Abstract:
A joining device including a clevis and a connecting member is disclosed. The connecting member includes a through hole which is housed between a first and a second lug of the clevis. These lugs respectively have a first clevis hole and a second clevis hole. The device further includes a shear pin system passing through each of the holes and includes a threaded end collaborating with a nut system which abuts against the second lug. The shear pin system includes a widened portion passing through the first hole and forming a shoulder situated between the two lugs. The member is situated away from the first lug. A first side of the member is pressed against the shoulder and a second side of the member is pressed against the second lug.

Description:
TECHNICAL FIELD 
   The present invention relates in general to a joining device for joining two assemblies of the type comprising a clevis intended to be attached to a first assembly and a connecting member intended to be attached to a second assembly. 
   The invention applies particularly although not exclusively to the field of turbomachines, preferably taking the form of a turbojet engine for an aircraft, for example for connecting together two annular and concentric assemblies of a turbine or compressor stator. 
   PRIOR ART 
   Various joining devices of the type mentioned hereinabove are known from the prior art. 
   First, a conventional device known as a two-lug clevis is known. This is used to clamp the connecting member between the two lugs using a screw/nut combination passing through the device. In this case, loads are transferred essentially by the rubbing of the two opposing faces of the connecting member against the respective internal faces of the two lugs between which this same member is gripped. 
   The disadvantage of this kind of set up lies in the fact that it is conceivable only with a very small amount of clearance between the various components before the screw/nut assembly is tightened. This is because an excessive initial separation between the lugs of the clevis would, upon tightening, squeeze these lugs together and stress them, thereby weakening them. 
   Furthermore, with this combination, it is only possible to bring the connecting member parallel to the lugs of the clevis as it is being introduced between these lugs, namely at right angles to the axes of the clevis holes, by applying a translational movement parallel to a direction known as the clevis orientation direction. This inevitably makes it difficult, if not impossible, under certain circumstances as described in the example below, for an operator to assemble and of necessity entails that the components be positioned very accurately relative to one another in order to be able to achieve the aforementioned introduction. 
   In effect, it is possible to envision a scenario in which the first annular assembly is positioned radially on the inside with respect to the second annular assembly, with the clevis of each of the joining devices with which this first annular assembly is equipped being arranged in such a way that, when viewed from above with respect to this clevis, the clevis is set at the same angle with respect to an axis of the first and second annular assemblies. In this configuration, it is evidently impossible to introduce each of the connecting members which are distributed circumferentially on the second assembly simultaneously into their associated clevis and this is true regardless of the nature of the relative movement applied to the first and second assemblies. 
   The prior art also discloses a conventional device also known as a two-lug clevis device but in which the connecting member is not clamped between the two lugs but separated therefrom. In this case, the loadings are then transferred through the shearing and bending of the pin system that passes through the various components of the joining device. Nonetheless, the major disadvantage with this type of setup stems from there being a degree of freedom associated with the connecting member situated some distance from the two clevis lugs, giving this same member the ability to move along the pin system. As a result, because this connecting member is not pressed against the clevis lugs, it is therefore impossible to guarantee accurate positioning of the second assembly with respect to the first assembly. 
   In addition, if a clearance is left between the pin system and the through hole made in the connecting member, particularly with a view to accommodating some degree of uncertainty over the positioning prior to the introduction of the pin system through this hole, the mechanical joint obtained then becomes extremely sensitive to vibrations. 
   Finally, the prior art also discloses another conventional device known as a single lug clevis, in which the connecting member is clamped against the single lug of the clevis. This configuration does of course have the advantage of introducing practically no accessibility constraints on the operator who has to bring the member onto the single lug. In other words, in contrast with the previous embodiments, the member can be fitted onto the clevis in some way other than by applying a translational movement parallel to orientation of the clevis, thus offering the operator more scope. 
   However, the lug and the member experience a significant amount of bending as a result of the asymmetry of the fastening, thus creating a high bending moment. In addition, in order to transmit loads of the same order of magnitude, this type of fastening requires components which are overengineered by comparison with those of which the abovementioned two-lug clevis devices are made, and as a result causes problems of space. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to propose a joining device that at least partially remedies the aforementioned disadvantages relating to the embodiments of the prior art. 
   To do this, a first subject of the invention is a joining device for joining two assemblies comprising a clevis intended to be attached to a first assembly and a connecting member intended to be attached to a second assembly, the connecting member pierced with a through hole being housed between a first and a second lug of the clevis, these lugs respectively having a first clevis hole and a second clevis hole, the device further comprising a shear pin system passing through each of the first clevis hole, second clevis hole and through hole and comprising a threaded end collaborating with a nut system bearing against a second clevis lug. 
