Abstract:
An elastic joint, in particular for a wheel suspension of a motor vehicle. The joint includes an inner armature, an outer armature surrounding the inner armature, wherein the armatures define an axial direction and two radial directions perpendicular to the axial direction as well as perpendicular to each other and disposed in a circumferential plane, and an elastomeric body for the mutual elastic retention of the armatures, wherein the elastomeric body consists of at least four connecting columns respectively extending from the inner armature to the outer armature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority benefits under 35 U.S.C. §119(a) to German Patent Application No. DE 10 2011 121 831.2, entitled “Elastic Joint, in Particular for a Wheel Suspension of a Motor Vehicle,” and filed Dec. 21, 2011, the contents of which are incorporated by reference herein in their entirety. 
     BACKGROUND 
     Aspects of the invention relate to an elastic joint, in particular for a wheel suspension of a motor vehicle, and may relate in particular to a rear wheel suspension of the vehicle. 
     In the modern motor vehicle technology it is known, in particular for the rear wheel suspension of a passenger car as well as for a motor lorry, to realize so called elastic mountings or elastic joints, the principal structure of which is formed by a rigid inner armature, in particular made of metal, like a rigid sleeve or a support rod, an outer armature like an outer sleeve, and an elastomeric body disposed between the armatures. The elastomeric body serves to separate, in particular acoustically insulate, the vehicle body from the vibration loaded wheels. Also the high occurring dynamic vehicle loads are to be born in the elastic joints. There is a large number of designs of elastic joints, the elastomeric bodies of which are usually formed by a purely elastic material, wherein hydraulic functional components may also be added. 
     Aspects of this disclosure are directed in particular towards the elastic joints having a spring body of merely elastomeric material between the rigid armatures. 
     From EP 1 505 311 A1 a bearing bush is known for a motor vehicle, the bearing bush having a sleeve-shaped, rigid inner armature as well as a sleeve-shaped outer sleeve of weaker form, between which an elastomeric body is injection molded. The outer sleeve is provided with a restriction for the adjustment of the spring characteristic of the elastomeric body, whereby two elastomeric sections are formed, the deformations of which influence each other respectively. In order to reduce the stiffness of the bearing bush in one radial direction so that the bearing bush is soft in one radial direction and stiffer in the other, a recess is realized in the elastomeric body along part of the circumference. 
     An elastically resilient pivot joint for the mutually pivoting connection of a wheel trunk with a guide member is known from DE 32 05 716 C2. The elastomeric body vulcanized between the armatures can be partitioned into two circular sections with different strength in the radial direction by means of a central bulge. An embodiment of an elastic joint, similar thereto, is known from KR 2009 009 8978, in which the partition by sections of the elastomeric body is realized by a restriction in the outer armature. 
     It became apparent in the known elastic joints, in particular for motor vehicles, that the ratio of axial stiffness versus radial stiffness, which is an important characteristic for automotive engineers, cannot be realized to be sufficiently high. Ratios of little above 1.0 are common. For automotive engineers it is of particular interest to have a high stiffness ratio, wherein a cardanic stiffness remains as low as possible. 
     In order to structurally optimize these characteristics, the cost effect and the weight/usage ratio is of course not to be neglected but in particular should also be optimized. 
     A need therefore exists for an elastic joint, in particular for a wheel suspension of a motor vehicle, in which the ratio of axial stiffness over radial stiffness is high for a low cardanic stiffness while using cost effective and light materials. 
     SUMMARY 
     In accordance with one embodiment, the elastic joint comprises an inner armature, an outer armature surrounding the inner armature, wherein the armatures define an axial direction and two radial directions perpendicular to the axial direction as well as perpendicular to each other and disposed in a circumferential plane, and an elastomeric body for the mutual elastic support of the armatures. According to certain embodiments, the elastomeric body consists of at least four connecting columns respectively extending from the inner armature to the outer armature. Herein “connecting column” signifies an arm-like or rod-like structure that does precisely not revolve in the circumferential direction of the elastic joint. The respective connecting columns extend in the radial direction in order to establish a respective stiffness in this direction. 
     With the connecting columns, which may be arranged in any way with respect to each other wherein preferred positions relative to each other are given in the following explanations, a reduction of the radial stiffness is achieved without having to accept reductions too large for the axial stiffness. For the elastic joint with an exclusively elastomeric spring, that is, without hydraulic damping measures, the connecting columns are in fact the means that elastically connect the armatures with each other for enabling elastic vibrations. In an embodiment of the elastic joint as a so-called hydro bushing or hydroelastic joint, the connecting columns serve as reinforced delimiting walls of the hydraulic working camber and connect the armatures, wherein the sections free of connecting columns are realized by membrane sections, whereby a very good hydraulic adjustability of the hydrodynamic joint can be achieved. 
