Abstract:
Device for assembly of a connecting rod ( 3 ) on the casing of a turbo-engine comprising, in addition to said suspension member, a clevis ( 4 ) fixed to the casing and comprising at least two coaxially bored lugs, and a shaft ( 9 ) traversing the bores of said lugs to which said suspension member is fixed, in a manner which is mobile in radial rotation, via a ball joint ( 10 ) surrounding the shaft, said shaft being held in place in the lugs of said clevis by connecting means ( 11, 12, 14 ) capable of being driven in rotation about the axis of said bores, characterized in that said ball joint and said connecting means are configured such that the rotation of said connecting means about the axis of the bore of the lugs causes an offset of the axis of rotation of the connecting rod ( 3 ) in a direction perpendicular to said axis of the bores.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The field of the present invention is that of turbojets and members providing the connection between the various parts thereof. The invention relates more particularly to members providing the mechanical support of the bypass flow duct of bypass engines. 
         [0002]    A propulsion engine, such as a turbojet, may be mounted in various locations of the aircraft, by fastening onto a mast or a pylon belonging to the structure thereof. It may also be suspended below the wings, fixed to the fuselage, generally at the rear, or mounted in the tail unit by appropriate fastening means. Said fastening means have the function of ensuring the transmission of mechanical forces between the engine and the structure of the aircraft. The loads to be taken into account are, in particular, the weight of the engine along the vertical Z-axis, its thrust along the X-axis of the engine and the lateral aerodynamic loads along the transverse Y-axis. The loads to be transmitted also include the torque pick-up about the shaft of the engine. Said means also have to absorb the deformations to which the engine is subjected during the different phases of the flight which result, for example, from dimensional variations due to thermal expansion or contraction, without transmitting said deformations to the mast. 
         [0003]    A method of suspension, for example in the case of a turbo-fan engine, consists in fastening the engine to a mast belonging to the structure of the wing of the aircraft by a front suspension or front fixing and a rear suspension or rear fixing. The front suspension is fixed, in particular, to the intermediate casing downstream of the fan casing and the rear suspension to the exhaust casing of the primary flow. Said two parts constitute the structural elements of a turbo-engine, on which all the forces are absorbed. 
         [0004]    Modern turbojets are bypass turbo-engines with a high by-pass ratio, the secondary air flow being compressed by a single compressor stage known as the fan. At the outlet of this stage the air flow is guided by a duct directly into a nozzle to contribute to the thrust of the engine. It circulates, therefore, between the principal body of the engine defined by the casings and a bypass flow duct (generally denoted by the English acronym OFD for Outer Fan Duct). For reasons of mass, said duct is commonly made from composite material. The fixing of said duct to the engine is carried out by connections at its two longitudinal ends, a first fixing being carried out upstream on the casing surrounding the fan and a second fixing to the rear on a support ring carried by the exhaust casing. 
         [0005]    The connection between the support ring and said exhaust casing is generally carried out by means of arms which pass through the bypass flow. In more recent embodiments, said connection may also be provided by profiled connecting rods, fixed, on the one hand, to the bypass flow duct and, on the other hand, to the exhaust casing, which permits a significant reduction in the mass of this connection. In this case of carrying out the fixing by connecting rods, the connection is made by a framework of connecting rods, which are generally six or eight in number and aligned in pairs, and which are attached at three or four points to the support ring, as shown in  FIG. 2 . 
         [0006]    Such an assembly is intentionally hyperstatic, in particular to ensure redundancy in the case of rupture of one of said elements. The drawback with such a choice is that the system is difficult to mount and it is necessary to provide devices for adjusting the length of the connecting rods, without which the mounting becomes impossible. Thus it is necessary to provide a system for adjusting the position of the ball joints as a function of the length of the connecting rods, to take into account the manufacturing tolerances of each of the connecting rods and clevises of the exhaust casing and, if required, to provide them with pre-stressing during the mounting. 
       DESCRIPTION OF THE PRIOR ART 
       [0007]    In the prior art, numerous devices for adjusting the length of the connecting rods have been conceived, such as for example those which provide a shaft carrier part screwed to one of the ends thereof; in this case the adjustment takes place by rotating said part by one or more half-turns about the principal axis of the connecting rod. To be able to obtain a precise adjustment it is thus necessary to produce a thread with a very fine pitch which complicates the production of the connecting rod and constitutes a system which is not particularly robust in terms of mechanical strength. 
         [0008]    The object of the present invention is to remedy said drawbacks by proposing a device for adjusting the length of the connecting rod which is simple to implement and which ensures an adjustment of the length which is perfectly adapted to requirements. 
