Patent Publication Number: US-8118144-B2

Title: Hydraulic dampers with pressure regulated control valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/958,149, filed Dec. 17, 2007, which is a continuation of patent application Ser. No. 11/228,284, filed Sep. 15, 2005, U.S. Pat. No. 7,308,976, which is a continuation of patent application Ser. No. 10/449,722, filed May 29, 2003, U.S. Pat. No. 6,978,872, which claims the benefit to U.S. Provisional Application Ser. No. 60/384,369, filed on May 29, 2002, which are incorporated herein by specific reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to hydraulic dampers which can be used independently or as part of a shock absorber, front fork or other suspension system. 
     2. The Relevant Technology 
     Dampers are used in conventional shock absorbers, front forks, and other suspension systems to dampen or absorb an impact or force applied to the suspension system. For example, a conventional damper includes a tubular housing bounding a sealed chamber. An incompressible hydraulic fluid is disposed within the chamber of the housing. One end of a piston rod having a piston mounted thereon is also disposed within the chamber. Orifices extend through the piston so that the piston can slide within the chamber of the housing as the hydraulic fluid passes through the orifices. 
     When a compressive force is applied to the damper, such as when an automobile having shock absorbers hits a bump, the force seeks to drive the piston rod into the chamber of the housing. The damper partially absorbs this force by using the force to compress the hydraulic fluid through orifices. When a rebound force is applied to the damper, such as through the application of a spring, the damper again regulates the rebound force by requiring the hydraulic fluid to pass back through the orifices in the piston in order for the piston rod to return to its original position. 
     Although conventional dampers impart some degree of damping to suspension systems, conventional dampers have significant shortcomings. For example, the damping properties of conventional dampers are directly related to the constant restriction of the hydraulic fluid flow through the orifices extending through the piston. As this variable does not change along the stroke of the piston rod, the damping properties are substantially constant independent of the force applied or the position of the piston rod. As a result, minimum damping performance is achieved. That is, what is needed in the art are dampers for suspension systems that can automatically adjust the damping characteristics throughout the range of piston movement to more efficiently dampen based on changing operating and road conditions. 
     Although attempts have been made to produce adjustable dampers, such dampers have had minimal effectiveness, are difficult and expensive to produce, and permit minimal selective adjustment based on use and condition requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1  is a cross sectional side view of one embodiment of a damper; 
         FIG. 2  is an exploded perspective view the distal end of the piston rod of the damper depicted in  FIG. 1 ; 
         FIG. 3  is an enlarged cross sectional side view of the components shown in  FIG. 2  in an assembled state; 
         FIG. 4  is a cross sectional side view of the damper shown in  FIG. 1  with the control valve in an open state; 
         FIG. 5  is a cross sectional side view of the damper shown in  FIG. 4  with the piston rod being advanced into the housing; 
         FIG. 6  is a cross sectional side view of the damper shown in  FIG. 5  with the piston rod fully advanced into the housing; 
         FIG. 7  is a cross sectional side view of the damper shown in  FIG. 6  with the piston rod being retracted out of the housing; 
         FIG. 8  is a cross sectional side view of a spring biased against the floating piston at the distal end of the damper shown in  FIG. 1 ; 
         FIG. 9  is a cross sectional side view of an inflated bladder disposed at the distal end of the damper shown in  FIG. 1 ; 
         FIG. 10  is a cross sectional side view of a flexible diaphragm disposed at the distal end of the damper shown in  FIG. 1 ; 
         FIG. 11  is a cross sectional side view of a boundary line between a hydraulic fluid and a compressible gas disposed at the distal end of the damper shown in  FIG. 1 ; 
         FIG. 12  is a cross sectional side view of an alternative embodiment of a damper having an adjusting piston; 
         FIG. 13  is a cross sectional side view of the damper shown in  FIG. 12  with the adjusting piston moved to a second position; 
         FIG. 14  is a schematic representation of a remote pressure regulated dampening system; 
         FIG. 15  is a cross sectional side view of an alternative embodiment of a damper having a fixed control valve assembly; 
         FIG. 16  is a cross sectional side view of the damper shown in  FIG. 15  with the piston rod being advanced into the housing thereof; 
         FIG. 17  is a cross sectional side view of the damper shown in  FIG. 16  with the piston rod being fully advanced into the housing; 
         FIG. 18  is a cross sectional side view of the damper shown in  FIG. 17  with the piston rod being retracted out of the housing; 
         FIG. 19  is a cross sectional side view of a twin tube damper; 
         FIG. 20  is a cross sectional side view of the twin tube damper shown in  FIG. 19  with the piston rod being advanced into the inner tube thereof; 
         FIG. 21  is a perspective view of a shock absorber; 
         FIG. 22  is an elevated front view of the shock absorber shown in  FIG. 21 ; 
         FIG. 23  is a an elevated side view of the shock absorber shown in  FIG. 21 ; 
         FIG. 24  is a cross sectional side view of the shock absorber shown in  FIG. 21 ; 
         FIG. 25  is a cross sectional view of the shock absorber shown in  FIG. 24  taken along section lines  25 - 25 ; 
         FIG. 26  is an enlarged cross sectional side view of the second end of the stem of the shock absorber shown in  FIG. 24 ; 
         FIG. 27  is an enlarged cross sectional side view of the gas volume adjuster assembly of the shock absorber shown in  FIG. 24 ; 
         FIG. 28  is a cross sectional side view of an alternative embodiment of a damper having a base valve assembly; 
         FIG. 29  is an enlarged cross sectional side view of the base valve assembly shown in  FIG. 28 ; 
         FIG. 30  is a cross sectional side view of the damper shown in  FIG. 28  with the piston rod being advanced in the housing thereof; 
         FIG. 31  is a cross sectional side view of the damper shown in  FIG. 30  with the piston rod being retracted from the housing; 
         FIG. 32  is a cross sectional side view of an alternative embodiment of the damper shown in  FIG. 28  with the floating piston being replaced by a flexible diaphragm; 
         FIG. 33  is a cross sectional side view of an alternative embodiment of the damper shown in  FIG. 28  with the base valve assembly being replaced by an alternative base valve assembly; 
         FIG. 34  is an elevated cross sectional side view of a front fork with a cartridge incorporating a damper of the present invention; 
         FIG. 35  is an elevated cross sectional side view of the front fork shown in  FIG. 34  with the piston rod being advanced into the upper tube thereof; 
         FIG. 36  is an elevated cross sectional side view of the front fork shown in  FIG. 34  with the cartridge removed, 
         FIG. 37  is an elevated cross sectional side view of the front fork shown in  FIG. 36  with the piston rod being advanced into the upper tube thereof; 
         FIG. 38  is an elevated cross sectional side view of the front fork shown in  FIG. 36  with the piston rod being retracted from the upper tube thereof; 
         FIG. 39  is an elevated cross sectional side view of a front fork having a fixed base valve in the upper tube; and 
         FIG. 40  is an elevated cross sectional side view of the front fork shown in  FIG. 39  with the piston rod being retracted from the upper tube thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to hydraulic dampers which can be used independently or as part of a shock absorber, front fork or other suspension system. Such dampers can be used in association with all types of vehicles or mechanical apparatus where it is desired to control suspension movement and/or vibration. Examples of vehicles on which the dampers can be used include bicycles, motorcycles, automobiles, all terrain vehicles, snowmobiles, airplanes, and the like. 
     Depicted in  FIG. 1  is one embodiment of a damper  10  incorporating features of the present invention. Damper  10  comprises a housing  12  having an interior surface  14  bounding a chamber  16 . Housing  12  comprises a cylindrical sidewall  18  that extends between a proximal end  20  and an opposing distal end  22 . An end wall  24  is formed at distal end  22  of sidewall  18 . A bracket  30  having a hole  32  extending therethrough is formed on end wall  24  for selectively attaching damper  10  to a structure. In alternative embodiments, bracket  30  can be replaced with any conventional attachment structure. 
     A cap  26  is removably threaded or otherwise attached onto proximal end  20  of sidewall  18 . Cap  26  has a passageway  28  centrally extending therethrough so as to communicate with chamber  16 . A piston rod  34  is slideably disposed within passageway  28  so as to extend into and outside of chamber  16 . Piston rod  34  has an exterior surface  36  extending between a proximal end  37  ( FIG. 2 ) and an opposing distal end  38 . An annular seal  40  extends between cap  26  and piston rod  34  so as to effect a sealed connection that enables piston rod  34  to freely slide relative to housing  12 . 
