Abstract:
This spider assembly comprises a spider which comprises a hub intended to be connected to a shaft and from which there project several arms ( 3 ). Each arm comprises a cylindrical runway surface ( 12 ), a roller ( 5 ) mounted to rotate and slide on each arm via a ring of needles ( 4 ), and a split elastic ring ( 8 ) for retaining the ring of needles and the roller on the arm. The ring is axially fixed by snap-fitting onto the arm, the width of the split in the ring after mounting being zero or very much smaller than the diameter of the needles. The ring comprises, on its interior face ( 16 ), both a needle-retaining surface ( 20 ) that is flared towards the free end of the arm and delimits the space in which the needles run, and a roller-retaining surface ( 22 ) that is flared towards the free end of the arm. The flared roller-retaining surface is more or less in the continuation of the flared needle-retaining surface ( 20 ).

Description:
BACKGROUND OF THE INVENTION 
   The subject of the present invention is a spider assembly for a universal joint of the type defined in the preamble of claim  1 . 
   The invention applies for example to constant-velocity tripod joints used in motor vehicle transmissions. 
   Such a spider assembly is known from French Patent FR-A-2 795 467 in the name of the Applicant Company. 
   The assembly described in the abovementioned document is intended to hold each roller on its arm when it is necessary for the spider equipped with rollers and needles, on the one hand, and the female element, on the other, to be delivered separately, these two parts being assembled on a vehicle assembly line. This assembly allows positive retention both of the rollers and of the needles, but the retaining ring in this assembly has, in cross section, a complex profile and this is an economic impediment to its manufacture and a technical impediment regarding tolerance bands. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to propose a suitable retaining ring for equipping the aforementioned type of spider assembly, which is of low cost while at the same time more or less maintaining the same functional advantages as those described in the aforementioned document, particularly in terms of roller and needle retention. 
   To this end, the subject of the invention is a spider assembly of the aforementioned type comprising the characteristics of the characterizing part of claim  1 . 
   The spider assembly according to the invention may have one or more of the characteristics described in claims  2  to  17 , taken in isolation or in any technically feasible combination. 
   Another subject of the invention is a universal joint comprising a spider assembly as defined hereinabove and a female element which comprises tracks in which the rollers are accommodated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from reading the description which will follow, given solely by way of example and made with reference to the appended drawings in which: 
       FIG. 1  is a view in meridian cross section of a spider assembly according to the invention; 
       FIG. 2  is a view from above of the spider assembly of  FIG. 1 ; 
       FIG. 3A  is a view on a larger scale of a detail ringed III in  FIG. 1 , with the roller in another position; 
       FIG. 3B  is a view similar to  FIG. 3 , but on a larger scale;  FIGS. 4  to  6  are views similar to  FIG. 3A  but of three alternative forms of embodiment of a spider assembly according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  depicts a spider assembly of a constant velocity universal joint of the tripot type. This spider assembly comprises a spider  1  consisting of a central body or hub  2  which is annular of axis X—X assumed to be horizontal and from which there project radially three arms  3  of axis Y—Y arranged angularly 120° apart; and, on each arm  3 , a ring of needles  4 , a roller  5  having a spherical exterior surface  6  and a cylindrical bore  7 , and a retaining ring  8 . 
   This spider assembly is designed to equip a female element  9  merely sketched in  FIG. 1 , the roller  5  of each arm  3  being housed in a corresponding pair of tracks  9 A that the female element comprises. 
   The retaining ring  8  alone provides positive axial retention of the needles  4  and also positive retention of the roller  5 . 
   The expressions “bottom”, “top”, “lower” and “upper” refer, in the description which follows, to the axis X—X and to the orientation of  FIGS. 1 ,  3 A,  3 B and  4  to  6 , which means that “lower” denotes a position closer to this axis. Likewise, the terms “inner” and “outer” are used with respect to the axis Y—Y which means that “inner” denotes a position close to this axis Y—Y. 
