Patent Publication Number: US-2002011697-A1

Title: Strut with an air-filled cushion

Description:
[0001] The present invention concerns a strut with an air-filled cushion as recited in the preamble to claim  1 . Struts of this genus are being increasingly employed in wheel suspensions for smooth-riding vehicles. One such device is known from German 19 819 642 A1 for example. The cushion is essentially a bellows that rolls down, has closing and fastening components at one end and accommodates a hydraulic dashpot. The interface between the bellows and the dashpot must be sealed, and O rings accommodated in grooves have proven satisfactory for this purpose. The grooves have always been preferably machined into the closing and fastening components, a complicated procedure that causes considerable wear on the tools. Finally, since the closing and fastening components are preferably plastic, machining them often leads to strain and fissuring.  
       [0002] The object of the present invention is accordingly a simpler approach to sealing the interface between the closing and fastening components and the dashpot that will still allow a reliable seal by means of O rings.  
       [0003] This object is attained in accordance with the present invention by the characteristics recited in the body of claim  1 . Advantageous and advanced embodiments are addressed in claims  2  through  4 .  
       [0004] The particular advantage of the present invention is that the accommodations for the O rings are not machined, which avoids the aforesaid drawbacks. Another advantage is that one stage of the manufacturing process is eliminated, considerably simplifying it. 
     
    
    
     [0005] One embodiment of the present invention will now be specified with reference to the accompanying drawing, wherein  
     [0006]FIG. 1 is a schematic illustration of an strut with an air-filled cushion,  
     [0007]FIG. 2 is a larger-scale illustration of the interface between the upper fastening component and the piston rod,  
     [0008] and  
     [0009]FIG. 3 is a larger-scale illustration of the interface between the lower fastening component, in the form of a surface that the bellows rolls down over, and the dashpot&#39;s cylinder. 
    
    
     [0010] The strut preferably consists of an air cushion with a hydraulic dashpot accommodated inside. As will be evident from FIG. 1, the cushion essential comprises a bellows  1  that rolls down and has closing and fastening components at each end. These components are represented in the present embodiment by a cap  2  at the top and by a surface  3  at the bottom that the bellows rolls down over. The dashpot consists of a shock-absorbing cylinder  4  and of a piston rod  5  that travels into and out of it. Cylinder  4  is secured at its upper end and piston rod  5  at its lower end to the vehicle&#39;s body or suspension by eyes  6 .  
     [0011] Cap  2  and surface  3  are preferably plastic, which may be reinforced with glass fiber or another material. These components are injection molded.  
     [0012] An elastic compression-accommodating stop  7  is positioned below cap  2  and around piston rod  5 . Stop  7  ensures that the rod will not be forced all the way through its potential stroke when subjected to a powerful impact, but will be resiliently braked.  
     [0013] As will be evident from FIGS. 2 and 3, bellows  1  is forced against and sealed off gas tight from cap  2  and surface  3  by tensioned bands  8 , and cap  2  is sealed off gastight from piston rod  5  and from surface  3  and cylinder  4  by O rings  9  and  10 .  
     [0014] As will be evident from the detail, FIG. 2, upper O ring  9  is accommodated in an axial recess in cap  2  that opens toward upper eye  6 . The inner edge of O ring  9  rests against piston rod  5 . The recess is dimensioned to deform the ring radially, resulting in tension that ensures a reliable seal.  
     [0015] The end of piston rod  5  next to eye  6  is provided with a collar  11  that accommodates cap  2 . Between cap  2  and collar  11  is a disk  12  that closes off the recess axially. This arrangement tensions upper O ring  9  in that direction. Disk  12  is provided with at least one and preferably with several radial slits that divide it into segments. The disk is secured at its outside circumference by tensioned hooks or by an outer bead  13 .  
     [0016] How the seal is assembled will now be specified. The air cushion and dashpot are fastened together, cap  2  positioned some distance below collar  11 . Upper O ring  9  is inserted into the recess and disk  12  below bead  13  segment by segment. Cap  2  is slid against collar  11 , permanently and reliably fixing it gas tight, axial fixation being ensured by the pressure inside the cushion.  
     [0017] Surface  3  is fastened to cylinder  4  as represented in FIG. 3. Lower O ring  10  is accommodated in the open recess in surface  3  and radially tensioned against the cylinder. Ring  10  is axially tensioned by a ring  14  that, like disk  12 , includes at least one and preferably several radial slits that divide it into segments. Here as well, ring  14  is secured axially by tensioned hooks or by a bead  15  at the lower end of surface  3 .  
     [0018] In one version of the strut that differs from the embodiment illustrated in FIG. 3, surface  3  or a similar closing and fastening component is not sealed off.