US3707124A

US3707124A - Vehicle speed control device actuating mechanism

Info

Publication number: US3707124A
Application number: US101927A
Authority: US
Inventors: William H Peterson
Original assignee: Pullman Inc
Current assignee: Pullman Standard Inc; Pullman Inc
Priority date: 1970-12-28
Filing date: 1970-12-28
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26
Also published as: CA938707A

Abstract

An actuating mechanism for initiating the operation of a speed control device which brakes a railroad vehicle should it exceed a predetermined speed. The actuating device consists of a flexible sensor hose containing a liquid subject to the weight of the railroad vehicle to operate and to close a pressure contact in an electrical circuit to energize a ground mounted or railside mounted tripping mechanism in the form of an electromagnet in the railroad classification yard which, in turn, trips the vehiclemounted speed control device on a railroad car passing over the electromagnet for slowing down the speed of the railroad car. The electromagnet will not be energized to the ''''on'''' condition until sufficient time has elapsed as determined by a timer in the electrical circuit of the electromagnet and thereby only ''''standing'''' cars rather than ''''passing'''' cars turn on the electromagnet. A modified form of the device utilizes two such sensor hoses and pressure switches in a common circuit whereby both pressure switches must be closed in order to energize the electromagnet, the spacing distance between the sensor hoses being greater than the distance between the fore and aft railroad car trucks and the length of each of the hoses or sensing units being greater than the distance between the trucks.

Description

United States Patent Peterson 1 51 Dec. 26, 1972 [54] VEHICLE SPEED CONTROL DEVICE ACTUATING MECHANISM [72] Inventor: William H. Peterson, I-Iomewood,

Ill.

[73] Assignee: Pullman Incorporated, Chicago, Ill.

[22] Filed: Dec. 28, 1970 [2]] Appl. No.: 101,927

52 us. 01. ..l04/26 R, 246/182 B, 246/271 51 161.01 ..B6lb 1/00, B611 3/12 58 Field 61 Search ..246/93, 95, 100, 116, 271,

246/182 B, 192, 201, 202, 24s; 104/26 R Primary Examiner-Gerald M. Forlenza Assistant Examiner-George l-l. Libman Attorney-Hilmond O. Vogel and Richard J. Myers [5 7] ABSTRACT An actuating mechanism for initiating the operation of a speed control device which brakes a railroad vehicle should it exceed a predetermined speed. The actuating device consists of a flexible sensor hose containing a liquid subject to the weight of the railroad vehicle to operate and to close a pressure contact in an electrical circuit to energize a ground mounted or railside mounted tripping mechanism in the form of an electromagnet in the railroad classification yard which, in turn, trips the vehicle-mounted speed control device on a railroad car passing over the electromagnet for slowing down the speed of the railroad car. The electromagnet will not be energized to the on condition until sufficient time has elapsed as determined by a timer in the electrical circuit of the electromagnet and thereby only standing cars rather than passing cars turn on the electromagnet. A modified form of the device utilizes two such sensor hoses and pressure switches in a common circuit whereby both pressure switches must be closed in order to energize the electromagnet, the spacing distance between the sensor hoses being greater than the distance between the fore and aft railroad car trucks and the length of each of the hoses or sensing units being greater than the distance between the trucks.

20 Claims, 7 Drawing Figures PATENTEflnEczs m2 3.707.124

sum 2 or 2 SPEED MAGNETICALLY T 15 RESPONSIVE JQGENERATOR J6RESPONSIVE \SWITCH I SWITCH a SPEED CONTROL L9 ,5 PRIOR ART DEVICE Z 7 RELAY 2$EM i saksa' 74%;, #firsm VEHICLE SPEED CONTROL DEVICE ACTUATING MECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention The field of art to which this invention pertains is the railroad car art and, in particular, relates to speed con trol devices for the railroad car, especially for use in the railroad classification yard.

2. Description of the Prior Art It is known in the prior art to provide for various types of speed control devices for regulating the speed of a rolling railroad car within a classification yard. It is important, however, to regulate the triggering or tripping devices by switches that initiate the operation of the railroad car speed control device such that these tripping devices will not operate until their operation is required. It is for this particular problem the invention finds the solution.

SUMMARY It isa'general object and purpose of this invention to provide for an actuating mechanism for operating carmounted speed control devices at various'points along the railroad track as, for instance, in a classification yard. More particularly, it is an object of this invention to provide for means for sensing the presence of a standing railroad car and then to energize groundmounted speed control device tripping mechanisms and to actuate the speed control device on the railroad car to limit the free rolling speed of the railroad car within the classification yard. The operation of such a speed control device has been previously described in U.S. Pat. No. 3,524,982 to William H. Peterson.

