Ngk Spark Plug Company, Limited

Kaori Kishimoto

Hiroyuki Kameda

Katsutoshi Nakayama

Yasushi Sakakura

Tomoaki Kato

Tomoaki Aoki

There is provided a spark plug for an internal combustion engine, including: a center electrode extending in the direction of an axis of the spark plug and having a core of higher thermal expansion coefficient than that of a front end thereof, the center electrode including a flanged portion radially outwardly protruding on a rear side thereof and a cylindrical portion located closer to a front end of the spark plug than the flanged portion and being smaller in diameter than the flanged portion; an insulator having an axial hole in the direction of the axis to retain the flanged portion in the axial hole with the cylindrical portion held in a loose-fit state in the axial hole; and a metal shell accommodating the insulator, wherein the spark plug satisfies the following condition: Cb&#x3c;Cf where Cb is a difference between an inner diameter of the axial hole and an outer diameter of the cylindrical portion at an arbitrary axial position B in the direction of the axis; and Cf is a difference between the inner diameter of the axial hole and the outer diameter of the cylindrical portion at an axial position F closer to the front end of the spark plug than the axial position B in the direction of the axis.

Spark plug for internal combustion engine

A spark plug is provided with a ground electrode, a noble metal tip made of a Pt alloy, and a relieving layer tip made of a Pt alloy which has a linear expansion coefficient between that of the ground electrode and that of the noble metal tip.

A spark plug includes a center electrode extending along an axial line, a ground electrode, and a noble metal tip. A center axis of the noble metal tip is displaced from a center axis of the ground electrode toward a base-end side in the axial line. The ground electrode includes an outer layer and an inner layer, and a distal end of the inner layer is closer to the axial line than a base end of the ground electrode. An overlap area between the inner layer and the noble metal tip occupies a ratio of 25% or more in a projective plane defined by projecting, along the center axis, a plane of the ground electrode viewed from a distal-end face on a cross section of the ground electrode in which a maximum cross-sectional area of the inner layer is achieved, among cross sections orthogonal to the center axis.

A spark plug including a ground electrode which has an excellent heat sinking ability. The ground electrode includes a core material therein. Heat received from a combustion chamber during a drive of an internal-combustion engine can be conducted to the core material. More effective heat sinking ability can be achieved because of the core material.

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Nagoya, Japan

Kaori Kishimoto