Abstract:
The housing of a shock absorber is constructed to include an inner chamber surrounded by an outer chamber. The inner chamber is divided by the piston to which the piston rod is connected into two portions. One of these portion has a number of orifices that fluidly connect that portion to the outer chamber. A piston slidably and movably fitted along the length of the outer chamber divides the outer chamber into two compartments, one of which is in fluid communication with the portion of the inner chamber to which it is connected by means of the orifices. An incompressible fluid is provided in the fluidly interconnected compartment and portion. A biasing force acts against the piston in the outer chamber by means of a pressurized gas provided in the other compartment of the outer chamber. With the shock absorber thus constructed, when the piston rod moves, the piston to which it is connected would force an exchange of fluid between the inner chamber and the outer chamber, which acts as a reservoir. Both the size of the orifices and the pressure of the gas that acts against the piston in the outer chamber contribute to defining the stiffness of the shock absorber, i.e., how much dampening is to be effected to the movement of the piston rod relative to the housing. Another embodiment of the shock absorber partitions the outer chamber into three compartments, with the two end compartments being in fluid communication with the inner chamber. An alternative embodiment of the shock absorber is constructed with coacting pairs of plunger/bore and plunger/cavity for enhancing the damping effect of the shock absorber.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of application Ser. No. 09/204,351 filed Dec. 4, 1998, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to shock absorbers and more particularly a shock absorber that utilizes different fluids for isolating or cushioning the ride of a vehicle to which the shock absorber is coupled. 
     BACKGROUND OF THE INVENTION 
     A suspension system for a vehicle typically includes the use of shock absorbers, shock absorbing struts and/or suspension springs to provide a cushioned ride for the driver and the passengers, if any, of the vehicle. A conventional shock absorber has a chamber filled with hydraulic oil in which a piston connected to a piston rod is moved. The viscosity of the oil in the cylinder provides damping for the movement of the piston rod relative to the cylinder so that any vibration or bump to either the cylinder or the piston rod that result from sudden jolts to the vehicle is modulated. 
     A second type of shock absorber consists of gas shocks that utilize pressurized gases for damping the movement of the piston rod. Yet a third type of suspension system comprises a combination of both oil and gas. For this type of suspension system, there is provided an external reservoir for the oil that is separate from the shock absorber cylinder. In this reservoir, there is stored, in addition to the oil, a pressurized gas that provides a biasing force against the oil so that, when oil is needed in the cylinder, the oil in the reservoir is forced by the pressurized gas to fill up the cylinder. When under pressure in the cylinder, the excess oil is forced out of the cylinder and stored in the reservoir. 
     Such external oil reservoir suspension system is taught for example in U.S. Pat. Nos. 4,593,921 and 5,486,018. These systems work well. However, due to its bulkiness, such system requires a large amount of space which may not be available for certain types of vehicles such as for example snowmobiles. Moreover, due to the need for the extra reservoir and the conduits necessary for connecting the reservoir to the shock absorber, the cost for such system is much higher and therefore could not be justified in most types of vehicles. Furthermore, due to the extra valves and controls that are required to regulate the flow of fluid between the shock absorber and the reservoir, not only is the cost high, the maintenance for such system likewise is greater than that required for a typical suspension system. Lastly, the chances of a breakdown for such suspension system are increased due to the additional components required. 
     SUMMARY OF THE INVENTION 
     The present invention shock absorber uses a combination of different types of fluids for effecting damping. In particular, the present invention shock absorber looks like a conventional shock absorber from the outside but is constructed to have an inner chamber and an outer chamber in concentric relationship with the inner chamber. For example, the outer chamber is constructed to surround at least a portion of the inner chamber. The inner chamber is filled with an incompressible fluid such as for example a hydraulic oil. A number of orifices are provided between the inner chamber and the outer chamber so as to enable fluid communication between the inner and outer chambers. A piston rod extends through an opening at one end of the inner chamber and is coupled or bolted to a piston that fits within the inner chamber in a fluid tight manner so as to separate the inner chamber into two portions. At the portion of the inner chamber where the orifices are located there is provided the incompressible fluid such as for example the hydraulic oil. 
     Concentrically fitted about the inner chamber is a moveable piston that provides a fluid tight seal within the outer chamber. This piston seal in the outer chamber, like its inner chamber counterpart, also separates the outer chamber into two portions or compartments. The compartment that is in fluid communication with the inner chamber by means of the orifices is likewise filled with hydraulic oil, while the compartment separated from the oil filled compartment is filled with a pressurized gaseous fluid. 
