Abstract:
A rotary actuator for controlling a flight control surface and a flight control surface actuation assembly including the rotary actuator. The actuator comprises a rotary output shaft for driving a flight control surface, a locking mechanism for selectively preventing rotation of the rotary output shaft and a torque limiter for allowing the locking mechanism to be bypassed upon the locking mechanism experiencing a torque above a predetermined limit.

Description:
FOREIGN PRIORITY 
       [0001]    This application claims priority to European Patent Application No. 14306776.7 filed Nov. 6, 2014, the entire contents of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a rotary actuator for controlling a flight control surface and a flight control surface actuation assembly comprising a rotary actuator. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is well known to use a rotary actuator to control the position of a flight control surface, such as a spoiler on an aircraft wing. It is also known to use a “no-back” device to prevent the flight control surface from back-driving the actuator. 
       SUMMARY 
       [0004]    There is disclosed herein a rotary actuator assembly for controlling a flight control surface, the actuator comprising a rotary output shaft for driving a flight control surface, a locking mechanism for selectively preventing rotation of the rotary output shaft and a torque limiter for allowing the locking mechanism to be bypassed upon the locking mechanism experiencing a torque above a predetermined limit. 
         [0005]    The use of the term ‘bypassed’ should be understood to mean that the torque limiter can allow the output shaft to operate normally (i.e. rotate freely) even though the locking mechanism is in a locked state (which without the bypass function of the torque limiter would cause the shaft to be prevented from rotating freely). If the torque experienced by the locking mechanism is at or below the predetermined level, the torque limiter will not bypass the locking function of the locking mechanism. 
         [0006]    The locking mechanism may prevent a flight control surface being moved by an external force such as high or low aerodynamic pressure acting on the surface. The locking mechanism may prevent the flight control surface being unintentionally extended. 
         [0007]    The torque limiter may allow the surface to be moved by such an external force if the force is so large that damage to the surface, or another part of the wing or the actuator (such as the locking mechanism) may occur should the surface be held in place by the locking mechanism. The torque limiter may therefore allow the surface to be extended by the external force. 
         [0008]    The rotary actuator may be a servo-controlled rotary actuator. 
         [0009]    The locking mechanism may be configured, when in the first operating state to allow rotation of the output shaft in both first and second rotational directions, and, when in the second operating state to prevent rotation of the output shaft in the first rotational direction and to allow rotation of the output shaft in the second rotational direction. 
         [0010]    The first rotational direction may be that direction in which the output shaft moves to actuate a flight control surface, i.e. to extend the flight control surface into a deployed position. As such, the second rotational direction may be the direction in which the output shaft moves to retract the surface to a stowed position. 
         [0011]    The locking mechanism may comprise a locking actuator for switching the locking mechanism between first and second operating states. 
         [0012]    The locking mechanism may be configured such that in the first operating state the locking actuator is activated and, upon deactivation of the second actuator, the locking mechanism is be switched from the first operating state to the second operating state. 
         [0013]    The locking mechanism may further comprise a ratchet wheel operatively connected to the output shaft and rotatable therewith and a pawl operatively connected to the locking actuator and being operable between a first position in its first operating state to a second position in the second state. The pawl may be out of contact with the ratchet wheel in its first position to allow rotation of the output shaft in the first rotational direction. The pawl may be in contact with the ratchet wheel in its second position to prohibit rotation of the output shaft in the first rotational direction. 
         [0014]    The locking mechanism may further comprise a pawl biasing member arranged to bias the pawl into its second position. The pawl biasing member may be a pawl spring. 
         [0015]    The locking actuator may be configured to switch the locking mechanism into its first operating state by overcoming the bias force of the pawl biasing member and moving the pawl into its first position. 
         [0016]    In its second operating state, the locking actuator may be deactivated to allow the pawl biasing member to bias the pawl into its second position. 
         [0017]    The torque limiter may be arranged or configured such that, upon the locking mechanism being in its second operating state and experiencing a torque above the predetermined limit, the torque limiter may allow the output shaft to rotate relative to the ratchet wheel (even though the pawl is in contact with the ratchet wheel). 
         [0018]    The torque limiter may comprise a ball detent torque limiter. 
         [0019]    The ball detent torque limiter may comprise a plurality of balls located in recesses in the ratchet wheel and a ball biasing member associated with each ball. 
         [0020]    Each ball biasing member may comprise a spring. 
         [0021]    The locking actuator may be a linear actuator (i.e. having a linear output) and may comprise a solenoid and a push rod. 
         [0022]    The present disclosure also extends to a flight control surface actuation assembly comprising a rotary actuator as described above and a flight control surface being operatively connected to the rotary output shaft. 
