Abstract:
In a central fastening element for an axially symmetric, vehicle gas spring, which includes a bellows that has central bores or cutouts in the region of its end faces, the fastening element being fixed to the vehicle body, protruding from the surroundings of the attachment point in a direction normal to it, and being encompassed by the bores or cutouts. The fastening element includes a shaped stud or a shaped cap, the maximum outer diameter of the stud or the cap being at least less than one fifth of the maximum outer diameter of the gas-spring bellows. 
     A device may be provided which allows a gas spring to be installed in a simple manner and allows the spring bellows to rotate with respect to the suspension and/or the vehicle body during the initial installation and/or the initial operation.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a central fastening element for an axially symmetric, vehicle gas spring, which includes a bellows that has central bores or cutouts in the region of its end faces, the fastening element being fixed to the vehicle body, protruding from the surroundings of the attachment point in a direction normal to it, and being encompassed by the bores or cutouts. 
       BACKGROUND INFORMATION 
       [0002]    Such a device is described in European Published Patent Application No. 0 123 171. The gas spring includes, inter alia, a vertical U-bellows and two axially symmetric bodies terminating it on the upper and lower sides. On the upper side, the gas spring is fixed to the vehicle body, e.g., to the vehicle frame, with the aid of a bolt. This bolt is seated in a bore of the frame and is screwed to the axially symmetric upper body, a so-called plug. The U-bellows itself is fastened to the axially symmetric, upper member with the aid of a tension band. In this case, the diameter of the plug is as large as the inner diameter of the U-bellows. 
         [0003]    This type of fastening requires that the bolthead on the upper side of the frame be accessible during installation. This makes it difficult to automate the installation of the gas spring. The gas spring tends to twist during installation, and while compressing and rebounding. Therefore, the tightening torque of the bolt must be selected to be high enough to prevent the connection between the gas spring and the vehicle body from loosening or releasing in response to vibrations and shock. 
         [0004]    It is an object of the present invention to provide a fastening element, which renders simple installation possible and allows the bellows to rotate with respect to the suspension and/or the vehicle frame during the initial installation and/or the initial operation. 
       SUMMARY 
       [0005]    This object may be achieved by providing a fastening element as described herein. To this end, the fastening element may include a shaped stud or a shaped cap, the maximum outer diameter of the stud or the cap being at least less than one fifth of the maximum outer diameter of the gas-spring bellows. The cap or the stud has at least one necked-down portion or waist, whose outer diameter is less than the above-mentioned, maximum diameter of the cap or stud. The end face is elastic in the zone in which it comes into contact with the stud or the cap. 
         [0006]    The central fastening element may be attached to the vehicle body prior to the installation of the gas spring and may protrude from the vehicle body in a direction normal to it. During installation, the gas spring is attached to, for example, the strut of the suspension and, e.g., pressed, together with it, against the shaped stud or the shaped cap. In the following, the term, stud, also includes the shaped cap. The elastic zone of the end face of the gas spring comes into contact with the stud in response to being slid up, and then engages with it in the manner of a snap fastener. The stud has a necked-down portion, which is encompassed by the bore or the cutout in a form-locked or force-locked manner. 
         [0007]    This type of fastening may allow the gas spring to be installed in an automated manner. In this case, and during initial operation, the gas spring may rotate on the stud, which means that the twisting of the U-bellows and the increased wear caused by it are prevented. The keyed connection between the stud and spring prevents vibrations and shock from detaching the fastening element. 
         [0008]    The base of the gas-spring bellows surrounds the stud axially and radially. Consequently, the gas spring is fixed in position in the axial and radial directions after installation. For example, it may not detach when the vehicle is jacked up, or in response to a pressure drop. 
         [0009]    The gas spring may be attached at its upper and lower ends in the same manner. Supply lines may be run through the fastening element into the interior of the gas spring. 
         [0010]    At least some regions of the base of the gas-spring bellows may be made of an elastic material, e.g., rubber. This may allow the base to act as a damping layer. The base may also be made up of multiple layers, e.g., a rubber layer and a metallic layer. In this case, the gas-spring bellows is attached to the metallic layer. The metallic layer is simultaneously used for increasing the strength of the gas-spring base. Several rubber and metallic layers may also be combined. 
         [0011]    To attach the gas spring, e.g., this rubber layer is compressed between two surface sections of the stud oriented in opposite, axial directions, or between a surface section oriented in the direction of the vehicle body, and the vehicle body. 
         [0012]    If the base of the gas spring is made out of multiple layers, the inner layer may be, for example, a metallic layer. The gas-spring bellows is then attached to this. This layer may be constructed in such a manner, that it supports the rubber layer and holds the position of the gas spring on the stud. 
         [0013]    Further details of the fastening element according to the present invention are set forth below in the subsequent description of several schematically represented, example embodiments. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  schematically illustrates the attachment of a gas spring to a vehicle body. 
           [0015]      FIG. 2  schematically illustrates an alternative manner of attaching a gas spring to a vehicle body. 