     By adjusting the pressure of the gas provided in the gas compartment of the outer chamber, a desired stiffness could be obtained for the shock absorber. To further define the stiffness of the shock absorber, the flow rate of the oil between the inner chamber and the outer chamber can be regulated by adjusting the size of the orifices that provide the fluid communicative passage between the inner chamber and the outer chamber. Such adjustment may be made by fitting to at least one of the orifices a conventional needle valve. Thus, the movement of the piston rod relative to the shock absorber cylinder is damped by the hydraulic oil in the inner chamber, the flow rate by which the oil is exchanged between the inner and outer chambers, and the pressurized gas that provides the bias force against the hydraulic oil. 
     The shock absorber of the present invention is further provided with an air cushion assembly in the form of an elastomeric boot that sealingly covers the portion of the piston rod that extends from the cylinder body. When the elastomeric boot, or bag, is pressurized with the appropriate amount of gaseous fluid such as for example air, an additional damping attribute is provided. To prevent the mounting bracket to which the piston rod is connected from collapsing into the shock absorber cylinder, a spring is fitted about the piston rod between the mounting bracket and the body of the cylinder. An additional spring may be provided about the portion of the piston rod within the inner chamber so as to prevent the rod from collapsing against the opening when the portion of the piston rod within the inner chamber is moved towards the opening. 
     A second embodiment of the shock absorber of the instant invention has the outer chamber thereof partitioned by a pair of moveable pistons into three separate compartments. The portions of the inner chamber that are separated by the piston connected to the piston rod in turn each have a number of orifices for forming fluid communication passages with their corresponding end compartments of the outer chamber. Thus, as the piston rod is moved by the bumps that the vehicle which the shock absorber is coupled to encounters, the oil in the inner chamber is exchanged with both end compartments of the outer chamber, with one of those end chambers storing the oil forced out of the inner chamber while the other end compartment outputting oil to the inner chamber, to thereby provide a balancing but yet damping influence on the vehicle. 
     Another embodiment of the shock absorber of the instant invention utilizes particular cavities or bores that coact with plunger mechanisms for providing additional damping attributes to the shock absorber. In particular, a cavity and a bore could be strategically formed in the inner chamber of the housing, and also in the mounting bracket of the shock absorber assembly. Corresponding puncher mechanisms are integrated to the piston of the piston rod and also to the housing so that when the plunger mechanism at the piston coacts or mates with the cavity formed inside the inner chamber, a damping resistance force is built up to act against the movement of the piston, thereby. damping the movement of the piston rod relative to the housing of the shock absorber. Such resistance force adds damping to the shock absorber in the event that the piston rod is being pulled away from the housing of the shock absorber. 
     In the event that the piston rod and the housing are being pushed toward each other, the bore formed at the mounting bracket will coact with a plunger mechanism formed at the housing so as to generate a resistance force when the plunger mechanism at the housing mates with the bore at the mounting bracket. Again, a resistance force is generated to provide damping for the shock absorber assembly, in this instance when the shock absorber assembly is being compressed. 
     It is therefore an objective of the present invention to provide a shock absorber that is highly effective in that it uses a number of interacting fluids for defining its stiffness. 
     It is another objective of the present invention to provide a shock absorber that has an outside appearance that looks substantially like a conventional shock absorber and yet contains therewithin an oil reservoir that prior art shock absorbers do not have. 
     It is yet a further objective of the present invention to provide a shock absorber that has the damping attributes of a combination air and oil shock isolation system but yet at the same time is structurally small enough to fit into small vehicles such as for example snowmobiles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned objectives and advantages of the present invention will become apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side view of the shock absorber of the instant invention; 
     FIG. 2 is a cross-sectional view of the shock absorber of the instant invention; 
     FIG. 3 is another cross-sectional view of the shock absorber of the instant invention equipped with an air spring subassembly; 
     FIG. 4 is a second embodiment of the shock absorber of the instant invention; 
     FIG. 5 is a cross-sectional view of an improved embodiment of the shock absorber of the instant invention in the extended position; and 
     FIG. 6 is a cross-sectional view of the improved embodiment of the shock absorber of the instant invention shown in compression. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 2, a shock absorber  2  of the instant invention is shown to have a main body that comprises a housing  4  having extending therefrom a mounting bracket or anchor means  6 . Mounting bracket  6  is meant to be coupled to a first part of a vehicle such as for example the frame thereof. Housing  4  has at its outer end an opening  8  through which a piston rod  11  extends. 
