Abstract:
An extension-type spark plug ( 10 ) is disclosed for igniting the air-fuel mixture in an internal combustion engine. The spark plug ( 10 ) includes an installation conduit ( 12 ), a contact button ( 34 ), an electrode extension ( 20 ), a firing electrode ( 60 ), a ground plate ( 66 ), a sleeve insulator ( 22 ), an upper insulator ( 90 ) and a lower insulator ( 50 ). The electrode extension ( 20 ) is axially aligned with and in communication with the firing electrode ( 60 ). The ground plate ( 66 ) is proximate the firing electrode ( 60 ) to define a spark gap between the firing electrode ( 60 ) and a first end of the ground plate ( 66 ). The sleeve insulator ( 22 ) surrounds the electrode extension ( 20 ). The upper insulator ( 90 ) surrounds an upper portion of the electrode extension ( 20 ) and is in contact with the sleeve insulator ( 22 ). The lower insulator ( 50 ) surrounds the lower portion of the electrode extension ( 20 ) and is in contact with the sleeve insulator ( 22 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     NONE. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to spark plugs for igniting combustion gases in a combustion chamber of an internal combustion engine, and more particularly toward an extension type spark plug as used chiefly in specialized applications. 
     2. Related Art 
     Spark plugs are used in a variety of applications and are configured along with other accessory parts to fit within a given environment. For example, in a particular application the depth of the bore in the engine may require the use of a separate spark plug extension to connect the spark plug to the spark plug wire. While designs with accessory pieces meet their intended purpose, many problems still exist. For example, spark plug designs having multiple pieces require complex training and cause logistic issues. Further, the more complex designs require retrofit instructions. Moreover, such designs having multiple pieces require field assembly and, thus, have a reduced reliability. 
     Therefore, it would be desirable to reduce the number of components necessary to install a spark plug in a given environment to reduce assembly complexity. Moreover, the new and improved designs should provide a more reliable spark plug. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, an extension-type spark plug is provided for igniting the air-fuel mixture in an internal combustion engine (ICE). The spark plug includes an installation conduit, a contact button, an electrode extension, a firing electrode, a ground plate, an insulator sleeve, an upper insulator, and a lower insulator. The installation conduit serves to mechanically contain the components and bears the torque of installing the plug to the engine. The contact button delivers the high voltage pulse from the external source and to the electrode extension. The electrode extension is both axially aligned and in communication with the firing electrode. The ground plate is proximate the firing electrode so as to define a spark gap between the firing electrode and a first end of the ground plate. The sleeve insulator surrounds the electrode extension. The upper insulator surrounds an upper portion of the electrode extension and is in contact with the sleeve insulator. The lower insulator surrounds the lower portion of the electrode extension and is in contact with the sleeve insulator. 
     In accordance with another aspect of the present invention, the spark plug includes a contact button axially aligned and in contact with the electrode extension. 
     In accordance with another aspect of the present invention, the spark plug includes a gasket disposed between the contact button and the firing electrode. 
     In accordance with still another aspect of the present invention, the contact button of the spark plug includes threads for engaging mating threads in the electrode extension. 
     In accordance with still another aspect of the present invention, the spark plug includes an installation conduit surrounding the upper and lower insulators. 
     In accordance with still another aspect of the present invention, the spark plug includes an end bushing secured to an end of the installation conduit for connecting an electrical conductor to the electrode contact button. 
     In accordance with still another aspect of the present invention, the upper insulator has a plurality of portions having different diameters. 
     In accordance with still another aspect of the present invention, the lower insulator has a plurality of portions having different diameters. 
     In accordance with still another aspect of the present invention, the upper insulator includes a cavity for receiving a first end of the sleeve insulator. 
     In accordance with still another aspect of the present invention, the lower insulator includes a cavity for receiving a second end of the sleeve insulator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
         FIG. 1  is a cross-sectional view through an extension spark plug, in accordance with an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view of an internal portion of the spark plug, in accordance with an embodiment of the present invention; 
         FIG. 2B  is an end view of the spark plug, in accordance with an embodiment of the present invention; and 
         FIG. 3  is a cross-sectional view of the insulator of the spark plug, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a cross-sectional view of an extension-type spark plug  10  is illustrated, in accordance with an embodiment of the present invention. The spark plug  10  is of the type used in industrial engine and other specialized applications where access to the spark plug  10  for maintenance and replacement purposes is severely limited. The spark plug  10  includes an installation conduit  12 . Installation conduit  12  is made of a metal material such as stainless steel or some alloy of steel. Installation conduit  12  houses a lower assembly, generally indicated at  14 , and an upper assembly, generally indicated at  16 . Both the lower  14  and upper  16  assemblies are made, at least in part, from a dielectric material such as ceramic. 
     Lower assembly  14  and upper assembly  16  together support an electrically conductive electrode extension  20  which, in one exemplary embodiment, comprises a stiff metallic wire. In one version of the invention, the electrode extension  20  comprises a 0.125 inch diameter wire made from a nickel-based alloy such as is commonly used in center electrode constructions for spark plugs. Electrode extension  20  is surrounded by a sleeve insulator  22  which, together with the dielectric portions of the lower  14  and upper  16  assemblies, prevents electrical conduction between the charged electrode extension  20  and the grounded installation conduit  12 . Sleeve insulator  22  is made of a non-conducting material such as a silicone rubber or polymer and as best illustrated in  FIG. 1 , has a first end surrounded by the upper assembly  16 , a second end surrounded by the lower assembly  14 , and a central section  23  which is directly exposed by the spacing between the assemblies  14 ,  16  to the surrounding metallic installation conduit  12 . 
