Hydraulic actuator system

Abstract: A hydraulic actuator system, for use in an aircraft, and in which the servo fluid supply to the system is used to provide for the operation and cooling of the system. The system comprises: - a hydraulically operated piston mechanism including at least one hydraulically operated piston means (2); - a servo fluid input to the system (8, 9), which is connected in a ring main to a first side of the hydraulically operated piston means; - a servo fluid output from the system (10-13), which is connected in a ring main to a second side of the hydraulically operated piston means; - a variable restrictor arrangement (14, 15) which provides an interface between the servo fluid input ring main and the servo fluid output ring main; and - a restrictor arrangement (18, 19) positioned in the servo fluid output side of the system. The position of the piston of the hydraulic piston means and the adjustment thereof, are controlled by the restriction applied on the system by the variable restrictor arrangement (14, 15).

Description: This invention relates to a hydraulic actuator systems, and in particular, to hydraulic actuator systems which are adapted for use in hostile environments, such as those experienced with aircraft. GB-A-1152228 discloses a hydraulic actuator system which is suitable for use in conjunction with aircraft, incorporating an actuator system including a plurality of hydraulically operated piston devices each of which piston devices having a piston which divides the piston device into a first side and a second side. There is a servo fluid input ring-main line connecting the second sides of the piston devices. An input and output supply fluid to respective ring-mains. the flow of hydraulic fluid through the system serves both to actuate and cool the system. However, the lack of control over the fluid flow through the system causes large problems with designing an actuator system having the desired minimum cooling flow under all operating/flight conditions throughout the aircraft. The present invention is concerned with providing an actuator system, having a readily controllable flow of fluid through the operating and cooling systems, and thereby alleviating or at least reducing the above mentioned problem. Accordingly, the present invention consists of a hydraulic actuator system in which the servo fluid supply to the system is used to provide for the operation and cooling of the system, comprising at least one hydraulically operated piston device having a differential area piston that divides the piston device into a first side and a second side, the first side having a smaller effective piston area than the second side; a servo fluid input ring main line connected to the first side and a servo fluid output ring main line connected to the second side; a servo fluid input connected to the input ring main line; a servo fluid output connected to the output ring main line; characterised in that a restrictor arrangement is positioned in the servo fluid output, and a variable restrictor arrangement is connected between the servo fluid input ring main line and the servo fluid output ring main line, said variable restrictor arrangement being adapted to provide in a first mode of operation a maximum throttling thereby allowing a predetermined amount of servo fluid flow throughput, and in a second mode of operation a significantly increased servo fluid flow throughput, and both said restrictor arrangements interacting to provide the actuator system in both modes of operation with a desired throughflow of fluid thereby creating a pressure differential between the servo fluid input ring main line and the servo fluid output ring main line forcing the pistons to the retracted and extended positions respectively. With this arrangement of the system, the rate of flow of hydraulic fluid through the system is controlled by the relative configuration of the restrictor arrangement and the variable restrictor arrangement. In practice the configuration of the restrictor arrangement relative to the variable restrictor arrangement is dependent on the amount of movement available in the system. It can be easily appreciated from this statement of invention that an actuator system made in accordance with the present invention, uses the same flow system to control the operation, and the cooling of the actuator system. Further, the actuator system may be adjusted between a fully extended position and a fully retracted position by simply adjusting the restriction/throttling placed on the system by the variable restrictor arrangement. Preferably, at least one of the hydraulically operated piston means provided includes a master/controlling hydraulically operated piston means. Each of the hydraulically operated piston means may comprise a simple landed piston in a chamber, the position of which piston in the chamber is adjusted by a pressure differential acting across the piston, i.e. a pressure differential between the first side and the second side of the hydraulically operated piston means. Preferably, the variable restrictor arrangement is incorporated within the master hydraulically operated piston means. Preferably, the restrictor arrangement is a fixed restrictive effect restrictor arrangement. However, alternatively the restrictor may include a variable restrictor. The restrictor arrangement may be positioned anywhere