Abstract:
A cover for the spark plug boot and an ignition wire connected with spark plug of an engine includes a woven fiberglass sheath surrounding the spark plug insulator and spark plug boot and having an entrance cuff formed with an inner end flap stitched to form a pocket for capturing the end strands of the sheath, forming a four plug end construction that maintains the circularity of the opening and reduces the harmonic vibration in the sheath during engine operation.

Description:
RELATED APPLICATION 
   This application is a continuation-in-part application of U.S. Ser. No. 10/753,285 filed on Jan. 9, 2004 now U.S. Pat. No. 6,810,847 Ernest T. Jefferson and entitled “Charge Dissipative Cover for Spark Plug, Ignition Wire and Boot”. 

   FIELD OF THE INVENTION 
   The present invention relates to ignition wire shielding and, in particular, covers for grounding spark plugs and ignition cable components. 
   BACKGROUND OF THE INVENTION 
   Ignition systems for automotive engines are conventionally provided with an elastomeric boot for covering and protecting the electrical connection between the ignition cable and the spark plug. As engine operating temperatures have increased over the years and as the cylinder heads were located closer to the exhaust manifolds, the temperatures to which the boot and spark plug are exposed have increased correspondingly. The high temperatures reduce the useful life of the boot elastomer, even when high temperature silicone products and protective lubricants are used. In addition, the high voltage ignition systems on current engines can create conditions exceeding the dielectric strength leading to external grounding that can cause further erosion of the boot as well as corrosion of the contact interfaces. It has further been determined that the ignition cables can create high potential gradients, with attendant high E-field intensities creating corona discharges that can further degrade the boots and contacts. 
   In an early approach, metal shields were used to surround the spark plug boot to shield against excessive heat as disclosed in U.S. Pat. No. 4,497,532 to Benzusko et al. and U.S. Pat. No. 4,671,586 to DeBolt. The shields, however, can provide an adverse grounding path when the dielectric strength is exceeded resulting in engine misfire and performance reduction. It has also been proposed to use high temperature ceramic sleeves to isolate the spark plug boot from high operating temperatures as disclosed in U.S. Pat. No. 6,305,954 to Aluise. The sleeves are rigid and difficult to mount on existing cables, and are limited to in-line boots, to the exclusion of commonplace inclined or right angle boot configurations. The ceramic material does not assist in dissipating electrical fields. It has also been proposed to reduce corona discharge by incorporating a conductive sleeve on the boot interior as disclosed in U.S. Pat. No. 5,716,223 to Phillips et al. All of the foregoing approaches are directed to original equipment limiting the ability to provide improved protection to existing as well as new engines. 
   It would accordingly be desirable to provide a universal design for ready integration with existing and new ignition cables to protect the boot and electrical connection from deterioration by increasing thermal and radiant insulation, and decreasing adverse electrical effects. 
   It would also be desirable to provide an improved cover for the cables and boots that increases resistance of the cover to operational and mechanical degradation 
   SUMMARY OF THE INVENTION 
   The present invention provides a flexible fabric cover for simple installation over the spark plug boot that is coated with a heat reflective electrical conductive base coat and a dielectric top coat to provide electric dissipation protection. The cover takes the form of currently available fiberglass sleeves having a restrictive mouth that fits over the sparkplug insulator and a sleeve body that covers the boot and connector area and extends therebeyond. The sleeve body has sufficient flexibility to accommodate in-line and angled boots. The base coat comprises a high temperature silicone resin containing electrically conductive aluminum flake that provides infrared reflectivity and a conductive exterior sheath with low break down voltage that dissipates static and corona charges to eliminate elastomer attack. The top coat includes a silicone resin containing a high temperature ceramic pigment effective for providing a dielectric outer coating and increasing thermal resistance. The top coat may include a color pigment for providing an appealing contrasting color to the basically gray/silver coloration of the standard sleeve material. The novel cover may be installed on existing high operating temperature engines to shield against electrical charges, extend life and function of the boot assembly, lower cable operating temperatures. The materials are porous and breathable to reduce heat buildup and reduce moisture retention, non-flammable and non-toxic, and not reactive with petroleum products. The flexible fabric construction allows the cover to be conveniently mounted in recessed plug ports. 
   In another aspect of the invention, it has been found that such covers, with or without the dissipative protection may be prone to operational degradation of the cover material, a glass woven material. In the basic design the upper end of the sleeve terminates with a reversely inwardly turned flap that is medially circumferentially stitched. Such construction under certain operating conditions can exhibit premature wear characteristics. For example, frequent removal of the boot and wire can fray the cut end of the flap resulting in extended unwoven ends. Under engine vibration, the ends tend to fracture resulting in debris that can affect ignition performance. Moreover, the ends may get reversed during installation, projecting outwardly of the sleeve and distracting from the aesthetic appearance. It has also been determined that the woven sleeve is subject to harmonic vibration during engine operation that can lead to glass strand fracture and an additional source of debris. Further, the end is subject to permanent distortion, assuming an ovate shape that reduces the thermal insulating characteristics 
   In a further embodiment, the above limitations are overcome by forming an initial flap at the free end of the outer layer which inverted against the inner sleeve and stitched so as to capture the strand ends in a containment pocket. The capture of the end thereby avoids the adverse effects of the unraveling. Further, the increased mass at the free end of the cover has been found to decrease the harmonic vibrations thereby extending the material life. Moreover, the additional layers greatly reinforces that circularity of the opening, even after repeated removals, thereby maintaining the insulating properties of the cover design. 
   Accordingly, it is an object of the present invention to provide an improved cover for protecting spark plug boot assemblies against thermal and electrical degradation. 
   Another object is to provide a flexible thermal and electrically protective cover for surface mounted and recessed port spark plug boots and connectors. 
   A further object is to provide a spark plug boot cover that dissipates static and corona charges to reduce degradation and operational impairment of spark plug boots and cable connections. 
   A still further object is to provide a protective spark plug boot cover that has improved resistance to operational material degradation. 

