Abstract: An ignition plug includes a center electrode; a cylindrical insulator that surrounds at least the circumference of a front end portion of the center electrode and that includes a bottom portion at the front side; and a cylindrical metal shell that holds the insulator from the outer circumference side. The center electrode includes a shaft portion that extends along an axial line and a head portion disposed at a front end of the shaft portion. The head portion has a width greater than that of the shaft portion in the radial direction. The insulator includes a first and second insulator. The first insulator has an axial hole and a diameter smaller than the maximum diameter of the head portion. The second insulator is joined to the first insulator. The shaft portion is disposed in the axial hole of the first insulator. The second insulator encloses the head portion.

Abstract: In an ignition plug, the volume V1 of a portion of an insulator, which projects from a metallic shell to a front side, is equal to or greater than 45 mm3; and an expression 0.18?V2/V1?0.37 is satisfied, where H is a length along which the insulator projects from the metallic shell to the front side in an axial direction, and V2 is a volume of a portion of the insulator, which projects from a front end of the insulator along a length H/2 in the axial direction.

Abstract: In an ignition plug, since a ground electrode is formed in a thin-rod-shape or a mesh-like shape, sufficiently strong radicals are locally generated by a barrier discharge, an anti-inflammation effect by the electrode is small, and the growth of a flame is hardly hindered. Furthermore, by making the thickness dimension of a second dielectric facing a discharge region uniform, the barrier discharge is spread over the surface of the second dielectric, the generation of the radicals is maintained, and combustibility after ignition is promoted. Furthermore, because an end portion of a high voltage electrode and a ground electrode are disposed to face each other within a combustion chamber, a fuel gas introduced into the combustion chamber is liable to flow into the discharge region, and is easily ignited by the radicals generated due to the discharge.

Abstract: An ignition plug includes a center electrode; a cylindrical insulator that surrounds at least the circumference of a front end portion of the center electrode and that includes a bottom portion at the front side; and a cylindrical metal shell that holds the insulator from the outer circumference side. The center electrode includes a shaft portion that extends along an axial line and a head portion disposed at a front end of the shaft portion. The head portion has a width greater than that of the shaft portion in the radial direction. The insulator includes a first and second insulator. The first insulator has an axial hole and a diameter smaller than the maximum diameter of the head portion. The second insulator is joined to the first insulator. The shaft portion is disposed in the axial hole of the first insulator. The second insulator encloses the head portion.

Abstract: An ignition plug capable of improving ignition performance while preventing pre-ignition includes a center electrode, a bottomed cylindrical insulator enclosing a front end portion of the center electrode and a cylindrical metal shell holding therein the insulator. The insulator has, on a front end side thereof, a protruding portion protruding from and located frontward of a front end of the metal shell. In the ignition plug, a difference between an outer diameter of the center electrode and an inner diameter of the insulator is 0.01 mm or more; an axial length of the protruding portion is 6.7 mm to 12.7 mm; and the following condition is satisfied: 1.07?S/V1?1.35 where S is an outer surface area of the protruding portion; and V1 is a volume of the protruding portion.

Abstract: An ignition plug capable of improving ignition performance while preventing pre-ignition includes a center electrode, a bottomed cylindrical insulator enclosing a front end portion of the center electrode and a cylindrical metal shell holding therein the insulator. The insulator has, on a front end side thereof, a protruding portion protruding from and located frontward of a front end of the metal shell. In the ignition plug, a difference between an outer diameter of the center electrode and an inner diameter of the insulator is 0.01 mm or more; an axial length of the protruding portion is 6.7 mm to 12.7 mm; and the following condition is satisfied: 1.07?S/V1?1.35 where S is an outer surface area of the protruding portion; and V1 is a volume of the protruding portion.

