US2252525A - Railway train control system - Google Patents

Description

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Patented Aug. 12, 1941 RAILWAY TRAIN CONTROL SYSTEM Oliver Walter Reid and Errol dn Preea Erasmus,

Africa Deiville, Germiston, Transvaal, Union of South Ammonium 31.1930, Serial No. 292,946 In the Union of South Africa September 18, 1938 8 Claims.

This invention relates to railway control systems concerned with such systems for the control oitrains independently of their drivers, tor the purpose primarily of preventing collisions.

the railway train control system according to the present invention comprises for each train an electric wave signaltransmitter and an electrio wave. signal receiver, means for rendering the transmitter and the receiver alternately operative and meansrcontrolled by the signal output of the receiver of a train due to signals received from the transmitter of another train, on reaching a predetermined strength due to relative approach of-the trains, to apply the brakes of the train. Thus, when in the operation of trains, two trains come within a predetermined range of one mother the brakes of both trains are automatically applied to stop the trains.

According to. a further feature of the invention means is provided for rendering the receiver: operative with decreased sensitivity during periods of transmission from the same trainand means is employed operated by the output of the receiver as av result of signals received from the transmitter on the trsinto determine the efliciency of operation of the installation. Preferably, meana i's automatically operated when the output of the receiver during the transmission periods falls below a predetermined value to put stand-by apparatus into operation. Therefore, if for. any reason the transmitter or the receiver fails: to operate with a predetermined emciency (c1. zit-29) the stand-by apparatus is put into operation.

Another feature of the invention consists in the provision of auxiliary signal receiving apparatus and means controlled by this receiving apparatus for rendering the receiver inoperative i'or'inooming signals of which the strength 1:

Th auxiliary receiving apparatus thus prevents the brakeafrom being operated as a result of a strong interfering signalsbeingreceived on the main receiver.

According to yctanother feature of the invention the transmitter comprises means for changing a frequency for example a modulation frequency, of the transmission, and the receiver comprises selective means for each frequency, andfurthermcre, means is provided adjacent the track for automatically effecting the change of the frequency of operation of both transmitter and: receiver when: the train. passes from one track to another. Conveniently, the means for eifecting a. change or frequency comprises light means of light sources on the track. Different signal frequencies maytherefore be employed forv trains working on different tracks so as to avoid mutual interference and by the provision of the automatic change-over as regards frequency a train operating on one track may be passed on to another track and automatically come under the control system for that track.

A further feature of the invention consists in the provision of light responsive means on the train for controlling the actuation of the brakes, which light responsive means is arranged for control by'means of light sources on the track. A train may thus be stopped at predetermined locations, for example, in station sections of the track.

Furthermore, light responsive means may also be provided on the train for rendering the transmitter and receiver inoperative in predetermined track sections, for example in stations under the control of light sources on the track. Under these conditions, means is provided for detecting the presence of a train in a section in which its transmitter and receiver are inoperative, together with light sources on the track remote from said section and controlled by the detecting means in order to render the installation an approaching traln operative to apply the brakes. In the case where the track comprises points for directing a train on to alternative tracks there are conveniently provided light sources on the track for stopping an oncoming train, which light sources are controlled by the position of the points, and by the presence of a train on the track, opened by the points for the oncoming train.

In one construction means to apply the brakes of the train comprises a brake operating motor, means for completing an energising circuit for the motor under the control of the output of the receiver, switch means automatically opening the motor circuit when the brakes have been aperated and means for re-energising the motor to release the brakes. Preferably, there is a stand-by brake operating motor and means such as a relay controlled by the output of the receiver and operating with a time delay for completing an energising circuit for the stand-by motor to apply the brakes.

For the alternate operation of the transmitterplete this circuit for putting the stand-by apparatus into operation if the monitoring relay is not operated to open the control circuit.

In one arrangement for efiecting a changeof frequency there are provided light responsive devices allocated to each of two alternative frequencies and means controlled by each of these light responsive devices to operate a change-over switch for effecting a change from one frequency to the other.

The light-responsive devices for controlling the brakes for rendering the transmitter and receiver inoperative in a predetermined track section and for determining the signal frequency and for operating the brakes are preferably mounted at different heights on the train so as to be responsive only to light sources disposed at'correspondingly different heights above the track.

One specific form of the train control system according to the invention is shown by way of example in the accompanying drawings. in which:

Figure 1 is a circuit diagram of the receiver;

Figure 2 is a circuit diagram of the transmitter;

Figure 3 is a circuit diagram of the auxiliary receiving means;

Figure 4 is a circuit diagram of a modulator for the transmitter;

Figure 5 is a circuit diagram of power supply apparatus for the transmitter;

Figure 8 is a circuit diagram of means for controlling alternate transmission and reception and the bringing into action of stand-by appa-.

of an antenna system to the receiver as hereinafter described. The valves VI, V2 and W are coupled by tuned transformers T2 and the valve V3 is in turn coupled by means of a tuned transformer T3 to a diode section of a valve V4 for detecting the modulation signal frequency which is amplified in a triode section of this valve Yl. The output from the valve V4 is applied throu'gh modulation signal selective means to the input of the signal frequency amplifying valve VI which is, in turn, transformer-coupled by means of a transformer T4 to a signal output valve V.

v For single track operation, in which only one signal frequency is used, the frequency selective means may simply consist of a filter for this frequency. Where different signal frequencies are used for multiple track operation the frequency selective means comprises filters for these Fig. 10a is a diagram showing the arrange- I ment of the photo-electric cells. V

Figure 11 is a diagram showing a particular arrangement of light sources on the track;

Figure 12 is a diagram showing control devices for a looped track, and

Figure 13 is a circuit diagram of control means for the light sources for track control, as shown in Figure 12.

