Actuator arrangement

An actuator arrangement comprises a plurality of linearly extendable actuators arranged to be driven by a common electrically driven motor, each actuator, being provided with limit stops to limit extension and/or retraction thereof, wherein the limit stops of the actuators are positioned such that a first one of the actuators has a smaller range of permitted extension than at least a second one of the actuators.

BACKGROUND OF THE INVENTION

This invention relates to an actuator arrangement and in particular to an actuator arrangement suitable for use in an electrically driven thrust reverser system for use in moving components of the thrust reverser system between stowed and deployed positions.

One form of thrust reverser system includes a pair of part generally cylindrical cowls each being arranged to be driven between stowed and deployed positions by a plurality of linearly extendable actuators. Commonly, the actuators used in this application have been hydraulically driven. However, the use of electrically powered thrust reverser systems is becoming more common.

One form of electrically powered thrust reverser system includes a cowl moveable by a plurality of ball or roller screw type actuators, for example three such actuators may be provided. A single electrically powered motor is used to drive all of the actuators associated with the cowl, an appropriate gear box and drive transmission system being provided to distribute and transmit power to the actuators and to ensure that the actuators operate in synchronism with one another at the same speed.

In normal use, the actuators are driven at high speed over the majority of their length, the motor being controlled to reduce the speed at which the actuators are driven as the actuators approach their stowed and fully deployed positions so that, when the stowed and fully deployed positions are reached, movement can be safely arrested by claw stops provided in the actuators. The stops are configured so that the stops of all of the actuators associated with the cowl engage to arrest further movement simultaneously.

There is a requirement for the stops provided in the actuators to be able to arrest movement even if the motor fails to slow the rate of operation of the actuators as they approach the stowed and fully deployed positions, for example as a result of a control failure in the thrust reverser control system resulting in the occurrence of a so called powered runaway condition in which the motor continues to be driven at full speed as these positions are approached.

One way in which the stops can be designed to be able to arrest such movement is to increase the radial height of the stops so as to enable them to withstand greater loadings as would occur in such circumstances. However, doing so would result in the diameter of the tail tube of each actuator being increased. As the actuators are approximately 1 m long, increasing the diameter of the tail tube even by a relatively small amount can result in a significant increase in the weight of the actuator arrangement, which is undesirable.

It is an object of the invention to provide an actuator arrangement in which the problem outlined hereinbefore is overcome or of reduced effect.

SUMMARY OF THE INVENTION

According to the present invention there is provided an actuator arrangement comprising a plurality of linearly extendable actuators arranged to be driven by a common electrically driven motor, each actuator being provided with limit stops to limit extension and/or retraction thereof, wherein the limit stops of the actuators are positioned such that a first one of the actuators has a smaller range of permitted extension than at least a second one of the actuators.

By arranging the limit stops in this manner, in normal use, only the limit stops of the said first one of the actuators will operate to arrest movement as the stowed and/or fully deployed positions are reached, the limit stops of the other actuators being redundant, in use, but useful during maintenance and fitting operations to avoid over extension of the actuator which may result in parts thereof becoming disengaged from one another. Consequently, only the limit stops of this one of the actuators need to be designed to withstand the increased loadings that may occur in the event of a control failure, and hence only the tail tube diameter of this one of the actuators needs to be increased. It will be appreciated, therefore, that a saving in the weight of the actuator arrangement can be achieved.

Conveniently, the limit stops of the first actuator engage to arrest movement both when the actuator reaches its fully deployed and stowed positions.

The first actuator is preferably provided with a position sensor, for example in the form of a linear variable differential transducer (LVDT), the output of which can be used by the control system of the thrust reverser actuator system to provide an indication of the position of the cowl thereof.

