US2331134A - Railway signaling system - Google Patents

Description

Oct. 5 19,43.l F; H. NICHOLSON ET AL. 2,331,134

RAILWAY S IGNALING SYSTEM Filed July 30, 1942 Patented Oct. 5, 1943 RAILWAY SIGNALING SYSTEBI Frank H. Nicholson, Penn Township, Allegheny County, and Crawford E. Staples, Pittsburgh, Pa., assignors to The Union Switch & Signal Company, Pennsylvania Swissvale, Pa.,

a corporation of Application July 30, 1942, Serial No. 452,894

13 Claims.

Our invention relates to railway signaling systems of the type employing coded energy in the track circuits thereof.

In signaling systems of the type employing frequency code it is customary to employ energy of 75, 120 and 180 code frequency to provide three distinctive proceed indications. These are adequate for most situations, but in some cases it is desired to provide another or fourth proceed indication.

It is an object of this invention to provide improved means for producing an additional indi cation in a coded signaling system.

A further object of the invention is to provide apparatus arranged so that when locomotives equipped with cab signal apparatus arranged to providev three proceed indications are operated over stretches where the wayside apparatus is arranged to provide four proceed indications, the locomotive cab signal equipment will operate at all times to provide an appropriate indication.

Another object of the invention is to provide a signaling system of the type described which will not interfere with the operation of a lockout eircuit if such a circuit is employed.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawing.

In practicing our invention we provide means for at times modifying the energy of '75 code frequency by substantially reducing the length of every third oi period in the code and correspondingly increasing the length of the succeeding on period. Means are provided to detect this special code, including a slow release detector relay to which an impulse of energy is supplied on release of the track relay contacts and which has a release period such that it remains picked up during the short off period but not throughout an ofi period of normal length. In addition, energy is supplied to this detector relay over a stick circuit if the relay is still picked up when the track relay contacts pick up again. When the contacts of the track relay and of the slow release detector relay are picked up, a circuit is established to supply energy to a second slow release relay which is sufliciently slow acting to remain picked up during the intervals between the short off periods in the modified code.

We shall describe one form of apparatus embodying our invention, and shall then point out the novel features thereof in claims.

In the drawing,

Fig. 1 is a diagram of a stretch of railroad track equipped with one form of signaling apparatus embodying our invention, and

Fig. 2 is a diagram of the modified coded energy employed in the system of this invention.

Referring to Fig. 1 of the drawing, there is shown therein a stretch of railroad track over which traffic normally moves in the direction indicated by the arrow, that is, from left to right. The track rails I and 2 of the track stretch are divided by insulated joints 3 into track sections for signaling purposes.

Electric current may be employed for propulsion purposes and where this is so alternating current energy is employed in the track circuits, and impedance bonds 4 of the customary form are provided to conduct the propulsion current around each pair of insulated rail joints. As the description proceeds, however, it will be apparent that the apparatus of this invention is equally well suited for use on a steam road in which either direct or alternating current may be employed in the track circuits, while the impedance bonds may be omitted.

In addition, as impedance bonds are employed the signaling apparatus includes means to check the insulated joints. As here shown, this means is the non-cascading lockout circuit of United States Patent No. 2,235,134 issued March 18, 194i, to Leslie R. Allison and Frank H. Nicholson. If our present invention is employed in a track stretch where impedance bonds are not required, the portions of the signaling apparatus relating to the lockout circuit may be omitted.

Similarly, the decoding means provided by this invention for detecting the modified code is not limited to use in wayside apparatus but may be incorporated in cab signal apparatus foruse on locomotives.

In the diagram forming Fig. l of the drawing one complete section I2T and parts of the two adjoining sections l IT and 13T, are shown. Each of these sections has located at the entrance end thereof a signal S for governing trafiic in the track stretch. The signais illustrated are of the familiar color light type and each signal has an upper and a lower portion each of which has a green, a yellow and a red lamp. The invention, however, is not limited to the use of signals of this type and any appropriate form of signal may be used. Likewise, the invention is not limited to a system employing wayside signals, but is equally applicable to track stretches without waysidle signals and having provision for cab signals on y.

The rails of each track section form a part of stretch by a transmission line, not shown. The

terminals of the power supply source are designated BX and CX, and it will be assumed that the energy supplied from this source is alternating current of a frequency of 60 cycles per second.

The signaling system shown in Fig. 1 makes use of track circuit energy coded at four different y This coded energy is provided by frequencies. code transmitters CT which interrupt the supply circuits for the associated track transformers a definite number of times per minute according to traiiic or other conditions ahead. As'shown,.

each code transmitter is provided with four circuit making and breaking contacts which are continuously actuated by a motor or other suitable mechanism. The rate of operation of the contacts l5, llEl and i8@ is such as' to provide 75, 120 and 180 energy pulses per minute, respectively,y which are separated by, periods of equal duration in which no energy is supplied.

Each code transmitter has another contact designated M which is so operated asv to produce two cycles of coded energy of 75 lcode frequency in which the on and off periods are of approximately equal duration, while every third code cycle is modified in suchv manner that the-off period is much shorter than normal and the length of the on periodV is correspondingly increased. The pattern of this code is shown in Fig. 2. Since the distinguishing characteristic of the 75M code occurs in every third code cycle of the 75 code, the '75M code is in eiect energyof 75 code frequency modulated 25 times a minute.

The details of construction of the code transmitters to cause them to produce the '75M code are not a part of this invention. However, this special coded energy may be generated by cam wheels of suitable design such as those shown in United States Patent No. 1,861,488,V issued June '7, 1932 to Leslie A. Allison and Frank H. Nicholson. v

Each track circuit includes a code following track relay connected across the section rails at the entrance end of the section. As shown, the relay IZTR is of the direct current type and is connected to the track rails through a resonant rectier unit IZRU. e This unit includes a transformer, a capacitorv and a reactor so arranged and proportioned as to freely pass cycle signal control energy but so as not to pass propulsion current of a different frequency. The unit RU includes, in addition, a rectifier which converts into direct current the alternating current supplied through the unit.

