Nippondenso Co., Ltd.

Denso Corporation

Kenji Horibe

Nobuo Abe

Keiji Kanao

Hironori Osamura

Akio Katoh

Takeshi Hanai

A spark plug including an insulation porcelain having a throughhole; a center electrode held at one end of the throughhole; a housing holding the insulation porcelain; a ground electrode disposed at a front end of the housing and facing the center electrode; a spark gap defined by the center electrode and the ground electrode; and at least one of the center and ground electrodes having a nobel metal member bonded to a discharging spot of its front end, wherein the nobel metal member consists of 90 wt % or more of an Ir&mdash;Rh alloy containing 1 to 60 wt % Rh and the balance substantially consisting of at least one of Pt, Pb, Ru, Au and Ni.

Spark plug for internal combustion engine

To improve the consumption resistance and lifetime, a spark plug for an internal combustion engine comprises: an insulation porcelain having a throughhole; a center electrode held at one end of the throughhole; a housing holding the insulation porcelain; a ground electrode disposed at an front end of the housing and facing the center electrode; a spark gap defined by the center electrode and the ground electrode; and at least one of the center electrode and the ground electrode having a noble metal chip bonded to a discharging spot of an front end thereof, wherein the noble metal chip consisting of an Ir-Rh alloy contains Rh in an amount of from 1 wt % to 60 wt %.

A composite chip formed by joining a discharging layer and a heat stress relieving layer at a joint interface therebetween beforehand is provided on at least one of a central electrode and a ground electrode in its discharge portion made of an electrode material. The discharging layer is made of a precious metal or a precious metal alloy having superior spark- and wear-resistance, and the heat stress relieving layer is made of a metal or an alloy having a linear expansion coefficient between those of the discharging layer and the electrode material. Formed at the joint interface between both the discharging layer and the heat stress relieving layer through mutual diffusion of those materials developed when the two layers are joined to each other is a diffusion layer, in which concentrations of materials of both the layers are continuously changed. A thickness of the diffusion layer is not less than 3 .mu.m in a state that the composite chip is welded to the discharge portion.

Growing community of inventors

Nishikasugai-gun, Japan

Kenji Horibe