Small spark plug with iridium-based central electrode tip

摘要

Spark plug has: (a) a nickel alloy central electrode (3) with a tip (3a); (b) an insulator (2) which covers the edge of the central electrode except for its tip and which optionally also has a tip (2b); (c) a fitting (1) which surrounds the insulator edge and which has an external thread, a space (7) formed between the fitting and the insulator and exposing the insulator tip (2b); (d) an iridium (alloy) tip (51) on the tip (3b) of the central electrode (3); and (e) an earth electrode (4) fixed on the fitting (1) and spaced from and facing the iridium (alloy) tip (51). Dimensions of the spark plug are as follows: discharge gap (6) length (A) = 0.9 to 1.35 mm.; space (7) width (B) /- (10/9)A; insulator (2) projection length (C) = 1.0 to 2.5 mm.; external diameter (D) of fitting threaded section = 10 to 12 mm.; central electrode tip diameter (F) = 2.0 to 2.7 mm.; iridium (alloy) tip (51) end diameter (G) = 0.6 to 0.9 mm.; and iridium (alloy) tip (51) projection height (H) = 0.3 to 1.0 mm.