US2272581A

US2272581A - Coded track circuit signaling system

Info

Publication number: US2272581A
Application number: US362636A
Authority: US
Inventors: Robert M Phinney
Original assignee: General Railway Signal Co
Current assignee: SPX Corp
Priority date: 1940-10-24
Filing date: 1940-10-24
Publication date: 1942-02-10
Anticipated expiration: 1959-02-10

Description

Feb. 10, 1942. PH|NNEY 2,272,581

CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Oct. 24, 1940 3 Sheets-Sheet 1 Fla 1.

SY 52 re; &

-12esponds to1000-only rp qi F lyqu 5 Gen. INVENTOR =="OC1-2 fi 0C BY J T 6 Tr 72M 1 5 1942. R. M. PHINNEY 72,581

CODED TRACK CIRCUIT SIGNALING SYSTEM I Filed Oct. 24, 1940 3 Sheets-Sheet 2 FIG. 2.

I! 3' Responds to IOOO'YOnIy 54 %VENTOR 60-AC intermittently Superimposed BY y by 1000-potential NW Feb. 10, 1942. R. M. PHINNEY 2,272,581

CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Oct. 24, 1940 3 Sheets-Sheet 5 MCMJFJ Uyq fi i I 4 s v W" !%1 i I fjlaofL 3 IL cM5-6 mvENTop 60-AC intermittently Superimposed I by 1000- potential ATTORNEY Patented Feb. 10, 1942 r'rs rsr cries CODE!) TRACK CIRCUIT SIGNALING SYSTEM Robert M. Phinney, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

29 Claims.

The present invention relates to signaling systems of the absolute-permissive-block type and more particularly to a double or duplex coded track circuit for such systems.

By coded track circuit is meant a track circuit of the coded type wherein impulses of current are repeatedly applied to one end of the track circuit and suitable code responsive apparatus detects the code at the other end of such track circuit. By a double coded track circuit or a duplex coded track circuit is meant a track circuit in which codes may be applied at both ends and code responsive apparatus may be connected at both ends wherein each code responsive apparatus only responds to the codes applied by the code applying apparatus at the other end of the track circuit.

In order to control a signal in accordance with trailic conditions in one or more blocks in advance without the requirement of signal control line wires it is desirable to have the track relay or the code responsive apparatus located adjacent the signal, namely, at the entrance end of the track section. Obviously, if traffic moves in both directions as is often the case for single track railroads, in which case there may be a signal at each end of such track section for governing traffic into the section, it becomes apparent that it is desirable to have a track relay or code responsive means at each end of the track section, which may be shunted out by a train in that section and if not shunted refleets trafiic conditions in advance. Since traffic conditions in opposite directions of such section may be different the codes transmitted in opposite direction may be different. Also when continuous inductive train control is employed it is found necessary to apply the code to the exit end of the section so that it may be detected in front of the train and for single track railroads both ends of each section are at times exit ends. These characteristics of a track circuit are desirable in order to avoid the need of line wires between the signal and the track relay or code responsive apparatus controlling thesame. In

view of these facts it is desirable to employ a double track circuit, so to speak, in which there is a track relay or code responsive means at each end controlled by energy applied to the opposite end.

In accordance with the present invention it is proposed to construct such a double track circuit by providing each end of a track section with synchronously operated contacts which simultaneously connect code creating apparatus to one end of the track circuit while code responsive apparatus is connected to the other end of the track circuit and vice versa. By reason of the fact that the code which is to be applied to one end of a track section may be different than the code applied to the opposite end of the track section it is not possible to alternate the use of the track rails to the two track circuits, once for each code element, because if this were done the code element spacing of the codes transmitted in opposite directions through the track would not synchronize when difierent rate codes are applied at opposite ends. In view of this fact, and in accordance with the present invention, it is proposed to alternately allow the use of the track rails of a track section for its two track circuits for time periods long enough to trans-' mit suificient elements of the rate codes transmitted to make interpretation possible. In other words, it is proposed to allow a code to be transmitted in one direction along the track section long enough to have its code responsive apparatus respond and to thereafter allow the transmission of a code in the opposite direction through the rails of the track section for a period long enough for its code responsive apparatus to respond and to employ code responsive apparatus which will manifest the reception of a continuous code in spite of the fact that the code is intermittently interrupted during the time when a code is being transmitted in the opposite direction.

