Patent Publication Number: US-7594489-B1

Title: High voltage extender

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
   Not applicable. 
   REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to high voltage extenders for connecting a high voltage source to a spark plug. More particularly, the present invention relates to extenders that are used for insulating a conductive rod that is connected to an ignition coil at one end and to a spark plug at an opposite end. 
   2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98. 
   Extenders are often used for the connection of high voltage sources, such as ignition coils, to spark plugs. These high voltage extenders are intended to pass the charge from the high voltage source (having a maximum voltage of 40 KV) to the ignition coils. Typically, these extenders are suitably insulated so as to prevent tracking from the conductive rod to the electrical ground created by the engine block. 
     FIG. 1  illustrates one example of a prior art high voltage extender utilized and sold by Caterpillar, Inc. The high voltage extender  10  has a machined stainless steel rod  12  that has a threaded end  14  and a connecting end  16 . The threaded end  14  is machined onto the stainless steel rod  12  so as to connect into the female thread of the high voltage connector of an ignition coil. The connection end  16  connects to the high voltage terminal of a spark plug. A spring  18  is affixed to the connection end  16  of the stainless steel rod  12 . The connection is accomplished by compressing the voluted spring  18  against the high voltage terminal of the spark plug. The spring  18  is received within a stainless steel cup  20  which is attached to the stainless steel rod  12 . The rod  12  is pressed into a machined sleeve  22  of “void free” polytetrafluoroethylene, otherwise known as TEFLON™. The sleeve  22  serves to insulate the stainless steel rod  12  from the electrical ground created by the ignition block. 
   As can be seen in  FIG. 1 , the sleeve  22  has a narrow diameter portion  24  overlying the threaded end  14  of the stainless steel rod  12 . A main section  26  of the sleeve  22  extends along the rod  12  from the narrow diameter portion  24 . The main section  26  has a greater diameter than the diameter of the narrow diameter portion  24 . The sleeve  22  defines a receptacle  28  at an end opposite the narrow diameter portion  24 . Receptacle  28  is suitable for receiving a portion of a spark plug therein. An O-ring seal  30  is received within a notch  32  formed in the interior wall of receptacle  28  at the end of the sleeve  22 . The sleeve  22  has a constant diameter extending from the narrow diameter portion  24 . 
   Experiments with the prior art of  FIG. 1  have determined that during extended periods of high-voltage (30-40 kV), the voltage punctures the polytetrafluoroethylene sleeve at a point where the stainless steel cup  20  is nearest the high voltage terminal of the spark plug. This occurs in an average of 5 to 10 hours when a grounded metal sleeve is placed over the extender  10 . During thermal cycling, the polytetrafluoroethylene expands and contracts lengthwise and creates a gap at the inner face surface of the extender  10  and the insulating surface of the high voltage connection of the ignition coil. This allow tracking along the surface to the electrical ground created by the engine block. During shipping, the extender  10  has a tendency to loosen. This also serves to create a gap at the area of the interface of the ignition coil and the extender  10 . The polytetrafluoroethylene material “cold flows.” This allows the extender  10  to loosen. 
   In the past, various U.S. patents have issued relating to such high voltage extenders. For example, U.S. Pat. No. 4,944,259, issued on Jul. 31, 1990 to R. D. Richardson, teaches an ignition system with an insulated and extendable extender. This extender resiliently biases the extender between the source of high energy and the spark plug to provide a positive and reliable electrical connection therebetween. The extender is of a relatively rigid construction so as to prevent bending. The extender is combined with a shield in the engine to further protect and increase the functional life of the components. 
   U.S. Pat. No. 5,060,624, issued on Oct. 29, 1991 to Bruning et al., provides an engine ignition system that has a transformer assembly and positioning means. The transformer assembly has an elongated body having a cup portion containing the coils, a base portion, and a stem portion. A conducting core extends through the stem and base portions. A suitable clip connects the core electrically to a spark plug installed in a profiled bore of the cylinder head. A positioning device is provided to positively align and contain the transformer assembly within a valve mechanism compartment defined between the cover and the cylinder head. A spring member connected to the cup portion. Depending guide members formed within the cover cooperate with each other. 