The track relay iZT?. has associated therewith auxiliary relays lZFSA, IPZBSA, IZHA, IZHB, 12K, |2J and l 2TRB, a decoding transformer IZDT, and a timing unit IZTU, while each of the other signals in the track stretch has associated therewith equipment corresponding to that associated with signal IES. l

Each signal also has associated therewith a source of direct current, such as a storage battery, not shown, the terminals of which arey designated B and C.

The equipment is shown in the condition which it assumes when the track stretch is vacant.v At

such times energy of 180 code frequency is sup-' plied to the track transformer NTT by theeqilipment associated with section 13T. The equipment for section IBT operates in the same manner as that for section IZT.

The coded energy Supplied to track transformer l2TT feeds to the track relay ITR and produces code following operation of this relay. As a result of operation of the relay EETR, energy is alternately supplied to the two portions of the primary 2li of transformer IZDT from the direct current source. During the picked-up periods of the track relay contacts energy is supplied from the transformer secondary winding 22 to the pick-up winding of the relay lEFSA over the circuit established by the track relay contact I6, while during the released periods of the track relay its contact i6 establishes a snubbing circuit for the relay IZFSA to keep the contacts of the latter relay picked up during the off periods in the code.

When the track relay contacts are released, energy is supplied to the relay I2BSA over a circuit which includes back contact Il of the track relay and front contact 26 of the relay IZFSA, while contact 26 also connects a snubbing resistor 28 across the terminals of the winding of relay IZBSA to make it slow in releasing.

At this time the relay IZHA is energized by current supplied over its stick circuit which is traced from terminal B through its own front contact 29, front contact 3i) of relay ZBSA, winding of relay I2HA and back contact i6 of relay l ZTRB to terminal C. A resistor 32 is connected across the terminals of the winding of relay IZHA to make the relay slow to release.

The relays IEK and I2J are energized from the decoding transformer through resonant units IZUDU andv lSDU, respectively, which include inductances and capactances arranged and proportioned to permit energy to ilow freely through the units when the frequency of the current supplied thereto is that which is present when the track relay is responding to energy of 120 and 180 code frequency, respectively, Vand to substantially prevent flow of energy at other times. 'Each of these units also includes arectier for rectifying the energy supplied through the unit. Y

As the track relay is responding to energy of 180 code frequency, energy is supplied through the unit ISEBDU to relay |2J and its contacts are picked up. Accordingly, contact 32 of relay I2J interrupts the circuit through which energy is supplied to the timing u nit l2TU, and as a result energy is not supplied from this unit to the relay IZTRB and its contacts remain released so that the contacts 0f relay IEHB also remain released.

As relays I2HA and I2J are picked up, energy is suppliedyto the upper green lamp G of signal 52S over a circuit which includes front contact 34 of relay IZHA and front contact 35 of relay IZJ, while energy is supplied to the lower red lamp R of this signal over a vcircuit which includes front contact 36 of relay i2I-IA and front contact 38 of relay l2J. Accordingly, the signal 12S displays a green over a red light which is its clear or least restrictive indication.

At this timeenergy 0f 180 code frequency is supplied to track transformer HTT over a circuit which is traced from terminal BX through contact H of the code transmitter IZCT, front contact 40 of relay 12J, front Contact l2 of relay IZHA, front contact 1&3 of relay IZBSA, front contact 44 of relay I2FSA, and the primary winding of the track` transformer IITT to terminal CX. Accordingly, energy of code frequency is supplied ,to the .rails of section l IT and the signal for that section is caused to display its clear indication.

When a train moving in the normal direction of trafficenters section I2T, the track relay I2TR is shunted and relay IZFSA releases so that its contact 26 interrupts the supply of energy to relay IZBSA and also interrupts the snubbing circuit for this relay, with the result that relay I2BSA quickly releases. On release of relay IZBSA its contact 30 interrupts the circuit of relay I2HA, while when the track relay ceases to follow code, energy is no longer supplied to relay I2J and its contacts release.

As a result of release of the relays IZHA and I2J, the circuit of the upper green lamp G of signal I2S is interrupted, and the upper red lamp R is lighted by current supplied over back contact 34 of relay I2HA; also the vcircuit traced above for the lower red lamp R is interrupted and this lamp is lighted by energy supplied over back contact 36 of relay I2HA. The signal now displays a red lamp over a red lamp which is its stop or most restrictive indication.

At this time energy of "I5 code frequency is supplied to the track transformer IITT over a circuit which is traced from terminal BX through back contact 43 of'relay IZBSA, back contact 44 of relay IZFSA, and contact of the code transmitter I2CT.

When thetrain enters section I3T, the equipy ment for that section operates in the same manner as the equipment for section I2T so that signal IBS provides its stop indication, while energy of '75 code frequency is supplied to the track transformer I2TT.

When thev train Vacates section I2T, coded enorgy feeds to the track relay I2TR, and on the iirst movement of the track relay contacts to their picked-up position an impulse of energy is supplied from the secondary winding 22 of transformer I2DT to the pick-upv winding of relay IZFSA.

At this time the holding Winding of relay IZFSA is short circuited by back contact 2l of the relay so that the relay is slow to pick up. The relay and transformer are proportioned so that the first impulse of energy supplied to the relay will not pick up the relay contacts. However, on the next or second picked-up period of the track relay contacts the contacts of relay IZFSA pick up and contact 25 establishes the circuit of the relay IZBSA so that on the next or second released period of the track relay contacts energy is supplied to the relay I2BSA and its contacts pick up.

