Improvements in Electric Brakes and Methods of Operating the same.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Electric Brakes and Methods of Operating the same.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to us from abroad by Frank E.
Case, of Schenectady, in the County of Schenectady, State of New York, United
States of America, Electrical Engineer), and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
The present invention relates to the art of braking electrically propelled
vehicles, and is especially designed for use with electric railways, in which that
system of braking has been most successfully developed. It has for its object to
obviate some difficulties attendant upon the operation of the ordinary systems of
electric braking, that stops may be made more easily, certainly and without undue
jolting of the car or strain upon the apparatus.
In the operation of the ordinary and now well known systems of electric
braking, in which one or a number of brake shoes act upon discs rotating with
the axle and are supplied with current from the motors operated as generators by
the momentum of the cars, a difficulty has arisen from the variations of braking
effect upon the same motor circuit resistance, due to variations in speed of the
car. If the vehicle, for instance, be travelling at a low speed, the current
generated in the motors is of only moderate volume and potential. Under these
conditions the amount of resistance in circuit must be much less to get the same
effect than that required when the speed of the car is higher; this is true
although the friction co-efficient rises very rapidly as the speed falls. It is also
the case that the first actuation of the brake-shoe requires a considerably larger
current than is necessary to maintain adhesion after the air gap between the
shoe and the disc has been closed.
66
In many braking systems there is provided what is called an emergency stop,"
to be used only when accident threatens the car. This has generally been arranged
so that the brake shoes are cut out of circuit and the motors operating as
generators are short-circuited. With this arrangement there is but little danger
of slipping the wheels and thus diminishing the braking effect, and grinding flats
on the wheel treads, but this method of braking is not applicable to ordinary
service conditions, although useful and valuable in emergencies, since it causes a
sudden stop disagreeable to passengers and capable of causing severe strains on
the motors and gears. Its principle may be applied in making ordinary steps
by inserting in the circuit of the motors a sufficient resistance to prevent undue
retardation; but it is then open to the objection of not bringing the car to a
stand, inasmuch as, after the speed has materially diminished, the generation of
current is so small as not to retard the rotation of the armatures sufficiently to
stop the car.
The method and apparatus which we have devised mitigate the difficulties

page_text: pointed out and in some degree utilize both of the methods indicated above. The
method consists in general of supplying the brake shoes from an auxiliary source
of electro-motive force, preferably a storage battery using the motors also to
affect a part of the retardation of the car, but supplementing this action by just
so much of the brake shoe effect as to render the braking effect practically con-
stant for any given motor circuit resistance. In this arrangement the motors
may or may not furnish part of the current for the brake shoes, and may be
utilized directly or indirectly to regulate the braking.
One particular arrangement of apparatus by which we are enabled to carry out
the indicated method we have shown as consisting of one or more motors, which
it is understood are operated as generators, and which have included in their
circuit a resistance regulable in amount so as to adjust the current flow in the
motors to the retarding effect desired; another source of substantially constant
electro-motive force such as a storage battery which may or may not be fed from
the line, the particular source of electro-motive force being unimportant; and
one or more brake shoes supplied from the storage battery. In one arrange-
ment, we include in the motor-circuit a current measuring coil which may be
either an electro-magnet or a solenoid coil, and within its influence an armature
or core as the case may be, operating an adjustable resistance in the brake shoe
circuit the arrangement being such that as the current generated by the motor
diminishes more and more resistance is cut out from the brake shoe circuit, so
that a greater current from the exterior source actuated the shoes, and thus, as
the braking action of the generators diminishes by the diminished output, the
action of the brake shoes increases proportionally so that we obtain substantially
a constant effect for any given motor-circuit resistance.
With this arrangement it will be seen that, while the actual output of the
generators will change substantially directly as the speed, and their braking
effect will accordingly vary, the sum of this effect and that due to the attraction
This does not mean, of course,
of the brake shoes will be practically constant.
that the breaking effect is constant irrespective of the position of the brake-
controller, because although the sum of the two effects just spoken of is constant,
it may be varied as a whole by changing the resistance of the motor-circuit.