Another object of the present invention resides in the provision of contacts at each end of each track circuit for alternately connecting the code creating apparatus and the code responsive apparatus to the track rails, and to provide means for operating the contacts at opposite ends of the track section in synchronism. More specifically it is proposed to operate these contacts by electro-responsive means connected through a suitable filtering means to a transmission line upon which is superimposed a special current which is intermittently applied for time intervals long enough to transmit a code through the rails of a track section and which is then removed for substantially the same time interval.

Other objects, purposes and characteristic features of the present invention will in part be described hereinaiter and will in part appear from the accompanying drawings, in which:

Figs. 1,2 and 3 when laid end-to-end constitute a portion of an absolute permissive block system embodying the present invention.

Referring to the drawings the track rails I have been shown divided by insulating joints 2 into track sections of which the sections X and Y and the adjacent ends of sections W and Z only have been shown. As illustrated the entrance end for eastbound trafiic to the blocks or sections X, Y and Z have been provided with signals S2, S4 and S6 respectively, and similarly the entrance end for west-bound traflic to the blocks Y, X and W have been provided with signals S5, S3 and SI, respectively. These signals S may be of any suitable construction such as semaphore signals, search-light signals, or multi-aspect signals and for convenience only multi-aspect signals each having a green lamp 9, a yellow lamp y, and a red lamp 1 have been illustrated. The green lamp signifies clear, the yellow lamp caution and the red lamp signifies danger traffic conditions ahead, when lighted.

Parallel to the railway track is preferably provided a transmission line Tr which supplies the necessary power for charging storage batteries, for operating code creating apparatus and for applying energy to the track rails. This transmission line preferably supplies power of commercial frequency such as current of 60 cycles per second. This 60 cycle current has preferably superimposed thereon a high frequency current, such as current of 1000 cycles per second, this high frequency current being applied intermittently for, say, two second intervals spaced by a period of two second intervals.

This intermittently applied high frequency cur rent is preferably derived from a suitable generator Gen and is preferably intermittently ap plied by suitable circuit interrupting means such as the contact 5 intermittently closed by a cam 6 which may be driven by a suitable motor, such as a synchronous motor operated from the 60 cycle source of current supply. In order to prevent the 60 cycle energy from flowing through the winding of the generator Gen a condenser C is preferably employed. At each track section junction there is provided a synchronizing relay SY which is connected to be responsive to the superimposed high frequency current, the circuit for each of these relays SY preferably having included in series therewith a condenser such as the condenser OCl-2 shown for the junction provided with signals Si and S2. This condenser is preferably of such a capacity that in combination with the inductance of the relay SY the circuit therethrough is tuned for the high frequency current.

Each track section junction is also preferably provided with a coding motor CM, the coding motor for the location of signals SI and S2 having been designated CMI--2. These coding mo tors CM are provided with coding contacts designated l and E80 and closed 75 and 180 times per minute, respectively, although coding contacts operating at other frequencies such as contacts which close 120 times a minute may be employed if desired.

Since the apparatus and wiring for the various signals is identical it is deemed sufficient to describe the apparatus associated with the signal S2 and to designate like parts of all other signals with like reference characters having distinctive suffixes and exponents corresponding to the sufiix of the associated signal.

Referring to the signal S2 and its associated apparatus located at the entrance end to the block X, this signal S2 is'controlled through the medium of code following relays CLZand CA2 as is readily apparent from the circuits for the signal lamps g, y and r for the signal S2 including contacts 35 and 36 During the periods of energization of the synchronizing relay SY the rails of the west end of the block X are connected to the secondary winding of the transformer TTZ. This transformer has its primary winding normally (under clear traffic conditions) connected to the transmission line Tr through a circuit including the front contact I0 of the track repeater relay TRI, the contact lSEl of the coder CMl--2, back contact H of the directional stick relay SRI and through back contact I2 of the directional stick relay SR2. Under caution traffic conditions for west-bcund traffic in block X this transformer TTZ is connected to the transmission line T1- through the back contact I0 of the track repeater relay TRI, through coding contact 15, through the front contact H of the directional stick relay SR9 and through back contact l2 of the directional stick relay SR2. When however the synchronizing relay SY is deenergized the west end of the track section X has its track rails connected to the track relay T2.

