Improvements in or relating to Electric Brakes.
Year: 1895

page_text: Date of Application, 24th Dec., 1895-Accepted, 14th Mar., 1896
COMPLETE SPECIFICATION.
Improvements in or relating to Electric Brakes.
I, JAMES DEVONSHIRE, Secretary of the British Thomson-Houston Limited of
38 Parliament Street, Westminster, London do hereby declare the nature of this
invention (a communication from abroad by William B. Potter, Electrical
Engineer, of Schenectady, in the State of New York, United States of America)
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
My invention relates to electric brakes; and has for its object to provide an
arrangement of circuits and of apparatus by which the effect of a plurality of
motors when converted into generators and used to operate a plurality of brake-
shoes, may be made more uniform and reliable. For this purpose I arrange the
fields of the motors and also their armatures in multiple; and across the leads
from the armatures and from the fields I place equalizers, so that each end of
the armatures is connected, and each end of the fields is also connected, the motors
thus connected as a whole feeding current into a local circuit including a variable
resistance and a plurality of brake-shoes. With the apparatus as thus arranged,
1 also combine an "emergency stop," actuated in a certain definite position of the
controller, preferably in the final position to which the braking switch or con-
troller may be thrown, so that in case of emergency, as when an obstacle is upon
the track, the motorman may throw the handle of his brake-switch to its final
position, with the assurance that he has done everything possible to stop the car.
By preference, this emergency stop is arranged to cut out the brake-shoes and
resistance altogether, leaving the motors short-circuited upon themselves with
resistance. This practically instantaneously stops the rotation of their armatures,
but as soon as the armatures are stopped, the current falls off, the resistance to
motion diminishes, and the car wheels begin again to revolve; with this revolution
the current again increases in the short circuit and the motors are again brought up
sharply this action is extremely severe, and is of course only to be used in case
of danger to the car or to some outside object; but is also proportionately effective
in stopping momentum, as it does away with the slipping or skidding" of the
wheels. In the apparatus I also arrange cutout switches for the brake-shoes
independent of any other switches, and by this means I am enabled to cut out a
defective shoe without impairing the operation of the remainder of the apparatus.
I also arrange cutout switches in the circuits of the motors so that a defective
motor may be cut out in the same way. The arrangement of the brake-shoes is
illustrated and described as a series arrangement. So far as I am aware, brake-
shoes have hitherto been arranged in multiple, as this causes the least drop of
potential across each shoe between the source of current and the ground. I have
found important advantages from arranging the shoes in series; the greatest of
these advantages is that the proper relation of braking effect between the motors
themselves and the different shoes in the traio, is preserved. As an illustration,
suppose that there be five ampères in the motor and five ampères in each brake
shoe, as giving the best effect; the amperage remains approximately constant in
this arrangement, the potential necessary to drive the current through different
amounts of resistance included in the circuit by including a greater or less number
of brake shoes in series, varying as required. This is an especial advantage,
nasmuch as the number of ampères obtainable from the ordinary railway motor
Iriven by momentum is comparatively limited, while its voltage may run up to a
"מ

page_text: very high point without injury; in practice if a sufficient amount of current be
taken from a railway motor to supply a large number of shoes in multiple, its
destruction would be almost inevitable. Another objection to the multiple
arrangement which is obviated by that in series, is that where the ampères rise
rapidly the motor acts with more energy to brake the train than do the brake-
shoes, and the train, as it is expressed amongst railway men,
piles up on the
motor car. This may become dangerous in braking when running around a curve,
where the tension of the train must be preserved.
"6
"
Another advantage which I have found for the shoes arranged in series is, that
the leads between the different cars, and in fact, the leads to convey current
throughout the system, may be of the same size, as the current will be substantially
alike at all points of the system; whereas, when shoes are connected up in
multiple, the leads must all be proportioned for the greatest number of cars that
may ever be put together on one train; while to obtain economy of distribution, it
would be necessary to make the leads of the car nearest the engine or electric
locomotive ten times as large as the tenth car back need be. This leads to either
waste of copper or waste of current. Ordinarily the waste of current is preferred,
but in any event the copper conductors must be kept of such a size as not to burn
out under the load or to become unduly heated; and no matter of what size they
are made, the risk of burning out the motor is not lessened.
