Abstract:
A sparkplug having multiple side discharge negative electrodes and employing an integral capacitor extending from the plug body to the area of the connector to the ignition system to effectively store the electrical energy normally lost during the rise time of the ignition transformer, and to discharge the stored energy across the electrode gap. The body ( 2 ) has a cylindrical extension which serves as the negative plate ( 10 ) of the capacitive element. A positive electrode ( 8 ) forms the interior portion of the sparkplug. One end of the positive electrode forms a spark gap ( 9 ) with two or more negative electrodes ( 7 ). The other end of the positive electrode ( 8 ) connects by means of a resistive connector ( 4 ) to a conventional high-voltage ignition cable. The positive electrode ( 8 ) serves as the positive plate of the capacitive element. A moldable dielectric material ( 11 ) completely fills the space between the positive and negative plates ( 8, 10 ) of the capacitive element for the length of the sparkplug, and also serves as the outer insulator of the spark plug.

Description:
FIELD OF THE INVENTION 
     The present invention relates to sparkplugs and, specifically, to a sparkplug having multiple side-discharge negative electrodes and a body constructed to effectively absorb the electrical energy normally lost during the rise time of the ignition transformer, a method to store electrical energy, and a method to discharge the stored energy across the electrode gap during the first few nanoseconds of the spark event. 
     BACKGROUND OF THE INVENTION 
     There have been many and various attempts at creating an ignitor, more commonly described as a sparkplug, for combusting fuel in an internal combustion engine. Behind these ignitors, in the ignition circuit, have been many devices designed to increase the effectiveness of the ignitor. The attempts at creating a more efficient ignitor or increasing the effectiveness of the ignitor can be described as conventional sparkplugs with modifications to the electrodes and/or electrode spacing, capacitors/condensers in parallel with the ignition circuit, or devices interrupting the high voltage ignition pulse. While these attempts do effect, to some degree, the dynamics of the spark event, they are unnecessarily complex, costly, and inefficient. 
     U.S. Pat. No. 3,683,232, issued to Baur, discloses a sparkplug cap designed to increase the sparking power. The cap has internal capacitance of an unknown quantity. Without knowing the size of the capacitor, it is impossible to determine the increase of power, and it is very likely that a capacitor of high capacitance as claimed would, in fact, deplete the ignition voltage, precipitating a misfire and causing the engine to cease operation. It is very likely the Baur device requires an ignition system which is significantly higher in output energy than is commonly found on internal combustion engines. 
     U.S. Pat. No. 4,751,430, issued to Muller et al., discloses a sparkplug connector comprising a storage capacitor coaxial with an ignition transformer, which is fitted onto a sparkplug disposed deep in a spark plug hole. Such an arrangement, for the same reason as in Baur, can cause the engine to cease operation. 
     In U.S. Pat. No. 5,272,415, issued to Griswold et al., the method is different from Muller et al. and Baur, but the purpose of inserting a capacitor in parallel with the ignition circuit at the sparkplug raises the same concerns as Muller et al. and Baur, and causes a further problem of excess radio frequency interference (RFI). In vehicles manufactured in the 1990&#39;s, there is an increasing use of microprocessors to monitor and modify engine functions based on present conditions. These microprocessors are very sensitive to RFI emanations, and they will misfunction or fail as the frequency of a ringing capacitive discharge occurs in the same range as the operating frequency of the microprocessors. 
     U.S. Pat. No. 1,148,106, issued to Lux, discloses the addition of a condenser arranged in the positive electrode of a sparkplug in combination with multiple sparkplug gaps by which the resistance is diminished at the sparkplug gap, thereby obtaining improved operation of the sparkplug. The resistance of the sparkplug gap, whether single or multiple, is directly related to the pressure at the gap and the distance between the positive and negative electrodes of the sparkplug. In the case of multiple electrodes, it is dependent on the distance between the closest positive and negative electrode. A “silent” capacitive discharge between a pair of opposing electrodes effectively reduces the resistance between that pair of electrodes and the ignition spark is generated there rather than at a different pair where no ionization occurred. In Lux, the reduction of the resistance at a spark gap distant from the fuel mixture through a “silent” discharge forces the spark to occur at the “silent” pair of electrodes, which might or might not have fuel present to ignite. It is possible to ensure the proper operation of the spark while not igniting the fuel charge at all. 
