# US 11,309,689 B2 · Spark plug and method for manufacturing spark plug

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- Number: US 11,309,689 B2
- Document ID: US11309689B2
- Status: Granted
- Kind: B2
- Application number: 17/405,189
- Filed: 2021-08-18
- Published: 2022-02-24
- Granted: 2022-04-19
- Earliest claimed: 2020-08-19
- Assignees: Ngk Spark Plug Co., Ltd.
- Applicants: Ngk Spark Plug Co., Ltd.
- Inventors: Junji Kimura
- Web page: https://patentgrep.com/patent/US11309689B2

## CPC

- H01T 13/58: Testing (testing characteristics of the spark in internal-combustion engine ignition F02P17/12)
- H01T 13/02: Details
- H01T 21/02: of sparking plugs
- B23K 26/359: by providing a line or line pattern, e.g. a dotted break initiation line
- H01T: SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES (overvoltage protection circuits H02H)
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM

## Abstract

A spark plug including an insulator and a metallic member such as a metallic shell. In the spark plug, a mark such as a two-dimensional code is provided on the surface of at least one of the insulator and the metallic member. Also, a protective layer covers the mark. The protective layer is optically transparent and contains a fluorescent substance.

## Claims

### Claim 1

A spark plug comprising:
an insulator;
a metallic member;
a mark provided on a surface of at least one of the insulator and the metallic member; and
a protective layer which covers the mark,
wherein the protective layer is optically transparent and contains a fluorescent substance.

### Claim 2

A method for manufacturing a spark plug including an insulator and a metallic member and having a mark on a surface of at least one of the insulator and the metallic member, the method comprising:
a mark forming step of forming the mark; and
a protective layer forming step of forming a protective layer containing a fluorescent substance which covers the mark.

### Claim 3 (depends on 2)

The method for manufacturing a spark plug as claimed in claim 2, further comprising a checking step of checking, after the protective layer forming step, a state of the protective layer by irradiating the mark with light.

### Claim 4 (depends on 3)

The method for manufacturing a spark plug as claimed in claim 3, wherein, in the checking step, the state of the protective layer is checked using, as a reference value, an amount of light emitted when a mark covered with a protective layer having a predetermined thickness is irradiated with the light, measuring an amount of light emitted when the spark plug to be checked is irradiated with the light, and comparing the measured light emission amount with the reference value.