Patent Publication Number: US-11376913-B2

Title: Shock absorber incorporating a floating piston

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/962,106, filed Apr. 25, 2018, which is a continuation of U.S. patent application Ser. No. 15/264,808, filed Sep. 14, 2016, now U.S. Pat. No. 9,981,712, which is a continuation-in-part of U.S. patent application Ser. No. 14/465,944, filed Aug. 22, 2014, now U.S. Pat. No. 9,731,574, which claims the benefit of U.S. Provisional Application No. 61/869,095, filed Aug. 23, 2013. These prior applications are hereby incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     (Not Applicable) 
     REFERENCE TO AN APPENDIX 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to suspension components on vehicles. More particularly, the present disclosure relates to a shock absorber with a gas spring seal arrangement with reduced friction during compression for use on bicycles. 
     Reducing friction in the compression stroke may improve suspension response and allow for finer control of compression damping. These improvements are of particular interest for off-road cycling, where the combination of light component weight and suspension compliance is highly valued. 
     Shock absorbers that support the weight of the vehicle with compressed gas instead of coil or leaf springs may be attractive for applications where the weight of components must be kept as low as possible. Moreover, gas spring shocks may allow for convenient adjustability of the spring rate of the suspension, in some cases by increasing or decreasing the volume of gas within the shock. Both of these advantages have made gas spring shock absorbers a popular choice for mountain bikes. However, precisely because the ratio of vehicle-to-passenger weight may be low for bicycles, jounce may be transmitted efficiently and may be felt keenly by the cyclist. Where terrain is rugged, as in off-road cycling, it may be desirable for the bicycle&#39;s suspension to be as responsive as possible. The difference in responsiveness between gas-sprung and coil-sprung shocks has proven great enough to limit the use of gas-sprung shocks in off-road cycling. 
     Turning to  FIGS. 1-4 , a conventional gas spring shock may be seen. A conventional gas spring shock absorber  10  for lightweight vehicles, including bicycles, employs a piston  16  with a gas seal  35  that engages a cylinder  12 . As the seal  35  on the piston  16  moves against the wall of the cylinder  12  during compression, the gas trapped in a compression chamber  22  between the seal  35  and the closed end  32  of the cylinder  12  offers progressively greater resistance to compressive movement as a simple function of rising pressure against the sectional area of the piston  16  and seal  35 . Secondarily, this rising gas pressure causes the piston seal  35  to press with progressively greater force against the cylinder  12 . The frictional adhesion of the seal  35  to the cylinder wall must be overcome before the shock absorber  10  will compress, decreasing responsiveness. 
     If an O-ring seal (not shown) is used on the piston of a conventional gas spring design, the contact area of the seal with the cylinder surface will be relatively large. The area of O-ring contact varies with pressure in the gas spring chamber, since pressure forces the O-ring axially toward one end of its gland and into conformity with the square-cornered sectional profile formed by the gland and cylinder wall. The relatively large contact patch of the O-ring under pressure adds significantly to the adhesion of the seal to the cylinder. 
     A u-cup or “X”-section seal (as shown in  FIGS. 1-4 ) will have a smaller area of contact with the cylinder compared to an O-ring. However, in order to contain gas pressure reliably, the projecting lip  35   a  of such a seal must be angled toward the cylinder in the direction of compression and in the direction of its own movement in relation to the dynamically sealed surface. The angular abutment of the seal lip against the cylinder wall  12  drives the pressure of the seal material at the contact patch to high values during compression. The chisel-action of the seal lip creates significant adhesion of the seal material to the cylinder wall, partially offsetting the advantage of a smaller area of contact as compared with an O-ring. 
     The need therefore exists for a gas spring shock absorber with reduced adhesion of the dynamic gas containment seal during the compression stroke, thereby improving responsiveness. 
     Further, in some prior embodiments, cavitation may occur in the damping portion of the shock absorber. The occurrence of cavitation creates a less desirable, rougher ride. Accordingly, the need exists for a shock absorber where gas pressure may be used to minimize or eliminate cavitation by increasing pressure on the substantially incompressible fluid in a damping chamber. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, a shock absorber for a vehicle includes a first end, a second end, and a dynamic gas seal. The first end may have an interior wall and may be adapted to be mounted to one of the frame and a first wheel of the vehicle. The second end may be reciprocally and slidably mounted to the first end. The second end may be adapted to be mounted to the other of the frame and the first wheel of the vehicle. A substantially gas-tight interior gas spring chamber may be defined between the first end and the second end. Gas pressure in the interior gas spring chamber may bias the first end and the second end away from one another. The dynamic gas seal may be attached to the first end. The dynamic gas seal may have at least one lip engaging the second end, thereby creating a substantially gas-tight barrier between the first end and the second end. Movement of the plunger into the interior gas spring chamber may reduce the size of the interior gas spring chamber by compressing gas in the chamber. This decrease in the interior volume of the interior gas spring chamber may cause the gas pressure in the interior gas spring chamber to rise in proportion to the decreased volume. Movement of the plunger out from the interior gas spring chamber may increase the size of the interior gas spring chamber and diminish the pressure on gas in the chamber. This increase in the interior volume of the interior gas spring chamber may cause the gas pressure in the interior gas spring chamber to fall in proportion to the increased volume. The dynamic gas seal may be the only dynamic seal attached between the first end and the second end and capable of creating a substantially gas-tight barrier between the first end and the second end. 
     The dynamic gas seal may further include a base portion disposed at a free end of the first end. The at least one lip of the dynamic gas seal may extend both radially and axially away from the base portion. The at least one lip may also sealingly contact the outer surface of the second end. Friction between the at least one lip and the second end may be lower when the plunger moves into the interior gas spring chamber than when the plunger moves out from the interior gas spring chamber. The at least one lip may extend axially farther than it does radially. 
     The vehicle may be a bicycle. The shock absorber may further include a hydraulic damper defined substantially within the second end. The hydraulic damper may further include a damper chamber within the second end. Air pressure from the interior gas spring chamber may pressurize fluid within the damper chamber. The hydraulic damper may further dampen movement of the plunger. 
     A suspension system may include a first suspension element, a second suspension element, and a dynamic seal. The first suspension element may include an interior wall. The second suspension element may be capable of reciprocating relative to the first suspension element and may have an exterior wall that slidingly interfits with and is capable of reciprocating relative to the first suspension element. The dynamic seal may have at least one lip and may minimize the escape of gas from within an interior gas chamber defined between the first suspension element and the second suspension element. The dynamic seal may be mounted on the first suspension element. The dynamic seal may be the only dynamic seal fixed to the first suspension element and capable of creating a substantially fluid-tight barrier between the first suspension element and the second suspension element. The interior wall of the first suspension element may fit closely with the exterior wall of the second suspension element regardless of the reciprocal position of the first suspension element relative to the second suspension element. The interior wall of the first suspension element may have a consistent circumference along its length. 
