IMPROVEMENTS IN THE CONSTRUCTION AND GOVERNMENT OF ELECTRO- MOTORS OR MACHINES WHICH CONVERT ELECTRICAL ENERGY INTO MECHANICAL ENERGY
Year: 1882

page_text: LETTERS PATENT to William Edward Ayrton Professor of Technical Physics,
Fellow of the Royal Society, and John Perry Professor of Mechanical
Engineering and Applied Mathematics in the City and Guilds of London
Technical College Finsbury in the county of Middlesex for an Invention
of IMPROVEMENTS IN THE CONSTRUCTION AND GOVERNMENT OF ELECTRO-
MOTORS OR MACHINES WHICH CONVERT ELECTRICAL ENERGY INTO MECHANICAL
ENERGY
PROVISIONAL SPECIFICATION left by the said William Edward Ayrton and
John Perry at the Office of the Commissioners of Patents on the 15th June
1882.
WILLIAM EDWARD AYRTON Professor of Technical Physics, Fellow of the Royal
Society, and JOHN PERRY Professor of Mechanical Engineering and Applied
Mathematics in the City and Guilds of London Technical College Finsbury
in the County of Middlesex IMPROVEMENTS IN THE CONSTRUCTION AND GOVERN-
MENT OF ELECTRO-MOTORS OR MACHINES WHICH CONVERT ELECTRICAL ENERGY INTO
MECHANICAL ENERGY."
The Machines commonly in use for converting electrical energy into mechanical
energy are generally dynamo electric or magneto electric machines which are
simply reversed in their action. For such purposes we are in the habit of using
machines which may or may not be capable of working as dynamo machines. We
consider that one condition for the satisfactory working of a dynamo machine is
that the part or parts which undergo no great magnetic change during the motion,
hereinafter called the "field magnet" should have a large magnetic moment in
comparison with that of the part or parts which are continually altering in their
magnetic properties herein-after called the "armature
"
Now in motors the condition required is quite different. It is important that
the magnetic moments of the moveable and fixed parts should not be very different
from one another.
One form of our Invention consists in the old form of. Siemens' bobbin, called by
us our field magnet, formed of soft iron or steel or some other magnetic material
and wound with wire, rotating on a spindle in the ordinary way inside a fixed soft
iron ring or hollow cylinder, like the ring of a Brush machine, called by us our

page_text: armature which is channelled out and can be wound with separate coils of wire in
the channels, the wires and channels being parallel to the axis. The fixed ring
may be built up of a number of pieces. Thus in some cases we build it up of a
number of pieces stamped out from sheet iron, fastened rigidly with wood or metal
separating pieces so as to leave air spaces between.
The bare parts of the iron between the channels project inwards so as nearly to
touch the surface of the rotating part. Fixed insulated pieces of brass, herein-after
called the commutator, are provided to which the separate coils are joined as in
the Gramme machine, except that these insulated brass pieces, and the coils, and
ring or cylinder, do not get any motion. We prefer that the commutator should
have the form and arrangement described in the Patent Specification No. 1178 of
1880. Preferably we let the rubbed parts of the brass pieces form a plane surface.
Brushes attached to the revolving part continually rub on the fixed commutator.
The revolving field magnet always receives the electric current in the same
direction, being supplied from two brushes which rub on two parts of the spindle,
one of which is insulated from the other except that they are connected by the
wire of the field magnet itself. Instead of the Siemens' bobbin any form of electro-
magnet, or a combination of electro-magnets may be employed; or a ring somewhat
similar to the outside ring may be used, or instead of the rings being placed one
inside the other, they may be placed side by side; their distinguishing characteristics
being that the magnetic polarity of a point in one of them, which we call the field
magnet, does not alter, whereas the magnetic polarity of the other, called the
armature, is continually being altered by means of the commutator. The
commutator is attached to the armature, the brushes to the field magnet, and either
the armature or the field magnet may form the fixed part of the machine.
Another form of our Invention consists in combinations of such rings as for
example we may imagine two Bürgin rotating parts placed one inside the other,
the outer being fixed, or a Bürgin rotating part fixed as the armature, with a
Siemens' bobbin or other electro-magnet or combination of electro-magnets rotating
inside it as the field magnet.
