Abstract:
An improved thermal relief vent for a fuel tank, and a method of manufacturing the same, includes a thermal relief ring that is used to create a mechanical seal within the vent. The thermal relief ring, at room temperature, is crimped in place by use of the vent cap itself. The crimped thermal relief ring creates a mechanical seal between the vent and the vent cap, up until a predetermined thermal relief point, at which time the thermal relief ring will soften and/or yield and release the vent cap from the vent body.

Description:
TECHNICAL FIELD 
   The present invention relates to an improved thermal relief vent for a fuel tank wherein a thermal relief ring creates a mechanical seal within the vent and, more particularly, to an improved thermal relief vent wherein a thermal relief ring is crimped in place by the vent cap. The crimped thermal relief ring creates a mechanical seal between the vent and the vent cap, up until a predetermined thermal relief point, at which time the thermal relief ring will soften and/or melt and release the vent cap from the remainder of the vent. 
   BACKGROUND OF THE INVENTION 
   Fuel tanks, such as those used on commerical vehicles, are subject to a number of safety requirements. One of these safety requirements is the inclusion of a thermal relief system that allows venting of pressure within the fuel tank when the tank reaches a predetermined temperature. One type of thermal relief system is disclosed in U.S. Pat. No. 5,111,837 to Morris, which discloses a termal relief valve including a ring of fusible material that is cast in situ within a chamber positioned between an abutment member and a plate. At elevated temperatures the fusible material melts to allow the plate and the abutment member to slide relative to each other such that the plate may move outwardly from the vent, thereby releasing pressure within the fuel tank. 
   There are several disadvantages with such an in situ casting method. In particular, molten fusible material, such as molten metal, is required which requires subjecting workers to the hazards of handling high temperature molten metals. There are costs in generating and maintaining the molten material, as well as the safety equipment that must be purchased to work with such molten material. Additionally, employers generally must monitor the level of toxic metals in employee&#39;s bodies to ensure the safety of the process. 
   The in situ casting method, which involves injecting molten metal into a cavity, could result in air bubbles or an otherwise imperfect fill of the cavity, rendering the cast ineffective. Moreover, an imperfectly filled cavity may not be readily visible or otherwise detectible, such that a defective thermal relief vent may be sold to end consumers and installed on a vehicle. Additionally, the releasable vent plate generally must be held in position before, during and for a short time period after the molten material is poured, so that the molten material will solidify with the plate correctly positioned. The logistics of holding the plate in place before, during and shortly after the molten material is poured adds complexity to the in situ casting process. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved thermal relief vent for a fuel tank, and a method of manufacturing the same, wherein a thermal relief ring is used to create a mechanical seal within the vent. More particularly, the improved thermal relief vent includes a thermal relief ring that, at room temperature, is crimped in place by the vent cap itself. The crimped thermal relief ring creates a mechanical seal between the vent and the vent cap, up until a predetermined thermal relief point, at which time the thermal relief ring will soften and/or melt and release the vent cap from the remainer of the vent. 
   The manufacturing process of crimping a solid ring of fusible material in place with use of the vent cap itself alleviates many disadvantages of the prior art. Namely, use of a room temperature ring of fusible material eliminates many hazards and expenses associated with the use of molten metal. Additionally, use of a ring of fusible material eliminates the problems associated with casting such as air bubbles and partially filled casting chambers. Moreover, crimping of the fusible ring by use of the vent cap itself eliminates the need for holding the cap in place during casting. 
   In a preferred embodiment the method comprises providing a ring of fusible material, such as lead, and crimping the lead ring in place between the body of the vent and a vent cap by applying pressure to the vent cap when seated on the vent body. Crimping of the ring of fusible material causes the ring to “flow” into and around one or more annular grooves positioned on an inside surface of the vent body and on an exterior surface of the vent cap, to create a mechanical seal between the body and the cap. 
   Accordingly, an object of the present invention is to provide a thermal relief vent that provides an airtight seal on a fuel tank during normal thermal conditions. 