   U.S. Pat. No. 5,357,233, issued on Oct. 18, 1994 to Z. Wada, teaches an extension device which extends from the ignition coil to supply the peak high-voltage output to a spark plug. A part of an outer periphery of the secondary coil at an intermediate position of the outer periphery of the secondary coil sinks in relation to the other part of the outer periphery of the secondary coil to form a groove extending in a radial direction of the secondary coil. The peak high-voltage output is transmitted from the secondary coil through the groove to the extension device. The extension device includes a first member extending from the ignition coil, a second member for being connected to the spark plug, and an elastic member connecting the first member to the second member so that the first member moves elastically in relation to the second member. 
   U.S. Pat. No. 5,577,921, issued on Nov. 26, 1996 to Philyaw et al., discloses an electrical connector system for electrically connecting a voltage source to a spark plug terminal. This transformer assembly has an elongate body including a cup portion containing primary and secondary coils, a base portion, and a stem that is adapted to be installed in a housing of a cylinder head. An electrical source extends through the stem and base portion. An electrical connecting system includes an electrical conductor adapted to receive the voltage source with a spring contacting the end of a spark plug terminal biasing the conductor in a direction away from the spark plug. The electrical connector system further includes a positioning device adapted to positively align and contain the transformer assembly within a valve mechanism compartment defined between a cover and the cylinder head. A spring member is connected to the cup portion so as to axially bias the electrical conductor in a direction toward the spring in contact with the spark plug terminal so as to ensure an electrical connection. 
   U.S. Pat. No. 5,685,282 issued on Nov. 11, 1997 to Murata et al., discloses an ignition device for an internal combustion engine. This ignition device has a spark plug including a high voltage terminal, an ignition coil for generating a high voltage, and adapter assembly for electrically connecting the ignition coil to the high voltage terminal of the spark plug. The adapter assembly has a support sleeve for accommodating and supporting the high voltage terminal of the spark plug against a transverse movement of the high voltage terminal. The support sleeve is either a continuous extension or a metal tube of the adapter assembly. The assembly may also include a wear-resistant material. 
   U.S. Pat. No. 6,068,495, issued on May 30, 2000 to F. Virchow, discloses a sparkg plug for an internal combustion engine. A connector sleeve is formed of an insulating material. An elastic member is connected to the connector sleeve so as to seal the gap between the connector sleeve and a spark plug well. A ceramic inlet is formed in the connector sleeve so as to enclose the plug-in contact and the ignition cable connection. 
   U.S. Pat. No. 6,340,303, issued on Jan. 22, 2002 to Hamada et al., describes a high tension connection for the spark plug of an internal combustion engine. This connection portion has a first high tension connection terminal, a second high tension connection terminal for electrically connecting with the first high tension connection terminal, a locking mechanism provided between the first high tension connection terminal and the second high tension connection terminal for restricting the separation therebetween in the axial direction, and a spring member disposed between the first high tension connection terminal and the second high tension connection terminal. This device serves to prevent an instantaneous breakdown of the connection if an external force is applied to the high tension portion. 
   U.S. Pat. No. 6,817,872, issued on Nov. 16, 2004 to S. M. Berg, describes a heat-protective spark plug extension. The extender includes an elongated body formed of heat resistant and electrically insulative material that extends between a spark plug engagement end and a spark plug wire connector end. A conductor is located within the body and includes a fitting adapted to releasably electrically connect to a spark plug wire. A receptacle is adapted for electrical connection to a spark plug. An adjustment part permits adjustable movement of the spark plug wire connector end relative to the conductive receptacle. 
   It is an object of the present invention to provide an extender which assures that the insulating material is void-free. 
   It is another object of the present invention to provide an extender which seals an interface between the extender and the ignition coil and serves to prevent high voltage leakage. 
   It is another object of the present invention to provide an extender which prevents movement of the rod within the sleeve rotationally and lengthwise. 
   It is still a further object of the present invention to provide an extender which is resistant to the corona created in the engine block. 
   It is a further object of the present invention to provide an extender which is easy to manufacture, easy to install and use, and relatively inexpensive. 
