Composite Spark Plug

Abstract

A composite ignition device includes a positive electrode having a tip formed thereon that is bonded to a first insulator to form a firing cone assembly. A second insulator having a negative capacitive element embedded therein is attached to the firing cone assembly. A positive capacitive element is disposed in the second insulator and is separated from the negative capacitive element by the second insulator. The positive capacitive element is coupled to the positive electrode. The positive and negative capacitive elements form a capacitor. A resistor is coupled to the positive capacitive element. An electrical connector is coupled to the resistor and attached to the second insulator. A shell includign a negative electrode having a tip is attached to the second insulator and the firing core assembly and coupled to the negative capacitive element. The negative electrode tip is spaced apart from the positive electrode tip.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein:

FIG. 1 is a cross sectional view of an embodiment of an ignition device for internal combustion spark ignited engines of the present invention;

FIG. 2A is a partially exploded cross sectional view of the individual components that are over-molded with the engineered polymer to create the insulator of the spark plug:

FIG. 2B is a top view of the capacitive element shown in FIG. 2A;

FIG. 3 is a cross sectional view of a composite insulator of the present invention;

FIG. 4 is a is a partially exploded cross sectional view of the individual components comprising the positive plate of the capacitor element and the central electrode assembly;

FIG. 5 is a cross sectional view of an insulator assembly of the ignition device of the present invention; and.

FIG. 6 is a circuit diagram for an ignition device in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, in particular FIG. 1, a spark plug or ignition device for spark ignited, internal combustion engines in accordance with the present invention is shown generally as 1. The spark plug or ignition device 1 consists of a preferably metal casing or shell 15 having a substantially cylindrical base 44, which may have external threads 18, formed thereon for engagement with the cylinder head (not shown) of the spark ignited internal combustion engine (not shown). The cylindrical base 44 of the spark plug shell has a generally flattened surface perpendicular to the longitudinal axis of the spark plug 1 to which a ground electrode 16 is affixed, preferably by conventional welding. In an embodiment of the invention, the ground electrode 16 has a preferably rounded tip 45 of Rhenium/Tungsten sintered compound, which resists the erosion of the electrode 16 due to high power discharge, as further disclosed herein.

The spark plug or ignition device 1 includes a preferably hollow, composite insulator 4 disposed concentrically within the shell 15, incorporating a combustion cone 5, preferably formed from ceramic or the like. The center or positive electrode 7 is disposed concentrically within the ceramic cone 5 that is disposed in the combustion chamber when installed in the engine (not shown).

The center electrode 7 is preferably constructed of a thermally and electrically conductive material with very low resistivity values such as, but not limited to, a copper or copper alloy, with or without an outer coating, cladding or plating preferred in a nickel alloy. The center electrode 7 preferably includes formed thereon, by weldment or by other suitable attachment, an electrode tip 17 preferably constructed of a Rhenium/Tungsten alloy (50%-75% Rhenium), which is highly resistant to erosion under high power discharge, as further disclosed herein.

The spark plug 1 includes a highly conductive spring 10 that is a component of the center conductor assembly and positive plate 43 of the capacitive element. The spring 10 is connected to one end of a preferably 5KΩ (or suitable resitance) resistor or inductor 11 and electrically and mechanically contacts the positive plate 43 of the capacitor, which is connected to the center electrode 7 by means of an interference fit of the stud 9 of the electrode 7 into the positive plate 43. Preferably, the resistor or inductor 11 is connected to a high voltage terminal 13 for further connection to an ignition coil (not shown) by a penetrating rod 14 of the terminal 13, as further disclosed herein.

The composite insulator 4 of the spark plug is inserted into the shell 15 and preferably crimped for positive alignment and seal against combustion gasses, as is customary practice in the industry. Preferably, during an over molding process of creating the insulator 4, a flange 3 of a negative plate 2 is left exposed. The exposed flange 3 of the negative plate of the capacitor 2 makes physical and electrical contact with the conductive shell 15 of the spark plug when the shell 15 is crimped with sideward and downward pressure onto the insulator 1 using conventional industry practice. The mechanical contact between the shell 15, which is electrically connected to the ground circuit of the engine ignition circuit and the negative plate 2 of the capacitor advantageously ensures that the negative plate 2 is electrically connected to the ground circuit of the ignition system.

