Spark plug and manufacturing method therefor
AssigneeNgk Spark Plug Co., Ltd.
InventorsTakahiro Suzuki, Tomoaki Kato
Life of this patent
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Abstract
Provided are a spark plug in which the occurrence of spark blowout or the like is restrained for improvement of ignition performance, and a method of manufacturing the spark plug. A ground electrode 27 of the spark plug has a protrusion 28 which faces a center electrode 5. The distal end surface of the protrusion 28 has a noble metal tip 32 provided at the center thereof and includes an annular fusion portion 33 adjacent to the periphery of the noble metal tip 32, and an annular electrode base metal surface located externally of the annular fusion portion 33. A spark discharge gap 35 is formed between the center electrode 5 and the distal end of the protrusion 28 including the noble metal tip 32.
Claims7
A spark plug comprising a center electrode extending in a direction of an axis, an insulator which holds the center electrode, a metallic shell which holds the insulator, a ground electrode whose proximal end portion is joined to a front end portion of the metallic shell and which is bent and fixed such that an inside surface of a distal end portion thereof faces a front end portion of the center electrode, and a noble metal tip joined to the inside surface of the ground electrode, a spark discharge gap being formed between the center electrode and the noble metal tip of the ground electrode,
- the spark plug being characterized in that:
- the inside surface of the ground electrode has a columnar protrusion projecting in the direction of the axis and formed of an electrode base metal of the ground electrode which contains nickel as a main component;
- the noble metal tip whose cross-sectional area is smaller than an area of a distal end surface of the protrusion is joined to the distal end surface of the protrusion, and a discharge allowance surface is a part of the distal end surface of the protrusion and is formed around at least a portion of a periphery of the noble metal tip, the discharge allowance surface is formed of the electrode base metal of the ground electrode;
- a dimension of the spark discharge gap, which is a distance between a discharge surface of the center electrode and a discharge surface of the noble metal tip of the ground electrode as measured along the direction of the axis, is 0.8 mm or greater;
- a projecting dimension of the noble metal tip of the ground electrode, which is a distance between the inside surface of the ground electrode and the discharge surface of the noble metal tip of the ground electrode as measured along the direction of the axis, is 0.5 mm or greater;
- and
- when the discharge surface of the center electrode and the discharge surface of the noble metal tip of the ground electrode are projected onto a plane orthogonal to the direction of the axis, a projected image of the discharge surface of the center electrode does not protrude from a projected image of the discharge surface of the noble metal tip of the ground electrode.
A method of manufacturing a spark plug comprising a center electrode extending in a direction of an axis, an insulator which holds the center electrode, a metallic shell which holds the insulator, a ground electrode whose proximal end portion is joined to a front end portion of the metallic shell and which is bent and fixed such that an inside surface of a distal end portion thereof faces a front end portion of the center electrode, a columnar protrusion provided at the inside surface of the ground electrode, and a noble metal tip joined to a distal end surface of the protrusion, a spark discharge gap being formed between the center electrode and the noble metal tip of the ground electrode and between the center electrode and the distal end surface of the protrusion,
- the method being characterized by comprising:
- a welding step of welding the noble metal tip to an original body of the ground electrode having substantially the form of a straight bar;
- a press working step of performing press working on the original body of the ground electrode at least in a region which encompasses the noble metal tip, from a side opposite a side from which the noble metal tip is welded, thereby forming the protrusion;
- and
- a bending step of bending the original body of the ground electrode in such a manner that the distal end surface of the protrusion including the noble metal tip faces the front end portion of the center electrode, thereby forming the spark discharge gap.
Dependencies are inferred from the claim text.