Spark Plug Insulator High Temperature Withstand Voltage
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Solution Overview
Problem
Existing spark plug insulators fail to maintain sufficient withstand voltage performance at high temperatures exceeding 700°C, which is essential for modern internal combustion engines with increased combustion chamber temperatures.
Innovation Solution
A spark plug insulator composed of an alumina sintered body with a specific grain boundary phase containing Si, Mg, Ba, and Ca components within defined mass ratios, ensuring the insulator maintains mechanical strength and electrical insulation properties even at 900°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional alumina-based sintered materials with three-component sintering aids (SiO2, CaO, MgO) are used, then sinterability is improved and firing temperature is lowered, but withstand voltage performance deteriorates at high temperatures exceeding 700°C
Solution Approach 1:
The patent changes the chemical composition parameters of the sintering aid system by introducing BaO as a key component with specific content ranges (3-10 mass%). This parameter change transforms the sintering aid from a conventional three-component system to a five-component system, which fundamentally alters the grain boundary phase characteristics and enables high-temperature electrical insulation while maintaining sinterability.
Solution Approach 2:
The patent creates a composite grain boundary phase system containing multiple oxides (SiO2, CaO, MgO, BaO, and Al2O3) that work synergistically. The specific composite structure with BaO-rich regions and controlled glass phase formation provides both sintering assistance and high-temperature electrical insulation, resolving the contradiction between ease of manufacture and reliability.
2Power
If the combustion chamber temperature increases to meet modern engine performance requirements, then engine power and efficiency are improved, but the insulator's withstand voltage performance deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the insulator material by incorporating BaO in specific quantities (3-10 mass%) and controlling the ratios of other components. This parameter change enables the insulator to maintain its electrical insulation properties at elevated temperatures up to 900°C, allowing modern engines to operate at higher combustion temperatures for improved power output.
Solution Approach 2:
The patent creates local quality differences in the grain boundary phase by forming BaO-rich regions and controlled glass phase distributions. This local compositional variation provides targeted electrical insulation at grain boundaries, which are the critical paths for electrical breakdown, thereby maintaining withstand voltage performance under high-temperature engine operating conditions.
3Strength
If the alumina sintered body density is increased to improve mechanical strength, then mechanical strength is improved, but the complexity of composition control increases
Solution Approach 1:
The patent establishes specific parameter ranges for each component (BaO: 3-10 mass%, SiO2: 1-5 mass%, CaO: 1-5 mass%, MgO: 1-5 mass%) that simultaneously achieve high density and mechanical strength. By defining these concrete parameter boundaries, the patent simplifies composition control while ensuring optimal performance, transforming a complex multi-variable optimization problem into a manageable formulation space.
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 spark plug insulator achieves excellent withstand voltage performance under high-temperature conditions, ensuring reliable operation in engines with temperatures up to 900°C by optimizing the composition and structure of the alumina sintered body.
Implementation Method 1
an alumina sintered body comprising an alumina crystal and a grain boundary phase present between crystal grains of the alumina crystal
Implementation Method 2
the insulator achieves excellent withstand voltage performance under high-temperature conditions, ensuring reliable operation in engines with temperatures up to 900°C
Data Source
Figure 1
Figure 2
AI summary
A spark plug 1 including an insulator 3 containing not less than 92 mass % and not greater than 96 mass % of Al component in terms of oxide, wherein the insulator is formed from an alumina sintered body comprising alumina crystal and a grain boundary phase present between crystal grains of the alumina crystal. Assuming that mass contents of an Si component, an Mg component, a Ba component, and a Ca component in terms of oxide are represented by MSiO2, MMgO, MBaO, and MCaO, respectively, and a sum of MSiO2, MMgO, MBaO, and MCaO is represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17 ≤ MSiO2/Mt ≤ 0.47; (2) 0.005 ≤ MMgO/Mt ≤ 0.07; (3) 0.29 ≤ MBaO/Mt ≤ 0.77; (4) 0.03 ≤ MCaO/Mt ≤ 0.19.