 7 should act, and to the aggregate section of which
the cross section of the said pole piece should be approximately equal, is deter-
mined by the details of the winding. For example if the number of sectors in the
commutator is equal to the number of teeth on the armature, then the pole pieces
and their connecting yokes y, should have a section equal to or greater than that
of one tooth. If the number of sectors in the commutator is equal to half the
number of teeth then the pole pieces p and their connecting yokes y should each
have a section equal to or greater than that of two armature teeth; or if the
number of sections in the commutator is equal to one third the number of teeth
in the armature, then the poles and their connecting yokes should have a section
equal to or greater than that of three armature teeth and so on.
Fig. 3 shows the relative arrangement of the pole pieces p and the commutator
coils B B. To avoid confusion only those coils of the main winding A¹ and
commutator coils B-B are shown, which are in the region of commutation.
The diagram represents a winding for a two pole machine some coils being repeated
at opposite ends of the diagram. The section of the main winding which has
just been reversed is shown by a somewhat thicker line than the others, while
the one which will next be reversed is shown by a broken line, the direction of
rotation being as shown by arrow a. The distance between the two pole pieces p
which are nearest each other is approximately equal to the distance between the
two side portions B-132 of the commutator coil which respectively lie in slots 1
and 8 and are in connection with the armature winding A at a point A thereof
located between the two main armature sections which lie in slots 4 and 6. The
arrows b indicate the path of the magnetic flux through each connected pair of
pole pieces p, yokes y and the portion of the armature core opposite them and
forming part of the magnetic circuit. The pair of pole pieces p, which n
nearest together but which are connected to different frames act to bring about
the reversal of the armature section that is about to be commutated, in the same
way that the polar extensions E and field magnet poles described in connection
with Figs. 3, 3, 3 and 3 of the said former specification No. 10298 of 1893 act
to bring about the reversal of the armature sections; but whereas in the arrange-
ment described in the said former specification one or both of the pole pieces or
tips of field magnets are magnetised by the field winding so that their magnetisa-
tion and therefore their aggregate effect on the commutator coils BB cannot
be proportional to the armature current although their magnetisation
strengthened thereby, in an arrangement according to the present invention both
the poles acting on a commutator coil BB are magnetised solely by the
is

page_text: armature current so that the magnetic flux acting to produce the reversal is pro-
portional to the armature current throughout the range in which the magnetic
reluctance of the poles p p frames y and the portion of the armature core forming
the magnetic circuit, as indicated by the arrows b in Fig. 3, is a negligable
quantity.
In Figs. 1, 2 and 3, each of the yokes y is made in two parts adapted to be
magnetically connected together by a block or piece z of iron which is adapted to
be adjusted nearer to or further from the adjacent ends of the parts of the yoke
and serves as a magnetic link by means of which the magnetic flux through the
pole pieces can be adjusted. If the blocks z are screwed close up to the yokes y,
then the magnetic flow will be at a maximum, but if they be moved to a greater
or less distance from the yokes, then the air gap between the said parts interposes
a magnetic reluctance. By thus varying the position of one or other or both of
the magnetic blocks z, the magnetic flow can be adjusted to the required amount
to secure sparkless commutation. Adjustment of the magnetic flow can also be
made by causing the pole pieces to approach or recede from the armature.
When sparkless commutation has been produced by the means above described,
the position of the brushes will be the same for all loads and for either direction
of rotation of the machine. In Figs. 4 and 5 each frame or yoke y is provided
with a single adjustable block z of iron for the same purpose as the two blocks
for each frame shown in Figs 1, 2 and 3.
Figs. 6 and 7 are similar views to Figs. 4 and 5 respectively, showing a modified
construction of multi-polar machine in which the polar projections or reversing
poles are connected magnetically to the yoke M' of the field magnet by
pieces of iron to which the pole pieces 7 may be separately secured
by bolts as shown, so as to allow of adjustment to and from the
armature A, but each pole piece may be made in one piece
with the corresponding yoke M. This arrangement is more liable to be disturbed
by variation in the permeability of the field magnets with varying degrees of
magnetisation than are the arrangements shown in Figs. 1, 2 and 3, and in
Figs. 4 and 5, but is sufficient in practice, in many cases, to enable the object of
this invention to be attained.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is:
1. In a dynamo electric machine of the kind herein referred to providing an
each of the two opposite sides as set forth of each pole of the field magnet or
magnets a polar projection the two such polar projections of each pole constituting
a pair being arranged longitudinally in relation to the cylindrical surface of the
armature but separate therefrom and connected together magnetically so as to
form with the armature core a magnetic circuit in which there will be produced,
when a current is flowing in the armature, a magnetic flux that will be propor-
tional to the armature current throughout a considerable range and will be in
the proper direction in the adjacent polar projections of successive pairs of polar
projections to bring about, by means of the commutator coils, the reversal of the
current in the armature sections at the required times in whichever direction the
armature be running and whether as a generator or as a motor, as set forth.
2. A dynamo electric machine of the kind referred to in the preceding claim
in which each pair of longitudinal polar projections is carried by an iron frame
of sufficient cross section to carry the requisite induction, and the frames with
polar projections are separately fixed around or at opposite sides of the armature
so as to be kept clear of the field magnet or magnets and of the armature and so that
the distance between the two adjacent polar projections of two frames, or of
successive frames, as measured over the surface of the armature or tangential
thereto, is rather greater than the distance between the two sides of each com-
mutator coil, substantially as herein described.

page_text: 3. Dynamo electric machines of the kind herein referred to constructed with
reversing means arranged and operating as herein before described with reference
to and shown in Figs. 1 to 3 inclusive, or modified according to Figs. 4 and 5
of the drawings annexed.
Dated this 20th day of Santambor 1907
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.