US2197416A - Signal system - Google Patents

Description

April 16.1940. y w. P., PLACEA l SIGNAL SYSTEM Filed Feb. 17, 1939 I5 Sheets-Sheet 1 April 16, 1940. `w, PLACE 2,197,416

SIGNAL SYSTEM Filed Feb. 17, 1939 s sheets-sheet 2 ler v 10? dmplfier TF# ""1] "if/04 B Decoding I/nit C pw Liquid F'Low Contc INVENTOR Tf1/Har Place.

BY v

HIS ATTORNEY Apnl 16, 1940.

One C ycLe 5 Sheets-Sheet 3 0n Period Off Period Coder GoncM? #AV-g Commun l 2F 011e Cycle. l 011, Peri 0d Qjf Period Uurren [1v1/pulses 0j A A A A [204%7560616 AA AA fh AA Ileguencies vv vv vv v 0n Period )j/ Period Elecrontilfe @ne ('ycle 0n Perid @jf/"Period Carrelli [mpwle Under/90 60de AAA 011e Oycl e -lNVENTOR Will dPPLaxce.

His .ATTORNEY Patented Apr. 16, 1940 UNITED .STATES PATENT yOFFICE SIGNAL SYSTEM Application February 17, 1939, Serial No. 256,946

12 Claims.

My invention relates to signal systems, and

more specifically to signal systems for railways.

I shall describe one form of apparatus embodying my invention, and I shall then point out the i" novel features thereof in claims.

Code signal systems have found widespread use, and in railway signaling code signal systems are now of common practice. In many of the code signal systems for railways an alternating current of a selected frequency, preferably 100 ,cycles per second, is coded by being periodically interrupted, the interruptions being preferably of the code frequencies of 180, 120 and 75 cycles per minute. Each of such code frequencies is assigned to reflect a lparticular traic condition. For example, as generally used, the 180 code frequency reflects a clear trafc condition, the 120 code frequency reflects an approach medium traffic condition, the 75 code frequency reflects an approach 2 traffic condition, and no current reflects a stop or slow speed condition. In such codes of a1- ternating current the on and oif" periods are of substantially equal duration` In the 180 code D frequency, for example, each cycle is one-third second in duration, and current is supplied (on period) for substantially one-sixth second, and no current is supplied (.off period) for substantially one-sixth second.

The alternating current is usually distributed from a central power station to the different signaling points along the railway by a transmission line formed by line Wires strung on a pole line along the right of way and line transformers one 'at eachsignaling point. The primary 'control circuit is the track circuit of an insulated track section, yand coding apparatus codes the alternating current supplied to the track circuit according to traffic conditions in advance of that track section. circuit is mounted on the train in inductive relation with the track rails to inductively receive an electromotive force in response to each period alternating current flows in the track circuit. A code following relay governed by the receiving circuit is operated to one position when the alternating current flows in the track circuit, and is operated to a second position when the alternating current ceases. Hence the code following relay has substantially equal on and off periods of operation. That is, the period the `relay remains at the position effected by the presence of current on period) and the period the relay remains at the position effected by the absence of current (off period) are substan- The decoding apparatus governed ""1 tially equal.

In such cab signal systems a receiving by the code following relay for selectively controlling a cab signal in accordance with the different codes of alternating current is constructed for most satisfactory operation when the code following relay is operated with substantially equal cn and off periods Again, when the track relay controlled by the track circuit of' each track section is a code following relay and this track relay governs a wayside signal through the medium of a decoding relay means, it is desirable to effect substantially equal on and oil pericds of operation for the code following track relay. That is to say, the decoding relay means now in general use in railway code signal` systems operates most effectively and satisfactorily when 15 the on and. off operation periods of the code following relay are equal.

Furthermore, the lter preferably associated with the receiving circuit of the present code signal systems for railways is sharply tuned to the frequency of the alternating current which, as stated hereinbefore, is preferably cycles per second,

Other code signal systems have been proposed for railways which use coded impulses of direct current. The direct current is supplied from batteries or other sources of unidirectional current located one at each signaling point, the control circuit vbeing the track circuit the same as in coded alternating current systems. The coding apparatus at each signaling point so interrupts the supply of unidirectional current to the track circuit of the associated track section that the current impulses of direct current have different code frequencies according to different traffic conditions in advance of that section. The current impulses of direct current would preferably be of the 180, and '75 code frequencies the same as under the coded alternating current systems. These systemsI using such coded direct `current do not require a constantly energized transmission line, and hence are free from delays 'to traffic should all line wires be destroyed by a storm. The direct current impulses are in each case of relatively high peak voltage and of short duration. 'I'he high peak voltage is an aid to the shunting sensitivity of the track circuit and also effects, when the section is occupied by a train, surges of current of high amperage which is an aid to the inductive transfer of energy to train 0 carried receiving circuits. The current impulses are, as stated above, of short duration, the duration of each current impulse being only a small portion of the code cycle, and hence the energy output required of the battery is relatively low.

With code following relays operated to a first position during the presence or" current and operated to a second position during the absence of current, it follows that in systems of the code impulse type (coded direct current) the on period or the code following relay is relatively short compared with the ofi period of the relay. Such limping operation of the code following relay may not, therefore, effectively operate the present decoding apparatus which, as stated hereine before, is constructed for substantially equal on and ofi periods or the code following relay.

