Patent Publication Number: US-10760528-B2

Title: Thrust reverser actuation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/893,459, filed Sep. 29, 2010, which claims benefit to GB Application No. 0917057.2 filed Sep. 29, 2009, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     This invention relates to thrust reverser actuation and in particular to a drive arrangement suitable for use in driving a movable component, for example a cowl, of a thrust reverser system between stowed and deployed positions. 
     A typical thrust reverser system includes a pair of movable cowls, each being movable between a stowed position and a deployed position in which it is exposed to the airflow through the aircraft engine with which it is associated to apply a braking load to the aircraft. Each cowl is guided for movement along a pair of guide tracks, and is driven for movement by a plurality of linearly extendable actuators, for example in the form of screw jack actuators. Usually an actuator will be located relatively close to each of the guide tracks, and one or more intermediate actuators will be positioned between the aforementioned actuators. The actuators are arranged to be driven in synchronism, conveniently by a single motor, drive from which is transmitted to all of the actuators. 
     In order to prevent deployment of the thrust reverser system other than when desired a number of locks are built into the system. Typically, a track lock or tertiary lock for example in the form of a hook-type lock is provided whereby the cowl is locked against movement relative to the fixed structure of the nacelle, the track lock being released when deployment of the actuator is commanded. The track lock is usually designed so as to be able to hold the cowl against movement in the event of, for example, a control failure resulting in the drive motor operating, erroneously, to drive the cowl for movement. It will be appreciated that, in order to prevent movement of the cowl in such circumstances, the track lock needs to be of robust form. 
     If there is a failure in the control system resulting in attempted deployment of the cowl when the track lock is engaged, or a failure in the track lock resulting in the track lock not releasing, when desired, or if the cowl becomes jammed relative to one or other of the guide tracks during deployment, for example as a result of the presence of a tool, safety locking pin or other foreign body in the guide track, then it will be appreciated that the actuator adjacent that guide track will be subject, very suddenly, to a large compressive load as movement of the cowl is arrested. There is a risk that such loads could result in permanent damage to the actuator, for example in buckling of the output shaft thereof. Obviously, it is desirable to avoid such damage and the inconvenience and cost associated with having to make repairs after such damage has occurred. It is an object of the invention to provide an arrangement in which the disadvantages outlined hereinbefore are overcome or are of reduced effect. 
     It is known to incorporate a torque limiter device which releases upon the application of an excessive torque thereto into an actuator. For example, WO2004/113707 describes a design of actuator in which a torque limiter assembly is incorporated to limit the torque applied to the actuator. 
     GB2408725 and EP1972548 both describe actuator schemes in which a plurality of actuators are provided. 
     According to the present invention there is provided a thrust reverser drive arrangement for use in driving a thrust reverser cowl for movement relative to first and second guide tracks, the drive arrangement comprising a first actuator located, in use, close to the first guide track, and a second actuator located, in use, close to the second guide track, the actuators being arranged to be driven in synchronism and at the same speed by a drive motor to drive the cowl for movement, wherein at least one of the first and second actuators is provided with a load limiter to limit the transmission of loads through that actuator in the event that that actuator is subject to a compressive loading greater than a predetermined level. 
     Conveniently both the first actuator and the second actuator are provided with a load limiter. 
     With such an arrangement, in the event of a failure of the nature outlined hereinbefore, the load limiter will serve to limit the loadings experienced by the associated actuator, preferably reacting or earthing excess loadings through the housing thereof, thereby reducing the risk of permanent damage to the actuator. 
     Each actuator conveniently comprises a rotatable actuator member, rotatable by the motor, in use, the actuator member being coupled through a ball or roller-screw coupling to an output member, rotation of the actuator member driving the output member for axial movement, the load limiter being operable to apply a braking load to the actuator member to resist rotation thereof, thereby reacting applied motor torque to a housing of the actuator rather than increasing the compression of the output member. 
     The load limiter conveniently comprises bearing means supporting the actuator member for rotary motion relative to the housing, resilient biasing means permitting limited axial movement of the actuator member in the event of the application of excessive loadings to the actuator, and abutment means co-operable in the event of axial movement of the actuator member beyond a predetermined distance to transmit torque loadings between the actuator member and the housing. 
     The abutment means preferably comprises a first stop member secured, in use, to the actuator member and co-operable with a first abutment surface associated with the housing, and a second stop member secured, in use to the actuator member and co-operable with a second abutment surface associated with the housing. The bearing means is conveniently located between the first and second stop members, and the resilient biasing means conveniently comprises first and second disc spring packs interposed between the bearing means and the first and second stop members, respectively. 