Under some conditions, as when running at high speed, it is manifest that the
retardation of the brake-shoes is unnecessary until the speed diminishes. Under
these conditions the action of the current measuring coil already referred to will
be to open the circuit of the brake shoes, so that they are not operated until the
speed has materially diminished and the current flow in the motor-circuit has so
far fallen as to no longer furnish the desired retardation; at which time the
brake shoes will be cut in to maintain the constancy of braking effect, and
finally, as the motor current falls so as to furnish practically no retardation, the
frictional retardation of the brake shoes will increase to an amount sufficient to
bring the car positively to rest.
Furthermore, by this method, of operation and the apparatus embodying it, we
are able to overcome another difficulty which has arisen with the electric brake;
that is, holding the car at rest after it has been stopped. It sometimes occurs that
stops are made on a grade sufficient to start the car in motion: it has heretofore
been necessary either to arrange the controller so that a limited trolley current
may be passed through the brake shoes by the last position of the controller, or
else to apply the hand brake. The first arrangement, while practical and useful,
involves an expenditure of energy, which electric braking is intended to avoid
as far as possible. In addition, it necessitates either winding the coils in the
brake shoes for 500-volt current, or else using an auxiliary coil wound for that
voltage. By the arrangement which is outlined however, neither of these alter-
natives is rendered necessary, for while the storage battery is to some extent a
consumer of energy, it need not be made large, and may be of as low voltage as
desired, rendering it possible to wind, the brake-shoe coils with wire as large as
may be convenient and to use only the ordinary winding in each shoe, in the

page_text: customary manner. The battery may, if preferred, be so connected as to be
charged by current from the motors, in which case no energy will be taken from
the ine and the main objection to it obviated.
So many different ways of applying the invention may be devised that we have
not attempted to indicate all of them, but only a few examples from which a
competent electrician may readily devise other ways of accomplishing the same
results; all of which we aim to include in the claims appended to this description.
The accompanying drawings therefore show in Fig. 1 a plan view of a car truck
equipped with a pair of motors and brake shoes and controllers by means of
which the invention may be applied either in any of the forms illustrated or
otherwise: Figs. 2 to 5 are diagrams of connections embodying the invention;
Fig. 6 shows a controller adapted to its exercise.
In Fig. 2 M1, M2 are the motors, of which A1, A2 are the armatures and F¹, F3
the fields. R is the motor regulating resistance, which is used in this case to
determine the output of the machines when operated as momentum driven
generators. S is the solenoid in the motor circuit operating a switch s by means
of which a second resistance R¹ is controlled so that various amounts of it may
be included in circuit. This resistance is in series with the brake shoes BS¹, BS2,
one of which is supposed to be upon the axle with each motor. The shoes are
supplied with current from the storage battery B, which may be charged in any
desired manner, not illustrated in the diagram.
The operation of these parts is as follows: the motors by their rotation retard
the motion of the car or other moving load, and at the same time generate in
the circuit including the resistance R and the coil S a current larger or smaller
in proportion to the speed of the car and the resistance of the circuit. We may
assume for instance, that the speed is considerable and the resistance a moderate
one, in which case so much current will be generated that the core of the solenoid
will be drawn up until the switch s opens the circuit of the brake shoes and
battery. Under these conditions the entire retardation will be that due to the
rotation of the motor armatures. If now, from a slackening of speed, current begins
to fall off, the circuit of the battery will be closed by the switch s, but with all
the resistance R in circuit, so that only a small current will flow through the
brake-shoes. Their attraction and consequent resistance to motion will be
added to the retardation effected by the motors: the current will still further fall
off, and more and more of the resistance R¹ will be cut out until finally it will be
cut out entirely, when the full current of the battery will pass through the
brake shoes, the car will be brought to rest, and as the brake shoes will be
attracted with full power, the car will be maintained stationary, even on a heavy
grade.
