Abstract:
Air spring, in particular for a commercial vehicle, comprising a plunger piston, an air bellows, and a cover, said air bellows being movable between a first compressed position and a second extended position by a compressing or extending movement, wherein the air bellows has an axle-side region with a fixing portion for fixing on the plunger piston, and a body-side region, wherein the fixing portion is fixed between the cover and the plunger piston, and wherein the cover has at least one guiding portion on the cover circumferential edge, said guiding portion extending away from the body-side region and outwards over or beyond the fixing portion and being used as a support for the axle-side region.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an air spring or pneumatic spring, in particular for a commercial vehicle. 
       BACKGROUND OF THE INVENTION  
       [0002]    Conventionally, a vehicle axle of a commercial vehicle comprises an axle body which on one side by means of at least one trailing arm forms an axle assembly and therefore is movably hinged on the vehicle frame and supported relative to the vehicle frame by means of a respective air spring arranged above or behind the crossing area of the axle body and the trailing arm. The air spring in turn comprises an air bellows arranged between a cover and a base plate, wherein for a mechanical coupling between the air bellows on the one hand and the axle assembly on the other hand there is provided a plunger piston which is arranged on the air bellows. At its axle-side region the air bellows is connected to the plunger piston, wherein an outer surface of the plunger piston serves as a rolling or unfolding surface for the air bellows so that a guided movement of the air bellows is ensured during operation when the plunger piston moves up and down. 
         [0003]    However, such air springs are to a limited extent only suitable for crane and train loading since due to the weight of the axle, which will then hang below the vehicle, the air bellows is completely extended or unfolded without further support devices so that a negative pressure is generated in the air bellows relative to its surroundings. When the vehicle is set down, there is the danger that the air bellows folds towards the inside or tilts relative to the plunger piston or folds in and, hence, does not unroll or unfold along the plunger piston, as would be normal operation, which might lead to damage. 
         [0004]    In order to avoid this problem, conventionally in crane and train loading the range of spring of the air spring is limited by means of a tensioning or gripping device attached to the vehicle frame, or a divided plunger piston is used. Alternatively, the air spring may also be designed such that the air spring is releasably connected to the body and, in the case of crane loading of the trailer, the air spring is separated from the body by means of a returning device, and by means of the returning device the cover, and thus the bellows as well, is held in a defined position relative to the plunger piston so that the bellows unrolls or unfolds along the plunger piston or is held in an unrolled or unfolded state. 
       SUMMARY OF THE INVENTION 
       [0005]    The object underlying the invention is to provide an air spring, which is in a simple manner suitable for a crane loading of vehicles. 
         [0006]    This object is achieved by means of an air spring according to claim  1 . Advantageous further developments of the invention are defined in the dependent claims. 
         [0007]    According to the present invention there is provided an air spring, in particular of a commercial vehicle, comprising a plunger piston, an air bellows which is movable between a first compressed position and a second extended position by a compressing or extending movement, respectively, and an axle-side region with a fixing portion for fixing on the plunger piston, and a body-side region. The air spring according to the invention further comprises a cover, wherein the fixing portion is fixed between the cover and the plunger piston, and wherein the cover has at least one guiding portion at its circumferential edge, which guiding portion extends away from the body-side region and outwards beyond the fixing portion and serves as a support for the axle-side region. The guiding portion preferably lies from above on that portion of the axle-side region which is adjacent to the fixing portion, which usually is held or supported, in particular clamped, between the cover and a respective groove or bead in the upper region of the plunger piston. 
