US2948234A - Remote control organization for a locomotive - Google Patents

Description

Aug. 9, 1960 J o. HUGHSON REMOTE CONTROL ORGANIZATION FOR A LOCOMOTIVE Filed Sept. 30, 1957 I5 Sheets-Sheet 1 GENERAL LAYOUT INVENTOR. J. D. HUGH SON H l ATTORNEY 1960 .1 D. HUGHSON 2,948,234

REMOTE CONTROL ORGANIZATION FOR A LOCOMOTIVES I Filed Sept 30 1957 3 Sheets-Sheet 2 STOP FIGZ.

IA CONTROL OFFICE TRANSMIT FORWARD: I'RE ROG v 23 TOgET .\L 11- GENE A o -,L

GF. ;,I 26 i 1 TONE 29: VOLTAGE ANTENNA sENllAToR m AMPLIFI E R MODULATOR POWER VOLTAGE AMPLIFIER AMPLIFIER FIG.3.

LOCOMOTIVE RECEIVER ANTENNA AUDIO AUDIO I AMPLIFIER AMPLIFIER I I CARRIER I I I RECEIVER LOCOMOTIVE AND DEMODULATOR BATTERIES MOTOR CONTROL AMPLIFIER INVENTOR. a. D. HUGHSON ZMW HIS ATTORNEY Aug. 9, 1960 J D. HUGHSON' REMOTE; CONTROL ORGANIZATION FOR A LOCOMOTIVE Filed Sept. 30, 1957 FIG.4.

5 Sheets-Sheet 3 LOCOMOTIVE CONTROL E WARNING 5| LIGHT l T l I I l I I I I 3f I I I I I I I I LOCOMOTIVE SPEED I I I. l I DETECTOR SWITCH I I I I I l M I 44I l I I I I: 1 I46 I I I II IR 4\ I l i I 11' I l I I R| I I 12 -I l ET I I I I l I- I I -IIz I I? III I I I AT I 9- I IST I I I m I I I 3%" I I +I I I 8; BRAKE RELEASE I 5 I I I I SOLENOID I I I I I I I l I I I I57 I I LOCOMOTIVE I I BRAKES I I 54I lfi' l I FT RT (-I I49 I 48 H 55 SPF 5:)

FORWARD REVERSE MOVEMENT OF MOVEMENT OF LOCOMOTIVE; LOCOMOTIVE INVENTOR. J.D.HUGHSON BY HIS ATTORNEY United States Patent-O REMOTE CONTROL ORGANIZATION FOR A LOCOMOTIV E i J Donald Hughson, Rochester, N.Y., assignor to General Railway Signal Company, Rochester, N.Y.

Filed Sept. '30, 1957, Ser. No. 687,008

4 Claims. (Cl. 104-26) This invention relates to a control organization for a remotely controlled locomotive, and more particularly relates to an improved control system for a remotely controlled trimming locomotive in a railroad classification yard.

In railroad classification yards, incoming freight cars are disconnected from their respective trains and reclassified as to future destinations. A typical railroad clas- I have different free rolling characteristics which are caused by weight, friction, and wind, the freight car will not in every instance freely roll to its intended destination. It is therefore necessary that one or more trimming locomotives be provided to forcibly push freight cars which have prematurely come to a stop to their intended des tination.

This invention provides for an improved control system for a remotely controlled trimming locomotive in a railroad classification yard, which locomotive is manually controlled from a centrally located control tower. Railroad classification yards normally extend over a large area, which, at times, makesit impossible for a control tower operator to visually ascertain the exact position of the trimming locomotive under his control. .There are times when inclement weather conditions, such as fog, rain, or the darkness of night prevent the control tower operator from accurately controlling the movement of the trimming locomotive. There are also times when his attention may be momentarily diverted from the operation of a particular trimming locomotive to the operation of another trimming locomotive under his control, or

possibly to the traffic conditions concerning other free rolling freight cars in the yard. i

There are other times when the control tower operator may inadvertently permit the remotely controlled trimming locomotive to travel a greater distance than intended, which may possibly place the receiving equipment located on the locomotive beyond the influence of the transmitter, which condition at the very least will cause unnecessary delay. There are also times when the operator, whose attention may be diverted, or who is unable to accuratelyjudge the exact position of the trimming locomotive, will permit the locomotive to.inadvertently return to a dangerous position in the switching area or inthe path of free rolling freight cars. 7

In other instances, a trimming locomotive may be operated to push a car, or a cut of cars which it is unable to ming locomotive. This condition may occur if thefric- 2,948,231 Patented Aug. 9, 1960 tion on the surface of the track rails is reduced by rain or moisture, or if the load to be pushed is extremely heavy.