On picking up of the track relay contacts after picking up of the contacts of relay IZBSA energy issupplied to the relay I2HA over a circuit which is traced from terminal B through front contact I1 of the track relay, front Contact 3|] of relay IZBSA, winding of relay IZHA, and back contact 4S of relay IZTRB to terminal C. On picking up of the contacts of relay IZHA its contact 29 establishes a circuit to maintain the relay energized as long as the relay IZBSA is picked up and the relay I2TRB is released, while contact 29 of relay IZHA interrupts the circuit for supplying energy to the holding winding of relay IZFSA.

On continued code following operation of the track relay energy is supplied to the relay IZFSA during the picked-up periods of the track relay and is supplied to the relay IZBSA during the released periods of the track relay. Accordingly, these relays are picked up and relay IZBSA maintains the circuit of the relay IZHA.

On picking up of the contactsrof relay IZFSA its contact 44 interrupts the circuit traced above for supplying energy of '15 code frequency to track transformer I IT'I, and establishes a circuit including back contact 43 of relay IZBSA for supplying steady uncoded energy to section I iT.

As explained in the patent to Allison and Nicholson referred to above, if the insulated joints separating sections IIT and I2T are defective, this steady energy will feed across the joints and prevent release of the track relay IZTR so energy is not supplied to relay IZBSA with the result that relays IZBSA and IZHA remain released, while energy is supplied to the holding winding of relay IZFSA to keep its contacts picked up.

However, if the insulated joints are intact so that the steady energy does not reach the track relay I2TR, the contacts of this relay will release at the end of the on period and cause energy to be supplied to the relay IZBSA so that its coni tact 43 picks up vand interrupts the supply of steady energy to track transformer I ITT. W hen the contacts of relay IZHA pick up, a circuit is established to supply energy of 75M frequency to track transformer IITT. This circuit is traced from terminal BX through contact 15M of the code transmitter, back contact 48 of relay IZHB, back contact 49 of relay I2K, back Contact 4i] of relay IZJ, front contact 42 of relay IEHA, front contact 43 of relay I2BSA, front contact 44 oi relay IZFSA, and primary winding of transformer I ITT to transformer CX.

On the supply of this energy to section IIT the equipment for that section operates as hereinafter explained to control the signal for that section to cause it to display its advance approach indication consisting of a yellow over a yellow lamp.

Similarly, when the train vacates section HET the energy supplied to section IET is changed from '75 to 75M code frequency and the relay is picked up as hereinafter explained in detail and causes the signal I2S to display its advance approach indication.

The construction of the timing unit IZTU is 5' not a part of our invention, but is shown and claimed in application Serial No. 452,9?12 of Carl Volz, led July 30, 1942. This unit includes a transformer having a primary winding which is energized in multiple with a condenser, while the secondary winding of the transformer is connected through a rectifier'to the winding of relay i2TRB. The various parts of the unit are proportioned so that the energy supplied to the transformer primary winding causes the transformer core to be saturated, while on interruption of the supply of energy to the transformer primary winding, this winding and the condenser associated therewith form a highly damped oscillating circuit. The energy circulating in the transformer primary winding causes energy to be induced in the transformer secondary winding from. which it is supplied through the rectifier to the relay IZTRB. The characteristics of the timingr unit and of the relay IZTRB are such that on interruption of the supply of energy to the timing unit, energy is supplied therefrom to the relay IZ'I'RB which'isl eifective to cause the contacts of relay IZTRB to pick up and to remain picked up for a time longer than the short off period in the '75M code but not as long as the off eriods .in the 75 code.

When the track relay I2TR is responding to energy of '75 code frequency, energy is supplied to the primary winding of the transformer of the timing unit I2TU over the circuit which is traced from terminal B c1 the source through iront con@ tact l of the track relay IZTR, asymmetric unit 5l, front contact 52 of relayv ItIZBSA, back Contact. S2 of relay ZJ, back contact 53 cui' relay MK. back contact ll of relay i-ZTRB, and'priinary winding of the timing unit. transformer to terminal C.

On movement of the track relay Contactate, their released positions the supply of energy toj the timing unit transformer is interrupted and thisA imit operates as explained` above tosupply energy through the. rectifier incorporated; in the unit to therelay EZTRB over the circuit which is traced from the positive output terminal or the rectier over back contact 5E. of track relay SETR, and winding ofrelay ltd-RB to terminal C, it being noted that the other output terminalof the rectilier is connected to termin-al O. The energy supplied to the winding of relay iTRB' causes the contacts` of this.v relay topick up and to remain picked up for a short time interval. However, as explained'ahove, this time interval is shorter than the olf periods in the 'i5' code. so that when the track relay is respond-ing to energy oi 75 code frequency the contacts of' relay lTRB release before the track relay contacts pick up again, and as a result contact 54 of relay lf2-TRB establishes the circuit for rsupplying energy to the unit IZTU on subsequent picking up of the track relay contacts. In addition, Contact 5S or" relay lZTRB is releasedl and interruptsthe circuit of relay itl-EB so that this relay remains released at this time, and its contact te maintains the circuit of the lower red lamp R of signal VES, while its contact lt'maintains the circuit for supplying energy of 75M code frequency to section IlT. n

On picking up of relay lZTRB its contact 46 interrupts the circuit of relay lilla, but this relay is suflicientlyV slow in releasing to remain picked up during the picked-up periodsr of con'- tact 46.

As the circuit oi relay IZHA includes a back contact Il@ of relay IZTRB', the relay I2HA will be released ii the contacts of lrelay l-ZTRBremain picked up for any reason. This arrangement checks the relay IQTRB to insure that it releases, and, therefore, permitsthe use of' a relay having metal to metal contacts for this purpose.

