US 8,217,561 B2Granted

Spark plug having laminated ground electrode

AssigneeNgk Spark Plug Co., Ltd.

InventorsReimon Fukuzawa, Tomoaki Kato, Akira Suzuki

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Abstract

A spark plug includes: a metal shell having a mounting thread formed with a nominal diameter of M12 or smaller; a ground electrode consisting of a first structural member and at least one ith structural member (i=2, 3, 4, 5) laminated to cover an outer surface thereof, the length of protrusion of the ground electrode from a front end face of the metal shell being 4.5 mm or larger, the ground electrode having a bent portion with a curvature radius of 2.3 mm or smaller; and an electrode tip joined thereto at a position facing the front end of the center electrode and having a protrusion length of 0.5 mm or larger and a cross sectional area of 0.20 to 1.13 mm2. The ground electrode has a total thermal conductivity of 35 W/(m·K) or higher at 20° C.

A spark plug, comprising:

a center electrode;
a ceramic insulator having an axial hole extending in an axial direction and retaining the center electrode in the axial hole;
a metal shell surrounding a radial outer circumference of the ceramic insulator and retaining therein the ceramic insulator;
a ground electrode joined at one end thereof to a front end face of the metal shell and having a bent portion formed between the one end and the other end thereof in such a manner that the other end of the ground electrode faces a front end of the center electrode;
and
an electrode tip joined to the other end of the ground electrode at a position facing the front end of the center electrode and having a protrusion length of 0.5 mm or larger from the other end of the ground electrode and a cross sectional area of 0.20 to 1.13 mm2,
the ground electrode consisting of a first structural member extending from the one end toward the other end of the ground electrode and at least one ith structural member (i=2, 3, 4, 5) laminated to cover an outer surface of the first structural member;
the minimum curvature radius of a side surface of the bent portion facing the center electrode being 2.3 mm or smaller;
the length of protrusion of a point of the other end of the ground electrode protruding most in the axial direction from the front end face of the metal shell being 4.5 mm or larger;
the metal shell having a mounting thread formed with a nominal diameter of M12 or smaller based on JIS standard;
and
the total thermal conductivity X of the ground electrode as expressed by the formula [1] being 35 W/(m·K) or higher at 20° C.
[
Formula
⁢
⁢
4
]
X
=
volume
⁢
⁢
of
⁢
⁢
first
⁢
⁢
structual
⁢
⁢
member
volume
⁢
⁢
of
⁢
⁢
ground
⁢
⁢
electrode
×
thermal
⁢
⁢
conductivity
⁢
⁢
of
⁢
⁢
first
⁢
⁢
structural
⁢
⁢
member
+
∑
i
=
2
n
⁢
(
volume
⁢
⁢
of
⁢
⁢
ith
⁢
⁢
structural
⁢
⁢
member
volume
⁢
⁢
of
⁢
⁢
ground
⁢
⁢
electrode
×
⁢
thermal
⁢
⁢
⁢
conductivity
⁢
⁢
⁢
of
⁢
⁢
ith
⁢
⁢
structural
⁢
⁢
member
)
(
1
)
where n is an integer of 2 to 5 indicating the maximum number of the structural members of the ground electrode.

113 more elements

Abstract

Claims6