in the output side of the system, however preferably is at the output from the system. Preferably, the actuator system further includes a means to vary the fluid output flow rate from the actuator system. In this way the output fluid flow rate from the system, at both of its operational positions, is easily controllable. Preferably, the means to vary the fluid output flow rate from the actuator system is incorporated into the restrictor means. Therefore, the restrictor arrangement preferably comprises a dual line output arrangement, each of which includes a fixed restrictor, and one of which is closed off when the actuator system is fully extended. Most preferably, this is achieved by one of the, or the, lands in the master hydraulically operated piston means as the piston moves to the fully extended position. The variable restrictor arrangement, preferably, comprises a solenoid valve and restrictor arrangement. The variable restrictor arrangement may be constructed so that the actuator system may be set to any of two or more positions. An actuator system of this kind may be used in any number of situations, and may be called upon to have a small or large degree of piston travel, and may be used so as to enable very accurate control of the piston travel. The present invention may be used in a large number of environments, and is particularly suited to use in environments where cooling and heat management need to be considered, for example, on rocket turbine or jet powered craft such as aircraft, and spacecraft. This type of actuator system is particularly suited to use in circumstances where the system is subjected to very harsh and hostile conditions. For example, conditions under which the system itself may be subjected to temperatures in excess of 200°C. This is typical of the conditions a variable air flow nozzle system for a modern jet engined aircraft would be subjected too, and the exact conditions this actuator system has been designed for. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of an actuator system made in accordance with the present invention. Now referring to the drawings, an hydraulic actuator system 1 made in accordance with the present invention includes: eleven hydraulic piston means 2, each of which has a piston 3 that divides the piston means into a first stage 4 and a second stage 5; a master hydraulic piston means 6 which has a double landed piston 7 which divides the master hydraulic piston means 6 into three stages, the first stage 21 and second stage 22 of which correspond to the first and second stages of the hydraulic piston means 2 and the second stage 22 and third stage 23 of which are interconnected by an annular means 24; a fluid input line 8 to the master hydraulic piston means 6; a fluid input ring main line 9 which connects the first stages 4, 21 of all the hydraulic piston means 2 and the master hydraulic piston means 6 in series; a fluid output line 10, having two branch output lines 11, 12 from the master hydraulic piston means 6; a fluid output ring main line 13 which interconnects the second stages 5, 22 of all the hydraulic piston means 2 and the master hydraulic piston means 6 in series; a cooling flow restrictor 14, and a solenoid valve 15 positioned in respective branch lines 16, 17 and which effectively separates the fluid input ring main line 9 and the fluid output ring main line 13; and two restrictors 18, 19 placed one in each of the two branch output lines 11, 12 and of differing sizes. This particular system is designed and constructed to have two positions of operation retracted and extended. Figure 1 of the drawings illustrates the system in a fully extended position, and, also, shows the relative positions of the retracted and extended positions for the actuator system 1. In one of the possible uses envisaged for this actuator system, i.e. in conjunctions with the nozzle of a jet engine, for fine control thereof, the total distance of travel of the piston between the extended and retracted positions may be as little as 1 cm. Therefore, it can be easily appreciated that such a system is very accurate in the control which it provides. In this particular usage the system will be regularly subjected to operating temperatures in excess of 200°C. Under which conditions the fluid temperatures within the system may rise above 200°C, hence a cooling system is required. An actuator in accordance with the present invention provides the necessary cooling system with efficient use of components and space. The two groups of restrictors, i.e. solenoid valve 15 with cooling flow restrictor 14, and the two restrictor 18, 19 are designed, and sized so that they fully interact with each other to provide the system with the desired throughput of fluid in both the fully retracted and fully extended positions of the system. Although, it may not be possible, due to the particular system design criteria, to provide the system with identical fluid throughputs for both the retracted and extended positions, these throughputs as far as is possible are substantially identical. In the fully retracted position, each of the pistons 3 of the hydraulic piston means and the piston 7 of the master hydraulic piston means abuts against a stop 20 provided in the respective piston means. In this position the solenoid valve 15 is closed and the cooling flow restrictor 14 provides maximum throttling across the