US2214924A

US2214924A - Railway signaling system

Info

Publication number: US2214924A
Application number: US210580A
Authority: US
Inventors: Griffiths John Balmain; Brown Andrew
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1937-06-01
Filing date: 1938-05-28
Publication date: 1940-09-17
Anticipated expiration: 1957-09-17

Description

Sept. l 7, 1 940.

J. B. GRIFFITHS Er Al.

RAILWAY SIGNALING SYSTEM 2 Sheets-Sheet l Filed May 28, 1936 TTORNE Y sept. 17, 1940.,

RAILWAY SIGNALING SYSTEM Filed May 28, 1936 Fig. 2.

Fig. 3.

J. B. GRlFFrrHs 'E- AL 2,214,924

2 Sheets-Sheet 2 Patented Sept. I7, 1940 RAILWAY SIGNALING SYSTEM John Balmain Griffiths and Andrew Brown, London, England, assignors to International Standard Electric Corporation,

Application 25 Claims.

This invention relates to railway signaling systems.

ing track section in turn as that section is approached. In such arrangements the stopping point of one tual position of sition of the beginning of preceding train the or any part of train 1s determined not by the acthe train ahead,

but by the po'- section in which a the preceding train happens to be standing. Further, the signals for stopping yof a train are not controlled dependent ing in question, nor on its own It is the object of the present invention on the speed at which the preceding train is movspeed.

to provide a system of train signaling and/or control in which trains are allowed to follow one another at the shortest intervals which are proved to be safe taking into account the distance apart of the trains irrespective of their positions on the track and/or the speed of a train itself and/ or the speed of the preceding train.

The main feature of the invention comprises a railway signaling system characterised by a continuous electrical signaling circuit along a track, electrical transmitting train on the track arranged along the circuit in which the train is travelling equipment on each to be connected to said signaling circuit to transmit information the opposite direction to on the track, electrical receiving equipment on each'train arranged to receive said information from the preceding train and to determine therefrom information concerning the relative positions of the two trains on the track, and control ment on each train adapted control of and/ or indicating equipto function under the receiving equipment 'to give an indication to the driver or to control the train in accordance with its safe margin of travel as determined by the distance between the trains irrespective of their positions on the track with respect to particular divisions thereof.

the following description of thereof shown in which:

The invention will be clearly understood from the embodiments the accompanying drawings, in

Fig. 1 shows a continuous signaling circuit SC connected at intervals to and also to trains T each the earthed rails ER provided with control circuits at the front and rear shunted between the continuous signal circuit SC and the rails ER;

Fig. 1A shows a modied f @55 apparatus of Fig. 1.

ormof part of the New York, N. Y.

May Z8, 1938, Serial No. 210,580. In

reat Britain June l, 1937 Fig. 2 shows a modication of the signaling circuit shown in Fig. 1, arranged for direct control of the driving motors of a train; while v Fig. 3 shows a train drivers speed indicator.

Referring first to Fig. l, the control circuit atthe 5 front of each train comprises a source of electric potential EP and a meter M the reading of which will be influenced by the distance between the train and the preceding train. The control circuit at the rear of eachtrain is either a direct short circuit or an impedance connection I which may if desired be variable under control of a speedometer.

The continuous signal circuit is divided into sections the length of which is determinedby the shortest individual vehicle or train which must pass over the track, under full control of the signaling equipment.

At the junction point between each pair of sections a resistance RS and rectifier RC in series are inserted into the signal circuit SC. The rectiers RC are so inserted that they pass current through the circuit SC in the direction in which trafc passes along the track. At the junction point of each resistance and rectifier pair (or at any other point in each section) a connection is made through high resistance HR to the rails ER or other dead earth. The resistances in the signal circuit are very small compared with the high resistance shunts but are large compared with the resistance of the rectifiers. For instance, an ordinary dry rectifier in the go direction has a resistance ofl about 3 ohms. The resistance in series therewith will be about 17 ohms, while the shunt resistance will be about 5000 ohms. When a train passes along the track with no other train in front of it a circuit is formed through the meter, through all of the shunts HR of the signal circuit sections ahead through the rails and the battery EP.

The resistances and the battery voltage are so chosen that in the worst condition a certain minimum current should pass through the meter and unless this minimum currentis indicatedby the meter thetrainisnotallowedtomove. 'I'hisminimum 45 current value is determined by the current which would be allowed to new by the shunt resistances of a number of signal circuit sections, which cover the maximum braking distance of a train.

It will be appreciated that the rectiers in the sections behind the train prevent the shunt resistance of these sections having any effect upon the meter current.

