Improvements in or relating to Electric Motors and the Transmission of Power therefrom.
Year: 1898

page_text: Date of Application, 4th June, 1898
Complete Specification Left, 23rd Feb., 1899-Accepted, 1st Apr., 1899
DIONAL DIECIFICATION.
Improvements in or relating to Electric Motors and the Transmission
of Power therefrom.
We, FAWCETT PRESTON & COMPANY LIMITED, of 17, York Street, Liverpool,
Engineers, and CHARLES ALPHONSO MATTHEY, of Russell Rise, Reading, Berks,
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to electric motors and the transmission of power there-
from.
Electric motors whether driven by continuous current or by alternating poly-
phase current, run cool, that is to say, without undue heating of their armature
windings at the speed (generally high) for which they are designed.
But at low speeds, and more especially at starting if the whole current is
turned on when the motor is at rest the armature winding and insulation of the
motor are very liable to get overheated and destroyed, before the motor has
attained the speed at which it is safe to allow the whole current to pass through
the machine.
In order to overcome this difficulty the motors have hitherto generally been
provided with resistance boxes containing resistance coils which are used to
increase the resistance of the armature coils by switching in all or some of the
resistance coils at starting by means of a suitable switch or contact making
device, and cutting out the resistance coils gradually one after the other as the
motor increases its speed.
This expedient entails the provision of a complete resistance box or set of
resistances with a suitable switch, and in the case of the polyphase motors a
costly form of construction of the armature shaft together with the provision of
rubbing contacts, brushes, brush-holders and their connections; whilst also the
attendant must have sufficient intelligence to know how much resistance to put
in for a start, and at which points to cut it out as the motor attains its full
speed. All the foregoing requirements considerably increase the cost of manu-
facture and up-keep of an electric motor, without however entirely obviating
the risk of burning out the armature.
Apart from this risk of destroying the armature of the motor at starting,
the polyphase motor has a further peculiarity which has hitherto also necessi-
tated the provision of a variable resistance. This is that in such motors the
torque or torsion effort at starting is extremely small, so that with a moderate
load even far below its normal full load, the motor in its normal condition will
not start at all. This peculiarity is due to the fact that the torque or moment
of torsion, i.e., the force with which the motor armature tends to twist or turn
its shaft is roughly proportional to the resistance of the secondary circuit, i.e.
of the armature coils. Hence the necessity for the introduction of a resistance
into the motor armature circuit at starting and the gradual cutting out of the
resistance as the speed increases.
Now the present invention has for its objects to dispense with the provision

page_text: and use of a resistance box or set of resistances, to do away with the above
stated complication and increased cost of construction of electric motors, and also
to dispense with the necessity for a skilled attendant whilst obviating all danger
of burning out the armature coils.
"
These objects are effected by allowing the electric motor to run idle for a time
at starting, that is to say, without any load other than that due to the friction
of its bearings, so that the armature can jump up so to speak, to its full
speed, or at least to a safe speed at once before it has time to become heated;
and by letting the machine driven by it attain its proper speed more gradually.
For this purpose, we introduce between the armature shaft or driv-
ing shaft of the motor and the shaft of the machine to be driven
by the latter a yielding or slipping, power-transmitting device prefer-
ably automatic in its action or capable of being placed into and out
of gear at will either with the electric motor or with the driven
machine. The type of device which we prefer to employ consists substantially
of a friction clutch operated by centrifugal action produced by and consequently
practically directly proportioned to, the square of the speed of the motor to
which it is applied.
Apparatus for carrying out this invention may be constructed in various ways.
According to one arrangement we employ a slipping pulley consisting of an
inner pulley or its equivalent keyed to the armature shaft of the electric motor,
and an outer pulley keyed or otherwise attached to or geared with the shaft
of the machine to be driven by the electric motor. The inner pulley is adapted
to drive the outer pulley by means of friction produced in the following way.
The inner pulley or its equivalent has in its rim or arms two or more recesses
or pockets into each of which there fits easily a block of wood or other material
which may be covered with leather, canvas, cotton, cloth or other material for
making considerable friction against the material of the outer pulley. When
the inner pulley is revolving, the blocks are caused by centrifugal action to press
against the inside of the rim of the outer pulley and thus drive the latter round
by friction.
The arrangement is such that in a position of rest, i.e. when the motor is about
to be started, the blocks do not press against the rim of the outer pulley, and
consequently transmit no torsion. At low speeds of the armature and inner
pulley, the torsion transmitted is very small, but rises more rapidly as the speed
gets up because as we have seen it varies as the square of the speed. Therefore
when the current is turned on, the armature meeting with such a small oppos-
ing torque at low speeds rushes up to a high speed where the torque it exerts
is balanced by the opposing torque, and at this speed its armature is safe from
overheating.
The inner pulley will continue to outrun the outer till the latter has
attained the same speed. In the case of a machine possessing great inertia this
period may last several minutes; and even if by accident the driven machine
were locked, and consequently the outer pulley remained stationary, the inner
pulley and the electric motor will revolve at a speed sufficiently high to prevent
heating in the motor, whilst any heat that may be produced will take place by
friction in the pulley where it can do no harm.
Where the machine is to be driven from the motor by means of a belt, it is
preferable to provide a separate belt-driving pulley keyed on a separate shaft
driven by the outer pulley; and by arranging bearings for this shaft between
the belt driving pulley and the said outer pulley all binding of the parts is
obviated.
Dated this 4th dose of Iun 1000
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.

