Patent Publication Number: US-2005127611-A1

Title: Piston ring, especially for a vibration damper

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention pertains to a piston ring, especially for a piston in a vibration damper, including a lateral wall with a lateral surface facing the piston, a pair of retaining segments extending radially inward from the lateral surface and having respective retaining surfaces which rest against the top and bottom of the piston, and a pair of sealing lips which extend radially outward from the lateral wall for engaging a cylindrical wall of the damper.  
      2. Description of the Related Art  
      A piston ring which covers a lateral surface of a flat piston is known from US 2003/0062687. In the axial direction, the piston ring is secured by support elements with retaining surfaces, which rest on the top and bottom surfaces of the piston. Within a groove in the piston ring, a tensioning ring is provided, which is intended to pretension the piston ring radially outward against the wall of the cylinder of the vibration damper. The groove is formed by the sidewalls of webs, which extend radially inward. In this design, the problem is that the locking ring can slide out of the groove during the axial movements of the piston, which can be very rapid at times. Although it is advisable for the groove to be as deep as possible, it is difficult if not impossible to remove a piston ring with a very deep groove from the mold after the injection-molding process.  
      FIG. 3 of U.S. Pat. No. 5,615,756 also shows a piston ring for a flat piston, where, starting from the support segments, a comparatively massive sealing lip extends toward the inside wall. Relatively high pretensioning forces against the cylinder wall can be achieved with a massive sealing lip without the need for a tensioning ring. The presence of such a large amount of material, however, leads to distortion when the piston ring cools down after injection molding, so that the shape of the sealing lip does not always have the desired precision.  
     SUMMARY OF THE INVENTION  
      The task of the present invention is to obtain a piston seal with a large amount of pretension against the cylinder wall.  
      Accomplished according to the invention in that the sealing lip is designed with a reinforcing profile radially on the inside, the web of which is perpendicular to the support segments.  
      The advantage of the reinforcing profile is that the wall thickness of the web does not represent a large concentration of material. In addition, it is easy to remove perpendicular webs from the mold.  
      Thus, for example, the sealing lip and the reinforcing profile can form a U-shaped cross section.  
      In another advantageous embodiment, the reinforcing profile is formed by a ring-shaped web. The sealing lip and the ring-shaped reinforcing profile are concentric and provide sufficient pretension against the cylinder wall. To simplify the design of the mold, the ring-shaped web begins directly above the support segment.  
      An especially high degree of dimensional rigidity can be obtained especially by providing transverse webs between the ring-shaped web and the sealing lip.  
      In a variant, the reinforcing profile is located axially between the support segment and the sealing lip and extends toward the surface against which the seal is to be formed. This design principle makes it possible to provide the sealing lip with very high rigidity, and at the same time the piston ring can be removed easily from the mold.  
      It is provided that the reinforcing profile is formed by a box profile, which is open radially toward the outside.  
      Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows how the piston ring is installed in a vibration damper;  
       FIG. 2  shows a piston ring on a piston; and  
       FIGS. 3-7  show diagrams of details of the inventive piston ring.  
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS  
       FIG. 1  shows by way of example a piston-cylinder assembly  1  in the form of a single-tube vibration damper. In principle, the invention can also be applied to other types of piston-cylinder assemblies.  
      The single-tube vibration damper  1  consists essentially of a pressure tube  3 , in which a piston  5 , mounted on a piston rod  7 , is installed with freedom of axial movement. At the exit end of the piston rod  7 , a piston rod guide  9  closes off a working space  11 , which is filled with damping medium. This working space is separated by a separating piston  13  from a gas space  15 , which has a bottom part  17  with an eye  19  at the end.  
      When the piston rod moves, damping medium is displaced through the damping valves  21  in the piston  5 , the valves being formed by valve disks  23 . A piston ring  25 , which covers a circumferential surface of the piston  5 , prevents the medium from flowing laterally around the piston.  
       FIG. 2  shows the piston  5  on the piston rod. The piston ring  25  has a U-shaped cross section, so that, starting from the lateral surface  27  of the piston ring, the retaining surfaces  33 ,  35  of the support segments  29 ,  31  rest on the top and bottom surfaces of the piston, thus holding the piston ring  25  axially in place on the piston  5 .  
       FIG. 3  shows a part of an inventive piston ring with part of the lateral surface  27  and the support segment  29 . Axially above the lateral surface, a sealing lip  37  or, in the simplest case, a sealing edge, rests against the inside wall of the cylinder  3 . Radially on the inside, the sealing lip is designed with a reinforcing profile  39 , which, in this exemplary embodiment, has, among other things, a radially inward extending, disk-shaped web  41 . This disk-shaped web  41  carries in turn a web  43 , which, with respect to the support segment  29 , proceeds in the axial direction, so that the sealing lip  37 , the disk-shaped web  41 , and the axially oriented circular ring-shaped web  43  describe a U-shaped cross section. As a result, the sealing lip  37  has a comparatively high degree of elastic stiffness while avoiding a large concentration of material. The circular ring-shaped web  43  and the radially oriented web  41  can also be divided into individual segments.  
       FIG. 4  shows a variant, in which the ring-shaped web  43  proceeds directly from a support segment. The sealing lip  37 , the support segment  29 , and the ring-shaped web  43  thus form a U-shaped profile. The sealing lip and the ring-shaped web can also be connected to each other by transverse webs  45 , as a result of which the spring rate of the sealing lip is increased significantly. It can be seen in  FIG. 5  that the sealing lip  37 , the transverse webs  45 , and the ring-shaped web  43  form pockets  47 , which are filled with damping medium in the case that the application involves a vibration damper.  
       FIGS. 6 and 7  show again parts of an inventive piston ring  25 , in which the reinforcing profile  39  is located axially between a support segment and the sealing lip and extends toward the surface against which the seal is to be formed. The sealing lip extends toward the cylinder  3  at a slant from the support segment  29 . The reinforcing profile  39 , which is designed as a box profile open radially toward the outside, is located in this space.  
      It is common to all the variants according to  FIGS. 3-7  that the piston ring  25  is slightly oversized when it is pushed into the cylinder; as a result, its sealing lip  37  rests with pretension against the cylinder  3 . This pretension is absorbed by the reinforcing profile  39 . In the embodiments according to  FIGS. 3-5 , the stresses are essentially compressive, whereas, in  FIGS. 6 and 7 , they are essentially tensile. The open box profile fulfills its function in spite of the pockets present in it, because the sealing lip remains free of distortion when the piston ring cools down after the injection-molding process.  
      Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be, understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.