     SUMMARY OF THE INVENTION 
     According to the present invention, an improved sparkplug with very low resistance and inductance is provided for use with internal combustion engines to initiate the combustion of the fuel mixture. The body of the sparkplug incorporates a capacitive element to effectively absorb the electrical energy normally lost during the rise time of the ignition transformer, to store such electrical energy, and to discharge the stored energy across the electrode gap during the first few nanoseconds of the spark event. 
     The sparkplug is comprised of an iron or steel body constructed so as to be threaded into conventional sparkplug holes, as found on cylinderheads of internal combustion engines. The body has a cylindrical extension which serves as the negative plate of the capacitive element. The body also provides for multiple negative electrodes. It is further comprised of a positive electrode which forms the interior portion of the sparkplug. One end of the positive electrode forms a spark channel with two or more negative electrodes in a plane perpendicular to the motion of the piston. The other end of the positive electrode connects by means of a resistive element to a high-voltage ignition cable of conventional design. The positive electrode also serves as the positive plate of the capacitive element. It is cylindrical, and it extends centrally through the body of the sparkplug within the negative plate of the capacitive element. The positive electrode receives the resistive element which connects the sparkplug to the ignition system. A moldable dielectric material completely fills the space between the positive and negative plates of the capacitive element for the length of the sparkplug. 
     The primary object of the invention is to provide a sparkplug with very low resistance and inductance and a properly configured and electrically sized capacitive means by which to peak the current of the electrical spark discharge. 
     Another object of the invention is to provide a sparkplug with a resistive element outside of the spark discharge circuit preventing the emanations of radio frequency interference and allowing for the use of very low resistance ignition cables. 
     Another object of the invention is to provide a sparkplug with a spark electrode configuration designed to expose the length of the spark channel to the top of the piston. 
     A further object of the invention is to provide a sparkplug with an electrode configuration by which the wearing away of the electrode material through the Coulomb Effect is diminished. 
     Still another object of the invention is to provide alternative sparkplug designs which are compact and require very little space above the cylinder head, while still maintaining the required capacitive element. 
     Still another object of the invention is to provide an alternate means by which to connect the high-voltage ignition cable to the sparkplug preventing the loss of energy due to the creation of corona and the unintentional creation of a spark between the cable and the body of the sparkplug. 
     Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form part of the specification, illustrate embodiments of the present invention and, together with the descriptions, serve to explain the principles of the invention. 
     FIG. 1 shows a schematic diagram of a sparkplug in accordance with the present invention. 
     FIG. 2 shows a longitudinal cross section of such a sparkplug. 
     FIG. 3 shows an end view of the such a sparkplug and details of the electrode disposition. 
     FIG. 4 shows the resistive connector of such a sparkplug. 
     FIG. 5 shows the positive and negative electrodes in a crown arrangement. 
     FIG.  6 . shows an alternate embodiment of the invention providing a ceramic cone which encases the positive electrode in the combustion chamber. 
     FIG. 7 shows a longitudinal partial cross section of an alternative embodiment of the invention and one means to connect the high-voltage ignition cable to the positive electrode within the capacitive element. 
     FIG. 8 shows a longitudinal partial cross section of the embodiment illustrated in FIG. 7 with an alterative means to connect the high-voltage ignition cable to the positive electrode within the capacitive element. 
     FIG. 9 shows a longitudinal cross section of yet another embodiment of the invention, one that provides two sets of opposing positive and negative plates to reduce the height of the sparkplug and to enable the use of higher spark energies, and that offers an alternative location of the installation hex for tightening the sparkplug to the cylinder head. 