When the train advances far enough to vacate section IST, energy of 75 code frequency feeds to the track relay for that section so that signal 53S displays its approach indication, while energy of 75M code frequency is supplied to section VET. On the supply of this energy to the track relay HTR it continues to follow code in such manner that the relays I,2FSA,.I2BSA and, S21-IA are maintained energized. As. explained above, each time the track relay contacts release the contacts of relay lZTRB` pick up, While when a short olf period in the '25M code is encountered, the contacts of the. track relay pickup. before the contacts of relay lZTRBrelease. v When this occurs, energy is supplied to relay LZTRB over a circuit which is traced from terminal B through front contact l5 of track relay IETR, asymmetric unit 5l, front contact 52 of relay I'ZBSA, back Contact 32 of relay 12J, back contact. 53 ot rel-aylEK, front contact 54 of relay I2TRB andv wind'- ing of relay IZTRB to terminal C. This energy,

keeps the contacts of relay lZTltB. pickedl up throughout the long on periodI in the '15M code followingy the short 01T period.

In; addition. on. picking up: of the. track relay contacts. while the contacts of relay l-ZTRB are still picked up, the relays 52E-TB and lZBSA are energized in series. over a. circuit'which is traced from terminal B through front. contact l5 cf .relay liZTR, asymmetric unit el, front Contact 52 of relay l'llBSA, back contact, 32 or"- relay E25, back contactl of relay 12K, iront contact 5d of relay Iii-TRB, front contact 5%y of relay lfTR,

winding of relay 12T-IB, iront Contact 53 of relay IZTRB, front contact Zitv of relay IEFSA, and winding of relay l2BSA to terminal C. The energy supplied to the relay IZBSA over this circuit insures that the contacts of relay IZBSA will remain picked up throughout the long on period in the 75M code, While the energy supplied to the relay llt-HB at this time causes the relay contacts to pick up. The relay IZHB is of a type the contacts of which are slow in releasing and when the relay isenergized throughout the long on period in the '75M code, the flux in the relay core isbuilt upto a value such that the relay contacts wil-l .remain pickedupduri-ng the intervals between the long on periods in the 75M code.

On picking up of the contacts' of relay Lil-.iB its contact 48 interrupts the circ-uit traced above for supplying energyl of 75M code frequency to track transformer ll TT, and establishes a circuit for supplying energy of v code frequency thereto. This circuit is traced from terminaly BX through contact l2@ of the code transmitter, front contact 5.8 of relay l-2HB, back Contact t9 of relay 52K, back contact ill of relay 12J, iront contact l2 ci relayr'i2I-IA, front contact 6301" relay IZBSA, front Contact M of relay lZFSA, and' primary winding of the track transformer NTT to terminal CX.

4When relay IZHB picks up,l its contact 5t interrupts the previously traced circuit for supplying energy to the lower red lamp. R; of signal 42S and establishes a circuit for supplying energy to the lower yellow lamp Y of this signal. This circuit is traced from terminal B through front contact 3.6 oi relay WHA, back contact 38 of relay lZJ, back contact 6l of relay 12K, front contact 6l! of relay lZHB, andjlamp Y to terminal C.V Accordingly,r the signal l2S displays its advance approach indication consisting of a yellow. lamp over a yellow lamp.

On release of the track relay lZTR after the long on period in the 75M code its contact l5 interrupts the supply of energy to the relays I2TRB, IZHB, and IZBSA and the relay EQTRB releases. The contacts ofY relay IZHB are maintained picked up because ofthe slow releasing characteristic of the relay, while on release of the track relay I 2TH. its contact Il establishes the previously traced circuit for supplying energy to the relay l ZBSA so its contacts remain picked up.

In addition, on release of relay l-Tli its contact 55A interrupts the previously traced circuit for energizing the relays lill-IB' and lBSA in series and establishes the circuit to permit energy 4to be supplied from the timing unit 92TH to the lished by back. contact 56 of thel track relay lZTR i and the contacts of relay I2TRB remain released.

On the first picked-up period of the track relay contacts after the long on period in the 75M code energy is supplied to the primary winding of the transformer incorporated in the timing unit IZTU over the circuit including back contact 54 of relay IZTRB so that on the next released period of the track relay contacts the timing unit I2TU operates as explained above to supply energy to the relay I2TRB and its contacts become picked up. However, the ofi period in the 75M code at this time is lonc`.,.` than the release period of the contacts of relay IZTRB so that its contacts release before the track relay contacts pick up again. Accordingly, energy is not supplied to `the relay I2HB at this time.

On the next or second picked-up period of the track relay contacts subsequent to the long on period energy is again supplied to the timing unit I2TU, while on the next released period of the track relay contacts, which occurs during a short off period in the 75M code, energy is again supplied from the timing unit I2TU to the relay IZTRB and its contacts pick up with the result that on picking up of the track relay contacts the contacts of relay IZTRB are still picked up so that energy is supplied over the holding circuit for relay IZTRB, and is also supplied to the relays IZHB and I 2BSA in series.

It will be seen, therefore, that when the track relay is responding to energy of 75M code frequency and the short off period in the code is encountered, the track relay contacts pick up before the contacts of relay IZ'I'RB release, and

as a result energy is supplied to relay IZTRB to maintain its contacts picked up during the long on period which follows the short off period. In addition, energy is supplied to the relay I2HB to pick up its contacts and to maintain them picked up during the time intervals between the long "on periods in the code, while energy is supplied to the relay I2BSA to maintain its contacts picked up during the long on period in this code. relay IZ'I'R responds to energy of 75M code frequency the contacts of relay lZHB are maintained picked up.