Referring to Figure 1 of the drawings, the main receiver of the train installation for receiving the modulated carrier wave signals has three valve amplifying stages VI, V2 and VI operating at the carrier frequency. An input is applied to the valve Vi through a tuned input transformer Tl from terminals 2i and 22 which are bridged with terminals 2i and 22 shown in Fig. 6 and these terminals are connected to relays frequencies and means for connecting them individually in circuit. In l'igu're 1 there are shown two filters FI and F! for two different signal frequencies arranged to be alternatively connected in circuit by-means. of relays Run and By. These relays are connected in parallel and to terminals I and 8 of the receiver through which they are 'energieed, as hereinafter described, according to the signal. frequency on which operation of the system is to be effected.

The be adi ted to the required value by. means of variable resistors RI and Rll in the cathode circuits of the valves VI and VI respectively and the output valve W of the receiver is biased to cut-oi! by means of a battery B. Thus, when no signals are being received, no current will flow in the output circuit of the valve V! but, on signals being received at the appropriate modulation signal frequency, the valve V. will pass current.

The anode of the valve or tube V1 is connected to a terminal H which is bridged to a terminal II in Fig. 8. The terminal 14 in Fig. 6 is connected to a contact a! of a relay Run. The contacts a! and al of. this relay are normally closed. The terminal 12 shown-in Fig. 6 is connected to the contact 03. The terminal I! of Fig. 8 is bridged tothe terminal I! in Fig. 7. The terminal I! in Fig. '7 is connected to the winding of a relay Ryll shown in Fig. '7. The other end of the winding of the relay Rull is connected to the terminal II which is connected to the terminal I! in' Fig. 8. The terminal il in Fig. 8 is connected to a contact 4a of a relay Hut. The contacts is and la of the relay Rel are normally closed. The contact la is connected to apositive terminal II of a high voltage supply. The relay Rgll is thus energized on signals of. sufiicient strength being received by the receiver.

The receiver is required to operate also in a comparatively insensitive condition and for this purpose the high tension current for the valves VI, V2, V3 and V4 is fed through a resistor Rll which, 101 normal operation is short-circuited by normally closed contacts lb and 2b of a relay Ry. The anode supply for these valves is applied through a terminal 5 which is bridged to a terminal I in Fig. 3. The terminal I in Fig. 3 is connected to a terminal I. in Fig. 3 through normally closed contacts of a relay Ry. a The terminal II in Fig. 3 is connected to the terminal II in Fig. 8 and' this terminal is connected to the positive terminal ii in Fig. 8 by R 35 and R3138 for controlling the connection means of the normally closed contacts is and 4a ormal sensitivity of the receiver may oi the relay R118. The anode oi the valve VI is connected to the terminal I in Fig. i which is bridged to the terminal I! in Fig. 8. Thus the anode oi the tube or valve ,Vl receives a positive potential irom the positiveterminal II in Fig. 8 through the normally closed contacts Ia and 4a. The cathodes oi the receiver tubes are oonnectedto a terminal II as shown in Fig. 1 and this terminal is connected to negative side oi' the high voltage supply. v r

Referring to Figure '1, a D. C.electric motor MI is arranged to operate a valve (not shown) to apply the brakes oi the train. Thismotor. is also arranged to rotate two commutators E and 1!, Y

The commutator F hasv diametrically opposite conducting'segments Si .and S! which are elec leased, through the .brushes BI and B2 and the commutator segment E2. The motor continues 4 to rotate until the segment E2 rides past the brushes BI and B2, or to the tion oi the segment El in Figure 'l, at the sametlme bringing the segment S2 oi commutator F into the position oi the segm'ent'Si as shown in Figure 7. The drive irom the motor is such that during this I 7 further rotation oi the commutators the braketrically bridged together and each extendingover oi the total periphery oithecomrnutator.

A stand-byelectric motor MI is provided also ior operating thevalve to apply the brakes'and this,

motor drives two commutators G and H oi'which the commutator .1! has diametrically opposite conductingsegments Hi and!!! .jbridgedtogfether and similar to the segmentssl and-'si'oritne commutator I". The commutator E has diametri- "cally opposite conducting "segments El and E2 and the commutator G has similar conducting segments GI and GIL Each oi these segments El, E2, GI andGlextends over 20% oi the periphery oi the commutator. In the position oi the motors Ml and M2 corresponding to the brakes being oii, brushes BI and Bi engage respectively the leading ends oi the segments Bi and 82 oi the commutator F and brushes B1 and Bl similarly engage the leading ends oi the seg-j ments HI and H2 oi the commutator H. Two brushes BI and B2 are arranged side-by-side'just past the training edge of the conducting segment El oi the commutator E and similarly two brushes B! and B0 engage the commutator G just behind the training edge 01! the segment GI. On the relay Bull being energized by a re-.