We employ various contrivances for the purpose of regulating or governing
electro-motors. Our Patent No. 55 of 1882 entitled "Improvements in the
apparatus used in the distribution of electrical energy "enables us in distributing
electrical power to maintain a constant electromotive force at the ends of parallel
circuits, in which motors or lamps are being worked; or again we are enabled
to maintain a constant current through a circuit in which a number of motors or
lamps are being worked in series, so that a number of motors or lamps are rendered
independent of one another. What our present Invention effects is that a motor
whose terminals are maintained with a constant electromotive force between them,
or with a constant current running, may be made to revolve at a constant speed
whatever mechanical work it may have to do. In the following description we
must be understood as referring not merely to the motors already described, but to
any electro-motors.
First When there is a constant electromotive force. One method is to use a
governor like an ordinary steam engine governor. When the speed is too great
the motion of the governor causes a resistance to be introduced. The motor has
been arranged to work at a certain speed when the greatest load is on, hence in
the normal state of things when there is only a medium load, a resistance is
continually being introduced and taken out from the circuit periodically. Now
when the load gets greater the governor causes the resistance to be introduced for
shorter intervals of time, and when the load gets less the governor allows the
resistance to be introduced for longer intervals of time. This corresponds some-
what with the automatic cut-off in steam engines, or more exactly with the
automatic cut-off in water-pressure engines. Many arrangements may be employed
to effect this purpose.
In one of these a cam or eccentrio moves a contact block
periodically over studs, so that contact is made during a portion of the periodic
time of revolution of the cam or eccentric. A lateral shifting of the contact block

page_text: places it on studs which are shorter or longer in the direction of the periodic
motion. In some cases we govern the motion by causing the governor to introduce
more or less resistance as the load is small or great, and this we regard as analogous
with the throttle valve governing the action of a steam engine, and we do not
approve of it except in special cases. The constant resistance which we prefer to
introduce for longer or shorter small periods is usually much greater than the
resistance of the motor itself and where possible we prefer that it should be an
infinite resistance.
Another method which we employ to effect the same object is to let the
governor alter the adjustment of the brushes, that is to cause a relative motion
of the brushes and the field magnet Another method which we employ is
to let the governor alter the positions of the field magnets or of a soft iron pole
piece or pole pieces Another method which we employ is to use several
independent circuits in the winding of the field magnets, and the governor cuts out
more or less of these from the circuit, or changes the way in which they are
combined. Another method which we employ consists in the use of a magneto-
electric machine. That is, the field magnet is made permanently magnetic, but it
is also wound with a coil of wire which is in the same circuit as the armature, and
whose effect is to diminish the magnetism of the permanent magnet when the
current passes through the motor. Such a machine might be called a "Combined
Magneto and Dynamo Electric Motor." The dynamo part helps the current and
uses up mechanical energy, thus acting as a governor to the magneto part, which
is really the motor, and which converts electrical energy into mechanical energy.
A magneto machine gearing into a very much smaller dynamo machine, both in the
same circuit and regarded as one motor may also be used. In any case the constant
electromotive force which is maintained externally, the resistance and constant of
the machine or machines, and the speed, are matters which we determine very
accurately by means similar to those described in the above mentioned Patent
Specification No. 55 of 1882. A shunted motor may also be employed, that is a
shunt circuit is coiled on the field magnet and produces a permanent magnetic effect;
but there is also a coil on the field magnet which is in series with the armature
and which is so arranged that when the current passes the magnetism is weakened
Second When the current is maintained constant we allow a governor like a
steam engine governor to shunt a considerable part of the current past the motor
periodically for longer or shorter small periods of time. Another method is the
Brush adjustment already described Another method which we employ is to
cause the governor to alter the relative positions of the field magnet and armature,
or the position of a soft iron pole piece or pole pieces. Another method is to use a
shunted motor whose field magnet cores are partly permanently magnetic, that is
the magnets are permanent magnets which are also wound with a shunt circuit.