     FIG. 10 shows a longitudinal cross section of a final embodiment of the invention, showing a wide, reduced height sparkplug and a connection between the high-voltage ignition cable and the positive plate where such connection is totally surrounded by ground to eliminate RFI emanations. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1, a sparkplug  1  in accordance with the present invention is shown, which is longer than a sparkplug of conventional design. The body  2  of the sparkplug is conventional in design. It can be constructed of iron, steel, or other conductive material commonly used in sparkplugs. Installation hexes of 1″, ⅞″, {fraction (13/16)}″, ¾″, ⅝″ and other common specifications may be utilized. The threaded portion and seat  6  are also conventional. The threads may be 18 mm, 14 mm, 12 mm, or 10 mm, and the seat may be either tapered- or washer-type. The insulator  3  can be of any suitable insulating material, such as ceramic, glass, or polymer, which provides high voltage insulation against the ignition pulse of up to 60 Kv. The resistive connector  4  is shown as a solid connector similar in shape to connectors found on conventional sparkplugs, but it can also be provided as a 4 mm threaded post. While similar in design to conventional connectors, the resistive connector of the present invention is different in material and in function as further discussed below. 
     The spark gap  9  is not conventional, as the spark channel is rotated to a position 90 degrees from the plane of the motion of the piston in the cylinder. Additionally, there are two or more negative electrodes  7 , instead of the normal single negative electrode. This is necessary to reduce the loss of electrode material due to the Coulomb effect. 
     Referring now to FIG. 2, the capacitive element can be seen in axial cross section. The negative cylindrical plate  10  is an extension of the body  2 . The positive cylindrical plate  8  is also the positive electrode. The dielectric insulation  11  is shown completely encasing the positive cylindrical plate  8 , inside the negative cylindrical plate  10 , except for where the center electrode is exposed at the spark gap  9 . 
     The dielectric constant, Dc, of the dielectric insulation  11  is critical to the design of the sparkplug. The spacing between the negative plate  10  and the positive plate  8 , in connection with the Dc of the insulating material and the length of the plates  10  and  8 , determine the capacitance of the invention. The optimum capacitance for ignition systems as currently offered by automobile manufacturers is between 80 and 120 picofarads, which is a very small capacitance. The material chosen for the insulator will dictate the length of the extended portion of the body. The greater the dielectric constant, the shorter the length of the extended portion of the body. For example, preferably using a derivative of the Liquid Crystal Polymer family (LCP), which has a dielectric constant of 4.5, the capacitance of the invention can be predetermined by formula: Capacitance is equal to the product of a constant (1.4122) multiplied by the dielectric constant (Dc) of the material (4.5 in the case of LCP) divided by the natural log of the quotient of the inside diameter of the negative plate  10  divided by the outside diameter of the positive plate  8 , multiplied by the length of the shortest plate. The values are calculated as follows to result in a capacitor of 80 picofarads:        Capacitance   =           (   1.4122   )     ×     (   4.5   )         N                 log                   .320   /   .250         =       6.35490   .24686     =   25.74292                              
     The calculated result of 25.74292 is the capacitance per inch. If such a device is to have 80 picofarads of capacitance, the length of the shortest plate must be 3.11 inches in length. The selection of a material such as Kapton™, with a greater dielectric constant than LCP, will allow the extended portion of the body to be shorter in length. LCP and Kapton are also desirable dielectric materials as each can be molded to completely encase the positive cylindrical plate  8 , inside the negative cylindrical plate  10 . Many otherwise suitable dielectric materials lack such moldability. 
     In selecting a dielectric material, it is critical to consider not only the dielectric constant, but also dielectric strength, which is the ability of the material to withstand a specified voltage. This property of a material is stated in volts per mil (V/.001). For our selected dielectric material, LCP, the dielectric strength is 950 v/mil. With a spacing of 0.070″ (70 mil), the total “voltage hold-off” of the material is 66.5 Kv, sufficient for an operating voltage of less than 20 Kv or a peak of less than 60 Kv. 
     The design of the capacitive element as discussed above reduces the inductance to almost zero and provides for the maximum delivery of stored energy in the shortest possible time. The frequency of the discharge and subsequent ringing is between 100 Mhz and 250 Mhz. In order to damp or eliminate the RFI associated with 250 Mhz emanations, a 2,000-5,000 ohm resistive connector  4  is permanently attached at the end of the positive cylindrical plate  8  connecting said plate to the high voltage cable of the ignition system. This resistive connector  4  can be of solid profile designed for snap on cable connectors, or can be of male threaded design, for example 4 mm X 0.7, as found on most European sparkplugs. The resistive connector can be constructed from various materials capable of providing the required resistance and being machined into the required shape. Carbon fiber materials are particularly suitable for such a purpose. 