input ring main line 9 and output ring main line 13 interface. Thereby the pressure differential across the input to output of the system is at its greatest and the pistons 3 and 7 are forced to contact the stops 20. Further, in this position both of the branch output lines 11, 12 are open to the third stage 23 of the master hydraulic piston means and output flow occurs via both of these lines. Now, when the actuator system is to be moved from the retracted position to the extended position, the solenoid valve 15 is activated to open, and thereby, the pressure drop/differential between the input ring main line 9 and the output ring main line 13 is reduced to a minimum. Effectively, this causes the pistons of the hydraulic piston means 2 and master hydraulic piston means 6 to move in direction A and away from the stops 20. Further, this significantly increases the fluid flow throughput of the actuator system, which means in order to attain an adequate balance this has to be brought down to an acceptable level. Once, the hydraulic piston means 2 and master hydraulic piston means 6 of the system have reached the respective positions, as shown in Figure 1, in which one of the lands 25 of the double landed piston 7 closes off the output branch line 11. This in turn, closes down the effective flow area for output flow of fluid from the system and with the restrictor 18 in line 12 being correctly sized reduces the fluid flow throughput of the system to the desired level. Thereby, the system in accordance with the present invention in addition to providing an accurate control means also provides effective cooling for a system which may be exposed to very hot and hostile environments, e.g. hot gases in a turbulent gas stream, i.e. the fuel nozzle on a jet aircraft. In one particular example of an actuator system in accordance with the present invention the following characteristics were typical for the system: Solenoid/Cooling flow Flow number restrictor 18 (opened in both extended/retracted mode) Flow number restrictor 19 (closed off in extended mode) Finally, in the above example the actuator system has been illustrated with the solenoid 15, cooling flow restrictor 14, and, the two restrictors 18, 19, as separate components. For the sake of space and weight, which are of prime importance in certain applications, it is possible, and in certain cases imperative that the solenoid 15, cooling flow restrictor 14 and the two restrictors 18, 19 are incorporated in the master hydraulic piston means 6.

Claims: A hydraulic actuator system (1) in which the servo fluid supply to the system is used to provide for the operation and cooling of the system, comprising at least one hydraulically operated piston device (2,6) having a differential area piston (3,7) that divides the piston device into a first side (4,21) and a second side (5,22), the first side having a smaller effective piston area than the second side; a servo fluid input ring main line (9) connected to the first side and a servo fluid output ring main line (13) connected to the second side; a servo fluid input (8) connected to the input ring main line; a servo fluid output (10) connected to the output ring main line; characterised in that a restrictor arrangement (18,19) is positioned in the servo fluid output (10), and a variable restrictor arrangement (14,15) is connected between the servo fluid input ring main line and the servo fluid output ring main line, said variable restrictor arrangement (14,15) being adapted to provide in a first mode of operation a maximum throttling thereby allowing a predetermined amount of servo fluid flow throughput, and in a second mode of operation a significantly increased servo fluid flow throughput, and both said restrictor arrangements (14,15,18,19) interacting to provide the actuator system (1) in both modes of operation with a desired throughflow of fluid thereby creating a pressure differential between the servo fluid input ring main line and the servo (9) fluid output ring main line (13) forcing the pistons (3,7) to the retracted and extended positions, respectively. A system as claimed in claim 1, wherein fluid flow rate means (11,12,25) are provided to vary the fluid output flow rate from the system, said means comprising a dual line output arrangement (11,12) each including a fixed restrictor (18, 19), a first line (11) of which arrangement is closed when the actuator is fully extended. A system as claimed in claim 2, comprising a plurality of piston devices (2,6) wherein the fluid flow rate means (11,12,25) are incorporated into one piston device which forms a master piston device (6). A system as claimed in claim 3, wherein the master piston device comprises a double landed piston (7), one of the lands (25) of which closes off the first line (11) when the master piston device (6) is fully extended. A system as claimed in any preceding claim wherein the variable restrictor arrangement (14,15) has a fixed restrictive effect. A system as claimed in claim 5 the variable restrictor arrangement (14,15) comprises a fixed restrictive effect restrictor (14) and a bypass valve (15) arranged in parallel. A system as claimed in claim 1 or claim 2 comprising a plurality of piston devices (2,6).

Inventors: PICKARD GERALD WILLIAM, PICKARD, GERALD WILLIAM
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1989
Main classification: F15B21
IPC codes: F15B21