Abstract:
A dashpot featuring amplitude-dependent shock absorption, especially intended for the wheel of a vehicle and including a hydraulically parallel cylindrical pressure-compensation chamber ( 8 ). The pressure-compensation chamber is partitioned by an axially displaceable floating piston ( 10 ). At least one face ( 25 ) of the floating piston is provided with a resilient bumper ( 18 ). 
     The object is a dashpot with a floating piston that arrives more gently at its limit inside the pressure-compensation chamber ( 8 ). 
     The bumper is accordingly accommodated in an axial hollow ( 17 ) that extends through the body ( 15 ) of the floating piston.

Description:
BACKGROUND OF THE INVENTION 
   The present invention concerns a dashpot, or shock absorber, featuring amplitude-dependent shock absorption and including a hydraulically parallel cylindrical pressure-compensation. 
   Dashpots with amplitude-dependent shock absorption have been developed for use with motor vehicle wheels in particular, to ensure that the level of shock absorption will decrease when the oscillations are both high in frequency and narrow in amplitude. A dashpot of this genus is known from EP 1 152 155 A1. The device features a hydraulically parallel cylindrical pressure-compensation chamber partitioned into two halves by an axially displaceable floating piston. At least one face of the floating piston is provided with a resilient bumper. The bumper is in the form of an O ring that fits into a groove. This is a drawback in that the bumper&#39;s performance curve is so hard that the floating piston&#39;s impact against the bottom of the pressure-compensation chamber will lead to jolts that are at least heard and in the worst case even felt inside the vehicle. The sudden impacts on the bumper also soon lead to wear. Furthermore, a hard bumper accelerates the transition between soft and hard dashpot-performance curves. This situation in turn can result in impermissibly steep acceleration of the piston rod at the transition point, perceived inside the vehicle as irritating noise or dissonant shock absorption. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is a dashpot of the aforesaid genus improved to ensure that the floating piston will arrive gently at its terminal position in the pressure-compensation chamber. 
   According to the present invention, the elastomeric bumper is accordingly accommodated in a hollow that extends axially through the body of the floating piston. This approach has several advantages. Any deformation will be distributed more uniformly over a wider area of the bumper, and hence there will be fewer local strains in the material. The performance curve can be softer. Another advantage is more reliable cementing or vulcanization to the floating piston&#39;s body. There will be less noise and less wear, considerably extending the component&#39;s life. In special applications, when the hollow through the body of the floating piston is very wide, the bumper can even be in one piece, with heads on each side that extend over each face. The bumper will accordingly be locked into position in the body of the floating piston in addition to any other means of fastening it. 
   One embodiment of the present invention features an alternative approach to shock absorption at one end of the floating piston. Here, the floating piston is provided with a central arbor that eventually enters the central hydraulic-fluid supply bore. The result is hydraulic shock absorption without the floating piston impacting the associated base of the pressure-compensation chamber. This embodiment as well ensures a soft start. The inward tapering of the arbor at one end allows adaptation of the shock absorption to individual requirements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the present invention will now be specified with reference to the accompanying drawing, wherein 
       FIG. 1  is a section through the vicinity of the working piston in a dashpot, 
       FIGS. 2 and 3  depict different versions of the floating piston, 
       FIG. 4  depicts an alternative version of the floating piston, which operates in conjunction with an associated pressure compensation chamber, 
       FIGS. 5 and 6  are sections similar to the section in  FIG. 1  with alternative versions of the pressure-compensation chamber housing, 
       FIG. 7  is a graph representing force over distance as the floating piston enters operation, and 
       FIG. 8  is a larger-scale illustration of a detail of  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a section through the vicinity of the working piston in a dashpot with, in the present case, a solid-walled cylinder. Cylinder  1  is closed at the top and bottom and charged with shock absorption fluid. Working piston  3  travels up and down inside cylinder  1  on one end of a piston rod  2 . The working piston  3  in the illustrated example is indirectly connected, and partitions cylinder  1  into two compression-decompression compartments  4  and  5 . Piston rod  2  travels into and out of cylinder  1  through a sealed port at the bottom. The fluid can flow out of one compression-decompression compartment and into the other through sloping bores  6 . The ends of sloping bores  6  are capped top and bottom by resilient stacks  7  of cupsprings, each stack  7  accordingly decelerating the flow. 
   Cylinder  1  and piston rod  2  are attached by unillustrated means to the vehicle&#39;s wheel at one end and to its chassis at the other. 
   When vibrations of narrow amplitude occur between piston rod  2  and cylinder  1 , only weak shock-absorption forces are needed to unnecessarily prevent deterioration of riding comfort, whereas the performance curve of the particular cupspring-capped valves employed will not allow corresponding compensation without simultaneously decreasing the shock-absorption force in the range of higher starting amplitudes, which would have a deleterious effect on driving dynamics. A cylindrical pressure-compensation chamber  8  is accordingly accommodated inside floating piston  10  in an extension  9  of piston rod  2  hydraulically parallel with working piston  3 . Pressure-compensation chamber  8  is partitioned into two half chambers  11  and  12  by a floating piston  10 . Half chambers  11  and  12  communicate hydraulically through ports, preferably bores  13  and  14 , with compression-decompression compartments  4  and  5 . 