Intermittent picking up of the track relay T2 in response to either a 75 impulse per minute code or a 180 impulse per minute code will cause its contact M to intermittently connect the posi tive terminal of a battery (conventionally represented by the terminals and to opposite ends of the primary winding of the transformer T82, which primary winding has its mid-point connected to the terminal of the same battery. This transformer is therefore in effect energized by alternating current of '75 or 180 cycles per minute, as the case may be. One secondary winding of this transformer TS2 has its midpoint connected to one terminal of the relay CA2 and has the two ends of its winding connected to the stationary front contact and the stationary back contact, respectively, associated with the movable contact I5 of the relay T2, so that this contact I5 constitutes a rectifying contact for the alternating current induced in this secondary winding of the transformer TS2. The transformer TS2 is provided with another secondary winding which is connected through a condenser lC2 to a full-wave rectifier REE which has its out-put direct current terminals connected to the clear relay CL2. The condenser |C2 is of such capacity as compared with the inductance in its circuit so as to resonate the circuit at a frequency of 180 cycles per minute, so that the relay CL2 will only pick up when a code of 180 cycles or impulses per minute is received by the track relay T2 and will not pick up if a code of either 75 or impulses per minute is received. As heretofore pointed out the synchronizing relay SY is energized for substantially a two second interval and is then deenergized for substantially a two second interval.

In order to be assured that the clear relay GL2 or the caution relay CA2 will remain energized during the two second off period intervals these relays CL2 and CA2 have been provided with stick circuits. These stick circuits for relays CLZ and CA2 include stick contacts [l and I8 respectively, which are included in series with condensers 2G2 and 302, respectively, through front contacts I9 and 20 respectively, of the relay SY during the .off code period. These condensers 2C2 and 302 are charged from a battery B2 through back contacts l9 and 20 respectively, when the relay SY is deenergized and are connected to the stick windings of the relays CLZ and CA2 when the relay SY is energized, so that a definite amount of energy is transferred from the battery B2 to an energized relay for each code transmitting period.

The track repeater relay TRZ is a slow dropping relay and may be energized through two circuits, one of which includes the front contact 22 of the relay CA2 and the other of which includes a front contact 23 of the relay GL2. Each of the signals S is provided with a directional stick relay of which the directional stick relay for the signal S2 has been designated SR2. This directional stick relay SR2 may be picked up by a circuit including the back contact 25 of the track repeater relay TRI, back contact 2'5 of the relay GL2, back contact 21 of the relay CA2, front contact 28 of the relay TRZ. This stick relay SR2 when once energized may be maintained energized through a stick circuit including the back contact BI of the relay GL2, back contact 32 of the relay CA2, and front stick contact 33 of. this directional stick relay SR2. There is also an auxiliary stick circuit for this relay including the back contact 3& of slow dropping track repeater relay TR2.

Operation Let us first assume that all of the signals governing east-bound trailic are in their normal clear traffic condition in which their green lamps g, are energized and that there is an east-bound train which just entered the block W. Since this east-bound train entirely shunts the track relay Tl the caution relay CA! and the clear relay CL! as well as the track repeater relay TRI will all assume their deenergized position. Also the back contact 215 of the relay TR2 is open as a result of which the directional stick relay SRI did not pick up in response to closure of back contacts 26 and 21 Under this condition since the contacts N3 of the relay TR! and contact I I of the relay SR! are both in their retracted position the transformer TT2 is entirely deenergized, because its two energizing circuits including the coding contacts 15 and H39, respectively, of the coding motor ClVll2 are open. This results in the signal S3 at the east end of the block X and governing west-bound trafiic assuming the stop position. Similarly, since the relays SR3, TRB, CA3 and CLS also all assume their deenergized position no coded current can be applied to the west end of the block Y and accordingly the signal S5 at the east end of this block Y and governing west-bound traffic will also assume its stop position. It is, of course, understood that the signal Si no longer assumes its clear condition because the relay CM is deenergized, the track relay Tl being shunted by the train occupying the block W, and since the green lamp g of the signal SI includes the front contact 35 this green lamp g will of course be extinguished. Also, since the lamp y for the signal SI includes a front contact 36 of relay CAI this lamp y will also be extinguished. The lamp r of this signal S! will be energized through a circuit including these back contacts 35 and'36 It is thus seen that the usual tumble down of track circuits is eifected upon entrance of a train resulting in all opposing signals in the single track section being put to stop.

