Abstract:
A suspension thrust-bearing device for a telescopic suspension strut of a motor vehicle which includes a rolling bearing forming an axial thrust stop, a metal cup for accepting a suspension spring, and an elastic support block. The rolling bearing is positioned between the metal cup and the elastic support block which is secured to the frame of the motor vehicle. The rolling bearing includes an upper race placed within a cap which is in contact with the support block, and a lower race. The cap is provided with means for axially retaining the metal cup, to form a unit assembly, and acts as an interface between the upper race and the elastic support block. An outer cylindrical portion of the cap covers the periphery of the metal cup.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of suspension thrust bearing used, in particular, in motor vehicles on the telescopic suspension struts of the steered wheels. 
     The suspension thrust bearing is generally placed at the top of the suspension strut between a lower metal cup which also acts as a seat for the suspension spring, and an elastic support block. The elastic support block is made up of metallic and elastomer elements and is secured to the vehicle body. The suspension spring is arranged around the rod of a damper piston whose end, generally the end of the piston rod, is secured to the elastic support block. The suspension thrust bearing thus allows axial loads to be transmitted between the spring and the vehicle body while at the same time allowing a relative angular movement between the spring cup, which is able to rotate, and the fixed elastic support block secured to the body. This relative angular movement may be the result of a turning of the steered wheel and/or compression of the suspension spring. 
     It is important to make the transportation and assembly of the suspension thrust bearing with the surrounding components, and in particular with the metal cup which forms the spring seat, easier. 
     2. Description of the Related Art 
     For this, document U.S. Pat. No. 4,995,737 proposes that each of the races of the suspension thrust bearing be equipped with a plastic cap. Each cap has projections for the axial retention of the other cap, and one of the two caps has hooks capable of interacting with apertures made in the lower cup. It is thus possible to produce the suspension thrust bearing and the lower cup as a permanently-assembled entity thus making easier the operations of transporting and handling the thrust bearing/cup subassembly, the operations of mounting the subassembly in the vehicle suspension strut system and the automating of at least some of these operations. 
     A device of this kind does, however, have certain drawbacks: 
     it dictates the use of two caps made of plastic, hence increasing the cost and axial bulk of the assembly. 
     it dictates the use of two races for the thrust bearing which, again, leads to an increase in the cost and axial bulk of the assembly. 
     it dictates that the lower cup must have, in a precise location, an opening to interact with the hook of the lower cap, hence increasing the cost. 
     on assembly, it is necessary angularly to orientate the lower cap of the thrust bearing relative to the opening in the cup, this making this operation and any automating thereof more complicated, thereby once again increasing the cost. 
     Document DE U 295 06 796 discloses a suspension thrust bearing device comprising a rolling bearing with two metal races, the lower race being in contact with a lower plastic cap which also acts as a spring seat, thus precluding the possibility of using the cup as a raceway for the rolling bodies. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention sets out to solve these problems using simple and inexpensive means, at the same time making it possible to reduce the number of parts, the axial bulk and the costs, and to simplify the assembly process. 
     The suspension thrust bearing device, according to the invention, is of the type comprising a rolling bearing forming an axial thrust bearing, a cup for a spring, and an elastic support block. The rolling bearing is placed between the cup and the elastic support block secured to the vehicle frame, and comprises an upper race placed inside a cap acting as an interface between said race and the elastic support block in contact with the cap, and a lower race. The cap has means of axially retaining the cup with a view to forming a unit assembly. Part of the cap covers the periphery of the cup and forms a means of axially retaining the cup relative to the cap, said cup being made of metal. Thus, the cap can be mounted on the cup without angularly orientating it beforehand, while at the same time allowing the use of a lower bearing race which is thin or is built into the cup. 
     In one embodiment of the invention, the cap comprises at least a radial protuberance directed inwardly arranged on the bore of a cylindrical part or the said cap, for example in the shape of a rim continuous or not, or of circumferentially distributed hooks, Advantageously, the cap comprises a sealing means adapted to cooperate with the cup, for example a sealing lip. The cylindrical part may form a narrow passage with the periphery of the cup. 
     Advantageously, the cap comprises a radial part adjacent to the cylindrical part and provided with a surface for bearing against the support block. 
     In one embodiment of the invention, the cap comprises a part of a shape that mates with the upper race. 
     In one embodiment of the invention, the cap comprises an inner cylindrical pan capable of interacting by its internal diameter with an axial part of the support block on which said cap comes for centering. 
