US3459136A

US3459136A - Automatic control for track surfacing machines

Info

Publication number: US3459136A
Application number: US636949A
Authority: US
Inventors: Colin St John
Original assignee: Conquip Ltd
Current assignee: Conquip Ltd
Priority date: 1966-05-12
Filing date: 1967-05-08
Publication date: 1969-08-05
Anticipated expiration: 1986-08-05
Also published as: CH456669A

Description

AUTOMATIC CONIROL FOR TRACK SURFAOING MACHINE S Filed May a, 1967 6.5T. JOHN Aug. 5, 1969 4 SheetwSheet 1 Aug. 5, 1969 4 Sheets-Sheet 2 FIG.3

L J 644W- @fluwlz 4,4115% c. ST. JOHN 3,459,136

AUTOMATIC CONTROL FOR TRACK SURFACING MACHINES Filed May a, 1967 1 Aug. 5, 1969 c, JOHN 3,459,136

AUTOMATIC CONTROL FOR TRACK SUBFACING MACHINES Filed May 8, 1967 4 Sheets-Sheet 3 FIG.4

AUTOMATIC CONTROL FOR TRACK SURFACING MACHINES Filed May a, 1967 C. ST. JOHN Aug. 5, 1969 4 Sheets-Sheet 4.

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United States Patent US. Cl. 1047 13 Claims ABSTRACT OF THE DISCLOSURE The provision of a control unit for automatically controlling the amount of lift applied to railway and the like tracks during the surfacing thereof by means of a railmounted track lifting and tamping unit.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to railway track surfacing machines of the type having a rail-mounted track lift- "ing and tamping unit which moves along the rails lifting the track at spaced intervals and tamping the ballast under the lifted track, and wherein the amount of lift applied is determined from reference planes or lines provided between the lifting and tamping unit and an associated trolley.

Description of the prior art Machines of the type to which this invention relates normally comprises a lifting unit which moves along the track lifting the rails at spaced intervals, e.g. at each sleeper or set multiples of sleepers, and tamping the ballast under the lifted sleeper or sets of sleepers to hold the track in its new position. The amount by which the rails are lifted at each point where lift is applied is determined from reference planes or lines provided from a trolley which is normally situated in advance of the lifting unit but which could be at the rear of the lifting unit or, alternatively, trolleys could be placed both in front of and behind the lifting unit. These reference planes or lines can either comprise tensioned cables stretched between the trolley and the lifting unit or beams of light or infrared rays which are projected from the trolley and provide a line of sight lift relative to:

(a) The position of the track to the rear of the lifting unit i.e., the track which has already been lifted and tamped;

(b) The elevation or position of the track well ahead of the machine and therefore ahead of any possible track disturbance while lifting or aligning; or

(0) Positions located above the rails adjacent to the point at which the track is being lifted and tamped.

In the operation of these machines the reference planes are first set, by adjustment of the height of the cables or the beam projectors on the trolley, to a position which will provide the minimum lift necessary to eliminate all the irregularities in the track, or to minimise the irregularities if it is not practicable to entirely eliminate them, and the track is then automatically lifted at each lifting point until the cut-off position is reached, i.e., until a shadow board on the lifting mechanism cuts the beam or until a contact plate touches the tensioned cable to complete a circuit and stop the lift. The track is then held at this position until the ballast under the lifted sleeper has been tamped when the machine advances to the next lifting station and repeats the same process.

3,459,136 Patented Aug. 5, 1969 These tr-ack surfacing machines, however, suffer from the disadvantage that in situations where there are large variations in track levels no lift will be obtained, i.e., the shadow board will be cutting the beam or the contact plate will be in contact with the cable, unless the reference planes are adjusted. This adjustment, which has to be done constantly as the machine advances along the track, has previously been done manually by altering the height of the cables or beam projectors on the trolley, or by adjusting the height of the rear plane or lines in an endeavour to provide enough lift at all points along the track to correct cross level errors and produce reasonably smooth longitudinal track surfacing. The manual control system was diflicult to operate at close to minimum lift and required an extra operator to calculate and com stantly re-set the amount of lift or, where the one operator worked both the surfacing machine and the manual controls, the machine was slowed down considerably.