     The dynamic seal may further include a base portion disposed at a free end of the first suspension element. The at least one lip of the seal may extend both radially and axially away from the base portion. The at least one lip may sealingly contact an exterior wall of the second suspension element. Friction between the at least one lip and the second suspension element may be lower when the two suspension elements move relatively in one direction than when the two suspension elements move relatively in a second direction. The at least one lip may extend axially farther than it does radially. 
     The vehicle may be a bicycle. The suspension system may further include a hydraulic damper defined substantially within the second suspension element. The hydraulic damper may further include a damper chamber within the second suspension element. Air pressure from the interior gas chamber may pressurize fluid within the damper chamber. Fluid pressure from the damper chamber may pressurize air from the interior gas chamber. 
     In one embodiment, a shock absorber for a vehicle includes a first end, a second end, a first piston, a second piston, and a floating piston. The first end may be annular along at least a portion of its length and may terminate at a first cap. The first end may at least partially define a gas spring chamber containing gas. The second end may be annular along at least a portion of its length and may terminate at a second cap. The first end and the second end may be configured to telescopically slidingly interfit with one another. The second end may at least partially define a damping chamber containing a substantially incompressible fluid. A first piston may be disposed in fixed relationship to the second end. Movement of the first piston within the first end may affect the gas in the gas spring chamber. A second piston may be disposed in fixed relationship to the first end. Movement of the second piston within the second end may affect the substantially incompressible fluid in the damping chamber. A floating piston may have a first side and a second side. The first side of the floating piston may be in fluid communication with the gas in the gas spring chamber and the second side of the floating piston may be in fluid communication with the substantially incompressible fluid in the second chamber. The vehicle may be a bicycle. 
     The floating piston may be substantially disc shaped. The floating piston may be positioned within the second end. 
     The floating piston may be substantially annular. The floating piston may surround a shaft attached to the first end. The second piston may be attached to the shaft. 
     The damping chamber may include a first cylindrical chamber, a second cylindrical chamber and an annular chamber. The damping chamber may be configured with a first valve allowing the substantially incompressible fluid to flow from the cylindrical chamber to the annual chamber during a compression stroke. The damping chamber may be configured with a second valve allowing the substantially incompressible fluid to flow from the cylindrical chamber to the annual chamber during a rebound stroke. The second valve may be substantially annular. The second cylindrical chamber may be adjacent the floating piston. 
     The gas spring chamber may include a first cylindrical chamber, a second cylindrical chamber, and an annular chamber. The annular chamber may allow passage of gas between the first cylindrical chamber and the second cylindrical chamber. The second cylindrical chamber may be adjacent the floating piston. 
     The floating piston may be configured to transmit pressure from the gas in the gas spring chamber to the substantially incompressible fluid in the damping chamber. The pressure from the gas in the gas spring chamber against the floating piston may be adequate to minimize cavitation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a side view of a prior art gas spring for a vehicle suspension; 
         FIG. 2  is an end view of the spring of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the spring of  FIG. 1  taken along line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is a detailed view of the area shown by a dashed circle in  FIG. 3 ; 
         FIG. 5  is a side view of one embodiment of a vehicle suspension according to the present disclosure; 
         FIG. 6  is an end view of the suspension of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of the suspension of  FIG. 5  taken along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is a detailed view of the area shown by a dashed circle in  FIG. 7 ; 
         FIG. 9  is a side view of another embodiment of a dynamic gas seal; 
         FIG. 10  is a cross-sectional view of an alternative embodiment of the suspension; 
         FIG. 11  is a cross-sectional view of another alternative embodiment of the suspension; 
         FIG. 12  is a cross-sectional view of the embodiment of  FIG. 11  taken on line  12 - 12  of  FIG. 11 ; 
         FIG. 13  is a perspective view of another alternative embodiment of the suspension; 
         FIG. 14  is an end view of the embodiment of  FIG. 13 ; 
         FIG. 15  is a cross-sectional view of the embodiment of  FIG. 13  taken along line  15 - 15  of  FIG. 14 ; 
         FIG. 16  is a cross-sectional view of the embodiment of  FIG. 13  taken along line  16 - 16  of  FIG. 14 ; 
         FIG. 17  is a cross-sectional view of the embodiment of  FIG. 13  taken along line  16 - 16  of  FIG. 14 , but with the shock absorber in a compressed condition; 
         FIG. 18  is a cross-sectional view of the embodiment of  FIG. 13  taken along line  18 - 18  of  FIG. 13 ; 
         FIG. 19  is a perspective view of one embodiment of the membrane assembly used in the embodiment of  FIG. 13 ; 
         FIG. 20  is a cross-sectional view of an embodiment showing an alternative embodiment of membrane assembly; and 
         FIG. 21  is a cross-sectional view of the embodiment of  FIG. 21  in compressed condition. 
     
    
    
     In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or terms similar thereto are often used. They are not limited to direct connection, but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In this detailed description, various terms relating to direction may be used. The elements discussed herein relate to a bicycle. Because, in its operable position, a bicycle is oriented generally vertically, i.e., perpendicular to the ground, the direction terms refer to the position of an element relative to gravity when the bicycle is in its operable position. Accordingly, for example, the term “downwardly” refers to the direction towards the ground when the bicycle is in its operable position, and the term “forwardly” relates to a direction towards a front wheel of the bicycle when it is in its operable position. Further, the terms “inboard” and “outboard” may be used. The term “inboard” describes a position between one item and a vertical plane substantially bisecting the bicycle. The term “outboard” describes a position of an object further from the vertical center plane of the bicycle. In addition, the terms “bicycle” and “bike” are used herein interchangeably. A person having ordinary skill in the art will understand that if something is referred to as one, it can refer to the other. 
     In the present disclosure, the suspension structure may be described as it relates to a bicycle. However, the suspension structure described in the present embodiments may instead be applied to other vehicles. The present suspension structure may be used with vehicles having a different number of wheels, for example. The suspension structure may be used in connection with a motorized vehicle. 
     The present embodiments may reduce seal adhesion in a gas spring shock absorber. In some embodiments, the gas-compressing element may be a plunger or large-diameter blind rod slidingly engaging a seal contained in the cylinder. The lip of the u-cup that forms the dynamic gas containment seal may be angled toward the gas spring chamber so that rising pressure pushes the seal progressively harder against the surface of the plunger, but because the plunger surface moves compressively in the same direction in which the lip of the seal is biased, there is no accompanying chisel-action of the seal lip to compound the pressure at the contact patch and contribute undesirably to adhesion. By eliminating a structural contributor to seal adhesion (“stiction”), the present invention may be more responsive to bumps than is a conventional gas spring shock absorber. 