A feature oi my present invention is the provision in signal systems of the code impulse type of novel and improved means for transmitting code impulses or" direct current of the present code frequencies which are eiective to operate code following relays with substantially equal on and oli periods and the present standard decoding means can be used, Another feature of my invention is the provision of novel and improved coding means wherewith the direct current code impulses transmitted thereby effectively inuence the present receiving circuits which are, as stated hereinbefore, sharply tuned for reception of alternating current oi 100 cycles per second. Thus a train equipped with standard train carried cab signal apparatus will be controlled when the train is moving over a track circuit using coded direct current supplied apparatus embodying my invention equally as well as when the train is moving over a track circuit supplied with the present coded alternating current. Still another feature of my invention is the provision in code signal systems of the impulse type oi novel means for checking the proper occurrence of the current impulses supplied to the 'track circuit. Other features and advantages oi my invention will appear as the specirlcation progresses.

For a better understanding of my invention, reference can be had to the accompanying drawings in which Figs. la and 1b are diagrammatic views of a preferred form of apparatus embodying my invention when applied to a railway signal system, Fig. la being the trackway portion of the apparatus and Fig. 1b being the train carried portion of the apparatus. Fig. 2 is a view partly diagrammatic and partly in plan of a coder or code transmitter that may be used in the trackway apparatus of Fig. la. Fig. 2a is a detail of the coder of Fig. 2. Fig. 3 is a diagram illustrating the operation of certain circuit controlling contacts of the coder of Fig. 2. Figs. 4a and 4b are diagrams illustrating operating characteristics of the direct current impulses produced by the coder of Fig. 2 under certain conditions and of the electromotive forces effected by such impulses. Figs. 5a and 5b are diagrams illustrating operating characteristics of direct current impulses produced by the coder of Fig. 2 under certain other conditions and of the electromotve forces effected by these latter impulses.

In each of the several views like reference characters designate similar parts.

It will be understood that I do not wish to limit my invention to signal systems for railways and this one application of apparatus embodying my invention will serve to illustrate the many places where the apparatus will be useful.

Referring to Fig. la, a railway over which trafric normally moves in the direction indicated by an arrow has its track rails la and lb formed by the usual insulated rail joints into consecutive track sections of which only section W-X and the adjoining ends of the two sections adjacent thereto are shown for the sake of simplicity. Each track section is provided with a track circuit which comprises means for supplying coded unidirectional current across the rails at the exit of the section and a receiving and decoding relay means connected across the rails at the entrance of the section. Looking at track section W-X, coded unidirectional current is supplied to the rails adjacent the exit of the section through the medium of a battery TB, a rst and a second track transformer TI and T2, coding apparatus indicated as a whole by the reference character CT, and associated circuits, the code frequency supe plied being governed by trailic controlled relays XA, XR and XL to be later described.

Before proceeding further with the description of the apparatus of Fig. la, it should be pointed out that in several instances the contact lingers oi relays XA, XR and XL are shown remote from the windings of the relays in order to simplify the drawings. 1n each such instance the Contact iinger is identified by the reference character of the relay and is shown in the position corresponding to the normal energized or deenergized condition of the relay winding.

The secondary windings of the transformers Tl and T2 are each connected across the track rails la and Ib over circuits which are so controlled that only one secondary Winding is connected with the rails at a time. The secondary nding 2 of track transformer TI has its lei'tliand terminal connected with rail Ia over wire and has its right-hand terminal connected with rail lb over four alternate paths, the first one of which includes wire 4, front contact 5 of relay XA and wire 6. The second path includes Wire il, back contact 7 of relay XA, front contact 8 of relay XR and wires 9 and 6. The third path includes wire 4, back contact l of relay XA, back Contact I of relay XR, lower winding II of a polar relay PR to be later described, front contact I2 of relay XL, wire I3, contact MI of a coder or code transmitter CI20 also to be later described, and wires 9 and 8. The fourth path is the same as the third path up to winding II of relay PR, thence over back contact I4 of relay XL, wire I5, contact MI of a code transmitter or coder C75 to be later described, and wires 9 and 6.

The secondary Winding I6 or transformer T2 has its left-hand terminal connected with rail I a over wires I'I and 3, while its right-hand terminal is connected with rail Ib over two alternate paths, a iirst one of which includes back Contact I8 of relay XA, back contact I9 of relay X'R, top winding 20 of polar relay PR, front contact 2I of relay XL, wire 22, contact M2 of coder C120 when closed as will later appear, and wires 9 and 5. The second path is the same as the rst path up to winding 20 of relay PR, thence over back contact 23 of relay XL, wire 24, contact M2 of coder C75 when closed, and wires 9 and 6. It follows that when either relay XA or XR is picked up the secondary winding 2 of track transformer TI alone is connected across the track rails, but when 30th relays XA and XR are released and relay XL is picked up the secondary winding 2 of transformer TI is connected across the rails serially with the lower winding II of relay PR and the contact MI of coder CI20, while the secondary winding I6 of transformer T2 is connected across the rails serially with the top winding 20 of relay PR and contact M2 of coder CI20. When relays XA, XR and XL are all released, the secondary winding 2 of transformer TI is connected across CFI the rails over a path serially including winding I I of polar relay PR and contact MI of coder C15, while the secondary winding I6 of transformer T2 is connected across the rails over a path serially including winding 20 of polar relay PR and contact M2 of coder C15. It should be here pointed out that when both relays XA and XR. are released a short circuit path across the rails Ia and Ib` can be traced from rail Ia over wires I1 and 83, back contact 84 of a relay 82 to be referred to later, back contacts and 86 of relays XA and XR, respectively, and Wires 81, 9. and 6 to rail Ib. The purpose of such short circuit path across the track rails will be more fully described hereinafter.