Referring now to FIG. 2, the negative plate is shown generally at 2 and includes at least one flange 20 extending therefrom. During the molding process, the negative plate 2 is encased in the engineered polymer of the insulator 4 and the tips of flange 20 are left exposed in order that they make mechanical and electrical contact with the shell of the spark plug (not shown) thereby ensuring the plate 2 is electrically connected to the ground of the ignition system. A scallop 21 of the flange 20, ensures a complete flow of the engineered polymer of the insulator 4 around the plate 19 during the molding process to encase and locate the plate 2 concentric to the ceramic cone 5.

The preferably ceramic cone 5 has an integral and concentric locking detent 27 wherein during the molding process, the engineered polymer of the insulator 4 flows into, which locks and locates the cone 5 in relation to and separated from the negative plate 2. A concentric cavity 26 in the ceramic cone 5 is formed to nestle the center or positive electrode 7.

The center electrode 7 is provided with a boss 23, stud 9 and an electrode tip 17 that is resistant to high power discharge. The boss 23 of the center electrode 7 nestles in the cavity 26 provided in the ceramic cone 5. During the manufacturing process, the cavity 26 is preferably filled with copper glass, ceramic epoxy or other suitable permanently sealing material on top of the installed center electrode 7 and boss 23 thereof, which provides a gas seal to protect the interior of the spark plug 1 from combustion pressures. The stud 9 of the electrode 7 is provided to engage the assembled positive plate of the capacitor (shown as 43 in FIG. 4) with an interference fit ensuring completion of the positive side of the ignition circuit.

Referring now to FIG. 3, the center electrode 7 is provided with an erosion resistant electrode tip 17 that is preferably formed from a Rhenium/Tungsten alloy of between about 50%-75% Rhenium. An end of the highly erosion resistive electrode tip 17 is preferably flush with the end 30 of the ceramic cone 5.

Within the ignition or spark gap pulsed-power industry, it is well-known that increasing the power (Watts) of the spark increases the erosion rate of the electrodes, with the spark-emanating electrode eroding faster than the receiving electrode. Industry standard has been to utilize precious or noble metals such as gold, silver, platinum and lately iridium as the electrode metal of choice to abate the electrode erosion of common ignition power. These metals, however, will not suffice to reduce the elevated electrode erosion rate of the high power discharge of the current invention. The electrode tip 17 of a sintered compound of rhenium by about 50% to 75% by mass sintered with tungsten in a preferably cylindrical configuration of 0.025″-0.060″ in diameter and 0.100″ in length is preferably affixed to the center electrode 7 by means of plasma, friction or electron welding or other suitable method by which permanency is achieved while delivering a low resistance juncture.

The use of pure tungsten as an electrode in a spark gap application is well documented within the pulsed-power industry as a preferred erosion resistant material. However, as used in an internal combustion engine where combustion temperatures reach beyond the oxidation temperature of tungsten, the electrode disadvantageously erodes at a faster rate than noble metals. Tungsten may be utilized as an electrode material in an automotive application by the isolation of the tungsten to the oxygen present in the combustion chamber. This is partially accomplished by the sintering of tungsten with rhenium and an appropriate binding agent such as, but not limited to, a non-oxidizing metal that melts at a temperature below that of rhenium and tungsten. The sintering process blends the two preferably powdered base metals with the binding agent and during the refractory process melts the binder and sinters the base materials into a form held together by the binder. The form, preferably rectangular in shape, is then extruded into wire of 0.025″ to 0.060″ in diameter to form the electrode tips 17 and 45. The bonding agent provides protection against the oxidation of the tungsten component by covering that portion of the tungsten not in contact with the rhenium.

