US2810611A - Train control system - Google Patents

Description

Oct. 22, 1957 H. P. FOLKER TRAIN CONTROL SYSTEM 5 Sheets-Sheet 1 Filed April 23, 1.951

, INVENTRL.

f/erberl P Fo/ker E 6) 2% Arron/5Y5 Oct. 22, 1957 H. P. FOLKER 2,810,611

TRAIN CONTROL SYSTEM Filed April 23, 1951 3 Sheets-Sheet 2 III.

| INVENTOR.

wdwaw States has TRAIN CONTROL SYSTEM Application April 23, 1951, Serial No. 222,432

1 Claim. (31. 303-18) This invention relates generally to pneumatic train control systems of the type adapted to effect automatic brake applications and having provision for a manual forestalling operation to prevent an automatic brake application under certain conditions.

In the past pneumatic train control systems have been employed which incorporate means on the locomotive adapted to receive a track impulse which serves to vent the main brake pipe of the pneumatic braking system of the train to thereby eifect an automatic brake application. Forestalling devices such as are used with such systems incorporate a time delay mechanism having an automatic cycle which is put in operation when the engineer actuates a forestalling lever. In the event a track impulse is received by the system during the time delay afforded by the forestalling mechanism, a brake application does not occur. Should the engineer fail to make timely operation of the forestalling lever, an automatic brake application occurs in response to a track impulse, and the train is then stopped, thus requiring the engineer to thereafter carry out a restoring operation. In train control systems of the type described in Folker et al. 1,439,081 and 1,690,816 a magnetic track impulse is utilized which directly operates one of a pair of valves incorporated in a duplex control valve, whereby a control line leading to an automatic train stop valve is vented to secure a brake application. A typical forestalling unit such as has been used with a system of the Folker type is shown in Patent 1,592,930, and serves to automatically shut off the line leading from the automatic stop valve to the duplex control valve, and to vent that portion of the line leading to the duplex control valve to thereby prevent operation of the same in response to a track impulse. A forestalling arrangement such as is adapted for remote operation is disclosed in Folker 2,486,271 and employs a small manually operated valve located a considerable distance from the time delay means of the forestalling unit.

In many train control systems for effecting automatic brake applications, a so-called speed recorder or speed governor has been employed to cause an automatic brake application when the train speed exceeds a predetermined speed limit. Such speed control means can be in the form of a speed governor which operates a switch when a predetermined speed limit has been reached, whereupon an electrical circuit is conditioned to cause an automatic brake application.

I have found that the margin of safety aflorded by a system of the Folker type, together with automatic speed control as described above, can be greatly enhanced by the provision of means whereby the locomotive engineer cannot resort to a forestalling operation to prevent an automatic brake application while passing a danger zone, unless the train speed is below a value which is substantially less than the speed limit for which the speed recorder causes an automatic application. It is an object of the present invention to provide such an arrangement and to make possible such additional safety with a minimum amount of additional operating parts.

A further object of the invention is to provide an imatent 2 ,810,611 Patented Oct. 22, 1957 proved train control system of the above character which is applicable to both remote and directly operated forethe preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure 1 is a diagrammatic view illustrating parts of a complete system incorporating the present invention.

Figure 2 is a schematic view illustrating a modification of Figure 1.

Figure 3 is a schematic view in section illustrating the forestalling means of Figure 1 and certain associated parts.

Figure 4 is a schematic view in section illustrating a modification of Figure 1 to incorporate direct operated forestalling means.

Figure 5 is a schematic view illustrating a modification of Figure 4.

The train control system illustrated in Figure 1 consists of a'duplex train control valve 10 of the type adapted.

tobe operated by a magnetic track impulse, and as disclosed for example in Letters Patents 1,439,081, 1,439,082, 1,592,930 and 1,690,816. This control valve is employed in conjunction with the release or restoring valve 11, the automatic train stop valve 12 (see 1,529,058) and the forestalling unit 13. Located at a point remote from the forestalling unit 13 there is a manually operated valve 14. In addition to'these parts the system can include an air strainer 16, a double heading interlocking valve 17, and a double heading cutout cock 18. The release or restoring valve 11 and valves 17 and 18, can be substantially as shown and described in Folker 1,690,816.