     The center electrode  8  can be constructed as a solid bar of conductive material or of hollow drawn or formed construction. The center electrode must be of highly conductive material and, where exposed to the arc channel of the spark, it must be of solid construction. It is desirable to apply a highly conductive material, such as platinum, silver, or gold, to the tip of the center electrode and to the negative electrodes to enhance the field effect, promote more consistent spark breakdown, and reduce electrode wear due to the effect of electron transfer. Such techniques are well-known in the art. 
     It also is desirable to protect the portion of the dielectric insulation  11  protruding into the combustion chamber from exposure to heat in excess of 1,000 degrees Fahrenheit. Particularly desirable is to coat the dielectric insulation with a heat and flame resistant material, such as ceramic, to prevent destruction. Ceramic coating processes are well known in the sparkplug art. Without a protective coating, otherwise desirable dielectric materials will commonly char on the surface exposed to flame. Such degradation ultimately leads to failure of the device. An alternative to coating is to employ a ceramic cone, which is discussed below. 
     Referring now to FIG. 3, it can be seen that the negative electrodes  7  are, and must be, equidistant from the positive center electrode  8  and terminate in an arc equal to the arc created by the circumference of the center electrode. There could be any number of negative electrodes  7 . However, a single electrode would experience excessive wear, which is reduced by the use of two or more electrodes. 
     Referring now to FIG. 4, a particularly preferred deployment of multiple negative electrodes around the positive electrode is shown. Illustrated is a “crown” of negative electrodes  12  maintaining a consistent spark gap with the tips of a positive electrode extension in the shape of a “petal”  13 . The distance between the positive and negative electrodes is adjusted by bending the negative electrode away from the positive electrode in order to conform to the automobile manufacturer specifications for spark gap spacing. This spacing is determined by the manufacturer of the engine and ignition systems conforming to the requirements for spark breakdown and ignition capability. It is not advisable to either increase or decrease the spacing from the specified factory setting. 
     Such a “crown” and “petal” arrangement of negative and positive electrodes provides a very stable field enhanced area for ionization to occur. The effects of heat induced ionization are reduced as are the effects of electrode wear, which would increase the voltage required for ionization. This electrode pattern will also reduce spark jitter, which are fluctuations of ionization voltages commonly found at idle in internal combustion engines. Any selected electrode pattern must provide smooth curves of the electrode tips for stable breakdown voltages in cylinders where the conditions are very inconsistent cycle-to-cycle, such as idle. The electrode pattern can be of any multiple from 2 to 10 or more individual arcing points. 
     FIG. 5 illustrates the resistive connector  4  of the current invention in greater detail. It can be constructed of any suitable material providing the desired resistance, e.g., 5,000 ohms. The resistive component can be of any number of configurations to attach to the high voltage cable originating from the transformer. Shown are the two most common connector configurations in use for sparkplugs. One is a solid hourglass shape  14  intended for use on cables having a snap ring detent as commonly found on United States automobiles. The threaded configuration  15  is more commonly found on European automobiles. A resistive connector in accordance with the present invention may be produced in either configuration to provide the required resistance to effectively shunt the RFI emanating from the discharge “ringdown” cycle of the current invention. 
     FIG. 6 illustrates the use of a ceramic cone  16  to shield the dielectric insulation  11  from the high temperatures and oxidizing conditions inside the combustion chamber. The Figure also illustrates an alternative design for the positive electrode  8  which is comprised of both hollow and solid sections. Also illustrated are details of preferable means to achieve a stable mechanical connection between the dielectric insulation  11  and both the cone  16  and the body  2 . 
     Dielectric insulation  11  suitable for use in the present invention generally is able to withstand the high temperatures present in the combustion chamber. However, such materials often degrade when exposed to the flame of combustion. Typically, the insulation material will char on the surface and provide a path for the spark to bypass the negative electrode and travel to ground by tracking along the charred surface. To prevent this result, it is desirable to employ a prefabricated ceramic cone  16 , which receives the positive electrode  8  and is inserted into the body  2 . As can be seen by reference to FIG. 6, once so positioned, the ceramic cone shields the dielectric insulation from the flame of combustion. 