Preferably a series of drive shafts are provided to transmit drive to at least some of the actuators. The drive shafts may be capable of undergoing limited torsional movement. In such an arrangement, when the stops of the first actuator arrest movement thereof, limited continued movement of the remaining actuators may occur, such movement resulting in ‘winding up’ or torsional movement of the drive shafts. Such winding up of the drive shafts will apply a braking load to these actuators, preferably arresting movement thereof before the limit stops of these actuators engage.

The limit stops conveniently comprise claw stops.

The limit stop of the first actuator operable as the actuator reaches its fully deployed position is conveniently compliant. The limit stop operable as the first actuator reaches its stowed position may also be compliant, but this need not always be the case as the provision of larger limit stops capable of withstanding the loadings applied in the event of control failure leading to a powered runaway condition as the actuator reaches its stowed position need not involve the use of an increased diameter tail tube.

In one arrangement, the actuator includes a screw shaft of hollow form, and the compliant stop is provided by locating a torsion bar within the screw shaft, a stop member being associated with the torsion bar, the stop member projecting through a slot formed in the shaft and engageable by a stop associated with a nut translatable along the screw shaft. Stop members may be provided at or adjacent both ends of the torsion bar. Alternatively, a stop member may be provided at or adjacent just one end thereof. In either case, winding up of the torsion bar occurs, in use, when the nut reaches its stowed and/or fully deployed position, thus slowing and arresting further movement.

In another arrangement, at least one of the compliant stops may comprise a stop member spring biased towards a stop position such that, in use, once the stop position is reached, the spring biasing applies a braking load prior to arresting actuator movement.

The stop member may be mounted on the actuator shaft by means of an acme screw thread. The spring could comprise, for example, a coiled spring or, alternatively, may comprise at least one disc spring.

If desired, a spring biased stop may be provided to arrest actuator movement in one direction, a torsion bar arrangement being used to arrest movement in the opposite direction.

The invention also relates to an electrical thrust reverser system comprising an extendable actuator driven by an electric motor, the actuator including a rotatable screw shaft and a translatable nut, the actuator being provided with limit stops to limit the permitted range of extension of the actuator, wherein at least one of the limit stops is compliant.

The compliant limit stop may comprise a stop member biased by a spring towards a stop position. The stop member may be mounted upon the screw shaft of the actuator by means of an acme screw thread. The spring may comprise a coil spring, or alternatively may comprise at least one disc spring.

Alternatively, the compliant limit stop may be provided by locating a torsion bar within the screw shaft, a stop member being associated with the torsion bar, the stop member projecting through a slot formed in the shaft and engageable by a stop associated with the nut translatable along the screw shaft. Stop members may be provided at or adjacent both ends of the torsion bar. Alternatively, a stop member may be provided at or adjacent just one end thereof.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1there is illustrated an actuator arrangement for use in a thrust reverser system. The actuator arrangement comprises an electrically driven motor10arranged to drive a first actuator12through a gearbox14. The first actuator12comprises a screw shaft16mounted to be rotatable by the operation of the motor10, but held against axial movement by bearings (not shown). A translating nut18cooperates with thread formations formed on the screw shaft16, the nut18being held against rotation but being free to undergo translational motion. It will be appreciated that, in use, operation of the motor10to drive the screw shaft16results in translation of the nut18, the direction of movement of the nut18being dependent upon the direction of rotary motion of the screw shaft16. In order to reduce frictional forces resisting movement of the nut18, the cooperation between the nut18and thread formations is conveniently in the form of a ball-screw or roller-screw type cooperation.

The translating nut18is connected to or forms part of a tail tube20which is formed with a mounting22whereby it is connected to a generally part cylindrical thrust reverser cowl24.

The motor10is controlled, in use, by an electrical trust reverser actuator system controller (not shown) which receives information representative of the position of first actuator12and the cowl24from a LVDT26driven from the gearbox14.

