Abstract:
An adapting part is designed to be held on a casing of a turbo-engine, partially covering the casing. The adapting part includes, in the extension of one of its axial ends, a first connector to engage with a first complementary connector associated with the casing to form a sliding connection. The adapting part also includes, at its other axial end, a second connector to be secured to a second complementary connector associated with the casing to form a rigid connection.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method for holding an adapting part on a tubular casing of a turbo-engine, and to a corresponding adapting part and holding system. 
     The present invention applies in particular, although not exclusively, to a suspension for a turbo-engine on a pylon of an aircraft, by means of which the turbo-engine can be attached entirely securely to the structure of the aircraft. 
     The term suspension designates, in general terms, all the various necessary parts for attaching the turbo-engine to the pylon, such as attachments, articulations, spindles, ball swivels, articulated rods, arms, hoops, fittings, etc., which are usually employed to that effect. 
     Description of the Related Art 
     As is known, the suspension of a turbo-engine below a wing of an aircraft is generally located and contained in specific suspension planes of the turbo-engine, which planes are mutually parallel and orthogonal to the longitudinal axis of the turbo-engine. 
     Thus, such a suspension may comprise:
         on one hand, a front suspension bracket in a front suspension plane located at the level of a structural intermediate casing of the turbo-engine and connecting the latter to the attachment bracket of the pylon; and   on the other hand, a rear suspension bracket in a rear suspension plane located at the level of the structural exhaust casing of the turbo-engine and connecting the latter to the attachment bracket of the pylon.       

     The front and rear suspension brackets are respectively attached to the intermediate casing and to the exhaust casing via the intermediary of simple or double articulated rods and clevises which are molded thereon. 
     It is further known that such a suspension comprises thrust uptake means in the form of struts which are inclined with respect to the axis of the turbo-engine. The thrust uptake struts connect an inner ring, in the front suspension plane, to an outer ring (or hoop) of the exhaust casing, in the rear suspension plane. The struts are fastened to the two rings by means of attachments. Each attachment consists of two simple or double clevises, of which one is secured to the end of the strut and the other is secured to the wall of the corresponding ring, a common spindle passing through these. 
     The purpose of the arrangement of the suspension is, in particular, to take up the forces which act in the three directions (roll, pitch and yaw) of an orthonormal reference frame connected to the aircraft, and the moments according to these three directions. 
     However, the bulkiness of the attachment devises molded onto the outer ring of the exhaust casing represents an important limiting factor when defining the lines of the nacelle surrounding the turbo-engine and causes problems for integrating the latter underneath the wing of an aircraft, in particular when trying to bring the turbo-engine as close as possible to the wings of the aircraft (for example in the case of increasing the bypass ratio of the engine for the same ground clearance). 
     Moreover, since attaching the pylon to the exhaust casing requires a structural exhaust casing, the latter has a large mass. 
     In addition, the considerable separation between the two suspension planes means that the thrust uptake struts must be long. In order to avoid any risk of buckling, the struts are dimensioned accordingly, which results in a large associated diameter and mass. 
     In order to compensate for these drawbacks, it is known for the rear attachment of the pylon to be on a structural inter-turbine casing of a turbo-engine. In particular, this rear attachment requires an intermediate structural outer ring which is bolted on the downstream flange of the inter-turbine casing via the intermediary of a single downstream flange of the intermediate ring. The thrust uptake struts are attached with the aid of a spreader which is connected to the rear suspension bracket by means of a pivot connection. This rear suspension bracket is, for its part, connected to the structural ring by struts. These are connected, on one hand, to the suspension bracket and, on the other hand, to the intermediate structural ring by means of molded attachment clevises. These clevises are arranged upstream of the downstream attachment flange of the inter-turbine casing and are thus arranged in a cantilever configuration with respect to the latter. It is then vital to reinforce the structure of the intermediate ring, either by increasing the thickness or with the aid of ribs, which makes the ring considerably heavier. 
     Moreover, attaching this intermediate outer ring to the only downstream flange of the inter-turbine casing subjects the flange to substantial forces, meaning that it too has to be strengthened, which once again leads to an increase in mass. 
