Abstract:
In order to reduce the width of the attachment between the rear portion of an aircraft engine and its attachment pylon, an engine assembly attachment include an assembly of rear engine attachments comprising a first connecting rod laid out in a longitudinal and median vertical plane, a second connecting rod substantially laid out tangentially to the inter-turbine case, and a rear engine attachment for transversely spreading the loads, axially shifted rearwards relatively to the first and second connecting rods, and comprising a shear pin oriented along a vertical direction of the engine assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to French Patent Application FR 15 59474 filed Oct. 5, 2015, the entire disclosure of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to aircraft engine assemblies comprising a pylon for mounting the engine on a structure of the aircraft, preferably beneath a wing of the aircraft. 
         [0003]    The present disclosure relates more specifically to an engine assembly in which a rear engine attachment links the primary structure of the pylon to an inter-turbine casing of the engine. 
         [0004]    The present disclosure applies preferably to commercial airplanes. 
       BACKGROUND 
       [0005]    On existing aircraft, engines such as dual-flow dual-body turbojet engines are suspended beneath the wing system by complex mounting systems referred to as engine mounting structures (EMS) or mounting pylons. The mounting pylons normally used have a rigid structure referred to as the primary structure. This primary structure usually forms a box, i.e. it is formed by assembling lower and upper longerons connected together by a plurality of stiffening transverse ribs positioned inside the box. The longerons are arranged on the lower and upper faces, while the side panels close the lateral faces of the box. 
         [0006]    In a known manner, the primary structure of these pylons is designed to enable the static and dynamic forces generated by the engines—such as weight, thrust and other dynamic forces—to be transmitted to the wing structure. 
         [0007]    In the solutions known in the prior art, the transmission of forces between the engine and the primary structure is conventionally ensured using mounting means comprising a front engine attachment, a rear engine attachment and a thrust spreading device. These elements together form an isostatic attachment system comprising primary attachments to cover nominal operating conditions and secondary attachments to cover operation in the event of failures/faults, also referred to as failsafe cases. 
         [0008]    Normally, the rear engine attachment links the primary structure to the exhaust casing of the engine, also referred to as the gas exhaust casing, which is located at the rear end of this engine. A conventional example embodiment of the rear engine attachment is shown in FIG. 1 and disclosed in patent application FR 3 014 841. 
         [0009]    This rear engine attachment  7   a  therefore links the exhaust casing of the engine to the primary structure  6  of the box-shaped mounting pylon. To do so, the attachment  7   a  comprises a body  100  and a plurality of connecting rods  102  articulated with the engine attachment body  100  and with the clevises on the exhaust casing. More specifically, the body  100  has one or more cross members  104 ,  106  stacked vertically. The three connecting rods  102  are spaced out transversally, which results in the overall width of the rear engine attachment being relatively large. 
         [0010]    It has recently been proposed to install the rear engine attachment level with the inter-turbine casing of the engine, with a view to reducing the deformations of this latter. Limiting such deformations helps to better control blade-tip clearance in high- and low-pressure turbines, and helps to improve overall performance of the engine. Indeed, the fact of moving the rear engine attachment forwards from the exhaust casing towards the inter-turbine casing makes it possible to arrange this attachment in a zone in which the inner aerodynamic fairings of the nacelle, or inner fixed structure (IFS), are wider and therefore facilitate better aerodynamic integration. 
         [0011]    However, for this type of installation on the inter-turbine casing, the rear engine attachment usually has a design similar to the one shown in  FIG. 1 . Consequently, the significant width of same is liable to require the overdimensioning of one or more of the structures inside the nacelle flow path, some of which are intended to streamline the rear engine attachment. Such overdimensioning increases the size of the rear attachment or rear mount fairing (RMF), which may take the form of local enlargements around the two lateral ends of the rear engine attachment, causing aerodynamic disturbances that have an adverse effect on the overall performance of the engine. 
       SUMMARY The present disclosure is therefore intended to disclose an aircraft engine assembly that at least partially overcomes the aforementioned problems found in the prior art solutions. 
       [0012]    To do so, the present disclosure relates to an aircraft engine assembly comprising: 
         [0013]    a dual-body engine comprising an inter-turbine casing, 
         [0014]    a pylon for mounting the engine on a structure of the aircraft, the pylon including a primary structure, 
         [0015]    a mount for mounting the engine on the primary structure of the mounting pylon, the mount comprising a system of isostatic or hyperstatic attachments, the system of isostatic attachments being preferred. 
