Abstract: A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. At least one of the center electrode and the ground electrode includes a projection having a columnar shape. The projection projects toward the other of the center electrode and the ground electrode and forms the discharge gap. A portion of a side surface of the projection has a recess. A melted portion is formed by melting the noble metal tip and an electrode base material. The recess is formed in the melted portion. When D is a depth of the recess from a side surface of the noble metal tip and R is a diameter of the noble metal tip, 0.05 mm?D?0.3×R is satisfied.

Abstract: A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. At least one of the center electrode and the ground electrode includes a projection having a columnar shape. The projection projects toward the other of the center electrode and the ground electrode and forms the discharge gap. A portion of a side surface of the projection has a recess. A melted portion is formed by melting the noble metal tip and an electrode base material. The recess is formed in the melted portion. When D is a depth of the recess from a side surface of the noble metal tip and R is a diameter of the noble metal tip, 0.05 mm?D?0.3×R is satisfied.

Abstract: A connection device for connecting a first power supply and a second power supply to an ignition plug has a first power supply side line which establishes electrical connection between the ignition plug and the first power supply and which is electrically connected to the second power supply, and a second power supply side line which establishes electrical connection between the ignition plug and the second power supply. The first power supply side line includes a first diode which prevents a current inflow from the second power supply into the first power supply or a current inflow from the first power supply into the second power supply, and an inductor disposed between the first diode and the ignition plug. The inductor is disposed around the second power supply side line while being separated from the second power supply side line. Thus, noise can be suppressed.

Abstract: A spark plug has a center electrode containing a shaft portion, a tip portion joined to a forward end portion of the shaft portion, and a joint portion joining the shaft portion and the tip portion together. In the spark plug, the distance between the surface of the center electrode and an inner edge of the insulator is 0.3 mm or greater. The inner edge is a forward-end-side edge of an inner circumferential surface of a small diameter portion of the insulator, the small diameter portion being a part of a portion of the insulator for accommodating the tip portion and having the smallest inner diameter.

Abstract: A plasma jet spark plug having increased capacitive discharge current, and thus improved plasma generation efficiency. The plasma jet spark plug includes an insulating body having an axial hole, a center electrode, a metal shell, and a cavity portion formed by the inner peripheral surface of the insulating body and the leading end face of the center electrode. A conductive layer formed from a conductive material is provided on at least one portion of at least one of: (a) a surface on the insulating body outer peripheral surface opposed to the inner peripheral surface of the metal shell, the conductive layer electrically connected to a ground electrode; and (b) a surface on the insulating body inner peripheral surface opposed to the outer peripheral surface of the center electrode, the conductive layer electrically connected to the center electrode.

Abstract: An ignition plug providing excellent ignition performance that can be maintained over a long period of time by restraining channeling. The ignition plug includes a ceramic insulator having an axial bore, a center electrode inserted into the axial bore, a metallic shell, and a ground electrode fixed to the metallic shell, and has a cavity defined by an inner circumferential surface of the axial bore and the forward end surface of the center electrode. The axial bore includes a first straight portion and a diameter-reducing portion. As viewed on a section which contains an axis (CL1) of the ignition plug, a relational expression ??10 is satisfied, where ? (°) is an acute angle formed by a straight line orthogonal to the axis (CL1) and the outline of the diameter-reducing portion.

Abstract: An ignition plug that reliably restrains generation of corona discharge for enhancing accuracy in detection of ionic current and method of manufacturing same. The ignition plug is configured such that a metallic shell and an insulator are fixed together by means of a crimped portion provided at a rear end portion of the metallic shell and bent radially inward. An electrically insulative filling member fills a space formed between the crimped portion and the insulator. The filling member covers at least a portion of an outer circumferential surface of a rear trunk portion of the insulator along the entire circumference and the entirety of a rear end surface of the metallic shell, which is a portion of the outer surface of the crimped portion and is visible from the rear side with respect to the direction of an axial line CL1.

Abstract: An ignition plug that reliably restrains generation of corona discharge for enhancing accuracy in detection of ionic current and method of manufacturing same. The ignition plug is configured such that a metallic shell and an insulator are fixed together by means of a crimped portion provided at a rear end portion of the metallic shell and bent radially inward. An electrically insulative filling member fills a space formed between the crimped portion and the insulator. The filling member covers at least a portion of an outer circumferential surface of a rear trunk portion of the insulator along the entire circumference and the entirety of a rear end surface of the metallic shell, which is a portion of the outer surface of the crimped portion and is visible from the rear side with respect to the direction of an axial line CL1.

Abstract: A connection device for connecting a first power supply and a second power supply to an ignition plug has a first power supply side line which establishes electrical connection between the ignition plug and the first power supply and which is electrically connected to the second power supply, and a second power supply side line which establishes electrical connection between the ignition plug and the second power supply. The first power supply side line includes a first diode which prevents a current inflow from the second power supply into the first power supply or a current inflow from the first power supply into the second power supply, and an inductor disposed between the first diode and the ignition plug. The inductor is disposed around the second power supply side line while being separated from the second power supply side line. Thus, noise can be suppressed.

Abstract: A plasma jet spark plug capable of preventing a channeling progress and having excellent heat conduction. The plasma jet spark plug comprised of: a ceramic insulator having a small diameter portion which assumes a linear shape in an axial direction, and a center electrode has an outer diameter increasing in the order of a frontmost portion, a step portion, a front end portion and a body portion.

