Electric lamp or space discharge component or device manufacturi – Process – Spark plug or spark gap making
Reexamination Certificate
1999-07-13
2003-03-18
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Spark plug or spark gap making
C313S141000
Reexamination Certificate
active
06533629
ABSTRACT:
BACKGROUND OF THE INVIENTION
1. Field of the Invention
The present invention relates To spark plugs for use in internal combustion engines. More particularly, the present invention relates to a method of making spark plugs which include wear-resistant electrode tips made from a co-extruded composite material, and to spark plugs incorporating such wear-resistant electrode tips.
2. Decription of the Background Art
Spark plugs are widely used to ignite fuel in internal combustion engines. Spark plug electrodes are subject to intense heat, and to a highly corrosive environment, generated by the exploding air/fuel mixture, To improve durability and erosion resistance, spark plug electrodes must be able to withstand the high temperature and corrosive environment resulting from the chemical reaction products between air, fuel, and fuel additives within a combustion chamber. The same chemical and thermal stresses also affect the interface between the ground electrode and the metal spark plug shell to which the ground electrode is bonded. Where this interface does not consist of a strong bond, these stresses can reduce spark plug performance or even cause the spark plug to fail.
Society of Automotive Engineers paper No. SAEJ312 describes the specification for automotive gasoline used as a fuel in the United States. The gasoline consists of blends of hydrocarbons derived from petroleum: 50-80 percent saturates, 0-15 percent olefins, and 15-40 percent aromatics. Leaded gasoline contains about 0.10 grams of lead per gallon of fuel (0.026 g Pb/liter), and 0.15 percent sulfur. In unleaded gasoline there is about 0.05 grams of lead per gallon (0.013 g Pb/l), 0.1 percent sulfur, and 0.005 g phosphorous per gallon (0.0013 g P/liter).
In addition, there are a number of additives incorporated into gasoline for various reasons. For example, tetramethyllead (TML) and tetraethyllead (TEL) are added as antiknock agents. Carboxylic acid compounds such as acetic acid are added as lead extenders. Aromatic amines and phenols are added as antioxidants. Organic bromine and/or chlorine compounds are added as scavengers and deposit modifiers. Phosphors and boron-containing compounds are added to reduce surface ignition, preignition, and as engine scavengers. Metal deactivators are added to reduce oxidative deterioration of fiel by metals, such as Cu, Co, V, Mn, Fe, Cr and Pb. In addition, carboxylic acids, alcohols, amines, sulfonates, and phosphoric acid salts of amines are used as nist-inhibiting additives.
Another factor which places a stress on spark plugs in the combustion chamber environment is the use of Exhaust, Gas Recirculation (EGR) back into the combustion chamber, to cool the combustion charge and to improve emissions, particularly by reducing oxides of nitrogen.
The manufacture of copper (Cu) and nickel (Ni) electrodes for spark plugs is a proven art and has been accomplished in various ways. For instance, U.S. Pat. No. 3,803,892 describes a method of producing extruded copper and nickel electrodes from a flat plate of the two materials. U.S. Pat. No. 3,548,472 discloses a method of cold-forming an outer nickel cup-shaped sleeve in several steps, inserting a piece of copper wire into the cup, and then lightly pressing the two materials together. U.S. Pat. No. 3,857,145 discloses a process for making a spark plug center electrode in which a central copper core is inserted into a nickel member and attached thereto by a collar portion, to assure that an electrical flow path is produced.
U.S. Pat. No. 4,093,887 to Corbach et al. discloses a design for a spark plug having a center electrode made of a composite material. In the design for the composite spark plug electrode as taught by this reference, the electrode is about 2.4 mm in diameter, and includes an outer cylindrical metal jacket, which may be made of nickel, a nickel alloy, or a material based on chromium or cobalt. Inside this outer metal jacket, according To the reference, a matrix material of high conductivity, such as copper or a copper alloy, has a plurality of parallel strands embedded therein. The embedded strands are each approximately 0.3 mm in diameter, and are formed from the same material as the outer jacket. The strands are preferred to be seven in number, are placed so that they do not touch each other, and are arranged so as to be distributed essentially uniformly over the cross-section of the matrix material. This reference does not specifically teach or suggest The use of a wear-resistant electrode tip, but rather, teaches that the entire center electrode be made of the described composite material.
The use of certain types of embedded and/or welded-on spark plug electrode tips, which are more wear-resistant than the main body of the electrode, is also known. In recent years, the practice of adding these wear-resistant tips to spark plug electrodes has become favored in the art. Such spark plug electrode tips may be added to the center electrode, to the side electrode, or to both of the center and side electrodes. Such wear-resistant electrode tips are made tougher and more erosion resistant than the balance of the electrodes, and since the wear-resistant electrode tips provide the points where the spark crosses over between the electrodes, they are among the most critical working parts of a spark plug. Sometimes these electrode tips are mechanically flattened out or ‘coined’, during or subsequent to the attachment thereof to the base electrode, to cover a larger surface area than would otherwise be the case.
Some illustrative examples of patents relating to various wear-resistant spark plug electrode tips, and to spark plugs including such electrode tips may be found in U.S. Pat. Nos. 4,324,588, 4,810,220, 4,684,352, 4,810,220, 4,840,594, 5,179,313, 5,456,624, 5,558,575, 5,574,329, and 5,869,921.
Some of the known wear-resistant spark plug electrode tips incorporate platinum and/or other noble metals, because of their excellent resistance to oxidation and erosion under exposure to a combustion chamber environment. However, platinum is a very expensive raw material, as are the other noble metals, and it is therefore advantageous to strictly control the amount of noble metal which is incorporated into each spark plug.
In addition, the welding together of two dissimilar metals may result in a mismatch of the relative coefficient of thermal linear expansion of each metal. Under high thermal stress, this mismatch can lead to weakening or fracture of the bond between the electrode and the tip, and may even lead to physical separation of the noble metal and base metal.
U.S. Pat. No. 5,510,667 to Loffler et al. discloses a design for a spark plug which incorporates a reinforced electrode tip made of a platinum-nickel fiber composite material. The disclosed material, in this reference, may be a platinum matrix in which nickel fibers are embedded, or a nickel matrix in which platinum fibers are embedded. No specific number of embedded fibers is discussed in this reference, although the drawings appear to show a large number of fibers in the matrix. Alloys, which include platinum and another metal or metals, are not specifically disclosed in this reference.
The Loffler et al. '667 patent cites to a German patent application number 2 508 490 as disclosing a suitable method of making a fiber composite material which is usable to pracice the invention thereof. The above-cited Gernan patent application also corresponds to Great Britain patent application number 1 528 514, filed Feb. 26, 1976. The method taught therein involves loosely placing solid wires inside hollow metal tubes formed from a dissimilar metal than that of the wires, and bundling multiple tubes and wires together, inside of a larger tubular jacket. The placement of the bundled tubes in a metal jacket is followed by cold plastic deformation of the jacket, tubes, and wires together, to produce a composite material. Different end products are obtained, depending on which materials are used for the component parts.
Society of Automotive Engineers Publication No. 1999
Boehler Jeffrey T.
Zulauf Gary B.
Allied-Signal Inc.
Haynes Mack
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