Patent ID: 7652413
Filing Date: 2010-01-26
Classification: H01T

Abstract:
1. A spark plug, comprising: a center electrode; an insulator disposed on an outer circumferential surface of the center electrode, the insulator having an end portion protruded from an end surface of a cylinder head of an internal combustion engine into a combustion chamber of the engine facing the end surface of the cylinder head; a metallic housing disposed on an outer circumferential surface of the insulator and fixed to the cylinder head, the housing having an end portion facing the combustion chamber, a pocket bore being formed between the insulator and the housing so as to face the combustion chamber; a ground electrode attached to the housing; a tip portion disposed on the center electrode so as to be placed in the combustion chamber; and another tip portion disposed on the ground electrode to form a spark discharging gap between the tip portions, wherein a spark position length H between the end surface of the cylinder head and the tip portion of the center electrode is set within a range from 6.5 mm to 10 mm, a spark discharging gap length G between the tip portions is set within a range from 1.1 mm to 2.0 mm, a housing position length J between the end surface of the cylinder head and the end portion of the housing, the spark position length H and an insulator position length F between the end surface of the cylinder head and the end portion of the insulator are set to satisfy a relation of J≦F≦H−1.0 mm, a sectional area S the tip portion of the center electrode is made of a first noble metal having a melting point equal to or higher than 2000° C. or is made of a first alloy containing the first noble metal, the tip portion of the ground electrode is made of a second noble metal having a melting point equal to or higher than 1700° C. or is made of a second alloy containing the second noble metal, and the spark discharging gap length G, the sectional area S when the areas S 1 and S 2 are expressed in mm 2 while the length G and the clearance P are expressed in mm.