Patent Publication Number: US-7588021-B2

Title: Spark plug circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 60/792,205, filed Apr. 14, 2006 which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to spark plugs for igniting the fuel/air mixture in a combustion chamber of an automobile and to systems and methods for reducing corrosion, clogging and fouling of the center electrode of the spark plug. 
     2. Discussion 
     Spark plugs, of course, are well known in the automotive and other industries for igniting the fuel mixture in the cylinders of internal combustion engines. Spark plugs are exposed to extremely high temperatures and corrosive environments which reduce their useful life. In order to increase the useful life of the spark plug, and especially the discharge portion of the spark plug, many spark plugs use metals containing predominately Platinum (Pt), Iridium (Ir) or alloys thereof. Nonetheless, corrosion mechanisms are still present with spark plugs using Ir. The corrosion mechanism on spark plugs using Ir occurs through the presence of calcium and/or phosphorus, both of which are often present in the oil used to lubricate the engine, which invariably enters the combustion chamber in internal combustion engines. Due to the high temperature of the combustion reaction it has been found that calcium and phosphorous may wear away or corrode the Ir on the electrode of the spark plug. Other problems with Ir include severe oxidation at certain temperature ranges. Though the discharge portion of the spark surface is typically immune from wear, over time corrosion or oxidation may cause pieces of the discharge portion to dissolve, erode and/or vaporize. It is believed that calcium and/or phosphorus is the cause of this wear. The source of the calcium and phosphorus is from the lubricating oil that is circulated throughout the engine. A small amount of lubricating oil is present in the combustion chamber as it moves past the piston rings. 
     Engine designers and manufacturers are continually pressured to increase the efficiency of the engine. One major source of loss of efficiency is in the form of friction. Major friction losses occur through the reciprocal movement of the pistons within the combustion chambers. In an effort to reduce the friction between the pistons and combustion chamber walls, engine designers are changing the piston ring designs to reduce friction, which tends to allow more oil to pass between the piston and combustion chamber walls, thus leading to an increase of engine lubricant entering into the combustion chamber. This increase in engine lubricant into the combustion chamber increases corrosive compounds, such as calcium and phosphorus, and exacerbate the corrosion and fouling of the Ir containing electrodes. 
     Further, it has been observed that during the combustion cycle, calcium and phosphorus is present in ionic form in the gas phase of the combustion cycle. The gas containing the calcium and phosphorus molecules condenses into a liquid onto the tip of the Ir electrode. Because the calcium and phosphorus ions are positively charged, they are attracted to the negatively charged electrode of the spark plug. Once on the tip of the electrode, the corrosion mechanism of the calcium and phosphorus ions acts to corrode and/or foul the electrode. Moreover, it is known that molten calcium dissolves Ir and leaves the Ir electrode vulnerable to oxidation. 
     Therefore, there is a need for a new and improved method and system for preventing or reducing the corrosion mechanism caused by the presence of calcium and phosphorus in the combustion chamber. 
     SUMMARY OF THE INVENTION 
     In view of the above, the described features of the present invention generally relate to a spark plug ignition circuit for igniting the fuel/air mixture in a combustion chamber of an internal combustion engine. The circuit comprises a battery having a positive terminal and a negative terminal, which is connected to a vehicle ground. The circuit further includes an ignition circuit having a first and second switch terminal, which is operably connected to the vehicle ground. The circuit also comprises an ignition coil having a primary coil and a secondary coil, wherein the primary coil has a first coil end operably connected to the first switch terminal of the ignition circuit and a second coil end operably connected to the positive terminal of the battery. The secondary coil has a first coil end and a second coil end, which is operably connected to vehicle ground. Additionally, the circuit comprises a spark plug having a center electrode and a ground electrode, wherein the center electrode is operably connected to the first coil end of the secondary coil and the ground electrode is operably connected to ground, wherein the center electrode and the ground electrode are separated by a gap and the secondary coil provides a first positive voltage across the gap between the center electrode and the ground electrode. 
     In another embodiment of the present invention, a method for reducing corrosion of spark plug electrodes in an ignition system is disclosed. The method comprises the step of providing a first positive voltage across the gap between the center electrode and the ground electrode. 