ceiv'ed signal itscontacts id and 2d are closed. and a circuit is completed irom terminal I operating valve is moved to the closed position l and the apparatus is ready ior a repetition oi its operation; A relay TDvRuIO is connected in parallel with the relay Bull, and on being'energised, operates with a time delay oi, ior example,

three to'iour seconds to close its contacts is and motor M! which is'also arranged to transmit a drive to the brake-operating valve in applying the brakes. Thus, should the main brake-operating' motor Ml iail to'operate, the application oi the brakes is assured and by the operation oi the stand-by brake-operating motor MI. Means may be provided ior rendering the stand-by brake operatlng motor MI inoperative when the main brake-operating motor Mi has operated to apply the brakes. ,With the operation oi .the stand-by brake-operating motor M2, the commutators G and H'driven thereby are rotated so that, when the brake-operating valve has been opened, the segments HI and H2 are moved clear oi the brushes B1 and BI respectively and the segment G2 oi the commutator G has moved to a position in whichv it nearly bridges brushes BI and BI. A

- tained, aiter the press-button is released, by the brushes BI and BI being bridged by the segment G1. Asin the case oi the main brake-operating motor Mi, the iurther operation oi stand-by motor M2 serves to return the valve tothe normally closed position and, in doing so, turns the commutators G and H to the position in which the j segment H2 occupies the position oi segment Hi Mi and the contacts to and 4c oi the relay 8112i back to the negative terminal 2.- The relay Rull being energised also closesv holding contacts ic and 20 to maintain the relay energised regardless oi iurther operation oi the reli y Rilll.

and B2 oi the latter pass beyond the brushes B3 and B4 respectively so as to open the circuit oi to the fully-open position to apply the brakes. In this position oi the commutators the segments El and El oi the commutator E are so arranged that the leading part 0! segment E2 is now just short oi a position bridging the brushes Bland BI. These brushes Bi and B2, when electrically bridged, serve to connect the motor Ml directly across the supply terminals i and I. A press-button switch P is connected in parallel with the brusheaBi and 55 The motor Mi continues to rotate and drives 1 the commutators E and 1" until the segments Si in Fig, l and the positions oi segments GI and G2 oi commutator G are reversed. The commutators vG and H are, thereiore, re-positioned ior a subsequent braking operation. It will be understood that the cornmutators E, F, G and H are rotated through ior each complete cycle operations oi the brake-operating valve.

A relay 'Rvlfl when energised closes contacts i l and, 2/ connected in parallel with the contacts id and 2d oi relay Ry". I This relay Ry" is connected by terminals Ha and "a to the output oi'a stand-by receiver which is a receiver oi the same form as that shown-in Figure 1 and is brought into operation as hereinafter described. Thus, the brake-operating motors MI and M2 may be put into operation either by relay Ryil or relay Rul9 being energised. A warning lamp RWL is connected in circuit with the contacts of, relays Evil and Ryls so as to give an indication when either of .these relays is energised.

For the purpose oi stopping the train ata predetermined location there is provided a photoelectric cell PEC3 associated with an amplifying valve V1 arranged to energise a relay R118 connectedin the anode circuit of .the valve. The anode circuit is completed through the commutators F and H to the positive supply terminal i and the cathode is connected directly with the negative terminal 2 of the supply. The relay R118, when energised, closes contacts lo and 29 serving to complete the circuits of the relays RyZi and TDyRyN. The photo-electric cell PEC3 is connected between the anode and a control grid of the valve V'l, the control grid being further connected by a terminal 1 to a source of control potential such as to bias the valve V1 to the cut-off. Thus, when the photo-electric cell PEC3 is energised, the valve V1 is made conductive to pass anode current through the relay RyG to effect this operation and, in consequence, the operation of the brakes of the train in the .manner hereinbefore described.

Referring to Figure 2 of the drawings, the transmitter of the train installation comprises a master oscillator V8 controlled by a quartz crystal Q which conveniently operates at onehalf of the required carrier frequency. The carrier frequency is selected by a tuned circuit Til in the anode circuit of the valve V8 and is applied through a resistance capacity coupling to an amplifying valve V8. The output of the valve V9 is applied through coupled tuned circuits TH and T18 to an output valve VII having a tuned output circuit T]! which is coupled to a feed coil connected to terminals l8 and Il as shown in Fig. 2 and these terminals are bridged to terminals i9 and 20 in Fig. 6 which are connected, under the control of relays R313! and R 136, to an antenna system connected to terminals i 7 and it (Figure 6). The anodes of the valves V8 and V9 are connected through terminal 26 (Figures 2 and 5) to the positive pole of a high tension supply. The valve Vl is shown as having a directly heated cathode of which the electrical centre is connected to the cathodes of the valves V8 and V9 and through terminal ib (Figures 2 and 5) to the negative pole of a high tension supply for the transmitter.

The transmitter is modulated by modulation signals applied to the electrical centre of tuned circuit Tfl via the terminal 21. This terminal 21 (Figures 2 and 4) is connected from the secondary winding of a modulating transformer "T30, terminal 4 (Figures 4 and 5) to the positive pole of a high tension supply for the output valve Vii) of the transmitter.