   Each arm  3  comprises, near its free end, a circular retaining groove  10  of axis Y—Y which separates the main part of the arm  3  from an end cap  11 . This cap  11  comprises a conical part  11 A converging upwards. The main part of the arm comprises a cylindrical runway surface  12  of axis Y—Y which ends towards the axis X—X near a shoulder  14  of the body  2 . This shoulder is chamfered so that it forms with the axis X—X an angle labelled β. At its upper end, the surface  12  is delimited by the circular groove  10 . 
   The needles  4  are accommodated in the space formed by the runway surface  12 , the shoulder  14  and the ring  8 . They run both along the runway surface  12  and along the bore  7  of the roller. In consequence, in the absence of the ring  8 , the roller and the needles could escape by sliding towards the outside of the arms  3  which carry them. 
   The ring  8  provides positive retention of the roller and of the needles on their arm before the spider assembly is mounted in the female element of the joint. For this, and as depicted in  FIG. 2 , the ring  8  has a vertical split  15  inclined at 45° to the radial direction, which passes through the entire cross section of the ring. 
   This ring  8  is a shaped annular washer, of more or less constant thickness, preferably made of a spring steel. Its inner end is snap-fitted into the retaining groove  10  of the arm, thus axially retaining the ring  8  on the arm. 
   As depicted in greater detail in  FIGS. 3A and 3B , the lower face  16  of the ring  8 , that is to say its face facing towards the hub  2 , comprises:
         a surface  20  for retaining the needles  4 , delimiting the space in which the needles run;   a surface  21  arranged on the inside of the groove  10 , situated internally with respect to the surface  20  and after the latter; and   a surface  22  for retaining the roller  5 , which surface is arranged plumb with the roller, situated externally with respect to the surface  20  and after the latter.       

   The surface  20  for retaining the needles  4  flares continuously upwards, that is to say towards the free end of the arm  3 . The surface  20  comprises an inner part  20 A designed to collaborate with the upper ends of the needles  4  and which is more or less frustoconical, forming with the axis X—X an angle labelled α measuring 18° for example. 
   The surface  21  is more or less frustoconical and flares upwards, meeting the surface  20  at a tangent. 
   The surface  22  is designed to collaborate with a mating chamfer  24  formed at the upper end of the cylindrical bore  7  of the roller  5 , when this roller is in an upper end position on the arm  3 , as depicted in  FIGS. 3 and 3A . This surface  22  is more or less frustoconical and flares upwards, forming with the axis X—X an angle γ greater than the angle α. 
   The surface  22  meets an outer part  20 B of the surface  20  at a tangent, this part  20 B being roughly frustoconical and connected to the inner part  20 A by a region the surface of which is curved. 
   Thus, the face  16  continuously flares along the entire width of the ring  8 , the snap-fitted surface  21  and the surface  22  for retaining the roller  5  extending in the continuation of the surface  20 , and meeting this surface  20  at a tangent. 
   The upper face  26  of the ring  8  flares continuously towards the free end of the arm. It comprises a first surface  26 A more or less parallel to the inner part  20 A of the surface  20  and a second surface  26 B more or less parallel to the surface  22 , which means that the thickness of the ring  8  is more or less constant. This ring thickness is designed so that, when the roller  5  is under maximum axial stress on the ring, this roller cannot deform the ring  8  to the extent that it leaves the groove  10  of the arm. 
   The ring is delimited on the inside by a cylindrical surface  27 A and on the top by a flat surface  27 B. In the position of  FIGS. 3A and 3B , the surface  27 B is more or less in the plane of the upper end face  5 A of the roller, and at the level of the conical surface  11 A. 