We find that there is a certain relationship between the magnetic and resistance
constants of such a motor, and the speed, which enables it to remain perfectly
constant in speed whatever mechanical work it may be giving out, if there is a
certain constant total current flowing through it. The same object is effected by
gearing together a shunted dynamo motor and a magneto electric motor, their
armature coils being in series and the shunt circuit of the dynamo being a shunt
to both the armatures, and regarding the whole as one motor with a certain
constant current and at certain speeds of the two machines our general object is
effected. Or again the magneto electric part of the combination may be in the
shunt circuit, that is in the circuit of the field magnet of the dynamo-electric part.
We have described methods of governing motors when a constant electromotive
force or a constant current is maintained. These are the supply conditions which
best satisfy the requirements of the various cases, but our methods are useful and
are employed by us under other supply conditions, that is, even when neither the
electro-motive force nor the current is maintained constant.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Edward Ayrton and John Perry in the Great Seal
Patent Office on the 15th December 1882.
WILLIAM EDWARD AYRTON, Professor of Technical Physics, Fellow of the Royal
Society; and JOHN PERRY Professor of Mechanical Engineering and Applied
Mathematics in the City and Guilds of London Technical College, Finsbury in
the County of Middlesex." "IMPROVEMENTS IN THE CONSTRUCTION AND GOVERNMENT
OF ELECTRO-MOTORS OR MACHINES WHICH CONVERT ELECTRICAL ENERGY INTO
MECHANICAL ENERGY."
The machines commonly in use for converting electrical energy into mechanical
energy are generally dynamo-electric or magnetic-electric machines which are
simply reversed in their action. For such purposes we are in the habit of using
machines which may or not be capable of working as dynamo machines.
We consider that one condition for the satisfactory working of a dynamo-machine
is that the part or parts which undergo no great magnetic change during the
motion, hereinafter called the "field magnets," should have a large magnetic
moment in comparison with that of the part or parts which are continually altering
in their magnetic properties, hereinafter called the "armature." Now in motors
the condition required is quite different It is important that the magnetic
moments of the movable and fixed parts should not be very different from one
another
One form of our Invention is shown in Figs. 1, 2 and 3. The shape of A. the
rotating part is there shown. We call it our "field magnet." It is formed of
soft iron, steel, or malleable cast iron, or some other magnetic material and is
wound with wire in coils which are nearly parallel to the axis. The iron part of
this bobbin may be in one solid piece with a spindle as shown in the Fig. 2, or the
two parts may be screwed into its two ends before winding, or again the bobbin
may first be wound and then fixed to the two parts of the spindle by end pieces
screwed on to it as shown in Fig. 4. This bobbin rotates inside a Pacinotti ring,
In the present case one end of the wire on the bobbin is fastened to the iron and
the other end passes insulated through a hole in the spindle to S where it is
connected to one of the rubbing brushes T. The Pacinotti ring we prefer to build
up in pieces, that is, two ends parts of soft iron E E and a considerable number of
plates of iron formed as shown in Fig. 2, bolted together with separating washers.
It will be seen that parts of the ring project inwards so as nearly to touch the
surface of the rotating part. Sometimes we make the ring of one piece of soft
iron cutting deep circular grooves, preferably in the form of very narrow screw-
threads, on the inside of the ring, the screw-threads being of small pitch, the axis of
the screw being the axis of the ring; leaving very little solid metal on the outer
part. In this case the ring may be of very malleable cast iron, but we prefer to
have it of the best wrought iron. The dotted lines in Figs. 1 and 2 show how the
wire coils are wound in the grooves of the ring so that they shall be clear of the
rotating part. There may be four or any greater even number of these coils.
the present example there are twelve of these coils and their ends are joined up to
the pieces C of the commutator as in the Gramme ring. In Figs. 2 and 3 this
cominutator is shown so that the rubbing surface is plain, the twelve pieces C
being fastened to the disc of wood Z. This disc of wood has on its surface also a
continuous ring of metal D to which is connected one terminal B of the machine.
