Patent Publication Number: US-2010127438-A1

Title: Plunger piston

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a plunger piston for an air spring, which plunger piston is formed as a hollow body and has a bottom to which a circumferential casing part is indirectly or directly coupled, and a plunger piston, in its cover region remote from a bottom, has a connecting edge for a bellows and at least one air passage opening. 
     2. Discussion of Related Art 
     A plunger piston of this kind is known from U.S. Pat. No. 6,386,524 B1, wherein a hollow body is formed by two circumferential walls. An inner circumferential wall is situated concentric to an outer circumferential wall. The two circumferential walls are supported in relation to each other by reinforcing ribs. The inner circumferential wall encompasses an air passage opening in the cover region of the plunger piston. The air passage opening is delimited by an edge to which a bellows can be fastened. The bottom region of the plunger piston can be sealed by a plate. The plate in this case is integrally joined, for example glued, to the lower edges of the circumferential wall. In order to provide the air spring with the greatest possible air volume, the inner circumferential wall has air passage openings that connect the individual volume regions of the hollow body to one another. When rapid load changes occur, undesirable air oscillations can occur in the region of these air passage openings. In addition, the inner circumference wall takes up space and thus limits the available air volume of the hollow body. 
     SUMMARY OF THE INVENTION 
     One object of this invention is to provide a plunger piston of the type mentioned above but which has a simple design and is easy to produce. 
     This object is achieved with a hollow body that has a cup-shaped lower part comprised of the bottom and the casing part. An upper part is placed onto the lower part and connected to the lower part in an airtight fashion, and the upper part has the connecting edge. 
     The cup-shaped lower part can be easily produced and forms the lower airtight closure of the hollow body. The upper part can be placed like a cover onto the lower part, thus delimiting the cavity defined by the hollow body. The upper part with its connecting edge forms the coupling point for the bellows. It is thus possible to control the introduction of force from the upper part to the lower part by the embodiment of the upper part. In particular, a load transfer can be carried out, if so desired, from the upper part directly into the circumferential casing part of the lower part. This permits a simpler and more stable design of the plunger piston. 
     According to one embodiment of this invention, it is possible for the casing part to have a cylindrical region that transitions into a circumferential, cylindrical side wall of the upper part having the same diameter. The cylindrical regions of the upper part and lower part that transition into each other can form the contact and rolling surface for the bellows. This embodiment also permits a kit-like design of the plunger piston. For example the upper part, embodied in the form of a universally usable component, can be placed onto various lower parts. Thus, it is possible for the various lower parts to enclose various air volumes. 
     The kit-like embodiment of the plunger piston can also be achieved within the scope of this invention if a standardized interface is provided between the lower part and the upper part. 
     An airtight connection of the lower part to the upper part can be achieved in a simple fashion if the lower part and the upper part each has a circumferential edge and the upper part with the lower part are joined to each other at the edges by a sealed connection. 
     In order to improve the load transfer, according to one embodiment of this invention, the lower part and/or the upper part each is reinforced by reinforcing elements. In this case, the reinforcing elements of the lower part can be embodied in the form of ribs that are formed integrally onto the casing part and extend in the radial direction. 
     The design of the upper part achieves a more stable structure because the reinforcing elements of the upper part are formed integrally onto the connecting edge and protrude into the air passage region enclosed by the connecting edge and because at least part of the reinforcing elements, in their region remote from the connecting edge, are connected to a reinforcing part. This design makes it possible to reliably absorb and transfer radially acting clamping forces of the bellows. 
     A further reinforcing of the plunger piston is achieved if at least part of the reinforcing elements of the cover part have a supporting part that is supported against a counterpart supporting part of the lower part. 
     In one embodiment of this invention, the reinforcing elements of the lower part and upper part are at least partially supported against one another. This promotes the shunting of force from the upper part to the lower part. 
     In one embodiment of this invention, the cover-like upper part encloses a partial cavity that combines with the partial cavity formed by the lower part to form a whole cavity, with the partial cavities communicating in an air-conveying fashion. 
     The lower part and upper part are preferably embodied in the form of injection-molded plastic parts. 
     If the upper part has a convex, rounded transition that adjoins the cylindrical, circumferential side wall and supports a transition section, the transition section is sloped toward the lower part, and the annular connecting edge adjoins the transition section by a concave rounded transition, then a transfer region between the side wall and the connecting edge deflects the bellows in an optimized fashion in terms of tension. 
     According to one embodiment of this invention, the bottom of the lower part has a reinforcing element coupled to the bottom or embedded into the bottom, for example during the plastic injection-molding process. The reinforcing element stiffens the bottom at least partially. The transmission of force to a connected axle or body component is thus improved. This is accompanied by advantages with regard to the distribution of force if the bottom is not resting with its entire surface area against the axle/body component. 
     The reinforcing element can advantageously be formed as a plate or ring, with the plane of the plate or ring oriented in the direction of the bottom plane. 
     If a plunger piston is embodied so that the reinforcing element has a greater hardness than the bottom and is comprised, for example, of metal, then the lower part can be produced in a cost-optimized way in the form of a composite component made of two different materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention is explained in view of an exemplary embodiment shown in the drawings, wherein: 
         FIG. 1  is a perspective, exploded view of a plunger piston having a lower part and an upper part; 
         FIG. 2  is an assembled view of the plunger piston according to  FIG. 1 , in a sectional side view; and 
         FIG. 3  is perspective, sectional view of the plunger piston according to  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a plunger piston comprised of a lower part  10  and an upper part  20 . The structural embodiment of these two components is shown in greater detail in  FIG. 2 . Accordingly, the lower part  10  has a bottom  12  onto which a circumferential casing part  11  is integrally formed. A fastening receptacle  13  is also formed centrally onto the bottom  12 . The fastening receptacle  13  encloses a receiving space into which a fastening element such as a nut can be inserted and the cylindrical fastening receptacle  13  transitions into a counterpart support part  14  that is centrally formed. 
