Abstract:
The invention pertains to an engine mount onto an aircraft structure comprising at least one connection means between a first and a second element such as an engine case and said structure, characterized by the fact that said connection means comprises an eccentric member housed in a bore of the first element, being rotational about a first axis, the eccentric member comprising a trunnion attached to the second element and of axis off-centred with respect to the first axis of rotation, the eccentric member being rotational about said off-centred axis. 
     The solution of the invention has the advantage of allowing a compact assembly.

Description:
BACKGROUND OF THE INVENTION 
   
       
       
         
           1. Field of the Invention 
         
       
     
  
   The present invention relates to the mounting of jet engines onto an aircraft structure.
         2. Description of the Related Art       

   A jet engine, such as a turbojet engine, may be mounted at various points of the aircraft being hung from a mast or pylon that is part of the aircraft structure. It may be mounted under the wings, attached to the fuselage, generally at the rear, or mounted in the tail unit by mounting means. The function of these mounting means is to ensure the transmission of mechanical loads between the engine and the aircraft structure. The loads to be taken into consideration are oriented along the three main directions of a reference frame related to the engine. These are the weight of the engine along the vertical axis Z, its thrust along axis X of the engine, and lateral aerodynamic loads along the transverse axis Y. The loads to be transmitted also comprise the rotational torque about the engine axis. These means must also absorb the deformations undergone by the engine during the different flight phases, without transmitting the same to the pylon, which are derived for example from dimensional variations due to thermal expansions or contractions. 
   The connection between the engine and the pylon is generally ensured, for turbofan jet engines, by two mounts, one forward of the engine and the other aft. Each of the mounting means is arranged to transmit part of the loads. For example, one of the mounts ensures the transmission of lateral forces along axis Y and vertical forces along axis Z, and transmission of the engine torque about axis X. The other transmits thrust and also lateral and vertical forces. 
   Generally a mounting means comprises a beam, optionally double, fixed to the pylon by bolts and joined to the engine case by links. These links swivel at their ends on devises or lugs, depending upon assembly, and are respectively integral with the case and beam. So that load transmission by the links is purely axial, a ball-joint bearing is provided for the cross pins, at each end of the links. With this assembly it is possible in particular to absorb radial and axial expansions of the engine. Provision is also made for connection means having a clearance, so-called standby connections, which become active when the clearance is reduced should one of the transmissions fail subsequent to failure of a part. 
   Patents EP 1216921 or FR 2820402 illustrate mounting modes of this type. 
   The beams are generally fairly massive and of complex shape. They ensure the transition between a horizontal plane of attachment to the pylon and a vertical plane comprising devises for connection to the engine. For wing mounting the height dimension of the beams depends upon the space that needs to be reserved for the attachment bolts to the pylon. 
   Also, a sufficient space must be set aside between the case and the beam to house the links and allow them free movement. 
   The attachment of the engines on some parts of the aircraft, for example on the wings, requires that the volume taken up by the mount should be as small as possible since the available space is fairly limited. 
   SUMMARY OF THE INVENTION 
   The applicant has therefore set itself the objective of developing a mount whose height is lower than is known in the prior art. 
   A further objective of the invention is to provide a mount consisting of parts whose shapes are simple and whose manufacture is relatively low-cost. 
   A still further objective of the invention is to provide a mount integrating failsafe means ensuring load transmission in the event of partial failure of a part. 
   According to the invention it is possible to attain these objectives with an engine mount for an aircraft structure comprising at least one connection means between a first and a second element such as an engine case and said structure, characterized by the fact that said connection means comprises an eccentric member housed in a bore of the first element and being rotational about a first axis, the eccentric member comprising a trunnion attached to the second element and having an off-centre axis relative to the first axis of rotation, the eccentric member being rotational about said off-centre axis. 
   The first or second element may also be a beam or any other intermediate part between the case and the structure. 
   The eccentric member is in the shape of a disc for example mounted via a bearing in the bore, and preferably the trunnion is mounted on the disc. 