         [0008]    This means that in case the axle-side region of the air bellows unrolls or unfolds on the outer side of the plunger piston during the compressing or extending movement, it is supported additionally by the at least one guiding portion, whereby there is provided a better control or definition of the unrolling and rolling or unfolding and folding operation of the axle-side region of the air bellows and, thus, a better and safer handling of the air spring. The upper side of the plunger piston is adjacent to the cover. The term “commercial vehicle” in the sense of the present invention is not meant to be limited to drawing vehicles such as trucks or tractors, but also the trailers or semi-trailers thereof. There are different ways of positioning the axle-side support of the air spring. The axle-side support may be a plunger piston attachment or an air spring carrier. The air spring carrier may be arranged on a suspension arm of the axle assembly, for example. The axle-side region in the sense of the present invention is the end portion of the air bellows which is connected to the axle-side support of the air spring by means of the plunger piston and, possibly, further arrangement means, i.e. the portion of the air bellows which is arranged on the plunger piston. The body-side region of the air bellows is that portion of the air bellows which is connected to the body by means of a cover and, possibly, further arrangement means. An air bellows according to the invention may be in different states. In a basic state of the air bellows, there are no external forces such as tensile or propulsive and/or shearing forces acting on the air bellows. In particular, the basic state of the air bellows is that state in which the air bellows is when the air bellows which is mounted in an air spring is once inflated using compressed air for example and then the compressed air is let off or deflated again from the air spring, i.e. inside the air spring there is again ambient pressure. In the basic state no further force is applied on the air spring after the inflation process, apart from its own weight force. The air bellows may also have different operational states. One of said operational states is for example when the air spring is arranged in conventional operation, wherein for example the internal pressure in the air bellows differs from the ambient pressure. Such an operational state is present for example when the vehicle is in conventional use. In use, as a result of compressing and extending movements, the air bellows may be moved into a first position in which it is—possibly even completely—compressed, as well as into a second position in which it is—possibly even completely—extended. Another operational state is a state in which the air bellows is deflated, for example when the device such as a trailer of a truck on which the air spring is arranged is parked over a longer period of time. In this case, there is ambient pressure inside of the air bellows, as in the basic state, and the air bellows is in the first position. In this operational state of the air bellows, the length of the air spring is regularly smaller than the length of the air spring in the basic state of the air bellows. Furthermore, the air bellows may have a loading state, wherein the loading state is present for example when the vehicle is crane-loaded onto a railway car, i.e. the axle assembly depends from the air spring. In this case the air bellows is in the second position. In the loading state of the air bellows, the air spring, when measured along its center line, is regularly longer than in the basic state of the air bellows. If a very high internal pressure is applied to the air spring in the operational state of the air bellows, it is also possible that the air spring has the same dimensions as in the loading state of the air bellows. The air bellows may also be in the basic state when it is decoupled from the plunger piston, for example, i.e. for example when the air bellows is supported alone. When a trailer on which the air spring is arranged is loaded onto a railway car, a ferry or the like, when the trailer is lifted over the chassis or the body, due to the axle weight, the air bellows is essentially completely stretched. As has already been described, the axle-side region of the air bellows is reliably rolled or folded or unrolled or unfolded due to the additional support by means of the at least one guiding portion. Consequently, at any time it is ensured that the unrolling or unfolding of the air bellows on the plunger piston functions reliably even if no pressure is applied to the air bellows. Thus, when the trailer is put down onto the railway car or onto the ferry, the air bellows is designed such that it automatically returns to the same state as before the lifting operation. This state may be the basic state, for example, when in particular the air bellows is deflated, or a state different from the basic state, when an internal pressure is applied to the air bellows for example. To put it differently, the air bellows may essentially be fully stretched during the lifting of the trailer when the trailer is loaded onto a railway car or a ferry. When the trailer is then put down on the railway car or the ferry, the air bellows unrolls or unfolds along the outside of the plunger piston even if there is only little internal pressure inside of the air bellows. Tilting or folding in of the air bellows is prevented by the at least one guiding portion of the cover. Therefore, advantageously, according to the invention it is not necessary to limit the maximum spring range during the loading operation, for example by means of an arrester cable as preferred gripping or tensioning device. In particular, it is advantageously neither necessary to design the plunger piston such that it is divided. Rather, due to the air spring according to the invention, the problems of the prior art are solved in a simple manner. 
