Ngk Spark Plug Company, Limited

Yoshihisa Sugiyama

Katsutoshi Nakayama

Kenichi Kumagai

Yoshitaka Sugiura

Tomoharu Suzuki

Takeru Wakamatsu

In a spark plug, the nickel content of a center electrodeis greater than that of a ground electrode. This enhances resistance to spark-induced consumption of the center electrode. Also, the ground electrodeto which a noble-metal chipis joined exhibits high resistance to spark-induced consumption. Accordingly, the spark plugcan be attached to either of a negative-polarity cylinder in which the center electrodeassumes a negative polarity, and a positive-polarity cylinder in which the center electrodeassumes a positive polarity. The noble-metal chipis joined only to the ground electrode, and a noble-metal chip is not joined to the center electrode

Spark plug and internal combustion engine equipped with the spark plug

In a spark plug ( ), at least one side face of the ground electrode ( ) is made of an electrode base material comprising an Ni alloy containing 21-25% by mass of Cr, 1-2% by mass of Al, 7-20% by mass of Fe and 58-71% by mass of Ni. The noble metal wear resistant portion ( ) is joined to the electrode base material via a welding portion (W). When the linear expansion coefficients at 800 K of the noble metal constituting the noble metal wear resistant portion ( ) and the electrode base material are represented by &agr;1 and &agr;2, respectively, &Dgr;&agr;&equiv;&agr;2&minus;&agr;1 is adjusted to be 4.55&times;10 /K or less. The outer diameter of the noble material wear resistant portion ( ) is set from 0.6 mm to 1.5 mm.

Spark plug having ground electrode made of NI alloy and noble metal wear resistant portion

A spark plug includes: a central electrode; an insulator surrounding the central electrode radially; a metallic shell surrounding the insulator radially; and a ground electrode having a first end connected to the metallic shell and a second end defining a side face. The ground electrode is so bent that the side face of the second end faces the central electrode. The ground electrode contains: a nickel in a range from 58% to 71% by weight, a chromium in a range from 21% to 25% by weight, an iron in a range from 7% to 20% by weight, and an aluminum in a range from 1% to 2% by weight. The ground electrode has a Vickers hardness in a range from Hv 140 to Hv 220 through a Vickers hardness test specified in Japanese Industrial Standard Z2244. A load 9.8 N is applied to the ground electrode in the hardness test.

Growing community of inventors

Gifu, Japan

Yoshihisa Sugiyama