US2150857A - Continuous inductive cab signaling and train control system - Google Patents

Description

March 14, 1939. D. v. EDWARDS CONTINUOUS INDUCTIVE' CAB SIGNALING AND TRAIN CONTROL S'ZSTEII Filed Feb. 18, 1937 3 Sheets-sheet l R. I N

L .L J. Jr 1W 3 fi/agmia fiwmm ATTORNEY March 14, 1939. v EDWARDS 2,150,857

CONTINUOUS INDUCTIVE CAB SIGNALING AND TRAIN CONTROL SYSTEM Filed Feb. 18, 1937 3 Sheetssheet 2 FIG. 2.

INVENTOR AZ. 7/ m- March 14, 1939. D. v. EDWARDS LING AND TRAIN CONTROL SYSTEM CONTINUOUS INDUCTIVE CAB SIC-NA Filed Feb. 18, 1957 3 Sheets-sheet 3 cpcbmbno catu numomE s n nozmm Ill.- "I'Ur BY A iaamz M. ATTORNEY Patented Mar. 14, 1939 NED S'FTES QONOUS INDUCTKVE'OAB SIGNALING TRAIN CONTROL SYSTEM Donald V. Edwards, Montclair, N. 3., assignor to General Railway Signal Company, Rochester,

Application February 18, 1937, Serial No. 1126,4118

ill Giaims.

This invention relates to an automatic cab signaling and train control system of the continuous inductive type, and more particularly to a system of this type wherein the distance of another train ahead within certain limits is at all times precisely indicated.

Generally speaking, not only in automatic train control and cab signaling systems, but also in railway signaling systems of the wayside signal in type, the condition of trafiic in advance has in the past been manifested or indicated in terms of the particular block in which such train ahead is located. For instance, a wayside railway signal, in such signal systems as are in common use, 5 indicates whether the first block in advance, the second block in advance or neither of these blocks is occupied. This is also true of cab signaling systems in common use. It is readily understood that if track occupancy in advance of a signal or go in advance of a train are expressed in terms of the block in which such track occupancy exists, the exact distance of such train in advance is uncertain to-an extent depending upon the length of the block. It is apparent from the foregoing discussion that if train presence is expressed in the term of the block in which such train is located, trains cannot'be spaced safely as closely as they can if the cab signal indicates precisely the distance that another train is in advance of the train in question.

In accordance with the present invention it is proposed to at all times indicate in the cab, as in feet or meters, the distance to'the next train in advance. More specifically, it is proposed to induce in the track rails. a momentary impulse of current, which impulse in accordance'with usual wave motion and propagation may flow down the track rails, and if this impulse or current wave is not interfered with it will be ab- 40 sorbed or dissipated by the'usual attenuation due to resistance losses; If this wave, however, encounters the axles of anothertrain in advance this wave will pass through these axles, so to speak, and will return on the other rail, the same thing being true of a similar wave which is propagated down the other rail, so that the current wave will be reflected back to the train which carries the transmitting apparatus. The reflected wave will. however be negative in character with respect to the transmitted wave, but since it moves in the opposite direction its efiect on'the receiving apparatus will be the same as the effect produced by. the transmitted wave. Also, a wave reflected back from an open circuit, such as a broken rail, will be of reverse polarity with respect to one reflected back from a short circuit. If now suitable apparatus is provided on the train to detect not only that this reflected wave has returned to the train but which also detects the time consumed for this wave to flow to the train in advance and back again to the train from which it started, and bearing in mind that current flowing in a suitable circuit flows at the same rate as the velocity of light, accurate information as to the distance of the train ahead is manifested on the train carrying the transmitting and receiving equipment. Other objects, purposes and characteristic features of the invention reside in the provision of means for controlling the air brakes of the train in accordance with the extent of unoccupied track in advance of the equipped train.

Other objects, purposes and characteristic features of the 'present invention will be understood from the following description when considered in connection with the drawings, in which:

Fig. 1 illustrates conventionally a cab signaling system embodying the present invention;

Fig. 2 illustrates graphically the voltage wave of the alternating current car-carried source, preferably of a frequency of about 200 cycles per second, together with the voltage applied to the grid of the sending tube;

Fig. 3 shows conventionally apparatus for controlling the air brakes of the train by apparatus similar to that shown in Fig. 1 of the drawings;

and

Fig. 4 shows how a railway track divided into blocks for wayside signaling purposes may be modified to function properly with a cab signaling system such as shown in Fig. 1 or Fig. 3.