The piping for the various parts mentioned above is as follows: A control pipe 20 extends from the duplex control valve 10 to the restoring valve 11. An extension 21 of the same pipe leads from the restoring valve to the shutoff valve 51. Line 22, which connects to the automatic train stop valve 12, is the brake pipe of a conventional pneumatic train braking system. Pipe 23 leads from the train stop valve 12 to the engineers brake valve, and is equipped with a double heading cock 18. Line 24 represents a connection to the main air supply reservoir of the braking system. Line 26 is an extension of line 24 beyond the air filter 16 and connects with a time delay means of the forestalling unit as will be presently explained. Pipe 27 connects from the stop valve 12 to certain parts of the forestalling unit as indicated and in effect is an extension of the control line 21. Another pipe 28 connects stop valve 12 with the air supply pipe 26. Pipe 29 connects the restoring or release valve 11 with the interlocking valve 17, and pipe 31 connects this device to th double heading cock 1%.

For a normal position of the various parts, that is a position in which the system is in condition to be responsive to a track impulse to effect an automatic brake application, thebrake pipe is maintained closed against venting to the atmosphere by the stop valve 12, while air pressure is maintained in control pipes 20 and 21, and cock 18 is open to permit control of'the braking system from the engineers cab. Pipe 28 leads to the main air reservoir and is in restricted communication with the control pipes 20 and 21. Each of the twovalv e s 'in the duplex control valve 10 is retained closed magnetically,

and when the control valve passes over a track magnet, the field of which has not beenv neutralized by a signal current, one of the two duplexv control valves (normally held closed magnetically) is opened to vent the control pipe, the particular valve operated depending upon the directionof movement of the train. The venting of control pipe 20 to the atmosphere resulting from opening of one of the two control valves reduces holding pressure upon the operating diaphragm of the train stop valve 12 and as a result the valve member of the train stop valve moves to a position to cause venting of the brake pipe 21 to the atmosphere; and the valve incorporated in the saine closes cornnjunication between pipes 23 andZZ The for estalling unit incorporated in Figure 1, together with the remote forestalling valve 13;, are illustrated in greater detail; in Eigure 3. The forestalling means illustfated consists-oi time delay means of the hydraulic type,

including a reservoir 33 adapted to contain a quantity of suitable liquid such as oil. Restricted orifice 34 establishes communication between the'lower portion of reservoir 33 and the lower portion of a vertically extending cylinder 36. A piston 37 is slidably fittedin cylinder 36 and is attached to the lower end of a rod 38. The upper end oi rod 33 is attached to a member-39' which can be termed a piston valve, and which is slidably fitted' in a second cylinder 41. Piston 37 is provided with suitable sealingmeans such as the cup leather-'42, and like meahs such as a cup leather'43; is providedfor piston 39." A compression spring 44 is shown positioned at the lower end of cylinder 36 and is adapted tobe compressed when the piston 39 completes its final downward movement; The lower portion of the cylinder 4.1 isprovidedwith ports 46 and 47 which are closed by the 'piston valve'39 for =the lowermost position of the same as illustrated in Figure 3 but which are exposed for communication with the upper portion of cylinder 36"whe'n'thepiston valve moves upwardly.

During a forstalling period piston 37 together with piston-valve 39 are caused to move upwardly'at a regulated rate by application of line pressure to the reservoir 33, and atterreaching the upper limit of their travel, these members move downwardly to their initial positions. The space above piston 37; is in continuous communicationwith the main reservoir supply line 26.