Another object of this invention is to provide for a sensor device which senses the presence of the standing railroad car and then operates a pressure switch'and timed relay device to operate an electromagnet mounted on the railroad car ladder track in a classification yard where such electromagnet is a considerable distance further removed upstream or uphill from the location of the standing car. The invention provides for sequential energization of these speed control device triggering electromagnets that are spaced further and further away upstream from the location where the first or initial standing cars came to rest. As a series of cars are formed into a train, as a particular car contacts a sensing arrangement, track-mounted electromagnets closer upstream toward the entrance of the ladder track in the classification yard are activated to control the speed of the railroad car at an earlier time during its entrance into the ladder track.

These and other objects of the invention will become more apparent by reference to the following description, appended claims and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a classification yard showing a series of tracks with a system of railroad car speed control device actuating mechanisms;

FIG. 2 is a view schematically showing a section of railroad track in a classification yard wherein there is provided the electromagnet actuating mechanism for operating a vehicle speed control device and the sensor unit or hose and pressure contact switch and timer to operate the electromagnet;

FIG. 3 is a sectional view illustrating the relation between the railroad car wheel and the sensor unit or flexible hose;

FIG. 4 schematically discloses the pressure-responsive switch arrangement of the actuating mechanism for the vehicle speed control device;

FIG. 5 is a schematic view of the electrical circuit including the electromagnet, the pressure switch and the timer;

FIG. 6 is'a schematic view of a railroad car speed control device of the type shown in U.S. Pat. No. 3,524,982; and

FIG. 7 is a modified arrangement of the actuating arrangement for initiating the operation of the railroad car speed control device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIGS. 1-6 and in particular with reference to FIG. 1, there is shown a classification yard 1 provided with a plurality of ladder tracks 2. Each ladder track 2 has a railroad car entrant or beginning portion 3 and main portion 4 following the entrant or upstream portion 3. In operation, a railroad car, such as shown in dotted line at 5, moves from the entrant portion along the track 2 and into the central area portion 4 to couple with a standing car 6 at the other end or downstream or downhill of the central portion 4 of the track 2. The ladder track 2 has a slight downhill grade to permit the railroad car 5 to roll along it and couple with the standing car 6 to form part of a train, as is the usual practice. Should the car 5 be traveling too fast, a speed control device 7 mounted on the car passes by the track-mounted magnet 8 and is actuated to apply the vehicle air brakes as, for instance, shown by U.S. Pat. No. 3,524,982 to W. H. Peterson, and incorporated herein by reference thereto. Consequently, the car 5 is slowed down to a desirable speed, say, between 3 and 4 m.p.h. and coupled with car 6 and overlies the novel inventive vehicle speed control device actuating mechanism 9 which, when tripped by the presence of the vehicle, operates its electromagnet unit 10 which will actuate the speed control device of the next car coming down the ladder track 2 to brake the vehicle as it passes over the electromagnet 10. Thus the next successive uphill cars are braked earlier in place and time by the electromagnet unit 10. After a number of cars have been coupled, eventually the last car of that group will be over another actuating mechanism 9 that is just to the right of the permanent magnet unit 8. This vehicle actuating mechanism 9 will then be activated by the standing car over it to operate its associated electromagnet unit 10 which is closest to the entrant portion 3 of the track 2 so that subsequent cars entering the track area will immediately have their speed control device activated by the entrant electromagnet unit 10 of the actuating mechanism 9 located closest to the entrant portion 3 of the track 2. The other ladder tracks 2 shown in FIG. 1 similarly contain a plurality of vehicle speed control device actuating mechanisms 9 provided with electromagnets 10 spaced up-track therefrom and connected by electrical wire means 11. By such an arrangement it is seen that as the left end of the ladder tracks fill up from left to 7 right (FIG. 1) with cars progressively the actuating mechanisms from left to right become activated because of the presence of a standing car thereat.

