Abstract:
A number of embodiments of piston sealing arrangements for shock absorbers having a hydraulic cylinder in which a piston is slidably supported to define a pair of fluid chambers. The piston is provided with a peripheral groove in which a sealing piston ring is provided. A number of different communicating passage arrangements are formed in the piston ring that communicate the exterior surface of the piston ring which engages the cylinder bore with the interior surface of the piston ring which faces the ring groove so as to balance the pressure therebetween. In each embodiment a seal is provided between the piston ring groove and the piston ring so as to preclude fluid flow from one fluid chamber to the other through the piston ring groove and the communicating passage arrangement.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a shock absorber construction and more particularly to an improved sealing piston ring arrangement for a shock absorber. 
     A common type of shock absorber used for suspension systems and other purposes employs a piston that is slidably supported within a hydraulic cylinder. The piston and/or cylinder are provided with passages that extend between opposite sides of the piston and which include an arrangement for damping the flow therethrough. This provides a hydraulic damping action, as is well known in the art. 
     With this type of arrangement, however, there is also provided a seal on the exterior surface of the piston which engages and seals with the cylinder so as to preclude fluid leakage past the seal that would permit fluid to bypass the damping arrangement mentioned. However, these types of arrangements provide certain problems, as may be best understood by reference to FIG. 1 which shows a conventional seal of the type utilized in shock absorbers. 
     FIG. 1 shows a portion of a shock absorber arrangement of the prior art type and this shock absorber mechanism is shown only partially and in cross-section to indicate the problems associated with the seal therein. The overall construction of the shock absorber in which the sealing mechanism is employed may be of any known type and such structures will be shown later in describing the preferred embodiment of the invention in FIG.  2 . 
     Nevertheless, the shock absorber includes an outer cylinder  21  which defines a cylinder bore  22  in which a piston  23  reciprocates. The cylinder  22  is filled with hydraulic fluid so as to form chambers above and below the piston  23 . In addition, flow passages are provided between the two chambers, normally in the body of the piston  23 , through which fluid may flow in a damped fashion so as to damp the suspension movement with which the shock absorber is associated. 
     In order to provide a seal and insure against leakage around this shock absorbing passage arrangement, at least one piston ring groove  24  is formed in the outer peripheral surface of the piston  23 . A piston ring  25  is provided in this piston ring groove  24 . This piston ring  25  may be of any type of construction and is pressed by its own resilience and by that of an O-ring  26  into sealing engagement with the cylinder surface  22 . The O-ring  26  is received in a groove  27  formed in the exterior surface of the piston  23  at the base of the ring groove  24 . 
     As may be seen in this Figure, if the piston  23  is forced downwardly relative to the cylinder  21  in the direction indicated by the force arrow F, the piston ring  25  will slide slightly upwardly and bottom against the upper side of the ring groove  24  of the piston  23 . 
     Thus, some fluid under pressure may enter into this area through a gap G that exists between the exterior surface of the piston  23  and the cylinder  22 . This pressure can then flow into a further gap area G 1  behind the piston ring  25 . 
     Thus, a hydraulic pressure is exerted which acts in conjunction with the pressure of ring  25  and the O-ring  26  to force the piston ring  25  into tight engagement with the surface  22  of the cylinder  21 . This restricts motion and can cause imprecise action of the shock absorber. 
     Arrangements have been proposed for reducing this effect by permitting a passage that will communicate the exterior surface of the piston ring with its interior surface. However, such passages then provide a path through which fluid may leak from one end of the piston ring to the other. Thus the shock absorbing system will be partially bypassed. 
     It is, therefore, a principal object of this invention to provide an improved piston ring arrangement that can be utilized with shock absorbers or other similar arrangements. 
     It is a further object of this invention to provide an improved piston ring arrangement wherein compressive pressure in one of the fluid chambers defined by the associated piston will not act on the piston ring to vary its sealing force with the cylinder in which it is received. 