     In addition, the downstream flange of the intermediate ring is attached to the downstream flange of the inter-turbine casing either by means of an axial bolted connection, obtained with the aid of bolts oriented axially (that is to say parallel to the axis of the turbo-engine), or by means of a radial bolted connection, obtained with the aid of bolts oriented radially (that is to say perpendicular to the axis of the turbo-engine). 
     In the case of an axial bolted connection of the flange of the intermediate ring, it is known to manage the manufacturing tolerances by providing peelable shims. However, such peelable shims are difficult and laborious to install since the manipulation thereof over the entire circumference of the intermediate ring is complex. 
     In the case of a radial bolted connection of the flange of the intermediate ring, where the bolts are subjected principally to shear loading, it is essential to use large-diameter bolts, which increases the mass associated with the intermediate ring. Moreover, in this latter case, it proves difficult to manage the expansion of the intermediate ring and of the inter-turbine casing. 
     It is an object of the present invention to remedy these drawbacks. 
     BRIEF SUMMARY OF THE INVENTION 
     To that end, according to the invention, the method for holding an adapting part on a tubular casing of a turbo-engine, said part being designed to partially cover said casing, 
     is noteworthy in that the following steps are carried out: 
     
         
         
           
             one of the axial ends of the adapting part is connected to a corresponding first axial end of said casing, so as to form an axially sliding connection in the extension of said axial end of the adapting part; and 
             the other axial end of the adapting part is attached to a corresponding second axial end of said casing, so as to form a rigid connection. 
           
         
       
    
     Moreover, the adapting part designed to be held on a casing of a turbo-engine according to the method set out is noteworthy in that it comprises:
         in the extension of one of its axial ends, a first connecting means configured so as to engage with a first complementary connecting means associated with said casing, so as to form the sliding connection; and   at its other axial end, a second connecting means configured so as to be secured to a second complementary connecting means associated with said casing, so as to form the rigid connection.       

     Thus, by virtue of the invention, the adapting part may be held, at its axial ends, on the casing of the turbo-engine by means of a rigid connection on one hand, and by means of a sliding connection on the other hand. It is thus possible, by means of the sliding connection, to absorb at least part of the expansion—in particular the axial expansion—of the adapting part and of the casing in question, when the turbo-engine is in operation. Management of the expansion is improved. Moreover, it is possible by means of the sliding connection to have radial centering of the adapting part which is more appropriate and more precise than with a flange-type rigid connection for which manufacturing tolerances are difficult to manage. The invention provides for larger contact surfaces by means of which the adapting part can be positioned radially. 
     It will be noted that the sliding connection may be arranged either upstream of said casing or downstream thereof. 
     Preferably, the first connecting means comprises at least one projecting tab, which is entirely circular or extends over a predetermined angular sector, preferably equal to 120°. Thus, no flange is used in order to form the sliding connection, which reduces the mass of the adapting part. 
     Moreover, the second connecting means is advantageously in the form of a flange, which is entirely circular or extends over a predetermined angular sector, preferably equal to 120°. 
     In addition, the adapting part may comprise a hoop portion of predetermined angular sector, preferably equal to 120°. In this case, the adapting part, limited to a given angular portion, is less massive than a full intermediate ring, of circular cross section, of the type described above. The mass added to the turbo-engine by the adapting part, and the associated bulkiness, are less than the mass and the bulkiness of such a full intermediate ring. Moreover, mounting the more compact adapting part on the turbo-engine is made substantially easier. It will also be noted that drawing the lines of a nacelle surrounding the turbo-engine is simpler, as is bringing the latter closer to the wings of an aircraft. 
     Furthermore, the present invention also relates to a system for holding, on a tubular casing of a turbo-engine, an adapting part of the type described hereinabove, which is noteworthy in that it comprises:
         the first complementary means associated with said casing, which is configured so as to engage with the first connecting means of the adapting part, so as to form the sliding connection; and   the second complementary means associated with said casing, which is configured so as to engage with the second connecting means of the adapting part, so as to form the rigid connection.       

     Preferably, the first complementary connecting means comprises a connecting member comprising at least one groove, which is entirely circular or extends over a predetermined angular sector, preferably equal to 120°. 
     Thus, the tab of the adapting part may be introduced into the groove of the connecting member so as to form the sliding connection. It is then much easier to mount and remove the adapting part, reducing the time required for carrying out these operations. 