When a train is on the track in front of the train under consideration, the meter current will per section is 300 ohms be determined by the shunt on the rear of the preceding train through which a much greater current can pass than would be passed through the shunt resistances HR between the trains, or

by all the shunt resistances HR where no train The reading of the meter will increase as the distance between the trains becomes less and the reading of the meter will be used to indicate to the driver the maximum safe speed at which he can proceed or to control the speed of the train in accordance with safe limits or automatically to prevent the train travelling at -a speed greater than the safe speed.

If, as has been suggested previously, the shunt resistance on the rear of the preceding train is increased under control of a speedometer as the speed of the train increases, it will be seen that the reading of the meter on the following train will be correspondingly decreased enabling that train to proceed at a greater speed and run closer behind the train in front by virtue of the fact that the preceding train is itself moving.

For the purpose of varying the resistance of the shunt placed on the signal circuit according to the speed of the train, a series of governorcontrolled contacts for cutting in and out resistance may be used.

If the driver attempts to run his train at a speed greater than that indicated under control of the meter or if the reading of the meter reaches a certain maximum, the train will be automatically stopped by any known means.

Let us assume as an example, that the maximum braking distance of the trains is 600 ft. and :that the signaling circuit section length is 40 ft., then the number of sections corresponding to the maximum braking distance is 15. The signal circuit resistance of 15 sections at 20 ohms and this corresponds roughly to fifteen 5000 ohm shunts in parallel.

The fundamental purpose of the shunt resistance is to guard against a disconnection ahead of the signal circuit. For this purpose it is necessary for the meter to show the minimum current reading before a train is allowed to move, whether or not there is a train on the track ahead.

It will have been noted that the resistance of is present.

each rectifier in the signal circuit is small compared with the value of its series resistance. The reason Yfor this is to prevent small changes in the rectifier resistance eiecting the system. However,k it is possible for the resistance of a rectifier Vin the go direction to increase to a value of the orderof 260 or 300 ohms although this is very unlikely as the-rectifier usually either becomes short-circuited or completely disconnected instead. However, if such a remote contingency Idid arise the response of the meter, circuit or train via the shunt of the preceding train would be artificially increased so that the preceding train appears much farther away than it actually is. This of course is a wrong side fault. In order to take care of this, the front control circuit on each train may be connected to the signal circuit SC by a pair of sliders SL, between l which a voltmeter V is connected and which are spaced so as to bridge each resistance and rectifier pair RS, RC, so that the voltmeter will read 'the voltage drop across each rectier and re- 4sistance pair in turn.

The voltmeter reading will be compared with the reading of the ampere meter M to show the actual resistance of each rectifier resistance pair. If this is high an alarm will be given and if considered necessary the train will be stopped.

' the meter needle The shunt connection on the rear of the train is a possible source of a wrong side fault because if it became disconnected the presence of the preceding train would no longer be indicated. In order to guard against this, several parallel shunt connections may be provided on each train asl shown in Fig. 11A, so that if one such connection comes adrift, no appreciable change in the resistance of the circuit between the two trains will arise. Provision can be made at suitable points on the track for testing that all the par- `allel circuits were intact.

As an alternative to the ammeter indicator, a chain of relays may be provided, the response of which would be graded so as to operatev in turn as the signal channel resistance decreases.

Another alternative is to control the driving motor or motors of trains directly by the signal channel resistance. Such an arrangement is shown in Fig. 2, and is a modication of the D. C. system described above. A source of direct current, CS, is connected between a wheel rail WR and a live rail LR. Between WR and the mid-points of the resistance-rectifier pairs RS, RC in the signal wire SW, the shunt circuits HR are connected.

The drivingfmotor MOis also connected between WR and SW by wheel WH and slider SLC in series with normally open contacts Zd and the relay LD controlling said contacts. Between Zd and LD is connected a current feed circuit via resistance FR and slider SLR.

For a train to start, a circuit for operating LD is completed via SLC, HR, CS, LR, SLR and FR. LD will only operate if the signal channel is in order, thereby closing contacts Zd to complete the circuit for motor MO. A shunt on motor MO is maintained via. LD, SLC, SW shunt circuits HR and WR, so that the excitation of the motor decreases as the resistance of the shunt decreases. In this way the speed of the trains' may be automatically controlled. Y

Automatic train speed control could of course be obtained by the provision of an intermediate control relaying means between, an ammeter or relay chain and a motor shunt or other automatic control means. For instance, the meter could be provided with power operated means toy operate one of a number of control circuit pairs via according to the position of the needle, the contacts being used to control a motor shunt or other motor control device.

Fig. 3 shows a train drivers speed indicator designed to give him detailed speed information and a very simple maximum speed check device.

