Abstract:
The invention relates to a monolith retainer for a fuel canister. The retainer has a head portion for retaining a monolith within a chamber of the fuel canister and a plurality of resiliently biased leg members, which extend from the head portion along a length of the monolith being retained. The legs are resiliently biased toward the inner wall of the chamber such that, when the monolith resides within the chamber, contact feet of the resiliently biased leg members abut against the monolith. A support ridge is also provided for preventing the monolith from traveling too far into the canister.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The present invention relates to a monolith retainer, particularly, but not exclusively for use in retaining a monolith in position within a fuel canister of an automobile. 
       BACKGROUND OF INVENTION 
       [0002]    Automobiles are typically provided with fuel canisters for reducing vapour emission from the fuel tank. This is often achieved using a carbon based monolith which is placed in line with the canister in order to adsorb vapours from the fuel tank. Such monoliths may be located remotely from the canister and connected via a pipe or may be installed in a suitable chamber integrated into the canister body. 
         [0003]    In order to secure the monolith within the integrated chamber and to ensure that vapour flows through the monolith (rather than around it) it is typically sandwiched between a pair of rubber seal plugs. However, the material required for these seals to retain the monolith securely and to ensure a sufficient seal to the vapour, is relatively expensive. Furthermore, the monolith (which is typically manufactured from a brittle material) is easily damaged during insertion into the chamber. 
         [0004]    Another problem with current monolith chamber arrangements is that, once in position, a resilient compensation system typically compresses the monolith arrangement from above. This can cause undesirable axial movement of the monolith within the chamber after manufacture of the fuel canister. 
       SUMMARY OF THE INVENTION 
       [0005]    According to the present invention there is provided a monolith retainer having a head portion for retaining a monolith within a chamber, at least one resiliently biased leg member which extends from the head portion along a length of the monolith and is resiliently biased toward the inner wall of the chamber such that when the monolith resides within the chamber at least a portion of the resiliently biased leg member abuts against a portion of the outer surface of the monolith. 
         [0006]    Further features and advantages of the invention will appear more clearly on a reading of the following detail description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    Embodiments of the present invention will be further described with reference to the accompanying drawings in which: 
           [0008]      FIG. 1  is a transverse partial cross sectional diagram illustrating the installation of a monolith into the monolith chamber using prior art sealing plugs; 
           [0009]      FIG. 2  is a transverse partial cross sectional diagram illustrating the installation of a monolith into the monolith chamber using the monolith retainer according to the present invention; 
           [0010]      FIG. 3  is a transverse partial cross sectional view of the monolith of  FIG. 2  installed in the canister; 
           [0011]      FIG. 4  is perspective partial cut-away view of the monolith of  FIG. 3  from the end side of the monolith; and 
           [0012]      FIG. 5  is a perspective partial cut-away view of the monolith of  FIG. 3  from the vapour end of the monolith. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0013]    In the following description the term “vapour end” is used to describe the end of the monolith closest to the vapour supply from the fuel tank, and the term “air end” describes the end of the monolith closest to the adsorbed output from the monolith. 
         [0014]    Referring to  FIG. 1 , in prior art canisters, the monolith  10  is inserted into a monolith chamber  12  by pushing it in the direction indicated by arrow A. The monolith chamber  12  has an upper section  11  and a lower, relatively small diameter section  18 . A filter  14  and seal  16  are placed at the air end of the monolith  10  during insertion. Once in position, the seal  16  ensures that no gases (vapour/air) may pass from the upper section  11  and out of the lower section  18  without having passed through the monolith  10 . Once in position in the lower section  18  of the chamber  12 , the air end of the monolith  10  sits in the seal  16  body and is discouraged from being pushed out of the bottom of the lower section  18  due a gradual taper in the walls of the lower section  18 . A further seal  20  is simultaneously pushed onto the vapour end of the monolith  10 . The seal  20  ensures that no vapour may pass from the upper section  11  and into the annulus between the monolith  10  and the inner walls of the lower chamber  18 . The seal  20  also retains the monolith  10  in the lower portion  18  of chamber  12  against the seal  16 . In order to prevent carbon from entering the monolith, a plate  22  is also inserted on top of the seal  20 . A screen  24  is then placed on top of this arrangement. 
         [0015]    A problem with the prior art arrangement of  FIG. 1  is that in order to ensure that the monolith is held securely in place within the lower section  18  of the monolith chamber  12 , it must be pushed in firmly. However, the tapered nature of the lower section  18  walls allows the seal  20  to be pushed too far into the monolith chamber  12 . This can jam the monolith into the lower section  18  and often results in damage to the monolith  10  and/or the seals  16 ,  20  resulting in a decrease in performance of the resulting canister arrangement. Furthermore, although the gradual taper in the walls of the lower section discourage the monolith from being pushed further into the monolith chamber, over time it may do so due to the resilience provided by compensation systems typically used to compress such monolith arrangements. 