     Piston rod  34  comprises a base rod  42  and a bolt  44 . As depicted in  FIG. 2 , base rod  42  comprises an exterior surface  45  extending between a proximal end  46  and an opposing distal end  48 . Distal end  48  terminates at a distal end face  50 . A substantially L-shaped channel  52  (see also  FIG. 3 ) extends from distal end face  50  to exterior surface  45  at distal end  48 . 
     Bolt  44  comprises a shaft  56  having a proximal end  58  and an opposing distal end  60 . Proximal end  58  of shaft  56  terminates at a proximal end face  64 . As depicted in  FIGS. 2 and 3 , distal end  60  of shaft  56  terminates at a distal end face  66 . Encircling and radially outwardly projecting from shaft  56  at distal end  60  is a head  70 . Head  70  also has a proximal end face  72  and an opposing distal end face  74 . Distal end face  74  of head  70  is spaced proximal of distal end face  66  of shaft  56 . A channel  78  extends through shaft  56  from distal end face  66  to proximal end face  64 . A plurality of radially spaced apart ports  79  extend from channel  78  to distal end face  74  of head  70 . Removably threaded into channel  78  at distal end face  66  of shaft  56  is a jet  80  having an opening  82  extending therethrough. For reasons as will be discussed below in greater detail, jet  80  can be replaced with other jets having different sized openings. Alternatively, jet  80  can be replaced with a plug so that the only access to channel  78  at distal end  60  of shaft  56  is through ports  79 . 
     One or more flexible metal spring shims  84  are mounted on distal end face  74  of head  70  so as to encircle shaft  56  and cover the openings to ports  79 . Shims  84  are secured in place by a C-clip  86  mating with a groove on shaft  56  distal of shims  84 . In an alternative embodiment, C-clip  86  can be replaced with a washer. Jet  80  can then be formed with an outwardly projecting flange at the end thereof. As jet  80  is screwed into channel  78 , the flange biases the washer against the shims  84  so as to secure shims  84  in place. 
     During assembly, proximal end  58  of bolt  44  is threaded into distal end  48  of base rod  42  so that channels  52  and  78  are in fluid communication. The combination of channels  52  and  78  are herein referred to as rebound channel  88 . In alternative embodiments, it is appreciated that base rod  42  and bolt  44  can be integrally formed as a single member. Furthermore, bolt  44  can be replaced with a nut that threads onto the distal end of base rod  42 . 
     Depicted in  FIG. 2 , mounted on distal end  38  of piston rod  34  is a main piston  102 , a control valve assembly  100 , and a stop plate  174 . Control valve assembly  100  comprises a valve guide  104  and a control valve  106 . Main piston  102  has a substantially circular disk shape configuration with a proximal face  108 , an opposing distal face  110 , and a peripheral side  112  extending therebetween. A groove  113  is formed on peripheral side  110  so as to receive an annular seal  114  ( FIG. 3 ). In the embodiment depicted, seal  114  comprises a flexible o-ring  96  that outwardly biases an annular band  98 . Band  98  is typically comprised of Teflon. Other conventional seal configurations can also be used. It is noted that in several of the other drawings showing pistons, the annular seal has been not been shown in the peripheral groove. This was done so as to help clarify the drawings. It is appreciated that in use, however, a seal is disposed within each peripheral groove. 
     A plurality of spaced apart, elongated pressure ports  118  extend through main piston  102  from proximal face  108  to distal face  110 . Pressure ports  118  extend at a substantially constant radius from the center of main piston  102 . Disposed on proximal face  108  between each adjacent pressure port  118  is an elongated shallow pocket  120 . Each pocket extends along a radial axis aligned with the center of main piston  102 . Extending from distal face  110  of main piston  102  to each pocket  120  is a corresponding rebound port  122 . Rebound ports  122  are disposed radially inward of pressure ports  118 . A central opening  116  also extends though main piston  102 . 
     In the assembled state depicted in  FIG. 3 , piston rod  34  is passed though central opening  116  of main piston  102  so that main piston  102  encircles and radially outwardly projects from piston rod  34  proximal of head  70 . Seal  114  is biased in sealed engagement against interior surface  14  of sidewall  18  so as to enable main piston  102  to freely slide within chamber  16  as piston rod  34  is moved within chamber  16 . 
     In one embodiment of the present invention means are provided for enabling fluid flow through rebound port  122  from proximal face  108  to distal face  110  while precluding fluid flow from distal face  110  to proximal face  108 . By way of example and not by limitation, a plurality of stacked shims  124  encircle piston rod  34  and bias against distal face  110  of main piston  102 . Stacked shims  124  cover the distal opening to rebound ports  122  but do not cover the openings to compression ports  118 . A washer  126  is disposed between head  70  and stacked shims  124  so as to provide space for the outer perimeter of stacked shims  124  to flex distally. Fluid can thus travel in a distal direction through rebound ports  122  by flexing shims  124 , but is precluded from traveling in a proximal direction through rebound ports  122  as a result of shims  124 . Shims  124  thus act as a type of one-way check valve during compressive movement of piston rod  34  and pressure sensitive valves during the rebound movement of piston rod  34 . That is, the greater the fluid pressure against shims  124  during the rebound stroke, the farther shims  124  flex and the more rebound ports  122  are opened. 
     In alternative embodiments of the means for enabling fluid flow through rebound port  122 , it is appreciated that shims  124  can be replaced with any number of alternative one-way check valve designs. For example, flexible shims  124  can be replaced with a solid washer or hinged flaps that are biased against distal face  110  over rebound ports  122  by a spring. One such example is discussed below with regard to  FIG. 29 . It is noted that there are a number of different elements and alternative designs disclosed herein which incorporate flexible shims as a one-way check valve. It is appreciated that each such use of shims is intended to have a corresponding means for enabling fluid flow in a select direction and that such shims can be replaced with alternative one-way check valve designs as discussed above. 
     Depicted in  FIG. 2 , valve guide  104  comprises an annular base  130  having a proximal face  132  and an opposing distal face  134 . Projecting from distal face  132  is an annular stem  136 . Stem  136  has an outer diameter smaller than the outer diameter of base  130 . A central opening  138  extends through both stem  136  and base  130 . In the assembled state depicted in  FIG. 3 , piston rod  34  is passed through central opening  138  so that distal face  134  of valve guide  104  rests against proximal face  108  of main piston  102 . Valve guide  104  only partially covers pockets  120  so that fluid communication is still made with rebound ports  122  though pockets  120 . It is noted that valve guide  104  is locked in place by being clamped between a shoulder  181  formed on piston rod  34  and main piston  102 . In alternative embodiments, it is appreciated that valve guide  104  can be directly secured to or integrally formed with main piston  102 . 
     Depicted in  FIGS. 2 and 3 , control valve  106  has an annular peripheral side  144  extending between an annular distal face  146  and an annular proximal face  148 . Distal face  146  has a surface area smaller than the surface area of proximal face  148 . In one embodiment, the aspect ratio of the surface area of distal face  146  to the surface area of proximal face  148  is in a range between about 0.3 to about 0.6 with about 0.3 to about 0.4 being more preferred. In general, control valve  106  comprises an annular collar  150  having an interior surface  152 . An annular flange  154  radially inwardly projects from interior surface  152  of collar  150  at a proximal end thereof. Flange  154  has a proximal face  155  that terminates at an interior surface  157 . A central opening  156  extends through both collar  150  and flange  154 . 
     In the assembled state, piston rod  34  is slideably received within central opening  156  so that control valve  106  slideably mates with valve guide  104 . Specifically, in the position depicted in  FIG. 3 , collar  150  of control valve  106  encircles base  130  of valve guide  104 . An annular groove  158  is formed on interior surface  152  of collar  150  and receives an annular first seal  160 . First seal  160  biases against base  130  of valve guide  104  so as to form a slideable sealed engagement between collar  150  and base  130 . 
