Various kinds of actuator arrangements are used to switch railway points or switchgear. A main drive actuator bears against the switch rail close to its free end or toe and acts to push this against the side of the fixed stock rail. Where the switch rail has a long curved section it may be necessary to have one, two or up to three additional actuators, or backdrive actuators, spaced along the switch rail to push it and hold it in position relative to the stock rail. The main drive actuator usually includes some form of clamp or latch that positively locks the switch rail against the stock rail. This ensures that the switch rail is held in the correct position even if the force applied by the actuator itself should fall. Because railway points may be held in a switched period for prolonged periods, perhaps for several days, there is inevitably some relaxation in the actuator, such as caused by leakage of hydraulic fluid and, therefore, a gradual loss of force. It is less easy to lock the switch rails in the desired position at the location of the backdrive actuators because the switch rails may be spaced from the stock rail. For this reason, the usual practice is to monitor displacement of the switch rails from the desired position and to correct for this as necessary by reapplying power from the backdrive actuator. Any detected deviation of the switch rails from their desired position will cause a momentary failure indication before repowering of the actuator has corrected for this. This can lead to the generation of a danger signal on the railway line with consequent interruptions to

rail traffic.

It is an object of the present invention to provide alternative actuator arrangements.

According to one aspect of the present invention there is provided an actuator arrangement for moving first and second members, the two members being interconnected with one another by a linkage extending between them, the arrangement including first and second actuator means arranged to bear against respective movable members such that actuation of the first actuator causes both movable members to move in one direction and actuation of the other actuator causes both movable members to move in the opposite direction, and a locking mechanism coupled with the first and second actuators, the locking mechanism being arranged to allow free movement in opposite directions caused by actuation of the first and second actuator means respectively but to prevent movement in either direction when not caused by actuation of the respective actuator means.

The actuator arrangement is preferably a hydraulic actuator. The locking mechanism preferably includes two rods movable along their lengths and having respective sliders movable along a channel, the sliders being arranged to apply an outward locking force on walls of the channel when one rod is pushed towards the other.

The sliders may have cooperating inclined faces. The first and second members are preferably switch rails.

A railway point actuator arrangement according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in

which: Figure 1 is a plan view of the arrangement ; Figure 2 is a more detailed view of the locking mechanism ; and Figures 3 to 5 show alternative locking mechanisms.

With reference first to Figures 1 and 2, the actuator arrangement is located between a pair of fixed stock rails 1 and 2 and a pair of movable members in the form of switch rails 3 and 4 extending between the stock rails. The switch rails 3 and 4 are linked together by a linkage or stretcher bar 5 extending laterally between the rails.

The actuator arrangement includes two conventional hydraulic actuator cylinders 6 and 7 fixed at their bases 8 and 9 to a sleeper 10, or other fixed structure, and extending laterally outwardly in line with one another. The cylinders 6 and 7 are driven by hydraulic fluid from a conventional supply indicated generally by the numeral 11. The pistons 12 and 13 of the cylinders 6 and 7 each support a respective bracket 14 and 15 the outer face of which carries a respective insulating nylon brush 16 and 17. The bushes 16 and 17 bear against the inside faces 18 and 19 of respective switch rails 3 and 4 so that the switch rails can be pushed outwardly by actuation of the appropriate actuator. The actuators 6 and 7 only make an abutting contact with the switch rails 3 and 4, enabling them to be pushed out, and are not attached with the switch rails. The brackets 14 and 15 also support opposite ends of two locking mechanisms 20 and 21 of identical construction.

Each locking mechanism 20 and 21 includes a first laterally-extending rod 22 connected at one end with left-hand bracket 14 by a pair of nuts 23. The opposite end of

the rod 22 extends about halfway across the gap between the two brackets 14 and 15 and carries a slider or wedge 24 having an outer face 25 extending parallel with the rod 22 and an inner face 26 inclined to the axis at an angle of about 30°. The slider 24 may carry a roller 27, as shown in Figure 2. The locking mechanisms 20 and 21 also include a second laterally-extending rod 28 extending inwardly from the opposite bracket 15. This rod 28 has its outer, right-hand end secured with the bracket 15 by a pair of nuts 29 and its inner, left-hand end carries a second slider wedge 30 shaped to cooperate with the first slider 24. The second slider 30 has an outer face 31 extending parallel with the rod 28 and an inner face 32 inclined parallel with the face 26 of the first slider 24. The two rods 22 and 28 extend in a fixed channel 34 in the sleeper 10 having facing sides 35 against which slide the outer faces 25 and 31 of the two sliders 24 and 30.