     In a preferred embodiment of the invention the connecting columns are made from one piece of elastomeric material. Therein the connecting columns, preferably their column bodies extending rectilinearly, are structurally separated from each other such that the mere deformation of a connecting column, for example in case of a radial loading, does not affect the deformation behavior of the other connecting columns, in particular of the neighboring connecting columns. 
     In this way it is possible to adjust the radial stiffness independently of the radial direction. In a preferred embodiment of the invention the column bodies of the connecting columns are essentially formed identically. 
     The connecting columns, in particular the column bodies, are arranged without contact along their column bodies in an extension direction so that a deformation of one connecting column does not affect the neighboring column. In a further development of certain embodiments, the at least four connecting columns are allocated to each other as pairs of connecting columns arranged axially symmetrically with respect to the axial direction. One pair of connecting columns is arranged circumferentially offset with respect to another pair of connecting columns. Therein the connecting columns of a pair are diametrically opposed in the radial direction. Preferably an offset angle between neighboring pairs is essentially equal, preferably about 90°. The connecting columns can extend about 30° in the circumferential direction so that seen in the axial direction soft areas free of elastomer with a circumferential width of 30° are realized for an offset angle of 90°. 
     For such an arrangement a particularly large stiffness ratio, notably of 1.4, of axial versus radial stiffness is realized. Therein a low cardanic stiffness is provided. Such a radial stiffness ratio can be achieved without using high grade materials or engaging in intensive production effort. 
     In a preferred embodiment the elastic joint has a central radial plane that preferably partitions the elastic joint into two equally dimensioned joint sections. One pair of connecting columns is arranged on one side of the central radial plane whereas another pair of connecting columns is disposed on the opposite side of the central radial plane. 
     In a preferred embodiment of the invention the connecting columns, in particular their column bodies define an extension direction, preferably a central axis, to be inclined with respect to the radial directions. Preferably a directional component of the extension direction in radial direction is larger than in axial direction, preferably between 50° and 70°. 
     In a preferred embodiment of the invention the angles of inclination of all the extension directions of the connecting columns are adjusted to each other, in particular selected to be of equal size, such that a stiffness of the elastic joint in axial direction increases when the elastomeric body, which elastically deforms under a load acting in radial direction, enables a relative movement between the inner armature and the outer armature in radial direction. Consequently, for a deformation of the elastomeric body in radial direction a stiffening of the elastomeric body in axial direction is realized. This quality of an increase in axial stiffness for an elastic deformation in radial direction is achieved in particular by the fact that the connecting columns are inclined with respect to the radial direction. 
     In a preferred embodiment of the invention the connecting columns respectively define an extension direction that is inclined with respect to the radial direction, and the directional component in radial direction of which is larger than in axial direction. This means that the connecting columns have a smaller angle of inclination in radial direction than in axial direction. The geometries, like the contours of the column bodies of the connecting columns and/or the angles of inclination of the extension directions are adjusted to each other such that the elastomeric body, which elastically deforms under a load acting in the radial direction, enables a relative movement between the inner armature and the outer armature in the radial direction. This means that the inner armature does not perform a movement in the axial direction with respect to the outer armature and vice versa in case that an elastic deformation in the radial direction of the elastomeric body is taking place simultaneously. In this way an abutment function of the elastomeric body in axial direction is realized. 
     In a preferred embodiment of the invention two respective connecting columns, preferably different pairs of connecting columns, are inclined in opposite direction to the radial direction such that deformation forces acting in axial direction, which build up inside the column bodies of the connecting columns owing to the relative movement in the radial direction between the inner armature and the outer armature, have opposite directions and preferably cancel each other out completely, so that, as desired, a relative displacement of the armature in the axial direction is prevented, whereby the desired abutment function is achieved. 
     Preferably the extension directions of all connecting columns are inclined with respect to the radial direction in an acute angle of between 25° to 65°. It is particularly preferred that all angles of inclination of the connecting columns with respect to the radial direction are selected to be equal. 
     In a preferred embodiment of the invention the column bodies of the connecting columns respectively define a center axis which, in case of a rotationally symmetric connecting column, may coincide with the axis of rotation. This center axis can be seen as the above mentioned extension direction. Preferably all center axes of the connecting columns meet each other essentially in a common area, preferably even at a common location in the three dimensional space. This area, preferably this location is disposed in particular on the axis of the axial direction of the elastic joint or at least in its vicinity. In a further development of the invention the shape of a cross-section of the column body increases in particular continuously along the center axis from a center section towards both armatures. The cross-sectional plane considered therein is disposed perpendicularly to the center axis. In this way enhanced coupling areas towards the respective armature can be achieved. 
     A special measure for reducing the radial stiffness without having to accept respective losses of stiffness in axial direction is achieved in that at least an outer surface of the column body facing towards the outside of the joint in axial direction has a concave shape. 
