Abstract:
A grommet for sealing the wires extending through the wall of a fuel tank is formed by first removing a portion of the covering exposing the strands of wires within. A liquid sealing agent is applied to the strands and the strands are compressed to displace the strands. A hardener is then applied and then the strands are encapsulated in the body of the grommet.

Description:
The present invention relates to an insulated grommet for fitting in an opening in a fuel tank, the grommet having a plurality of covered electric wires passing therethrough, with each of said wires being made of a plurality of strands. 
     BACKGROUND OF THE INVENTION 
     The fuel tanks of vehicles have certain electrical apparatus therein, including a detector for detecting the volume of liquid in the tank and a pump for pumping fuel from the tank to the engine of the vehicle. Wires extend from outside the tank through an opening and into the tank to connect the electrical devices inside the tank with the apparatus of the vehicle. Each of the wires typically consists of about twenty smaller strands of copper wire wound together and surrounded by a plastic insulation layer, which is gasoline resistant. The wires passing through the walls of the tank are sealed against leakage by a grommet. 
     It has been found that the chemicals of a hydrocarbon fuel form a vapor which migrates between tiny gaps in the strands of wire, inside the insulating coating surrounding the wire. Regulations of the United States government prohibit virtually any leakage of fuel from the fuel tank and therefore, if wires passing through the walls of a fuel tank are not adequately sealed, the vehicle will violate government regulations. 
     To prevent all of the forgoing, it is desirable to provide a grommet fitted into the opening of a fuel tank that permits the wires to pass therethrough, but provides a seal to prevent gasoline vapors from migrating between the strands and outside of the tank. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention is embodied in a grommet having a body with an exterior configuration sized and shaped to seal against an opening in the fuel tank of a vehicle. The grommet has an inner end and an outer end with a plurality of stranded covered wires extending from the inner end, through the grommet and outward of the outer end. The covering is removed from a portion of the wires exposing the bundle of strands that make up each of the wires and a sealing agent permeates into the gaps between the strands and surrounds the circumference of the bundle of strands to seal the bundle against the inner surface of the body of the grommet. 
     To make a grommet in accordance with the invention, a portion of the covering of each of the wires that is to be enclosed within the grommet is removed exposing the individual strands. A gasoline resistant sealing agent is then applied to the surface of the exposed strands. The gaps between the strands are very small and the bundle of strands is dense, and as a result, the application of a liquid to the outer surface of the bundle will not result in the liquid permeating the bundle and wetting all the surfaces of all the strands. To facilitate this wetting of all the strands, the exposed strands, while in the presence of the liquid sealant, are displaced with respect to one another such that each of the exposed strands becomes coated with a portion of the liquefied sealing agent. 
     In the preferred embodiment, the bundle of strands is compressed for a short period of time between a pair of parallel spaced apart planar surfaces thereby causing the various strands to become displaced during the interval of time that the compression occurs. When the bundle is subsequently released from compression, the strands may return to their original configuration causing the strands to again displace with respect to one another and further coating the surfaces of the strands. It should be appreciated that the purpose of applying a compressive force to the bundle is to cause displacement of the strands and not to compress the strands into a single mass. 
     After the strands have been coated with the liquefied sealing material, the strands are treated to cause the liquefied sealing agent to harden. Where the liquefied sealing agent is in the form of a gasoline resistant liquefied polymer, the treating agent will cause the liquefied polymer to crosslink and harden into a mass that will fill the gaps between the individual strands of the bundle and will surround the exterior of the bundle. Where the liquefied sealing agent is in the form of a liquefied rubber, the strands are subjected to a vulcanizing agent to cause the liquefied rubber to solidify. 