The train under consideration may of course proceed, at speed, into the block X because signal S2 is clear and has its green lamp g energized. This green lamp g for signal 2 isenergized, as indicated in the drawings, because its associated clear relay 0L2 is in its energized position. This, relay CL is in its energized condition because intermittently for two seconds at a time, spaced by two second intervals, the track relay T2 is energized at a coding rate of 1'80 impulses per minute. These.- intermittent energ-izations of the track relay T2 occur when: the synchronizing relay SY is deenergized. Since these intermittent energizations cause the contact It? to apply 180 cycle per minute. current to thetransformer TS2 for which the input circult for the rectifier REZ is tuned sufficientcurrent will be. supplied by this rectifier to pick upv the relay GL2. energized condition and its stick circuit includ-= ing its stick" contact [1 closed, the lower winding of the relay GL2. is energized by the currents which were stored in the condenser 202 during the period of. deenergization of the synchronizing relay SY and which current is applied to this winding during the period of deenergization of its upper winding.

The caution relay CA2 is also energized under this condition but this is of no importance since the circuit for the clear lamp G does not include a contact of the caution relay CA2. east-bound train moving in the block W the track repeater TRI is deenergized but this is of no importance at the present time insofar as the pickup circuit for the directional stick relay SR2 is concerned because its pick-up circuit is open at back contacts 26 and 21 of relays CLZ and CA2, respectively. As the train in question however passes the signal S2 and enters the block X the track relay T2 will remain continuously deenergized thereby resulting in the deenergization and dropping of the relays CLZ and CA2. With the relays GL2 and CA2 both in their retracted posi-' tion the signal S2, for reasons heretofore given, indicates danger. With both of these relays GL2 and CA2 deenergized, and with the track repeater relay TRI' also deenergized, for reasons heretofore given, a pick-up circuit for the directional stick relay SR2 is closed through back contacts of these relays TRI, GL2 and CA2 and front contact 28 of the track repeater relay TRZ. This track repeater relay TR2 is sufficiently slow dropping to allow the directional stick relay SR2 to pick up before its contact 23 is opened. As soon as the directional stick relay SR2 has assumed its picked up position a stick circuit for this directional stick relay SR2 is closed which includes the back contacts 31 and 32 of the relays CL2 and CA2, respectively, and also includes the stick contact 33 of the relay SR2. Upon dropping of' the repeater track relay TRZ a second stick circuit is closed for the directional stick relay SR2 which includes the back contact 34 of this relay TRZ. As soon as the train has fully left the block W the code following relay CAI and CLI, as well as the repeater track relay TRI, will again be energized. The picking up of the track repeater re lay TR! opens its back contact 25 so that the pick-upcircuit for the relay SR2 is now broken. It should be remembered that with relay TR2 assuming its retracted position and the relay SR2 assuming its energized position a 75 impulse per minute code is applied to the east end of block W, so that the signal at the entrance end (west end) of the block W indicates caution, as illustrated for the signal S4 in the drawings. apparatus associated with the signalS2 is now in With the clear relay GL2- in its.

With the The the same condition as that illustrated for the signal S6 in the drawings.

As the train passes the signal S4 the same operations, as just explained for the signal S2 when the train passed the signal S2, take place. That is, the signal S4 is operated to its stop condition and the directional stick relay SR4 is picked up and stuck up. As the train in question now passes entirely out of the block X the relays CA2 and TRZ pick up and thereby open the pickup circuit and both stick circuits for the directional stick relay SR2. The Picking up of caution relay CA2 (relay CL2 still down) closes an energizing circuit for the yellow lamp Y of the signal S2. The dropping of the directional stick relay SR2 (relay TRZ being up) causes the entering signal (not shown) at the west end of the block W to give a clear indication.

Similar operations take place when the train under consideration passes the signal S6.

Let us now assume that the train in question has passed entirely through the blocks X and Y and is now occupying the block Z. Under this condition the apparatus is in the condition as illustrated in the drawings. It will be noted that with the directional stick relay SR6 energized by its stick circuit that its contacts II and I2 will be in their raised condition. Under this condition the transformer TTG will be deenergized, whereas the transformer TT5 will be energized by current coded at the 75 impulse per minute rate. The circuit for the winding of the transformer TT5 may be traced as follows: starting at the one terminal of the transmission line Tr through the winding of the transformer TT5, back contact 12 of the relay SR5, front contact I l of the directional stick relay SRt, coding contact 15 of the coding motor CM56, back contact it of the track repeater relay TRB, to the other wire ofthe transmission line Tr. This application of the 75 impuls per minute rate code to the east end of the track section Y causes the track relay T4 at the west end of this section Y to be intermittently picked up at the 75 impulse per minute code rate for substantially two seconds, after which the track relay T4 remains deenergized for substantially two seconds. This intermittent picking up of the track relay T4 at the 75 per minute impulse code rate for alternate two second periods causes the relay CA4 to pick up but does not allow sufficient current to flow to the clear relay CL l through the medium of the rectifier RE4 so that this clear relay GL4 remains deenergized. The caution relay CA4 will, however, be picked up by this '75 impulse per minute code rate, even though only applied intermittently, as