     In one embodiment of the invention, the lower race and the cup form a single piece. 
     In another embodiment of the invention, the two races of the rolling bearing are identical. 
     The cup may be made of steel or light alloy. 
     The cap is made of a synthetic material, preferably a plastic material. The cap may be made of a material different from the one forming the elastic support block. 
     In one embodiment of the invention, the axial retaining of the bearing cup with the cap is made by diametral interference between the means of axially retaining of the cap and the periphery of the bearing cup. 
     In another embodiment of the invention, the axial retaining of the bearing cup with the cap is made by diametral interference between the means of axially retaining of the cap and tho periphery of an intermediary bearing seat of the spring arranged axially between the spring and the bearing cup. 
     The sealing of the thrust bearing is carried out, independently from the elastic support block, by means joined with the cage and/or the cap. There is thus obtained in a particularly economical way an assembly which combines the suspension thrust bearing and the lower cap forming a seat for the spring. What is more, this assembly is not very bulky, and is easy to assemble, to transport, to handle and to build into the vehicle suspension system. 
     The invention will be better understood from studying the detailed description of a number of embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a view in axial section of the upper part of a vehicle suspension system including a thrust bearing in accordance with the invention; 
     FIG. 2 is a half view in axial section of a suspension thrust bearing in accordance with the invention; and 
     FIGS. 3 to  5  show alternative forms of the embodiment of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The damper comprises a cylinder  1  in which a piston is able to slide, the rod  2  of the piston being bonded by the upper end to an elastic support block  3 . The elastic support block  3  bears on an element of the frame  4  forming a seat, and is joined therewith. The elastic support block  3  includes: 
     a metallic internal binding element  5 , formed of two parts  5   a  and  5   b  and on which is mounted the end of the rod  2  or the damper piston by means of a nut  6 . 
     a metallic external binding element  7  used for the joining with the frame  4 , 
     a metallic upper cup  8  used for supporting seat for the thrust bearing  9 , 
     a block of rubber  10  bonded to the surface of the above three elements and binding them together with filtering of the vibrations. 
     One end of the external binding element  7  is fixed on the frame  4 , for example by screwing, and the other end is arranged axially between the two parts  5   a  and  5   b . The upper cup  8  is arranged axially on the level of the internal binding element  5  but is of a greater diameter. 
     Also visible is the suspension spring  11 , the upper end of which bears against the lower cup  12  which, in turn, also bears against the thrust bearing  9 . The cup  12  is made of sheet steel. 
     As better seen in FIG. 2, the upper cup  8  comprises a cylindrical portion  8   a  extending downwards, away from the frame  4 , and a radial portion  8   b  extending outwards the entire upper cup  8  being embedded in the elastic material used in the elastic support block  10  which close to the said upper cup  8  offers a radial part forming a bearing surface  16  and an axial part  17  defined by a radial annular projection  18 . 
     The suspension thrust bearing  9  proper comprises an upper race  13  and a lower race  14  both made of sheet steel, between which balls  15  are housed. 
     The balls  15  of the thrust bearing  9  are held by a cage  19  made of synthetic material, which is extended an one side by a sealing lip  19   a  which rubs against the lower race  14 , and on the other side by a lip  19   b  which rubs against a surface of the bearing cup  12 . A lip  19   c  adjacent to the lip  19   b  rubs against the upper race  13 . 
     The lower race  14  and the spring  11  are in contact with the cup  12 , on each side of a radial portion  12   a . This radical portion  12   a  is extended outwards and upwards towards the frame  4  in the form of a curved portion  12   b  which is concave on the side of the lower race  14  and which in terms of shape mates with the said curved portion  12   b , this making it possible to use a thin sheet from which to make the said lower race  14 . 
     Placed between the upper race  13  of the thrust bearing  9  and the elastic support block  3  is a cap  20  made of synthetic material, preferably a material that can be moulded. The material forming the cap  20  will be choosen among plastics, for example a polyamide loaded or not with glass fibers. The cap  20  comprises a cylindrical internal portion  21  mounted in contact with the radial part  16  by means of one of its ends, and with the axial part  17  on which the cylindrical internal portion  21  comes for centering by means of its internal diameter. 
     The cap  20  is extended from the cylindrical internal portion  21  by a radial portion  23  having a toroidal concave surface  22  on the side and at the level of upper race of the bearing and mating with said race and a radial plane surface  23   a  on the side of the radial part  16  of the elastic support block  3 . A plane surface  23   b  is fitted together on the concave surface  22  and forms a rubbing surface for a sealing lip  19   a  of the cage  19 . 