         [0016]    According to the present disclosure, the mount includes a rear engine attachment assembly comprising: 
         [0017]    a first connecting rod articulated at one of the ends of same with a bracket rigidly connected to the inter-turbine casing and articulated at the other end with a bracket rigidly connected to the primary structure of the pylon, the first connecting rod being arranged in a median vertical and longitudinal plane; 
         [0018]    a second connecting rod articulated at one of the ends of same with a bracket rigidly connected to the inter-turbine casing and articulated at the other end with a bracket rigidly connected to the primary structure of the pylon, the second connecting rod being arranged substantially tangential to the inter-turbine casing; and 
         [0019]    a rear engine attachment for transverse force spreading, shifted axially backwards in relation to the first and second connecting rods, and including a shear pin oriented in a vertical direction of the engine assembly and rigidly connected to either the engine or the primary structure, as well as a seating bracket for the shear pin that is rigidly connected to the other of the elements and that has a seating orifice for the shear pin, the shear pin being seated in the seating orifice with a clearance in the longitudinal direction of the engine assembly. 
         [0020]    Thus, the mount of the rear portion of the engine is split into several engine attachments that are preferably split between two or three parallel planes normal to the longitudinal axis of the engine. A rear plane including a shear pin is shifted axially along the longitudinal axis of the front plane (or of the front planes) including the first and second connecting rods. This novel distribution of attachments between several axially shifted planes advantageously reduces the overall width of this rear engine attachment assembly. This in turn reduces the width of the surrounding secondary structures, thereby increasing the overall performance of the engine. 
         [0021]    Furthermore, the rear attachments are simplified, resulting in a reduction in mass. Also with a view to reducing overall mass, simple connecting rods are used between the primary structure and the inter-turbine casing, which obviates the need for an intermediate structure attached between the primary structure of the pylon and the inter-turbine casing, as in the prior art. 
         [0022]    The present disclosure incorporates at least one of the following optional features, individually or in combination. 
         [0023]    According to a first embodiment, the first and second connecting rods are arranged in the same transverse plane of the engine assembly. 
         [0024]    According to a second embodiment, the first and second connecting rods are arranged respectively in two different transverse planes of the engine assembly. In this case, it is possible that, when viewed axially, the first and second connecting rods cross one another to further reduce the overall transverse width of the rear engine attachment assembly. 
         [0025]    Each of the first and second connecting rods is associated with an emergency connecting rod that is only stressed in the event of the related connecting rod suffering an accident. 
         [0026]    The shear pin is seated movably in vertical translation in the seating orifice, and the free end of the pin is provided with vertical stopping member arranged vertically distant from a complementary stopping member rigidly connected to the primary structure. The arrangement provides a failsafe function for spreading forces in the vertical direction in the event of damage being caused to the first and second connecting rods, for example in the event of rotor break-up, the objective then being to keep the rear portion of the engine on the airplane (to withstand the weight and dynamic forces). 
         [0027]    The primary structure of the mounting pylon is in the form of a box fitted with a lower longeron, the vertical stopping member is positioned inside the box, and the complementary stopping member is formed by the lower longeron. 
         [0028]    The rear engine attachment for transverse force spreading is positioned on an exhaust casing of the engine, although a more forward position towards the connecting rods is possible without thereby moving outside the scope of the present disclosure. 
         [0029]    The shear pin is preferably rigidly connected to the engine, although it may alternatively be rigidly connected to the primary structure of the pylon. 
         [0030]    The shear pin comprises: 
         [0031]    a base; 
         [0032]    a vertical shaft rigidly connected to the base; 
         [0033]    a male ball-joint element formed on the vertical shaft; 
         [0034]    an outer bearing member inside the pin seating orifice; the outer member having an inner surface defining a female ball-joint element cooperating with the male element. 
         [0035]    The mount also has a front engine attachment, as well as a thrust spreading device oriented in the longitudinal direction of the engine assembly. 
         [0036]    The rear engine attachment, the front engine attachment and the thrust spreading device thus make up the mount of the engine, forming an isostatic force-spreading system. 
         [0037]    The thrust spreading device comprises: 
         [0038]    a supporting element attached to the primary structure; 
         [0039]    two thrust-spreading lateral link rods; and 
         [0040]    a swing bar articulated with the supporting element, both lateral link rods being articulated with the two opposite ends of the swing bar respectively. 
         [0041]    The supporting element is positioned in front of the first and second connecting rods. 
         [0042]    The present disclosure also relates to an aircraft including at least one such engine assembly. 
