Improvements in Dynamo Electric Machines and Motors.
Year: 1895

page_text: Date of Application, 28th Feb., 1895
Complete Specification Left, 28th Nov., 1895-Accepted, 25th Jan., 1896
PROVISIONAL SPERATION.
Improvements in Dynamo Electric Machines and Motors.
I, LLEWELYN BIROHALL ATKINSON, of 3 Whitehall Place, Westminster,
S.W. Civil Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to improvements in dynamo-electric machines and motors,
and has for its object, the increasing of the output for a given weight of machine,
and enabling the brushes to be fixed at au invariable point on the collector for all
lourls.
In dynamos and motore, as ordinarily constructed, the reversal of the current in
each coil of the armature as it passes the collecting point, is offected, by giving the
brushes a "lead" relatively to the neutral magnetic axis, so as to bring the coil
within the magnetic field of the leading pole corner.
When however the armature ampere turns are, relatively to the field maguet
ampere turns, large, this leading pole coruer is demagnetized and the result is that
sparking at the brushes ensues.
To overcome this, independent pole pieces, called reversing poles have been
applied, excited by a circuit in series with the armature; or independent coils
wound on the armature, and carried under that pole corner which is strengthened,
have been used.
The first of these methods has the disadvantage that it entails a considerable
weight of copper to excite the reversing pole magnetism; the second lins the
objection that the magnetic strength of the pole corner is not proportional, as it
should be, to the current in the armature.
To overcome these objections, and to provide means for applying a reversing
E.M.F. to the coil to be commutated, proportional to the current in the armature
is the object of the present invention.
In order to carry out this invention, I utilize the ampere turns on the armature
to produce a magnetic field, acting on independent coils, which are connected
between the commutator sections and the point of junction of successive armature
coils.
To carry this into effect a direct or differential method may be adopted.
The direct method consists in providing, outside the main magnetic field, an
independent armature, carrying the reversing coils. On the circumference of this
said armature are a pair (in a 2 pole machine) of small pole pieces, of a width
corresponding to about the width of one commutator coil. These poles are con-
nected magnetically to two similar narrow poles, which are on the circumference of
the main armature, between the main poles, but not covering the coil which is
being commutated.
In the differential method, a commutator coil or coils are wound on the circum-
ference of the main armature, and so placed that they are in the main magnetic
field at the time the coil on the armature is to be commutated, but 30 placed that
there is no resultant E.M.F., except that due to the difference in strength between
the leading and trailing pole-piece of the magnets, which is proportional to the
armature current; and in order to maintain the differential or balanced. action
when one such coil, or side of a coil, passes from under the magnet, a groove or
space is provided in the pole-piece corresponding to the other coil or side of a
انمه

page_text: In certain forms of multipolar machines, where the number of poles is one more,
or one less, than the number of coils, the cross magnetic action enables the same
results to be obtained without any slots or grooves in the poles, still maintaining
the required differential action.
Dated this 28th day of February 1895.
FELL & WILDING,
1 Queen Victoria Street, E.C., Agents for the Applicant.
improvements in Dynamo Electric Machines and Motors.
I, LLEWELYN BIROHALL ATKINSON of 3 Whitehall Place, Westminster,
8.W. Civil Engineer, do hereby declare the uature 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 relates to improvements in dynamo-electric machines and motors,
and has for its object, the increasing of the output for a given weight of machino
and enabling the brushes to be fixed at an invariable point on the collector for all
loads.
In dynamos and motors, as ordinarily constructed, the reversal of the current in
each coil of the armature as it passes the collecting point, is effected, by giving the
brushes a "lead" relatively to the neutral inagnetic axis, so as to bring the coil
within the magnetic field of the leading pole corner.
When however the armature ampere turns are. relatively to the field magnet
ampere turns, large this leading pole corner is demagnetized, and the result is that
sparking at the brushes ensues.