When the train advances far enough to vacate the section in advance of section IST, energy of 75M code frequency is supplied to section IST and the equipment for that section operates as explained above in connection with section I2T to cause energy of 120 code frequency to be supplied to the rails of section I2T. When the track relay IZTR responds to this energy, the frequency of the current induced in the secondary winding 23 of decoding transformer IZDT is such that it is freely passed by resonant unit I20DU and the re- Accordingly, as long as the track lay IZK picks up so that contact 53 interrupts the circuit for supplying energy to the timing unit I2TU, and for supp ying energy to relay IZTRB and to relays IZHB and IZBSA in series. v

Accordingly, relays IZTRB and IZHB thereafter remain released.

On picking up of the relay I2K its Contact SI interrupts the circuit traced above for supplying energy to the lower yellow lamp Y of signal IZS and establishes a circuit including front contact 35 of relay IZHA, back Contact 38 of relay IZJ,

and front contact 6I of relay I2K for supplying energy to the lower green lamp G of signal |255. The signal I2S, therefore, displays its approach medium indication consisting of a yellow lanp over a green lamp.

When the relay I2K picks up, its contact 49 interrupts the circuit traced above for supplying energy of 120 code frequency to transformer I I TT and establishes a circuit for supplyingf energy of 180 code frequency thereto. This circuit is traced from terminal BX through contact I8!) of the code transmitter I2CT, front contact 49 of relay I2K, back contact 4D of relay I2J, and front contacts of the relays IZHA, IZBSA and IZFSA to the transformer IIT'I.

When the train advances far enough to vacate two sections in advance of section IST, energy of 120 code frequency is supplied thereto and the equipment for that section operates to supply energy of 180 code frequency to track transformer IZTT. When this energy feeds to the track relay I2TR, the frequency of the energy induced in transformer secondary winding 23 is such that it is no longer passed by the resonant unit IZGDU, but is freely passed by the unit lSDU so that relay IZK releases and relay I2J picks up. On picking up of relay I2J its contact 32 interrupts the circuit of the timing unit IZTU, and of the relays ITRB, IHB, and I ZBSA, while its contacts 38 interrupts the circuit traced above for supplying energy to the lower green lamp G and establishes the circuit including front contact 38 of relay IEHA for supplying energy to the lower red lamp R of signal I2S. In addition, at this time contact S5 of relay I2J interrupts the circuit of the upper yellow lamp Y of signal IZS and establishes the circuit including front contact 34 of relay IZHA for supplying energy to the upper green lamp G of signal I2S, Accordingly, vthe signal IES displays its clear indication consisting of a green lamp over a red lamp.

On picking up of relay IZJ contact 49 interrupts the previously traced circuit for supplying energy of 186 code frequency to transformer II'I'I and establishes another circuit for supplying energy of this code frequency to the transformer IITT.

From the foregoing it will be seen that the system of this invention operates to provide four distinct proceed indications. rihree of these indications are provided by the usual coded energy of '75, 120 and 180 code frequencies, while one of these indications is provided by the special '75M code which is a modification of the standard '75 code.

It has been found that when locomotives construction and having decoding means for detecting energy of 75, 120 and 180 code frequency are operated in sections supplied with the special 75M code, the cab 'signal apparatus gives the same response to the '75M code as it gives when supplied with energy of 75 code frequency. Accordingly, when a locomotive equipped with standard four indication cab signal apparatus is operated in a track stretch equipped with the ve indication apparatus provided by this invention, the cab signal equipment will provide its approach indication through the two blocks in the rear of an occupied block. In such situations the wayside signal at the entrance to the second section in the rear of an occupied block will display itsadvance approach indication, while when the locomotive enters this section, the cab signal will provide its approach indication.

If desired, the locomotive cab signal apparatus may include means for detecting the special 75M code, and if this is done, the cab signal will provide its advance approach indication when the locomotive is in a section to which energy of 75M code frequency is supplied.

Operation of equipment when an insulated .'ioint is defective' if the insulated joints separating two sections are defective.

lf a train breaks down one of the insulated joints 3 separating sections IIT and IZT, energy of 75 code frequency supplied to transformer l ITT may pick up the track relay I2TR when the train advances far enough for the rear of the train to be located some distance in advance of the track relay.

On initial movement of the track relay contacts to their picked-up positions an impulse of energy is supplied through the decoding transformer iZDT to the pick-up winding of relay IZFSA, but the contacts of this relay remain released and maintain the supply of energy of 75 code frequency to the transformer IITT, while they interrupt the circuit of relay iZBSA. At this time contact 52 of relay I2BSA is released and prevents the supply of energy through the asymmetric unit 5I to the timing unit I-ZTU. As relay IZFSA remains released energy is not supplied to the relay IZBSA on release of the track relay.

On the next or second movement of the track relay contacts to their picked-up positions another impulse of energy'is supplied to the pick-up Winding of relay SEF-SA and its contacts pick up with the result that contact 44 interrupts the oircuit for supplying energy of '75 code frequency to the transformer IiTT and establishes the circuit including back contact is of relay IZBSA for supplying steady uncoded energy to the transformer IITT. This energy feeds across the defective joints and keeps the track relay contacts picked up.

As the track relay contacts and the contacts of relay IEFSA are picked up, energy is supplied to the holding Winding of relay IZFSA over the circuit Which is traced from terminal B through front contact Il of the track relay, back contact 2Q of relay I lfHA, front contact 2'! of relay IEFSA, and holding Winding of the relay IZFSA to terminal C. The energy supplied to the holding winding of relay IZFSA keeps the relay contacts picked up so that its contact 2l maintains the circuit of the relay holding Winding, While its contact it maintains the circuit for supplying steady energy to the transformer IITT. This energy feeds across the defective joints and keeps the track relay contacts picked up with the result that energy is not supplied to the relay IZBSA and its contacts remain released and interrupt the circuit `of relay IZHA so that relay IZHA remains released and causes signal I2S to continue to display its stop indication.