   Another object of the present invention is to provide a thermal relief vent that releases pressure within a fuel tank upon the tank reaching a predetermined temperature. 
   Still another object of the present invention is to provide a thermal relief vent that is installed without the use of molten fusible material. 
   Yet another object of the present invention is to provide a thermal relief vent that is manufactured by a mechanical crimping operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of the thermal relief vent with the vent cap and ring of fusible material crimped therein, with the vent shown in a pressurized configuration; 
       FIG. 2  is a cross-sectional view of one embodiment of the vent cap; 
       FIG. 3  is an isometric view of the ring of fusible material; 
       FIG. 4  is a cross-sectional view of the thermal relief vent with the vent cap and ring of fusible material crimped therein, with the vent shown in a non-pressurized configuration; 
       FIG. 5  is a detailed cross-sectional view of one embodiment of the cap and ring of fusible material prior to crimping thereof; 
       FIG. 6  is a detailed cross-sectional view of the cap and ring of fusible material after crimping thereof; and 
       FIG. 7  is an isometric view of the float and the float seal of the thermal relief vent. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the figures,  FIG. 1  shows a cross-sectional view of the thermal relief vent  10  with the vent cap  12  positioned on the vent body  14 , and a ring of fusible material  16  crimped therein, with the vent shown in a pressurized configuration. In the embodiment shown, vent body  14  comprises an elongate float section  18 , also referred to as a cage tube section  18 , which houses a ball  20  and a float  22 . Cage body  18  includes a crimped end portion  24  which prevents the exit of ball  20  and float  22  from an interior  26  of cage body  18 . The crimped end portion  24  and apertures  28  allow fuel and pressure within the fuel tank to communicate with interior  26  of cage body  18 . In a pressurized configuration, i.e, when the interior of the fuel tank and therefore the interior  26  of the cage body  18  is subject to a pressure above a first predetermined value, or in the condition of partial tank rollover, the fuel level will cause float  22  to move in a direction  30  within vent body  14  such that a seal  32  positioned on float  22  will contact a vent valve  34 , having a lower opening  34   a , positioned within a neck portion  36  of vent body  14 . A spring  38  is positioned within neck portion  36  of the vent body  14 , and, up until a second predetermined pressure is exerted against the spring in direction  30 , the spring  38  exerts a pressure on vent valve  34  in a direction  40 , forcing an O-ring  42  of the vent valve  34  against a seat  44 , or shoulder  44 , of neck portion  36  of vent body  14 . Once the pressure within the tank exceeds the second predetermined pressure, float  22  moves further in direction  30 , thereby forcing vent valve  34  further in direction  30 , thereby slightly compressing spring  38  in direction  30 . This movement of vent valve  34  in direction  30 , so that O-ring  42  is no longer in contact with shoulder  44 , allows fuel or pressurized gas within the fuel tank and vent to escape from the vent  14  through an aperture  46  of neck portion  36  and out of the vent body  14  through a hose barb  48 . 
   Still referring to  FIG. 1 , spring  38  is retained within neck portion  36  of the vent body  14  by vent cap  12  and ring of fusible material  16 . In particular, during assembly of thermal relief vent  10 , ring of fusible material  16  (shown more clearly in  FIG. 3 ) is positioned in an annular recess  50  of vent neck portion  36 . Vent cap  12  is then crimped on the vent body  14 , i.e., vent cap  12  is forced in direction  40  against ring of fuisible material  16 . Ring  16  typically is manufactured of a thermal relief material, i.e, a material that will soften or otherwise yield upon reaching a predetermined temperature. In a preferred embodiment, ring  16  is manufactured of an alloy of lead, but other thermal relief materials may be utilized for particular applications. As vent cap  12  is forced or crimped in direction  30 , fusible ring  16  “flows around” one or more threads  52  on vent cap  12 , one or more threads  54  in annular recess  50  of vent neck portion  36 , and throughout annular recess  50  of neck portion  36  and throughout recess  51  of vent cap  12 . Vent cap  12  is crimped on vent body  14  until a shoulder  56  of the vent cap  12  abutts the top portion  58  of vent body  14 . With the cap  12  in this crimped position on body  14 , the ring of fusible material  16  has “flowed” around threads  52  and  54 , and typically has filled annular recesses  50  and  51  such that ring  16  creates a mechanical and an airtight seal between vent cap  12  and vent body  14 . Accordingly, in the method of manufacturing the thermal relief vent  10  of the present invention, vent cap  12  itself is used as the force mechanism to seat ring  16 . 