While this offers some protection for the tungsten against oxidation, the bonding metal erodes during the high-power discharge process, exposing the raw tungsten of the electrode tips 17 and 45 to ambient oxygen in the combustion chamber and thereby accelerating tungsten erosion. However, the erosion rate due to oxygen exposure is significantly reduced by the use of the bonding agent. Additionally, as the tungsten erodes, the rhenium is now closer to the opposing or negative electrode, and as proximity and field effect dictate where the spark emanates from, the rhenium, also highly resistant to high-power erosion, becomes the source of the spark streamer.

Additionally, tungsten may be utilized as an electrode material in an automotive application by the placement of the electrode tip 17 with respect to the ceramic cone 5. In this placement, only the extreme end of the electrode tip 17 is exposed to the elements in the combustion chamber. The remainder of the cylindrical electrode tip 17 has been bonded to the ceramic cone 5, sealing off the electrode tip 17 against any combustion gasses including oxygen. In this fashion, only the extreme end of the electrode tip 17 will erode, as it will under the high power discharge of the current invention.

As the electrode tip 17 gradually wears away, electrons from the ignition pulse will emanate from the recessed electrode tip 17 and ionize the ceramic cone wall 31 and creep to the edge 30 of the ceramic cone 5 before ionizing the spark gap (not shown) and creating a spark (not shown) to the ground electrode 16. The voltage required to ionize the ceramic cone wall 31 just above the eroding electrode tip 17 is very small resulting in the total voltage required to breakdown the spark gap and create a spark being minimally more than the voltage required to break down the original, un-eroded spark gap.

In this fashion, the electrode tip 17 can erode to the point where the distance from the ground electrode 16 to the center or positive electrode tip 17 has doubled, while the voltage required to break down the doubled gap is slightly more than the breakdown voltage of the original spark gap and well under the available voltage from the original equipment manufacturer ignition system. This advantageously assures proper operation of the engine for a minimum of 10⁹ cycles of the spark plug or 100,000 equivalent miles.

Referring again to FIG. 3, there is shown a molded composite insulator assembly indicated generally at 19, center electrode 7 with erosion resistant tip 17, ceramic cone 5 and binding and insulating engineered polymer 4, forming the assembly 19. Referring now to the composite insulator 19 and center electrode 7 of FIG. 3, and the center conductor 43 of FIG. 4, when the hollow center conductor 43 is inserted into the cavity 32 of the composite insulator 19, the stud 9 of the center electrode 7 engages the undersize hole 46 of the center conductor providing a highly conductive path from the ignition coil output (not shown) to the spark plug gap (not shown). Once connected to the center electrode 7, the center conductor 43 becomes the positive plate of the capacitive element and a capacitor or capacitive element, indicated generally at 28 in FIG. 5, is formed by definition, i.e.: a capacitor being two conductive plates (plates 43 and 2) of opposite electrical charge separated by a dielectric, the dielectric being the engineered polymer 4.

Capacitance can be mathematically arrived at by formula;

$C=\frac{1.4122\times D_c}{L_n\left(D_i/D_o\right)}$

Where C is the capacitance per inch of cylindrical plates, D_c is the dielectric constant of the polymer 4, L_n is the natural log, D_i is the inside diameter of the negative plate 2, and D_o is the outside diameter of the positive plate 43 in FIG. 4. Capacitance can be increased by decreasing the separation of the oppositely charged plates 43 and 2 or by increasing the surface areas of the plates 43 and 2. Capacitance can also be affected by the dielectric constant of the engineered polymer. Dielectric constants can vary from four to over twelve depending on the material selected.

Attention is now directed in FIG. 3 to the center or positive electrode 7 and the cavity 26 of ceramic cone 5 into which the electrode 7 is embedded concentrically. Once the electrode 7 has been inserted into the ceramic cone 5, a pressure or gas seal is accomplished by completely filling the cavity 26 with ceramic epoxy, copper glass or other suitable high temperature sealant.