If an insulated joint separating sections IIT and 52T breaks down when section 12T is vacant, the coded energy feeding from transformer I ITT across the defective joint to track relay I ZTR combines with energy supplied from transformer $2TT to the track relay IZ'TR. If at the time the insulated joint becomes defective the impulses of coded energy supplied to transformersV I ITT and NTT are out of step, the contacts of track relay I2TR Will be held picked up an abnormally large proportion of the time. If at the time the insulated joint becomes defective the impulses of coded .energy supplied to the transformers IiTT and I2TT are in step, they Will soon become out of step as the code transmitters controlling the supply of energy to the two sections are operated by induction motors and these Will not run at exactly the samC` speed for any substantial period of time.

As a result of the increase in the picked-up periods of the track relay contacts, the circuit of the relay IZBSA is interrupted so much of the time that this relay will release with the result that its contact i3 interrupts the circuit for supplying coded energy to the transformer I ITT and establishes a circuit to supply steady energy thereto. This energy feeds across the defective joint and keeps the track relay contacts picked up so that energy is no longer supplied through the decoding transformer I2DT to the relay iFSA, nor to the relay IZK or I2J, so that these relays release.

In addition, on release of relay IEBSA its contact 3U interrupts the circuit of relay ill-IA and the contacts of this relay release, but because of the slow releasing characteristic of this relay its contact 29 remains picked up and interrupts the circuit for supplying energy to the holding Winding of relay 'l EFSA until after contact 2 of relay IZFSA has released and interrupted this circuit.

On release of relay IZBSA its contact 52 interrupts the circuit for supplying energy to the timing unit IZTU, and also to relays iTRB, IZHB and I'BSA.

On release of relay IEFSA its contact liLl interrupts the supply of steady energy to transformer IITT and causes energy of 75 code frequency to be supplied thereto over the circuit which is traced from terminal BX through back Contact 43 of relay IZBSA, back contact 4d of relay IZFSA, and Contact 'i5 of the code transmitter IECT to the transformer IITT. Energy from the transformer feeds across the defective joint to track relay I2TR and combines With the energy supplied from transformer IZTT.

The impulses of coded energy supplied to the track relay I2TR from the transformers IITT and I2TT will cause the contacts of the track relay to be picked up most of the time, but a time will soon be reached When the relationship of the two codes is such that the track relay contac'ts will pick up twice in rapid succession. When 55'tained picked up. In addition, on picking up of this occurs, the relay IEFSA Will pick up and its contact 21 will establish the circuit traced above for supplying energy to the relay holding Winding so that the relay contacts are thereafter mainthe relay IZFSA its contact it interrupts the circuit for supplying energy of 'l5 code frequency to transformer I ITT and establishes the circuit for supplying steady energy thereto. This energy keeps the track relay IZTR` picked up so that energy is not supplied Vto relay IZBSA. Accordlingly, the contacts of relay i2BSA remain redecoding means, and if a locomotive equipped with existing cab signal apparatus is operated in a section to which the modified coded energy is supplied the locomotive cab signal apparatus will operate to provide a suitable proceed indication.

Furthermore, it has been found that energy of the code pattern employed for the '7 5M code frequency has a minimum effect on the decoding units for energy of 120 and 180 code frequency.

It will be seen also that the decoding means for detecting the energy of 'llcode frequency is arranged so that it does not interfere with the lockout circuit. The relay BSA has a release time just long enough to bridge the picked-up periods of the track relay when the track relay is supplied with energy of 75 code frequency so that this relay will release quickly and establish the lockout circuit if energy feeds across a defective joint and keeps the track relay picked up an abnormally large proportion of the time. The decoding means for the '75M code frequency includes means for supplying energy to the relay ESA during the long on periods in this code to thereby prevent release of this relay at such times and resultant interference with the supply of energy to the adjacent section in the rear. This means for supplying energy to the relay BSA is effective only during the long on periods in the 75M code so that there is a minimum of interference with the release of the relay BSA.

In addition, the 75M decoding means is controlled by the relays which detect the other code frequencies so that the '75M decoding means is prevented from functioning if the relays which detect energy of 120 and 180 code frequency are picked up. This reduces the period of operation of the 75M decoding means, while it prevents operation of this means in response to momentary release of the track relay contacts occurring when the track relay starts to follow code, when there is a change in the frequency of the energy supplied to the track relay, or when the track relay is supplied with energy of 120 or 180 code frequency- Similarly, the decoding means for the 75M code is controlled by the relay BSA so that this decoding means will function only when the track relay is responding to coded energy.

The modified code employed in this system and the decoding means for this code are of such nature that coded energy resulting from modications of the standard code due to track circuit or other conditions will not operate this decoding means. The short off period in the 75M code must be present to cause the contacts of the track In the modified code employed in this system the short off period is followed by a long on period and energy is supplied to the relay HB throughout this long on period so that enough energy is supplied to the relay to keep it picked up during the interval between the long on periods. These long on periods are substantially longer than the "on periods present in any of the standard codes and will not be produced by modifications 0f those codes by track circuit conditions.

In addition, the special code employed in this system is arranged so that the modified code cycles are of the same length as the code cycles of standard pattern, and the code can be generated by existing types of motor driven code transmitters with only a slight modification thereof consisting of the addition of another cam.

Although We have herein shown and described only one form of apparatus embodying our 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 our invention.

Having thus described our invention, what we claim is:

1. In a coded signaling system, combination, a code following relay, means for at times supplying to said relay recurring cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an off period during which no energy is supplied, means for at times period-A ically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle, a first relay responsive to op eration of said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on response of said code following relay to said predetermined code periods to supply to said auxiliary relay energy effective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a circuit including a front contact of said auxiliary relai.T and a contact of said code following relay closed on response of said relay to said other code periods for supplying energy to a second relay, and signaling means governed by said rst and sccond relays.