Referring to Fig. 1 of the drawings the numeral i designates track rails of a railway track, which rails are preferably bonded together and which rails are preferably not divided into blocks by insulating joints as is usually the case, such insulating joints only being employed where diverging tracks lead from the main track as by a track switch, such as shown in Fig. 4. These track rails preferably are provided with a distributed capacity by having small condensers a connected between the track rails. These condensers are preferably so small and are located correspondingly close together, so that the least attenuation of the impulse for the particular frequency chosen occurs, that is, the capacity is distributed in small enough units to prevent reflecting the impulse and to afford propagation of short impulse electric current waves through the track rails. In accordance with one preferred form of the present invention there are provided, to define certain points along the track, suitable wayside current reflecting devices WR, which will be more specifically described hereinafter.

On this track illustrated by rails I has been illustrated a train "i3 equipped with car-carried apparatus embodying one form of the present invention, in advance of which there is illustrated another train T trafi'ic preferably being from left to right, as indicated by an arrow.

Transmittingequipment In accordance with the embodiment of the invention illustrated, the transmitting apparatus comprises a transmitting .coil TC, a discharge condenser DC, and a sending tube ST, together with suitable auxiliary apparatus associated therewith. In practice, this transmitting coil TC preferably comprises a substantially closed-loop of square tubing preferably several inches on each side connected through the discharge condenser DC to the cathode and plate, respectively, of the sending tube ST, so coordinated that this circuit is as short as possible. In other words, the discharge condenser DC and the sending tube ST are preferably located just above the rails and in front of the locomotive and included in series with the transmitting coil TC. This sending tube ST may be of any suitable construction to perform the desired result, but is preferably a tube of the gas filled type known in the trade as a grid controlled rectifier. A grid controlled rectifier of this type acts to prevent flow of plate ,current until the gas in the tube is ruptured by the flow of current, as by a control voltage applied to the grid, and when plate current once flows it continues to 'fiow until the plate circuit energy has been dissipated. Tubes of this kind are also known as electrostatics-11y controlled gaseous arc discharge tubes. This sending tube ST has its filament f. energized from a filament transformer secondary 9, which is a secondary winding of the main transformer MT having a primary winding III, the midpoint of this secondary winding 0 is connected to the negative terminal of the plate source lI-ii which has its positive terminal connected to the plate 9 of this sending tube ST. This plate source comprises a plate rectifier PR of the Flemming valve type energized from the secondary coil ll of the transformer MT, the output leads being bridged by a resistance unit I! to constitute a potentiometer, this resistance I: .being shunted by condenser 13. The grid 0 of this sending tube ST is connected through the usual grid resistance It, through the secondary winding of a peaking transformer PT, to a point on the potentiometer to bias the grid 9 slightlypositive as compared with the filament 'f. This normal bias is,however, not sumcient to cause discharge of the tube ST.

The peaking transformer PT is employed to apply a sudden positive trigger voltage to the grid 9' of the sending tube ST at the time when the voltage of the car-carried source, which is preferably a 200 cycle alternating current source, one cycle of which is shown by the graph II in Fig. 2, passes through zero in a particular direction, as illustrated by the short peak voltage curvel8 shown in Fig. 2 of the drawings. The voltages generated in the output of transformer PT are illustrated by curve SI of Pig. 2. It will be noted that the discharge condenser DC is connected directly across the plate source i2-I3 through a series resistance i1. From this 'it is apparent that if the discharge condenser DC has Just been discharged, this condenser may be recharged by current flowing through this resistance l1, and that for this reason the re-charging of the condenser DC will take place rather slowly. This fiow of re-charge current through the series resistance l'l causes a negative potential to be applied to the grid g of the sending tube ST, and this negative grid potential varying in accordance with the fiow of current to the condenser DC has been illustrated by the curve i8 in Fig. 2 of the drawings. The grid potential for the sendin tube ST and shown by curve l8 in Fig. 2 is of saw-tooth shape. The vertical part l8 of this curve illustrates the building up of current flowing to the discharge condenser DC, the inclined portion of this curve indicating that the charging current to the condenser DC gradually decreases, whereas the negative peak i8 and the positive peak l8 illustrate the voltage generated in the secondary winding of the peaking transformer PT. If these various values are properly chosen the grid 9 of the sending tube ST will rise to a potential equal to the trigger-off value of this sending tube ST, at the time the grid potential is being raised by the peaking transformer. When this critical grid voltage is reached an electron discharge stream flowing from the filament to the plate of the sending tube ST takes place, causing the resistance within this tube and between the filament f and the plate p to suddenly fall substantially to zero, whereby the discharge condenser DC is very suddenly discharged actually flows fromthe plate 11 to the filament f.

