Spark Plug Electrode Concave-Convex Structure Gap Prevention
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Solution Overview
Problem
The difference in thermal expansion coefficients between the cover and core portions of spark plug electrodes leads to gaps during thermal cycles, hindering heat transfer and potentially causing voids or breakage.
Innovation Solution
The spark plug design incorporates a core portion with a concave-convex shape and a diameter reduction portion, increasing the contact area with the cover portion, which suppresses gap formation by forming a larger diffusion layer and preventing the cover portion from coming off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a core portion made of material with high thermal conductivity is used, then heat transfer performance is improved, but gap formation between cover portion and core portion occurs during thermal cycles
Solution Approach 1:
A concave portion is formed at the front end of the core portion before assembly, and a convex portion is formed on the inner surface of the cover portion. These pre-formed geometric features ensure proper alignment and contact between the cover portion and core portion during thermal expansion and contraction cycles, preventing gap formation while maintaining the high thermal conductivity of the core portion
Solution Approach 2:
The core portion is designed with a concave portion at its front end, creating a localized geometric feature that corresponds to the convex portion on the cover portion. This local quality modification ensures that the cover portion remains firmly attached to the core portion during thermal cycles, preventing gap formation at the critical interface while preserving the overall high thermal conductivity of the core portion material
2Productivity
If electrode diameter is reduced, then productivity is improved, but gap occurrence between cover portion and core portion increases
Solution Approach 1:
The concave portion at the front end of the core portion and the corresponding convex portion on the cover portion are pre-formed during manufacturing. This preliminary action ensures that even in reduced-diameter electrodes, the cover portion and core portion maintain proper contact and alignment during thermal cycles, preventing gap formation while enabling smaller electrode diameters for improved productivity
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
This design effectively suppresses gap occurrence between the cover and core portions, enhancing heat transfer performance and preventing electrode breakage during thermal cycles.
Implementation Method 1
a relatively large diffusion layer is formed between the core portion and the cover portion
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(b)
AI summary
In a spark plug including an electrode having a cover portion and a core portion, the occurrence of a gap between the cover portion and the core portion is suppressed. In a spark plug including a center electrode and a ground electrode that forms a gap between the center electrode and the ground electrode, at least one of the center electrode and the ground electrode has a cover portion and a core portion covered with the cover portion and formed of a material having a thermal expansion coefficient different from that of the cover portion. The core portion of the at least one electrode has a concave portion and a convex portion formed at the front end thereof. The convex portion is such that, in a cross section passing through the barycenter of the front surface of the electrode and also passing through the convex portion, the area of the convex portion delimited by a line perpendicular to the bisector of the convex portion and passing through a point 0.2 mm shifted from the front end of the convex portion in the direction of the bisector is smaller than the area of a triangle formed by connecting the front end of the convex portion and intersections of the line perpendicular to the bisector and the contour of the convex portion.