         [0009]    It may be advantageous if the fixing portion extends at least up to the radial outer side of the plunger piston or even beyond. This offers the advantage that the guiding of the axle-side region of the air bellows in particular in the area of the maximum extension is particularly good and precise since a particularly large contact surface and a close contact between the at least one guiding portion and the axle-side region result. 
         [0010]    Expediently, the fixing portion of the air bellows is directed preferably diagonally downwards in each position of the air bellows. That portion of the air bellows which is positioned or guided by the fixing portion or which is adjacent to the fixing portion may be directed diagonally downwards, i.e. away from the body-side region downwards and outwards. 
         [0011]    The guiding and support of the axle-side region of the air bellows between the at least one guiding portion and the upper side of the plunger piston is even further improved if the plunger piston has an inclined surface on its upper side, which at least partially corresponds to the at least one guiding portion. In particular, the guiding portion and the inclined surface may be designed to be essentially parallel to one another at least in certain areas. 
         [0012]    A particularly simple embodiment of the guiding portion results when it is designed as a surface which is rotationally symmetrical relative to the axis of symmetry of the air spring. To put it differently, this means that the guiding portion is designed as a ring surface inclined downwards from the edge of the cover, for example as a lateral surface of a cone or of a truncated cone. 
         [0013]    In an alternative embodiment, the at least one guiding portion is designed as a plurality of partial surfaces, which relative to the axis of symmetry of the air spring are arranged at the same circumferential angle distance relative to one another. The individual guiding portions are designed for example like petals of a blossom—each one with its outer edges inclined downwards, assuming a normal mounting position of the cover or of the air spring. In this context it should be noted that such an air spring usually is largely rotationally symmetrical to an axis of symmetry, which, however, does not apply to each individual component. Thus, the individual guiding portions strictly speaking are not rotationally symmetrical to the axis of symmetry. 
         [0014]    It may be advantageous if the at least one guiding portion comprises a curveless partial portion which is arranged at an angle a of about 0° to 70° relative to the axis of symmetry of the air spring. Preferably, however, the angle α is about between 20° and 50°, wherein an angle of about 35°-45° is particularly preferred. Thus, the at least one guiding portion may be ideally adapted to the shape of the upper side of the plunger piston and be optimized with respect to its guiding and supporting properties. 
         [0015]    It is advantageous if the at least one guiding portion extends over a range of about 10% to 40%, preferably about 15% to 35%, and in particular about 20% to 30% of the radial expansion of the plunger piston. In this way it is possible to optimize the guiding and supporting properties of the at least one guiding portion. 
         [0016]    It may be advantageous if the cover radially within the at least one guiding portion forms an at least essentially plane surface. To put it differently, there is not provided a downwards recess in the cover, but the latter is plane. 
         [0017]    Alternatively, the cover may be designed concavely at least in certain areas within the at least one guiding portion. Here, the curvature may extend into the air bellows. Preferably, however, the curvature is oriented from the inside of the air bellows towards its outside. 
         [0018]    If the at least one guiding portion comprises at its radial outer end a rounding or portion which curves back towards the body-side region, said end rests particularly well and “softly”, i.e. without the danger of injuries, against the axle-side region of the air bellows and guides the latter particularly well. Said properties may be even further improved if the rounding forms a chamfer which is open towards the upper side—i.e. towards the body-side region. Therefore, in this embodiment the air bellows may adapt or conform or adhere to the chamfer and is thus particularly well guided and supported. 