In view of theabove considerations, this invention provides for a remotely controlled trimming locomotive organization which will automatically cause the trimming locomotive traveling in a forward direction to come to a complete stop before it can be inadvertently operated beyond its control area. After coming to a stop under this condition the locomotive cannot be operated in a forward direction.

Italso provides for automatically stopping the locomotive traveling in a reverse direction, if it is allowed to be operated beyond another predetermined point in the classification yard system. However, in this situation,.the operator is able to further operate the locomotive in either direction.

The present invention also includes a means for preventing the locomotive from continually attempting to push a load which it is incapable of moving thereby causing the wheels of the locomotive to slip on the track rails.

Under all of the above conditions, the locomotive will automatically shut itself off and apply its brakes, thus requiring the operator to exercise control over any further movements of the trimming locomotive. 7

One of the objects of this invention is to provide an improved control organization for a remotely controlled trimming locomotive in a railroad car classification system. t a

Another object of this invention is to provide a means for preventing a remotely controlled trimming locomotive from repeatedly attempting to move a load which it is incapable of moving.

A further object of this invention is to provide an improved remotely controlled trirnrning locomotive control system having means for automatically causing the locomotive to come to a stop at predetermined locations in the railroad classification yard. t

A further object of this invention is to absolutely prevent the locomotive from being remotely operated beyond the area in which it can be effectively controlled.

A still further object of this invention is to provide a means for shutting off the locomotive in the event that its Wheels should slip while attempting to move a load which it is incapable of moving. V

Other objects, purposes and characteristic features of the present invention will be, in part, obvious from the accompanying drawings and, in part, pointed out as the description of the invention progresses.

In describing the invention in detail, reference is made to the accompanying drawings, in which similar letter 60 :to the receiving apparatus of the trimming locomotive;

Fig. 3 illustrates in block form the organization of the apparatus located on the trimming locomotive, and also shows the organizationof the apparatus located adjacent the classification tracks; and i Fig. 4 illustrates diagrammatically the apparatus and circuits located on the trimming locomotive in' one embodiment of this invention.

For the purpose of facilitating the disclosure of the present invention as to its mode of operation, schematic wire diagrams have been used to illustrate the circuit organization rather than-attempting to show the specific structure and arrangement of parts that will be employed in practice. Rather than show the wiring connections to l all sources of energy, the symbols and have been .used to indicate connections to therespective posie tive and negative terminals of suitable batteries, or other sources of direct current. V

Referring to Fig. l, the general organizationfor a railroad classification yard is illustrated wherein the cars to be classified travel towards the classification tracks CLT from the hump crest over the main track MT in the direction of the arrow D. A trimming locomotive T is shown at rest on a spur track SCT which is so located as to not interfere with the normal movement of the freight cars down the inclined track MT. It is understood, however, that the locomotive T may have a normal storage or resting place at any point in the classification yard according to the individual needs of practice. A control tower CTO contains the control equipment for actuating the various switches in accordance with the intended destination of a respective freight car to a respective classification track CLT. The control tower CTO also contains the manual and transmitting apparatus for controlling tJhe remotely controlled trimming locomotive T. Located at a predetermined point along the classification tracks CLT and adjacent thereto, are suitable stop tripping ramps, or track instruments, TA. The tripping ramps TA cooperate with certain apparatus on the locomotive, which apparatus will be described in detail as the description of the invention progresses. Located along the classification track and closer to the main track MT are the reverse stop tripping ramps, or track instruments, TB which serve to automatically stop the locomotive in a reverse direction. The tripping ramps TB are positioned to cooperate with certain other ap paratus on the locomotive T which will be hereinafter described in detail. The ramps TA-and TB can be any conventional raised projection securely affixed near the track rails. Although the particular location of the various forward and reverse stop tripping ramps TA and TB are shown as being located in a definite position in the classification yard, it is to be understood that they may be placed atany position therein as the dictates of practice may require.