SUMMARY OF THE INVENTION The object of the present invention is to overcome the abovementioned difiiculties is known types of railway track surfacing machines by providing an automatic control which constantly adjusts the height of reference levels or planes to compensate for variations in the levels of the untreated track.

Broadly, in accordance with the present invention, there is provided a railway track surfacing machine of the type having a rail-mounted track lifting and tamping unit, said track lifting and tamping unit having an electrically controlled lifting mechanism, a rail-mounted trolley spaced from said track lifting and tamping unit, reference planes above the rails between said trolley and said track lifting and tamping unit, and sensing elements mounted on said lifting mechanism, said sensing elements cooperating with said reference planes to determine the height to which the track is lifted, characterized by a control unit operatively connected to height adjusting means for altering the distances between said reference planes and said sensing elements, said control unit receiving electrical signals from the electrical circuit of said lifting mechanism indicating the positions of said sensing elements relative to said reference planes and operating said height adjusting means in response to said signals to thereby automatically adjust the height to which the track is lifted independently of variations in the unsurfaced track ahead of the machine.

In a preferred form of the present invention the height adjusting means are hydraulically operated, and in a particularly preferred form of the invention, the hydraulic circuit therefor includes a metering valve to control the rate at which the height adjustment is effected. Although any known form of metering valve can be used in conjunction with the control unit provided by this invention it is preferred to use a metering valve which comprises a metering cylinder having a self-centering spring-loaded piston mounted therein, said metering cylinder receiving high pressure oil when the control unit is set to increase the height to which the track is to be lifted, with said high pressure oil displacing said spring-loaded piston from its central position to thereby transmit a predetermined amount of oil from said metering valve at a controlled rate to the hydraulically operated height adjusting means.

The present invention also provides a control unit for a railway track surfacing machine of the type wherein an electrically controlled lifting mechanism lifts the track to a height determined by sensing elements carried on said lifting mechanism cooperating with reference planes provided above the track and wherein hydraulically operated height adjusting means are provided for altering the distances between said reference planes and said sensing elements, said control unit comprising electrical contact means connected to a source of electric current, a hydraulic control valve operatively connected to said contact means and a hydraulic metering valve, said electrical contact means being adapted to receive electrical signals from the electrical circuit of said lifting mechanism indicating the positions of said sensing elements relative to said reference planes and to actuate said hydraulic ocntrol valve in response to said signals, said contact means actuating said hydraulic control valve in response to a first set of signals to transmit hydraulic fluid through said metering valve to said hydraulically operated height adjusting means and actuating said hydraulic control valve in response to a second set of signals to withdraw hydraulic fluid from said hydraulically operated height adjustment means through said metering valve, said metering valve controlling the rate at which hydraulic fluid is passed therethrough to thereby control the rate at which said hydraulically operated height adjusting means are adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a track levelling machine and an advance trolley, viewed from ahead of the advance trolley;

FIGURE 2 is a side elevation of the machine and trolley illustrated in FIGURE 1;

FIGURE 2A is a schematic perspective view depicting infrared ray transmitter and receiver means for establishing reference planes, similar to the general illustration of FIG. 4.

FIGURE 3 is a diagrammatic representation of the control circuit of this invention illustrating the adjustment of the reference planes by adjustment of the trolley crossarm;

FIGURE 4 is a diagrammatic representation of a modification of the invention wherein the adjustment of the reference planes is achieved by adjustment of the trolley cross-arm and/or the contact plates (or shadow boards) and/or the rear measuring stanchions; and

FIGURE 5 is a diagrammatic representation of a preferred form of oil metering valve for use with the control unit of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGURES 1 and 2 the track surfacing machine consists of a trolley 6 situated in advance of a lifting unit 7. The lifting unit 7 is of known construction and need not therefore be described in detail for the purposes of explaining the present invention. Briefly, the lifting unit 7 comprise a rail-mounted car 8 which is progressively moved, under its own power, along the track lifting each sleeper or set of sleepers in turn, by means of lifting arms 9, to a predetermined height (as will hereinafter be described) and tamping the ballast under the lifted sleeper or sets of sleepers, by means of tamping arms 10, to hold the track in its new position.