page_text: Improvements in or relating to Electric Motors and the Transmission
of Power therefrom.
We, FAWCETT PRESTON & COMPANY LIMITED, of 17, York Street, Liverpool,
Engineers, and CHARLES ALPHONSO MATTHEY, of Russell Rise, Reading, Berks,
Engineer, 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 relates to electric motors and the transmission of power there-
from.
Electric motors whether driven by continuous current or by alternating poly-
phase current, run cool, that is to say, without undue heating of their armature
windings, at the speed (generally high) for which they are designed.
But at low speeds, and more especially at starting if the whole current is
turned on when the motor is at rest, the armature winding and insulation of the
motor are very liable to get overheated and destroyed before the motor has
attained the speed at which it is safe to allow the whole current to pass through
the machine.
In order to overcome this difficulty the motors have hitherto generally been
provided with resistance boxes containing resistance coils which are used to
increase the resistance of the armature coils by switching in all or some of the
resistance coils at starting by means of a suitable switch or contact making
device, and cutting out the resistance coils gradually one after the other as the
motor increases its speed.
This expedient entails the provision of a complete resistance box or set of
resistances with a suitable switch, and in the case of the polyphase motors a
costly form of construction of the armature shaft together with the provision of
rubbing contacts, brushes, brush-holders and their connections; whilst also the
attendant must have sufficient intelligence to know how much resistance to put
in for a start, and at which points to cut it out as the motor attains its full
speed. All the foregoing requirements considerably increase the cost of manu-
facture and up-keep of an electric motor without however entirely obviating
the risk of burning out the armature.
Apart from this risk of destroying the armature of the motor at starting,
the polyphase motor has a further peculiarity which has hitherto also necessi-
tated the provision of a variable resistance. This is that in such motors the
torque or torsion effort at starting is extremely small, so that with a moderate
load even far below its normal full load, the motor in its normal condition will
not start at all. This peculiarity is due to the fact that the torque or moment
of torsion, i.e., the force with which the motor armature tends to twist or turn
its shaft is roughly proportional to the resistance of the secondary circuit, i.e.
of the armature coils. Hence the necessity for the introduction of a resistance
into the motor armature circuit at starting and the gradual cutting out of the
resistance as the speed increases.
Now the present invention has for its objects to dispense with the provision
and use of a resistance box or set of resistances, to do away with the above
stated complication and increased cost of construction of electric motors, and also
to dispense with the necessity for a skilled attendant, whilst obviating all danger
of burning out the armature coils.
According to our invention the electric motor is allowed to run idle for
a time at starting, that is to say, without any load other than that due to the

