US3737718A - Ignition noise suppression center electrode assembly for spark plugs - Google Patents

Abstract

An improved resistance element for suppressing random radio frequency radiation from the high voltage ignition circuit of an internal combustion engine. The resistance element is produced by sintering an extruded or compressed rod consisting essentially of copper oxides plus a heat destructible binder and from 0 to 10 percent of an inert plasticizer. The resulting element consists essentially of a combination of cupric oxide (CuO) and cuprous oxide (Cu2). Optional contact terminals may be formed on the element by applying a metallic coating to opposed ends of the capsule. The suppression element may be placed in the center electrode assembly of a spark plug electrically in series between a high voltage terminal and an electrode tip or at any suitable location in the high voltage ignition circuit for the internal combustion engine.

Description

Rempes, Jr. et al.

[54] IGNITION NOISE SUPPRESSION CENTER ELECTRODE ASSEMBLY FOR SPARK PLUGS [75] Inventors: Paul E. Rempes, Jr., Royal Oak, Mich.; Le Roy H. Houghton, Toledo, Ohio [73] Assignee: Champion Spark Plug Company,

Toledo, Ohio [22] Filed: Aug. 20, 1971 [21] Appl. No.: 173,409

[52] U.S. Cl ..315/58, 313/136 [51] Int. Cl ..H 0lt 13/20 [58] Field of Search ..252/518; 315/58 [56] References Cited UNITED STATES PATENTS 2,071,571 2/1937 Rabezzana et al ..3l5/58 2,633,521 3/1953 Becker et al. "252/518 2,837,487 6/1958 Huttar ..252/5l8 1 June 5, 1973 Primary ExaminerRoy Lake Assistant ExamjnerDarwin R. l-lostetter Att0rney-Carl F. Schaffer, Allen Owen, Henry K. Leonard et al.

57 ABSTRACT An improved resistance element for suppressing random radio frequency radiation from the high voltage ignition circuit of an internal combustion engine. The resistance element is produced by sintering an extruded or compressed rod consisting essentially of copper oxides plus a heat destructible binder and from 0 to 10 percent of an inert plasticizer. The resulting element consists essentially of a combination of cupric oxide (CuO) and cuprous oxide (Cu Optional contact terminals may be formed on the element by applying a metallic coating to opposed ends of the capsule. The suppression element may be placed in the center electrode assembly of a spark plug electrically in series between a high voltage terminal and an electrode tip or at any suitable location in the high voltage ignition circuit for the internal combustion engine.

10 Claims, 2 Drawing Figures IGNITION NOISE SUPPRESSION CENTER ELECTRODE ASSEMBLY FOR SPARK PLUGS BACKGROUND OF THE INVENTION This invention relates to resistance elements and more particularly to an improved resistance element for suppressing radio frequency radiation from the high voltage ignition circuit of an internal combustion engine.

The problem of eliminating radio frequency radiation from high voltage ignition systems of internal combustion engines has been of increasing concern in recent years because of its interference with the use of the radio channels for communications and for navigation. This problem has been accentuated by the increasing number of automobiles, boats and aircraft and the simultaneous increase in the use of radio frequency equipment in both communications and navigation.

The typical ignition system for an internal combustion engine includes a set of breaker points, a capacitor, an ignition coil, a spark plug, and connecting wires. When the breaker points are closed, a battery is connected to cause a current to flow in a primary winding of the ignition coil, thereby establishing a magnetic field about, and storing energy in, a ferrous core in the ignition coil. When the breaker points are opened, the magnetic field collapses to produce a high voltage across a secondary winding of the ignition coil. The high voltage is applied to, and arcs across, a spark gap in the spark plug, greatly decreasing the impedance of the gap. The secondary coil winding and the low impedance spark gap form a resonant circuit which oscillates as the energy stored in the core is dissipated. The oscillations are in the radio frequency spectrum and may cause severe noise and interference in both communications equipment and navigational equipment.

In the past, it has been found that random radio frequency radiation from the ignition system of internal combustion engines may be greatly reduced or eliminated by placing a resistance element in the high voltage ignition circuit for each spark plug. The resistance element may be positioned in the bore of a spark plug insulator in series with the spark plug center electrode or it may be placed at some other convenient location in the ignition system, such as in a distributor rotor or distributed in the high voltage ignition cables.