Inconjunction with the timing means" there is a shutoiivalye 51 and; a valve actuator 52; "The shutofi valve is double seated andlconsists of a movable valve member 3 carried by the fluted; stem 54. The valve member in its one limiting positio'nbloses upon a'stationary seat" 56 and in its other-limiting'position it closes onse at 57' whiph surrounds stem 54:' The orifice through seat 56 connects -'with the pipe line27tas'illustrated, and an orifice" between seats 5 6 a'nd' STcomi'ects withthecontrol line 21. lustratedin fiigureli, lines- 21 and are plac'e'dfin free communication,- However when stetn 54 is actuated' to close valvememberSS upon seat 56;'line 21 is vente'd to the atmosphere past stem 54 and line 27 is closed;

The actuator 52;'can* consistofa body forming a cylinder 5 andfitted with'a piston 59L The space on one side of piston 5 9 iconnects withthe'signalwhistle' 61, and with pipe 62; which-connects with"th e"port 47 of the tirriihg' means. 5 Thus-when-airpressure is applied to pipe""(oi' duct);62 the piston S9-is-urged1in a direction to movestem 54 and thereby close valve member 53 "upon seat" 56. *While such; pressure is appliedto'pipe 62' the signal whistle6 l is operated.

The forestalling-unit also includes pneumatic actuator 63 and a combination vent andclosure valve 64. Actuator 63' 'consists of abody 615 fitted with a cylinder 67. A piston 68 is fitted in"cylinder67 andis attachedto' the" rod;69 A tube 71'is"als'o attachedto rod 69 and extends to the exterior ofthe device. A plunger" 72 provided with a-projecting 'stud'73'is slidably fitted within tube71 and-is-yieldably urged toward projected position bythe: compression spring 74. Another 'compressionspi'ilig 76 urges-the piston together with the tubiiIa -membe'r 711mwardjretracted position. Duct '77 communicating with one-'side-of piston68 is connected by pipe 78 to the-port 46 ofthe timing means, and also by pipe 79 to the mote valve 14;

Valve 64 consists of a valve member 81 adapted to 'In thenormah'position'ofthe shutolflvalve as il-' 4 a close upon the stationary seat 82 and carried by the stem 83. The valve stem is provided with a duct 84 which communicates with the orifice 86 formed on the outer end of the stem. The outer end of the stem loosely carries a cup 87 provided with vent openings 88, and with a seating disc 89. One side of the seat 82 is connected by pipe 91 with the line Z'Zleaiiirig to the automatic train stop valve. The other side of seat 82 is connected by line 92 to a duct 93in"the timing means whereby this p p in mmunicatiomwith the space in the u r part otheiiquidreservoir 3 3. f v 1 The timing means, the pneumatic actuator 63 and the valve 64 are correlated by latching means as follows: A latch lever 94' (Figiii'e"3),hasastationary pivotal 'mounting 95 and a portion of. are same is interposed in the path of movement of the piston valve 39. The free end of lever 94 carries what can be termed a latch bolt 96, the lower end of which for purposes of schematic illustration is normally interposed between the aligned stud 73 and the cap 87.. The "arrangement of parts'in this connection can be similar to that illustrated in Patent 1,592,930 (see Figures 5 and 6 of same), assuming that plunger stem '69gcorresponds' to the plunger stud 73: in the presentinstance.

The latching means functions as follows: When no pressure is being appliedto the piston'68 of the pneumatic actuator 63, the parts occupy the operating positions'illustratedv in'Figure 3, while member 81 is closed upon its seat 82, andline' 92 is vented to the atmosphere through ducts 84, 86 and 88. When pneumatic pressure is applied to piston '68 by way of duct 77, movement ofi'this pistomtransmits motion t'o' the stud 73 and uch motion is transmitted through the lower end of latch bolt 96, to close cap 87 upon orifice 86 and to move the valve member 31 to open position with respect to seat 82. Thereafter when piston valve 39- strikes latch lever 94 and swings the same upwardly a limited distance, latchbolt 96 is retracted froniits'normal position between Stud 73; and cap '87, whereby'valvejrnember 81 is permitted to:

close'and cap 87 permitted to move to open the venting orifice '86. This initiatesa' downward movement of'tlie piston" valve 39, andafter" pis'ton'37 has completed its downward movement, pneumatic pressure upon piston 68 its initialposition under the urge of "compression spring,

