Abstract:
A method and apparatus for a shock absorber having a damping fluid compensation chamber with a gas charge. In one aspect, a partition separates a first chamber portion from a second chamber portion, wherein the first portion of the chamber is at a first initial gas pressure and the second portion of the chamber is at a second initial pressure. A valve separates the first and second chamber portions and opening the valve commingles the first and second chamber portions so that the combined chamber portions are at a third pressure. In another aspect, a piston disposed through a wall is in pressure communication with the gas charge and is biased inwardly toward a pressure of the charge, whereby an indicator is movable by the piston in response to the pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 61/254,947, filed Oct. 26, 2009, and U.S. provisional patent application Ser. No. 61/267,646, filed Dec. 8, 2009, both of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to shock absorbers for vehicles. More particularly, the invention relates to fluid dampers. More particularly still, the invention relates to methods and apparatus for controlling and managing pressurized gas used in a fluid damper reservoir. 
         [0004]    2. Description of the Related Art 
         [0005]    Suspension systems (e.g. “shock absorber”) for vehicles, including motor vehicles and bicycles, include a spring portion and a damper portion. The spring portion creates resistance to a shock absorber&#39;s compression, and that resistance may increase non-linearly as the spring is compressed. In some instances, springs are coil springs or leaf springs and in other instances they are gas springs that produce a non-linear compression curve due to the compression of a given quantity of gas. Dampers, on the other hand, produce resistance as a piston moves through substantially incompressible fluid, making the operation of the damper dependent upon shock absorber compression velocity rather than the stroke position of the suspension system. A fluid damper typically involves a chamber having a damping fluid disposed therein and a piston and rod which together move in and out of the fluid chamber as the suspension system compresses and rebounds. The piston is equipped with fluid passages, usually including shims, which restrict the flow of fluid through the piston from one side of the chamber to the other and provide the damping effect as the piston and rod move into and out of the chamber. 
         [0006]    When the piston and rod enter the fluid chamber, a volume of fluid equal to the volume of the incoming piston rod must be displaced from the chamber. In order to compensate for the reduction in space for the fluid, a reservoir is used which typically consists of a floating piston that operates with a volume of gas behind the piston. As the volume in the fluid chamber decreases, the floating piston moves against the volume of gas which thereby becomes compressed. In this manner, the reservoir volume available for the damping fluid can increase and decrease during each respective compression and retraction stroke of the shock absorber. A reservoir can be integrally included as a part of the damper chamber or can be a separate chamber, usually adjacent the main damper chamber. 
         [0007]    In some instances, especially for larger capacity dampers used with motor vehicles, it is not unusual to have the gas volume of the remote reservoir pressurized for use to 200 psi. Due to the physical size and weight of the damper and the tendency of the charged gas reservoir to extend the piston and rod, these shocks can be difficult to mount when the gas volume is charged with pressure, due to an individual&#39;s inability to compress the rod and piston by hand. This problem has been addressed by providing the damper to the customer in a pre-charged condition, but with a strap or other temporary restraining member retaining the damper in a partially compressed position. After the damper is installed on a vehicle, the strap is removed to permit the damper to extend to its fully extended position. 
         [0008]    Because the gas pressure of the gas volume in a damper affects the overall performance of the damper, maintaining appropriate gas pressure is important. In some instances, however, the mere act of checking the pressure results in a gas volume which is under-pressurized due to the small gas volume and the necessity of utilizing at least a small part of the gas while checking the pressure. Constant checking only exacerbates the issue and often results in an underpressured reservoir. 
         [0009]    What is needed is a way to facilitate the installation of dampers on vehicles while ensuring that the damper will be provided with the appropriate gas pressure in the reservoir portion. Additionally, there is a need for a safe and easy way to determine whether a gas volume in a damper is appropriately charged with the desired amount of gas pressure. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention generally comprises a damper having a damping fluid compensation chamber, or reservoir, with a gas charge. In one aspect, a partition separates a first chamber portion from a second chamber portion, wherein the first portion of the chamber is at a first initial gas pressure and the second portion of the chamber is at a second initial pressure. A valve or frangible member separates the first and second chamber portions and opening the valve commingles the first and second chamber portions so that the combined chamber portions are at a third pressure based on their respective initial pressures and volumes. In another aspect, a piston disposed through a wall of the shock absorber is in pressure communication with a reservoir gas chamber and is biased inwardly toward an interior volume of the chamber, whereby an indicator is movable by the piston (or comprises the piston) in response to a gas pressure in the chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    So that the manner in which the above recited features can be understood in detail, a more particular description, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0012]      FIG. 1  is a section view of a damper with a remote reservoir. 