     Flange  154  of control valve  106  encircles stem  136  of valve guide  104 . An annular groove  162  is formed on interior surface  157  of flange  154  and receives an annular second seal  164 . Second seal  164  biases against stem  136  of valve guide  104  so as to form a slideable sealed engagement between flange  154  and stem  136 . It is noted that in several of the other drawings showing control valve assembly  100 , first seal  160  and second seal  164  are not shown in their corresponding grooves. This was done so as to help clarify the drawings. It is appreciated that in use, however, seals  160  and  164  are disposed within their corresponding grooves in each control valve assembly  100 . 
     An annular groove  166  is also formed on the interior surface of control valve  106  between first seal  158  and second seal  164 . In part, groove  166  bounds a valve chamber  170  formed between control valve  106  and valve guide  104  and which is sealed closed by first seal  158  and second seal  164 . Disposed within valve chamber  170  is a compressible gas such as air. In one embodiment, as control valve  106  is received over valve guide  104 , air is captured within valve chamber  170  at a first pressure, i.e., atmospheric pressure. In alternative embodiments, it is appreciated that a resiliently compressible member such as a spring or compressible material can also be disposed within valve chamber  170  so as to bias between valve guide  104  and control valve  106 . 
     As depicted in  FIG. 2 , annular stop plate  174  has a distal side  176  and an opposing proximal side  178 . A central opening  180  and a plurality of radially spaced apart ports  182  extend through stop plate  174  between opposing sides  176  and  178 . As depicted in  FIG. 3 , distal end  48  of base rod  42  is passed through central opening  180  such that stop plate  174  is captured between a shoulder  181  of base rod  42  and valve guide  104 . 
     Stop plate  174  functions as a stop for control valve assembly  100 . Specifically, control valve assembly  100  operates at various states between an open position and a closed position. In the closed position depicted in  FIG. 3 , distal face  146  of control valve  106  biases against proximal face  108  of main piston  102  so as to cover the proximal openings to compression ports  118 . However, a portion of pockets  120  on main piston  102  are not covered by control valve  106  or valve guide  104  so that open fluid communication is provided to rebound ports  122  through pockets  120 . As discussed below in greater detail, it is also noted that when control valve  106  is in the closed position, valve chamber  170  is collapsed so as to have a first volume. 
     Depicted in  FIG. 4 , control valve assembly  100  is in the fully open position. In this configuration, control valve  106  has slid proximally relative to valve guide  104  so that proximal face  148  of control valve  106  is biased against stop plate  174 , thereby stopping further proximal movement of control valve  106 . In this open position, control valve  106  is spaced apart from main piston  102  so that fluid is free to travel through the compression ports  118  and through a flow channel  167  formed between control valve  106  and main piston  102 . It is also noted that in the open position, distal face  155  of flange  154  of control valve  106  is spaced apart from proximal face  132  of base  130  of valve guide  104 , thereby expanding valve chamber  170  so as to have a second volume that is lager than the first volume. The pressure in valve chamber  170  is greater in the collapsed state than in the expanded state. As such, the pressure within valve chamber  170  has the natural tendency to push control valve  106  into the open position under a force corresponding to the relative pressure within valve chamber  170 . 
     Returning to  FIG. 1 , slideably disposed within chamber  16  distal of piston rod  34  is a floating piston  184 . Floating piston  184  has a peripheral side  186  that extends between a distal face  188  and an opposing proximal face  190 . A seal  192  is disposed on peripheral side  186 . Seal  192  biases in sealed engagement against interior surface  14  of sidewall  18  of housing  12  so as to enable floating piston  184  to selectively slide within chamber  16  but substantially precluding fluid or gas from passing through or around floating piston  184 . 
     Floating piston  184  divides chamber  16  into a distal compartment  196  and a proximal compartment  198 . Compartments  196  and  198  each change in relative size as floating piston  184  slides within chamber  16 . Disposed within distal compartment  196  is a compressible gas, such as air, while disposed within proximal compartment  198  is a hydraulic fluid. As used in the specification and appended claims, the term “hydraulic fluid” is intended to include all types of fluids that can be used to transfer hydraulic pressures. Although hydraulic fluids are generally considered as being substantially non-compressible, it is appreciated that hydraulic fluids can be emulsified or have entrained gas, thereby making them slightly compressible. 
     The gas within distal compartment  196  is disposed at a second pressure that is greater than the first pressure of the gas within valve chamber  170 . Accordingly, in the static position shown in  FIG. 1  with piston rod  34  retracted out of chamber  16 , control valve  106  is in the closed position. That is, the pressure within distal compartment  196  is transferred through floating piston  184  and the hydraulic fluid within proximal compartment  198  so to collapse valve chamber  170  and move valve guide  106  into the closed position. 
     In general, control valve  106  is closed because of the opposing forces applied by the hydraulic fluid on distal side  134  of valve guide  104  and on proximal face  148  of control valve  106 . Although not required, it has been empirically determined that control valve assembly  100  more effectively operates under the applied pressures to move between the open and closed positions if the surface area of distal side  134  of valve guide  104  is at least 50%, preferably at least 60% and more preferably at least 70% of the surface area of proximal face  148  of control valve  106 . 
     During operation, when a force is applied to proximal end  37  of piston rod  34  which is greater than the force which is maintaining control valve assembly  100  in the closed position, piston rod  34  with main piston  102  and control valve assembly  100  begin to move distally within chamber  16 . Specifically, as depicted in  FIG. 4 , as piston rod  34  moves distally within chamber  16 , the hydraulic fluid within proximal compartment  198  travels through compression ports  118  and pushes against distal face  146  of control valve  106 , thereby causing control valve  106  to at least partially slide into the open position. 
     Control valve assembly  100  meters the flow of hydraulic fluid through compression ports  118  during the advancement of main piston  102 . The extent to which control valve  106  slides distally in part depends on the rate and magnitude of the force applied to piston rod  34 . For example, if a large force is rapidly applied to piston rod  34 , i.e., sharp hi-speed bump force, control valve assembly  100  is quickly moved to the fully open position as a result of the high pressures that are produced in proximal compartment  198  and applied to distal face  146  of control valve  106 . The hydraulic fluid can thus freely travel through compression ports  118  and around control valve  106 , thereby allowing piston rod  34  to rapidly and easily advance within chamber  16 . As such, the impact of the initial force on piston rod  34  is quickly absorbed by movement of piston rod  34 . In contrast, if a gradual small force is applied to piston rod  34 , control valve  106  is only partially moved to the open position so that flow passageway  167  remains partially constricted. This constriction of flow passageway  167  decreases the flow of hydraulic fluid through compression ports  118  and thus slows of movement of main piston  102  within chamber  16 . 
     As depicted in  FIG. 5 , as more of piston rod  34  enters proximal compartment  198 , piston rod  34  displaces a corresponding volume of the hydraulic fluid therein. Because the hydraulic fluid does not significantly compress, the hydraulic fluid causes floating piston  184  to slide distally and compress the gas with distal compartment  196 . As the gas pressure increases within distal compartment  196 , the fluid pressure within proximal compartment  198  increases and the fluid pressure begins to collapse valve chamber  170 , thereby moving control valve  106  into the closed position. As control valve  106  moves into the closed position, flow channel  167  constricts making it more difficult for the hydraulic fluid to pass therethrough. Accordingly, the farther piston rod  34  advances into chamber  16 , the greater the resistance force that is applied against piston rod  34 . 
     As depicted in  FIG. 6 , piston rod  34  is stopped from further advancement into chamber  16  when control valve assembly  100  returns to the closed position. This occurs when a sufficient length of piston rod  34  has entered proximal compartment  198  such that the hydraulic fluid pressure tending to move control valve assembly  100  into the closed position, thereby precluding fluid travel through compression ports  118 , is greater than the external force applied to piston rod  34  which tends to cause the hydraulic fluid to move the control valve into the open position. 
     As will be discussed below, in alternative embodiments the initial pressure within and the volume of distal compartment  196  can be selectively adjusted. The initial pressure and volume of distal compartment  196  has a number of effects on the damping. For example, by increasing the initial pressure within distal compartment  196 , increased force is initially applied by the hydraulic fluid to maintain control valve assembly  100  in the closed position. As such, greater force to piston rod  34  is required to initially move control valve assembly  100  into the open position. 