Condensers 21 and 28 are preferably connected across the primary windings 25 and 26, respectively, of transformers TI and T2. The circuits by which current from battery TB is supplied to the primary windings 25 and 26 of transformers TI and T2, respectively, will be taken up and pointed out in detail hereinafter.

The coding apparatus CT may take different forms and as here shown it comprises three separate code transmitters or coders C|80, CI20 and C15 of the well-known torsional type. For example, these coders may be of the form covered by the United States Letters Patent No. 1,858,- 876, granted May 17, 1932, to Paul N. Bossart for Coding apparatus, the coders CI2IJ and C15 being modified by an improvement to be later described. Reference is made to the above Bossart Patent No. 1,858,876 for a full description of such coding apparatus, and the coders CI8IJ, CI20` and C15 will be in the instant application described only to the extent necessary for a full understanding of my present invention and to describe the improvements herein provided for the coders CI20 and C15.

Referring to Fig. 2, a magnetic core structure 29 is mounted on a frame 30 of suitable nonrnagnetic material such as brass. The core 29 terminates in two spaced pole pieces 29a and 29h and has mounted thereon a winding 3 I. An oscillatable armature 32 is secured to a shaft 33 in any convenient manner here shown as by set screw 32a in a hub of the armature. Shaft 33 is journaled in frame 35 so that the armature 32 is disposed for rotatable movement between the pole pieces 23a and 29h. The armature 32 is cylindrical in shape and is provided with an outer surface (see Fig. 2a) so shaped that when the armature is rotated in a rst direction (counterclockwise in Fig. 2a) from a normal or biased position the air gaps between the outer surface of the armature and the pole pieces 29a and 29h are gradually decreased, but if the armature is rotated in the opposite or second direction (clockwise in 2o) from. such normal position the air gaps are at first gradually increased and then abruptly increase. The armature 32 is biased to its normal position by a spiral spring 34 the outer end of which is secured to the frame 3|] by screws 35 and its inner end is secured to the hub of armature 32 by screws IUS. The coder is provided with a contact KI for controllingr the supply of current to winding 3I and which Contact comprises a contact member 36 disposed for operation by rotation of shaft 33, and a stationary contact member 31, the arrangement being such that contact member 35 engages contact member 31 to close the contact KI at the normal position of armature 32 and the contact member 38 moves out of engagement with contact member 31 to open the contact KI when the armature 32 swings in its first direction away from the normal position. The contact member 36 is connected with a terminal 38 through a suitable flexible connection 38a, while the contact member 31 is connected with one i terminal of winding 3|. When a source of direct current is connected at terminals B and C of Fig. 2 the winding 3l is energized and a magnetic flux is built up in the core 29 which attracts armature 32 against the force of the bias spring 34 in its first direction from its normal position, that is,

armature 32 swings in the direction of the decreasing air gap. After a limited rotation of armature 32, the contact KI is opened and the winding 3l is deenergized. Bias spring 34 now causes armature 32 to swing back toward its normal position and contact KI is closed to again energize winding 3I. Due to the inertia of the parts, armature 32 swings past the normal position in its second direction a limited distance before it is again rotated in its first direction due to the attraction created by the energization of winding 3I. The parts are so constructed that armature 32 swings substantially equal distances each side of its normal position. It is clear that as long as the current source is connected at teri:

minals B and C the armature 32 will oscillate at a frequency governed by the mass of the armature 32 and the stiffness of the spring 34. The parts of coder Cl of Fig. la are so proportioned and adjusted that its armature oscillates at the frequency of 180 cycles per minute or three cycles per second. Coder Cl2 and coder C15 are so proportioned and adjusted that their respective armatures oscillate. at the code frequencies of and '75 cycles per minute, respectively.

A contact Mt is carried on shaft 33 by means of clips 3S. Contact M4 is preferably of the liquid flow type such as a mercury switch, a common construction of which consists of a glass envelope having two spaced metal electrodes and a quantity of mercury sealed therein, the arrangement being such that the mercury bridges the electrodes at certain positions of the envelope and the mercury ows away from the. electrodes when the envelope is tilted. Contact M4 for each of the coders of Fig. la is so positioned on shaft 33 that the contact is closed at the normal position of the armature 32 and is tilted to open the contact as the armature swings in its first direction, and is reclosed as the armature swings back to its normal position and remains closed while the armature swings in its second direction. Hence, as illustrated in Fig. 3, where the black area represents the closed position of the contacts, contact M4 opens at the start of each operating cycle of the coder (armature starts to swing in said one direction), is reclosed at the end of the first half period of the cycle (armature returned to normal position) and remains closed during the second half period of each operating cycle (armature swings in said second direction and returns to normal position).

The construction thus far described for the coder is common for eachy of the coders CIBQ, CI20 and C15 and is substantially the construction of the coding apparatus covered by the aforementioned Bossart Patent No. 1,858,876 except for the liquid ow type of contact. Coders C120 and C15 are each provided with an improvement which I shall now describe.

