Electric heating – Heating devices – Resistive element: igniter type
Reexamination Certificate
2000-01-11
2001-09-04
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Resistive element: igniter type
C313S141000
Reexamination Certificate
active
06285008
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to ignition plugs, such as igniter and spark plugs, used in internal combustion engines to ignite the combustion gases in the combustion chamber, and more particularly to the seal provided between the insulator and the electrode which serves to prevent the escape of combustion gases through the plug.
2. Related Prior Art
A hermetic seal is required between the internal electrode and surrounding tubular insulator body of igniter and spark plug devices for preventing high temperature, high pressure combustion gases from passing through the plugs. Some seals are typically made by fusing glass to the adjacent surfaces of the electrode and insulator. The glass fusion process is labor intensive, costly and subjects the components of the plug to elevated temperatures above 1000° F.
The internal electrodes of such plug devices are typically of a multi-part construction. The electrode components, including upper and lower electrodes, are assembled within the insulator in abutting contact across axially opposed electrode surfaces of the components. While applying an axial compressive load to the components, the confronting surfaces are locally heated and melted by resistance welding to fuse the material of the electrode components together across the interface. Resistance welding imparts only localized heating of the electrode components at the weld interface, and avoids subjecting the other components to high temperatures associated with the glass fusion sealing. With resistance welding, the mating electrode components are locally melted and the materials fused together at the interface without the use of any foreign filler metal. Joining techniques such as brazing and soldering employ low melting point filler metals different than that of the electrode materials being joined, which could impair the electrical properties of the electrode.
U.S. Pat. No. 2,874,208 to Pierce discloses an igniter plug having a single piece center electrode formed with an enlarged firing button at its lower end that is external to the surrounding tubular insulator body. A sleeve of heat-expandable metal is disposed about the center electrode and is urged against an interior shoulder of the insulator by a tensioning nut that is either threaded or brazed about the center electrode. A washer is compressed between the firing button and the external end face of the insulator body to provide a gas-tight seal. There is no teaching or suggestion of incorporating such a compressed washer sealing system in ignition plugs having multi-piece electrodes joined by resistance welding.
SUMMARY OF THE INVENTION AND ADVANTAGES
An ignition plug according to the invention used for igniting combustion gases in an internal combustion engine comprises a tubular insulator body having a passage therein extending between axially opposite ends of the insulator. Within the passage are upper and lower sealing shoulders spaced from the ends of the insulator and facing in opposite directions generally axially outwardly toward the ends. A multi-piece electrode assembly is disposed within the passage and includes an upper electrode, a lower electrode aligned axially with an extending end axially prolongation of the upper electrode, and an expansion sleeve disposed about at least one of the electrodes. The upper and lower electrodes have opposed confronting surfaces extending transversely of the axis of the electrodes joined by a resistance weld joint, with the expansion sleeve being joined to one or more electrodes. When so joined, the electrode assembly presents a pair of axially inwardly facing sealing surfaces adjacent the sealing shoulders of the insulator, with one of the sealing surfaces being provided on the expansion sleeve and the other of the sealing surfaces being provided on one of the electrodes.
According to a characterizing feature of the invention, the ignition plug is provided, in addition to the inner shoulders of the insulator and the expansion sleeve, with compressible metal gaskets disposed in constant axial compression between the sealing shoulders of the insulator and the sealing surfaces of the electrode assembly as a result of the joining of the electrodes by the resistance weld joint to provide a gas-tight seal between the electrode assembly and the insulator to prevent the leakage of combustion gases through the ignition plug.
According to a method of the invention for manufacturing such ignition plugs, an insulator is formed with the opposing interior shoulders, and, the sealing washers are disposed against the shoulders, often which a first electrode with expansion sleeve are extended into the insulator from one end thereof and a second electrode is extended into the insulator from the other end such that the electrodes are aligned axially and confront across transversely disposed surfaces. While forcing the electrodes axially into confronting engagement with one another under a compression load so as to place the washers under axial compression, the electrodes are welded or joined together by a resistance weld across their confronting surfaces to permanently maintain the washers under constant axially compression thereby perfecting a gas-tight seal between the multi-part electrode assembly and the surrounding insulator.
The invention has the advantage of utilizing the compressive loading forces normally imparted on the upper and lower electrodes during resistance welding for securing the electrodes together to compress metal sealing gaskets between the multi-piece electrode and insulator to provide a gas-tight seal therebetween, without the need for glass fusion sealing or the introduction of foreign filler materials in the joining of the upper and lower electrodes that could disrupt the electrical properties. In addition, the high thermal expansion sleeve provides an increasing compressive load as operating temperatures increase. This increasing load is unique in that most prior art has decreased sealing capabilities because of the inability of the designs to take advantage of thermal expansion properties of the components.
REFERENCES:
patent: 1328147 (1920-01-01), Genn
patent: 1363380 (1920-12-01), Zimmermann et al.
patent: 1511937 (1924-10-01), Bentley
patent: 1512564 (1924-10-01), Rogers
patent: 1812438 (1931-06-01), Hurley
patent: 1996422 (1935-04-01), Hurley
patent: 2630107 (1953-03-01), Field
patent: 2874208 (1959-02-01), Pierce
patent: 3229032 (1966-01-01), Willis
patent: 5589091 (1996-12-01), Muller
Fleetwood Charles T.
Runge Michael A.
Federal-Mogul World Wide Inc.
Jeffery John A.
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
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