     Furthermore, having a higher initial pressure within distal compartment  196  causes control valve assembly  100  to close earlier as piston rod  34  is advanced into proximal compartment  198 . That is, the gas pressure within distal compartment  196 , and thus also the hydraulic fluid pressure within proximal compartment  198 , increases exponentially as the volume of distal compartment  196  is compressed. The increase in pressure is based on the compression ratio of distal compartment  196 , i.e., the starting volume of distal compartment  196  versus the final volume of distal compartment  196  when piston rod  34  is advanced into chamber  16 . For example, if the starting volume of distal compartment  196  is 100 cc and the final volume is 25 cc, the compression ratio is 4:1. As a result, the gas pressure and thus also the hydraulic fluid pressure in the final volume is four times the gas pressure in the starting volume. The pressure continues to increase exponentially as the volume of distal compartment  196  decreases by compression. 
     It is also appreciated that the starting volume of distal compartment  196  can be adjusted separately from the initial pressure therein so as to separately effect the damping properties. For example, in a first embodiment the initial volume of distal compartment  196  can be 100 cc while in a second embodiment the initial volume can be 75 cc. Assuming the starting gas pressure in each embodiment is the same, the same initial force is applied to control valve  100  as discussed above. However, for the same advancement of piston rod  34  in each of the embodiments, the compression ratio for the second embodiment is greater because the initial volume is smaller. As such, the rate of pressure increase and resulting damping force is greater for the second embodiment relative to the first embodiment. 
     In view of the foregoing, during a compressive movement of main piston  102 , a virtually infinite combination of pressures can be applied to control valve assembly  100  as a result of: displacement of piston rod  34  and the resulting pressure changes within chamber  16 ; varying bump loads and resulting pressures that are generated within the chambers on each side of main piston  102 ; and the resulting pressures that are variably generated upon distal face  134  of valve guide  104  and proximal face  148  of control valve  106  through out the stroke of piston rod  34 . 
     The resulting metering of hydraulic fluid flow through pressure ports  118  on main piston  102  by control valve assembly  110  during a compressive movement of main piston  102  thus produces damping effects which are: position sensitive as a result of the position of piston rod  34  within proximal compartment  198 ; variable position and load sensitive depending on the position of main piston  102 , speed/force of the bump input, and pressure within the distal compartment  196 ; and position and/or load adjustable, by varying the volume and force of the pressure within distal compartment  196 . 
     Depicted in  FIG. 7 , during rebound when piston rod  34  is being drawn out of chamber  16 , the pressure applied by the hydraulic fluid keeps control valve assembly  100  closed, thereby preventing the hydraulic fluid that is now proximal of control valve  106  from passing through compression ports  118 . Rather, the hydraulic fluid flows through one of possibly three rebound paths. In a first path, the hydraulic fluid enters rebound channel  88  proximal of stop plate  174 , travels centrally through piston rod  34  along rebound channel  88 , and then travels out through ports  79  by distally flexing shims  84 . In a second rebound path, rather then traveling out through ports  79 , the hydraulic fluid within rebound channel  88  travels out through jet  80 . In the third rebound path, the hydraulic fluid travels around the exterior of control valve  106  and enters pockets  120  of main piston  102 . The hydraulic fluid then travels out through rebound ports  122  by distally flexing shims  124 . 
     By adjusting the stiffness and/or number of shims  84 ,  124  and the size of opening  82  in jet  80 , the hydraulic fluid can simultaneously flow through one, two, or all three of the rebound paths. For example, by having shims  124  stiffer than shims  84 , the hydraulic fluid may flow only through jet  80  at low rebound forces. At a higher rebound force, the hydraulic fluid may flow through both the first and second rebound path or through all three rebound paths. 
     The rebound force, typically produced by an opposing spring, is generally greatest when piston rod  34  is fully inserted into chamber  16  ( FIG. 6 ) and initially begins to move in the rebound direction. As such, all of the rebound paths may initially be used as piston rod  34  begins to retract. However, as piston rod  34  continues to move in the rebound direction, one or more of the rebound paths may close off, thereby slowing the rebound as piston rod  34  approaches the fully retracted position. As will be discussed below with regard to alternative embodiments, rebound channel  88  can also be selectively restricted or closed so as to enable manual control of the hydraulic fluid therethrough based on operating parameters. 
     As discussed above, the compressible gas is sealed within distal compartment  196  so as to enable piston rod  34  to travel into chamber  16  through the compression of the gas and to at least partially control the operation of control valve assembly  100  by producing variable pressure thereon. It is appreciated, however, that there are a number of alternative ways in which these same functions can be achieved. 
     For example, depicted in  FIG. 8  a resiliently compressible member  246  is disposed within distal compartment  196 . Member  246  extends between floating piston  184  and distal end wall  24 . Although member  246  is shown as being a coiled spring, in alternative embodiments member  246  can comprise other forms of mechanical springs or blocks of resiliently compressible material such as rubber or polymeric foam. As the hydraulic pressure increases in proximal chamber  198 , floating piston  184  slides distally resiliently compressing member  246 . In this regard, compressed member  246  functions similar to the compressed gas. 
     It is appreciated that member  246  can be used in addition to or independent of filling distal compartment  196  with a gas at elevated pressure. Where member  246  is independently used to provide the compressive resistance, distal compartment  196  need not be sealed closed within housing  12 . For example an opening depicted by dashed lines  248  can be formed through distal end wall  24 . Opening  248  facilitates proper placement of floating piston  184 . In other embodiments, it is appreciated that member  246  need not be disposed within chamber  16  but can be disposed outside of chamber  16 . For example, a rod can extend from floating piston  184  through distal end wall  24  where it connects with member  246  outside of housing  12 . 
     In another alternative embodiment depicted in  FIG. 9 , a flexible bladder  250  is disposed within the distal end of chamber  16 . Bladder  250  communicates with the exterior of housing  12  through a fill valve  252  such as Schrader charge valve. Fill valve  252  enables bladder  250  to be selectively inflated with gas to a desired pressure. It is noted that bladder  250  can be used in association with or independent of floating piston  184 . That is, floating piston  184  can be eliminated so that the hydraulic fluid directly bears against inflated bladder  250  so as to compress bladder  250 . In this embodiment, bladder  250  bounds distal compartment  196 . Bladder  250  can also be filled with resiliently compressible material such as rubber or polymeric foam. 
     Depicted in  FIG. 10 , floating piston  184  is replaced with a flexible diaphragm  254 . Diaphragm  254  is mounted to interior surface  14  of sidewall  18  of housing  12  so as to divide chamber  16  into distal compartment  196  and proximal compartment  198 . A fill valve  256  is formed on sidewall  18  and enables distal compartment  196  to be filled with a compressible gas to a desired pressure. Again, as piston rod  34  is advanced into chamber  16 , the hydraulic fluid presses against diaphragm  254  causing it to flex distally, thereby compressing the gas within distal compartment  196 . 
     It is appreciated that in other embodiments no mechanical barriers are required. For example, depicted in  FIG. 11  chamber  16  is filled with a gas  260 , such as air, and a hydraulic fluid  262 . A boundary line  264  is formed therebetween. As piston rod  34  enters chamber  16 , hydraulic fluid  262  compresses gas  260 . In some uses, however, this embodiment is less desirable as the gas and hydraulic fluid can mix or emulsify within chamber  16  and diminish operating properties. 
     Set forth below are a number of alternative embodiments of dampers wherein like elements are identified by like reference characters. In one embodiment of the present invention means are provided for selectively adjusting the size of distal compartment  196 . By way of example, depicted in  FIG. 12  is a damper  210 . Damper  210  is substantially identical to damper  10  except that damper  210  includes an adjusting piston  212  disposed within chamber  16  distal of floating piston  184 . Adjusting piston  212  includes a peripheral side  214  having a seal  216  formed thereat. Seal  216  is biased in sealed engagement against interior surface  14  of sidewall  18  of housing  12  so as to enable adjusting piston  212  to selectively slide within chamber  16  without allowing fluid to pass through or around. 
     Centrally mounted on adjusting piston  212  is a sleeve  218 . Sleeve  218  has a threaded bore  220  which opens distally. In alternative embodiments, it is appreciated that threaded bore  220  can be formed directly on the distal face of adjusting piston  212 . 
