Patent Publication Number: US-2011049829-A1

Title: Suspension Strut and Thrust Bearing Device

Description:
The present invention relates to the field of suspension thrust bearing devices used, particularly on motor vehicles, in suspension struts for the steered wheels. 
     As is known, from document US 2007/0009190, a suspension thrust bearing may comprise a rolling bearing equipped with two rings and with a row of rolling elements covered by a flange extending around the upper ring and around part of the lower ring. The end plate ends at the bottom in an inwardly directed rim. 
     This type of thrust bearing presents the problem of possible contamination by the ingress of water or of other contaminants. A suspension thrust bearing is actually positioned at a location that is particularly exposed to being splashed with water and other contaminants. When this type of thrust bearing is subjected to fierce sprays of water, for example when the vehicle is driving along a flooded road or alternatively when the vehicle is being cleaned with a high pressure jet of water, water may enter the rolling bearing to the detriment of the life of the said bearing. The ingress of water may be via the lower part of the thrust bearing, between the cover and the lower ring, or may equally well be via the upper part, infiltrating between the cover and the upper ring. 
     Document FR 2 665 494 discloses an axial rolling bearing, the cage of which is fitted with sealing lips. However, the material of a cage has to be rigid, while the material of a sealing lip needs to be flexible. 
     Document U.S. Pat. No. 5,344,241 discloses a tapered thrust bearing fitted with a seal. However, the shape of the component encourages water retention and is therefore unable effectively to guard against infiltration of water. 
     Document FR 2 866 085 relates to a flywheel axial thrust bearing provided with a rubbing lip. This device is ill-suited to use along a substantially vertical axis and therefore presents risks of water ingress. 
     It is a particular object of the invention to overcome the abovementioned disadvantages. A particular object of the invention is to reduce the probability of the ingress of water or other contaminants into a suspension thrust bearing. It is an object of the invention to avoid the ingress of water from the top and from the bottom of the thrust bearing. 
     The suspension thrust bearing device comprises a rolling bearing and an annular end plate provided with means of axial retention of the elements of the thrust bearing. The rolling bearing comprises an upper ring, a lower ring and a plurality of rolling elements positioned between the rings. The device comprises both a dynamic seal between the end plate and the lower ring, and a static seal between the end plate and the upper ring. This therefore spares the interior of the rolling bearing from the ingress of undesirables. 
     In one embodiment, the end plate bears the dynamic seal and the static seal. The mounting of the thrust bearing is facilitated thereby. 
     In one embodiment, the dynamic seal comprises at least one lip bearing against the lower ring of the thrust bearing. 
     In one embodiment, the static seal comprises a layer of flexible material at least partially coating an interior surface of the end plate, the said layer being in contact with the upper ring. In other words, the static seal comprises a packing positioned between the end plate and the upper ring. The packing may comprise a radial portion and a substantially toroidal portion. 
     In one embodiment, the dynamic seal and the static seal are overmoulded onto the end plate. Overmoulding can be done simultaneously to make manufacturing easier. 
     In one embodiment, the dynamic seal and the static seal are made of the same material. The said material may comprise an elastomer, for example of the synthetic rubber type. 
     In one embodiment, the dynamic seal and the static seal are connected to one another by flexible material. The end plate and the upper ring may be positioned a short distance apart, delimiting a space in which the static seal is positioned, this static seal also attenuating the transmission of noise and vibration. 
     In one embodiment, the dynamic seal is set back axially from the free end of an axial portion of the end plate. 
     In one embodiment, the end plate comprises an axial portion provided with an end bent back obliquely towards the lower ring. Means of axial retention are thus formed. The risk that components will become lost while the thrust bearing is being handled prior to its being mounted in a strut is thus lessened. 
     The invention also relates to a strut comprising a suspension thrust bearing device and a shock absorber. The suspension thrust bearing device may be mounted around a rod of the shock absorber. A spring may be positioned around the shock absorber and connected to the thrust bearing by a spring cup. 
     By virtue of the invention, the risk of water or contaminant ingress into the suspension thrust bearing rolling bearing part of the suspension thrust bearing is particularly low. 
    
    
     
       The present invention will be better understood from reading the detailed description of one embodiment taken by way of entirely nonlimiting example and illustrated by the attached drawings, in which: 
         FIG. 1  is a view in axial section of a strut; 
         FIG. 2  is a view in axial section of a suspension thrust bearing device; and 
         FIG. 3  is a detailed view of  FIG. 2 . 
     