   According to the invention, the shear pin system comprises, at the opposite end to the threaded end, a widened portion passing through the first clevis hole and forming a shoulder situated between the first and second clevis lugs, the connecting member situated some distance from the first clevis lug being pressed, on one side, against the shoulder and, on the other side, against the second clevis lug. 
   The joining device according to the invention has the particular feature of enjoying all of the advantages relating to the embodiments of the prior art, without suffering from their disadvantages. 
   Specifically, it should first of all be emphasized that the joining device is of a design which allows it to be made of small-sized elements, in that the presence of a two-lug clevis avoids the detrimental bending effects encountered in the single-lug solutions of the prior art. 
   In addition, it is advantageously possible to achieve accurate final positioning of the connecting member with respect to the clevis given that this member is kept fixedly in contact with one of the two lugs of this clevis. As a result, this makes it possible to obtain very precise relative positioning between the first and second assemblies bearing this joining device according to the invention. 
   Furthermore, even if some clearance is preferentially left between the shear pin system and the through hole made in the connecting member, particularly with a view to accommodating some uncertainty over the positioning prior to the introduction of the shear pin system through this hole, the mechanical connection remains advantageously insensitive to vibrations insofar as the connecting member is held fixedly by friction between the shoulder of the shear pin system and one of the two lugs. 
   Finally, it must therefore be understood that the separation between the two lugs is far greater than the thickness of the connecting member because this connecting member is situated some distance from the first clevis lug in the assembled position. Thus, this particular feature offers the advantage of giving the operator a great deal of scope as to how he introduces the member into the clevis, this insertion of course now no longer being restricted to the application of a translational movement parallel to the orientation of the clevis as it was before. 
   By way of indicative example, the invention applies to a case in which the first annular assembly is positioned radially on the inside with respect to the second annular assembly on which it is fixedly mounted using several circumferentially distributed joining devices, with the clevis of each of these devices with which the first assembly is equipped positioned in such a way that, when viewed from above with respect to this clevis, the clevis is set at the same angle with respect to an axis of the first and second annular assemblies. In this configuration which is, for example, encountered on a turbomachine stator, simultaneous introduction of each of the connecting members into their associated clevis becomes possible simply by applying to the first and/or second assemblies a relative movement of the twisting type about the axis of these assemblies. 
   By way of example, the thickness (e) of the connecting member in one direction of the shear pin system satisfies the condition 1.3&lt;E/e&lt;2.5 where (E) corresponds to a separation between the first and second clevis lugs in the same direction. Naturally, this ratio can be altered by those skilled in the art to suit the requirements encountered. In particular, in the preferred case indicated hereinabove in which each of the connecting members is to be introduced simultaneously into its associated clevis by applying to the first and/or second assembly a relative movement of the twisting type about the axis of these assemblies, the ratio E/e that allows such “screw-fastening” may then be set according to various parameters such as the magnitude of the angle at which the lugs are set, their height and thickness, the radius of the first assembly bearing the clevises, etc. 
   In other words, it was mentioned that the invention can be applied wherever the assembly movement requires a clearance which is greater, even if only very slightly, than the mere clearance associated with manufacturing tolerances. For example, if the setting angle is very small, of the order of 5°, then the ratio E/e may possibly be less than 1.3 but the assembly movement will nonetheless need to be a twisting movement, namely a movement of the type mentioned hereinabove. 
   According to a first preferred embodiment of the present invention, the shear pin system comprises a head and a bushing bearing at one of its ends against the head, the bushing constituting the widened portion passing through the first clevis hole and forming the shoulder at the other of its ends. In such a scenario, provision is therefore made for the diameter of the screw head to be smaller than or equal to the outside diameter of the bushing, which for its own part corresponds more or less to the diameter of the first clevis hole. Nonetheless, when the screw head is entirely externally offset with respect to the clevis, that is to say is not in any way in contact therewith, it may have a diameter greater than the outside diameter of the bushing, and therefore greater than the diameter of the first clevis hole, without departing from the scope of the invention. 
   According to a second preferred embodiment of the present invention the shear pin system is in the form of a pin made as a single piece, having a head that constitutes the widened portion passing through the first clevis hole. In this second embodiment, it is therefore the screw head which passes right through the first clevis hole and which forms the shoulder against which the connecting member is clamped at its end bearing the threaded part. 
   In these two preferred embodiments, arrangements are preferably made to ensure that the shear pin system does not butt against the first clevis lug, in order to be certain of obtaining contact between the shoulder and the connecting member. 
   As a preference, in order to ensure ease of fitting, provision is made for the first clevis hole to be larger than the second clevis hole. 
   Finally, it must be noted that the connecting member may be in the form of an arm. 
   Furthermore, a further subject of the invention is, a joint for a turbomachine comprising first and second assemblies fixedly attached to one another by at least one joining device as described hereinabove. More preferably, the first and second assemblies are annular and concentric and attached fixedly to one another by a number of joining devices as described hereinabove, spaced circumferentially apart, preferably uniformly. 