page_text: friction of its bearings, so that the armature can "jump up" so to speak, to its
full speed, or at least to a safe speed at once before it has time to become heated;
and the machine driven by it is allowed to attain its proper speed more gradually.
For this purpose, we introduce between the armature shaft or driving shaft
of the motor and the shaft of the machine to be driven by the latter, an auto-
matic friction clutch operated by centrifugal action produced by, and consequently
practically directly proportioned to the square of, the speed of the motor to
which it is applied.
To effect this we employ a slipping pulley consisting of an inner pulley or
its equivalent keyed to the armature shaft of the electric motor, and an outer
pulley keyed or otherwise attached to or geared with the shaft of the machine
to be driven by the electric motor. The inner pulley is adapted to drive the
outer pulley by means of friction produced in the following way:-
The inner pulley or its equivalent has in its rim or arms two or more recesses
or pockets into each of which there fits easily a block of wood or other material
which may be covered with leather, canvas, cotton, cloth or other material for
making considerable friction against the material of the outer pulley. When
the inner pulley is revolving, the blocks are caused by centrifugal action to press
against the inside of the rim of the outer pulley and thus drive the latter round
by friction.
The arrangement is such that in a position of rest, i.e. when the motor is about
to be started, the blocks do not press against the rim of the outer pulley, and
consequently transmit no torsion. At low speeds of the armature and inner
pulley, the torsion transmitted is very small, but rises more rapidly as the speed
gets up because as we have seen it varies as the square of the speed. Therefore
when the current is turned on, the armature meeting with such a small oppos-
ing torque at low speeds rushes up to a high speed where the torque it exerts
is balanced by the opposing torque, and at this speed its armature is safe from
overheating.
The inner pulley will continue to outrun the outer pulley until the latter has
attained the same speed. In the case of a machine possessing great inertia this
period may last several minutes; and even if by accident the driven machine
were locked, and consequently the outer pulley remained stationary, the inner
pulley and the electric motor will revolve at a speed sufficiently high to prevent
heating in the motor, whilst any heat that may be produced will take place by
friction in the pulley where it can do no harm.
Where the machine is to be driven from the motor by means of a belt, it is
preferable to provide a separate belt-driving pulley keyed on a separate shaft
driven by the outer pulley; and by arranging bearings for this shaft between
the belt driving pulley and the said outer pulley all binding of the parts is
obviated.
Referring to the accompanying diagrammatic drawings:-
Figure 1 is a side elevation partly in central vertical section of one arrange-
ment of apparatus for carrying out this invention.
Figures 2 and 3 are respectively a front end view and a plan of the slipping
pulley shown separately.
Figure 4 is a side elevation, partly in central vertical section of a modified
arrangement of the apparatus.
A represents the armature of the electric motor, and B is the armature shaft.
C is a pulley which is keyed on the armature shaft and which is provided with
a number (two are shown) of recesses D formed in its rim. E E are blocks
which fit loosely in the recesses D and which are preferably covered as shown
with a strip F of leather, hemp or other material for making friction when the
blocks are pressing against the inner surface of the rim of the pulley G. The
speed of this pulley G is intended to be equal to or proportional to the speed
of the machine (not shown) to be driven by the armature shaft B of the electric
motor.

page_text: In Figure 1, this pulley G is shown keyed on a shaft H which may drive
the machine to be driven either directly or through suitable gearing.
In Figure 4 the pulley G is shown mounted so as to run loose on the arma-
ture shaft B; it is constructed to take a belt H for transmitting the power to
the driven machine. A stop collar I serves to keep the pulley G on the shaft B.
In both arrangements when the electric motor and consequently its armature A
are at rest the blocks E will be either quite away from or else barely touch the
inner surface of the rim of the pulley G.
On starting the electric motor, its armature which has only to overcome the
inertia of the armature shaft B and the pulley C with its blocks E and the
friction corresponding to the small centrifugal force of those blocks at low speeds,
will be able to attain a safe speed before the coils are burnt by the large initial
current. The centrifugal action produced by such speed causes the blocks E to
fly outwards and press against the inner surface of the rim of the pulley G with
sufficient friction to drive the said pulley G and consequently also the machine
to be driven.
In this way all risk of burning out the armature coils is obviated, and the
motor will be enabled to drive the machine at its full load in a very short time
after starting from a state of rest.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that
what we claim is:
The combination with an electric motor and a shaft or pulley to be driven
thereby of an automatic centrifugal action friction clutch such as is herein before
described and represented in the accompanying drawings between the motor
armature shaft and the shaft or pulley to be driven, whereby the motor armature
can jump up at once to its normal or full speed, or to a safe speed before it has
time to become heated, substantially as and for the purpose set forth.
TY
00
1000
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.