A spark plug having an insulating body defining a longitudinal axis and including a base portion and an obstruction portion, a first electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the first electrode extending through the base portion of the insulating body, and a second electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the second electrode extending through the base portion and the obstruction portion of the insulating body, wherein the obstruction portion axially extends beyond the distal portion of the first electrode.

A spark plug having an insulating body defining a longitudinal axis and including a base portion and an obstruction portion, a first electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the first electrode extending through the base portion of the insulating body, and a second electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the second electrode extending through the base portion and the obstruction portion of the insulating body, wherein the obstruction portion axially extends beyond the distal portion of the first electrode.

An ignition accelerator is used in conjunction with an igniter. The ignition accelerator includes a magnetic shielding conductive element and a magnetic element. The magnetic shielding conductive element has a first disposing portion and a second disposing portion. One end of the igniter is disposed inside the first disposing portion and electrically connected with the magnetic shielding conductive element. The magnetic element is disposed at the second disposing portion, and has a north-seeking pole and a south-seeking pole. The north-seeking pole is located at one side of the magnetic element near the igniter. The south-seeking pole is located at another side of the magnetic element away from the igniter. The magnetic shielding conductive element shields a magnetic force of the magnetic element in a direction toward the igniter. The invention has higher ignition efficiency.

A spark plug having a resistor disposed between a metal terminal and a center electrode so as to be electrically connected to the metal terminal and the center electrode, wherein the resistor is in contact with an inner circumferential surface of the insulator. On a cross section taken along the axial line so as to include the axial line, in a case where a plurality of points are plotted at predetermined intervals in a direction of the axial line so as to be present on a partial boundary line, within an arbitrary range in the direction of the axial line, of a boundary line between the insulator and the resistor, and a regression line is drawn by a least-squares method with use of the plurality of points, an average value of distances in a direction perpendicular to the regression line between the regression line and the partial boundary line is 0.1 to 0.3 m.

A spark plug having a resistor disposed between a metal terminal and a center electrode so as to be electrically connected to the metal terminal and the center electrode, wherein the resistor is in contact with an inner circumferential surface of the insulator. On a cross section taken along the axial line so as to include the axial line, in a case where a plurality of points are plotted at predetermined intervals in a direction of the axial line so as to be present on a partial boundary line, within an arbitrary range in the direction of the axial line, of a boundary line between the insulator and the resistor, and a regression line is drawn by a least-squares method with use of the plurality of points, an average value of distances in a direction perpendicular to the regression line between the regression line and the partial boundary line is 0.1 to 0.3 m.

A sensitivity enhancement wearable having at least one aperture possessing unique attributes so that a sensitivity enhanced region of a body extends through the aperture thereby creating increased sensitivity in the sensitivity enhanced region.

By grounding a metal first housing, radiation noise generated from the coupling circuit is shielded. Further, by enclosing the first housing in a metal second housing in a manner such that the first housing and the second housing do not come into contact with each other, and grounding the second housing by connecting the second housing to an engine block, radiation noise generated by the capacitive component between the coupling circuit and the first housing is shielded by the second housing. As a result, the influence of this noise on peripheral devices of the high frequency discharge ignition device can be suppressed.

By grounding a metal first housing, radiation noise generated from the coupling circuit is shielded. Further, by enclosing the first housing in a metal second housing in a manner such that the first housing and the second housing do not come into contact with each other, and grounding the second housing by connecting the second housing to an engine block, radiation noise generated by the capacitive component between the coupling circuit and the first housing is shielded by the second housing. As a result, the influence of this noise on peripheral devices of the high frequency discharge ignition device can be suppressed.

A spark plug includes: an insulator having an axial hole formed therein in an axial direction; a center electrode extending in the axial direction and having a rear end located within the axial hole; a metal terminal extending in the axial direction and having a front end located rearward of the rear end of the center electrode within the axial hole; a resistor arranged between the center electrode and the metal terminal within the axial hole; and a conductive seal layer that fills a space between the resistor and the center electrode in the axial. The conductive seal layer has a first layer portion located adjacent to the center electrode and a second layer portion located between the first layer portion and the resistor. The second layer portion has a thermal expansion coefficient different from and falling between those of the first layer portion and the resistor.

One example provides a spark plug having a center electrode including first material and a second material, the second material having a hardness rating greater than a hardness rating of the first material. The center electrode includes an electrode head, wherein at least a portion of the electrode head is disposed beyond an end surface of an insulative nose toward the firing end and has a cross-sectional area perpendicular to an axial centerline greater than a cross-sectional area of the end surface of the insulative nose. The center electrode has a region of first material disposed axially beyond the end surface of the insulative nose, and includes a shield element of the second material which covers exposed surfaces of the region of first material disposed beyond the end surface of the insulative nose. An electrode wire extends from the electrode head into a central bore of the insulative nose.