Abstract:
A spark plug designed for fitting in tight spaces of an engine compartment is disclosed. The spark plug has a conductive terminal attached to one end of a flexible central electrode and has a ceramic insulator partially encasing the flexible central electrode. The part of the flexible central electrode between the ceramic insulator and the conductive terminal is encased in a flexible insulator. The flexible part of the central electrode may be bent away from the axis of the ceramic insulator accommodating both installation and servicing of the spark plug in tight spaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the U.S. Provisional Patent Application No. 61/209,048 filed Mar. 3, 2009 by the present inventor. This provisional patent application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to spark plugs, more particularly to spark plugs that are used in small cramped spaces. 
     BACKGROUND OF THE DISCLOSURE 
     A spark plug for an internal combustion engine generally is comprised of a rod-like central electrode, a hollow cylindrical ceramic insulator encasing the central electrode, a conductive terminal attached to the central electrode at the spark plug terminal end, a hollow cylindrical metal shell partially encasing the ceramic insulator having threads for mating the spark plug with the engine block, a hexagonal nut for gripping the plug with a wrench, and an L-shaped ground electrode attached to the ignition end of the metal shell. 
     When the spark plug is installed in the engine compartment, the threads are mated to the engine block with the ignition end accessing the combustion chamber. The ignition coil is connected to the terminal end of the spark plug via ignition wires going from the ignition coil to the spark plug terminal end. The ignition coil wire is attached to the spark plug terminal with a clip. 
     In some cases, space around the spark plug is severely limited. Therefore, installation, removal and servicing of the spark plug can be difficult. There are several ways of handling this problem. Sometimes, other components in the engine compartment need to be removed to give access to the spark plug. Another solution uses a modified clip design that limits the space required for the plug stem plus clip. Still other methods use special spark plug wrenches that permit working in a limited space. Another approach is to use special spark plug designs that shorten the length of the spark plug between the spark plug hexagonal nut and the terminal end. All these solutions have utility in some situations. However none of these solutions are totally satisfactory. 
     SUMMARY OF THE DISCLOSURE 
     The flexible spark plug embodiments of the present invention presented herein solve the problem of accommodating a spark plug in an engine compartment where access to the spark plug is limited. The flexible spark plug employs a ceramic insulator with a shortened length above the spark plug&#39;s hexagonal nut at the terminal end of the plug as compared to a standard spark plug. It uses a flexible conductive wire instead of a central electrode rod. The flexible conductive wire has the same conductivity and diameter as a central electrode rod, and is covered by an insulating flexible covering. When installing an embodiment, the flexible electrode may be bent away from the axis of the ceramic insulator. This novel design allows the spark plug to be installed in the engine block in a way that provides less vertical clearance than required for a standard plug, and allows the spark plug terminal to be attached to the ignition wire clip in a location that is easier to access. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a perspective view of a first prior art spark plug. 
         FIG. 1B  is an exploded view of the first prior art spark plug. 
         FIG. 1C  is a sectional view of the first prior art spark plug. 
         FIG. 2A  is perspective view of the spark plug of a first embodiment. 
         FIG. 2B  is an exploded of the first embodiment of the present invention. 
         FIG. 2C  is a sectional view of the first embodiment of the present invention. 
         FIG. 3A  is a perspective view of a second prior art spark plug 
         FIG. 3B  is an exploded view of the second prior art spark plug. 
         FIG. 3C  is a sectional view of the second prior art spark plug. 
         FIG. 3D  is an expanded sectional view of a portion the second prior art spark plug. 
         FIG. 4A  is perspective view of a second embodiment of the current invention. 
         FIG. 4B  is an exploded of the second embodiment of the current invention. 
         FIG. 4C  is a sectional view of the second embodiment of the current invention. 
         FIG. 4D  is an expanded sectional view of a portion of the second embodiment of the current invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, the terms top, upper, bottom and lower are interpreted as viewed in the figures. A spark plug has a terminal end, where a clip from in ignition wire is attached, and an ignition end where a spark is generated. 
       FIG. 1A  illustrates a perspective view of a first prior art spark plug  102 .  FIG. 1B  illustrates an exploded view of first prior art spark plug  102 .  FIG. 1C  is a sectional view of first prior art spark plug  102  along a central axis A 1 . Referring to  FIGS. 1A ,  1 B, and  1 C, first prior art spark plug  102  has a rod-like central electrode  104  of length B 1 , a hollow cylindrical ceramic insulator  106  encasing central electrode  104 , a conductive terminal  108  having length N 1  attached to central electrode  104  at the top end, a hollow cylindrical metal shell  110  partially encasing ceramic insulator  106 , and an L-shaped ground electrode  112  attached to the bottom of metal shell  110 . The spark plug components are disposed along a central axis A 1 . 
     Central electrode  104 , having length B 1 , is composed of a highly conductive material such as copper. It transmits a high voltage received from the ignition system&#39;s ignition coil via ignition wires that attach to first prior art spark plug  102  at terminal  108  located at the terminal end of first prior art spark plug  102  and delivers the high voltage to the tip located at the lower end of central electrode  104 . The high voltage causes a spark to jump across a gap G to ground electrode  112 . The ignition system, ignition coil and ignition wires are not shown in the figures. 
     Ceramic insulator  106 , is retained in metal shell  110 , encases and supports central electrode  104 , insulates central electrode  104  from metal shell  110 , dissipates heat from first prior art spark plug  102  and provides mechanical strength to protect first prior art spark plug  102  from engine vibration. Ceramic insulator  106  protrudes from the upper end of metal shell  110  and from the lower end of metal shell  110 . The portion of ceramic insulator  106  protruding above the metal shell  110  has length L 1 . 