2. In a coded signaling system, in combination, a code following relay, means for at times supplying to said relay recurrinor cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an off period during which no energy is supplied, means for at times periodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle, a first relay responsive to operation of said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on response of said code following relay to said predetermined code periods to supply to said auxiliary relay energy effective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response of said relay to said other code periods for also supplying energy to said auxiliary relay, and signaling means governed by said code following relay and said auxiliary relay and by said rst relay.

3. In a coded signaling system, in combination, a code following relay, means for at times supplying to said relay recurring cycles of coded energy,` each of said cycles consisting oftwo periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an off period during which no energy is supplied, means for at times periodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle, a rst relay responsive to operation 'cf said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on response of said'code following relay to said predetermined -code periods to supply to said auxiliary relay energy effective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a slow releasing relay, a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response of said relay to said other code periods for supplying energy to said slow releasing relay and for also supplying energy to said auxiliary relay, and signaling means governed by said first relay and by said slow releasing relay.

4. In a coded signaling system, in combination, a code following relay, means for at times supplying to said relay recurring cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to saidV relay and the other of said periods being an off period during which no energy is supplied, means for at times periodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle and correspondingly increasing the length of the other period of said code cycle, a first relay responsive to operation of said code following relay by either normal or modied coded energy, an auxiliary relay, means operative on response of said code following relay to said predetermined code periods to supply to said auxiliary relay energy eiective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response of said relay to said other code periods for supplying energy to a second relay, and signaling means governed by said first and second relays.

5. In a coded signaling system, in combination, a code followingrelay, means for at times supplying to said relay recurring cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an oi period during which no energy is supplied, means for at times periodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle and correspondingly increasing the length of the other period of said code cycle, a rst relay responsive to operation of said code following relay by either normal or modied coded energy, an auxiliary relay, means operative on response of said code following'relay to said predetermined code periods to supply to said auxiliary relay energy effective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response of said relay to said other code periods for also supplying energy to said auxiliary relay, and signaling means governed bysaid code following relay and said auxiliary relay and by said first relay.

6. In a coded signaling system, in combination, a code following relay, means for at times supplying to said relay recurring cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an off period during which no energy is supplied, means for at times perivodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle and correspondingly increasing the length of the other period of said code cycle, a rst relay responsive to operation of said code following relay by either normal or modiiied coded energy, an lauxiliary relay, means operative on response of said code following relay to said predetermined code periods to supply to said auxiliary relay energy elective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a slow releasing relay, a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response Vof said relay to said other code periods for supplying energy to said slow releasing relay, and signaling means governed by iirst relay and by said slow releasing relay.

7. In a coded signaling system, in combination, a code Yfollowing relay, means for at times supplying to said relay recurring cycles of coded energy, each of said cycles consisting of two periods of substantially equal length, one of said periods being an on period during which energy is supplied to said relay and the other of said periods being an oif period during which no energy is supplied, means for at times periodically modifying the cycles of coded energy supplied to said relay by substantially reducing the length of a predetermined one of the periods of said code cycle and correspondingly increasing the length of the other period of said code cycle, a rst relay responsive to operation of said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on response of said code following relay to said predetermined `code periods to supply to said auxiliary relay energy effective to pick up the contacts of said auxiliary relay and to maintain them picked up for a time longer than a period of reduced length but not as long as a period of normal length, a slow releasing relay, a circuit including a front contact of said auxiliary relay and a contact of said code following relay closed on response of said relay to said other code periods for supplying energy to said slow releasing relay and for also supplying energy to auxiliary relay, and signaling means governed by said rst relay and by said slow releasing relay.

8. In a coded signaling system, in combination, a code following relay, means for supplying to said relay coded energy consisting of alternate onl and off periods of substantially equal duration, means for at times periodically modifying the coded energy supplied to said relay by substantially reducing the length of an on period and correspondingly increasing the length of the succeeding on period, a first relay responsive to operation of said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on release of the contacts of said code following relay to supply to said auxiliary relay energy effective to pickup the contacts of said auxiliary relay and to maintain them picked up for a. time longer than an oi period of reduced length but'shorter than an off period of normal length, a circuit including front contacts of said code following relay and of said auxiliary relay for supplying energy to said auxiliary relay, a second relay governed by said code following relay and said auxiliary relay, and signaling means controlled by said first and second relays.

9. In a coded signaling system, in combination, a code following relay, means for supplying to said relay coded energy consisting of alternate on and off periods of substantially equal duration, means for at times periodically modifying the coded energy supplied to said relay by substantially reducing the length of an ofi period and correspondingly increasing the length of the succeeding on period, a first relay responsive to operation of said code following relay by either normal or modified coded energy, an auxiliary relay, means operative on release oi" 'the contacts of said code following relay to supply to said auxiliary relay energy eiiective to pick up the `contacts of said auxiliary relay and to maintain them picked up for a time longer than an 01T period vof reduced length but shorter than an oif period of normal length, a circuit including front contacts of said code following relay and of said auxiliary-relay for supplying energy to said auxiliary relay, a slow releasing relay, a circuit including front contacts of said code following relay and of said auxiliary relay for supplying energy to said slow releasing relay, and signaling means governed by said first relay and by said slow releasing relay.

