Spark plug for e.g. or engine combustion engine of automotive vehicles, includes iridium alloy firing tip made of rod-like iridium alloy that is connected to portion of the center electrode and the ground electrode

摘要

A spark plug comprises center electrode, insulator, insulator housing, and ground electrode. The ground electrode has one end portion connected to the housing and other end portion opposed to the center electrode via a discharge gap. An iridium alloy-firing tip made of a rod-like iridium alloy is connected to a portion of at least one of the center electrode and the ground electrode facing to the discharge gap. A spark plug comprises center electrode (30), insulator holding the center electrode, housing holding and fixing the insulator, and ground electrode having one end portion (31) connected to the housing and the other end portion opposed to the center electrode via a discharge gap. An iridium (Ir) alloy firing tip (50) made of a rod-like Ir alloy is connected to a portion of the center electrode and the ground electrode facing to the discharge gap. The cross-sectional area of Ir alloy firing tip taken along a plane perpendicular to an axis of the iridium alloy-firing tip has an out-of-round configuration. When the firing tip is assumed that a circumscribed circle has a largest diameter A among virtual circles each contacting the portions of a visible outline of the cross- sectional area and an inscribed circle has a largest diameter B among inscribed circles each being coaxial with the circumscribed circle, a ratio of the diameter B to the diameter A (B/A) is 0.8-1. The visible outline of the cross-sectional area is constituted by a serial joint of at least 7 straight or curved line elements, and the angle between each line element and adjacent line element is 125-235 degrees. An Independent claim is also included for a method for manufacturing a spark plug comprising configuring the cross-sectional area of the Ir alloy firing tip in such a manner that the visible outline is constituted by a serial joint of at least 7 straight or curved line elements and an angle between each line element and an adjacent line element is 125-235 degrees, and welding an entire circumferential surface of the Ir alloy firing tip by laser welding to the portion of the center electrode and the ground electrode facing to the discharge gap.