Improvements in and relating to Electric Brakes for Railway and Tramway Vehicles.
Year: 1896

page_text: Date of Application, 3rd Mar., 1896-Accepted, 18th Apr., 1896
COMPLETE SPECIFICATION.
Improvements in and relating to Electric Brakes for Railway and
Tramway Vehicles.
I, JAMES DEVONSHIRE, Secretary of The British Thomson Houston Limited, of
38 Parliament Street, Westminster, London, (a communication from abroad by
William B. Potter, Electrical Engineer, of Schenectady, in the State of New
York, United States of America), 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 :-
My invention relates to electric brakes for railway and tramway vehicles, and
has especial reference to devices designed to prevent such brakes operating with
too great power, or with such excessive power as, to altogether stop the rotation of
the wheels. It is well known in railway circles that a maximum braking effect is
obtained when the wheels are allowed to run at a rate nearly or quite that of the
progress of the car, while the friction of the brake-shoe is kept as great as possible
consistent with the continuance of this rotation; and that when the wheels skid,
not only is a flat spot worn in the tread, but the surface of the flat spot becomes
polished, so that the momentum of the car carries it much further than if the
wheels be allowed to turn. For the purposes of my invention, I arrange electric
means designed to limit the current which may be supplied to braking magnets of
any desired form, though preferably of the now well known disc form, applied to
the axle of the car. Such current-limiting-devices for the purpose designed have
heretofore been devised, but all such with which I am acquainted are open to
objection; first, in the form in which they are applied by hand, their operation is
uncertain and is to so great a degree dependent upon the judgment of the motorman
or operator that they become superfluous, and it is safer as well as cheaper and
simpler to trust to the same man's judgment in operating the brake handle to get
the particular effect desired; and second, in their automatic form, they have been
beyond the control of the motorman, and have operated to cut in resistance and
thus limit the current positively and definitely, without indicating to the operator
the condition of the current-limiting device. In all such appliances with which
I am acquainted this current-limiting effect has not been dependent upon the rotation
of the wheels or the condition of the track; nor can it be adjusted for variations
of load with any degree of certainty.
To overcome the objections thus pointed out, I have devised my present
apparatus, which consists, first, of a solenoid having its core connected directly to
the brake handle; this solenoid is normally short-circuited by contacts which
themselves are controlled by a relay magnet in the inain circuit. Upon increase of
current to a certain maximum, the relay magnet attracts its armature, opens the
contacts, and throws the solenoid into the main circuit; the current passing
through the solenoid attracts the core so that the brake handle is itself drawn back
or its further operation practically prevented. It is of course feasible to so construct
the apparatus that it will be beyond the power of the motorman to actuate the
brake handle at all while the current passes in the solenoid; normally, however,
I do not so design to construct it. I prefer, for reasons which will be well under-
stood, to employ just such strength of magnetic attraction as will act to check the
rotation of the handle but not to absolutely stop it if the motorman exerts his
strength. With this degree of attraction I have found that if (with the ordinary
application of power to the handle) it be moved so far as to cut in the solenoid, the

page_text: handle will be drawn a notch or two back, and more resistance will be inserted in the
circuit. At the same time, where the emergency stop such as I have described and
illustrated in my British Patent, No. 14639, dated August 1, 1895, is incorporated
in the braking apparatus, it is possible for the motorman by a single quick motion
to throw the handle so its last. position, or the position which is ordinarily not used,
and in which the motors are short-circuited and the braking magnets cut out.
By limiting the current in the manner just described, I am enabled to keep the
wheels always turning and to do this without undue complication. It is of course
designed to inake the relay mngnet adjustable for different amounts of current, not
only because this enables me to construct standard apparatus which may be
adjusted to adapt it to different requirements without alteration, but because by
this means the apparatus may he quickly and readily adjusted after installation for
the different conditions of track which obtain in electric railway operation. For
instance, upon some days when the track is wet and slippery, a less amount of
current is suflicient to slip the wheels, while where the track is rough and sandy,
a very great amount of current will be necessary.
I have illustrated the improved safety appliance of my invention as applied to a
controller like that shown and claimed in iny Patent above referred to, but I do not
menn thereby to exclude its application to other forms of apparatus.
The accompanying drawings show embodiments of my invention, Fig. 1 being a
diagram of the controller and circuits of the car wiring, with my improved safety
appliance attached, outy one end of the car being shown, and Fig. 2 being an
enlarged detail of the solenoid showing its connection with the braking switch or
controller.
I will first describe Fig. 2; therein A is the solenoid, B its core, attached to the
shaft M of the braking switch; C is the arm to which the solenoid is secured, and
which supports it in position. The magnetic circuit of the apparatus is through
the core B, the shaft of the switch and the arm C, which is of magnetic material
Lis the handle of the braking switch, shown in dotted lines. The braking switch
is ordinarily operated in practice by drawing the handle from right to left or in the
same direction as the hands of a watch revolve, and when the switch is thrown on
the handle L. and attached parts unke the dotted line position of the figure.
Referring now to Fig. 1, E is the braking switch or controller with the shaft M;
the solenoid of Fig. 2 is shown at the bottom of the switch to indicate its proper
attachment. The contacts of the switch are numbered from 1 to 16, the contacts
11 to 14 being those shown and described in my Patent before referred to, and also
in my British Patent No. 15225, dated August 13, 1895, as forming part of the motor
controlling switch. R is the resistance serving to limit the current flow. The
motor armatures are designated by the reference letters A', A³, and the field
magnets by FM, F M'. The letters C F indicate the controller frame. E' is a
blow-out magnet coil connected between the contacts 3, 4, upon the braking switch,
as indicated in my prior Applications; I, I are the brake shoes. All of these parts
are such as are commonly used in the art, and my invention does not reside in
them.
The controller or relay-inngnet is illustrated between the braking switch E and
the brake shoes; D is the controlling or relay-magnet proper; K is its armature;
the motion of the armature is opposed by the spring F, and the adjusting screw G
is provided for the spring, arranged in any suitable manner to increase or diminish
its tension according to circumstances. It is manifest that when the tension of the
spring is diminished, the magnet D will act with less current than when it is
increased, and within reasonable limits the action of the current may be pre-
determined. N is a set-screw of brass or other non-maguetic substance, designed
to prevent the hysteresis in the magnet-core holding the armature down after the
current has fallen below the predetermined maximum. H shows the contacts
controlled by the armature K. I shall trace only two of the circuits in this
apparatus, inasmuch as all of them are traced in detail in my Patents before referred
to, and they do not form the essence of the present invention.

