US2068254A

US2068254A - Crossing signal

Info

Publication number: US2068254A
Application number: US36710A
Authority: US
Inventors: Mercer D Wilson
Original assignee: Individual
Current assignee: Individual
Priority date: 1935-08-17
Filing date: 1935-08-17
Publication date: 1937-01-19
Anticipated expiration: 1954-01-19

Description

Jan. 19, 1937. M. D. WILSON 7 2,068,254 CROSSING SIGNAL Filed Aug. 1'7, 1955 3 Sheets-Sheet 1 Inventor iflerflerD. 10:75am

III

Jan. 19, 1937. I 5 WILSON 2,068,254

. CROSSING SIGNAL Jan. 19, 1937.

M. D. WILSON CROSSING SIGNAL Filed Au 17, 1955 5 Sheets-Sheet 3 Patented Jan. 19, 1937 UN! ED STATE 11 Claims.

My invention relates to traffic signals, particularly to automatic signal mechanisms for railroad crossings, and is directed to an improvement based on the device shown in my Patent Number 1,890,352, issued December 6, 1932, entitled Cl'OSSlIlg signals, and the disclosure of my copending application, serially numbered 11,597, filed March 18, 1935, entitled Crossing signal.

The present invention embodies the same general principles as those disclosed in the aforesaid patent and patent application. The signal means adapted to control traffic across a railroad track reciprocates between a stop position and a go or clear position, one movement of the reciprocation being effected by a power-driven mechanism and the opposite movement being accomplished by gravity. By this arrangement, the powerdriven movement not only moves the signal memher from one position to another, but also, by

" displacing a suitable weight against the force of gravity, stores energy in the form of energy ofv position to be used in accomplishing the opposite movement of the signal member.

Preferably the signal member indicates go when it is at the end of the power-driven movement, energy then being stored for the opposite movement of the signal member to the stop position. In other words, when the signal is in the clear position potential energy is available for H10 the signal movement, and an approaching train or control vehicle merely releases the stored energy. After the departure of the train, the reverse power-driven movement is automatically initiated and completed to place the parts of the signal mechanism in their normal go position.

The word normal, as hereinafter used, will refer to the position of the mechanism at the go or clear position of the signal.

An important advantage of this arrangement is that, if the power-driven mechanism fails, the

ous accident can be caused by the breakdown.

An additional safety feature is that the signal is maintained in the go position only so long as an electric control circuit is energized. Con- 5O sequently, whenever the controlcircuit fails,.or is broken by accident, the signal member will immediately move to the stop position, regardless of the proximity of a train. thereby calling attention to the need for immediate repair. As in my .55 previous disclosures, I prefer that the powerdriven mechanism comprise a hydraulic lift actuated by an electrically driven pump.

Important objects of my invention include the provisions of a new cam arrangement and an improved form of weight, whereby the cost of manu facturing the device will be lowered and the amount of energy-expenditure and expense to operate the signal will be substantially reduced. These and other objects and advantages of my invention will be apparent in the following detailed description.

In its broadest aspect my improvement comprises a signal-actuating shaft in combination with two cam means operatively associated with the shaft and adapted, respectively, to rotate the shaft in opposite directions, together with means to cause relative movement between .said cam means.

In the accompanying drawings Fig. 1 is a side elevation of my invention;

Fig. 2 is an enlarged side elevation with the outer housing or casing shown in section;

Fig. 3 is a vertical, medial section of Fig. 2;

Fig. 4 is a fragmentary vertical section taken as indicated by line 5- 8 of Fig. ,3;

Fig. 5 is a side elevation of a portion of the device, with the casing shown in section to reveal the latch mechanism in the normal position;

Fig. 6 is a view similar to Fig.5, showing the latch mechanism in an alternate position;

Fig. '7 is a horizontal section taken as indicated by line 1-1 of Fig. 5, showing the mechanism in the normal latched position;

Fig. 8 is a horizontal section of the signal mechanism, taken as indicated by the line 88 of Fig. 6;

Fig. 9 is a vertical section, taken as indicated by 99 of Fig. 8;

Fig. 10 is a vertical section, taken as indicated by the line Hllll of Fig. 9, with the signal mechanism in the stop position;

Fig. 11 is a vertical section taken as indicated by line lI-H of Fig. 8, with the signal in the stop position;

Fig. 12 is a wiring diagram, indicating one of a platform 23 that supports the major part of the mechanism. This mechanism includes a hydraulic cylinder 24, having a vertically extended cylinder head 25.