         [0023]    Rotating the rotary output shaft in the first direction may cause the flight control surface to be extended into a deployed position. Rotating the rotary output shaft in the second direction may cause the flight control surface to be moved into a stowed position. 
         [0024]    The flight control surface may be a spoiler. 
         [0025]    The present disclosure also extends to an aircraft comprising a flight control surface actuation assembly as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    An exemplary embodiment of the present disclosure will now be described by way of example only and with reference to  FIGS. 1 to 4 , of which: 
           [0027]      FIG. 1  is an overview of an exemplary rotary actuator in accordance with an embodiment of the present disclosure; 
           [0028]      FIG. 2  is an end view of the exemplary rotary actuator of  FIG. 1 ; 
           [0029]      FIG. 3  shows a first cross-sectional view through part of the rotary actuator of  FIGS. 1 and 2 ; and 
           [0030]      FIG. 4  shows a second cross-sectional view through a part of the rotary actuator of  FIGS. 1 to 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]      FIG. 1  shows a schematic overview of a rotary actuator  100  for controlling a flight control surface (not shown). The actuator  100  comprises, in serial operative connection, a motor module  10 , an anti-extension module  12 , a gearbox  14  and an output lever  16 . The output lever  16  is connected to a connecting rod  18 , via a pivot point  17  ( FIG. 2 ). The connecting rod  18  has a connection point  19  at its free end that can be connected to a flight control surface (not shown), as is known in the art. 
         [0032]      FIG. 2  shows an end view of the actuator  100  of  FIG. 1 . The pivot point  17  between output lever  16  and connecting rod  18  is shown. 
         [0033]      FIG. 3  shows cross-section A-A of  FIG. 1 , through the anti-extension module  12 . The cross-section shows an output shaft  11  of the actuator  100  surrounded by a ratchet wheel  22 , which is operatively connected thereto. The ratchet wheel  22  comprises holes  26  and ball bearings  36  located therein, which will be explained in more detail below, in relation to  FIG. 4 . The ratchet wheel  22  is disposed in a ratchet wheel housing  28 , which is secured within actuator housing  8  using fasteners  25   a,    25   b,    25   c.    
         [0034]    A pawl  20  is disposed adjacent to the ratchet wheel  22  between the wheel  22  and the actuator housing  8 , in a gap  29  in ratchet wheel housing  28 . The pawl  20  is pivotally mounted within the actuator  100  via a pin  21 . The pawl  20  is in operable communication with an electrical locking (linear) actuator  24  and a pawl spring  23 . The locking actuator  24  comprises a solenoid and a push-rod  24   a  disposed between the pawl  20  and actuator housing  8 . The pawl spring  23  is also disposed within actuator housing  8  in gap  29 , between the pawl  20  and the ratchet wheel housing  28 . 
         [0035]    As shown in  FIG. 3 , the pawl spring  23  biases the pawl  20  about its pivot point at pin  21  in an anti-clockwise direction such that it is forced into engagement with ratchet wheel  22 . When the pawl  20  is engaged with the ratchet wheel  22 , rotation of the wheel  22  in a clockwise direction is prohibited. When the electrical actuator  24  is activated, push-rod  24   a  pushes the pawl  20  about its pivot point in a clockwise direction, overcoming the bias of spring pawl  23 , such that the pawl  20  disengages from the ratchet wheel  22 . When the pawl  20  is disengaged from the ratchet wheel  22 , the wheel  22  is free to rotate in either rotational direction. In this way, the ratchet wheel  22  and pawl  20  act as a locking mechanism, to selectively lock rotation of the ratchet wheel  22  in one rotational direction. 
         [0036]    Although a pawl  20  and ratchet  22  locking mechanism is used within this embodiment, any suitable locking mechanism, as would be understood by one skilled in the art, may be used. 
         [0037]    In this embodiment, the locking actuator  24  comprises a solenoid, however, any other suitable electrical actuator, as would be understood by one skilled in the art, may be used. 
         [0038]    In this embodiment, the locking actuator  24  is activated to disengage the locking mechanism, and deactivated to engage it. It should be understood, however, that the opposite mode of operation could be used within the scope of this disclosure. 
         [0039]      FIG. 4  shows cross-section B-B of  FIG. 2 , which shows ratchet wheel  22  operatively connected to a torque limiter  30 . The torque limiter  30  comprises a plate  38  having a plurality of recesses  37 . The plate  38  is operatively connected to the output shaft  11 . A plurality of springs  32  are held in the recesses  37  on the plate  38 . Each spring  32  is biased to push against a respective thrust bearing  34 . The thrust bearings  34  are in turn biased into contact with respective ball bearings  36 . 