page_text: Starting, for instance, from the armature A', at the plus brush, the current
passes through the resistance R, to the contact plate 4, through the blow-out
magnet coil E to the contact plate 3, thence by the lead to the point a, thence
down the lead e, across the contacts H, by the lead c to the point b, thence around
the relay-magnet D, through the brake-shoes I, I, to the controller frame, re-
entering from the controller frame to the field magnet F M', thence to the contact
plate 11, by cross-connection to contact plate 12, and back to the minus brush of
the armature. The path of the current from the armature A may be similarly
traced from the plus brush to contact plate 15, thence to contact plate 16, thence
through the resistance, and then as before to the controller frame through the relay
and the brake-shoes; re-entering from the controller frame to contact plate 1,
thence through the field magnet F M2, to contact plate 14, to contact plate 13, and
back to the minus brush of the armature.
Thus it will be seen that the relay magnet D is in series in the brake shoe circuit
at all times, while the solenoid A is in a circuit from the poiut a by the lead f,
returning by the lead d to the point b, the leads d and e closing this circuit at the
contact H. Ordinarily, therefore, no current will flow in the solenoid A, and
its core will be unattracted and the motion of the switch will be free. When,
however, the current in the circuit rises to such a point as to overcome by the relay-
magnet the resistance of the spring F, the contacts H open, the solenoid A. is then
cut in, as the current passes by the lead through the solenoid, and returns by the
lend d to the point 6, and thence around the relay magnet. The motion of the
solenoid core B is then opposed by the attraction in the solenoid, and in practice
this opposition is such as to control the motion of the handle L; so that, if the
operator applies only moderate strength, the handle will even be drawn back a
notch or two, thus cutting in more of the resistance R by the operation of the
contacts 5 to 9, in ways well understood in the art. As soon, however, as the
current falls below the predetermined maximum, the contact H closes, the solenoid
is cut out, and the switch may be freely turned. As outlined in my Patent
No. 14639 A.D. 1895 before referred to, the contacts 2 and 10 act to apply an
emergency stop by cutting out all the resistance in the circuit of the motors; if it
is desired to apply this stop, a quick throw of the handle L, will enable the solenoid
core to be withdrawn before the current has had time to rise to such a point as to
affect the relay-magnet D. All of this apparatus will then be cut out of the
circuit, and can have no effect upon the operation of the brake.
I believe myself to be the first to have devised means for controlling the opera-
tion of the braking switch by excess of current in the local circuit which the switch
controls, and therefore the claims which I make in this particular I wish to be
liberally construed. I am aware that mechanical appliances may be used, but as
these are independent of the current in the circuit, they have not been found
efficacious. Where such mechanical appliances however, are controlled by the
current and are cut in by excess of current and cut out when the current falls off,
1 consider them within the scope of the claims I have made.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me from.
abroad I declare that what I claim is :
1. A safety appliance for an electric brake, comprising a braking switch, brake-
magnets and a source of electro-motive force in circuit with the braking switch, and
means controlled by the current in the circuit for preventing the too rapid
manipulation of the braking switch.
2. A safety appliance for an electric brake, comprising a braking switch, a
circuit including brake magnets and a source of electro-motive force, a solenoid
having its core attached to and controlling the braking switch, and means for
actuating the solenoid by excess of current in the circuit.
3. A safety appliance for au electric brake, comprising a braking switch, a circuit
including brake magnets and a source of electro-motive force controlled by the

page_text: braking switch, a solenoid, a core for the solenoid controlling the movements
of the braking switch, and adjustable means for actunting the solenoid by a
predetermined excess of current.
4. A safety appliance for an electric brake, comprising a braking switch, a
circuit including the braking switch, brake magnets and a source of electro-
motive force, a solenoid, contacts norinally short-circuiting the solenoid, a core for
the solenoid controlling the braking switch, a magnet in the circuit controlling the
short-circuiting contacts, the means for adjusting the magnet for different amounts
of current.
5. A. safety appliance for an electric brake, compromising a braking switch,
braking magnets and a source of electro-motive force in circuit with the braking
switch, a solenoid, a core for the solenoid controlling the braking switch, contacts
normally short-circuiting the solenoid, a magnet in the circuit controlling the
contacts by the movements of its armature, a spring opposing the motion of the
armature under the magnetic pull, and means for adjusting the pull of the spring to
correspond to different amounts of current and conditions of use.
Dated this 3rd day of March 1896.
For the Applicat
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.