Abstract:
The fastening element connects two parts in a chassis of a vehicle. The fastening element has a central axle on which two opposing paired support elements of damping material are arranged at an axial distance from one another. In order to achieve an improved performance at least one of the support elements is composed of two different components and/or of different material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims the priority of DE 2007 005 567.8 which was filed on Feb. 5, 2007. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a fastening element, in particular for connecting two parts in a chassis, which fastening element has a central axle on which at least two support elements of damping material are arranged at an axial distance from one another. 
     Fastening elements of this type are required in order, for example in vehicle wheel suspension systems, to secure two parts, which execute certain movements in operation, relative to each other. Fastening elements of this type are also referred to as coupling rods. They ensure that the parts which are to be secured relative to one another are held in a manner low in vibrations. An example of a coupling rod is shown in U.S. Pat No. 4,944,523. As shown therein, the coupling rod is provided with a central axle in the form of a steel bolt 112. See U.S. Pat. No. 4,944,523, Col. 5, 11. 8-16. The coupling rod of U.S. Pat. No. 4,944,523 is also provided with support elements molded of an elastomeric material, referred to as “grommets.” U.S. Pat. No. 4,944,523, Col. 5, 11. 35-45. 
     Consequently, in previously known solutions, a central metal axle is provided onto which support elements of rotationally symmetrical design are pushed. In this case, the support elements are shaped in such a manner that two support elements can secure between them a part which is to be retained. The support elements here are composed of a suitable plastics material such that adequate damping behaviour can be obtained. The use of polyurethane has proven successful here. 
     In this case, limits which are defined by the forces to be absorbed are to be taken into consideration both in the selection of material for the support elements and in the formation thereof. 
     It has emerged that coupling rods of the type mentioned at the beginning still leave something to be desired in this regard. In particular, it has been found to be negative that undesirable effects in the form of bending moments occur if the fastening element has to be dimensioned in such a manner that it can absorb high retaining forces. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the object of developing a fastening element of the type mentioned at the beginning in such a manner that it is capable of absorbing high forces and nevertheless the introduction of undesirable forces and moments is kept small. A further endeavour is for the support element to be able to be easily produced and fitted, thus resulting in a cost-effective realization. The performance of the vehicle equipped with the chassis in which the fastening element is installed is therefore to be improved. 
     The achievement of this object by the invention is characterized in that at least one of the support elements of the fastening element is composed of at least two different components and/or of different materials. 
     Accordingly, the support element is therefore composed either of two components which interact; these components may be composed, but do not have to be composed, of different materials. It is just as possible that, although the component is of single-part design, it is constructed from different materials; the last-mentioned possibility is of interest in particular in conjunction with multicomponent injection-moulding. 
     In this case, the two different components are preferably arranged concentrically about the axle and axially adjacent to each other. The one component may be composed of an elastic, damping material which has a greater hardness than the other component. In this case, a plastic is preferably provided. Particularly preferably, the plastic may be polyurethane. In order to increase the strength of this component, it can be provided that it is provided with reinforcing fibres, with glass fibres or carbon fibres being particularly in mind. The other component is preferably likewise composed of an elastic, damping material. In this case, an elastomeric material, in particular a material based on rubber or based on silicone, is preferably provided. 
     According to a particularly preferred embodiment, the two components are produced by a two-component injection-moulding process. Alternatively, the two components may be, of course, assembled to form the support elements only by an installation process. 
     One of the components, namely the one composed of softer material, can have an annular form with a rectangular shape in radial section. Alternatively, an annular form with a wedge-shaped, circular or elliptical contour in radial section may also be provided. In the case of the wedge-shaped structure, the axial extent of the component can increase with increasing distance from the axle. 
     Furthermore, a continuation of the invention provides that one of the components has a centring surface, in particular one with a cylindrical shape, for the other component. The centring surface may be configured in such a manner that it forms a bearing surface for the radially inner edge of one of the components. It is also possible that, in order to centre the one component, use is made of a separate component which has the centring surface. 
     At least one support element can be enclosed at its radially outer edge by a component which is sleeve-shaped at least in some sections. The effect achieved by this configuration is that the radially outwardly directed displacement in particular of soft material of one of the components is limited. In this case, the component which is sleeve-shaped at least in some sections is generally composed of metal or of plastic. In the event of the sleeve-shaped component being formed from plastic, polyamide is preferably provided. The said component can be reinforced with reinforcing fibres, in particular with glass fibres or carbon fibres. Furthermore, the component which is sleeve-shaped at least in some sections can have an axial bearing surface for one of the components. 
