ACTUATOR SYSTEM FOR AEROSPACE CONTROLS AND FUNCTIONS

Abstract: The invention provides an actuator (12) having a piston (18) moveable within a cylinder (20), and a piston rod (22) extending from the piston and providing an actuator ram (14). The piston divides the cylinder into a cylindrical chamber (24) and an annular chamber (26), and a fluid direction control valve (34) controls the supply of fluid between these chambers and a fluid supply line (30) and a fluid return line (32). The actuator is arranged to have first and second modes of operation during extension of the piston rod, the actuator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected directly or indirectly to the cylindrical chamber. The actuator system also includes means (36, 38; 102, 104, 106) for automatically switching the actuator from one mode to the other mode.

Description: ACTUATOR SYSTEM FOR AEROSPACE CONTROLS AND FUNCTIONS This invention concerns actuator systems for aerospace controls and for other aerospace functions, for example for operating the control surfaces of an aircraft such as the ailerons, elevators, spoilers, rudder, and wing leading edge and trailing edge flaps and slats, or for controlling the airbrakes, arrester hook, flight refuelling probe, the undercarriage or pallets, doors and locks generally. Fluid pressure operated actuator systems for powering aircraft control surfaces and for other aerospace functions are well known and basically comprise a piston and cylinder arrangement in which a piston rod is extended for actuating the control surface and retracted for returning the control surface to its original condition. In particular, a known actuator system comprises an actuator having a piston moveable within a cylinder and a piston rod extending from the piston for actuating the aircraft control surface, the piston dividing the cylinder into a cylindrical chamber and an annular chamber. The system also comprises a fluid supply line, a fluid return line, and a fluid direction control valve for controlling the supply of fluid to the cylindrical and annular chambers respectively for extension and retraction of the piston rod. This known actuator system has two different modes of operation during actuator rod extension, which offer different maximum no-load rates of rod extension, and for the purposes of selecting and controlling the mode of operation the actuator system includes a number of control valves operable by the overall control system of the aircraft under pilot control. In one mode of operation, the fluid supply line is arranged to supply pressure to the cylindrical chamber and the annular chamber is arranged to exhaust to the fluid return line. In this mode of operation, the effective piston area is the full circular area of the piston exposed to the cylindrical chamber. In the other mode of operation, the fluid supply line is arranged to supply pressure to the cylindrical chamber, while the annular chamber is connected to the cylindrical chamber. In this mode of operation, the supply pressure is therefore supplied simultaneously both to the cylindrical chamber and to the annular chamber, and the effective piston area is the difference in area between the full circular area of the piston exposed in the cylindrical chamber and the annular area of the piston exposed in the annular chamber, ie it is the cross-sectional area of the piston rod. In the second mode of operation, the resultant net thrust is reduced, but so also are the flow requirements, since fluid is recycled from the annular chamber into the cylindrical chamber, and as a result a higher maximum no-load rate of extension can be achieved. When applied to the leading edge slats of an aircraft, the actuator system is normally required to extend the leading edge slats much more rapidly than the rate at which it is required to retract them, and rapid extension usually takes place at high angles of attack where the air loads tend to encourage extension. Since the air loads are assisting extension, the rapid rate of the second mode of operation may be employed in these conditions. However, at high aircraft speeds, extension of the leading edge slats often takes place at low angles of incidence and rapid deployment is undesirable. In these circumstances, high air loads tend to oppose extension of the leading edge and then the first mode of operation is preferable since a higher thrust is possible. This known actuator system possesses a number of advantages in terms of its versatility but, nonetheless, it incorporates a number of significant disadvantages in terms of the complexity of the control system required for determining and selecting the preferred mode of operation and for then controlling the actuator system to operate in the desired mode. Actuator systems for use in other applications are also known from GB-A-2 313 413, EP- A-0 629 781 and US-4 434 708. GB-A-2 313 413 and EP-A-0 629 781 both relate to hydraulic circuits for construction vehicles, such as hydraulic excavators, in which a regeneration device is provided for feeding fluid back from a return line extending from the actuator to a supply line extending to the actuator. In each case, the actuator is controlled by a direction changeover valve, and a separate recovery control valve is provided for operating the regeneration device in dependence upon the delivery pressure in the supply line. US-4 434 708 concerns a control valve for double acting piston and cylinder assemblies, for raising a load against the force of gravity and lowering the same, for example. The aim of this patent is to prevent cavitation on the expanding side of the piston and cylinder assembly when the capacity of the hydraulic pump in the system is