To overcome this, independent pole pieces, called reversing poles have been
applied, excited by a circuit in series with the armature, or independent coils
wound on the armature, and carried under that pole corner which is strengthened
have been used.
The first of these methods has the disadvantage that it entails a considerable
weight of copper to excite the reversing pole inagnetism; the second has the
objection that the magnetic strength of the pole corner is not proportional, as it
should be, to the current in the armature.
To overcome these objections, and to provide means for applying a reversing
E.M.F. to the coil to be commutated, proportional to the current in the armature
is the object of the present invention.
In order to carry out this invention, I utilize the ampere turns on the armature
to produce a magnetic field, acting on independent coils, which are connected
between the commutator sections and the point of junction of successive armature
coils.
To carry my invention into effect a direct or differential method may be adopted.
By direct method I mean the adoption of such means as shall produce in the
reversing or commutating coils a single E.M.F. proportional to the armature
currents; by a differential method mean the adoption of such means as shall
while admitting other E.M.F.'s, in the reversing or commutating coils, produce a
resultant E.M.F. proportional to the armature current.
In its simplest form the direct method consists in providing outside the main
magnetic field, an independent armature, carrying the reversing coils connected
between the armaturo coils and the commutator bars. On the circumference of
this armature is a pair (in a 2 pole machine) of small pole pieces of a width
corresponding to about the width of one commutator coil. Each of these poles are
connected magnetically to two similar narrow poles, which aro on the circumference

page_text: of the main armature, between the main poles, but not covering the coil which u
being commutated.
And in order that this part of my invention may be better understood I will now
proceed to describe it with reference to Fig. 1. (a) (b) (c) (d).
In these figures N. S represent the two poles of a dynamo machine or motor
(1) is the main armature wound with either drum or gramme winding, but in Fig. 1.
(d) the winding shewn diagramatically is a gramme winding Fig. (1) c shews in plan.
the main armature (1) and subsidiary armature carrying the reversing coils (2),
und pole piece (3) b'ig. 1 (a) shewing a section on m'm, and Fig. 1 (6) a section
On 17.
In Fig. 1(a) and Fig. 1 (d) 4 represents the coil on the main armature in which
the current is to be commutated, and which is not under the pole piece 3, whilst in
Fig. 1(b) and Fig. 1 (d) 5 shews the coil on the subsidiary armature, which is..
nuder the pole piece, and in which the necessary E.M.F. is set up to reverse
the current in four.
The diagram Fig. (1) shews by curved lines and arrows the path of the
magnetic induction excited by and proportional to the ampere turns on the
armature not cutting the coil 4, but cutting the coil 5, and the connections are.
shewn through coil 6 to the commutator. The action of such commutating coils.
being well understood need not be further described.
Although the pole piece (3) on the main armature as shewn Fig. (1) a is shewn,
divided into two halves with intervening gap one auch half is sufficient, and may
in some cases be preferable.
Figure (2) a shews in plan a modified arrangement securing the same results.
In this case in place of a main armature, and subsidiary armature carrying the-
reversing coils, two main armatures are used, each forming the subsidiary armatures.
for the other.
The two armatures 8. 9 revolve together in fields placed oppositely as shewn.
The pole piece 3 in this case shown as referred to previously; that is single instead
of double, covers both armatures. The main coils are shewn by full lines, the-
subsidiary coils by dotted lines, and the armature coils of 8 are connected through
the commutator coils on 9, to commutator 7, whilst the armature coils of 9 are-
connected through the commutator coils on 8 to commutator 6.
Fig. 2 (b) shews how by carrying the commutator coil back over the same
armature core, the subsidiary armature may be dispensed with, and Figure (2) (c).
shews diagramatically the connections in such an arrangement.
It is to be noted that in this case the magnetic circuit through the armature and
pole pieces (3), must be completed externally to the armature, shewn in Figure (2) -
by 10, it being understood that any convenient path may be adopted through the
frame of the machine or otherwise, provided that there is no other resultant.
magnetic force along the path of the magnetic circuit than that due to the armature
ampere turns.