a result of which the caution lamp y for the signal 4 will be energized through back contact 35 of the relay CM and front contact 36 of the relay CA4. The picking up of the caution relay CA4 following unoccupancy of block Y caused the stick circuit for the relay SR4 (which was closed during the occupancy of the block Y) to be broken. Also with the caution relay CA4 in its energized condition even though the clear relay GL4 is in its deenergized condition will cause energization of the track repeater relay TBA, thereby causing the 180 impulse per minute code rate circuit for the transformer TT3 to be closed, this circuit including the back contact I2 of the relay SR3, back contact H of the relay SR4, the 180 impulse per minute coding contact of the coder CM3 l and the front contact Ill of the relay TR4. It is thus seen that the block X is provided at the east end with coded energy of the 180 impulse per minute coding rate as a result of which the signal S2 will again assume its clear condition.

Since the coding impulses of current flowing in the track rails constitute alternating current they can be inductively detected on the locomotive, as for instance, through the medium of receivers RI one located over each track rail and supported in front of the locomotive. These receivers comprise a core of laminated iron on which there is wound a coil. These coils are connected in series and to an amplifier A and also include in series therewith a condenser C which tunes this circuit to the frequency of the alternating current flowing in the track circuit cycle in this instance). The output side of this amplifier A feeds current of amplified quantity to the code following relay CR so that this code following relay CR follows the code pulses in the track rails in the same Way as the track relay of the block occupied by the train would have done had the train not entered the block. This code following relay CR controls the carcarried signals 9, y and r in exactly the same way and by similar apparatus as that employed to control the wayside signals. For this reason like parts have been designated by like reference characters except that exponents or suffixes t have been substituted for the numeral exponents and sufiixes. There is, however, one difference between the car-carried apparatus and the trackway apparatus in that the stick circuits of the relays CA and CL employed along the trackway have been omitted from corresponding relays carried on the locomotive. It will be remembered that stick circuits were employed to hold these relays CA and CL energized during the periods when the alternate track circuit is in use. In order to prevent the car-carried relays CM and CRt from dropping during this period, these relays CLt and CM have been made specially slow dropping.

Although no brake control apparatus or other means for retarding the speed of the train have been illustrated, it should be understood that suitable automatic brake control apparatus controlled by the car-carried relays CM and CM may be employed, if desired.

The applicant has thus disclosed an absolutepermissible-block signaling system for railroads capable of operating either wayside or cab signals and which does not require any line wires except the usual power transmission line along the trackway, and which employs double or duplicate track circuits, one track circuit having a track relay at one end of the block and the other track circuit having a track relay at the other end of the same block. In each block, track circuits are made available alternately by durations of time sufficiently along to allow an entire code to be transmitted and received. Although the applicant has disclosed only one specific embodiment of the present invention, it should be understood that this has been done only for the purpose of disclosing the nature of the invention by illustrating one specific form thereof, and should not be construed to limit the number of embodiments in which the invention may take form, and it should be understood that various changes, modifications, and additions may be made to adapt the invention to the particular problems encountered in practicing the same and without departing from the spirit or scope of the invention except as required by the scope of the following claims.

What I claim as new is:

1.- In a duplex track circuit of the coded type comprising, a section of track, code applying apparatus at each end of said section, code responsive apparatus at each end of said section, and double throw contacts at each end of said section operating in synchronism to connect the code applying apparatus at one end to the code responsive apparatus at the other end through the rails of said section and connect the code applying apparatus at the other end to the code responsive apparatus at said one end through the rails of said section alternately, said double throw contacts assuming alternate positions at such a slow rate that a complete code comprising a plurality of impulses may be transmitted in opposite directions through the rails of said section during such single alternate connection by said double throw contacts.

2. In a duplex track circuit of the coded type comprising, a section of track, code applying apparatus at each end of said section, code responsive apparatus at each end of said section, and double throw contacts at each end of said section operating in synchronism to connect the ternately in opposite directions through the rails of said section during each alternate connection, and said code responsive apparatus having slow acting operating characteristics such as to manifest a continuous code in spite of its intermittent interruption due to such alternation.