   In order to assemble such an arrangement, the ring of needles  4  and the roller  5  are mounted first of all, followed by the ring  8  which is fitted by deforming it elastically. The conical part  11 A of the cap of the arm  3  makes the ring  8  easier to mount: it allows the ring to be opened up when it is pushed axially downwards, the edges of the split  15  then parting from one another appreciably. When the conical part  11 A of the cap has been negotiated, the inner end of the ring  8  snap-fits into the groove  10 , the inside diameter of the ring and the outside diameter of the groove being dimensioned such that the split  15  closes up sufficiently that the needles  4  cannot enter it during operation. 
   During operation, the axial forces exerted by the needles  4  on the ring  8 , and possibly by the roller  5 , tend to close this ring up by virtue of the flared conical shapes of the surfaces  20  and  22 . The width of the split  15  is therefore small in operation. 
   The gradual flaring of the upper and lower faces of the ring  8  makes it possible to limit the bulk of the joint, at the free end of the arm. The ring  8  does not impede the free movement of the tripod in the female element of the joint, the needles  4  have sufficient clearance for axial translation, and the rollers  5  have sufficient freedom for axial translation, very much greater than the clearance of the needles. 
   The profile of the cross section of the ring  8  thus makes it possible to maintain appreciably the same functional advantages as those in the spider assembly of the aforementioned document FR-A-2 795 467, while at the same time offering great simplicity of manufacture of this ring. 
   Advantageously, the values of the angles α and β may be chosen to be more or less equal, so as in particular to improve the frictional behaviour of the needles  4  on the ring  8  and the hub  2 . 
   In addition, the angle α is large enough and the axial clearance of the needles is small enough to limit the risk of the ring  8  becoming extracted during operation. In particular, the flaring of the surface  20  allows the inner end of the lower face  16  of the ring  8  to be positioned appreciably below the level of the upper ends of the needles  4  in the direction of the axis Y—Y. 
     
     FIGS. 4  to  6  respectively depict three alternative forms of the spider assembly according to the invention. These assemblies differ from the one depicted in  FIG. 3A  only in the shape of the retaining ring  8 . The elements which are common to all these alternative forms and to the assembly of  FIG. 3A  bear the same references. 
   In  FIG. 4 , the surfaces  20 ,  21  and  22  of the lower face  16  of the ring  8  are inclined more or less at the same angles, the part  20 A of the surface  20  being wider than before. Furthermore, the upper face  26  runs roughly parallel to this part  20 A across the entire width of the ring. 
   In  FIG. 5 , the lower  16  and upper  26  faces of the ring  8  are more or less spherical or toric, which means that the angle α of inclination of the needle-retaining surface  20  is therefore defined by means of the tangent to this surface  20  at the inner end of this surface. The roller  5  is retained by the surface  22 , consisting of the outer end part of the lower face  16  and meeting the outer end of the surface  20  at a tangent. The surface  22  defines a contact of the sphere-plane or torus-plane type with the chamfer  24  of the roller when this roller is in its extreme upper position on the arm  3 . 
   In  FIG. 6 , the lower  16  and upper  26  faces of the ring  8  run more or less in a straight line and converge towards each other in the direction of the outside. Also, the thickness of the ring  8  decreases slightly, continuously, from its inner end snap-fitted into the groove  10  towards its outer end resting against the chamfer  24  of the roller  5 . The thickness of the ring  8  is dimensioned in the same way as in the embodiment of  FIG. 3 , that is to say such that even when the roller  5  is under maximum stress on the ring  8 , the ring does not deform to the extent of leaving the groove  10  of the arm. It will be noted that, in this alternative form, the angles α of inclination of the surface  20  and γ of inclination of the surface  22  are more or less equal. 
   This last alternative form of the embodiment makes it possible to achieve a retaining ring profile which is particularly simple to produce and fit, while at the same time enjoying practically the same functional advantages as those described previously. 
   It will be noted that it is conceivable, in order to observe particular joint geometries, for the lower  16  and upper  26  faces of the ring  8  to extend such that they diverge from one another in the direction towards the free end of arm  3 .