Let us suppose the current enters at B to the rings D-The broad brush t bridges
across from the ring to one of the commutator pieces C, so that the current passes
in this way and circulates through the two sides of the ring, coming out at the
diametrically opposite contact piece on to the second narrower brush T thence to S,
In

page_text: and through the hollow spindle to the coils of the rotating bobbin and then to
the metal of the bobbin; from this it passes through the bearings of the machine, or
in some cases through another brush rubbing on a part of the spindle to the general
frame of the machine on which may be fixed the other binding screw. Sometimes
the binding-screw is insulated and then the rolling brush which takes the current
from the revolving bobbin and the collar on which it rubs are insulated from the
frame and from the spindle. The disc of wood, or vulcanised fibre, or other insu-
lating material which carries the commutator pieces C is shown in Fig. 2 rigidly
fastened to the frame of the machine. In some cases, however, we make it capable
of revolving to some extent for the purpose of adjusting the lead. In this case
the connections of the commutator pieces with the coils of the Pacinotti ring are
made flexible. Another form of this movable commutator is shown in Fig. 4 where
the commutator pieces are arranged to have a cylindric rubbing surface, but it is
obvious that they may be arranged to form any surface of revolution. The two
ends of two neighbouring coils, which must be joined to a certain piece of the
commutator, are soldered together on the outside, and only one cable like P Q
comes from the coils to the screw Q on the commutator piece. The commutator is
supported by the frame B beyond the end of the spindle. The brush-holder K is,
as before, fastened to the spindle. The brush t pressed by springs on the com-
mutator pieces and on the continuous insulated ring D is like the broad brush of
Fig. 2. In this case it is easy to fasten all the wires to the commutator at places
which are near the axis, so that when the commutator is moved round by means
of the handle there is less risk of entanglement of the wires. J shows a guard
which we use in many of these cases to protect the long connecting wires from
the rotating brush-holder. The Drawing shows sufficiently well without further
description how a relative motion may be given to the commutator and the
Pacinotti ring by means of the handle A. This figure also shows the arrangement
of brush-holder K that seems most suitable when the commutatur is cylindrical,
It is obvious that the theory of arrangement is exactly the same as in the case of
the flat commutator.
In Fig. 2 the brush-holder is a disc of wood, or vulcanised fibre, or other insu-
lating material fastened to the spindle by means of a set-screw passing out at the
circumference of the disc. This enables a very easy means to be employed for
adjusting the brushes so that they shall have the proper lead for the particular
5 speed at which the motor is supposed to be driven. In Fig. 5, however, we show a
means of adjusting the position of the brushes and giving the proper lead to them
even when the machine is in motion. In this case A is an ordinary clutch lever.
The clutch F when withdrawn from the position in which it is shown is con-
strained by one or more spiral feathers on the spindle, not only to move along
the spindle but to have a relative motion round it. GG are straight slots so that
the motion round the spindle which F gets is communicated to the brush-
holder K by means of the screws H. We usually give a total relative motion of
180 degrees so that when the motor is employed for the driving of tramcars or
railway carriages or in any case where it is required to go at very different speeds
5 in either direction, it is possible to give the brushes the best lead.
Sometimes instead of using the field-magnet shown at A in Figs. 1 and 2 as the
rotating part, we combine several electro-magnets as shown in section Fig. 6 to
form a magnet which is not unlike the field magnet A of Figs. 1 and 2 when the
winding is all finished. In some of our larger motors we employ many ribs of this
b character although only three are shown in the Drawing, and sometimes we only
employ the two side-magnets leaving out the central one. In this Figure the pole
pieces are cylindric surfaces, but we sometimes arrange that the whole, or part, of
the surfaces of the poles are in planes at right angles to the axis of rotation. One
of the simplest of such rotating magnets is shown in Figs. 7 and 8 where N N,
5 S S, are two pairs of pole pieces of this character, and in this case the part which is
wound with wire may be a diametrical piece, or two side pieces, or combinations of
many pieces with their like poles coming towards the pole pieces. When the pole.

page_text: pieres are of this character we employ Pacinotti rings placed with their planes at
right angles to the axis of rotation, and there may be one of them on each side of
the rotating field-maguet, or one on one side only. Thus in Figs. 9 and 10 A is the
rotating field magnet with pole pieces whose surfaces are at right angles to the
axis of rotation and shaped as shown by the dotted lines. at N N, SS, Figure 9. The
two Pacinotti rings E E are on each side of the field-magnet. These may be built
up of many pieces, or, as shown in these figures, each ring may be in a solid picce
shaped out with the proper Pacinotti projections shown in Fig. 9 and with many
deep circular grooves cut into it to prevent induction currents. The brushes T
and t, the commutator pieces C, the ring D, and the insulating disc of the com-
mutator Z are of much the same construction as in Fig. 2. In these Drawings the
field-magnet is shown consisting of two semi-circular electro-magnets fastened
together at their ends, or made in one solid piece without any fastening and carried
by the spindle P by means of a brass centre."