The trolley 6 carries a cross-arm 11 which has a central pulley 12 and outer pulleys 13 and 14, respectively. As illustrated in FIGURE 1 central pulley 12 carries a tensioned cable which provides reference lines and 16 to indicate the amount of lift available above the right hand rail 17 and the left hand rail 18, respectively, at the point of lift at the front of the car 8. Instead of using central pulley 12, the tensioned cable could be passed around outer pulleys l3 and 14 so that

reference lines

15 and 16 would be above the rails 17 and 18, respectively, throughout their length. Again, the tensioned cable could be replaced by infrared transmitters IRT on the trolley projecting beams of infrared rays onto receivers IRR in car 8 mounted above rails 17 and 18, respectively, as shown schematically in FIG. 2A, which includes other apparatus as depicted and described in conjunction with FIGS. 1 and 4.

In the operation of these track surfacing machines when the height of cross-arm 11 has been set, to thereby set the height of

reference lines

15 and 16 above rails 17 and 18, respectively, then at each point where lift is to be applied the hydraulic lifting arms 9 will lift the track until

contact plates

19 and 20, which are carried on the lifting mechanism of car 8, contact the reference planes (i.e. the tensioned cables) 15 and 16 to complete electrical circuits and stop the lift. (Where infrared transmitters 1- RT and receivers IRR, respectively, are used instead of tensioned cables to provide reference planes 15' and 16, the

contact plates

19 and 20 are replaced by

shadow boards

19 and 20, respectively which cut the infrared beams and stop the lift.)

The description given to date has been solely concerned with the operation of conventional track surfacing machines. As previously mentioned, the present invention provides an automatic control for adjusting the height of

reference planes

15 and 16, and therefore of the amount of lift provided at each point where lift is applied to the track. In the embodiment illustrated in FIGURES 1 to 3 the cross-arm is carried on a vertical column 21, which is hydraulically operated by means of hydraulic cylinder 22, and which has a manual adjustment 23 for the initial adjustment of the basic minimum lift. The control circuit (which is diagrammatically illustrated in FIG- URE 3) operates at the end of each forward movement of the lifting unit 7 and serves to raise or lower vertical column 22 to thereby raise or lower

reference planes

15 and 16, where necessary, towards the exact height necessary for imminent cut-off on one or both planes.

Referring now to FIGURE 3, the control circuit receives current from the automatic tamp switch of the lifting unit 7, which is fed to terminal 24, and also receives current from the lifting control circuit of unit 7 when current is flowing therein i.e., when lift is available above one or both of the rails 17 and 18. Thus when lift is available above rail 17, i.e. when contact plate 19 is clear of reference plane (or cable) 15, current will be fed to terminal 25, and when lift is available above rail 18, i.e., when contact plate 20 is clear of reference plane (or cable) 16, current will be fed to terminal 26. The control circuit is brought into operation by depressing switch 27, which is depressed by means of the operator depressing a foot control pedal to move the lifting unit 7 forward.

The control circuit has an off/ automatic control switch consisting of interlinked switches S S and S the control switch being shown in the off position in FIGURE 3. Relays R and R control contact banks C C C38. 411 C521 C623. and 11 211 C311 41 51 fib: spectively, when they receive current from

terminals

26 and 25, respectively. Relays R and R operate a 4-way oil control valve 27 to respectively raise and lower vertical column 21 by pumping oil through pipe-line 28 to bydraulic cylinder 22 to raise column 21 or by withdrawing oil from hydraulic cylinder 22 to lower column 21. A needle valve 29, control valve 30 and check valve 31 are provided in pipe-line 28. The control circuit also includes a manual raise/lower/hold switch S to enable the operator to manually control the height of vertical column 21 Where necessary. Indicator lights L and L are also provided to give a visual indication of when lift is available above the left hand rail 18 and the right hand rail 17, respectively.