     In yet another embodiment of the present invention, a spark plug ignition circuit for igniting the fuel/air mixture in a combustion chamber of an internal combustion engine is disclosed. The circuit comprises a battery having a positive terminal and a negative terminal, which is connected to a vehicle ground. The circuit further includes an ignition circuit having a first and second switch terminal, which is operably connected to the vehicle ground. The circuit also comprises an ignition coil having a primary coil and a secondary coil, wherein the primary coil has a first coil end operably connected to the first switch terminal of the ignition circuit and a second coil end operably connected to the positive terminal of the battery. The secondary coil has a first coil end and a second coil end, which is operably connected to vehicle ground. Additionally, the circuit comprises a spark plug having a center electrode and a ground electrode, wherein the center electrode is operably connected to the first coil end of the secondary coil, the ground electrode is operably connected to ground, and the ground electrode has a portion made of Iridium or an alloy of Iridium, wherein the center electrode and the ground electrode are separated by a gap and the secondary coil provides a negative voltage across the gap between the center electrode and the ground electrode. 
     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a conventional automotive ignition system; 
         FIG. 2  is a schematic diagram of a spark plug ignition system, in accordance with one embodiment of the present invention; and 
         FIG. 3  is a schematic diagram of an alternate embodiment of a spark plug ignition system, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a conventional automotive ignition system is shown schematically. Prior art ignition circuit  10  generally includes a battery  12 , an ignition coil  14 , a spark plug  16 , and an ignition switch  18 . The battery  12  includes two terminals: positive terminal  20  and negative terminal  22 . The ignition coil  14  includes a primary coil  24  and a secondary coil  26 . Primary coil  24  has a first coil end  28  connected to the positive terminal  20  of battery  12 . Primary coil  24  also has a second coil end  30  connected to switch  18 . Switch  18  has a first switch terminal  32  and a second switch terminal  34 . Connected to the second switch terminal  34  is negative terminal  22  of battery  12 . Secondary coil  26  has a first end  36  connected to spark plug  16  and a second end  38  connected to negative terminal  22  of battery  12 . 
     Spark plug  16  generally includes a first end  40  having an electrical connector for attaching, as is conventionally known, a distributor wire connecting the first end  36  of secondary coil  26  to spark plug  16 . As is conventionally known, the electrical connector at the first spark plug end  40  is in communication with a center electrode, which is insulated from the grounded body of spark plug  16  at second spark plug end  42 . Generally, second spark plug end  42  has a ground electrode and is connected through the engine and body of the vehicle to the vehicle ground or the negative terminal  22  of battery  12 . Circuit  10  may have multiple grounding points, such as grounding point  44 , which connect the circuit  10  to vehicle ground. 
     In operation, battery  12  energizes the primary coil  24  of ignition coil  14 . Once the primary coil  24  is fully energized and the appropriate time in the combustion cycle is reached, that is, when a spark is required, switch  18  is activated to disconnect primary coil  24  from ground  44 . Upon disconnection of the primary coil  24  from ground, the energy stored in primary coil  24  is released through a collapsing magnetic field. As the magnetic field collapses, voltage is induced in secondary coil  26 . The polarity of the voltage induced in secondary coil  26  is dictated by polarity set up in primary coil  24 . Secondary coil  26  will have the opposite polarity of primary coil  24 . In other words, if the first end  28  of the primary coil  24  is the positive end, then the first end  36  of secondary coil  26  will be the negative end of secondary coil  26 . If the first end  36  of secondary coil  26  is the negative end of secondary coil  26 , which is the case for circuit  10  shown in  FIG. 1 , the electrode of spark plug  16  will be negatively charged with respect to ground  44 . The second end  42  of spark plug  16  is connected to ground  44 , which has a positive polarity with respect to first end  40 , and the spark will be created between the negatively charged electrode and end  42  of spark plug  16 . 
     Referring now to  FIG. 2 , a schematic diagram illustrating a spark plug ignition circuit  60  in accordance with one embodiment of the present invention is shown. Ignition circuit  60  includes a battery  62 , an ignition coil  64 , a spark plug  66 , an ignition switch  68 , and at least one ground point  70 . Battery  62 , as is conventionally known, has a positive terminal  72  and a negative terminal  74 . 
     Ignition coil  64  includes a primary coil  76  and a secondary coil  78 . Primary coil  76  has a first coil end  80  and a second coil end  82 . First coil end  80  is connected to ignition switch  68 , and second coil end  82  is connected to positive terminal  72  of battery  62 . Secondary coil  78  has a first coil end  84  connected to spark plug  66  and a second coil end  86  connected to ground point  70 . Ignition switch  68  has a first switch terminal  88  connected to the first end of primary coil  76  and a second switch terminal  90  connected to a negative terminal  74  of battery  62 . 
