Patent ID: 8164243

Claim:
A spark plug for an internal combustion engine, comprising: a rod-like center electrode; a tubular insulator having an axial hole extending along the direction of an axis of the center electrode and holding the center electrode placed in the axial hole; a tubular metallic shell provided radially outward of the insulator; a ground electrode extending from a front end portion of the metallic shell and bent such that a distal end of the ground electrode is directed toward the axis; a center-electrode-side chip joined to a distal end of the center electrode and extending from the center electrode along the direction of the axis; and a ground-electrode-side chip joined to a distal end surface of the ground electrode, the ground-electrode-side chip being thinner than the distal end surface of the ground electrode and having a distal end surface which faces a side surface portion of the center-electrode-side chip, wherein an angle θ 1 formed between a first straight line and a second straight line falls within a range of 120° to 140° inclusive, the first straight line passing through the center of a proximal end surface of the ground electrode which borders on the front end portion of the metallic shell and the center of a cross section of the ground electrode at a position separated from the center of the proximal end surface toward the distal end by 0.5 mm as measured along the direction of the axis, and the second straight line passing through the center of a distal end surface of the ground electrode and the center of a cross section of the ground electrode at a position separated from the center of the distal end surface of the ground electrode toward the proximal end portion of the ground electrode by 0.5 mm as measured along a direction perpendicular to the axis; an angle θ 2 formed between the axis and a plane including the distal end surface of the ground-electrode-side chip falls within a range of 0° to 3° inclusive; and a minimum distance between the insulator and the ground electrode is greater than a minimum distance between the distal end surface of the ground-electrode-side chip and the side surface portion of the center-electrode-side chip so as to generate a spark discharge between the ground-electrode-side chip and the center-electrode-side chip.