Spark Plug Tip Composite Structure for Erosion Resistance
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Solution Overview
Problem
Spark plugs used in high-temperature and harsh heating/cooling cycle environments experience abnormal erosion due to increased internal combustion engine temperatures and frequent heating/cooling cycles, leading to reduced durability and maintenance intervals.
Innovation Solution
A spark plug design featuring a tip with a body portion primarily composed of Ir, Rh, and Ru, a high specific resistance layer with a Ni content greater than the body portion, and a Ni-rich coating layer, optimized in thickness and composition to inhibit abnormal erosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tip made of Ir or Ir alloy is used to improve spark erosion resistance, then erosion resistance is improved, but abnormal erosion occurs where the outer peripheral surface is hollowed into an arc shape
Solution Approach 1:
The tip is constructed as a composite structure with a body portion containing Ir as main component and a coating layer containing Ni. This composite structure combines the excellent spark erosion resistance of Ir with the abnormal erosion resistance of Ni, resolving the contradiction between the two types of erosion resistance.
Solution Approach 2:
Different portions of the tip have different material compositions optimized for different functions: the body portion uses Ir for spark erosion resistance at the discharge surface, while the outer peripheral surface uses Ni coating for abnormal erosion resistance. This local differentiation resolves the contradiction by assigning appropriate materials to specific locations.
2Power
If the internal temperature of the combustion chamber is increased to improve power output or fuel efficiency, then engine performance is improved, but the heating/cooling cycle environment becomes harsher
Solution Approach 1:
The material composition parameters of the tip are changed from single-phase Ir to a two-phase composite (Ir body + Ni coating). This parameter change enables the tip to withstand the harsher thermal environment resulting from increased combustion chamber temperatures, thereby maintaining spark plug durability while allowing higher engine performance.
Data Source
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AI summary
An object of the present invention is to provide a spark plug having excellent durability in which when the spark plug is used in a combination of a high-temperature environment and a harsh heating/cooling cycle environment, the abnormal erosion of the tip is inhibited for a long time. The spark plug includes a tip provided on at least one of a center electrode and a ground electrode. The tip includes a body portion, a coating layer, and a high specific resistance layer. The body portion contains mostly Ir, and also contains 2 mass% or more of Rh or Pt, and none of group-A elements or a total content of the group-A elements of 24 mass% or less, the total content of the group-A elements excluding Ru being less than 7 mass%, where the group-A elements are metal elements having a crystal structure different from the crystal structure of Ir, Rh, and Pt at room temperature. The high specific resistance layer is provided on a side peripheral surface of the body portion, has a Ni content greater than the Ni content of the body portion and less than 50 mass%, and has a thickness of 2 µm or greater and 45 µm or less. The coating layer is provided on a side peripheral surface of the high specific resistance layer, contains 50 mass% or more of Ni, and has a thickness of 3 µm or greater and 20 µm or less. The tip has a specific resistance of 20 × 10-8 Ωm or less at room temperature.