Abstract: A spark plug having a ground electrode, a noble metal tip having a front end that projects forward of a front end portion of the ground electrode, and a center electrode. When S1 represents an area of an overlap region in which a region onto which the center electrode is projected overlaps a region onto which the noble metal tip is projected when the center electrode and the noble metal tip are projected onto an imaginary plane perpendicular to a center line of the center electrode, and S2 represents an area of an overlap region in which a region onto which the noble metal tip is projected overlaps a region onto which the ground electrode is projected when the noble metal tip and the ground electrode are projected onto the imaginary plane, 0.22?S1/S2?0.68 is satisfied.

Abstract: An ignition system that uses a technique capable of restraining radiation of noise caused by discharge of a spark plug in the ignition system. The ignition system includes a spark plug and a power supply section. The spark plug is attached to an engine head. The power supply section has a battery having a ground terminal, and an ignition coil which transforms a voltage of the battery and supplies a transformed voltage to the spark plug. In the ignition system, a metallic shell of the spark plug is fixed to the engine head while being electrically insulated from the engine head through an insulator an electrically conductive path is connected to the metallic shell, and the electrically conductive path is electrically connected to the ground terminal of the battery while being electrically insulated from the engine head.

Abstract: A non-thermal equilibrium plasma ignition plug including a tubular metallic shell having an axial hole extending along an axial line, an insulator disposed in such a manner as to form a gap in cooperation with a wall surface of the axial hole at a forward end portion of the metallic shell, and a center electrode held at the center of the insulator, and generates nonequilibrium plasma in response to voltage applied thereto from a power supply. The insulator has a plurality of depressions or protrusions formed on a surface thereof which faces a discharge space therearound.

Abstract: A spark plug having a ground electrode, a noble metal tip having a front end that projects forward of a front end portion of the ground electrode, and a center electrode. When S1 represents an area of an overlap region in which a region onto which the center electrode is projected overlaps a region onto which the noble metal tip is projected when the center electrode and the noble metal tip are projected onto an imaginary plane perpendicular to a center line of the center electrode, and S2 represents an area of an overlap region in which a region onto which the noble metal tip is projected overlaps a region onto which the ground electrode is projected when the noble metal tip and the ground electrode are projected onto the imaginary plane, 0.22?S1/S2?0.68 is satisfied.

Abstract: A sparkplug includes: an insulator with an axial hole extending along an axial line; a metal shell covering the insulator; and a shelf part inside the metal shell. The insulator includes a second column part formed in the front end side of a tapering part. When a volume surrounded by a first plane that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line, a curved surface extending from an outer circumference of the second column part, and an outer circumferential surface of the insulator is defined as A, and a volume surrounded by the first plane, the curved surface, a second plane that passes through the front end of the metal shell and is orthogonal to the axial line, and the axial hole of the insulator is defined as B, a relational expression 0.9?A/B?2.4 is satisfied.

Abstract: In an ignition plug, the volume V1 of a portion of an insulator, which projects from a metallic shell to a front side, is equal to or greater than 45 mm3; and an expression 0.18?V2/V1?0.37 is satisfied, where H is a length along which the insulator projects from the metallic shell to the front side in an axial direction, and V2 is a volume of a portion of the insulator, which projects from a front end of the insulator along a length H/2 in the axial direction.

Abstract: An ignition plug that promotes expansion of flame and enhances spark corrosion resistance, said plug includes a center electrode; a tubular insulator holding the center electrode; a tubular metallic shell holding the insulator; and a ground electrode having a bent portion and a facing end surface. A plurality of peak voltages can be applied to the center electrode after application of a voltage for trigger discharge thereto. When a forward end surface of the center electrode and the facing end surface are projected onto a plane orthogonal to axial direction of the center electrode, the projection of the center of the forward end surface and the projection of the facing end surface overlap with each other, and the projection of a remote-side edge portion of the facing end surface which is located on the side remote from the bent portion is located within the projection of the forward end surface.

Abstract: A non-thermal equilibrium plasma ignition plug including a tubular metallic shell having an axial hole extending along an axial line, an insulator disposed in such a manner as to form a gap in cooperation with a wall surface of the axial hole at a forward end portion of the metallic shell, and a center electrode held at the center of the insulator, and generates nonequilibrium plasma in response to voltage applied thereto from a power supply. The insulator has a plurality of depressions or protrusions formed on a surface thereof which faces a discharge space therearound.