The actuator arrangement further comprises a pair of second actuators28which are identical to one another, the first actuator12being located between the second actuators28. The second actuators28are driven from the gearbox14through drive shafts30and gear arrangements32. Each second actuator28, like the first actuator12, comprises a rotatable screw shaft34which cooperates through a ball-screw or roller-screw type arrangement with a translatable nut36. The nut36is connected to or forms part of a tail tube38which, like the tail tube20of the first actuator12, is connected to the cowl24.

The first actuator12is provided with limit stops operable to determine the range of extension thereof. The limit stops comprise first claw stop members40a,40bassociated with the shaft16and nut18, respectively, and engageable with one another to limit movement of the nut18in the stow direction, and second claw stop members42a,42bassociated with the shaft16and nut18, respectively, and engageable with one another to limit movement of the nut18in the deploy direction. Similarly, the second actuators28are each provided with corresponding first and second claw stop members44a,44b,46a,46b. However, the positioning of the stop members44a,44b,46a,46bof the second actuators28is chosen such that the permitted range of extension of the first actuator12as determined by the first and second stop members40a,40b,42a,42bis smaller than the permitted range of movement of the second actuators28as determined by the stop members44a,44b,46a,46b. InFIG. 1, the permitted range of extension of the first actuator12is denoted by ‘A’, and the range of extension of the second actuators28is denoted by ‘a’, these dimensions being exaggerated inFIG. 1for clarity. It will be apparent that range ‘a’ extends beyond range ‘A’ at both limits of movement. Thus, as the actuator arrangement is driven towards and reaches both its stowed limit position and its deployed limit position, the claw stop members40a,40b,42a,42bof the first actuator12engage to arrest movement, the stop members44a,44b,46a,46bof the second actuators remaining out of engagement with one another. As only the stop members of the first actuator12serve to arrest movement, in use, only these stops need to be of sufficiently large dimensions to be able to withstand the loadings applied in a powered runaway event. The stop members of the second actuators serve primarily to prevent overextension of the second actuators, and associated disengagement of components thereof, during servicing, fitting and maintenance operations, and so can be of relatively small dimensions as the loadings applied thereto are relatively small.

In normal use, when the cowl24is to be moved to its deployed position, the motor10is operated to drive the first and second actuators12,28towards their deployed positions. As the deployed position is approached, as sensed by the LVDT26, the controller reduces the operating speed of the motor10such that the rate of extension of the actuators12,28is reduced, extension being arrested when the fully deployed position is reached by engagement of the second stop members42a,42bof the first actuator12with one another. The stop members of the second actuators28remain spaced apart from one another.

To return the cowl24to its stowed position, the motor10is driven in the reverse direction. As the stowed position is approached, the motor operation is controlled to slow the actuator speed, and movement is arrested once the stowed position is reached by the cooperation of the first stop members40a,40bof the first actuator12. The stop members of the second actuators again remain spaced apart from one another.

In the event of a control failure leading to a powered runaway condition during movement in either the stow direction or the deploy direction, the motor10will drive the actuators12,28at high speed, and the appropriate ones of the stop members40a,40b,42a,42bof the first actuator12will engage one another (depending upon the operating direction of the actuator when the powered runaway condition arises) to arrest the movement of the first actuator12when its limit position is reached. Continued movement of the second actuators28will result in torsional movement or winding up of the drive shafts30. Such winding up of the drive shafts30will apply a braking force to the second actuators28which will result in movement of these actuators being slowed and arrested before the stop members thereof engage, and subsequently the drive shafts30will return to their unwound condition.

It will be appreciated that as only the stop members40a,40b,42a,42bof the first actuator12serve to arrest actuator movement at the stowed and deployed positions, only these stop members need to be sufficiently large to bear the loading applied in a powered runaway event, thus only the first actuator12needs to have a tail tube of increased diameter. Consequently, significant weight savings can be made.

In the arrangement described hereinbefore, the claw stop members are all fixed stops. Rather than provide fixed stops, it is thought that the use of compliant stops to reduce the actuator operating speed before it is finally arrested will allow a reduction in the radial dimensions of the limit stops provided on the first actuator12. Consequently, a small diameter tail tube may be used which may result in further weight savings being possible.