The indicator comprises two red indicator segplied full braking power. The segment S is controlled by the speedometer and yrotates anticlockwise as the speed increases. The pointer HLP on H indicates on a scale the maximum per- `missible speed while pointer SP on S indicates the actual speed of the train.

As the trainy speed approaches the maximum allowable speed, 'the visible greerr background G decreases in size and is blotted out completely when the train reaches the kmaximum speed. The indicator is arranged 'to `operate contacts SW, shunt circuits C and when the vgreen disappears to cause automatic application of the brakes. The main features of the indicator are the variable indication of the margin of speed and the automatic brake control.

Signaling between trains may be performed by measuring the resistance of a direct current circuit via the intervening signal circuit between two trains, or the resistance or phase angle of an alternating current circuit.

Inductive connections between the trains and the signal circuit may be used.

Instead of using a constant potential to measure variable line resistance or impedance, it is possible for each signal section to insert additional D. C. or A. C. voltage in the circuit between two trains so that the voltage is a measure of the degree of freedom ahead.

i It is sometimes necessary to apply either temporary or permanent speed restrictions on a portion of a track, for instance a newly-laid portion or a sharp curve. A condition can then be connected to the signal channel near the beginning of the section in question, which will cause a train to slow down to the required speed before entering the section. If the section is long, it may be necessary to apply two or more such conditions spaced along the section to be restricted. In the case of the D. C. system, this condition could be a resistance leak by additional resistance units HR.

If it is desired to pass locomotives or trolleys shorter in length than the signal channel sections along the track, they can be provided with equipment for short-circuiting the channel for instance, to safeguard their rear, but will not be provided with detector equipment for testing the condition of the portion of the signal channel ahead.

An important facility offered by the system is the possibility of governing the approach speed and distance of trains according to the gradient of the track. This :facility is obtained in the D. C. system for example, by varying the values of the shunt resistances across the signal channel to allow relatively greater speeds and shorter spacings on up-gradients than on level track sections, and on level sections than on down-gradients.

What is claimed is:

1. A railway signaling system comprising a continuous electrical signaling circuit along a track including as a part thereof the track rails, means in said circuit for conducting current in one direction only along a portion of said circuit, electrical receiving means and a current source on each train connected to said circuit, a transmission modifying means on each train connected to said circuit for modifying the current f path for the current source on a following train,

said receiving means on each train for receiving current from. the current source of a preceding train, and responsive to its position relative to the transmission modifying means on said preceding train for indicating the distance between said trains in accordance with the safe margin of travelfunder control of said current'source.

2. A railway signaling system as claimed in claim 1, wherein means is provided to control said transmission modifying means according to the speed of travel of the train on which it is mounted and said receiving equipment is arranged to control the indicating equipment in accordance with the combined distance from the preceding train and the speed of movement of the preceding train.

3. A railway signaling system as claimed in claim 1, characterised in this that said indicating and control equipment includes a maximum safe speed indicator for the driver.

4. A railway signaling system as claimed in claim 1, characterised in this that said indicating and control equipment includes a maximum safe speed indicator, and automatic braking equipment brought into operation in response to speeds exceeding said maximum safe speed.

5. A railway signaling system as claimed in claim 1, characterised in this that the continuous signaling circuit comprises a rst continuous electric conductor formed by short conductor sections each adjacent pair comprising a recti` iier, a second continuous electrical conductor parallel to said interconnected conductor sections, and a high resistance bridge per section of the first conductor between the first and second conductors, that said transmission modifying means on each train comprises a movable bridge connection between the two conductors of the con tinuousI signaling circuit, and that the receiving equipment is also bridged across the conductors.

6. A railway signaling system characterised by a continuous signaling circuit comprising a first continuous electric conductor formed by short conductor sections each adjacent pair of which is connected by a resistance and rectier in series said rectiers being poled to transmit current .in one direction only along said conductor, a second continuousl electrical conductor parallel to said interconnected conductor sections, and a high resistance bridge per section of the first conductor between the nrst and second conductors, the resistances in the iirst conductor being small compared with the bridge resistances, transmission modifying equipment on the rear of each train comprising a movable bridge connection between the two conductors of the con tinuous signaling circuit and equipment on the front of each train also bridged across the conductors of the signaling circuit comprising a source of direct current potential and an indicator, the rectiiiers in the rst conductor of the continuous signaling circuit being poled to allow current to flow therein from the direct potential source of one train over the transmission modifying equipment of the preceding train and to the indicating means of said one train.

7. A railway signaling lsystem as claimed in claim 6, characterised in this that saidgsecond conductor is formed by the running rails'.

8. A railway signaling system as claimed in claim 6, characterised in this, that each high resistance bridge on the continuous signaling circuit is connected to the rst conductor at the junction between a resistance and rectifier interconnecting a pair of conductor sections.