     Turning now to  FIG. 5 , a shock absorber or suspension system  110  may be seen. The suspension system  110  may have a first housing member, portion or end  112  and a second housing member, portion or end  114 . A first eye hole  124  may extend from a closed end  140  of the first portion  112 . A second eye hole  126  may extend from a closed end  142  of the second portion  114 . In some vehicles, one of the first eye hole  124  and the second eye hole  126  may be directly or indirectly secured to a vehicle frame (not shown) in conventional fashion. The other of the first eye hole  124  and the second eye hole  126  may be secured directly or indirectly to a vehicle wheel (not shown) in conventional fashion. 
     As may be seen most clearly in  FIG. 7 , the suspension system may include two components. The first is a conventional hydraulic damping portion  144  and an air spring portion  146 . While various components are illustrated of the hydraulic damping portion  144 , these components are relatively conventional. The second end  114  may be annular along at least a portion of its length and may terminate at a second cap  708 . The hydraulic damping portion  144  may, for example, include a second piston  706  that may extend from and be disposed in a fixed relationship to the first end  112 . In some embodiments, a shaft  123  may have a first end  712  attached to the first end  112  and a second end  714  attached to the second piston  706 . The second end  114  may at least partially define a damping chamber  704  that may contain or be at least partially filled with a substantially incompressible fluid, such as oil. The damping chamber  704  may be configured so that the substantially incompressible fluid remains within the second end  114 . In many embodiments, the shaft  123  may be positioned such that a first portion  716  of the shaft  123  may be within the gas spring chamber  122  and surrounded by gas and a second portion  718  of the shaft  123  may be within the damping chamber and surrounded by substantially incompressible fluid. Because the first end  112  and the second end  114  telescopically slide with respect to one another in functioning as a shock absorber, the proportion of the shaft  123  that is within each of the gas spring chamber  122  and the damping chamber  704  may vary depending on the relative position of the first end  112  and the second end  114 . Many other configurations of hydraulic damping may be substituted therefor by a designer or other person having ordinary skill in the art. Accordingly, these components are not further described in detail. 
     Turning now to the air spring portion  146 , it may be seen that the first portion or first end  112  may include an inner wall  148  and the second portion  114  may include an outer wall  158 . The first end  112  may be annular along at least a portion of its length and may terminate at a second cap  710 . The inner wall  148  and the outer wall  158  may be configured to be of similar shape and size, while allowing the inner wall  148  and the outer wall  158  to telescopically slidingly interfit with one another to allow the first portion  112  and the second portion  114  to reciprocate relative to one another. 
     The first portion  112  may terminate in a free end  162 . The free end  162  may be open to allow the insertion of the second portion  114 . The second portion  114  may terminate in a plunger or other closed end structure  164 . An interior gas spring chamber  122  may be defined between the first portion  112  and the second portion  114 . The gas spring chamber  122  may be defined between the inner wall  148  of the first portion  112  and the plunger  164 . The gas spring chamber  122  may be filled with any desirable gas through a conventional port to a desired pressure level. The pressure in the gas spring chamber  122  may desirably be selected to be sufficient to bias the plunger  164  away from the closed end  140  of the first end  112 , thereby biasing the first end  112  and second end  114  relatively away from one another. The plunger  164  may be a first piston. The first piston  164  may extend from and be disposed in a fixed relationship to the second end  114 . A portion of the first piston  164 , such as the end face  165  of the first piston  164 , may be in contact with gas in the gas spring chamber  122 . 
     When the wheel of the vehicle encounters an obstacle, the impact may be at least partially absorbed by the suspension element  110 . The impact may cause the plunger  164  to move toward the closed end  140  of the first portion  112 . This movement may reduce the size of the gas chamber  122 , thereby causing the gas in the gas chamber  122  to compress and increasing the gas pressure in the chamber  122  in proportion to the reduction in the interior volume of the chamber  122  caused by the plunger. Upon removal of the impact force, the gas pressure force may exceed the impact force and move the plunger  164  away from the closed end  140  of the first portion  112 . This movement may cause an increase in the size of the gas chamber  122  and a decrease in the gas pressure in the chamber  122  in proportion to the increase in the interior volume of the housing by the plunger  164 . 
     In many embodiments, it is desirable for there to be only one gas spring chamber. In contrast to the prior art embodiment shown in  FIGS. 1-4 , no supplemental chamber is used between the plunger  16  and the cap  30 . In the prior art embodiment, there is included an outward-facing flange  31  on the second portion  14  and an inward-facing flange  33  on the first portion  12 . This set of flanges cooperated to create a first gas cylinder  22  and a second gas cylinder  23 . The second gas cylinder  23  is often used to oppose extension of the first and second portions relative to one another. It is also noted that in such a design, there are two dynamic seals used between the first portion  12  and the second portion  14 . One dynamic seal is attached to the first portion  12  on its inward-facing flange  33  and contacts the outer surface of the second portion  14 . A second dynamic seal is attached to the second portion  14  on its outward facing flange  31  and contacts the inner surface of the first portion  12 . 
     In the present embodiment, instead of including cooperating flanges, there may be no need for a secondary gas cylinder. The outer circumference of the second portion  114  may be substantially the same along its length. Similarly, the inner circumference of the first portion  112  may be substantially the same along its length. This close fit may allow for a minimum of binding between the parts. 
     Other features of the device are also conventional and are illustrated. For example, in  FIG. 7 , there is illustrated a structure  700  that allows for adjustment of air pressure within the gas spring chamber  122 . This structure  700  may incorporate a variety of static seals that may serve to contain air pressure within the interior gas chamber  122 . Similarly, there is illustrated a structure  702  that allows for adjustment of hydraulic pressure within the damper chamber  704 . This structure  702  may also incorporate a variety of static seals that may serve to contain air pressure within the damper chamber  704 . 
     In some embodiments, it may be desirable to include a structure that serves to keep the pressure of the substantially incompressible fluid  720  and the pressure of the compressible fluid  722  in equilibrium. In some embodiments, it may be desirable to incorporate a membrane assembly  724  positioned between substantially incompressible fluid  720  and the compressible fluid  722  in a manner that does not interfere with the movement of the first piston  164  and the second piston  706 . It is desirable for the membrane assembly to be sealingly engaged with a portion of the shock absorber to minimize or prevent the introduction of substantially incompressible fluid  720  into the air spring chamber  122  and of compressible fluid  722  into the damping chamber  704 . In the embodiment shown in  FIGS. 7 and 8 , the membrane assembly  724  is shown as being positioned in an annular chamber  726  that may radially surround the damping chamber  704 . The membrane assembly  724  may include a first edge  728  that may be sealingly engaged to the second end  114  adjacent the first piston  164 . The membrane assembly  724  may also include a second edge  730  that may be sealingly engaged to the outer wall  158  of the second end  114 . While this configuration is shown, the membrane assembly  724  may be attached in other locations as well on the shock absorber. A person having ordinary skill in the art can select an appropriate attachment structure and location depending on the materials selected for the membrane  732  and the desired structures in the remainder of the shock absorber. 