Prior art resistors, other than distributed resistances found in ignition cables, are generally either of a carbon rod type, of a wire wound type, of a sintered resistive rod type or of a resistive mass fired between glass seals in the center electrode bore through a spark plug insulator. Each of the different types of resistors has advantages and disadvantages. The carbon capsule resistor is, for example, relatively inexpensive compared to a wire wound resistor. However, when the carbon capsule resistor is placed in a spark plug and is heated to perhaps over 450F. or more during operation of the engine, the carbon tendsto oxidize, resulting in an open circuit. For this reason, carbon resistors are not used in aircraft engines, which operate at higher temperatures than automobile engines and cannot tolerate a failure. The carbon resistor is also subject to failure since the resistance value depends upon how tightly the carbon particles are compacted and thermal and electrical stresses may loosen the particles, causing failure. The wire wound resistor does not have as large a decrease in resistance at higher temperatures as carbon resistors and, therefore, is a much more effective suppressor. However, the wire wound resistor is expensive compared to the carbon resistor and it presents problems both in arcing and in connecting terminals to the wire ends. Wire wound resistors are also bulky and, therefore, difficult to use in smaller size spark plugs.

Resistance elements have also been formed directly in the center electrode bore in a spark plug insulator. One such type consists of a resistor formed by tamping a resistance composition in the bore of a spark plug insulator. Such compositions generally consist of a heterogenous mixture of a conducting or semi-conducting material, such as carbon, metals, metal oxides, metal carbides, or combinations thereof. The mixture is typically held in place by a pair of conductive glass seals. In another embodiment, the resistance composition is suspended in a glassy matrix and the spark plug insulator is heated to fuse the composition into a solid resistor element.

SUMMARY OF THE INVENTION According to the instant invention, an improved resistance element for suppressing random radio frequency radiation from internal combustion engines is formed essentially from copper oxide. The copper oxide, a heat destructible binder and up to 10 percent by weight of a plasticizer are compressed, extruded or otherwise formed into a rod or capsule which is heated sufficiently to sinter the copper oxide into a coherent resistance element and to simultaneously destroy the binder. The element may be provided with contact terminals by applying metal coating to ends of the resistance element.

When the resistance element is heated to perhaps as high as 450F. or more during operation of an internal combustion engine, the resistance value will fall to approximately 5 percent of the cold or room temperature resistance. In spite of this drastic decrease in resistance, the element is effective in suppressing radio frequency radiation from ignition systems in internal combustion engines. The drastic decrease in resistance as the resistor element is heated necessitates the use of resistor elements having a significantly higher room temperature resistance than is used with carbon resistors. The high cold resistance results in a high suppression during starting, when an engine may produce higher than normal radio frequency radiation. When the resistance element is heated during operation of the engine, the resistance drops into or below the normal resistance range for suppressor resistors while maintaining its effectiveness as a suppressor. Copper oxide suppression elements having a cold resistance on the order of 25,000 to 30,000 ohms and higher have been found to be much more effective than a 5,000 ohm carbon resistor and to be at least as effective as a 5,000 ohm wire wound resistor at a lower cost and at a significantly smaller size than a 5,000 ohm wire wound resistor.

Accordingly, it is the primary object of this invention to provide an improved resistance element for suppressing radio frequency radiation from ignition systerns in internal combustion engines.

Another object of the invention is to provide an improved spark plug having an internal ignition noise suppression element formed essentially from copper oxide.

Other objects and advantages of the invention will become apparent from the following detailed description, reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view, in partial section, of a spark plug including an internal noise suppression element constructed in accordance with the present invention; and

FIG. 2 is an enlarged section of one embodiment of a suppression element constructed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a conventional spark plug is shown with an internal resistor element 11 for suppressing radio frequency radiation which may interfere with communications and navigational equipment. The spark plug 10 generally comprises a tubular metal shell 12, an insulator 13 mounted in the shell 12 and a center electrode assembly 14. The lower end of the shell 12 has a threaded portion 15 for threadably engaging the head of an internal combustion engine. A ground electrode 16 is welded to the lower end of the shell 12 for defining a spark gap with a center electrode tip 17. The center electrode assembly 14 is mounted in an axial bore 18 extending through the insulator 13 and typically comprises the center electrode tip 17, a terminal 19, the suppression element 11, and a spring 20. The spring 20 is compressed either between the element 11 and the electrode tip 17 or between the element 11 and the terminal 19 to maintain a series electrical path between the terminal 19 and the electrode tip 17.