In FIGS. 2-5 there is shown a first embodiment which comprises a particular actuating mechanism 9 which includes a electromagnet 10, a sensor 18, a trigger or pressure-responsive switch 20, power source or battery 21, and time delay relay 23, and how a car 5 effects the operation of the actuating mechanism 9 which, in turn, has its electromagnet unit 10 trigger the speed control device 7 on the vehicle 5 to brake the speed of the vehicle as disclosed in the aforementioned patent. The speed control device 7, (see FIG. 6) as disclosed by the said patent includes a brake system 12 which is operated by air pressure funneled by the solenoid valve 13 when the ladder is energized by therailroad car driven generator 14 when the centrifugal or speed-responsive switch 15 is closed when the vehicle exceeds approximately 4 mph and the magnetically responsive switch 16 has been acted upon by the permanent magnet 8 or an energized electromagnet 10 to operate relay l7 attendant to energizing the solenoid 13. When the vehiclespeed falls below the speed of 4 m.p.h., the centrifugal switch 15 opens the circuit and de-energ izes the holding relay l7 de-energizing the solenoid valve and preventing further application of air brake pressure to the vehicle brake system.

The components of an actuating mechanism 9 are shown in FIG. 2 and include the compressible or flexible member or hose 18 which acts as a sensor which senses the presence of the railroad car in that it contains enclosed within it a fluid such as a liquid 19 which acts on the pressure-responsive switch means 20 to close the circuit to the power source or electric battery 21 and the electromagnet means 10. The pressureresponsive switch means 20 is responsive to the sensor 18 and triggers or energizes the circuit 22 containing the battery 21, the electrom agnet 10 and the time delay relay means 23. In FIG. 3 it is seen that the railroad wheel 24 of the car 5 has its outer portion 25 compressing the flexible hose 18 while the main body portion 26 of the railroad wheel 24 rests on the upper part 27 of the rail 28 while the upright flange portion 29 of the rail 28 carries a Z-shaped bracket 30 by bolt means 31 which supports lengthwise of the track the hose or sensor 18. The outer end 18a of the hose 18 is closed and the inner end 18b of the hose is open (see FIGS. 2 and 4) and exposed to the flexible diaphragm 20a of the pressure-responsive switch means 20 which also includes a housing 20b and a micro-switch or contact button 20c which moves contact 20d into engagement with contact arm 20c for closing the circuit 22 at the place where the pressure-responsive switch 20 is located, the contact arms 20:: and 20d being mounted in the housing 32 which also contains the time delay relay means 23.

The time delay relay mechanism 23 is best seen in FIG. 5 and includes the relay unit 33, the potentiometer or a variable resistance control means 34, motor means 35, cam means 36, first timer contact means 37 and second timer contact means 38. The polarity or direction of current flow of circuit 22 in FIG. 5 is shown as positive with a plus sign and as negative with a minus sign and electrical ground is designated by the letter G.

When the pressure responsive switch means 20 is closed, the relay coil 33a of relay 33 is energized and moves its contact members 33b and 330 from the solid line position of engagement with contacts 39 and 40 respectively to the dotted line position of engagement with

contacts

41 and 42 to operate motor means 35 causing rotation of motor means and cam means 36 in a clockwise direction. Such movement of the

relay contact arms

33b and 33c also places the variable resistance means 34, which permits adjustment of the length of time of operation of the delay means 23, in the circuit. The variable resistance means 34 is set at a desired position to control the current flow where a smaller amount of current is sent to the motor means to rotate it more slowly in the clockwise direction than in the counter-clockwise direction when the resistance means 34 is not in the circuit. As cam means 36 rotates clockwise, the bufl'er portion 370 of the spring contact member 37b rides out of cam slot 36a to move contact member 37b against spring contact member 370 to close the circuit between

line portions

43 and 44. Contact members 37bv and 370 function to later terminate reverse rotation of the motor means 35 during subsequent rotation. When cam slot 36a rotates from that position shown in FIG. 5, the buffer 38a of spring contact member 38b of contact means 38 enters the slot 36a (because the spring element 38b is biased towards the cam means 36) and spring contact element 380 which is also biased toward cam means 36 engages and closes with contact element 38d, the electromagnet 10 is energized. As this happens, previously closed

contacts

38c and 38f of members 380 and 38b, respectively, separate and open the circuit to motor means 35 and stop clockwise rotation of the motor means 35. As the completed train is pulled out of the classification yard carrying the car 5 away from the sensor 18, the pressure switch means 20 opens the circuit causing the relay 33 to release with contacts 33b and 330 going to the solid line position illustrated which reverses polarity of the motor means 35, thereby causing motor to move in a counter-clockwise direction. Since resistance means 34 is now out of the circuit which is operating the motor means, motor means 35 causes a rapid or fast movement of the cam slot 36a away from buffer 38a to de-energize the electromagnet 10 by opening the engaged

