Abstract:
A ball and socket joint has high stability of the bearing shell and hence of the joint and reduces the transmitted structure-borne noise from the viewpoint of increased comfort with a bearing shell design with at least two layers. The inner layer is formed of a metal and the outer layer of a plastic such as polyoxymethylene.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase application of International Application PCT/DE 2006/001047 and claims the benefit of priority under 35 U.S.C. § 119 of German Patent Application DE 10 2005 030 747.7 filed Jun. 29, 2005, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a ball and socket joint. It pertains, in particular, to the special embodiment of the ball shell or bearing shell of such a ball and socket joint for reducing sound transmission. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ball and socket joints transmit and absorb forces from a plurality of directions. They are used in automotive engineering, for example, in the area of the steering or track rod. Ball and socket joints of this class comprise a ball pivot, i.e., a bolt with a ball formed at an axial end, a bearing shell accommodating the ball and a housing accommodating the bearing shell and parts of the ball pivot. The ball of the ball pivot slides within the prestressed, permanently lubricated bearing shell, which is protected by the housing against moisture and dirt as well as against the escape of lubricant. In the case of use in a motor vehicle, especially the inner surfaces of the bearing shell accommodating the ball are exposed to high loads. The bearing shells are therefore manufactured, as a rule, from a metal. However, steadily increasing requirements are also imposed on comfort in modern automotive engineering, which can sometimes be met by ball and socket joints with a metallic bearing shell only insufficiently. One drawback is that structure-borne noise is transmitted from the chassis to the passenger compartment or released into the environment to an undesired extent by ball and socket joints with a metallic shell. Ball and socket joints with a plastic shell offer considerable advantages in respect to the transmission of structure-borne noise. Such joints can also meet the requirements concerning loadability in many cases if modern plastics are used. However, their drawback is that their emergency running properties are considerably limited, i.e., total failure of the ball and socket joint can be observed within a short time in case of a defect or failure of the housing seal of a corresponding ball and socket joint, as a consequence of which dirt enters the joint or the lubricant escapes from the bearing site proper, i.e., from the intermediate space between surfaces of the ball of the ball pivot and the bearing shell, which surfaces slide on one another. 
         [0004]    A ball and socket joint with a non-metallic bearing shell, in which the bearing shell has a two-layer design, has become known from DE 103 29 804 A1. According to the solution described in that document, the two layers forming the shell have different moduli of elasticity, the outer layer located away from the ball consisting of an elastically springable material and the inner layer located close to the ball consisting of a material with a wear-resistant surface. However, aside from the reference that the bearing shell consists of a non-metallic material, no concrete data are specified concerning the materials of the two layers forming the bearing shell. It can therefore be assumed here from a manufacturing technological point of view that both layers consist of a plastic, but the plastics have different moduli of elasticity and surface strengths, because such layers consisting of different plastics can be manufactured in a two-stage injection molding process and connected to one another in a favorable manner. The requirement that the structure-borne noise be reduced is certainly also met with the use of a corresponding plastic for the inner layer for many applications. However, the problem of insufficient emergency running properties is certainly present with this solution as well, because, unlike in the case of metals, dirt, which can be observed, for example, when leaks develop in ball and socket joints in the area of the running surfaces, tend to dig into the material surface to a certain extent in the case of plastics and materials comparable to plastics. At any rate, metals thus have emergency running properties that can hardly be attained by plastics. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is therefore to provide a ball and socket joint, which meets the increasing requirements imposed in terms of comfort, especially the reduction of the transmission of structure-borne noise, on the one hand, and possesses good emergency running properties, besides high loadability for the forces introduced into the joint, on the other hand. 
         [0006]    The ball and socket joint according to the invention accomplishes the object. The ball and socket joint comprises a joint housing, which is open on one side, a pivot pin with a joint ball, which is formed at one of the ends, and a spherical bearing shell, which is likewise open on one side. The joint ball of the pivot pin is accommodated by the joint housing, and the bearing shell, which has permanent lubrication on its inner surface, is arranged between the joint ball and the joint housing, as a result of which a sliding surface is formed for the joint ball. The joint housing is closed by a closing ring and sealed by a sealing bellows to prevent the penetration of dirt and the escape of the lubricant in the area of the transition between the joint ball and the shaft of the pivot pin. The shaft protrudes from the joint housing. The bearing shell is formed by at least two layers. The inner layer of the bearing shell according to the present invention is metallic and the outer layer is plastic. High wear resistance of the ball and socket joint is achieved due to this design, and the ball and socket joint has, moreover, good emergency running properties because of the metallic inner surface of its bearing shell. On the other hand, a marked reduction of the transmission of structure-borne noise is achieved compared with ball and socket joints with a purely metallic bearing shell due to the outer plastic layer of the bearing shell. 
         [0007]    If the bearing shell of the ball and socket joint according to the present invention is made, as is preferred, of two layers, the outer, absorbing plastic layer used to uncouple sound is preferably injected on the metallic inner layer of the bearing shell. However, it is conceivable that the inner metallic layer and the outer plastic layer are connected to one another by a bonded connection. 
         [0008]    Corresponding to an especially advantageous variant of the present invention, the bearing shell has a two-part design. The two parts of the bearing shell, which comprise two or more layers each, are connected to one another via a web acting as a hinge. The mounting of the ball and socket joint, i.e., the fitting together of its components, is simplified by this form of embodiment. The joint ball can be easily inserted into the bearing shell even in case of a thick metallic cover between the joint housing and the joint ball, as it is desirable and is embodied in this embodiment. This is quasi folded up for this and closed after the insertion of the joint ball. Higher resistance to tearing out results for the pivot pin from the increased metallic coverage, so that a higher tensile load is possible for the joints. 