9. A railway signaling system as claimed in claim 1, characterised in this that the receiving means is provided with means responsive to the received currents to automatically control the speed of the train.

10. A railway signaling system as claimed in claim 6 characterised in this that each section resistance of a direct current circuit, between two trains.

12. A railway signaling system as claimed in claim 6, characterised in this that the indicating equipment of each train is connected to the first conductor by two sliders spaced sufliciently to bridge each rectier in the rst conductor in turn, and a voltmeter connected between said sliders by means of which the condition of the rectiers may be determined,

13. A railway signaling system as claimed in claim 6, characterised in this that each transmission modifying equipment comprises a plurality of parallel bridge connections.

14. A railway signaling system as claimed in n claim 6, characterised by a variable resistance in said bridge connection of each transmission modifying equipment and means for varying said resistance in accordance with the speed of the train.

15. A railway signaling system as ciaimed in claim 1, characterised in this that the signaling circuit is divided into sections each of which is e shorter than the distance between transmitting and receiving equipment on the shortest train which is to pass over the track under full control of the system.

16. A railway signaling system as claimed in claim 6 characterised in this that the signaling circuit is divided into sections each of which is shorter than the distance between transmitting and receiving equipment on the shortest train which is to pass over the track under full control of the system, and in this that a rolling stock unit or group of units which is' to pass over said track and which is shorter than a signaling circuit section is provided with transmitting equipment only.

17. A railway signaling system as claimed in claim 1 characterised in this that the electrical characteristics of the signaling circuit vary from portion to portion of said circuit in accordance with the gradient of the track for instance.

18. A railway signaling system as claimed in rclaim 6 characterised in this, that the indicating equipment on a train comprises a chain of relays graded to operate in turn as the distance between trains decreases.

19. A railway signaling system as claimed in claim 1 characterised in this that means are provided to control the driving motor or motors' of an electric train directly by the variable re` sistance of the signaling circuit between said train and the preceding train.

20. A railway signaling system as claimed in claim 6 characterised by an electric driving motor for each train forming part of an indicator bridge circuit, a live rail together with the second conductor of the signaling circuit forming the driving current feed circuit and a feed connection from a point on the indicator bridge circuit of each train between the first signaling circuit conductor and the motor to a shoe contacting with the live rail.

2l. A railway signaling system as claimed in claim 6, characterised by an electric driving motor for each train forming part of the receiving bridge circuit, a live rail which together with kthe second conductor of the signaling circuit forming the driving current feed circuit and a feed connection from` a point on the receiving bridge circuit of each train between the rst signaling circuit conductor and the motor to a shoe contacting with the live rail, a relay connected in the indicating equipment of each train between the rst conductor of the signaling circuit and said feed connection, and contacts controlled by said relay, closed when thev relay is energised, in the motor feed circuit portion of indicator equipment bridge.

22. A railway signaling system as claimed in claim 1, characterised by an indicator on each train comprising two the receiving equipment to indicate maximum permissible speed, the other controlled by a speedometer to indicate actual speed.

23. A railway signaling system( as claimed in pointers, one controlled by claim 6, characterisedby an indicator on'each train comprising two pointers', one controlled by said indicating equipment to indicate maximum permissible speed, the other controlled by a speedometer to indicate actual speed, said pointers of the indicators carrying screens which approach one another when the margin between train speed and permissible speed decreases, and by doing so decrease the amount of a background visible between said screens, so lthat the safety margin indication is reduced to an arbitrary minimum when the train is travelling at the maximum permissible speed.

24. A railway signaling system as claimed in claim 6, characterised by an indicator on each train comprising two pointers, one controlled by said receiving equipment to indicate maximumi permissible speed, the other controlled by a speedometer to indicate actual speed, said pointers of the indicators carrying screens which approach one another when the margin between train speed and permissible speed decreases, and by doing so decrease the amount of a background visible between said screens, so that the safety margin indication is reduced to an arbirninimum when the train is travelling at the maximum permissible speed, and contacts on said indicator closed when the maximum: permissible speed is reached and which cause application of the train brakes.

25. A railway signaling system as claimed in claim 6, characterised by an indicator on each actual speed, pointers of the indicators carrying screens which approach one another when the margin between train speed and permissible speed decreases, and by doing so decrease the amount of a background visible between said screens, so that the safety margin indication is reduced to an arbitrary minimum when the train is travelling at the maximum permissible speed, and means, controlled by the indicating equipment to indicate that the signal circuit is out of order, comprising a section of the background which is of different color displayed independently of the position of the screen which indicates actual speed.

JOHN BALMAIN GRIFFI'IHS.

ANDREW BROWN.