FIG. 2illustrates one way of providing the first actuator12with compliant stops. As illustrated inFIG. 2, the screw shaft16is of hollow form. Within the screw shaft16is located a multi-part torsion bar50to which are secured pins52, the pins52each passing through slots54formed in the screw shaft16, the projecting parts of the pins52defining or having the stop members40a,42asecured thereto. As best seen inFIGS. 3aand3b, the slots54are each shaped so as to allow the pins52to undergo angular movement about the axis of the screw shaft16. Although illustrated as lying in the same plane as one another, the pins52may be angularly displaced relative to one another. The torsion bar50is prestressed in that, during assembly, the torsion bar50is introduced into the screw shaft from the free end thereof and one of the pins52furthest from the free end of the shaft16is introduced through the corresponding slot54and through an opening in the bar50. A torque is then applied to the bar50to prestress the bar50by a predetermined amount, and the other pin52is then introduced axially into its respective slot54and coupled to the bar. The torque may be applied by using an appropriate tool to engage, for example, flats formed at an end of the bar50.

In use, when the actuator is being driven towards and approaches its deployed position, the stop member42bmoves into engagement with the stop member42a, urging the corresponding pin52to undergo angular movement as permitted by the slot54. The arrangement is such that, in order for such angular movement to occur, further stressing of the torsion bar50must occur, the other pin52already being located hard against the corresponding end of its slot54and so being unable to undergo further angular movement. The further stressing of the torsion bar50serves to apply a braking load, slowing and subsequently arresting movement of the actuator12. Similarly, movement of the actuator12towards its stowed position is slowed and arrested by stressing of the torsion bar50, in this case by engagement between the stop members40a,40b.

The arrangement illustrated inFIGS. 2 and 3uses the torsion bar50to apply a braking load to slow and arrest movement in both directions. However, if desired, one end of the torsion bar50could be anchored against movement relative to the screw shaft12, for example by a pin received in a correspondingly sized opening formed in the screw shaft16, so that the torsion bar50serves to slow and arrest movement in only one direction. Such an arrangement may be advantageous where there are concerns that the formation of a slot54may unduly weaken the screw shaft16.

Although the arrangement illustrated inFIG. 2has two separate pins52, an arrangement is envisaged in which one of the pins52(the one adjacent the free end of the screw shaft16) is integral with the torsion bar50, the prestressing of the torsion bar being achieved by applying a torque to the other end thereof prior to introduction of the corresponding pin52.

FIG. 4shows an arrangement in which the compliant stop is formed by a stop member60mounted upon the screw shaft16by an acme screw thread62. The stop member40ais formed on the stop member60. A spring64is engaged between the stop member60and a shoulder66formed on the screw shaft16.

In use, as the actuator12is moved towards its stowed position, the stop member40bengages the stop member40a. The acme screw thread62allows the stop member60to move relatively freely on the screw shaft16, but movement of the stop member60is resisted by the spring64. It will be appreciated, therefore, that upon engagement of the stop members40a,40b, movement of the actuator is slowed and subsequently arrested. The spring64is illustrated as comprising a series of disc springs, but could alternatively comprise a coiled spring, for example.

The arrangement shown inFIG. 4is intended for use in slowing and arresting movement to the stowed position, but could alternatively or additionally be used to slow and arrest movement to the deployed position. Further, theFIG. 4arrangement could be used in combination with, for example, a torsion bar arrangement. For example, the torsion bar arrangement could be used to slow and arrest movement to the deployed position whilst the spring biased arrangement is used to slow and arrest movement to the stowed position.

The position of arrangements using compliant stops is thought to allow a reduction in the radial size of the stops, thus permitting a smaller size of tail tube to be used.

It will be appreciated that a wide range of modifications and alterations may be made to the arrangements described hereinbefore without departing from the scope of the invention.