Improvements in or connected with Automatic Brakes for Electri- cally Driven Machines.
Year: 1897

page_text: Date of Application, 8th Sept., 1897
Complete Specification Left, 4th June, 1898-Accepted, 13th Aug., 1898
PROVISIONAL SPECIFICATION.
Improvements in or connected with Automatic Brakes for Electri-
cally Driven Machines.
We, ALEXANDER BEWICKE BLACKBURN, Manager of the Electric Construction
Company, Limited, of Wolverhampton, in the County of Stafford, and WILFRID
L. SPENCE, of Dunluce, Tettenhall Road, Wolverhampton aforesaid, Civil
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention has for its object the automatic application of a dynamo electric
brake to elevators, winding machines, tramway, or road, cars, or any other
mechanism which is normally driven by, and takes power from, an electric motor,
but which, at other times, is liable to over-run the speed of the said motor.
According to this invention the brake is so arranged that the braking effect tends
to return energy to the feeding line with a minimum variation from the normal
speed of running.
The following description of an arrangement according to this invention will
serve to explain the nature of the said invention, but the invention is not limited
to the details of this arrangement. The electric motor, (which is preferably one
with a powerful shunt field and low armature resistance), is connected to the
driven gear through a mechanical clutch, or coupling, having a predetermined
amount of backlash, or play, say, for example, 90 degrees. When the motor
is running normally, and transmitting power, the driven part will follow, with
the said backlash, or play, behind it, but if, while still running in the same
direction, the load on the mechanism becomes negative, the speed of the driven
part will increase beyond that of the motor, and the part which was previously
lagging will now lead, and drive the motor as a generator.
This relative motion between driver and follower is taken advantage of in any
suitable way, at times of negative load, to operate electrical contacts by means of
which the field of the dynamo machine is strengthened beyond the normal thus
causing the electro-motive force to rise so as to be equal to, or greater than,
that of the line and so return current thereto without involving objectionable
rise in speed.
This effect can be graduated by the interposition of springs in the coupling
and by a multiplication of contacts but usually this will not be necessary as
the braking effect increases both with the driving power and with the speed.
The arrangement will act both ways; for example, in an elevator it will act
whether the cage be ascending too rapidly through overbalancing, or descending
too rapidly through overload.
A suitable operative arrangement for the field strengthening contacts, accord-
ing to this invention (to which, however, we do not limit ourselves) is as
follows:-
The end of the motor-shaft, adjacent to the coupling, is screwed with a thread
of quick pitch, and carries a nut which is, (except as hereinafter mentioned,),
free to traverse thereon. A stud fixed to the follower half of the coupling

page_text: at right angles thereto, and parallel with the main shaft, engages with a slotted
recess in the nut and drives it.
The slot may extend through an arc of any suitable length, say one of
90 degrees, and, in the case of a like amount of play in the main clutch, the nut
will take up four positions along the screwed part of the shaft corresponding
with the following conditions:-
A. Motor driving right handedly. Coupling lagging.
B. Motor being driven right handedly. Coupling leading.
C. Motor driving left handedly. Coupling lagging.
D. Motor being driven left handedly. Coupling leading.
Of these A and C will be extremes to right and left of the traverse of the nut,
whilst B and D will be mean positions which may coincide.
A switch, or contact, can readily be arranged to, say, short circuit a resistance
in series with the shunt field when operated on by the nut in positions B and D.
The nut may rest in contact with a brake shoe with just enough friction to
prevent it rotating except when driven by the stud.
When the conditions of driving are such that there is considerable starting
friction to overcome, or when a rapid acceleration of the load is necessary, the
starting switch contacts may be so arranged as to control, independently of
the position of the coupling controller, the supplementary field excitation of the
motor until the machine is under way; or, alternatively, a cumulative series
winding on the field may be cut in and out for starting alone, exactly as a dead
resistance is ordinarily used for the like purpose.
The usual accessories of stopping brake, limit switches and the like can be
employed and they are in no way interfered with by this improved brake, which
is less employed for stopping than for speed regulation, and which will ordinarily
come into action only when the main switch is closed, this switch having to be
opened to apply the stopping brake.
The foregoing arrangement is we consider one of the simplest, but we do not
confine ourselves thereto as the relative motion between driving and following
parts of the coupling may, according to this invention, be utilised in other ways,
both mechanically and electrically, to effect the strengthening of the field at
times of negative load on the motor.
Dated this 8th day of September 1907
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.
Improvements in or connected with Automatic Brakes for Electri-
cally Driven Machines.
We, ALEXANDER BEWICKE BLACKBURN, Manager of the Electric Construction
Company Limited, of Wolverhampton, in the County of Stafford, and WILFRID
L. SPENCE, of Dunluce, Tettenhall Road, Wolverhampton aforesaid, Civil
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 has for its object the automatic application of a dynamo electric
brake to elevators, winding machines, tramway, or road-cars, or any other
mechanism which is normally driven by, and takes power from, an electric motor,