     In some embodiments, it may be desirable to include a bushing  121  adjacent the first piston  164 . The bushing  121  may have slots or passageways (not shown) oriented generally in an axial direction which allow compressible fluid  722  to enter the compressible fluid passageway  734  and contact a first face or side  736  of the membrane  732 . In addition, in some embodiments, it may be desirable to include a compression ring  738  adjacent the second edge  730  of the membrane assembly  724 . The compression ring  738  may include one or more passageways that allow the substantially incompressible fluid to flow from the first supplemental chamber  740  through the second supplemental chamber  742  and into the substantially incompressible fluid passageway  744  and contact a second face or side  746  of the membrane  732 . The relative positions of these structures may be more clearly seen in  FIGS. 7 and 8 . 
     The flexible membrane  732  may be annular, as is shown in  FIGS. 7 and 8 . However, in some configurations, it may be desirable for the flexible membrane to extend only partially around the circumference of the circumference of the second end  114 . 
     The flexible membrane  732  may serve as a barrier between the gas spring chamber  122  and the damping chamber  704 , because the first edge  728  and the second edge  730  are sealingly engaged to other structures. This allows the first side  736  to be in fluid communication with one of the chambers, in this embodiment the gas spring chamber and the second side  730  to be in fluid communication with the other chamber, in this case the damping chamber  704 . 
     The membrane  732  may be permitted to move in a generally radial direction, such as the radial direction  745 . The first edge  728  and the second edge  730  may remain in sealing engagement with the shock absorber. However, the remainder of the barrier  732  may be permitted to deform to minimize or substantially equalize any pressure or force difference between the compressible fluid  722  in the gas spring chamber  122  and the substantially incompressible fluid  720  in the damping chamber  704 . By moving in this way, the barrier  732  may serve to maintain the pressure in the gas spring chamber  122  and the pressure in the damping chamber  704  substantially in equilibrium. 
     As an example, during a compression stroke, the first piston  164  may move into the first or gas spring chamber  122  towards the cap  710 . This movement may reduce the volume of the first chamber  122 , thereby compressing the substantially compressible fluid  722  in the first chamber  122  and the compressible fluid passageway  734 . This pressure increase in the compressible fluid passageway may increase the pressure or force on the first face  736  of the flexible membrane  732  and may tend to urge the membrane to deform in a radial direction  746  towards the axis  168 . However, at the same time, the second piston  706  may move into the damping or second chamber  704  towards the second cap  708 . This movement may displace the substantially incompressible fluid  722  within the first chamber  704  and through the first supplemental chamber  740  through the second supplemental chamber  742  and into the substantially incompressible fluid passageway  744 . When the substantially incompressible fluid  722  contacts the barrier  732 , the pressure on the second face  746  of the flexible membrane  732  may increase and may tend to urge the membrane to deform in a radial direction  746  away from the axis  168 . The deformation of the flexible membrane  732  may be governed, therefore, by the relative pressures within the gas spring chamber  122  and the damping chamber  704 . The flexible membrane therefore may be able to minimize pressure differences between the chambers and thereby to maintain the pressures substantially in equilibrium. 
     Turning now to  FIG. 8 , a more detailed view may be seen of the seal  150   b  that is attached and extends between the first portion  112  and the second portion  114 . The seal  150   b  may include a base portion  160   a  that may be inserted into or otherwise secured to a finger  160  disposed at or adjacent the free end  162  of the first end  112 . The seal  150   b  may further include at least one lip portion  166  that extends both axially (along the axis  168  of the suspension system  110 ) and radially (towards the axis  168  of the suspension system  110 ). In some embodiments, it may be desirable for the at least one lip portion  166  to extend axially a greater distance than it extends radially. The seal  150   b , and in many embodiments, the lip portion  166 , may be configured to sealingly engage the outer surface  158  of the second portion  114 . The use of such a seal may minimize the escape of gas from the gas spring chamber  122 . The lip portion  166  may have a thickness  802  and the base  160   a  may have a thickness  804 . The thickness  802  of the lip portion  166  may be less than about half of the thickness  804  of the base  160   a . The lip portion  166  may have a length  806 , and the base  160   a  may have a length  810 . The length  806  of the lip portion  166  may be less than about half of the length  810  of the base  160   a . In many embodiments, it may be desirable for a free end  812  of the lip portion  166  to engage the second housing member  114 . In many embodiments, the lip portion  166  may be axially deformable to allow axial movement, particularly of the free end  812  towards and away from the axis  168 . 
     An alternative embodiment of the seal may be seen in  FIG. 9 .  FIG. 9  illustrates a seal  950   b  that has a base portion  960   a . The seal  950   b  also includes a first lip  966  and a second lip  967 . As may be seen in  FIG. 9 , the first lip  966  and the second lip  967  may be of similar size and shape and may project from the base portion at substantially the same angle. However, a designer may choose to vary the thickness and angle of protrusion of each of the lips  966 ,  967  away from the base portion  960   a . The lips may each extend both radially and axially from the base portion and may extend the same or different lengths radially and axially. Further, any number of lips may be used instead of those illustrated in  FIGS. 5-10 . The embodiments shown are merely exemplary. 
     The configuration of the seal  150   b  in  FIG. 8  may allow for improved relative reciprocation of the first portion  112  and the second portion  114 . When the first portion  112  moves towards the second portion  114  (reducing the size of the gas spring chamber  122 ), the lip portion may deform in an inward direction relative to the axis  168  (away from the second portion  114 ) and minimize the surface area of the seal that contacts the second portion  114 . This inward deformation may cause the seal to take a chisel shape that may allow for adequate containment of the gas. In the orientation shown in  FIG. 8 , the compression stroke will involve the first end or portion  112  moving towards the left, towards the second end or portion  114 . As may be apparent, when the first end  112  moves towards the second end, the lip portion  166  may deform outwardly and partially into the cavity  170  within the seal  150   b . This deformation may minimize contact and friction between the seal  150   b  and the outer surface  158  of the second end  114 . This deformation may allow the compression stroke to occur with a minimum of friction between the seal  150   b  and the second end  114 . 
     However, during the rebound stroke, the seal  150   b  has an opposite effect. When the first end  112  moves away from the second end  114  (towards the right in  FIG. 8 ), the lip portion  166  may move inwardly (towards the axis  168 ). This inward movement may create an increased drag or friction between the seal  150   b  and the second end  114 . This friction may prevent or minimize the effects of premature rebound of the shock absorber. 
     The precise design of the seal  150   b  and its attachment to the first end  112  may be modified by a person having ordinary skill in the art. While the seal  150   b  is attached to a finger  160  adjacent a dust guard (wiping seal)  153  at the free end  162  of the first end  112 , this structure may be modified. For example, the finger  160  may be configured differently. The finger  160  may be thicker or thinner than that shown. It may be positioned at a different angle relative to the axis  168 . It may be curved or have any other desirable profile. 
