Spark Plug Insulator Segmentation for Heat Conduction
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Solution Overview
Problem
Conventional spark plugs experience reduced anti-fouling performance and heat conduction issues due to carbon deposition, leading to flashover and irregular spark discharges, despite extensions and double tapered designs.
Innovation Solution
A spark plug design featuring a metal shell with a convex inner portion and an insulator with double tapered shapes, ensuring efficient heat transfer and extended insulation distance, along with specific dimensions for the spark discharge gap and inner diameters to prevent flashover and maintain stable combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulator nose is extended to improve anti-fouling performance, then the resistance to carbon deposition is improved, but the heat conduction from insulator to metal shell deteriorates
Solution Approach 1:
The insulator is divided into multiple sections with different diameters: a large-diameter section adjacent to the metal shell for heat conduction, and a small-diameter insulator nose section for extended anti-fouling protection. This segmentation allows each section to optimize its function independently.
Solution Approach 2:
Different sections of the insulator have different local properties: the section adjacent to the metal shell has a larger diameter to ensure good thermal contact and heat conduction, while the insulator nose has a smaller diameter to extend the protected area against carbon deposition. Each local region is optimized for its specific function.
2Reliability
If the insulator nose is extended further, then the anti-fouling performance is improved, but the risk of flashover to the metal shell increases
Solution Approach 1:
The insulator is segmented into different diameter sections, creating a stepped profile that extends the insulation path. The small-diameter insulator nose section increases the distance carbon must travel to cause flashover to the metal shell, while the large-diameter base section ensures proper heat conduction.
Solution Approach 2:
The insulator profile changes in the radial dimension with different diameter sections, creating a stepped structure. This dimensional variation allows the insulator nose to extend further into the combustion chamber while maintaining thermal contact at the base, effectively increasing the flashover path length without compromising heat conduction.
3Reliability
If the gap between metal shell and insulator is reduced to prevent unburnt gas intrusion, then the sealing performance is improved, but the heat conduction path is shortened
Solution Approach 1:
The insulator is segmented with a large-diameter base section that maintains adequate gap distance for heat conduction, while the small-diameter nose section provides sealing protection. This segmentation allows the gap to be optimized for both sealing and thermal functions at different locations.
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 significantly improves anti-fouling performance and heat conduction, preventing flashover and ensuring stable combustion by maintaining sufficient heat transfer and insulation distance, while preventing side sparks and maintaining withstand voltage performance.
Implementation Method 1
heat is not smoothly transferred from the insulator to the metal shell because the length of a portion of the insulator adjacent to the metal shell and disposed at a front end side with respect to the plate packing is necessary to be reduced. Thus, heat conduction of the insulator is likely to be deteriorated.
Implementation Method 2
a center electrode inserted in the axial bore, a metal shell disposed on an outer circumference of the insulator and a ground electrode provided at a front end face of the metal shell and forming a spark discharge gap with the center electrode
Data Source
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AI summary
To improve heat conduction and anti-fouling performance of a spark plug used for combustion engines. A spark plug 1 includes an insulator 2, a metal shell 3, a center electrode 5 and a ground electrode 27. A spark discharge gap 33 is formed between a front end portion 28 of the center electrode 5 and the ground electrode 27. The metal shell 3 has a through hole 29 therein and a metal convex portion 21 inwardly radially projecting in the through hole 29. The metal convex portion 21 includes a convex rearward face 30, a convex inner circumferential face 31 and a convex forward face 32. The through hole 29 has an inner diameter A (mm) at a front end side inner circumferential face 40, which is located at the front end side with respect to the convex forward face 32. The insulator 2 is inserted in the through hole 29 and has a first insulator taper portion 14, a second insulator taper portion 36 and a base 37 between the taper portions. The present invention satisfies the following representations: G ≤ (A-B)/2; A ≥ 7.3; and 2 ≤ XX ≤ 4, where "B"(mm)is an outer diameter of a border K between an insulator front end portion 38 and the second insulator taper portion 36, where "G"(mm) is a distance of a spark discharge gap 33, and where "XX" (mm) is a length from a very-end portion FF of the convex inner circumferential face 31 to the border K in the axial C1 direction.