Abstract:
A bearing assembly for mounting a pair of spaced parallel actuators ( 3 ) between a wing and a control surface of an aircraft so that the actuators control deployment of said control surface from the wing in tandem is disclosed. The bearing assembly comprises a fixed member ( 18 ) for attachment to the aircraft and a movable member ( 8 ) attachable to the actuators. The fixed and movable members are coupled via a part-spherical bearing ( 14 ) and are configured such that the part-spherical bearing is located in the space between the actuators ( 3 ).

Description:
INTRODUCTION 
       [0001]    The present invention relates to a bearing assembly for mounting an actuator to an aircraft wing and to an actuator system assembly comprising the bearing assembly of the invention and the actuators. 
       BACKGROUND 
       [0002]    Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge control surfaces are used to control the wing coefficient of lift. The leading edge control surface is known as a slat and a trailing edge control surface is known as a flap. During normal flight the slats and flaps are retracted against the leading and trailing edges of the wing, respectively. However, during take-off and landing they are deployed from the wing so as to vary the airflow across and under the wing surfaces. By varying the extent to which the slats and flaps are deployed from the wing, the lift provided by the wing can be controlled. Other trailing edge control surfaces include ailerons and spoilers. 
         [0003]    The control surfaces are moved using hydraulic actuators mounted within the wing structure and coupled at each end to the wing and to the control surface via spherical bearing assemblies at both ends of the actuator. 
         [0004]    As demands for thinner, more efficient wing profiles increase, it becomes increasingly difficult to fit all the necessary systems, structure and actuation devices within the wing outer mould line and the size of actuator that may be employed for controlling deployment of various control surfaces is severely limited. In particular, the length of conventional hydraulic cylinders is a problem, especially as the spherical bearing at each end of the actuator each add between 50 to 200 mm to the length of the actuator which is often unacceptable due to the tight space constraints within the wing structure. 
         [0005]    To address the problems referred to above, it is known to employ trunion mounted cylinders as these are shorter in length. However, as these actuators rely on only one spherical bearing at the moving end of the hydraulic cylinder, the fixed end of the actuator is mounted for movement about one axis, and so they suffer from high wear on the cylinder bushes and seals resulting in premature failure due to hyperstatic loading caused by wing bending and manufacturing tolerances. Therefore, regular inspection and maintenance is necessary to avoid a potential failure. 
         [0006]    It is therefore desirable to provide an assembly in which the actuator is mounted via a spherical bearing at both ends but which does not have the additional length suffered by conventional bearing assemblies. Embodiments of the present invention therefore seek to provide an actuator which substantially overcomes or alleviates the known problems with conventional bearing assemblies and to provide an actuator of reduced length that can withstand hyperstatic loads caused by wing bending. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the invention, there is provided a bearing assembly for mounting a pair of spaced parallel actuators between a wing and a control surface of an aircraft so that the actuators control deployment of said control surface from the wing in tandem, the bearing assembly comprising a fixed member for attachment to the aircraft and a movable member attachable to the actuators, wherein the fixed and movable members are coupled via a part-spherical bearing and are configured such that the part-spherical bearing is located in the space between the actuators. 
         [0008]    Each actuator may comprise a hydraulic cylinder and a piston slideably received in the cylinder. The bearing assembly preferably comprises a first movable support member attachable to the hydraulic cylinders to couple each actuator together in spaced parallel relation, said first movable support member including a shaft that extends across the space between the cylinders and a first part-spherical bearing being mountable to said shaft. 
         [0009]    In a preferred embodiment, a first fixed support member comprises an arm that extends into the space between the cylinders, the arm having an opening that forms a bearing seat to receive the first part-spherical bearing mounted on the shaft of the first movable support member such that the fixed and movable support members are rotatable relative to each other about the first part-spherical bearing. 
         [0010]    The arm of the first fixed support member may be formed in two separable parts that combine to form the bearing seat and enclose the first part-spherical bearing. 