3. In combination, a track section separated by insulating joints from the adjacent track, code creating apparatus and code responsive apparatus at each end of said sections, double throw contacts at each end of said section operated substantially in synchronism, and circuit wires including said contacts to alternately connect the code creating and code responsive apparatuses to the ends of said section in such a manner that the code creating apparatus at one end is connected to the track section when the code responsive apparatus at the other end is connected to the track section, the timing of said contacts being such that a complete code consisting of a plurality of current impulses is transmitted first from one end to the other and then from the other to said one end of said track section.

4. In combination, a track section separated by insulating joints from the adjacent track, code creating apparatus and code responsive apparatus at each end of said sections, double throw contacts at each end of said section operated substantially in synchronism, and circuit wires to alternately connect the code creating and code responsive apparatuses to the ends of section,

apparatus being so constructed that it will manifest continuous reception of a code in spite of e the interruption during which a code consisting of a plurality of current impulses is being transmitted to the opposite end.

5. In combination, a railway track divided into sections by insulating joints, a transmission line extending along said railway track, code creating apparatus and code responsive apparatus at each end of each track section,contacts at each end of each track section for alternately connecting said code creating and said code responsive apparatus to the rails of such track a distinctive current intermittently superimposed upon the transmission current of said transmission line, and electro-responsive means controlled by said intermittently superimposed current for intermittently closing said contacts in such a manner that the code creating apparatus is connected to a particular end of each track section while the code responsive apparatus is connected to the opposite end of such track section for a time during which a complete code consisting of a plurality of current impulses is transmitted and so that the code responsive apparatus is connected to said particular end of each track section while the code creating means is connected to the Opposite end of such track section for a time during which a complete code consisting of a plurality of current impulses is transmitted.

6. In combination, a railway track divided into sections by insulating joints, a transmission line extending along said railway track, code creating apparatus and code responsive apparatus at each end of each track section, contacts at each end of each track section for alternately conmeeting said code creating and said code responsive apparatus to the rails of such track section, a distinctive current intermittently superimposed upon the transmission current of said transmission line, and electro-responsive means controlled by said intermittently applied distinctive current for intermittently closing said contacts in such a manner that the code creating apparatus is connected to a particular end of each track section while the code responsive apparatus is connected to the opposite end of such track section and so that the code responsive apparatus is connected to said particular end of each track section while the code creating means is connected to the opposite end of such track section said intermittently applied distinctive current being applied and removed for sufiiciently long time periods to allow a complete code consisting of a plurality of impulses to be sent in opposite directions alternately.

'7. In combination, a railway track divided into sections by insulating joints, a transmission line extending along said railway track, code creating apparatus and code responsive apparatus at each end of each track section, contacts at each end for intermittently closing said contacts in such a manner that the code creating apparatus is connected to a particular end of each track section while the code responsive apparatus is connected to the opposite end of such track section andso that the code responsive apparatus is connected to said particular end of each track section while the code creating means is connected to the opposite end of such track section said intermittently applied distinctive current being applied and removed for sufficiently long time periods to allow a complete code comprising a plurality of code elements to be sent in opposite directions alternately and said code responsive apparatus being constructed to manifest the continuous reception of a code in spite of its intermittent nature.

8. In a duplex track circuit of the coded type comprising, a section of track, code applying apparatus at each end of said section, code responsive apparatus at each end of said section, and double throw contacts at each end of said section operating in synchronism to connect the code applying apparatus at one end to the code responsive apparatus at the other end through the rails of said section and connect the code applying apparatus to the other end to the code responsive apparatus at said one end through the rails of said section alternately, said double throw contacts assuming alternate positions at such a slow rate that complete codes each comprising a plurality of impulses will be transmitted alternately in opposite directions through the rails of said section during such connection.

9. In a duplex track circuit of the coded type comprising, a section of track, code applying apparatus at each end of said section, code responsive apparatus at each end of said section responsive distinctively to different codes each consisting of a plurality of impulses, and double throw contacts at each end of said section operating in synchronism to connect the code applying apparatus at one end to the code responsive apparatus at said one end through the rails of said section and connect the code applying apparatus at the other end to the code responsive apparatus at said one, end through the rails of said section alternately, said double throw contacts assuming alternate position at such a slow rate that a complete code comprising a plurality of impulses may be transmitted alternately in opposite directions through the rails of said section during such connections made repeatedly, and said code responsive apparatus having slow acting operating characteristics such as to manifest a continuous code in spite of its intermittent interruption due to such alternation.

