US1700703A - Train control - Google Patents

Description

Jan. 29, 1929. v 1,700,703

R. c. LEAKE ET AL TRAIN CONTROL Filed Sept. 21. 1923 2 Sheets-Sheet IN V EN TORS Kama/ M Jan. 29; 1929. 1,700,703

R. c. LEAKE ET AL TRAIN CONTROL 2 Sheets-Sheet 2 Filed Sept. 21, 1923 BY MTT%NEY:

Patented .lan. 29, 1929.

RICHARD o. LEAKE AND onAaLns r. ES'IWICK, or Roonnsriin, m zo x, nss'reiiorls T0 GENERAL RAILWAY SIGHALCOMPANY, or :aocnnsrna'nuw YORK;

TRAIN CONTROL.

Application filed September 21, 1923. Serial No. 664,045.

This invention relates to automatic train control systems oi the continuous alternating current inductive type, and more particularly to means for tuning the various circuits of the car-carried apparatus so that this apparatus will respond substantially to the same degree for various frequencies within a certain range.

Generally speaking, in the type of system to which the present invention relates alter nating current is transmitted through one or more suitable traclrway circuits which inductively influence suitable amplifying apparutus on the train for maintaining a relay energized in accordance with the flow of such current. More specifically, one particular type of train control system of this general character includes a receiving; element located in front of the first axle of the tram which is in inductive relation with the rails of the tracltway and responds to the flow of current in one direction in one or" the rails, and in the other direct-ion in the other rail correspondto the usual track circuit current and conveniently called the loop circuit current; and another receiving element in inductive relation with the track rails and constructed to respond to the flow oi current in the same direction in the two rails in multiple, conveniently called the simplex circuit current. On account 01" the limited current which may be applied in practice to the usual tracliway circuit, and on account of the difficulty of inductively detecting such a small track circuit current throuon an intervening; air gap, it is V I .whereby the currents in the windings of the v relay are caused to be shifted in the opposite found desirable to tune the windings of the inductive influence receiving; elements, to. a degree at least, in order to be able to .ints the r lay ener ed by the use of ordinary amplifying apparatus. in practice, the on in the track rails is derived from a trans scion line supplied "from corniuerciulapparatusg and the flCqllC. -y varies slightly. Consequently, it the rec 3 ele- ..ve the' r winding gs tuned 7 7 "ply to e at the frequency of the Slglltlllllff rd that ch-s 'ht variations chain of circuits and devices betvee'n the in accordance with track or loop circuit influence receiving element and one element of atwo-element carcarried relay, 1n which the winding ofthe receiving element is tuned to a frequency higher than the frequency of the-proposed signaling current; and to provide a suitable series or-chain of circuits and devices between the other orsimplex receiving element and the otherIe-lement-of the relay, in which the winding of the simplex receivingelement is resonant to a frequency lower thanthe proposed signaling i'requency, so that two overlapped resonance characteristics are obtamed 1n the detectmg and amphfying apparatus for energizing the polyphase relay,

The provision of apparatu'stuned in a man- I ner as thus far described 1s, however, not 'entirely -satisfactory, because the two. trackway circuits mentioned preferably have currents flowing therein which are substantially in quadrature (displaced electrical degrees) so as to make them distinctive, and

with two influence receiving elements tuned above and below the frequency of the signaling currents, respectively, the reproduced current for operating the relay will not be correspondingly displaced (in quadrature) unless'a compensatin shift in the phase of these currents is made in a suitable manner. Therefore, as a further object o t-the present invention, it is proposed to provide means direction so as to bring them into quadrature,

or displace them substantially the same mun Figure 1. illustrates conventionally and in 1 a diagrammat c manner the devices ofthe manner in which they cooperate;

2'graphically. illustrates the variation in phase relationfof the currents in the-re I car carr-ied andtrackway apparatus and the Y ceiving elemcntsvas comparedwith,theinnected to suitable contact fingers and which is biased to assume a neutral position. contacts for such a relay R are shown conventionally in the drawings as comprising a plurality of fingers, cooperating with stationary contacts indicated by arrows, these fingers having a middle or neutral position and movable in eitherdirection to a normal and a reverse posit-ion, respectively. This relay R also has two field coils or windings L'W and SW of suitable construction. If both of these windings are energized with alternating current displaced in phase, the rotor or vane of the relay is shifted in opposition to its bias in one direction or the other. If either ofthese windings is deenergized, the movable element of the relay assumes its biased or neutral position. For reasons well recognized by those skilledin the art, the torque or operating force of the movable element insuch a relay depends upon the product of the currents in the two field windings and also the phase displacement of these currents, the torque being a maximum for a given product of currents in the field windings when the phase displacement of these currents is 90 degrees.