   Use of cap  12  itself to apply a force to ring  16  eliminates the positioning problems posed by the prior art wherein the cap must be held in place while molten metal is injected around the cap. Moreover, the crimping method of the present invention eliminates the need for the use of molten metal, thereby eliminating the hazards and costs associated with molten metal casting operations. Additionally, the ring  16  of fusible material utilized in the present invention typically has a circumference that matches the circumference of annualar recess  50  of neck portion  36  such that the mechanical seal of fusible material positioned between vent cap  12  and vent body  14  fills the entirety of annualar recesses  50  and  51  and does not include air pockets, as do some cast seals of the prior art. 
   As stated above, ring  16  typically is manufactured of a thermal relief material, i.e, a material such as a lead alloy that will soften or otherwise yield upon reaching a predetermined temperature. For example, when thermal relief vent  10 , or the contents within a fuel tank on which the vent is mounted, reaches a predetermined temperature, the fusible material will also be subjected to the predetermined temperature. Upon reaching this predetermined temperature, fusible material  16  will soften or yield, thereby allowing cap  12  to become loosened with respect to vent body  14 . Upon softening of fusible material  16 , the mechanical seal created by the fusible material is weakened such that spring  38 , or pressure within interior  26  of vent body  14 , will force vent cap  12  from vent body  14  in direction  30 . Once vent cap  12  is forced from vent body  14 , pressure within interior  26  of the vent body is vented out an opening  60  of vent body  14 . 
   Each of the components of vent  10  typically are manufactured of a material that will withstand the high temperatures and pressures, and the harsh environmental conditions associated with the commercial trucking industry. In one embodiment, cap  12 , body  14  and hose barb  48  are manufactured of brass. Float ball  20  and spring  38  may be manufactured steel. Float  22  typically is manufactured of plastic or another like bouyant material. Seal  32  and O-ring  42  typically are manufactured of a flexible material, such as rubber, plastic or the like. 
     FIG. 2  shows a cross-sectional view of vent cap  12  including shoulder  56 , external threads  52 , annular recess or groove  51 , and an interior recess  62  for receiving spring  38 . Annular groove  51  defines a diameter  64  and shoulder  56  defines a slightly larger diameter  66 . 
     FIG. 3  shows an isometric view of the ring of fusible material  16 . Ring  16  typically has a diameter  68  approximately the same size as diameter  64  of cap  12 , and smaller than diameter  66  of cap  12 . Ring  16  may be manufactured by taking an elongate piece of fusible material, cutting it to a preferred length, and then bending it into a circular shape as shown in  FIG. 3  such that ends  70  and  72  abutt one another. In another embodiment, ring  16  may be manufactured by taking an elongate piece of fusbile material, cutting it in a preferred length, and then bending it into a circular shape such that ends  70  and  72  overlap one another. In yet another embodiment, ring  16  may be stamped, such as in the circular shape as shown, from a sheet of fusible material. In still another embodiment, ring  16  may be cast from molten material. Applicants note that such a casting method may be conducted for the fabrication of ring  16 , prior to placement of the solid, previously formed ring  16  within body  14 . In a preferred embodiment, a lead “wire” is wound into a helix on a mandrel. The helix is then cut along the length of the mandrel to form many lead rings with a single cut. 
     FIG. 4  shows a cross-sectional view of the thermal relief vent  10  in a nonpressurized configuration. In particular, float  22  is shown in a lowered position such that seal  32  on the float is not in contact with vent valve  34 . 