     Moreover, the circumferential ends of the groove, of predetermined angular sector, may advantageously be closed in order to avoid any rotation of the adapting part with respect to the casing in question and in order to make the angular positioning of said adapting part easier. 
     According to one embodiment in accordance with the present invention, the connecting member is fitted on one end flange of said casing. In this case, the connecting member may either extend, in the radial direction, a flange of a casing adjacent to said casing in question, or form a separate and independent element of the turbo-engine. 
     As a variant, the connecting member may radially extend one upstream or downstream end flange of said casing. 
     Furthermore, the present invention also relates to a suspension for a turbo-engine on a pylon of an aircraft, comprising a front suspension bracket which is designed to be mounted on an intermediate casing of the turbo-engine and a rear suspension bracket designed to be mounted on an inter-turbine casing of the turbo-engine, and an adapting part of the type specified hereinabove, in order to connect the rear suspension bracket to the inter-turbine casing of the turbo-engine. 
     The present invention also relates to a turbo-engine attached to a pylon of an aircraft via the intermediary of a suspension comprising a front suspension bracket mounted on an intermediate casing of the turbo-engine and a rear suspension bracket mounted on an inter-turbine casing of the turbo-engine, which is noteworthy in that:
         the suspension further comprises an adapting part of the type described hereinabove, in order to connect the rear suspension bracket to the inter-turbine casing of the turbo-engine; and in that   it comprises a system for holding said adapting part as mentioned above.       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The figures of the appended drawing will make it easy to understand how the invention may be embodied. In these figures, identical references designate similar elements. 
         FIG. 1  shows, very schematically and in profile, a turbo-engine attached to an attachment pylon of an aircraft via the intermediary of a suspension in accordance with the present invention. 
         FIG. 2  shows, in a schematic perspective view, an example of a suspension implementing an adapting part in accordance with the present invention. 
         FIG. 3  is a schematic axial section of the adapting part of  FIG. 2 , once mounted on the inter-turbine casing of the turbo-engine. 
         FIG. 4  shows, in a schematic perspective view, the adapting part of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a suspension  3  is provided for mounting and attaching a turbo-engine  1 , of longitudinal axis L-L, to a pylon  2  of an aircraft below the wings of the latter, so as to form an interface between the turbo-engine  1  and the pylon  2 . 
     Thus, the suspension  3  of the invention is positioned between the pylon  2  having a box-type attachment bracket (partially represented in  FIG. 2 ) and intermediate  4  and inter-turbine  5  outer casings of the turbo-engine  1 . 
     Moreover, the suspension  3  is positioned and contained in two suspension planes P1 and P2 of the turbo-engine  1 , which are mutually parallel and orthogonal to the longitudinal axis L-L thereof. 
     With respect to an orthonormal reference frame XYZ (corresponding to that of the aircraft  1  with X being the roll axis, Y being the pitch axis and Z being the yaw axis), the longitudinal axis L-L of the turbo-engine  1  is parallel to X and the suspension planes, front P1 and rear P2, are contained in planes formed by the Y and Z axes. 
     The front suspension plane P1 is arranged level with the intermediate casing  4  downstream of the fan of the turbo-engine  1  and the rear suspension plane P2 is, for its part, located level with the frustoconical inter-turbine casing  5 , arranged between a high-pressure turbine casing  6  and a low-pressure turbine casing  7 . 
     The front suspension  3 A and the rear suspension  3 B—forming the overall suspension  3 —are represented by rectangles  3 A and  3 B ( FIG. 1 ) connecting the casings  4  and  5  corresponding to the attachment bracket of the pylon  2 . 
     As shown in  FIG. 2 , the suspensions, front  3 A and rear  3 B, respectively comprise a front suspension bracket  8 , in the front suspension plane P1, and a rear suspension bracket  9 , in the rear suspension plane P2. 
     In particular, the front suspension bracket  8  comprises a fitting  10  and three articulated rods  11 A and  11 B. The upper portion  10 A of the fitting  10  defines a platform for receiving the attachment bracket of the pylon  2  in the front suspension plane P1. 
     The fitting  10  extends on either side of the engine axis L-L via two double clevises  12  into which are inserted, respectively, the ends of the lateral struts  11 A, so as to form an articulated connection having a common spindle  13  passing through the two lugs of each of the clevises  11 A and the ends of the corresponding struts  11 A. 