page_text: but which, at other times, is liable to over-run the speed of the said motor.
According to this invention the brake is so arranged that the braking effect tends
to return energy to the feeding inne with a minimum variation from the normal
speed of running.
The following description of an arrangement according to this invention will
serve to explain the nature of the said invention, but the invention is not limited
to the details of this arrangement. The electric motor, (which is preferably one
with a powerful shunt field and low armature resistance), is connected to the
driven gear through a mechanical clutch, or coupling, having a predetermined
amount of backlash, or play, say, for example, 90 degrees. When the motor
is running normally, and transmitting power, the driven part will follow, with
the said backlash, or play, behind it, but if, while still running in the same
direction, the load on the mechanism becomes negative, the speed of the driven
part will increase beyond that of the motor, and the part which was previously
lagging will now lead, and drive the motor as a generator.
This relative motion between driver and follower is taken advantage of in any
suitable way, at times of negative load, to operate electrical contacts by means of
which the field of the dynamo machine is strengthened beyond the normal thus
causing the electro-motive force to rise so as to be equal to, or greater than,
that of the line and so return current thereto without involving objectionable
rise in speed.
This effect can be graduated by the interposition of springs in the coupling
and by a multiplication of contacts but usually this will not be necessary as
the braking effect increases both with the driving power and with the speed.
The arrangement will act both ways; for example, in an elevator it will act
whether the cage be ascending too rapidly through overbalancing, or descending
too rapidly through overload.
A suitable operative arrangement for the field strengthening contacts, accord-
ing to this invention, (to which however we do not limit ourselves) is as
follows: The end of the motor-shaft, adjacent to the coupling, is screwed with
a thread of quick pitch, and carries a nut which is, (except as hereafter mentioned),
free to traverse thereon. A stud fixed to the follower half of the coupling at
right angles thereto, and parallel with the main shaft, engages with a slotted
recess in the nut and drives it. The slot may extend through an arc of any
suitable length, say one of 90 degrees, and, in the case of a like amount of play
in the main clutch, the nut will take up four positions along the screwed part of
the shaft corresponding with the following conditions:
A. Motor driving right handedly. Coupling lagging.
B. Motor being driven right handedly. Coupling leading.
C. Motor driving left handedly. Coupling lagging.
D. Motor being driven left handedly. Coupling leading.
Of these A and C will be extremes to right and left of the traverse of the nut,
whilst B and D will be mean positions which may coincide.
A switch, or contact, can readily be arranged to say, short circuit a resistance
in series with the shunt field when operated on by the nut in positions B and D.
The nut may rest in contact with a brake shoe with just enough friction to
prevent it rotating except when driven by the stud.
When the conditions of driving are such that there is considerable starting
friction to overcome, or when a rapid acceleration of the load is necessary, the
starting switch contacts may be so arranged as to control, independently of
the position of the coupling controller, the supplementary field excitation of the
motor until the machine is under way; or, alternatively a cumulative series
winding on the field may be cut in and out for starting alone, exactly as a dead
resistance is ordinarily used for the like purpose.
The usual accessories of stopping brake, limit switches and the like can be
employed and they are in no way interfered with by this improved brake, which