         [0040]    The effective bias on the ball bearings  36  retains them in a ring  35  containing a plurality of cup washers. The ring  35  is located adjacent to the ratchet wheel  22  and is operatively connected to the output shaft  11  via flange  11   a.  The engagement of the ball bearings  36  and the cup washer ring  35  allows the ratchet wheel  22  and torque limiter  30  to rotate with the output shaft  11 . The operation of the torque limiter  30  will be described in more detail below. Larger, secondary bearings  40  are also provided to secure the output shaft  11  and associated components to the actuator housing  8 , and to allow rotation of the shaft  11  and its associated components within the housing  8 . 
         [0041]    The actuator  100  of the present disclosure features two modes of operation: an operating mode and an anti-extension mode. 
         [0042]    In operating mode, actuation of a flight control surface is desired. The locking actuator  24  is activated (i.e. power is supplied to the solenoid), causing push-rod  24   a  to push on pawl  20 , such that the biasing force of pawl spring  23  is overcome (as described above in relation to  FIG. 3 ). This allows free rotation of the ratchet wheel  22  and, through engagement with torque limiter  30 , the output shaft  11 . The motor module  10  is simultaneously activated to turn output shaft  11 , which in turn drives the connecting rod  18  via the anti-extension module  12  and gearbox  14  to extend or retract a flight control surface, for example, to move a spoiler upwardly or downwardly on an aircraft wing. 
         [0043]    In anti-extension mode, the extension of a flight control surface is undesirable and is to be prohibited. This can be, for example, when a flight control surface is in a stowed position and it is undesirable for it to be actuated, or a flight control surface has been actuated to a desired position, and any further actuation is undesirable. Such undesirable actuation can be caused by an external force e.g. low pressure over a wing surface. In this mode, the locking actuator  24  is deactivated (i.e. no power is supplied to the solenoid  24 ). This allows the push-rod  24   a  to retract and allows the pawl spring  23  to push pawl  20  into engagement with ratchet wheel  22 , which prohibits its rotation in a clockwise direction. As ratchet wheel  22  is connected to output shaft  11  via engagement with cup washers  35 , this also prohibits rotation of the output shaft  11  in the clockwise direction, which prevents the connecting rod  18  and thus, any flight control surface attached thereto, from being extended. 
         [0044]    In this configuration it is important to point out that the ratchet wheel  22  only prohibits rotation in an extension direction of the flight control surface, and not in the reverse direction. Therefore, in an anti-extension mode the flight control surface is still permitted to be retracted (using the actuator  100 ) to a lower or stowed position, as anti-clockwise rotation of the ratchet wheel  22  will merely cause pawl  20  to skip along the teeth of the ratchet wheel  22 . In this embodiment, anti-clockwise rotation of the output shaft  11  and ratchet wheel  22  cause retraction and clockwise rotation causes actuation of the connecting rod  18 . It should be understood that within the scope of this disclosure, either rotation direction could be used for actuation or retraction. The output shaft  11  and ratchet wheel  22  could even be configured to counter rotate, if desired. 
         [0045]    In either mode, the torque limiter  30  is configured to engage the ratchet wheel  22  (as described in relation to  FIG. 4 ) with cup washer ring  35 , such that the wheel  22  and limiter  30  are rotatable with the output shaft  11  (and able to block rotation of the shaft  11  when desired). 
         [0046]    In anti-extension mode, the torque limiter  30  serves to disconnect the ratchet wheel  22  from the output shaft  11 , should the ratchet wheel  22  experience a torque force, in the direction of rotation that is opposed by the pawl  20  (i.e. clockwise in this embodiment), that is above a predetermined limit T limit . Such a force may occur due to the output shaft  11  being urged in that direction by an external load trying to lift (or deploy) the flight control surface. Such a load may damage the locking mechanism or other actuator/flight control surface components if the ratchet wheel  22  remained locked in place. 
         [0047]    When a torque greater than T limit  is experienced, the tendency for the output shaft  11  to rotate against the locked ratchet wheel  22  is great enough to cause the springs  32  to be compressed such that ball bearings  36  slide out of engagement with the cup washer ring  35 . This disengages the ratchet wheel  22  from the output shaft  11 . This prevents the locking mechanism and/or other actuator/structural components from being damaged by torque above T limit . The torque T limit  at which the output shaft  11  disengages ratchet wheel  22  can be tuned, as known in the art, for example, using smaller or larger spring bias from springs  32 . 
         [0048]    In this embodiment, the torque limiter  30  described above will be readily recognised to those skilled in the art as a ball detent torque limiter. It should, however, be understood that any other suitable torque limiters may be used within the scope of this disclosure, for example, a shear pin torque limiter, a synchronous magnetic torque limiter, or a friction disk and spring torque limiter. 
         [0049]    Although the figures and the accompanying description describe a particular embodiment, it is to be understood that the scope of this disclosure is not to be limited to such an embodiment, and is, instead, to be determined by the following claims.