           [0016]      FIGS. 3 to 7  schematically illustrate alternative example embodiments of the fastening elements for the arrangements illustrated in  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  illustrates the attachment of a gas spring  70  to a vehicle body  5 , or to a strut. In this case, gas spring  70 , e.g. an air spring, is made up of, inter alia, a U-bellows  72 , which is attached to a damper plate  50 . In this connection, damper plate  50  forms the base of gas-spring bellows  72 . A fastening element  10  is mounted to vehicle body  5 , e.g., to the vehicle frame, a body member, or a reinforced part of the body paneling. 
         [0018]    On vehicle body  5 , a bolt  15  is situated in a concave and, optionally, axial asymmetric depression  6 . For example, this bolt  15  may be welded on. Bolt  15  has a thread  16 . A mushroom-shaped cap  19  is screwed onto this thread  16  via an internal thread  21 . 
         [0019]    Cap  19  is axially asymmetric and has a cylindrical outer contour  23  in the upper region. In the middle region, the contour changes, e.g., discontinuously, into a circular arc  24 . This transition is referred to in the following as  35  necked-down portion  25 , undercut, or waist. In this case, the center point of circular arc  24  is, e.g., on the radius of cylindrical outer contour  23  or below it. 
         [0020]    Curved section  24  is referred to below as a toroid. Cap  19  changes continuously or discontinuously between toroid  24  and a conical section  28  and tapers to approximately three quarters of its upper diameter. 
         [0021]    Instead of being semicircular, the contour of the partial cross-section of toroid  24  may also be triangular. In the case of this contour, toroid  24  has a frustoconical lateral surface, whose imaginary apex points to the center of the U-bellows interior. For example, the bottom surface of this frustoconical apex discontinuously joins up with necked-down portion  25  to form a barb-shaped undercut. 
         [0022]    The frustoconical apex may also be an imaginary enveloping surface for a series of resilient barbs positioned about cap  19 . After installation, these barbs sink into optionally sharp-edged groove  54  of damper plate  50 , while elastically recovering. 
         [0023]    For example, a hexagonal recess  26  is centrally situated in cap  19 , cf.  FIG. 3 . 
         [0024]    Damper plate  50  is positioned around cap  19 . The upper side of damper plate  50  is designated as outer side  59  and the lower side is designated as inner side  58 . Cylindrical damper plate  50  is made of rubber and has a central bore  52 , which is smaller that the maximum outer diameter of cap  19 . A recess in the form of a circular groove  54  is situated approximately halfway up bore  52 . This has a contour opposite to that of toroid  24  and therefore may ensure that damper plate  50  grips cap  19  from behind. In this connection, the region of damper plate  50  between groove  54  and outer side  59  may be compressed. Bore  52  changes into a chamfer  57  at the upper end face of damper plate  50 . Damper plate  50  is also chamferred at the lower end face. The thickness of damper plate  50  in the middle region approximately corresponds to the length of cap  19 , but the thickness in the outer region is reduced to approximately two thirds of the overall height. In this connection, inner side  58  is approximately planar. 
         [0025]    A metallic disk  62  and a thin rubber layer  63  are situated on the outer side  59  of damper plate  50 . The two parts may be cemented on or vulcanized on. A machined disk  64 , whose central region is formed in the shape of a frustoconical shell in the direction of the center, is situated on inner side  58 . The top edge of the frustoconical shell may be oriented, e.g., along groove  54  and may thus reinforce the rubber layer between bore  52  and machined disk  64 . This improves, for example, the rear gripping action. For example, this machined disk  64  may be vulcanized into damper plate  50 . 
         [0026]    At least two bores  65  are situated in damper plate  50 . These are cylindrical in the region of upper metallic disk  62 , thin rubber layer  63  and damper plate  50 . The diameter of bores.  65  in machined disk  64  is adapted to cover bolts  68 . Gas-spring bellows  72  is attached to damper plate  50  by these cover bolts  68 . Damper plate  50  rests against vehicle body  5  in the region of vehicle-frame depression  6 , and in the region of rubber sheet  63 . 
         [0027]      FIG. 2  illustrates an alternative manner of attaching gas spring  70  to vehicle body  5 . As in the exemplary embodiment illustrated in  FIG. 1 , a bolt  15  having external thread  16  is situated in a depression  6  of vehicle body  5 . 
         [0028]    A cap  19  is screwed onto a bolt  15 . In this case, this cap  19  has two circumferential toroids  24  at the transition from conical part  28  to cylindrical outer contour  23 , the outer diameter being greater in the region of the cap  19  of the two circumferential toroids than in the region of cylindrical outer contour  23 . The spacing of the two toroids  24  is, for example, approximately as large as half the difference of the diameter of a toroid  24  and cylindrical outer contour  23 . Conical part  28  of cap  19  is tapered in the downward direction. 
         [0029]    Damper plate  50  of gas spring  70  is a cylindrical, axially symmetric rubber sheet, which has a central bore  52 . Bore  52  has two circumferential grooves  54 . These have a contour opposite to that of toroids  24  and therefore may ensure that damper plate  50  elastically grips cap  19  from behind. In this connection, the region of damper plate  50  between grooves  54  is optionally compressed. 