With reference to Fig. 2, the control office apparatus for the transmission of locomotive controls is illustrated in block form. A locomotive control lever LC, which is located on a suitable control panel in the control tower CTO, is capable of being manually operated to a forward, stop, or reverse position. In the present embodiment of the invention the lever 'LC remains in the position to which it is moved until it is manually operated to a different position. When the lever LC is in an extreme right-hand position, the locomotive T is operated in a reverse direction, and when it is in an extreme left-hand position, the locomotive T is operated in a forward direction. When the lever LC is intermediate between the left and right-hand positions, the locomotive T is deenergized and at rest.

The system described herein for the purpose of eifecting a'remote control of the locomotive T comprises apparatus for transmitting a continuous carrier wave which is modulated by two distinct frequencies. The output of a respective tone generator GF or GR is effective to apply its output to a suitable voltage amplifier. The amplified output is applied to the modulator and its output is applied to the carrier wave oscillator. The modulated carrier wave is further amplified and the output of the amplifier is supplied to the antenna A-1 and radiated to an appropriate receiving antenna A2 located on the locomotive T. The forward office control relay FOC, when in its energized position, serves to apply the particular tone generated by the tone generator GP to the voltage amplifier for controlling the movement of the locomotive T in a forward direction. The relay lFOC is energized by moving the control lever LC to its forward position only and not the tripping ramp TB.

4 completes a circuit which extends from and-includes left-hand contact 21 of the lever LC and the Winding of relay FOC, to

The reverse oflice control relay ROC, when energized, causes the tone generator GR to apply its output to the voltage amplifier for operatingthe locomotive T in a reverse direction. The relay ROC is energized by positioning the lever LC to its extreme right-hand position completes a circuit which extends from and includes the right-hand contact 22 of the lever LC and the winding of relay ROC, to

It is readily seen in Fig. 2 that the closing of the front contacts 23 and 24 of relay FCC and the closing of the back contacts 25 and 26 of relay ROC completes an output circuit to the voltage amplifier. Similarly, the closure of the back contacts 27 and 28 of the relay FOC and the closing of front contacts 2 and Stlof relay ROC. completes a circuit for app-lying the output of the tone generator GR to the Voltage amplifier. An inspection of Fig. 2 reveals that only the output of one tone generator is applied to the voltage amplifier at any one time.

With the position of the lever LC intermediate between the forward and reverse position, the relays FOC and ROC are both 'deenergized, thereby preventing the output of the tone generator GF and GR from bein applied to the voltage amplifier.

With reference to Fig. 3, the locomotive receiving apparatus is adapted to receive the modulated tones of the transmitting carrier wave through the antenna A2 located on the locomotive T. The modulated carrier wave is then amplified by the carrier amplifier, demodulated by a conventional demodulator and further amplified by a tuned audio amplifier. The audio amplifier AF is distinctively tuned to receive and amplify the demodulated audio frequency waves generated by the tone generator GF, and the amplifier AR is distinctively tuned to receive and amplify the demodulated audio frequency waves generated by the tone generator GR. The output of the audio amplifier AF is rectified to energize the relay F for controlling the locomotive motor control circuit. The output of the audio amplifier AR is rectified to energize the relay R for controlling the locomotive motor control circuit. Thus, it is apparent from the preceding description that the movement of the lever LC to its forward position results in the energization of relay F and movement of the lever LC to its reverse position results in the energization of the relay R.

As further shown in Fig. 3, the locomotive -T is provided with a forward tripping switch SPF which effectively governs the motor control circuit when it comes in contact with the forward stop tripping ramp TA, as will be more fully described. Similarly the reverse stoptripping switch "SPB is provided to effectively control the motor control circuit when it comes in contact with the reverse tripping ramp TB. The tripping switches SPF and SPB located on the locomotive are of the conventional centering variety with motion allowed in either direction. It should be noted that the trip switch SPB is so positioned on'the locomotive relative to the location of the tripping ramp TB that it will come in contact with the tripping ramp TB only, and not with the tripping ramp TA. Similarly, the trip switch SPF is so positioned that it will contact the tripping ramp TA It should be also noted in Fig. 3 that the trip switch SPB is effective to govern the motor control circuit concerned with the 're- .a forward and're verse direction for reasons which will be more fully-explained as the description progresses. With reference to Fig. 4, the locomotive is provided with a motor M which comprises an armature AT and a field DI. It is assumed that the motor M is suitably connected to drive the wheels of the locomotive in either a forward or reverse direction depending upon the direction of rotation of the motor.

