Abstract:
The assembly comprises a fixed fork ( 10 ) of which the lugs ( 22, 30 ) support a rod ( 60 ) onto which a spherical ball is slipped ( 46 ) about which a cage ( 44 ) and a support ( 42 ), of the part which is mobile in rotation, swivel. The maintaining of the axial and angular positions of the spherical ball ( 46 ) in the fork is ensured, in particular, by a tight fit (A 3 ) which replaces conventional screw and nut systems positioned at the end of the rod and which project disadvantageously. 
     According to the invention, a pair of planar facets which are opposing and in abutment (including 23) carry out a blocking of one of the assembly pieces in rotation. 
     Application to bell cranks for the transmission of movement, in particular in aircraft engines.

Description:
TECHNICAL FIELD 
   The present invention relates to the field of assemblies of devices swiveling on bell crank forks. 
   It relates to an assembly of a device swiveling on a bell crank fork. 
   It also relates to a control system for a variable pitch flow-straightener comprising such an assembly of a device swiveling on a bell crank fork. 
   It finally relates to an aircraft engine provided with at least one such assembly of a device swiveling on a bell crank fork. 
   PRIOR ART 
   The assembly of a device swiveling on a bell crank fork is known, for example in the document U.S. Pat. No. 4,174,137. In the known manner, the bell crank fork comprises two parallel lugs, each penetrated by a bore aligned with the bore of the other lug. In a similarly known manner, the swiveling device comprises a spherical internal ring, or ball joint ball, penetrated by a ring bore, which is surrounded by an external ring of spherical shape corresponding to the ball or ball joint cage, itself carried by a support. The support is thus mobile in all rotational directions, or “swiveling”, relative to the fork. 
   Said document reveals a conventional assembly of the device swiveling on the bell crank fork, in which the internal ring is tightened between the two lugs of the fork by means of a screw-nut coupling. The rod of the screw successively passes through the bore of one of the lugs of the fork, then the bore of the ring, then the bore of the other lug of the fork and the nut is tightened onto the end of the screw, which is threaded to this end. The size of such an assembly is large in the axial direction of the screw. More specifically, the height of the head of the screw and the height of the nut are added to the size of the fork in this direction. 
   In some specific configurations, the space available to house an assembly of this type is reduced. More specifically, as is the case, for example, for control systems for variable pitch flow-straighteners of a turbomachine compressor, the assembly of the swiveling device on the bell crank fork is inserted into a volume of reduced width, in the order of several centimeters. 
   The diameter of the spherical ball is generally dictated by the application and, in particular, by the forces which it has to undergo. The lugs of the fork between which the ball is mounted, have to be at a distance allowing sufficient angular clearance of the swiveling support. The ends of the ball and the nut add to the transverse spatial requirement of the device, which may become excessive within small housings. 
   The need, therefore, exists to propose an assembly of a device swiveling on a bell crank fork which may be implemented with a restricted spatial requirement. 
   U.S. Pat. No. 5 5 501 421, FR-A-2 005 524 and U.S. Pat. No. 2,728,975 illustrate designs which are quite close to the invention. 
   DESCRIPTION OF THE INVENTION 
   A first object of the invention is to propose an assembly of a device swiveling on a bell crank fork which may be implemented with a restricted spatial requirement. This is the case, for example, for assemblies of devices swiveling on bell crank forks which are implemented in the control systems for variable pitch flow-straighteners of a turbomachine compressor. 
   A second object of the present invention is to propose an assembly of the device swiveling on a bell crank fork which respects certain restrictions of assembly. The spherical ball thus has to remain fixed. However, in order to avoid seizing, it is not desirable that it is forcibly mounted on the rod passing through the fork. This is why it is mounted by a close sliding fit on the rod and maintained in place by tightening the parts in the direction of the axis of the rod, which is carried out by the nut. 
   The elimination of the nut has to be made by maintaining the spherical ball in position against the rotational and axial movements. It is also noteworthy that the jamming of the spherical ball between the two lugs of the fork is not a perfect solution, since it also requires strict manufacturing tolerances and may also lead to deformations which are detrimental to the service life of the bell crank. 
   The type of invention relates to an assembly of a device swiveling on a bell crank fork by assembly means, said assembly means comprising an assembly rod and other assembly means, 
   in which said swiveling device comprises an internal ring (the spherical ball) penetrated by a ring bore, 
   in which said bell crank fork comprises two lugs each penetrated by one respective lug bore, said lug bores being aligned with one another according to an assembly axis, and 
   in which said assembly rod passes successively through one of the lug bores, then the ring bore, then the other lug bore, 
   where said other assembly means have a tight fit of one portion of the rod on a surface in which said portion is engaged. 