This relay R has its field windings LW and SW connected to respond to loop circuit and simplex circuit currents, respectively. The loop circuit field winding lfW of the relay R derives its current from suitable amplifying apparatus including thermionic amplifiers or audions LA and LA and a trans former LT; and the simplex circuit field winding SW derives its current from a similar amplifying apparatus, including the audions SA and 8A and a transformer ST. Since the various circuit connections between the influence receiving element LE and the field winding law of the relay Rare substantially the same as that between the influence receiving element SE and the field winding SW the circuits for the simplex circuit receiving element only will be traced; and the like parts for the loop circuit receiving element LE will be given the same reference numbers with distinctive exponents L.

The filament circuit for the audio-ins Sil and A may be traced as follows :--beginning' at the positive side of the filament battery 33, which in the particular system illustrated preferably comprises a 82 volt oat tery, wires 34, 85, 36 and 37, filament of the audion 8A wire 38, resistance unit 39, wire 40, filament of the audion SA wire ll, resistance unit 42, wires 48, i l, a5 and d6 back to the filament battery 33. it should be noted that this circuit includes resistances 39 and 42. These resistances ar used to provide the necessary negative bias oi the grids of the audions SA? and Sr? with respect to their respective filaments, so that these gric s do not draw current. In the particular system disclosed good results have been obtained The by choosing resistances which cause't' e voltage of the grid of audion SA tobe n'e tive to the midpoint of its filament b volts; whereas the grid of the audion S negative with respect to the said poin filament to the extent of 27 volts. I

The grid circuit for the audion gA may be traced as follows :beginning at the'windine' l8 of the simplex element SE, wi stare sistance unit 50, wires 51 and 52, grid ofthc audion 6A to the-filament of this aud'ion, througl i the wire 41, resistance unit 42, wires 4-3, 53, 54 and 55 backto the winding 48- of the simplex element SE. The winding 48 in series with resistance unit 50 is shunted by a condenser 56 for purposes more clearlydescribed hereinafter. q

The plate circuit forthe audion Sil may be traced as follows :begi-nningat the plate battery 60, wires 6l, 62,63 and 64, primary winding of the transformer ST, wire 65, plate of the audion 5A to the filament of this au'dion, to the filament battery 33', wires- 3-1 and 66 back to the plate battery 60.

The grid circuit for the audion 8A may be traced as follows :'beginning at the secondary winding of the transformer ST, wires 67 and 68, grid of the auction SA to the filament of this audion, through the filament circuit and wires 69 and 70 back to the secondary winding of thetransformer ST. The

secondary winding of this transformer'Sl is shunted by a condenser 71, for the reason more clearly described hereinafter;

, The plate circuit for the audion Si-i may be traced as follows :beginning at the plate battery 60', wires :61, 62,- 63 and 77, inductance or choke 78, wires 79 and 80, plateof the audion 8A to the filament of this audion, through the wires 37, 36, 35 and 66 baclr to the plate battery-60. p j

lheinductance 7,8 is shunted by' a partial circuit including the winding SW of there lay The circuit for this winding SW which permits the flow of alternating current, due to changes of uni-directional current fiow int'he inductance 78, may be tracedas follows :beginning at the positive side of the plate battery 60, wires 61, 62, 63and W, inductance 78, wires 7, 9 and 81, blocking" condenser 82, wire 83, winding SV/ of the re-- i, la v battery 60. r

. ln order to llliI OTi'lTtllQ enginer of tra'liic conditions ahead, suitable signals are preferably provided at a convenient point in the locomotive cab or anyother suitable place,

wires 84, 3'5 and 66 back to the plate. I I

vhichrespond to the different. indicating" as shown, the caution lamp Y is energized when the relay is energized in the reverse direction, and the red lamp Rd is energized if the relay is deenergized.

Suitable apparatus is preferably provided on the railway vehicle to control the train in any suitable manner. his apparatus preferably includes a speed-responsive device and an elcctro-pneumatic brake control device, and suitable means for actuating the brake control device and applyin the brakes of the vehicle if the speed of the train is excessive. In order to simplify the description of the present invention, a caution device Ca has been illus fated to properly control the train in a' caution block. control device is of the normally deenerg'ized type, and is n'iaintained energized under clear traliic conditions by energy flowing from one terminal B of a suitable source of supply to the other terminal C of said source as readily traced in the drawings. This device Ca is only energized when the relay it is in its normal energized condition.

Another control device adapted to control the train in anynianner desired when movin throu h a dan er block has been L: C t) illustrated by the device Dr, as shown. This device is energized when the relay R is energized in either its normal or its reversedirectiorn This device preferably limits the speed of the train eventually to a predetermined low value of, say miles per hour, and then maintains the speed so limited as long'as this device Dr is deenergized.