There are three combinations of signals which can be fed into the control circuit, viz.:

(1) Both reference planes clear of the contact plates;

(2) One plane clear of contact plate and one plane cut-off; and

(3) Both planes cut-off.

In the first case, i.e., where lift is available on both rails, current will flow through

terminals

26 and 25 to relays R and R respectively, which will open contacts C C and C C and simultaneously close contacts C 4) C C s, C C and C C Current from terminal 24 will therefor flow to relay R, which will switch the hydraulic control valve 27 to withdraw oil from hydraulic cylinder 22 to thereby lower vertical column 21 to reduce the amount of lift towards the basic minimum. In the second case, i.e., where lift is available on one rail only, current will be fed to only one of the relays, for example relay R which will open contacts C C however, as contacts C C will still be closed current from terminal 24 will flow via these latter contacts to relay R; which will reverse hydraulic control valve 27 to pump oil into hydraulic cylinder 22 and raise vertical column 21 to a position where lift is available above both rails. In the third case, i.e., where no lift is available on either rail, no current will flow to either relay R or R and contacts C ,C and C -C will remain closed to again set the controls to raise vertical column 21 towards a position where lift is available above both rails. Where the reference planes are at the basic minimum lift position and lift is available on both rails, the control system will always sense and change the plane at which minimum lift is available on both rails but not necessarily equal lift. The automatic control enables the track surfacing machine to ramp the track where necessary for surfacing operations and at the same time retains near minimum lift on the high rail enabling and achieving perfect rail cant control.

As shown in FIGURE 4 the control circuit, which is indicated generally at C, can be used to adjust the amount of lift obtained by adjusting the heights of the rear measuring stanchions and/or of the heights of the contact plates (or shadow boards) in addition to, or instead of, adjusting the height of the vertical column on the trolley. Thus, oil from control valve 27 flowing through pipeline 28 instead of, or in addition to, being passed to hydraulic cylinder 22 to raise vertical column 21 can be by-passed to either or both of pipe-lines 32 and 33. Pipelines 32 and 33, when used, pass oil to

hydraulic cylinders

34, 35 and 36, 37, respectively to thereby adjust the heights of

contact plates

19, 20 and rear measuring stanchions 38, 39, respectively. In the case where infrared or other forms of transmitter are used in place of tensioned cables and 16, hydraulic cylinders 34 and 35 would be used to adjust the heights of the shadow boards while

hydraulic cylinders

36 and 37 would be used to adjust the heights of the receivers in car 8.

FIGURE 5 illustrates a preferred form of metering valve for controlling the rate of lift and lower of vertical column 21 and/ or contact plates 19, and/ or rear measuring stanchions 38, 39 so as to avoid any sudden oil surges to or from the hydraulic cylinders and thereby obtain a more gradual adjustment of the lift. The metering valve, and the hydraulic circuit therefor, comprises a metering cylinder 40, having a piston 41 therein, a 4- way impulse control valve 42 operated by an oil pilot valve 43, throttle valve 44, by-pass valve 45, shuttle valve 46, pilot operated check valve 47 and a normally closed by-pass valve 48. Metering cylinder 40, which is selfcentering, has a heavy spring 49 and a light spring 50 to control the rate of movement of piston 41, and adjustable stops 51 and 52 to adjust the amount of travel of piston 41 in each direction.

In the operation of the metering valve, when the control circuit sets hydraulic control valve 27 to raise vertical column 21 i.e., when relay R is energized, high pressure oil will flow through line 53, shuttle valve 46 and line 54 (which has a fixed restriction 55 therein) to oil pilot valve 43 which will set control valve 42. At the same time high pressure oil from the line 53 will flow through line 56, by-pass valve 45 and line 57 to control valve 42 and from there, via line 58, to metering cylinder 40. The high pressure oil entering metering cylinder 40 through line 58 will displace piston 41, against the action of spring 49, until it comes against stop 51 thereby displacing a controlled amount of oil from cylinder 40. The oil displaced from cylinder 40, which will be at a lower pressure than that coming from control valve 27,

will flow through

lines

59 and 60 to check valve 47 and thence via line 61 to hydraulic cylinder 22 to thereby raise vertical column 21 and adjust the height of

reference planes

15 and 16. Alternatively, or additionally, the low pressure oil could be passed via line 62 to either or both of

hydraulic cylinder

34, 35 and 36, 37 so as to adjust

contact plates

19, 20 and/or rear measuring stanchions 38, 39.