     The fitting  10  also comprises a central clevis  14  so as to form an articulated connection with the central strut  11 B with a common spindle  13 . The front suspension bracket  8  is designed to take up the forces taking up the torque of the turbo-engine  1  in particular via the intermediary of the central strut  11 B. In this case (torque uptake at the front), the forces acting in the formed rear suspension  3 B are reduced. Indeed, taking up the torque on the intermediate casing  4  at the front of the turbo-engine  1 —which has a larger radius than the inter-turbine casing  5 —allows a reduction of the torque uptake forces. Such an attachment configuration prevents any torque uptake at the rear of the turbo-engine  1  at the level of the rear suspension  3 B, such that the latter is subjected to less force. 
     Moreover, the rear suspension bracket  9  comprises a fitting  15  and two lateral articulated rods  16 . The upper portion  15 A of the fitting  15  forms a platform for receiving the attachment bracket of the pylon  2  in the rear suspension plane P2. 
     The fitting  15  extends on either side of the engine axis L-L via two double clevises  17 A into which are inserted, respectively, the ends of the lateral struts  16 , so as to form an articulated connection having a common spindle  18  passing through the two lugs of each of the lateral clevises  17 A and the ends of the corresponding struts  16 . 
     The fitting  15  also comprises a double central clevis  17 B so as to form an articulated connection with a single clevis of an adapting part  19  in accordance with the invention, as is set out hereinbelow. 
     Furthermore, as shown in  FIG. 2 , once mounted on the turbo-engine  1 , the rear suspension bracket  9  is attached to the adapting part  19  designed to be fitted on the inter-turbine casing  5 , in the rear suspension plane P2. 
     As shown in  FIGS. 2 and 4 , the adapting part  19  is formed of a frustoconical hoop portion  20  of angular sector α approximately equal to 120°. The hoop portion  20  has a longitudinal extent along the axis L-L which is substantially equal to that of the inter-turbine casing  5 . 
     The adapting part  19  further comprises a tab  21  which extends, in the upstream direction, the axial end of the hoop portion  20 . The upstream tab  21 , which is partially cylindrical, extends over the angular sector α. It is inclined with respect to a generatrix T-T of the frustoconical portion  20 . 
     The adapting part  19  also comprises a downstream flange  22  secured to the downstream end of the hoop portion  20  and designed to be connected to the downstream flange  5 B of the inter-turbine casing  5  (see  FIG. 3 ). The downstream flange  22 , in the form of a collar portion, extends over the angular sector α. In other words, when it is attached to the corresponding flange  5 B of the inter-turbine casing  5 , the attachment is effected only over an angle portion. 
     Once the adapting part  19  is fitted on the inter-turbine casing  5 , the downstream flange  22  is in a plane orthogonal to the longitudinal axis L-L, such that it is inclined with respect to the generatrix T-T. 
     As shown in  FIG. 3 , the high-pressure turbine casing  6  comprises, at its downstream end, a circular flange  6 A which extends axially via a connecting member  23  comprising a groove  24  which is circular in shape. The connecting member  23  extends over an angular sector equal to the angular sector α. 
     The groove  24 , delimited by two concentric ribs  23 A and  23 B, defines a receiving recess designed to accommodate the tab  21  of the adapting part  19 . The depth of the groove  24  is such that, once the adapting part  19  is fitted on the inter-turbine casing  5 , a clearance remains between the free end of the tab  21  and the bottom of the groove  24 . 
     Moreover, the circumferential ends of the groove  24  are closed, such that the angular extent of the groove  24  corresponds to that of the tab  21 . Thus, once the tab  21  is accommodated with adjustment in the groove  24 , it is possible to prevent any rotation of the adapting part  19  with respect to the inter-turbine casing  5  and high-pressure casing  6 . Closing the circumferential ends of the groove  24  also facilitates the angular positioning of the adapting part  19 . 
     As a variant, the tab of the adapting part could comprise a plurality of notches, defining sub-tabs, and the groove of the connecting member could comprise radial walls, defining sub-grooves designed to accommodate the corresponding sub-tabs. In another variant, the sub-tabs could be flat and the sub-grooves straight. 
     It will be noted that the connecting member  23  may comprise a shoulder  23 C which is annular or partially annular and against which the upstream flange  5 A of the inter-turbine casing  5  is designed to press, in order to facilitate the centering of the latter. 