The signal member utilized may be in the form of a barrier, generally designated by numeral 26, carried by a horizontally extending arm 2?, the arm being rigidly mounted to a floating, vertical signal shaft 28. Preferably, barrier 26 is counterbalanced by a suitable weight 29 carried by an arm 30 mounted on shaft 28 diametrically opposite from arm 21. A cable 3| braces arm 21, and a second cable 32 braces arm 30, as shown.

Floating shaft 28 is slidingly journaled in two bearings, one bearing 33 being built into conical top 2!, the other bearing 34 being incorporated in cylinder head 25. For weather protection, shaft 28 may be provided with a conical hood 35 extending over the top of the casing in spaced relation thereto, the hood having a depending annular portion 36.

Shaft 28 is supported by two rollers, or ,camfollowers 3'! mounted on a pair of stub shafts 39 that extend diametrically from signal shaft 28. These rollers are positioned to rest in turn on either or both of two cooperating arcuate cams concentric with the shaft, these being a stationary cam all and a movable cam ll. I prefer to split each of these rollers into two units, one for each cam, as shown.

Stationary cam 4!! is of cylindrical configuration, and is enlarged at the lower end to engage and rest upon cylinder-head 25, suitable screws 40a being employed for assembly. The cylindrical body of the cam is provided with two longitudinal slots 42 positioned diametrically from each other. The upper edge of the cylindrical body provides an arcuate cam having two diametrically disposed

low points

43 and 44 and, alternating therewith, two diametrically disposed

high points

45 and 46 as may be understood by referring to Figs. 13 and I l. The shape shown provides two normally effective diametrically disposed cam surfaces 4! inclined in one circumferential direction, and two diametrically disposed cam surfaces 48 of opposite inclination.

Movable cam ll, likewise of cylindrical configuration, slidingly embraces stationary cam 40. The top edge of movable cam ll is divided into two effective cam surfaces 58, both of which are inclined in the opposite circumferential direction from the aforementioned effective surfaces It will be noted that low points of movable cam M are positioned in staggered relation to low points 43 and M of the stationary cam, i. e., the low points of the movable cam are closer to the high points of the stationary cam than to the low points of the stationary cam.

To prevent cam-followers 31 from passing over the

high points

45 and 46 of the stationary cam, suitable stops may be provided on either cam. In the drawings the stops comprise fingers 52 integral with movable cam 4|.

Movable cam M is mounted on a suitable plate 53, and is prevented from rotating by virtue of end portions 54 of the plate extending through aforementioned slots 52 of the fixed cam. Plate 53 is centrally apertured to surround signal-shaft 28, in spaced relation. The mass of movable cam 4|, together with plate 53, is such that the cam will gravitate downward freely and in a positive manner.

When the preferred form of my device is in operation, signal-shaft 28 is normally held in a first signal position by latch means that will be described later, the movable cam being latched in its elevated position with the cam-followers at the upper ends of inclined cam surfaces 4'! of fixed cam 40.

When the signal moves from its normal go position to the stop position, cam H gravitates downward, rollers 31 following down inclined surfaces 41, thereby rotating the signal-shaft 90 degrees to place barrier 26 across the traffic lane to be controlled. If the progress of the signal barrier towards the stop position is impeded by some obstacle, such as a vehicle in the traffic lane, the rollers will be delayed on cam surfaces 41, and, upon removal of the obstacle, will continue towards the stop position.

If, while in the stop position, barrier 26 is struck from the front, rollers or cam-followers 3'! will be forced up cam surfaces 41; and if the signal barrier is struck from the opposite side, rollers 3'! will pass up either cam surfaces 48 of the stationary cam or cam surfaces 50 of the movable cam, whichever of these cam surfaces is the higher. In either situation, fingers 52 will prevent the signal passing over

high points

45 and 46 of the stationary cam, and, in either situation, inclined surfaces will cause the signal to gravitate to the desired stop position.

The power means in the preferred form of my invention for moving cam 4| upward includes a hydraulic lift.

In the construction shown in the drawings, bydraulic cylinder 24 embraces a suitable piston 56, from which two spaced piston rods 51 extend upward through piston-head 25, terminating in plate 53.

