Patent ID: 6225752
Filing Date: 2001-05-01
Classification: F02B,H01T

Abstract:
A spark plug for an internal combustion engine comprising:an insulating member having an axial hole formed along a central axis;a rod-shape central electrode accommodated in said axial hole; anda ground electrode with which an igniting portion opposite to the outer surface of said central electrode is formed;wherein said spark plug satisfies at least one of the following conditions (a) and (b):(a) when said insulating member is cut along said central axis and a first extension line in the form obtained by outwards extending a line indicating an end surface of said insulating member adjacent to said igniting portion and a second extension line in the form obtained by extending a line indicating the outer surface of said insulating member in the vicinity of said igniting portion are drawn, the distance tp from an intersection between said first and second extension lines to a line indicating an inner surface of said axial hole adjacent to said igniting portion is 1.0 mm or shorter (tp.ltoreq.1.0 mm); and(b) the difference (.phi.d.sub.2 -.phi.d.sub.1) between diameter (.phi.d.sub.1 of said central electrode and diameter .phi.d.sub.2 of said axial hole is 0.08 mm or shorter.