Abstract: A spark plug wherein an outer diameter of a first face that is a gap foliating face of the center electrode tip is denoted as R1, an outer diameter of a second face that is a gap forming face of the ground electrode tip is denoted as R2, a length of the gap is denoted as G1, and an average distance of a distance between an end in the first direction of the first face and an end in the first direction of the second face and a distance between an end in the second direction of the first face and an end in the second direction of the second face is denoted as G2, R1<R2, 0.5 mm?R1?1.1 mm, 0.7 mm?R2?1.2 mm, 0.6 mm?G1?1.3 mm, and 1.4?(R2/R1)×(G2/G1)?1.8 are satisfied.

Abstract: An ignition system includes an ignition plug, a discharge power supply for applying a high voltage to the gap of the ignition plug, a high-frequency power supply for supplying a high-frequency current to the gap, a matching unit provided between the ignition plug and the high-frequency power supply, and a mixer through which currents output from the two power supplies flow. An oscillation frequency fs (Hz) which maximizes the current flowing between the matching unit and the mixer when spark discharge is generated and an oscillation frequency fo (Hz) which maximizes the current flowing between the matching unit and the mixer when spark discharge is not generated satisfy a relation fs/fo?0.85. Thus, a current whose oscillation frequency is equal to the oscillation frequency fs flows between the matching unit and the mixer when spark discharge is not generated.

Abstract: An ignition system that sufficiently utilizes the energy output from a power supply, to thereby realize excellent ignition performance. The ignition system includes an ignition plug having a spark discharge gap formed between a center electrode and a ground electrode, and a power supply for supplying electric energy to the spark discharge gap. Electric energy output from the power supply for producing spark discharge of one unit is set to 100 mJ or greater. S1?[{?30 (mm?1)×G1+60}/100]×S2 and G1<2.0 are satisfied wherein G1 represents the size (mm) of the spark discharge, S1 represents an area (mm2) defined with a region obtained by removing, from a projection region of the center electrode, a region where the projection region overlaps with a projection region of the ground electrode and S2 represents an area (mm2) defined with the projection region of the center electrode.

Abstract: A spark plug wherein an outer diameter of a first face that is a gap foliating face of the center electrode tip is denoted as R1, an outer diameter of a second face that is a gap forming face of the ground electrode tip is denoted as R2, a length of the gap is denoted as G1, and an average distance of a distance between an end in the first direction of the first face and an end in the first direction of the second face and a distance between an end in the second direction of the first face and an end in the second direction of the second face is denoted as G2, R1<R2, 0.5 mm?R1?1.1 mm, 0.7 mm?R2?1.2 mm, 0.6 mm?G1?1.3 mm, and 1.4?(R2/R1)×(G2/G1)?1.8 are satisfied.

Abstract: A sparkplug includes: an insulator with an axial hole extending along an axial line; a metal shell covering the insulator; and a shelf part inside the metal shell. The insulator includes a second column part formed in the front end side of a tapering part. When a volume surrounded by a first plane that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line, a curved surface extending from an outer circumference of the second column part, and an outer circumferential surface of the insulator is defined as A, and a volume surrounded by the first plane, the curved surface, a second plane that passes through the front end of the metal shell and is orthogonal to the axial line, and the axial hole of the insulator is defined as B, a relational expression 0.9?A/B?2.4 is satisfied.

Abstract: A spark plug in which a front end portion of a ground electrode is positioned outside of a virtual outer circumferential face that is formed by extending a front and outer circumferential face of a center electrode in the axis direction, and positioned on a front end side in the axis direction with respect to a virtual face including a front end face of the center electrode. Further, the equation 1.1?b/a?1.6 is satisfied, where “a” (mm) represents a first minimal distance between the front end portion of the center electrode and the front end portion of the ground electrode and, where “b” (mm) represents a second minimal distance between the front end portion of a ceramic insulator and the front end portion of the ground electrode.