Improvements in Surface Contact Railway Systems.
Year: 1898

page_text: Date of Application 25th June, 1898-Accepted, 30th July, 1898
COMPLETE SPECIFICATION.
Improvements in Surface Contact Railway Systems.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by William B.
Potter, residing at Schenectady, 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 follow-
ing statement:
The present invention relates to surface contact railway systems; and has for
its object to provide a time overlap for the switches, which are actuated by current
from the contact-shoes, and this is attained by insuring the prompt closing of
each switch in succession. When running at any considerable speed, in systems
in which the switch in advance of the one furnishing current to the car motors is
closed by a portion of the motor current passing from one of the contact-shoes
around its coil, in a way well understood in the art, it sometimes occurs that,
owing to the low resistance of the circuit through the shoe and the ground circuit
established through the switch already energized, current goes to ground almost
entirely through the last-named switch, while the switch in advance does not receive
sufficient current to insure its moving with promptness; since it takes more
current to close a switch than to hold it closed.
To obviate this difficulty, the resistance of the contact-shoe which actuates
the switches, is artifically increased so that the path of the current through the
switch which has been actuated will have increased resistance relatively to the
one which is about to be actuated, and thus the latter switch receives a larger
share of the current and moves promptly.
There are several ways in which the resistance in the circuit can be increased
for the purpose described; the shoe may have an external or artificial resistance
connected to it, the shoe itself being cut in two and the sections insulated, or its
cross section may be diminished at a point near its middle; or the whole shoe may
be made of comparatively small section, or of high-resistance metal, so that, as
it is drawn over the contact, the resistance in the circuit of the closed switch
steadily increases until the second contact touches the shoe. The essence of the
invention, therefore, consists more in the method of operation outlined than in
the apparatus, though there is material novelty in that also; the method consist-
ing in closing the switch with a certain current, then increasing the resistance of
the circuit of the closed switch, so as to compel the current to seek the path
through the coil of the switch which is about to close; then, after that switch
closes, cutting down the current by the added resistance, and so on.
The accompanying drawings show ways of carrying out the invention, Fig. 1
showing in diagram the system, now well known, to which it is applied, and
Fig. 2 illustrating different ways of carrying out its purposes.
In Fig. 1, A A are the track rails, B the high potential or positive studs or con-

page_text: tacts, C the negative or low potential studs or contacts, D, D₁ the wheels of the
E the storage battery, S a switch by which the battery may be thrown into
or out of circuit, and R S a reversing switch for reversing the motor M.
car,
All of these parts are well known; H is a feeder supplying current to operate
the road, G, Gare switches by which successive connection between the studs B
and the feeder is effected. These switches are provided with contacts g, g¹, g³,
and an operating coil G¹ connected between the contacts or studs C and ground.
F, F¹ are the contact-shoes.
So far the parts are of ordinary construction, and operate as follows; at starting,
the switch S is thrown, and current passes from the storage battery E directly
to the shoe F, thence by contact C upon which the shoe rests, through the coil G
to ground, closing the switch G. From ground, current passes back to the
battery E, one end of which is grounded on the car wheel D. Current then passes
from the feeder H, by contacts g, etc., to the positive studs B, B, upon which the
shoe F rests, and thence through the field and armature of the motor M. The
switch S may be then opened, and current from the motor circuit will energize
the switches G in succession as the shoe F touches each of the contacts G, the
main motor current passing to the ground through these contacts in multiple.
At this point the operation of the present invention begins. The shoe Fi is
divided into two parts f, f, between which is connected the resistance R, a
section I of insulating material being placed between the parts of the shoe. As
soon as the shoe F¹ touches the contact C next the one upon which it is resting, a
great part of the motor current will pass to ground through this contact, on account
of the insertion of the resistance R. Sufficient current, however, will still pass
the resistance to hold the switch G closed; it being well known that it takes more
current to effect the closing of the switch than it does to hold it closed, on account
of the diminution of the air-gap when the switch is closed.
To get the full advantage of the present invention, the current should enter the
shoe at its front end. This result is attained by a switch K, preferably connected
to the reversing switch R S, so that the two are thrown together; thus, whenever
the direction of motion of the car is reversed, the switch J is also operated to con-
nect the front end of the shoe to the source of current, either the battery E or the
negative terminal of the motors as the case may be. Both the switch S and the
switches R S and K may be placed on the car controller, as will be obvious to one
skilled in the art.
In Fig. 2 are illustrated three forms of contact shoe to which reference has been
made in the statement of invention. The first of these shows in diagram the
resistance connected in between the parts f, f¹ of the shoe F¹, while in the second
form, a part of diminished section answers the same purpose. In the third
form shown, the shoe itself is formed of smaller section, or of some resistance
material or both. Other arrangements will of course readily suggest themselves.
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. The method described of insuring the successive closing of a number of
electrically-operated switches, which consists in increasing the resistance in the
circuit of a switch already closed, and thus increasing the current in the switch
about to close.
2. The method described of insuring the prompt closing of the successive
switches in a surface contact railway system, which consists in closing a switch
at full current, and increasing the resistance in the circuit of the switch until the
shoe makes contact with the switch in advance of the one already closed, thereby
diverting to that switch the greater part of the current, and insuring its closing.
3. The method described of operating in sequence a number of electro-magnetic
switches, which consists in closing each switch with full current, gradually

page_text: diminishing the current in that switch until about the time of closing the next
switch in advance, and then breaking the circuit, as set forth.
4. The combination with a number of electro-magnetically-operated switches,
and a contact device furnishing current to close the switches in succession, of
means for increasing the resistance in the circuit of each switch after its closure.
5. In a surface contact railway system, a number of electro-magnetically-
operated switches, a contact device taking current at its forward end in either
direction of movement, and means for increasing the resistance in the circuit of
the contact device after each switch is operated.
6. In a surface contact railway system, a number of electro-magnetically-
operated switches to be closed in succession, a contact-shoe, a resistance in the
circuit of the contact-shoe, and a switch for connecting the forward end of the
contact-shoe in either direction of movement to the source of current by which
the switches are actuated.
7. In a surface contact railway system, a contact-shoe carried by a moving
vehicle, a reversing switch, and a switch for connecting the front end of the shoe
in either direction of movement with the source of current, the two switches
being combined in one or having a connection by which they are simultaneously
operated.
THE BRITISH THOMSON-HOUSTON CO. LTD.
A R. MONKS,
Director.
ALFRED CLEMENTS,
Assistant Secretary.