A method for implementation with the operation of an internal combustion engine, having an ignition plug, which is arranged on a combustion chamber of a cylinder of the internal combustion engine, wherein: in a first step, a cylinder pressure at the ignition time at the combustion chamber is detected, as well as a breakdown voltage at the ignition plug; and in a second step, a current electrode distance of the ignition electrodes, representing a current ignition electrode wear state, is determined based on the detected cylinder pressure, the detected breakdown voltage and a constant of proportionality.

A method for manufacturing a spark plug that includes preparing an assembly fitted with a cylindrical insulator, and a main metal fitting disposed on an outer periphery of the insulator; photographing the assembly by using a camera disposed on the axis while turning on a first lighting equipment disposed; photographing the assembly by using the camera while turning on a second lighting equipment; specifying a position of an outer peripheral surface of the insulator by using one of photographed images; specifying a position of an inner peripheral surface of the main metal fitting by using the other of the photographed images; and specifying a size of a clearance between the insulator and the main metal fitting by using the position of the outer peripheral surface of the insulator and the position of the inner peripheral surface of the main metal fitting.

In order to test a semiconductor spark plug, a test method comprises a step consisting of depositing water on the head of the spark plug, between the two electrodes of same, so that the water forms a water meniscus covering the semiconductor element of the head, a step consisting of applying, between the first terminal and the second terminal of the spark plug, a voltage equal to the operating voltage of the spark plug, a step consisting of identifying at least a first characteristic of electric arcs induced between the electrodes during the application of the voltage, and a step consisting of determining the operational or defective character of the spark plug according to the first characteristic of the electric arcs. This test method is particularly reliable and does not require constraining provisions in order to ensure the safety of the operators implementing the method.

In order to test a semiconductor spark plug, a test method comprises a step consisting of depositing water on the head of the spark plug, between the two electrodes of same, so that the water forms a water meniscus covering the semiconductor element of the head, a step consisting of applying, between the first terminal and the second terminal of the spark plug, a voltage equal to the operating voltage of the spark plug, a step consisting of identifying at least a first characteristic of electric arcs induced between the electrodes during the application of the voltage, and a step consisting of determining the operational or defective character of the spark plug according to the first characteristic of the electric arcs. This test method is particularly reliable and does not require constraining provisions in order to ensure the safety of the operators implementing the method.

A spark plug inspection method and a spark plug manufacturing method that enable evaluation for the position of a ground electrode of a tapered-seat-type spark plug. The spark plug inspection method includes: a contact step of screwing an external thread of a metal shell to an internal thread of a gauge so as to bring a part of a tapered portion of the metal shell into line-contact or point-contact with an inner edge of the gauge; and a determination step of determining whether or not a ground electrode is present within a predetermined range in a circumferential direction of the gauge when the tapered portion comes into line-contact or point-contact with the inner edge of the gauge in the contact step.

A spark plug inspection method and a spark plug manufacturing method that enable evaluation for the position of a ground electrode of a tapered-seat-type spark plug. The spark plug inspection method includes: a contact step of screwing an external thread of a metal shell to an internal thread of a gauge so as to bring a part of a tapered portion of the metal shell into line-contact or point-contact with an inner edge of the gauge; and a determination step of determining whether or not a ground electrode is present within a predetermined range in a circumferential direction of the gauge when the tapered portion comes into line-contact or point-contact with the inner edge of the gauge in the contact step.

A spark plug electrode wearing rate estimating method for a spark plug in which spark discharge occurs between two electrodes by application of voltage generated by an ignition coil, includes the step of estimating a wearing rate of a first electrode in one spark discharge based on a temperature of the first electrode, and a spark discharge voltage and supply energy from the ignition coil. The first electrode contains any one of Ir, Ru, W, and Ni as a main component.

A spark plug electrode wearing rate estimating method for a spark plug in which spark discharge occurs between two electrodes by application of voltage generated by an ignition coil, includes the step of estimating a wearing rate of a first electrode in one spark discharge based on a temperature of the first electrode, and a spark discharge voltage and supply energy from the ignition coil. The first electrode contains any one of Ir, Ru, W, and Ni as a main component.

An ignition device for an internal combustion engine with an ignition plug that ignites an air-fuel mixture in a combustion chamber, wherein a discharge current i provided by the ignition plug to the air-fuel mixture is controlled to be greater than a discharge current reference value ibf, which is a minimum current value at which a spark discharge blow-out phenomenon does not arise.

A method for manufacturing a spark plug including a reference standard imaging step of imaging a plurality of reference standards to obtain a plurality of reference images, each reference standard having a reference part with a predetermined known dimension; a reference standard measuring step of measuring a measured dimension or a measured number of pixels of the reference part in the plurality of reference images; a regression line deriving step of obtaining a regression line by the least squares method from: the measured dimension or the measured number of pixels of the plurality of reference standards; and the known dimensions; and a determining step of determining whether a target part in a target image is within a predetermined range based on a correction value obtained by correcting a measured dimension of a target part by using a relational expression describing the regression line.