Electric train signaling system

Oct. 29, 1935.

2,019,166

L. D. WHITELOCK

ELECTRIC TRAIN SIGNALING SYSTEM

Filed Feb. 17, - 1934

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Patented Oct. 29, 1935

2,019,166

UNITED STATES PATENT OFFICE

2,019,166 ELECTRIC TRAIN SIGNALING SYSTEM Leland D. Whitelock, Wilkinsburg, Pa., assignor to The Union Switch &amp; Signal Company, Swissvale, Pa., a corporation of Pennsylvania

Application February 17, 1934, Serial No. 711,788

Claims.

My invention relates to signaling systems for railway trains, and particularly to systems for telephone communication for railway trains.

An object of my invention is the provision, in 5 systems of the type here involved, of novel means for transmission of signaling currents between spaced points on a train, or between two trains, οι- between a train and a wayside station. Other objects and advantages of my invention will ap10 pear as the specification progresses.

I will describe certain forms of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. l.is a dia15 grammatic view showing one form of signaling apparatus embodying my invention. Fig. 2 is a diagrammatic view of a modified form of the signaling apparatus of Fig. 1 and which also· embodies my invention. Fig. 3 is a diagrammatic 20 view of a wayside station equipped with apparatus embodying my invention.

Similar reference characters refer to similar parts in each of the views.

My present invention is an improvement on 25 the invention disclosed and claimed in application for Letters Patent of the United States, Serial No. 450,135, filed May 6, 1930, by Lars O. Grondahl for Electric train signaling systems.

Referring first to Fig. 1, the reference charac30 ters i and l^a designate the traffic rails of a stretch of railway track which is occupied by a railway train designated as a whole by a reference character TN. The forward vehicle of the train TN is indicated at 2 and the rear vehicle 35 is indicated at 3, for example, the vehicles 2 and 3 may be the locomotive and caboose of the freight train, respectively. This particular make-up of the train TN has no significance, however, in so far as my present invention is concerned, and the 40 vehicles 2 and 3 may be any two vehicles of the train. Furthermore, as will appear hereinafter, the vehicles 2 and 3 may be vehicles of two separate trains, respectively.

When my invention is to be utilized for signal45 ing between two spaced points on the same train, for example, between the locomotive and caboose of a freight train, one equipment will be mounted on the locomotive and a second and similar equipment will be mounted in the caboose. Each 50 of such equipments preferably comprises a transmitter, a receiver, a coupling transformer, a circuit controller for connecting said transformer with either the transmitter or receiver and an electrical conducting member or counterpoise. 55 The transmission circuit between the two spaced (Cl. 246—8) locations preferably includes the traffic rails in a manner to more fully appear hereinafter. The transmitter T of the locomotive equipment includes a source of alternating current, such as a generator G. One terminal of the generator 5 G is connected with a contact 8 of a manually operated circuit controlling switch SW, while the opposite terminal of the generator G is connected with a second contact 9 of the switch SW, the secondary winding 10 of a transformer Ti being 10 interposed in the connection between the generator G and the contact 9. The primary winding ί I of the transformer Ti is included in a circuit which also contains a battery 12 and a control device, such as a microphone M. It follows that 15 sound impulses produced by speaking into the microphone M will cause variations in the current flow in the primary winding 11 of the transformer TI which will induce an electromotive force of corresponding frequencies in the sec- 20 ondary winding 10 with the result that the alternating current supplied by the generator G will be modulated by the voice frequencies. It will be understood that the microphone M may be a control device adapted to produce a single given 25 frequency of variation of the current flow should it seem desirable. In this latter case, the alternating current will be modulated by a single frequency corresponding to the frequency produced by the control device. 30