     With respect to the armatures it is to be noted that they are not necessarily the radially most internal or most external armature, but can also be formed by intermediate armatures like intermediate rings. 
     In a preferred embodiment of the invention the connecting columns are fixed at an intermediate ring that is coupled via a further elastomeric body of either the outer or the inner armature to the outer or inner armature. 
     For each connecting column the inner as well as the outer armature may form support surfaces diametrically opposed to each other and in particular axially symmetrical, the perpendiculars of which are disposed parallel to the extension direction of the respective connecting column. 
     Preferably the outer armature has the shape of an in particular closed housing ring, at the inside of which a protrusion is formed respectively for the formation of a support surface for the connecting column. Therein the ring structure and the protrusion may be made of one plastic piece. 
     In an embodiment of the elastic joint the outer armature may be realized by a combination of an intermediate ring sleeve of lesser strength and an outer ring sleeve that are coupled to each other by a completely circumferential elastomeric body section. 
     In a preferred embodiment of the invention the inner armature is formed by a rod-like basic structure, the center area of which is formed with a point-symmetrical radial bulge for the formation of support surfaces for the connecting columns. The bulge may be preferably axially symmetrical with respect to a radial direction that may be defined by a radial center plain. The support surfaces are preferably formed only in a transition area between a base of the bulge and a bulge maximum. 
     In a preferred embodiment of the invention a ball joint is inserted into the inner sleeve in order to reduce the cardanic stiffness and the rotational stiffness for the inner armature. In this way the service life and the strength can be increased significantly. 
     In an alternative embodiment of the elastic joint as a hydroelastic joint the at least four connecting columns form support spring elements that simultaneously form the delimiting walls of the hydraulic working chambers, wherein the areas without connecting column are realized by membrane segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, qualities and features will become clear from the following description of preferred embodiments of the invention in conjunction with the accompanying drawings. 
         FIG. 1  is an exploded view of a first embodiment of the invention; 
         FIG. 2  is a partial perspective sectional view of the embodiment of the elastic joint according to  FIG. 1 ; 
         FIG. 3  is a side view in axial direction of the elastic joint according to  FIGS. 1 and 2 ; 
         FIG. 4  is a cross-sectional view along the section line A-A according to  FIG. 3 ; 
         FIG. 5  is a sectional view along the section line B-B according to  FIG. 4 ; 
         FIG. 6  is an exploded view of a second embodiment of the invention; 
         FIG. 7  is a partial perspective sectional view of the elastic joint according to  FIG. 6 ; 
         FIG. 8  is a side view in axial direction of the elastic joint according to  FIGS. 6 and 7 ; 
         FIG. 9  is a sectional view along the section line A-A according to  FIG. 8 ; 
         FIG. 10  is a sectional view along the section line B-B according to  FIG. 9 ; 
         FIG. 11  is an exploded view of a third embodiment of the invention; 
         FIG. 12  is a partial perspective sectional view of the elastic joint according to  FIG. 11 ; 
         FIG. 13  is a side view in axial direction of the elastic joint according to  FIGS. 11 and 12 ; 
         FIG. 14  is a sectional view along the section line A-A according to  FIG. 13 ; 
         FIG. 15  is a sectional view along the section line B-B according to  FIG. 14 ; 
         FIG. 16  is an exploded view of a fourth embodiment of the invention; 
         FIG. 17  is a side view in axial direction of the elastic joint according to  FIG. 16 ; and 
         FIG. 18  is a sectional view along the section line A-A according to  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following figure descriptions, components of the elastic joint according to embodiment of the invention are first explained by means of the  FIGS. 1 to 5 . The description of the further embodiments refers, if necessary, to corresponding same or similar components without explaining them anew for the respective embodiment. 
     In  FIG. 1  the elastic joint for a wheel suspension of a motor vehicle is generally given the reference numeral  1 . The elastic joint, which has a purely elastomeric spring component without an additional hydraulic function, consists essentially of three components, that is, an inner armature  3 , an outer armature  5  and an elastomeric spring body  7  arranged between the armatures  3 ,  5 , which, besides elastomer material, may also have rigidification components made of metal or plastic. 
     As evident from  FIGS. 1 to 5 , the elastomeric body has no fully circumferential coupling structure between the armatures  3 ,  5 , but is realized in sections by recess  11 , that may extend completely in axial direction through the elastic joint. By means of this recess it is possible that a vulcanizing tool can enter the inside of the elastomeric body from both sides of the elastic joint, whereby the manufacturability of the elastic joint is simplified. 
     The elastomeric body  7  has four connecting columns  13  to  19 , the column bodies of which are structurally separated from each other, so that they can deform elastically without influencing the other connecting columns. The connecting columns  13  to  19  present a center axis M that is inclined with respect to the radial direction R as well as to the axial direction Z. 