     Mounted on housing  12  is a knob  222 . Knob  222  has a first end with an enlarged head  224  formed thereat. Head  224  is at least partially exposed outside of housing  12  so as to enable selective, manual rotation of head  224 . A threaded shaft  226  is formed at an opposing second end of knob  222 . Threaded shaft  226  is threadedly engaged with bore  220  on piston  212 . Accordingly, as depicted in  FIGS. 12 and 13 , by selectively rotating head  224  of knob  222 , adjusting piston  212  is selectively advanced and retracted within the distal end of chamber  16 . 
     In this embodiment, distal compartment  196  is bounded between adjusting piston  212  and floating piston  184 . By manually advancing adjusting piston  212  toward floating piston  184 , distal compartment  196  becomes smaller. By making distal compartment  196  smaller, the gas pressure can be increased therein and the rate at which the pressure increases within proximal compartment  198  as floating piston  184  moves distally increases. Alternative embodiments of the means for selectively adjusting the size of distal compartment are discussed below. 
     Also mounted on housing  12  so as to communicate with distal compartment  196  is a fill valve  228 . As previously discussed, fill valve  228  can comprise a conventional air valve such as used on car and bike tires. Fill valve  228  can thus be used to selectively increase or decreases the gas pressure within distal compartment  196 . For example, air can be added to or removed from distal compartment  196  so as to selectively increase or decrease the gas pressure therein. Again, as previously discussed, the gas pressure affects the operation of control valve  100  and thus the movement of piston rod  34 . Accordingly, adjusting piston  212  and fill valve  228  enable an end user to selectively adjust dampening properties of damper  210  based on current or expected operating parameters. 
     In one embodiment of the present invention, means are provided for remotely adjusting the fluid pressure of the hydraulic fluid within proximal compartment  198  of damper  10 . By way of example and not by limitation, depicted in  FIG. 14  is one embodiment of a pressure regulated damping system  232 . Dampening system  232  includes means for providing a compressed gas. Examples of such means includes air source  234  which can comprise a compressor or tank holding compressed gas. Damping system  232  further comprises a pressure regulator  235  and one or more of dampers  10 . A port  238  is provided in gas communication with distal compartment  196  of each damper  10 . Supply lines  240  provide gas communication between air source  234  and pressure regulator  235 . In turn, supply lines  242 , such as tubes or any other form of conduit, provide gas communication between pressure regulator  235  and distal compartment  196  of each damper  10  by way of port  238 . 
     Regulator  235  can be manually, electronically, and/or computer controlled so as to selectively or automatically adjust the pressure independently within distal compartment  196  of each damper  10  as the operating environment for dampers  10  change. By increasing the pressure in distal compartment  196 , the pressure differential is transferred through floating piston  184  so as to increase the fluid pressure of the hydraulic fluid within proximal compartment  198 . In turn, increasing the hydraulic fluid pressure adjusts the operation of control valve  100  and thus the damping properties of damper  10 . It is appreciated that regulator  235  can come in a variety of different configurations and can be comprised of multiple discrete components. 
     As one example of use, one or more dampers  10  can be incorporated into the shock absorbers of an automobile or any other type of vehicle. As road and operating conditions change, for example, straight versus curvy, on-road versus off-road, accelerating versus breaking, the rapid remote adjustment of the hydraulic fluid pressure can be used to provide optimum suspension performance. It is appreciated that optimum performance will often be obtain by simultaneously separately adjusting the hydraulic fluid pressure in each of dampers  10  on a vehicle. 
     To facilitate automatic damping adjustment, one or more sensors  243 , such as a gyroscopic sensor or other movement sensitive sensors, can be mounted on the vehicle and in electrical communication with a central processing unit (CPU)  244 . CPU  244  may be separate from or form a portion of regulator  235 . Based on inputs from the one or more sensors  243 , CPU  244  can control regulator  235  so as to accordingly adjust the gas pressure and resulting hydraulic fluid pressure in one or more of dampers  10  on the vehicle. 
     As an alternative to automatic adjustment, a manual input mechanism  245 , such as a switch or control panel, can be electrically coupled with CPU  244 . Inputs provided to manual input mechanism  245  can be used to set the hydraulic fluid pressure in each of dampers  10  to a predefined valve. 
     The use of gas pressure is only one example of the means for remotely adjusting the fluid pressure of the hydraulic fluid within proximal compartment  198  of damper  10 . As an alternative embodiment, spring  246  of  FIG. 8  can be disposed between floating piston  184  and adjusting piston  212  of  FIG. 12 . In turn, a motor or other form of gear mechanism is attached knob  222  in  FIG. 12 . Central processing unit  244  is electrically coupled with the motor such that based on sensor or manual input signals the motor adjusts the compression on spring  246  so as to remotely adjust the hydraulic fluid pressure in dampers  10 . 
     It is appreciated that there are a variety of different systems that can be used to remotely adjust the fluid pressure of the hydraulic fluid within dampers  10  by selectively adjusting the pressure applied to floating piston  184  or one of the alternatives discussed thereto. 
     In view of the foregoing the suspension of a vehicle can be controlled by providing a vehicle having a suspension system including at least one pressure regulated damper; and automatically or selectively delivering a gas to or withdrawing a gas from the at least one damper during operation of the vehicle so as to automatically or selectively control suspension performance properties of the at least one damper. Such suspension control can be performed during movement of the vehicle. 
     Likewise, suspension control can be obtained by automatically or selectively altering the fluid pressure of the hydraulic fluid within the at least one damper during operation of the vehicle so as to automatically or selectively control suspension performance properties of the at least one damper, the automatic or selective altering of the fluid pressure being based on automatic sensor signals or manual input signals. 
     Depicted in  FIG. 15  is another alternative embodiment of a damper  270  incorporating features of the present invention. Damper  270  includes housing  12  bounding chamber  16 . Chamber  16  is divided by floating piston  184  into distal compartment  196  and proximal compartment  198  which contain a compressed gas and hydraulic fluid, respectively. Again, floating piston  184  can be replaced with any of the alternatives as previously discussed. 
     A piston rod  272  slideably extends into the proximal end of housing  12 . Piston rod  272  includes a base rod  278  and a bolt  280 . Bolt  280  is screwed onto the distal end face of base rod  278  so as to secure main piston  102  therebetween. Seal  114  is mounted on the peripheral side of main piston  102  and forms a slideable sealed biased engagement against interior surface  14  of sidewall  18 . 
     Secured between an enlarged head  281  of bolt  280  and distal face  110  of piston  102  is a first shim  282 . First shim  282  is biased against distal face  110  of piston  102  so as to cover the distal openings to rebound ports  122 . A second shim  284  is disposed between the distal end of base rod  278  and proximal face  108  of piston  102 . Second shim  284  is biased against proximal face  108  of piston  274  so as to cover the proximal openings of compression ports  118 . However, second shim  284  only covers a portion of pockets  120  leading to rebound ports  122 . As previously discussed with regard to shims  124  in  FIG. 3 , shims  282  and  284  function as one-way check valves which control the direction of flow through rebound ports  122  and compression ports  118 , respectively. The alternatives as previously discussed with regard to shims  124  are also applicable to shims  282 ,  284 , and the flexible shims disclosed in other embodiments of the present invention. 
     In contrast to damper  10  wherein control valve assembly  100  is mounted to the moveable piston rod, in the present embodiment control valve assembly  100  is mounted on a secondary piston  274  disposed within proximal compartment  198  between piston rod  272  and floating piston  184 . Secondary piston  274  has the same configuration as main piston  102  and thus like reference characters are used to identify like elements. It is noted, however, that secondary piston  274  and control valve assembly  100  are rotated 180° relative to the corresponding structures in damper  10 . As such, the proximal and distal orientations are reversed relative thereto. 
     Secondary piston  274  is secured in place by clips  292  which are received in grooves on interior surface  14  of sidewall  18  so as to bias against opposing sides of secondary piston  274 . In alternative embodiments, clips  292  can be further spaced apart to allow some longitudinal sliding of secondary piston  274 . In yet other embodiments, secondary piston  274  can be integrally formed with housing  12  so as to eliminate the need for seal  114  and clips  292 . A shaft  288  extends through secondary piston  274  and control valve assembly  100  so as to secure the two elements together. Shims  124  bias against proximal face  110  of secondary piston  274  and are secured thereat by a head  290  of shaft  288  and washer  126 . Stop plate  174  is mounted at the distal end of shaft  288  to control the distal movement of control valve  106 . The combination of secondary piston  274 , control valve  100  and stop plate  174  secured together by shaft  288  is herein referred to as base valve  286 . 
