Ngk Spark Plug Company, Limited

Shoichiro Ito

Yoshihiro Matsubara

Makoto Yamaguchi

Naomichi Miyashita

Kazumasa Yoshida

Hiroaki Kuki

Akio Kokubu

Kazuya Iwata

Hiroshi Ono

Yuji Hirano

An ignition system has a spark plug and a positive voltage applying unit. The spark plug includes a central electrode, a porcelain insulator for holding the central electrode, a main metallic shell for holding the porcelain insulator, and a ground electrode electrically connected to the main metallic shell. The positive voltage applying unit applies a positive voltage to the central electrode of the spark plug in comparison with the ground electrode, so that an ignition high voltage is applied between the central electrode and the ground electrode. In the spark plug, a spark discharge gap is formed between the ground electrode and a distal end portion of the central electrode. The ground electrode is positioned so that a rear edge of a mating face opposed to a peripheral side of the central electrode is positioned in the side of the distal end of the central electrode in comparison with an end face of the porcelain insulator.

Ignition system

In a creeping discharge type spark plug, the firing surface forming portions of a center electrode and a ground electrode are made of a metallic material containing a corrosion impeding component consisting of one or more of Fe, Cr and Cu. The spark plug is attached to an internal combustion engine. When it is operated under conditions of a predetermined high speed and high load, a corrosion impeding layer containing a corrosion impeding component is formed on the surface of the top end of an insulating member, with progression of spark discharge in spark discharge gaps. The corrosion impeding layer thus formed protects the center electrode from the attack by the creeping discharge spark. Therefore, the channeling is considerably effectively prevented or restricted.

Spark plug with a corrosion impeding layer

A spark plug includes a spark portion of an Ir-based metal and a resistor disposed between a center electrode and a metallic terminal and adapted to establish an electric resistance of not less than 10 k&OHgr;, preferably not less than 15 k&OHgr;, but not greater than 25 k&OHgr; as measured between the center electrode and the metallic terminal. Thus, even in a system in which an ignition coil is connected directly to the spark plug without use of a high tension cable, an electrical discharge with a relatively weak current, such as a glow discharge, can be maintained stably, so that even at high speed or heavy load operation, consumption of the spark portion caused by volatilization of Ir through oxidation can be suppressed, thereby extending spark plug life.

Spark plug and ignition system for use with internal combustion engine

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Toki, Japan

Shoichiro Ito