Spark Plug Ground Electrode Bilayer Structure for Heat Sinking
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Solution Overview
Problem
Conventional spark plugs experience unstable ignitability due to air-fuel mixture disturbance and poor durability caused by heat sinking issues, particularly at high speeds, due to the design of the ground electrode, which affects the spark discharge gap and leads to erosion and deformation.
Innovation Solution
A spark plug design featuring a ground electrode with a two-layer structure, where the outer layer is made of nickel alloy for oxidation resistance and the inner layer is made of pure copper or copper alloy for better thermal conductivity, with a specific cross-sectional area ratio and geometry to ensure efficient air-fuel mixture flow and heat dissipation, reducing erosion and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ground electrode is formed with a two-layer structure (outer nickel alloy layer for oxidation resistance, inner copper layer for thermal conductivity), then heat sinking ability is improved, but deformation (spring back) occurs due to difference in thermal expansion coefficients
Solution Approach 1:
The patent applies parameter changes by carefully controlling the thickness ratio between the outer nickel alloy layer and inner copper layer. The outer layer thickness is set to 0.05-0.5mm and the inner layer thickness to 0.05-1.0mm, with specific ratio ranges that optimize both heat sinking performance and minimize thermal expansion differential effects, thereby reducing spring back deformation while maintaining effective heat dissipation
Solution Approach 2:
The patent uses composite materials by combining nickel alloy (outer layer) and copper (inner layer) in a two-layer structure. This composite approach leverages the oxidation resistance of nickel alloy and the superior thermal conductivity of copper, achieving both goals while managing the inherent compatibility issues through controlled layer thicknesses
2Productivity
If the ground electrode cross-sectional area is reduced to improve air-fuel mixture flow, then ignitability is improved, but heat sinking ability deteriorates
Solution Approach 1:
The patent applies local quality by creating a ground electrode with non-uniform cross-sectional area along its length. The front-end portion (near the spark discharge gap) has a smaller cross-sectional area to facilitate air-fuel mixture flow and improve ignitability, while the rear portion has a larger cross-sectional area to maintain effective heat sinking ability. This gradient structure optimizes both local and global performance
3Temperature
If the ground electrode is formed with a rectangular shape in cross-section, then heat sinking ability is improved, but air-fuel mixture flow to the spark discharge gap is disturbed
Solution Approach 1:
The patent applies dynamics by transitioning from a static uniform rectangular cross-section to a dynamic gradient structure. The cross-sectional area varies continuously or in steps along the length of the ground electrode, creating an optimized flow path for air-fuel mixture while maintaining adequate heat sinking surface area. This dynamic geometry adapts to different functional requirements 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 enhances ignitability by ensuring consistent air-fuel mixture flow to the spark discharge gap, improves durability by effective heat sinking, and prevents deformation and erosion of the ground electrode, thereby extending the spark plug's lifespan.
Implementation Method 1
an inner layer made of pure copper or a copper alloy having a better thermal conductivity than that of the outer layer
Implementation Method 2
an outer layer made of a nickel alloy...which is excellent in oxidation resistance
Data Source
AI summary
A spark plug 100 comprised of a metal shell 1, an insulator 2, a center electrode 3 and a ground electrode 4. A rear-end face of the ground electrode 4 is welded to a front-end face of the metal shell 1, and a bent portion 5 located at the intermediated position in the longitudinal direction is bent toward the center of the spark plug 100. The ground electrode 4 assumes a circular-shape with a diameter of 2 mm or less whereby an inflow of an air-fuel mixture is not disturbed even when the air-fuel mixture directly flows into a back face of the ground electrode 4. The ground electrode 4 is comprised of an outer layer 4A made of a nickel alloy and an inner layer 4B made of pure copper with an excellent thermal conductivity, in which a ratio of a cross-sectional area of the inner layer 4B to the entire cross-sectional area of the ground electrode 4 is 10% or more to 35% or less. Thus, the spark plug 100 which is excellent in heat sinking ability and can prevent a spring back phenomenon due to a difference in a coefficient of thermal expansion.