76, thereby enabling the latch bolt 96 to again drop tdown ating rod is attached to'a piston 109 fitted in the cyliildierw 1113" One 'side of the piston '109 is vented to theatfnosphere through the space abourrqd 107, The othei 'iside" is normally in cbinmunicationwith the outflow passage 112. The'iinlet passage 113 of th'e valve'is connected re the 'mainfres efvpii-siipply' pipe 115% while the ou tfiow pa' s'sag'"112 connects with the line 79, which in turn connects'witli'the pneumatic actuators and withthe timing means.

"The system insofar as described above is the same as disclosed iri'iiiy"Patent"2,486,27l. Iii conjunction with this systenfIhave shown afspeeid recorder 116 This speed recorder can 'be offlthe typ e'manufactured by Barco Manufacturing Co, Chicago, Illinois, and includes cenmargin governi means OpelfQKlVI lY connected to a'wheel I of thetrain andse'r vingtop operate an electrical switch when fthe' train speed exceeds for which the 111 sti'ument is set. Iria typical instance this limiting s maybe In a dditi on to .the regular jspjeeii; limit switch, I provide a second electrical ,s'ivitchfl'lf whichis likewise arranged toQbeoperate'dby the 'cen 'tnfugal governor of the instrument, and which can be set to be operated when the speed exceeds a somewhat lower value, such as 40 M. P. H. Switch 117 is shown connected to control an electrical circuit including the battery 118 or other source of current, and the operating solenoid 119 is for the valve 121. Pipe 122 serves to connect this valve with the pipe 79, which connects the remote valve 14 with the timing means. Valve 121 when opened by energizing the solenoid 119 vents to the atmosphere.

Operation of the system described above is as follows: Assuming that the system is in normal operation ready to receive a track impulse, and that the double heading cock 18 is turned to open position to permit control from the engineers cab as desired, the two valves ofthe duplex control valve are in closed position and are retained closed against the pressure of air in control pipe 20 by the magnetic field of a permanent magnet as described in Patent 1,548,593. The parts of the forestalling unit are substantially in the position as illustrated in Figures 1 and 3, and the double seated shutoff valve 51 is in the position illustrated whereby pipes 21 and 27 are in free communication. By virtue of pressure maintained in pipe 27 the valve member of the automatic train stop valve 12 is maintained in such a position that the valve means of the same maintains pipe 22 in non-venting condition. At the same time however pipes 20, 21 and 27 are in restricted communication with the main source of air supply through the train stop valve.

Assuming that the train is proceeding at a speed below the limiting speed for which the speed recorder 116 is set (e. g. 78 M. P. H.) and that a track impulse is received by the duplex control valve without operation of the forestalling unit, line 20 is vented to the atmosphere by the opening of one of the valve members of the duplex control valve, and this serves to vent line 27 from the stop valve 12, whereby the train stop valve automatically operates to vent the brake pipe 22 to the atmosphere. This serves to effect an automatic brake application. To restore the system to normal operation the engineer moves the handle of the restoring valve 11 to the restoring position, whereby pipe 20 is vented to the atmosphere and temporarily disconnected from pipe 21, and pipe 21 is connected to pipe 29 and thereby vented to the atmosphere through the interlocking valve 17. This retains the brakes applied and permits the pressure in pipe 20 to drop to atmospheric, whereby the valve member of the duplex control valve which has been actuated to open position, is permitted to return to closed position. Thereafter the handle of the restoring valve 11 is returned to normal position and pipe 20 is reconnected with pipe 21.

