Abstract: 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.

Abstract: 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.

Abstract: A spark plug includes an insulator; a center electrode; a metal shell; and a ground electrode whose base end is fixed to the metal shell. A distal end of the ground electrode includes a first surface facing the center electrode, a second surface facing a side opposite to the first surface, and an inclined surface that is inclined with respect to the second surface. A noble metal tip is partially buried in the inclined surface. A width of the inclined surface is larger than that of the noble metal tip. In this spark plug, A B is satisfied, where A is a distance from a distal end of the ground electrode to a proximal-end-side end portion of the inclined surface and B is a distance from the distal end of the ground electrode to a proximal-end-side end portion of the noble metal tip.

Abstract: A spark plug includes an insulator; a center electrode; a metal shell; and a ground electrode whose base end is fixed to the metal shell. A distal end of the ground electrode includes a first surface facing the center electrode, a second surface facing a side opposite to the first surface, and an inclined surface that is inclined with respect to the second surface. A noble metal tip is partially buried in the inclined surface. A width of the inclined surface is larger than that of the noble metal tip. In this spark plug, A B is satisfied, where A is a distance from a distal end of the ground electrode to a proximal-end-side end portion of the inclined surface and B is a distance from the distal end of the ground electrode to a proximal-end-side end portion of the noble metal tip.