     Metal shell  110  has a hollow cylindrical shape, except for hexagonal nut  116 , and is made of a conductive metal material such as low carbon steel. It has a threaded portion  114  for installation in the engine block and has hexagonal nut  116  that accepts a wrench to allow first prior art spark plug  102  to be installed and removed from the engine block. 
       FIGS. 2A ,  2 B, and  2 C display a first embodiment  302  of the present invention, a first flexible spark plug  302 . Referring to  FIGS. 2A ,  2 B, and  2 C, central electrode  104  of first prior art spark plug  102  is replaced by a flexible wire  304  of the same diameter as central electrode  104 . It has length B 2  approximately equal to the length B 1  of the first prior art central electrode. As an example, if the central electrode  104  of first prior art spark plug  102  is a  10  gauge rigid copper rod, central electrode  304  of first embodiment  302  of the present invention is a  10  gauge flexible copper wire. 
     Ceramic insulator  106  of first prior art spark plug  102  is replaced by a shorter ceramic insulator  306  of a different shape than ceramic insulator  106  of first prior art spark plug  102 . Specifically, the portion of ceramic insulator  306  above metal shell  110  of first embodiment  302  has length L 2  that is considerably shorter than length L 1  of ceramic insulator  104  above metal shell  110  of first prior art spark plug  102 . 
     Referring now to  FIGS. 1C and 2C , the portion of flexible wire central electrode  304  between the top of ceramic insulator  306  and the bottom of terminal  108  has length M 2  and is covered by a flexible insulating material  308  such as a spark plug ignition wire cover. The total length of the portion spark plug  302  of first embodiment  102  above metal shell  110  has length P 2 =L 2 +M 2 +N 2  that is the same length P 1 =L 1 +N 1  of the portion spark plug  102  of first prior art spark plug  102  above metal shell  110 . The remaining components and structure of the first embodiment spark plug  302  are the same as first prior art spark plug  102 . 
     Spark plugs in use on many modern vehicles have significant improvements as compared to the first prior art spark plug  102 . A second embodiment  702  of the present invention is presented herein that illustrates how the present invention may be adapted to a second prior art spark plug design. A second prior art spark plug  502  design is given here as an example for illustrative purposes only. The design can be adapted from the implementation of the second flexible spark plug  702  presented herein to other modern spark plug designs. 
       FIGS. 3A ,  3 B,  3 C, and  3 D illustrate the details of second prior art spark plug  502 .  FIG. 3A  is a perspective view of second spark plug  502 .  FIG. 3B  gives an exploded of second prior art spark plug  502  and  FIG. 3C  gives a sectional view of second prior art spark plug  502 .  FIG. 3D  gives an exploded view of a portion of  FIG. 3C . 
     Referring to  FIGS. 3A through 3D , first prior art spark plug  102  has single rod central electrode  104  that runs the full length of spark plug  302  with length B 1 . Second prior art spark plug  502  replaces single rod central electrode  104  by several electrode components disposed along central axis A 2 : a top central electrode  504 , a resistor  508 , two glass seals  506 , a lower central electrode  510  and a central electrode tip  512 . 
     Referring now to  FIG. 3C , top central electrode  504  of second prior art spark plug  502  is made of a single copper rod. Resistor  508  is made of a carbon-based material; two glass seals  506  are made from a copper glass material. Lower central electrode  510  is made from a highly heat conductive metal material such as Cu as the core material and a highly heat-resistant, corrosion-resistant metal material such as Ni (Nickel)-based alloy as the clad material. Tip  512 , made from a precious-metal alloy, welded to central electrode  510 , improves spark creation and reduces wear. 
       FIGS. 4A ,  4 B,  4 C, and  4 D illustrate a second embodiment  702  of the current invention: a second flexible spark plug  702 . Second flexible spark plug  702  is a modification of second prior art spark plug  502 . Most of the new components of second flexible spark plug  702 , viz. resistor  508 , two glass seals  506 , lower electrode  510  and lower electrode tip  512  are the same as in second prior art spark plug  502  as illustrated in  FIG. 3C . 
     The changes made in second flexible spark plug  702  as compared to second prior art spark plug  502  are as follow. Referring to  FIGS. 3A ,  3 B,  3 C,  4 A  4 B, and  4 C, top central electrode  504  of second prior art spark plug  502  is replaced by a flexible wire  704  of the same diameter and length as top central electrode  504 . Ceramic insulator  106  of second prior art spark plug  502  is replaced by shorter ceramic insulator  306  and flexible wire cover  308 . 
     Referring to  FIGS. 3A ,  3 B,  3 C,  4 A  4 B, and  4 C, only wire central electrode  504 , ceramic insulator  106  needs to be replaced by flexible wire  704  , ceramic insulator  306  an flexible insulator  308  to convert second prior art spark plug  502  into second flexible spark plug  702 . The remaining components of s second flexible spark plug  702  are incorporated without change to second prior art spark  502  design as shown in  FIG. 3C . 
     The spark plug presented in the first and second embodiments are used is the same situations where the prior art spark plugs are used. However, the flexible nature of the central electrode design allows the invention embodiments to be used is tight situations where the flexible electrode may be bent to a convenient position. This is not possible with the prior art designs. 
     In the two embodiments presented herein, the overall length of each embodiment is set to the same length as the prior art spark plug they are based on. Modification of the length of the two embodiments may easily be made by changing the length of the flexible central electrode and adjusting the size of the flexible insulator accordingly. 
     The disclosure presented herein gives two embodiments of the invention. These embodiments are to be considered as only illustrative of the invention and not a limitation of the scope of the invention. Various permutations, combinations, variations, and extensions of these embodiments are considered to fall within the scope of this invention.