   These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is an extender for connecting a high voltage source to a spark plug. The extender of the present invention comprises a conductive rod having a first end and a second end, with an injection-molded sleeve over the conductive rod so as to be in void-free relation with an exterior surface of the conductive rod. The first end of the conductive rod is suitable for electrical connection to the high voltage source. The second end of the conductive rod is suitable for electrical connection to the spark plug. The conductive rod has the first end extending outwardly of the sleeve. The sleeve defines a spark plug-receiving receptacle at the second end of the conductive rod. 
   The sleeve has a narrow diameter portion adjacent the first end of the conductive rod. This narrow diameter portion has a notch extend therearound. An O-ring is received in the notch and extends around the narrow diameter portion. The sleeve has an abutment ring formed on a side of the O-ring opposite the first end the conductive rod. This abutment ring is integrally formed with the sleeve. The abutment ring has a greater diameter than a diameter of the narrow diameter portion. The sleeve has a main section extending around the conductive rod from the abutment ring to the receptacle. This main section is of generally constant diameter less than the diameter of the abutment ring. This sleeve has an end section extending around the receptacle. The end section has a greater diameter than the diameter of the main section. 
   A spring is connected to the second end of the conductive rod. The spring is suitable for contacting a terminal of the spark plug. The receptacle has a notch formed around a wall thereof. An O-ring is received in the notch. The receptacle extends outwardly beyond the second end of the conductive rod so as to form a compartment wherein the spark plug can be received and in which the O-ring is in contact with the exterior surface of the spark plug. 
   The present invention is also a method of forming an extender used for connecting a high voltage source to a spark plug. This method includes the steps of: (1) placing a conductive rod in a mold; (2) injection-molding a sleeve of polymeric material around the conductive rod such that a first end of the conductive rod extends outwardly of an end of the sleeve and such that a spark plug-receiving receptacle is formed at an opposite end of the sleeve; and (3) removing the injection-molded sleeve and conductive rod from the mold. 
   The method of the present invention also includes forming a narrow diameter portion of the sleeve adjacent to the end of the conductive rod. A notch is formed around the exterior surface of this narrow diameter portion. An elastomeric O-ring is placed into the notch. Also, in the method of the present invention, a notch is formed around an inner wall of the receptacle. An elastomeric O-ring is inserted into this notch such that a portion of the O-ring extends inwardly of the inner wall of the receptacle. A conductive spring is affixed to a second end of the conductive rod. The first end of the conductive rod is threadedly connecting to the high voltage source. The spark plug is inserted into the receptacle such that a terminal of the spark plug is electrically connected to the conductive rod. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view showing a prior art extender. 
       FIG. 2  is a perspective view of the extender of the present invention. 
       FIG. 3  is a side elevational view of the extender of the present invention. 
       FIG. 4  is a cross-sectional view of the extender of the present invention with the O-ring seals at opposite ends thereof omitted. 
       FIG. 5  is detailed view showing the O-ring seal as placed within the end of the receptacle of the extender of the present invention. 
       FIG. 6  illustrates the connection of the extender with an ignition coil and a spark plug. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 2 , there is shown the high voltage extender  40  in accordance with the teachings of the present invention. The high voltage extender includes a conductive rod  42  with a sleeve  44  injection molded thereover. As shown in  FIG. 2 , the sleeve  44  includes a receptacle  46  suitable for the receipt of a spark plug therein. A threaded connection  48  is formed at the end of the conductive rod  42 . The sleeve  44  is injection molded over the conductive rod  42  so as to have a void-free connection with the exterior surface of the conductive rod  42 . 