    
    
     As may be seen in  FIG. 1 , the strut  1  comprises a shock absorber  2  provided with a rod  3 , a spring  4 , a thrust bearing  5  mounted around the rod  3 , a cap  6  forming the interface between the spring  4  and the thrust bearing  5  and an elastic block  7  mounted between the thrust bearing  5  and the body  8  of a vehicle in which the strut  1  is mounted. The shock absorber  2  is visible only in part, the shock absorber cylinder not having been depicted through lack of space. The rod  3  of the shock absorber has a large-diameter axial exterior surface  3   a , a small-diameter axial exterior surface  3   b , the axial surfaces  3   a  and  3   b  being separated by a shoulder  3   c.    
     The strut  1  also comprises an axial spacer piece  9  positioned around the small-diameter axial surface  3   b , a clamping cup  10  and a nut  11  collaborating with a threaded portion of the small-diameter axial surface  3   b  near the free end of the rod  3 . The nut  11  provides the axial connection between the elastic block  7 , the spacer piece  9  and the thrust bearing  5 , the spacer piece  9  being positioned in the space radially bounded by the small-diameter axial surface  3   b  of the shock absorber rod  3  and a bore  7   a  in the elastic block  7 . 
     The cap  6  is in the form of a sheet metal annular component comprising a small-diameter radial portion  6   a  in contact with the thrust bearing  5 , a frustoconical portion  6   b  extending outwards and downwards, that is to say away from the free end of the shock absorber rod  3 , a large-diameter radial portion  6   c , against which the end turn of the spring  4  rests, and a rim  6   d  of axial overall shape serving to centre the end turn of the spring  4 . 
     The elastic block  7  may be made of a flexible material such as an elastomer, into which, as an option, one or more strengthening rigid inserts  12 , for example metal inserts, may be inserted. In the embodiment of  FIG. 1 , the insert  12  is in the form of an annular component, comprising a small-diameter axial portion  12   a , a substantially toroidal portion  12   b  and a frustoconical portion  12   c  extending outwards and towards the spring  4 . The insert  12  may be embedded in the elastic material while at the same time lying a short distance away from the thrust bearing  5 . 
     The elastic block  7  has an annular radial surface  7   b  adjacent to the bore  7   a  and in contact with a radial surface of the clamping cup  10 , an annular groove  7   c  open at the top, towards the body  8 , a short upper annular radial surface  7   d  in contact with a radial surface of the body  8 , a frustoconical surface  7   e  extending outwards and downwards, towards the spring  4  from the exterior edge of the radial surface  7   d  and in contact with the body  8 , a substantially axial surface  7   f  extending from the body  8  towards the spring  4 , a lower radial portion  7   g  positioned a short distance away from the large-diameter radial portion  6   c  of the bearing cap  6  and directed inwards from the exterior axial surface  7   f , a frustoconical surface  7   h  substantially parallel to the frustoconical portion  6   b  of the bearing cap  6  and extending inwards and upwards from the interior edge of the lower radial surface  7   g , and a substantially toroidal surface  7   i  where the lower frustoconical surface  7   h  and the axial bore  7   a  meet. If appropriate, a small-sized radial surface  7   g  may be provided between the substantially toroidal surface  7   i  and the bore  7   a.    
     The thrust bearing  5  comprises an upper ring  15 , a lower ring  16 , a row of rolling elements  17 , in this instance balls, a retaining end plate  18  and a sealing packing  19 . The upper ring  15  is in the form of an annular component in which there is formed a central bore  15   a  that creates a passage for the upper portion of the shock absorber rod  3 , particularly for the small-diameter axial surface  3   b.    
     The upper ring  15  also comprises a radial upper surface  15   b  extending outwards from the bore  15   a , a toroidal surface  15   c  extending outwards and downwards from the radial upper surface  15   b , a small-sized frustoconical surface  15   d  extending inwards and downwards from the toroidal surface  15   c , a lower radial surface  15   e  extending inwards from the frustoconical surface  15   d , a toroidal surface  15   f  which in meridian axial section is of concave shape and which forms a raceway for the rolling elements  17 , and a radial surface  15   g  extending between the toroidal surface  15   f  and the bore  15   a.    
     The upper ring  15  may be of one piece. The upper ring  15  is axially clamped between the spacer piece  9  and the shoulder  3   c.    
     The lower ring  16  is made in two parts and comprises a cup  21 , for example made of a synthetic material, and an attached track  20 , for example made of sheet metal. The attached track  20  is of annular overall shape. The attached track  20  may be produced by cutting and pressing a sheet metal blank, and this is a particularly economical way of producing it. The attached track  20  offers a concave surface  20   a  forming a raceway for the rolling elements  17  and a lower surface  20   b  which in meridian axial section is of convex shape. 
     The cup  21  is able to offer shapes that are more complex than the attached track  20  and has a bore  21   a  in contact with the large-diameter axial surface  3   a  of the shock absorber rod  3 , an upper toroidal surface  21   b  in contact with the lower surface  20   b  of the attached raceway track  20 , and an annular projection  21   c  of axial overall shape between the bore  21   a  and the toroidal surface  21   b . The projection  21   c  extends axially upwards towards the upper ring  15 . 