         [0043]    Other advantages and features of the present disclosure are set out in the non-limiting detailed description given below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    This description is made with reference to the attached drawings, in which: 
           [0045]      FIG. 1 , as described above, shows an aircraft engine assembly according to the prior art including a mounting pylon and a rear engine attachment; 
           [0046]      FIG. 2  shows an aircraft fitted with an engine assembly according to the present disclosure; 
           [0047]      FIG. 3  is a schematic side view of the engine assembly shown in the previous figure, according to the present disclosure; 
           [0048]      FIG. 4  is a more detailed side view of the rear engine attachment assembly shown in the previous figure; 
           [0049]      FIG. 5  is an axial front view of the first and second connecting rods forming an integral part of the rear engine attachment assembly shown in  FIG. 4 ; 
           [0050]      FIG. 6  is a cross section taken along the line VI-VI in  FIG. 5 ; 
           [0051]      FIG. 7  is a side view of the rear engine attachment for transverse force spreading, forming an integral part of the rear engine attachment assembly shown in  FIG. 4 ; 
           [0052]      FIG. 8  is an axial front view of the first and second connecting rods according to another embodiment of the present disclosure; 
           [0053]      FIG. 9  is a cross section taken along the line IX-IX in  FIG. 8 ; and 
           [0054]      FIG. 10  is a schematic perspective view showing the force spreading by the mount of the engine on the pylon. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]      FIG. 2  shows an aircraft  200  including a fuselage  3  to which are attached two wing system elements  2  (only one visible in  FIG. 2 ), each wing system element bearing an engine assembly  5  according to the present disclosure. This engine assembly  5  includes a dual-flow dual-body engine  10 , such as a turbojet, and a mounting pylon  4  for the engine  10 . 
         [0056]      FIG. 3  shows one of the engine assemblies  5  in greater detail. The wing system elements  2 , the turbojet engine  10  and the mounting pylon  4  are shown. Furthermore, mounts  8  for the pylon  4  are provided on the wing system element  2 , and mounts  7   a,    7   b,    7   c  for the turbojet  10  are provided on the pylon. These mounts  7   a,    7   b,    7   c,  the pylon  4  and the turbojet  10  form the engine assembly  5  according to the present disclosure. 
         [0057]    The mounts  8 , located at the interface between the pylon  4  and the wing system element  2 , is formed in a conventional manner. As a result, they shall not be described in further detail. 
         [0058]    The mounts  7   a - 7   c  are formed by a rear engine attachment assembly  7   a , a thrust spreading device  7   b,  and a front engine attachment  7   c.  In this regard, it can be seen that the front end of the primary structure  6  of the pylon, also referred to as the primary structure, is attached using the front engine attachment  7   c  to an external shroud  13  of an intermediate casing  15  of the turbojet  10 . This shroud  13  forms a rearward axial extension of the fan casing  17  of substantially the same diameter. Alternatively, the front engine attachment  7   c  may be attached to the compressor casing  18  closer to the longitudinal axis  30  of the turbojet  10 . 
         [0059]    In the remainder of the description, the direction X shall correspond to the longitudinal/axial direction of the pylon  4 , which is also similar to the longitudinal direction of the turbojet  10  and of the engine assembly  5 . This direction X is parallel to the longitudinal axis  30  of this turbojet  10 . Furthermore, the direction Y corresponds to the direction oriented transversely in relation to the mast  4  and also similar to the transverse direction of the turbojet  10  and of the engine assembly  5 , while the direction Z corresponds to the vertical direction or height. These three directions X, Y and Z are mutually orthogonal and form a right trihedron. 
         [0060]    Furthermore, the terms “front” and “rear” shall be understood in relation to the direction of forward movement of the aircraft following the thrust exerted by the turbojets  10 , this direction being represented schematically by the arrow  19 . 
         [0061]      FIG. 3  shows only the primary structure  6  of the mounting pylon  4 . All of the component parts of this pylon  4  that have not been shown, specifically secondary structures ensuring the segregation and attachments of systems while carrying the aerodynamic fairings, are elements known in the prior art. Consequently, no detailed description shall be made thereof. 
         [0062]    The primary structure  6  is usually made up of a “box”, i.e. formed by assembling upper and lower longerons  20 ,  22  and two side panels  24  (only one being visible due to the side view), these elements  20 ,  22 ,  24  being connected together by internal stiffening transverse ribs (not shown), which are usually oriented along the parallel planes YZ. These ribs are preferably uniformly distributed inside the box  6  in the direction X. Other embodiments of the primary structure are nonetheless possible without thereby moving outside the scope of the present disclosure. 
