Ngk Spark Plug Company, Limited

Ryuichi Ono

Tomoaki Kato

Nobuaki Sakayanagi

Shinya Mitsuda

A spark plug includes: a rod-shaped center electrode extending in an axial direction; an insulator including a shaft hole that holds the center electrode inside of the shaft hole; a metal shell surrounding and holding a part of the insulator; and a ground electrode including a base end welded to the metal shell. The metal shell and the ground electrode are joined via a fusion portion formed by welding the ground electrode and the metal shell together. When the smallest thickness of the fusion portion in the axial direction is A, when, in a cross section that includes a center line of the ground electrode and is parallel to the axis, a length of a ground-electrode-side melted boundary formed between the fusion portion and the ground electrode is B, and when the ground electrode thickness is C, conditions of A&#x2267;0.2 mm and B&#x3e;C are satisfied.

Growing community of inventors

Niwa-gun, Japan

Ryuichi Ono