'10. In combination, a railway track divided into sections by insulating joints, a transmission line extending along said railway track, code creating apparatus and code responsive apparatus at each end of each track section, contacts at each end of each track section for alternately connecting said code creating and said code responsive apparatus at that end to the rails of such track section, a distinctive current intermittently superimposed upon the transmission current of said transmission line, and electroresponsive means controlled by said intermittently applied distinctive current for intermittently closing said contacts in such a manner that the code creating apparatus is connected to a particular end of each track section while the code responsive apparatus is connected to the opposite end of such track section and so that the code responsive apparatus is connected to said particular end of each track section while the code creating means is connected to the opposite end of such track section said intermittently applied current being applied and removed for sufficiently long time periods to allow a complete code consisting of a plurality of impulses to be sent first in one direction and then in an opposite direction through the track section.

11. In combination, a railway track divided into sections by insulating joints, a transmission lineextending along said railway track, code creating apparatus and code responsive apparatus at each end of each track section, said code creating apparatus creating one of two distnctive kinds of codes each comprising a plurality of impulses distinctive in character and said code responsive apparatus manifesting which of the two distinctive codes is being received, contacts at each end of each track section for alte nately connecting said code creating and said code responsive apparatus to the rails of such track section, a distinctive current intermittently superimposed upon the transmission current of said transmission line, and electro-responsive means controlled by said intermittently applied current for intermittently closing said contacts in such a manner that the code creating apparatus is connected to a particular end of each track section while the code responsive apparatus is connected to the opposite end of such track section and so that the code responsive apparatus is connected to said particular end of each track section while the code creating means is connected to the opposite end of such track section said intermittently applied distinctive current being applied and removed for sufiiciently long time periods to allow a complete code consisting of a plurality of impulses to be sent in opposite directions alternately and said code responsive apparatus being constructed to manifest the continuous reoeption of a code in spite of its intermittent nature.

12. In an absolute-permissive-block signaling system, the combination with a railway track divided into blocks by insulating joints, a signal at each end of each block to govern the movement of trafiic into such block from that end, code responsive means associated with each signal and controlling the same and governed through the rails of the block in advance by code creating means located at the exit end of such block, and synchronously operated contacts at opposite ends of each block for alternately connecting the code creating means and the code responsive means across the rails at such end of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating at a sulficiently slow rate to allow complete codes each consisting of a plurality of code elements to be sent alternately in opposite directions through the rails of such block to control the code responsive means at the ends of the block.

13. In an absolute-permissive-blocl: signaling system, the combination with a railway track divided into blocks by insulating joints, a signal at each end of each block to govern the movement of traffic into such block from that end, code responsive means associated with each signal and controlling such signal and governed through the rails of the block in advance by code creating means located at the exit end of such block, and synchronously operated contacts at opposite ends of each block for alternately connecting the code creating means and the code responsive means across the rails at such end of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating at a sufiiciently slow rate to allow complete codes each consisting of a plurality of current impulses to be sent alternately in opposite directions through the rails of such block, and said code responsive means being constructed to manifest the continuous reception of a code in spite of its intermittent reception.

14. In an absolute-permissive-blocl; cab signaling system, the combination with a railway track divided by insulating joints into blocks,

code responsive means at each end of each block governed through the rails of such block by code creating means located at the opposite end of the block, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its end of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating sufficiently slow to allow a complete code consisting of a plurality of current impulses to be transmitted during each closure of such contacts, means for controlling each code creating means by the code responsive means at the adjacent end of the block next in advance, and car-carried apparatus including a cab signal controlled by the coded current flowing in the track rails in advance of the vehicle carrying such car-carried apparatus.

15. In absolute-permissive-block cab signaling system, the combination with a railway track divided by insulating joints into blocks, code responsive means at each end of each block governed through the rails of such block by code creating means located at the oppoposite end of the block, said code responsive means being constructed to continuously manifest a code even though the code is intermittently absent for a time period to allow a complete code comprising a plurality of current impulses to be transmitted in the opposite direction, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its end of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating sufficiently flow to allow a com plete code comprising a plurality of current impulses to be transmitted during each closure of such contacts, means for controlling each code creating means by the code responsive means at the adjacent end of the block next in advance, and car-carried apparatus including a cab signal controlled by the coded current flowing in the track rails in advance of the vehicle carrying such car-carried apparatus.