           [0013]      FIG. 2  is a section view of the remote reservoir of  FIG. 1  showing a pre-charge assembly. 
           [0014]      FIG. 3  is a section view of the remote reservoir of  FIG. 2 , with the pre-charge assembly in a shifted position. 
           [0015]      FIG. 4  is a section view of a remote reservoir showing a gas pressure indicator. 
           [0016]      FIG. 5  is a section view of the remote reservoir of  FIG. 3  with the pressure indictor incorporated therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is a section view of a fluid damper  100  embodiment, typically for a motor vehicle. The main parts for the damper include a fluid chamber  105  and a rod  110  with a piston  115  disposed at the end thereof for extending into the fluid chamber  105 , thereby dividing the chamber into compression and rebound portions respectively on opposite sides of the piston  115 . In  FIG. 1 , the rod and piston are shown in their fully extended position as they would appear at the beginning of a compression stroke (e.g. an uncompressed damper). The damper also includes a remote reservoir  125  or compensation chamber, constructed and arranged to receive damping fluid via a communication, or fluid flow, path  130 . The remote reservoir is divided into a damping fluid  135  and a compressed gas portion  150  with the two portions separated by a floating piston  155  which, as described herein, is sealed with an O-ring  230  and moves against the volume of compressed gas in the gas portion  150  as fluid displaced from the fluid chamber  105  during a compression stroke of the damper moves into the fluid portion  135  of the remote reservoir  125 . 
         [0018]    In one embodiment the damper of  FIG. 1  is often installed as part of a vehicle suspension system and a mounting lug or “eyelet”  160  formed at an end of the fluid chamber is connected to the vehicle frame while another mounting lug  162  disposed at an end of the rod is attached to the vehicle wheel (not shown). As the damper operates, the piston  115  and rod  110  move into and out of the fluid chamber  105 , metering fluid through communication paths  170  and shims in the piston. An annular bumper  175  is disposed at an end of the piston rod  110  to prevent the assembly  100  from reaching a bottom-out condition. 
         [0019]    In addition to the components of the damper described, the damper of  FIG. 1  includes a pre-charge assembly  200  disposed at an end of the remote reservoir  125  (note that if the reservoir were in line with the damper so to would be such a pre-charge assembly). The pre-charge assembly includes a pre-charge gas portion  210  which is separated from the compressed gas portion  150  of the remote reservoir  125  by a partition  215 . The assembly  200  also includes a fill/communication valve  220  constructed and arranged to permit initial charging of the pre-charge gas portion and to allow a user to permit fluid communication between the pre-charge portion  210  and the compressed gas portion  150 . 
         [0020]      FIG. 2  is a section view of the pre-charge assembly  200  of  FIG. 1 . In the embodiments of  FIGS. 1 and 2 , the assembly  200  is located at one end of the remote reservoir  125  of the damper  100  and the pre-charge portion  210  houses a volume of pressurized gas which is retained between an end cap  225  and partition  215 . Both the end cap and the partition are sealed with O-rings  230  or other suitable seals and each is retained axially by structural rings  235  acting against shoulders  240  formed in the cap  225  and partition  215  to maintain structural integrity against the highly pressurized gas (e.g. 600-800 psi in one embodiment) that will be housed in the pre-charge portion  210 . In one embodiment, the compressed gas portion  150  is isolated from the pre-charge portion and gas pressure in portion  150  is limited to atmospheric pressure. The gas pressure in portion  150  may be any suitable low pressure, preferably such that the net extension force acting on rod  110  due to the pressure may be overcome manually. 
         [0021]    Disposed in the pre-charge assembly is a fill/communication valve  220  intended to facilitate initial filling of the pre-charge portion  210  and to provide selective communication between the pre-charge portion  210  and the compressed gas portion  150  of the remote reservoir. Thereafter, the valve  220  provides a way to further fill or adjust the combined gas portion of the reservoir with pressurized gas. The valve is shown with a protective cap  245  threaded onto an end thereof. 