page_text: is less employed for stopping than for speed regulation, and which will ordinarily
come into action only when the main switch is closed, this switch having to be
opened to apply the stopping brake.
The foregoing arrangement is we consider one of the simplest, but we do not
confine ourselves thereto as the relative motion between driving and following
parts of the coupling may, according to this invention, be utilised in other ways,
both mechanically and electrically to effect the strengthening of the field at
times of negative load on the motor.
We will now describe with reference to the accompanying drawings, more
particularly, arrangements according to this invention, premising that we do
not limit ourselves to the precise details shewn.
Figure 1 shews a form of claw coupling which may be used, for the purposes
of this invention, to connect the motor to the driven shaft. It has 90 degrees of
backlash, or play, between the driving and driven, (that is, motor and generator)
positions. The two halves E and F may be alike, but we prefer to form one,
say that on the driven shaft D as a brake drum B which also serves to protect
the stud or pin P, as hereinafter described with reference to Figure 2.
The motor shaft M, behind the coupling, or it may be the boss of the coupling
to which the shaft is rigidly attached, is screwed with a thread, or threads, pre-
ferably of quick pitch, or angular lead, upon which runs a disc, or loose collar, C
driven by the pin P, which is fixed to the other half of the coupling-as shewn
in Figure 2.
The disc or loose collar C is slotted, or recessed, as shewn in Figure 3, to
engage with the pin P and this connection may have a degree of back-lash, or
play, the same as, or different, from that of the principal coupling. Under the
control of the pin P, the disc C will take up different positions along the shaft M
according as the motor half of the coupling leads, or lags behind the other half,
and also according to the direction of rotation.
With 90 degrees play the positions will be a mean (intermediate) position for
the two generating cases and extreme positions (to right and left) for the two
motoring cases.
If, with the particular form of contact device employed to control the motor
field, these positions are not found convenient, then by increasing the play to
270 degrees the positions will be reversed, namely the two motoring cases will
give the mean (intermediate), and the two generating cases will give extreme
positions to right and left of the travel of the disc C.
The various relative positions of the two half-couplings and of the disc O on
its screwed shaft can be readily traced by means of the diagrams, Figures 4*, 4,
4°, and 4º, which represent elevations of the inner face of the motor half coupling.
The motor shaft with fixed key (to represent its half coupling, F) is shewn in the
centre, the other half of the coupling (E) is indicated by the 90 degrees slot, E¹,
engaging with the key e, and the screw bushed disc (C) is indicated by the
270 degrees slot shewn dotted at C¹ engaging with the pin P which is fixed
to the half coupling E or E¹.
A full line arrow on the shaft and the dotted arrow on the disc indicate the
relative displacements.
Figure 4 represents the motor driving clockwise (normal).
Figure 4 represents the motor being driven clockwise (abnormal).
Here the disc C has been turned on its shaft through 90 degrees to give the
corresponding longitudinal traverse.
Figure 4 represents the motor driving counter-clockwise, (normal), the disc C
being in the same position as in Figure 4.
Figure 4 represents the motor being driven counter-clockwise (abnormal),
the disc C having been turned through 180 degrees from the position Figure 4"
and being therefore at the opposite limit of its travel on the screwed shaft.
One method by which the field strengthening contacts may be operated accord-

page_text: ing to this invention is shewn diagrammatically in Figure 4. The disc C has
fixed to each face near the periphery an insulated metal ring R, (see Figure 2,)
which makes contact between two fixed stops, or buttons, at either end of its
longitudinal travel. These stops are permanently connected by a fixed resist-
ance O in series with the shunt field winding S, of the motor N, so that whenever
the load tends to over-run the motor in either direction, this resistance is short
circuited, the counter electro-motive force of the motor correspondingly raised
and a braking current generated which prevents undue rise of speed.
It will be obvious the movement of the disc C may be utilised in other ways
to mechanically operate a switch of any convenient description and, that instead
of short-circuiting a resistance, various other means may be employed for increas-
ing the field strength of the motor, which may be excited otherwise than as a
plain shunt.
To insure the sufficiency of this improved braking apparatus in the case of
lifts, and like apparatus, it is essential that the supply system be capable of
absorbing the return current at such times as the load is negative. If the supply
be given by a generator and prime motor badly governed, or by a storage battery
of high internal resistance, without other load on the circuit, then cases may
arise when the return current will not be absorbed and no effective braking will
result even with considerable increase of speed. To provide for such contingency
we furnish a bye-pass for the braking current which only comes into operation
on a predetermined speed being attained. A centrifugal governor of any suitable
tvpe driven preferably from the motor shaft is arranged to control a throw over
switch so as to disconnect the main supply and close the motor terminals over
a fixed resistance of such amount and capacity that the motor may be adequately
retarded. The same device acts also as a safety governor on the occurrences,
due to any cause, as for example an abnormal rise of voltage on the circuit, of
excessive speed.
We may also in certain like cases arrange that the said governor shall at
the same, or at any different speed, open the brake release circuit, or
interpose therein additional resistance, in amount sufficient to require motoring
current from the line, or to effect an approximate balance between the, frictional
braking effect together with the available electrical braking effect on the one
side and the power due to net weight being lowered on the other. This speed
safety device may either be wholly under control of the speed governor, which
will then both make and brake the contacts, or it may be under partial control
only, so that when once put in action (for example by the release of a latch) it
cannot be automatically withdrawn by any consequent reduction of speed.
We
have in the foregoing description dealt with the brake release circuit as being
in parallel with the supply system, but it may be in series with the motor, or
partly in series and partly in parallel, in which cases the necessary modifications
will be obvious to electricians.
We have referred only to the mechanical applications of electric motors, but
this invention may usefully be employed in other cases, for example in connection
with motor alternators, motor generators, motor driven boosters, and the like,
where the power of the motor is consumed, either wholly or in part, in the
production of electricity in another form, or at a different pressure. We will
describe one of these cases as being typical-namely the use of a motor-driven
booster in an installation with a storage battery auxiliary for the purpose of
obtaining a high load factor on the generating plant. Figure 5 shews diagram-
matically an arrangement of connections which may be employed. It is assumed
that the load is a variable one. B is the battery having such a number of cells
that its terminal electro motive force bears any desired relation to that of the
booster, M is the motor end, and G the generator end of the booster, the two
machines being connected through the special coupling C. D, D, are the main
dynamos, S, S, are shunt fields, S¹ the series field of the booster V, R, variable