     SUMMARY OF THE INVENTION 
     This invention is adapted to be embodied in a piston sealing arrangement for a shock absorber having a hydraulic cylinder in which a piston is slidably supported. The piston is provided with a peripheral groove in which a sealing piston ring is provided. A communicating passage arrangement is formed in the piston ring that communicates the exterior surface of the piston ring which engages the cylinder bore with the interior surface of the piston which faces the ring groove so as to balance therebetween. A seal is provided between the piston ring groove and the piston ring so as to preclude fluid flow from one fluid chamber to the other through the piston ring groove and the communicating passage arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged, cross-sectional view taken through a portion of a shock absorber constructed in accordance with a prior art type of configuration. 
     FIG. 2 is a side elevational view, with a portion broken away and shown in cross-section, of a shock absorber constructed in accordance with an embodiment of the invention and shows the general environment in which the various embodiments hereinafter described may be employed. 
     FIG. 3 is an enlarged cross-sectional view looking in the same direction as FIG.  2  and taken along the same plane and shows the shock absorber piston valving arrangement. 
     FIG. 4 is an enlarged perspective view showing the piston ring of this embodiment. 
     FIG. 5 is a further enlarged cross-sectional view taken along the line  5 — 5  of FIG. 
     FIG. 6 is an enlarged perspective view, in part similar to FIG.  4  and shows another embodiment of the invention. 
     FIG. 7 is an elevational view showing the end joint in the piston ring of this embodiment. 
     FIG. 8 is an enlarged cross-sectional view taken along the line  8 — 8  of FIG. 7 but shows the sealing ring in position in the cylinder. 
     FIG. 9 is a side elevational view, in part similar to FIG. 7, and shows a further embodiment of invention. 
     FIG. 10 is an enlarged cross-sectional view taken along the line  10 — 10  of FIG.  9 . 
     FIG. 11 is an enlarged cross-sectional view taken along the line  11 — 11  of FIG.  9 . 
     FIG. 12 is an enlarged side elevational view, in part similar to FIGS. 7 and 9 and shows a yet further embodiment of the invention. 
     FIG. 13 is an enlarged cross-sectional view taken along the line  13 — 13  of FIG. 
     FIG. 14 is an enlarged cross-sectional view taken along the line  14 — 14  of FIG.  12 . 
     FIG. 15 is an enlarged cross-sectional view taken along the line  15 — 15  of FIG. 
     FIG. 16 is an enlarged cross-sectional view taken along the line  16 — 16  of FIG. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first in detail to FIG. 2, a shock absorber and vehicle suspension unit that forms the environment in which the invention is adapted to be employed is identified generally by the reference numeral  51  and also shows a first embodiment of the invention. Although the invention is described in conjunction with a shock absorber for a wheel suspension unit of a vehicle, it should be readily apparent that the sealing ring or piston ring constructions described herein can be utilized in a wide variety of other uses, particularly those utilized to pressurize fluid chambers. 
     The shock absorber  51  includes a main cylinder unit  52  that carries a trunnion  53  at one end thereof for attachment to an associated vehicle body. The cylinder unit  52  includes a tubular body member  54  that defines a cylinder bore  55  in which a piston assembly, indicated generally by the reference numeral  56  is slidably supported. 
     The piston  56  has affixed to it a piston rod  57  and which extends through an end closure assembly, indicated generally by the reference numeral  58 , that is positioned adjacent an open end of the tubular member  54 . The opposite end thereof is closed by an integral end wall to which the trunnion  53  is affixed. 
     The end closure  58  provides a seal arrangement, in a manner to be described, so as to form an upper fluid chamber O 1  and a lower fluid chamber O 2  each of which is filled with hydraulic fluid and which are separated by the piston  56  in a manner to be described. 
     The piston rod  57  is adapted to be affixed to a suspension element for a vehicle grounding engaging element such as a vehicle wheel or the like. In addition, a spring retainer  59  is affixed to the cylinder member  52  and one end of a coil compression spring  60  bears against the spring retainer member  59 . The other end of the coil spring  60  bears against the ground engaging element, suspension unit so that as the vehicle travels along the ground and meets of obstacles, the piston  56  will move upwardly and downwardly in the cylinder bore  55 . It should be understood, of course, that the connections can be reversed, i.e., the trunnion  53  can be connected to the vehicle ground engaging element suspension unit and the piston rod  59  can be connected to the vehicle frame. 
