Patent ID: 8928213
Filing Date: 2015-01-06
Classification: H01T

Abstract:
1. A spark plug for an internal-combustion engine, comprising: a central electrode; an insulator that holds the central electrode inside; a housing that holds the insulator inside; a ground electrode that forms a spark gap with the central electrode, the ground electrode including a ground base member connected to the housing, and a ground protrusion protruding from a confronting face of the ground base member confronting the central electrode, the ground protrusion having a diameter of 0.9 to 1.4 mm, the spark plug being configured to satisfy the following inequality: wherein R [mm] is a curvature radius of a base member corner and θ[degrees] is an angle formed by a shortest connecting line between the base member corner and a protrusion corner and a plane perpendicular to an axial direction of the ground protrusion, the base member corner being a widthwise directional edge of the confronting face of the ground base member and the protrusion corner being an edge of a spark face of the ground protrusion confronting the central electrode.