To limit the upward movement of the piston under hydraulic action, the piston may be provided with a suitable relief valve 58, that normally covers relief passages 59. The valve includes a stem 69, extending upward a suitable distance towards cylinder-head 25. The valve is normally maintained in a closed position by virtue of a suitable helical spring 6| confined between piston 56 and a stop 62 on stem 60.

It may be noted here that in the construction shown, the piston reciprocates only over the lower portion of cylinder 24. The pump, generally designated by numeral 63, is mounted below the cylinder in the space between platform 23 and base plate 22. The pump may be of the gear type, comprising two interlocking rotary elements 64 and 65, in pump chamber 66. The two rotary elements are mounted, respectively, on shafts 61 and 68, shaft 68 being driven by a suitable motor 69.

Any fluid may be used in the hydraulic lift, preferably a suitable grade of oil. The space in cylinder 24, above the piston, is utilized as a resvoir, the oil being pumped out of the reservoir into the cylinder under the piston to raise the movable cam, and being returned to the reservoir when the movable cam forces the piston down. The drawings show an arrangement that may be employed to provide such a cycle of fluid movements.

From a port l0 in the cylinder wall just above the upper position of piston 55 (Fig. 11) a downflow passage H (Fig. leads to pump chamber 66. From the outlet side of the pump a pressure passage 12 leads to the bottom of a vertically disposed valve chamber 13, in which a valve 14 is free to move longitudinally from a normal lower position, shown in Fig. 10, to an alternate higher of the cylinder through passage 84.

flow of oil through up-flow passage 84. -erably, adjustment of degree of restraint of oilposition, the valve moving upward by-fiuid pressure from the bottom. The valve includes an extensive stem 15, terminating in a valve head 16.

Preferably, the gravitational return of the valve is facilitated by a helical spring Tl, confined between valve head 16 and the upper end wall 18 of off from both pump pressure passage 12 and lower cylinder passage 8|. In the lowermost position of the valve (Fig. 10) pressure passage 12 is out 01f, and communication is established between the space in the cylinder under piston 56 and the space in the cylinder above piston 56, as follows: port 82, lower cylinder passage 8|, port 88, valve chamber 13, upper valve port 83, up-fiow passage '84, and spaced ports and 86 in the cylinder wall above the uppermost position of the piston. It will be noted that the arrangement is equivalent to an ordinary three-way valve responsive to fluid pressure, i. e., when a pump is in operation fluid pressure forces the valve to its uppermost position, thereby placing the pump in communication withthe cylinder under the piston, and when the pump ceases operation the valve automatically returns to a position placing the lowermost portion of the cylinder in communication with the uppermost portion of the cylinder.

Since oil trapped in pump pressure passage 12 may hinder, if not prevent, the downward return of valve member 14, either the pump must permit sufiicient reverse leakage to release the trapped oil, or a suitably dimensioned bleeder passage 81 must be provided between pressure passage 12 and down-flow passage 1 I.

Normally, the movable cam is held at its uppermost position, independent of the hydraulic lift by virtue of a latch means to be described later. When a train or control vehicle enters the control zone of the track, the movable cam is released to gravitate downward, thereby turning the signal to the stop position, and forcing oil from the bottom of the cylinder to the top Relatively fast movement of the signal barrier for the first 30 degrees of rotation, and slower movement for the remaining 60 degrees, may be accomplished 'by controlling the flow of fluid through passage 84,

in accordance with the desired rate of movement of the signal.

For this purpose, the upper portion of passage 84 is enlarged to a time-control cylinder 88, in

which reciprocates a time-control plunger 89.

By means of a connecting rod 98, extending upward through a suitable packing gland 9|, timecontrol plunger 89 is connected to a bracket 92, the bracket being secured to movable cam 4| by screws 92a (Fig. 4).

Plunger 89 has one or more longitudinal passages 93, dimensioned to suitably restrain the Prefflow is provided by a complementary disk 94, having suitable apertures corresponding to passages 93 in the time-control plunger. This disk may be held fixed by a nut 95 in any of various positions partially closing passages 93.