     In manufacture, the ceramic cone  16  is fitted into a tapered seat  17  in the body  2  and the positive electrode  8  is inserted into the cone. The assembly is then injected molded with the dielectric insulation  11 . The tapered seat  17  prevents the injected internal components of the invention from falling into the combustion chamber. Conversely, to prevent the internal components of the invention from being ejected from the body  2  during the high pressures of combustion, a retaining backcut  18 , in the body may be utilized. The backcut or indent can have a pointed shoulder, as illustrated, or have a round or oval shape, so long as it is sufficient to restrict the backward movement of the ceramic cone  16  and positive electrode  8  during the high pressures of the combustion process. It also is desirable to provide means for a mechanical connection between the ceramic cone  16  and the dielectric insulation  11 . It is particularly desirable to employ a series of conical ridges  19 , however, alternative mechanical connections well known in the art may also be used. 
     FIG. 6 also illustrates the construction of the positive electrode  8  employing a hollow section. This section can be of any highly conductive material such as steel, iron, copper, or other materials as is known in the sparkplug art. The section of the positive electrode  8  which is received by the ceramic cone  16  is solid in construction and fashioned from a material of better than average conductivity, such as copper or other material commonly employed in the manufacture of sparkplugs. 
     The embodiment of a current peaking sparkplug disclosed above is considered to be the best mode of practicing the invention. However, it is recognized that alternative embodiments of the invention may be desirable in applications where a more compact sparkplug is called for, particularly for multi-valve cylinder heads where physical space often is very limited. In cramped physical spaces, it further is desirable to provide means for the attachment of the high-voltage ignition cable to the positive electrode inside the capacitive element, which also offers the advantage of reducing any RFI or electromagnetic emissions from the sparkplug. It some applications it is desirable to provide for an installation hex as far removed from the cylinder head as possible, so as to ease installation of the sparkplug and eliminate the need for special tooling. It also is desirable to provide a sparkplug with multiple positive and negative capacitive plates. This capability is essential to accommodate future developments in ignition systems. The presently preferred embodiment discussed above provides between 80 to 120 picofarads of capacitance, which electrically matches current ignition offerings from manufacturers and after market suppliers. The development by these companies of future, higher energy ignition systems will require sparkplugs of increased capacitance to retain high electrical transfer efficiency while at the same time retaining physical size. 
     FIGS. 7 through 10 each illustrate alternative embodiments of the current peaking sparkplug invention to provide these enhancements. FIG. 7 discloses a compact sparkplug with one means for the attachment of the high-voltage ignition cable to the positive electrode inside the capacitive element. FIG. 8 discloses a similar compact sparkplug with alternative means for the attachment of the high-voltage ignition cable to the positive electrode inside the capacitive element. FIG. 9 discloses an even more compact sparkplug with multiple positive and negative capacitive plates, which is capable of delivering extremely high spark energies. FIG. 10 discloses a very compact sparkplug, one which can be physically smaller than conventional sparkplugs, that is particularly useful for restricted physical spaces. FIG. 10 also discloses another means for the attachment of the high-voltage ignition cable to the positive electrode inside the capacitive element and means to shield the connection so as to reduce RFI or electromagnetic emissions to a minimum. FIGS. 9 and 10 disclose alternative locations for installation hexes. 
     It should be understood that each of the embodiments illustrated in FIGS. 7 through 10 include bodies, threads, sparkgaps, positive and negative electrodes, capacitive elements, and dielectric materials as discussed above for the preferred embodiment. For sake of clarity, such design elements are not repeated in the discussions below, but, a reader should consider the embodiments illustrated in FIGS. 7 through 10 as modifications to the preferred embodiment illustrated in FIGS. 1 through 6 and discussed above. 
     Referring to FIG. 7, the positive electrode  20  is cylindrical and open at the end, exposing a central cavity to allow for the insertion of a high-voltage ignition cable (not shown). Attached to the electrode  20  by conventional means is a clip  21  made of a conductive material with two or more spikes  22  to make electrical contact with the high-voltage cable. A 2,000-5,000 ohm resistor  23  is placed between the clip and a conductive connector  24  to capture the center conductor of the HV ignition cable. An insulator  25  is located as to insulate the electrode from clip  21  to avoid electrical connection there between until the electrical charge passes through the resistor  23 . The connector  24  allows electrical connection of the resistor with electrode  20 . Preventing moisture or other elements from entering the open cavity is a weather seal  25  tightly formed around the high-voltage ignition cable and outside diameter of the sparkplug. The resistor  23  may be constructed of a resistive material, as discussed above for resistive connector  4 , or be a resistor wired between the clip  21  and the connector  24  by conventional means. Particularly desirable would be a clip, resistor, and connector molded as a single element. The negative plate  26  of the invention can be seen totally encapsulated be the dielectric insulating material  27 . 