   The body  15  of floating piston  10  rests radially by way of a low friction sleeve  16  against the cylindrical inner surface of pressure-compensation chamber  8 , allowing the piston to travel up and down axially inside the chamber. 
   Floating piston  10  is provided with an axial hollow  17 , in the form of a central bore in the present example. A bumper  18  in the form of a shaft with a head  19 , at each end in the illustrated embodiment, extends through hollow  17 , Each head  19  is in the form of a shallow cone, its base covering the adjacent face of body  15 . The shaft and heads in the embodiment illustrated in  FIG. 1  are in one piece and are vulcanized or molded onto the faces of floating piston  10 . 
   The bore  14  between the lower half chamber  12  of pressure compensation chamber  8  and the lower compression-decompression compartment  5  of cylinder  1  extends along the central axis of piston-rod extension  9 . As floating piston  10  comes into action accordingly, and strikes the base represented at the bottom of  FIG. 1 , bore  14  would ordinarily close too suddenly, inducing impacts in the overall system. This behavior is not desirable, and the bumper would be rapidly destroyed by the edge of the bore. The pressure-compensation end of the bore  14  is accordingly capped with an isolating disk  20 . The fluid can flow out of bore  14  and into the lower half chamber  12  of pressure-compensation chamber  8  by way of several ports  21  along the edge of isolating disk  20 . In the embodiment illustrated in  FIG. 1  as well, accordingly, floating piston  10  will be ensured of a soft start against the base, i.e. isolating disk  20  in the present case, of pressure compensation chamber  8 . This function is ensured at any event in relation to the upper base  22  by a radially outward bore  13 . Isolating disk  20  will in one alternative not be necessary if the bore  14  through a bolt  23  that working piston  3  is mounted on is a blind bore and does not extend through the lower base. In this event, the bore will communicate with the lower half chamber  12  of floating piston  10  through several supplementary channels. Since the openings into these channels are positioned radially outward in the lower base, bumper  18  will not be able to block them and will not be damaged by the edge of the openings. 
   The piston-rod extension  9  that accommodates the pressure compensation chamber  8  in  FIG. 1  is welded. Its lower end is provided with a bolt  23  whereon working piston  3  is mounted, secured by a nut  24 . 
     FIG. 2  illustrates an alternative version of floating piston  10 . The floating piston&#39;s body  15 , low-friction sleeve  16 , and axial hollow  17  are similar to the ones illustrated in  FIG. 1 . Bumper  18  on the other hand is provided with integral annular ridges  26  that rest against the faces of floating-piston body  15 . To prevent them from adhering to base  22 , each annular ridge  26  is provided with at least one radial intersection  27 . The shaft of bumper  18  does not completely occupy hollow  17 , simplifying installation in a housing with a central intake channel. Each head of bumper  18  will be thoroughly embedded in a recess provided in each face of floating piston  10 . Floating-piston body  15  will impact the base of the cylinder by way of annular ridges  26 , limiting the deformation of bumper  18  and accordingly prolonging its life. 
   The floating piston  10  illustrated in  FIG. 3  is similar to the one illustrated in  FIG. 1 . In this embodiment, however, hollow  17  is very wide, and the head is provided with a spherical bulge  19 . This species of floating piston allows bumper  18  to be separate from floating-piston body  15 , and the two components can snap together, resulting in an interlocking attachment. Floating piston  10  will accordingly be easier to adapt to various requirements. Various embodiments of bumper  18  can be combined with various embodiments of floating-piston body  15  as desired. Floating piston  10  can be cemented or vulcanized or fabricated by bicomponent plastic injection molding. The outer annular surface in this embodiment of floating piston  10  can also act as a terminating stop, limiting the extent of deformation of bumper  18 . In this event, however, the mass of the bumper will not, as in the embodiment illustrated in  FIG. 2 , be forced into the depressions in the faces of floating-piston body  15  but will mainly be deformed axially by the body as a whole. 
   The piston-rod extension  9  depicted in  FIG. 4  differs from the one depicted in  FIG. 1  in that it is not welded but screwed together. The essential difference, however, is in the terminating shock absorption. Instead of the mechanical shock absorption represented in  FIGS. 1 through 3 , that is, at least one end features hydraulic shock absorption. One face of floating piston  10  is provided with a central arbor  28  that, as the piston approaches lower base  29 , enters the bore  14  through the center of the bolt  23  that working piston  3  is mounted on. The hydraulic flow through the bore will accordingly be impeded. Arbor  28  can, as illustrated in  FIG. 4 , taper in toward its end. In this event, bore  14  will accordingly gradually close as floating piston  10  comes to rest against lower base  29 . 
   The hollow for the pressure-compensation chamber  8  illustrated in  FIG. 5  is particularly economical to produce. The hollow itself is in the form of a blind bore in the end of piston rod  2 . The bore can be conventionally produced by machining. Cold forging can also be employed. 