In Figs. 12 and 13 it is one Pacinotti ring which revolves and the rotating field
magnet of Fig. 10 is shown now cut into two halves one being placed on each side
of the rotating ring. In this case the brushes are fixed and the commutator is
movable. The commutator and brushes of these machines are shown in Fig. 14.
We employ various contrivances for the purpose of regulating or governing
electro-motors. Our English Patent No. 55 of 1882 entitled " Apparatus used in
the distribution of "Electric Energy" enables us in distributing electrical power
to maintain a constant electro-motive force at the ends of parallel circuits in which
motors, or lamps, or both, are being worked. Or again we are enabled to maintain
a constant current through a circuit in which a number of motors, or lamps, or both,
are being worked in series; so that the working of a number of motors or lamps
are rendered absolutely independent of one another
What the second part of our new and present Invention effects is that a motor
whose terminals are maintained with a constant electro-motive force between them
or with a constant current running may be made to revolve at a constant speed
whatever mechanical work it may have to do.
In the following description we must be understood as referring not merely to
the motors already described but to any electro-motors
First when there is a constant electro-motive force-Suppose that a motor has
been arranged to work at a certain speed when the greatest load is on; then when
there is only a medium load we arrange that a resistance shall be introduced and
taken out from the circuit periodically. When the load gets greater the "governor "
causes the resistance to be introduced for shorter intervals of time, and when
the load gets less the governor allows the resistance to be introduced for longer
intervals of time. This corresponds somewhat with the automatic "cut-off"
in a steam engine, or more exactly with the automatic "cut off" in a water-
pressure engine. Many arrangements may be employed to effect this purpose.
one of these a cam or eccentric moves a contact block, or brush, or roller, periodically
over studs so that contact is made during a portion of the periodic time of revolution
of the cam or eccentric. A lateral shifting of the contact block or of the cam by
means of the governor, places on studs which are shorter or longer in the direction
of the periodic motion than before. Again in Figs. 15 and 16 A is a piece which
makes contact between B and C M, and let us suppose that when there is contact
between B and C M the motor is fed with electricity CM is a rotating piece
In
and A is fastened to it at M, by means of a spiral spring. A is guided so that it
can only move radially on C M. At a normal speed as A is carried round, it con-
tinually makes contact between B and C M, but at greater speeds, A moves out
from the centre by centrifugal force and may not make contact between B and C M
but between K and C M, the rubbing surface on K being in the same plane as the
rubbing surface on B, and K and B being connected with one another through a
resistance. Again in Fig. 17 A is a brush lying on the rotating piece B K, the
cylindric surface of this piece is formed of two conducting portions connected with
one another through a resistance, and the brush A may move along the cylinder B K

page_text: under the action of the governor balls shown in the Figure. Let us suppose that
when the brush A is touching the contact part B the motor is receiving current
directly, but when A rests on the part K then the motor receives current through
a resistance which is interposed between B and K. If the governor-balls fly out
the brush is moved along B K so that it is in contact with K during a greater
portion of a revolution than before; and if the governor balls come together, the
speed of the motor being too small, the brush is moved in the opposite direction so
that it gets more contact with B during each revolution. It is obvious that we
can make B K, as a sleeve, move in the direction of the length of the spindle under
the action of the governor, instead of the brush, the relative motion being all that
is required: and it is also plain that the surfaces of BK may be that of any other
surfaces of revolution besides the cylindric. The same object is effected in Figs. 18.
19. 20 & 21 which show a flat commutator such as has already been described.