   
     DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become apparent upon reading the following detailed description taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a side cross sectional view of a charge dissipative cover installed over an ignition line including an ignition cable, a spark plug boot and a spark plug; 
       FIG. 2  is a side elevational view of the cover of  FIG. 1  on the ignition line; 
       FIG. 3  is a sectioned side view of the cover of  FIG. 1 ; and 
       FIG. 4  is a fragmentary cross sectional view of the cover wall including the conductive base coat and dielectric top coat: 
       FIG. 5  is a side cross sectional view of a cover installed over an ignition line including an ignition cable, a spark plug boot and a spark plug according to another embodiment of the invention; 
       FIG. 6  is an enlarged fragmentary cross sectional view of the end cuff of the cover taken along line  6 — 6  in  FIG. 5 ; and 
       FIG. 7  is an enlarged fragmentary cross sectional view of the end of the cover of  FIG. 5  prior to forming of the end cuff. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings for the purpose of describing the preferred embodiments only and not for limiting same,  FIGS. 1 and 2  show a charge dissipative cover  10  for the ignition line  12  for a combustion chamber  14  of an internal combustion engine  16 . As conventional, the ignition line  12  includes an ignition cable  20  terminating with a socket terminal  22  attached to the stud terminal  24  of a spark plug  26 . An elastomeric spark plug boot  28  is carried at an upper end on the ignition cable  20  and includes a lower skirt  30  having an interior socket engaging and sealing the spark plug insulator  32 . The spark plug  26  is received in a recessed port  34  in the cylinder head  36  of the engine with a threaded shank  38  conventionally screwed into a threaded opening interfacing with the combustion chamber  14 . 
   The ignition line components employed differ by engine, model and manufacturer. The cover as herein described finds application in the vast majority of engines designs for use as original or aftermarket equipment. The cover has sufficient flexibility for use with in-line as well as angular offset boots and cables. 
   The cover  10  overcomes the problems associated with high operating temperatures, high voltage, and static and corona charges. The cover  10  includes a tubular cover body  40  formed of a high temperature resistant braided fabric having a thermally insulating and electrically conductive coating system  42  on the outer surfaces thereof. The cover body  40  is preferably formed of braided fiberglass sleeving, preferably E-type glass. Suitable fabric is available as product no. 2F-120-18 from Atkins &amp; Pearce, Inc. of Covington, Ky. A 1-inch inner diameter tube accommodates the majority of current ignition assembly configurations. Prior to assembly, the tubing is heat treated and annealed to remove resins and reduce fraying. 
   Referring to  FIG. 3 , the body  40  includes an inner layer  44  and an overlying outer layer  46  folded and gathered around a retaining ring  48  thereby defining a cylindrical upwardly opening socket  50  downwardly terminating with an inwardly curved annular mouth  52  having a coaxial circular port  54  establishing a sliding fit with the spark plug insulator  32 . The upper end of the outer layer  46  is inwardly folded over the inner layer  44  at cylindrical hem  56 . The upper ends of the layers and the hem  56  are interconnected at circumferential stitching  58 . 
   Referring to  FIG. 4 , the coating system  31  comprises an electrically conductive, heat reflective base coat  44  and a heat resistant, dielectric top coat  46 . The base coat  44  comprises a sprayed silicone resin having a substantial portion of electrically conductive flake. The base coat  44  is characterized by a low breakdown voltage that functions to bleed static and corona charges under engine operating conditions. The base coat  44  is spray applied and ambiently dried to the touch without curing. Final curing takes place under engine operating conditions. Alternatively, the base coat  44  may be cured prior to use. The top coat  46  is spray coated over the dried base coat  44 . The top coat  46  comprises a silicone resin containing an effective amount of high temperature ceramic material sufficient to provide infrared reflectivity and dielectric protection from external sources. 
   A suitable base coat formulation comprises a silicone component, in powder and/or liquid resin form, in a solvent and carrier base and containing an amount of metallic particulate, in flake or otherwise finely dispersible form, for providing the desired electrical characteristics in the base coat  44 . Suitable catalysts and fillers may be added. The dried base coat contains about 15 to 35% metallic particulate based on weight, with 25 to 30% preferred. A preferred metallic particulate is aluminum flake having a particulate size of around 50 microns. 
   An effective formulation for the base coat is set forth below: 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Item 
                Vendor 
                  Product No. 
                Amount (gr.) 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Aluminum 
                 