It is also assumed that the locomotive braking apparatus as shown in block form is controlled by a brake release relay BR in such a way that the deenergized position of relay BR is effective to apply the brakes to the locomotive.

A locomotive speed detector switch LW is provided to detect the movement of the trimming locomotive. The speed detector switch LW is a conventional zero speed detector switch which is capable of closing its front contact 31 in response to the movement of the locomotive T. The speed detector switch can be of any well known type which will adequately detect rotational movement to close an electrical contact. In a practical application a well known zero speed switch utilizing the basic principle of induction by rotating a permanent magnet which rotates a cup-like'conductor thereby causing an appropriate electrical contact to close. The detector switch LW may be operated, for example, by an auxiliary free riding detector wheel (not shown) which rotates only when the locomotive is moving or may be operated from a wheel of the locomotive which is not only of the driving wheels.

A warning light TB is suitable mounted on the locomotive to warn the operator of a slipping condition of the wheels of the locomotive.

With reference to the motor control circuit, a forward repeater relay FP repeates the operation of the forward control relay F. A reverse repeater relay RP repeats the operation of the reverse control relay R.

A slow release starting relay ST is provided to prevent a heavy surge of current when the locomotive is being started and also permits the gradual increase of speed of the locomotive motor M when it is being started in either a forward or reverse direction.

A normally energized warning relay WR having slow drop away characteristics is provided to shut off the motor M and light the warning light TB in the event that the locomotive should be in a stalled and-slipping condition.

A forward trip relay FT serves to shut off the motor M in response to the operation of the trip switch SPF as will be more fully described. In the operation of the locomotive motor control circuit, a reverse trip relay RT serves to shut off the motor in the response to the operation of the trip switch SPB as will be hereinafter more fully described.

Although double wound neutral relays having opposing magnetic fields are utilized for the relays FT and RT in the illustrated embodiment of this invention, it is thereby understood that conventional magnetic stick relays can be substituted without departing from the spirit or scope of this invention.

Assuming that the locomotive T is at rest on the spur track SCT (see Fig. 1) and the locomotive operator wishes tocause the movement of the locomotive in a forward direction to one of the classification track CLT, the locomotive control lever LC is moved to its forward position which causes the pick-up of the relay F as hereinbefore described. The picking-up of the relay F energizese the forward repeater relay FP by a circuit which extends from and includes front contact 33 of relay F, back contact 34 of relay PT, the winding of the forward repeater relay FP, the back contact 35 of the reverse repeater relay RP and the front contact 36 of the warning relay WR to The picking-up of the relay FP energizes the relay BR by a circuit which extends from and includes front contact 37 of relay PP and the winding of relay BR to The picking-up of relay BR opens its back contact 38 which releases the brakes of the locomotive. In response to the picking-up of relay the motor is energized in a forward direction by a circuit which extends from and includes front contact 39 of relay FP, winding DT, back contact 40 of relay RP, armature AT, and resistor R1 to Simultaneously, the relay FP removes energy from the normally energized starting relay ST. The energizing circuit of relay ST extends from and includes the back contact 41 of relay FP, the back contact 42 of relay RP, and the winding of relay ST to Because of the slow dropaway characteristics of the relay ST, the back contact 42 of the starting relay ST is not closed until after a predetermined time has elapsed. With the closure of the back contact 42 of relay ST, the resistor R1 is shunted out of the motor control circuit, thereby permitting the motor to increase in speed.

When the relay F was picked-up as hereinbefore described, the energizing circuit for the relay WR was interrupted by the opening of the back contact 44 of relay F. Prior to the picking-up of relay F, the normal energizing circuit for the relay WR extended from and included back contact 44 of relay 'F, back contact 45 of relay R, and the winding of relay WR to When this circuit was interrupted as hereinbefore described, the only possible means of maintaining the relay WR energized is by a stick circuit which extends from and includes front contact 44 of relay F, front contact 31 of the speeddetector switch LW, front contact 46 of relay WR and the winding of relay WR to As previously described the detector switch LW closes its front contact in response to the movement of the locomotive T, therefore, if the wheels of the locomotive should rotate and slip on the track rails without the resultant movement of the locomotive, which may be caused by attempting to push an excessive load without sufficient friction between the locomotive driving wheels and the track rails, the previously described stick circuit for WR is not completed and the relay WR drops-away after a predetermined period of time as measured by the drop-away characteristics of relay WR. The dropping-away of the relay WR causes the relay FP to drop-away by opening the front contact 36 of relay WR in the previously described energizing circuit of relay FP, thereby removing energy from the motor M and simultaneously removing energy from the relay BR which, as previously described, causes the application of the brakes of the locomotive T. Similarly, with the dropping-away of the relay WR, its back contact 47 closes to energize the warning light TE by an obvious circuit.