In Fig. 3 we have shown another form of the invention which also employs a
storage battery. In this case the connections are such that the battery need take
no energy from the line and thus practically the only objection to its use is
avoided. Here the reference letters are the same as before, but the battery is
placed in parallel with the shoes in the motor circuit and in series with the
resistance R.
The motion of this combination of apparatus is as follows:-so long as the
current generated by the motor is considerable, the drop through the brake shoes
will be sufficient to force a considerable part of the current through the battery B.
and thus charge it. This action will continue so long as the drop in potential across
the brake-shoes is greater than the electro-motive force of the battery. When
these two potentials are equal, however, the battery neither receives current
from the motors nor sends current through the shoes. As soon as the current
from the motors falls to such a point that the drop across the shoes is less than
the electro-motive force of the battery, the battery sends current through the
shoes in the direction of the arrow, thus maintaining their adhesion after the
car comes to rest and supplying any deficiency of current which may exist.
In Fig. 4 we have shown another combination of apparatus for producing a

page_text: similar result. In this case we have shown the shoes as fed from the trolley T,
the circuit being grounded at G; but the storage battery may be used in the
place of the trolley circuit, or the trolley circuit might be employed with the
other combinations of apparatus shown in place of the storage battery, it being
immaterial what source of current is used. In Fig. 4, in addition to the motor
regulating resistance R, we connect in multiple with the shoes a somewhat high
resistance R¹, the shoes should equal in resistance the resistance R', at least
approximately.
The circuit from the trolley or other source of current leads through the
resistance R to the brake shoes and to the motor fields, so that, irrespective of
the motor armatures there will be a strong field maintained. The arrows show
the course of current, and the action of this combination of apparatus is as
follows the motor armature will be revolved by the momentum of the car. so as
to give an electro-motive force in the direction of the arrow. If the speed be
somewhat high, this electro motive force may, owing to the strong field already
mentioned, be sufficient to send current through the resistance. R¹ and the brake
shoes, reinforcing the current from the trolley. At a certain critical speed,
which may be anything desired, according to the proportioning of the apparatus,
the electro motive force generated by the motor armatures will equal that from
the exterior source of current, and no current will pass through the resistance R³,
while the entire current from the trolley or other exterior source will pass through
the brake shoes and the motor fields. As the speed diminishes, the trolley cur-
rent will divide through the resistance R¹ and the brake-shoes until, when the
car has nearly come to rest, a substantial portion of current may pass through the
resistance and the motor armatures (the ohmic resistance of which is practically
negligible), thus shunting the shoes and tending to drive the armatures as motors
in the reverse direction, with this arrangement of apparatus, while the retarda-
tion due to the motor armatures is still present, it does not play so important a
part as in the other arrangements illustrated, the armatures acting more as a
regulator for the braking current.
In Fig. 5 we show still another arrangement of apparatus in this the motor
armatures are in multiple, while their fields are in series, and shunting the
fields are the storage battery and the brake-shoes, these being arranged in series.
The motor regulating resistance completes the circuit both of the fields and
brake shoes, etc.
In all of the diagrams we have shown a grounded connection, but this is to be
understood as representing the "ground wire" of the controllers, which is
ordinarily employed in completing these circuits, and unless the trolley current
be used, the ground performs no necessary function.
In the arrangement shown in Fig. 5 the battery acts as a resistance in series
with the brake shoes, and tends to maintain the fields so that even at moderate
speeds the motors have considerable effect in checking the car.
In this arrange-
ment at high speeds the fields F1, F2 being quite strong, some current will be
shunted through the battery, charging it, and then passing through the brake
shoes; but the principal part of the retardation will be that due to the revolu-
tion of the motor armatures. As the current falls off, at a certain critical speed,
the electro-motive force of the battery will balance that of the armatures, and no
current will pass through the brake-shoes; but when the speed falls a little
lower, the electromotive force of the battery will preponderate and while still
sending current through the fields to maintain the magnetization, it will also
send current through the brake-shoes in the reverse sense, first demagnetizing
them and then re-applying them, so that, when the car comes to rest, the shoes
will still be applied to hold it. At the same time, a strong field will be
generated, so that a quick stop may be made immediately after the car starts,
even though still at low speed, an emergency which sometimes arises, and which
has not been provided for with some forms of electric brake.
