Patent ID: 7145287

Claim:
A spark plug comprising: a center electrode ( 3 ); an insulator ( 2 ) surrounding the center electrode ( 3 ) such that a distal end portion ( 51 ) disposed on the center electrode ( 3 ) projects from the insulator ( 2 ); a metallic shell ( 1 ) holding the insulator ( 2 ); and a ground electrode ( 4 ) comprising a base metal ( 4 b ) fixed to the metallic shell ( 1 ) and having a discharge portion ( 52 ) projecting from and laser-welded to an electrode base metal surface ( 4 a ) of the ground electrode ( 4 ), a discharge gap ( 6 ) being formed between a distal end surface ( 52 a ) of the discharge portion ( 52 ) and a distal end surface ( 51 a ) of the distal end portion ( 51 ) of the center electrode ( 3 ); and the spark plug satisfying 0.36 mm≦φB≦0.8 mm, φ B/φA≧ 1.2, and 0.5 mm≦C≦1.2 mm, where φA (mm) is a diameter of the distal end portion ( 51 ) formed of a noble metal tip ( 51 b ), which contains a predominant amount of a noble metal; φB (mm) is a diameter of the discharge portion ( 52 ) formed of a noble metal tip ( 52 b ), which contains a predominant amount of a noble metal and having a survival rate of 90% or higher after being subjected for 100 hours in an air atmosphere to a temperature of 1,000° C. in an electric furnace; and C (mm) is a projection length of the discharge portion ( 52 ) from the electrode base metal surface ( 4 a ).