Assuming that the engineer is alert and carries out a forestalling operation to prevent brake application by a track impulse, button 108 of the remote forestalling valve 14 is depressed whereby valve 102 is unseated to permit application of air pressure from the main supply through pipe 79 to the pneumatic actuator 63. Operation of the actuator 63 serves to close the venting orifice 86 and unseat the valve member 81, whereby pressure from line 27 through line 91 is applied through pipe or duct 92 and duct 93 of the timing means to the space above the liquid in the reservoir 33. Liquid from reservoir 33 now commences to flow through the restricted orifice 34 to the space beneath'the piston 37. The initial movement of this piston is aided by the compression spring 44. Piston valve 39 moves upwardly within cylinder 41, and when port 46 is exposed this port together with line 78 is placed in free communication with the space above the piston 37. In connection with the upward movement of piston 37 the full pressure of the main reservoir supply is applied to the space above the piston 37. However the upper area of piston 37.minus the upper area of piston 39 is less than the bottom area to which the liquid pressure is applied. Therefore a differential force acts to urge the piston upwardly. Exposure ofport, 46 to the space 6 above the piston applies a full main reservoir pressure to the pipe 78, to pipe 79 and to the pneumatic actuator 63. The pressure thus applied to the actuator can be termed the holding pressure and thereafter the operator may release the button 108, without interfering with automatic continuation of the forestalling cycle. Release of button 108 permits it to raise to an elevated position above the normal position shown in Figure 3 due to the fact that piston 109 is urged upwardly by pressure applied to passage 112. Valve 102 is also returned to its normal position shown in Figure 3 by action of spring 103.

Simultaneously with exposure of port 46 the port 47 is likewise exposed to the line pressure existing in the upper portion of cylinder 36. Therefore main reservoir pressure is applied through pipe 62 to the pneumatic operator 52 whereby the piston 59 of this operator operates the shutoff valve 51 to close the valve member 53upon seat 56. Thus shortly after the commencement of the forestalling period the control line 21 is shut off from communication with the remainder of the control line '27, andlikewise that part of the control line leading to the duplex control valve by way of pipe 21 is vented to the atmosphere.

As a result a track impulse will not'operate either one of the two control valves.

The piston 37 moves upwardly at a predetermined speed and when it reaches substantially the upper limit of its travel, piston'valve 39 strikes the latch lever 94 with the result that latch bolt 96 as diagrammatically illustrated is effectively withdrawn from between stud 73 and the cap 87 (ignoring for the sake of diagrammatic illustration the additional lever 85 shown in Patent 1,592,930 which would customarily be used in place of a single latch bolt). This serves as a motion transmitting element to permit closure of valve member 81 and to cause venting of line 92 through orifice 86. Reduction of pressure upon the liquid in the reservoir 33 to atmospheric results in downward movement of the piston 37 under the urge of air pressure from the main reservoir supply. During the last portion of the downward travel of the piston 37, communication between ports 46 and 47 and line 26 is interrupted by seal 43 and the pressure in both 46 and 47 is reduced to atmospheric because of leakage past piston 39. Thus the shutoff valve 51 is permitted to open to re-establish communication between pipes 21 and 27. Also air is no longer supplied from line 114 to pneumatic actuator 63, and the closure valve 64 is therefore permitted to open to vent pipe 92 to the atmosphere through orifice 86. Button 108 is'therefore permitted to drop down to its normal position shown in Figure 3 by gravity. This serves to indicate to the operator that the forestalling period has en ed.