Operation-Let us assume that "he block J is occupied by another train, or is in a dangerous condition for some other reason,

and the track relay 5 is deenergized. With the track relay 5 at the entrance to the block J deenergized, the three sections from the beginning to the ex; end of the block I are provided with normal simplex current, reverse simplex current, and zero simplex current, respectively.

With the simplex circuit current flowing in the normal direction, that is, in a predetermined phase relation to the track circuit or loop circuit current, both field windings of the relay R are energized by currents di placed in phase sub. tantially the sameas the phase displacement of the loop and simplex circuit currents, and consequently the movable element of the. relay assumes its normal position shown, lighting the green lamp G and energizing: both the caution control device Ca and the danger control device Dr. In other words, with the relay R in its normal position, a clear or proceed cab signal is displayed and the speed restrictions or other control enforced by the danger and caution control devices are not in eii'ect. The speed of the train under such clear trahic conditions may be unlimited, or if desired, this normal running speed may be limited to some arbi- This caution train 7 if) M. ll.) comes to a weaves t-rary maximum, such as miles per hour. The relay R is maintained in the normalconditicn, with the results just noted, while the train is travelingthrough the block H under the clear tratlic conditions assumed to exist.

As the train moves into the block I, the block J next in advance being assumed to be occupied, there is no change in the position of the relay 3 during the travel of the train over the first section of this block 1. between the balancing resistances 7 and 8, for the reason that the simplex circuit current is still of the normal relative polarity or phase relation. This p rticular arrangement has been selected to illustrate how the caution control may be made effective at some selected point beyond the caution signal itself,.or the actual entrance to the caution block, this condition existing more particularly in the case of long blocks that are longer than the braking distance necessary; but it should be;

understood that the balancing resistances 7 and 8, together with transformer 9, may be omitted, and the balancing resistance l5 located at the joints 2 marking the entrance to the caution block.

[is the train moves beyond the balancing resistance 15, the relation between the loop and simplex circuit currentdetected by the car-carried apparatus is reversed; and the relay llchangcs to shift its contact fingers to the reverse position, thereby deenergizing' the caution train control device Ca but maintaining the danger control device Dr energized. Also, the green lamp G is extinguished and the yellow lamp Y is lighted. lhe engineer will. therefore, be required to reduce or govern the speed of the train in accordance with the permissive speed set up by the caution speed device Ca. In one arrangement, the action of the caution speed device compels reduction in speed to intern'iediate speed of, say, 40 miles per hour.

As the train passes the point D, it is entirel; leprived of simplex circuit current and the ielay is deenerg'izcd, its field winding Fil having no current therein. 7 The engineer is now required to govern his speed in accordance with the requirements of "he danger train control device or there is an autom tic applicationof the brakes. The danger cemrol device is made effective at the point D and before the ii, i. of the blocl; l: is read in Ol'tlQllO assure that the train reaches prodeterinined safe low speed (say stop before reachthe end of the block.

[is he train proceeds intothe block J, this lo i tillbeinp; occupied by said another ain, the relay ismaintained deenergized re rdle s of simplex current flowing in the simple circuit of the block J. Thisis true because no loop circuit current, or at least not an appreciab'le amount, will be flowing, so that the relay it is deenergized primarily on account of the lack of current flowin in the Winding IIW of the relay R. Consequently, the restriction in the movement of the train is Continued so that it can not exceed said minim 'im speed limit until the said an other train leaves the block J. i As soon as this occurs the train in question is no longer restricted to this low limiting speed unless the train has passed the point D of the block J. Net, since the present system is based on the principle of continuous control, or a permanent communicating link between the train and track relays ahead, the train Will be immediately released andpermitted to proceed as soon as tralfic conditions ahead become more favorable, all in the manner Well known by those familiar with this type of continuous inductive train control system. 1

'Co nstrmts of elements of the mucous carcarried decides-in order to obtain the desired performance of the car-carried apparatus under varying frequencies, a varying amount of current fiowin in the simplex and loop circuits, respectively, reasonable variation in the phase displacement between these lTWO currents and other varying conditions encountered in practice, the various circuit portions of the car-carried circuits are tuned and adjusted in a predetermined manner to be presently described. The variation in the frequency of the alternating signaling current to be picked up and amplified exists and must be compensated for, because this current will in practice be derived from a transmission line supplied With current from commercial apparatus and Willhave the small frequency variations ordinarily found in commercial power sources. The amount of current in the loop or track circuit varies in accordance With the location of the train in the block, being a maximum with the train at.

the exit or feed end of the block and a minimum at the entrance end'ot the block. Variation in the phase relation of the currents in tire tracku'ay loop and simplex circuits is occasioned by the differentelectrical characteristics of the blocks, due tochanges in ballast resistance, location of the train in the block, and other i'actoi's.

