Patent ID: 6523515
Filing Date: 2003-02-25
Classification: H01T

Abstract:
A spark plug for internal combustion engines, which is provided with an earth electrode having a front end facing to a center electrode (30) of the spark plug, a noble metal chip being welded to the front end via a melted portion formed therebetween, whereinthe earth electrode has a cladding member made of metal having corrosion resistance and oxidation resistance, a first core member not only made of metal higher in heat conductivity than the cladding member but also contained in the cladding member, and a second core member not only made of metal higher in melting point than the first core member and superior in heat conductivity as compared to the cladding member but also contained in the first core member (44), the second core member protruding, within the earth electrode, from a tip of the first core member to a side of the front end of the earth electrode; and a tip of a protruding portion of the second core member being located at a position satisfying a distance L1 of not less than 0.3 mm and not more than a distance L0, the distance L1 being defined by a distance between the tip of the protruding portion of the second core member and the front end of the earth electrode and the distance L0 being defined by a distance between a farthest located edge of the melted portion including the noble metal chip from the front end of the earth electrode and the front end of the earth electrode.