     Continuing to refer to FIG. 2, the end closure  58  includes a piston rod guide  61  that carries a seal  62  at its lower end to affect a seal between a closure plate and the end of the cylinder bore  55 . A rod seal  63  sealingly engages the piston rod  57  and is held in place by a retainer ring  64 . Finally, a rebound stopper  65  is positioned to be engaged by a stopper holder  66  so as to engage the underside of the piston  56  to provide a snubbing action for final movement in the extreme extended position. 
     The piston  56  carries a damping arrangement that may be best understood by reference to FIG.  3  and which will now be described by reference thereto. The piston  56  is mounted on a reduced diameter end portion of the piston rod  57  and is engaged at its lower end with a spacer plate  67  that is affixed in abutment with a shoulder  68  formed at the step between the piston rod portions. 
     The piston  56  includes a main body member  69  that is formed with a piston ring groove  71  in which a piston ring and seal assembly, indicated generally by the reference numeral  72  and having a construction best shown in FIGS.  4 - 6  is mounted to affect a fluid tight seal with the cylinder bore  55 . 
     A first set of damping passages  73  extend from the lower face of the piston body  69  to the upper face so as to permit flow from the chamber O 2  to the chamber O 1  under certain conditions. A stacked leaf spring arrangement  74  valves the upper end of these passages  73  and is held in place by a nut  75  on a threaded upper end of the piston rod  57  and washers or shims  76 . This arrangement permits flow from the chamber O 2  to the chamber O 1  when sufficient force is encountered. Reverse flow, however, is precluded through the passages  73 . 
     In a like manner, a shim spring arrangement  77  is positioned on the underside of the piston body  69  and cooperates with another series of damping passages  78  that permit flow from the chamber O 1  to the chamber O 2  but preclude flow in the opposite direction. These types of damping mechanisms are well known in the art and it is believed that further description of the actual damping arrangement is not necessary to permit those skilled in the art to practice the invention. 
     Because of the fact that the piston rod  57  occupies a portion of the fluid chamber O 2 , the amount of fluid displaced from the chamber O 1  by the upward movement of the piston assembly  57  will be greater than can be accommodated in the chamber O 2 . Therefore, there is provided a makeup reservoir (not shown) that communicates with the chamber O 1  through a conduit  79 . This chamber may be partially filled with hydraulic fluid that is pressurized by an inert gas over a floating piston. 
     The construction of the shock absorber  51  as thus far described may be considered to be conventional and, for that reason, further description of it is not believed to be necessary to permit those skilled in the art to practice the invention. 
     The sealing structure provided by the piston ring assembly  72  will now be described by particular reference to FIGS. 4 and 5. As may be best seen in FIGS.  4  and the piston ring  72  is formed as an annular member, which may be split, and is formed from a suitable material such as a nylon or the like. 
     This member  72  is fitted with a clearance in the piston groove  71 . The ring member  72  has a main body  81  that has a generally cylindrical outer surface  82  in which a pair of circumferentially extending, axially spaced grooves  83  are formed. The grooves  83  are actually spaced at a distance so that they will be normally positioned on opposite sides of a further groove  84  formed in the piston at the base of the piston ring groove  71 . 
     An O-ring element  85  is positioned in this groove  84  and bears against a cylindrical inner surface  86  of the piston ring  72  so as to establish the sealing pressure between its outer surface  82  and the cylinder bore surface  55 . 
     Positioned at spaced circumferential locations around the piston ring  72  and communicating with the grooves  83  are upper and lower relief passages  87  and  88 , respectively. These passages  87  and  88  perform the function of balancing the pressure between the inner and outer surfaces  86  and  82  of the piston ring  72  so that no fluid pressure acts to augment the sealing pressure exerted by the O-ring  85 . 
     This may be understood by reference to FIG. 5 which shows a loading condition the same as that shown in FIG.  1 . This is a situation where the piston assembly  56  is being forced downwardly by a force indicated by the force vector F. 