Again referring to Fig. 2, a second armature 40 is xed on a hollow shaft 41 which is slipped over and rotates freely on shaft 33. Armature 4I) is joined to the shaft 33 through a spiral spring 4I, the outer end of spring 4I being secured to armathe wave form of the track circuit current impulse is of relatively high peak voltage which, as is well known, aids the shunting sensitivity of the track circuit and which effects when the section is occupied by a train a current surge of high amperage which is an aid to the transfer of energy inductively to train carried apparatus. Furthermore, the duration of the current impulse is only a small portion of the cycle which in the case of the 180 code frequency is substantially .3 second. In the event that both relays XA and XR are released and relay XL is picked up so that back contacts 56, 64 and 68 of relay XA; back contacts 55, 65 and 69 of relay XR; and front contacts 54, 66 and 1l) of relay XL are closed, the coder'CIZ is operated and the battery TB is intermittently connected with the primary windings 25 and 2G of transformers TI and T2 through the medium of the contacts M4 and M3 of coder CI20. During the time contacts M4 and M3 of coder CIZII are closed, current flows to the primary windings 25 and 26 and energy is stored in the magnetic circuits of transformers TI and T2. When contact M4 is opened. the energy stored in transformer TI decays and a current impulse is supplied to the track rails because the secondary winding 2 is connected to the rails over back contacts 1 and Il) of relays XA and XR, winding II of relay PR, front contact I2 of relay XL, and contact MI of coder CI20 and since contact MI remains closed until after contact M4 of coder CIZB is opened. It is to be noted because relays XR and XA are released, closing back contacts 85 and 85, the current impulse flows through the short circuit path rather than through the track rails of the section. The current impulse flowing through winding Il of polar relay l PR energizes that relay, the energization being such as to cause polar contact members 1B and 11 to be operated to the right-hand positions. Shortly after this current impulse is supplied'by transformer TI, the contact MI of coder CI20 is opened and contact M2 is closed so that the secondary winding 2 of transformer TI is disconnected from the track rails and the secondary Winding I6 of transformer T2 is connected thereto. A little later in the operating cycle of coder CI25 the contact M3 is opened tovinterrupt the circuit to the primary winding 26 of transformer T2 and condenser 28, with the result that the energy stored in transformer T2 quickly decays and induces an electromotive force in the secondary winding I6 of transformer T2 which causes an impulse of current to be applied across the track rails because relays XA and XR are released closing their back contacts I8 and I9. Transformer T2 and condenser 28 are preferably similar to transformer TI and condenser 21, respectively,

. E and hence the current impulse supplied through transformer T2 is substantially of the same characteristics as that supplied through transformer TI. At the start this current impulse supplied through transformer T2 flows in the short circuit path rather than in the rails. This current impulse from transformer T2 flows in the winding 20 of polar relay PR in a direction to cause the polar contact members 16 and 11 to be operated to the left-hand positions. It follows that two current impulses are supplied during each operating cycle of coder CIZ!) and relay PR is operated in step with. the current impulses. With f relay PR operated current is reversibly supplied to the two half portions of the primary winding 18 of a transformer T3, the circuit for primary winding 18 being completed over back contacts 19 and 80 of relays XR and XA, respectively. The electromotive forces induced in the secondary winding 8I of transformer T3 are rectified by contact member 11 of relay PRvand are sup- .plied to the relay 82 as rectified current. After a few current impulses relay 82 is energized and plcked up, opening back contact 84 to remove the short circuit path across the track rails. From ,l

relay PR, transformer T3 and relay 82 function therefore to check the presence of two impulses each operating cycle of coder CIZQ. Ii impulsesA are supplied from transformer TI only, then polar relay PR remains at its righthand position and relay 82 is released tor complete the short circuit path across the track rails. Likewise, if impulses are supplied through transformer T2 only, polar relay PR is held at its left-hand position and relay 82 is released to complete the short circuit path across the track rails.

If relay XL is released closing back contacts 58, 61 and 13 at the same time that relays XA and XR are released, current from battery TB is supplied intermittently to the primary windings and 26 of transformers TI and T2 over the contacts M4 and M3 of coder C15. Since the contacts of coder C15 are positioned similarly to the contacts ofl coder CI20, two current impulses are supplied to the track rails during each operating cycle of coder C15. the windings II and 28 of polar relay PR being interposed in the connection withthe track rails and relay PR operated by each current impulse. Again it should be noted that at the start of the operation of coder C15 the track rails are short circuited over the path including back contact 84 of relay 82, but that the relay 82 is shortly picked up to remove the'short circuit if the Acurrent impulses are alternately supplied by the transformers TI and T2. i

From the foregoing description it is to be seen that under trafiic conditions that cause relay XA or relay XR to be vpicked up, codery C180 is operated and a single current impulse is supplied to the track circuit of section W-X each operating cycle of the coder, the wave form of the current impulse being as illustrated byv Fig. 5a. Under traffic conditions that cause relays XA and XR'to be released and relay XL to be picked up, coder CI2!) isoperated and two current impulses are supplied to the trackcircuit each operating cycle ofthe coder, 'the two current impulses being spaced apart by a predetermined time interval by virtue of the setting of the contacts MI, M2 and M3 of coder CIZII. The relationship of the setting of the contacts of coder CI20 and the spacing of the two current irnpulses supplied each operating cycle is illustrated by Figs. 3 and 4a. As illustrated in Fig. 4a, each current impulse has a damped wave form the same as explained in connection with the current impulse supplied to the track circuit when the coder CI8S is operated.