     The first and second stop members are preferably each provided with fingers, the fingers of the first stop member being interleaved with those of the second stop member, the bearing means encircling the fingers, each finger including a lip at its free end co-operable with the bearing means to hold the first and second stop members captive to the bearing means. 
     Such a design of load limiter is advantageous in that it can be pre-assembled and tested, if desired, prior to introduction into the actuator. 
    
    
     
       The invention will further be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view of a thrust reverser arrangement incorporating a drive arrangement in accordance with one embodiment of the invention; 
         FIG. 2  is a sectional view illustrating part of one of the actuators of the arrangement of  FIG. 1 ; 
         FIG. 3  illustrates part of the load limiter of the actuator of  FIG. 2 ; and 
         FIGS. 4 to 7  are diagrams illustrating various operating conditions of the actuator of  FIG. 2 . 
     
    
    
       FIG. 1  illustrates, diagrammatically, part of a thrust reverser system for use with an aircraft. The thrust reverser system comprises a cowl  10  guided for movement relative to an aircraft engine by a pair of guide tracks  12 . The cowl  10  is arranged to be driven for movement along the guide tracks  12  by a drive arrangement  14  which comprises three linear actuators  16  arranged to be driven by a single, common electric motor  18 . Each actuator  16  is in the form of a screw-jack actuator. 
     A first one of the actuators  16 , actuator  16   a , is located adjacent one of the tracks  12 , a second one of the actuators  16 , actuator  16   b , being located adjacent the other of the tracks  12 . Intermediate the first and second actuators  16   a ,  16   b  is located a third, intermediate actuator  16   c . Each actuator  16  is secured by a respective mounting  20  to the cowl  10 , and is also secured by gimbal mounting means  22  to a fixed part of the engine housing or wing structure (not shown). 
     The electric motor  18  is arranged to drive the third actuator  16   c  directly, and flexible drive transmission shafts  24  are arranged to transmit drive from the third actuator  16   c  to the first and second actuators  16   a ,  16   b.    
     The first and second actuators  16   a ,  16   b  are substantially identical to one another and incorporate stops  26  operable to limit extending and retracting movement of the actuators  16   a  and  16   b , lock arrangements  28  operable to lock these actuators against movement, and sensors  30  operable to output signals indicative of the operating status of the lock arrangements  28  to an associated control unit (not shown). 
     The thrust reverser system further comprises a track lock or tertiary lock  32  operable to lock the cowl  10  against movement relative to one of the tracks  12 , the track lock  32  having sensors  34  associated therewith to output signals representative of the status of the track lock  32  to the control unit. The track lock  32  comprises a pivotally moveable hook member  32   a  which, in a locked condition retains a lock pin  32   b  secured to the cowl, to resist movement of the cowl  10 . Lock arrangements of this general type are well known and so the track lock  32  will not be described herein in greater detail. 
     A position sensor in the form of an RVDT or an LVDT  36  monitors the operation of one of the actuators  16  to provide a signal indicative of the position of the actuators  16  and hence the cowl  10  for use by the control unit. 
     It is apparent from  FIG. 1  that the third actuator  16   c  is of a different design to the first and second actuators  16   a ,  16   b . This arises from the fact that the loadings experienced by the third actuator  16   c  are considerably smaller than those experienced by the first and second actuators  16 ,  16   b , in use. As a consequence, the third actuator  16   c  can be of reduced size and weight compared to the first and second actuators  16   a ,  16   b , thereby achieving a weight saving. There is also no need to provide the third actuator  16   c  with the stops  26 , lock  28  or associated sensors  30 , thereby achieving further weight and cost savings. As mentioned hereinbefore, the third, smaller and/or lighter actuator  16   c  is capable of withstanding only smaller loadings than can be withstood by the first and second actuators  16   a ,  16   b.    
     In use, when deployment of the cowl  10  is required, the track lock  32  and locks  28  are instructed to release, and the outputs of the sensors  30 ,  34  are used by the control unit to determine that the system is unlocked. The motor  18  is then operated to drive the actuators  16 , and hence the cowl  10 , for movement. 