     FIG. 5  shows a detailed cross-sectional view of the cap  12 , body  14  and ring  16  of fusible material prior to crimping thereof. Prior to crimping of cap  12  to vent body  14 , cap  12  is positioned above opening  60  of the vent body. Cap  12  may be held in such a position, for example, manually by a assembly device  73  that has a recess  75  into which the top portion  74  of cap  12  seats. Recess  75  generally is similar in shape to cap  12  such that device  73  is self aligning. Cap  12  is held in this seated and centered posiiont by the force of spring  38  (not shown in this figure). Ring  16  is positioned on shoulder  44 , within annular recess  50  and adjacent threads  54  of of vent body  14 . A diameter  76  of threads  54  and recess  50  of vent body  14  typically is slightly larger than diameter  64  of threads  52  and recess  51  of cap  12  such that the threads  52  and  54  do not mate with one another but are positioned adjacent one another. In this manner, fusible material  16  may “flow” around threads  52  and  54 , and through recesses  50  and  51  so as to secure cap  12  on vent body  14 . In another embodiment, threads  52  and  54  may mate with another another (such that diameters  64  and  76  are approximately the same size), thereby requiring cap  12  to be twisted or turned with respect to body  14 , in order for cap  12  to be received within annular recess  50  of vent body  14 . In this embodiment wherein the threads mate with one another, a sufficient amount of space will still remain between the mating threads so that ring  16  will “flow” around threads  52  and  54  during crimping of cap  12  to body  14 . 
     FIG. 6  shows a detailed cross-sectional view of cap  12 , body  14  and ring  16  of fusible material after crimping thereof wherein assembly fixture  73  has been removed. In particular, to secure cap  12  to body  14 , cap  12  is moved in direction  40  toward body  14  by assembly  73  with a force great enough to cause fusible material  16  to flow, i.e., to deform, such that fusible material  16  conforms to the shape of annular recesses  50  and  51 , and threads  52  and  54 . Of course, body  14  can be moved toward cap  12  or both the body and cap may be moved toward each other. The force exerted against cap  12  and body  14  should preferrably be sufficient to cause deformation of ring  16  but less than the force required to deform cap  12  and body  14 . The amount of force required for any particular application will depend on, for example, the size and shape of threads  52  and  54 , the size of annular recesses  50  and  51 , the type of fusible material used to manufacture ring  16 , the size of ring  16 , and the depth of threads  52  and  54 . As shown in  FIG. 6 , ring  16  forms a mechanical and an airtight seal between cap  12  and body  14  such that cap  12  will not become displaced with respect to body  14  until ring  16  is softened thereby allowing cap  12  to be removed therefrom. 
     FIG. 7  shows an isometric view of the float  22  and the float seal  32  of the thermal relief vent  10 . In the embodiment shown, float  22  comprises an elongate float having a generally square cross sectional shape wherein top surface  78  is solid and a lower surface  80  allows access to a hollow interior  82  of the float. A tab  84  extends outwardly from a side surface  86  of the float and engages an aperture  88  of seal  32 . Seal  32 , in the embodiment shown, is manufactured with a bend  90  in a midsection thereof, such that an end region  92  of the seal is positioned overlying top surface  78  of float  22 . Due to bend  90  of the seal, and due to the flexible and resilient nature of the material from which seal  32  is manufactured, end region  92  of the seal is flexibly positioned on top surface  78  of the float. As shown more clearly in  FIG. 1 , top surface  78  of float  22  may include an upwardly extending projection  94  sized to be received within opening  34   a  of vent valve  34 . Accordingly, in the pressurized condition shown in  FIG. 1 , projection  94  is aligned with opening  34   a  such that seal  32  contacts the lip of opening  34   a  around a circumference thereof. Moreover, due to bend  90  of the seal  32  on float  22 , the seal is loosely positioned above top surface  78  of the float such that the seal will be correctly positioned for contact with opening  34   a  of the vent valve. Because seal  32  is secured to side surface  86 , tab  84  is positioned away from top sealing surface  78  of the float and, therefore, will not interfere with sealing of the vent. 
   In the above description numerous details have been set forth in order to provide a more through understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced using other equivalent designs.