     As best shown in FIG. 2, housing  4  includes an inner chamber  10  through which a portion of piston rod  11  is moveable. The end of piston rod  11  that resides in inner chamber  10  is coupled, per its end, to a piston  12  that is sealingly fitted within inner chamber  10 . Since piston  12  is fixedly mounted to end  14  of piston rod  11 , when piston rod  11  moves longitudinally along axis  16  of shock absorber  2 , piston  12  likewise moves with it. And since piston  12  sealingly fits within the interior circumferential surface of inner chamber  10 , it separates inner chamber  10  into two portions, namely portion  18  that is interposed between the top surface  20  of inner chamber  10  and the upper surface  22  of piston  12 , and portion  24  which is interposed between lower surface  26  of piston  12  and the end surface  28  of inner chamber  10 . 
     Inner chamber  10 , at least a portion thereof, is shown to be surrounded by an outer chamber  30  in coaxial relationship therewith. For the embodiment shown in FIG. 2, a piston  32  is concentrically mounted about inner chamber  10  within outer chamber  30  and is slidable therealong. With the appropriate sealing gaskets, such as for example  34 , piston  32  partitions outer chamber  30  for the FIG. 2 embodiment into two counterparts  36  and  38 . O-ring seals  40  and  42  isolate compartment  36  from the environment outside of shock absorber  2 . 
     Returning to inner chamber  10 , note that portion  24  thereof has at its lower portion a plurality of orifices  44  each forming a fluid communication passage between portion  24  of inner chamber  10  and compartment  38  of outer chamber  30 . A conventional type of valve, for example a needle point valve, designated  46 , is fitted to at least one of the orifices so that the flow rate of fluid between portion  24  and compartment  38  can be regulated. 
     To isolate portion  18  from the environment, a seal  48  is provided at the neck of housing  4  relative to opening  8 . As a consequence, even though piston rod  11  is moveable coaxially along axis  16 , portion  18  of inner chamber  10  nonetheless is isolated from the outside environment. 
     The portion of piston rod  11  that extends beyond opening  8  has its end integrated to an anchor means such as for example a mounting bracket  50  that has a bore  52 , through which mounting bracket  50  can be bolted to another part of a vehicle by means of a bolt. Bracket  50  has a flange extension  54  whereat an air inlet  56  is provided. The purpose of air inlet  56  will be discussed with reference to FIG.  3 . 
     An incompressible fluid such as for example a hydraulic fluid is provided in inner chamber  10 , and specifically in portion  24  thereof. This incompressible fluid likewise is provided in the compartment, namely compartment  38 , of outer chamber  30  that is in fluid communication with portion  24 , via orifices  44 . 
     For the FIG. 2 embodiment of the instant invention shock absorber, in compartment  36  there is provided another fluid such as for example a pressurized gas. The pressure of the gas provided in compartment  36  can be regulated by means of some valve, not shown, so that a force is continuously being biased against piston  32 , which in turn continuously forces the hydraulic oil in compartment  38  into portion  24  of inner chamber  10  by means or orifices  44 . And since the hydraulic oil within portion  24  of inner chamber  10  acts against surface  26  of piston  12 , a desired stiffness of shock absorber  2  can be obtained by setting the pressure of the gas within compartment  36  to a predetermined amount. 
     By adjusting the flow rate of the fluid between portion  24  and compartment  38 , the stiffness of shock absorber  2  can also be regulated. Thus, the pressure of the gas provided in compartment  36 , as well as the size of the opening of each of the orifices  44 , can both contribute to defining the stiffness of shock absorber  2 . 
     In operation, when a bump is encountered by the vehicle to which the shock absorber of the instant invention is mounted, a relative movement is effected between piston rod  11  and housing  4 . Consequently, assuming that the movement of piston  12  is away from opening  18 , then piston  12  would force the hydraulic oil within portion  24  of inner chamber  10  into compartment  38  by way of orifices  44 . Note that when additional fluid is forced by the movement of piston  12  from portion  24  into compartment  38 , piston  32  within outer chamber  30  is moved in a direction toward the neck of housing  4 . The pressurized gas in compartment  36  naturally acts against the movement by piston  32  to thereby damp its movement. The net effect of course is that the ride provided to the driver and passengers, if any, in the vehicle is cushioned. 