         [0030]    In the region of the cap, the thickness of damper plate  50  corresponds to approximately two-thirds of the length of cap  19 . In this case, outer side  59  of damper plate  50  is planar. 
         [0031]    Situated in damper plate  50  is a, e.g., metallic, machined disk  80 , which may be vulcanized in. It has a central bore  82 . Near the bore  82 , the thickness of this machined disk  80  is approximately twice as much as in the remainder of machined disk  80 . The diameter of bore  82  is approximately one third of the overall diameter of machined disk  80 . A recess  83  is situated approximately in the center of this cylindrical bore  82 . Damper plate  50  engages with the former and thus allows axial, form-locked engagement. Bore  82  of machined disk  80  surrounds damper plate  50  to provide stiffness in the region of grooves  54 . 
         [0032]    Machined disk  80  has at least two countersunk bores  86  in the outer region. Cover bolts  68  are situated in these countersunk bores  86 , cf.  FIG. 1 . In the exemplary embodiment illustrated in  FIG. 2 , metallic disks  62 ,  64  and/or rubber disks  63  illustrated in  FIG. 1  may also be vulcanized into damper plate  50 . 
         [0033]    In the two exemplary embodiments, gas-spring bellows  72  pre-mounted to damper plate  50  is installed in the designated position. In this connection, central bore  52  of damper plate  50  is aligned with and centered on cap  19 . Chamfer  57  of bore  52  is then seated on conical part  28  of cap  19 . For installation purposes, damper plate  50  is pushed, optionally together with spring bellows  72 , against cap  19 , and pushed over toroid(s)  24 , as damper plate  50  elastically expands. Cap in this case, grooves  54  rest against toroid(s)  24 . 
         [0034]    During the automatic assembly of the axle, this gas spring  70  may be snapped into place in the nonpressurized state. Additional fastening measures, such as bonding or the application of a torque, may not be necessary for installation. In addition, a special tool may not be required for the installation or the detachment of gas spring  70  in the exemplary embodiments. 
         [0035]    During installation, gas spring  70  centers itself on cap  19 , using chamfer  57  of damper plate  50 . No torsional stress is generated in spring bellows  72  in response to it being filled with gas, since spring  70  may align itself about fastening element  10 . Due to its rear engagement, gas spring  70  may not detach from its mounting in response to a drop in pressure. 
         [0036]    If gas spring  70  is equipped, on its end faces, with one of the mountings described in the exemplary embodiments, upper or lower damper plate  50  of gas spring  70  may also be arranged to have a blind hole in place of a bore  52 . In this case, the sealing of the interior of gas spring  70  may be eliminated in the region of attachment. 
         [0037]    Damper plate  50  may also be part of spring bellows  72 . In this case, the need for pre-mounting spring bellows  72  to damper plate  50  may be eliminated. In this exemplary embodiment, the need for the upper and/or lower gaskets in the region of the cover bolts may be eliminated. 
         [0038]    The rubber-elastic seating of damper plate  50  on vehicle body  5  allows it to acoustically decouple vehicle body  5  from the suspension. 
         [0039]      FIGS. 3 to 7  illustrate exemplary embodiments of the form and the attachment of bolt  15 , i.e., of the shaped stud, and cap  19  to vehicle frame  5 . 
         [0040]    In  FIG. 3 , bolt  15  is welded, for example, to vehicle frame  5 . Bolt  15  may also be arranged as a sleeve. Cap  19  has a cylindrical inner bore  22 . As seen from above, the final third of inner bore  22  is arranged to be a tapped hole  21 . 
         [0041]    In  FIG. 4 , stud  15  is screwed into a thread in vehicle frame  5 . To secure the connection, stud  15  is braced against vehicle frame  5  at collar  17 . 
         [0042]      FIG. 5  illustrates a bolt  95 , which is inserted from above, through a bore  8  of vehicle frame  5 . Bolt  95  may have a special head shape. Head  96  of bolt  95  is welded to vehicle frame  5  from the top. Cap  19  is screwed onto bolt  15  from below. In this case, this cap  19  has the same exemplary embodiment as in  FIG. 3 . Cap  19  is fastened to bolt  95  by bracing it. 
         [0043]    In  FIG. 6 , a nut  93  is welded to vehicle frame  5 . Stud  15  is screwed into the nut. In this connection, stud  15  may be arranged to have or not have a collar. When stud  15  is constructed without a collar, stud  15  is secured by bracing stud  15  against the root of the thread. When stud  15  has a collar, stud  15  is secured by bracing the shaft collar against nut  93 . 
         [0044]      FIG. 7  corresponds to  FIG. 6 , the difference being that a weld nut  92  is attached to the upper side of vehicle frame  5 . Stud  15  is secured, for example, by tack-welding it to weld nut  92 , or by cold-working the ends of the thread, e.g., using a special tool. 
         [0045]    Other attachment variations are possible. These may combine, for example, the elements described above.