     A bushing  18  is connected at a first bushing end  24  to installation conduit  12  by welding, crimping, or other attachment means. The other end  26  of bushing  18  includes threads  28  for connecting to a spark plug wire (not shown). As conventionally known, the spark plug wire is connected to an external energy source. The bushing  18  possesses a hexagon segment configuration compatible with industry standard socket wrench tooling for installation/removal purposes. The bushing  18  is preferably metallic and is electrically connected to ground through the metallic installation conduit  12 . 
     Electrode extension  20  includes a threaded first end  29  and a threaded second end  30 . First end  29  of electrode extension  20  is threaded into a terminal stud  32 , whereas the second end  30  is threaded into a contact button  34 . The contact button  34  is provided for establishing electrical contact with a leading end of an ignition wire (not shown) according to known coupling techniques. Terminal stud  32  and contact button  34  are generally made of aluminum or a similar metal alloy; however, any electrically conductive material suitable for the purpose may be used as indicated. 
     Referring now to  FIGS. 2A and 2B , lower assembly  14  will now be described in further detail, in accordance with one exemplary embodiment of the present invention. Lower assembly  14  includes the firing end of spark plug  10 . A high voltage pulse from an external ignition system is applied to lower assembly  14  through the electrode extension  20 . Lower assembly  14  includes a lower insulator  50  for preventing the high voltage pulse supplied to spark plug  10  from leaking between electrode extension  20  and installation conduit  12 . Lower insulator  50  has a cavity  49  for receiving a first end  51  of sleeve insulator  22 . Lower insulator  50  is typically made of alumina ceramic or a similar material. Lower insulator  50  is captured by a lower shell  52 . Lower shell  52  has a first end  54  that is threaded to engage a bore in the engine (not shown). Lower insulator  50  has a lower seat  55 . Lower seat  55 , when positioned within lower shell  52 , is pressed against a complementary ledge or seat in lower shell  52 . A second end  56  of lower shell  52  engages lower insulator  50  at an upper shoulder  58  of insulator  50 . Thus, the insulator  50  is retained within lower shell  52  by crimping end  56  over shoulder  58  while the lower seat  55  bears against the complementary ledge. An annular groove  57  is disposed in lower shell  52  to define a narrowed wall section  59 . Narrowed wall section  59  is influenced by electrically applied localized heat along with overwhelming pressure applied to the ends of lower shell  52  to cause wall  59  to deflect or buckle outward. The affected wall section  59  causes lower shell  52  to decrease in length. The decreased length of lower shell  52  creates a predefined pressure on lower insulator  50  holding the insulator firmly in place within the lower shell  52 . 
     A firing electrode  60  is disposed near first end  54  of lower shell  52 . Electrode extension  20  is connected to and supplies voltage to firing electrode  60  through the terminal stud  32 , a compression spring, a radio frequency suppressor capsule  64 , and a conductive glass seal. Those of skill will appreciate various other intermediate conduction path configurations between the terminal stud  32  and the firing electrode  60 . For one example, a fired-in suppressor seal pack may be substituted. Other constructions are also possible. The suppressor capsule  64  or other RFI device is provided to reduce the effects of electromagnetic interference (EMI) on peripheral devices such as radios. A ground plate  66  surrounds firing electrode  60  and is welded, crimped, or otherwise attached to end  54  of shell  52 . As will be described hereinafter, a spark gap is defined by the clearance between firing electrode  60  and ground plate  66 . The tip of the firing electrode  60  facing the spark gap may be provided with a precious metal insert to improve service life. 
     An end view of firing electrode  60  and ground plate  66  is shown in  FIG. 2B . The ground plate  66  includes a plurality of prongs  70  which extend inwardly toward firing electrode  60 . The clearance between each end of the inwardly extending prongs  70  and the firing electrode  60  defines the spark gap over which a spark is created. The tips of the prongs  70 , like that of the firing electrode  60 , may be fitted with precious metal for durability. Also, other constructions of the ground electrode  66  may be used, such as a full annular spark gap or other than four prongs  70 . 
     Referring now to  FIG. 3 , upper assembly  16  is further illustrated, in accordance with an embodiment of the present invention. Upper assembly  16  includes an upper insulator  90  which has a first end  92 . Near first end  92  is an annular groove  94 . Annular groove  94  is configured to receive an o-ring style sealing gasket (not shown). The sealing gasket seals and positions upper insulator  90  within the installation conduit  12 . Near the other end  96  of upper insulator  90  is a series of stepped-down portions having progressively smaller diameters. More specifically, upper insulator  90  includes a first diameter portion  98 , a second diameter portion  100 , a third diameter portion  102 , and a fourth diameter portion  104 . The inner diameter of portions  100 ,  102  and  104  are the same dimension, whereas the inner diameter of portion  98  is larger than the diameter of portions  100 ,  102  and  104 . As shown in  FIG. 1 , the various diameter changes in the upper assembly  16  cooperate with corresponding features in the bushing  18 , installation conduit  12 , sleeve insulator  22  and lower assembly  14  so as to combine into a nested arrangement of components that form a unitary structure. Further, upper insulator  90  includes a transitional region or seat  106  disposed within a cavity  91 . Seat  106  is configured to receive a seating gasket (depicted as an o-ring) to seat sleeve insulator  22  thereagainst. 
     During assembly, upper insulator  90  is positioned within installation conduit  12  and moved toward lower assembly  14  until sleeve insulator  22  contacts seat  106 . The contact of sleeve insulator  22  and seat  106  prevents further movement of upper insulator  90  toward lower insulator  50 . Bushing  18  is then placed into installation conduit  12  until the interior walls of bushing  18  contact the exterior walls of upper insulator  90  at end  96 . Bushing  18  is then welded or otherwise mechanically fastened to installation conduit  12  so as to secure upper insulator  90  within installation conduit  12 . 
     The foregoing invention has been described in accordance with relevant legal standards; thus, the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.