Spark plug

Abstract

Provided is a spark plug with which depletion of the base material of a grounding electrode can be suppressed, and abnormal combustion can be suppressed. A spark plug 100 comprises: an insulator 10; a main metal fitting 50 covering the outer periphery of the insulator 10; a center electrode 20 which is arranged within a shaft hole 12 of the insulator 10 and a distal end 22a of which is exposed from a distal end section 10a of the insulator 10; and a grounding electrode 30 which has a fixed end 31 fixed to the main metal fitting 50 and a free end 32 spaced apart at a predetermined distance SG from the center electrode 20, and which is provided with an inside surface 30c facing the center electrode 20 and insulator 10. The spark plug is provided with a covering section 80 formed of a noble metal or noble metal alloy and covering at least a region spanning from a first crossing line section including an intersection between the grounding electrode 30 and a virtual line extending from an outer periphery of a center electrode base material 21 on the fixed end side to the grounding electrode 30, to a second crossing line section at which a virtual plane parallel to an end surface of the distal end 22a passing through a midpoint of the predetermined distance intersects with the grounding electrode 30.

Description

technical field [0001] The present invention relates to a spark plug used in an internal combustion engine for igniting an air-fuel mixture. Background technique [0002] Conventionally, in order to improve ignitability and flame propagation, various techniques have been proposed to focus on the shape of the ground electrode in the spark plug or to suppress wear of the electrode in the spark plug (for example, Patent Document 1, Patent Document 2). [0003] prior art literature [0004] patent documents [0005] Patent Document 1: Japanese Patent Laid-Open No. 2008-204882 [0006] Patent Document 2: Japanese Patent Laid-Open No. 2007-265842 [0007] However, in recent years, in order to improve the fuel economy performance of the vehicle, and in order to adapt to the increasingly strict exhaust gas limit value, as the air-fuel ratio when the vehicle is running, there is a tendency to use an air-fuel ratio in a lean region that is smaller than the theoretical air-fuel rati...

AI Technical Summary

Problems solved by technology

[0008] On the other hand, the increase in the size of the spark or the prolongation of the energization time will easily lead to the jet of sparks. As the frequency of exposure to the jet of sparks increases, the consumption of the base material of the ground electrode will increase.

As a result, problems such as misfire or breakage of the ground electrode may occur due to peeling of the noble metal tip joined to the ground electrode.

In particular, there is a problem that the wear of the root portion of the ground electrode causes breakage of the ground electrode, and the performance as a spark plug cannot be exhibited.

On the other hand, in order to protect the ground electrode, when the ground electrode is simply covered with a noble metal or the like, there is a problem that abnormal combustion is likely to occur.

In the prior art, these problems have not been fully considered

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