Abstract: A current of sufficient size to form plasma at ignition of a plasma jet ignition plug flows to a spark discharge gap while suppressing noise occurrence. There is provided an ignition apparatus of a plasma jet ignition plug, which includes a resistor R1, with one end connected to a diode D1 disposed between the plasma jet ignition plug 100 and a high-voltage generation circuit 210 and with the other end electrically connected to a center electrode 40 of the plasma jet ignition plug 100, and a capacitor C1, with one end connected to the center electrode 40 of the plasma jet ignition plug 100 and with the other end grounded.

Abstract: An ignition plug providing excellent ignition performance that can be maintained over a long period of time by restraining channeling. The ignition plug includes a ceramic insulator having an axial bore, a center electrode inserted into the axial bore, a metallic shell, and a ground electrode fixed to the metallic shell, and has a cavity defined by an inner circumferential surface of the axial bore and the forward end surface of the center electrode. The axial bore includes a first straight portion and a diameter-reducing portion. As viewed on a section which contains an axis (CL1) of the ignition plug, a relational expression ??10 is satisfied, where ? (°) is an acute angle formed by a straight line orthogonal to the axis (CL1) and the outline of the diameter-reducing portion.

Abstract: An ignition plug that maintains excellent ignition performance over a long period of time through effective prevention of channeling. The ignition plug includes an insulator having an axial bore, a center electrode inserted into the axial bore, a metallic shell disposed externally of the outer circumference of the insulator, and a ground electrode fixed to a front end portion of the metallic shell. A cavity is defined by the wall surface of the axial bore and the front end surface of the center electrode. The ground electrode includes a body whose distal end portion is disposed away from the front end of the insulator, and a protrusion protruding from the body.

Abstract: A plasma jet spark plug for igniting an air-fuel mixture in a conventional combustion device such as an internal combustion engine.

Abstract: A plasma jet spark plug having increased capacitive discharge current, and thus improved plasma generation efficiency. The plasma jet spark plug includes an insulating body having an axial hole, a center electrode, a metal shell, and a cavity portion formed by the inner peripheral surface of the insulating body and the leading end face of the center electrode. A conductive layer formed from a conductive material is provided on at least one portion of at least one of: (a) a surface on the insulating body outer peripheral surface opposed to the inner peripheral surface of the metal shell, the conductive layer electrically connected to a ground electrode; and (b) a surface on the insulating body inner peripheral surface opposed to the outer peripheral surface of the center electrode, the conductive layer electrically connected to the center electrode.

Abstract: A plasma jet ignition plug that reliably prevents current leakage with restraint on variation in the position of a ground electrode relative to an insulator and on overheat of the ground electrode, for stable generation of plasma. The plug includes an insulator having an axial bore extending in the direction of an axis CL1, a center electrode inserted in the axial bore, a metallic shell disposed externally of the outer circumference of the insulator, and a ground electrode fixed to the metallic shell, and has a cavity defined by the wall surface of the axial bore and the front end surface of the center electrode. Supports intervene between the insulator and the ground electrode. A space formed radially outward of the supports and a space formed radially inward of the support communicate with each other.

Abstract: A plasma jet ignition plug having high ignition performance and high durability. The plasma jet ignition plug comprises a center electrode wherein at least a front end portion including a front end surface of the center electrode contains an oxide of at least one of the rare earth elements in a total amount of 0.5% by mass to 10% by mass inclusive and tungsten (W) in an amount of 90% by mass or greater, or contains iridium (Ir) in an amount of 0.3% by mass to 3% by mass inclusive and W in an amount of 97% by mass or greater.

Abstract: A plasma jet ignition plug including an insulator having an axial hole extending therethrough in the direction of an axis CL1, a center electrode inserted into the axial hole, and a ground electrode disposed frontward of the front end of the insulator. The insulator has a cavity defined by the wall surface of the axial hole and the front end surface of the center electrode and opens frontward. The ground electrode has a through hole for establishing communication between the cavity and an ambient atmosphere. A front end portion of the center electrode is formed into a taper portion whose diameter reduces frontward in the direction of the axis CL1. The outside diameter of a front end of the taper portion is smaller than the diameter of the through hole. The cavity has a substantially constant diameter with respect to the direction of the axis CL1.

Abstract: An ignition system including a plasma jet spark plug, a discharge power source, and an energy input portion. The spark plug includes a center electrode inserted and installed in the axis hole of an insulator, a ground electrode forming a clearance with the center electrode in between, and a cavity defined by an inner peripheral surface of the axis hole and a top end surface of the center electrode. A plasma is generated in the cavity as the discharge power source generates a spark discharge by applying a voltage to the clearance and the energy input portion inputs electric power into the clearance. The energy input portion inputs electric power into the clearance more than once in a single spark discharge.

Abstract: A plasma jet ignition plug that reliably prevents current leakage with restraint on variation in the position of a ground electrode relative to an insulator and on overheat of the ground electrode, for stable generation of plasma. The plug includes an insulator having an axial bore extending in the direction of an axis CL1, a center electrode inserted in the axial bore, a metallic shell disposed externally of the outer circumference of the insulator, and a ground electrode fixed to the metallic shell, and has a cavity defined by the wall surface of the axial bore and the front end surface of the center electrode. Supports intervene between the insulator and the ground electrode. A space formed radially outward of the supports and a space formed radially inward of the support communicate with each other.