Under traffic conditions that cause relay XL as well as therelays XA and XR to be released, the coder C15 is operated and two current impulses are supplied to the track circuit each operating cycle of coder'C15, the impulses being spaced apart by a predetermined time interval by virtue E9 is connected across of the setting of the contacts of coder C15. The relationship of the setting of the contacts of coder C and the spacing of the current iinpulses supplied to the track circuit is illustrated by Figs. 3 and ea the same as in connection with coder Cill except for the fact that the two current impulses supplied when coder C75 is operated are spaced somewhat farther apart than the two current impulses supplied when the coder C I2?) is operated. The use of such spacing of the two current impulses supplied each operating cycle of coder CE2@ or coder C75 will be described more fully hereinafter. Furthermore it is to be recalled that the fact that two current impulses are supplied each operating cycle of coder CI'ZO or coder Cll is checked through the medium of polar relay PR and its associated apparatus.

The arrangement of a track transformer having a condenser connected across its winding and the two connected with the track rails so that the track circuit thus formed is an oscillatory circuit and the current impulse supplied to the track circuit when a direct current owing in the transformer winding is interrupted has a damped wave form is disclosed and claimed in my cepending application, Serial No. 239,523, iiled November 3 1938, for Signal systems.

Still referring to Fig. 1a, the receiving and decoding relay means for the track circuit of section Y -X includes a lter WF, a code following relay WT, decoding unit DUI and three control relays WA, WR and WL. As shown in Fig. lo, the iilter WF consists of an inductor .'39 and two condensers and 9! A portion o1 inductor the rails lo and Ib over condenser' 90 and wires 92 and 33, and the full inductor 89 is connected with the winding of relay WT through a full wave rectifier 94. The i'llter WF is tuned to resonance at the frequency of cycles per second. In other words, the circuit by which relay WT is connected across the track rails of section W-X is tuned to resonance at the frequency of the oscillations of the wave form of the current impulses supplied to the track rails through the medium of the apparatus located at the exit end of the track section. Since the current impulses supplied to the track circuit have a damped wave the oscillations of which are of the order of 100 cycles per second, the energy applied to filter WF sets up oscillation which persists in the iilter circuit for several cycles longer than the current impulse. Fig. 5u illustrates the damped wave of the track circuit current impulses under the 180 code frequency, and 5b illustrates the oscillation set up in the lter WF by each such current impulse. I have found that at the 180 code frequency a single current impulse of relatively high peak voltage causes oscillation to persist in the filter circuit for an interval which is substantially equal to one-half of the cycle interval. In other words, the on period of the oscillations created by a single current impulse is substantially equal to the oli period of the oscillations. The oscillations created in lter WF are rectified by rectier and are applied to the winding of the code following relay WT, with the result that the code following relay WT is operated at substantially equal on and olf periods when the code impulses of the track circuit are of the 180 code frequency. At the or '75 code frequency "de on period of the oscillations created in the filter is not long enough to avoid a limping operation of the code following relay if only one current impulse is transmitted each cycle. For this reason coders CI20 and C15 are constructed to provide two current impulses each code cycle. Looking at Figs. 4a and 4b, when the oscillations set up by the rst current impulse begin to they are supported by fresh energy from the second current impulse. The two current impulses transmitted each code cycle are so spaced by Virtue of the positioning of the contacts of the coder that the oscillations set up in the filter WF of the associated receiving means persist for sub- 1 stantially the rst half period of the cycle interval and the code following relay of the receiving means is operated for substantially equal on and off periods. The diference between the two current impulses transmitted through the medium of coder CIZD and the two transmitted through the medium of coder C75 lies in the fact that the two impulses thi' 7 code frequency are spaced slightly farther apart than. the spacing of the two current linnn...) under the 120 code frequency, this spacing being readily obtained by a proper setting of the contacts MI, M2 and M3 of the coder C15. The contact member 95 of code following relay WT is therefore operated at the code frequency of 180, 120 or 75 according to the cede frequency of the current impulses supplied to the track circuit, the on and ofl7 periods of operation of relay WT being substantially equal for each of the different code frequencies.

Code following relay WT controls over its contact member 95 the supply of current to the decoding unit DUI, the current impulses supplied to the decoding unit DUI being of a frequency corresponding to the code of the current impulses of the track circuit and being of substantially equal on and oil periods because of the operation effected for the code following relay WT. The decoding unit DUI may be oi standard construction and it is deemed suicient to say that relay WA connected with the output terminals of the unit DUI is eiectively energized and picked up only at the code frequencx7 of 180, relay WR connested with the output terminals of the unit DUI is effectively energized and picked up only when the code following relay is operated at the 120 code frequency, and relay WL connected with the output terminals of the unit DUI is effectively energized and picked up at either the '75, 120 or code frequency.

Control relays WA, W'R and WL correspond to the control relays XA, XR and XL, respectively, and control the supply of track current to the coding apparatus for the track circuitl for the section next in the rear of section W-X in the same manner that relays XA. XR and XL control the supply of current to the coding apparatus for the track circuit of section W-X Furthermore, the control relays XAy XR and XL are contr'olled by the track circuit for the section in advance of section W-X through a lter XF, code following relay XT and decoding unit DU?? in the same manner that relays WA, WR and WL are controlled by the track circuit of section W-X.

As shown at the lower right-hand portion of Fig. la, the relays XA, XR and XL govern the operating circuits of a wayside .signal XS, as will be readily understood by an inspection of Fig. la, and a detailed description of such operating circuits is not necessary since they are in accordance with standard practice and form no part of my present invention.