The broad brush t now becomes two brushes, t¹ which rub on the continuous ring now
made cylindric, and t which becomes part of a heavy arm which can move readily
about the pin R which is fastened to the brush-holder, so that the place of contact
of the brush with the commutator tends to be further out from the centre when
the speed is great, on account of centrifugal force. It is restrained from flying out
from the centre by means of a spring-N N are a second set of commutator
pieces connected with the first by means of more or less resistance so that when
the brush, by centrifugal force, is urged too far out from the centre the commutator
pieces do not always receive electricity directly from the brush, but periodically
through a certain amount of resistance. When this arrangement is employed with
the cylindric form of commutator an independent governor is employed to shift
the brushes
We do not think it necessary to give a detailed account of how the centrifugal
action, either in the case of these brushes or in the case of the speed-governor,
employed in any method of effecting our object is so arranged as to give a very
considerable amount of motion for small alterations in speed, because these matters
are sufficiently well known already to mechanical engineers.
We have now described a few of the methods in which this part of our Invention
is carried out, viz the continual introduction and taking out of a resistance from
the circuit periodically in such a way that the governor causes the resistance to be
introduced for shorter or longer periodic intervals of time. We have found in
practice that any mechanical engineer can suggest and carry out practically
numerous ways of effecting this object besides those which we have described, and
it is to avoid a multiplicity of Drawings that we only describe the way shown in
Figs. 15 to 21.
In governing motors we also employ a method in which we use several circuits
in the winding of the field-magnet and the centrifugal or other governor cuts out
more or less of these from the main circuit, or changes the way in which they are
joined when the speed alters.
"
Another method which we employ consists in the use of a magneto-electric
machine. That is, the field-magnet is made permanently magnetic but it is also
wound with a coil of wire which is in the same circuit as the armature and whose
effect is to diminish the magnetism of the permanent magnet when the current passes
through the motor. Such a machine might be called a "Combined Magneto and
Dynamo Electric Motor." The dynamo part helps the current and uses up
mechanical energy, thus acting as a "governor to the magneto part, which is
really the motor, and which converts electrical energy into mechanical energy. A
magneto machine gearing into a very much smaller dynamo machine, both in the
same circuit and regarded as one motor, may also be used. In any case the
constant electro-motive force which is maintained externally, the resistance and
constant of the machine or machines, and the speed, are matters we determine very
accurately by means similar to those described in the above mentioned Patent Speci-
fication of No. 55 (1882). A shunted motor may also be employed, that is a shunt
circuit is coiled on the field-magnet & produces a permanent magnetic effect, but

page_text: there is also a coil on the field-magnet which is in series with the armature and
which is so arranged that when the current passes the magnetism is weakened.
The theory of this method of governing may be roughly given as follows. If E
is the constant difference of potentials maintained between the terminals of the
motor. If C is the current flowing through it, then the back electro-motive force e
is en (a K C) if n is speed of motor and a and K are constants.
-
but e= E-RC
where R is resistance of the motor (neglecting any shunt circuit which may be
employed to produce the permanent magnetism); Now the power given out by
the motor is proportional to e C, and the condition we wish to arrive at is that e C
shall be independent of n the speed.
Now e C is n (a-K C) C and it must also be (ERC) C.
Without any alteration in n. This condition is evidently effected if we make
na E and n K = R
The constant a relates to the permanent magnetism of the field-magnet in one
case, or to the permanent magnetism of the coupled magneto machine in another
case, or to the permanent magnetism produced by the shunt circuit in another case;
whereas K relates to the dynamo-electric part of any of the arrangements.
We shall now show how we practically produce the above mentioned conditions
in a given motor wound in the ordinary way (this may be any typical machine)
and experiments made on this one motor will tell us how to wind all motors of
the same class and size.
Let its present field-magnet resistance be r. its armature resistance R₁ pass
a current c₁ through the field-magnet, drive the machine at n₁ revolutions
per minute; and let us measure the electro-motive force e, in the armature
produced by rotation. If there is any permanent magnetism in the field-magnet
two experiments of this kind must be made. The armature ought first to be
run when there is no current through the field magnet, then run when there is
a current c, and it is then the difference of the two electro-motive forces that is
taken as e₁.
