Spark plug for internal combustion engine having a shaped composite chip on center electrode and/or ground electrode

A spark plug for an internal combustion engine, comprising:

• a center electrode held inside a cylindrical insulator and protruding from a tip of the insulator toward a distal end;
• a ground electrode provided on a distal end of a housing holding the insulator, the ground electrode facing the center electrode in an axial direction;
• and
• a composite chip formed on at least one of the center electrode and the ground electrode and protruding in the axial direction,
• wherein the composite chip includes a core having a mount formed integrally with an electrode base material, and a cup-shaped surface layer having a discharge portion covering a protrusion end surface of the core and a side surface coating covering a side surface continuous to the protrusion end surface,
• the surface layer includes a thick portion along a connection area between the discharge portion and the side surface coating, the thick portion having, in the radial direction, a maximum coating thickness S1 greater than the coating thickness S of the side surface coating,
• the core is formed from a Ni alloy material, and the surface layer is formed from a Pt alloy material, and
• in the surface layer, a coating thickness S of the side surface coating in a radial direction, an outer diameter D1 of the discharge portion, and a coating length L1 of the side surface coating in the axial direction satisfy a relation represented by expression 1:
• S≥D1/20+L1/10−0.005 mm;
• and Expression 1:
• the coating thickness S of the side surface coating, the outer diameter D1 of the discharge portion, the coating length L1 of the side surface coating in the axial direction, and a coating thickness maximum difference Q being a difference between the maximum coating thickness S1 and the coating thickness S of the side surface coating satisfy a relation represented by expression 1A:
• S≥D1/20+L1/10−Q/10−0.005 mm Expression 1A.