     Furthermore, as shown in  FIGS. 2 to 4 , orifices  25  are regularly distributed over the downstream flange  22  of the part  19  such that, for example, they may be bolted to the corresponding downstream flange  5 B of the inter-turbine casing  5 . Of course, other attachment means could equally be employed, such as for example rivets, so as to replace the bolts. 
     When it is assembled on the turbo-engine  1 , the adapting part  19  is first fitted on the inter-turbine casing  5  by inserting the tab  21  into the corresponding groove  24  of the connecting member  23 . Once the tab  21  is accommodated in the groove  24 , the downstream flange  22  is fixed, by bolting, to the downstream flange  5 B of the inter-turbine casing  5  and to the upstream flange  7 A of the low-pressure turbine casing  7 . The connecting member  23  and the upstream flange  5 A of the inter-turbine casing  5  then define a system for holding the adapting part  19  on the turbo-engine  1 . 
     Thus, once the adapting part  19  is fitted on the inter-turbine casing  5 , the tab  21  engages with the groove  24  so as to form, on the upstream side, an axially sliding connection. On the downstream side of the adapting part  19 , a rigid connection, obtained by bolting, is formed by assembling the flanges  22 ,  5 B and  7 A, respectively in this order. 
     The differential expansion of the casings and of the adapting part is thus better managed, with at least part of the axial expansion being absorbed by the upstream sliding connection. 
     Moreover, the forces supplied by the rear suspension bracket  9  on the adapting part  19  are transmitted directly to the sliding and rigid connections arranged at the axial ends of the inter-turbine casing  5 . 
     Furthermore, as shown in  FIG. 4 , the adapting part  19  also comprises three suspension clevises  26  and  27 , of which two are lateral double clevises  26  and one is a central single clevis  27 . It goes without saying that, as a variant, the number and shape of the clevises (single or double) could be different. 
     The suspension clevises  26  and  27  are arranged on that face of the hoop portion  20  which faces outwards. 
     Moreover, as shown in  FIG. 2 , the lateral articulated rods  16  which are articulated on the rear suspension bracket  9  are designed to form an articulated connection with the corresponding lateral clevises  26  of the part  19 . The free ends of the articulated rods  16  are inserted between the two lugs of the lateral clevises  26  and a common spindle  28  passes through them, thus forming an articulated connection. 
     The double central clevis  17 B of the rear suspension bracket  9  receives the single clevis  27  of the adapting part  19 , such that a common spindle  29  passes through it and thus forms an articulated connection. 
     Furthermore, in the example shown, the hoop portion  20  comprises a plurality of rectangular cutouts  30  which are designed to lighten the adapting part  19  and to allow cables, equipment or any other element to pass through. 
       FIG. 2  also shows two thrust uptake struts  31  which are connected to the rear suspension bracket  9  via the intermediary of a spreader  32 . 
     It is to be noted that, when mounting the suspension  3  on the turbo-engine  1 , the adapting part  19  is preferably first attached to the inter-turbine casing  5 . The rear suspension bracket  9  is then mounted on the adapting part  19  which is positioned in this manner. The attachment bracket of the pylon  2  is finally bolted to the corresponding platform of the rear suspension bracket  9 . 
     Of course, the present invention is in no way limited to the exemplary embodiment described hereinabove. 
     Thus, in a first variant which is not illustrated, the connecting member may axially extend the upstream flange  5 A of the inter-turbine casing  5  (and not the downstream flange  6 A of the high-pressure turbine casing  6 ). 
     In a second variant which is not illustrated, the connecting member may be independent and distinct from the flanges  5 A and  6 A, such that it can be fitted and attached to these flanges  5 A and  6 A, for example when they are assembled by bolting with one another. In this case, the distinct connecting member may be fitted on the upstream face of the downstream flange  6 A of the high-pressure turbine casing  6 , or on the downstream face of the upstream flange  5 A of the inter-turbine casing  5 . In this variant, shear pins may also be provided on one of the flanges  5 A or  6 A in order to facilitate the positioning thereon (in particular the angular centering) of the connecting member. 
     Furthermore, the invention may equally apply to an adapting part and a tab of entirely circular shape. 
     It will finally be noted that the adapting part in accordance with the invention is not limited to use in a rear suspension of a turbo-engine of an aircraft.