previously stated, it is desirable to time more or less sharply the coils ofthe receiving elements so as to obtain the maximum voltage for application to the grids of the vacuum tube amplifiers for the minimum amount of signaling current in the track rails. Roughspealring, it has been found that, by the arrangement shown I and hereinafter eX- plained, the tuning of the coils of the receiving elements serves to give an input voltage for the vacuum tube amplifiers which is from to 10 times the voltage induced in these coils. Such voltage increase or manifestation is characteristic of voltage resonance and very desirable in train control systems of this type. Hence, a condenser, such as 56, is-connected in cries Withthe coil, as 48, of each receiving element.

lVith such an arrangemenu it is evident that there is a particular frequency ilorw'hich the combination is resonated and the voltage equallyevident that for other frequencies the voltage Wlll be lower. Similarly, for the particular frequency for which the receiving coil is tuned, the induced voltage and current in this coil are in phase With each other and have a definite phase relation to the current in the track rails producing such voltage and current; Whereas for a different frequency, the current in the coil of the receiving element and the voltage across the condenser which is the potential applied to the amplivtier) does not have the same definite phase relation to the inducing current in the trac'l Way circuit, due to the fact that for such different'trequency there is more inductive reacross the condenser is a maximum; and it is actance in the tuned circuit than condensive reactance, or vice versa. the receiving coils are tuned sharply to resonate at a predetermined frequency, such as 60' v practice. it may be said that the present invcntion deals principal-lyivith the problem of arranging or ad usting the circu ts and devices on the locomotive or other vehicle, so as to attain substantially uniform torque tor the relay under the varying conditions of frequency encountered in practice.

For the purpose oi explaining the nature and iuulerlying principle Of'illllS'lllVGHlTlOll, it is assumed that the normal signaling frequency is 60 cycles, and that compensation should he; made for variation of '2 cycles either way. In other words, in this explanation, it is assumed that the equipment is designed to give a substantially uniform torque for the relay R for a range of frequencies be tween '58 and 62 cycles per second,'it being understood of course that this is merely illustrative. v f

As a further aid in explaining this inven tion, certain curves or graphs have "been shown Figs. 2 and these being drawn on the basis of certain assumed conditions which are of course susceptible of considerable variation in practice. Fig. 2 illustrates the phase relation of the current in the coils of the loop and simplex circuit elements with respectto the voltage'induced in these respective coils -lor different frequencies. Thehorizonta-l distances or abscissa represent fre- 1 Consequently, if

quencies, and the vertical distances or ordinates denote phase an le, positive phase angles or leading current being on the upper half of the figure above the horizontal line, and a negative phase angle or lagging current below said line. 1

Fig. 8 illustrates in two separate groups of curves to different ordinates, the variation in the current in the coils and also in the tuning condenser of the loop and simplex circuit elements, as the frequency varies, and also the voltage across the tuning condenser for said elements.

As previously stated, the torque of the relay R depends upon the product of the currents in its respective field windings. [assuming proportionate amplification throughout. the working range of voltages, the currents in the field windings of the relay are proportional to the voltages impressed upon the input circuits of their respective ampl tiers. In other words as the voltage across the condenser 56 for the simplex circuit re ceiving element SE increases or decreases, it may be assumed that the current in the field windings SW of the relay It corre spondingly increases or decreases. It has been pointed out, however, that this voltage changes with the frequency, and hence the current in said field winding likewise varies. Thus, if both of the receiving elements are tuned by their respective condensers to resonance for the same frequency, an increase r decrease in this frequency would result in diminution of the current in both field windings of the relay and result. in a lower torque. It is this condition that the particular arrangement of this invention, among other things, is proposed to remedy.

Generally stated, according to this invention, the condenser 56 in series with the coil 48 of the simplex circuit receiving element SE for tuning thiscoil, is preferably chosen,

or adjusted, to a capacity approximately 20% more than that. required to produce resonance for the normal frequency of (it) cycles; and similarly, the condenser 56 is adjusted with about 20% less capacity than required to produce resonance for said normal frequency. In other words, the coils of the two receiving elements are tuned, not to the same frequency, but to different frequencies. More specifically, on the basis of the assumptions hereinbefore mentioned, for a range'offrequencies from 58 to 62 cycles, one satisfactory arrangement is to tune the coil of the simplex element SE for resonance at about 54 cycles and the coil of the loop circuit element LE for resonance at about 65% cycles. This particular arrangement hasbeen indicated in the illustrative curves, as apparent from Fig. 2, the points of resonan'ce being shown for the frequency producing zero phase displacement.

