A semi-creeping discharge type spark plug

摘要

In a semi-creeping discharge type spark plug, a cylindrical metal shell (1) and an insulator (2) are provided, the latter of which has an axial bore (22) and placed within the metal shell (1) so that a front end of the insulator (2) extends beyond the metal shell (1). A center electrode (3) is placed within the axial bore (22) of the insulator (2) so that a front end surface edge (311) of the center electrode (3) retracts by 0.1 &tilde& 0.6 mm behind from a front end surface (23) of the insulator (2) . A ground electrode (4), one end of which is connected to a front end (11) of the metal shell (1), and the other end of which is bent to oppose an outer surface of the insulator (2) so as to form an air-gap (g1) therebetween while permitting creeping spark discharges running along said front end surface (23) of said insulator (2). A foward edge portion (42) of a front end surface (41) of the ground electrode (4) extends by 0.0 &tilde& 1.0 mm forward from the front end surface (23) of the insulator (2). <IMAGE>