In Figure 4 there is shown modulating means for two frequencies corresponding to the frequencies of the filters Fl and F2 of the main receiver. The modulator comprises a valve oscillator Vi I having an oscillating circuit comprising an inductance L and either a condenser C or a condenser CI in parallel therewith. The

selection of the condensers C and C l is effected by a relay R115 of which contacts ill and 271. are normally closed connecting the condenser CI in circuit for the production of a modulation frequency of, say 10 kilocycles. When the relay R115 is energised relay contacts Hz and in are opened and relay contacts 2h and in are closed connecting the condenser C in circuit for producing another modulation frequency of, say, 85 kilocycles. The valve Vii is coupled by means of a resistance coupling to a valve Vl2, this, in turn, being coupled by means of a transformer Tl l to a further amplifying stage comprising valves W3 and Vi connected in push-pull. The output of this stage is applied through a transformed coupling T2 to a push-pull output stage comprising valves W5 and Vii feeding the primary winding of the transformer T1. The valves VI i, VII and VII of the modulator have their anodes connected through terminal I! (Figures 4 and 6) to the positive pole of a high tension supply, the cathodes of the valves being connected through terminal I! (Figures 4 and 6) to the negative pole of the high tension supply. The relay R 15, which controls the modulation frequency is connected through terminals 2 and 3 (Figure 4) to means for effecting a change of modulation signal frequency, as hereinafter described.

The power supply for the transmitter and modulator is derived from the power supply means illustrated in Figure 5. In Figure 5 an alternating current supply applied to terminals II and ii feeds the transformers T800, T4", T5" and TI" through normally closed contacts 8!: and lie of a relay Ryl. The output for the transformer TIN is applied through terminals 28 and 2! (Figures 5 and 2) to the directly heated cathode of thetransmitting valve Viii. The transformer T4" feeds a rectifier Vil applying, through a smoothing circuit LICI, L404, a high tension supply through terminal 20 (Figures 5 and 2) to the valves VI and VI of the transmitter. The transformers TI and T8" feed a rectifier comprising valves VII and Vi! for providing a high tension supply applied through a smoothing circuit LlCl, LICZ through the terminal 4 (Figures 5 and 4) to the anode of the transmitting valve Vil by way of the transformer T30 of the modulator. A relay TDgR N, operating with a time delay. serves to close its contacts lm and In. which are in circuit with the primary windings of the transformers TI and TI", so that current is only supplied to these transformers after the valves of the transmitter have reached the required operating temperature. The circuit through the primary of the transformer Till is also controlled by contacts In and In and In and in of relays Ry and Ry connected in a circuit from the positive terminal 2 of the D. C. supply, through the relays Ru and R11 to terminal II (Figures 5 and 8) through normally closed contacts la and 2a of relay R118, through terminal 24 (Figures 8 and 6) and after described for controlling the alternate operation of the transmitter and receiver.

The supply to the transformers T3, Till, T5" and Tilili is effected through normally closed contacts 87c and k of the relay Rvl and this relay, when energised opens this pair of contacts and closes another pair of contacts 4k and II: to apply the A. C. supply to a stand-by high tension supply apparatus like that shown in Figure 5. The relay Ryl is energised through the terminal I for the positive pole of the D. C. supply terminal 23 (Figures 5 and 6) and control means, hereinafter described with reference to Figure 6, and on being energised also closes contacts ik and 2! connecting the relay Ryi directly across the terminals i and 2 of the D. C. supply.

A high tension supply for the receiver and modulator is obtained through a transformer TIA (Figure 6) of which the primary winding is connected through normally closed contacts In and 3p of a relay R11 to terminals iii and ii for the A. 0. supply. The secondary winding of the transformer TIA feeds a rectifier V20 from which the D. C. output is applied through a smoothing circuit L503 and L5G! to terminal ii to the receiver and modulator as hereinbefore described, the negative pole of the high tension supply bethrough means herein ing connected through terminal IE to the cathodes of the valves of the receiver and modulator. When energised, as hereafter described, R1134 opens its contacts 2p and 3p and closes contacts In and 2p to connect the primary another transformer TIA to the supply. The secondary of this transformer feeds another valve rectifier V2l of which the D. C. output is applied through a smoothing circuit LTC'I and L8C8 to a,. terminal lid for connection to the stand-by receiver and modulator (not shown).

Each train is provided with the, transmitting and receiving apparatus .herelnbelore described and, for single track operation, a single modulation frequency is employed. As" one train approaches another the field strength of a transmitter in one of the trains increases at thereceiver of the other train and, when it reaches a value predetermined by the sensitivity of the receiver, Rylt or Rul! or the braking apparatus becomes operative to apply the brakes and stop the train. The distance apart of the trains when the brakes become operative is dependent upon the requirements of the railway system and may, ior example, be 1,200 yards. Thus, in this case, having regard to the power of the transmitter, the sensitivity of the main receiver would be such as to effect an operation of the brakes by reception of the transmission when the trains are this distance apart.

In order that the transmitter shall not interi'ere with the operation or the receiver of the same inc allation, th transmitter is energised periodically for instance, for periods of 4 seconds separated by non-operative intervals of 4 seconds and the receiver is operated with reduced sensitivity, as hereinbeiore referred to during the periods of operation of the transmitter. The operation 01' the transmitter and receiver are controlled by means of a keying motor MI (Figure 6) which rotates two commutators A and C at a speed of one revolution per 8 seconds. The motor is connected to D. C, supply terminals I and 2 through a relay R112! and normally closed contacts lr and 2r of a relay R1128. These commutators each have a single conducting segment, the segment of commutator A extending through 50% or the circumference and that oi commutator C through a lesser angle, for instance 40% of the circumference. The commutator A co-operates with brushes Bill and EH and the commutator C with brushes Bl2 and BI 3 and the arrangement is such that the conducting segment 01 commutator A electrically connects the brushes Bill and BH for an interval before the brushes Bl2 and BI! are connected by the segment of commutator C and for an interval after the brushes Hi2 and Bit leave the conducting segmentot the commutator C. The commutator A renders the transmitter operative and reduces the sensitivity of the receiver during the one-halt 01' each revolution in which its conducting segment bridges the brushes Bill and BI l. The commutator C serves to bring the stand-by apparatus into operation should a fault occur. During the period in which the brushes are not bridged by the conducting segment of the commutator A the receiver is operative with its normal sensitivity. It is connected by terminals 2| and 22 (Figures 1 and 6) through normally closed contacts 4s and Us and Is and 23 of relay R112 and normally closed contacts'4t and It and It and 2t of relay Ry" to the antenna terminals l1 and II. The high tension supply is also provided and the output of the receiver includes the brake-operating relay By".