The reasons for providing two

ports

85 and 86,

spaced as shown, will now be apparent. In the prises a rotary latch member normal position of the signal, time-control plunger 89 clears lowermost port 85 by a distance corresponding ,to the first 38 degrees of the signal movement. When the movable cam is released t6 gravitate downward, the time-control plunger will not restrict the flow of fluid through passage 85 until it begins to cut off port 85. Thereafter, however, the downward movement of the cam will be retarded by the restricted flow of the oil through apertures 93, until the time-control pis ton reaches its lowermost position indicated in Fig. 10. Two spaced portsare required so that when the time-control plunger is passing over lowermost port 85, uppermost port 88 will be available for oil passage.

The latch means to hold signal shaft 28 in the normal first signal position may be associated either with the shaft directly or with movable cam 4|. In my preferred form of the invention set forth in the drawings, two latches are employed: one associated with the shaft, and the other effective to hold up the movable cam independently. If thelatch associated with the shaft should fail, obviously the device will still function by virtue of the latch associated with the movable cam. If the latter latch should fail the first latch would suffice to hold the signal member at the normal first position, but, desirable control of the speed of rotation of the shaft to the second signal position will be lacking.

A rack member 98 assembled to fixed cam 48 and cylinder head 25 by suitable bolts 91 is curved concentric to shaft 28. The upper edge of this member is formed as a spiral rack 98, corresponding to an effective cam surface 4"! on fixed cam 48, and a longitudinal edge of the member is formed as a vertical rack 99.

A latch member generally designated by numeral I88 to releasably hold signal shaft 28 at the normal firstposition is rotatably mounted on one of stub shafts 39 and secured thereto by a suitable screw Illi. This latch member com- !92, having a latch tooth I83, and a pinion HM fixed to said rotary member and adapted to mesh with spiral rack 98. A second latch member generally designated by numeral N25 to releasedly hold movable cam H at its elevated position, is rotatably mounted on a stub shaft I88 extending radially from movable cam H, the latch member being secured to the shaft by a suitable screw I51. This second latch member is similar to the first, comprising a rotary latch member E88, having latch tooth I58, and a pinion H8 fixed to said rotary member in a position to mesh with vertical rack 99.

A shelf having a central aperture M2 to clear signal shaft 28, extends diametrically across casing 28, resting at its ends on an inwardly extending flange I I3 integral with the casing wall. The shelf may have a depending arcuate flange H4 near each end position to abut said casing flange H3. Preferably, a pair of rods Ilia. extend upward from platform 23 to shelf as shown.

Mounted on the lower side of shelf III is a latch bracket H5, having a lateral arm 6 integral therewith. Arm 6 is vertically aper turecl to slidingly embrace and guide a longitudinal movable latch-release H1. Latch-release H is a bar provided with laterally extending pins H8 and H 9, and has a reduced lower end bent to form a finger i28. Finger I28 extends laterally into a vertical slot |2| in a latch weight |22.

ill)

Mounted on the lower end of latch bracket H5 is a suitable motor cut-off switch I23, operated by a plunger I24, the plunger being fixed to a bracket I attached to latch weight I22. This switch is closed when the plunger is down (Fig. 6) and is open when the plunger is up (Fig. 5).

Journaled in standard II5 are two arbors I26 and I2'I. Keyed to the inner end of arbor I26 is a pawl I28, positioned to engage latch tooth I03; and keyed to the outer end of the arbor is a latch arm I29 having a large slot I30 to receive pin H3 on latch-release II'I. Keyed to the inner end of arbor I 21 is a second pawl I3I positioned to engage latch tooth I09; and keyed to the outer end of arbor I2! is a latch arm I32 having a slot I33 to receive lower pin I I9 of latch release II'I. Both pawls I28 and I3I are relatively heavy to overbalance their respective latch arms H8 and H9.

In the normal positions of the various parts of the latch mechanism shown in Fig. 5, latch weight I22 is held at its uppermost position by virtue of electro-magnetic coupling between an armature I34 integral with the top end of the weight, and an electro-magnet I35 mounted on the under side of shelf III. The electro-magnet shown is U-shaped, with a coil I36 around one leg. By virtue of the fact that finger I20 rests against the lower end of slot I2I in the latch weight, latch-release I II is held at an elevated position that permits pawls I28 and I3I to rest in engagement with their respective latch teeth.

When the electro-magnet is de-energized by a train entering the control zone of the track, latch weight I22 is released to gravitate downward. Slot I2I is of sufficient length to provide a substantial degree of lost motion between latchweight I22 and finger I20, with the result that the released weight strikes the finger with sufficient force to jar pawls I28 and I3I from their latched. positions. As long as a train is in the control zone, weight I22 will remain suspended from finger I20 in the position shown in Fig. 6.