Assuming now that the coils'of the two receiving elements are tuned off resonance for the normal signaling frequency, as just stated, and referring to Fig. 2, it will be seen that the induced current and likewise the voltage across the tuning condenser is not the maximum for the normal frequency of 60 cycles but is an intermediate value. Referring particularly to the voltagecurves in Fig. 3, it will be noted that these curves have substantially'the same general form and slope, especially over the range of frequencies for which the equipment is designed, namely, between 58 and 62 cycles. It will also be. noted that, as the normal frequency of 60 cycles is increased, for example, to 62 cycles, the voltage across the condenser 56 for the simplex element SE decreases, while the voltage across the condenser 56 for the loop circuit receiving element LE increases; and on account of the similarity in this va riation, the product of the voltage remains practically constant throughout the band of frequencies in question. For example, at 58 cycles the voltages are 2.2 and 2.4 with a product of 5.2; at a frequency of 60 cycles, the voltages are 1.7 and 2.9 with a product of 41-.93; and at 62 cycles, the voltages are 1.3 and 3.7 with a product of 4.81. In short, the products of the voltages or potentials in pressed on the amplifiers remain substantially constant, one increasing as the other decreases with a change in frequency, and vice versa, so that the currents in the field windings of the relay R change, one increasing and the other decreasing, with a change-of frequencies, their products remaining substantially constant and the torque nearly uniform.

The arrangementjust described for maintaining uniform relay torque for different frequencies, consisting of tuning the receiving elements to higher and lower frequencies respectively than the normal frequency,

serves admirably for this particular purpose.

but introduces additional factors and consideratirms. Mention has been made of the fact that the phase relation of the induced currents in the coils of the receiving elements varies with respect to the induced voltage as the frequency varies. If such variation in phase relation were truthfully reproduced proportionally throughout the amplifiers and up to the field windings of the relay R, the net effect upon the relay would be substantially the same, the currents in its field Windings both becoming more leading or lagging, as the case may be, and to the samedegree. Exact similarity and faithful reproduction of phase relation throughout an amplifier arrangement, particularly with apparatus built in quantity on a commercial basis, is not easy to obtain or maintain, with the result that compensating adjustments are desirable and almost essential.

Another desirable attribute of the car equipment for a system of the character un-- der consideration is that there should be no ultimate change in phase relation produced by the car apparatus by itself, that is, the phase relation of the currents in the windings of the relay B should be the same as the phase relation between the currents in the simplex and loop circuits. This is desirable for several reasons, and more particularly to avoid the possibility of false operation under peculiar conditions. To illustrate, suppose that the balancing resistance 16, for example, should have its connection to one of the track rails broken. This Would cause all of the simplex circuit current to flow in the other rail and pass under'one of the loop circuit receive-rs'LE. Such current Would induce a corresponding voltage in the coils of the receivers LE and apply it to the grid ofthe vacuum tube LA, the current being confined to one rail so that there could be nobalancing effect due to the Way in Which these coils are Wound. If the existance of such abnormal simplex current and its action upon the amplifier for the loop circuit produces upon the Winding Ll/V of the relay R the same effect as the regular or authorized loop circuit, then false operation of the relay might occur, that is,the relay might be energized directly behind a train in the same block Which would shunt out the loop circuit current but Would not change the flovv of the false simplex current all in one rail. As aremedy for this possibility, it is proposed to arrange the loop and simplex circuit receiving elements and their amplifiers so as to have inherently no phase displacementand produce all of the phase displacement, necessary for operation of the relay R, in the trackway circuits. With such an arrangement, false application of the simplex circuit to the loop circuit receiving elements could not produce any improper effect upon the relay, since this current would he in phase with the regular simplex circuit current in the other Winding of the relay, and this relay, as already explained, requires a phase displacement in the currents in its iield windings in; order to operate.

Generalizing, it is desirable, for the reasons indicated, and others not requiring specific discussion, to provide an organization of circuits for receiving loop circuit current, and also for receiving simplex circuit current,

which produces no phase shift on the can.

in order, however, to maintain substantially uniform torque on the relay, the coils for the simplex and loop circuit elements have already, as previously explained, been tuned oft resonance for the signaling frequencies, so

to speak, with the result that at the signaling I frequency one is lagging andthe other is leading With respect to the currents in the track rails producing such currents.

This condition just discussed is bestexplained by referring to Fig. 2, from which it natin current in the coil of the loop circuit ie condenser, leads its induced voltage by about 4:8 degrees at the normal frequency of on account of the. smaller value of i 60 cycles, Whereas the current in the 'coil of i the 316K receiving element lags behind its ind cing voltage by'about 59degrees. In order to bring the currents applied to the windings of the relay R back into phase, it is necessary to make a similar compensation in another part of the operative chain be tween the receiving coil and the relay Windings, more specifically in the amplifier. This is accomplished by using an inductive or rear sive coupling between the first and second I 1 stages of the amplifier, namely, a transformer 81 or LT, and tuning these in an opposite fashion by a condenser 71 or 71%. I

To illustrate, assuming the'condenser 56 adjusted to resonate the coils of the loop cir-' cuit receivers for a frequency higher than the normal frequency and the condenser 56 adjusted to tune the coil of the simplex. receiver for a frequency lower. han the normal frequency, then the condensers 71 and 71 can be selected or adjusted in either of two Ways to produce the desired compensation. Ac-

cording to the first method, the condenser 71 is selected to make the current derived from the first amplifier LA of the loop circuit device still more leading, and the condenser 71 Elli to give a still more lagging current, so as to bring about a phase difference of 180 degrees.