The brushes Bil and Bl2 are electrically con nected together and are also connected through normally closed contacts 3w and 420 of a relay Ry and normally closed contacts l1: and 2;! of a relay TDyR-y29 to the terminal I for the positive pole of the D. C. supply. The relay TDyRyZS is connected across the D. C, supply and 01erates with a time delay after .the installation has been switched on to close its contacts ly and 2y. When the brushes Bill and Eli are electrically bridged, a circuit is completed throu h terminal 24 of Fig. 6 to the relay R1 24 01 Fig". 1 to terminal 2 for the negatve pole of the D. 0. supply. Another circuit is completed through terminal 24 of Fig. 6 and normally closed contacts la and 2a of R119 in Fig. a terminal 25, relays R1139 and Ry" in Fig. 5 back. to terminal 2 or the D. C. supply. A further circuit is completed from the brushes BIO and Bil through relays E4132 and R1138 direct to terminal 2 (Figure 6) .By Ru and R1140 in Fig. 5 being energised, their contacts are closed to complete the circuit or the transformers T400 and T600 through contacts in to 4n and the contacts lm and 2m of the relay TDuRyJB normally closed during operation or the system. The high tension supply from terminals 4 and 26 thus becomes available and is applied, as hereinbefore described, to the transmitter to enable it to operate. The modulating means, being in operation, the modulated carrier wave signal is propagated by the transmitter. Relay R 136 being energised closes its contacts 2s and Is, and 5s and is to connect antenna terminals l1 and I! through normally closed contacts It and 2t and 3t and 4t respectively or a relay R1135 to terminals l8 and 20 oi the trans,- mitter. v

0n R1132 being energised its contacts a2 and al are opened to interrupt the output circuit of the receiver through the brake-operating relay Rulfl and, by closing of its contacts al and a2, completes another output circuit 01. the receiver from terminal l4 (Figures 1 and 6) through a relay Ru3l to the terminal la the high tension supply. By relay R1124 being energised, its contacts lb and 2b are open to decrease the sensitivity of the receiver as a result or the resistance of B being introduced into the circuit and this reduced sensitivity is such that the receiver output is sufficient to operate Rz/3l by the output derived from the transmitter oi the same installation only it the installation is otherwise operating with proper elliciency.

As rotation of the commutators A and C proceeds, the brushes Bl2 and Bl3 are bridged by the conducting segment of commutator C and a circuit is completed through a relay R1130 causing its contacts is and 2a to close, thus connecting the brush Bl2 with contact la: oi Rull. Should there be any defect in the transmitter or the receiver, rendering either or them ineflicient or inoperative, the output of the receiver will not be suflicient to energise the relay Ry3l so that its contacts la: and 21: will remain closed and thus connect relays R1133, R 28 and Ry! (Figure 5) in circuit with the terminals I and 2 oi? the D. C. supply, Ryl being connected to these terminals through terminal 23 (Figures 5 and 6). Ry" will remain energised by the closing or holding contacts lw and 2w and Ryl (Figure 5) will also remain energised by the closing 01 its holding contacts I]: and 2k. Moreover, R1128 is maintained energised being in circuit with the holding contacts of relay Rul R 28 being energised, opens its contacts I r and 21- and closes its contacts 2r and 31' thus connecting a standby keying motor M4 to the D. C. supply and disconnecting the motor M! from the supply. Ry33 being energised, its contacts 3w and 4w are opened to interrupt the circuits of Ru, Run, R1136, R113! and R1140 restoring the condition for normal reception. Contacts 4w and 5w of relay R 33 are closed to complete circuits through relays R113 and R1135. R1134 thus being energised opens its contacts 2p and 3p and closes its contacts ip and 2p so that the transformer T2A of the stand-by receiver high tension supply unit is energised to put the standby receiver into operation. Relay Ryi on being energised closes its contacts 41: and 5k to connect the A. C. supply to a stand-by power supply apparatus for ieeding the stand-by transmitter and modulator so as to bring these into operation. R1135 on being energised, opens contacts It and 2t and 4t and 5t and closes contacts 2t and 3t and 5t and it to transfer the connection of the antenna feeders i1 and I8 from the control relay R 138 to a stand-by antenna control relay R1131. This relay R1131 performs the same functions as the relay Rm! for the stand-by apparatus, serving to change the antenna connections from transmitter to receiver.

The motor M4 drives a commutator Z, serving to bridge brushes Bil and BIS. This commutator serves to render the stand-by transmitter alternately operative and inoperative in the same way as th commutator A for the primary apparatus. The brush BIS is connected through contacts 410 and 5w, now closed, of relay R1133 and contacts ly and 23/ of relay TDyRyZS to the terminal i of the D. C. supply, the circuit being completed, when the brushes are electrically bridged, from Bil through relay means not shown for eiIecting the change over in stand-by transmission and reception. The circuit of the relay R1131 controlling the antenna connections for stand-by operation is also energised under the control of the commutator Z and brushes Bil and BIS. The relay R1121 is energised by current taken by the main keying motor M3 so that should any defect develop causing fuses in the circuit with the motor to fail, the relay is deenergised to bring the stand-by apparatus into operation.