It is further assumed that the locomotive T is under the control of an operator in the control tower CTO and is moving in a forward direction toward a classification track CLT. When the locomotive reaches a point adjacent one of the tripping ramps TA which are located at a predetermined position along a respective classification track, the tripping switch SPF is actuated by the ramp TA, thereby closing the right-hand contact 48 of the tripping switch SPF. The closure of the right-hand contact 4S energizes the forward tripping relay FT by a circuit which extends from and includes right-hand contact 48 of tripping switch SPF and the winding of relay FT to The picking-up of the relay FT interrupts the previously described energizing circuit for the forward'repeater relay FP at the back contact 34 of the relay FT, thereby shutting off the motor and applying the brakes to the locomotive T as previously described. After the locomotive has passed the tripping ramp TA, the tripping switch SPF returns to its neutral position, however, the relay FT remains in its energized position by a stick circuit which extends from'(+) and includes the front contact 49 of the relay FT and the winding of relay FT to At this point in the operation of the locomotive, it can be readily seen that the motor M cannot be energized to move in a forward direction because of the open condition of the previously described energizing circuit for the forward repeater relay FP at; the back contact 34 of relay FI.

7 Assuming that the operator wishes to start the operation of the locomotive T in a reverse direction after having been automatically stopped by the actuation of the switch SPF, it is necessary that the control lever LC be moved to the reverse position. A reverse nrovement of the lever LC energizes the reverse control relay.

R in the manner previously described. The picking-up ofthe relay R energizes the reverse repeater relay RP by a circuit which extends from and includes front contact of relay R, back contact 51 of relay RT, the winding of relay RP, back contact 52 of relay PP, and the front contact 36 of relay WR to The pickingnp of the relay RP energizes the motor M in a reverse direction by a circuit which extends from (-1-) and includes front contact of the relay RP, the field winding DT, back contact 39 of relay FP, the armature AT and the resistor R1 to The closing of front contact 53 of relay RP releases the brakes of the locomotive T as heretofore described. The motor starter circuit is actuated in the same manner described in connection with the forward movement of the locomotive T. When the locomotive T has traveled a sufficient distance in a reverse direction to cause the switch SPF to again come in contact with the tripping ramp TA, the trip switch SPF closes its left-hand contact 48 which deenergizes the relay FT by a circuit which extends from (-1-) and includes left-hand contact 48 of switch SPF, front contact 54 of relay FT, and the upper winding of relay FT to It is noted that the current passing through the upper winding of the relay FT opposes the polarity of the current flowing through the lower winding of relay FT which results in the dropping away of the relay FT. This reverse action of the forward tripping switch SPF conditions the controlling circuit so that the locomotive can be once again manually operated in a forward direction if it is so desired.

Assuming that the locomotive is traveling in a reverse direction and reaches a point in the classification yard whereby a reverse tripping ramp TB actuates the reverse tripping switch SPB, the resulting movement of the'tripping switch SPB energizes the reverse trip relay RT by a circuit which extends from and includes left-hand contact 55 of the switch SPB and the lower winding of relay RT to The relay RT is also provided with a stick circuit for holding it in an energized condition after the switch SPB has assumed a normal position which stick circuit extends from (-1-) and includes front contact 56 of relay RT and the lower winding of relay RT to The picking-up of the relay RT interrupts the energizing circuit for the reverse repeater relay RP by opening the back contact 51 of the relay RT, thereby bringing the locomotive T to a stop in the manner previously described, and prevents any further reverse movement of the locomotive T without subsequent manual operation of the lever LC. When the locomotive has come to a stop because of the actuation of the tripping switch SPB it is necessary that the operator move the lever LC to its intermediate or stop position in order to re-acquire control over the locomotive T. When the lever LC is moved to its stopped position the reverse relay R is deenergized as previously described, thereby deenergizing the relay RT by closing a circuit which extends from (-1-) and includes the back contact 57 of relay F, back contact 58 of relay R, front contact 59 of relay RT and the winding of relay RT to The circuit for the upper winding of relay RT affects the lower winding of the relay RT in a manner similar to that described in connection with the relay FT. At this point it is apparent that the movementof the lever LC to its intermediate position again puts the motor control circuit of the locomotive in condition for further manual control.

