Abstract:
A suspension for suspending of a turbine engine from the structure of an aircraft using a beam with an attachment device which attaches to the structure and at least one link rod articulated via one end to a journal secured to the beam and via the other to a fitting secured to the turbine engine is disclosed. This suspension is one wherein the journal is mounted on the beam via a flexible coupling formed of two preloaded laminated, elastomer and metal, cylinders.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the suspending of a turbine engine from the structure of an airplane and is aimed more specifically at a means of attenuating vibrations between the engine and the bearing structure. 
     A turbine engine suspended, for example, from an airplane wing via a pylori comprises a forward hard point that reacts the loads passing through the intermediate casing in particular and a rear hard point at the exhaust casing. In a statically determinate suspension, the loads are transmitted via link rods suitably distributed between the two fastening components and which generally work in tension and in compression. The link rods are secured at one end to a beam secured to the structure of the airplane and at the other end to fittings on the engine casing or to the casing directly. The end attachments of the link rods used ball joints so that load can be transmitted only along the axis of these link rods. The loads reacted by these fasteners are the engine torque and the loads applied in the transverse plane of the engine such as the weight, lateral loads and engine thrust. 
     DESCRIPTION OF THE PRIOR ART 
     In order to reduce the vibrations introduced into the structure and the noise introduced into the cabin as a result of engine operation, it is known practice for vibration isolators to be introduced into the attachment systems. For example, patent EP 250659 describes a suspension for suspending a turbine engine from the structure of an airplane incorporating a transverse spindle between a beam from which the engine is suspended via link rods and the pylori under the wing of the airplane. The transverse spindle is supported by a first pair of isolators at its ends, working in vertical compression, and a second pair working in transverse compression. The two pairs are independent of one another and may have different coefficients of elasticity. This solution occupies a certain amount of space in the heightwise direction. 
     Other arrangements are known and are relatively complicated. These are generally applied to systems of the statically indeterminate type. This type of attachment has the chief disadvantage that the levels of load transmitted through the parts at any given moment are not known. This being the case, the isolators are harder to engineer with certainty. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to produce a suspension for suspending a turbine engine in an aircraft structure that is both of the statically determinate type and incorporates a flexible vibration isolator, it being necessary for the unit to remain as compact as possible. 
     This objective is achieved with a suspension for suspending from the structure of an aircraft comprising a beam with means of attachment to said structure and at least one link rod articulated via one end to a journal secured to the beam and via the other to a fitting secured to the turbine engine, wherein said journal is mounted on the beam via a flexible coupling formed of two laminated cylinders combining layers of elastomer and of metal bonded together, supporting the journal at each end. 
     The load on the coupling is thus restricted to that exerted by one link rod. Further, as there are generally a number of link rods, this ensures that the load is spread. Furthermore, this arrangement makes it possible to know with certainty what path the loads are taking and the dimensions of the parts of the flexible coupling can be optimized. 
     In particular, the laminated cylinders comprise an annular rigid first armature secured to the journal, a second armature coaxial with the journal and a layer of elastomeric material between the two armatures, said elastomer layer being preloaded. 
     According to a preferred embodiment, the first and second armatures each have a frustoconical surface with the same axis as the journal, said preloaded layer being positioned between the two frustoconical surfaces. 
     More specifically, a flexible coupling means comprising a low number of parts is obtained, this at the same time being very compact with the rigid first armature of at least one of the two laminated cylinders mounted such that it can slide on the journal, compression being obtained by moving the first armature toward the second armature. 
     Advantageously, the frustoconical surfaces of the two laminated cylinders are symmetric with respect to the plane perpendicular to the journal passing through the link rod, and the two first armatures are slidably mounted on the journal. The elastomeric material is preloaded by moving the two first armatures toward one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One nonlimiting embodiment of the invention is now described with reference to the drawings in which: 
         FIG. 1  shows one embodiment of a suspension according to the invention, viewed in perspective, 
         FIG. 2  is a view in section on II-II of the suspension of  FIG. 1 , 
         FIG. 3  shows a suspension of the invention while it is in the process of being assembled. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The suspension of  FIG. 1  is made up of a beam  2  with an upper platform  21  in which holes have been drilled for the passage of fasteners such as bolts, not depicted, for attaching the beam to the structure of an aircraft. This structure may be a pylori for mounting under the wing, but the invention more generally covers attachment to any part of the aircraft. A central peg  23  reacts shear loads. 