Now if this motor is rewound with wire so that its field magnet
of its volume wound with a resistance r, and if through this we pass a
has
1th
1th
current c, and if of its equally useful volume is wound with a resistance p, and if
through this we pass a current C, then the electro-motive force produced by the
rotation of the armature, if the armature resistance is R is nearly
e
☑ C
e=
this is obviously of the shape
22
R
e = n (a + b c
-
K C₁)
and reasoning as before, if we wish with a constant difference of potentials E at
terminals of machine to drive at a constant speed n whatever be the power given
out, c being the constant current produced round the field magnet by the shunt
circuit of resistance r we must have
(1) n (a + h) - Mr-
which is the game
E
na

page_text: These conditions may be satisfied in many ways-Numerical Example. In an
experiment suppose we find
If now we assume that our constant difference of potentials is say 100 volts,
and we make r =
nb = na
100, c = 1 from (1) we have 100
=
-
Let us make R
= 0.16 and n = 1000. Also arrange that regulating coil is to
occupy say 1/6th of the field magnet coil space, then y = 5 and x = 1.25, so we find
that b 0.053 and a = 0.113 K = 0.00016 and p = 0.000132 ohms
When therefore the regulating coil p has this resistance and occupies one-fifth of
the volume of the field-magnet winding: and when the shunt part occupies four
times as much of the equally useful volume, and has a resistance of 100 ohms:
when armature resistance together with that of regulating coil is 01601 ohms,
this motor will run at, 1000 revolutions if a constant difference of potentials
100 volts is maintained between its terminals.
Second. When motors are in series with one another, or with lamps, heating
apparatus, electro-plating baths, or other contrivances; in governing our motors we
allow a governor like a steam engine governor to shunt a considerable part of the
current past the motor periodically for longer or shorter small periods of time in
ways which must be quite clear from the descriptions given of Figs. 15 to 21.
Thus in Fig. 17 if when the brush A is in contact with the piece B the motor
receives its electricity in the ordinary way, and if K is insulated from B but is
connected with a circuit on the other side of the motor through no resistance, or
through a greater or less resistance, than when the brush is touching K the motor
is receiving no electricity. A governor which causes a relative motion of the
part BK and the brush will effect the object we have described.
Another method which we employ for the governing of a motor in series with
others is (A) to use a shunted motor whose field magnet cores are partly
permanently magnetic, that is, the magnets are permanent magnets which are
also wound with a shunt circuit, the permanent magnetism being opposite to that
produced by the shunt circuit. We find that there is a certain relation between the
magnetic and resistance constants of such a motor and the speed, which enables it
to remain perfectly constant in speed, whatever mechanical work it may be giving
out, if there is a certain constant total current flowing through it. The same object
may be effected by (B) using an ordinary motor with part of its field-magnet
circuit in series with its armature circuit, but besides this its field-magnet is mainly
wound with wire which is a shunt to the armature part only; the series coil on the
field-magnet diminishing the magnetic field. The same object is effected by (D)
gearing together a shunted dynamo motor and a magneto-electric motor, their
armature coils being in series and the shunt circuit of the dynamo being a shunt
to both the armatures and regarding the whole as one motor,-the magneto part
really reconverting mechanical into electrical energy however-with a certain

page_text: constant current, and at certain speeds of the two machines, our general object is
effected. Or again (F) the magneto-electric part of the combination may be in the
shunt circuit, that is, in the circuit of the field-magnet of the dynamo electric part.
Instead of speaking here of a magneto-electric motor it is obvious that we may
speak (G) of a dynamo motor round whose field-magnet the whole constant current
passes, as this causes its magnetism to be permanent
The theory of this method of governing may be roughly given as follows;-
Let R and be the resistances of the direct and of the shunt parts respectively, C
and c the currents through these parts, and let C¹ be the total current through motor
which is kept constant. The back electromotive force e in the armature is,—
e = n (a + b c - KC)
where a is what permanent magnetic field there is, and n is the speed
Now ecrCR, and as e C the power given out by the motor is
n (a+be K C) C, and also (cr - CR) C
-
-
Orn lab (CC) -KCJ C and also 1r (C' - C) - CRI C
If this power is to vary whilst n remains constant we must satisfy the conditions
na + nb C = C
nb + n K
=+R
-
(1)
(2),
and if these conditions are satisfied the motor will maintain a constant speed for
very different amounts of power given out by it. When a motor is given us we
can, in much the same way as that already described-by making an experiment
with it at any speed and with anỹ winding, determine the proper kind of winding
for working at a certain constant speed under the action of a constant current.