Referring now to FIG. 4, a center conductor assembly is indicated generally at 33 consisting of the tubular positive plate or conductor 43, resistor 11, conductive spring connector 10, terminal insert 12, and high tension cable or coil terminal 13. The resistor 11 is inserted into the cavity 41 of the terminal insert 12 and preferably retained by means of a high temperature ceramic epoxy or other high temperature adhesive suitable to retain the resistor 11 in place under operation of the engine. The high tension cable or coil terminal 13 is attached to the terminal insert 12 by means of a threaded portion 48 of the terminal 13 into the threaded cavity 40 of the terminal insert 12. The pointed shaft 47 of the terminal 13 makes physical and electrical contact with the resistor 11 once the terminal 13 is installed by screwing into the terminal insert 12. The end of the resistor 11 opposite the terminal 13 makes physical and electrical contact with the conductive spring 10, which is under compression when the center conductor assembly is inserted into the composite insulator 19 of FIG. 3.

The spring 10 end opposite the resistor 11 makes mechanical and electrical contact with the tubular positive plate or conductor 43 completing the positive circuit for the ignition pulse. The placement of the resistor 11 in the positive circuit before the positive plate 43 of the capacitive element of the spark plug 1 allows the capacitor 28 to discharge at a very high transfer efficiency rate and deposit a very high percentage, greater than 95%, of the stored energy into the fuel charge. Normally this hard deposition of energy would create an abnormal amount of radio frequency or electromagnetic interference, which is incompatible with the operation of automobile engine management computers. Placement of the resistor 11 before the capacitor 28 in the circuit allows for the deposition while elimination the interference.

FIG. 6 illustrates an exemplary circuit 30 for the ignition device 1 of the present invention and shows a coil 35, such as an ignition coil or the like, connected to the resistor 11 through a secondary circuit 37. The capacitor 28 is connected to the resistor 11 and connected in parallel with the secondary circuit 37 and ground 34. The resistor 11 advantageously suppresses high frequency electrical noise generated by the circuit 30 while not affecting the high power discharge of the capacitor 28.

There is abundant prior experimentation with related results, see Society of Automotive Engineers Paper 02FFFL-204 titled “Automotive Ignition Transfer Efficiency”, concerning the utilization of a current peaking capacitor, such as the capacitor 28 wired in parallel to the high voltage circuit such as the circuits 30 and 37 of the ignition system to increase the electrical transfer efficiency of the ignition and thereby couple more electrical energy to the fuel charge. By coupling more electrical energy to the fuel charge, consistent ignition relative to crank angle is accomplished reducing cycle-to-cycle variations in peak combustion pressure, which increases engine efficiency. An additional benefit of coupling the current peaking capacitor 28 in parallel is the resultant large robust flame kernel created at the discharge of the capacitor 28. The robust kernel causes more consistent ignition and more complete combustion, again resulting in greater engine performance. One of the benefits of utilizing a peaking capacitor 28 to improve engine performance is the ability to ignite fuel in extreme lean conditions. Today, modern engines are introducing more and more exhaust gas into the intake of the engine to reduce emissions and improve fuel economy. The use of the peaking capacitor 28 will allow automobile manufacturers to lean air:fuel ratios with additional levels of exhaust gas beyond levels of current automotive ignition capability.

Referring now to FIG. 5, there is shown the completely assembled composite insulator assembly indicated generally as 6, consisting of the over-molded insulator 19 with ceramic cone 5 and center electrode 7 with erosion resistant electrode tip 17, negative plate 2 of the capacitive element 28, and insulating engineered polymer 4. Also shown is a cross sectional view of the completely assembled component string of the center conductor assembly 33 shown in FIG. 4 consisting of the tubular positive plate or conductor 43 of the capacitor or capacitive element 28, resistor 11, conductive spring connector 10, terminal insert 12, and high tension cable or coil terminal 13. This view illustrates the completed assembly of the composite insulator assembly 6 prior to insertion and crimping into the spark plug shell 44 of FIG. 1.

Gas seal and ground contact washer 22 of FIG. 5 is placed into the shell 15 of FIG. 1, resting in the transition of diameters, ensuring the negative plate 43 makes contact with the shell 15 and completing the ground circuit of the capacitive element of the current invention.