     As described hereinbefore, in the event that the motor  18  operates to drive the cowl  10  for deployment at a time when the track lock  32  is still engaged, for example as a result of a control system failure or resulting from a failure of the track lock  32 , then the track lock  32  will operate to hold the cowl  10  against deployment. The nature of the track lock  32  is typically such that there is a clearance between the hook-shaped lock member  32   a  thereof and the associated lock pin  32   b  secured to the cowl  10  when the cowl is locked in its stowed position. This is advantageous in that wear of the components of the track lock  32 , for example arising from vibrations, is reduced. However, as a result, if the motor  18  is operated to drive the cowl  10  for deployment at a time when the track lock is engaged, a small amount of extension of the actuators  16  and movement of the cowl  10  will occur before movement is arrested by the track lock  32 , and during this period momentum will have built up, and the drive shafts  24  will have become stressed. Once this small amount of movement has occurred, further extension of the adjacent actuator  16  is suddenly prevented, and the continued application of motor drive to that actuator  16 , in combination with the effects of the aforementioned momentum and stressing, will place that actuator  16  under a significant compressive load. In accordance with the invention, in order to avoid damage to the actuator  16 , a load limiter device  40  is incorporated in the actuator  16 , the load limiter device  40  being operable, under such conditions, to applying a braking load to the actuator  16 , reacting the applied torque to the housing of the actuator  16  rather than attempting to continue extension of the actuator  16 . It will be appreciated that the load limiter device  40  thus serves to reduce the risk of damage of the actuator in such circumstances. 
     Although the failure mode outlined hereinbefore involves deployment of the cowl at a time when the track lock is engaged, it will be appreciated that a number of other scenarios could have similar results. For example, if a maintenance tool or mechanical safety locking pin, or other foreign body, is located within one of the guide tracks  12  at a time when the cowl  10  is moved towards its deployed position, sudden arresting of the movement of the cowl  10 , and corresponding arresting of the extension of the actuators  16  will occur, albeit with the cowl  10  in a part deployed, rather than stowed, position. Such arresting of the actuators  16  has much the same result as described hereinbefore, and the presence of the load limiter device  40  will serve to reduce the risk of actuator damage under such circumstances. 
     As the third actuator  16   c  is spaced by a relatively large distance from the guide tracks  12 , slight flexing of the cowl  10  allows this actuator to decelerate at a lower rate than the first and second actuators  16   a ,  16   b , thus damage thereto is less likely. Consequently, in the arrangement illustrated, the third actuator  16   c  is not provided with a load limiter  40 . However, there may be circumstances in which this is desirable. 
     In the arrangement illustrated, the first and second actuators  16   a ,  16   b  are conveniently of the form illustrated in  FIG. 2 . The actuator shown in  FIG. 2  comprises a rotatable actuator member  42  supported for rotation within a housing  44 . The actuator member  42  includes a region  46  of tubular form having, at an end thereof, a threaded nut (not shown) secured through a ball or roller-screw coupling to a threaded output shaft  48 . The output shaft  48  is secured to the associated mounting  20  in such a manner that the output shaft  48  is unable to rotate. It will be appreciated that, in use, rotation of the actuator member  42  under the control of the electric motor  18  results in axial displacement of the output shaft  48  relative to the housing  44 , and thus results in displacement of the cowl  10 , in use. 
     The load limiter device  40  is interposed between the tubular part  46  of the rotary actuator member  42  and the housing  44 . The load limiter device  40  comprises a first stop member  50  which is secured to the rotary actuator member  42  so as to be rotatable therewith and to be axially fixed relative to the rotary actuator member  42 , in use, by being abutted against a shoulder formed thereon. A key, spline or other connection arrangement may be used to ensure that rotary movement of the first stop member  50  relative to the rotary actuator member  42  is not permitted. The first stop member  50  includes a radially outwardly extending flange  52  which, in the position illustrated in  FIG. 2 , is spaced by a small distance from an abutment surface  54  of an abutment member  56  rigidly secured to the housing  44 . 
     A second stop member  58  is also secured to the rotary actuator member  42  in such a manner that rotary movement thereof relative to the actuator member  42  is not permitted. This is conveniently achieved by a spline, key or other similar coupling. The second stop member  58  includes a radially outwardly extending flange  60  which in the position illustrated in  FIG. 2  is spaced by a small distance from a second abutment surface  62  of an abutment member  64  also rigidly secured to the housing  44 . 
     As best shown in  FIG. 3 , the first stop member  50  includes a series of fingers  64  which are interleaved with similar fingers  66  provided on the second stop member  58 . Bearing means  68  encircle the fingers  64 ,  66 , the bearing means  68  comprising inner races  70  supported on the fingers  64 ,  66  for rotation therewith, outer races  72  secured to the fixed abutment member  56 , and ball bearings  74  located therebetween. 
