US 8,575,828 B2 · Spark plug

Abstract

A corner of a distal end of a ground-electrode-side noble metal tip of a spark plug is taken as a first corner; a corner of a leading end of a center-electrode-side noble metal tip is taken as a second corner; a corner formed at a starting point where a diameter of the center electrode is reduced is taken as a third corner; a corner of the ground electrode is taken as a fourth corner; a corner closest to the third corner of the corners on the distal end of the ground-electrode-side noble metal tip is taken as a fifth corner; a length of a virtual flying spark path defined between the first corner and the second corner is taken as L1; a length of a virtual flying spark path defined between the third corner and the fourth corner is taken as L2; a length of a virtual flying spark path defined between the third corner and the fifth corner is taken as L3; and L2 or L3, whichever is shorter, is taken as L4, the spark plug fulfills a relational expression of L4/L1≧1.1.

A spark plug comprising:

a center electrode extending in an axial direction of the spark plug;
a center-electrode-side noble metal tip joined to a leading end of the center electrode;
a fused portion is formed between the center electrode and the center-electrode-side noble metal tip,
an obtuse angle achieved in a boundary portion between the center-electrode-side noble metal tip and the fused portion is taken as θ1, and
an obtuse angle achieved in a boundary portion between the fused portion and the center electrode is taken as θ2,
a relational expression of θ1>θ2 and a relational expression of θ1<180° are fulfilled;
a ground electrode opposing a side surface of the center-electrode-side noble metal tip;
and
a ground-electrode-side noble metal tip joined to a distal end of the ground electrode, wherein:
of corners of a distal end of the ground-electrode-side noble metal tip, a corner closest toward a leading end direction of the center-electrode-side noble metal tip is taken as a first corner;
of corners of the leading end of the center-electrode-side noble metal tip, a corner closest to the ground-electrode-side noble metal tip is taken as a second corner;
of corners formed at a starting point where a diameter of the center electrode is reduced, a corner closest to the ground electrode is taken as a third corner;
of the corners of the ground electrode, a corner closest to the third corner is taken as a fourth corner;
of the corners on the distal end of the ground-electrode-side noble metal tip, a corner closest to the third corner is taken as a fifth corner;
of corners formed in a boundary portion between the center electrode and the fused portion, a corner closest to the ground electrode is taken as a sixth corner;
a virtual flying spark path established between any two of the corners is defined, on condition that:
a line passing through a vertex of one corner and bisecting the one corner is taken as a first line,
a line passing through a vertex of another corner and bisecting the another corner is taken as a second line,
a circular arc tangent to the first line and having end points at the vertex of the one corner and the vertex of the another corner is taken as a first circular arc, and
a circular arc tangent to the second line and having end points at the vertex of the one corner and the vertex of the another corner is taken as a second circular arc,
as a combination of:
a path extending along the first circular arc which connects the vertex of the one corner to a middle point of the first circular arc;
a straight path that connects the middle point of the first circular arc to a middle point of the second circular arc;
and a path extending along the second circular arc which connects the middle point of the second circular arc to the vertex of the another corner;
and
a relational expression of L4/L1≧1.1 is fulfilled on condition that:
a length of a virtual flying spark path defined between the first corner and the second corner is taken as L1,
a length of a virtual flying spark path defined between the third corner and the fourth corner is taken as L2,
a length of a virtual flying spark path defined between the third corner and the fifth corner is taken as L3, and
L2 or L3, whichever is shorter, is taken as L4;
a relational expression of L7/L4≧0.5 is fulfilled on condition that:
a length of a virtual flying spark path defined between the fourth corner and the sixth corner is taken as L5,
a length of a virtual flying spark path defined between the fifth corner and the sixth corner is taken as L6, and
L5 or L6, whichever is shorter, is taken as L7.

31 more elements

Spark plug

Life of this patent

Spark plug

Life of this patent

Abstract

Claims14