         [0022]    The fill/communication valve  220  includes a central member  250  having external threads  255  which interact with internal threads  260  formed in the end cap  225 , whereby rotation of the central member  250  provides axial movement (corresponding to the thread pitch) of the communication valve  220  relative to the end cap  225 . The central member  250  includes a seal  230  at each end of the threaded portions  255 ,  260 . In one embodiment the cap gland interior seal  230  engages a relatively smooth outer diameter of the central member  250  and seals initial pressure of the pre-charge portion  210  prior to movement of the central member  250  and corresponding gas commingling between the pre-charge portion  210  and the compressed gas portion  150 . An interior portion  265  of the central member is hollow and a first communication path including apertures  270  is formed between the hollow portion of the central member  250  and the pre-charge portion  210  therearound. For example, in  FIG. 2 , gas communication exists only between the pre-charge portion and the central member (permitting the pre-charge portion to be initially charged without introducing gas pressure elsewhere). A second communication path apertures  275  extending from the interior portion  265  of the central member is blocked in the position shown in  FIG. 2 . The result is that in the position of  FIG. 2 , there is no fluid communication from the pre-charge portion to any other operative portion of the damper  100  (i.e. the pre-charge is isolated by the central member  250  and the partition  215 . 
         [0023]      FIG. 3  is another section view of the pre-charge assembly  200  of  FIG. 2  showing the central member  250  in a shifted position, whereby fluid communication, illustrated by arrows  280 , is permitted between the pre-charge portion  210  and the compressed gas portion  150  of the reservoir  125  (via apertures  270 , bore  265  and apertures  275 ). The pre-charge assembly  200  has been shifted by rotation of the central member  250  to provide axial movement of the fill/communication valve relative to the end cap  225  and relative to the partition  215 . In the position shown in  FIG. 3 , compressed gas flows through the first communication path, through the interior portion  265  of the central member and exiting the second communication path  275  which has been placed into fluid communication with the compressed gas portion  150 . Once communication is complete, portions  210  and  125  are combined to effectively form a single larger-volume gas portion at a pressure corresponding to a volume weighted combination of the pressures of the pre-charge and the compressed gas portions. 
         [0024]    In one embodiment, partition  215  comprises a rupture disk or frangible membrane. The membrane contains the pre-charge pressure under initial circumstances with the central member in its initial position. In such an embodiment an end of the central member is proximate the partition but does not necessarily penetrate it. The central member includes a relatively sharp end (end near apertures  275 ) that is capable of piercing the partition upon axial movement of the central member. The central member is axially moved toward the membrane as described herein (or in other suitable fashion) and the sharp end of the central member pierces the partition thereby communicating the pre-charge portion gas with the compressed gas portion gas. That results in gas commingling as described herein. 
         [0025]    Because the operational reservoir pressure (e.g. the combined pressure of the pre-charge and the compressed gas portions) is initially isolated from the active portions of the damper, the rod and piston length can be easily adjusted (for example manually) for installation. Once the damper is installed between mounting points in a vehicle, the central member of the fill/communication valve is threaded inwards, placing the second communication path apertures  275  in communication with the compressed gas portion of the damper, thereby permitting gas communication between the portions. In one aspect, the pre-charge assembly  200  is utilized whereby an end user receives a damper with effectively no gas pressure acting upon the floating piston in the remote reservoir and hence no pressure acting on an end area of the piston rod  110 . In fact, the gas pressure (a higher pressure designed to be commingled at a lower equilibrium pressure) is all stored in the pre-charge portion  210  of the reservoir. With this arrangement, the piston and rod are easily manipulated back and forth in the fluid chamber which facilitates mounting of the damper relative to mounting locations on the vehicle. Thereafter, the pre-charge assembly is shifted and the damper operates normally utilizing the combined gas portions  210 ,  125  as a single gas volume. 
