GB2408725A

GB2408725A - Thrust reverser actuation system

Info

Publication number: GB2408725A
Application number: GB0327868A
Authority: GB
Inventors: Terry Jones
Original assignee: Goodrich Actuation Systems Ltd
Current assignee: Goodrich Actuation Systems Ltd
Priority date: 2003-12-02
Filing date: 2003-12-02
Publication date: 2005-06-08
Also published as: GB0327868D0

Abstract

An actuation system for a thrust reverser cowl 11a comprising at least two linear actuators at least one of which is an hydraulic actuator 12a and at least one of which is a mechanical actuator 14a being driven from a mechanical output of said at least one hydraulic actuator 12a. Two hydraulic actuators 12a, 13a may be provided, the mechanical actuator 14a being driven by the mechanical output of both hydraulic actuators 12a, 13a, all three actuators 12a, 13a, 14a being synchronised. The actuation system may actuate a plurality of cowls 11a, 11b in a synchronised manner. The mechanical actuator 14a may be driven by the mechanical output of the hydraulic actuator 12a via a flexible drive shaft and a gearbox 15a. Each actuator 12a, 13a, 14a may comprise a screw mechanism driven by a piston.

Description

THRUST REVERSER ACTUATION SYSTEM

This invention relates to a thrust reverser actuation system for a gas turbine engine, particularly but not exclusively an aircraft engine.

A number of different forms of gas turbine engine thrust reverser are known, and share the common concept of two elements which are deployed from a rest position to an actuated position, to reverse the thrust produced by the gas turbine engine, usually for braking purposes. When thrust reversal is no longer required the deployed elements are retracted back to their rest position. The movable elements can take inter alla the form of hinged doors, shells, vanes and cowls, and for convenience the thrust reverser elements will be referred to herein as cowls. It is to be understood however that the invention is applicable to a wide range of thrust reverser elements.

The thrust reverser cowls are deployed and retracted by actuation systems which may be electrically or hydraulically operated, and the present invention is concerned with hydraulically operated thrust reverser actuation systems.

In a known reverser system each cowl of the thrust reverser is deployed or retracted by simultaneous operation of a plurality of hydraulic actuators.

Each hydraulic actuator includes a piston and cylinder arrangement, hydraulic fluid under pressure being admitted to the cylinder to cause movement of the associated piston. Often the hydraulic actuators are double acting in that they can be extended and retracted by appropriate admission of hydraulic pressure to the same cylinder. - 2-

Conventionally the plurality of hydraulic actuators of each cowl are mechanically linked to ensure that they operate in synchronism, and so do not apply twisting or other unbalanced loads to their cowl during operation.

Usually each hydraulic actuator includes a screw mechanism whereby linear movement of the piston of the actuator is converted by the screw mechanism into rotational movement of an output spindle of the actuator, the output spindles of the actuators of each cowl being interconnected by a common drive shaft (synchronising shaft) ensuring that the actuators move in synchronism with one another.

One or more hydraulic pumps provide the pressurised hydraulic fluid for application to the actuators of each cowl. Conventionally the actuators are operated at around 2O,OOO to 21,000 kPa (around 3,000 psi). With a view to saving weight in the thrust reverser system as a whole it has been proposed to increase the operating pressure of the actuators to around 34,000 to 35,000 kPa (around 5,000 psi) as it is believed that this will allow the use of lower capacity, and therefore smaller hydraulic actuators associated with each cowl, and by virtue of the reduction in pressurised fluid volume which is necessary in order to operate smaller actuators, it is believed that smaller pumps can be used, leading to a significant reduction in the overall weight of the thrust reverser actuation system.

However, a problem has been encountered in implementing such weight savings. The provision, within each hydraulic actuator, of a screw mechanism operated by the piston, to provide a rotary output for synchronization purposes, limits the physical size reduction which can be achieved in the actuators. In other words, there is a minimum actuator diameter, and therefore piston and cylinder diameter, which can be achieved given the need to incorporate the screw mechanism. It is found that because of their size, the hydraulic fluid volume needed to supply the conventional number of actuators (two or three per cowl) is not significantly reduced and so does not provide the pump weight savings which are theoretically possible.