     After the sealing agent has surrounded the various strands of the exposed wires and the liquefied sealing agent has been treated to cause the liquefied sealing agent to harden, the strands are then encapsulated in a hermetically sealed body that forms a portion of the grommet. Where the grommet is to be made of a plastic material formed by injecting a heated liquefied plastic material into a mold and allowing the plastic material to cool and harden, and where the treatment required to harden the liquefied sealer also requires the application of heat, the heat required to harden the sealant may at least in part be derived from the heat released in the formation of the plastic body of the grommet. Where the heat needed to form the plastic body also hardens the sealing agent, the outer surface of the bundle of strands will become securely bonded to the mass of plastic forming the body of the grommet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be had after a reading of the following detailed description taken in conjunction with the drawings wherein: 
         FIG. 1  is a cross-sectional view of a grommet manufactured in accordance with the method of the present invention and fitted into an opening in a fuel tank; 
         FIG. 2  is an enlarged side elevational view of one of the covered wires that pass through a grommet made in accordance with the present invention with a portion of the covering removed to expose the strands that make up the wire; 
         FIG. 3  is an enlarged side elevation view of a portion of the wire shown in  FIG. 3  being subjected to a compressive force to displace the various strands thereof after the outer surface of the bundle has been moistened with a liquefied sealing agent; 
         FIG. 4  is an enlarged cross-sectional view of the strands being compressed taken through lines  4 - 14  of  FIG. 3 ; 
         FIG. 5  is another side elevational view of the several lengths of wire such as is shown in  FIG. 2  after the strands have been released from compression and returned to their original orientation and inserted into a mold for forming the body of the grommet. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , to prevent gasoline vapors from escaping from a fuel tank  10  by migrating under a cover surrounding the strands that make up the lengths of wire  12 ,  13 ,  14 ,  15  that extend from inside the fuel tank  10  to an outside location, a grommet  16  manufactured in accordance with the present invention is provided. The grommet  16  has a body  18  made of a suitable gasoline resistant plastic having inner and outer surfaces  24 ,  26  respectively and a generally cylindrical outer wall  20  that tightly fits within a cylindrical opening  22  in the wall of the fuel tank  10 . Between the cylindrical outer wall  20  of the grommet  16  and the opening  22  in the fuel tank  10  is an O-ring  27  for sealing against leakage of fuel out of the tank  10 . 
     Referring to  FIGS. 2 ,  3 , and  4 , each of the various lengths of wire  12 - 15 , of which wire  12  is representative of all such lengths of wire  12 ,  13 ,  14 ,  15 , consists of a plurality of strands of copper wire with the strands wound together to form a bundle that extends through a covering  30 . Each of the lengths of wire  12 - 15  extends into an aperture in the inner surface  24  of the grommet  16 , through the body  18 , and out of the outer surface  26  thereof. 
     To seal the various conductive strands  28 - 28  that make up the bundle enclosed within the covering  30 , a portion of the covering  30  is removed leaving an uncovered portion  32  having a first end  34 , beyond which the covering extends around the portion of the wire passing through the inner surface  24  of the grommet  16 , and a second end  36  beyond which the covering extends around the portion of the wire  12  passing through the outer surface  26  of the grommet  16 . To seal the various strands  28 - 28  so as to prevent molecules of gasoline from migrating between gaps separating adjacent strands, a small amount of liquefied sealing agent  38  is applied to the outer surface of the bundle of strands  28 - 28 . Blended into the sealing agent  38  is a suitable curing agent that will, with the passage of time and sometimes with the application of heat, cause the liquid sealant to harden and become resistant to gasoline. 
     When the liquefied sealing agent  38  is first applied to the outer surface of the bundle of strands  28 - 28 , the innermost strands may not become wetted by the liquefied sealing agent where the number of strands  28 - 28  that make up the wire are numerous, perhaps eight or more. To moisten the surfaces of all the strands  28 - 28  that make up such a bundle, the outer surface of the bundle is compressed between a pair of opposing spaced apart parallel surfaces  40 ,  42 . The surfaces  40 ,  42  may be made of a suitable steel or other hard material that will not become distorted over time as pressure is applied to the strands and may have any of a number of shapes. The surfaces  40 ,  42  may be planar as depicted, but regardless of the shape, the surfaces must not define sharp edges that could damage one or more of the strands  28 ,  28 . One of the wires  12  is positioned between the surfaces  40 ,  42  such that the wire  12  and the strands  28 - 28  thereof extend generally parallel to the surfaces  40 ,  42 . In accordance with the invention, pressure is applied across of the surfaces  40 ,  42  to compress the strands  28 - 28  and cause them to become displaced with respect to one another. The displacement of the strands  28 - 28  causes small gaps to open between the various strands and causes the movement of one strand relative to another strand such that the liquefied sealing agent  38  is drawn between the strands and applied to the surfaces of various strands  28 - 28  thereby moistening them with the liquefied sealing agent. 
     It should be appreciated that where there are only a few strands  28 - 28  that make up the conductive elements of the wire, perhaps five, six, or less, it would not be necessary to displace the strands. In this case, the liquefied sealing agent will wet the strands and fill the cavities between the strands  28 - 28  without requiring that the strands be displaced. 