Referring now to Fig. lb, the train carried apparatus includes two inductors 96 and 9'! mounted on the train in inductive relation with track r'ails |a and Ib, respectively. Inductors 96 and 91 are connected through a condenser 98 with a portion of an inductor winding 99 of a filter TF, the connection of inductors 96 and 91 being such that electromotive forces induced therein by current formed in the rails in opposite directions add their effects. A condenser is connected across the inductor winding 99 and the full winding 99 is connected with the input terminals of an amplifier AM over wires |02 and |03, the amplifier AM being preferably of the electron tube type. The output terminals of amplifier AM are connected over wires |00 and |05 with the winding of a master code following relay MR. Relay MR in turn controls over its contact inember |0|` the supply of current to input side of a decoding unit DU3 whose output terminals are connected with control relays TA, TR and TL. The decoding unit DU3 is preferably of standard construction and the arrangement is such that relay TA is effectively energized and picked up only in response to operation of the code following relay MR at the code frequency of 180 cycles per minute, relay TR is effectively energized and picked up only in response to operation of relay MR at the code frequency of |20. and relay TL is effectively energized and picked up when relay MR is operated at either the |80, |20 or 15 code frequency. The control relays TA, TR and TL are used to control train governing means here shown as a cab signal CS of the four indication position light type. 'I'he operating circuits for' the cab signal CS' will be readily understood by an inspection of Fig. 1b and the circuits need not be described in detail since they are of standard practice and form no part of my present invention.

The train carried apparatus of Fig. 1b is substantially that of standard practice in present day use in coded alternating current systemsy It should be noted that filter TF interposed in the receiving circuit of amplifier AM is tuned to resonance at the frequency of 100 cycles per second. Furthermore, the decoding unit DUS is, as stated hereinbefore, constructed for substantially equal on and off periods of operation of the associated code following relay MR.

I shall now point out the operation of the train carried apparatus of Fig. 1b by the trackway apparatus of Fig. la. I shall lrst assume that the train enters the track section W--X from the left and the traffic conditions in advance of section W-X are such as to cause relay XA to be picked up so that coder C|80 is operated and current im- 'f pulses of the code frequency of 180 are supplied to the track rails, a single current impulse being supplied each operating cycle of the coder C |80 and the current impulse having a damped wave as illustrated in Fig. 5a. Each such current impulse induces an electromotive force in the train carried inductors 96 and 91 of relatively high peak voltage because oi' the high amperage of the current surge produced by the high peak voltage of the rail current impulse. The electromotive force induced in the inductors 96 and 91 set up in filter TF oscillations that persist for several cycles after the rail current impulse ceases because the filter TF is tuned to resonance at 100 cycles per second and the oscillation of the current impulse is of 100 cycles per second. As illustrated in Fig. 5b, the oscillations set up in filter TF persist for substantially one-half of the cycle interval. The energy of filter TF is applied to amplifier AM and after amplification the energy is effective to operate relay MR to its left-hand position, relay MR being operated to its righthand position when the oscillations in the filter TF cease. Hence the master relay MR is operated at the code frequency of 180 and the on and ofi periods of the operation of the relay are substantially equal the same as if the train on which the apparatus of Fig. 1b is mounted is moving over a track circuit supplied with alternating current coded at the 180 code frequency. With relay MR thus operated by the 180 code frequency, the relay TA is selected and the corresponding signal indication is effected for the cab signal CS.

I shall next assume that the traiiic conditions in advance of section W-X are such as to cause relay XR to be picked up while relay XA is released. The coder C|80 is operated and code impulses of current of the 180 code frequency are supplied to the track circuit of section W--X the same as previously described with the result that the cab signal CS displays the same signal indication. That is to say, the 180 code frequency for the track circuit of section W-X is effected in response to clear traflic conditions in advance and relay XA is picked up and is also effected in response to approach medium traffic conditions in advance and relay XR is picked up.

Assuming that the traffic conditions in advance of section W-X are such as to cause relays XR and XAto both be released while relay XL is picked up, the coder C|20 is operated to` cause two current impulses to be supplied to the track circuit each code cycle, the impulses being spaced apart a. predetermined time interval by the positioning of the contacts of the coder C|20 as illustrated by Figs. 3 and 4a. Each such current impulse induces electromotive forces in the inductors 96 and 91 that in turn set up oscillations in the filter TF, the oscillations effected by the second impulse beginning before the oscillations effected by the first impulse cease so that as illustrated in Fig. 4b the oscillations applied to amplifier AM for operating relay MR persist for substantially one-half period of the code cycle. Hence the relay MR is operated for substantially equal on and off periods in response to the track circuit current impulses supplied by the apparatus of Fig. la under the 120 code frequency the same as it would be operated'if the train was moving over a track circuit supplied with coded alternating current of the 120 code frequency. The current impulses supplied to the decoding unit DU3 will select relay TR which in turn will cause a corresponding signal indication for the cab signal CS.

In the event the traffic conditions in advance of section W-X are such relays XA, XR and XL are all released, the coder C15 is made active and two current impulses are supplied to the track circuit each code cycle, the two current impulses being separated a predetermined time interval by virtue of the setting of the contacts of coder C15.

Again, the oscillations set up in filter TF by the f section W-X is occupied by a train in advance, then the track circuit is shunted by the leading train and no electromotive force is induced in the inductors 9G 9i, with the result the relay MR is not operated the control TA, TR and TL are all released to establish a corresponding signal indication for the signal CS.

It is clear from the foregoing description that the train carried apparatus of Fig. lo, which is substantially that oi standard practice for the present code signal system for railways, is effectively operated by tl e rackway apparatus ci Fig. lb equally as Well as by track circuits using coded alternating current.