Furthermore, because the actuators, operating at 34,000 - 35,000 kPa are larger than they need to be, they are heavier than they theoretically need to be and the force generated by the actuators is in excess of that which is required. The system must be able to withstand a "full load lock" that is to say must be able to accommodate, without damage, the full force available from the actuators being applied against a locked and immovable cowl. In order to achieve this, the actuator output rods, the mounting points of the actuators on the cowl, and in some instances the structure of the cowl itself and its connection to the engine, must be strengthened and thus the system is made stronger and heavier than would otherwise be necessary.

It is an object of the present invention to provide a thrust reverser actuation system in which the aforementioned disadvantages are obviated or minimised.

In accordance with the present invention there is provided an actuation system for a thrust reverser cowl comprising at least two linear actuators at least one of which is an hydraulic actuator and at least one of which is a mechanical actuator driven from a mechanical output of said at least one hydraulic actuator. - 4-

Preferably where each cowl has two actuators one of which is mechanical and the other of which is hydraulic then a mechanical drive connection is provided between the actuators of one cowl of the engine and the actuators of a second cowl of the same engine.

Conveniently, where in association with a single cowl two hydraulic actuators drive a single mechanical actuator, the mechanical actuator is disposed, in relation to the cowl that is driven thereby, between the two hydraulic actuators.

Preferably a mechanical drive connection interconnects the mechanical actuator and mechanical outputs of both of the associated hydraulic actuators whereby the three actuators of the cowl are synchronized.

Preferably said mechanical drive connections incorporate flexible drive shafts.

Desirably the actuators of each cowl of an engine are synchronized by linking synchronizing shafts so that the cowls operate in unison.

The use of synchronizing mechanical connections between cowl actuation systems in addition to providing operational synchronism also permits one or more hydraulic actuators of one cowl to drive a mechanical actuator of a second cowl of the engine in the event of failure of the or one of the hydraulic actuators of the first cowl. - 5 -

It will be understood that a thrust reverser actuation system in accordance with the invention can achieve weight savings consequent upon increasing operating pressure by virtue of the replacement of one or more hydraulic actuators by a mechanical actuator which inherently will be of lower weight.

Moreover, even though the hydraulic actuators may not be reduced in size to their theoretical minimum, the pump needs to provide hydraulic fluid for a lesser number of hydraulic actuators, and thus can be of a smaller size commensurate with the lower volume needed to operate the actuators.

The accompanying drawing is a diagrammatic representation of a hydromechanical thrust reverser actuator system in accordance with one example of the present invention.

The drawing illustrates left and right cowls 1 la, 11_ which together constitute the thrust reverser of an aircraft gas turbine engine. The cowls are hinged, in known manner, to the body of the gas turbine engine, and are intended to be moved in unison with one another between rest and deployed positions by means of an hydraulic actuation system, and the thrust reverser assembly including the cowls 11_, 11b and the actuation system is equipped with primary, secondary, and tertiary locking systems operated in known manner. The safety locking systems associated with the actuators and the cowls form no part of the present invention.

The actuation systems of the cowls 11_, 1 lb are identical, and consist of first and second hydraulic, linear actuators 12_, 12_ and 13_, 13_ respectively, together with a mechanical, linear actuator 14_, 14_. Each of the hydraulic linear actuators 12, 13 is conventional, comprising a piston and cylinder - 6- arrangement the piston of which is capable of being driven in an extend or a retract direction by appropriate admission of hydraulic fluid under pressure to the cylinder. Each actuator 12, 13 includes a screw mechanism driven by movement of the respective piston to provide a mechanical, rotational output at a synchronizing spindle adjacent to one end of the actuator.

Each mechanical actuator 14a, 14_ is shown extremely diagrammatically in the drawing, and usually will consist of a ball-screw mechanism the rotatable input shaft of which is axially fixed, and the non-rotatable nut of which moves axially as a result of rotation of the shaft relative thereto and is connected to the respective reverser cowl in use. It will be recognised however that it would be possible to produce a mechanical linear actuator in which the shaft is the axially movable, non-rotatable output member and the nut is rotatable, but held against axial movement.

