Spark plug

Patent metadata

Field	Value
Publication number	US-12095233-B1
Application number	US-202218567541-A
Country	US
Kind code	B1
Filing date	Jun 14, 2022
Priority date	Jun 14, 2021
Publication date	Sep 17, 2024
Grant date	Sep 17, 2024

Abstract

A spark plug 1 of the present invention includes: an insulator 2 made from an alumina-based sintered body; a center electrode being a bar-like electrode inserted in the insulator 2 and having, on a rear end side of the center electrode, a diameter-enlarged portion enlarged in a radial direction and engaged with an inner wall of the insulator; and a conductive sealing material provided on the rear end side of the center electrode 3 inside the insulator. In a mirror-polished surface obtained by mirror-polishing a cut surface obtained by cutting the insulator in a direction perpendicular to the axial line direction, at a position 2 mm from a portion having a maximum diameter of the diameter-enlarged portion to the rear end side along the axial line direction, when 20 observation regions each being 192 μm×255 μm are set so as to each overlap a reference position being a center position between an inner peripheral surface and an outer peripheral surface of the insulator and so as not to overlap each other, an average of a proportion (porosity) of pores included in each observation region is not greater than 3.5% and, with respect to a variation in the proportion (porosity), when a standard deviation is defined as σ, σ is not greater than 0.36.

First claim

A What is claimed is:

1. A spark plug comprising:
an insulator having a tubular shape extending along an axial line direction thereof and made from an alumina-based sintered body;
a center electrode being a bar-like electrode inserted in the insulator such that a front end of the bar-like electrode is exposed from the insulator and a ear end of the bar-like electrode is housed inside the insulator, the center electrode having, on a rear end side thereof, a diameter-enlarged portion enlarged in a radial direction and engaged with an inner wall of the insulator; and
a conductive sealing material provided on the rear end side of the center electrode inside the insulator, wherein
in a mirror-polished surface obtained by mirror-polishing a cut surface obtained by cutting the insulator in a direction perpendicular to the axial line direction, at a position 2 mm from a portion having a maximum diameter of the diameter-enlarged portion to the rear end side along the axial line direction,
when 20 observation regions each being 192 μm×255 μm are set so as to each overlap a reference position being a center position between an inner peripheral surface and an outer peripheral surface of the insulator and so as not to overlap each other,
an average of a porosity of pores included in each observation region is not greater than 3.5% and, with respect to a variation in the porosity, when a standard deviation is defined as σ, σ is not greater than 0.36.

2. The spark plug according to claim 1 , wherein, in the observation region, an average of the number of large pores, out of the pores, each having an area of not less than 0.05 μm 2 is not less than 200 and not grater than 600.

3. The spark plug according to claim 2 , wherein, with respect to a variation in the number of the large pores in the observation region, when a standard deviation is defined as σ, 3 σ is not greater than 100.

4. The spark plug according to claim 3 , wherein the 3σ is not greater than 50.

5. The spark plug according to claim 2 , wherein, in the observation region, the average of the porosity of the pores is not less than 1.0% and the average of the number of the large pores is not less than 240.

6. The spark plug according to claim 2 , wherein, in the observation region, with respect to a variation in the number of the large pores, when a standard deviation is defined as a, a value of “the average of the number +3σ” is less than 330.

7. The spark plug according to claim 2 , wherein
in the mirror-polished surface, when a region provided between the inner peripheral surface and the outer peripheral surface of the insulator is divided such that a length thereof in the radial direction is trisected, with respect to an inner side region provided on an innermost side, 20 inner side observation regions each being 192 μm×255 μm are set so as not to overlap each other, and with respect to an outer side region provided on an outermost side, 20 outer side observation regions each being 192 μm×255 μm are set so as not to overlap each other,
an average of a porosity of pores included in each inner side observation region is smaller by 0.1 to 2% than an average of a porosity of pores included in each outer side observation region.

Assignees

• Niterra Co Ltd

Inventors

• Tamura Noriyuki
• Yoshida Haruki
• Shimada Hiroki
• KUKINO Tomoya
• KOBA Takuto
• Fujimura Kengo

Classifications

• H01T21/02

  of sparking plugs · CPC title

• H01T13/34 Primary

  characterised by the mounting of electrodes in insulation, e.g. by embedding · CPC title

• H01T13/20 Primary

  characterised by features of the electrodes or insulation · CPC title