insufficient. For this purpose, the control valve includes a regeneration check piston responsive on the one hand to the delivery pressure supplied by the hydraulic pump to the expanding side of the piston and cylinder assembly and on the other hand to fluid pressure in a chamber of the control valve connected between the retracting side of the piston and cylinder assembly and the return line. All of these latter actuator systems are of complex design, including separate regeneration control valves and arrangements, and furthermore are unsuited to the rigours of the aerospace industry. It is an aim of the present invention to provide an actuator system which overcomes these disadvantages of the known arrangements. Another aim of the present invention is to provide an actuator system having two modes of operation during actuator extension and having a reliable and simple method of converting between these two modes of operation. The invention, at least in its preferred form, further seeks to provide an actuator system having two modes of operation during actuator extension and an automatic switch over arrangement for converting from one mode of operation to another. According to one aspect of the present invention, there is provided an actuator system, comprising: an actuator having a piston moveable within a cylinder, and a piston rod extending from the piston and providing an actuator ram, the piston dividing the cylinder into a cylindrical chamber and an annular chamber, a fluid supply line, a fluid return line, a fluid direction control valve for controlling the supply of fluid to the cylindrical and annular chambers, respectively, for extension and retraction of the piston rod, the actuator being arranged to have first and second modes of operation during extension of the piston rod, the actuator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected directly or indirectly to the cylindrical chamber, and means for automatically switching the actuator from one mode to the other mode in response to a change in pressure in the annular chamber. According to another aspect of the present invention, there is provided an actuator system, comprising: an actuator having a piston moveable within a cylinder, and a piston rod extending from the piston and providing an actuator ram, the piston dividing the cylinder into a cylindrical chamber and an annular chamber, a fluid supply line, a fluid return line, a fluid direction control valve for controlling the supply of fluid to the cylindrical and annular chambers, respectively, for extension and retraction of the piston rod, the actuator being arranged to have first and second modes of operation during extension of the piston rod, the actuator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected directly or indirectly to the cylindrical chamber, a non return valve provided between the annular chamber and the cylindrical chamber and openable in response to a build up of pressure in the annular chamber to connect the same to the cylindrical chamber, and means for providing a restricted fluid flow between the annular chamber and the return line. The combination of the non return valve and the means for providing a restricted flow ensures that the actuator switches automatically from the first mode to the second mode of operation in response to a build up of pressure in the annular chamber. In a preferred form of the invention, a restrictor is provided in a fluid flow passage between the annular chamber and the return line to permit a restricted flow of fluid therebetween. It is an important feature of the invention that, with this arrangement, the actuator system will effectively revert automatically from the second mode of operation to the first mode of operation whenever the opposing load provided by the aircraft control surface increases during actuator extension to the point where the velocity of the actuator slows and the actuator approaches a stall situation, because at this point substantially all the fluid emerging from the annular chamber will leak via the restrictor to the return line and so the non return valve will close as the pressure in the annular chamber drops. As a result, the effective area of the piston becomes the full circular area and the thrust of the actuator may be several times higher than in the second mode of operation. By appropriate selection of the size of the restrictor, the actuator characteristics may be matched to the required aerodynamic rate and load requirements. Although the preferred form of means for providing a restricted fluid flow is a permanent constriction in a fluid flow passage leading from the annular chamber, it is alternatively possible to employ an adjustable valve or a constant flow device operable to provide the fluid flow restriction. The advantage of such an arrangement is that the restriction can be set to suit the system requirements. However, a possible disadvantage in instances where the constant flow device or valve have to function in other states than as a restrictor is that an additional control device may be necessary in order to achieve the desired mode of operation. The invention is described further, by way of example, with reference to the accompanying drawings in which: Figures 1 to 3 illustrate diagrammatically the operation of an actuator system for aircraft control surfaces according to the invention; and Figures 4 and 5 illustrate schematically a preferred embodiment of actuator system according to the invention. Referring initially to Figures 1 to 3, these show in schematic form an actuator system 10 for controlling an actuator 12 having an actuator ram 14, which in use is connected by way of a linkage (not shown) to an aircraft control surface