     Another feature of the instant invention is shown in FIG.  3 . For this embodiment and the to be discussed embodiment shown in FIG. 4, all components that are the same as those shown in FIGS. 1 and 2 are labeled the same. 
     Continuing, note that the embodiment of the shock absorber of the instant invention as shown in FIG. 3 comprises an elastomeric tube means, such as for example a rubber boot  56  positioned to cover the portion of piston rod  10  that extends beyond opening  8 . Elastomeric tube  56  is fixedly coupled to flange  54  by way of a nut  58  or equivalents thereof. The other end of elastomeric tube  56  is similarly secured to an extension  61  of housing  4 , although the nut or equivalents thereof used for securing that end of elastomeric tube  56  to housing  10  is not shown for the sake of simplicity. Since tube  56  is elastomeric, it can expand or contract with the movement of piston rod  11 . By way of air inlet  57 , a fluid, such as for example air, can be pumped into elastomeric tube  56  under pressure so that the inflated elastomeric tube  56  acts as an air spring to further enhance the shock absorbing ability of shock absorber  2 . 
     To prevent the collapse of piston rod  11  to inner chamber  10 , a coil spring  60  is provided about piston rod  11 , and interposed between bottom surface  62  of flange  54  and surface  64  of extension  60  of housing  4 . With coil spring  60  thus situated, even when the vehicle to which the shock absorber  2  of the instant invention is mounted comes upon a bump suddenly, such sudden shock would not cause piston rod  11  to collapse into housing  10 . 
     For the embodiment shown in FIG. 3, the stiffness of shock absorber  2  is contributed by the hydraulic oil or any other equivalent incompressible fluid in portion  24  of inner chamber  10  and compartment  38  of outer chamber  30 , the pressurized gas in compartment  36  of outer chamber  30 , and the air cushion provided by the elastomeric bag  56 . It should be appreciated that the stiffness can be defined by regulating either the amount or the pressure of any one of those components. 
     For the FIG. 3 embodiment, a coil spring  66  can be added about piston rod  11  at the portion thereof that is inside of inner chamber  10 . Spring  60  further prevents the collapse of piston rod  11  when piston rod  11  is suddenly pulled in a direction away from the closed end of inner chamber  10 . With spring  66  in place, piston  12  is prevented from coming into contact with surface  68  of inner chamber  10  even were piston rod  11  to be pulled suddenly away from the closed end of inner chamber  10 . 
     FIG. 4 illustrates another embodiment of the instant invention shock absorber. As before, inner chamber  10  is partitioned by piston  12  into 2 portions  18  and  24 . But unlike the earlier embodiments, outer chamber  30  now has two circumferential pistons, namely piston  32  and newly added piston  68 . Each of pistons  32  and  68  is slidably movable along the length of outer chamber  30 , which in turn is divided into three compartments, namely the previous end compartments  36  and  38 , as well as a new central or middle compartment  70 . For the FIG. 4 embodiment, compartment  36  is filled with an incompressible fluid such as for example a hydraulic oil. Portion  24  of inner chamber  10  likewise is filled with the same incompressible fluid. And orifices  72  which are similar to orifices  44  are introduced to the wall that separates inner chamber  10  and outer chamber  30  so that fluid communication passages are established between portion  24  and compartment  36 . For the FIG. 4 embodiment, a pressurized gaseous fluid is provided into central compartment  70  so that biasing forces are asserted against both pistons  32  and  68  toward both ends of housing  4 . 
     In operation, the shock absorber of the FIG. 4 embodiment has the movement of piston rod  11  relative to housing  4  damped by the hydraulic oil in portions  18  and  24 . For example, if piston rod  11  were to move towards the closed end of inner chamber  10 , the fluid in portion  24  would flow from orifices  44  into compartment  38 . At the same time, the fluid in compartment  36  is fed, by means of orifices  72 , into portion  18 . The sizes of orifices  72  are likewise adjustable so that the flow rate of the fluid between portion  18  and compartment  36  can be regulated. 
     In the converse scenario, were piston rod  11  to move piston  12  in the direction towards opening  8 , then the fluid in portion  18  will be forced into compartment  36  while the fluid in compartment  38  of outer chamber  30  is fed into portion  24  of inner chamber  10 . With the configuration provided in the FIG. 4 embodiment, the relative movement between piston rod  11  and housing  4  is readily damped. 