The receiver R of the locomotive equipment includes in this instance a demodulator-amplifier DA and a signaling device shown as a loud speaker LS. The upper right-hand input terminal of the demodulator-amplifier DA is connected with 35 a contact 13 of the switch SW and its lower right-hand input terminal is connected with a second contact 14 of the switch SW. The output of the demodulator-amplifier is connected with the operating winding of the loud speaker LS 40 over wires 15 and 16. The demodulator-amplifier DA may take different forms several of which are well known to the signaling art, and as its specific structure forms no part of my present invention, this device is shown conventionally 45 only for the sake of simplicity. It is deemed sufficient for the present application to say that this demodulator-amplifier DA demodulates alternating current modulated by voice frequencies or modulated by a given single frequency when 50 such currents are applied to its input circuit and causes to appear in its output circuit the voice frequencies or the single frequency only greatly increased in amplitude. As stated above, the output circuit of the demodulator-amplifier DA is 55

2,019,166 connected with the operating winding of the loud speaker LS, and hence alternating current modulated by the voice frequencies of a telephone message and applied to the receiver R will be re5 produced by the loud speaker LS. The loud speaker LS may be a signaling device selectively responsive to a single given frequency should it seem desirable. In this latter case, alternating current modulated with the given single frequency 10 and applied to the receiver R will be effective to operate the signaling device.

The contact members IT and 18 of the circuit controlling switch SW are connected with the opposite terminals respectively, of the winding 19 of 15 a coupling transformer T2. Consequently, when the switch SW is set in the position illustrated by the full lines in Fig. 1 and the contact members 17 and 18 engage the contacts 13 and 14, respectively, the receiver R is connected with the wind20 ing 19 of the transformer T2. When the switch SW is depressed to the position illustrated by the dotted lines in Fig. 1 and the contact members 17 and 18 make engagement with the contacts 8 and 9, the transmitter T is connected with the 25 winding 19 of the transformer T2.

A second winding 20 of the coupling transformer T2 is included in a circuit connection extending from the traffic rails to an electrical conducting member or counterpoise. This circuit 30 connection extends from the lower terminal of the winding 20 over wire 21 to the traffic rails ί .and l^a in multiple through the medium of the wheels and axle 4 of the locomotive or vehicle 2. The electrical connection of the wire 21 with the 35 wheels of the locomotive may be through the journal boxes or may be through a contact ring mounted on the axle and a contact brush adapted to engage therewith, .as may be desired. Furthermore, the wire 21 may make connection with 40 the rails i and i^a through the medium of a pair of contact shoes, one riding on each rail, if found desirable to do so. The specific manner of connecting one terminal of the locomotive circuit with the traffic rails forms no· part of my 45 invention, and the form here shown will serve to illustrate the many ways direct connection with the traffic rails may be made. This circuit connection on the locomotive extends from the top terminal of the winding 20 of the transformer 50 T2 over a wire 22 to one end of an electrical conducting member A—B, the other end of which is dead-ended and is free from connection with the equipment and from the metallic parts of the locomotive. The electrical conducting member 55 A—B may be a single wire of some length, a loop of several turns, a network or a metal sheet of considerable area as desired, one terminal of which, as stated above, is dead-ended. This conducting member A—B may be located .at any con60 venient place on the locomotive and preferably is located below the body of the locomotive and relatively close to the road bed. It is clear that the conducting member A—B serves as one plate of a condenser of which the earth is the other plate, 65 and also serves as one plate of another condenser of which the traffic rails is the other plate. This latter capacity, however, will be relatively small in comparison with the capacity between the conducting member A—B and the earth, and hence 70 the conducting member A—B serves as a counterpoise for a circuit which includes the above traced circuit connection and the traffic rails in multiple extending in either or both directions from the locomotive.

A tuning condenser 23 is preferably connected across the winding 20 of the transformer T2 to tune this circuit connection. The condenser 23 may be used in series with the winding 20 if found desirable.

From the foregoing description it is to be seen g that with the switch SW on the locomotive set in the position illustrated in Fig. 1, alternating current picked up from the traffic rails will be impressed upon the receiver R through the medium of the transformer T2, and that with the switch 10 SW depressed, alternating current will be sup- . plied to the traffic rails from the transmitter T of the locomotive equipment through the medium of the coupling transformer T2 and that this alternating current may be modulated with voice 15 frequencies by speaking into· the microphone M.