       SUMMARY OF THE INVENTION 
       [0009]    To this end, the subject of the invention is a device for assembly of a suspension member on the casing of a turbo-engine comprising, in addition to said suspension member, a clevis fixed to the casing and comprising at least two coaxially bored lugs, and a shaft traversing the bores of said lugs to which said suspension member is fixed, in a manner which is mobile in radial rotation, via a fixing means surrounding the shaft, said shaft being held in place in the lugs of said clevis by connecting means capable of being driven in rotation about the axis of said bores, characterized in that said fixing means and said connecting means are configured such that the rotation of said connecting means about the axis of the bore of the lugs causes an offset of the axis of rotation of the suspension member in a direction perpendicular to said axis of the bores. 
         [0010]    The offset created by the rotation of the connecting means permits the compensation of clearance left during the mounting of the suspension member and its pre-stressing to avoid peening of the parts due to vibrations. 
         [0011]    In a preferred embodiment, the fixing means is a ball joint fixed at one of the ends of said suspension member, and bored along an axis which is offset relative to the axis of symmetry of its spherical part, the axis of rotation of said connecting means being merged with the axis of the bore of said lugs. 
         [0012]    Advantageously, the ball joint comprises at least one cutout on a radial face facing said connecting means and in which said connecting means comprise a longitudinal extension capable of cooperating with said cutout to fix in rotation said ball joint with said connecting means, about the axis of the bore of said lugs. 
         [0013]    Preferably, the connecting means comprise a bushing and a support ring for said extension, both extending about the support shaft of said suspension member and comprising means for reciprocal fixing in rotation, said bushing and said ring each comprising a radial shoulder configured to be positioned on both sides of one of the lugs of the clevis. 
         [0014]    Preferably, the ring comprises two longitudinal extensions located on both sides of the radial shoulder thereof, a first longitudinal extension being capable of cooperating with the cutout of the ball joint and a second longitudinal extension being capable of cooperating with a cutout formed in said bushing. 
         [0015]    Advantageously, said bushing comprises two parallel flat portions positioned on its circumference, permitting its rotation using a tool about the axis of the bore of said lugs. 
         [0016]    Preferably, the support shaft is hollow and traversed by an assembly consisting of a screw and a nut capable of providing the clamping of the radial shoulder of said bushing against the corresponding lug of the clevis, so as to block the rotation of the bushing about the axis of the bore of said lugs. 
         [0017]    More preferably, the device further comprises a washer positioned between the bushing and the nut, said washer comprising two parallel flat portions capable of being positioned opposite the flat portions of said bushing. 
         [0018]    In an alternative embodiment, said connecting means are bored along an axis offset relative to the axis of the bore of said lugs in a direction perpendicular thereto. 
         [0019]    The invention also relates to a turbo-engine comprising a device for assembly as disclosed above. 
         [0020]    The invention will be understood more clearly and further objects, details, features and advantages thereof will appear more clearly during the following detailed explanatory description of an embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the drawings: 
           [0022]      FIG. 1  is a schematic view of a bypass turbojet, with a connection via connecting rods between the exhaust duct and the bypass flow duct; 
           [0023]      FIG. 2  is a perspective view of an exhaust casing and the support ring of the bypass flow duct of a turbojet; 
           [0024]      FIG. 3  is a perspective view of the end of a connecting rod for supporting a turbojet and its fixing clevis, according to an embodiment, 
           [0025]      FIG. 4  is a sectional view of the connecting rod and of the clevis of  FIG. 3 , and 
           [0026]      FIG. 5  is a perspective view of the screw of the clevis of  FIG. 3  and its bushings. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    With reference to  FIG. 1 , a stylized view of a bypass turbojet may be seen, comprising a fan  101 , a primary body  102  comprising downstream thereof an exhaust casing  1  which forms part of the structure of the engine, and a rear cone  103 . The primary flow which passes through the primary body is ejected into a primary nozzle  104  surrounding the rear cone, whilst the secondary flow which originates from the fan is guided downstream thereof by a bypass flow duct  105  terminated by a secondary nozzle  106 . The bypass flow duct  105  is attached to the exhaust casing  1  by a framework of connecting rods  3  which are inclined relative to a radial plane of the engine, the fixing to the bypass flow duct being positioned upstream relative to that on the exhaust casing. 
         [0028]    With reference to  FIG. 2 , an exhaust casing  1  of a turbojet is seen surrounded by a support ring  2  designed to retain the bypass flow duct  105  of said turbojet. Said forces associated with this retention are transmitted to the exhaust casing by a set of six connecting rods  3  which are fixed at one of their ends to the ring  2  and at the other end to the exhaust casing  1  by fixings in the form of clevises. As shown in the figure, the connecting rods  3  are arranged in pairs, tangentially to the exhaust casing  3  and thus form a triangle of which the apexes are located on the support ring  2 . 