   The mount that is the subject of the claim may be applied both to the forward part of the engine and to the aft part. By replacing the link rod connection between the two elements by a connection with a member of eccentric type, it is possible to achieve a more compact assembly since the connection, with its at least two degrees of freedom, can be housed within the contour of one of the elements. In this way, the height dimension of the mount is reduced by several centimetres without losing out on radial mobility. The ground clearance of the rotating assembly can be increased, or a space may be reserved for positioning shock-absorbing elastomers. 
   This new connection means may be widely applied. 
   According to one embodiment, the invention is applied to the connection between the engine case and a beam. The connection means comprises at least one eccentric member and a pin distant from said eccentric member swivelling between the case and the beam. In this manner the transmission of vertical and lateral loads is ensured and the transmission of engine torque, while allowing free expansion of the engine case. 
   According to one variant of this embodiment, the connection means comprises at least one first and one second eccentric members. Preferably, it comprises three thereof in this embodiment for transmission of engine torque. Said connection then finds advantageous application as a forward engine mount between the aircraft structure and the intermediate case, or an aft mount. 
   According to a further characteristic, the means of the invention form a connection between the beam and the aircraft structure. It comprises a structural eccentric member and a pin distant from said structural eccentric member swivelling between the beam and the structure. As in the preceding solution for the connection between the case and the beam, this connection means enables both the transmission of vertical and lateral loads and the transmission of engine torque, while allowing radial dimensional variations between the beam and the aircraft structure. 
   According to one variant, the connection means between the beam and aircraft structure comprise at least one first and one second structural eccentric members. 
   In this embodiment, the mounting of the engine to the aircraft structure preferably comprises a connection means between the case and the beam and a connection means between the beam and the structure. 
   Advantageously, the disc of at least one of said eccentric members is mounted in its housing on the element by means of a bearing forming a ball-joint, or else the trunnion with off-centre axis of at least one of the discs is mounted in the eccentric member by the bearing means forming a ball-joint. Preferably, at least one of said distant pins is also mounted in its housing by means of a bearing forming a ball-joint. 
   This ball-joint function is obtained for example by mounting the trunnion on its eccentric member in a bearing housed in a retainer having a spherical surface and forming a ball-joint, as is known to persons skilled in the art. This ball-joint function may also be obtained by mounting the eccentric member in a bearing with spherical surface. 
   According to one particular embodiment, a double ball-joint function is imparted to the eccentric member by providing a ball-joint both for the trunnion pin and for the rotating disc. In this way freedom of rotation is ensured over a wide angle. 
   Preferably, the distant pin is also mounted in a bearing forming a ball-joint. With this embodiment, it is possible to absorb axial expansions or contractions of the case during transitory operating phases of the engine. In particular, in the first embodiment, through the similar arrangement of the beam with the engine structure, it is made possible through the combined movements of the beam relative to the engine case and of the beam relative to the aircraft structure, to absorb efficiently the axial expansions or movements of the engine with respect to the aircraft structure. 
   Further preferably, it is provided that one of the pins or trunnions is able to slide with respect to one of the elements: case, beam or structure. In this way it is ensured that the loads involving rotation of the engine case about the vertical axis Z are not transmitted, and a fully isostatic assembly is provided. 
   According to a further characteristic, the mount comprises a first standby connection member between the beam and the engine case, arranged between the first and second trunnions. 
   According to a further characteristic the mount comprises a second and a third standby connection member between the beam and the aircraft structure. 
   Preferably, the standby connection members are formed by a trunnion housed in a bore with a set clearance. According to one embodiment, at least one of the pins or trunnions is mounted in its bearing being axially mobile. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages will become apparent on reading the following description of a non-restrictive embodiment of the invention, accompanied by the drawings in which: 
       FIG. 1  shows an engine mount attached to an aircraft pylon with its forward and aft attachments, 
       FIG. 2  shows a mount according to a first embodiment of the invention, 
       FIG. 3  shows a cross-section view of  FIG. 2  along direction  3 - 3 , 
       FIG. 4  shows a cross-section of  FIG. 2  along direction  4 - 4 , 
       FIG. 5  shows just the beam of the mount according to the first embodiment of the invention, 
     FIGS.  6 A 1  and  6 B 1  show a front view of part of the mount according to the first embodiment in cold engine and hot engine position, 
     FIGS.  6 A 2  and  6 B 2  show a side view of the mount according to the first embodiment in cold engine and hot engine position, 
       FIG. 7  gives a perspective view of a second embodiment of the invention, 
       FIG. 8  is a front view of the eccentric member in  FIG. 7 , 
       FIG. 9  is a cross-section of  FIG. 7  along direction  9 - 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  very schematically shows a turbojet engine  1  mounted on a pylon  3  which is part of the wing structure of the aircraft and is not visible. The mount generally comprises a forward attachment  5  at the intermediate fan case, and an aft attachment  7  at the exhaust case. Both cases are structural elements of the engine through which mechanical loads transit between the aircraft structure and the engine. 