When the control circuit sets hydraulic control valve 27 to lower vertical column 21, i.e., when relay R is energised, high pressure oil will fiow through line 63 to check valve 47 and simultaneously through line 64, shuttle valve 46 and line 54 to pilot valve 43. Oil will be displaced from hydraulic cylinder 22, by means of piston 65 and spring 66 acting downwardly, and this oil will pass via line 61, check valve 47 and

lines

60 and 59 to metering cylinder 40, thereby displacing piston 41 against the action of spring 50. The movement of piston 41 will displace oil from metering cylinder 40 and this oil will be returned to an oil tank via line 58, control valve 42,

lines

57 and 53 and control valve 27.

The oil metering valve illustrated in FIGURE 5 operates to alter the lift height by a pre-set amount at a precise point of time during each working cycle of the track surfacing machine. The valve operation is almost instantaneous regardless of temperature and operating conditions, i.e., it is independent of factors such as changes in the viscosity of the oil. It is these special features which distinguish this metering valve from other hydraulic metering devices.

The use of an oil metering valve, and particularly of the preferred form thereof illustrated in FIGURE 5, in conjunction with the control circuit obviates any sudden changes in the height of the reference planes which might otherwise occur and enables the track surfacing machine to eliminate high spots from the track by gradually ramping the track up to such high spots.

In the case of a track levelling and surfacing operation both planes or

lines

15, 16 are raised or lowered simultaneously by exactly the same height relative to the plane through the rear measuring stanchions and are not dependent on the varying rail elevation ahead of the machine. The same principle also applies when the rails are being aligned. This control unit consequently always provides sufiicient lift on the low rail (either left or right) to match exactly the height of the high rail and will continue to operate in the same plane either horizontal, on straight stretches, or at any required angle to the horizontal on curved stretches.

In the operation of this control system, if the basic minimum lift is set at /2" and the track variations ahead of the machine as far as the trolley terminals of reference planes or lines (15, 16) amount to /2 or more, then the control circuit will operate whenever the line of sight at the middle (or lifting point) cuts below the head of the rail or rails and will raise the reference planes, or reduce the heights of the measuring or cut-off stanchions, simultaneously and equally until the pulsating or constantly reversing point of cut-olf/cut-on is achieved above the rail which is high relative to the rear lifting plane through the rear terminals of the two reference planes. As soon as this hump has been negotiated the automatic control will return the reference planes to the preset basic minimum lift and the machine will then surface the track normally until another hump tends to cut above the reference planes.

With these control units the basic minimum lift can actually be set to below zero (negative lift) in which setting the automatic control will be constantly working and the low rail only will be lifted so as to align this with the high rail.

The control units of this invention can be used with either a fixed or movable target, i.e., with the trolley fixed in position and the lifting unit being gradually moved toward the trolley or with the trolley moving with the lifting unit and thereby being maintained a fixed distance from the lifting unit.

Although the previous detailed description has been give in relation to mechanisms wherein the height of the 7 reference planes and/or of the contact plates (or shadow boards) is adjusted hydraulically it is to be understood that the invention is not restricted to this particular mode of operation since the automatic control of the height of the reference planes and/or of the contact plates (or shadow boards) could be effected by means of power operated screws, electrically pneumatically or by combinations of such means.