     In one modification of the invention, one of the planar surfaces  40  may be moved in a linear direction parallel to the second horizontal surface  42  and perpendicular to the axial length of the strands of wire  28 - 28 , as shown in  FIG. 4 , while the strands are compressed to further displace the strands, if it is found that the mere compression of the strands is insufficient to moisten all of the surfaces of the strands. 
     It should be appreciated that it is not the intent of the compression process to distort the cross-sectional configuration of the various strands or to compress them together into a single mass because such compression could damage the strands and reduce the overall conductivity of the wire  12 . It should also be appreciated that after the compression applied by the surfaces  40 ,  42  has been released, the wires will generally reconfigure and at least partially resume their original shape thereby causing further displacement of the strands and further contributing to the wetting of the surfaces thereof. Accordingly, once the strands  28 - 28  are removed from the compressive force applied by the planar surfaces  40 ,  42 , the reconfigured strands  28 - 28  will be wetted throughout and a coating of sealing agent will also surround the outer circumference of the bundle. 
     Once the bundle of strands  28 - 28  has been fully wetted, the sealing agent  38  can be re-applied, if necessary, to the outer surface of the bundle of strands  28 - 28 . The sealing agent may include one or more solvents, in which case the sealing agent should be dried in the air or heated in an oven. The dried sealing agent should then be cured, where the curing process is a crosslinking or vulcanizing process. Depending upon the kind of sealing agent employed, the curing process can be achieved by ultraviolet light, baking the strands in the oven, or curing by the heat needed to form the body of the grommet  20 . 
     It should be appreciated that any of a number of sealing agents may be used to seal the strands  28 - 28  in accordance with the invention. For example, the strands may be sealed using a liquefied polymer which becomes fuel resistant when subjected to a crosslinking agent. One such liquefied polymer is sold under the trademark Kraton and manufactured by The Kraton Polymers Group of Companies. Kraton and the associated crosslink agents can be mixed and dissolved in a solvent then coated on the stripped area of the wire as described above. The coating is then dried in the air or oven and the coated wires are then baked in the oven to achieve the crosslinkage of the polymer, thereby forming a fuel resistant seal. 
     It should also be appreciated that certain rubbers, such as hydrogenated nitride butadiene rubber (HNBR) or NBR can be mixed with a suitable curing agent, or vulcanizing agent, and dissolved in a suitable solvent. The various strands  28 - 28  can then be coated with the mixture after which the coated strands are dried. 
     It should also be appreciated that many fluro silicones are soluble in suitable solvents such as DC730 RTV sold by Dow Corning and the Sifel series sold by Shin-Etsu. These liquids may also be used to coat and seal the strands  28 - 28  to form a fuel resistant seal. 
     In all cases, the sealing agent should be resistive to gasoline. Gasoline resistant polymers are know to swell in some measure when exposed to gasoline, but where the polymer occupies the spaces between the strands  28 - 28  that make up the length of wire  12 , the slight expansion of the polymer will assist in further sealing the gaps between the strands and prevent the migration of molecules of gasoline from escaping the interior of the gas tank  10 . 
     Referring to  FIGS. 1 and 5 , after the surfaces of the various strands  28 - 28  have been wetted by the liquefied sealant  38 , the length of wire  12  and other wires  13 ,  14 ,  15  are inserted into a mold  46 , the inner surface of which is complementary to the outer shape of the grommet  16 . Thereafter, the mold  46  is filled with a suitable liquefied plastic material  48  which when hardened will form the body  18  of the grommet  16 . As the material  48  that forms the body  18  of the grommet  16  hardens, the plastic of the body  18  will adhere to the hardening sealant  38  that permeates the bundle of strands  28 - 28 , further sealing the bundle against migration of gasoline molecules. 
     It should be appreciated that the chemistry employed to form the plastic body  18  of the grommet  16  may include the adequate applications of heat required to cause the liquefied sealing agent  38  to harden. It should also be appreciated that, certain liquefied sealing agents  38  may require only the application of heat to cause the sealing agent to harden to a solid and that a separate hardening agent, other than the application of heat, may not be required. 
     While the present invention has been described with respect to a single embodiment, it will be appreciated that many modifications and variations may be made without departing from the true spirit and scope of the invention. It is therefore the intent of the following claims to cover all such variations and modifications that fall within the true spirit and scope of the invention.