Assuming that the operator wishes to continue the operation of the locomotive in a reverse direction, he positions the lever LC to its extreme right-hand position 7 8 which starts the locomotive running in the manner previously described.

Although one embodiment of the invention is shown herein, it isunderstood that various changes and modification may be made therein, within the scope ofthe appended claims without departing from the spirit or scope of this invention. Having thus described this invention, what I claim is: V

1. In a system for the automatic operation of a vehicle having a reversible motive power means and running over a stretch of track, the combination comprising, radiation communication apparatus including transmitting means at a fixed location and receiving means on said vehicle, means for controlling said transmitting means to transmit distinctive signals to said receiving'means, said receiving means being differently controlled by said distinctive signals respectively for selectively operating said motive power means alternatively to forward and reverse and deenergized conditions, control communicating apparatus including trackside means positioned along said track at at least one designated point defining a terminus of an operating zone on said stretch of track for said vehicle and also including vehicle-carried means operated by said trackside means only as said vehicle passes said designated point, said trackside means operating said vehicle-carried means from a normal first condition to a second condition as said vehicle moves out of said operating zone, means controlled by said vehicle-carried means when in its said second condition for deenergizing said motive power means and preventing further operation of said motive power means in the direction taken by said vehicle as it passes out of said zone past said designated point, and means being distinctively controlled by said receiving means to restore said vehicle-carried means to its said normal first condition when once operated to said second condition only when said receiving means receives a control from said transmitting means normally effective to deenergize said motive power means, whereby said motive power means is deenergized when said vehicle moves out of said operating zone and can subsequently be energized to effect forward or reverse motion of said vehicle only by first transmitting a deenergizing control to said receiving means.

2. The system defined in claim 1 wherein said trackside means includes a track instrument and said vehiclecarried means includes, a switch having an operating member coming in contact with said track instrument and closing a contact means when said vehicle passes.

said track instrument as it moves out of said operating zone, said vehicle-carried means being operated to its said second condition by closure of said contact means.

3. In a system for the automatic operation of a vehicle having a reversible motive power means and running over a stretch of track, the combination comprising, radiation communication apparatus including transmitting means at a fixed location and receiving means on said vehicle, means for controlling said transmitting means totransinit distinctive signals to said receiving means, said receiving means being differently controlled by said distinctive signals respectively for selectively operating said motive power means alternatively to forward and reverse and deenergized conditions, control communicating appar-atus including trackside means positioned along said track at at least one designated point defining a terminus of an operating zone on said stretch of track for said vehicle and also including vehicle-carried means operated by said trackside means only as said vehicle passes said designated point, said trackside means operating said vehicle-carried means from a normal first condition to a second condition as said vehicle moves out of said operating zone, means controlled by said vehicle-carried means when in its said second condition for deenergizing said motive power means and preventing further operation of said motive power means in the direction taken by said vehicle as it passes out of said zone past said designated point, motion detector means mounted on said vehicle and being operated to a distinctive condition whenever said vehicle is in motion, and means being operated to a distinctive condition when a reverse or forward operating control has been received by said receiving means for a predetermined interval throughout which said motion detector means is not in its said distinctive condition, said last-named means deenergizing said motive power means whenever operated to its said distinctive condition.

4. The system as defined in claim 1 and further including additional control communicating apparatus comprising second trackside means positioned along said track at a second designated point defining a second terminus of said operating zone and also comprising second vehicle-carried means, said second vehicle-carried means being operated from a normal first condition to a second condition by said second trackside means as said vehicle moves out of said zone past said second desig- 10 nated point, said second vehicle-carried means being restored to its normal first condition by said second trackside means as said vehicle re-enters said zone past said second designated point, and further means controlled by said second vehicle-carried means in its said second condition for preventing energization of said motive power means in the direction taken by said vehicle in moving out of said zone past said second designated point.

References Cited in the file of this patent UNITED STATES PATENTS Re. 22,588 Kew Jan. 9, 1945 746,463 Clark Dec. 8, 1903 1,653,172 Hammond Dec. 20, 1927 2,078,001 Joly Apr. 20, 1937 2,215,341 Weybrew Sept. 17, 1940 2,321,059 Anderson June 8, 1943 2,700,728 Brixner Jan. 28, 1955

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