contact members

38c, 38d and for fast return of the cam slot 36a to engage with the buffer 37a and opens contacts 37b and 370 to stop motor means 35. Similarly, any time the car leaves the sensor before the electromagnet 10 is energized by the buffer 38a entering the slot 37a, i.e. when cam means 36 rotates less than 180 or, say, approximately two or three minutes to indicate a car is merely temporarily over or passing over the sensor 18, as distinguished from being a standing or stopped car on the sensor 18, the motor polarity is reversed to cause a rapid reverse rotation of the cam means to place the cam slot 36a in engagement with the buffer 37a. The length of a particular hose or standing railroad car sensor unit 18 should be greater than the distance between the railroad car trucks of the largest railroad car in the classification yard.

In the modification shown in FIG. 7, there is shown two such sensor units 18' and 18" connecting with pressure-responsive switches 20' and 20" respectively. The switches 20' and 20" are in a common circuit 45 and are connected to one another by a common electrical line 46. There is a battery 21 adjacent each pressure switch 20' or 20", their polarity being the same so that their output is additive. It will be appreciated that only one battery would be effective to operate the circuit 45. The circuit 45 also is provided with a groundmounted or railside mounted tripping mechanism or electromagnet 101. By this arrangement, not only is the length of the sensor hoses 18' and 18" greater than the distance between the trucks at each end of the car or between the fore and aft pair of car trucks but the spacing distance between each of the sensors 20' and 20" is greater than the distance between said fore and aft railroad car trucks. If the distance between the sensors and the length of the sensors exceeded the length of the longest railroad car, this, of course, would provide for an adequate sensing arrangement in the actuating mechanism 9. The actuating mechanism 9' of the modified form shown in FIG. 7 requires that two railroad cars must be coupled together and standing over the

respective sensor units

18 and 18" before the associated electromagnet 10' is energized. The distance between the sensor 18" and the electromagnet 10 should be not less than three or four railroad car lengths in order to give the braked railroad car sufficient stopping distance but actually it would be preferable to have the electromagnet spaced considerably more up toward the entrant portion of the ladder track and could also be true in the case of the first embodiment shown in FIGS. 1-5. One preferred arrangement in the classification yard would be to use one perv manent magnet or an electromagnet for braking the speeds of the free rolling cars half-way down (or more) of a particular ladder track and then to have the sensor of the first embodiment or the sensors of the second embodiment located just adjacent the permanent magnet and between the permanent magnet and the entrance of the ladder track and then to have an electromagnet that is to be energized by a particular sensor or sensors be located at the entrance of the ladder track. As a train builds up to where cars are'standing anywhere along the length of the hose of the first em bodiment or a pair of hoses of the second embodiment, then the electromagnet will activate the car-mounted speed control device as the cars enter the ladder track. In the first mentioned embodiment only a car standing anywhere along the length of the sensor or hose closes the pressure switch which energizes the time delay relay and if the pressure switch remains closed for longer, say, than three minutes, then the contacts in the time delay relay close, completing the circuit and energizing the electromagnet at the head end of the ladder track.

The foregoing description and drawings merely explain and illustrate the invention and the invention is not limited thereto, except insofar as the appended claims are so limited, as those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

What is claimed is:

l. A ground-mounted actuating mechanism for a vehicle-mounted speed control device comprising:

sensor means in the path of a first vehicle sensing thepresence of the first vehicle in a first location,

triggering means in said path and spaced upstream from said first location at a second location for operation the vehicle-mounted speed control device of a second vehicle passing said second location,

power means connected with said triggering means and said sensor means,

sensor switch means connected with said sensor means, said power means and said triggering means and responsive to said sensor means to energize said triggering means after a time delay greater than the normal time for a moving vehicle to pass said sensor means, whereby switching will occur only when a vehicle is standing at said sensor means.

2. The invention according to claim 1, and

the length of said sensor means being at least the extent of the distance between the fore and aft wheelsof the vehicle.

3. The invention according to claim I, and

a second triggering means spaced downstream from said first mentioned triggering means for actuating the speed control device on said first vehicle prior to the energizing of said first mentioned triggering means by said sensor means sensing the first vehicle in the first location.

4. The invention according to claim 3, and

said second triggering means spaced downstream from said first triggering means in a third location.

5. The invention according to claim 1, and

said sensor means including a flexible tube having a fluid therein and said sensor switch means including a pressure-responsive switch responsive to the pressure on the tube exerted by the presence of the first vehicle.