It may be pointed out that the constants of this discharge .circuit are preferably such that this discharge takes place in the form of a single highfrequency alternating current wave train of which each cycle of the alternating current consumes one micro second (one millionth of a second) or even less, and each of these trains preferably continue for a period less than half of a cycle of the supply voltage, that "is a period of less than a four hundredth part of a'second. In other words, the arc gap in the tube ST corresponds to the arc gap in the air of the old are type oscillator. Although the resistance of the arc gap of the tube. ST is, in a.broad sense, unidirectional, it actually allows this ultra-hish frequency train of .altemating current to flow.

because this alternating current is superimposed voltage, so that of a series of such current wave trains an in-coming current wave train will not conflict with an out-going current wave train except for very closely spaced trains.

The peaking transformer PT generates the short waves of potential I l and I8 (see Fig. 2) by reason of the fact that the iron of the peaking transformer PT is fully saturated substantially throughout the entire cycle of the 200 cycle alternating current preferably applied thereto. Since source.

current is generated in a secondary winding of this transformer PT only when there is a. change of flux in the magnetic circuit of this transformer PT, and since a change of flux in the magnetic circuit of this transformer PT takes place only momentarily as the magnetizing current passes through zero, voltage is generated only for an instant as this magnetizing current reverses and passes through zero. It will be noted that one of these peaks BB -E is in a negative direction and that the other peak is in a positive direction. For this reason, among other reasons, the sending tube ST will fire, or discharge, only once for each cycle of the car-carried alternating current Even though this alternating current source is presumably of a fairly low frequency, such as 200 cycles per second, the frequency of the impulse applied to the transmitting coil TC comprises a wave train of very high frequency current. For instance, if a wave of this wave train is present only for one micro second the frequency of the alternating current wave train would be in the neighborhood of 500,000 cycles per second.

Receiving equipment In order to accurately indicate by suitable cab signal indication the exact distance of a train or other obstruction ahead, the invention contemplates suitable time measuring means for measuring and indicating the time elapsed between the transmission and reflection of an impulse of current:

the usual indicating plate or fluoroscope including suitable fluorescent material 25, a filament or heater 2%, a grid or focusing electrode 21, a plate or target 28, as well as sweep plates SP and control plates CP.

The sweep plates SP are connected directly across the secondary winding 30 of the main transformer MT. The control plates CP are connected directly across the secondary winding of the out-put transformer 0T having its primary winding included in the plate circuit of the output amplifier A3 of the receiving apparatus. It may be pointed out that the plate or target is supplied by plate circuit voltage from the plate circuit source 82-43, heretofore described, and that the sweep plates SP and the control plates CP have one of their plates connected to the common wire which in turn is connected to the plate or target 28.

In addition to the plate source l2-I3, here- I tofore mentioned, there is provided a similar grid source 32-43 including a grid rectifier GR. This grid source supplies current of negative potential to grid 21, with respect to the filament or heater 26 of the oscillograph CRO, this in order to permit a higher voltage to be applied between the filament 26 and the plate 28, thereby causing the electron velocity to be increased. In addition to the plate source l2-|3 and the grid q source 32-43, there is also provided a plate source PS for the amplifiers Al, A2 and A8. This plate source PS comprises a double-wave rectifier DWR.

of well known thermionic tube construction, and

including condensers 31 and 38 and an inductance 39 comprising the usual elements for excluding the alternating current ripples which would otherwise be supplied to the plate circuits of the amplifiers Al, A2 and A3.