Assuming now that the train enters a danger zone at'a speed suflicient to cause the switch 117 to be operated by the speed recorder and governor 116 (e. g. above 40 M. P. H.) the open condition of valve 121 serves to automatically make it impossible for the engineer to avoid a brake application by a track impulse, by operating the forestalling valve. Thus if the engineer should operate the remote forestalling valve 14, under such conditions, the discharge side of the valve 14 would be vented to the atmosphere through pipe 122, and insufiicient pressure would exist in pipe 79 to operate the'pneumatic actuator 63. As a result the combination vent and closure valve 64 would not be operated to cause pressure to be applied to the timing means through pipe 92. Thus upon receipt of a track impulse by the duplex control valve 10, an automatic brake application would occur irrespective of I whether or not the engineer had attempted to prevent such application by operating the remote forestalling valve 14.-

It will be evident that my invention provides an added factor of safety in automatic train control systems; be-

cause it places a penalty upon entering a danger zone atv a speed above thatwhich would normally be wandered a ate 5 9 1 si t GQ SliliQ S- Penal y s h same s hat vtt has, isst b tl n th te e em a fl at nts. t at te th tra n. ha been s ppe by i athe sts ake an iea en t is n cessa y o the. w tness 9 P 4 w th. r s or perat on, w ich n: s sss ttms e. h s ca to. p rate. the res ing. etta slseen do s no a er he the tu t ens the s eed esqtt e .6.. n me y to c use n utom ic t a l' at qn n he. event t e a n at any ime @X".

' Mat L mit ash) as .8. H-

nother mar ner. of; connecting the, valve 121 is shown n, E s e .5 n. t is. nsane-e the. valv 1; has its ine i qennss ed; n. t epipe .4, h uppl a r p tent s.manning a ve .4;- W th t is r gement. h Switch A s do ed ol no d: 9. s ne ze to a an z hiss ves q interrupt pp y of r it ane. 5 'Ehusv en e. v l 1 is p r d ally-n9 ai Pr ssman. ran m t e r gh ine. 19

QRQF P Q efflt f i stall n ea am 4. ll s r tes. nether mb d ment; or the nvenw ncgrpora tes, a directmanually operated fore.- stalling means he heme. n e ter. .3,, t em is. a ha d le er 1 6 mounted upon the rotatable shaft 127;. As, diagram: a i a ty. lust ated; he ha c r es a spring p s l s l es. W

1218 adapted toengageandtransmitforce, to theflower end.

ofgt he latch bo l tfl 29 'lghuswhen the, handlever is. turned cloclgvv ise 27.Q from the position viewed in Figure 4, the cap 8:7; of the valve, 64 is operated whereby the, valve r 8,1 is unseate d. This operation is the, same as when thepneumatioactuator 6 3 of Figure 1 is operated ya t P 1lesanfiiitefiet c mmen m nt f a res llingcycle Latch bolt 1Z9-is pivotally attachedto the. latch bolt 131, corresponding to the latch arm 94 of Fig- "L lL Whenhflw P ston-"7 reaches. the up ofv its.

travellatch, leyer 1 31 is operatedto retract, the bolt 129,

Figure 5 illustrates a modification of the arrangement described above-with; referenpe to..Fignre 4. In 1 this .in-

esse s lbe' devel oped: l

zone at a excessive speed, (e, g. above, 40 P. H.-)

' rnov n eremgphgsnhrgn valvejl.isnotoperated. With- The valye 14 is omitted, and, in placeof lt th va lve 6,4 is permitted to return to its, pos on, and: the, forestalling. lever. 126.

the pipe 92. when the valve121 is. opened pipe'. 92

u 3 lzlgleading from the; solenoid operated connec tgd tojh ep ipe 62; Thus ,whentheI closed tqopep thegsolenoid valvelzl, pipe.

.togethe gwith pipe 62, whereby no, pressure.

' pipefipfor operationofthevalve. 91: 52.; 'Thusjfan engippe r; should attempttodefcat a tg matic ,bral e appli catiqn I when. entering a danger Pisto 7 u o he Passa 1v result u ipperation of. the pneumatic operator 52,

W n pf th h mainline 51,, the control iinez remains in com municatlongwiih. the line ,27, and. that part of 'tliejc'ontrol 'lihe leading to the duplexcontrol, valve.

is 'not vented to the atmosphere. Asfa result a ,trac'k im-,

pulse' ca'tises anautomatip brake application.