   A tight fit is relied upon to replace the screw and nut system, generally combined with other assembly means to guarantee the immobilization of the spherical ball or internal ring in rotation and in translation along the rod. By stopping the rod passing through the fork by a tight fit generally located via the lug bores, the end of the screw where the threaded portion was made and which had to project beyond the fork to receive the nut becomes unnecessary. 
   The surface which provides the tight fit with the portion of the rod may belong to a bushing engaged in one of the lug bores of the fork. Such a bushing often has the advantage of contributing to the retention of the internal ring in the axial portion. 
   The rod portion having a tight fit will often oppose a head of the rod resting on an external face of one of the two lugs of the fork and forming part of the other assembly means, more precisely defining an abutment of the rod. 
   The tight fit constitutes a means for blocking the rod in translation as well as in rotation. Further assembly means also have to be added to retain the internal ring. These means may be located on the additional parts, which also have to be held in translation and in rotation and which are of different types, as will be seen according to the disclosed examples. These assembly means may thus comprise a bushing engaged in one of the lug bores of the fork around the rod and comprising an end face bearing against the external ring; or two bushings of this type, which are thus engaged in each of the lug bores of the fork. Such bushings have a principal function of holding the internal ring in translation along the axis. The axial position of the internal ring is determined and invariable if it is pushed against the internal face of a fork lug or against the spacer which is itself pushed against the fork lug. 
   The invention is characterized by specific assembly means allowing blocking in rotation, which consist of a pair of planar facets opposing one another, one thereof being made at the bottom of an indentation of one of the lugs of the fork. The other facet is made, according to the embodiments, on a head of the rod, on one of the bushings, or on a circular collar positioned at one polar end of the lower ring, to hold one or other of these parts in rotation. One significant advantage of these pairs of facets is the volume which is saved, since no additional part is required and this arrangement involves nesting of the existing parts, with no protuberance relative to the designs where it does not exist. It is also reliable and durable. 
   Further assembly means, intended to block the rotational movements, comprise matching lugs and steps joining the internal ring to other parts of the assembly, which may be the aforementioned bushings or even the bushing when there is only one, and a head of the rod. As the rod is held in rotation by the tight fit and at least one of the bushings is held in rotation by a further means such as a second tight fit, the internal ring is thus also held in rotation. A considerable number of means for blocking in translation and in rotation is thus necessary to retain the parts of the assembly and obtain the desired stability during installation. 
   Other assembly means are to be envisaged, amongst which crimping may be cited, carried out between adjacent parts by folding a deformable portion of one of these parts onto the other. The crimping may be carried out with sufficient force to produce both means for blocking in translation and blocking in rotation. Said means are more reliably guaranteed if the crimping only relates to deformable angular portions, which are folded back into the angular slots of the adjacent part. Examples of crimping may be carried out by folding back a collar at one end of the rod onto the bushing, tabs of the bushing into the slots of the rod, or a collar at one end of the rod onto one of the lugs of the fork. 
   Certain arrangements of the assembly make it possible to reduce further the lateral spatial requirement by limiting the lengths projecting beyond the fork which remain after the elimination of the screw and nut system. It is in this manner that when the rod comprises a head, it may be housed in an indentation on the external face, or comprise a truncated shape being forced into a conical recess of the lug of the fork. In other designs, the rod comprises a head and one of the fork lugs comprises a recess into which the head is partially forced, instead of abutting against the lug of the fork. It is thus a different means from the head of the rod which define the position for blocking the assembly in translation. 
   If the rod is forced completely into the bore of the fork lug, the assembly is thus completely incorporated within the fork and the greatest saving in space is obtained. 
   A particularly simple embodiment is characterized in that the internal ring is retained between a head of the rod and either one of the fork lugs, or a spacer located between the internal ring and one of the fork lugs. 