In all these cases the pole pieces may be fixed or movable, in the latter case-
the E.M.F. of the machine may be varied either by varying the position of the
brushes on the commutator the main field being maintained constant, or by allowing
such variations of position to weaken or strengthen the main field in manner well.
understood.
In the preceeding descriptions the E.M.F. set up in the commutating coil is.
that due to a magnetic field produced by the armature ampere turns and this is the-
only E.M.F. acting in the commutating coils.
In the differential methods now to be described commutator coils are wound on.
the circumference of the main armature, and so placed that they are in the main.
magnetic field at the time the coil on the armature is to be commutated but so
placed that there is no resultant E.M.F. except that due to the difference in
strength between the leading and trailing pole corners of the magnets, which is
proportional to the armature current, and in ordor to maintain the differential or
balanced action. When one such coil or side of a coil passes from under the

page_text: magnet a grove or space is provided in the pole piece corresponding to the other
coil or side of a coil. In this case therefore no subsidiary pole pieces are
required.
Figure 3 shews diagrammatically this arrangement. The main coils are shewn
by wires of circular section wound in drum manner, the commutating coils
belonging to these main coils are shewn by wires of square section. The coil 12
is in the position in which the current is to be commiated, the reversing coil 14,
will normally have no E.M.F. in it, as both wires of the coil are in the same
field and hence the E.M. F. is balanced. The pole tip 16 however is stronger
than the pole tip 17 by an amount proportional to the current in the armature
and hence a differential E.M.F. is produced, applicable to reverse the current
in coil 12. When coil 12 passes into position 13, the cominutating coil is as 15,
one side being out of the field the other side being in the gap in the pole, so
that there is no E.M.F. in the coil.
In reversible motors both pole pieces may be notched and neaus provided by
moving the brushes to produce the reversal in a coil on the opposite side of the
neutral line to that shown.
Figure 4 shews the application of the differential method to that class of dynamo
originally devised by Hefner Alteneck in which there are independent coils on the
arinature, the number of pairs of which differ by one from the number pairs
of poles.
In the figure there are three pairs of poles and four pairs of coils. The arrange-
ment of such coils and their commutation is understood by those versed in the art.
Those poles in which the coil is approaching the central position are weakened, and
those in which the coil is receding from the central position are strengthened, by
the currents in the coils.
Thus in Figure 4 pole 1 is strengthened, pole 2 weakened by the currents in the
coils.
If therefore subsidiary or reversing coils 3. 4 are wound and so connected as to
normally balance their E.M.F., a resultant E.M.F. will be set up proportional
to the armature current and may be used for the purpose of reversing the current
in the coil 5.
It will be understood that where a two pole machine has been described, the
description cæteris paribus, may be applied to multipolar machines.
Having now particularly described and ascertained the nature of my invention
and in what manner the same is to be performed 1 desire to state that I do not
claim the use of reversing coils, nor reversing coils in combination with a magnetic
field proportional to the armature current, but I declare that what I do claim is :-
1st. In continuous current dynamos or motors the combination with main
armature coils of subsidiary reversing or commutating coils, acted on by a magnetic
field produced by and proportional to the current in the main armature coils,
substantially as and for the purposes described.
2nd. In continuous current dynamos or motors the combination with main
armature coils of subsidiary reversing or commutating coils acted upon both by the
main magnetic field, and by the cross magnetic field produced by and proportional
to the armature current, so arranged that the resultant E.M.F. in the subsidiary
reversing or commutating coils is due to the cross magnetic field only, substantially
as and for the purposes described.
3rd. The construction and arrangement of continuous current dynamo electric
machines and motors substantially as described and illustrated by Figures 1 to 4.
ALL
1002
FELL & WILDING,
1 Queen Victoria Street, London, E.C., Agents for the Applicant.