While electro-magnet I35 is of sufficient strength to hold the latch weight suspended in the position shown in Fig. 5, it is not of sufficient strength to draw the weight upward against gravity from the position shown in Fig. 6. I have, therefore, provided automatic means for restoring the latch weight to its normal position upon the arrival of movable cam 4! at its uppermost position.

Below the weight, a vertically disposed cut-ofif cylinder I39 communicates with main cylinder 24 by an upper passage I 40 and a lower passage I4I, lower passage MI opening to a chamber I42 on the wall of main cylinder 24. Towards the upper end of chamber I42 a bore, or group of bores, generally designated by numeral I43, extends through the wall of cylinder 24, and a similar bore, or group of bores, generally designated by numeral I44, extends through the wall of the main cylinder near the lower end of chamber I42.

A suitable cut-off plunger I45, slidably mounted in cut-01f cylinder I39, is mounted on a rod I46. The rod extends upward through a packing gland I4! into a vertical bore I40, in weight I22. A suitable helical spring I49 embraces rod I below weight I22, the spring resting upon a suitable sleeve I50 adjustably mounted on the rod.

Normally, i. e., when the signal is in the clear position and no train is in the control zone of the track, rod I46 rests upon a bottom end plate I5I, holding cut-off plunger I45 at a position just above passage MI, and no effective pressure Is exerted by spring I49 against the bottom of latch weight I22.

When latch weight I22 is released by a train entering the control zone, it may fall far enough to contract spring I49, partially as shown. in Fig. 6. As soon as the train clears the control zone, motor 60 is energized and pump 63 begins to deliver oil to the bottom of cylinder 24 beneath piston 56. When piston 56, on its upward movement, opens the lowermost of bores I44, oil under pressure escapes into chamber I42 and passage I4I to exert pressure on the under side of cut-off plunger I45. The full force of the oil pump is not delivered against the cut-01f plunger initially, however, because bores I43 and bores I44 are so spaced that momentarily oil flows both outward from underneath the piston through one or more of bores I44 and inward above the piston through one or more of bores I43. This momentary condition ceases as piston 56 moves upward to completely cover bores I43, and to completely uncover all of bores I44, so that the full force of the pump is thereafter delivered against cut-off plunger I45.

The cut-01f plunger is forced upward, carrying with it rod I40, the upward'movement forcing weight I22 into the normal position shown in Fig. 5. It will be noted that spring I49 serves as a shock-absorber and permits a certain latitude in the adjustment of sleeve I50.

If, for any reason, motor cut-01f switch I23 is not closed by the arrangement described to stop the pump, damage to the mechanism will be prevented by the action of relief valve 58, as previously described.

As soon as pump 63 stops, cut-off plunger I45 returns to its normal position at the lower end of its range of reciprocation, and latch weight I22, except for the attraction of electro-magnet I35, is again free to drop down upon finger I20. It is contemplated that all pressure in cylinder 24 beneath the piston, will be released immediately after the pump stops, by virtue of valve I4 returning to its lowermost position and thereby providing free communication from port 82 at the bottom of the cylinder to

ports

85 and 86 at the top of the cylinder.

An electrical arrangement that may be employed to operate the signal includes two control switches, both of which must be closed to energize the signal motor, one being a mechanically operated switch that opens only when the signal is in the go position, the other being an electrically operate-d switch open only when a train is in the control zone. Both switches in such an arrangement will be closed to operate the motor whenever the signal is in the stop position and no train is in the control zone. Of these two switches, the mechanically operated switch is motor cut-01f switch I23 described above.

A wiring diagram showing the essential fea tures of such an electrical arrangement is shown in Fig. 12. Relay I52 is normally energized in a closed position by wires I33 and I34 that are part of a circuit associated with the control zone of the railroad track. Whenever a train enters the control zone this circuit is sho-rt-circuited to deenergize relay I52, thereby breaking the normal circuit through electro-magnet I35. This last named normal circuit includes wire I55, battery I56, wire I51, relay member I58, and wire I59 to the other side of the electro-magnet.