   The invention further relates to a control system for a variable pitch flow-straightener and an aircraft engine provided with an assembly in accordance with the preceding information. As this system and this engine are not modified, moreover, relative to the known designs, they will not be described in detail here. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be understood more clearly by reading the detailed description of embodiments that follow, which are given by way of illustrative example and are not limiting in any sense, by referring to the accompanying drawings, in which: 
       FIG. 1  shows, in section according to a longitudinal plane of symmetry, a first embodiment of the assembly (according to the invention); 
       FIG. 2  shows, in perspective, an assembly rod according to the first embodiment; 
       FIG. 3  shows a perspective view of an internal ring of the swiveling device according to the first embodiment; 
       FIG. 4  is a perspective view of the two connecting bushings according to the first embodiment; 
       FIG. 5  shows, in section according to a longitudinal plane of symmetry, a second embodiment of the assembly (according to the invention); 
       FIG. 6  shows, in section according to a longitudinal plane of symmetry, a third embodiment of the assembly (not according to the invention, per se); 
       FIG. 7  is an exploded perspective view of the third embodiment of the assembly; 
       FIG. 8  is a further perspective view showing the two connecting bushings according to the third embodiment; 
       FIG. 9  is a further perspective view of the assembly according to the third embodiment in the configuration prior to the assembly; 
       FIG. 10  shows, in section according to a longitudinal plane of symmetry, a fourth embodiment of the assembly (according to the invention); 
       FIG. 11  shows, in section according to a longitudinal plane of symmetry, a fifth embodiment of the assembly (according to the invention); 
       FIG. 12  shows, in section according to a longitudinal plane of symmetry, a sixth embodiment of the assembly (according to the invention); 
       FIG. 13  shows, in section according to a longitudinal plane of symmetry, a seventh embodiment of the assembly (according to the invention); 
       FIG. 14  shows, in section according to a longitudinal plane of symmetry, an eighth embodiment of the assembly (according to the invention); 
       FIGS. 15 to 17  show, respectively, three variants of surfaces for blocking in rotation, which are common to the sixth, seventh, eighth, tenth and fourteenth embodiments; 
       FIG. 18  shows, in section according to a longitudinal plane of symmetry, a ninth embodiment of the assembly (not according to the invention, per se); 
       FIG. 19  shows, in an exploded perspective view, the internal ring, a connecting bushing, and the assembly rod, for the ninth embodiment; 
       FIG. 20  shows a perspective view of the ninth embodiment, 
       FIG. 21  shows, in section according to a longitudinal plane of symmetry, a tenth embodiment of the assembly (according to the invention); 
       FIG. 22  shows, in section according to a longitudinal plane of symmetry, an eleventh embodiment of the assembly (not according to the invention, per se); 
       FIG. 23  shows, in section according to a longitudinal plane of symmetry, a twelfth embodiment of the assembly (not according to the invention, per se); 
       FIG. 24  shows, in section according to a longitudinal plane of symmetry, a thirteenth embodiment of the assembly (not according to the invention, per se); 
       FIG. 25  shows, in section according to a longitudinal plane of symmetry, a fourteenth embodiment of the assembly (according to the invention); 
       FIG. 26  shows, in section according to a longitudinal plane of symmetry, a fifteenth embodiment of the assembly (not according to the invention, per se). 
   

   DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
   Firstly, referring to all the figures, the elements common to all the embodiments of an assembly of a device swiveling on a bell crank fork will be described. In the remainder of the description, and in order to simplify said description, an assembly of a device swiveling on a bell crank fork will be referred to as an “assembly”. 
   The assembly  10  according to the invention is arranged inside a housing  12  (only sketched here) of which the internal dimensions are fixed. In particular, the housing  12  comprises a first internal face  14  and a second internal face  16  arranged opposite one another and parallel to one another, which are separated by a fixed distance D 12 . The housing  12  is, for example, a housing forming part of a control system for one or more stages of variable pitch flow-straighteners. 
   The assembly  10  comprises a fork  20  and a swiveling device  40  which are assembled to one another by assembly means. These assembly means comprise an assembly rod  60  and other assembly means which will be defined below. 
   The fork  20  comprises a first fork lug  22  penetrated by a first lug bore  24  and a second fork lug  30  penetrated by a second lug bore  32 . The two lug bores  24 ,  32  are aligned in the direction of an assembly axis  2 . 
   The fork  20  comprises a first external face  26  which is located opposite the first internal face  14  of the housing  12  at a distance D 1  therefrom, and a second external face  34  which is located opposite the second internal face  16  of the housing  12  at a distance D 2  therefrom. 
   The swiveling device  40  comprises, in a manner known per se, a support  42  on which an external ring  44  is fixed, also known as a cage, in which an internal ring  46  is arranged, also known as a ball. The external ring  44  comprises a concave and spherical internal face which cooperates with a convex and spherical face of the internal ring  46  to permit three degrees of freedom in rotation between the external ring  44  and the internal ring  46 . The internal ring  46  is penetrated by a ring bore  48 . 
   The assembly rod  60  comprises a substantially cylindrical body. It has a first end  64  and a second end  66 . 
   The fork  20  and the swiveling device  40  are assembled by means of the assembly rod  60  which passes successively through the first lug bore  24 , the ring bore  48  and the second lug bore  32  according to the assembly axis  2 . 
   In the examples illustrated in the figures, the assembly rod  60  is dimensioned such that its axial length L (illustrated in  FIG. 3 ) is slightly greater, equal to or less than the distance D (illustrated in  FIG. 1 ) which separates the first external face  26  and the second external face  34 . As a result, when the assembly rod  60  is in position in the three bores  24 ,  48 ,  32 , it is entirely arranged between these two external faces  26 ,  34 . In other words, its first end  62  does not protrude or hardly protrudes beyond the first external face  26  and its second end  64  does not protrude or hardly protrudes beyond the second external face  34 . 