6. The invention according to claim 1, and

said sensor means including a compressible member and said sensor switch means including a switch member responsive to the compression of said compressible member by the presence of the first vehicle.

7. The invention according to claim 1, and

time delay relay means connected with said sensor switch means and upon actuation of the sensor switch means by the sensor means being operative to measure a predetermined duration of the presence of the first vehicle at the first location attendant to energizing of the triggering means at the termination of said duration.

8. The invention according to claim 7, and

said time delay relay means including means for resetting said time delay relay means should said sensor means de-activate said sensor switch means prior to the first vehicle leaving the first location before completion of the predetermined duration.

9. The invention according to claim 1, and

said sensor means including a pressure-responsive tube means containing a fluid and said sensor switch means including a pressure-responsive switch operative to a closed position by the pressure of said fluid thereon when the first vehicle exerts a force on the sensor means.

10. The invention according to claim 9, and

said triggering means including an electromagnet energized by the closing of said pressure-responsive switch.

1 1. The invention according to claim 10, and

said power means including a battery for supplying electricity to energize said electromagnet.

12. The invention according to claim 3, and

said second triggering means including a permanent magnet and operative on the speed control device of said first vehicle attendant to braking the speed of said first vehicle.

13. A ground-mounted actuating mechanism for vehicle-mounted speed control devices;

each vehicle mounted speed control device including a magnetically-responsive switch triggered by said ground-mounted actuating mechanism for applying the associated vehicle brakes attendant to slowing down the vehicle speed,

said ground-mounted actuating mechanism including sensor means in the path of a first vehicle for sensing the presence of the first vehicle in a first location, 1

triggering means in the form of an electromagnet in said path and spaced upstream from said first location at a second location for operating the vehiclemounted speed control device of a second vehicle passing said second location,

a source of electrical power connected to said electromagnet and said sensor means, and

sensor switch means connected with said sensor means, said source of electrical power and said electromagnet and acted upon by said sensor means to energize the electromagnet when said first vehicle stands at the first location a predetermined time greater than the normal time for a moving vehicle to pass said sensor means, whereby when the second vehicle passes by the energized electromagnet the speed control device of the second vehicle is energized by the electromagnet to brake the speed of the second vehicle.

14. The invention according to claim 13, and

said switch means including a time delay relay means for determining said predetermined time.

15. The invention according to claim 13, and

a second magnet located downstream of said electromagnet to activate the speed control device on said first vehicle.

16. In a railroad classification yard, an arrangement for controlling the speed of free rolling railroad cars on a downwardly sloping railroad track wherein the cars are provided with speed control devices activated for car braking in excess of a predetermined car speed,

a trackside electromagnet located uphill toward the entrance of the track and adapted when energized to activate a speed control device on a first railroad car at a first location near the electromagnet,

a railroad car sensor located at trackside and downhill from the electromagnet and adapted to sense the presence of a second railroad car located at a second location proximate the sensor,

a time delayed sensor switch and a power source associated with the sensor and the electromagnet in a common circuit whereby the first railroad car located at the sensor for a time'greater than the delay time energizes the electromagnet which activates subsequent speed control devices on cars passing by said electromagnet whereby only cars at rest at said sensor will cause actuation of said sensor switch.

17. The invention according to claim 16, and

a magnet member at trackside downhill from the electromagnet for activating the speed control d ic ofac r ass hereb. 18. i iie inventiem acc r ing to c laim l7, and

said magnet member being between the sensor and the electromagnet.

19. The invention according to claim 16, and

said sensor switch including a timer means determining the duration of the presence of the second railroad car at the second location attendant to energizing the electromagnet at the termination of said duration.

20. The invention according to claim 16, and

said sensor comprising a pressure-responsive fluid bearing tube and said switch comprising a pressure-responsive member and a switch member closed thereby with closing of the circuit before the power source and the electromagnet.

Claims

1. A ground-mounted actuating mechanism for a vehicle-mounted speed control device comprising: sensor means in the path of a first vehicle sensing the presence of the first vehicle in a first location, triggering means in said path and spaced upstream from said first location at a second location for operation the vehiclemounted speed control device of a second vehicle passing said second location, power means connected with said triggering means and said sensor means, sensor switch means connected with said sensor means, said power means and said triggering means and responsive to said sensor means to energize said triggering means after a time delay greater than the normal time for a moving vehicle to pass said sensor means, whereby switching will occur only when a vehicle is standing at said sensor means.

