Spark Plug Insulator Vibration Crack Prevention
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Solution Overview
Problem
The reduction in size and diameter of spark plugs leads to thinner insulators, making them prone to cracking due to vibrations, which complicates ensuring resistance to cracking.
Innovation Solution
A spark plug design featuring an insulator with a specific axial bore configuration, including a cylindrical first portion, a second portion with a larger diameter, and a third portion with a rear end located distant from the rear end of the insulator, along with a metal terminal structure that reduces impact on the insulator by increasing the distance from the fulcrum of vibration to the point of impact, thereby minimizing the applied impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the spark plug diameter and size are reduced, then the spark plug becomes more compact and suitable for modern engines, but the insulator becomes thinner and more prone to cracking due to vibration
Solution Approach 1:
The insulator is segmented into multiple cylindrical portions (first, second, and third portions) with different diameters along the axial direction. This segmentation allows each portion to serve a specific function: the first portion provides structural support, the second portion accommodates the metal terminal, and the third portion provides a transition zone that reduces stress concentration, thereby preventing cracking while maintaining a compact overall size.
Solution Approach 2:
Different portions of the insulator are designed with different local qualities - specifically different diameters and wall thicknesses. The first portion has a smaller diameter, the second portion has a larger diameter to accommodate the metal terminal, and the third portion has an intermediate diameter. This local variation in geometry allows the insulator to maintain strength where needed while reducing overall size, preventing cracking in thin-walled regions.
2Volume of moving object
If the insulator wall thickness is reduced to decrease spark plug size, then the spark plug becomes more compact, but the insulator becomes more susceptible to impact from metal terminal vibration
Solution Approach 1:
The third portion of the insulator acts as a pre-designed cushioning element between the metal terminal and the rear end of the insulator. By positioning this portion with intermediate diameter and appropriate wall thickness, the design anticipates and absorbs the impact forces generated during metal terminal vibration, preventing these forces from reaching the rear end of the insulator where they could cause cracking.
Solution Approach 2:
The insulator design employs parameter changes in the form of varying diameter and wall thickness across different axial portions. The first portion has diameter D1 and wall thickness T1, the second portion has diameter D2 and wall thickness T2, and the third portion has diameter D3 and wall thickness T3, where D1 < D2, D3 < D2, and T3 ≤ 6.1mm. These parameter variations optimize the balance between compactness and impact resistance.
3Ease of manufacture
If the metal terminal is positioned closer to the rear end of the insulator to simplify structure, then manufacturing becomes easier, but the impact from vibration is transmitted more directly to the insulator rear end
Solution Approach 1:
The third portion of the insulator serves as an intermediary element between the metal terminal and the rear end of the insulator. This intermediate structure with its specific diameter and wall thickness characteristics acts as a buffer zone that decouples the direct transmission of vibration impact, allowing the metal terminal to be positioned effectively while protecting the insulator rear end from harmful forces.
Data Source
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AI summary
A spark plug with an insulator (10) that includes: a first portion (10A) having a first inner diameter (Ra) with a front end of a trunk portion (43) of a metal terminal (40) disposed therein; a second portion (10B) having a second inner diameter (Rb) larger than the first inner diameter (Ra), and including a portion 1 mm or more forward of a rear end of the insulator (10); and a third portion (10C) disposed between the first portion (10A) and the second portion (10B) and having a third inner diameter (Rc) larger than the first inner diameter (Ra) and smaller than the second inner diameter (Rb). The trunk portion (43) of the metal terminal (40) includes: a front trunk portion (43A) and a rear trunk portion (43C) with a front end of the rear trunk portion (43C) positioned forward of a rear end of the third portion (10C) of the insulator (10), the rear trunk portion (43C) having an outer diameter (Re) larger than the outer diameter (Rd) of the front trunk portion (43A).