   In addition to the rod  60 , the assembly  10  comprises further assembly means, which comprise:
         means for blocking the rod  60  in axial translation according to the assembly axis  2 ,   means for blocking in rotation which prevent a rotation of the internal ring  46  relative to the rod  60  about the assembly axis  2 .       

   These other assembly means are entirely arranged between the two external faces  26 ,  34  of the fork  20 . In other words, none of said assembly means project beyond the first external face  26 , nor beyond the second external face  34 . 
   It follows from the above that the distance D 1  which separates the first external face  26  and the first internal face  14  of the housing  12  may be reduced to a minimum. In a similar manner, the distance D 2  which separates the second external face  34  and the second internal face  16  of the housing  12  may be reduced to a minimum. As a result, for a fixed value of the distance D 12  between the two internal faces of the housing  12 , it is possible to dimension the fork  20  such that the distance D between the two external faces  26 ,  34  of the fork  20  is very similar to this distance D 12 . 
   Now the means for blocking in translation and the means for blocking in rotation belonging to each embodiment of the assembly  10  according to the invention will be described. 
   FIRST EMBODIMENT 
   By referring to  FIG. 1 , a first embodiment of the assembly  10  according to the invention is shown in section according to a longitudinal plane of symmetry. 
   The first fork lug  22  comprises an indentation  38  on its external face opposite the first internal face  14  of the housing  12 . This indentation  38  extends from the free end of the first lug  22 , passes through the first lug bore  24 , extends beyond the first lug bore over a certain distance, and is interrupted when joining the first external face  26  of the fork  20 . This indentation  38  defines, on the exterior of the first lug  22 , a substantially planar facet  23  which is perpendicular to the longitudinal plane of symmetry (plane of  FIG. 1 ) of the fork  20  and parallel to the assembly axis  2 . 
   The internal ring  46  of the swiveling device  40  is shown in perspective in  FIG. 2 . It has a substantially spherical shape penetrated by a ring bore  48  and cut off at its two poles, defining a first transverse ring face  50  and a second transverse ring face  52  which are perpendicular to the direction of the ring bore  48 . Each transverse face  50 ,  52  carries two diametrically opposed steps  54 . 
   The assembly rod  60  is shown in perspective in  FIG. 3 . It carries, at its first end  62 , a rod head  66  which has a substantially “D” shape. This rod head  66  has a substantially planar facet  68  parallel to the direction of the assembly rod  60 . The second end  64  of the assembly rod  60  has a smaller diameter than that of the remainder of the assembly rod  60 . 
   The assembly  10  comprises a first connecting bushing  70  and a second connecting bushing  80  which are shown in perspective in  FIG. 4 . The two connecting bushings  70 ,  80  are respectively provided with a cylindrical body  72 ,  82  and a radial end shoulder  74 ,  84 . Each shoulder  74 ,  84  carries on its face opposing the body  72 ,  82 , two diametrically opposed lugs  708 . 
   The method for installing the assembly  10  will now be described by referring to  FIG. 1 . 
   The first connecting bushing  70  is arranged in the first lug bore  24  with its shoulder  74  oriented towards the second lug  30 . The second connecting bushing  80  is arranged in the second lug bore  32  with its shoulder  84  oriented towards the first lug  22 . The two connecting bushings  70 ,  80  are oriented about the assembly axis  2  such that their respective lugs  708  are opposite one another. 
   Then the swiveling device  40  is introduced between the lugs  22 ,  30  of the fork  20 , such that the internal ring  46  is positioned between the two shoulders  74 ,  84  of the connecting bushings  70 ,  80  and that the four lugs  708  of the two bushings  70 ,  80  are located respectively in the four steps  54  of the internal ring  46  and such that the ring bore  48  is aligned with the two lug bores  24 ,  32 . 
   The assembly rod  60  is then introduced by its second end  64  into the first bushing  70 , then into the ring bore  48 , then into the second bushing  80  according to the direction of the assembly axis  2 , until the head of the rod  66  bears against the indentation  38 . The assembly rod  60  is oriented about the assembly axis  2  such that the planar facet  68  of the rod head  66  is parallel with the planar facet  23  of the indentation  38 . 
   The head of the rod  66  and the indentation  38  are dimensioned such that the planar facet  68  of the rod head  66  is in abutment against the planar facet  23  of the indentation  38 . 
   The head of the rod  66  and the indentation  38  are dimensioned such that said rod head  66  does not protrude beyond the first external face  26  of the fork  20 . 
   The assembly rod  60  is dimensioned such that its second end  64  does not protrude beyond the second external face  34  of the fork  20  or protrudes very little. 