     As depicted in  FIG. 16 , as piston rod  272  advances into distal compartment  198  of chamber  16 , the hydraulic fluid causes second shims  284  to proximally flex allowing the hydraulic fluid to travel through compression ports  118  of main piston  102 . Simultaneously, the hydraulic fluid also moves control valve  106  of control valve assembly  100  into an at least partially open state so that the hydraulic fluid can pass through compression ports  118  of secondary piston  274 . The hydraulic fluid then pushes floating piston  184  distally, thereby compressing the gas within distal compartment  196 . 
     Depicted in  FIG. 17 , when the compressive movement of piston rod  272  has stopped within chamber  16 , the fluid pressure within proximal compartment  198  collapses valve chamber  170 , thereby moving control valve  106  into the closed position. As depicted in  FIG. 18 , during the rebound stroke the hydraulic fluid travels through secondary piston  274  by flowing through pockets  120  and out through rebound ports  122  by proximally flexing shims  124 . Similarly, the hydraulic fluid travels through main piston  102  by traveling through pockets  120  and out through rebound ports  122  by distally flexing shims  282 . 
     Depicted in  FIG. 19  is another alternative embodiment of a damper  300 . Damper  300  includes a double tube housing  302 . Specifically, housing  302  comprises a distal cap  304  and an opposing proximal cap  306 . Extending between caps  304  and  306  and secured thereto is an outer tube  308 . Disposed within outer tube  308  is an inner tube  310  which also extends between opposing caps  304  and  306 . Inner tube  310  has an interior surface  312  that bounds an inner compartment  314 . Bounded between the exterior surface of inner tube  310  and the interior surface of outer tube  308  is an outer compartment  316 . Inner compartment  314  communicates with outer compartment  316  through a port  318 . 
     Inner compartment  314  is filled with a hydraulic fluid. Disposed within outer compartment  316  is an inflatable bladder  320 . Bladder  320  is selectively inflated through a fill valve  322  projecting through outer tube  308 . Disposed within the distal end of inner compartment  314  is base valve  286  as previously discussed with regard to damper  270  in  FIGS. 15-18 . In this embodiment, however, shaft  288  is used to secure base valve  286  directly to distal end cap  304 . It is appreciated that alternative mounting methods can be used to secure base valve  286  within inner tube  310 . Piston rod  272  with main piston  102 , as also discussed with damper  270 , are slideably disposed within inner compartment  314 . 
     As depicted in  FIG. 20 , damper  300  operates similar to damper  270 . Specifically, as piston rod advances into inner compartment  314 , control valve  106  moves to the open position and the hydraulic fluid travels through compression ports  118  on both main piston  102  and secondary piston  274 . As the fluid passes secondary piston  274 , the hydraulic fluid enters outer compartment  316  thorough port  318  where it compresses bladder  320 . The hydraulic fluid continues to compress bladder  320  until piston rod  272  is retracted. During retraction, the hydraulic fluid flows back through main piston  102  and secondary piston  274  in substantially the same ways as previously discussed with regard to damper  270 . In an alternative embodiment, it is appreciated that bladder  320  can be replaced with a floating piston which encircles inner tube  310  and slides within outer compartment  316 . In yet another alternative, damper  320  can be inverted and bladder  320  removed. In this embodiment, a gas, such as air, is trapped within outer compartment  316 . The hydraulic fluid directly contacts the gas, such as previously discussed with regard to  FIG. 11 , so as to selectively compress the gas. 
     Depicted in  FIG. 21  is one embodiment of shock absorber  350  incorporating features of the present invention. As depicted in  FIGS. 22 and 23 , shock absorber  350  comprises a piggy-back housing  352  which includes a primary tube  354 , a secondary tube  356  and a stem  358  extending therebetween. As depicted in  FIG. 24  primary tube  354  has an interior surface  430  bounding a primary chamber  432  while secondary tube  356  has an interior surface  437  bounding a secondary chamber  438 . Returning to  FIGS. 22 and 23 , stem  358  has a substantially U-shaped configuration that extends between a first end  359  and an opposing second end  361 . An opening  357  extends through stem  358  at first end  359  for selective attachment to a structure. 
     Primary tube  354  has an exterior surface  360  extending between a distal end  362  and an opposing proximal end  364 . Distal end  362  of primary tube  354  is threaded into first end  359  of stem  358 . A proximal end cap  366  is threaded into proximal end  364  of primary tube  360 . Adjustably threaded onto distal end  362  of primary tube  360  is an annular distal spring retention collar  368 . 
     A piston rod  370  has a distal end  372  ( FIG. 24 ) and an opposing proximal end  374 . A bracket  376  having an opening  378  extending therethrough is threaded onto proximal end  374  of piston rod  370 . Positioned on bracket  376  is an annular proximal spring retention collar  380 . A coiled spring  382  extends between distal spring retention collar  368  and proximal spring retention collar  380 . The tension on spring  382  is selectively adjusted by adjusting distal spring retention collar  368  along the length of primary tube  354 . 
     Encircling piston rod  370  between proximal end cap  366  and proximal spring retention collar  380  is a bottom-out cushion  382 . Cushion  382  is made of a resiliently flexible material such as rubber or polymeric foam. 
     As depicted in  FIG. 24 , piston rod  370  includes a tubular base rod  384  and bolt  44  as previously discussed with regard to damper  10 . Base rod  384  has an interior surface  390  bounding a channel  392  that longitudinally extends between a distal end  386  and an opposing proximal end  388 . Bolt  44  is threaded onto distal end  386  of base rod  384  so that channel  78  of bolt  44  is in fluid communication with channel  392  of base rod  384 . A port  394  extends through base rod  384  so as to provide fluid communication between primary chamber  432  of primary tube  354  and channel  78 . A pin  396  is slideably disposed within channel  392  of base rod  384 . Pin  396  has a tapered nose  398  disposed at the distal end thereof. Nose  398  is configured to complementary fit within the proximal opening of channel  78  of bolt  44 . As a result, pin  396  can be used to selectively restrict or close off fluid communication between primary chamber  432  and channel  78  by advancing and retracting pin  396  within base rod  384 . 
     Bracket  376  has a distal end face  410  having a bore  412  recessed thereon. A passageway  400  transversely extends across bracket  376  so as to intersect with bore  412 . Bracket  376  is screwed onto base rod  384  such that pin  396  extends down through bore  412  and partially into passageway  400 . A regulator  414  is adjustably disposed within passageway  400 . Regulator  414  includes a shaft  416  having a distal portion  418  in threaded engagement within passageway  400  of bracket  376 , a substantially frustuconical transition portion  420 , and a substantially cylindrical central portion  422  formed therebetween. Regulator  414  also includes a selectively removable knob  424 . Selective rotation of knob  424  advances and retracts regulator  414  within passageway  400 . As regulator  414  is advanced within passageway  400 , frustuconical transition portion  420  biases against the distal end of pin  396  causing pin  396  to advance toward bolt  44 , thereby restricting or closing off the proximal opening to channel  78 . In turn, as regulator  414  is retracted, pin  396  is lowered, thereby opening the flow path to channel  78 . Alternative adjustment systems may also be used to move pin  396 . 
     Mounted on the distal end of piston rod  370  is main piston  102 , control valve assembly  100 , and stop plate  174 . These elements are substantially the same as previously discussed with regard to damper  10  and operate in the same manner. The only distinction is that control valve assembly  100  of the embodiment shown in  FIG. 24  has a slightly different configured valve chamber  170 . This is due to different grooves formed on valve guide  104  and control valve  106 . 
     Formed at first end  359  of stem  358  is a threaded bore  446 . Distal end  362  of primary tube  360  is threaded within bore  446 . A threaded sleeve  450  projects from an end face  451  at second end  361  of stem  358 . A threaded central bore  453  is formed on end face  451 . The distal end of secondary tube  356  is coupled with threaded sleeve  450 . Alternative attachment methods may also be used to secure primary tube  360  and secondary tube  356  to piggy back housing  352 , including use of a 1-piece forged or cast assembly which includes all of the aforementioned parts. 
