Spark Plug Ground Electrode Composite Structure
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Solution Overview
Problem
Spark plugs face challenges in maintaining performance under high temperatures due to increased temperature of the ground electrode, leading to oxidation and cracking issues, especially with high Ni-based alloys used for improved thermal conductivity.
Innovation Solution
A spark plug design featuring a ground electrode with a core portion made from high thermal conductivity material and an outer layer composed of a specific alloy with high Ni content, optimized with Y, rare earth elements, Al, Si, Cr, Mn, Ti, and C, to enhance mechanical strength and prevent oxidation and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the ground electrode is made thinner for miniaturization, then the spark plug size is reduced, but the heat conduction capability deteriorates causing ground electrode temperature increase
Solution Approach 1:
The ground electrode is constructed as a composite structure with a core portion made of high thermal conductivity material (such as copper or copper alloy) and an outer layer made of electrode material (such as Ni-based alloy). This composite structure enables the thin ground electrode to maintain excellent heat conduction through the high thermal conductivity core while preserving the functional properties of the electrode material outer layer.
2Temperature
If high Ni-based alloy is used to improve thermal conductivity, then heat conduction is enhanced, but oxidation resistance deteriorates leading to grain boundary oxidation and cracking
Solution Approach 1:
The ground electrode combines a core portion made of high thermal conductivity material (copper or copper alloy) with an outer layer made of electrode material (Ni-based alloy). This composite structure allows the core to provide excellent heat conduction while the outer layer maintains oxidation resistance, thereby resolving the contradiction between thermal conductivity and oxidation resistance.
3Temperature
If the outer layer thickness is reduced to 0.5mm or less for improved heat conduction, then thermal performance is enhanced, but oxidation and cracking resistance deteriorates
Solution Approach 1:
The ground electrode employs a composite structure where the outer layer (0.5mm or less in thickness) is made of electrode material and the core portion is made of high thermal conductivity material. This allows the thin outer layer to achieve excellent heat conduction while the specific composition of the electrode material outer layer (containing Ni: 96 mass% or more, Si: 0.5-1.5 mass%, and specific amounts of Al, Cr, Mn, Ti, and rare earth elements) provides sufficient oxidation and cracking resistance.
Solution Approach 2:
The invention optimizes the chemical composition parameters of the electrode material outer layer, specifically setting Ni content at 96 mass% or more, Si content at 0.5-1.5 mass%, and controlling the content of Al, Cr, Mn, Ti, and rare earth elements within specific ranges. These parameter changes enhance both the heat conduction efficiency and the resistance to oxidation and cracking in the thin outer layer.
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 effectively suppresses cracking and corrosion in the outer layer, maintaining thermal conductivity while preventing grain boundary oxidation and foreign material formation, thus improving the spark plug's durability and performance.
Implementation Method 1
the core portion is formed from a material having higher thermal conductivity than that of the outer layer
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
AI summary
An object of the invention is to provide a spark plug capable of suppressing the occurrence of cracking with a grain boundary oxidized in an outer layer as the starting point under a cold and/or hot environment while decreasing temperature increase of a ground electrode. A spark plug of the invention including a center electrode and a ground electrode having a gap between the center electrode and the ground electrode in which the ground electrode has at least a core portion and an outer layer covering the core portion, and the core portion is formed from a material having higher thermal conductivity than that of the outer layer, wherein at least a portion in which thickness of the outer layer is 0.5 mm or less exists at a cross-section perpendicular to a direction in which the ground electrode is extended, and the composition of the electrode material forming the outer layer is as follows: Ni is 96 mass% or more, total of at least one kind selected from a group consisting of Y and rare earth elements is 0.05 mass% or more, Al is 0.5 mass% or less, and Si is 0.5 mass% or more and 1.5 mass% or less (here, the total of Ni, Y, rare earth elements, Al, Si does not exceed 100 mass%).