References haveb'emmade to the operation of the solenoid operated valve 121- r'esponsive' tothe closing or the switch 117. As is well understood by electrical en giheefis, the-.circuit; canlbe arranged to obtain the desired netetionhwhen.switch ll'jnis opened? Also it-is' possiple to sulgsti utgrpneumatiqor;other, type- {of control i En q 'oz fii lfimvel; circuit arrangement. Force);-

ample, I can'employ a valve having a pneumatic operator in, place of a solenoid and such a valve can have its operator connected to a source of air pressure controlled: by" a pilot valve, which is substituted for the. switch. 117;

It will be evident that my invention is capable 0% ad'- ditional embodiments and variations. Thus if desired either the remotely operated or directmanually operated forestalling means maybe employed in conjunction with a line charger. in. the manner disclosed and claimed in my Patent 2,486,271.

It will be evident that my invention. can be incorporated in the, pneumatic train control system of the Folker type with a amount ofi additional equipment. When aninstallation is, made as'described above, certain hazards in theoperation ofthe. train aredefinitely minimized. The engineer is forced to enter danger zones at a speed well below the maximum limiting speed. for which the speed recorder is set, and only when the train is-proceeding at sucha safespeed, can. the forestalling means-be effective.

In a. pneumatic. train. braking system, a control valve adaptedi tobe. actuated-.byia track impulse, a control line connected. to. said: control valve whereby said line'- is ventedupon actuation of the controlvalve by a track impulse, anautomatic train stop valve connected'to said control linefor .causinga. brake application when the control line invented, a manually initiated forestalling unit, said unit including. fluid. pressure operated timing means having a timing cycle and a shutoif' valve connected to the control line, fluidzpressureoperated means having a fluid pressureconnectionto the forestalling unit and arranged, when actuatedeby fluid pressure from said forestalling unit during a timingcycle, to move said-shutoif valve from a first toa second operating position, said shutoff valve in its. first operating position establishing: communication betweenthefcontrol valve and the automatic train stop valvel throughthecontrol line and in its second operating positioninterrupting such communication and venting tothe atmosphere-that portionof the control line extending from the. shutoff valve to the control valve, said I shutoff valve being .so arranged that fiuiclpressure in the controlline serves .tourgethe sbutofi valve toward said first'operating position, .manual initiation o f-a timing cycle of the fore stalling. unibwh'enthe train is proceeding at or below a predetermincdsafetrain speed and before receipt 'of'a trackimpulse serving to prevent an automatic brake application when the track-impulse; is received, and control meansresponsive-to a train speed in excess of a predeterminedssafe-speed and arranged to prevent actuation of I saidifiuid pressure operated means to position said shutoff valve insaidsecondposition whereby under such condition of:excessive train speed manual initiation of-the forestalling:unit timing cycle does not prevent an automatic brake-application'by a subsequently received track impulse, and inwhich a remote forestalling valve is providedihaving a pneumatic connection to the forestalling; unit,= said .forestalling valve when manually actuated serv ingto apply fluidpressure to the forestalling unit to initiate a forestalling unit timing cycle, and in which said control.

'means responsive to a train speed in excess of a predeter-' mined safespeedincludes a valve having a fluid connection to the connection between the forestalling. valve and the forestalling unit and serving to vent said last.connection when the train speed is in excess of a. predetermined safe speed.- i I References Cited inthe file of {this patent UNITED .STATES PATENTS 1,515,825. Bissell. Nov- 18, 1924 1,991,889 Farmeret'al Feb. 19," 1935 2,017,682 Cook, Oct-15, 1935 2,036,589: Loughridge Apr. 7, 1936 2,-052,944 1 schweyer-u; Sept. 1; 1936-; 2,486,271 Fo1ker, Oct-." '25;"1949-"

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