Each of these amplifiers has its heater h energized from the secondary winding 40 of the main transformer MT, which secondary winding 50 also supplies energy to the filament or heater 26 of the cathode ray oscillograph CRO. Each of the amplifiers A2 and A3 is provided with the usual grid condenser 42 and grid resistance 43 the grid 9 of the amplifiers A2 and A3 being fed respectively from the plates 1) of the amplifiers Al and A2. The amplifier Al is fed from the secondary winding of an impedance matching transformer IMT. This impedance matching transformer IMT preferably has its primary and secondary windings tuned as by condensers 44 to approximately resonate with the frequency of the electric impulse wave transmitted down the track and reflected back to the train, as heretofore pointed out. This tuning not only aids the entrance of the'reflected waves into the receiving equipment but also serves as a band pass filter which keeps waves of other frequencies suppressed. The primary side of the impedance matching transformer IMT is connected to two receivers R. connected in series. These receivers B, one located over each of the track rails, are preferably designed to most efliciently receive the reflected impulse returned from the train ahead, and for this reason preferably have their magnetic cores constructed of powdered iron or other suitable material of low reluctance which has low hysteresis and low eddy current losses.

Referring to the fluorescent portion of the cathode ray oscillograph CRO, it will be noted that a scale has been shown thereon illustrating the distance of a train or other impulse reflecting devicein advance of the equipped train in thousands of feet. The numeral 4, for instance, indicates that that point signifies 4000 feet in advance of the train. The horizontal portion of the curve shown thereon is due to the sweep voltage applied to the sweep plates SP, whereas the portion of any part of the curve above or below this line is due to the voltage applied to the control plates CP. It is of course understood that electrons are emitted by the heater 26 moving in a direction toward the plate 28. By reason of the small hole, constituting a target, in this plate a 1 very narrow stream of electrons strikes the screen 25. Were it not for the sweep plates SP and the control plates CP these electrons would hit near the zero part of the scale. The sweep plates, however, cause this electron stream to pass from left to right way beyond the end of the scale and back again. The control plates CP of course cause vertical vibration of the electron stream in accordance with the potential applied to the plates By looking at this graph 45 it will be noted that near the zero point on the scale this graph 45 raises abruptly making a peak 45 and then falls back to normal. This is due to the impulse induced in the receivers R by the transmitting coil TC either directly or indirectly through the medium of the track rails I. The peak portion 45" inthis graph illustrates a reflected impulse, which was reflected back from the train T in advance of the equipped train T, whereas the next peak lli which is negative illustrates an impulse that was reflected from the .wayside reflector WR located between the trains T and broken rail, are not continuous, the energy in the out-going impulse is not wholly dissipated 'when it reaches the broken portion of the rail Although thiswayside reflectorWlR. is loicated nearer the train Tl than is thetrainTh nevertheless, the impulse 45 reflected back from the train T reaches the receiverR before the negative impulse 45 reflected back from the wayside reflector WR reaches the receiver R. The reason for this apparent discrepancy is due tothe fact'tha't the: wayside reflectors :WRl and WR are so constructed that the time consumed for a. wave to enter this reflector WR or WR.

and again leave the same'con'sumes substantially the same amount of time that would be required for an impulse to travel a distance of 5000 feet down the track rails and back again. From this it is readily apparent that the negative peaks in the graph 45 due to wayside reflectors WR or WR can-'neverreach a lower part of the scale on the cathode ray oscillograph than the 5000'= feet point illustrated. These reflectors have been provided: to avoid confusionv between a reflected impulse reflected back from a wayside reflector 4 a distance aheadof thetrain indicated on'the oscillograph field 2,5 thegr'aph 45 would 'be'd'e pressed belowthe horizontal sweep line. This negative wave is due to the fact that reflection back from an open circuit produces the opposite I effect from that of the reflection back from a short, circuit. I Since the track rails, due to a and the remaining energy, through .a reflecting a or condenser effect, possibly with the other rail,

returns ina manner similar to that occurring with the wayside reflectors It can be con- I sldered that the high frequency impulses are reflected much, inthe same manner thatoccurs with sound and with'light, that is when such a wave meets a changed medium such as a short circuit or an open circuit, the wave is reflected much as is light and sound when they encounter a diflerent medium, such as a denser medium.