Thus, summarising the operation of the apparatus, as so far described, the transmitter of the installation operates for alternate periods of, say 4 seconds under the control of the commutator A. If the receiver is energised by an incoming signal from the transmitter of another installation within a given distance, the brakes are operated to stop the train. During the period of operation of the transmitter the receiver operates with less sensitivity such that the pick-up transmitter provides an output which is of the same order as the output which would be obtained from the receiver on receipt of signals from another installation at such a distance away as to operate the brakes. However, during the transmission period, the output of the receiver is not applied to operate the brakes but is directly connected to a monitoring relay Ryii which serves to maintain the normal operation of the system. Should either the transmitter or the receiver fail to perform adequately, this relay, being energised, brings the stand-by apparatus into operation. It would be very improbable that any two installations would operate with their periods of transmission coinciding in time but any such possibility may be overcome by effecting a changeover of operation by the commutator A at different intervals for diiiferent installaitons. When it is required that the train shall be stopped at a specific location a light source may be provided at the side of the track to operate the photoelectric cell PECI of the train installation so as to operate the brakes in the manner described with reference to Figure 6 and independently oi the receiver.

It is possible that a strong signal, even though not coming from another train installation on the same track, may be sumcient to cause the application of the brakes and such a signal may, for example, be caused by a lightning discharge or be produced by a train passing on an adjacent track. For instance, if the installation of one train is working on .85 kc. and the other on 10 kc., the filters provided in the receiver may, due to the very large field strength provided when the trains are passing, produce sumcient output to' actuate the brakes. In order to avoid this possibility there is provided an auxiliary receiver. as shown in Figure 3. This receiver comprises a radio frequency amplifying valve VI! to which alternative antennae AI and A! may be connected, a valve detector V2! and a modulation signal output valve V, in the output circuit oi which there is included the winding of a relay Ryll. The valve V24 may be biased by a battery BB to the cut-oil. When, on a signal being received, Ryi is energised and contacts IR: and 47: are open to interrupt the high tension supply circuit to the valves Vi to V4 of the main receiver. The relay RI is also provided with other contacts H: and 2k which provide a similar control for the stand-by receiver hereinbeiore referred to.

The auxiliary receiver is controlled, as regards sensitivity, for example, by means oi resistances R2: and Ru so that no current flows in the output circuit of the valve V as a result oi signals received from the installation on another train on the same track at a distance of, say, greater than 900 yards. With trains approaching on the same track, when this separation is reached, the brakes will have already been applied but, with trains passing on adjacent tracks, should the signal strength at the main receiver trains pass within this distance to a value which the brakes, this auxiliary receiver comes into operation to deenergise and thus safeguard the main receiver and, moreover, prevent the brakes being applied under such circumstances.

In the case of a railway system having more than one track, in which a train is required to pass from one track to another, means is provided automatically to change the signal frequency on which the apparatus works from that allocated to one track to the frequency allocated to the other track. This change of modulation signal frequency is controlled by photo-electric devices operated by means 01 light sources arranged at the side 01' the track.

In Figure 1, the relays Run and Ryil are de-energised and so connect the filter F2 operating at say 10 kc. in circuit. Similarly, in the modulator shown in Figure 4, R is de-energised and relay contacts In and 2h are closed completing the tuned circuit Lcl also for a irequency 01' 10 kc.

For a change-over oi the filters of the receiver and the frequency oi the modulator to the other signal frequency 0! say .85 kc., the train installation comprises (as shown in Figure 9), a photoelectric cell PECI connected across the anode and grid of a thermionicvalveVilthe cathode of the valve being. connected through the termi-- nal i to the. negative pole of the-.D.'C. supply- The positive pole, which is connected to terminal .i, appliesa positive potential through normallyclosed contacts mi and :sioii a relay B d and through a relay Ruilto the' anode of the valve Vii. Thevalve is arranged normally to-benonconducting. When. energised, the photo-electric cell PEClapplies' apositive potentialto the grid of the valve V25 and:current=ilows through the winding of Ri/ii thereby'closingthe contacts zi,

zi and 23, a4 01 this relay. Current is therefore applied from the terminal. i, contacts :4 and 2i of R1!" to energise a relay'Rul' through normally closedcontactswi and mi 01a relay By.