The equipment mounted on the caboose or vehicle 3 of Fig. 1 is similar in .all respects to the equipment mounted on the locomotive and it is thought unnecessary to repeat the description. 20 It will be noted that as long as the manually operated switch SW on the caboose occupies the position illustrated by the full lines in Fig. 1, its receiver R is connected with the winding 26 of the caboose coupling transformer T3 and hence 25 is coupled with the circuit connection extending between the traffic rails and the caboose counterpoise A—B. With the switch SW on the caboose depressed, the winding 26 is disconnected from the receiver R and is connected with the caboose 30 transmitter T which is now coupled with the circuit connection between the traffic rails and the counterpoise through the medium of the transformer T3.

When the switch SW of either the locomotive 35 or the caboose is reversed and its transmitter T is connected with the winding of the coupling transformer, an electromotive force of corresponding frequency will be induced in the winding of the transformer interposed between the 40 member A—B and the traffic rails with the result that an alternating difference of potential is created between the counterpoise on that vehicle and the traffic rails, and a corresponding current is supplied to the rails which returns in part 45 through the distributed impedance between the rails and ground, the ground and the capacitance existing between the counterpoise and earth. A portion of such current flowing in the traffic rails will be picked up by the wheels of the other ve- 50 hide and will flow through the circuit connection between the rails and the counterpoise on that vehicle, thence over the capacitance between the counterpoise and earth, the ground path and the capacitance existing between the counterpoise 55 and earth on the sending vehicle. Such current flowing in the coupling transformer winding interposed in the circuit connection on the second vehicle will induce a corresponding electromotive force in the other winding of the coupling trans- 60 former with the result that energy of corresponding frequency will be applied to the receiver of the second vehicle. It is to be seen, therefore, that a transmission circuit between the equipment on the locomotive and the equipment on the 65 caboose is provided through the medium of which energy corresponding to that supplied by the transmitter of the sending vehicle is impressed upon the receiver of the second vehicle. Furthermore, this transmission circuit will be effective to 70 transfer energy between the two equipments in either direction.

To aid in visualizing this transmission circuit between the two vehicles, fictitious condensers 27 and 28 are shown by dotted lines in Fig. 1 be- 75

2,019,166 tween the counterpoise A—B and ground of the two vehicles, respectively; and arrows have been added to the drawing to indicate the flow of current at some particular instant. To be explicit, 5 this transmission circuit can be traced as consisting of the following element: counterpoise A—B of vehicle 2, wire 22, winding 20 of the transformer T2, wire 21, wheels and axle 4 of vehicle 2, rails ί and l^a in multiple, wheels and axle 6 10 of vehicle 3, wire 25, winding 24 of transformer

T3, counterpoise A—B of vehicle 3, capacitance between counterpoise A—B and earth (fictitious condenser 21), ground and capacitance between counterpoise A—B of vehicle 2 and earth (ficti15 tious condenser 28). It is clear that when an electromotive force is induced in the winding 20 of the transformer T2 of vehicle 2, a corresponding electromotive force will be induced in the winding 26 of the transformer T3 on the ve20 hide 3, and conversely, when an electromotive force is induced in the winding 24 of the transformer T3 of vehicle 3, a corresponding electromotive force will be induced in the winding i9 of the transformer T2 on the vehicle 2.

In the event the locomotive operator desires to telephone to the operator in the caboose, he will depress his switch SW and speak into the microphone M. An electromotive force corresponding to the alternating current of the locomotive gen30 erator G modulated by the voice frequencies will be induced in the winding 20 of transformer T2 and a corresponding current will be supplied to· the traffic rails. A portion of this modulated current will be picked up from the traffic rails by 35 the wheels of the caboose and will flow through the connection between the rails and the counterpoise on the caboose and thence back to the locomotive through the capacitance and ground path. An electromotive force of corresponding fre40 quencies will now be induced in the winding 26 of the transformer T3 which will be applied to the input circuit of the demodulator-amplifier on the caboose. After demodulation and amplification, the voice frequencies will be caused to 45 appear in the output of the demodulator-amplifier and the telephone message will be reproduced by the caboose loud speaker LS. To· telephone from the caboose to the locomotive, the operator at the caboose will depress his switch SO SW to couple the caboose transmitter with the transmission circuit and he will speak into his microphone. This modulated alternating current will induce a corresponding current in the winding 24 of the transformer T3 and current will 55 flow in the transmission circuit to induce a corresponding current in the winding !9 of the locomotive transformer T2. The locomotive operator having subsequently restored his switch SW to its normal position, this modulated cur60 rent induced in the winding 19 will be applied to the locomotive receiver, and, after demodulation and amplification, the telephone message will be reproduced by the locomotive loud speaker.

