Spark plug
To prevent a sealant from intruding between a flange and a stepped portion during manufacture of a spark plug and to prevent cracking of an insulator during use of the spark plug, a spark plug includes a center electrode including a flange, an insulator having a through-hole extending in an axial-line direction and holding the center electrode, and a sealant filled in the through-hole to fix the flange and the insulator to each other; the insulator including a stepped portion in which the through-hole reduces a diameter toward a front end side and that supports the flange, and a small-diameter portion that is continuous with a front end side of the stepped portion and in which the diameter of the through-hole is smaller than in the stepped portion; an angle θ 1 formed by the stepped portion and a plane perpendicular to the axial line and an angle θ 2 formed by the plane perpendicular to the axial line and an opposing surface of the flange opposing the stepped portion satisfies θ 1−θ2 ≥6°, and in a cross section including the axial line, a maximum diameter D 1 of the flange and a diameter D 2 of the through-hole at a rear end of the small-diameter portion in the axial-line direction satisfy 0.15 mm≤(D 1 −D 2 )/2.
1. A spark plug, comprising:
a center electrode including
a leg extending in an axial-line direction parallel to an axial line, and
a flange that is continuous with a rear end side of the leg in the axial-line direction and protrudes radially outward beyond the leg;
an insulator having a through-hole extending in the axial-line direction, the insulator holding the center electrode in the through-hole; and
a sealant filled in the through-hole to fix the flange and the insulator to each other,
wherein the insulator includes
a stepped portion in which the through-hole reduces a diameter toward a front end side in the axial-line direction, the stepped portion supporting the flange, and
a small-diameter portion that is continuous with a front end side of the stepped portion and in which the diameter of the through-hole is smaller than in the stepped portion,
wherein an angle θ 1 formed by the stepped portion and a plane perpendicular to the axial line and an angle θ 2 formed by the plane and an opposing surface of the flange opposing the stepped portion satisfy θ 1 −θ 2 ≥6°, and
wherein, in a cross section including the axial line, a maximum diameter D 1 of the flange and a diameter D 2 of the through-hole at a rear end of the small-diameter portion in the axial-line direction satisfy 0.15 mm (D 1 −D 2 )/2.
2. The spark plug according to claim 1 ,
wherein the angle θ 1 satisfies 25°≤θ 1 ≤35°.
3. The spark plug according to claim 1 ,
wherein the angle θ 1 and the angle θ 2 satisfy θ 1 −θ 2 ≤20°.
4. The spark plug according to claim 2 ,
wherein the angle θ 1 and the angle θ 2 satisfy θ 1 −θ 2 ≤20°.