The rotatable input shaft of each screw actuator 14a, 14_ is driven through a respective gearbox 15_, 15_ which may simply be a bevel gear train which turns the axis of rotation through 90 .

Drive for the mechanical actuators 14a, 14_ is derived from the synchronising output spindles of the respective hydraulic actuators 12, 13, the output spindles of the actuators 12, 13 being connected to the gearbox 15 of the respective mechanical actuator 14 through respective drive shafts (not shown). The drive shafts interconnecting the output spindles of the actuators 12, 13 with respective input shafts of the associated gearbox 15 can be of the same form as conventional synchronizing shafts, consisting of a torsionally rigid, but longitudinally flexible shaft running within a protective outer sleeve 7- in the manner of a "Bowden Cable". Furthermore, the shafts from the two hydraulic actuators are interconnected through the respective gearbox 15 so that the shafts not only drive the respective mechanical actuator, but also act to synchronise the associated hydraulic actuators with one another and with their respective mechanical actuator. If desired the shafts of the actuation system of the cowl Ha can be linked to the synchronising/drive shafts of the actuation system of the cowl 11_ so that the cowls are operated in synchronism and the hydraulic actuators of one cowl can assist driving the other cowl in the event of failure of one or more of the hydraulic actuators of that cowl.

Figure 1 also illustrates the hydraulic supply and return lines through which hydraulic fluid under pressure is supplied to the actuators 12, 13. As shown a known aircraft thrust reverser interface 16 receives control signals which may be electrical, hydraulic or both, indicating that the thrust reversers are to be deployed. The interface 16, and the main engine electronic control system 17 (FADEC) interchange information in known manner to determine whether or not it is safe to deploy the thrust reversers, and to release the safety locking systems of the thrust reversers in a predetermined sequence.

Hydraulic fluid under pressure is supplied from a pump (not shown) through the interface 16 to an isolator control valve 18. The isolator control valve 18 receives control signals from the FADEC 17, and as shown the FADEC 17 may be a two-channel device in which case the isolation control valve 18 will receive control signals from both FADEC channels. Assuming that all safety criteria have been met then pressurised fluid will be supplied from the interface 16 to the valve 18, and through the valve 18 to a distribution control valve 19. The distribution control valve 19 determines the cylinder parts for - 8- admission of pressurised fluid to the cylinders of the actuators 12, 13 to control whether or not the actuators 12, 13 are operated in a deploy mode or a retract mode. It can be seen that the valve 19 also receives control signals from the FADEC in this regard. In the event that the FADEC instructs that no fluid is to be supplied to the distribution control valve 19 then isolation control valve 18 closes to isolate valve 19 from pressurised fluid in the main supply line 21.

When the valve 19 is operative to supply fluid to extend the actuators 12, 13 the supply from the line 21 is directed into a valve output line 23 which is divided into branch lines 24_, 24_ supplying the actuators of the cowls 11, 11b respectively. It can be seen that the branch lines 24, 24_ are divided respectively into actuator lines 25a, 26_ supplying the actuators 12_, 13_ respectively and 25b, 26b supplying the actuators 12b, 13b respectively.

Similarly return lines 27a, 28_ from the actuators 12_, 13_ connect to a branch return line 29_. The return lines 27b, 28b from the actuators 12b, 13b drain into a branch return line 29b, and the return lines 29, 29_ feed into a common return line 31 to the valve 19, and through the valve 19 and the valve 18 into the main return line 22. In practice the actuator lines 25_, 26a and 25b, 26b supply pressurised fluid to both ends of the cylinder of their respective actuator so that the same pressure is applied to opposite faces of the respective pistons. However the screw shaft extending from one face of each piston is of smaller diameter than the piston rod extending from the opposite face of the piston and so the effective areas of the opposite faces of each piston exposed to pressure is different and the piston moves in the direction to extend its piston rod and so deploy the associated reverser cowl.