     The counterpart support part  14  encloses a receiving region. A fastening screw that is screwed into the nut of the fastening receptacle  13  is accommodated with its thread in the counterpart support part  14 . 
     The circumferential, cylindrical casing part  11  has a circumferential edge  15 . The edge  15  is formed by a step-like cross-sectional reduction of the casing part  11 . 
     Reinforcing elements  16  are situated in the cavity enclosed by the lower part  10 . The reinforcing elements  16  are embodied in the form of ribs and extend radially inward from the casing part  11 . They are integrally connected to the fastening receptacle  13 , the casing part  11 , and the bottom  12 . As shown in  FIG. 1 , one part of the reinforcing elements  16  is formed only onto the fastening receptacle  13  while another part of the reinforcing elements  16  is formed onto both the fastening receptacle  13  and the counterpart support part  14 . The different reinforcing elements  16  are arranged in a constantly alternating fashion. The lower part  10  is embodied in the form of an injection-molded part and is constructed without an undercut in the direction of its central longitudinal axis, the dot-and-dash line shown in  FIG. 2 , so that it can be demolded in this direction without requiring a slide mold. 
     The upper part  20  has a circumferential edge  21  and is embodied with a step-shaped shoulder like the edge  15  of the lower part  10 . The edge  21  is adjoined by a cylindrical, circumferential side wall  22 . The side wall transitions via a convex rounded transition  23  into a transition section  24 . The transition section  24  is sloped toward the lower part  10 . The transition section  24  ends in a concave rounded transition  25 . The rounded transition  25  is adjoined by a connecting edge  26 . The connecting edge  26  is embodied in an annular form. The connecting edge  26  ends with a bead  27  and encompasses an air passage region. 
     As shown in  FIG. 1 , reinforcing elements  28  are formed onto the connecting edge  26 . The reinforcing elements  28  extend radially inward. At their end remote from the connecting edge  26 , the reinforcing elements  28  are connected to an annular circumferential reinforcing part  29 . 1 . The reinforcing elements  28  and the reinforcing part  29 . 1  stiffen the connecting edge  26 . As shown in  FIG. 2 , the reinforcing elements  28  are also integrally formed onto the side wall  22 , the rounded transitions  23  and  25 , and the transition section  24 . The reinforcing elements  28  thus extend in the radial direction. At their ends remote from the side wall  22 , the reinforcing elements  28  are formed onto the reinforcing part  29 . The reinforcing part  29  has a hollow, cylindrical support part  29 . 2 . The support part  29 . 2  transitions via a wall element  29 . 1  into a conical region of the reinforcing part  29 . 
     Like the lower part  10 , the upper part  20  is embodied in the form of an injection molded part. The demolding again occurs along the central longitudinal axis, along the dot-and-dash line shown in  FIG. 2 . In this direction, the upper part  20  is constructed without an undercut so that it can be removed from a mold without requiring a slide element. 
     The reinforcing elements  28  of the upper part  20  and the reinforcing elements  16  of the lower part  10  are matched to one another in their circumferential distribution and are spaced apart from one another by the same distances. It is thus possible for the reinforcing elements  28 ,  16  of the upper part  20  and lower part  10  to be aligned with one another. As shown in  FIGS. 2 and 3 , the reinforcing elements  28  of the upper part  20  rest on the reinforcing elements  16  of the lower part  10 , thus permitting a load transfer. 
     During assembly, the upper part  20  is placed with its edge  21  onto the edge  15  of the lower part  10 . As shown in  FIG. 2 , the side wall  22  and the casing part  11  transition into one another without a step. The edges  15  and  21  form respective abutting surfaces  15 . 1  and  21 . 1  that rest against each other, thus achieving a definite and limited assembly movement. In the region of the edges  15  and  21 , a suitable connecting technique is used that makes it possible to produce an airtight connection. For example, an integrally joined connection can be used, in particular a glued connection, a welded connection, or the like. 
     As also shown in  FIG. 2 , the support part  29 . 2  rests against the counterpart support part  14  when the upper part  20  and lower part  10  are in the joined state. In this case, the support part  29 . 2  surrounds the counterpart support part  14  and fixes it laterally in position. To permit a good load transfer, the wall element  29 . 1  rests on top of the counterpart support part  14 . 
     As shown in  FIGS. 2 and 3 , between the reinforcing elements  16  and  28 , there is sufficient open space so that all of the interior regions of the lower part  10  and upper part  20  communicate with one another in an air-conveying fashion. 
     A bellows  30  is shown in  FIG. 2 . For the sake of a clearer depiction, the bellows  30  is only shown on the left side of the plunger piston. The bellows  30  is arranged circumferentially in a known fashion. The bellows  30  has a fastening ring  31  that rests against the connecting edge  26  and is fastened to it. After its fastening ring  31 , the bellows  30  is continuously deflected by the rounded transitions  23  and  25  of the upper part  20  and laterally guided along the side wall  22  and the casing part  11 . The cylindrical region formed by the side wall  22  and the casing part  11  form a contact and rolling surface for the bellows  30 . The cavity enclosed by the bellows  30  is spatially connected to the cavity of the hollow body composed of the upper part  20  and lower part  10 . This spatial connection is produced by the air passage opening  27 . 1  in the region of the connecting edge  26 .