Niterra Co., Ltd.

Takuto Koba

Hiroki Shimada

Kengo Fujimura

Noriyuki Tamura

Tomoya Kukino

Yuichi Yamada

Takeshi Sakuma

Shoma Tsumagari

When a force to bend a spark plug insulator is applied to the spark plug insulator to fracture the spark plug insulator, for a range including a starting point of the fracture out of two ranges into which a fracture surface created by the fracture is divided by a plane which is a plane perpendicular to a direction of the force and includes the axial line, an average of areas of particles appearing in a planar image of the range is 4.4 μmor larger and 8.0 μmor smaller, and a maximum area of the particles is 600 μmor smaller. The particles include large particles having an area of 60 μmor larger and 600 μmor smaller, and, as the large particles, 0.1 particles/mmor more are present per unit area of the planar image.

Spark plug insulator and spark plug

A spark plugof the present invention includes: an insulatormade from an alumina-based sintered body; a center electrode being a bar-like electrode inserted in the insulatorand 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 electrodeinside 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.

Spark plug

A spark plugof the present invention includes an insulatormade from an alumina-based sintered body and including: a leg portionprovided on a front end side; a middle trunk portionprovided on a rear end side of the leg portionand having a larger diameter than the leg portion; and a flange portionprovided on the rear end side of the middle trunk portionand having a larger diameter than the middle trunk portion. In the spark plug, in a state where a cut surfaceobtained by cutting the middle trunk portionin a direction perpendicular to an axial line AX direction at an arbitrary position in the axial line AX direction is mirror-polished, when 20 observation regions X each being 185 μm×250 μm are set so as not to overlap each other, and with respect to each of a plurality of pores included in the 20 observation regions X, a square value P[μm] of a length P [μm] of a circumference of the pore is obtained, an average value of the square values P[μm] of top 20 pores having the largest square values P[μm] is not greater than 2200 μm, and a proportion T [%] of a total area of all pores included in the 20 observation regions X relative to a total area (100%) of the 20 observation regions X is not greater than 5%.

In a spark plugof the present invention, in a mirror-polished surfaceobtained by mirror-polishing a cut surfaceobtained by cutting an insulatorin a direction perpendicular to an axial line AX direction, at a position separated by 2 mm from a portion having a maximum diameter of a diameter-enlarged portionto a rear end side along the axial line AX direction, when 20 first observation regions X each being 192 μm×255 μm are set so as to each overlap a reference position mbeing a position 0.2 mm in a radial direction from an inner peripheral surfaceside of the insulatorand so as not to overlap each other, a proportion (porosity) of an area of all of pores included in the 20 first observation regions X relative to a total area (100%) of the 20 first observation regions X is not greater than 3.5%, and in a thermally etched surfaceobtained by subjecting the mirror-polished surfaceto thermal etching, when 20 second observation regions Y each being 32 μm×43 μm are set so as to each overlap the reference position mand so as not to overlap each other, a particle size distribution of alumina particles included in the 20 second observation regions Y is regarded as a normal distribution, an average particle diameter of the alumina particles is defined as A, and a standard deviation of a particle diameter of the alumina particles is defined as σ, A is not less than 1.9 μm and not greater than 2.8 μm, and (A+3σ) is not greater than 3.0 μm.

Growing community of inventors

Aichi, Japan

Takuto Koba