page_text: resistances in series and V¹, R', variable resistances in. shunt with the correspond-
ing field windings.
The series coil S₁ of the booster (generator) may be so proportioned to the
corresponding shunt coil S that, at normal load, the battery is neither charging
nor discharging, as the total electro motive force in this circuit just equals that
of the line. With an increase of load the booster electro-motive force is raised
and the battery discharges while with a decrease of load the booster electro motive
force falls and the total electro motive force in this circuit then becomes suffi-
ciently low to be overpowered by the line, at which time the generator end G
of the booster becomes a notor, and tends to overrun the motor end M, so that
the coupling C comes into action, and may be used to specially strengthen the
shunt field S, of the motor end M, so that it becomes a generator and also sends
charging current through the battery.
Another application of this invention is in connection with motor driven fly
wheels which have been used or proposed, for the purpose of relieving the gene-
rating plant, in electric traction, and like systems of sudden variations of demand
to which it is ordinarily exposed. Such motor fly wheels are described in the
Specification of Letters Patent No. 4841 of 1892. In this connection this inven-
tion may be applied in various ways to both alternating and direct current motors,
according as the principal object of the motor fly wheel is to maintain the
closest possible voltage regulation, or to give out the largest amount of energy
to the system under a fixed percentage variation of pressure.
The variation in field strength under control of the coupling may either be
proportioned to the difference between the speed when acting as a motor and
when acting as a generator, or to the difference between the motor counter electro
motive force and the generator terminal voltage under the given conditions.
We are aware that proposals have been previously made to use electro-dynamic
braking and to return such braking currents to line so as to be available for
useful purposes and we make no broad or general claim to such use.
We are also aware that various proposals have been previously made to regulate
dynamos and motors by means of spring dynamometers which give a measure
of the torque exerted on or by such dynamo or motor. This class of regulator as
stated in the Specification of Letters Patent No. 5003 of 1894 which is typical
"consists essentially in causing the transmission of the power from the motor to
the work to be done, to compress a spring and to actuate an electric switch
arrangement for regulating the current to the motor corresponding to the com-
pression of the spring." Although certain springs may be so used according
to the present invention they are not required and are generally undesirable,
the objects of the present invention being entirely outside the scope of those
involving springs as an essential part of the coupling, we therefore disclaim
specifically the use of any arrangement of which the regulator described in the
said Specification No. 5003 of 1894 is typical.
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 :-
1. An automatic brake for electrically driven machines the said brake being
arranged substantially as herein before described so that the braking effect tends
to return energy to the feeding line with a minimum variation from the normal
speed of running substantially as herein before described.
2. In electric motor driven mechanism in which the load is liable to become
negative the combination with a coupling having back lash play or dead travel,
of a secondary coupling having back lash play or dead travel and arranged to
operate a field regulating or equivalent device substantially as and for the
purposes herein before described.
3. The combination with a coupling having back lash, play or dead travel
used as the operative connection between an electric motor and mechanism the

page_text: speed of which is liable to over run that of the motor, of a mechanical device
controlled by the said coupling and adapted, by means of switch gear, to effect
changes in the generated or counter electro motive force of the motor substantially
as and for the purposes hereinbefore described.
4. The combination with the subject matter of the preceding claiming clause
of means for effecting simultaneous changes in the electro motive force of a
dynamo, as well as or instead of in the electro motive force of the motor, to
which the said dynamo is coupled substantially as herein before described.
5. In automatic electric braking apparatus a bye pass for the braking current
the said bye pass being of resistance and capacity commensurate with the avail-
able energy and coming into operation only when the supply system is unable
to absorb such braking current, or upon the attainment of abnormal speed,
substantially as and for the purposes, hereinbefore described.
6. The application of our improved electric braking apparatus in connection
with a motor fly wheel used as a means of regulation on an electric circuit sub-
stantially as and for the purposes set forth.
Dated thie 3rd day of June 1898
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.