         [0019]    Further advantages and features of the invention result from the following description of preferred embodiments with reference to the appended Figures, wherein individual features of individual embodiments may be combined to form new embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The Figures show: 
           [0021]      FIG. 1  a schematic sectional view of a first embodiment of the air spring according to the invention in its compressed position; 
           [0022]      FIG. 2  a schematic sectional view of a second embodiment of the air spring according to the invention in its compressed position; 
           [0023]      FIG. 3  a schematic sectional view of the second embodiment in its extended position; 
           [0024]      FIG. 4  a schematic sectional view of a third embodiment of the air spring according to the invention in its compressed position; and 
           [0025]      FIG. 5  a schematic sectional view of the third embodiment in its extended position. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows an air spring  10  according to the invention. The air spring  10  comprises a plunger piston  30  as well as an air bellows  14 . The plunger piston  30  may be made of any material, for example a plastic material or a metal such as steel. The air bellows comprises a body-side portion or a body-side region  16  as well as an axle-side portion or axle-side region  18 . Between the axle-side region  18  and the body-side region  16  there is provided a central portion  17 . 
         [0027]    The body-side region  16  is closed by means of a cover  40 . The cover  40  may be connected to a structure or body of a trailer (not shown in the Figures), for example. 
         [0028]    The axle-side region  18  of the air bellows  14  ends in a fixing portion  19  which forms a thickened ring into which a reinforcing ring  19   a  is embedded. At the upper side  31  of the plunger piston  30 , there is a ring bead  32  into which the fixing portion  19  is inserted. In order to close the plunger piston  30  there is placed onto its upper side  31  a cover  20 , which forms a plane surface  25  in its central region. 
         [0029]    At the circumferential edge  21  of the plane surface  25  the cover  20  continues in a guiding portion  26 , which is designed in the form of a circular ring surface the outer edge of which is tilted downwards, i.e. away from the body-side region  16 . To be more exact, the guiding portion  26  forms a part of a conical surface. 
         [0030]    At the radial outer end  27  of the guiding portion  26  there adjoins a relatively slightly curved rounding  28  which is open towards the body-side region  16  and which is curved back towards the body-side region  16 . The guiding portion  26  forms an angle a of about 40° to the axis of symmetry of the air spring  10 . With regard to the overall radial expansion of the cover  20  the guiding portion  26  takes up about a quarter thereof, wherein the rounding  28  is not taken into account. 
         [0031]    The arrangement is such that the fixing portion  19  and the adjacent portion of the axle-side region of the air bellows  14  comes to rest between the guiding portion  26  and an inclined surface  36  of the plunger piston  30 , which inclined surface  36  is formed below the ring bead  32 . Thus, the fixing portion  19  is supported or held, usually clamped, between the guiding portion  26  and the inclined surface  36 . The clamping is achieved by a clamping device  22  which connects or bolts the cover  20  to the plunger piston  30  by means of fastening means  24 , such as in particular bolts and nuts. Thus, a secure, however releasable, connection between the air bellows  14  and the plunger piston  30  is ensured. Otherwise, the plunger piston is of the conventional type as it is used for conventional air springs  10 . The basic embodiment of the air bellows  14  is also conventional, as it is known from conventional air springs  10 , wherein the air bellows  14  may be easily removed from the plunger piston  30 , for example by at least partially releasing the bolts and nuts  24  and by spacing apart the clamping device  22  from the plunger piston  30 . Consequently, the fixing portion  19  of the air bellows  14  is no longer clamped between the clamping device  22  and the plunger piston  30 , and it is possible to remove the air bellows  14  and to replace it by a new air bellows  14 . 
         [0032]    Thus, according to the invention the axle-side region  18  of the air bellows  14  is at any time securely guided and supported or held in the neighborhood of the fixing portion  19 , in particular, however, when the air bellows rolls or folds or unrolls or unfolds during a compressing or extending movement. 
         [0033]      FIGS. 2-5  show two further advantageous embodiments of the invention. In said Figures, identical or similar parts are designated by the same or similar reference numerals, and in order to avoid repetition, they are not explained anew. The statements made with respect to the first embodiment also apply to the further embodiments, unless it is explicitly explained differently or technically unfeasible. 