Although I have herein. shown and only ore of apparatus embed., venticn, it is inde. od that various changes and modifications .may made therein within the scope of the appended claims 'without departing from the spirit and scope of my invention.

Havingr thus di my iiivention, 'ivhat I claim is:

l. In a signal system for a railway whose track is formed into consecutive track se tions each of which is provided with a track circuit including a source of unidirectional current and each of which sections has associated therewith a conL ol relay governed by trafic conditions in advaie of the section the combination comprising, a coder for a section operative to divide time into successive operating cycles of a selected interval and provided with a rst and a second contact which are operated a predetermined interval apart during the rst half period of each of said cycles, and circuit means including a Contact cf the control relay for said section and said st and sec nd contacts of said coder to eiectively couple the current source of the section with its track circuit to cause to now in the track circuit during the iirst half period of each cycle two current impulses separated from each other by a predetermined interval.

2. In a signal system for a railway whose track is formed into consecutive track sections each of which is provided wtih a track circuit including a source of unidirectional current and each of which sections has associated therewith a control relay governed lcy traffic conditions in advance of the section the combination comprising, a first and a second track transformer for a section. each having a secondary winding connected across the track rails of the section, a coder operative to divide time into success've cycles or aselected interval and provided idth a nrst and a second contact which are closed the start of each cycle and are opened a predetermined interval apart during the first `iali period of each cycle, a first circuit inclue ng a contact of the control relay for said section and said first contact of the coder to connect the current source of said s cti-on with he prim :'y iifindirig of said st transformer', and a second circuit cluding Contact of the control relay and said second contact of the coder to connect the current source with the primary winding of said second transformer.

3. In a signal system for a railway whose track is formed into consecutive track sections each of which is provided with a track circuit including a source of unidirectional current and each of which sections has associated therewith a control relay governed by trailic conditions in advance of the section the combination comprising, a coder for a section having a cyclic operation of a predetermined frequency and provided with described a first and a second contact which are closed at the start of each said operation cycle and are successively opened at selected points oi the rst half period of the cycle,l and circuit means controlled by the control relay ol said section and including said rst and said second contacts supply from said source ci current to the track circuit of said section current impulse one when said first contact is opened and one when said second contact is opened to cause to flow in said track circuit during each said operation cycle two current impulses which are separated from each other.

In a signal System for a railway whose track is formed into consecutive track sections each of which. is provided with a track circuit including a source of unidirectional current and each of which sections has associated therewith a conn trol relay governed by trafhc conditions in advance of the section the combination comprising, a nrst i and a second track transformer for a section each having a secondary Winding connected across the track rails of said section, a polar relay having a first and a second winding, a coder for said section having a cyclic operation of a predetermined frequency and provided with two contacts which are closed at the start of each operation cycie are successively opened at selected points of the rst halt" period of the cycle, ineens controlled by the control relay of said section including said nrst winding of said polar relay and a first one of said coder contacts to con* nect the current source of said section with the primary winding of said first transformer to supply to the track rails during each said cycle a nrst current impulse, other means controlled by said control relay including said second winding of said polar relay and the other one of said coder contacts to connect said current source with the primary winding of said second transformer to supply to the track rails during each said cycle a second current impulse, said first and second windings of said polar relay poled to operate that relay to a iirst position in response to each of said first current impulses and to operate that relay to a second position in response to each of said second current impulses, and means controlled by said polar relay to check the successive occurrence of said nrst and second current impulses.

5. In a signal system for a railway whose track is formed into consecutive track sections each of which is provided with a track circuit including a source of unidirectional cur ent and each of which sections has associated therewith a control relay governed by traic conditions in advance of the section the combination comprising, a coder for a section having a cyclic operation of a predetermined frequency and provided with a pair of contacts which are closed at the start oi erich said operation cycle and are successively opened at selected points of the first half period of the cycle, a first circuit means controlled by the control relay of said section including a reactance device and a iirst one of said coder contacts to supply from the current source oi said section to the track rails a rst current impulse when said one contact is opened, a second circuit means controlled by said control relay including another reactance device and the other one of said coder contacts to supply from said current source to the track rails a second current impulse when said other coder Contact is opened, a pola-r relay having a rst winding interposed in said nrst circuit means and a second winding interposed in Vsaid second circuit means, said first and second windings poled to operate said polar relay to a first-position in response to said first current impulse and to operate that relay to a second position in response to lsaid second current impulse, and means controlled by saidpolar relayl to check the successive occurrence of said first and second current impulses.

6. In a signal system for a railway whose track is formed into consecutive track sections each of which is provided with a track circuit including a source of unidirectional current and each of which sections has' associated therewith a control relay governed by traffic conditions in advance of the section the combination comprising, a coder for a sectionhaving a cyclic operation ofy a predetermined frequency and provided with a pair of contacts which are closed at the start of each said operation cycle and are successively opened during the iirst half period of each cycle, a first and a second reactance device for said therewith, a first circuit including a contact of the control relay of said section and a first one of said coder contacts to connect the current source of said section with said first reactance device to cause to ow in the track rails when said one coder contact is opened a first current impulse having a damped wave, a second circuit including a contact of said control relay and the other one of said coder contacts to connect said current source with said second reactance device to cause to flow in the track rails when said other coder contact is opened a second current impulse having a damped wave.