     The seal  150   b  may be secured adjacent the free end  162  in a number of different ways. The seal  150   b  may be affixed to the first end  112  by an adhesive. Alternatively, it may be positioned within a cavity, such as the cavity  172 , without any adhesive. Alternatively, it may be secured with a fastener. Other methods and structures for attaching or securing the seal  150   b  in or to the first end  112  are within the capabilities of a person having ordinary skill in the art. 
     The relative size and shape of the seal  150   b  and the apparatus as a whole may also be modified by a person having ordinary skill in the art. A designer will be able to modify the size and shape of the seal  150   b , along with the extents of its axial and radial extensions in order to produce a desired friction. Further, the seal  150   b  may be made from a variety of materials capable of substantially producing a seal to enclose air within the shock absorber  110 . A designer is able to select an appropriate material to provide an appropriate durability, adhesion, and friction, based on the designer&#39;s criteria. In some embodiments, the material may be selected from nitrile, polyurethane, and fluorocarbon. In some embodiments, the material of the seal may have a Shore A hardness between about 60 and about 90. 
     In many embodiments, the dynamic seal  150   b  may be the only dynamic seal attached to the first end  112  capable of creating a substantially fluid-tight barrier between the first end  112  and the second end  114 . Other seals may, of course be present and may be attached to the first end  112 . For example, the dust wiping seal  153  may also be secured adjacent a free end  162  of the first end  112 . However, the dust wiping seal  153  is not capable of creating a substantially fluid-tight seal between the first end  112  and the second end  114 , due to its orientation and purpose. As also noted above, there may be static seals elsewhere in the design that may be attached to the first end  112  and that may contribute to the creation of a substantially gas-tight chamber  122 . As will be described below in connection with  FIG. 10 , there may be some embodiments where a passageway is created through or around the plunger  164  to create an interaction between the interior gas spring chamber  122  and the damper chamber  704 . In such embodiments, additional dynamic seals may be incorporated into the design. However, these dynamic seals are not attached directly to the first end  112  and do not serve to create a substantially gas-tight barrier directly between the first end  112  and the second end  114 . Accordingly, such other seals are attached differently and may serve very different purposes than that of the dynamic gas seal  150   b.    
     The remaining features of the design may also be modified as a designer wishes. The present embodiments may be used with a variety of hydraulic dampers. The design shown may be modified in a variety of ways known to a designer of ordinary skill to achieve the desired damping characteristics. 
     For example, an alternative embodiment is shown in  FIG. 10 . In the alternative shock absorber or suspension system  1000  illustrated in  FIG. 10 , there is a first end  1002  and a second end  1004 . The dynamic sealing structures  1005  and overall configuration are substantially the same as those described above in connection with  FIGS. 5-8  and this description will not be repeated here. However,  FIG. 10  illustrates a further feature that may be incorporated. 
       FIG. 10  illustrates an interior gas spring chamber  1006  defined substantially within the first end  1002  and further bounded by a plunger  1008 . The suspension system  1000  further includes a hydraulic damping chamber  1010  defined substantially within the second end  1004  and further bounded by a piston  1012 . In some embodiments, it may be desirable to incorporate a secondary gas chamber  1014  adjacent the hydraulic damping chamber  1010  and fluidly connected to the interior gas spring chamber  1006  by a gas passageway  1016 . A floating ring  1020  may be positioned between the secondary gas chamber  1014  and the hydraulic damping chamber  1010  to separate the gas and the hydraulic fluid and to allow force to be mutually created between the gas and the hydraulic fluid. In many embodiments, it may be desirable to incorporate one or more seals  1018  on the floating ring within the second end  1004  to minimize interaction between the gas and the hydraulic fluid. When a vehicle, such as a bicycle, encounters an obstacle, the first end  1002  and the second end  1004  move relatively toward one another, i.e., the free end  1024  of the first end  1002  moves left as illustrated and the free end  1026  of the second end  1004  moves right as illustrated. This movement causes the plunger  1008  to compress the gas in the interior gas chamber  1006  and the plunger  1012  to compress the fluid within the damper chamber  1010 . Upon such movement, the gas under pressure flows into the interaction chamber  1014  and presses on a first side  1022  of the floating ring  1020 . Similarly, pressure from the hydraulic fluid in the damper chamber  1010  presses on a second and opposite side  1023  of the floating ring  1020 . This pressure from each side serves to damp movement of the piston and the plunger. Accordingly, fluid pressure from the damper chamber  1010  may damp movement of the plunger  1008  into the gas chamber  1006  and gas pressure from the gas chamber  1006  may damp movement of the piston  1012  into the damper chamber  1010 . The inclusion of such an interaction chamber may, therefore, allow for better tuning of compression and rebound of the shock absorber  1000 . 
       FIGS. 10 and 11  may be compared to demonstrate different ways a shock absorber can be configured to permit a beneficial interaction between a gas spring chamber and a damping chamber. In both embodiments, gas from the gas spring chamber is in fluid communication or contact with one side of a floating piston. Substantially incompressible fluid from the damping chamber is in fluid communication or contact with an opposite side of the floating piston. In this manner, pressure from the gas in the gas spring chamber can be used to pressurize the substantially incompressible fluid in the damping chamber, thereby, among other things, minimizing or preventing vacuum bubbles within the substantially incompressible fluid. 
     As previously described, the shock absorber  1000  in the embodiment of  FIG. 10  may include a first end  1002  and a second end  1004 . The first end  1002  and the second end  1004  are configured to slidingly interfit with or be telescopic with one another. The first end  1002  may be annular along at least a portion of its length and may terminate in a first cap. The first cap may include an eye  1024  that may be used to secure the first end  1002  to a vehicle (not shown). The first end  1002  may at least partially define a positive gas spring chamber  1006 . The gas spring chamber  1006  may be filled with gas to a conventional pressure in a conventional manner. The second end  1004  may be annular along at least a portion of its length and may terminate in a second cap. The second cap may include an eye  1026  that may be used to secure the second end  1004  to a different portion of a vehicle (not shown). The second end  1004  may at least partially define a damping chamber  1010 . Upon compression, a first piston  1008  secured or otherwise disposed in a fixed relationship to the second end  1004  may move towards the first end  1002 . This movement of the first piston  1008  may affect the gas in the gas spring chamber  1006 . In many embodiments, the movement of the first piston  1008  may compress the gas in the positive gas spring chamber  1006 . Simultaneously, a second piston  1012  secured or otherwise disposed in a fixed relationship to the first end  1002  may move towards the second end  1004 . This movement of the second piston  1012  towards or within the second end  1004  may affect the substantially incompressible fluid in the damping chamber  1010 . In many embodiments, the movement of the second piston  1012  may create a displacement of oil or other incompressible fluid in the damping chamber  1010 . This oil displacement is done in a conventional manner with valving in the piston or in the second end  1004  to allow the substantially incompressible fluid to move from one damping chamber to the other. 