We may regard the formula as applying either to one motor or to two or more
coupled motors. Thus for (A) given above, a shunted motor, its field magnets being
permanently magnetic, the formule answer if we make K = 0 Again, the second
machine (B) above mentioned is represented if we assume, as we must, that there
is some permanent magnetism in the field magnets. Again we have the
combination (D) or (F) if we imagine K = O. Obviously also (G) is the same
as (A).
In all when we practically apply the method, whether we use one machine, or
two or more coupled together, n may be taken as the speed of the one machine, or
of any rotating part of the combination.
We have described methods of governing motors when a constant electro-motive
force or a constant current is maintained. These are the supply conditions which
best satisfy the requirements of the various cases but our methods are useful, and
are employed by us, under other supply conditions, that is, even when neither the
electro-motive force nor the current is maintained constant.
Having now described and particularly ascertained the nature of our said
Invention and the manner in which the same is to be performed or carried out
in practice, we hereby declare that what we consider to be novel or original and
therefore claim as the Invention secured to us by the hereinbefore in part recited
Letters Patent is
(1) A fixed Pacinotti ring, with four or any greater number of coils, inside which
rotates a field-magnet of the shape shown in Figs. 1 and 2 substantially as described,
or any mere moditication of the same.
(2) A fixed Pacinotti ring inside or alongside which rotates a bobbin shaped like
Figs. 6. 7 or 8 substantially as described, or any mere modification of the same.
(3) The arrangements shown in Figs. 9. 10 and 11, and in 12, 13 and 14
substantially as described
(4) The arrangement shown in Fig. 5, by means of which the relative positions
of the brushes and field-magnet may be altered, substantially as described, or any
mere modification of the same
(5) The arrangement shown in Fig. 4 by means of which the relative positions of
the commutator and the Pacinotti ring may be altered, substantially as described,
or any mere modification of the same.

page_text: (6) The regulation of a motor by continually introducing or taking out of the
circuit a resistance (which may be infinite), or shunting the current past the
machine or any portion of it periodically in such a way that a governor, like an
ordinary steam-engine governor, alters the fractional part of the whole periodic
time during which introduction of the resistance, or the shunting occurs.
(7) Effecting the novel object of our fifth claim by apparatus shown in Figs. 15
and 16-in Fig. 17-in Figs. 18. 19-20 and 21, substantially as described, or any
mere modification of the same.
(8) The use of a magneto-electric and a dynamo-electric motor coupled or geared
together in the manners described for obtaining constant speed independent of the
load when there is constant or nearly constant electro-motive force or constant or
nearly constant current respectively.
(9) The construction of a motor whose field-magnet is permanently magnetic
and is also wound with wire in the same circuit as the arinature in such a way
that the current diminishes the magnetism of the field-magnet, for obtaining constant
speed independently of the load where there is a constant or a nearly constant
difference of potentials maintained between the terminals of the motor.
(10) The construction of a motor whose field-magnet is mainly wound with a
shunt circuit to the whole machine, but is also partially wound with wire in the
same circuit as the armature in such a way that the current diminishes the
magnetism produced by the shunt circuit, for the purpose of obtaining constant
speed independently of the load, when there is a constant or a nearly constant
difference of potentials maintained between the terminals of the motor, or when
there is a constant or a nearly constant current supplied through the motor,
substantially as described
(11) The use of a shunted motor whose field magnet cores are partly permanently
magnetic, but which are also wound with a shunt circuit, the permanent magnetism
being opposite to that produced by the shunt circuit for the purpose of obtaining
constant speed when there is a constant or nearly constant current supplied through
the motor, substantially as described.
(12) The construction of a motor whose field-magnet and armature circuits are
in series, but whose field-magnet is also partly wound with wire which is a shunt
to the armature part only, the permanent magnetism produced by the series circuit
being opposite to that produced by the shunt circuit, for the purpose of obtaining
constant speed independently of the load when there is a constant current supplied
to the motor, substantially as described.
In witness whereof we the said William Edward Ayrton and John Perry
have hereunto set our hands and seals this fifteenth day of December in
the year of our Lord one thousand eight hundred and eighty two