     The component which is sleeve-shaped at least in some sections can furthermore have an undercut for the interlocking securing of at least one of the components. The effect achieved by this configuration is that a preassembled unit can be provided, which can be handled in a manner secure against being lost. It can also be provided for there to be a press fit between the sleeve-shaped component and at least one of the components in the fitted state in order to create a fixed composite. 
     At least two support elements which are axially adjacent to one another can be provided with corresponding guide surfaces which guide the two support elements during a relative axial displacement with respect to each other. These guide surfaces additionally also serve for better guidance of the support elements into the through hole of the two parts, which are to be clamped, in the chassis, as a result of which the installation of the fastening element in accordance with the function thereof is made more secure. In this case, the guide surfaces can interact in the manner of a male-female configuration and can thus ensure good guidance of the two components when they are moved axially towards each other. The guide surfaces preferably have a conical shape in radial section. Finally, the guide surfaces can be arranged on axial projections of the support elements. 
     Two of the support elements can be held at a defined distance by a further, partially sleeve-shaped component. 
     The effect which can be achieved by the configuration of the support elements as at least a two-part component with the use of materials of differing hardness is that—particularly in interaction with the further measures mentioned—undesirable forces and moments, in particular bending moments, are reduced, with it nevertheless being possible for relatively large forces to be easily absorbed. 
     It is possible to provide a preassembled unit which is secure against being lost, and therefore it is significantly less difficult to handle in comparison to previously known solutions. It is therefore made possible, in particular, to positively influence the logistics of the coupling rod and its assembly parts, in particular the support elements, since complete units can be prepared and delivered to the installation site. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing illustrates an exemplary embodiment of the invention. In the drawing: 
         FIG. 1  shows, schematically, a fastening element for holding two parts of a vehicle suspension system, in a cut away, perspective view, 
         FIG. 2  shows the right upper end region of the fastening element in an enlarged view and in radial section, with a variant embodiment of somewhat alternative design to  FIG. 1  being illustrated, and 
         FIG. 3  shows the upper region of the fastening element according to  FIG. 2  in an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A fastening element  1  which is referred to as a coupling element can be seen in the figures; it is sold under the trademark Pogostik, registered with the United States Patent and Trademark Office on Feb. 11, 2003, Registration No. 2,686,834. The fastening element serves to secure two parts  2  and  3  (see  FIG. 1 ) of a chassis relative to each other, which has to take place in a vibration-damping and secure manner. The parts  2  and  3  are only indicated schematically in  FIG. 1 . 
     To this end, the fastening element  1  has a central axle  4  of steel, on which a plurality of support elements  5 ,  6 ,  7 ,  8  are arranged. Each support element  5 ,  6 ,  7 ,  8  is of rotationally symmetrical design. In radial section, the support elements  5 ,  6 ,  7 ,  8  have a shape tapering to a point on one side. A simple cylindrical shape is also possible. Every two support elements, namely the support elements  5  and  6  and the support elements  7  and  8 , are arranged on the axle  4 , in such a manner that they are directed towards each other with their regions tapering to a point. Accordingly, the support elements  5  and  6  and  7  and  8  form receiving regions for the parts  2  and  3 , respectively, between them. 
     The axle  4  has a head  20  in the upper region. A thread with a nut can also be provided there. In the lower region—which is not illustrated specifically—a thread is provided onto which a nut  21  is screwed. A fixed composite, to which the two parts  2  and  3  can be fixedly mounted, is therefore produced in the fitted state of the fastening element  1 . 
     It is preferred that the support elements  5 ,  6 ,  7 ,  8  in the exemplary embodiment are each composed of two different components  9  and  10 , with the components  9 ,  10  being composed of different materials. 
     The component  9  is manufactured from a material which is softer than that of the component  10 . The material of the component  9  is preferably an elastomeric material which can be based on rubber or based on silicone. 
     By contrast, the component  10  is relatively hard. In the exemplary embodiment, it is composed of polyurethane, the degree of hardness of which is selected specifically for the application. Other thermoplastics are certainly also possible. The support elements  5 ,  6 ,  7 ,  8  and therefore the components  9  and  10  are partially accommodated in sleeve-shaped components  12  and  13 , respectively. In the exemplary embodiment, the sleeve-shaped component  12  is composed of metal. Manufacturing it from a fibre-reinforced plastic, preferably of polyamide with reinforcing fibres of glass or carbon, is also possible. In the exemplary embodiment, the sleeve-shaped component  13  is composed of a fibre-reinforced plastic, preferably of polyamide with reinforcing fibres of glass or carbon. Manufacturing it from metal is also possible. 