2. The invention according to claim 1, and the length of said sensor means being at least the extent of the distance between the fore and aft wheels of the vehicle.

3. The invention according to claim 1, and a second triggering means spaced downstream from said first mentioned triggering means for actuating the speed control device on said first vehicle prior to the energizing of said first mentioned triggering means by said sensor means sensing the first vehicle in the first location.

4. The invention according to claim 3, and said second triggering means spaced downstream from said first triggering means in a third location.

5. The invention according to claim 1, and said sensor means including a flexible tube having a fluid therein and said sensor switch means including a pressure-responsive switch responsive to the pressure on the tube exerted by the presence of the first vehicle.

6. The invention according to claim 1, and said sensor means including a compressible member and said sensor switch means including a switch member responsive to the compression of said compressible member by the presence of the first vehicle.

7. The invention according to claim 1, and time delay relay means connected with said sensor switch means and upon actuation of the sensor switch means by the sensor means being operative to measure a predetermined duration of the presence of the first vehicle at the first location attendant to energizing of the triggering means at the termination of said duration.

8. The invention according to claim 7, and said time delay relay means including means for resetting said time delay relay means should said sensor means de-activate said sensor switch means prior to the first vehicle leaving the first location before completion of the predetermined duration.

9. The invention according to claim 1, and said sensor means including a pressure-responsive tube means containing a fluid and said sensor switch means including a pressure-responsive switch operative to a closed position by the pressure of said fluid thereon when the first vehicle exerts a force on the sensor means.

10. The invention according to claim 9, and said triggering means including an electromagnet energized by the closing of said pressure-responsive switch.

11. The invention according to claim 10, and said power means including a battery for supplying electricity to energize said electromagnet.

12. The invention according to claim 3, and said second triggering means including a permanent magnet and operative on the speed control device of said first vehicle attendant to braking the speed of said first vehicle.

13. A ground-mounted actuating mechanism for vehicle-mounted speed control devices; each vehicle mounted speed control device including a magnetically-responsive switch triggered by said ground-mounted actuating mechanism for applying the associated vehicle brakes attendant to slowing down the vehicle speed, said ground-mounted actuating mechanism including sensor means in the path of a first vehicle for sensing the presence of the first vehicle in a first location, triggering means in the form of an electromagnet in said path and spaced upstream from said first location at a second location for operating the vehicle-mounted speed control device of a second vehicle passing said second location, a source of electrical power connected to said electromagnet and said sensor means, and sensor switch means connected with said sensor means, said source of electrical power and said electromagnet and acted upon by said sensor means to energize the electromagnet when said first vehicle stands at the first location a predetermined time greater than the normal time for a moving vehicle to pass said sensor means, whereby when the second vehicle passes by the energized electromagnet the speed control device of the second vehicle is energized by the electromagnet to brake the speed of the second vehicle.

14. The invention according to claim 13, and said switch means including a time delay relay means for determining said predetermined time.

15. The invention according to claim 13, and a second magnet located downstream of said electromagnet to activate the speed control device on said first vehicle.

16. In a railroad classification yard, an arrangement for controlling the speed of free rolling railroad cars on a downwardly sloping railroad track wherein the cars are provided with speed control devices activated for car braking in excess of a predetermined car speed, a trackside electromagnet located uphill toward the entrance of the track and adapted when energized to activate a speed control device on a first railroad car at a first location near the electromagnet, a railroad car sensor located at trackside and downhill from the electromagnet and adapted to sense the presence of a second railroad car located at a second location proximate the sensor, a time delayed sensor switch and a power source associated with the sensor and the electromagnet in a common circuit whereby the first railroad car located at the sensor for a time greater than the delay time energizes the electromagnet which activates subsequent speed control devices on cars passing by said electromagnet whereby only cars at rest at said sensor will cause actuation of said sensor switch.

17. The invention according to claim 16, and a magnet member at trackside downhill from the electromagnet for activating the speed control device of a car passing thereby.

18. The invention according to claim 17, and said magnet member being between the sensor and the electromagnet.

19. The invention according to claim 16, and said sensor switch including a timer means determining the duration of the presence of the second railroad car at the second location attendant to energizing the electromagnet at the termination of said duration.

20. The invention according to claim 16, and said sensor comprising a pressure-responsive fluid bearing tube and said switch comprising a pressure-responsive member and a switch member closed thereby with closing of the circuit before the power source and the electromagnet.