'7. In a signal system for a railway Whose track is formed into consecutive track sections each of which is provided with a track circuit including a source of unidirectional current and each of which sections has associated therewith a control relay governed by traflic conditions in advance of the section the combination comprising, a, coder for a section having a cyclic operation of a predetermined frequency and provided with a pair of contacts which are closed at the start of each said operation cycle and are successively opened during the first half period of each operation cycle, a first and a second reactance device havingconnections with the track rails of said section and each proportioned to form an oscillatory circuit therewith, circuit means controlled by the control relay of said section and including said pair of coder contacts to connect the current source of said section with said reactance devices to cause when said coder contacts are opened during the first half period of each said cycles two spaced current `impulses to flow in the track rails each of which impulses has a damped wave of predetermined oscillation frequency, a code following relay, a receiving circuit to couple said code following relay with the track rails of said section and including a filter tuned to resonance at said oscillation frequency to supply to said code following relay in response to said two spaced current impulses of each said operation cycle an energizing impulse that persists for substantially the first half period of the cycle, and a signal controlled by said code following relay.

8. In a signal system for a railway whose track is formed into consecutive track sections each of which is provided with' a track circuit including a source of unidirectional current and each of which sections has associated therewith a control relay governed by traflic conditions in ad- Vance of the section the combination comprising, a coder for a section having a cyclic operation of a predetermined frequency and provided with a pair of contacts which are closed at the start of each said operation cycle and are successively opened during the first half period of each operation cycle, energy storing means including capacity and reactance connected across the track rails of said section to form an oscillatory circuit therewith, circuit means including a contact of the control relay of said section and said pair of coder contacts to connect the current source of said section with said energy storing means to canse to iiow in the track rails of said section during the first half period of each said operation cycle twc spaced `current impulses each of which impulses has a dampedwave of predetermined oscillaticn frequency, a code following relay, receiving circuit means to couple said code following relay with the track rails of said section and including capacitance and inductance to tune the circuit means to resonance at said oscillation frecarried amplifying and decoding means connected to said receiving circuit through said filter for operating a cab signal in response to recurrent electrornotive forces induced in the receiving circuit by current of a predetermined code flowing in the track rails when each cycle of such code current consists of substantially equal on and off periods of current, a track section, va coder having an operation cycle equal to the cycle of said code current and provided with a first and second contact which are successively opened in the order named during the rst half period of each operation cycle, a source of direct current, and traflic controlled circuit means including capacitance and inductance to connect said source with the rails of said section over said contacts to 'supply to the rails during the rst half period of each said yoperation cycle two spaced current impulses which induce in said receiving circuit electromotive forces which are effective to cause oscillations of said predetermined frequency to persist in said filter during substantially the first half period of each cycle.

10. In a signal system for a railway whose track is formed with a track section to the rails of which a receiving circuit including a filter tuned to resonance at a predetermined frequency is coupled and which receiving circuit has a decoding means connected therewith for operating a signaling device when alternatingcurrent of said predetermined frequency coded at a particular code rate is applied to said receiving circuit and such coded current has equal on and off periods, the combination comprising, a source of direct current, a coder having an operation cycle equal to thecycle period of said particular code rate and including a contact which is opened at the start of each operation cycle and reclosed at a selected point of the cycle, a transformer and a condenser, and circuit means including said transformer and condenser to conneet said source oi direct current to the rails of said section over said coder contact for supplying to said rails at the start of each said operation cycle a current impulse of a voltage and duration eiiective to shock excite said lter for causing current oscillations to persist therein for a period substantially equal to one-half of said code cycle period whereby said decoding means is effectively controlled to operate said signaling device.

ll. In a signal system for a railway Whose track is formed with a track section to the rails of which a receiving circuit including a filter tuned to resonance at a predetermined frequency is coupled and which receiving circuit has a decoding means connected therewith for operating a signaling device when alternating current of said predetermined frequency coded at a particular code rate is applied to said receiving circuit and such coded current has equal on and off periods, the combination comprising, a source oi direct current, a coder having an operation cycle equal to the cycle period of said particular code rate and including a contact which is opened at the start of each operation cycle and reclosed at a selected point of the cycle, a transformer having a secondary winding con.- nected with the rails of said section, and circuit means including said coder contact to connect said source of direct current to the primary Winding of said transformer for storing up niagnetic energy when the contact is closed and for supplying a current impulse to the rails when said contact is opened and which current impulse is characterized by a peak voltage eiective to shock excite said filter for causing current oscillations to persist therein for a period substantially equal to one-half of said code cycle period and said decoding means is eiectively controlled to operate said signaling device.

12. In a signal system for a railway whose track is formed with a track section to the rails of which a receiving circuit including a filter tuned to resonance at a predetermined frequency is coupled and which receiving circuit has a decoding means connected therewith for operating a signaling device when alternating current of said predetermined frequency coded at a particular code rate is applied to said receiving circuit, the combination comprising, a source of direct current, a coder having an operation cycle equal to the cycle period of said particular code rate and including a contact opened at the start of each operation cycle and reclosed at a selected point of the operation cycle, a transformer having a secondary winding connected with the track rails of said section, and circuit means including said coder contact to connect said direct current source with a primary winding or' said transformer, said circuit means and transformer proportioned so that magnetic energy builds up slowly in said transformer when said contact is closed and decays rapidly when the contact is opened for supplying to the track rails unidirectional current impulses at said particular code rate with each impulse of a voltage and duration effective to shock excite said lter to Cause current oscillations to persist therein for a preselected interval after the current impulse ceases whereby the decoding means is controlled in operate said signaling device.

WILLARD P. PLACE.

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