   The two connecting bushings  70 ,  80  are dimensioned such that the two transverse faces  50 ,  52  of the internal ring  46  are in abutment against their shoulders  74 ,  84 . The lugs  708  of the bushings  70 ,  80  and the steps  54  of the internal ring  46  are formed and dimensioned such that the lugs  708  come into engagement in the steps  54  and prevent an axial rotation between the internal ring  46  and each of the two bushings  70 ,  80 . 
   The two connecting bushings  70 ,  80  are also dimensioned such that the height of the body  72  of the first connecting bushing  70  is less than or substantially equal to the height of the first lug  22  of the fork  20  in the region of the indentation, such that the rod head  68  may abut against the indentation  38 . 
   The internal diameter of the body  84  of the second connecting bushing  80  is less than the internal diameter of the body  72  of the first connecting bushing  70 , in a substantially similar manner to the variation in diameter between the second end of the rod  64  and the first end of the rod  62 . 
   The internal diameter of the first bushing  70  and the part of the rod  60  of greater diameter are dimensioned so as to allow a first close sliding fit A 1 , for example of the standard type H7g6, between these two parts  60 ,  70 . 
   The body  72  of the first bushing  70  and the first lug bore  24  of the first lug  22  are dimensioned so as to produce a second tight fit A 2 , for example of the standard type H7p6, between these two parts  22 ,  70 . 
   The second end  64  of the assembly rod  60  and the internal diameter of the second connecting bushing  80  are dimensioned so as to produce a third tight fit A 3 , for example of the standard type H7p6, between these two parts  60 ,  80 . 
   The body  82  of the second bushing  80  and the second lug bore  32  of the second lug  30  are dimensioned so as to allow a fourth close sliding fit A 4 , for example of the standard type H7g6, between these two parts  32 ,  80 . 
   The part of the assembly rod  60  of greater diameter and the ring bore  48  of the internal ring  46  are dimensioned so as to allow a fifth close sliding fit A 5 , for example of the standard type H7g6, between these two parts  46 ,  60 . 
   The first embodiment of the assembly  10  comprises means for blocking the assembly rod  60  in translation relative to the fork  20 , which are the rod head  66  and the indentation  38  in cooperation. 
   The first embodiment of the assembly  10  comprises means for blocking in rotation to prevent a rotation of the internal ring  46  relative to the assembly rod  60  about the assembly axis  2 . 
   These means for blocking in rotation comprise first means for blocking in rotation of the internal ring  46  relative to each of the connecting bushings  70 ,  80 , which are the lugs  708  and the steps  54  in cooperation. 
   These means for blocking in rotation comprise second means for blocking the assembly rod  60  in rotation relative to the second connecting bushing  80 , which are the tight fit between these two parts. 
   These means for blocking in rotation comprise third means for blocking the first connecting bushing  70  in rotation relative to the fork  20 , which are the tight fit between the first connecting bushing  70  and the first lug  22 . 
   The first embodiment of the assembly  10  comprises, moreover, the fourth means for blocking the rod  60  in rotation relative to the fork  20  about the assembly axis  2 , which are planar facets  68  and  23  in cooperation. These fourth means for blocking in rotation reinforce the third means for blocking in rotation. 
   As may be seen, and as will be found in the other embodiments of the invention, the fits such as A 1  to A 5  are a combination of tight fits to introduce the required blocking in rotation and close sliding fits to allow easy installation, but without the risk of allowing an offset of the internal ring  46  and an error in the transmission of the movement. 
   A fifth sliding fit A 5  will be found, in particular, in the other embodiments. The reason is that it should be avoided that the internal ring  46  seizes on the rod  60 . 
   The axial tightening of the system is carried out at the end of the installation by bringing together as closely as possible the second bushing  80  of the rod head  66  and by maintaining said rod head in abutment with the surface of the indentation  38 . The second bushing  80  slides into the second lug bore  32  by allowing a final clearance J to be produced, measured in the direction of the axis  2  between the second lug  30  and the flange  81  of the bushing  80 . The internal ring  46  ends up being gripped between the flanges  71  and  81  of the bushings  70  and  80  oriented towards one another, the flange  71  of the first bushing  70  abuts against the first lug  22  and the tightening in the third fit A 3  retains the system in this position. 
   It has been mentioned that the second fit A 2  was tight. It is possible to select it to be sliding, since the rotations of its first bushing  70  are prevented by the lugs  708 , the tightening of the third fit A 3  and the abutment between the facets  68  and  222 . 
   FURTHER EMBODIMENTS 
   In a general manner, the reference numerals of similar elements of different embodiments will carry the same reference numerals of two numbers preceded by 200, 300, etc. 