In Fig. 6 we show a controller well adapted for the exercise of our invention.

page_text: This particular controller embodies the connections illustrated in Fig. 3, and
engineers will readily understand the methods of utilizing the other systems
shown. Of course the one controller is to be taken as typical of all of those
which may be employed. It comprises a motor controlling switch K which is
used when the motors are operated by current from the trolley T, a reversing
Bwitch RS, and a brake controller BK, which connects the apparatus so that the
motors act as generators in a now well understood way. The fixed contacts of
the different switches are numbered from 1 to 36 consecutively and the moving
contacts bear the same numbers with additional reference letters, such as 1ª, etc.;
this being a well known system used in lettering such diagrams. The con-
troller K connects the motor in series or in parallel, the contacts 4" to 7b, etc.,
shifting the resistance in ways now well understood in the art, while the lower
contacts from 8 to 12 serve to connect the motors in different combinations. When
the contacts 9 to 12, for instance, are just touching the contacts 9", 10" and 11b
and 12b, a shunt is thrown around one of the motors and its circuit is then opened,
as contact 9 and 10 pass off the contact plates until when contacts 8 and 9 touch con-
tacts 8 and 9, the second motor is connected in multiple with the first and in
series with a portion of the resistance, which is progressively cut out by the
contacts 4b and 7b. This is a well known system of control, and not claimed in
this application. The reversing switch is of the usual construction, and consists
of certain cross-connected contacts by which the relation of armature and field
in the motors may be reversed. The brake switch BK is provided with three
sets of contacts, those on the left simply serving to shift the resistance R in a
well known way; the intermediate contacts upon which the brushes rest at the off
position of the brake switch are simply for convenience in effecting the necessary
connections; while those contacts upon the right connect the motors, brake-
shoes BS, BS2 and battery B, as presently to be described.
.
We will trace only the first circuit from the controller K, with the motors in
series and full resistance in circuit, the others being unnecessary to describe and
readily determined.
Current passes from the controller K to contact 1, to contact 2, through the
resistance R to the point r, thence to contact 30 of the brake switch, by cross-
connection to contact 34, contact 16 of the reversing switch, contact 14, through
the armature A¹, contacts 15 and 13 of the reversing switch, contact 32 of the
brake switch, contact 33, through the field F¹, contact 10 of the controller K,
contact 9, contact 20 of the reversing switch, contact 18, armature A², contact 19
of the reversing switch, contact 17, contact 31, thence by cross connection to
contact 24, and through the cross connections to contact 36, through the field F³
and out to ground. The other functions of the controller have already been
briefly described.
When now the brakes are to be operated, the controller K will be in its off
position in which the brushes 1 to 12 are inoperative, while the contacts 21 to 36
of the brake switch will be each shifted to the right to connect with the contact
plates, brushes 29 to 36 passing off the contacts upon which they are illustrated
and touching contacts 29b to 36b. In the first position the contacts 21 to 23 touch
their respective moving contacts, the reversing switch being, as before, with the
cross connected contacts touching the brushes 13 to 20. As a convenient starting
point in this circuit, we may take the end r of the resistance R, from which the
circuit passes to contact 30, 30b, and by the cross connections to 31 and 32b.
These contacts lead respectively to the armatures, as follows: from 31 to con-
tact 17 of the reversing switch, contact 19, through armature A2, (which it will be
observed is in reverse relation to its field, as will presently be noted), to contact 18,
to contact 20, back to the brake switch at contact 35. Starting again from 32, a
similar circuit is traced through armature A¹, as follows: to contact 13 of the
reversing switch, contact 15, through armature A¹. contact 14, contact 16, back
to the brake switch at contact 34: these contacts being connected by the cross-
connection between the contacts 34 and 35b, form the equalizer at the armature

page_text: end of the fields. The fields are in circuit respectively with contacts:33 and 36,
as follows: from contact 33 through the field F in the same direction as when
the machine acts as a motor, and to ground by way of contacts 29 and 29, from
contact 26 through the field F and to ground directly. Of course it is under-
stood that in this case ground" means the ground wire of the controller, as
already explained.
