Spark Plug Insulator Bore Design for Force Distribution
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Solution Overview
Problem
Conventional spark plugs face issues with insulator breakage and reduced durability due to excessive force transmission during the fabrication process, which affects the connecting portion's longevity.
Innovation Solution
A spark plug design featuring a rod-shaped center electrode, an insulator with varying bore diameters, and a metallic terminal with a roughened surface, where the metallic terminal's Vickers hardness is between 200 Hv and 320 Hv, and specific ratios of diameters are maintained to distribute force effectively and prevent insulator breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic terminal is inserted into a through hole to press material for a connecting portion, then the connecting portion's durability is improved, but the insulator may break due to excessive force transmission
Solution Approach 1:
The insulator is designed with different bore diameters at different locations: a first bore diameter in the front end side portion and a second bore diameter (larger than the first) in the rear end side portion. This local variation in geometry allows the metallic terminal to be pressed with sufficient force to ensure good contact with the connecting portion material at the rear end, while the smaller front end bore provides structural support to prevent insulator breakage during the pressing operation.
2Reliability
If the material for the connecting portion is pressed sufficiently to improve durability, then the connecting portion's loaded life properties are improved, but the insulator breakage risk increases
Solution Approach 1:
The patent changes the geometric parameters of the insulator's through hole by defining two different bore diameters along its length. The first bore diameter (smaller) and second bore diameter (larger) create a tapered configuration that modifies the force distribution during metallic terminal insertion, enabling sufficient pressing of the connecting portion material without causing insulator breakage.
3Strength
If the first bore diameter is reduced to prevent insulator breakage, then the insulator strength is improved, but the metallic terminal may not be pressed sufficiently against the connecting portion material
Solution Approach 1:
The through hole of the insulator is segmented into two distinct portions with different bore diameters: a front end side portion with a first bore diameter and a rear end side portion with a second bore diameter. This segmentation allows each portion to serve a different function - the front end provides structural strength while the rear end enables sufficient pressing force for the metallic terminal.
Solution Approach 2:
Different sections of the through hole are given different geometric properties - the front end has a smaller bore diameter for structural support, while the rear end has a larger bore diameter for effective terminal pressing. This local differentiation resolves the contradiction between insulator strength and connecting portion durability.
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
The design reduces the likelihood of insulator breakage while maintaining the durability of the connecting portion, enhancing the spark plug's loaded life properties and reducing fabrication-related failures.
Implementation Method 1
a roughened surface portion formed at a position of the metallic terminal which corresponds to at least a part of the first portion, at least a part of the second portion and the middle portion of the insulator in the direction of the axis when the metallic terminal is inserted into the thorough hole in the insulator, the roughened surface having at least one of one or more projecting portions and one or more recess portions on an outer circumferential surface thereof
Implementation Method 2
an insulator having a through hole which extends from a front end side to a rear end side in the direction of the axis... a first portion which accommodates a front end of the metallic terminal and which has a first bore diameter of 2.9 mm or smaller; a second portion which is disposed closer to the rear end side than the first portion and which has a second bore diameter which is greater than the first bore diameter; and a middle portion which is disposed between the first portion and the second portion and a bore diameter of which increases towards the rear end side
Implementation Method 3
a Vickers hardness of a portion of the metallic terminal which is disposed in the through hole and is disposed closer to the rear end side than the roughened surface portion is 200 Hv or greater and 320 Hv or smaller
Data Source
Figure 1
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AI summary
A spark plug having an insulator that includes a first portion which accommodates a front end of the metallic terminal. A portion of the metallic terminal has a roughened surface portion with a Vickers hardness of 200 Hv or greater and 320 Hv or smaller. A first ratio of an outside diameter of the roughened surface corresponding to at least a part of the first portion of the insulator to the first bore diameter of the insulator is 0.90 or greater. A second ratio of the first bore diameter to the second bore diameter of the insulator is 0.80 or greater and 0.98 or smaller.