According to the other method, Which is con- 7 sidered to be preferable, the'condensers '71 and 71 are selected or adjustedto bring the currents back into phase, that is, With the current in the loop'circuit chain of devices leading as shown in Fig. 2, the condenser 71 1's justed to give a compensating lag. It is, of

course, evident that if the condenser 56 gives a lead of L8 degrees, the condenser not necessarily give a lag of the same angle, so long as'the condensers 71 and 71 together compensate for the total phase angle difienence. In other Words, assuming the condenser 56 gives a lead of 4.8 degrees, as shown in Fig. 2, the condenser 71 may beadjusted to give a lag of,say, 58 degrees, instead of 48 degrees, or a 10 degree over-compensation, but'in that case thecondenser 71 Would be adjusted to give a lead of 10 degrees less, or

.1.8 degrees, instead of 58 degrees, accordingto i the values assumed andshovvn in Fig. 2.

The transformers ST and LT have been referred to as used for. the purpose of obtain,- ing a compensation in the amplifiers to bring about zero degree phase displacement; but it should be understood thatthese transformers have other advantageous characteristics. For example, these transformers introduce an additional tuned element in the operative chain of devicesbetween the currents in the 71v need trackway circuits and the windings of the car relay; and consequently these transformers give greater selectivity and render the whole system less susceptible to operation by currents of frequencies widely different from the normal signaling frequency. It may be said that this feature ofselectivity is desirable more particularly in the case of railroads emwith the same effect as described in connection with the coils of. the receiving elements. Qhe curves or graphs in the case of the trans formers, being similar to those shown in Figs. 2 and 8, have not been illustrated; and in view of the foregoing explanation it .is thought to be unnecessary to discuss this scheme of selection or adjustment of the constants for these transformers.

The desired phase displacement of the currents in the simplex and loop circuits on the trackway may be obtained in accordance with any one of the well-known expedients employed in connection with alternating current track circuits. According to the arrangement illustrated, which is preferable for ordinary conditions, the simplex circuit is made resistive, so that the current therein is substantially in phase with the transmission line voltage; whereas the loop circuit is made reactive, so that the current therein lags behind the transmission line voltage. Forthis reason, the reactance l is introduced in series with the secondary of the transformer 3, this reactance serving the purpose of the usual limiting reactance or resistance employed to limit'the flow of current as a train approaches and stands directly over the feed end of the track circuit.

It may be explained here that the invention hasbeen shown in connection wit-h alternating current track circuits,.but the same principles are applicable to direct current track circuits, the alternating current used for train control purposes eing superimposed upon the direct current, as for example, by connecting the transformer feed in series with the track batter As previously stated, it is considered to be desirable in systems of this character to have no phase shifting by the car apparatus, and have the phase displacement of the currents in the field windings of the relay correspond with the phase displacement of the currents flowing in the simplex circuits on the track way. Based on this pren'iise, the car apparatus may be readil adjustedto function in the desired manner in the following fashion First, the coils of the receiving elements are tuned off resonance to frequencies higher and lower than the norn'ial frequency. Then with these receiving elements energized by currents exactly in phase, the condensers Ti and 71 are adjusted so thatthere is no torque produced by the relay, These adjustments, it may be added, are preferably made after trial with variations in frequency and strength of current in the tracl-zway circuits, such as would be encountered, in practice. After obtaining an adjustment of the car apparatus in this manner, the currents in the trackway and loop circuits are thrown out oi' phase through angles corresponding to that likely to be encountered in practice, these currents respectively reversed and cut oil, and the to que of the relay R noted.

Mention has been made of the fact that there is considerable variation in the amount of loop circuit current influencing the receiving elements LE as the train travels through block. So long as the car equipment is sulliciently sensitive toproduce reliable operation of the car relay with the minimum amount of loop circuit current, existing when the train first enters a block, the additional energization of the relay .by the increase of loop circuit current is not particularly objectionable; but it may be explained that this condition is under control and may be duly compensated for by reason of the saturation or overload characteristics of the vacuum tube amplifier. In other words, the amplifiers for the loop circuit particularly may be worked at such a point that excessive loop circuit current does not produce excessive relay current.