         [0063]    With reference to the mounts  7   a - 7   c,  the thrust spreading device  7   b  is also formed in a conventional manner using two lateral link rods  9  designed to spread forces in the direction X. These link rods  9  are arranged symmetrically about a median plane XZ of the engine assembly  5 . The link rods are articulated at the front end with an internal shroud of the intermediate casing  15 , and are articulated at the rear end respectively with the two opposing lateral ends of a swing bar  32 . The swing bar  32  is in turn articulated at the center of same with a supporting element  34  that is attached beneath the lower longeron  22  of the primary structure  6 . 
         [0064]    The supporting element  34  is located in front of and close to the rear engine attachment assembly  7   a,  which links the casing of the turbojet  10  to the lower longeron  22 . 
         [0065]    The design of the rear engine attachment assembly  7   a  is given below with reference to  FIGS. 4 to 7 . The assembly comprises three separate attachments, specifically a first connecting rod  7   a   1 , a second connecting rod  7   a   2 , and a rear engine attachment  7   a   3  for transverse force spreading. 
         [0066]    The rear portion of the engine that cooperates with these attachments  7   a   1 ,  7   a   2 ,  7   a   3  has, from front to back, a high-pressure turbine casing  44 , an inter-turbine casing  46 , a low-pressure turbine casing  48 , and an exhaust casing  50 . 
         [0067]    The first connecting rod  7   a   1  is arranged in a medium vertical and longitudinal plane  52  of the engine assembly  5 , and is preferably oriented in the direction Z to spread only the forces exerted in this vertical direction. The upper end of same is articulated with a bracket  54  attached statically to the lower longeron  2  of the primary structure  6 , and more specifically is articulated with a clevis  54 - 1  provided on the bracket. The lower end of same is articulated with a clevis-shaped bracket  56  attached statically to or formed as a single part with the inter-turbine casing  46 . 
         [0068]    The second connecting rod  7   a   2  is arranged substantially tangential to the inter-turbine casing  46 , and is preferably arranged in a transverse plane XZ. From an axial view such as the one shown in  FIG. 5 , the angles of inclination between the second connecting rod  7   a   2  and each of the two directions Y and Z is for example around 20° to 70°. 
         [0069]    The upper end of the second connecting rod is articulated with the bracket  54  at a point different to that of the first connecting rod  7   a   1 , and more specifically is articulated with a clevis  54 - 2  also provided on the bracket. The lower end of same is in turn articulated with a clevis-shaped bracket  58  attached statically to or formed as a single part with the inter-turbine casing  46 . 
         [0070]    On account of the substantially tangential arrangement of same, the second connecting rod  7   a   2  is provided exclusively to spread the moment exerted in the direction X. 
         [0071]    The joints of the connecting rods  7   a   1 ,  7   a   2  are made using jointing members oriented in the direction X. These jointing members are preferably doubled up to deal with accident conditions, thereby providing the failsafe function in the event of failure of the jointing members active during normal operating conditions. 
         [0072]    Each of the two connecting rods  7   a   1 ,  7   a   2  may also be doubled up, also for safety reasons. More specifically,  FIG. 6  shows how a first emergency connecting rod  7   a   1 ′ may be associated with the first connecting rod  7   a   1 . This first emergency connecting rod is mounted such that it is inactive under normal operating conditions, but is able to spread the vertical forces in the event of an accident occurring to the first connecting rod  7   a   1 . Similarly, and also with a view to providing the failsafe function, a second emergency connecting rod  7   a   2 ′ may also be associated with the second connecting rod  7   a   2 . The second emergency connecting rod is mounted such that it is inactive under normal operating conditions, and stressed in order to spread the moment exerted in the direction X in the event of an accident occurring to the second connecting rod  7   a   2 . 
         [0073]    The connecting rods  7   a   1 ,  7   a   2  are therefore preferably arranged in a first transverse plane YZ  59  of the engine assembly  5 , while the emergency connecting rods  7   a   1 ′,  7   a   2 ′ are preferably arranged in a second transverse plane YZ  60 , located very close axially to the first plane  59 . Preferably, the connecting rods  7   a   1 ,  7   a   1 ′,  7   a   2 ,  7   a   2 ′ are arranged so as to be perfectly superposed in pairs when viewed axially. 
         [0074]    The rear transverse spreading attachment  7   a   3  is positioned axially behind the connecting rods  7   a   1 ,  7   a   2 . It attaches the exhaust casing  50  to a rear end of the lower longeron  22  of the primary structure  6 , in a small vertical gap or space between the turbojet  10  and the primary structure  6  of the pylon. This attachment  7   a   3  is designed exclusively to spread the forces exerted in the direction Y. The attachment is traversed symmetrically by the median plane  52 , as shown more clearly in  FIG. 7 . 