16. In an absolute-permissive-blocl; signaling system, the combination with a railway track end of the block and said code responsive means being capable of manifesting the reception of any one of a plurality of codes each consisting of a plurality of current impulses distinctive from the current impulses of any other code and being constructed to continuously manifest a code even though the code is intermittently absent for time periods each period of which is long enough to allow a complete code consisting of a plurality of current impulses to be transmitted in the opposite direction through the track rails, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its ends of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two enw of the block are alternately controlled by the Code creating means at the opposite end of the block, said contacts operating sumciently slow to allow a complete code comprising a plurality of current impulses to be transmitted during each closure of such contacts, means for controlling each code creating means by the code responsive means at the adjacent end of the block next in advance, and signals at each end of the block for governing the movement of traffic into that end of the block controlled by the associated code responsive means.

1'7. In an absolute-permissive-block cab signaling system, the combination with a railway track divided by insulating joints into blocks, code responsive means at each end of each block governed through the rails of such block by code creating means located at the opposite end of the block, said code responsive means being capable of manifesting the reception of any one of a plurality of codes each consisting of a plurality of current impulses distinctive from the current impulses of any other code and being constructed to continuously manifest a code even though the code is intermittently absent for time periods each period of which is long enough to allow a complete code consisting of a plurality of current impulses to be transmitted in the opposit direction through the track rails, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its end of the block in such synchronous relation wtih the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating sufiiciently slow to allow a complete code consisting of a plurality of current impulses to be transmitted during each closure of such contacts, means for controlling each code creating means by the code responsive means at the adjacent end of the block next in advance, and car-carried apparatus including a cab signal controlled by the coded current flowing in the track rails in advance of the vehicle carrying such car-carried apparatus.

18. In an absolutepermissiveblock cab signaling system, the combination with a railway track divided by insulating joints into blocks, code responsive means at each end of each block governed through the rails of such block by code creating means located at the opposite end of the block, said code responsive means being capable of manifesting th reception of any one of a plurality of codes each consisting of a plurality of current impulses distinctive from the current impulses of any other code and being constructed to continuously manifest a code even though the code is intermittently absent for time periods each period of which is long enough to allow a complete code consisting of a plurality of current impulses to be transmitted in the opposite direction through the track rails, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its end of the block in such synchronous relation with the operation of the contacts at the opposit end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts operating sufliciently slow to allow a complete code consisting of a plurality of current impulses to be transmitted during each closure of such contacts, means for controlling each code creating means by the code responsive means at the adjacent end of the block next in advance, and a wayside signal at each end of such block for governing the movement of trafiic into such block from that end controlled by the associated code responsive means.

19. In an absolute-permissive-block signaling system, the combination with a railway track divided by insulating joints into blocks, code responsive means and code creating means at each end of each block, said code responsive means being governed through the rails of such block by the code creating means located at the opposite end of the block and said code responsive means being capable of manifesting the reception of any one of a plurality of codes each consisting of a plurality of current impulses distinctive from the current impulses of any other code and being constructed to continuously manifest a code even though the code is intermittently absent for time periods each period of which is long enough to allow a complete code consisting of a plurality of current impulses to be transmitted in the opposite direction through the track rails, synchronously operated contacts at the two ends of each block for alternately connecting the code creating means and the code responsive means across the rails at its ends of the block in such synchronous relation with the operation of the contacts at the opposite end of the block that the code responsive means at the two ends of the block are alternately controlled by the code creating means at the opposite end of the block, said contacts being sufficiently slow to allow a complete code comprising a plurality of current impulses to be transmitted during each closure of such contacts, a directional stick relay at each end of each block having a pick-up circuit and a stick circuit each controlled by the associated code responsive means, means for controlling each code creating means by the directional stick relay of the adjacent end of the block next in advance, and signals at each end of a block for governing the movement of trafiic into that end of the block controlled by the associated code responsive means.

20. The combination with a track section connected to adjacent track by insulating joints, code creating and code responsive apparatus at each end of said section, said code creating apparatus being constructed to transmit any one of a plurality of codes each code including a plurality of impulses which distinguish in character from the impulses of any other of said plurality of codes and said code responsive means being constructed to distinctively manifest the reception of any one of said plurality of codes, double throw contacts at each end of said section operated substantially in synchronism, and circuit wires including said contacts to alternately connect the cod creating and code responsive apparatuses to the ends of said section in such a manner that the code creating apparatus at one end is connected to the track section when the code responsive apparatus at the other end is connected to the track section, the timing of said contacts being such that a complete code consisting of a plurality of current impulses is transmitted first from one end to the other and then from the other to said one end of said track section, and a signal at each end of said track section controlled by the associated code responsive means.

ROBERT M. PHINNEY.