Abstract In a spark plug including an insulator mounted in a tubular shell and an electrode assembly mounted within a bore through the insulator and projecting from a nose portion of the insulator to define a spark gap with a ground electrode, a method for improving the resistance of the nose portion to cracking caused by thermal stresses. The electrode assembly includes a high heat conducting portion in close proximity with the wall of the portion of the bore extending through the nose portion of the insulator. The method comprises applying a coating of a glaze slip to the interior wall of the portion of the insulator bore which will be in proximity with the heat conducting portion of the electrode and then firing the glaze at a controlled time and temperature to form an uninterrupted glassy coating on at least the portion of the nose bore adjacent the end of the insulator. The fired glaze must have a lower coefficient of thermal expansion than the insulator, an appreciably lower thermal conductivity than the insulator and a softening temperature above the highest operating temperature encountered by the glazed bore wall.
Inventors
👤 F Westenkirchner
👤 P Rempes
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-30 17:05
CPC Classifications
H; H01; H01T; H01T13/00; H01T13/20; H01T13/34
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
167 words
A spark plug for an internal combustion engine which is resistant to insulator cracking caused by thermal stresses comprising, in combination, a shell having a threaded end for engaging an internal combustion engine, an elongated insulator mounted within said shell, said insulator having a nose portion forming an end adjacent the threaded end of said shell, a terminal end and a bore extending through said insulator between said nose portion and said terminal end for mounting an electrode assembly, a glaze forming a continuous glassy coating on at least the wall of the bore within and adjacent the exterior end of said insulator nose portion, said glaze having a thickness within the range of 0.0005 inch and 0.0025 inch and having a softening temperature above the highest operating temperature encountered by said glaze during operation of said spark plug in such engine, and an electrode assembly mounted within said insulator bore, said electrode assembly including a high thermally conducting portion cast directly within said insulator nose bore.
Claim 2
Dependent Claim
167 words
A spark plug for an internal combustion engine which is resistant to insulator cracking caused by thermal stresses comprising, in combination, a shell having a threaded end for engaging an internal combustion engine, an elongated insulator mounted within said shell, said insulator having a nose portion forming an end adjacent the threaded end of said shell, a terminal end and a bore extending through said insulator between said nose portion and said terminal end for mounting an electrode assembly, a glaze forming a continuous glassy coating on at least the wall of the bore within and adjacent the exterior end of said insulator nose portion, said glaze having a thickness within the range of 0.0005 inch and 0.0025 inch and having a softening temperature above the highest operating temperature encountered by said glaze during operation of said spark plug in such engine, and an electrode assembly mounted within said insulator bore, said electrode assembly including a high thermally conducting portion cast directly within said insulator nose bore.
Claim 3
Dependent Claim
23 words
A spark plug, as defined in claim 1, wherein said high thermally conducting portion of said center electrode assembly is cast from silver.
Claim 4
Dependent Claim
32 words
A spark plug, as defined in claim 2, wherein said cast silver portion of said center electrode assembly is in contact with said glaze on the wall of said insulator nose bore.