   The invention such as illustrated in the description of the first embodiment given below is applied to the aft attachment, but it could also be applied to the forward or other attachment. 
   Mount  7  comprises a beam  10  positioned transverse to axis X of engine  1  between the annular frame  20 , that is here integral with the turbine case, and the base  30  of the pylon. 
   A more detailed description will now be given of the mount with reference to  FIGS. 2 to 5 . The beam  10  here is in the general shape of an arc of a circle with attachment means to the annular frame of case  20  which itself is in the shape of an arc of a circle and perpendicular to the engine axis. This annular frame forms two radial devises  21  and  23  spaced apart on the arc of a circle with bores and bearings to receive two trunnions or pins. The connection means of a first element such as the beam  10  to a second element such as the case  20  comprises an eccentric member  13  at one end of the beam  10  and a pin  11  at the opposite end. As can be seen in more detail in  FIG. 3 , the eccentric member  13  consists of a disc  131  housed in a bore provided in the beam  10  and having a rotational axis  131 A. 
   In this embodiment, the disc is rotationally mounted about the sole rotational axis  131 A perpendicular to its plane. This disc may also, in one variant such as shown  FIGS. 7 to 9 , be mounted so as to form a ball-joint. 
   Also the disc is shown to be solid; however, it may be of any other shape, all that is required is that it should be housed in a bore provided in the beam  10 . 
   On this disc  131 , a trunnion pin  133  is mounted of axis  133 A off-centred with respect to axis  131 A, via a bearing  134  forming a ball-joint and housed in a retainer  135 . The external surface of the bearing  134  is spherical enabling the trunnion  133  to pivot and tilt at a certain angle with respect to the plane of the disc  131 . The trunnion  133  crosses through the two branches of the clevis  23  in which it is supported by bearings  123 . In operation, axis  131 A may rotate about axis  133 A, and axis  133 A may rotate about axis  131 A. 
   On the opposite side of beam  10 , a pin  11  is swivel-mounted in the beam and the two branches of the clevis  21 . Advantageously, the pin  11  is housed in a bearing  11 R whose outer surface is spherical to enable pin  11  to rotate about itself around its rotational axis  11 A. The rotational axis  11 A through the ball-joint is able to tilt at a certain angle with respect to the plane of the beam  10 . 
   It can be seen in  FIG. 2  that the mount comprises a connection means for the beam to the aircraft structure  30  also formed by an eccentric member  43  on one side of the beam and by a pin  41  on the other end of the beam  10 . 
   The eccentric member  43  is formed of a disc  431  mounted in a cylindrical housing of axis  431 A. Like member  13  it is rotationally mounted about the sole axis  431 A but in another embodiment it may be swivel mounted. The disc comprises a trunnion  433  of axis  433 A off-centred with respect to axis  431 A. Axis  433 A rotates about rotational axis  431 A of disc  431 . 
   The trunnion  433  is supported in disc  431  by a bearing with a spherical outer surface  434  via a retainer  435 . 
   The distant pin  41 , like distant pin  11 , swivels through clevis  31  and is mounted on the beam via a bearing forming a ball-joint  41 R. 
   To meet safety constraints in the event of partial failure of a part, the solution makes it possible to provide standby connection members. As can be seen in  FIG. 2 , a first standby connection member  101  consists of a trunnion which is housed in a bore passing through a central clevis  24  of annular frame  20  and the beam  10  with a set clearance. For reasons related to clarity of the drawing the trunnion is not shown. Only the bore  102  can be seen in which it is housed. In normal operation, the trunnion is not subjected to any load on account of the clearance. 