A circuit is also completed through-thecontacts of R 12! and terminal i energising Rut shown Referring again to. Fig. 9, the relay R110 is provided withholding contacts ti and ti com pletingthe circuit of Ru! through the normally ciosed'contacts of Evil so that, although Rid! may become de-energisedRul is maintained energised whiletherequiredisignal frequency is .85 kc. For efiecting a change back to the first modulation signal frequency another photo-elemtric cell PECI-is provided associated with a valve Vil inthe same way'as'the photo-electric cell PECl is associated withvalve Vii. The anode" of the valve -Vi0-is connected' through R1126 and contactsti and vid of Rul,1through terminal I to the positlve'pole of the D. C. supply,'the cathode being connected through terminal i to the negative pole. Thephoto-electric cell PECB is'energised by means of a light-source'suitably disposed at the sideof'the traclcand, when so energised, causes current tofiowin the anode circuit or the valve Vit thus energising' Ru" and opening its contacts. The opening of contacts wi and wi 01 Rui'i opens the-circuit of R114, thereby opening the anodeccircult of thevalve V2 and opening the circuit-otfRutiforchanging the tuned signal circuit backto *k'c. The valves V and Vi may be of the gas-filledtypewhich, having been set in operation, require their anode circuits to be interrupted inorderto restore the original 'operatingconditions. The provision oi such valves ensures that R. has operated its holding contactsandinterruption of the anode circuits is efi'ectedby arelay TDuRui coming into operation after, say, iseconds and closing contacts di and di incircuit' with Ryi and thereby interrupting the supply to the valve Vil throughRyiI. The-circuitot the valve Vii will be interrupted-by R114 being energised, as Moresaid.

The train installation comprises three devices,

as shownin Figure 9; one '1 tor controlling. the

change-over irequencyior the modulation oi the transmitter, as hereinbeiore described, another ior'controlling the chansemveroi the filters FI and F2 oi the receiverandyetanother'for'eflecting the change-over in the modulator and the receiver filters oi-the stand-by apparatus. In this way a high factor oi-saietyisachieved.

A rurth'er arrangement'oi' photo electric cells 70:- is provided in the train installation for rendering the transmitter and receiver inoperative in sta-- tions. For this purpose thereareprovided, as shown in Figure 8, an electric motor Ml driving two commutator: D and-K". The commutator D has a conducting segment Di extending through of its periphery and the commutator K has a conducting segment Ki extending through 15% of its periphery. Cooperating with the commutator D there are two pairs or brushes Bil, Bil and Bit, B20, the two pairs being diametrically opposite one another. Co-operating with the commutator K there is a single pair oi brushes Bil and 322. The arrangement is such that, when the brushes Bii and Bii are on the conducting segment Ki oi the commutator K, the brushes Bi! and 1320 are disposed between the ends of the conducting segment Di of the commutator D. A photo-electric device PECi con- 1 trols the operation of the valve Vi'l and another to the anode oi the valve, the cathode oi the valve being connected through terminal 2 to the negative pole of the D. C. supply. On being energised, Rz/l closes its contacts 00 and 00 to complete a circuit energising the motor M8, also through the brushes BIO, B20. The motor thus rotates the commutators D and K until the insulating part of the commutator D, between the ends of the segment Di, comes into register with the brushes Bit and B20 thus interrupting the motor circuit. A circuit is, however, now completed from terminal i through brushes Bil and B22 short-circuited by the segment Ki or the commutator K and through Ry! back to the terminal i. This relay R110, on being energised, opens its contacts iaand ia which are connected through terminals 20 and ii 01' Fig. 5 to open the circuit of the primaries of transformers T400 and T000 for the high tension supply to the trans- The opening of contacts to and la 0! through terminal I! Fig. l interrupts the high tension supply to the receiver.

On leaving the station, a light source is arranged to energise the photo-electric cell PECI causing current to how in the anode circuit of valve Vii from the terminal i connected to the positive pole oi the D. C. supply, through R111 to the anode of valve Vii, the cathode being connected through terminal 2 to the negative pole oi the D. C. supply. R111, by being energised, closes its contacts pi and pi and completes a circuit through brushes BH and Bit, which at this time will engage with the conducting segment Di oi the commutator D, and through contacts of R111 to again energise the motor M0. The motor thus rotates the commutators D and K through another revolution and then the motor circuit is broken by the insulating part of the commutator D arriving beneath the' brushes Bil and Bit. Also the conducting segment K i will have moved away from the brushes Bil and Bii to its original position, thus deenerglsing R119 and closing its contacts, thus restoring the transmitter and receiver to the operating condition. Press-button switches FBI and .932 may be provided in parallel with the contacts of R111 and R118 respectively for manual operation in case oi an emergency. Thus, the photo-electric cells PECi and PECi ceiver to put them out 01' operation on the train entering a station and to reinstate them in operation on the train leaving the station. The grid electrodes of the valves associated with the photo-electric cells are connected through a terminal 1 to a source of biasing potential such as to render the valves normally non-conducting.

As shown in Figure 10, the photo-electric cells may conveniently be housed in recesses in the cars of a train directed downwardly for control by light sources indicated at Ltl, L132, L153 and Lil at the side of the track. Thus, the photoelectric cell PEC3 and stand-by cell 3A may be arranged for operation by a light source Ltl, the photo-electric cells PEG! and PEG! for disconnection and connection of the transmitter and receiver may be arranged for operation by the light source Lt? at a. different height, the photoelectric cells PECl at one level for operation by the light source Lt3 at another height and the photo-electric cells PECS for introducing the other modulation signal frequency are in line for operation by the light source Lt at yet another height. It will be understood that the light source Lti to Ltd will be arranged at standard heights throughout the train systems.

Arrangements of the light sources on the track are shown in Figures 11 and 12. In Figure 11 there is shown a portion of a. railway system in which a track M runs into another track N. In this case, alongside the track M, at a suitable distance from the points, light sources Lt3 are arranged at the height necessary for operating the photo-electric cells PEG for changing the modulation signal frequency from that allocated to track M to that allocated to track N.