     Stem  358  is configured to provide fluid communication between primary chamber  432  of primary tube  360  and secondary chamber  438  of secondary tube  356 . Specifically, a transition channel  448  communicates with bore  446  at first end  359  of stem  358 . As depicted in  FIG. 25 , a first valve chamber  452  and a second valve chamber  454  are each bored into stem  358  from second end  361  toward first end  359 . A first pathway  456  extends from first valve chamber  452  to transition channel  448  while a second pathway  458  extends from second valve chamber  454  to transition channel  448 . A bore  460  intersects with first valve chamber  452  and extends to end face  451  at second end  361  of stem  358 . A bore  462  transversely intersects with both second valve chamber  454  and central bore  453  so as to provide fluid communication therebetween. A plug  463  is secured in the opening of bore  462  to prevent fluid from escaping thereat. 
     A first valve  466  is adjustably disposed within first valve chamber  452 . First valve  466  comprises a head  468  having a socket  470  formed on the end thereof to selectively receive a tool for rotating first valve  466 . First valve  466  also has a central body  472  having threads thereon that engage with the inner wall of first valve chamber  452 . One or more seals  474  encircle body  472  and provide sealed engagement with the inner wall of first valve chamber  452 . Projecting from body  472  is a shaft  474  having a tapered nose  476 . Tapered nose  476  is configured to selectively engage with the opening to first pathway  456 . Accordingly, by selectively rotating first valve  466 , shaft  474  advances or retracts so as to selectively restrict or open the opening to first pathway  456 . 
     A second valve  480  is adjustably disposed within second valve chamber  454 . Similar to first valve  466 , second valve  480  comprises head  468 , threaded body  472 , and seal  474 . A piston  482  is movably disposed within second valve chamber  454  at the opening to second pathway  458 . A spring  484  extends between body  472  and piston  482  so as to bias piston  482  against the opening to second pathway  458 . A rod  486  extends from piston  482 , centrally through spring  484 , and freely into a channel  487  formed in the end of body  472 . As piston  482  is pushed back, rod  486  is free to retract within body  472 . 
     By advancing second valve  480  within second valve chamber  454 , spring  484  is compressed, thereby providing greater biasing force against piston  482 . Second pathway  458  is thus only open when sufficient force is applied to piston  482  to overcome the applied spring force. Accordingly, by selectively adjusting first valve  466  and second valve  480 , dampening properties can be adjusted for operating conditions. 
     Returning to  FIG. 24 , movably disposed within secondary chamber  438  is a floating piston  490 . Floating piston  490  divides the enclosed area bounded by primary tube  354 , secondary tube  356  and stem  358  into a proximal compartment  492  and a distal compartment  493 . Again, proximal compartment  492  is filled with a hydraulic fluid while distal compartment  493  is filled with a compressible gas. Other alternatives as previously discussed can also be used to replace or use in conjunction with floating valve  490  and the compressible gas. 
     Turning to  FIG. 26 , a tubular bolt  508  having an enlarged head  509  is threaded into central opening  453  at second end  361  of stem  358 . Tubular bolt  508  has an interior surface  510  bounding a channel  512 . Central opening  453  and channel  512  provide fluid communication between second valve chamber  454  and secondary chamber  438 . Alternative attachment methods may be used in place of bolt  508 . 
     Encircling bolt  508  and biased against the interior surface of sleeve  450  is a fixed piston  494  having a configuration similar to piston  102  as discussed with damper  10 . Fixed piston  494  has a proximal face  496  and an opposing distal face  498 . Extending between faces  496  and  498  are a plurality of radially spaced apart damping ports  500 . A plurality of radially spaced apart pockets  502  are recessed on proximal face  496 . A compression port  504  extends from distal face  498  to each pocket  502 . 
     A first shim  514  encircles bolt  508  and biases against proximal face  496 . First shim  514  covers the proximal opening of damping ports  500  but only covers a portion of pockets  502 . A washer  516  encircles bolt  508  and is disposed between shim  514  and end face  451  of stem  358 . Washer  516  provides spacing between end face  451  and first shim  514  so that first shim  514  can flex proximal during operation. 
     A second shim  518  encircles bolt  508  and biases against distal face  498  of fixed piston  494 . Second shim  518  covers the distal opening of compression ports  504  but only covers a portion of the distal openings of damping ports  500 . A washer  520  is disposed between bolt head  509  and second shim  518  to enable second shim  518  to flex distally during operation. As previously mentioned, bore  460  extends between first valve chamber and end face  451  of stem  358 . As such, the hydraulic fluid passing through bore  460  must necessarily pass through fixed piston  494  as it enters secondary chamber  438 . 
     Depicted in  FIG. 24 , threaded into the distal end of secondary tube  356  is a volume adjuster assembly  520 . Depicted in  FIG. 27 , volume adjuster assembly  520  comprises an annular sleeve  522  having an interior surface  528  and an exterior surface  526 . Sleeve  522  is threaded into the distal end of secondary tube  356 . Adjustably threaded into sleeve  522  is a tubular stem  530 . Stem  530  has a proximal end  532  and a distal end  534 . Mounted on proximal end  532  of stem  530  so as to encircle and radially outwardly project therefrom is a piston  536 . Piston  536  is secured to stem  530  by a clip  538  mounted on stem  530  proximal of piston  536 . Piston  536  outwardly projects so as to seal in slideable engagement against interior surface  437  of secondary tube  356 . Distal compartment  493  is bounded between floating piston  490  and piston  536 . By selectively rotating stem  530  relative to sleeve  522 , stem  530  and thus piston  536  advance or retract relative to sleeve  522 . Thus by advancing stem  530  and piston  536 , distal compartment  493  becomes smaller. In turn the rate at which the gas compresses, i.e., the compression ratio, within distal compartment  493  increases. 
     A cavity  540  is recessed on a distal end face  541  of stem  530 . A passageway  542  extends from cavity  540  to a proximal end face  544  of stem  530 . Positioned within cavity  540  in communication with passageway  542  is a fill valve  546  through which pressured gas can be fed into distal compartment  493 . One example of valve  546  is a Schrader charge valve. Thus, fill valve  546  can be used to selectively adjust the gas pressure within distal compartment  493 , thereby adjusting the related dampening properties. 
     It is appreciated that shock absorber  350  operates using the same principals as discussed in detail with regard to the other embodiments. 
     Depicted in  FIG. 28  is another alternative embodiment of a damper  550 . Damper  550  has a piggy-back housing  552  comprising a primary housing  554 , a secondary housing  556 , and a tubular stem  558  extending therebetween. A sealed hose, pipe, or other conduit may be substituted for stem  558  for establishing fluid communication between primary housing  554  and secondary housing  556 . Primary housing  554  is the same as housing  12  previously discussed with regard to damper  10  except for the attachment of stem  558 . Furthermore, as also discussed with damper  10 , coupled with primary housing  554  is piston rod  34  having a main piston  102 , control valve assembly  100 , and stop plate  174  mounted thereon. As such like elements between damper  550  and damper  10  are identified by like reference characters. 
     Secondary housing  556  comprises a tubular, cylindrical sidewall  560  extending between a proximal end  562  to an opposing distal end  564 . Proximal end  562  terminates at a proximal end wall  563 . Threadedly disposed within distal end  564  of secondary housing  556  is volume adjuster assembly  520  as previously discussed with regard to  FIG. 25 . Alternative methods for attaching volume adjustor assembly  520  can be used. Sidewall  560  has an interior surface  566  that bounds a secondary chamber  568  extending between proximal end wall  563  and piston  536  of volume adjuster assembly  520 . Tubular stem  558  bounds a channel  576  that extends between primary chamber  16  and secondary chamber  568 . Primary chamber  16 , secondary chamber  568 , and channel  576  of stem  558  combine to form a total chamber  578 . 
     Inwardly projecting from sidewall  560  at proximal end  562  of secondary housing  556  is a retaining wall  570 . Slideably disposed within secondary chamber  568  distal of retaining wall  570  is a floating piston  574 . Floating piston  574  divides total chamber  578  into a proximal compartment  580  and a distal compartment  582 . Proximal compartment  580  is filled with a hydraulic fluid while distal compartment  582  is filled with a compressible gas. 