   Similarly, a second and a third standby connection member  105  and  107  are arranged on the annular frame  30  of the aircraft structure. The two members consist of two trunnions housed in two bores  106  and  108  with a set clearance either side of the vertical plane in which the member  101  is located, passing through the annular frame  30  and the beam that is housed between the two branches of the clevis. The two trunnions are not shown. 
     FIG. 5  shows the beam alone fitted with its eccentric members  13  and  43 , and with the respective distant pins  11  and  41 . The trunnions  133 ,  433  and the pins  11  and  41  are mounted on the discs and respectively the beam via spherical surface bearings  134 ,  434 ,  41 R and  11 R to form ball-joints. 
   A description is now given of the relative positioning of the parts in two different phases of engine operation. 
   In FIG.  6 A 1  the engine is cold, the left end of the mount shows the two eccentric members  13  and  43  with their eccentric trunnions  133  and  433 . In FIG.  6 A 2  which is a side view of the mount, the beam inclines towards the left. Tilting of the beam makes it possible to maintain an isostatic connection between the case  20  and the aircraft structure  30 ; this tilting is made possible by the two ball-joints. 
   In FIG.  6 B 1 , which corresponds to the situation when the engine is very hot, in a transitory engine operating phase, the eccentric member  133  with its trunnion has rotated to adapt to expansion of the case  20 . At the same time, the engine has become elongated and cambered. The beam then occupies the position seen in FIG.  6 B 1 . It can be seen that the annular frame  20  has shifted leftwards with respect to structure  30 . 
   The failsafe system functions as follows. 
   Failure of the trunnion  133  or pin  11  imposes partial rotation about pin  11  or trunnion  133  respectively, and reduces the clearance in the standby connection member  101 . Loads are then transmitted via this newly active connection. 
   Failure of the pin  41  on the structure side imposes rotation and reduced clearance in the standby connection member  107 . Transmission of loads passes through the newly active connection  107  and connection  433  is undamaged. Transmission is symmetrical in the event of a failure at the connection by the eccentric member  433 . 
   The invention is not limited to this embodiment such as described. It is possible, for example, to position the ball-joint assembly not on the off-centred trunnion but on the disc itself of the eccentric member. 
   It is also possible, especially if the tilt angle between the two end positions of the beam is not too great, to make provision for a double ball-joint for the eccentric member. 
   A second embodiment is now described of a mount incorporating eccentric members. 
   This concerns the forward mount of a turbofan jet engine for example. As can be seen in  FIGS. 7 ,  8  and  9  an intermediate cross piece in the form of a beam or hanger  1010  is made integral with the aircraft structure, a pylon for example that is not shown, using appropriate attachment means. This first element  1010  is joined to a second element  1003 , the intermediate case for example, by a connection means that here consists of an eccentric member  1013  at each end. The member  1013  is mounted on one side on element  1010  and on the other side on element  1003  via a trunnion which is not shown for reasons of figure clarity. The trunnion is mounted on the branches of a clevis  1023  that is part of the case. 
   The eccentric member comprises a disc  1131  of axis  1131 A swivel-mounted in a bore of element  1010  via a bearing with spherical surface  1132  housed in a retainer  1136  that is integral with the bore. On this disc  1131  a ball-joint is mounted of axis  1133 A with a spherical bearing  1134  housed in a retainer  1135  that is integral with a bore of disc  1131 . The two axes  1131 A and  1133 A are separate. The trunnion of axis  1133 A, which is not shown, passes through the two branches of clevis  1023 . 
   Said eccentric member may comprises means such as a groove enabling dismounting of a ball-joint head for maintenance. 
   This arrangement is equivalent to a link rod connection insofar as it is arranged so as to transmit loads in one direction only. This property is reproduced in this assembly with eccentric members. The first advantage with respect to links is the compactness of the connection. In addition it offers a weight gain. 
   This type of connection makes it possible to absorb variations due to thermal expansions and to make up for differences due to manufacturing tolerances.