     For the FIG. 4 embodiment, the factors that contribute to the regulation of the desired stiffness of shock absorber  2  include the amount of pressurized gas in central compartment  70 , the flow rate that the respective sets of orifices  44  and  72  set for the exchange of fluid between the two end compartments  36 ,  38  of outer chamber  30  with the two portions  18 ,  24  of inner chamber  12 , as well as the air cushioning provided by elastomeric boot  56 . For the sake of simplicity, spring  66  shown in FIG. 3, which can also be placed around the portion of piston rod  11  within portion  18  of the FIG. 4 embodiment, is not shown in FIG.  4 . 
     Another embodiment of the present invention shock absorber or damping device is shown in the cross-sectional views as illustrated in FIGS. 5 and 6. The same components, or equivalents thereof, for the shock absorber  80  shown in FIGS. 5 and 6 that are the same as those components. As illustrated in FIGS. 1-4 are labeled the same. 
     FIG. 5 shows shock absorber  80  being in its extended position in which mounting bracket  50  and housing  4  have moved away from each other to their respective most distant positions, as designated by the expansion arrows  82 . FIG. 6, on the other hand, per signified by compression arrows  85 , illustrates mounting bracket  50  and housing  4  having moved towards each other so as to compress the shock absorber assembly to its most compact configuration. For ease of illustration and understanding, spring  66  shown in FIG. 3 is not shown in either of FIGS. 5 and 6. 
     For the embodiment of the shock absorber of the present invention as illustrated in FIGS. 5 and 6, there is a bore  84  formed at the side of mounting bracket  50  that faces housing  4 . As further shown, an elastomeric tube or boot  56  has one end thereof secured to mounting bracket by means of its flange extension  54  threadedly coacting with a nut  58 . The other end of elastic boot  56  is mounted to flange  86  of housing  4 , and secured thereto by means of a coacting threaded nut  88 . Thus, elastic boot  56  acts as an enclosure means for enclosing the portion of piston rod  11  that extends beyond inner chamber  10  of housing  4 . Since elastomeric boot  56  is flexible, a gaseous fluid such as for example air could be input via port  56  to a space  90  that is enclosed by elastomeric boot  56 . The gaseous fluid input to space  90  has a predetermined pressure. Note that bore  84  is an extension of space  90 . 
     For the embodiment shown in FIGS. 5 and 6, housing  4  has further extending from the side that opposes mounting bracket  50  an extension  92  that has a dimension that corresponds to the opening of bore  84 . Extension  92  could also be considered as an extension of inner chamber  10 . In any event, the respective dimensions of bore  84  and extension  92 , which acts as a plunger that mates with bore  84 , could be varied depending on the amount of resistance force that is desired, when plunger  92  mates with bore  84 . This is due to the fact as housing  4  and mounting bracket  50  are moved relatively towards each other, the gaseous fluid in space  90  tends to be compressed so that the pressure in space  90  tends to increase as plunger  92  moves closer and closer towards bore  84 . 
     In fact, by empirical studies, when the front surface  94  of plunger  92  reaches the entrance or mouth  96  of bore  84 , the pressure in space  90  becomes equal to the pressure inside bore  84 . And as housing  4  and bracket mount  50  continue to move towards each other so that plunger  92  continues to advance into bore  84 , a correspondingly increasing pressure is built up inside bore  84 , so that a proportionally greater resistive force acts against plunger  92  to thereby enable shock absorber  80  to provide an ever increasing cushioning effect for the vehicle to which shock absorber  80  is mounted. Such compressive damping is due to the fact that the space in bore  84  becomes ever decreasing due to the advancement of plunger  92 . 
     As best shown in FIG. 6, the embodiment of the damping device shown in FIGS. 5 and 6 has a cavity  98  that is formed as an extension of inner chamber  10 . Further, piston  100  of shock absorber  80  of FIGS. 5 and 6, unlike piston  12  of the earlier embodiments, is configured to have at least one passage  102  extending therethrough so as to effect a fluid communication path between portion  18  and portion  24  of inner chamber  10 . Thus, when inner chamber  10  is filled with a fluid such as for example an incompressible hydraulic oil, when shock absorber  80  is in its compressive mode, as shown per FIG. 6, the fluid in portion  24  will pass through passage  102  to portion  18 , per shown by directional arrows  104 . 