                 552750 
                       545 
             
             
                 
               Acetone 
                 
                 
               1,135 
             
             
                 
               Xylene 
                 
                 
               200 
             
             
                 
               Silicone Resin 
             
             
                 
                  Powder 
               Seegott 
               SILREZ 604 
               1,360 
             
             
                 
                  Liquid 
               Seegott 
               SY-409 
               130 
             
             
                 
               Talc 
                 
                 
               27 
             
             
                 
               Catalyst 
             
             
                 
               Iron Hex 
               6% 
               OMG 
               7 
             
             
                 
                 
             
           
        
       
     
   
   The formula is prepared by mixing the acetone and xylene and gradually adding and dissolving the silicone powder. Thereafter the silicone liquid and aluminum flake are added and mixed thoroughly, the talc added and the catalyst slowly added and mixed. The mixture is blended sufficiently to avoid settling and transferred to a spray apparatus for application. 
   The top coat is based on the above formulation, with a suitable ceramic pigment substituted for the metallic particulate. For a red color, for example, a red ceramic pigment is used. A suitable pigment is available from General Color as product no. GR0660. Depending on the engine operating temperatures and proximity to the exhaust manifold, the ceramic content may be in the range of about 15% to 45% based on the weight of the silicone components. 
   The coating system  42  has been determined to provide both conductive and dielectric properties in covers using the above formulations. Covers containing only the base coat system have been tested in accordance with accepted protocols and were determined to have relatively low breakdown voltages of around 500 volts, well below that necessary for the effective grounding of the charges experienced in high voltage ignition systems. Covers containing the top coat withstood greater than 4,000 volts without any indications of breakdown, demonstrating substantial dielectric properties resisting outside interference. 
   Referring to  FIGS. 5 through 7  for the purpose of describing an additional embominent wherein the prior components are identified by like numerals, there is shown an improved wear and operation resistant cover  100  for the ignition line  12  for a combustion chamber  14  of an internal combustion engine  16 . The ignition line  12  includes an ignition cable  20  terminating with a socket terminal  22  attached to the stud terminal  24  of a spark plug  26 . An elastomeric spark plug boot  28  is carried at an upper end on the ignition cable  20  and includes a lower skirt  30  having an interior socket engaging and sealing the spark plug insulator  32 . The spark plug  26  is received in a recessed port  34  in the cylinder head  36  of the engine with a threaded shank  38  conventionally screwed into a threaded opening interfacing with the combustion chamber  14 . 
   The cover  100  includes a tubular cover body  140  formed of a high temperature resistant braided fabric. The cover body  140  is formed of a single length of fabric with cut ends. The cover body includes an inner layer or sleeve  142  extending from a free upper end conformally formed about an annular ring  144  and reversely formed to provide an outer layer or sleeve  146  overlying the inner sleeve and upwardly terminating with a circular entrance cuff  148  having an inwardly turned hemmed flap  150  that is circumferentially attached the sleeves  142 ,  146  by stitching  152 . As shown in  FIG. 6 , the flap  150  and stitching  150  form annular enclosure  153  capturing the free ends  154 ,  156  of the inner sleeve  142  and the outer sleeve  146 , respectively. 
   Referring to  FIG. 7  illustrating the cover prior to formation of the cuff  148 , the ends of the sleeves  144 ,  146  include frayed end strands  160 . Such end strands are prone to further unraveling under engine operating conditions and through repeated installation and removal of the cover. To overcome this problem, after formation of the sleeves about the ring  144 , the length of the outer sleeve  146  is sufficiently longer than the inner sleeve  142  thereby allowing the free end  156  to be reversely folded at hem  162  and conformed to the inner surface of the outer sleeve  146  thereby forming the flap  150 . Thereafter the flap  150  is reversely folded at hem  164  and conformed to the inner surface of the inner sleeve  142 . Thereafter the stitching is applied to form the enclosure  153  and capture the end strands  160 . 
   In addition to enclosing the end strands to prevent unraveling and disintegration, the enlarged and strengthened end cuff  148  provides further performance and durability benefits. The hems  162  and  164  and the four ply cuff  148  increase the hoop strength of the entrance end of the cover  100  and maintains the circularity of the opening by resisting creasing, ovating and other non-circular distortions. This maintains an open air circulation annulus to reduce heat transfer to the ignition components. Further, the four ply cuff increase the unsupported mass at the end of the cover thereby reducing the harmonic vibrations at the sleeve that can lead to glass strand fracture. 
   As a result of the foregoing, the cover  100  has been found to extend the life span of the cover, maintain the structural and insulative properties under extreme operating conditions, and retain the aesthetic appearance notwithstanding active maintenance. 
   While the present embodiment has been described with reference to the preferred embodiments, other modifications and changes thereto will become apparent. Accordingly, the invention is to be interpreted solely with reference to the following claims.