         [0026]    In one example, the fluid damper is intended to operate with 200 psi in the compressed gas portion of the remote reservoir  125 . In one embodiment, 800 psi of pressure is placed into the pre-charge portion. Once the damper is installed and the pre-charge portion shifted, the volume of pre-charge gas at 800 psi commingles with the volume of the compressed gas reservoir at atmospheric pressure resulting in 200 psi is available throughout the reservoir for normal operation in the damper. While the central member  250  is no longer needed to permit or restrict communication between the portions, the fill/communication valve  220  (e.g. Schader type) operates as a fill valve to check and maintain required gas pressure in the remote reservoir  125  throughout the life of the damper. 
         [0027]      FIG. 4  is a section view of a compressed gas portion  150  of a remote reservoir  125  having a gas pressure indicator assembly  300 . As described with reference to the other embodiments of the invention, the compressed gas portion  150  shown in  FIG. 4  is part of a remote reservoir that operates with a floating piston (not shown) acting against a source of pressurized gas to provide increasing and decreasing volume for fluid displaced from a main fluid-filled dampening chamber. Shown in  FIG. 4  is an end of the reservoir housing  305 , an end cap  225  that is sealed with O-rings  315  and retained with structural rings  235 , a fill valve  310  with a cap  311  for communicating pressurized gas into the compressed gas portion  150  and the gas pressure indicator assembly  300 . The purpose of the assembly  300  is to provide a visual indicator of the gas pressure in the gas portion. 
         [0028]    Gas pressure indicator assembly  300  includes a shaft  315  with a piston surface  320  formed at a first end and exposed to the interior of the gas portion  150 , whereby pressurized gas in the gas portion acts upon piston surface  320 . The shaft  315  is sealed in an aperture  330  formed in end cap  225  and sealed with O-ring  230 . The shaft and piston surface are biased towards the interior of the housing by a spring  325 . Opposite the piston surface is an indicator  340  constructed and arranged to be visible only when the shaft/piston surface are depressed against the spring  325  hence allowing  340  to extend beyond a surface of cap  225 . In use, the assembly  300  is designed whereby the spring  325  is overcome and the piston  320  is depressed when a predetermined pressure exists in the gas portion  150  of the reservoir. Such a position is shown in  FIG. 4  with the shaft  315  urged in direction of arrow  316  and the indictor  340  in an extended position where it would be visible to a user. Instead of checking the pressure with a gauge and depleting the gas portion of pressure in doing so (because a pressure gauge requires a volume of the gas being testing and consumes that volume for each test instance), the indicator provides visual assurance of the presence of a certain minimum amount of gas pressure. 
         [0029]      FIG. 5  is a section view of the remote reservoir  125  of  FIG. 3  with pressure indicator assembly  300  incorporated therein. The pre-charge assembly  200  with its pre-charge portion  210  operates as described with reference to  FIGS. 1-3  wherein the pre-charge portion retains the working gas pressure until an end user manipulates a fill/communication valve  220  to permit fluid communication between the pre-charge portion  210  and the compressed gas portion  150  (as described herein). Thereafter, the reservoir functions normally with a predetermined gas pressure available in both portions and both portions combined and functioning as one, larger volume compressed gas portion. Also included is the gas pressure indicator assembly  300 . In the embodiment shown in  FIG. 5 , a portion of the shaft  315  including the piston surface  320  is extended to communicate with the compressed gas portion  150  of the reservoir. The pre-charge portion  210  does not act axially on the shaft  315  because the shaft  315  runs entirely though the portion  210  and protrudes through each end with a diameter equal at each end (i.e. no net piston area on shaft  315  vis a vis volume of portion  210 ). In one embodiment the arrangement shown in  FIG. 5  operates as described herein regarding selective commingling of a pre-charge  210  and a gas compression chamber  150 . In the embodiment of  FIG. 5  the indicator shaft is moved when compressed gas of portion  150  acting on piston area  320  overcomes spring  325  force. As such the indicator provides a visual indication that commingling has been successful following movement of the central member. In this manner, the indicator  340  not only provides a visual indicator of working gas pressure in the reservoir, but is useful in confirming that initial communication has taken place between the portions  210 ,  150  after manipulation of the central member. In  FIG. 5 , the pressure indicator  340  is shown in its extended position indicating the presence of at least a minimum amount of pressure in the compressed gas portion  150 . 
         [0030]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.