The condensers 82 and SQ in series with the iield wind ings of the relay 1%, are provided primarily to prevent the direct current from the plate battery 60 flowing through these windings, and these condensers are essentially blocking condensers. These blocking con densers 82 and 82 of course reduce the inipedance of the circuits including the hold windin of the relay by compensating for the reactive component; and in practice these conden ers are preferably of the value to produce resonance for the normal frequency, that is, the condensive reactance of these condensers made equal to the inductive reacta'nce of the field windings of the relay. The tuning of the field windings of the relay, however, does not produce very sharp resonance because there is included in the tuning circuit the high internal resistance of the vacuum tube amplifier. In other words, the field windings of the relay do not have a sharp or peaked resonant curve and respond much the same over the range of frequencies applied thereto.

This well known fact thatresistancein the tuning circuit flattens or broadens the resonance curve may also be utilized in connection with'the receiving elements and it is found desirable in many instances to include in series with these elements a resistance unit 50 which may be selected or adjusted to give a more flexible control'ov'er the constants of these two circuits and promote stability of thesystemf Summarizing the features of this inven tion, it will be observed'that the system of train control of the continuous inductive type employs two separate trackway circuits, being conveniently termed the loop and simplex circuits. The currents inthese circuits are derived from a transmission line of 'cornmerout departing-from the nvention.

cial characteristics with the usual frequency variations, and these currents are displaced in phase" by any one of the well known expedients and are'individually controlled in the specific manner described to give three distinctive controlling conditions, namely, simplex circuit current normal, simplex circuit current reversed, and simplex circuit or loop circuitfcurrent cut off. Uniform torque for the car'relay is maintained by adjusting thereceiving elements to frequencies higher and lower than the normal frequency; or, in other I words, these receiving elements are tuned ofi resonance. These tuningconditions are selected to give a substantiallyuniforin product of the voltages impressednpon'the amplifiers throughout the range; of frequency variation to heencountered'. v

In order to have 'thedesired' feature of zero degreephase displacement by the car-apparatus an additional reactive device (coupling transformers) is introducedin each operative chain between the receiving -elements and relay, and-this ad'ditional'device is tuned 0E resonance to give a constant procluct of voltage and uniform relay torque and also so as to compensate for the phase change produced by the tuning of the receiving ele ments. In a sense, it may be said that each of" the chain of devices for the loop and simplex circuits has one link thereoflthe receiving coil) tuned to resonance for a frequency con siderably different than the normal signaling frequency, and another link (coupling transformer) tuned fora frequency also considerably butoppositely different from the signaling frequency. These tunings are such that the ultimate result is proper operation of the relay in producing substantially uniform torque for a. range of frequencies, say from 58 to 62 cycles, without'sacrificing the efficiency 'andadvantages of tuned circuits and without departing from the safety principle of having car apparatus operable only by trackway currents which are. displaced in phase. I

The present inventlon provides, a for trai'ismittlng induct vely any one therefore,

fof threedistinctive] control influences to a vehicle at any and all-poin-tsxin. its-travel,v with due allowance and compensation to meet the conditions: actually encountered in prac-- tice, more particularly variations-in frequency, and without sacrificing ith'eiadvantages' of tuned circuits. t should be understood that.

the specific organization of devices and cir cuitsherein shown and describedismerely illustrative of 1 the invention, and that the ,invention is not limited to this specificiembodiment. Forexample,whileapolyphase relay What-we'claimis V. v

1. In ail-automatic train control system, the combination ortrackway means for transmitting currents in two distinct trackway circuits, one of. which consists of the usual 'trackcircuit; and car-carried apparatus including influence receiving elements having windings located in'inductive relation with said trackway circuits, condensers connected in multiple with sa'idvwindings having capacities to tune these windings to higherand lower frequenciesrespectivelytha n the "pro- 'posed signaling -;frequency,- af two element electro-respons'ivedevice operated in res onse to currents flow ng in the-windings o said elements, andtr'ain control means governed by said electro responsivedevice.

2. In air automatic train-- control system,

the combination of trackwa-y means for transm tt ng currents in two distinct rtrackw ay circuits, one of which consists of the-usual track circuit; and car-carriedapparatus including influence receiving elements having windings located ininduct-ive relation with said trackway circults, condense-rscon-nected in:-,multip'le with said Windingshaving capacities-to time these windings to higher and lower frequencies respectively than I the proposed signaling frequency, two am lifying Qdevices having-their input circuits connected to the terminals of said condensers, atwo element,

relay having its windings connected'tothe output circu-its ofsaid amplifying devices, v andtrain control apparatus governed-by said relay;

3.- In an automatic train control system,

the combination of trackway means for transmitting currents in'two distincttrackway circuits, one 'o-fwhichconsists of the usual track circuit; and'car-carried apparatus including infiuence receivingelements havlng windings locatedininductive relation with said trackway circu ts, condensers connected in multiple with said windingsrh-aving cai pacities to tune these windings to higherv and the prolower frequencies respectively than posed signaling frequencygtwo' amplifying devices connected to respond to the potentialsacross said condensers having inductive output Circuits, a polyphase relay having its wmdmgsconnected to said output circuits,

and means for tuning said output circuits so as to cause the phase displacement between I the currents flowing in the two windings of the relay to be substantially the same as the phase displacement of the currents flowing in-the trackway circuits.