         [0011]    In one embodiment, the first fixed support member has a flange at one end remote from the bearing seat, the flange having means to enable the arm to be fixed to the aircraft. 
         [0012]    Preferably, the first movable support member comprises a collar at each end of the shaft to receive a cylinder of each actuator in respective collars. 
         [0013]    A reinforcing plate may be coupled to, and extend between, each collar. 
         [0014]    In a preferred embodiment, a second movable support member is attachable to the free end of each piston extending from their respective cylinders such that the pistons slide in unison into and out of their respective cylinders. 
         [0015]    The second movable support member may have a central region that extends between the pistons and an aperture extending through said central region to receive and mount a second part-spherical bearing between said pistons. 
         [0016]    The central region preferably has a hole in the central region to receive and mount a pin extending laterally through the aperture, the second part-spherical bearing being mountable on the pin. 
         [0017]    In a preferred embodiment, a second fixed support member comprises an arm configured to extend into the aperture in the central region of the second movable support member, the arm having an opening that forms a bearing seat to receive the second part-spherical bearing mounted in said aperture in the second movable support member such that the second fixed and movable support members rotate relative to each other about the second part-spherical bearing. 
         [0018]    The arm of the second fixed support member may be formed in two separable parts that combine to form the bearing seat and enclose the second part-spherical bearing. 
         [0019]    Preferably, the second fixed support member has a flange at one end remote from the bearing seat, the flange having means to enable the arm to be attached to the aircraft. 
         [0020]    In a preferred embodiment the bearing assembly comprises a manifold to fluidly connect a single fluid source to both cylinders. Preferably, a separate manifold is mountable at each end of the pair of cylinders. 
         [0021]    The ends of each cylinder may be closed by a plate and the manifold is attachable to the plates at one end of the pair of cylinders so as to extend therebetween, the plates each having a passage therethrough to fluidly connect the manifold to the cylinders. 
         [0022]    According to another aspect of the invention, there is provided an actuator system comprising the bearing assembly of the invention, the actuator system comprising a pair of spaced parallel cylinders each having a piston slideably received therein, a first movable support member being mounted to said cylinders and having a first part spherical bearing mounted on a shaft extending therebetween, a first fixed support member being coupled to said first part spherical bearing such that the first fixed and movable support members are rotatable relative to each other about said first part-spherical bearing. 
         [0023]    In a preferable embodiment, the second movable support member is mounted to the free end of each piston and a second part-spherical bearing is mounted in the aperture in the central region of said second movable support member, the second fixed support member extending into said aperture and being coupled to the second-part spherical bearing such that the second fixed and movable support members are rotatable relative to each other about the second part-spherical bearing. 
         [0024]    In one embodiment, a spring element is disposed in each cylinder to bias the pistons to a neutral position in the absence of hydraulic pressure acting on the pistons. 
         [0025]    In one embodiment, the first fixed support member is mountable to an aircraft wing and the second fixed support member is mountable to a control surface. 
         [0026]    In another embodiment, the first fixed support member is mountable to a control surface and the second fixed support member is mountable to an aircraft wing. 
         [0027]    According to another aspect of the invention, there is provided an aircraft wing and a control surface coupled to said wing for deployment during take-off and/or landing, and an actuator system according to the invention extending between and coupled to said control surface and the wing to control deployment of said control surface from said wing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0029]      FIG. 1  is a front perspective view of an actuator system assembly according to the invention, including the bearing assembly of the invention, with the pistons of the hydraulic cylinders shown in a retracted state; 
           [0030]      FIG. 2  is a rear perspective view of the actuator system of  FIG. 1 ; 
           [0031]      FIG. 3  is a front perspective view of the actuator system shown in  FIG. 1 , but with the pistons of the hydraulic cylinders shown in their extended state; and 
           [0032]      FIG. 4  is an exploded perspective view of the actuator system shown in  FIGS. 1 to 3 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Referring now to the drawings, there is shown in  FIGS. 1 and 2  an actuator system assembly  1  including a bearing assembly according to a preferred embodiment of the invention. The actuator system assembly  1  comprises a pair of spaced hydraulic cylinders  3  whose longitudinal axes (A-A in  FIG. 4 ) are arranged parallel to each other. Each cylinder  3  comprises a cylinder housing  4  with a piston  5  (see  FIG. 4 ) slideably received in the cylinder housing  4  to drive a control surface (not shown) towards and away from an aircraft wing (not shown) as the piston  5  slides into and out of the cylinder housing  4  in response to changes in hydraulic pressure on one side of the piston  5 . Each piston  5  has a shaft  6  that extends through a plate  7  closing an end of each cylinder housing  4 . 