The accompanying drawings show diagrammatic embodiments of my invention.
The controller in which I prefer to embody it is like that shown in my British
Patent No. 15225 dated August 13th 1895. I have therefore not illustrated it in
full, the brake switch resembling that shown therein, and the other parts not being
illustrated, as there is no charge in their construction.
Fig. 1 of the drawings is a general diagram of the circuits, the brake-switch
being shown developed in plane;
Fig. 2 is a diagram, showing the operation of the motors and brake-shoes and
their connections, in a form more readily understood;
Fig. 3 shows the circuits as they appear when the "
operation.
emergency stop" is in
A is the brake-switch of brake-controller, provided with contact-plates 1 to 16
inclusive A', A2 are the armatures of the motors, F1, F2 being the fields; S, S₁ are
the braking magnets; C, C are the cut-out switches for the motors; C₁, C² are
corresponding switches for the braking magnets. B to B indicate the blades of
the cutout switches; C, C, and D is a set of cross-connected contacts co-operating
with one of the switches. At V I have indicated the usual reversing switch in
which only one set of contacts is numbered, the other set operating in the well-
known way to reverse the relation of armature and field and permit the backward
rotation of the motors. R is a resistance in series with the two motors.
At CF
I have indicated certain connections made to the controller frame in the manner
pointed out and claimed in my Patent above referred to.
Except for the equalizer connections, E, E, E², the arrangement is like that
of my former Patent, but in addition to the two contact plates operating the
resistance in the way therein pointed out, I provide at 2 an auxiliary contact-
plate acting to make direct short-circuit between one side of the armatures and the
other side of the fields, thus throwing the motors into the condition shown in Fig. 3.
The circuits in the apparatus are as follows:-
Starting from the armature A2, passing in the direction of the arrow, the current
passes to the contact-plate 20 upon the reversing switch V, thence to the switch-
blade B, then to the contact-plate 13 upon the brake-switch A, by cross-connection
to the contact-plate 14, to the switch-blade B³, thence through the field F' to the
point a, then by the lead to the contact-plate 1 upon the brake-switch A, thence
to the controller-frame at C F. The other path of the current from the point a is
open-circuited upon the blade B of the switch. The current from the other
armature A passes likewise to the contact-plate 18 upon the reversing switch V,,
thence by the lead to the blade B of the cut-out switch, then to the contact-

page_text: plate 12 upon the brake-switch A, by cross-connection to the contact-plate 11,
thence by the lead to the blade B of the cut-out switch, thence through the
field F to the controller-frame. It will be seen that the current from the
armature A passes to the contact-plate 13, while that from the armature A¹
passes to the contact-plate 12. These two plates are joined by a cross-connection,
so that at this point the current is joined. The current re-enters at the controller-
frame adjacent to the brake-magnets S, passes through those magnets to the
contact-plate 3, through the blow-out coil I, to contact plate 4, thence through the
resistance R to the point b; at this point it passes to the left over the lead to
the contact-plate 17 upon the reversing switch V, and back to the armature A¹;
and from the point bit also passes to the contact-plate 16 upon the brake switch A,
by cross-connection to the contact-plate 15, thence to the contact-plate 19 upon
the reversing switch V, back to the armature A2. The contacts 4 to 10 inclusive
by the rotation of the cylinder, cut out more or less of the resistance to vary the
braking effect. The equalizer E connecting one end of the two field-magnet coils,
consists in part of the lead to which the connection a is made, and in part of the
controller-frame. The equalizer E is the connection between the contact-plates 12
and 13 upon the brake-switch A, while the equalizer E' is the lead from the point b
to the contact-plate 16. It is to be understood that the contacts 11° to 14ª have
the usual office of connecting the controller and the brake-switches, as in my
application already referred to. So also the cut-out switches C, C are found therein
fully described. The cut-out switches C', C² connected with the braking coils,
however, are illustrated particularly in Fig. 1, and consist each of a double-pole
switch provided with a pair of cross-connected contacts c, c. When the switch is
thrown so as to connect with these cross-connected contacts, the path of the
current would of course go through it in that way, and the braking magnet coil
will be cut out.