When the electro-magnet releases weight I60 of the wiring diagram, which represents latch weight I22 in the device itself, a switch member I60a connects contacts Iiiland I62, the switch member and two contacts representingcut-off switch I23 previously described. The dropping of switch member Ililla against contacts MI and I62 does not, however, close motor relay I53 because the circuit required to do so includes relay member I58. When, however, the train leaves the a control zone and relay I52 automatically closes,

motor relay I63 is energized through the following circuit; battery I55, wire I5'I, relay member I58, wire I59, wire I6 3, switch member IBlla, wire I65, coil of relay I63, wire I56, and wire I55 back to battery I56. When relay I63 is thereby energized, the following motor circuit is established: battery I56, wire I51, wire I51, relay member I68, wire I69, motor 65 and wire I55 back to battery. I56.

The operation of my invention may be readily understood from the foregoing description. When the various parts are in their normal positions, with the control zone of the track clear, relay I52 is closed; electro-magnet I35 is energized; cut-01f switch I25is open; the signal is in the go position; movable cam II and piston 56 are held at their uppermost positions by the lowermost of the two latches; the signal shaft isheld at its normal position by the uppermost of the two latches; latch weight I22 is held at its highest position by electro-magnet H5; cutoff plunger I 45 rests at its lowermost position; and, since the motor and pump are idle, valve I4 is at its lowermost position, providing free communication between the portion of the cylinder below the pistonand the portion of the cylinder above the piston.

As soon as a train enters the control zone, thereby de-energizing the track relay, electromagnet I35 is de-energized, releasing latch weight I22. The latch weight drops with suitable impact against finger I25, thereby disengaging both. latches with a jerk, and at the same time closing motor cut-off switch I23. Latch pawls I28 and I3I are then held in suspended position by pins H8 and I I9, respectively, as shown in Fig. 6. Pinion I04 being free to rotate, moves downward around rack 98 as the two cam-followers gravitate down cam surfaces 41 of stationary cam 40. Pinion IIEI also being free to rotate, moves down rack 59 as the movable cam gravitates downward. The downward movement of the cam-followers is governed by the oil-controlled downward movement of cam M. The signal swings rapidly degrees untiltime-control plunger 39 becomes effective, and then proceeds more slowly the remaining 60 degrees to the stop position.

As soon as the control zone of the track is again clear, the motor circuit is re-established, as heretofore described, and pump 63 begins to deliver oil through the cylinder under piston 55, valve I4 being moved to its upper position automatically. The pump continues to force piston 55 and movable cam 4| upward to permit pawls I28 and ISI to drop into position for engagement with their respective latch teeth, and then to close cut-off switch I25.

For the purpose of completely disclosing my invention and illustrating the principles involved, I have restricted my description to the preferred form of my invention; but the principles involved may be embodied in other forms, and I, therefore, reserve the right to all changes and modifications that properly come within the scope of my appended claims.

Having described my invention, I claim:

1. A signal having in combination: a signal member; a vertical floating shaft operatively connected with the signal member; an arcuate cam adjacent the shaft, having a cam surface sloping downward in one circumferential direction to a lowest level, a second arcuate cam adjacent the shaft having a cam surface sloping downward in the opposite circumferential direction to a lowest point, said two lowest points being staggered; a cam-follower associated with the shaft to support the shaft on either or both said cams; and means to cause relative axial movement of said camsto rotate the shaft in alternate directions.

2. A signal of the class described, having in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a stationary arcuate cam concentric to the shaft having a cam surface inclining downward in one circumferential direction; a second arcuate cam concentric to the shaft having a cam surface inclining downward in the opposite circumferential direction, said second cam being movable vertically; a cam-follower radially mounted upon the shaft to support the shaft uponeither or both of said cam surfaces; and means to raise the second cam to rotate the shaft in one direction and vice versa.

3. A signal of the class described, having in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a stationary arcuate cam concentric to the shaft having a cam surface inclining downward in one circumferential direction; a second arcuate cam concentric to the shaft having a cam surface inclining downward in the opposite circumferential direction, said second cam being movable vertically; a cam-follower radially mounted upon the shaft to support the shaft upon either or both of said cam surfaces; and power actuated'means to raise the second cam thereby causing the shaft to rotate in one direction, said second cam being adapted to gravitate downward from its raised position thereby permitting the stationary cam to rotate the shaft in the opposite direction.

