An ignition control apparatus applied to an internal combustion engine including a spark plug includes an in-cylinder pressure acquisition section, a frequency signal transmitting section which transmits a frequency signal having a predetermined frequency to a switching element, and a weak discharge generating section which causes the frequency signal to be transmitted during an intake stroke and controls the frequency signal such that a weak discharge is generated at the spark plug a plurality of times. The weak discharge generating section controls the frequency signal so as to cause a duty ratio of the switching element to be changed in accordance with the in-cylinder pressure, such that the frequency of generating weak discharges during a time period in which the frequency signal is transmitted becomes higher than a predetermined frequency.

An ignition control apparatus applied to an internal combustion engine including a spark plug includes an in-cylinder pressure acquisition section, a frequency signal transmitting section which transmits a frequency signal having a predetermined frequency to a switching element, and a weak discharge generating section which causes the frequency signal to be transmitted during an intake stroke and controls the frequency signal such that a weak discharge is generated at the spark plug a plurality of times. The weak discharge generating section controls the frequency signal so as to cause a duty ratio of the switching element to be changed in accordance with the in-cylinder pressure, such that the frequency of generating weak discharges during a time period in which the frequency signal is transmitted becomes higher than a predetermined frequency.

A spark plug enabling suppression of reduction in the strength of an insulator. In the spark plug, a rear end portion of an engagement portion formed on an outer peripheral surface of a tubular insulator extending along an axial line from a front side to a rear side, is engaged with a to-be-engaged portion of a tubular metal shell disposed on the outer peripheral surface of the insulator. The insulator is made from ceramic such as alumina. On at least a part of the outer peripheral surface of the insulator, a projected and recessed portion is formed on the front side relative to the engagement portion so as to helically extend in a circumferential direction of the insulator.

An ignition apparatus for an internal combustion engine includes a center electrode, a ground electrode, an insulator, a housing, and an insulator protective wall portion. The ground electrode is disposed such that a discharge gap is formed between the ground electrode and the center electrode. The insulator holds the center electrode on an inner side of the insulator. The housing holds the insulator on an inner side of the housing. The insulator protective wall portion is arranged to surround an outer circumference side of a distal end portion of the insulator. A distal end of the insulator protective wall portion is positioned further towards a distal end side than a distal end of the insulator is and further towards a proximal end side than a distal end of the center electrode is. The insulator protective wall portion includes an inward protruding portion that protrudes towards a side surface of the center electrode.

A spark plug for internal combustion engines is provided which includes a porcelain insulator which is disposed inside a housing and extends outside a front end of the porcelain insulator. An annular ground electrode is secured to a front end portion of the housing. A pocket is created between a nose of the porcelain insulator and the housing. The housing has formed therein a plurality of vent holes which are located outside the ground electrode in a radial direction of the housing and communicate between the pocket and a combustion chamber of the engine. The vent holes include a first vent hole and a second vent hole which are different in opening area from each other, thereby enhancing scavenging of the pocket to ensure the stability of operation of the spark plug.

A spark plug enabling suppression of reduction in the strength of an insulator. In the spark plug, a rear end portion of an engagement portion formed on an outer peripheral surface of a tubular insulator extending along an axial line from a front side to a rear side, is engaged with a to-be-engaged portion of a tubular metal shell disposed on the outer peripheral surface of the insulator. The insulator is made from ceramic such as alumina. On at least a part of the outer peripheral surface of the insulator, a projected and recessed portion is formed on the front side relative to the engagement portion so as to helically extend in a circumferential direction of the insulator.

A spark plug is described as including an insulator which is situated in a spark plug housing and which has a longitudinal axis and an opening along the longitudinal axis. Furthermore, a center electrode is situated in the opening of the insulator. Furthermore, at least one ground electrode is provided at the spark plug housing. The insulator has a first insulator section and a second insulator section, the first insulator section extending in the direction of the longitudinal axis over a first insulator section length having a first inner diameter. The second insulator section extends in the direction of the longitudinal axis over a second insulator section length having a second inner diameter. Here, the first inner diameter is smaller than the second inner diameter, the first insulator section merging directly into the second insulator section. The center electrode has a center electrode section which extends in the direction of the longitudinal axis over a center electrode section length having a center electrode outer diameter at least over the entire insulator section length of the first insulator section and of the second insulator section.

Provided is a spark plug capable of ensuring fouling resistance with a simple configuration. An insulator includes a step portion formed on an outer circumferential surface thereof. A center electrode is arranged in an axial hole of the insulator. A cylindrical metal shell having a shelf portion formed on an inner circumferential surface thereof is arranged radially outside the insulator. The insulator further includes a front end portion located frontward of the step portion. An outer circumferential surface of the front end portion has an arithmetic average roughness of 0.5 m or smaller in a circumferential direction. A recess is formed with a depth of 3 to 20 m in at least part of an end surface and the outer circumferential surface of the front end portion so as to extend from the front toward the rear.

A spark plug is disclosed that includes at least one bore extending through a shell of the spark plug in order to form a passageway between an annular volume around the spark plug insulator nose and a pre-chamber volume of a pre-chamber device, thus directing a purge of exhaust gases trapped in the annular volume to a space formed by the exterior of the spark plug body and the interior of the pre-chamber device.

A spark plug includes an insulative sleeve. A glaze coating is disposed on an exterior surface of the insulative sleeve. The glaze coating includes a boric acid, a borosilicate glass, a barium borate glass, a phosphorous glass, a silicate glass, or a combination thereof. The glasses are independently modified with a modifier selected from the group consisting of alkali group metals, alkali earth group metals, aluminum, silicon, a halogen, or a combination thereof. The glaze coating has a softening point between about 650 C. and about 1100 C.