While, in the particular adaptation of my in65 vention here disclosed, telephone communication is provided, it is apparent that by coding the alternating current supplied by the transmitters according to a prearranged code, code impulses of alternating current will be transmitted between 70 the two vehicles over the transmission circuit.

By further providing the receivers with decoders and signaling devices responsive to the prearranged code, control between the two vehicles may be established as desired.

The frequencies of each generator G may be of any suitable value, and is preferably high enough to avoid interference due to currents of commercial frequencies. Each receiver R will, of course, be provided with a filter so proportioned and adjusted as to· pass the frequency sent out 5 by the transmitter at the other location and to substantially suppress all other frequencies.

In order to signal between two· trains, each train may be provided with one or more equipments located at any convenient location or io- 10 cations on the trains. For example, the vehicle 2 of Fig. 1 and its equipment may be included in one train and the vehicle 3 and its equipment may be included in another train. With this arrangement, communication between the oper- 15 ators on the two· trains may be carried on in exactly the same manner as described above between the locomotive and the caboose of a freight train. In. the case of two· trains, the transmission circuit passes over the traffic rails in multiple 20 and returns to the sending vehicle through the capacitance and ground path. In this latter case, however, it will be understood that, the two trains are within reasonable distance of each other. 25

When it is desired to signal between a train and a wayside station along the track, the train may be provided with one or more, equipments in the manner previously described, and another equipment may be located at some convenient 30 point along the track. The equipment located along the track may, for example, be constructed as illustrated in Fig. 3. As here shown, the wayside equipment is provided with a receiver and a transmitter which are preferably the same as 35 the corresponding devices provided on the train and are selectively connected with the winding 23 of a coupling transformer T4 over a manually operated circuit controlling switch SW. The second winding 30 of the coupling transformer T3 40 is included in a connection extending from the rails I and i^a over a resistor 32 to its mid point, wire 3 i, winding 30 and thence to a ground electrode 33. Assuming the vehicle 2 with its equipment occupies the traffic rails I and i^a within 45 reasonable distance of the wayside station of Fig. 3 and that communication between the operators is desired, the operator on the vehicle 2 by depressing his switch SW will supply alternating current to the traffic rails which will flow over 60 the rails in multiple to the station equipment and thence it will pass to ground through the connection including the winding 30 of the transformer T4 and back to· the equipment on the vehicle 2 over the ground and counterpoise path. 55 A corresponding electromotive force will be induced in the winding 29 of the transformer T4 which will be applied to the receiver of the wayside station equipment. It is clear that alternating current may be transmitted from the way- 60 side station transmitter to· the vehicle 2 by the operator at the wayside station depressing the switch SW to connect his transmitter with the winding 29 of the coupling transformer T4.

Since the impedance of the circuit connection ^Gobetween the traffic rails and the counterpoise on a vehicle contains capacitance, it may be tuned by means of an inductive reactance in series with the connection as well as by a condenser. In γθ Fig. 2, the condenser 23 of the locomotive equipment is replaced by an inductor 34 which is interposed between the winding 20 of the coupling transformer T2 and the counterpoise A—B. It is clear that the equipment of Fig. 2 will function 75

8,019,166 in exactly the same manner as the locomotive equipment of Fig, L

Although I have herein shown and described only certain forms of apparatus embodying my 5 invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.