     When this occurs, as with the prior art construction, the piston ring  72  will move upwardly in the piston ring groove  71  and engage the upper surface thereof. Hydraulic pressure can be exerted therefore through the gap at the lower end which is again indicated at G and flow into the area G 1 . behind the piston ring body  81 . 
     This fluid however, can flow through the relief passages  88  into the groove area  83  so that the pressure on both sides of the piston ring  72  is balanced and the ring sealing pressure will not be increased. However, any substantial leakage past the piston ring  72  is precluded by the O-ring seal  85 . If the forces are in the opposite direction, the pressure would be relieved in the relief passages  87  with the same effect. Thus, this embodiment reduces the drag existent with prior art constructions and solves the problem of the prior art constructions. 
     The communicating passages  87  and  88  of the embodiment just described can be eliminated and cost reduction enjoyed by utilizing an arrangement as shown in the embodiment of FIGS.  6 - 8 . The sealing ring of this embodiment is identified generally by the reference numeral  101  and has basically the same construction as the previously described ring  72 . Thus, components are the same they have been identified by the same reference numerals and will not be described again. 
     This embodiment also includes the circumferential grooves  83  and the outer surface  82  of the ring body. However, the ring body is split by a staggered split arrangement shown in these figures and which comprises a first axially-extending portion  102  that extends upwardly from the lower edge of the ring  101  and to an area engaged by the O-ring seal  85  contained within its groove  84 . Thus, this slot portion  102  serves the same function as the pressure balancing passages  88  of the previously described embodiment. 
     A further axially extending slot portion  103  extends down from the upper edge of the ring  101  and terminates at a circumferentially extending shoulder  104  that bridges the slot portions  102  and  103 . Again, the slot  103  terminates in the area engaged by the O-ring seal  85  and this replaces the pressure relief passages  87  of the previously described embodiment. Thus, this embodiment has also the same effects as the previously described embodiment. Further description of this embodiment is not believed to be necessary to permit those skilled in the art to practice the invention. 
     FIGS.  9 - 11  show a seal ring constructed in accordance with a further embodiment of the invention which is identified generally by the reference numeral  121 . This ring  121  differs from the ring  101  of the embodiment of FIGS.  6 - 8  in having a pair of grooves  122  that extend circumferentially above the lower terminus of the slot portion  103  at the shoulder  104  which provide the function of permitting fluid to flow circumferentially around the sealing ring  121  to improve its pressure balance. 
     In a like manner, a pair of lower grooves  123  are formed in the area below the slot portion  104  and these also further assist in the pressure balance. FIGS.  12 - 16  show a final embodiment in which the sealing ring is identified generally by the reference numeral  141 . This sealing ring employs a slot arrangement like the embodiment of FIGS.  6 - 8  and, therefore, components of this ring which are the same as that embodiment have been identified by the same reference numerals. 
     In this embodiment, however, the slot is formed by a three-part arrangement as best shown in FIG.  12 . Because of this, a pair of O-ring grooves, indicated by the reference numerals  84   u  and  84   l  are employed. O-rings  85   u  and  85   l  are positioned in the grooves  84   u  and  84   l , respectively. This construction appears best in FIGS.  13 - 15 . 
     A lower slot portion  141  extends upwardly to an area that terminates adjacent the O-ring  85   l  as seen clearly in FIG. 13. A circumferentially extending portion  143  is formed at the termination of the slot  142  and a further axially extending slot  144  is formed there. A pressure balance groove  145  is associated with this slot  144  and covers the area between the O-rings  85   l  and  85   u.    
     Finally, at the upper termination of the slot  144 , there is a further radially extending shoulder portion  146  that is defined at the lower terminus of a final upper slot portion  147 . The O-ring seal  85   u  is positioned at the area where the shoulder portion  146  is provided so as to provide a good seal and achieve the results aforenoted. 
     Thus, from the foregoing description it should be readily apparent that the described embodiment of the invention provide a very effective piston ring seal and on in which the sealing pressure will be maintained constant regardless of pressurization of the chambers above or below the piston ring groove. 
     It will be readily apparent to those skilled in the art that the foregoing description is that of preferred embodiments of the invention and the various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.