Spark Plug Insulator Pore Control for High Withstand Voltage
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Solution Overview
Problem
The miniaturization of spark plugs for internal-combustion engines poses a challenge in maintaining high withstand voltage due to the thinning of insulators and reduction in diameter, which increases the likelihood of dielectric breakdown from giant pores or densely packed small pores.
Innovation Solution
A spark plug design with an insulator that excludes giant pores and aggregate pore groups occupying over 40% of the judgment area, combined with a manufacturing method involving slurry defoaming and the use of alumina powder with an average particle size of 1.0µm or less to prevent air bubbles from forming pores, ensuring a dense and reliable insulator structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the insulator is made thin and the diameter is reduced to miniaturize the spark plug, then the mounting space is reduced, but the likelihood of dielectric breakdown increases and withstand voltage decreases
Solution Approach 1:
The patent applies parameter changes by strictly controlling the pore size distribution in the insulator material. It specifies that pores with a maximum diameter of 15μm or more must occupy 4% or less of the total volume, and pores with a maximum diameter of 5μm or more must occupy 1% or less. This quantitative control of pore parameters enables the insulator to maintain high withstand voltage even when miniaturized, resolving the contradiction between reduced size and maintained reliability.
2Length of stationary object
If the insulator thickness is reduced to enable miniaturization, then the spark plug diameter is reduced, but the dielectric breakdown resistance decreases
Solution Approach 1:
The patent changes the pore size parameters to resolve the contradiction. By limiting large pores (≥15μm) to occupy ≤4% of volume and medium pores (≥5μm) to occupy ≤1% of volume, the insulator maintains dielectric strength even with reduced thickness. This parameter control prevents dielectric breakdown while enabling thinner insulator design.
Solution Approach 2:
The patent applies local quality by creating a non-uniform pore distribution pattern. The insulator has a controlled pore structure where large pores are minimized and medium pores are also restricted, creating a locally optimized structure that provides enhanced dielectric resistance in critical areas while maintaining overall miniaturization.
3Ease of manufacture
If small pores are densely present in the insulator, then the manufacturing process allows it, but dielectric breakdown is likely to occur from these dense pores
Solution Approach 1:
The patent changes the pore size parameters to resolve this contradiction. Instead of allowing dense small pores, it specifically limits medium-sized pores (5μm or more) to occupy only 1% or less of the total volume. This parameter restriction prevents the formation of dense pore groups that could initiate dielectric breakdown, while still permitting a controlled pore structure that is manufacturable.
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 solution effectively prevents dielectric breakdown, allowing the spark plug to maintain high withstand voltage even under high electrical fields, with the insulator capable of withstanding a spark discharge waveform voltage of up to 36kV without failure.
Implementation Method 1
a sintered body obtained by sintering the press-molded body
Implementation Method 2
the likelihood of causing a dielectric breakdown generated between the metal shell and a center electrode increases when the insulator is made thin and the diameter is reduced
Data Source
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AI summary
The present invention provides a highly reliable spark plug used for an internal-combustion engine and including an insulator with a high withstand voltage, and a method for manufacturing the same. Namely, it provides a spark plug containing a cylindrical metal shell having an insulator holding hole, a cylindrical insulator including an axial hole therein which extends in an axial direction, and engaging with said insulator holding hole of said metal shell, and a center electrode held in said axial hole of said insulator, wherein said insulator has a texture in which one or more pores exposed in a judgment area with 50µm in diameter occupy 40% or less of said judgment area at any locations in an observation area, in the case where a predetermined mirror-finishing section of an enclosed portion surrounded by said metal shell is used as said observation area to observe pores exposed in said observation.