# US 2014/0152169 A1 · Spark plug

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- Number: US 2014/0152169 A1
- Document ID: US20140152169A1
- Status: Published application
- Kind: A1
- Application number: 14/131,937
- Filed: 2012-05-15
- Published: 2014-06-05
- Earliest claimed: 2011-07-11
- Assignees: Ngk Spark Plug Co., Ltd.
- Inventors: Kaori Suzuki
- Web page: https://patentgrep.com/patent/US20140152169A1

## CPC

- H01T 13/20: characterised by features of the electrodes or insulation
- H01T 13/32: characterised by features of the earthed electrode
- 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)

## Abstract

A spark plug includes a center electrode a ceramic insulator provided with an axial hole, a metal shell, and a ground electrode having a facing surface that faces a leading end surface of the center electrode. An annular space is formed between an outer peripheral surface of the center electrode and an inner peripheral surface of the axial hole and is opened toward a leading end side, and when C (mm) is a distance between the outer peripheral surface of the center electrode and the inner peripheral surface of the axial hole in the opening of the annular space, C≧0.2 mm is satisfied. In a cross-section which includes the axial line and is orthogonal to the center axis of the ground electrode, a contour line of lateral surfaces of the ground electrode has a curved shape convexed outward.

## Claims

### Claim 1

A spark plug comprising:
a center electrode extending in an axial direction;
a cylindrical insulator provided with an axial hole into which the center electrode is inserted;
a cylindrical metal shell disposed on an outer periphery of the insulator; and
a ground electrode having one end fixed to a leading end of the metal shell and another end having a facing surface that faces a leading end surface of the center electrode,
wherein the spark plug has an annular space which is formed by an outer peripheral surface of the center electrode and an inner peripheral surface of the axial hole and is opened toward a leading end side in the axial direction,
wherein, when C (mm) is a distance between the outer peripheral surface of the center electrode and the inner peripheral surface of the axial hole in an opening of the annular space along a direction orthogonal to the axial line, C≧2 mm is satisfied, and
wherein, in a cross-section which includes the axial line and is orthogonal to the center axis of the ground electrode, a contour line of a lateral surface of the ground electrode, which is adjacent to the facing surface, has a curved shape which is convexed outward,
wherein a contour line of the facing surface is linearly shaped in the cross-section, and
wherein, when B (mm) is an outer diameter of the leading end surface of the center electrode, and D (mm) is a length of the contour line of the facing surface in the cross-section, D≦B is satisfied.

### Claim 2

(canceled)

### Claim 3 (depends on 1)

The spark plug according to claim 1,
wherein 0.72×B≧D is satisfied.

### Claim 4 (depends on 1)

The spark plug according to claim 1,
wherein |(D−B)/2|≦0.25 mm is satisfied.

### Claim 5 (depends on 1)

The spark plug according to claim 1,
wherein an outer peripheral surface of the metal shell includes a screw portion configured to be screwed with a fitting hole of a combustion device,
wherein the ground electrode includes a gap correspondence portion which is a portion at the leading end side of the leading end surface of the center electrode in the axial direction and at a rear end side of the facing surface of the ground electrode in the axial direction, and
wherein, when M (mm) is a screw diameter of the screw portion, and X (mm) is a width of the gap correspondence portion, M/X≧5.25 is satisfied.