     The fingers  64 ,  66  are provided, at their free ends, with outwardly extending lips  64   a ,  66   a  which are engageable with the inner races  70  to hold the first and second stop members  50 ,  58  captive to the bearing means  68 . 
     Resilient biasing means in the form of first and second disc spring packs  76 ,  78  are located between the flanges  52 ,  60  of the first and second stop members  52 ,  58  respectively, and the bearing means  68 . The biasing means urges the second stop member  58  against a no-back device  80  secured to the actuator member  46 , and the first stop member  50  against the associated shoulder on the actuator member  46 . The first and second disc spring packs  76 ,  78  may have different spring rates to provide different overload tensile and compressive limit settings for the load limiter device  40 . 
     In normal use, the biasing means serves to hold the rotary actuator member  46  in a substantially fixed axial position relative to the housing  44 , the bearing means  68  supporting the actuator member  46  for rotation. 
     If, during movement of the cowl  10  the actuator  16   a  or  16   b  is under compression or tension at levels sufficiently low that the accompanying axial movement of the actuator member  46  against the net biasing load applied by the biasing means does not result in co-operation between either of the stop members  52 ,  58  and the associated abutment surfaces  54 ,  62 , then the compressive or tensile load is reacted through the biasing means and bearing means  68  to the housing  44 , but the load limiter device  40  does not operate to resist rotation of the actuator member  46 . These operating conditions are illustrated in  FIGS. 4 and 5 ,  FIG. 4  illustrating the load path  82  by which compressive loads are reacted to the housing and  FIG. 5  illustrating the load path  84  by which tensile loads are reacted to the housing. 
     If larger compressive or tensile loads are experienced, sufficient to cause significant axial movement of the actuator member  46  relative to the housing  44  against the action of the biasing means then the load limiter device  40  will operate to react torque between the actuator member  46  and the housing  44 . The spring packs  76 ,  78  are sized so as to ensure that, during normal deployment conditions, such axial movement does not occur, but that if loads higher than those normally experienced during deployment occur, then axial movement of this degree occurs.  FIG. 6  illustrates the case where a large magnitude compressive load is experienced, as would occur in the failure mode outlined hereinbefore. In such a situation, the compressive load is sufficient to move the actuator member  46  to the left, in the orientation illustrated, against the net biasing load applied by the biasing means to a position in which the flange  52  of the first stop member  50  abuts the first abutment surface  54  of the abutment member  56  which is secured to the housing. As the first stop member  50  is, effectively, axially and rotationally fixed to the actuator member  46 , the co-operation between the flange  52  and the first abutment surface  54  serves to react both input torque and additional compressive loads between the actuator member  46  and the housing  44 . This load path is identified in  FIG. 6  as load path  86 , and it will be apparent that this load path is in addition to the load path  82 . 
       FIG. 7  illustrates the case where a large tensile load is applied, illustrating a load path  88  which serves, in addition to load path  84 , to react tensile loadings, and additionally to react torque loadings to the housing  44 . If a track jam, failure or obstruction is encountered during retraction of the cowl  10 , then the load limiter device  40  will operate to avoid the application of excessive stresses to the actuator mounting points. Consequently, the risk of damage is again reduced. 
     In both cases, as torque is reacted or earthed to the housing  44 , it will be appreciated that the load limiter device  40  operates as a brake, resisting rotation of the actuator member  46  when the tensile load or compressive load exceeds a predetermined level. As a result, the application of excessive compressive loads via the output shaft  48  as would otherwise occur in the failure mode outlined hereinbefore is avoided and so the risk of permanent damage to the actuator is reduced. It will be appreciated that this manner of operation is quite different to the operation of a torque limiter which releases upon the application of an excessive torque thereto. 
     The specific form of load limiter device  40  illustrated in  FIGS. 2 to 7  is advantageous in that, as the first and second stop members are held captive to the bearing means, the load limiter device  40  can be pre-assembled and tested as a module prior to mounting on the actuator. However, the invention is not restricted to the use of this specific type of load limiter device. 
     It will be appreciated that by using such load limiters, it may be possible to use actuators of reduced size, weight and strength without unnecessarily increasing the risk of component failure, and that the strength, and hence size and weight, of the track lock may also be reduced without any reduction in the overall performance and/or safety of the system. 
     The arrangement described hereinbefore is merely one embodiment of the invention and it will be appreciated that a wide range of modifications and alterations may be made without departing from the scope of the invention.