According to the present invention, the suppression element 11 is formed from a composition consisting essentially of copper oxides. Particles of cuprous oxide (Cu O) or a mixture of cuprous oxide and cupric oxide (CuO), having a size of less than 44 microns, and preferably an average size within the range of 6 to 13 microns, are formed into the desired resistor shape and are heated for a sufficient time and at a sufficient temperature to sinter into a coherent mass. A copper oxide mixture within a range of from 70 to lOO percent by weight of cuprous oxide and 0 to percent by weight of cupric oxide has been found to produce a satisfactory ignition noise suppressor. A small quantity of heat destructible binder, such as wax, starch, carboxycellulose, polyvinyl alcohol, or natural and synthetic gums, may be added to the copper oxide particles to maintain the desired resistor shape until the particles are sintered together. In a preferred embodiment, the binder ranges from 0.1 to 4 percent. In addition, up to 10 percent of an inert plasticizer, such as bentonite, colloidal silica or ball clay, may also be added to the copper oxide particles to increase the workability of the particles as they are formed into the final shape of the suppression element.

The final composition of the finished suppression element 1] is determined by several factors, primarily the initial composition and particle size of the copper oxides, the forming pressure, the firing temperature, atmosphere and the firing time. If, for example, the initial mixture comprises essentially cuprous oxide, the tinished element 11 may have a cored structure. During firing, oxygen from surrounding air combines with the cuprous oxide to form cupric oxide. As shown in the vertical section through a cylindrical element 11 in FIG. 2, a cupric oxide layer 21 is formed initially at the surfaces of the element 11. A core portion 22 of the element 11 remains essentially cuprous oxide, the composition of the starting mixture. The thickness of the outer cupric oxide layer 21 is determined by the firing time and temperature. If the element 11 is fired for a sufficiently longperiod of time at a sufficiently high temperature, the core 22 will disappear and the element 11 will consist essentially of cupric oxide. It has been found, for example, that all of the cuprous oxide as indicated by X-ray diffraction in a 0.142 inch diameter element will be converted to cupric oxide if the element is heated to l550F. for 30 minutes, while only about 20 percent of the cuprous oxide in a similar element was converted to cupric oxide when the element was heated to 850F. for 30 minutes. The core 22 of the element 11 will, of course, include cupric oxide if cupric oxide was present in the initial mixture from which the element was formed. In addition, when the element is heated to perhaps 1500F. or more the bentonite plasticizer is dehydrated into aluminum silicate. How ever, the aluminum silicate is also essentially inert in the suppression element.

The actual resistance value of a copper oxide element is difficult to measure accurately due to the variable effect of contact resistance at both ends of the element. Where a uniformity in measured resistance is desired, conductive coatings may be placed on the ends of the element 11 which contact the spring 20 and either the terminal 19 or the electrode tip 17 to form contact terminals. The coating reduces the likelihood of having resistive contacts between the suppressor element 11 and either the terminal 19 or the electrode tip 17 and the spring 20. The coating is applied after the copper oxide particles are sintered into a coherent mass. The coating may, for example, consist of a silver powder suspended in a resin or paste. The coating is applied onto the ends of the resistor and the element is tired at a sufficient temperature to fuse the silver to the ends of the sintered copper oxide element. However, when the suppressor element 11 is mounted in the center bore of a spark plug and a voltage comparable to ignition voltage is impressed, contact resistance is negligible, making the conductive coating unnecessary. The high voltage applied to the spark plug terminal 19 will arc across or break down any high resistance contact between the resistor element 11 and either the terminal 19 or the electrode tip 17 or the spring 20. Such arcing does not affect or destroy the copper oxide element.

The suppression element may be shaped by any conventional method. However, in the preferred embodiments, the element is shaped either by extrusion or by pressing into a die. The preferred methods of forming the resistance elements are described in detail in the following examples.

EXAMPLE I Resistance elements were formed by extrusion from a slip consisting essentially of cuprous oxide particles plus a binder and a plasticizer. The cuprous oxide particles were of a commercial quality at least percent pure and including free copper and cupric oxide as impurities. The cuprous oxide particles were screened to a size less than 44 microns and having an average size within the range of 6 and 13 microns. At least 0.1 percent and up to 4 percent by weight of a binder consisting of approximately 15 percent fish glue and 85 percent glycerin and from 1 to percent by weight bentonite as a plasticizer were added to the cuprous oxide particles. To this mixture, water was added to establish a moisture content between 6 and percent. The mixture was then passed through a 0.140 inch die in a ram extruder and cut into rods having a length of approximately 0.25 inch. The cuprous oxide particles were sintered into coherent rod shaped resistance elements by heating in a furnace for minutes at 1350F. The effects of contact resistance between the resistance elements and an external circuit were reduced by coating the contact ends of the resistance element with a silver paste. The resistance elements were then refired at 1000F. to fuse the silver to the ends of the elements.