such as an aileron, an elevator, the rudder, or a wing leading edge slat or trailing edge flap, for extending and retracting the same. More particularly, the actuator 12 comprises a piston and cylinder arrangement 16, having a piston 18 slideably received in a cylinder 20. A piston rod 22 extends from one surface of the piston 18 and emerges from the cylinder 20 to serve as the actuator ram 14. Consequently, the piston 18 divides the cylinder 20 into a cylindrical chamber 24 which is expandable to extend the actuator ram 14 and an annular chamber 26 which is expandable to retract the actuator ram 14. As shown in Figures 1 to 3, the actuator system 10 further comprises a fluid supply line 30 for supplying fluid to the actuator 12 at high pressure, and a fluid return line 32 for receiving fluid back from the actuator 12 at low pressure. The fluid supply and return lines 30, 32 may, for example, be connected to a fluid supply (not shown), eg a hydraulic supply, which may typically consist of a pump and a fluid reservoir. The fluid supply line 30 and the fluid return line 32 are both in communication with the actuator 12 by way of a fluid direction control valve 34, which is responsive to the aircraft control system for controlling the supply of fluid to and the exhaustion of fluid from the cylindrical chamber 24 and the annular chamber 26 of the actuator 12 for effecting extension and retraction of the actuator ram 14. In Figure 1, the actuator system 10 is shown with the fluid supply line 30 in communication with the cylindrical chamber 24 and with the annular chamber 26 in communication with the fluid return line 32 for extending the actuator ram 14. Retraction of the actuator ram 14 involves switching over the fluid direction control valve 34 to place the fluid supply line 30 in communication with the annular chamber 26 and the cylindrical chamber 24 in communication with the fluid return line 32. The actuator system 10 of Figures 1 to 3 also includes firstly a return line isolation valve 36 located in the return line 32, and secondly a non-return valve 38 situated between the fluid supply line 30 and the fluid return line 32. The non-return valve 38 is normally resiliently biased into a closed position, but is openable in response to an increase of pressure in the remrn line 32 upstream of the return line isolation valve 36 to communicate this portion 40 of the return line 32 with the fluid supply line 30. In the normal mode of extension shown in Figure 1 , the return line isolation valve 36 is open and the non-return valve 38 remains in its closed position. However, when the return line isolation valve 36 is closed during the extension mode of the actuator ram 14, as shown in Figure 2, a situation arises where a build-up of pressure occurs in the annular chamber 26 and hence in the line portion 40. In response to this build-up of pressure, the non-return valve 38 opens automatically to place the annular chamber 26 in communication with the cylindrical chamber 24. Once the annular chamber 26 has been placed in communication with the cylindrical chamber 24 in this way, a second mode of operation of extension of the actuator ram 14 occurs, since now fluid is being recycled from the annular chamber 26 into the cylindrical chamber 24. This allows either a much faster rate of extension of the actuator ram 14 for a given fluid flow rate in the fluid supply line 30 or a significantly reduced fluid consumption for a given extension rate for the piston 18. Consequently, by alternating between the normal mode of extension of the actuator ram 14, obtained by maintaining the return line isolation valve 36 open and represented in Figure 1, and the alternative mode of extension of the actuator ram 14, obtained by closure of the return line isolation line 36 and represented in Figure 2, the actuator system can be adapted both to the prevailing flight conditions and to the loads exerted on the aircraft control surface being operated by the actuator system. A further situation is represented in Figure 3, which enables the actuator system 10 to switch between the normal and alternative modes of extension of the actuator ram 14 automatically, as opposed to switching between these modes through opening and closing of the remrn line isolation valve 36 in response to signals from the aircraft control system. In Figure 3, the remrn line isolation valve 36 is set to a nearly closed position. As a result, the actuator system 10 will operate mainly in the alternative mode of extension described with reference to Figure 2, in which pressure build-up in the annular chamber 26 forces open the non-return valve 38 to re-circulate fluid from the annular chamber 26 to the cylindrical chamber 24. As already explained, this produces a high ram extension velocity suitable for low loads on the aircraft control surface being operated by the actuator ram 14. However, as soon as the actuator ram 14 encounters opposition to extension so that its velocity begins to fall, ie the load on the actuator ram 14 increases, then the fluid flow from the annular chamber 26 will diminish. As the ram 14 approaches a stall condition, then the fluid exhausted from the annular chamber 26 will approach the amount capable of leaking through the return line isolation valve 36 to the return line 32 and as a result the fluid pressure in the line portion 40 will drop and the non-return valve 38 will close. At this point, the actuator 12 has automatically switched from the alternative mode of extension in which the effective area of the piston 18 is the difference in areas between that of the circular face 42 presented to the cylindrical chamber 20 and the annular face 44 presented to the annular chamber 26, ie the area