   The second embodiment is disclosed in  FIG. 5 . It is largely identical to the preceding embodiment such that its complete description is not advantageous and in that only the original elements thereof will be described. The internal ring  246  is thus the same as the preceding one. The rod  260  now comprises a head  266  lacking a planar abutment facet such as at  68  creating a blocking in rotation; it may, however, be perfectly circular. It is the first bushing, referenced by  270 , which now carries a similar means, namely a planar facet  273  on a columnar part of the flange  271 ; this planar facet  273  bears against a planar facet  275  created at the bottom of a second indentation  277  which the first lug  222  now carries, opposing the indentation  238  similar to that already described with the reference numeral  38 . The fits A 1  to A 5  are identical to the preceding one, i.e. the fit A 3  between the end (in this case  264 ) of the rod (in this case  260 ) and the second bushing (in this case  280 ) is tight and the others may be sliding, even if it is possible to select tightening for the second fit A 2  between the first lug  222  and the first bushing  270  as in the preceding embodiment. The concentricity of the mechanical systems is even better if the second fit A 2  is tight. 
   The third embodiment shown in  FIGS. 6 ,  7 ,  8  and  9  involves the use of a rod  360  and the first lug  322  does not need to be indented. The first bushing  370  is provided with tabs  371  which may be deformed on the external side of the first lug  322 , projecting in the direction of the axis  2 , which may be folded back laterally toward one another onto the beveled slots  361  in the rod head  366 , so as to create crimping. In a similar manner, the opposing end of the rod  360  carries a narrowed portion  363  following the shape of a bore  365 , being forced in to a certain depth into the rod  360  and this narrowed portion  363  may be folded back onto a bevel  381  made on the internal face of the second bushing  380 , on the external side of the second lug  330 . This double crimping fixes the rod  360  in rotation and in translation against the bushings  370  and  380 . The fit A 2  is tight or sliding. The rotations of the assembly of the rod  360 , the bushings  370  and  380  and the internal ring  46  are prevented by the engagement of planar faces  391  of the rod head  366  on a dividing wall  392  of the first lug  322  ( FIG. 9 ). The fit A 3  is tight to retain the bushing  280  in an identical orientation to that of the bushing  270 . The other fits A 1 , A 4  and A 5  are sliding as before. In this embodiment, the bushing  370  as well as the ends of the rod  360  have to project slightly outside the lugs  322  and  330  so that a crimping tool reaches them easily. The internal ring  346  is the same as before. 
   The fourth embodiment, shown in  FIG. 10  combines the characteristics of the two previous embodiments, namely the use of crimping similar to that of the third embodiment and the interaction of a planar end facet  473  made on the flange  471  of the first bushing  470  on a corresponding planar facet  475  at the bottom of an indentation  477  on the internal face of the first lug  422 . The fits A 2  and A 3  are again tight, the three others A 1 , A 4  and A 5 , sliding. 
   The fifth embodiment is illustrated in  FIG. 11  as a variant of the fourth, but it could be applied to the other preceding embodiments: it is distinguished in that the rod  560  comprises a head  566  which is not planar but truncated, with an upper planar face  567  and a lower face  569  bearing against a bevel  571  made at the external end of the bore  524  of the first lug  522 . The fits are the same as before. The advantage of this solution is that the arrangement is more compact since the head  566  hardly projects beyond the first lug  522 . 
   The following embodiment, the sixth, is illustrated in  FIG. 12 . The bushing, known as the first bushing in the preceding embodiments and located on the rod head side, no longer exists, and the rod  660  is engaged directly in the bore  624  of the first lug  622 . The internal ring  646  is extended to the upper pole by a flange  647  in contact with the internal face of the first lug  622  and which is provided on one part of its periphery with a planar facet  649  which opposes a planar facet made at the bottom of an indentation  677  hollowed out in the first lug  622 . This device for blocking in rotation between the fork and the internal ring  646  resembles that which had been used, for example, in the second embodiment between the first bushing  270  and the fork. 
   The rod  660  comprises a truncated head  666  engaged in a bevel  671  of the first lug  622  in order to touch its surface only slightly and to limit the spatial requirement. Finally the remainder of the device is similar to that of the first embodiment, for example with a bushing  680  similar to the second bushing  80  and one narrow end  664  of the rod  660  enters into this bushing  680 . 
   The fits A 1  and A 2  of the preceding embodiments are replaced by a fit A 6  between the rod  660  and the bore  624  of the first lug  622 . The fit A 3  remains tight, the others A 4 , A 5  and A 6  are sliding. The rotation of the elements of the system is prevented by the abutment between the planar faces  649  and  675 , by the lugs between the internal ring  646  and the bushing  680  (they are similar to those of the first embodiment), by the tightening of the fit A 3 , whilst it is ensured that they are maintained in translation by the abutment of the flange  681  of the bushing  680  against the internal ring  646 , the abutment of the internal ring  646  against the bottom of the indentation  677  by the flange  647  and the abutment of the head  666  at the bottom of the bevel  671 . 