   As mentioned hereinabove, provision may then be made for the first annular assembly to be positioned radially on the inside with respect to the second annular assembly, and for the clevis of each of the joining devices with which the first annular assembly is equipped to be arranged in such a way that, when viewed from above with respect to this clevis, it has its clevis set at the same angle with respect to an axis of the first and second annular assemblies. Thus, it is then possible to conceive of introducing each of the connecting members into their associated clevis simultaneously by applying to the first and/or second assembly a relative movement of twisting type about the axis of these assemblies, as indicated earlier. 
   As a preference, the first and second assemblies between them define an annular space that forms a portion of a primary duct for the gases of the turbomachine. 
   Again as a preference, the joint constitutes a portion of a stator of the turbomachine. 
   Furthermore, a further subject of the invention is a turbomachine module comprising at least one joint as set out hereinabove. 
   As a preference, the module is a high-pressure or low-pressure turbomachine turbine or compressor. 
   Finally, a further subject of the invention is a turbomachine such as an aircraft turbojet engine comprising at least one module like the one described hereinabove. 
   Other advantages and features of the invention will become apparent from the nonlimiting detailed description given below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This description will be given with reference to the attached drawings in which: 
       FIG. 1  depicts a sectional part view of a turbomachine according to one preferred embodiment of the present invention; 
       FIG. 2  shows a face-on part view of a stator joint belonging to the turbomachine shown in  FIG. 1 , this joint constituting part of the stator; 
       FIG. 2   a  depicts a schematic part view from above of the first annular assembly belonging to the stator joint shown in  FIG. 2 ; 
       FIG. 3  shows a view in section on III-III of  FIG. 2 , and depicting a joining device according to a first preferred embodiment of the present invention; and 
       FIG. 4  shows a view similar to that of  FIG. 3  in which the joining device is in the form of a second preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows part of a turbomachine  1  according to one preferred embodiment of the present invention and, more particularly, a turbomachine module  2  which in this instance is a high-pressure or HP turbine of the turbomachine, which for its part is in the form of an aircraft turbojet engine. 
   The module  2  comprises a stator partially composed of a joint  4  which also forms part of the subject of the present invention, this joint  4  in general comprising a first assembly  6  and a second assembly  8  which are annular and concentric about an axis of the turbomachine (not depicted) which also corresponds to the axis of these assemblies  6 ,  8 . As will be detailed hereinbelow, the assemblies  6 ,  8  are fixedly attached to one another by a number of joining devices  10  spaced circumferentially apart, uniformly, also termed as “cyclically”. 
   As is visible in  FIG. 1 , the first and second assemblies  6 ,  8  between them define an annular space  12  forming a transverse portion of the primary duct for the gases  14  of the turbomachine. In other words, the gases escaping from the combustion chamber (not depicted) of the turbomachine travel along the annular primary gas duct  14  partially defined between the annular assemblies  6  and  8 , causing them to flow through the annular space  12  of the stator joint  4  toward the downstream end of the turbomachine. The annular space  12  that forms a transverse portion of the primary duct for the gases  14  could be directly radially delimited not by the two assemblies  6 ,  8  but by inner and outer annular covers  16 ,  18  attached fixedly to these same assemblies respectively, between said assemblies. 
   More specifically, with reference to  FIG. 2 , it is possible to see part of the stator joint  4  showing the plurality of joining devices  10  circumferentially spaced apart about the axis  20  of the turbomachine and of the assemblies  6 ,  8 . 
   It is noted that one of the particular features of the joining devices  10  which will be detailed later is that each of them is provided with a clevis  22  set at a non-zero angle with respect to the axis  20 , this angle at which the clevis is set being identical for each of the devises  22  produced. In other words and with reference to  FIG. 2   a , which is a view of any arbitrary clevis  22  from above, the clevis setting  24  is inclined by a setting angle A with respect to the axis  20 , the magnitude of which angle may range between 0 and 90°. By way of indication, this clevis setting  24  corresponds to an axis parallel to each of the two clevis lugs  26   a ,  26   b  and therefore extends along the inter-lug space. As mentioned hereinabove, the diagram given in  FIG. 2   a  is valid for all of the devises  22  fixedly attached to the first assembly  6  as an integral part of which they may optionally be formed. Thus, the setting angle A is of the same magnitude and in the same direction for all of the devises  22  which may then also be inclined in a radial direction, as clearly visible in  FIGS. 2 and 2   a.    
   As will be detailed later, the clevis  22  of a joining device  10  is designed to accept between its two lugs the internal radial end of a connecting member  28  in the form of an arm passing through the annular space  12 , this member  28  having an external radial end fixedly attached to the second assembly  8 , for example by screwed fittings. 