         [0009]    The bearing shell, which is open on one side, is preferably divided into two axially symmetrical halves. These are formed, according to a practical embodiment, by two deep-drawn, metallic half shells, which are covered by a plastic layer on their outer circumference and are connected to one another by a web. The edges of the half shells located next to each other within the joint housing close a round opening on the open side of the bearing shell, while the symmetry axis dividing the bearing shell extends at right angles through the diameter of this round opening. 
         [0010]    A collar web extending circumferentially on the circumference of the bearing shell is arranged in parallel to the edge of the opening of the bearing shell in a likewise advantageous variant of the ball and socket joint according to the present invention. The bearing shell arranged in the joint housing is fixed in the joint housing and secured against twisting by this collar web. which is pressed in between the closing ring and the joint housing. 
         [0011]    The inner metallic layer of the bearing shell has, preferably on its surface facing the joint ball, at least one groove, which forms a reservoir for a lubricant. 
         [0012]    To increase the wear resistance even more, the surface of the inner metallic layer of the bearing shell, which surface faces the joint ball, may be chromium-plated or additionally hardened. A QP treatment, i.e., nitriding of the metallic inner surface of the bearing shell, advantageously also leads to an improvement of wear resistance. 
         [0013]    For example, polyoxymethylene (POM) or polyamide (PA) or polyether ether ketone (PEEK) may be considered for use as plastics for the outer layer of the bearing shell of the ball and socket joint designed according to the present invention. 
         [0014]    The present invention shall be explained in more detail below once again on the basis of an exemplary embodiment. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the drawings: 
           [0016]      FIG. 1  is an axial half-section of a ball and socket joint designed according to the present invention; and 
           [0017]      FIG. 2  is an isometric view of the bearing shell of the ball and socket joint according to  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    Referring to the drawings in particular,  FIG. 1  shows a possible embodiment of a ball and socket joint designed according to the present invention in a half-section. The ball and socket joint comprises essentially the pivot pin  4 ,  5 , the bearing shell  1 ,  1 ′, the joint housing  6  and a sealing bellows  7 . The joint ball  4  of the pivot pin  4 ,  5  is accommodated by the joint housing  6 , which is open on one side. The permanently lubricated and spherically shaped bearing shell  1 ,  1 ′, which is likewise open on one side and whose inner surface forms the sliding surface for the joint ball of the pivot pin, is arranged between the joint housing  6  and the joint ball  4 . The bearing shell  1 ,  1 ′ has a two-layer design. Corresponding to the present invention, the inner layer  2  consists of a metal, while the outer layer  3  consists of a plastic. 
         [0019]    High stability of the ball and socket joint is guaranteed by the metallic inner layer  2  of the bearing shell  1 ,  1 ′. Compared to ball and socket joints whose bearing shell consists exclusively of non-metallic materials, i.e., usually plastic, the ball and socket joint designed according to the present invention possesses, moreover, improved emergency running properties. Leaks that may occur in the sealing bellows, as a consequence of which dirt penetrates into the joint or lubricant escapes from the bearing site thereof, do not lead, as a result, to rapid destruction of the ball and socket joint, unlike in the case of ball and socket joints with a plastic bearing shell. The risk of dirt particles digging into the running surface of the bearing shell  1 ,  1 ′ is reduced compared to bearing shells made of plastic. 
         [0020]    The bearing shell  1 ,  1 ′ has a two-part design in the embodiment shown in  FIG. 1 . It comprises two axially symmetrical halves, which are connected to one another via a connecting web  8  acting as a hinge. The mounting of the ball and socket joint is simplified as a result. In addition, a collar web  11 , which extends over the circumference of the bearing shell  1 ,  1 ′ and is pressed in between the closing ring  13  and the joint housing  6 , is formed in the lower area of the bearing shell  1 ,  1 ′. The bearing shell  1 ,  1 ′ is fixed in the joint housing  6  during mounting by the collar web  11  arranged in parallel to the edge  9 ,  9 ′ of the opening of the bearing shell and thus secured against accidental twisting during the use of the ball and socket joint as intended. 
         [0021]    The surface of the inner metallic surface  2  of the bearing shell  1 ,  1 ′ is, for example, hardened or QP-treated, i.e., nitrided, in order to further increase its wear resistance. Its outer layer  3  consists, for example, of POM (polyoxymethylene). The vibrations, especially the structure-borne noise, which are transmitted from the pivot pin  4 ,  5  via the bearing shell  1 ,  1 ′ to the joint housing  6 , are advantageously absorbed due to the elasticity of this material. Due to the design of the bearing shell  1 ,  1 ′ according to the present invention, the ball and socket joint thus outstandingly combines the meeting of the requirements imposed in terms of its loadability with the meeting of the requirements existing concerning comfort. The outer layer  3  of the bearing shell  1 ,  1 ′, consisting of a plastic, is applied to the inner metallic surface  2  preferably by injection. However, preliminary tests have shown that it could also be possible to bond the outer layer  3  to the inner one. 
         [0022]      FIG. 2  shows the bearing shell  1 ,  1 ′ designed according to the present invention in a two-part design once again in an isometric view. As can be recognized, both half shells are of a two-layer design and are connected to one another via web  8 , which acts as a hinge. The collar web  11  already mentioned, which extends circumferentially over the circumference of the bearing shell, can also be recognized in the view. Moreover, it can be seen that a groove  12  is milled into the metallic inner surface of the bearing shell  1 ,  1 ′. A grease reservoir is formed by this groove  12  for the permanent lubrication of the joint. 
         [0023]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.