   The seventh embodiment is shown in  FIG. 13  and shows a variant of the sixth embodiment, where the bushing  680  with a flange is replaced by a bushing  780  without a flange. The rod  760  comprises a crimping collar  763  at its lower end due to the creation of a bore  765  over a sufficient height. The crimping collar  763  is pushed back onto the bushing  780 , which is provided with a lower bevel  781  on its internal face. The crimping and the tight fit between the part  764  of the rod at the location of the bushing  780  and said bushing, in this case further reinforces the connection between the bushing  780  and the rod  760  against movements in rotation or in translation. 
   The eighth embodiment is shown in  FIG. 14  and is distinguished from the preceding embodiment in that there is no longer any bushing. The crimping of the rod  860  takes place by pushing back a collar  863  placed in a similar manner to the collar  763  in a bevel  831  at the external end of the bore  832  of the second lug  830 . The fits A 3  and A 4  are replaced by a single tight fit A 7  between the rod  860  and the bore  832  of the second lug  830 ; the fits A 5 , A 6  are both sliding. 
   The rod  860  is held in rotation and in translation with a sufficient force between its head and the crimping, and the internal ring  846  now comprises a flange  849  bearing against the internal face of the second lug  830 . An arrangement for blocking by a planar facet, similar to that of the sixth and seventh embodiments, blocks the internal ring  846 . In this embodiment, it is accepted that the internal ring  846  is retained immediately between the lugs  822  and  830  of the fork.  FIGS. 15 ,  16  and  17  illustrate certain possible shapes of the internal ring  846 , which might be also given to the internal rings  646  and  746  of the sixth and seventh embodiments. 
   All the flanges  847  at the poles of the sphere have these shapes, where said sphere is truncated, and indentations on these flanges  847 . These indentations are used to form the planar facet for blocking in rotation. One of the two flanges  847  has to be indented but it is not difficult to indent the two flanges to provide an additional possibility for installation and this is what has been illustrated here. 
   In  FIG. 15 , a planar facet  887  is machined on one part of the circumference of the flange  847  and a bevel  889  is added to the junction of the planar facet  887  and the upper face of the flange  847  to eliminate a sharp edge and to avoid the connecting radius R made in the bottom of the bevel of the first bushing  822  (it is illustrated in  FIG. 14 ). In  FIG. 16 , a machining of the upper face of the flange  847  has been added to form at that point an upper step  883 ; this design is advisable when the existing thickness of the flange  847  is too small near the bevel  889  in the embodiment of  FIG. 15 . Finally,  FIG. 17  shows a situation which is obtained if the flange  847  has a thickness which is too small to be able to apply the preceding embodiments thereto: it is then machined over its entire thickness, opened up, and the planar facet  887  is replaced by a pair of smaller planar facets  885 , which are separate and extend in a common plane; as above, bevels  891  are advantageously machined at the junctions of the planar facets  885  and the upper face of the flange  847 . 
   The ninth embodiment is described in  FIGS. 18 ,  19  and  20 . The device principally comprises, apart from the fork, a rod  960 , an internal ring  946 , an external ring  944  and a bushing  970 . The rod  960  comprises a head  966  forced into the bore of the first lug  922  of the fork and touching its surface for a reduced spatial requirement. The rod  960  comprises a collar  963  at its opposing end, to be crimped onto a bevel  931  of the second lug  930 . The rod  960  comprises two successive circular bearing surfaces  955  and  957  and respectively resting on the bores of the bushing  970  of the internal ring  946  and of the second lug  930 . The bushing  970  is also engaged in the bore of the first lug  922 . The fits present on the bearing surfaces  955  and  957  as well as between the bushing  970  and the first lug  922  are denoted A 1 , A 2 , A 5  and A 7  in accordance with the various preceding embodiments. The fit A 1  is tight and the fits A 2 , A 5  and A 7  are sliding. The internal ring comprises two circular planar end surfaces  950  and  952  respectively bearing against the bushing  970  and against the internal face of the second internal lug  930 . As the bushing  970  abuts against the head  966 , the system is perfectly blocked in translation and maintained in position by the crimping. 
   The blocking in rotation of the internal ring  946  and other elements of the system is ensured by the fit A 1  and also by lugs  975  and  977  on the two opposing end faces of the bushing  970 , which penetrate, for the lugs  977 , into recesses  954  associated with the internal ring  946  ( FIG. 19 ) and, for the lugs  975 , into recesses  967  associated with the rod head  966  by means of their internal portion ( FIG. 19 ) and into grooves  991  associated with the first lug  922  by means of their external portion ( FIG. 20 ). 