What I claim is:

1. A railway track surfacing machine of the type having a rail-mounted track lifting and tamping unit, said track lifting and tamping unit having an electrically controlled lifting mechanism, a rail-mounted trolley spaced from said track lifting and tamping unit, reference plane means for establishing reference planes above the rails extending between said trolley and said track lifting and tamping unit, and sensing elements mounted on said lifting mechanism, said sensing elements cooperating with said reference plane means to determine the height to which the track is lifted, characterized by a control unit including means operatively connected to height adjusting means for altering the distances between said reference planes and said sensing elements, said control unit including means for receiving electrical signals from the electrical circuit of said electrically controlled lifting mechanism indicating the positions of said sensing elements relative to said reference planes and including means for operating said height adjusting means in response to said signals to thereby automatically adjust the height to which the track is lifted via said lifting and tamping unit independently of variations in the unsurfaced track ahead of the machine, and wherein said reference plane means comprise tensioned cables stretched between means disposed on said trolley and said track lifting and tamping unit, said sensing elements on said lifting mechanism comprise contact plates adapted to complete an electrical circuit and stop the track lifting mechanism upon contacting said tensioned cables, characterized in that said height adjusting means comprises a hydraulic cylinder and piston means mounted on said trolley and vertical column carrying the trolley-supported ends of said tensioned cables and connected to the piston of said hydraulic cylinder means, and said control unit further includes and is operative to actuate a hydraulic control valve connected to said hydraulic cylinder, whereby actuation of said hydraulic control valve will serve to raise and lower said vertical column to thereby raise and lower the trolley-supported end of said tensioned cables in response to said signals.

2. A railway track surfacing machine as claimed in claim 1, characterized in that said height adjusting means comprises a pair of rear measuring stanchions spaced above said tracks, a first pair of interconnected hydraulic cylinders each of which is inserted in a rear measuring stanchion mounted in said track lifting and tamping unit, said rear measuring stanchions carrying the machine mounted ends of said tensioned cables, whereby actuation of said hydraulic control valve will serve to raise and lower said rear measuring stanchions to thereby raise and lower the machine mounted ends of said tensioned cables in response to said signals.

3. A railway track surfacing machine as claimed in claim 1, characterized in that said height adjusting means comprises a pair of interconnected hydraulic cylinders, each of which is connected to one of said contact plates, whereby actuation of said hydraulic control valve will serve to raise and lower said Contact plates in response to said signals.

4. A railway track surfacing machine as claimed in claim 2, characterized in that said height adjusting means comprises a second pair of interconnected hydraulic cylinders, each of which is connected to one of said contact plates, whereby actuation of said hydraulic control valve will serve to raise and lower said contact plates in response to said signals.

5. A railway track surfacing machine as claimed in claim 1 characterized in that a metering valve means is inserted into the hydraulic circuit between said hy draulic control valve and said hydraulic cylinder, said metering valve means comprising a metering cylinder having a self-centering spring-loaded piston mounted therein, said metering cylinder including means for receiving high pressure hydraulic fluid from said hydraulic control valve when said control unit is set to increase the height to which the track is to be lifted, said high pressure hydraulic fluid displacing said spring loaded piston from its central position to thereby transmit a predetermined amount of hydraulic fluid from said metering cylinder at a controlled rate to said hydraulic cylinder.

6. A railway track surfacing machine of the type having a rail mounted track lifting and tamping unit, said track lifting and tamping unit having an electrically controlled lifting mechanism, a rail mounted trolley spaced from said track lifting and tamping unit, reference plane means for establishing reference planes above the rails and extending between said trolley and said track lifting and tamping unit, and sensing elements mounted on said lifting mechanism, said sensing elements cooperating with said reference plane means to determine the height to which the track is lifted, characterized by a control unit including means operatively connected to height adjusting means for altering the distances between said reference planes and said sensing elements, said control unit including means for receiving electrical signals from the electrical circuit of said electrically controlled lifting mechanism indicating the positions of said sensing elements relative to said reference planes and including means for operating said height adjusting means in response to said signals to thereby automatically adjust the height to which the track is lifted via said lifting and tamping unit independently of variations in the unsurfaced track ahead of the machine, and wherein said reference plane means comprise spaced beams of electro-magnetic radiation projected from projectors mounted above said rails on said trolley onto receivers aligned therewith and mounted in said track lifting and tamping unit, and said sensing elements on said lifting mechanism comprise movable shadow boards adapted to stop the track lifting mechanism when they are moved to interrupt said beams, characterized in that said height adjusting means comprises a hydraulic cylinder and piston means mounted on said trolley and a vertical column which is adapted to carry said projectors is connected to the piston of said hydraulic cylinder, and said control unit includes and is operative to actuate a hydraulic control valve connected to said hydraulic cylinder, whereby actuation of said hydraulic control valve will serve to raise and lower said vertical column to thereby raise and lower said projectors.