Typical resistance elements produced by the above example were evaluated and showed that the elements had a resistance at room temperature of 6500 ohms plus or minus 1500 ohms. When the resistor elements were heated to a temperature within the normal operating range of 200F to 450F., the resistance dropped to between 250 and 400 ohms, or about 5 percent of the room temperature resistance.

EXAMPLE II Resistance elements were pressed from a mixture comprising essentially pure cuprous oxide particles including nor more than 5 percent impurities, 2 percent by weight of a paraffin binder and 1 percent by weight of bentonite as a plasticizer and a suspension agent. Prior to pressing, the mixture was formed into spherically shaped pellets of a 200 micron nominal size by a conventional spray drying process to enhance the flow properties of the mixture. The spherical pellets were then placed in a die, where they were pressed at pressures between 5 and tons per square inch to form resistance elements having a diameter of 0.140 inch and a length of approximately 0.25 inch. As in Example I, the resistance elements were heated for 30 minutes at 1350F. to sinter the cuprous oxide particles and simultaneously to burn out the binder.

Typical resistance elements produced by the above example were evaluated and again showed a resistance at room temperature in the range of 6500 ohms plus or minus 1500 ohms. At an operating temperature within the range of 200F. to 450F. the resistance dropped to approximately 5 percent of the room temperature resistance.

For suppressing radio frequency radiation from the ignition system of an internal combustion engine with the efficiency of a 5000 ohm wire wound resistor, sintered copper oxide elements having at least a 25,000

ohm room temperature resistance were formed for placement in series in the center electrode of a spark plug. When the spark plug insulator and the internal resistor were heated to an operating temperature range of approximately 200F. to 450F., the resistance value dropped to about 5 percent of the cold value, or to about 1250 ohms or more depending upon the cold temperature resistance. The resistance elements were effective as ignition noise suppressors at the lower resistance value.

EXAMPLE Ill Several different suppression elements were formed from essentially cuprous oxide and from mixtures comprising essentially cuprous oxide and up to 30 percent by weight cupric oxide. The cuprous oxide particles of 10 microns. In each case, 1 percent by weight bentonite was added as an inert plasticizer and 2 percent by weight polyvinyl alcohol was added as a temporary binder. The elements were pressed at from 15 to 47.5 tons per square inch into cylinders having a 0.142 inch diameter and a 0.250 inch length and were then sintered by firing first at 850F. for a 30 minute soak and then at 1500F. for a 6 minute soak.

In analyzing the sintered elements, bulk resistances were found to range from 30,000 ohms to 120,000 ohms, as measured by a 500 volt megger with a 20 pound terminal pressure applied at opposite ends of each cylinder. When the elements were placed in center electrode assemblies in spark plugs and operated in internal combustion engines, they were found to be at least comparable in efficiency to 5000 ohm wire wound resistors for suppressing ignition noise. The efficiency of the various elements as suppressors and the resistances of the elements did not appear to be related to the final composition of the elements. An X-ray analysis indicated that the overall composition of the finished elements ranged from a 50:50 mole ratio to a :30 mole ratio of cuprous oxide to cupric oxide. The final composition was affected by the forming pressure. A first group of elements formed from essentially percent cuprous oxide and pressed at 15 tons per square inch showed a cuprous oxide to cupric oxide mole ratio of 54:36, while a second group of elements formed from the same initial mixture and pressed at 25 tons per square inch had a mole ratio of 63:37 and a third group of elements formed from the same initial mixture and pressed at 42 tons per square inch had a mole ratio of 70:30. The forming pressure also affected the mechanical strength of the finished elements. For the above three groups of elements, the elements formed at 15 tons per square inch were crushed by axial loads of about 41 pounds; the elements formed at 25 tons per square inch were crushed by axial loads of about 50 pounds; and the elements formed at 42 tons per square inch were crushed by axial loads of about 64 pounds.

EXAMPLE lV Two groups of elements were formed essentially from cuprous oxide particles having an average diameter of 6 microns. To the particles, 1 percent by weight bentonite and 2 percent by weight polyvinyl alcohol were added as a plasticizer and as a temporary binder, respectively. This mixture was then formed into spherical pellets having a 200 micron nominal size. The elements were formed into 0.142 inch diameter cylinders 0.250 inch long by pressing at 15 tons per square inch. The first group was heated to 1500F. for a 6 minute soak and the second group was heated to 1500F. for a 30 minute soak.