     Disposed between retaining wall  570  and proximal end wall  563  of secondary housing  556  is a base valve  586 . Depicted in  FIG. 29  is an enlarged cross sectional view of base valve  586 . As depicted therein, base valve  586  comprises a secondary piston  584  having compression ports  118  and rebound ports  122  extending therethrough. A tubular shaft  583  extends through secondary piston  584  and beyond the proximal face thereof. A washer  585  encircles shaft  583  so as to cover the openings to rebound ports  122  while leaving the openings to compression ports  118  open. A retention collar  587  is threaded onto the proximal end of shaft  583 . A spring  588  extends between retention collar  587  and washer  585  so as to bias washer  585  against the openings to rebound ports  122 . Washer  585  and spring  588  function as a one-way check valve to regulate the fluid flow through rebound ports  122  and are an alternative embodiment to the flexible shims as discussed in other embodiments. 
     Disposed against the distal face of secondary piston  584  and encircling tubular shaft  583  is control valve assembly  100 . Control valve assembly  100  controls the fluid flow through compression ports  118  in substantially the same method of operation as discussed in the other embodiments. That is, based on the force of the fluid passing through compression ports  118  and the pressure of the hydraulic pressure, control valve assembly  100  is moved to some extent between the open position shown in  FIG. 30  and the closed position shown in  FIG. 31 . Unlike the prior embodiments, however, control valve assembly  100  can be selectively adjusted through the application of a spring force. 
     Specifically, a collar  589  is inserted within secondary housing  556 . Collar  589  encircles tubular shaft  583  so that an annular spring cavity  591  is formed therebetween. Disposed within spring cavity  591  is an annular first bias plate  592  disposed against control valve  106  and an annular second bias plate  593  disposed against a portion of collar  589 . A spring  594  extends between bias plates  592  and  593  so as to bias first bias plate  592  against control valve  106 . Posts  595  extend from second bias plate  593  to an end cap  596 . End cap  596  is configured such that rotation of end cap  596  causes posts  595  to advance into spring cavity  591 , thereby further compressing spring  594 . As spring  594  is compressed greater force is applied to control valve  106 , thereby altering the operation thereof. 
     To enable the hydraulic fluid to access the distal side of control valve assembly  100 , a fluid path  597  extends through shaft  583  and communicates with spring cavity  591  and chamber  581 . Ports  598  are formed on first bias plate  592  so as to enable the hydraulic fluid to directly contact control valve assembly  100 . The hydraulic fluid thus assists in the opening and closing of control valve assembly  100  of base valve  586  based on the pressure of the hydraulic fluid. To selectively control the flow of hydraulic fluid into and out of spring cavity  591  and chamber  581 , a pin  599  is threadedly disposed within fluid path  597  so as to selectively constrict fluid path  597 . 
       FIG. 30  shows the flow path of the hydraulic fluid as piston rod  34  is advanced within primary chamber  16 .  FIG. 31  shows the flow path of the hydraulic fluid as piston rod  34  is retracted out of primary chamber  16 . 
     Depicted in  FIG. 32  is a damper  600  that is substantially identical to damper  550 . Damper  600  is distinguished over damper  550  in that floating piston  574  has been replaced with a flexible diaphragm  602 . 
     Depicted in  FIG. 33  is another alternative embodiment of a damper  610  that is similar to damper  550 . Damper  610  is distinguished over damper  550  in that base valve  586  which contains a control valve assembly  100  has been replaced with a conventional base valve  612  that does not incorporate a control valve assembly  100 . 
     Depicted in  FIGS. 34 and 35  is one embodiment of how an inventive damper can be incorporated into a front fork of a bicycle, motorcycle, or the like. Specifically, depicted in  FIG. 34  is a front fork  630  having an upper tube  632  slideably received within a lower tube  634 . Disposed within lower tube  634  so as to resiliently bias against upper tube  632  is a spring  633 . Spring  633  provides the rebound force for the damper and can be positioned at different locations. Alternative methods of producing a rebounding force may also be used, i.e., compressed gas, microcellular foam, and the like. Disposed within upper tube  632  is a tubular cartridge  636  which bounds a chamber  638 . A tubular piston rod  640  has a proximal end  642  mounted on a base floor of lower tube  634  and an opposing distal end  644  slideably extending up through upper tube  632  and cartridge  636 . Mounted within chamber  638  on distal end  644  of piston rod  640  is main piston  102 , control valve  100 , and stop plate  174  as previously discussed with regard to damper  10  in  FIGS. 1-7 . 
     Rebound channel  88 , as disclosed with regard to damper  10 , is also formed on piston rod  640  so as to extend between opposing sides of main piston  102 . In contrast to rebound channel  88  for damper  10 , however, in the embodiment depicted in  FIG. 34  a regulating pin  641  having a tapered nose is movably disposed within piston rod  640 . That is, by selectively rotating regulating pin  641  outside of lower tube  634 , pin  641  can be adjusted to selectively restrict the flow of hydraulic fluid through rebound channel  88 . In part, the slower the flow of hydraulic fluid through rebound channel  88 , the slower the rebound of piston rod  640 . 
     Screwed into the distal end of cartridge  636  is a hollow sleeve  646 . In turn, screwed into sleeve  646  is an end plug  648  having a stem  650  proximally projecting therefrom within chamber  638 . A first piston  652  encircles and is slideably disposed on stem  650 . First piston  652  forms a sealed engagement with stem  650  and cartridge  636 . As such, first piston  652  forms a barrier that divides chamber  638  into a relative proximal chamber  654  and a relative distal chamber  656 . Proximal chamber  654  is filled with a hydraulic fluid while distal chamber  656  is filled with a compressible gas such as air. 
     Mounted against end plug  648  so as to also encircle stem  650  is a second piston  660 . Second piston  660  is also in sealed engagement with stem  650  and cartridge  636 . By rotating end plug  648 , second piston  660  advances into distal chamber  656  effectively decreasing the size of distal chamber  656 . This also increases the pressure within both proximal chamber  654  and distal chamber  656  and the compression ratio within distal chamber  656 . 
     A fill valve  662  is mounted on end plug  648 . A passageway  664  extends through end plug  648  from fill valve  662  to distal chamber  656 . As such, fill valve  662  can be used to selectively adjust the volume and pressure of gas within distal chamber  656 . 
     Finally, although not required, a base valve piston  668  is rigidly disposed within proximal chamber  654  between first piston  652  and piston rod  640 . Base valve piston  668  is sealed against cartridge  636  and, except for having a solid center, has substantially the same configuration as main piston  102 . Specifically, base valve piston  668  has compression ports  118  and rebound ports  122  extending therethrough. Flexible shims  670  and  672  are mounted on opposing sides of base valve piston  668 , as previously discussed in other embodiments, to control the flow of hydraulic fluid through compression ports  118  and rebound ports  122 , respectively. Base valve piston  668  thus further controls the flow of hydraulic fluid and transfer of pressure which partially controls the damping properties. 
       FIG. 35  shows front fork  630  with piston rod  640  being advanced into chamber  638 . 
     The use of cartridge  636  as discussed above with regard to front fork  630  is for ease in manufacture and assembly. The use of cartridge  636  also enables the dampers of the present invention to be retrofit into existing forks. Depicted in  FIG. 36 , however, is a front fork  676 . Front fork  676  is the same as front fork  630  except that cartridge  636  has been removed.  FIG. 37  shows front fork  676  with piston rod  640  being advanced into chamber  638  while  FIG. 38  shows front fork  676  with piston rod  640  being withdrawn from chamber  638 . 
     It is appreciated that all of the different damping configurations disclosed herein can be incorporated in a front fork. As a further example, depicted in  FIGS. 39 and 40  is a front fork  680  where control valve  100  has been moved from main piston  102  to base valve piston  668 . This system operates similar to the damper discussed with regard to  FIGS. 15-18 . 
     The above discussed dampers of the present invention provide automatic adjustment of damping properties based on operating conditions, thereby optimizing damping. Different embodiments provide for a variety of selective manual damping adjustments and/or remote damping adjustments. Such adjustability enables the dampers to be effectively used in a variety of different conditions and on a variety of different vehicle or other systems. The design of the dampers also facilitates ease in manufacture and assembly. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, disclosed herein are numerous examples of different dampers having different features for controlling damping properties. It is appreciated, however, that the different features can be mixed and matched so as to form a variety of other unique assemblies. Accordingly, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.