of the piston rod 22, to the normal mode of extension in which the effective piston area is the full circular area of the face 42 presented to the cylindrical chamber 20. Consequently, the available thrust of the actuator ram 14 is automatically increased to its full capacity. This is a significant advantage by comparison with the situation that would have arisen had the return line isolation valve 36 been fully closed, because in that case an hydraulic lock would probably have built up in the annular chamber 26 as the actuator ram 14 approached a stall condition and the thrust of the actuator ram 14 would have been further reduced. Once the load on the actuator ram 14 reduces again, the ram will start to accelerate as it extends. As the actoator ram 14 gathers speed, the pressure in the annular chamber 26 will increase, as fluid is forced through the return line isolation valve 36 at an increasing rate, while the pressure in the cylindrical chamber 24 will drop, until the non-return valve 38 starts to open to re-circulate fluid once more from the annular chamber 26 to the cylindrical chamber 24. In both cases, the switch over between one mode of extension for the actuator ram 14 and the other is gradually and smoothly achieved without abrupt transition, which would in any event be unacceptable in an aerospace application such as the present one. It will be understood that the remrn line isolation valve 36 may in practice be implemented by a permanent restrictor or by a flow control device such as a constant flow device operable in the automatic switching situation to provide a restricted flow, subject to appropriate connections of the fluid supply line 30 and fluid return line 32 through the fluid direction control valve 34 to permit the actoator 12 to operate solely in the normal mode of extension and of retraction when required. If a constant flow device is employed, its effective orifice size may be variable in order to maintain a constant leakage flow to the fluid return line 32. The advantage of this would be that at high ram extension speeds the size of the orifice is reduced in order to ensure that more oil is re-circulated to increase efficiency, while at lower ram extension speeds the size of the orifice is increased in order to ensure that the thrust delivered, above stall, is greater. Turning now to Figures 4 and 5, a preferred embodiment of actuator system according to the invention will be described. This actoator system 100 features some of the same elements as the actoator system 10 described with reference to Figures 1 to 3 and the same parts are designated by the same reference numerals. Only the differences will be described in detail. More particularly, the actoator system 100 features an actoator 12 connected by way of a fluid direction control valve 34 to a fluid supply line 30 and fluid return line 32 as before. Figure 4 shows the actoator 12 connected for the automatic switching mode of extension indicated above, and Figure 5 shows the actuator 12 connected for retraction of the actuator ram 14. Referring initially to Figure 5, in retraction of the actoator ram 14, the fluid direction control valve 34 connects the fluid supply line 30 to the annular chamber 26 of the actuator 12 by way of a non-return valve 102. The cylindrical chamber 24 of the actoator 12 is connected directly to the fluid return line 32 through the fluid direction control valve 34. Consequently, fluid is supplied under pressure to the annular chamber 26 and is exhausted from the cylindrical chamber 24 to the fluid return line 32 so that the actuator ram 14 is retracted. Turning now to Figure 4, in the automatic switching mode of extension of the actoator ram 14, the fluid direction control valve 34 connects the fluid supply line 30 directly with the cylindrical chamber 24 while the annular chamber 26 is connected firstly with the fluid supply line 30 by way of a non-return valve 104, which is normally biased into a closed position, and secondly to the fluid return line 32 by way of a restrictor 106, for example a viscosity compensating restrictor, and the fluid direction control valve 34. It will be apparent that the principle operation of the actoator 12 in the condition shown in Figure 4 is the same as that shown in and described with reference to Figure 3. The main differences inherent in the embodiment of Figures 4 and 5 are that in the latter: i) Firstly, the return port of the fluid direction control valve 34 and adjacent return line pipe work is not subjected to a pressure equivalent to the supply line pressure. ii) Secondly, the retraction rate of the actoator ram 14 is not limited by the restrictor since a second non-return valve 104 is provided as a bypass. Various practical means for implementing the invention have been described, including the use of a return line isolation valve set into a nearly closed position as a restricting means, and the use of a fixed restrictor providing a permanent constriction in a fluid flow passage from the annular chamber. It will be apparent that other restricting means may equally well be used. In particular, in the embodiment of Figures 4 and 5, the combination of two non-return valves and a fixed restrictor may be replaced by one non-return valve and a one-way restrictor, ie a device which allows a free flow of fluid in one direction while restricting the flow of fluid in the other direction. Other forms of restricting means which may also be employed include a constant flow device or a valve of alternative construction. The invention as described has the advantage that commercially available components may be built into standard or existing hydraulic fittings and pipework without the need for overall system re-design.