The wayside reflectors WE. are preferably spaced apart such a distance that there will always be indicated upon the screen of the cathode ray oscillograph at least one impulse reflected from a wayside reflector. This feature of applicants system afl'ords a continuous check upon the operativeness of his transmitting and receiving apparatus. Furthermore, these impulses reflected from the wayside reflectors WR afford a means of showing by their movement on the screen the actual speed of the train so equipped, and by comparing the rate of movement between such reflected impulses as 45 and 45 a direct indication of the speed .01 the train-in advance is also indicated. Stating this more specifically, since impulses 45 45 and 45 on the screen 25 show the relative locations of the trains T, T

and wayside reflector WR at any and every instance, then it follows that the speed of each of the trains is directly proportional to the speed at which wayside reflected impulse 45 approaches the impulse representative of that particular train. That is, the rate of approach of impulse 45 toward impulse 45 on the screen 25 is proportional to the speed of train T and the rate of approach 01' the impulse 45 on the screen 25 toward the impulse 45 is proportional to the speed of train '1.

Referring now to Fig. 3 of the drawings, it is ate relays connected to these amplifiers. amplifiers are provided with theusual filament circuit of the amplifier A 2 a check relay CK.

'forecaution trafiic limitations are now imposed desired to point out that the modified device CR shown therein comprises a cathode ray oscillograph, such as illustrated in Fig.1, ex-

cept that the inside Of'this oscillograph hasbeen provided with Faraday collecting plates I50, l5l and. I52. These plates 150, I51 and I52 are re-' spectively connected with the cathodes of am- ,plifiers A A 'and A 2, to illustrate how the cathode ray which pictorially indicates the position of a train in advance may be usedto oper- These battery a, plate battery band grid bias battery co. As illustrated there is included in the plate This relay CK preferably controls through its front'contact 53 a suitable normally energized brake control device Even I the train, so that deenergization of'this check "relay CK causes deenergization of device BV and an application of the brakes of the train. In accordance with this embodiment of applicants invention the wayside reflectors WR are located sufficiently energized in the event of failure of any portion of the car-carried or wayside apparatus. The

Faraday collector plates I51 are so located in the distance of the equipped train. 'As illustrated I I I the caution relay CA is now' energized, thereon the train in question. The's top relay S. on the other hand, is only energized in the event that the train in advance is within a dangerously close distance in advance of the; equippedtraln, and as illustrated'this stop relay :8 is deenergized because the path of electron emission does not strike one of the plates I which control the energization of the stop relay S. This stop relay has a back contact 54 included in series in the energizing circuit of the brake control device BV.

The various lines connecting to the elements of the cathode ray tube of Fig, 3, have been given reference characters corresponding to Fig. 1, to indicate that the tube in Fig. 3 is operated similar to the tube in Fig. 1. Wire 96 is added and is the common return for the Faraday plate circuits.

I In Fig. 4 of the drawings has been illustrated a track of the usual construction including track rails 50 divided by insulating joints 6| into blocks in the usual manner ior the purpose of controlling wayside signals. In this figure of the drawings one way has been illustrated in which a railway system of the insulated block type may be modified to adapt it for use in conjunction with the car-carried apparatus shown in Fig. 1, without interfering with the track circuits and close together so that at leasto'ne of these're- I flectors reflects an impulse to, throw the beam of the oscillograph on the Faraday collector plate I I52- In other words, the'checkrelay CK'is dc- I 30 cathode ray oscillog'raph CRO 'tha't the caution y y wayside signal control already installed. This low frequency track circuit current when alter- Y nating current track circuits are used for way- 7 gated wave will pass into the rails of the diverg-' ing route.