10. In a coded railway signaling system, in combination, a stretch of railway track over which traine normally moves in one direction, the rails of said section being divided by insulated joints into a forward and a rearward section, a, code following track relay at the entrance end of the forward section and having a winding receiving energy over the rails of said section, means at the exit end of said forward section for supplying to the rails of said section coded energy consisting of alternate on and ofi periods of substantially equal duration, means for at times periodically modifying the coded energy supplied to said section by substantially reducing the length of an off period and correspondingly increasing the length of the succeeding on period, means including a from; contact of said track relay for supplying energy to a first auxiliary relay, means including a back contact of the track relay and a front contact of said first auxiliary relay for supplying energy to a second auxiliary relay, said second auxiliary relay being slow enough in releasing to remain picked up for a period approximately as long as an on period of normal length after the supply of energy thereto is interrupted, means for supplying coded energy to the rails of said rearward section, a circuit complete when the contacts of the first auxiliary relay are picked up and the contacts of the second auxiliary relay are rreleased and over which steady energy may be supplied to the rails of said rearward section, means operative on release of the contacts of the track relay to supply to a third auxiliary relay energy effective to pick up the contacts of said relay and to maintain them picked up for a time longer than an oil period of reduced length but shorter than an off period of normal length, a circuit including front contacts of said track relay and of said third auxiliary relay for also supplying energy to said third auxiliary relay, a circuit including front contacts of said track relay and said third auxiliary relay vfor supplying energy to said second auxiliary relay, and means governed by said third auxiliary relay for supplying coded energy to the rails .of said rearward section.

11. In a coded'railway signaling system, in combination, a stretch of railway track over which traffic normally moves in one direction, the rails of said section being divided by insulated joints into a forward and a rearward section, a code following track relay at the entrance end of the forward section and having a winding receiving energy over the rails of said section, means at the exit end of said forward section for supplying to the rails of said section coded energy consisting of alternate on and off periods of substantially equal duration, means for at times periodically modifyingthe coded energy supplied to said sectionV by substantially reducing the length of an oii period and correspondingly increasing the length of the succeeding on period, means including a front contact of said track relay for supplying energy to a first auxiliary relay, means including a back contact of the track relay and a front contact of said first auxiliary relayfor supplying energy to a second auxiliary relay, said second auxiliaryrelay being slow enough in releasing to remain picked up for a period approximately as long as an on period Hof normal length after the supply of energy thereto is interrupted, means for supplying coded energy to the rails of said rearward section, a circuit complete when the contacts of the first auxiliary relay are picked up and the contacts of the second auxiliary relay are released and over which steady energy may be supplied to the rails of said rearward section, means operative on release of the contacts of the track relay to supply to a third auxiliary relay energy effective to pick up the contacts of said relay and to maintain them picked up for a time longer than an oli period of reduced length but shorter than an off period of normal length, means effective when the contacts of said track relay and said third auxiliary relay are picked up to supply energy to said third auxiliary relay, to said second auxiliary relay, and to a slow releasing relay, and means governed by said slow releasing relay for supplying coded energy to the rails of said rearward section.

l2. In a coded railway signaling system, in combination, a stretch of railway track over which trame normally moves in one direction, the rails of said section being divided by insulated joints into a forward and a rearward section, a code following track relay at the entrance end of the forward section and having a winding receiving energy over the rails of said section, means at the exit end 0f said forward section for supplying to the rails of said section coded energy consisting of alternate on and off periods of substantially equal duration, means for at times periodically modifying the coded energyA the track relay and a front contact of said-first I auxiliary relay for supplying energy to a second auxiliary relay, said second auxiliary relay being slow enough in releasing to remain picked up for a period approximately as long as an on period of normal length after the supply of energy thereto is interrupted, means for supplying Coded energy to the rails of said rearward section, acircuit complete when the contacts of the rst auxiliary relay are picked up and the contacts of the second auxiliary relayare releasedvand over which steady energy may be supplied to the rails of said 'rearward section, means operative on release. of the contacts of the track relay to supply to a third auxiliary relay energy efectiveI to pick uptheV ,contacts of said relay and to maintain them picked up for a time longer than an oi period of reduced length but shorter than an off .period of normal length, means eiective when the contacts of the track relay and of .the third auxiliary relay are .picked up to supply energy to 'said' third auxiliary Vrelay/and to a slow releasfingrelay, meansl effective when the contacts of the track relay and of said third auxiliary relay are picked up to prolong the picked-up periods of the contacts of` the second auxiliary relay, and

.means governed bysa'id slowreleasing relay for :supplying energy to the rails of said rearward section. 13. In a coded railway signaling system, in combination, a stretch of railway track lover -'Which traffic. normally moves inl one direction,

the rails of said section being divided by insulated joints into a forward and a Irearward section, a code following track relay at the entrance end of the forward section and having a winding receiving energy over the rails of said section, means at the exit end of said forward section for supplying to the rails of said section coded energy consisting of alternate. .on and on periods of substantially equal duration, 'means for at times periodically modifying the `c'oded'errergy supplied to said section by substantially ree ducing the length of an oiperiod 'and correspondingly increasing the length of the'succeeding on period,`means including a front contact of said track relay for-supplying energy to a rst auxiliary relay, lmeans including a back contact of the track relay and afront contact or said'rst auxiliary relay for supplying energy to a second auxiliary relay, said second auxiliary relay being ,slow enough in releasing to remain picked up for a period approximately as long `as an on period of normal length after the supply of energy thereto is interrupted, means for supplying coded energy to the rails of said rearward section, a circuit complete when the contacts of the first auxiliary relay are picked up and the contacts of the second auxiliary relay are released and over which steady energy may be supplied to the rails of said rearward section, means operative on release of the contacts `of the track relay provided the contacts ofthe second auxiliary re lay are picked up to supplyto a third auxiliary relay energy effective to pick up the'contacts of said relay and to maintain them picked up for a time longer than an oir period lof reduced length but shorter than an oli period of normal length, means effective when the contacts oi the track relay and of said second and third auxiliary relays are picked up to supply energy to said third auxiliary relay and to a slowreleasing relay, and means governed by said slow releasing relay for supplying coded energy to said rearward section. 1

n, H. NICHOLSON. "CRAWFORD E. STAPLES.

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