An embodiment of the spark plug or ignition device 1 of the present invention provides a spark plug that has an insulator 4 and 5 that is a composite of dissimilar materials. An embodiment of the spark plug or ignition device 1 includes a very fine cross sectional electrode tips 17 and 45 of a material and design to effectively reduce the erosion of the electrode tips 17 and 45 prevalent in high power discharge, spark-gap devices. An embodiment of the spark plug or ignition device 1 an insulator 4 constructed in such a manner as to create a capacitor 28 in parallel with the high voltage circuit 30 of the ignition system, and placement of an inductor or resistor 11 in the electrical circuit 30 of the spark plug whereby the resistor or inductor 11 suitably shields any electromagnetic or radio frequency emissions from the spark plug 1 without compromising the high power discharge of the spark. An embodiment of the spark plug or ignition device 1 also completes the capacitor 28 and high voltage circuit 30 of the ignition system to provide a path for the high power discharge to the electrode 17 of the spark plug 1.

Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above and/or in the attachments, and of the corresponding application(s), are hereby incorporated by reference.

Claims

1. A composite ignition device for an internal combustion engine, comprising: a positive electrode bonded to a first insulator to form a firing cone assembly, said positive electrode having a tip formed on an end thereof;a second insulator attached to said firing cone assembly, said second insulator including a negative capacitive element embedded therein;a positive capacitive element disposed in said second insulator and separated from said negative capacitive element by said second insulator, said positive capacitive element coupled to said positive electrode, said positive capacitance element and said negative capacitive element forming a capacitor;a resistor disposed in a resistor insulator and coupled to said positive capacitive element by a resistor connector;an electrical connector coupled to said resistor and attached to said second insulator; anda shell attached to said second insulator and said firing core assembly and coupled to said negative capacitive element, said shell including a negative electrode having a tip formed thereon and spaced apart from said positive electrode tip.

2. The device of claim 1 wherein said second insulator is attached to said firing cone assembly and said negative capacitive element is embedded in said second insulator by injection molding.

3. The device of claim 1 wherein said second insulator is attached to said firing cone assembly said negative capacitive element is embedded in said second insulator by insert molding.

4. The device of claim 1 wherein said second insulator comprises an engineered polymer.

5. The device of claim 4 wherein said engineered polymer comprises liquid crystal polymer.

6. The device of claim 4 wherein said engineered polymer comprises polyetheretherketone.

7. The device of claim 4 wherein said engineered polymer has a dielectric constant from between about 5 to about 10.

8. The device of claim 1 wherein said first insulator comprises an alumina material.

9. The device of claim 7 wherein said alumina material comprises from about 88 percent to about 99 percent pure alumina.

10. The device of claim 1 wherein said resistor connector comprises a spring member.

11. The device of claim 1 wherein said positive and negative electrode tips comprise a sintered rhenium and tungsten material.

12. The device of claim 11 wherein said material is formed from about 50 percent rhenium and about 50 percent tungsten.

13. The device of claim 11 wherein said material is formed from about 75 percent rhenium and about 25 percent tungsten.

14. The device of claim 1 wherein said positive electrode further comprises a coating of conductive ink on an exterior surface thereof, said coating having a predetermined thickness.

15. The device of claim 14 wherein said conductive ink comprises a precious metal or precious metal alloy.

16. The device of claim 1 wherein said capacitor has a predetermined capacitance in the range from about 30 to about 100 pf.

17. The device of claim 1 wherein said positive capacitive element is coupled to said positive electrode by an interference fit.

18. A circuit for an ignition device for an internal combustion engine, comprising: a power source operable to intermittently activate said circuit;a positive electrode having a tip on an end thereof;a ground electrode connected to ground and having a tip on an end thereof, said ground electrode tip spaced apart from said positive electrode tip by a predetermined spark gap;at least one resistor connected in series with said power source and said positive electrode; andat least one capacitor directly connected to said resistor and connected in parallel with said positive electrode and ground.

19. The circuit of claim 18 wherein said at least one resistor reduces radio frequency interference (RFI) when said circuit is active.