     On the other hand, in the expanding mode as shown in FIG. 5, the fluid in portion  18  will flow through passage  102  to portion  24  of inner chamber  10 , per shown by directional arrow  106 . By adjusting the diameter of passage  102 , the speed with which piston  100  traverses along inner chamber  10  could be regulated, as the amount of fluid that flows through passage  102  in inner chamber  10  relates to the amount of damping the fluid has on the movement of piston  100 . 
     Piston  100  has mounted thereto or extending therefrom a member  108  that acts as yet another plunger for the embodiment of the shock absorber of the present invention as shown in FIGS. 5 and 6. Plunger  108  has a dimension that is configured to correspond with the opening of cavity  98  that faces it so that plunger  108  could readily mate with cavity  98 . 
     Similar to the coaction between plunger  92  and bore  84 , when bracket mount  50  and housing  4  are moved relatively away from each other, plunger  108  extending from piston  100  is moved by piston rod  11  towards cavity  98 . Again, by empirical studies and calculation, by the time that face  110  of plunger  108  reaches substantially the mouth  112  of cavity  98 , the pressure of the fluid in inner chamber  10  and the pressure of the fluid remaining in cavity  98  are substantially equaled. Note that as plunger  108  and cavity  98  are further moved relatively towards each other, the fluid in inner chamber  10  tends to flow from portion  18  to portion  24 , as indicated by directional arrows  106  shown in FIG.  5 . Moreover, the fluid also tends to flow from portion  18  to compartment  36  of outer chamber  30  via passages  114 . 
     And as plunger  108  further advances into cavity  98 , the openings to passages  114  are covered by the side wall of plunger  108 . Accordingly, the pressure of the fluid inside cavity  98  increases in proportion to the distance that plunger  108  has advanced into cavity  98 . This increasing resistive pressure therefore provides damping against the movement of plunger  108 , and therefore the movement of piston  100  and of course the movement of piston rod  11 . As a consequence, a cushioning effect is provided to the vehicle to which shock absorber  80  is mounted when shock absorber  80  is in the expanding mode as shown in FIG.  5 . 
     Although the embodiment shown in FIGS. 5 and 6 provides for the coaction of plunger  92  with bore  84 , both of which are outside inner chamber  10 , it should be appreciated that additional cavities similar to cavity  98  could be formed at the other side of inner chamber  10 , such as for example at the bottom of inner chamber  10  as shown in FIG.  5 . Similarly, an additional plunger could be added to piston  100  in place of the nut  116  that secures piston  100  to piston rod  11 . Thus, instead of plunger  92  coating with bore  84  in the compressing mode as shown in FIG. 6, the additional plunger added to piston rod  11  could coact with the additional cavity that is formed at the bottom of inner chamber  10  to provide damping for shock absorber  80  as discussed above with respect to plunger  92  and bore  84 . Of course, in place of only the replacement plunger and cavity, plunger  92  and bore  84  could continue to coact with each other in conjunction with the additional pair of plunger and cavity in inner chamber  10  so as to provide even more damping for shock absorber  80 . The amount of damping in turn could further be regulated by varying the dimension of the respective sets of plunger/bore and/or plunger/cavity. 
     Similar to the embodiments of the present invention as shown in FIGS. 1-4, the embodiment of the shock absorber shown in FIGS. 5 and 6 also has a separator piston  32  that partitions outer chamber  30  into at least two compartments, namely compartment  36  and compartment  38  as shown. As discussed above, inner chamber  10  and outer compartment  36  are filled with a fluid such as for example incompressible hydraulic oil. To provide additional damping, a gaseous fluid under pressure is input to compartment  38 . The pressurized air in compartment  38  tends to react against the hydraulic oil in compartment  36 , and therefore inner chamber  10 . Of course, instead of the hydraulic oil filling inner chamber  10  and compartment  36  and a pressurized gas filling compartment  38 , the reverse is also applicable in that inner chamber  10  and compartment  36  could instead be filled with a pressurized gas while compartment  38  is filled with the incompressible hydraulic oil. 
     Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter described throughout this specification and shown in the accompanying drawings be interpreted as illustrative only and not in a limiting sense. Accordingly, it is intended that the invention be limited only by the spirit and scope of the hereto appended claims.