Spark Plug Discharge Member Diffusion Layer Control
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Solution Overview
Problem
Spark plugs used in internal combustion engines face challenges in wear resistance and peeling resistance under high-temperature environments due to embrittlement and decreased thermal conductivity of the diffusion layer between the discharge member and the intermediate member, leading to increased wear and peeling.
Innovation Solution
A spark plug design featuring a center electrode and ground electrode with a discharge member containing at least 45 wt.% platinum and one of nickel and rhodium, an intermediate member with a higher nickel content than the discharge member, and a diffusion layer with a thickness between 0.002 mm and 0.065 mm, optimizing the composition and structure to enhance oxidation resistance and suppress interdiffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diffusion layer thickness is increased to reduce thermal stress, then peeling resistance is improved, but embrittlement increases and wear resistance decreases
Solution Approach 1:
The patent precisely controls the diffusion layer thickness within the range of 5-20 μm to optimize the balance between peeling resistance and wear resistance. This parameter optimization ensures that the diffusion layer is thick enough to provide bonding strength and reduce thermal stress, yet thin enough to prevent excessive embrittlement and maintain wear resistance of the discharge member.
Solution Approach 2:
The patent creates a localized diffusion layer with specific compositional gradient and thickness characteristics at the interface between the discharge member and intermediate member. This localized quality control ensures that the diffusion layer provides the necessary bonding function without causing excessive embrittlement that would compromise the overall wear resistance of the spark plug components.
2Strength
If interdiffusion between the discharge member and intermediate member progresses to form a diffusion layer, then bonding strength is improved, but Kirkendall voids increase and embrittlement occurs
Solution Approach 1:
The patent optimizes the thickness of the diffusion layer to a specific range (5-20 μm) to balance bonding strength and structural integrity. By controlling the diffusion process to achieve this optimal thickness, the patent ensures sufficient interdiffusion for strong bonding while preventing excessive interdiffusion that would lead to Kirkendall void formation and embrittlement, thus maintaining structural integrity.
Solution Approach 2:
The patent replicates the optimal diffusion layer structure with controlled thickness and composition gradient. By carefully controlling the diffusion process parameters, the patent creates a reproducible diffusion layer structure that achieves the desired balance between bonding strength and resistance to embrittlement, ensuring consistent performance across production batches.
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 improves wear resistance and peeling resistance by reducing thermal stress and embrittlement, maintaining thermal conductivity, and preventing grain growth, thus extending the lifespan of the spark plug under high-temperature conditions.
Implementation Method 1
a diffusion layer formed between the discharge member and the intermediate member, suppresses peeling or falling off of the discharge member due to thermal stress between the members
Implementation Method 2
maintaining thermal conductivity
Data Source
AI summary
An electrode base material of the spark plug contains not less than 50 wt. % of Ni. A discharge member contains not less than 45 wt. % of Pt, and at least one of Ni and Rh. An intermediate member contains Pt and Ni. In the discharge member, a content of Pt is highest, and a total content of Pt, Rh, and Ni is not less than 92 wt. %. In the intermediate member, a content of one of Pt and Ni is not less than 50 wt. %, a content of Ni is higher than a content of Ni in the discharge member, and a total content of Pt, Rh, and Ni is not less than 85 wt. %. A thickness of the diffusion layer formed between the discharge member and the intermediate member is not less than 0.002 mm and not more than 0.065 mm.