Semi-creeping discharge type spark plug

A semi-creeping discharge type spark plug, comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• and
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator,
• wherein an inner edge portion of said front end surface of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, is beveled by greater than 0.5 mm to 1.0 mm in terms of chamfer length (C).

A semi-creeping discharge type spark plug, comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• and
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator,
• wherein an outer diameter of a front end of said center electrode is 1.0-2.0 mm, a front end portion of which opposes said ground electrode and is enclosed by said insulator;
• and
• wherein an inner edge portion of said front end surface of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, is beveled by greater than 0.5 mm to 0.1 mm in terms of chamfer length (C).

A semi-creeping discharge type spark plug, comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• and
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator,
• wherein an inner edge portion of said front end surface of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, is rounded by 0.1˜1.0 (1/mm) in terms of radius of curvature (R).

A semi-creeping discharge type spark plug, comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• and
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator,
• wherein an outer diameter of the front end of said center electrode is 1.0-2.0 mm, a front end portion of which opposes said ground electrode and is enclosed by said insulator;
• and
• wherein an inner edge portion of said front end surface of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, is rounded by 0.1˜1.0 (1/mm) in terms of radius of curvature (R).

A semi-creeping discharge type spark plug comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell and having an inner edge portion of the front end surface of said insulator rounded by 0.1˜1.0 (1/mm) in terms of radius of curvature (R);
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• said center electrode having an erosion resistant metal tip made of a metal selected from the group consisting of Pt, Pt-based alloy, Ir-based alloy and Ir—Rh based alloy;
• and
• a plurality of ground electrodes, first ends of which are connected to a front end of said metal shell, and second ends of which are bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surfaces of said ground electrodes extending by 0.0˜1.0 mm forward from said front end surface of said insulator.

A semi-creeping discharge type spark plug comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator;
• and
• an inner edge portion of said front end surface of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, being beveled in terms of chamfer length (C), the chamfer length (C) being defined as (t) mm<C<(t+0.1) mm,
• where (t) is a retraction length in which said front end surface edge of said center electrode is retracted from said front end surface of said insulator.

A semi-creeping discharge type spark plug comprising:

• a cylindrical metal shell;
• an insulator having an axial bore provided within said metal shell so that a front end of said insulator extends beyond said metal shell;
• a center electrode provided within said axial bore of said insulator so that a front end surface edge of said center electrode is retracted by 0.1˜0.6 mm from a front end surface of said insulator;
• at least one ground electrode, one end of which is connected to a front end of said metal shell, and the other end of which is bent to oppose an outer surface of said insulator so as to form an air-gap therebetween while permitting creeping spark discharges running along said front end surface of said insulator, a forward edge portion of a front end surface of said ground electrode extending by 0.0˜1.0 mm forward from said front end surface of said insulator;
• and
• an inner edge portion of said front end surfaces of said insulator which is subjected to the spark discharges from said ground electrode to said center electrode, being rounded in terms of radius of curvature (R), the radius of curvature (R) being defined as (t) mm<R<(t+0.1) mm,
• where (t) is a retraction length in which said front end surface edge of said center electrode is retracted from said front end surface of said insulator.