         [0034]    Referring to the bearing assembly, it comprises a first movable support element  8  having a pair of collars  9  spaced from each other by a shaft  10 , which is just visible in  FIG. 4  between the collars  9 . The collars  9  are sized so as to receive and mount hydraulic cylinder housings  4  close to one end, and with their longitudinal axes (A-A in  FIG. 4 ) parallel to each other. The longitudinal axis of the shaft  10  (B-B in  FIG. 4 ) intersects and extends perpendicular to the longitudinal axis A-A of each cylinder housing  4 . The collars  9  and shaft  10  are all rigidly connected together and/or integrally formed so that there is no relative movement between them. The cylinders  4  are therefore held in fixed relative positions by the collars  9 . To further reinforce and maintain the relative positions of the cylinders  4 , two plates  12  extend between and are connected directly to the collars  9  at each end by screws  13 . 
         [0035]    A first part-spherical bearing element  14  has inner and outer race portions  14   a ,  14   b . The inner race portion  14   a  is received on the shaft  10  and the outer race portion  14   b  is seated within an aperture  15  formed in an arm  17  of a first fixed support member  18  that has a flange  19  with apertures  20  for attaching the first fixed support member  18  to a structural part of a wing of an aircraft using bolts inserted through said apertures  20 . Therefore, the first movable and fixed support members  8 ,  18  are coupled so that they can rotate relative to each other about the first part-spherical bearing  14 . 
         [0036]    It will be noted that the first fixed support member  18  may be formed in two parts  18   a ,  18   b  that attach to each other and together form the aperture  15  that encloses the first part-spherical bearing  14 . The two parts  18   a ,  18   b  may be coupled using bolts  21   a  that locate in hollow dowels  21  in the arm  17  for accurate alignment between the two parts  18   a ,  18   b . The bolts pass through the dowels  21  into the threaded arm  17  to provide purely a clamping force. It will be appreciated that the first spherical bearing  14  is located between the cylinders  4  and so does not contribute to an increase in the overall length of the assembly  1 . 
         [0037]    It is possible for only one end of the assembly  1  to be provided with a spherical bearing assembly of the invention that does not contribute to the overall length of the assembly to the same extent as a conventional assembly would. However, in a preferred embodiment, both ends of the system are equipped with a bearing assembly of the invention in which a part-spherical bearing is mounted and positioned between the cylinders  4  so as to provide maximum reduction in the overall length of the assembly. In this case, the bearing assembly further includes a second movable support member  25  which is attached to the ends of both pistons  6  using, for example, bolts  26 . The pistons  5  are therefore constrained so that they slide in unison into and out of their respective cylinders  4 . 
         [0038]    The second movable support member  25  has a central region  27  that extends inwardly towards the cylinders  4  between the piston shafts  6 . A generally rectangular shaped aperture  28  extends through the central region  27  in the same direction as the longitudinal axis A-A of the cylinders  3 . A hole  28  also extends laterally, at right-angles to the longitudinal axis A-A, through the central region  27 , intersecting the aperture  28 . 
         [0039]    A second fixed support member  29  has an arm  30  with an aperture  31  in which is received a second part-spherical bearing  32  having inner and outer bearing races  32   a ,  32   b . The arm  30  may be formed in two parts  30   a ,  30   b  which together combine to form the aperture  31  and enclose the second part-spherical bearing  32 . The two-parts of the arm  30  may be connected together using bolts  33 . that locate in hollow dowels  33   a  in part  30   b  for accurate alignment between the two parts  30   a ,  30   b . The bolts  33  pass through the dowels  33   a  into the threaded part  30   b  to provide purely a clamping force. 