     The radial portion  23  extends beyond the periphery of the lower cup  12  and is extended downwards by a cylindrical portion  24  which surrounds the periphery of the lower cup  12 . Inwardly facing hooks  25  are provided on the inner edge and at the lower end of the cylindrical portion  24  and have a similar diameter than the periphery  12   c  of the lower cup  12  for forming a diametral interference between those two elements. 
     The cap  20  transmits axial loads from the thrust bearing  9  to the elastic support block  3  via the radial surface  16 , the mating between the surfaces in contact guaranteeing a good apportionment of the load. The axial part  17  assures a correct centring of the bearing  9  relative to the elastic support block  3 . The cylindrical portion  24  of the cap  20  forms, with the periphery  12   c  of the lower cup  12 , a seal on account of the narrow passage which supplements the action of the lip  19   a  of the cage  19 . Prior to the mounting of the suspension thrust bearing on tile elastic support block  3 , the cap  20  prevents the lower cup  12  from becoming separated from the various elements of the thrust bearing  9  and of the cap  20  itself thanks to its hooks  25  which limit any axial movement with respect to the lower cup  12 . 
     To assemble these elements, the lower race  14  is placed in the lower cup  12 . The cage  19  equipped with its balls  15  is placed in the lower race  14 . The assembly is capped with the upper race  13  then with the cap  20 , which snap-fastens by means of its hooks onto the periphery  12   c  of the lower cup  12 . Assembly requires no angular orientation of the various components with respect to one another. The axial portion  17  of the elastic support block  3  is designed to exert a slight radial preload on the cylindrical portion  21  of the cap  20  so that the said cap  20  is retained axially with respect to the elastic support block  7  during assembly. 
     The embodiment illustrated in FIG. 3 is similar to the one in FIG. 2 except that the lower race is formed as one piece with the lower cup  12 , the balls  15  coming directly into contact with a toroidal surface  12   d  of the lower cup  12 , which fulfils the function of a lower race. The toroidal surface  12   d  may have undergone a surface hardening treatment. The cap  20  comprises a more or less cylindrical sealing lip  26  of a diameter smaller than that of the outer cylindrical portion  24  and extending downwards from the radial portion  23  to come into rubbing contact with the lower cup  12  close to its periphery  12   c . The scaling lip  26  replaces the sealing lip  19   a  of FIG.  2 . 
     The embodiment illustrated in FIG. 4 is similar to the one in FIGS. 1 and 2, except that the lower cup  12  forming a seat for the spring is made of light alloy, for example an aluminium-based alloy, which allows an appreciable saving in weight compared with pressed steel and allows more complex shapes to be obtained. The upper race  13  and lower rare  14  of the thrust bearing  9  are identical, which results in an additional saving. The lower cup  12  may comprise an annular portion  27  extending between the thrust bearing  9  and the inner cylindrical portion  21  of the cap  20  upwards in the direction of the curved portion  22 , to form a seal thanks to a narrow passage with the said cylindrical portion  21 . On the other side of the rolling bearing  9 , the lower cup  12  is provided with an extension  28  extending between the said bearing  9  and the outer cylindrical portion  24  of the cap  20  and here too, allowing a seal to be formed by making a narrow passage between the periphery  12   c  and the said outer cylindrical portion  24 . 
     In the embodiment of FIG. 5, the spring  11  bears on the metallic bearing cup  12  by means of an inserted bearing seat  29  made of synthetic material and axially arranged between the cup  12  and the spring  11  as to provide a better support between spring and cup and to eliminate the risks of parasitic noises that could arise from steel/steel friction between spring and cup. In this embodiment, one takes advantage of the intermediary bearing seat  29  for carrying out the axial bind between lower cup  12  and bearing  9 . 
     Generally speaking, the carrying out of the cup  12  in metal (steel or light alloy) allows a space saving in the axial direction with regard to a cup made of plastic material that must be relatively thick so as to bear the mechanical loads, exerted on said cup. Like that, the axial dimension of the device is reduced. 
     Thanks to the invention, an assembly combining the suspension thrust stop and the lower cup forming the spring seat is obtained in a particularly economical way. This assembly has a small axial bulk and can be transported without any fear of the components becoming lost while at the same time allowing automated assembly.