20. The circuit of claim 18 wherein said at least one capacitor increases peak current to said spark gap when said circuit is active.

21. The circuit of claim 18 wherein said positive and negative electrode tips comprise a sintered rhenium and tungsten material.

22. The device of claim 22 wherein said material is formed from about 50 percent rhenium and about 50 percent tungsten.

23. The device of claim 22 wherein said material is formed from about 75 percent rhenium and about 25 percent tungsten.

24. The circuit of claim 18 wherein said resistor has a predetermined resistance in the range from about 2 kohms to about 20 kohms.

25. The circuit of claim 18 wherein said capacitor has a predetermined capacitance in the range from about 30 to about 100 pf.

26. A method for forming a composite ignition device for an internal combustion engine, comprising: bonding a positive electrode with a first insulator to form a firing cone assembly, said positive electrode tip including a tip formed thereon;embedding a negative capacitive element in a second insulator and attaching said second insulator to said firing cone assembly;coupling a positive capacitive element to said positive electrode in said second insulator, said positive capacitive element separated from said negative capacitive element by said second insulator, said positive capacitance element and said negative capacitive element forming a capacitor;disposing a resistor in a resistor insulator;coupling said resistor to said positive capacitive element by a resistor connector;coupling an electrical connector to said resistor;attaching said electrical connector to said second insulator;attaching a shell to said second insulator and said firing cone assembly, said shell including a negative electrode having a tip formed thereon, said negative electrode tip spaced apart from said positive electrode tip; andcoupling said shell to said negative capacitive element.

27. The method of claim 26 further comprising sealing a top of said electrode in said insulator.

28. The method of claim 26 further comprising coating said positive electrode with a conductive ink prior to bonding said positive electrode with said first insulator.

29. The device of claim 28 wherein said conductive ink comprises a precious metal or precious metal alloy.

30. The method of claim 26 wherein said step of attaching said shell to said second insulator and said firing cone assembly comprises crimping said shell to said second insulator and said firing cone assembly.

31. The method of claim 26 wherein said step of coupling said shell to said negative capacitive element comprises crimping said shell to said negative capacitive element.

32. The method of claim 26 wherein said step of bonding said positive electrode with said first insulator comprises heating said positive electrode and said first insulator at a predetermined temperature for a predetermined time.

33. The method of claim 27 wherein said predetermined temperature is about 750 degrees Celsius to about 900 degrees Celsius.

34. The method of claim 27 wherein said predetermined time is about 10 minutes to about 60 minutes.

35. The method of claim 26 wherein said step of embedding a negative capacitive element in a second insulator and attaching said second insulator to said firing cone assembly second insulator comprises injection molding.

36. The method of claim 26 wherein said step of embedding a negative capacitive element in a second insulator and attaching said second insulator to said firing cone assembly second insulator comprises insert molding.

37. The method of claim 26 wherein said second insulator comprises an engineered polymer.

38. The method of claim 37 wherein said engineered polymer comprises liquid crystal polymer.

39. The method of claim 37 wherein said engineered polymer comprises polyetheretherketone.

40. The method of claim 37 wherein said engineered polymer has a dielectric constant from between about 5 to about 10.

41. The method of claim 26 wherein said first insulator comprises an alumina material.

42. The device of claim 41 wherein said alumina material comprises from about 88 percent to about 99 percent pure alumina.

43. The method of claim 26 wherein said resistor connector comprises a spring member.

44. The method of claim 26 further comprising forming said positive and negative electrode tips by sintering rhenium and tungsten to form a sintered material.

45. The method of claim 44 wherein said material is formed from about 50 percent rhenium and about 50 percent tungsten.

46. The method of claim 44 wherein said material is formed from about 75 percent rhenium and about 25 percent tungsten.

47. The method of claim 26 wherein said capacitor has a predetermined capacitance in the range from about 30 to about 100 pf.

48. The method of claim 26 wherein said step of coupling a positive capacitive element to said positive electrode said positive capacitive element is performed by an interference fit.