Claims: CLAIMS 1. An actoator system for use in an aircraft control or operating system, comprising: an actoator (12) having a piston (18) moveable within a cylinder (20), and a piston rod (22) extending from the piston and providing an actoator ram, the piston dividing the cylinder into a cylindrical chamber (24) and an annular chamber (26), a fluid supply line (30), a fluid return line (32), a fluid direction control valve (34) for controlling the supply of fluid to the cylindrical and annular chambers, respectively, for extension and retraction of the piston rod, the actoator being arranged to have first and second modes of operation during extension of the piston rod, the actuator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected to the cylindrical chamber, and characterised by means (36, 38; 104, 106) for automatically switching the actuator from one mode to the other mode in response to a change in pressure in the annular chamber. 2. A system according to claim 1 characterised in that the automatic switching means are fluid operated. 3. A system according to claim 1 or 2 characterised in that the automatic switching means are arranged to switch the actoator from the second mode to the first mode in response to a reduction in pressure in the annular chamber. 4. A system according to claim 1 , 2 or 3 characterised in that the automatic switching means comprise a non-return valve (38; 104) arranged to connect the annular chamber to the cylindrical chamber, which non-return valve (36; 106) is resihently biased towards a closed position, and a flow restrictor provided between the annular chamber and the return line. 5. An actuator system for use in an aircraft control or operating system, comprising: an actoator (12) having a piston (18) moveable within a cylinder (20), and a piston rod (22) extending from the piston and providing an actuator ram, the piston dividing the cylinder into a cylindrical chamber (24) and an annular chamber (26), a fluid supply line (30), a fluid return line (32), a fluid direction control valve (34) for controlling the supply of fluid to the cylindrical and annular chambers, respectively, for extension and retraction of the piston rod, the actoator being arranged to have first and second modes of operation during extension of the piston rod, the actoator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected to the cylindrical chamber, and characterised by a non return valve (38; 104) provided between the annular chamber and the cylindrical chamber and openable in response to a build up of pressure in the annular chamber to connect the same to the cylindrical chamber, and means (36; 106) for providing a restricted fluid flow between the annular chamber and the return line. 6. A system according to claim 5 characterised in that the means for providing a restricted fluid flow comprise a control valve operable (36) to provide a restricted fluid flow. 7. A system according to claim 5 characterised in that the means for providing a restricted fluid flow comprise a constant flow device operable to provide a restricted fluid flow. 8. A system according to claim 5 in which the means for providing a restricted fluid flow comprise a restrictor (106) such as constriction in a fluid passage connected or connectable between the annular chamber and return line. 9. A system according to claim 4 or 8 characterised in that the restrictor is a one- way restrictor. 10. An aircraft control or operating system incorporating an actoator system according to any preceding claim.

Inventors: UTTLEY ANDREW EDWARD, UTTLEY, ANDREW, EDWARD
Applicants: BRITISH AEROSPACE, UTTLEY ANDREW EDWARD, BRITISH AEROSPACE PLC, UTTLEY, ANDREW, EDWARD
Application year: 1999
Main classification: F15B11
IPC codes: B64C13, F15B11