         [0075]    This figure shows an example design of the attachment  7   a   3 . It includes a shear pin  64  oriented in the vertical direction Z and mounted statically on the exhaust casing  50 . This attachment, which is a spigot attachment, also includes a bracket  66  for seating the shear pin, that is attached statically to the lower longeron  22  of the box  6  and outside the latter. This bracket  66  is provided with a seating orifice  68  for the shear pin  64 . 
         [0076]    The shear pin  64  is preferably formed of several elements, which are described below. Firstly there is a base  70  used for attachment to the exhaust casing  50 , and a vertical shaft  72  preferably formed as a single part with the base  70 . This shaft  72  is formed to define a male ball-joint element  74  by a spherical outer shape. 
         [0077]    Furthermore, an outer member  76  completes this shear pin  64 . This is a bearing member inside the seating orifice  68 , that has an inner surface defining a female ball-joint element  78  cooperating with the male element  74 . 
         [0078]    The outer bearing member  76  is in contact with the wall of the seating orifice  68  in the direction Y. Conversely, a clearance  81  is provided between these two elements  68 ,  76  in the direction X to ensure that force is only transmitted in the direction Y, since the presence of the ball-joint elements  74 ,  78  also filters out spurious moments. 
         [0079]    To provide a failsafe function related to the attachment  7   a   3 , instead of being made of a single part, the base  70  and the vertical shaft  72  may be made of two symmetrical parts attached to one another, as shown in  FIG. 7 . 
         [0080]    Furthermore, a failsafe function in the direction Z may also be associated with this attachment  7   a   3 . Indeed, the free end of the vertical shaft  72  located inside the box  6  is provided with a vertical stopping member  80  that is for example in the form of a nut. This member  80  is arranged vertically distant from the lower longeron  22 , which forms a complementary stopping member. Consequently, under normal operating conditions, the spreading of forces in the direction Z by the attachment  7   a   3  is not active on account of the vertical gap between the stopping member  80  and the lower longeron  22 . Conversely, in the event of an accident occurring to the connecting rods  7   a   1 ,  7   a   1 ′, since the outer bearing element  76  of the pin  64  is mounted movably in vertical translation in the seating orifice  68 , the vertical clearance  83  is closed until the elements  80 ,  22  come into contact. The latter may also spread forces in the vertical direction Z. 
         [0081]    According to another preferred embodiment further reducing the transverse footprint related to the two connecting rods  7   a   1 ,  7   a   2 , these latter cross one another when viewed axially, as shown in  FIG. 8 . To achieve this, these two connecting rods are arranged in different transverse planes YZ that are spaced out axially. Again in this case, the connecting rods  7   a   1 ,  7   a   2  arranged in the transverse planes  59 ′,  59 ″ may be doubled up to provide the failsafe function, as shown in  FIG. 8 . 
         [0082]    The mounts  7   a - 7   c  described above are the only elements in the engine assembly  5  that transfer loads between the turbojet  10  and the primary structure of the pylon. They form an isostatic force-spreading system under normal operating conditions. Indeed, as shown schematically in  FIG. 10 , the front engine attachment  7   c  only spreads forces in the directions Y and Z, while the device  7   b  only spreads forces in the direction X. In the rear engine attachment  7   a,  which is split into three separate attachments, the first connecting rod  7   a   1  only spreads forces in the direction Z, while the attachment  7   a   3  only spreads forces in the direction Y. 
         [0083]    Moreover, the forces exerted in the direction X are spread using the device  7   b,  the forces exerted in the direction Y are spread using the front engine attachment  7   c,  the second connecting rod  7   a   2  and the rear attachment  7   a   3 , while the forces exerted in the direction Z are spread jointly using the front engine attachment  7   c  and the first connecting rod  7   a   1 . 
         [0084]    Furthermore, the moment exerted along the axis X is spread using the force components oriented in the directions Y and Z using the three attachments formed by the first connecting rod  7   a   1 , the second connecting rod  7   a   2  and the rear attachment  7   a   3 , the moment exerted in the direction Y is spread using the force components oriented in the direction Z using the two attachments formed by the first connecting rod  7   a   1  and the front engine attachment  7   c,  and the moment exerted in the direction Z is spread using the force components oriented in the direction Y using the two attachments formed by the rear attachment  7   a   3  in combination with the front engine attachment  7   c.    
         [0085]    Naturally, a person skilled in the art may make different modifications to the present disclosure described above purely by way of non-limiting example. 
         [0086]    While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.