When the emergency stop, preferably operated only by the last position of the
brake-switch, is put on, the different circuits are as before, except that the
resistance is all cut out, the lowest brush of the resistance resting upon the contact-
plate 10, and the lowest brush shown being connected to that brush and resting
upon the contact-plate 16, so that the brake-shoes will also be cut out; and the
current, instead of entering at the controller-frame to the lead connected with the
brake-shoe, will enter from the controller-frame to the contact-plate 2.
The use of the equalizers prevents oue motor building up at the expense of the
other or faster than the other, and therefore prevents, in the application of the
brake, the "bucking" of one motor against the other.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to me
from abroad I declare that what I claim is:
1. In an electric braking apparatus, a plurality of electric motors arranged in
multiple, equalizing connections connecting similar terminals of the field-magnet
coils at each end of such coils, and equalizing connections connecting similar
terminals upon both sides of the armatures, in combination with braking-magnets
in circuit with the motors.
2. In an electric braking apparatus, a plurality of electric motors having
equalizing connections across similar terminals of the field-magnets and the
armatures, in combination with brake-inagnets and a resistance included in the
ocal circuit with the motors.
3. In an electric braking apparatus, a plurality of electric motors arranged in
multiple with their field-magnet and armature terminals respectively connected by
equalizing connections, in combination with brake-magnets arranged in series in
a local circuit with the motors.
4. In combination, a plurality of electric motors, means adapted to cut out
either oue of the motors at will, a plurality of brake-magnets arranged in
series, means for cutting out individual brake-magnets without interrupting

page_text: the continuity of the circuit, and a local circuit including the motors and
brake-magnets.
5. In combination, in an electric braking apparatus, a source of electro-motive
force, a local circuit, and brake-magnets arranged in series in the local circuit with
the source of electro-motive force.
6. In an electric braking apparatus, a plurality of electric motors arranged in
multiple and provided with equalizing connections for similar terminals of their
field-magnets and armatures, a local circuit and regulable resistance in the local
circuit, a plurality of brake-magnets arranged in series with the resistance and the
motors in the local circuit, and means for cutting out either of the motors or of the
brake-magnets without interrupting the continuity of the circuit.
7. In combination, a source of electro-motive force, brake-magnets actuated
thereby, means for regulating the current supplied to the brake-magnets by the
source of electro-motive force, and means for cutting out the brake-magnets and
short-circuiting the source of electro-motive force upon itself.
8. In an electric braking apparatus and in combination, a motor or motors
furnishing current when driven by the momentum of a moving vehicle, a local
circuit for such motors, brake-magnets in the local circuit, a controller and a
resistance also in the local circuit, contacts and cross-connectious upon the
controller adapted to vary the amount of resistance in circuit or to open the
circuit, and auxiliary contacts and cross-connections arranged to cut out
the brake-magnets and resistance and to short-circuit the motor upon itself at a
certain definite position of the braking controller.
9. In combination, a motor or motors furnishing current when driven
by the momentum of a car, a controller for regulating the action of the current in
the braking apparatus, and contacts and cross-connections upon the controller
acting to short-circuit the motors and cut out the braking apparatus, and thus
apply an emergency stop at a certain definite position in its rotation.
10. In combination, a plurality of motors, a brake-magnet, a local circuit
including the brake-magnet and the motors, the motors being provided with
equalizers for their fields and armatures, a controller regulating the action of the
current supplied by the motors when driven by the momentum of the moving
vehicle, contacts and cross-connections upon the controller regulating the braking
action, and auxiliary contacts and cross-connections cutting out the braking
apparatus and short-circuiting the motors upon themselves without resistance in
the last position only of the braking switch or controller.
Dated this 24th day of December 1895.