         [0029]      FIG. 3  shows a connecting rod  3  installed in a clevis  4  according to the invention, fixed to the exhaust casing  2 . The clevis and the connecting rod are traversed by a screw  5  which is clamped against the lugs of the clevis  4  via a nut  6 . A first conventional washer  7  is positioned between the head of the screw  5  and a first lug of the clevis whilst a second washer  8  having on its periphery two parallel flat portions is positioned between the second lug of the clevis  4  and the nut  6 . 
         [0030]    With reference to  FIGS. 3 and 4 , the clevis  4  is seen, the lugs thereof each being perforated by a bore through which a traversing shaft  9  passes. Said shaft is hollow and is in turn traversed on both sides by the screw  5 , which is free in terms of rotation in the shaft  9 . 
         [0031]    The connecting rod  3 , as explained above, is a pivoting connecting rod, i.e. it is connected to the shaft  9 , about which it pivots, by a ball joint  10 . The connection between the connecting rod  3  and the ball joint  10  is a free connection, the connecting rod being able, on the one hand, to rotate about the ball joint in a plane vertical to the shaft  9  of the clevis  4 , and on the other end, to have misalignments relative to said vertical plane. It is noteworthy that the bore formed in the ball joint  10  to permit the shaft  9  to pass through is not aligned with the axis of symmetry of its spherical shape. Said hole is off-centered in a direction perpendicular to the support shaft  9  of the connecting rod or the screw  5  so that a rotation of the ball joint  10  is associated with the connecting rod moving further away or closer relative to the axis of the bore of the lugs of the clevis  4 . The connection between the ball joint  10  and the shaft  9  is also a connection which is free in terms of rotation, the ball joint being able to rotate about said shaft  9  in the absence of a blocking device formed by a dog-clutch as explained below. 
         [0032]    The support shaft  9  is held laterally in position, in the conventional manner, by bushings which slip over the shaft and extend radially, on the side of their external end, via shoulders which bear against external lateral faces of the lugs of the clevis  4 . The first and second washers  7  and  8  are then placed outside the shoulders of said bushings to retain them in translation, in the same manner as the shaft  9 , and thus permit the fixing of the assembly formed by the shaft  9 , the bushings  11  and  12  and the washers  7  and  8 , by tightening the screw  5  and the nut  6 . 
         [0033]    The first bushing  11  located on the side of the screw head  5  is a conventional bushing of which the longitudinal part bears directly against a radial face of the ball joint  10  of the connecting rod  3 , whilst the second bushing  12  located on the side of the nut  6  is an engaged bushing which bears against the other radial face of the ball joint  10  only by means of an annular part, known as a dog-clutch  14 , which will be described in more detail with reference to  FIG. 5 . 
         [0034]    The ball joint  10  has, on the side of the engaged bushing  12  and the dog-clutch  14 , an indentation  13  which is hollowed out of the radial face thereof so as to form a housing for a longitudinal extension of the dog-clutch  14 , of which the cooperation with the indentation  13  ensures the fixing in rotation of the ball joint  10  and said dog-clutch  14 . 
         [0035]    With reference now to  FIG. 5 , starting from the right of the figure the second washer  8  is seen, said washer carrying two parallel flat portions on its circumference, for the purpose of being able to be driven in rotation using a wrench. 
         [0036]    The shoulder of the second bushing which bears against the external face of the second lug has in turn two flat portions, which are identical to those of the second washer  8  such that said two parts may be driven simultaneously in rotation by the same wrench. The longitudinal part of the second bushing  12  has a cylindrical shape which surrounds the shaft  9  and has at its end one or two rectangular cutouts  15  located symmetrically relative to one another, for the purpose of providing a housing with one or two longitudinal extensions, called the second extensions  16  of the dog-clutch  14 . 
         [0037]    The dog-clutch  14  has an annular shape surrounding the support shaft  9  and has a shoulder or collar  17  extending radially and from which two extensions extend longitudinally on both sides of the collar  17 . Said longitudinal extensions each have the shape of a cylindrical angular sector, of which the amplitude corresponds to that of the cutouts made for the first extension  18  in a radial face of the ball joint  10  and for the second extension  16  in the second bushing  12 . During the mounting of the assembly, the penetration of the first and second longitudinal extensions  18  and  16  of the dog-clutch, respectively, in the cutouts  13  and  15 , of the ball joint  10  and of the second bushing  12  permit the fixing in rotation about the shaft  9  of the ball joint  10  with the dog-clutch  14  and with the bushing  12 . By preventing any possibility of rotation to the second bushing  12  via a simple wrench, it is thus possible to immobilize the ball joint  10  in rotation about the shaft  9 . 