   As can be seen in  FIG. 3 , the extender  40  has the threaded end  48  of conductive rod  42  extending outwardly of a narrow diameter portion  50  of the sleeve  44 . An abutment ring  52  is formed on a side of the narrow diameter portion  50  opposite the threaded connection  48  of the conductive rod  42 . An elastomeric O-ring  54  is fitted over the narrow diameter portion  50 . The elastomeric O-ring  54  will form an insulating seal with the inner wall of the connection of the ignition coil. The abutment ring  52  will provide an abutment surface against the end of the connection portion of the ignition coil. The abutment ring  52  has a greater diameter than that of the narrow diameter portion  50  and is integrally formed with the sleeve  44  during the injection-molding process. A main section  56  extends from the side of the abutment ring  52  opposite the narrow diameter portion  50 . The main section  56  has a generally constant diameter extending longitudinally along the conductive rod  42 . The main section  56  has a diameter that is greater than that of the narrow diameter portion  50  and less than that of the abutment ring  52 . An end section  58  is formed at the end of the main section  56  opposite the abutment ring  52  and the narrow diameter portion  50 . The end section  58  defines the exterior of the receptacle  46 . The end section  58  has a diameter slightly greater than that of the main section  56 . The narrow diameter portion  50 , the abutment ring  52 , the main section  56  and the end section  58  are integrally formed together of a polymeric material and in void-free relation with the conductive rod  42 . Since a polymeric material is used in the present invention instead of polytetrafluoroethylene, the material used in the present invention is much less expensive than the polytetrafluoroethylene material. Additionally, because of the relatively narrow diameter main section  56 , less material is required for the protective sleeve  44  than that of the constant diameter polytetrafluoroethylene sleeve of the prior art. 
     FIG. 4  illustrates the conductive rod  42  as received within the sleeve  44 . As can be seen, the threaded end  48  extends outwardly of the narrow diameter portion  50  of the sleeve  44 . The conductive rod  42  should be formed of a stainless steel material (or any other highly conductive material). Because the sleeve  44  is injection molded over the exterior surface of the conductive rod  42 , there can be no voids in the space between the exterior surface of the conductive rod  42  and the inner surface of the sleeve  44 . A spring  60  is affixed to the end of the conductive rod  42  within the interior of the receptacle  46  at the end of the conductive rod  42  opposite the threaded connection  48 . Spring  60  assures a strong electrical connection with a spark plug introduced into the receptacle  46 . 
   In  FIG. 4 , it can be seen that there is a notch  61  formed on the exterior surface of the narrow diameter portion  50 . Notch  61  provides an area into which the O-ring  54  can be received. Similarly, a notch  62  is formed on an inner wall of the receptacle  46 . Notch  62  will also be suitable for receiving an O-ring  54  therein. 
     FIG. 5  illustrates the O-ring  64  as positioned within the notch  62  in the receptacle  46 . The O-ring  64  is positioned adjacent to the end  66  of the sleeve  44 . 
     FIG. 6  illustrates how the extender  40  of the present invention is used to connect with a spark plug  80  and an ignition coil  82 . The ignition coil  82  has a connection end  84 . The threaded connection  48  of the conductive rod  42  is received within the connecting section  84  of the ignition coil  82  and threadedly introduced into a female threaded connector on the interior of the sleeve  86  of the ignition coil  82  extending over the connection section  84 . The abutment ring  52  will rest against the end of the connection section  84  of the ignition coil  82 . The spark plug  80  has a high voltage terminal  88  that is compressed against the spring  60  so as to establish a strong electrical connection with the conductive rod  42  on the interior of sleeve  44 . A portion  90  of the spark plug  80  is introduced into the receptacle  46  at the end of sleeve  44 . The O-ring seal  64  will further seal portion  90  within the receptacle  46 . 
   In the present invention, the stainless steel conductive rod  42  is injected molded as an insert in the insulated polymeric sleeve  44  using injection molding techniques so as to ensure that the high voltage insulating material of the sleeve  44  is void free. The surface between the high voltage connection of the ignition coil  84  and the extender  40  utilizes the O-ring  54  on the extender  40  to seal the interface and to prevent high voltage leakage. Because the rod  42  is injection molded as an insert into the high voltage insulating material of sleeve  44 , the rod  42  cannot move within the sleeve  44  rotationally or lengthwise. This keeps the surface of the extender  40  at the ignition coil  82  and further prevents high voltage leakage at this point. The materials used in the extender  40  of the present invention are more resistant to the corona created in the engine block. During testing, the extender  40  of the present invention endured 240 hours without failure compared to a maximum of 10 hours for the extender  10  of the prior art. 
   The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction, or in the steps of the described method, can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.