     It is desirable to connect the high-voltage ignition cable to the positive plate by means of a resistor in the range of 2,000-5,000 ohms. This assembly provides an electrical shield for any incidental radio frequency interference that may emanate from the connection of the ignition cable terminal to the positive plate. This resistor is essential in shunting the RFI emissions created during the spark event. This interference is an oscillating, positive-negative, frequency in the same band width as the operating frequency of engine management computer systems, and such interference will cause a malfunction of the computer if not eliminated, or shunted to ground at the source. It further is desirable to locate the ignition cable inside the capacitive elements, as this offers further protection to RFI emissions. 
     Referring now to FIG. 8, an alternative means of connecting the center electrode  20  and a high-voltage ignition cable  28  is shown. As in FIG.7, the positive electrode  20  of the invention is hollow and open at the end to allow for the insertion of the ignition cable  28 . Attached to positive electrode  20  by conventional means is a non-conductive connector  30 , which provides a conductive spike  29  that is connected by conventional means to a 2,000-5,000 ohm resistor  31 . The resistor  31  is attached by conventional means to the connector  24  which is connected to the positive electrode  20 . Preventing moisture or other elements from entering the open cavity is a weather seal  25  tightly formed around the ignition cable  28  and outside diameter of the invention. The negative plate  26  of the invention can be seen totally encapsulated be the dielectric insulating material  27 . 
     Referring now to FIG. 9, the multiple positive plates  35  and negative plates  36  are shown in a relationship that provides significantly more opposing oppositely charged surfaces by which to enable the retention of capacitive electrical size while shortening the overall length of the invention for applications where physical size constraints are placed. Tower  37  is provided to prevent arcing over the installation hex  38 , which allows for installation of the sparkplug to the cylinder head. Connection to the ignition cable  28  is provided by spike  39 . This connection could alternatively be accomplished by means of a snap or ring connector, or other means common to the industry. Attached directly to the spike  39  is a 2,000-5,000 ohm resistive material  40  that connects the ignition cable  28  to the positive electrode  35 . The dielectric insulating material  43  can be seen completely isolating the multiple positive plates  35  from the negative plates  36 . The resistor  40  is attached to the positive electrode  35  by conventional means. Also illustrated is an interlock  41  which helps to secure the capacitive elements to the body  42 , preventing movement or even ejection of the elements during the high pressures of the combustion process. 
     FIG. 10 illustrates another means to connect the ignition cable  28  to the positive electrode  54 . A detent and ring clip retainer is shown at  50 , which is used to secure the connector  49  to the retaining cup  51 . The connector  49  may be constructed of a resistive material, as discussed above for resistive connector  4 . The retaining cup  51  is shown attached to the positive electrode  54  by means of copper staples  52 , providing both secure and conductive attachment. Any other conventional means of attaching cup  51  to the positive electrode  54  may be used. The dielectric material element  55  extends nearly the length of the sparkplug and separates the body of the sparkplug from the positive elements of the sparkplug. 
     FIG. 10 also illustrates an alternative means for the interlocking of the capacitive elements of the invention to the body of the sparkplug. The positive interlock can be seen as  46  and  47  whereby the combination of an expanded center electrode  48  with the intrusion of the body  45  serve to effectively lock the capacitive elements at the base of the sparkplug. The upper interlock  46  serves to restrict movement of the capacitive elements during the operation of the invention, maintaining the relationship of the positive plate to the negative plate, which serves to prevent operating losses due to changes in capacitance during the temperature changes resultant from operation. 
     Modifications may be made in the invention without departing from its spirit and purpose. Various such modifications have already been set forth and others will undoubtedly occur to one skilled in the art upon reading this specification. Accordingly, it is not intended that the invention shall be limited other than in the manner set forth in the claims which follow.