     The cup  21  also comprises an exterior axial surface  21   c  positioned axially on the same side as the spring  4  and capable of being in contact with the bore of the bearing cap  6 , a radial bearing surface  21   d  for the small-diameter radial portion  6   a  of the bearing cap  6  substantially aligned with the rolling elements  17  so that the cup  21  essentially transmits axial load, an exterior rounded surface  21   e  meeting outwards and upwards with a hook  21   f  equipped with a lower radial surface  21   h  that extends outwards. The cup  21  also comprises a frustoconical surface  21   g  extending upwards and inwards from the hook  21   f.    
     The end plate  18  may be in the form of a thin sheet metal component. The end plate  18  is of annular overall shape. The end plate  18  comprises a small-diameter radial portion  18   a  positioned in at least partial contact with the elastic block  7 , particularly with the radial surface  7   g , a substantially toroidal portion  18   b  extending outwards and downwards from the radial portion  18   a  also in contact with the elastic block  7 , particularly with the toroidal surface  7   i , a substantially axial portion  18   c  extending downwards from the toroidal portion  18   b  and surrounding the hook  19   f  of the cup  19  of the lower ring  16 , and a frustoconical rim  18   d  extending downwards and inwards for the purpose of interfering diametrically with the hook  19   f  if there is any accidental axial movement of the lower ring  16  with respect to the upper ring  15 , particularly during handling and transport prior to the fitting of the strut. 
     The suspension thrust bearing  5  thus forms a ready-to-fit subassembly with a low likelihood of components being lost. The rim  18   d  may start out substantially axial, see reference  18   e  in  FIG. 3 , then be bent into its definitive frustoconical shape once the thrust bearing  5  has been assembled. 
     The packing  19  is positioned partly between the upper ring  15  and the end plate  18 . The sealing packing  19  may comprise a flexible material, for example an elastomer such as a synthetic rubber. The sealing packing  19  comprises a part  19   a  that forms a static seal, clamped between the upper ring  15  and the end plate  18  and conforming shape-wise to the toroidal surface  15   c  and the toroidal portion  18   b , and a part  19   b  forming a dynamic seal, of a greater thickness than the static seal part  19   a , and that has a lip  19   c  that rubs against the frustoconical surface  21   g  of the cup  21  of the lower ring  16 , thus providing a high level sealing for the rolling bearing. 
     In this description, the expression “static seal” means sealing between two elements that is afforded by a contact that involves no relative motion and the expression “dynamic seal” means sealing afforded by a contact or a collaboration that does involve relative motion. 
     Water or other undesirables cannot infiltrate between the upper ring  15  and the end plate  18  because of the presence of the static seal part  19   a  which in particular comprises a small-diameter radial portion  19   e  and a large-diameter toroidal portion  19   f . Likewise, water or undesirables are prevented from infiltrating downwards, particularly through the narrow passage formed between the frustoconical rim  18   d  and the surface  21   h  of the hook  21   f  and especially via the dynamic seal part  19   b , the lip  19   c  of which rubs against the frustoconical surface  21   g  of the cup  21  of the lower ring  16 . This then prevents the ingress of water, particularly when driving along very wet or flooded road or alternatively when cleaning with a water jet, particularly a high pressure one. 
     The upper ring  15  is clamped between the shoulder  3   c  of the shock absorber rod  3  and the spacer piece  9  against which the cup  10  and the nut  11  bear. The end plate  18  has an inside diameter greater than the outside diameter of the spacer piece  9 . The end plate  18  provides axial retention of the lower ring  16  before the strut is fitted and acts as a support framework for the dynamic part  19   b  of the sealing packing  19 . Advantageously, the sealing packing  19  is overmoulded into the end plate  18 . In the embodiment depicted, the sealing packing  19  is of one piece. The sealing packing  19  comprises a portion  19   d  where the static seal part  19   a  and the dynamic seal part  19   b  meet. In an alternative that has not been depicted, the sealing packing is made as a static seal part and a dynamic seal part, which parts are separate from one another. 
     For reasons of ease and cost of manufacture, it is preferable for the static and dynamic seal parts to be made of the same material. 
     In other words, the suspension thrust bearing device comprises an upper ring and a lower ring between which rolling elements, such as balls or rollers, are positioned. The rings may have in-built or attached raceways. One ring may comprise a cup made of plastic and an attached raceway made of steel. The suspension thrust bearing may bear against the body of the vehicle directly or via a cup and/or an elastic block that filters out vibration in particular. The spring positioned around the shock absorber bears via its lower end against a lower cup secured to the shock absorber cylinder and bears directly or indirectly via its upper end against the lower cap. The upper end of the rod of the shock absorber piston is secured to the elastic support block so as to filter out vibration travelling up towards the body of the vehicle. The bump stop thrust bearing is thus able to transmit axial load between the spring and the body of the vehicle while at the same time allowing a relative angular movement between the spring and the body of the vehicle as the steered wheels of the vehicle are turned and/or as the spring compresses. 
     The sealing lip  19   c  of the dynamic seal part  19   b  of the sealing packing  19  may be vulcanized onto the interior surface of the cylindrical axial portion of the end plate approximately mid-way up the said portion. Of course, the dynamic seal part  19   b  may, by way of an alternative, comprise a plurality of rubbing lip seals. 
     By virtue of the invention, the risk of water finding its way into the rolling bearing and therefore of causing the rapid deterioration of the suspension thrust bearing is greatly reduced.