     The upper and the lower sleeve-shaped components  12  have an L-shaped and therefore cup-like contour in radial section and therefore form axial bearing surfaces  14  for the softer component  9 . The harder component  10  is accordingly adjacent to the component  9 , with the two components  9 ,  10  bearing against each other in a sheetlike manner via an annular surface. 
     The central sleeve-shaped component  13  has axial bearing surfaces  14  for two components which are also spaced apart axially from each other by the component  13  (and, as a result, component  13  shall also be referred to as a spacer  13 ). 
     Since, caused by the construction, the sleeve-shaped sections of the components  12  and  13  engage in the axial and radial direction around the—soft and correspondingly easily deformable—components  9 , they constitute an edge enclosure for the edge  11  of the components  9  and  10  to this extent or within the scope of their axial extent. 
     When an axial force is applied to the fastening element  1 , the sleeve-shaped components  12  and  13  therefore prevent the relatively soft material of the component  9  from being displaced or squeezed radially. This achieves a high degree of damping comfort and low undesirable forces and moments, in particular bending moments, and, nevertheless, a high degree of axial rigidity of the fastening element  1  is maintained without losses of function occurring. 
     A number of details of the proposed solution emerge from the exemplary embodiment according to  FIG. 2 . Here, the components  9  of soft material are not—as in FIG.  1 —of rectangular design in radial section; on the contrary, they have a wedge shape. The axial extent of the components  9  is greater with increasing distance from the axle. 
     The sleeve-shaped components  12 ,  13  here have an undercut  15  (only illustrated for the component  12 ) which can be produced by a forming operation. This undercut  15  creates the possibility of preassembling a unit which is secure against being lost, which substantially simplifies the logistics. Similarly, the desired function of the undercut—namely the preassembly of the individual components which are secure against being lost—can be achieved by a simple interference fit between the components  10  and  12  and  10  and  13 . 
     So that the two support elements  5  and  6 , and  7  and  8  are guided neatly relative to each other when they meet each other axially, axial projections  18  and  19  which are respectively provided with guide surfaces  16  and  17  are arranged on the components  10 . The guide surfaces  16 ,  17  correspond to each other, i.e. in the present case they have conical surfaces with the same angle of taper. If the support elements  5 ,  6 ,  7 ,  8  meet one another, they are therefore securely guided by the conical surfaces. Similarly, these guide surfaces additionally also serve for better introduction of the support elements into the through hole of the parts  2  and  3 , which are to be clamped, in the chassis, as a result of which the installation of the fastening element  1  in accordance with the function thereof is made more secure. 
     In  FIG. 3 , an alternative configuration of the invention can be seen insofar as here the support element  5  composed of the components  9  and  10 —the same of course can also apply to the other support elements  6 ,  7 ,  8 —is configured in such a manner that the component  10  has a cylindrical centring surface  22  which ensures that the component  9  is centred. The centring surface  22  also serves here as a radial edge enclosure of the component  9  to the inside—in a similar manner to that of the edge  11  by the components  12  and  13 . A conical design of the centring surface  22  is just as possible. Since the component  9  is preferably composed of softer material than the component  10 , the component  9  is readily kept in position by the component  10  and the sleeve-shaped component  12  when forces are applied. 
     The various individual parts are joined together by the proposed configuration in such a manner that preassembled units are produced which make it easier for the user to install the fastening element in the chassis on the assembly belt, since there is a smaller number of parts to be handled than previously. The proposed support elements with guide surfaces together with projections increase the reliability of installing the fastening element on the chassis. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  Fastening element 
           2  Part 
           3  Part 
           4  Axle 
           5  Support element 
           6  Support element 
           7  Support element 
           8  Support element 
           9  Component 
           10  Component 
           11  Edge 
           12  Sleeve-shaped component 
           13  Sleeve-shaped component 
           14  Axial bearing surface 
           15  Undercut 
           16  Guide surface 
           17  Guide surface 
           18  Axial projection 
           19  Axial projection 
           20  Head 
           21  Nut 
           22  Centring surface