Patent ID: 8952602
Filing Date: 2015-02-10
Classification: H01T

Abstract:
1. A spark plug comprising: a center electrode extending in the direction of an axial line; an insulator disposed around the center electrode such that a forward end portion of the center electrode is exposed; a metallic shell disposed around the insulator; and a ground electrode whose one end portion is joined to the metallic shell and which has a noble metal tip at the other end portion thereof, wherein a gap is formed between a forward end portion of the center electrode and a discharge surface of the noble metal tip, and wherein on a cross section which passes through the center of the discharge surface and includes the axial line, an acute angle formed by a forward end surface of the center electrode and the discharge surface of the noble metal tip is defined as θ1, a point on the forward end surface of the center electrode closest to the noble metal tip is defined as a point A, opposite end points of the discharge surface are defined as points B1 and B2, a line segment connecting the point A and the point B1 is defined as a first line segment, a line segment connecting the point A and the point B2 is defined as a second line segment, and an angle formed by the first line segment and the second line segment is defined as θ2; and under the above definitions, 35°≦θ1≦55°, 85°≦θ2≦90°, and a difference in length between the first and second line segments is equal to or less than 10% of the length of a longer line segment.