Spark plug, particularly for internal combustion engines having composite center electrode

US4093887A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Rainer Corbach · Olfen, DE
• Leo Steinke · Waiblingen, DE
• Walter Benedikt
• Rudolf Jurinke

Key dates

• Filing date: Nov 4, 1976
• Grant date: Jun 6, 1978
• Expiry date: Nov 4, 1996

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01T13/39
• WIPO field: Electrical machinery, apparatus, energy
• WIPO sector: Electrical engineering

Abstract

The spark plug center electrode is a composite of a jacket of corrosion resistant material, central filamentary core electrode elements, likewise of corrosion resistant material, and a matrix of thermally and electrically highly conductive material in which the corrosion resistant filamentary elements are embedded, filling the electrode within the outer jacket; in accordance with the present invention, the matrix material is recessed with respect to the jacket and the sparking ends of the corrosion resistant filamentary material to increase lifetime and to provide protection for the electrically and thermally highly conductive material and ensure ignition of even comparatively lean fuel-air mixtures. The electrode has an overall diameter in the order of about 2.4 mm, the recess of the matrix material being between 50 to 500 .mu. m, preferably about 100 to 250 .mu. m; a platinum coating having a thickness of preferably between 40 and 50 .mu. m can be provided to cover the exposed end of the electrode. The recess can be effected by etching selective to the matrix material and not attacking the corrosion resistant jacket and filamentary elements.