As pointed out above the wayside reflectors WR W12 etc., are preferably so constructed that the same time will be consumed from the time that an impulse enters such reflector until it again leaves the same as would be required for an impulse to move down the track rails 5000 feet and again return. These wayside reflectors or repeat-back stations are preferably located not over 2000 ft. apart, so that there will at all times be at least one of these reflectors indicated on the screen of the cathode ray oscillograph. These wayside reflectors comprise a composite filter composed of a number of sections of parallel condensers or capacities l3 and series inductances it connected between successive condensers it. These condensers and inductances' preferably have such time constants that substantially five micro seconds are required for a wave to penetrate to the end of the filter and five micro seconds are required for it to be reflected back. This consumption of micro seconds of time is substantially the equivalent of the time required for a wave of current to flow down the track 5000 feet and back again.

The series resistance ll limits the amount of energy taken from the impulse as it passes down the tracks and attenuates the out-going repeatback impulse to correspond to track and shunting conditions which would cause the greatest attenuation of the impulse. A non-linear resistor may be connected across the first condenser 13 so that when the, locomotive is directly above the wayside reflector the feed back or reflected impulse signal will be reduced in strength to approach more closely the relatively weaker signals received when the locomotive is 2000 feet away. The non-linear resistor 15, above mentioned, is a resistance unit in which the ohmic resistance falls very rapidly as current passing therethrough increases.

The applicant has thus shown a rather unique system of cab signaling and automatic train control which permits closer spacing of trains and affords facilities not afiorded by wayside signaling, cab signaling and train control systems of the former type in which the track is divided into blocks, and although a rather detailed embodiment of this invention has been illustrated it is to be understood that the applicant is not limited to the particular apparatus shown to exemplify his invention. It is further desired to be understood that many other adaptations and expedi-' cept as demanded by the'scope of the following claims,

What I claim is:--

1. In a train control system of the continuous inductive type, the combination with a railway track and a railway vehicle thereon, of another vehicle in advance of said first vehicle, means on the first vehicle for transmitting a current wave down the track rails, stationary reflecting means on the track for reflecting an image of the wave back to said first mentioned vehicle another image of said wave being reflected back to said first mentioned vehicle from the axles of said another vehicle in advance, means on said first mentioned vehicle for receiving said reflected waves, and means in the cab of said first mentioned vehicle for visually measuring the lapse of time between the transmission of said wave and the reception of the two reflected waves, whereby the relative locations of said stationary reflecting means and said another vehicle may be definitely ascertained.

2. In a train control system of the continuous inductive type, the combination with a railway track and a railway vehicle moving thereon, of means on the vehicle for intermittently transmitting current waves down the track rails, stationary reflecting means on the track for reflecting a portion of the waves back to said ,vehicle another portion of said waves being reflected back to said vehicle from the axles of another moving vehicle in advance, receiving means on said vehicle for receiving said first mentioned reflected waves, indicating means in the cab of said first mentioned vehicle for continuously visually indicating the time elapsed between the trans-.

mission of successive waves and the reception of portions thereof reflected back from said stationary reflecting means and from said another vehicle, whereby the position and motion of said another vehicle with respect to said stationary reflecting means is continuously indicated in the cab of the first mentioned vehicle, and means controlled by said receiving means for applying the brakes of said first mentioned vehicle when it too closely approaches said another vehicle.

3. In combination, a railway vehicle, a cathode ray oscillograph on said vehicle having sweep plates and control plates for sweeping an electron stream over a screen, means for impressing potentials on said sweep plates in accordance with electric waves transmitted from the vehicle to the trackway on which said vehicle moves, means in the trackway in advance of the vehicle for reflecting said waves back to said vehicle, and means for impressing potentials on said control plates in accordance with the waves reflected back from said means in the trackway.

- 4. In combination, a railway vehicle, a cathode ray oscillograph on said vehicle having sweep plates and control plates for sweeping an electron stream over a screen, another vehicle in advance of said vehicle, means for transmitting current waves down the track rails ahead of the first mentioned vehicle which will be reflected back from the axles of said vehicle in advance, means for impressing potentials on said sweep plates in accordance with the electric waves transmitted from the first mentioned vehicle to the trackway, and means for impressing potentials on said control plates in accordance with the waves reflected back from said vehicle in advance, whereby the image on said screemwill indicate the distance from said first-mentioned vehicle to said vehicle in advance.

