Patent ID: 9548592
Date: 2017-01-17
CPC Classifications: H01T

Claim:
1. A sparkplug comprising: an insulator having an axial hole extending along an axial line; a center electrode inserted in the axial hole; a metal shell disposed in an outer circumference of the insulator; and a ground electrode disposed at a front end of the metal shell, wherein the metal shell has a shelf part that protrudes inward in a radial direction and is formed on an inner circumference thereof, the insulator includes: a first column part facing at least a part of the shelf part; a taper part formed at a front end side of the first column part and having a decreasing diameter; and a second column part formed at the front end side of the taper part, said taper part diameter decreasing toward said second column, and when a volume of the insulator surrounded by a first plane that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line, a curved surface extending from an outer circumference of the second column part, and an outer circumference surface of the insulator is defined as A, and a volume of the insulator surrounded by the first plane, the curved surface, a second plane that passes through the front end of the metal shell and is orthogonal to the axial line, and the axial hole of the insulator is defined as B, a relational expression is satisfied.