US 4,539,503 AGranted

Rapid-heating, high-temperature-stable spark plug for internal combustion engines

AssigneeRobert Bosch GmbH

InventorsFriedrich Esper, Karl-Hermann Friese, Walter Gohl, Peter Sternad

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Abstract

In order to obviate the necessity for design compromise of spark plugs with respect to their operating temperature, so that the ceramic insulator (18) of the spark plug will rapidly reach the temperature at which deposits thereon will inherently burn off (about 400.degree. C.-450.degree. C.) while not becoming so hot as to cause spurious glow ignition within the combustion chamber of an internal combustion (IC) engine, the end portion of the insulator is formed with a central opening (19/3) within which a metal core (24) is included which has a temperature coefficient of expansion such that, at temperatures below between 400.degree. C.-450.degree. C. it is spaced by a narrow gap (25) from the inner surface of the insulator (see FIG. 1) but, as the spark plug becomes hot, the gap 25 closes (FIG. 2), thereby providing good heat transmission from the insulator to the center electrode structure (21, 23, 24) and thereby maintaining the insulator at a temperature below that at which it might glow. Suitable materials for the center electrode are aluminum bronze, or other materials having a heat transmission characteristic of at least 90 W/mK. The insulator, preferably, has a higher-than-usual flux content so that, at low temperatures, its heat transmission characteristics are poor, to insure rapid heating to free combustion temperature of possible deposits.

Claims20

Dependent claims

Rapid-heating, high-temperature-stable, long-lifetime spark plug with self-adjusting variable heat conductivity, for an internal combustion (IC) engine, having

a combustion chamber end and an external connection end;
a hollow metal housing (11,12);
a chassis or ground electrode (30) connected to the metal housing at the combustion chamber end;
an insulator (18) sealingly retained in the hollow metal housing, and formed with a central opening (19) therein;
and
a center electrode (21, 23, 24, 27, 28) located in the central opening (19) of the the insulator and including
a connection post (21);
a spark tip (27,28) located opposite the chassis or ground electrode (13), a solid metal spark plug core segment (24), electrically connected to the spark tip, and an electrical circuit connection means (23) for electrically connecting the metal core and the connection post,
wherein the solid metal core (24-24"') comprises a metal which is solid under all operating conditions of the spark plug, and said solid metal core is shaped to fit into the central opening (19) of the insulator and has a temperature coefficient of expansion such that,
(A) at temperatures above the deposit burn-off temperature of said insulator a major portion of the surface of the metal core (24) expands into surface engagement with the portion (19-19"') of the wall of the insulator (18) defining said opening therein, and such that,
(B) below said deposit burn-off temperature, said surface of said solid metal core is spaced from said portion of the wall surface of the insulator by a gap (25) thereby effecting rapid heating of said insulator to deposit burn-off temperature, by inhibiting rapid heat transfer from the insulator to said metal core, but preventing, by heat transfer to the center electrode including said metal core, excessive heating of the insulator tip portion to glow ignition temperature.

8 more elements

Dependencies are inferred from the claim text.