An analysis of the elements showed that elements in the first group had a cold resistance on the order of 300,000 ohms and elements in the second group had a cold resistance on the order of 50,000 to 55,000 ohms. Elements in both groups were comparable to 5000 ohm wire wound resistors for suppressing ignition noise from internal combustion engines when installed in center electrode assemblies of spark plugs. An X-ray analysis also showed that the overall composition of elements in the first group consisted essentially of copper oxide having a mole ratio of 20:80 of cuprous oxide to cupric oxide. Elements in the second group were essentially 100 percent cupric oxide, plus aluminum silicate from the dehydrated bentonite. Stronger mechanical binding resulted from the longer heating in the second group. An average axial force of 66 pounds was required to crush elements in the second group, while an average axial force of only 52 pounds was required to crush elements in the first group.

The sintered copper oxide suppressor element has several unexplainable properties. It has been found that many resistance materials that have a drop in resistance similar to sintered copper oxides are ineffective as suppressors. For example, a barium ferrite resistor having the same resistance under operating conditions did not function as a radio frequency noise suppressor. It has also been found that the suppression characteristics of sintered copper oxide elements appear to be nonlinear, as measured with a low voltage. In other words, a 30,000 ohm (cold) resistor may not be as effective as either a 20,000 ohm (cold) or a 40,000 ohm resistor (also cold). The reason for the apparent non-linearity has not yet been explained. The apparent non-linearity may, however, result from a difficulty in taking accurate low voltage resistance measurements of the copper oxide elements.

Suppression elements have also been integrally formed in spark plug insulators by compacting mixtures consisting essentially of copper oxide into the center electrode bore and firing the insulator. Since the insulator prevents oxygen in the air from contacting the mixture during firing, cuprous oxide is not converted to cupric oxide during firing. As a result of this, better results have been obtained by using cupric oxide or a mixture of cupric oxide and cuprous oxide as a starting material. However, cupric oxide alone is difficult to sinter and higher firing temperatures and longer firing times may be required, for example, firing from minutes to 2 hours at 1500F. to l800F.

It will be appreciated that various modifications and changes may be made in the method of producing a sintered copper oxide ignition noise suppression element and in the use of such an element without departing from the spirit and the scope of the claimed invention.

What we claim is:

l. in a spark plug for an internal combustion engine including a hollow tubular shell and an insulator positioned within the shell, said insulator having a bore for holding a center electrode assembly, an improved center electrode assembly comprising, in combination, a firing tip, a terminal, an ignition noise suppression element comprising a sintered mass consisting essentially of copper oxide, and means connecting said sintered copper oxide mass electrically in series between said tip and said terminal.

2. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass of copper oxide has a cylindrical shape with opposed ends for electrically connecting to said tip and said terminal.

3. An improved center electrode assembly for a spark plug, as defined in claim 2, wherein said connecting means includes electrically conductive coatings on said opposed ends of said cylindrical shaped mass of copper oxide.

4. An improved center electrode assembly for a spark plug, as defined in claim 3, wherein said conductive coating is of silver.

5. The improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass includes up to 10 percent of an inert plasticizer.

6. An improved center electrode assembly for a spark plug, as defined in claim 5, wherein said plasticizer is bentonite.

7. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said connecting means comprises a spring, said spring being compressed between said sintered copper oxide mass and one of said tip and said terminal.

8. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass consists essentially of cupric oxide.

9. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass consists essentially of cuprous oxide and cupric oxide.

10. An improved center electrode assembly for a spark plug, as defined in claim 9, wherein the surfaces of said sintered mass are essentially cupric oxide and a core portion of said sintered mass is essentially cuprous oxide.

Claims (9)

1. 2. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass of copper oxide has a cylindrical shape with opposed ends for electrically connecting to said tip and said terminal.
2. 3. An improved center electrode assembly for a spark plug, as defined in claim 2, wherein said connecting means includes electrically conductive coatings on said opposed ends of said cylindrical shaped mass of copper oxide.
3. 4. An improved center electrode assembly for a spark plug, as defined in claim 3, wherein said conductive coating is of silver.
4. 5. The improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass includes up to 10 percent of an inert plasticizer.
5. 6. An improved center electrode assembly for a spark plug, as defined in claim 5, wherein said plasticizer is bentonite.
6. 7. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said connecting means comprises a spring, said spring being compressed between said sintered copper oxide mass and one of said tip and said terminal.
7. 8. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass consists essentially of cupric oxide.
8. 9. An improved center electrode assembly for a spark plug, as defined in claim 1, wherein said sintered mass consists essentially of cuprous oxide and cupric oxide.
9. 10. An improved center electrode assembly for a spark plug, as defined in claim 9, wherein the surfaces of said sintered mass are essentially cupric oxide and a core portion of said sintered mass is essentially cuprous oxide.

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