     Spark plug  66  may have various configurations suitable for use in a variety of applications. The configuration of spark plug  66  shown in the Figures is for illustrative purposes only. The present invention contemplates the use of a variety of spark plug types and configurations, including spark plugs having a center electrode having an Ir or Ir alloy discharge portion. Spark plug  66  has a center electrode and a ground electrode  94 . The center electrode is in communication with an electrical connector  92 . Electrical connector  92  is configured to connect to an electrical cable (shown schematically) such as a distributor wire. The center electrode via electrical connector  92  of spark plug  66  is connected to first coil end  84  of secondary coil  78 , and the ground electrode  94  of spark plug  66  is connected to ground point  70  or vehicle ground. 
     In operation, primary coil  76  of ignition coil  64  is energized by battery  62 . The connections previously described with regard to the primary coil  76  of ignition coil  64  sets up a voltage polarity where the first end  80  of primary coil  76  is at vehicle ground and coil end  82  of primary coil  76  is at positive twelve volts or positive battery voltage. When a spark is required, which occurs at a specified time in the combustion cycle usually called spark timing, ignition switch  68  is opened to disconnect the first end  80  of primary coil  76  from vehicle ground. Once the vehicle ground connection of primary coil  76  is interrupted by switch  68 , the magnetic field developed in primary coil  76  collapses, and the resulting change in magnetic flux induces a voltage across secondary coil  78 . The polarity of voltage induced in coil  78  is the opposite of the polarity set up in primary coil  76 . That is, first coil end  84  is at a positive voltage and second coil end  86  is at vehicle ground. When secondary coil  78  is fully charged, a spark is developed across the gap between the center electrode of spark plug  66  and the ground electrode  94 . Since the first end  84  of secondary coil  78  is at a positive voltage, then the center electrode of spark plug  66  is positively charged, and the ground electrode  94  of spark plug  66  is at vehicle ground. 
     It has been observed that spark plugs having a portion of their center electrode made of an iridium or an alloy thereof enhances the life and durability of the discharge portion of the spark plug. Further, the inventor has determined that the combination of iridium and a positively charged electrode significantly reduces corrosion of the electrode. The corrosion mechanism is caused by the presence of calcium and phosphorus ions present in the combustion chamber. During combustion, the calcium and phosphorus ions are positively charged. The present invention, as described herein, provides a center electrode that is positively charged that, therefore, repels the positively charged calcium and phosphorus ions. Thus, the spark plug of the present invention is configured to significantly reduce or eliminate the impingement and/or collection of calcium and phosphorus ions on the center electrode. The inventor has also determined that, in a conventional spark plug ignition system in which a negative polarity is utilized as the sparking voltage, a reduction in corrosion of the spark plug can be achieved by utilizing an iridium or iridium alloy on the ground electrode only. 
     Referring now to  FIG. 3 , a schematic diagram of an alternate embodiment  100  of an ignition circuit, in accordance with the present invention, is illustrated. Ignition circuit  100  shown in  FIG. 3  includes the same components as shown and described above with respect to  FIG. 2  and includes the same connections to those components. However, alternate ignition circuit  100  includes a voltage source, illustrated in  FIG. 3  as DC to DC converter  102 . The DC to DC converter  102  provides a voltage source that will energize secondary coil  78  and provide a voltage across the gap of spark plug  66 . While the embodiment illustrated in  FIG. 3  includes DC to DC converter  102 , the present invention contemplates the use of any secondary voltage source to provide this constant voltage, e.g., a capacitor or battery. The DC to DC converter  102  has a first terminal  104  and a second terminal  106 . First terminal  104  of converter  102  is connected to the second end  86  of secondary coil  78 . Second terminal  106  of DC to DC converter  102  is connected to ground point  70 . Thus, converter  102  provides a constant positive voltage drop across the electrodes of spark plug  66  throughout the combustion cycle. Advantageously, the application of converter  102  provides a positive charge on the center electrode of spark plug  66  over the duration of the combustion cycle, thereby repelling the positively charged corrosive elements throughout the combustion cycle. Of course, the present invention contemplates the activation of DC to DC converter  102  over a time less than the entire combustion cycle as well. 
     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.