   It is important for the wall  31  at the end  30  of piston rod  2  to be in one piece with the piston rod. 
   Hydraulic communication between the upper half chamber  11  of pressure-compensation chamber  8  and the upper compression decompression compartment  4  of cylinder  1  is provided, as in the aforesaid embodiments, by a transverse bore  13 . 
   The bolt  23  that the working piston  3  is mounted on in a further development of this embodiment can be cold forged for example and, as illustrated in  FIG. 5 , provided with a connector flange  32 . In this event, the central bore  14  in bolt  23  is blind and does not extend through connector flange  32 . Transverse bores  33  slope through the flange and open into the blind end of central bore  14  on the one hand and, on the other, into the edge of the lower base  29  of pressure-compensation chamber  8 . 
   The floating piston  10  in the embodiment illustrated in  FIG. 5  is similar to the one illustrated in  FIG. 3 . 
   How the piston rod and its extension illustrated in  FIG. 5  are assembled will now be specified. Floating piston  10  is inserted into the blind bore that constitutes pressure-compensation chamber  8 . Connector flange  32 , which is rimmed by a wider lip  34 , is inserted into the end of pressure-compensation chamber  8 . The wall  31  that demarcates pressure-compensation chamber  8  at the bottom of end  30  is at this stage already being forced powerfully against the circumference of connector flange  32 , and the resulting joint between the wall and the flange will be tight of itself. This joint, however, is further reinforced by a weld  35 , especially a laser or electron-beam weld. 
   The tightness of the joint before welding will go far to prevent the inclusion of air during that procedure. As will be evident from  FIG. 5 , weld  35  is deeper than wall  31  is thick, enuring that the base of the joint will also melt. 
   The overflow from weld  35  is subjected to lower welding power, preventing the pokeholes that would cause weakness, especially subject to bending stress. 
   To improve the roundness tolerance between the two components, the joint is welded in at least two passes, with less power during the first. This approach minimizes heat default. Generally the welding speed will be high to keep as much heat as possible out of the work and accordingly to prevent damage to the floating piston. 
   The embodiment illustrated in  FIG. 6  is similar to the one illustrated in  FIG. 1 . The end  30  of piston rod  2  and the adjacent housing  36  for pressure-compensation chamber  8  are aligned by a centering pin  37  before being finally fastened in place by a weld  38 . This measure maintains the two components concentric. 
     FIG. 7  is a graph representing force over distance in a floating piston  10  like the one illustrated in  FIG. 3 . The piston&#39;s gentler approach to upper base  22  or lower base  29  is obvious. Before, however, the bumper can deform enough to generate a steep progressive increase  39  in force, one face  25  of floating piston  10  will have come to rest against its adjacent base  22  or  29 . The force-to-distance behavior of bumper  18  will accordingly be very sensitive to tolerances. 
     FIG. 8  is a larger-scale rendering illustrating how an isolating disk  20  can be secured in a piston-rod extension and to the bottom  40  adjacent to working-piston accommodating bolt  23  and capping lower half chamber  12 . 
   The bottom  40  in this embodiment is provided with a recess with more or less the same diameter as isolating disk  20 . The recess also has a depth  41  that exceeds the thickness  42  of isolating disk  20 . 
   Isolating disk  20  is embedded in the recess and the projecting edge  43  crimped onto it with an overhead punch  44 , reliably securing the disk to the bottom  40  of piston-rod extension  9 . The disk does not need to be secured as effectively axially because the difference in pressure between lower half chamber  12  and central bore  14  is not very great. 
   As will be evident from  FIG. 8 , punch  44  travels laterally along the inner surface of pressure-compensation chamber  8 . 
   Isolating disk  20  can be continuously or discontinuously crimped along its circumference. 
   List of Parts 
   
       
         1 . cylinder 
         2 . piston rod 
         3 . working piston 
         4 . upper compression-decompression compartment 
         5 . lower compression-decompression compartment 
         6 . sloping bore 
         7 . stack of cupsprings 
         8 . pressure-compensation chamber 
         9 . piston-rod extension 
         10 . floating piston 
         11 . upper half chamber 
         12 . lower half chamber 
         13 . transverse bore 
         14 . central bore 
         15 . body of floating piston 
         16 . low-friction sleeve 
         17 . hollow 
         18 . bumper 
         19 . bulge 
         20 . isolating disk 
         21 . port 
         22 . upper base 
         23 . working-piston accommodating bolt 
         24 . nut 
         25 . face 
         26 . annular ridge 
         27 . intersection 
         28 . arbor 
         29 . lower base 
         30 . end 
         31 . wall 
         32 . connector flange 
         33 . transverse bores 
         34 . lip 
         35 . weld 
         36 . housing 
         37 . centering pin 
         38 . weld 
         39 . increase 
         40 . bottom of piston-rod extension 
         41 . depth 
         42 . thickness 
         43 . projecting edge 
         44 . punch