5. In combination, a railway vehicle, a cathode ray oscillograph on said vehicle having sweep plates and control plates for sweeping an electron stream over a screen, another vehicle in advance of said vehicle, means for transmitting current waves down the track rails ahead of the first mentioned vehicle which will be reflected back from the axles of said vehicle in advance, means for impressing potentials on said sweep plates in accordance with the electric waves transmitted from the first mentioned vehicle to the trackway, means for impressing potentials on said control plates in accordance with the waves reflected back from said vehicle in advance, and means responsive to said electron stream to apply the brakes of the vehicle if the time elapsed between the transmission of a wave to the track rails and the reception of its reflected wave is less than a predetermined time.

6. In an automatic train brake control system, the combination with a railway vehicle, brake control means on the vehicle, means on the vehicle for sending out over the track rails in advance of said vehicle trains of current waves time spaced so that a particular train of waves may be reflected from the axles of a vehicle in advance greater than braking distance before a following train of waves is transmitted into the track rails, said trains of waves being transmitted for measuring the distance of travel of induced waves and the distance from the first mentioned vehicle to such vehicle in advance from the axles of which they are reflected, and detecting means on said first mentioned vehicle for detectin'g the refiected waves and actuating said brake control means when the reflected waves from said vehicle in advance by their time of arrival indicate that said vehicle in advance is less than a predetermined distance in advance of said first mentioned vehicle.

7. In an automatic train control system, the' combination of means for transmitting trains of current waves from a first vehicle down the track rails and time spaced so that a particular wave train may be reflected back from another vehicle more than braking distance ahead of the first vehicle and this same wave train received back on the first vehicle before a second wave train is transmitted down the track rails, detecting means on the first vehicle for detecting on the first vehicle the reception of a reflected wave train; and indicating means controlled by said detecting means. a

8. In an automatic train control system, the combination of means for transmitting successive series of current waves from a train down the track rails, said-series of waves being time spaced so .that -a particular series may be reflected back from another train more than braking distance ahead of the equipped train and this same series received back on the first mentioned train before a second series is transmitted down the track rails, and means for detecting on the first mentioned train the reception of a reflected series each series being so short that there is no over-lap between out-going and incoming series for the most closely spaced trains of which said another train is to be indicated on said first mentioned train, whereby out-going and in-coming series of waves cannot conflict with each other.

9. In combination, a railway track, a railway vehicle, another vehicle in advance of said vehicle, apparatus on said first mentioned vehicle for transmitting an electric current wave train down the rails which same wave train is of such short duration-that when reflected back from the'short circuit from rail to rail produced by said another vehicle more than braking distance in advance of said first mentioned vehicle the 3 front end of such wave train will be reflected back to-the first mentioned vehicle after the rear end of such wave train has been transmitted into the track rails, receiving apparatus on said first mentioned vehicle for manifesting the reception of this same reflected wave train on said first mentioned vehicle, means on the first mentioned vehicle for measuring the time elapsed between the transmission and the reception of this said wave train, and visualindicating means onthe first mentioned vehicle for indicating this' time.

the reception of a reflected wave train, and indicating means controlled by said detecting means for indicating on the vehicle the distance to the reflecting means andthespeed at which said train is moving toward such reflecting means.

11. In combination, a railway track, a railway vehicle, another vehicle in advance of said vehicle, apparatus on said first mentioned vehicle for transmitting an electric current wave train down the rails which same wave train is of such short duration that when reflected back from the short circuit from rail to rail produced by said another vehicle more than braking distance in advance of said first mentioned vehicle the front end of such wave train will be reflected back to the first mentioned vehicle after the rear end of such wave train has been transmitted into the track rails, receiving" apparatus on said first mentioned vehicle for manifesting the reception of this same reflected wave train on said first mentioned vehicle, means on the first mentioned vehicle for measuring the time elapsed between i the transmission and the reception of this said wave train, and visual indicatingmeans on the first mentioned vehicle for indicating this time on a scale calibrated to directly indicate the distance to such another vehicle.

DONALD V. EDWARDS.

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