4. In an automatic train control system,

the combination of trackway means for transmitting currents in two distinct trackway substantially the same amount as are the cur-.

rents flowing in said trackway circuits.

5. Car-carried apparatus for automatic train control systems of the type in which two distinctive trackway currents are transmitted along the trackway, one of which flows in the usual track circuitahead of the train comprising, a two-element alternating current relay each element having a winding,

two inductive influence receiving elements located in inductlve relation with said trackway circuits, two chains of circuits and devices connecting said-receiving elements and the windings of said relay, certain of the elements of said chains being resonated to frequencies different from the frequency of the proposedtrackway currents. 6. Car-carried apparatus for automatic train control systems of the type in which two distinctive trackway currents are transmitted along the trackway, one of which flows in the usual track circuit ahead of the train comprising, a two-element alternating current relay each element having a winding, two inductive influence receiving elements located in inductive relation with said trackway circuits,tw0 chains of circuits and devices connecting said receiving elements and the windings of said relay, certain elements of eachrchain being resonated 'to different fr equencies both above and below the proposed frequency of said trackwaycurrents, and the corresponding elements of the two chains being resonated to frequencies above and below, respectively, the proposed frequency of said trackway currents.

. '7. Car-carried apparatus for automatic train control systems of the type in which two distinctive trackway currents are transmitted alongthe trackway, one of which ourrents flows in the usual track circuit ahead of the train comprising; a two-element alternating currentrelay each element having a winding; two inductive influence'receiving elements located in inductive relation with said trackway circuits; two chains of circuits and devices connecting said receiving ele ments to the windings of said relay; each of said chains including, two audions having their filaments connected in series, and a resistance unit in the circuit of said filaments contained between said filaments'a'nd having an ohmic resistance of a value so that the filament current flowing therethrough will produce the proper grid bias in one of said a-udions with respect to the gridbias of the other audion. f q p 8. In an automatic train control system, the combination with separate trackway cir-. cuits including track rails and energized subjectto control in accordance with traffic cOnditions by alternating currentsof-thesame frequency but different in phase, a two-element alternating current relay on a vehicle,

and means on the vehicle inductively influenced by the alternating currents in said trackway circuits for amplifying the energy manifestations produced by such currents and applying the energy so amplified to said relay without phase distortion and giving a substantially uniform torque for" the relay for all frequencies throughout a predetermined range. 1

'9. In a continuous inductive impulse communicating means fortrain control purposes,

the combination with a two-element alternating current relay on a vehicle, of receiving coils and amplifiers supplying current to the field windings of said relay, and means tuning said receiving coils and amplifiers to pro- .vide a substantially constant product of the currents in the field windings'of said relay for all frequencies throughout a predetermined range.

10. In a train control system of the char-ace ter described including track rails normally having alternating signaling current flowing therein, separate receiving elements having coils and condensers tuning said coils, one to a lower and the other to a higher frequency; than the normal signaling frequency. 7

11. In a train control system, the combina- 'tion with trackway circuits energized with alternating current differing in frequency from a normal throughout a range of fre-. quencies, of a car-carried two-elementalternating current relay, and amplifying means detecting the flow of alternating current in said trackway circuits and supplying current to the field windings of said relay, said currents in said field windings having the characterized by the provision of means for producing a substantially constant torque in the moving element of said relay throughout a predetermined range of frequencies.

13. In an automatic train control system of the character described, in Which the 0peration of a two-element alternating current relay on a vehicle is controlled by the presence and absence and also relative phase relation of alternating currents in two trackway cir-v cuits, the provisionof means for maintaining a substantially uniform torque for said relay throughout a predetermined range of frequency variation.

' 14. Car-carried apparatus for automatic train control systems of the type in which two distinctive trackway currents are transmitted along the trackway, one of which flows in the usual track circuit ahead of the traincomprising; a two-elementalternating current relay each element havlng a w1nd1ng; tw'o 1n-. ductlve influence receiving elements located in inductive relation with said trackway circuits; two chains of circuits and devices con necting said receiving elements to the windings of said relay; each of said chains includin an audion having its plate circuit divided into two branches in multiple one of which includes an inductive reactance and the other of which includes a winding of said relay and a condenser in series, whereby the di-. rect current component'of the plate circuit current does not flow through the winding of said relay.

In testimony s gnatures.

. RICHARD o. Luann; CHARLES F. "ESTWICK.

whereof we hereby .affix our

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