CONTROL SYSTEM FOR A FLUID ACTUATED MOTOR

Abstract: A control system for a fluid actuated motor, such as that driving the prime mover of a winch, said system comprising a conduit for feeding fluid to the motor, a valve actuable to open and close the conduit, and means for actuating the valve to open or close the conduit when a predetermined condition, such as an upper or a lower limit of a load, is achieved through operation of the motor. The actuating means may comprise a second conduit for feeding fluid to the valve, and means for closing the second conduit for feeding fluid to the valve, and means for closing the second conduit when said predetermined condition is achieved; the closure of the second conduit results in actuation of the first valve to close the main conduit.

Description: This invention relates to a control system for a fluid actuated motor. Fluid actuated motors may be used to provide the prime movers of, for example, winches which are widely used for raising and lowering equipment. It is often very important to limit the action of a motor, and thus in the given example the action of the winch, so that the cable around the winch drum or the like does not pay out to its full extent thereby placing the entire weight of the equipment on the anchorage of the cable to the winch, or so that the cable does not overwind around the winch drum thereby causing the cable to leave its winding path on the drum. To solve the above problems, prior art EP-A-101 743 provides a winch driven by a motor fed with fluid from a main conduit. A valve, actuable to open and close the main conduit, is activated so as to close the valve when a predetermined travel of the winch is achieved. However, methods of controlling the limit load on the winch have not been entirely satisfactory and yet this is important in practice. According to the present invention there is provided a control system for a fluid actuated motor used to drive a winch, comprising a main conduit for feeding fluid to the motor, a first valve actuable to open and close the main conduit and valve actuating means, wherein said valve actuating means comprises a second conduit for feeding fluid to the valve, a cam movable with the winch and engagable with a cam follower operatively connected to a second valve for closing the second conduit when a predetermined condition is achieved, wherein closure of the second conduit results in actuation of the first valve to close the main conduit, characterised in that said valve actuating means also includes a pressure sensor which monitors the load on the winch and actuates a third valve to close the conduit on achievement of a predetermined load. Preferably, the pressure sensor comprises a first monitor which causes the said pressure sensor to close the third valve at winch loads above a first predetermined value and a second monitor which causes it to close the third valve at winch loads below a second predetermined value. Preferably, the pressure sensor includes a piston which is connected to the winch and movable within a cylinder so that pressure of fluid in the cylinder is increased or decreased in response to the load on the winch; this provides a safety system for deactivating the motor in the event of the cable, or the equipment being winched up or down, becoming snagged on an obstruction, and prevents continued tensioning or paying out of the cable. Preferably, a reactivating valve which is normally closed but is manually openable by a plunger, is connected to said second conduit in parallel with said second valve, wherein opening said reactivating valve causes opening of said first valve. Preferably, a pneumatic horn and a horn actuating valve are connected to said second conduit in parallel with said actuating means, wherein said actuating valve is closed when said second valve or said reactivating valve is open, and wherein said actuating valve is open causing the pneumatic horn to sound when said second valve and said reactivating valve are closed. The fluid may be for example air or hydraulic fluid. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a flow diagram of a control system for a fluid actuated motor, in accordance with the invention; Fig. 2 is a side view of a gearbox and one embodiment of an actuator for a winch driven by the motor of Fig. 1; Figs. 3a and 3b are views on A-A of two embodiments of the actuator of Fig. 2; Fig. 4 is an alternative embodiment of a control system for a fluid actuated motor, allied to the system of Fig. 1, having an actuator in the form of a limit load valve assembly for cutting off the motor on reduction of load on the winch; Fig. 5 is a flow diagram of the system of Fig. 1 incorporating the limit load valve assembly of Fig. 4; Fig. 6 is a diagrammatic representation of an alternative embodiment of the limit load valve assembly of the system