| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve a performance of a spark plug by realizing both of durability and ignitability.SOLUTION: A spark plug comprises a center electrode, an insulator arranged on an outer periphery of the center electrode, a main body metal fitting arranged on an outer periphery of the insulator, and a ground electrode jointed to the main body metal fitting at one end and having a noble metal chip at the other end. A gap is formed between a tip of the center electrode and a discharge face of the noble metal chip. An acute angle among angles formed by a tip face of the center electrode and the discharge face of the noble metal chip on a cross section passing through a center of the discharge face and including an axial line is designated asθ1. Also, on the tip face of the center electrode, a point nearest the noble metal chip is designated as a point A, and both end points on the discharge face are designated as points B1 and B2. An angle formed by a first segment connecting the point A and the point B1 and a second segment connecting the point A and the point B2 is designated asθ2. Here, 35°≤θ1≤55° and 85°≤θ2≤90° are satisfied, and a difference between length of the first segment and length of the second segment is 10% or less of the length of the longer segment.</p> |