   One of the special features of the present invention is that it offers a design that allows each of the connecting members  28  to be introduced simultaneously into their associated clevis  22  by bringing the first and second assemblies to face each other followed by the application of a simple relative movement of the twisting or screwing type about the axis  10 . To do this, a great separation between the lugs  26   a ,  26   b  of the clevis is provided in particular as will now be described with reference to  FIG. 3 . 
   This figure, which shows a device  10  in its assembled position, shows that the connecting member pierced with a through hole  30  at the internal radial end is housed between a first clevis lug  26   a  and a second clevis lug  26   b  which have a first clevis hole  32   a  and a second clevis hole  32   b  respectively. 
   In addition, the device  10  comprises a shear pin system  34  passing in succession through the first clevis hole  32   a , the through hole  30  and the second clevis hole  32   b . On the whole, this system  34  comprises a screw  36  which has a head  38  preferably equipped with a torque reacting system which performs a rotation-proofing function for the tightening of the associated nut system, and with a shank  40  which is threaded at its free end. The system  34  also comprises a clamping bushing  42  pushed onto the shank  40  and bearing against the screw head  38 . Finally, the device also comprises a nut system  44  which may be in the form of a simple nut, screwed onto the threaded end  46  of the screw shank and bearing against the outer face of the second clevis lug  26   b.    
   In this configuration, at the opposite end to the threaded end  46 , the clamping bushing  42  of the shear pin system  36  constitutes a widened portion that passes right through the first clevis hole  32   a , in particular meaning that the screw head  38  has to remain outside and some distance away from the clevis  22  against which it does not abut. In this respect, provision is preferably made for the diameter of the screw head  38  to be smaller than or equal to the outside diameter of the bushing which for its part corresponds more or less to the diameter of the first clevis hole  32   a.    
   Thus, the bushing  42  that forms the widened portion therefore extends into the inter-lug space  48  in order at its end situated within this space  48  to constitute a shoulder  50  which therefore also lies between the first and second clevis lugs  26   a ,  26   b.    
   This shoulder  50  butts against one of the faces of the connecting member  28 , the other of its faces, the opposite one to the first, bearing against an inner face of the second lug  26   b.    
   As a result, the connecting member  28  is held fixedly by nipping/friction some distance away from the first lug  26   a , thanks to the pressure exerted by the shoulder  50 . 
   By way of indication, provision is preferably made for the screw shank  40 , the second clevis hole  32   b  and the interior surface of the clamping bushing  42  to have more or less the same diameter, it being possible for the diameter of the through hole  30  for its part to be slightly larger in order to accommodate any uncertainty as to the positioning prior to the introduction of the shear pin system  36  through the hole  30 . Nonetheless, it should be noted that the shear pin system  36  is preferably designed to operate essentially in shear in collaboration with the through hole  30  and, as a secondary function, in friction through the contact between the opposing faces of the member  28  and the interior face of the lug  26   b  and the shoulder  50 , respectively. 
   In the scenario depicted in  FIG. 3 , the screw shank  40  having a constant diameter between its free end and the end that is fixedly attached to the screw head  38 , it is therefore obvious that the diameter of the second clevis hole  32   b  is smaller than that of the first clevis hole  32   a  through which the shear pin system  36  can slide freely upon assembly, along the axis  52  of the clevis holes  32   a ,  32   b.    
   Naturally, in order to allow the joint to be assembled simply through a relative twisting movement between the first assembly  6  and the second assembly  8  about the axis  20 , the person skilled in the art will be able to adjust the ratio E/e between the separation E between the first and second clevis lugs  26   a ,  26   b  in a direction of the shear pin system  36  that coincides with the axis  52  of the clevis holes and the thickness e of the connecting member  28  in that same direction  52 . By way of indicative example, this ratio may be such that it satisfies the condition 1.3&lt;E/e&lt;2.5. 
   Reference is now made to  FIG. 4  which depicts a joining device according to a preferred second embodiment of the present invention. It has strong similarities with the first embodiment described hereinabove and, in this respect, it is emphasized that the elements which bear the same numerical references in the figures correspond to elements which are identical or similar. 
   Thus, it may be seen that the only difference lies in the fact that there is a shear pin system  36  made as a single piece, of which the head  38  bearing the screw shank  40  coincides with the widened portion  42  that forms the shoulder  50  and passes through the first clevis hole  32   a . Here again, in the jointed state as depicted, there is no abutment between the first lug  26   a  and the screw head  38  passing through it. 
   Of course, various modifications can be made by those skilled in the art to the invention as just described merely by way of nonlimiting examples. In this respect, it may be possible to conceive of fitting the devises on the second assembly and the connecting members on the first assembly without departing from the scope of the invention.