   The tenth embodiment illustrated in  FIG. 21  is different and comprises a rod  1060 , which is substantially smooth, without a head, and no bushing. The internal ring  1046  is a ball, known as a ball with large clearance from the external ring, which comprises opposing flanges  1047 ,  1051  provided with planar peripheral facets  1049  and  1053  which bear against corresponding planar facets  675  and  679  at the bottom of indentations  1077  and  1081  made on the internal faces of the lugs  1022  and  1030 . The fits A 5 , A 6  and A 7  are similar to others already encountered between the rod  1060 , the bores of the lugs  1022  and  1030  and the internal ring  1046 . The fit A 7  between one distal end of the rod  1060  and the second lug  1030  is tight, the two others are sliding. The rod  1060  is maintained in the second lug  1030 , and the internal ring  1046  is held in translation between the two lugs  1022  and  1030 , on the internal faces of which it bears by a close sliding fit. The rotation of the internal ring  1046  is blocked by the contact of the planar facets  1049  and  1053 . 
   The eleventh embodiment will be described by referring to  FIG. 22 . It is similar to the ninth embodiment, with, amongst others, a bushing  1170  gripped in the bore of the fork lugs between a rod head  1166  forced completely into this bore and the internal ring  1146 , apart from the fact that a ring  1180  is introduced around the rod and retained between the internal ring  1146  and the second lug  1130  of the fork. The fits and their characteristics are identical. The ring  1180  is used as a spacer to obtain a position for the internal ring  1146  which is more centered in the fork in the direction of the axis  2 . 
   The twelfth embodiment is described by means of  FIG. 23 . It differs from the previous embodiment in that the bushing is absent and replaced by a solid head  1266  of the rod  1260 , which is provided with a planar surface  1267  at right angles to the bearing axis  2  of a polar planar face of the internal ring  1246 . Similar fits are found to those already encountered with the reference numerals A 5 , A 6  and A 7  and in which the fit A 7  between the rod  1260  and the bore of the opposing lug at the rod head  1266  is tight, the others are sliding. The rotation may be blocked simply by ensuring a compression of the internal ring  1246  against the rod  1266  and the spacer ring  1280  (similar to the preceding ring  1180 ) and by maintaining the whole in position by the crimping of the end of the rod  1266 . 
   A thirteenth embodiment will be described by means of  FIG. 24 . The spacer ring is omitted and the internal ring  1346  is in this case provided with two opposing flanges  1347  and  1351  to ensure the bearing against the rod head  1366  and the second lug  1330  of the fork. Similar fits to the preceding fits exist. 
   A fourteenth embodiment is described by means of  FIG. 25 . The arrangement of the internal ring  1466  resembles that of  FIG. 21  with, at its polar ends, a pair of flanges  1447  and  1451  each provided with a planar facet  1449  or  1453 , blocked in rotation against a corresponding planar facet at the bottom of an indentation of the adjacent fork lug. The flanges  1647  and  1451  abut respectively against the head  1466  and the second fork lug  1430 . The rod  1460  is, however, different and instead is reminiscent of that of  FIG. 23  with a solid rod head  1466  bearing against one end of the flange  1447  and a collar to be crimped onto a bevel of the fork lug opposing the rod head  1466 . This arrangement makes it possible to avoid maintaining the internal ring  1246  between the two fork lugs. The fits are similar to those in  FIG. 23 . The blocking in translation and in rotation are ensured by the tightness of the fit at the end of the rod  1460 , by the crimping and by the planar facets. 
   A fifteenth embodiment will be described in connection with  FIG. 26 . It corresponds to a particularly simple design, with a rod  1560  without a head, engaged directly in the bores  1524  and  1532  of the lugs  1522  and  1530  and where the internal ring  1546  is retained axially between the internal faces of the two lugs, by bearing thereagainst by means of smooth surfaces, i.e. deprived of flanges or lugs. A standard internal ring is shown as in the other embodiments and in particular the tenth; an internal ring with lateral flanges, known as a ball with large clearance, could be used. As in embodiments of this type where the internal ring is fitted directly between the two lugs, as in the eighth embodiment, the fit of the internal ring  1546  on the rod  1560  is marginally sliding and the internal ring  1546  is retained axially by a close fit, as H7g6 or H7h6 between the lugs  1522  and  1530  of the forks. The rod  1560  is retained in one of the bores  1532 , for example, of the fork lug by a tight fit which holds it in place. In such designs, the rod  1560  may be entirely contained within the fork, without touching the surface of the lugs, which constitutes an advantage which is able to compensate for the uncertainty of providing sufficient retention of the internal ring  1546 . Such a system is, moreover, very simple to produce. 
   In all the embodiments from the ninth embodiment, the rod is entirely contained within the two fork lug bores. The mountings are the least space-consuming. That said, in all the examples of the figures, the rod may be entirely contained within the space taken up by the fork lugs, on condition that a slightly greater spatial requirement for the crank forks is tolerated. 
   All the embodiments of the assembly which have been described here may be provided, for example by combining them together.