     Connected to this platform are, in this instance, two arms  25  and  27  arranged in a V and on which the link rods  3 ,  4  and  5  are mounted. These link rods are articulated on journals  6  which are parallel to one another and mounted via flexible couplings in the arms  25  and  27 . The beam may have a different structure or geometry; that depicted is nonlimiting. The free end of the link rods is holed for the passage of a fastener for attachment to the fitting of the engine casing, not depicted. Link rods in this instance are positioned in the transverse plane with respect to the axis of the engine. They may also be close to this plane. The two outer link rods  3  and  5  are connected to a transverse flange of the casing in such a way that the hard points form a trapezium. Because of the ball joint attachments, these two link rods transmit load along the axes  0 Y and  0 Z perpendicular to the axis of the engine. In this set-up, the purpose of the central link rod  4  is, in conjunction with the other link rods, to transmit loads associated with engine torque. The axis  0 X in the frame of reference associated with  FIG. 1  is the axis of the engine: the axis  0 Z is the vertical axis and the axis  0 Y is transverse. Reference is made to  FIG. 2  which shows, in greater detail, the mounting of a link rod on the beam. This is the central link rod  4  but this method of mounting is valid also for the other two link rods  3  and  5 . Two cylindrical housings  27 A and  27 B have been machined in the arm  27  according to this embodiment. The axis XX of these housings is perpendicular to the plane formed by the arms  25  and  27 . These two housings are separated by a slot  27 C which opens to the opposite side to the platform  21 . The slot houses the link rod  4  and is wide enough to allow this link rod some freedom to travel within it. The link rod is articulated on a journal  6  of axis XX parallel to the engine axis via a ball-jointed bearing  46 . This bearing allows the link rod to move about the axis XX mainly and about two further axes parallel to the axis XX; that is to say the transverse axis YY and the vertical axis ZZ. The movement permitted is within the limits of the clearance formed between the link rod  4  and the walls of the slot  27 C. 
     According to the invention, a flexible coupling  7 , the purpose of which is to damp out vibrations between the source that is the engine and the beam, connects the journal  6  to the arm  27 . This flexible coupling consists of two laminated cylinders  71  and  72  comprising layers of elastomeric material alternating with rigid metal layers. The cylindrical elements are positioned in the housings  27 A and  27 B respectively. Each of the cylinders  71  and  72  comprises a rigid first armature, particularly one made of metal,  71 A and  72 A; a rigid second armature  71 B and  72 B, respectively, and, between these two, layers  71 C,  72 C of elastomeric material alternating as appropriate with one or more metal layers  71 D,  72 D. The cylinder may comprise just a single elastomeric layer between the two armatures, and therefore have no metal layer. This example depicts three elastomeric layers  71 C,  72 C and two metal layers  71 D,  72 D. All the layers are bonded to one another. Reference hereinafter is made to the elastomeric layer  71 C,  72 C. The first annular armature is mounted on the journal  6  and its external surface is frustoconical of axis XX. The second annular armature is wedged via its external surface into the housing  27 A and also has a frustoconical surface, although this is an internal surface. The two conical surfaces have the same vortex angle and the same axis XX. Between them they form a space filled with the elastomeric layer. According to one feature of the invention, this layer is preloaded. This characteristic is obtained by moving the two frustoconical surfaces closer to one another along the axis XX. This compression allows the elastomer not to be subjected to any depression regardless of the relative movement of the journal with respect to the beam along any one of the axes XX, YY and ZZ. 
     The frustoconical shape has the advantage that the preload can be achieved easily. A preloaded cylindrical shape, although more difficult to produce, could also be conceivable. 
     This arrangement is particularly simple to implement both in terms of the structure and in terms of the assembly of the suspension. As can be seen in  FIG. 3 , the two cylinders  71  and  72 , prior to assembly, have their elastomeric layer  71 C,  72 C noncompressed, the two armatures being axially parted from one another because of the mobility of the first armature which is able to slide on the journal. Once the laminated cylinders  71 ,  72  have been fitted into their respective housings  27 A and  27 B, the link rod is positioned in the slot  27 C then the journal  6  is inserted into the armature from one side until a shoulder  61  of the journal comes into abutment; a washer  62  is slipped onto the other end of the journal, which is threaded. A nut  63  is fitted onto the threaded part and tightened.  FIG. 3  shows the assembled part prior to tightening. The two first armatures  71 A and  72 A are offset with respect to the second armatures  71 B and  72 B which are wedged in their respective housings  27 A and  27 B. By tightening the nut, the two washers are moved closer to one another carrying the two first armatures with them. It therefore follows that the elastomeric layer  71 C and  72 C between each first and second armature is subjected to axial compression. 
     The solution of the invention makes it possible to produce a flexible coupling between the journal and the beam through which the loads applied by the link rod to the journal pass.