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Spark plug

A spark plug and ground electrode technology, applied in the field of spark plugs, can solve the problems of ground electrode breakage resistance degradation, ground electrode heat dissipation reduction, internal stress breakage, etc.

Active Publication Date: 2009-10-28
NGK SPARK PLUG CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

On the other hand, since the heat dissipation path of the ground electrode (i.e., the heat dissipation path from the other end of the ground electrode to the end and then to the metal shell) increases with the length of the ground electrode, the heat dissipation capability of the ground electrode decreases.
Therefore, in the state where the metal fatigue strength of the ground electrode is reduced under thermal load, especially in the bent portion, there is a possibility that the internal stress exceeds the fatigue limit and breakage occurs.
This can lead to a deterioration in the breakage resistance of the ground electrode

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0058] In Example 1, an evaluation test was performed to verify the relationship between the curvature of the bent portion 34 of the ground electrode 30 and the life of the ground electrode 30 . For this evaluation test, a plurality of ground electrodes each having a three-layer structure composed of first, second and third structural members and showing a value of 15 W / (m·K ) or a total thermal conductivity X of 45W / (m K). In addition, the preparation cross-sectional area S is 0.38mm 3 ( 0.7mm) and a needle-shaped electrode tip with a protruding length H of 0.8mm and a cross-sectional area S of 0.38mm 3 And the protruding length H is a plate-shaped electrode tip of 0.2 mm, and the needle-shaped electrode tip and the plate-shaped electrode tip are joined to two kinds of ground electrodes having the above-mentioned total thermal conductivity X. Spark plug samples were assembled using these grounded electrodes with tip. In each spark plug sample, the ground electrode was be...

Embodiment 2

[0063] In Example 2, an evaluation test was performed to verify the relationship between the total thermal conductivity X of the ground electrode 30 and the life of the ground electrode 30 . For this evaluation test, a plurality of ground electrodes each having a three-layer structure of first, second and third structural members as in the case of Example 1 and showing the Total thermal conductivity X in the range of 15W / (m·K) to 110W / (m·K). Here, three ground electrodes are prepared for each thermal conductivity level X. In addition, the preparation cross-sectional area S is 0.38mm 3 ( 0.7 mm) with a protruding length H of 0.8 mm and bonded to each ground electrode. Spark plug samples were completed by forming a bend in the ground electrode in such a manner as to control the radius of curvature R of the ground electrode's inner surface for each thermal conductivity level X to three different levels: 1.0 mm, 1.5 mm, and 2.0 mm. An evaluation test was performed by applying...

Embodiment 3

[0067] In Example 3, an evaluation test was performed to verify the relationship between the protruding length L of the ground electrode 30 from the front end face 57 of the metal shell 50 and the life of the ground electrode 30 . For this evaluation test, a plurality of ground electrodes each having a three-layer structure of first, second and third structural members as in the case of Example 1 and showing the Total thermal conductivity X of 15W / (m·K) or 45W / (m·K). These ground electrodes are cut to such an entire length that the ground electrodes are bent to form a bend with a radius of curvature R of 1.5 mm and the protruding length L of the ground electrodes is controlled within the range of 4.0 mm to 10.0 mm (see figure 2 ). The preparation cross-sectional area S is 0.38mm 3 A needle-shaped electrode tip with a protruding length H of 0.8 mm was used, and the prepared electrode tip was bonded to each ground electrode. Spark plug samples were completed using these tipp...

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Abstract

Provided is a spark plug manufactured to have a small nominal diameter of M12 according to the JIS standards of a mounting screw formed in a main fitting. An earth electrode is covered, on the outer face of a first member extending from one end side to the other end side, with at least one or more i-th members (wherein i = 2, 3, 4 and 5) individually in stratified shapes. The other end has a protrusion length of 4.5 mm or more from the leading end face of the main fitting. The earth electrode has a bent portion bent with a radius of curvature of 2.3 mm or less between the one end and the other end. An electrode tip, which is sized to have a protrusion length of 0.5 mm or more and a sectional area of 0.20 to 1.13 mm2, is jointed at the other end to the position to confront the leading end of the center electrode. The heat extracting performance can be improved to suppress the reduction of the fatigue strength, if the material to constitute the earth electrode is selected such that the synthesized thermal conductivity (X), as expressed by Formula (1), of the earth electrode at 20 DEG C. is 35 W / (mK) or higher.

Description

technical field [0001] The invention relates to a spark plug, which has: a ground electrode formed with at least one inner layer of high thermal conductivity material; and a needle-shaped electrode head joined to the ground electrode. Background technique [0002] There is known a spark plug comprising: a center electrode; a ground electrode; and a needle-shaped electrode tip joined to an inner face (side surface) of an end portion of the ground electrode facing the center electrode and between the electrode tip and the center electrode. A spark discharge gap is defined between them. This type of spark plug allows the ground electrode to be located farther from the spark gap than conventional spark plugs and reduces the tendency of flame nuclei generated in the spark gap to contact the ground electrode during the initial stages of flame growth. Thereby, the quenching effect of the ground electrode can be reduced, and the ignition performance of the spark plug can be improve...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H01T13/32H01T13/16H01T13/20
CPCH01T13/32H01T13/16H01T13/39H01T13/20
Inventor 福泽怜门加藤友聪铃木彰
Owner NGK SPARK PLUG CO LTD
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