         [0016]    Referring to  FIG. 2 , apparatus according to the present invention will now be described. It should be noted that the present embodiment requires minimal or no modification of the monolith chambers typically provided in current fuel canisters. 
         [0017]    In the embodiment of the present invention shown in  FIG. 2 , the monolith retainer  33  has a circular head portion  34  (best illustrated in  FIGS. 4 and 5 ) with a central hole  35  passing there through. Support struts  36  extend across the hole. Four resiliently biased elongate securing members in the form of legs  38  project downwardly and outwardly from the head portion  34  and are circumferentially spaced there around. Securing lips  40  flare outwardly from the end of the legs  38 . Contact feet  42  also extend from the middle of each leg  38  toward the central axis of the monolith retainer  33 . 
         [0018]    The circular head portion  34 , support struts  36 , legs  38 , lips  40  and contact feet  42  are all integrated into a simple component which may be manufactured from a suitably resilient plastic material. 
         [0019]    The monolith chamber shown in  FIG. 2  is also provided with a support ridge  37  at the lower inner circumference of upper section  31 . Alternatively, an equivalent support could be provided by integrating support ridges into the monolith retainer  33 . 
         [0020]    When installing the monolith  30  into the monolith chamber of a fuel canister, the monolith retainer  33  is pushed in the direction indicated by arrow A on  FIG. 2  against the monolith  30  seal  44  and filter  46 . This causes the monolith  30  and seal  44  to progress from the upper section  31  to the lower section  50  of the monolith chamber  32  until the seal  44  and filter  46  are prevented from moving further down the lower section  50  past a pre-determined point (chosen to avoid damage of the monolith  30 ) by contact between the head portion  34  of the monolith retainer  33  and the support ridge  37 . The lips  40  of the legs  38  are prevented from splaying outwards by the inner surface of the lower section  50  and all of the insertion force in the direction A is transferred to the monolith  30 . At this point the contact feet  42  create a high level of frictional contact against the outer surface of the monolith and prevent it from moving relative to the monolith retainer  33 . Once the filter  46  and seal  44  are prevented from moving further down the lower section  50 , the monolith  30  is also prevented from traveling any further into the lower section  50 . At the same time lips  40  align with recesses  48  provided in the monolith chamber lower section  50 . The resilient nature of each lip  40  (which are an extension of legs  38 ) causes them to flare outwardly into each corresponding recess  48 , as shown in  FIGS. 4 and 5 . 
         [0021]    The above described arrangement secures the monolith  30  within the lower section  50  of the monolith chamber  32 . This is shown in  FIG. 3  along with the typical location of the chamber  32  relative to the canister body  54 . In this regard the contact feet  42  on each leg  38  also centralises the monolith  30  in the lower section  50 . 
         [0022]    An important feature of this arrangement is that any further application of force in the direction A will no longer result in any force being applied to the monolith  30  but will instead simply press the head portion  34  of the monolith retainer  33  against the support ridges  37 . This prevents damage to the monolith  30 /seal  44 . Furthermore, the abutment of ridge  37  and head portion  34  spaces the head portion  34  from the lower section  50  when installed. Another effect of this arrangement is that the monolith retainer  33  and monolith  30  will not be moved further into the monolith chamber under the effect of spring compensation systems which are typically provided above the monolith. 
         [0023]    Once in position, a screen  52  equivalent to screen  24  of the prior art may placed on top of the monolith retainer  33 . 
         [0024]    The circular head portion  34  may have a seal around its outer circumference in order to provide a sealing action equivalent to the that provided by seal  20  of the prior art. However, such a seal is not essential since any flow of vapour from the fuel tank toward the monolith chamber can only escape there from by passing through the monolith  30  and out from the lower section  50 . In this case, the skilled reader will note that recesses  48  should be enclosed to prevent any escape of vapour flow there from. 
         [0025]    Modifications and improvements may be made to the foregoing, without departing from the scope of the present invention, for example: 
         [0026]    Although four legs are circumferentially spaced around the monolith retainer in the embodiment shown, this may be altered to a minimum number in order to minimise the cost of producing the monolith retainer or may be increased to, for example, eight legs, in order to maximise the support provided by the monolith retainer whilst spreading the pressure exerted by the feet over a greater surface area of the monolith. 
         [0027]    While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.