of Figs. 4 and 5 for cutting off the motor on reduction or increase of load on the winch; Fig. 7 is a diagrammatic representation of an alternative embodiment of the limit load valve assembly of Figs. 4, 5 and 6; and, Fig. 8 is a perspective view of the apparatus of the system of Fig. 7. Referring to the drawings, and in particular Figs. 1 to 3a, the system of this embodiment of the invention has a pneumatically-driven motor 2 which is fed with pressurised air through an air line 4. A valve 6 is spring-biassed into a closed position in which it cuts off flow through the air line 4. A branch air line 8 in the form of a pilot line extends from a T-piece in the main air line 4 through a control box 10 to the valve 6, the air pressure in the branch line 8 holding the valve 6 open against its bias to allow flow of air to the motor 2. A quick-exhaust valve 12 is provided in the branch line 8 for bleeding off air instantaneously in the event of closure of the branch line 8, and a pneumatic horn 14 and actuating valve 16 are built into a pilot line 18 which short-circuits the branch line 8 in parallel with the control box 10. The valve 16 closes off flow to the horn when the air pressure in the branch lines 8a and 8b are equal, and opens flow when the pressure in the line 8a exceeds that in the line 8b. The control box 10 houses two valves 20, 22 each of which has an outwardly-biassed piston 24 (Fig. 3) which bears against a peripheral surface of a respective rotatable actuator plate 26, 28. Each plate 26, 28 has a recess 29 into which the piston 24 can move, and on such movement the valve 20, 22 switches from an open to a closed mode, cutting off flow of air through the control box 10 by way of the branch line 8. A further pilot line 30 extends across the branch lines 8a and 8b through a valve 32 which is normally closed but which is manually openable by means of a plunger 34. The actuator plates 26, 28 are mounted on an output shaft 36 of a 1960:1 gearbox 38 (Fig. 2) whose input shaft 40 is driven from the main winch gearbox connected to the motor 2. The plates 26, 28 are held on the shaft 36 by a lock nut 42, and are calibrated at 44 to relate to the movement of the winch. In use, pressurised air is pumped along the main air line 4 through the open valve 6 to the motor 2 which thus drives the winch. The air also passes along the branch line 8 through the control box 10 to the valve 6, maintaining it in its open position. As the winch rotates, its mechanical drive through the gearbox actuates the plates 26, 28 through the shaft 40, gearbox 38 and shaft 36, causing the plates to rotate very slowly. When the winch is at the limit of its safe travel in one direction the plates 26, 28 have rotated to an extent where the piston 24 of the valve 20 enters the corresponding recess 29 in the plate 26, closing the valve 20 and cutting off air flow through the branch line 8. The air in the line 8b then bleeds off through the quick-exhaust valve 12 and the pressure in the line 8b drops to atmospheric. As a result there is insufficient air pressure in the line 8b to hold the valve 6 open against its spring bias, so the valve 6 closes and cuts off air flow to the motor 2. The winch therefore stops at its predetermined limit. Similarly at the other end of the winch's desired travel the valve 22 enters the corresponding recess 29 in the other actuator plate 28, with the same result. When air pressure in the line 8b drops, the pressure from the line 8a opens the valve 16 and actuates the pneumatic horn 14 which thus gives a continuous audible warning that the winch's limit has been reached. To reactuate the winch, the plunger 34 on the valve 32 is depressed, thus opening the valve and providing air flow from the line 8a to the line 8b through the line 30, closing the valve 16 and silencing the horn 14. This opens the valve 6 against its spring bias and reactuates the motor 2, taking the piston 24 out of the recess 29 as the plates 26, 28 rotate, and re-opening the valve 20, 22. The plunger can then be released. As an extra safety feature the motor or gearbox may be provided with means which automatically reverses the direction of the winch each time cut-off occurs, with a manual switch for overriding it. Referring now to Fig 3b, there is shown an alternative embodiment of the actuator plate 26, of Fig. 3a, wherein the recesses 29 are replaced with cam projections 31 that may extend to 25% of the plate circumference. The valve 45 of Fig. 3b operates in reverse of those of Fig. 3a and thus on movement of cam follower 47 over the cam projection 31 and a consequent insertion of the piston 44 into the valve body, the valve 45 switches from an open to a closed position. Referring now to Fig. 4, the winch cable runs over a sheave 46 which is pivotally mounted on a support 48 through an arm 50. A shaft 52 is pivotally