When the left-hand switch rail 3 is to be moved over to its adjacent stock rail 1, a pump 40 in the supply unit 11 is operated to that fluid is supplied to the left-hand actuator 6, thereby causing its piston 12 to extend, pushing out its bracket 14 and hence pushing the switch rail 3 against the side of the stock rail 1. As it does this, it also pulls the rod 22 and its slider 24 in both locking mechanisms 20 and 21 to the left along the channels 34, along which they are free to slide. The stretcher bar 5 pulls the right-hand switch rail 4 to the left. The inside surface 19 of the right-hand switch rail 4 bears against the bush 17 on the bracket 15 and pushes in the piston 13 so that fluid in the cylinder 7 flows back to the supply unit 11. The two switch rails 3 and 4, therefore, both move over to the left as a pair. The pump 40 is then turned off and a pilot-operated check valve 41 locks the left-hand actuator 6 in this position by preventing flow of fluid out of the

actuator until the valve is opened. The locking mechanisms 20 and 21 prevent any movement of the switch rails 3 and 4 to the right as a result of leakage of fluid from the actuator 6. Movement of the switch rail 3 to the right will move the rod 22 slightly inwardly so that the inclined surface 26 of its slider 24 slides along the inclined surface 32 on the slider 30 of the other rod 28. This causes the two sliders 24 and 30 to exert an outward locking force on the surfaces 35 of the channel 34, so that the two sliders wedge or jam with one another. It should be noted that the right-hand rod 28 will not be displaced as a result of movement of the right-hand switch rail 4 to the right because the bracket 15 supporting the rod is not attached to the rail. Thus, the switch rails 3 and 4 will remain in the left-hand position until the supply unit 11 supplies fluid to move the piston 13 of the right-hand actuator 7 to the right. This moves the rod 28 and its slider 30 out of jamming engagement with the other slider 24.

The roller 27 of the slider 24 reduces friction between the two inclined surfaces 26 and 32 so that these can slide freely over one another. Alternatively, the inclined surfaces 26 and 32 could be provided with a low friction by other means, such as by a suitable coating. The outer surfaces 25 and 31 of the sliders 24 and 30 are given a higher coefficient of friction with the surfaces 35 of the channel 34, such as by roughening, so that they do not slide along the channel when jammed locked.

Various other forms of locking mechanism are possible that allow free movement when pulled back but lock when pushed. For example, as shown in Figure 3, the rods 50 and 51 support a respective slider in the form of a clutch plate 52 and 53 with facing surfaces 54 and 55 having profiled recesses 56 and 57 engaging an eccentric cam 58. The

cam 58 is rotatable about an axis transverse to the rods 50 and 51 and is shaped such that a pushing movement of one rod towards the other causes rotation of the cam in a sense tending to force the two clutch plates 52 and 53 outwardly against the walls 59 of the channel 60 in which they slide.

Figure 4 shows a locking mechanism having two rods 70 and 71 displaced laterally with respect to one another and having their ends interconnected by a pivoted linkage 72 extending at an angle to the rods. The rods 70 and 71 each have a high friction bearing surface 73 on their outer faces so that movement of the rods longitudinally towards one another causes them to be pushed laterally apart into locking contact with the walls 74 of the channel 75 in which they slide.

Figure 5 shows a locking mechanism similar to that of Figures 1 and 2 except that the sliders 124 and 130 have been modified each to have a hook portion 224 and 230 respectively at their ends, directed inwardly of the channel 134 towards one another. A roller 127 is located between opposed faces 126 and 132 of the sliders 124 and 130. It can be seen that, when either rod 122 or 128 is moved axially towards the other it will cause the roller 127 to roll along the surfaces 126 and 132 on the sliders 124 and 130, thereby applying a lateral force pushing them outwardly of the channel 134 and locking the rods in position. If, however, either rod 122 or 128 is moved away from the other, it will cause the roller 127 to locate between the two hook portions 224 and 230 so that the slider on the moved rod will act to pull the other slider, and hence its rod along the channel 134. This arrangement has the advantage that it will function without the need for a stretcher bar.

It will be appreciated that the invention is not confined to railway points systems but could be used in other applications where it is necessary to lock two members against movement. The actuator need not be hydraulic but could, for example, be electromechanical or pneumatic.