         [0038]    On the opposing side, i.e. on the side of the screw head, without the choice of the side which carries the cutouts and the longitudinal extensions having any importance, there is no part forming the dog-clutch, the radial face of the ball joint  10  not having a cutout and the first bushing  11  not having any longitudinal extension. The first bushing  11  bears against the first lug of the clevis by its radial shoulder whilst its longitudinal part traverses the first lug of the clevis  4  over its entire thickness to come directly into contact with the radial face of the ball joint  10 ; in contrast, on the side of the screw head it leaves a clearance J between the internal face of its shoulder and the external radial face of the first lug of the clevis, for the purpose of permitting the expansion of all of the parts forming the assembly of the connecting rod  3  with the clevis  4 . 
         [0039]    The mounting and operation of a connection according to the invention between a connecting rod  3  bearing an eccentric ball joint and a clevis  4  will now be described. The solution of the technical problem which is proposed by the invention consists in the use of monolithic connecting rods with eccentric ball joints, i.e. connecting rods of which the axis of the bore of the ball joint is offset relative to the center of its spherical surface. Thus the use of such an eccentric ball joint, in the first instance, enables mounting clearance of the connecting rod on the axis of the clevis to be compensated and, in the second instance, to be able to apply a pre-stressing to the connecting rod by using a simple torque wrench. 
         [0040]    The positioning of the connecting rod takes place in the following manner:
       the dog-clutch  14  is positioned in the second lug of the clevis  4  and the connecting rod  3  is positioned so that the bore of the ball joint  10  thereof is substantially aligned with the axis of the bore of the lugs of the clevis,   the shaft  9  provided with the first (disengaged) bushing  11  is introduced via the bores of the clevis  4 , the ball joint  10  and the dog-clutch  14 , the first bushing bearing, on the one hand, against the external face of the first lug and, on the other hand, against a radial face of the ball joint  10 . At the same time, the dog-clutch  14  is positioned in rotation on the shaft  9  so that the first longitudinal extensions  18  thereof penetrate the cutout(s)  13  formed on the corresponding radial surface of the ball joint  10 .   the second (engaged) bushing  12  is in turn passed about the shaft  9  and pivoted about said axis until its cutout(s)  15  cooperate with the second longitudinal extension(s)  16  of the dog-clutch  14 .   the screw  5  provided with the first washer  7  is slid inside the shaft  9  and the second washer  8  is positioned against the second bushing  12  and then pre-tightening is carried out by positioning the nut  6  on the thread of the screw  5 . During this positioning, the second washer  8  is positioned so as to align its flat portion(s) thereon or on those of the second bushing  12 . The pre-tightening is carried out so that it holds the elements together but it does not prevent rotation of the disengaged elements relative to one another. It is necessary to provide clearance between the parts so that, on the one hand, it is possible to mount them and, on the other hand, during use it is avoided that they are under stress relative to one another, which would generate wear during the relative movements thereof.   as the ball joint  10  is engaged on the dog-clutch  14 , which is itself engaged on the second bushing  12 , an action by the torque wrench on the flat portions of the second bushing and the second washer causes a rotation of the ball joint  10  about the shaft  9 . As said ball joint is eccentric relative to said shaft  9 , the rotation of the ball joint initially causes the compensation of the clearances which potentially exist between the connecting rod  3  and the shaft  9  of the clevis  4  and then, once the clearances have been compensated, the pre-stressing of the connecting rod  3  which makes it possible to avoid the peening of said parts by vibrations occurring on the engine or the aircraft. The use of a torque wrench makes it possible to calibrate the level of pre-stressing applied to the connecting rods.   once the ball joint  10  has been rotated by the angle which provides the desired level of pre-stressing, the tightening of the nut  6  ensures the retention of the assembly by the immobilization of the second bushing due to the clamping of the collar  17  and the radial shoulder of the second bushing  12  on the lug of the clevis  4 . The screw, by the shoulders of the first and second bushings  11  and  12  bearing against the lugs of the fork  4 , henceforth prevents said bushings from rotating about their axis, and as the ball joint  10  is engaged on the second bushing  12  it is blocked in rotation, as are the bushings.       
 
         [0047]    So as to improve the adhesion of the bushings on the radial faces of the lugs of the clevis, it is conceivable to place splines on the clevis or to create roughness on the shoulders of the bushings on the side where they come into contact with the lugs of the clevis  4 . 
         [0048]    By way of a variant, it is possible to use a conventional ball joint, having an axis of symmetry which is aligned with that of the shaft  9  of the clevis, and a second bushing  12  which in turn is eccentric, the rotation by the torque wrench of said bushing causing an offset of the shaft  9  parallel with itself and consequently an offset of the ball joint  10  which produces the desired compensation of clearance and pre-stressing of the connecting rod  3 .