     The shock absorber  1000  may further include a floating ring or piston  1020  having a first side  1022  and a second side  1023 . Gas in fluid communication with the positive gas spring chamber  1006  may be capable of contacting the first side  1022  of the floating piston  1020 . Substantially incompressible fluid in fluid communication with the damping chamber  1010  may be capable of contacting the second side  1023  of the floating piston  1020 . The floating piston  1020  may be responsive to the relative pressures of the gas in the positive gas spring chamber  1006  and of the substantially incompressible fluid in the damping chamber  1010  and may be permitted to move to maintain the pressures substantially in equilibrium. 
     As shown in  FIG. 10 , the air spring chamber  1006  may include a first substantially cylindrical chamber  1050 , a secondary chamber or interaction chamber or second substantially cylindrical gas chamber  1014 , and an annular chamber  1016 . Additional chambers or passageways may be included in fluid communication between these chambers, if desired or deemed appropriate by a person having ordinary skill in the art, such as the passageways  1052 . Gas within the gas spring chamber  1006  is permitted to move without restriction between the first substantially cylindrical chamber  1050 , the second substantially cylindrical gas chamber  1014 , and the annular chamber  1016 . In many embodiments, such as the illustrated embodiment, gas may flow freely between the chambers and passageways. In other embodiments, one or more valves may be incorporated within the gas spring chamber  1006 . Gas within the second cylindrical gas chamber  1014  may be in contact with one side of the floating piston  1020 , such as the first side  1022  as illustrated in this embodiment. 
     During a compression stroke, the first end  1002  and the second end  1004  may telescopically slide towards one another. The first piston  1008  may move into the gas spring chamber  1006 . This motion of the first piston  1008  may cause gas to move between the sub-chambers of the gas spring chamber  1006  and may also increase the pressure in the gas spring chamber  1006 . This fluid movement and pressure increase may increase the pressure of the gas in the second cylindrical chamber  1014  against the first side  1022  of the floating piston  1020 . At the same time, the second piston  1012  may move into the damping chamber  1010 . The movement of the second piston  1012  may cause the opening of a valve within the second piston  1012  to create a damping of the movement of the shock absorber  1000 . Such valving and damping is well known by persons having ordinary skill in the art and is not further described in detail. One embodiment of relevant valving is shown in  FIG. 10  and identified as  1054 . The pressure applied by the gas in the gas spring chamber  1006  to the floating piston  1020  may minimize or prevent vacuum bubbles from forming (i.e., cavitation) in the fluid of one or more damping chambers  1010  as the second piston  1012  moves during extension and compression of the shock absorber  1000 . The prevention of vacuum bubbles in the damping fluid may be desirable to maintain a substantially consistent damping force, as is known in the art. In addition, varying the gas pressure within the gas chamber  1006  may vary the tension on the seal  1018  of the floating piston  1020  that may be overcome in order for the floating piston  1020  to move and permit the shock absorber  1000  to compress. In this manner, gas pressure from the gas spring chamber  1006  may be used to affect the damping of the shock movement. 
     A person having ordinary skill in the art and a related user can easily adjust the shock absorbing and damping characteristics of the shock absorber  1000  merely by adjusting the air pressure within the gas spring chamber  1006 . There is an interrelationship between the pressure in the gas spring chamber  1006  and the pressure in the damping chamber  1010  through the equalizing effect and movement of the floating piston  1020  (as will be described in greater detail below). Accordingly, by adding or removing gas from the gas spring chamber  1006  alone, the damping characteristics will also change as described above. This interrelationship, particularly by allowing adjustment of the pressure of the gas in the gas spring chamber  1006  through a conventional Schrader valve open to the gas spring chamber  1006 , may allow a user to easily adjust these characteristics. 
     A similar configuration may be seen in  FIGS. 11 and 12 . The shock absorber  1100  in the embodiment of  FIG. 11  may include a first end  1102  and a second end  1104 . The first end  1102  and the second end  1104  may be configured to slidingly interfit with or be telescopic with one another. The first end  1102  may be annular along at least a portion of its length and may terminate in a first cap. The first cap may include an eye  1124  that may be used to secure the first end  1102  to a vehicle (not shown). The first end  1102  may at least partially define a positive gas spring chamber  1106 . The gas spring chamber  1106  may be filled with gas to a conventional pressure in a conventional manner. The second end  1104  may be annular along at least a portion of its length and may terminate in a second cap. The second cap may include an eye  1126  that may be used to secure the second end  1104  to a different portion of a vehicle (not shown). The second end  1104  may at least partially define a damping chamber  1110 . Upon compression, a first piston  1108  secured or otherwise disposed in a fixed relationship to the second end  1104  may move towards the first end  1102 . This movement of the first piston  1108  may affect the gas in the gas spring chamber  1106 . In many embodiments, the movement of the first piston  1108  may compress the gas in the positive gas spring chamber  1106 . Simultaneously, a second piston  1112  secured or otherwise disposed in a fixed relationship to the first end  1102  may move towards the second end  1104 . This movement of the second piston  1112  towards or within the second end  1104  may affect the substantially incompressible fluid in the damping chamber  1110 . In many embodiments, the movement of the second piston  1112  may create a displacement of oil or other incompressible fluid in the damping chamber  1110 . This oil displacement may be done in a conventional manner with valving in the piston or in the second end  1104  to allow the substantially incompressible fluid to move from one damping chamber to the other. 
     The shock absorber  1100  may further include a floating piston  1120  having a first side  1122  and a second side  1123 . The floating piston  1120  may be annular and may surround a portion of a shaft  1121 . The second piston  1112  may be secured to the shaft  1121 . The shaft  1121  may also be attached to the first end  1102 . Gas in fluid communication with the positive gas spring chamber  1106  may be capable of contacting the first side  1122  of the floating piston  1120 . Substantially incompressible fluid in fluid communication with the damping chamber  1110  may be capable of contacting the second side  1123  of the floating piston  1120 . The floating piston  1120  may be responsive to the relative pressures of the gas in the positive gas spring chamber  1106  and of the substantially incompressible fluid in the damping chamber  1110  and may be permitted to move to maintain the pressures substantially in equilibrium. 
     As shown in  FIG. 11 , the damping chamber  1110  may include a first cylindrical chamber  1160 , a second cylindrical chamber  1162 , a third cylindrical chamber  1164  and an annular chamber  1166 . The damping chamber  1110  may include a first valve or set of valves  1168 , as best shown in  FIG. 12 . This first valve  1168  may be a substantially one-way valve that permits the substantially incompressible fluid to flow from the first cylindrical chamber  1160  into the annular chamber  1166 . The substantially incompressible fluid may be permitted to flow without restriction between the annular chamber  1166  and the second cylindrical chamber  1162 . The damping chamber  1110  may include a second valve or valve adjuster  1170 . This valve adjuster  1170  may control restriction of a port that permits the substantially incompressible fluid to flow from the first cylindrical chamber  1160  into the annular chamber  1166  and consequently into the third cylindrical chamber  1164  during rebound. In some embodiments, the restricting element  1172  controlled by the valve adjuster  1170  may be substantially annular. In some embodiments, the restricting element  1172  may be a sleeve. 
