Actuator arrangement

This invention relates to an actuator arrangement, and in particular to a linear actuator arrangement of the type including a rotatable shaft upon which is located a translatable nut, a roller or ball screw coupling being provided therebetween such that rotation of the shaft drives the nut for translation along the shaft. Such an actuator is suitable for use in a number of applications, for example in driving the thrust reverser cowls or other components of an aircraft between stowed and deployed positions.

The actuators used in driving a thrust reverser cowl typically include a so-called no-back device operable to apply a braking load to the actuator to counter externally applied aiding loads and thereby reduce the risk of uncontrolled movement of the cowls or other components moved using the actuator. Such no-back devices include friction brake components which wear, in use, and one object of the invention is to provide an actuator arrangement including a sensor arrangement operable to detect whether or not the no-back device is operating correctly.

According to the present invention there is provided an actuator arrangement comprising a rotatable shaft, a no-back device operable to apply a braking load to the shaft, a drive arrangement operable to drive the shaft for rotation, and an indicator member, wherein the drive arrangement includes a differential drive operable to drive the indicator member for movement.

Such an arrangement is advantageous in that, during operation, when the braking load applied by the no-back device is less than expected and less than the resistance to movement of the indicator member, the differential drive will drive the indicator member for movement relative to the shaft, the movement providing an indication that the no-back device is not operating correctly. Preferably, the indicator member is movable axially of the shaft.

A sensor may be provided, the sensor monitoring the position or movement of the indicator member.

Preferably, stop means are provided to limit movement of the indicator member. The stop means are important in that, once the indicator member has reached the stop means, the differential drive operates to increase the magnitude of the driving load applied to the shaft.

A translatable nut is conveniently mounted upon the shaft, the nut being arranged to translate along the shaft upon rotation of the shaft.

A lock arrangement is preferably provided to lock the nut and shaft against relative rotation. The lock arrangement preferably includes a lock component mounted for axial movement relative to the shaft but held against angular movement relative to the shaft, the lock component being co-operable with the nut to lock the nut to the shaft and thereby prevent relative rotation therebetween. The drive arrangement is preferably operable to drive the lock component axially relative to the shaft to release the lock arrangement. The indicator member conveniently forms part of or is associated with the lock arrangement, for example it may form the lock component.

According to another aspect of the invention there is provided an actuator arrangement comprising a rotatable shaft, a nut mounted upon the shaft and translatable along the shaft upon rotation of the shaft, and a lock arrangement operable to lock the shaft and nut against relative rotation, the lock arrangement comprising a lock component mounted upon one of the shaft and the nut for axial movement but held against angular movement relative thereto, the lock component being co-operable with the other of the shaft and the nut, or a component associated therewith, to lock the shaft and nut to one another.

The actuator arrangement illustrated in the accompanying drawings comprises a shaft 10 which is mounted to a housing 12 and supported by bearings 14 for rotation. Axial movement of the shaft 10 is prevented or limited by the bearings 14. A nut 16 is mounted upon the shaft 10 by a ball screw type coupling 18. The nut 16 is connected to a cowl or other component to be moved by the actuator arrangement, in use, the nature of the connection of the nut 16 to the cowl or other component being such that the nut 16 is held against angular or rotary motion. It will be appreciated that, in use, rotation of the shaft 10 causes the nut 16 to translate axially along the shaft 10, the direction of rotary movement of the shaft 10 determining the direction in which the nut 16 translates, thus rotation of the shaft 10 drives the cowl or other component for movement.

A no-back device 20 is connected between the shaft 10 and the housing 12, the no-back device 20 having a friction brake 22 and being operable to apply a braking load to the shaft 10, resisting rotary movement of the shaft 10 in one rotary direction, the no-back device 20 further incorporating a ratchet mechanism 24 which is operable to avoid the application of the braking load when the shaft 10 is rotated in the opposite direction. A no-back device 20 of this general type is described and illustrated in EP 1378685. Although the illustrated no-back device is of the type incorporating a ratchet mechanism 24, a no-back device of the type in which no such ratchet mechanism is provided and a braking load is applied in both rotary directions of the shaft 10 could be used, if desired. No-back devices of this and other forms are well known and the no-back device will not be described in further detail as the specific design of the no-back device is not of relevance to the invention.

The shaft 10 is arranged to be driven for rotation by a drive arrangement 26 including a differential drive 27 in the form of a rotatable carriage 28 arranged to be driven by a motor (not shown), for example via a bevel gear from a synchronising shaft, or via a worm gear or directly by the motor. The carriage 28 carries a plurality of pairs of first planet gears 30 and second planet gears 32, each pair of planet gears 30, 32 being in meshing engagement with one another, as shown in FIG. 2. It is envisaged that three or more pairs of planet gears 30, 32 may be provided, but more or fewer may be present. The first planet gears 30 each further mesh with the teeth of a drive gear 34 mounted upon the shaft 10. It should be noted that the second planet gears 32 do not engage the drive gear 34. Rather, the second planet gears 32 are in meshing engagement with teeth formed on or associated with a secondary drive gear 36, the first planet gears 30 not cooperating with the secondary drive gear 36. The differential drive 27 applies the input drive load to the drive gear 34 and secondary drive gear 36 in an inverse relationship to the resistance to rotation thereof, ie drive is preferentially applied to the gear experiencing least resistance to rotation at any time.

The secondary drive gear 36 is mounted for rotation within the housing 12 by bearings 38, the secondary drive gear 36 being coaxial with, and encircling part of, the shaft 10. The secondary drive gear 36 is provided, internally, with recesses supporting balls 40 which ride in axially extending grooves 42 formed in the periphery of a coupling 44, the balls 40 and grooves 42 serving to drive the coupling 44 for rotation with the secondary drive gear 36 whilst permitting the coupling 44 to move axially. The coupling 44 is provided with an inwardly extending formation or series of formations 46 which cooperate with a shallow pitch helical recess 48 formed in the shaft 10 such that rotation of the secondary drive gear 36 and coupling 44 relative to the shaft 10 drives the coupling 44 for limited axial movement relative to the shaft 10, the movement being limited by the engagement of the formations 46 with the ends of the recess 48.

A lock and indicator member 50 encircles the shaft 10 and is splined thereto by formations 52 such that the member 50 is movable axially relative to the shaft 10, the spline formations 52 preventing rotation of the member 50 relative to the shaft 10. A spring 54 is engaged between the member 50 and the coupling 44, the spring 54 urging the member 50 to the right, in the orientation illustrated. The member 50 includes, at its left-hand most end, in the orientation illustrated, an outwardly extending flange 56 which is co-operable with a bearing 58 carried by the coupling 44 so that the member 50 is held captive to the coupling 44.