4. A signal having in combination: a vertical longitudinally movable shaft; a signal member operatively connected to the shaft; a cam-follower mounted on the shaft; a stationary cam adapted to cooperate with the follower to support the shaft, said cam having an inclined cam surface to cause the shaft to gravitate from a normal first signal position to a second signal position; latch means responsive to the approach of a control vehicle to releasably retain the follower at the normal first position; and a powerdriven cam. adapted to be energized upon departure of the control vehicle to force the follower up said inclined surface to the normal latched position.

5. A signal having in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a stationary arcuate cam concentric to the shaft having a cam surface inclining downward in one circumferential direction; a second axially movable arcuate cam concentric to the shaft having a cam surface inclining downward in the opposite circumferential direction; a cam-follower associated with the] shaft to support the shaft on either or both said cams; power actuated means to raise the second cam, thereby causing the shaft to rotate in one direction, said second cam being adapted to gravitate downward from its raised position thereby permitting the stationary cam to rotate the shaft in the opposite direction; and latch means responsive to a passing vehicle to releasably retain the shaft at the position resulting from the upward movement of said movable cam.

6. A signal having in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a follower mounted on the shaft; a stationary cam in position to support the follower and thereby the shaft, said cam having cam surfaces inclined in one direction whereby the shaft will rotate by gravitation from a first signal position to a second signal position; a second cam having a cam surface inclined in the opposite direction, said second cam being adapted when moved upward to engage the follower, thereby rotating the shaft in the reverse direction from the second signal position to the first signal position, said cam being adapted to gravitate from its raised position; a latch means to releasably hold the signal shaft at its first position, said latch means being adapted to release the signal shaft in response to the approach of a control vehicle; and power means adapted to be energized upon departure of the control vehicle to raise said second cam.

7. A signal having, in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a follower mounted on the shaft; a stationary cam in position to support the follower and shaft, said cam having cam surfaces inclined in one direction whereby the shaft will rotate by gravitation from a first signal position to a second signal position; a second cam having a cam surface inclined in the opposite direction, said second cam being adapted when moved upward to engage the follower, thereby rotating the shaft in the reverse direction from the second signal position to the first signal position, said cam being adapted to gravitate from. its raised position; a latch means to releasably hold the follower at its first position; a second latch means adapted to releasably hold the second cam at its raised position, both of said latch means being adapted to be released in response to the approach of a control vehicle; and power means adapted to be energized upon departure of the control vehicle to raise said second cam.

8. A signal having in combination: a signal member; a floating vertical shaft operatively connected with the signal member; a follower mounted on the shaft; a stationary cam in position to support the follower and shaft, said cam having a cam surface inclined in one direction whereby the shaft will rotate by gravitation from a first signal position to a second signal position; a second cam. having a cam surface inclined in the opposite direction, said second cam being adapted when moved upward to engage the follower, thereby rotating the shaft in the reverse direction from the second signal position to the first signal position, said cam being adapted to gravitate from its raised position; a latch means to releasably hold the follower at its second position; a second latch means adapted to releasably hold the second cam at a raised position free from the latched follower, both of said latch means being adapted to be released in response to the approach of a control vehicle.

9. A signal having in combination: a signal member; a vertical shaft operatively connected to the signal member; two arcuate cams adapted respectively to rotate the shaft in opposite directions; a follower connected to the vertical shaft and partially supporting the shaft on each said cams; and means to cause axial movement of one of said cam means relative to the other whereby said cam means will be alternately effective to rotate the shaft.

10. A signal having in combination: a signal member; a vertical shaft operatively connected to the signal member; a cam inclined to rotate the shaft in one direction; a second cam inclined to rotate the shaft in the opposite direction, said two cams being disposed to form a valley; a camfollower operatively connected with the shaft and resting in said valley; and means to cause relative movement between the two cams, thereby causing the vertex of the valley to shift for the purpose of rotating the shaft.

11. A signal having in combination: a signal member; a vertical shaft operatively connected with the signal member; a pair of diametricallydisposed followers extending radially from the shaft; an arcuate cam concentric to the shaft having two cam surfaces sloping in one circumferential direction; a second cam concentric to the shaft having two cam surfaces sloping in the opposite circumferential direction, said cam surfaces being disposed to form two diametricallyopposite valleys to support said cam-followers; and means to cause relative axial movement between the two cams, thereby causing the low points of said valleys to shift for the purpose of rotating said shaft.

MERCER D. WILSON.