connected to the arm 50 and carries limit load valve assembly 48 including a piston 54 at its lower end. The piston 54 is located in a cylinder 56 and hydraulic fluid 58 is pressurised by the piston 54. An aperture in the cylinder wall communicates with a valve 60 which is disposed in the fluid circuit of Fig. 1 in series with the valves 20, 22. The valve 60 is held open by the pressure of the fluid 58 and closes when the pressure drops. Normally the valve 60 is open in use as the weight of a load being winched pulls the sheave 46 downwards, pressurising the fluid 58, but if the load becomes snagged on an obstruction, or reaches a support at the end of its travel, its weight is released from the sheave 46 and the pressure of the fluid 58 drops, closing the valve 60 and thus stopping the winch motor 2 as described in relation to Fig. 1. Referring now to Figs 5 and 6, in an alternative embodiment to that of Fig. 4, the single valve 60 of the limit load valve assembly 48 of Fig. 5 is replaced by a dual-valve system comprising a normally-closed low-pressure valve 61 and a normally-open high-pressure valve 62 fitted to branch line 8b and in series with the control box 10. The valve 61 may be selected to open at a load in excess of 400 lbs, while the valve 62 may be selected to close at a load in excess of 4000 lbs. Both valves are adjustable, the switching mechanisms 67, 68, being shown in detail in Fig. 7. In Figs 7 and 8, the limit load valve assembly 48 is on a branch line 63 which runs in parallel to the branch line 8; the hydraulic fluid 58 of the assembly 48 is provided with a top-up reservoir 64 which is supplied via a one-way valve 65, and an alternative pressure source 66 to give override if selected. During normal operative procedure, both valves 61,62 are open as the weight of the load being winched pulls the sheave downwards, pressurising the fluid 58. However, if the cable or the load being winched snags when winching in, the increased tension on the cable tends to pull the sheave downwards, increasing the hydraulic pressure in cylinder 56 and closing the high pressure valve 62, thus cutting off air flow to the winch motor 2. Similarly, if the load drops below a predetermined level, as described in relation to Fig. 4, the low pressure valve 61 closes, also shutting down the winch motor. Modifications and improvements may be made without departing from the scope of the invention.

Claims: A control system for a fluid actuated motor (2) used to drive a winch, comprising a main conduit (4) for feeding fluid to the motor (2), a first valve (6) actuable to open and close the main conduit (4) and valve actuating means (10,48), wherein said valve actuating means comprises a second conduit (8,63) for feeding fluid to the valve (6), a cam (31,29) movable with the winch and engagable with a cam follower (47,24) operatively connected to a second valve (20,22,45) for closing the second conduit when a predetermined condition is achieved, wherein closure of the second conduit (8,63) results in actuation of the first valve (6) to close the main conduit (4), characterised in that said valve actuating means (48) also includes a pressure sensor which monitors the load on the winch and actuates a third valve (60,61,62) to close the second conduit (8,63) on achievement of a predetermined load. A control system as claimed in Claim 1, wherein the pressure sensor comprises a first monitor which causes the said pressure sensor to close the third valve (60,61,62) at winch loads above a first predetermined value and a second monitor which causes it to close the third valve at winch loads below a second predetermined value. A control system as claimed in Claim 1 or 2, wherein the pressure sensor includes a piston (54) which is connected to the winch and movable within a cylinder (56) so that pressure of fluid (58) in the cylinder is increased or decreased in response to the load on the winch. A control system as claimed in any one of the preceding Claims, wherein a reactivating valve (32) which is normally closed but is manually openable by a plunger (34), is connected to said second conduit (8,63) in parallel with said second valve, (20,22,45), wherein opening said reactivating valve causes opening of said first valves (6). A control system as claimed in any one of the preceding Claims, wherein a pneumatic horn (14) and a horn actuating valve (16) are connected to said second conduit (8,63) in parallel with said actuating means, wherein said actuating valve (16) is closed when said second valve (20,22,45) or said reactivating valve (32) is open, and wherein said actuating valve is open causing the pneumatic horn to sound when said second valve and said reactivating valve are closed.

Inventors: ROGERSON, JAMES
Applicants: MONYANA ENGINEERING SERVICES
Application year: 1987
Main classification: B66D1
IPC codes: B66D1