In Figure 12 there is shown a track section comprising a loop at a railway station. In this case. at a distance of, say, 500 yards from the points at each end of the loop, light sources Ltl are provided for energising the photo-electric cell PEC3 or stand-by PECSA of the train installation to apply the brakes should there be a train already in the station on the required track. At each end of the station area of both the loop and through tracks, there is provided light sources LtZ for energising the photo-electric cells PECI and PEC2 for dis-connecting the transmitter and 'receiver as the train enters the station section and re-connecting them for operation as the train leaves the station section.

The light sources Ltl, (Figure 12) may be controlled by photo-electric cell detectors on the track within the station area. These detectors may consist of a pair of light sources J at each end of the station section spaced apart along the tracks. the spacing being less than the length of any truck or carriage which is employed and cooperating wlth photo-electric cells PEG! and PEC8 arranged at the opposite sides of the two tracks. The photo-electric cells are employed to control light sources Lti in order to extinguish these light sources when there is no train in the station section so that, under these conditions, the brakes of the train are not automatically applied.

In Figure 13 there is shown an apparatus for controlling the light sources Ltl by means of the photo-electric cells PEG? and PEC8 according to the position of the points. For each end 01' the station section each photo-electric cell PEG! and photo-electric cell PECB is connected in circuit respectively with valves V30 and V29 having in their anode circuits relays R1120 and Rylfl, such that light falling on the photo-electric cells produces an increase in valve current. The relay 7 switch Pl closed by the points when they are set to open the straight track through the station section. The relay R1120 when energised closes its contacts fl and f2 to complete a circuit with the relay R1150 and a switch P2 closed by the points when they are set to open the loop through the station section; The relay R1150 when energised closes contacts It! and kl for completing a circuit to energise the light sources Lti beyond the station section. Thus, if a train occupies the straight or loop tracks of the station section the light from the source J on to photo-electric cells PECI or PEC8 as the case may be is interrupted and the corresponding relay Rylll or R1120 is energised. Ii, at the same time, the points are set to open the same track on which the train stands, the relay R1150 is energised to operate the light source Ltl which serves to apply the brakes 01. an approaching train, as hereinbetore described. The relay Ryfll may be provided with additional contacts kl and k2 in circuit with a warning lamp W and switches 80 and 10 may be provided in circuit with the contacts kl and kl for emergency control or the light source on the track.

What we claim is:

l. A railway-train control system comprising for each train an electric wave signal transmitter and an electric wave signal receiver. brakes for each train, means for rendering the transmitter and the receiver alternately operative, and means controlled by the signal output of the receiver of a train due to signals received from the transmitter of another train, on reaching a predetermined strength due to relative approach of the trains. to apply the brakes of the train.

2. A railway train control system as claimed in claim 1, including means for rendering the receiver operative with decreased sensitivity during periods of transmission from the same train, and means operated by the output of the receiver as a result of signals received from the trans: mitter on the train to determine the efficiency of operation of the control system.

3. A railway train control system comprising, an electric wave signal transmitter and an electric wave signal receiver carried by each train, brakes for each train. means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a. predetermined strength present in the receiver of one train from the transmitter 01 another train resulting from the relative approach of the trains for applying the brakes of the trains, and standby means for applying the brakes of the trains upon failure of the last mentioned means.

4. A railway train control system comprising, an electric wave signal transmitter and an electric wave signal receiver carried by each train, brakes for each train, means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a predetermined strength present in the receiver of 'one train from the transmitter of another train resulting from the relative approach or the trains for applying the brakes of the trains, an auxiliary signal receiver carried by each train, and means controlled by the output of the auxiliary receiver for rendering the first receiver inoperative to incoming signals of a strength greater than a predetermined value.

5. A railway train-control system comprising an electric wave signal transmitter and an electrio wave signal receiver carried by each train, brakes for each train, means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a predetermined strength present in the receiver of one train from the transmitter of another train resulting from the relative approachct the trains for applying the brakes of the trains, means for altering the frequency of signals emitted by the transmitters ot the trains when the same pass from one track to a second track, and means rendering the receivers carried by trains passing onto the second track responsive to said altered frequency.

6. A railway train control system comprising, an electric wave signal transmitter and an electric wave signal receiver carried by each train, brakes for each train, means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a predetermined strength present in the receiver of one train from the transmitter 01 another train resulting from the relative approach of the trains for applying the brakes of the trains, light responsive means carried by each train for rendering the transmitters and receivers inoperative, and a light source adjacent the track for controlling said light responsive means.

7. A railway train control system comprising, an electric wave signal transmitter and an electric wave signal receiver carried by each train, brakes for each train, means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a predetermined strength present in the receiver of one train from the transmitter of another train resulting from the relative approach oi. the trains for applying the brakes of the trains, light responsive means carried by each train for rendering the transmitters and receivers inoperative, a light source adjacent the track for controlling said light responsive means, means for detecting the presence of a train in a track section on which the transmitters and receivers are inoperative, and a light source adjacent the track remote from said section controlled by said detecting means for rendering the second mentioned means carried by an approaching train operative to apply the brakes.

8. A railway train control system comprising, an electric wave signal transmitter and an electric wave signal receiver carried by each train, brakes for each train, means rendering the receiver and transmitter of each train alternately operative, means responsive to signals of a predetermined strength present in the receiver of one train from the transmitter of another train resulting from the relative approach of the trains for applying the brakes of the trains, stand-by means for applying the brakes, and time delay means for rendering said stand-by means operative at a predetermined interval after failure of said second mentioned means.

ERROL DU PREEZ ERASMUS. OLIVER WALTER REID.

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