Spark Plug Tip with Ni-Rich Front Layer for Erosion Resistance
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Solution Overview
Problem
Spark plugs used in direct-injection gasoline engines experience abnormal erosion at the side surfaces of tips made from Pt-Rh alloys due to high oxygen concentration and temperature fluctuations, leading to reduced durability.
Innovation Solution
A spark plug design featuring a tip with a front surface layer containing at least 8 mass% Ni and a thickness of 2 µm or more on the outer peripheral surface, which reduces abnormal erosion by forming a Ni oxide film that stabilizes the Rh oxide and prevents peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Pt-Rh alloy tip is used to improve oxidation resistance, then oxidation resistance is improved, but abnormal erosion occurs at the side surface due to high oxygen concentration and temperature fluctuations
Solution Approach 1:
The tip is constructed as a composite structure with a Pt-Rh alloy core material and a Ni-containing front surface layer. This composite structure combines the oxidation resistance of Pt-Rh with the erosion resistance of Ni, resolving the contradiction between oxidation resistance and abnormal erosion resistance.
Solution Approach 2:
Different regions of the tip are given different material compositions: the core maintains Pt-Rh for oxidation resistance, while the front surface layer contains 3-15 mass% Ni to prevent abnormal erosion. This local differentiation allows each region to perform its specific function optimally.
2Reliability
If Rh content in Pt-Rh alloy is increased to improve spark erosion resistance, then spark erosion resistance is improved, but abnormal erosion at side surface worsens due to oxide peeling
Solution Approach 1:
The Ni-containing front surface layer acts as an intermediary between the Rh oxide and the external environment. It stabilizes the Rh oxide and prevents direct interaction with intake air gas, thereby preventing peeling while maintaining the spark erosion resistance provided by Rh.
Solution Approach 2:
The front surface layer converts the potentially harmful effect of Rh oxide formation (which causes peeling) into a beneficial stable structure. By containing and stabilizing the Rh oxide within the Ni-containing layer, the harmful peeling effect is eliminated while preserving the benefits of Rh.
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 significantly reduces abnormal erosion and enhances the durability of the spark plug by preventing oxidative cycles that cause surface peeling, maintaining the spark plug's performance over time.
Implementation Method 1
forming a Ni oxide film that stabilizes the Rh oxide and prevents peeling
Data Source
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AI summary
This invention solves a problem by providing a spark plug featuring excellent durability. The spark plug includes a tip at least one of a center electrode and a ground electrode. The spark plug with excellent durability can be achieved by reducing abnormal erosion of the tip. The spark plug includes the center electrode and the ground electrode. The center electrode is disposed providing a gap with the center electrode. At least one of the center electrode and the ground electrode includes a tip forming the gap. The tip includes a main body portion and a front surface layer. A composition of the main body portion is Pt as a main constituent and Rh of 5 mass% or more and Ni of 0 mass% or more to less than 8 mass%. The front surface layer is disposed at least at a surface radially outside of an axial line extending in a direction from a center of the main body portion to the gap. The front surface layer contains Ni of 8 mass% or more and has a thickness of 2 µm or more.