     During a compression stroke, the first end  1102  and the second end  1104  may telescopically slide towards one another. The first piston  1108  may move into the gas spring chamber  1106 . This motion of the first piston  1108  may increase the pressure in the gas spring chamber  1106 . This pressure increase may increase the pressure of the gas in the gas spring chamber against the first side  1122  of the floating piston  1120 . At the same time, the second piston  1112  may move into the damping chamber  1110 . The movement of the second piston  1112  may cause the opening of the first valve  1168  to create a damping of the movement of the shock absorber  1100 . The movement of the fluid within the damping chamber  1110  and its related chambers may be further affected by the pressure applied by the gas in the gas spring chamber  1106  to the floating piston  1120 . The pressure against, and movement of, the floating piston  1120  may resist movement of the substantially incompressible fluid within the damping chamber  1110 . Similarly, during a rebound stroke, pressure may continue to be applied to the substantially incompressible fluid in the damping chamber  1110  through the force on the gas in the gas spring chamber  1106  and the floating piston  1120 . The pressure applied by the gas in the gas spring chamber  1106  to the floating piston  1120  may minimize or prevent vacuum bubbles from forming in the fluid of the damping chamber  1110  in the same way as described for the embodiment of  FIG. 10 , above. Likewise, varying the gas pressure in the gas chamber  1106  may vary the tension on the seal  1118  of the floating piston  1120  that may be overcome in order to allow compressive movement of the shock absorber  1100 , also as described for the embodiment of  FIG. 10 . In this manner, gas pressure from the gas spring chamber  1106  may be used to and may affect the damping of the shock movement. 
     A further embodiment is shown in  FIGS. 13-19  and is the shock absorber  1300 . The shock absorber  1300  may include a first end  1312  and a second end  1314 . The first end  1312  and the second end  1314  are configured to slidingly interfit with or be telescopic with one another. The first end  1312  may be annular along at least a portion of its length and may terminate in a first cap  1313 . The first cap may include a first eye  1324  that may be used to secure the first end  1312  to a vehicle (not shown). The first end  1312  may at least partially define a positive gas spring chamber  1306 . The gas spring chamber  1306  may be filled with a compressible fluid  1316 , such as gas, to a conventional pressure in a conventional manner. The second end  1314  may be annular along at least a portion of its length and may terminate in a second cap  1315 . The second cap  1315  may include a second eye  1326  that may be used to secure the second end  1314  to a different portion of a vehicle (not shown). The second end  1314  may at least partially define a damping chamber  1310 . The damping chamber  1310  may be at least partially filled with a substantially incompressible fluid  1318 . 
     A first piston  1308  may be secured or otherwise disposed in a substantially fixed relationship to the second end  1314 . The first piston  1308  may include a first face or portion  1309  in contact with the compressible fluid or gas  1316  in the gas spring chamber. A second piston  1320  may be secured or otherwise disposed in a substantially fixed relationship to the first end  1312 . The second piston  1320  may have a first face or portion  1322  in contact with the substantially incompressible fluid  1318  in the damping chamber  1310 . In some embodiments, the second piston  1320  may be secured to a shaft, such as the shaft  1326 , that may be further secured to the first end  1312 . In some embodiments, it may be desirable to allow the shaft  1326  to rotate with respect to the first end  1312 , and accordingly, the shaft  1326  may be rotationally secured to the first end  1312 . 
     As may also be seen in  FIG. 17 , upon compression, the first piston  1308  may move within the first end  1312  and towards the first cap  1313 . This movement of the first piston  1308  may affect the gas  1316  in the gas spring chamber  1306 . In many embodiments, the movement of the first piston  1308  may reduce the volume and thereby compress the gas  1316  in the positive gas spring chamber  1306 . Simultaneously, the second piston  1320  may move within the second end  1314  towards the second cap  1315 . This movement of the second piston  1320  within the second end  1314  may affect the substantially incompressible fluid in the damping chamber  1310 . In many embodiments, the movement of the second piston  1320  may displace oil or other substantially incompressible fluid in the damping chamber  1310 . 
     In some embodiments, it may be desirable to include a structure that serves to keep the pressure of the substantially incompressible fluid  1318  and the pressure of the compressible fluid  1316  in equilibrium. In some embodiments, it may be desirable to incorporate a membrane assembly  1328  positioned between substantially incompressible fluid  1318  and the compressible fluid  1316  in a manner that does not interfere with the movement of the first piston  1308  and the second piston  1320 . It is desirable for the membrane assembly to be sealingly engaged with a portion of the shock absorber to minimize or prevent the introduction of substantially incompressible fluid  1318  into the air spring chamber  1306  and of compressible fluid  1316  into the damping chamber  1310 . In the embodiment shown in  FIGS. 13-19 , the membrane assembly  1328  is shown as being positioned in the annular air spring chamber  1306 . The membrane assembly  1328  may include a first edge  1330  that may be sealingly engaged to the second end  1314  adjacent the first piston  1308 . The membrane assembly  1328  may also include a second edge  1332  that may be sealingly engaged to the first end  1312 . In some embodiments, it may be desirable to allow the membrane assembly  1328  to rotate with respect to the first end  1312 , and accordingly, the membrane assembly  1328  may be rotationally secured to the first end  1312 , such as with the rotational connector  1334 . In some embodiments, when the membrane assembly  1328  is permitted to rotate relative to the first end  1312 , it may be desirable for the membrane assembly  1328  to remain in a particular rotational position with respect to the remainder of the shock absorber  1300 . Accordingly, in many embodiments, it may be desirable for the first edge  1330  to be sealingly engaged to the second end  1314  with a rotationally fixed connection. 
     While one configuration is shown, the membrane assembly  1328  may be attached in other locations as well on the shock absorber  1300 . A person having ordinary skill in the art can select an appropriate attachment structure and location depending on the materials selected for the membrane  1338  and the desired structures in the remainder of the shock absorber. In the illustrated embodiment, the membrane  1338  is annular in a roughly diamond shape along at least a portion of its length. However, in other embodiments, a different shape may be selected, depending on the desires of the designer. 
     In some embodiments, the membrane assembly  1328  may function as one side of the gas spring chamber. In such an embodiment, the compressible fluid  1316  in the gas spring chamber  1306  may contact the first face  1350  of the membrane  1338 . In addition, in some embodiments, it may be desirable for the second end cap  1315  of the second end  1314  to include one or more passageways that allow the substantially incompressible fluid to flow from the damping chamber  1310 , through the first supplemental chamber  1342  and into the substantially incompressible fluid passageway  1344  and contact a second face or side  1346  of the membrane  1338 . 
     The flexible membrane  1338  may serve as an additional barrier between the gas spring chamber  1306  and the damping chamber  1310 , because the first edge  1330  and the second edge  1332  are sealingly engaged to other structures. This allows the first side  1350  of the membrane  1338  to be in fluid communication with one of the chambers, in this embodiment the gas spring chamber  1306  and the second side  1346  to be in fluid communication with the other chamber, in this case the damping chamber  1310 . 