         [0034]      FIGS. 2 and 3  show a second embodiment of the air spring according to the invention. The second embodiment differs from the first embodiment on the one hand in that the plunger piston  30  does not have at its upper side  31  a linear or plane inclined surface  36 , as is the case in the first embodiment, but a curved surface  36 ′ which, however, is also inclined or slant. Thus, the plunger piston  30  of this embodiment is designed like a bell at its upper side. As can be readily seen from  FIGS. 1 and 2 , the present invention can be used for different embodiments of plunger pistons and does not depend on a certain design of the upper side of the plunger piston. On the other hand, the second embodiment differs from the first one in that the rounding  28  adjacent to the radial outer end  27  of the guiding portion  26  is designed as a chamfer which is open towards the body-side region  16 . By contrast, the respective rounding  28  of the first embodiment is considerably less curved and thus less pronounced than in the second embodiment. As can be seen from  FIG. 3 , which shows the air spring according to the invention in its largely extended state, the axle-side region  18  of the air bellows  14  rests closely against the rounding  28  in this state and is even better guided and supported thereby than in the first embodiment. 
         [0035]      FIGS. 4 and 5  show a third embodiment of the air spring according to the invention. Unlike in the first two embodiments the cover  20  is not designed as a plane surface  25  in its central portion, but forms a downwards recess, i.e. away from the body-side region  16 . As can be seen, the guiding portion  26  extends beyond the fixing portion  19  of the axle-side region  18  and in this area radially towards the outside forms a surface ascending to the body-side region  16 , which radially even further outside continues in a portion  29  which is curved away from the body-side region  16  (i.e. downwards). As a result, the plunger piston  30  is encompassed at its upper side  31 , and the axle-side region  18  is particularly well supported and guided between the guiding portion  26  with the portion  29  and the upper side  31  of the axle-side region  18  of the air bellows  14 . The radially outermost end of the guiding portion  26 , i.e. of the portion thereof, is designed in the form of a circumferential rounding  28  in the form of a chamfer open towards the top, which is even more pronounced than in the second embodiment. As can be seen from  FIG. 5 , the axle-side region  18  of the air bellows  14  in the completely or almost completely extended state of the air spring  10  rests very closely and over a large surface against the bottom side of the rounding  28  and is thus securely and precisely guided and supported by the rounding  28 . The diagonally downwards directed portion  29  of the guiding portion  26 —i.e. that portion immediately radially within the rounding  28 —is arranged very steeply and has only an angle α of about 10-20° with respect to the axis of symmetry S. 
         [0036]    In contrast to the first two embodiments, in the third embodiment of the air spring  10  according to the invention a ring bead  23  is provided not at the upper side of the plunger piston  30 , but in the cover  20 , in which ring bead  23  the fixing portion  19  of the outer region  18  of the air spring  14  comes to rest. 
         [0037]    It should be noted that according to the invention, in all embodiments, the axle-side region  18  of the air bellows  14  is at any time guided and supported or held in the neighborhood of the fixing portion  19 , in particular however during the rolling or folding and unrolling or unfolding of the air bellows during a compressing or extending movement. 
       LIST OF REFERENCE SIGNS 
       [0038]      10  air spring 
         [0039]      14  air bellows 
         [0040]      16  body-side region 
         [0041]      17  central portion 
         [0042]      18  axle-side region 
         [0043]      19  fixing portion 
         [0044]      19   a  reinforcing ring 
         [0045]      20  cover 
         [0046]      21  circumferential edge 
         [0047]      22  clamping device 
         [0048]      23  ring bead 
         [0049]      24  fastening means/bolts and nuts 
         [0050]      25  plane surface 
         [0051]      26  guiding portion 
         [0052]      26 ′ guiding portion 
         [0053]      27  radial outer end 
         [0054]      28  rounding 
         [0055]      29  portion 
         [0056]      30  plunger piston 
         [0057]      31  upper side 
         [0058]      32  ring bead 
         [0059]      36  inclined surface 
         [0060]      36 ′ slant surface 
         [0061]      40  cover 
         [0062]    α angle 
         [0063]    S axis of symmetry