.
Starting again at the point r of the resistance, the circuit passes in the other
direction through the resistance to contact 23 of the brake switch BK, which is
cross-connected to contacts 21 and 22. From contact 21 the circuit passes
through the storage battery B to ground; and from 22 through the brake-
shoes BS, BS in series, and in multiple with the battery B to ground. As the
brake switch is rotated, the resistance contacts gradually cut out the entire
resistance in a way well understood.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is :-
1-In an electric braking apparatus, the combination of one or more motors
retarding the moving load by their action as momentum-driven generators, one
or more electric brake-shoes also retarding the load, and means for compounding
the two retardations in the desired ratio.
2-In an electric braking apparatus, one or more motors and electric brake
shoes, means for retarding the moving load by the action of the motors as
momentum driven generators and by the brake shoes, and means for so propor-
tioning the two retardations that for any given motor-circuit resistance their sum
is practically constant.
3-In an electric brake, the combination of brake-shoes, a source of current,
and means for generating and applying a regulating electro-motive force for
controlling the effect of the shoes when fed from the source of current.
4-The combination, with electric brake-shoes and motors operated as genera-
tors by the momentum of the load, of means for generating and applying an
electro-motive force other than that of the motors, and breaking the load by the
composition of the two forces in the desired proportion.
5 As a means of electrically retarding a moving load, the combination of a
source of electro-motive force, another source of an electro-motive force opposed
to the first, means for compounding the two electro-motive forces in desired pro-
portions, and means for causing the resultant energy to resist the momentum of
the load.
6 In an electric brake, motors retarding the load by their action as momen-
tum-driven generators, an exterior source of electro-motive force, brake shoes,
and means for supplying to the brake shoes current from the exterior source
sufficient in amount to afford, in addition to the retardation of the motors, the
desired braking effect.
7 In an electric brake, the combination of electric brake shoes, with motors
furnishing current when operated as momentum-driven generators to energize the
brake shoes, and an exterior source of electro-motive force also in circuit with
the brake shoes; the arrangement being such that the resultant energy of the
two electro-motive forces, in coincidence or opposition as desired, acts in the
brake shoes to retard the load.
8 In an electric braking apparatus, the combination of a motor or motors
driven as generators by the momentum of the moving load and one or more
electric brake shoes, with means for regulating the braking effect of the shoes in
inverse ratio to that due to the current in the motors.
9 In an electric braking apparatus, the combination with one or more motors
and electric brake shoes, of a source of current separate from the motors supplying
the shoes, and means for regulating the current supplied from the separate source
in inverse ratio to that generated by the motors.

page_text: 10 In a braking apparatus, the combination of one or more electric motors
and brake-shoes, with an exterior source of electro motive force, means for supply-
ing to the shoes a current which is a function of the electro-motive forces pro-
duced by the motors and the exterior source, and means for regulating the two
components so that the retarding effect of the motors plus the retarding effect of
the shoes is practically a constant.
11-In an electric braking apparatus, the combination of brake shoes in series
with the motors, and a storage battery in shunt to the shoes.
12 In an electric braking apparatus, the combination of one or more electric
motors and brake shoes, with a source of electro-motive force in series with the
motors and in shunt to the brake shoes, acting as a regulator of the braking
effect.
13 In an electric braking apparatus, a controlling device provided with con-
tacts for regulating the motors from rest to full speed, and contacts and connec-
tions for throwing the motors in a local circuit to act as braking generators
through brake shoes and regulating a resistance, with a storage battery in
multiple with the brake shoes and in series with the motors.
D
1
8511
1
1000
THE BRITISH THOMSON-HOUSTON CO. LTD.
J. J. MANHEIM,
A. R. MONKS,
}
ALFRED CLEMENTS,
Directors.
Assistant Secretary.