     The connecting columns  13  to  19  extend along the center axis M essentially rectilinearly from the inner armature  3  to the outer armature  5 . 
     The inner armature  3  is formed by a sleeve having a rotational shape. The rotational shape is realized by a bulge  21  formed in the middle section and axially symmetrical with respect to a radial center plane Y. The bulge continuously decreases from a bulge maximum, that has no inclination in axial direction Z, towards ends of the sleeve, which are realized essentially cylindrically. 
     Cambered support surfaces are provided for the respective connecting column in the bulge area between the bulge maximum  23  and the cylindrical end section  25 . Therein the inclination of the bulge  21  is realized such that the connecting column, in particular its center axis, points perpendicularly into the inner armature  3 . 
     Also the outer armature is realized by a point-symmetrical rotational sleeve shape that presents a protrusion or offset section  27  at its ends in the area of the connecting columns, wherein the support surface is realized essentially by an area of transition between the offset section and the remaining section of the sleeve. The center axis of the connecting column is also disposed perpendicularly with respect to the area of transition towards the offset section  27 . 
     As visible in  FIG. 3 , the respective connecting columns extend in circumferential direction within an angular range of about 30°. Two pairs of connecting columns  13 ,  15  and  17 ,  19  are provided, wherein the connecting columns  13 ,  15  and  17 ,  19  are disposed in the radial direction in diametrically opposed positions. The pairs themselves are offset to each other by 90° so that when seen in the axial direction the transition spaces  11  are formed. 
     The embodiment according to  FIGS. 6 to 10 , shown generally by reference numeral  101 , differs from the elastic joint according to  FIGS. 1 to 5  with respect to the structure of the outer armature. This outer armature has additionally an intermediate ring  41  presenting an inclined section  43  at an axial end in order to realize the support surface for the respective connecting column  13  to  19 . 
     Approximately radially externally a revolving outer sleeve  45  is disposed which is coupled elastically with the intermediate ring  41  via a completely revolving ring body  47 . 
     The embodiment according to  FIGS. 11 to 15 , shown generally by reference numeral  201  differs from the basic embodiment according to  FIGS. 1 to 5  in that the cardanic stiffness and the rotational stiffness is reduced, whereby the service life and the strength of the elastic joint is improved. To this end the elastic joint additionally has a ball joint realized in the inner armature. To this end a ball head  51  is inserted into the slotted inner armature  53 . A retainer ring  55  belts the slotted inner armature  53  after insertion of the ball head  51 . The elastic joint is covered at its axial ends by a top cap  71  and a bottom cap  73  closing the space between the armatures  203 ,  205  and thereby preventing dirt from entering the joint. 
     The embodiment according to  FIGS. 16 to 18 , shown generally by reference numeral  301 , differs from the basic embodiment according to  FIGS. 1 to 5  in that alongside the purely elastomeric spring function it has integrated a hydraulic damping mechanism, into which a hydraulic working chamber  61  is fitted. The hydraulic working chamber is delimited into sections by the connecting columns  13  to  19 . Additionally the hydraulic working chamber is delimited by a membrane structure  63  at the sections where no connecting column is formed. Further, a removable closure element  65  is provided to allow filling of the hydraulic working chamber with a fluid in a pre-installation condition and sealingly closing of the hydraulic working chamber in an installation condition. Circumferential serrations  69  are formed on the elastomeric spring body  307  to fit into corresponding serrations  59  formed on the outer armature  5 . A bedstop  67  protrudes axially and radially from the elastomeric spring body  307 . In contrast to the embodiment according to  FIGS. 1 to 5  a radial abutment  23  made of elastomer material is now realized at the bulge  21  of the inner armature. This outer armature  5  has an intermediate ring  41   a  presenting an inclined section  43   a  at an axial end in order to realise the support surface for the respective connecting columns. 
     The features disclosed in the above description, the figures and the claims may be relevant for the realization of the invention in its different embodiments individually as well as in any combination. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  elastic joint 
           3  inner armature 
           5  outer armature 
           7  elastomeric spring body 
           11  recess 
           13 ,  15 ,  17 ,  19  connecting columns 
           21  bulge 
           23  bulge maximum 
           25  cylindrical end section 
           27  offset section 
           41  intermediate ring 
           43  inclined section 
           45  outer sleeve 
           47  ring body 
           51  ball head 
           53  slotted inner armature 
           55  retainer ring 
           59  serrations 
           61  hydraulic working chamber 
           63  membrane structure 
           65  closure element 
           67  bedstop 
           69  serrations 
           71  top cap 
           73  bottom cap 
           101  elastic joint 
           201  elastic joint 
           203  inner armature 
           205  out armature 
           301  elastic joint 
           307  spring body 
         M center axis 
         R radial direction 
         Z axial direction 
         Y radial center plane