Spark Plug Solid Annular Gasket Design for Stable Ignition

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Solution Overview

Problem

Conventional spark plugs with gaskets experience variations in ignition point due to large crushing deformation, leading to unstable combustion and potential gas-tightness issues, and existing solutions either fail to prevent gasket coming off or result in gas leaks.

Innovation Solution

A spark plug design featuring a solid annular gasket with a groove portion and tapered inner peripheral side, where the inside diameter is smaller than the outside diameter of the externally threaded portion, and the thickness of the outer peripheral side is greater than the inner peripheral side, minimizing deformation and preventing gasket rotation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a hollow-shaped gasket with large crushing deformation is used, then the gasket can be securely fitted, but the ignition point varies and combustion becomes unstable

Engineering Contradiction:

Improvegasket fitting securityVSAvoidignition point position

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The gasket shape is changed from hollow to solid, fundamentally altering its deformation characteristics during crushing. This parameter change reduces the variation in crushing amount, thereby stabilizing the ignition point position while maintaining secure fitting.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using a hollow gasket that deforms significantly, the invention inverts the approach by using a solid gasket with minimal deformation. This inversion of the gasket structure resolves the contradiction between secure fitting and ignition point stability.

Inventive Principle:

Principle #13The other way round (Inversion)

2Manufacturing precision

If a solid annular disk gasket is used, then the ignition point variation is suppressed, but the gasket may come off during operation

Engineering Contradiction:

Improveignition point positionVSAvoidgasket retention

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The solid annular gasket is segmented by forming pawl portions that project radially inward. These segmented structures engage with the threaded portion to prevent the gasket from coming off, while the overall solid structure maintains minimal deformation and stable ignition point.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The gasket transitions from a symmetric annular disk to an asymmetric structure with pawl portions projecting in specific directions. This asymmetry provides mechanical engagement with the threaded portion, preventing gasket removal while maintaining the solid structure's deformation advantages.

Inventive Principle:

Principle #4Asymmetry

3Reliability

If pawl portions are formed by cut bending after gasket fitting, then the gasket is prevented from coming off, but local recesses form causing gas leaks

Engineering Contradiction:

Improvegasket retentionVSAvoidgas leakage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The gasket is designed with differentiated local qualities: the main body remains solid and annular to prevent gas leakage, while specific localized pawl portions are formed to provide retention. This local differentiation resolves the contradiction between retention and gas-tightness.

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This design stabilizes the ignition point, prevents gasket coming off, and ensures gas-tightness by uniformly deforming the gasket, reducing the likelihood of gas leaks and thin-walled issues during threaded securing.

Implementation Method 1

the gasket is compressed between the gasket receiving portion and a peripheral edge portion of the opening of the threaded hole so as to be crushed, thereby sealing the gap

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 2

the thickness of the outer peripheral side is greater than the inner peripheral side, minimizing deformation and preventing gasket rotation

Methodology Applied

Scientific EffectDeformation: Deformation

Data Source

PatentEP1919047B1Spark plug for internal combustion engine and method of manufacturing the same

Publication Date: 2009.07.01 NITERRA CO LTD

Figure 1
Figure 2~3B
Figure 4A~4B

AI summary

A spark plug (1) for an internal combustion engine includes: a cylindrical insulator (2) as defined herein; a center.electrode (5) as defined herein; a cylindrical metal shell (3) as defined herein; and a ground electrode (27) as defined herein, an annular gasket receiving portion (16a) projecting radially outward being provided on a rear end side of the externally threaded portion (15) of the metal shell (3), and a metallic gasket (18) capable of abutting against the gasket receiving portion (16a) being provided on the outer periphery of the metal shell (3), wherein the gasket (18) has a solid annular shape, an inside diameter (A) of the gasket (18) is smaller than an outside diameter (D) of the externally threaded portion (15), and a groove portion (54) whose depth coincides with the direction of the axis (C1) is provided over an entire circumference of the gasket (18).