         [0040]    Once the second part-spherical bearing  32  has been located in the arm  30  with the outer bearing race  32   b  seated in the aperture  31 , the arm  30  is inserted through the rectangular shaped aperture  28  in the central region  27  of the second movable support member  25  so that the second part-spherical bearing  32  is positioned in the aperture  28  in the central region and aligned with the holes  28 . A pin  33   b  having a hollow female threaded shaft  34  is then inserted through the holes  28  and second part-spherical bearing  32  and retained in place by a plug  35  having a threaded male shaft  35   a . The female thread in the shaft  34  is engaged with the male thread on the shaft  35   a . The two components together act as one but are expected to fail individually and so act as a failsafe pin arrangement. The inner race  32   a  is thereby mounted on the shaft  34  and the second part-spherical bearing  32  is mounted in position within the aperture  28  of the central region  27  between the ends of the piston shafts  6 . Consequently, the second movable and fixed support members  25 ,  29  are now connected via the second part-spherical bearing  32  so that they can rotate relative to each other about the second part-spherical bearing  32 . It will be appreciated that the arm  30  is a relatively loose fit in the rectangular shaped aperture  28  so that there is sufficient clearance to enable relative rotation between the second movable and fixed support members  25 ,  29  through a limited angular range of movement. 
         [0041]    The second fixed support member  29  has a flange  34  at the free end of the arm  30  remote from the aperture  28  that receives the second part-spherical bearing  32  to enable the second fixed support member  29  to be attached to a control surface of an aircraft using bolts that extend through apertures  35  in the flange  34 . 
         [0042]    The cylinders  3  are configured so that they operate in tandem and so that the piston  5  associated with each cylinder housing  4  moves by exactly the same amount. Rigid twinning of the two cylinders  4  ensures that any asymmetry is eliminated or reduced. However, it is also envisaged that front and rear balance manifolds can be utilised to ensure that cylinders  4  do not fight each other and pressure equalisation is maintained. The use of a balanced manifold could also provide faster actuator response times. 
         [0043]    With reference to the drawings, a manifold  36  is attached to each end of the cylinder housing  4 . Each manifold  36  has a fluid flow conduit therethrough to connect both cylinder housings  4  to a single fluid supply pipe  37  attached to each manifold  36 . This ensures that exactly the same amount of fluid is pumped into, and withdrawn from, each cylinder housing  4 . Movement of the pistons  5  may be monitored using a linear velocity displacement transducer (LVDT). If two LVDT&#39;s are used, feedback on each piston position can be obtained through a comparator. The comparator may be configured to actuate a shut-off valve in the event of any asymmetry between the cylinders  3 . Alternatively, LVDT&#39;s could inform a twinned servo valve arrangement so that corrections are made on a continuous basis. 
         [0044]    In one unillustrated modified embodiment, a spring may be located in each cylinder housing  4  to bias the pistons  5  to a neutral position in the absence of hydraulic pressure acting on the pistons  5 . 
         [0045]    It will be appreciated that as at least one spherical bearing element  14 ,  32  is now disposed between a pair of cylinders  3 , rather than protruding from one end of the assembly. Therefore, the overall length of the actuator system  1  is reduced providing more design flexibility. Although the width of the actuator  1  is increased as a result of employing two cylinders  3  in side-by-side relation, the space in the across-wing direction is of less concern and so this is considered to be an acceptable compromise with the two cylinders  3  being more easily accommodated within the wing. 
         [0046]    Reference is made above to movable and fixed support members. Movable support members are those that are coupled to and move together with the cylinders  3 , whereas the fixed support members are those that are coupled to the aircraft structure or control surface. 
         [0047]    It will be appreciated that the foregoing description is given by way of example only and that modifications may be made to the support assembly of the present invention without departing from the scope of the appended claims.