The force developed by the pressure/area differences is sufficient for deploying the cowls but insufficient to result in piston rod and cowl damage in the event of a jam preventing cowl movement. When retraction of the piston rods and cowls is required pressure to the faces of the pistons from which the piston rods extend is maintained but the cylinder regions at the opposite faces of the pistons are vented by operation of the valve 19 to the return line 22 so that the pistons of the actuators are driven in a retract direction.

It is to be understood that in a conventional system the mechanical actuators 14_,14_ would normally be hydraulic actuators identical to the actuators 12, 13. The hydraulic supply pressure would be of the order of 20,000 to 21, 000 kPa (3,000 psi) in a conventional system, and the dimensions of the three hydraulic actuators of each cowl would be such that the three together provide the desired force to move the respective cowl. Furthermore, in the event of failure of one of the three hydraulic actuators in the conventional system the remaining actuators would provide sufficient power to actuate the cowl.

By comparison with such a conventional system, increasing the hydraulic supply pressure to 34,000 to 35,000 kPa (5,000 psi) and replacing the centre one of the three hydraulic actuators by a mechanical actuator 14 effects significant savings even though the remaining two hydraulic actuators 12, 13 of each cowl actuation system may not be any smaller than the actuators in the conventional system. The savings arise from the significant weight saving effected by replacing an hydraulic actuator with a mechanical actuator, and in the reduction in size of hydraulic supply pump which can be achieved by virtue of a one-third reduction in the volume of hydraulic fluid necessary - 10 to operate the system. Furthermore, it may be possible to reduce the size of the hydraulic actuators 12, 13 down to the minimum which can be achieved for an hydraulic actuator including a screw mechanism to provide the rotational movement of the actuators synchronising spindle. System redundancy is maintained, in that a single hydraulic actuator will still provide drive to the mechanical actuator in the event of failure of one of the two hydraulic actuators of the cowl.

While many large gas turbine engines have hydraulic thrust reverser systems utilising three hydraulic actuators for moving each cowl, it will be recognised that there are known smaller engine thrust reverser systems having only two hydraulic actuators associated with each cowl. It is believed that in a conventional two actuator per cowl system it would be possible, when increasing system hydraulic pressure, to substitute a mechanical actuator for one of the two hydraulic actuators of each cowl. However it is believed that such a substitution will most probably prove practical only if the actuation systems of both cowls of the engine are interconnected by one or more synchronising shafts so that both cowls move in unison and failure of the remaining hydraulic actuator of one cowl can be accommodated by that cowl being driven through its mechanical actuator from the hydraulic actuator of the other cowl.

Conventionally thrust reverser system employ two opposite cowls. However it is conceivable that future larger engines could employ three or more cowls and the present invention would be applicable thereto, references herein to first and second cowls being construed accordingly.

Claims

- 11 - Claims: 1. An actuation system for a thrust reverser cowl

comprising at least two linear actuators at least one of which is an hydraulic actuator and at least one of which is a mechanical actuator, said mechanical actuator being driven from a mechanical output of said at least one hydraulic actuator.
2. An actuation system as claimed in claim 1 wherein a mechanical drive connection is provided between said mechanical output and said mechanical actuator.
3. An actuation system as claimed in claim 1 or claim 2 having at least two hydraulic actuators and at least one mechanical actuator, and a mechanical drive connection between the mechanical outputs of said hydraulic actuators and said mechanical actuator whereby the three actuators of the cowl are synchronised.
4. An actuation system as claimed in claim 3, wherein said mechanical actuator is disposed, in relation to the cowl that is driven thereby, between the two hydraulic actuators.
5. An actuation system as claimed in any one of claims 1 to 4, for a plurality of cowls of an engine, and wherein each cowl has at least two actuators one of which is mechanical and the other of which is hydraulic, and a mechanical drive connection is provided between the actuators of one cowl of the engine and the actuators of a second cowl of the same engine whereby - 12 the actuators of each cowl of the engine are synchronised so that the cowls operate in unison.
6. An actuation system as claimed in any one of claims 2 to 5 wherein each said mechanical drive connection incorporates a flexible drive shaft.