7. A railway track surfacing machine as claimed in claim 6 characterized in that said height adjusting means comprises a pair of interconnected hydraulic cylinders, each of which is connected to one of said shadow boards, whereby actuation of said hydraulic control valve will serve to raise and lower said shadow boards in response to said signals.

8. A railway track surfacing machine as claimed in claim 6 characterized in that a metering valve means is inserted into the hydraulic circuit between said hydraulic control valve and said hydraulic cylinder, said metering valve means comprising a metering cylinder having a self-centering spring-loaded piston mounted therein, said metering cylinder including means for receiving high pressure hydraulic fluid from said hydraulic control valve when said control unit is set to increase the height to which the track is to be lifted, said high pressure hydraulic fluid displacing said spring loaded piston from its central position to thereby transmit a predetermined amount of hydraulic fluid from said metering cylinder at a controlled rate to said hydraulic cylinder.

9. A railway track surfacing machine as claimed in claim 6 characterized in that said height adjusting means comprises a first pair of interconnected hydraulic cylinders, each of which is connected to one of said receivers, whereby actuation of said hydraulic control valve will serve to raise and lower said receivers in response to said signals.

10. A railway track surfacing machine as claimed in claim 9 characterized in that said height adjusting means comprises a second pair of interconnected hydraulic cylinders, each of which is connected to one of said shadow boards, whereby actuation of said hydraulic control valve will serve to raise and lower said shadow boards in response to said signals.

11. An automatic control unit for a railway track surfacing machine of the type wherein an electrically controlled lifting mechanism including an electrical control unit with means to lift the track to a height determined by sensing elements carried on said lifting mechanism cooperating with reference plane means provided to establish reference planes above the track and wherein hydraulically operated height adjusting means including a hydraulic metering valve are provided for altering the distances between said reference planes and said sensing elements, said control unit comprising an electrical circuit with electrical contact means connected to a source of electric current, a hydraulic control valve operatively connected to said electrical contact means and the hydraulic metering valve, said electrical contact means being adapted to receive electrical signals from the electrical circuit of said lifting mechanism indicating the positions of said sensing elements relative to said reference planes and to actuate said hydraulic control valve in response to said signals, said electrical contact means actuating said hydraulic control valve in response to a first set of signals to transmit hydraulic fluid through said'metering valve to said hydraulically operated height adjusting means and actuating said hydraulic control valve in response to a second set of signals to withdraw hydraulic fluid from said hydraulically operated height adjustment means through said metering valve, said metering valve controlling the rate at which hydraulic fluid is passed therethrough to thereby control the rate at which said hydraulically operated height adjusting means are adjusted.

12. A control unit as defined in claim 11 characterized in that said metering valve comprises a metering cylinder having a self-centering spring loaded piston mounted therein, said metering cylinder including means receiving high pressure hydraulic fluid from said hydraulic control valve when said electrical contact means receives said first set of signals, said high pressure hydraulic fluid displacing said spring loaded piston from its central position to thereby transmit a predetermined amount of hydraulic fluid from said metering cylinder at a controlled rate to said hydraulically operated height adjusting means.

13. A control unit as claimed in claim 12 characterized in that said metering cylinder has adjustable stops for adjusting the amount of travel of said spring loaded piston from its central position to establish a predetermined minimum amount of lift or lowering of said reference plane establishing means.

References Cited UNITED STATES PATENTS 3,141,418 7/1964 Clayborne et al. 104-7 3,144,834 8/1964 Steward a... 104--7 3,198,135 8/1965 Plasser et al. -t. l()47 3,298,105 1/1967 Stewart et al. 104-7 3,301,198 1/1967 Bick 104-7 3,334,593 8/1967 Plasser et al 104--7 ARTHUR L. LA POINT, Primary Examiner RICHARD A. BERTSCH, Assistant Examiner US. 01. xx. 1o4- s