     The membrane  1338  may be permitted to move in a generally radial direction, such as the radial direction  1360 . The first edge  1330  and the second edge  1332  may remain in sealing engagement with the shock absorber  1300 . However, the remainder of the barrier  1336  may be permitted to deform to minimize or substantially equalize any pressure or force difference between the compressible fluid  1316  in the gas spring chamber  1306  and the substantially incompressible fluid  1318  in the damping chamber  1310 . By moving in this way, the barrier  1336  may serve to maintain the pressure in the gas spring chamber  1306  and the pressure in the damping chamber  1310  substantially in equilibrium. 
     As an example, during a compression stroke, the first piston  1308  may move into the first or gas spring chamber  1306  towards the first cap  1313 . This movement may reduce the volume in the first chamber  1306 , thereby compressing the substantially compressible fluid  1316  in the first chamber  1306 . This pressure increase in the first chamber  1306  may tend to urge the membrane to deform in a radial direction  1360  towards the axis  1368 . However, at the same time, the second piston  1320  may move into the damping or second chamber  1310  towards the second cap  1315 . This movement may displace the substantially incompressible fluid  1318  within the second chamber  1310  through the first supplemental chamber  1342  and into the substantially incompressible fluid passageway  1344 . The additional fluid adjacent the second face  1346  of the flexible membrane  1338  may tend to urge the membrane to deform in a radial direction  1360  away from the axis  1368 . The deformation of the flexible membrane  1338  may be governed, therefore, by the relative pressures within the gas spring chamber  1306  and the damping chamber  1310 . The flexible membrane therefore may be able to minimize pressure differences between the chambers and thereby to maintain the pressures substantially in equilibrium. 
     The shock absorber  1300  is shown in its fully compressed position in  FIG. 17 . When the shock absorber  1300  is in its fully compressed position, the long inner portion of the flexible membrane  1338  may also be compressed into a roughly cylindrical shape of relatively short length. The diameter of the compressed inner portion of the membrane may remain small enough to allow the outer portion of the flexible membrane to bulge radially inward and accommodate fluid displaced from the damping chambers, thereby maintaining the appropriate pressure equilibrium. 
     An alternative embodiment of a membrane structure may be seen in  FIGS. 20 and 21 . In some embodiments, it may be desirable to incorporate a membrane assembly  2028  positioned between substantially incompressible fluid  2018  and the compressible fluid  2016  in a manner that does not interfere with the movement of the first piston  2008  and the second piston  2020 . It is desirable for the membrane assembly to be sealingly engaged with a portion of the shock absorber to minimize or prevent the introduction of substantially incompressible fluid  2018  into the air spring chamber  2006  and of compressible fluid  2016  into the damping chamber  2010 . In the embodiment shown in  FIGS. 20-21 , the membrane assembly  2028  is shown as being positioned in the annular air spring chamber  2006 . The membrane assembly  2028  may include a first edge  2030  that may be sealingly engaged to the second end  2014  adjacent the first piston  2008 . The membrane assembly  2028  may also include a second edge  2032  that may be sealingly engaged to the first end  2012 . In some embodiments, it may be desirable to allow the membrane assembly  2028  to rotate with respect to the first end  2012 , and accordingly, the membrane assembly  2028  may be rotationally secured to the first end  2012 , such as with the rotational connector  2034 . In some embodiments, when the membrane assembly  2028  is permitted to rotate relative to the first end  2012 , it may be desirable for the membrane assembly  2028  to remain in a particular rotational position with respect to the remainder of the shock absorber  2000 . Accordingly, in many embodiments, it may be desirable for the first edge  2030  to be sealingly engaged to the second end  2014  with a rotationally fixed connection. 
     In some embodiments, the membrane assembly  2028  may function as one side of the gas spring chamber  2006 . In such an embodiment, the compressible fluid  2016  in the gas spring chamber  2006  may contact the first face  2050  of the membrane  2038 . In addition, in some embodiments, it may be desirable for the second end cap  2015  of the second end  2014  to include one or more passageways that allow the substantially incompressible fluid to flow from the damping chamber  2010 , through the first supplemental chamber  2042  and into the substantially incompressible fluid passageway  2044  and contact a second face or side  2046  of the membrane  2038 . 
     The flexible membrane  2038  may serve as an additional barrier between the gas spring chamber  2006  and the damping chamber  2010 , because the first edge  2030  and the second edge  2032  are sealingly engaged to other structures. This allows the first side  2050  of the membrane  2038  to be in fluid communication with one of the chambers, in this embodiment the gas spring chamber  2006 , and the second side  2046  to be in fluid communication with the other chamber, in this case the damping chamber  2010 . 
     The membrane  2038  may be permitted to move in a generally radial direction, such as the radial direction  2060 . The first edge  2030  and the second edge  2032  may remain in sealing engagement with the shock absorber  2000 . However, the remainder of the barrier  2038  may be permitted to deform to minimize or substantially equalize any pressure or force difference between the compressible fluid  2016  in the gas spring chamber  2006  and the substantially incompressible fluid  2018  in the damping chamber  2010 . By moving in this way, the barrier  2032  may serve to maintain the pressure in the gas spring chamber  2006  and the pressure in the damping chamber  2010  substantially in equilibrium. 
     As an example, during a compression stroke, the first piston  2008  may move into the first or gas spring chamber  2006  towards the first cap  2013 . This movement may reduce the volume in the first chamber  2006 , thereby compressing the substantially compressible fluid  2016  in the first chamber  2006 . This pressure increase in the first chamber  2006  may tend to urge the membrane to deform in a radial direction  2060  towards the axis  2068 . However, at the same time, the second piston  2020  may move into the damping or second chamber  2010  towards the second cap  2015 . This movement may displace the substantially incompressible fluid  2018  within the second chamber  2010  through the first supplemental chamber  2042  and into the substantially incompressible fluid passageway  2044 . The additional fluid adjacent the second face  2046  of the flexible membrane  2038  may tend to urge the membrane to deform in a radial direction  2060  away from the axis  2068 . The deformation of the flexible membrane  2038  may be governed, therefore, by the relative pressures within the gas spring chamber  2006  and the damping chamber  2010 . The flexible membrane therefore may be able to minimize pressure differences between the chambers and thereby to maintain the pressures substantially in equilibrium. 
     The shock absorber  2000  is shown in its fully compressed position in  FIG. 21 . Because this embodiment lacks the long inner portion of the flexible membrane  1338  of earlier embodiments, the flexible membrane  2038  may remain substantially in the same longitudinal position during the entirety of the stroke. The diameter of the membrane  2038  may remain small enough to allow the outer portion of the flexible membrane to bulge radially inward and accommodate fluid displaced from the damping chambers, thereby maintaining the appropriate pressure equilibrium. 
     This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.