Spark Plug Center Electrode Curvature for Lower Bending Stress
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Solution Overview
Problem
Existing spark plugs experience high bending stress in the front end portion of the center electrode due to combustion pressure, which affects durability and ignitability.
Innovation Solution
The spark plug design includes a center electrode with a front end portion that has a proximal end and an electrode tip end with a smaller width, featuring recessed portions and a melt portion between them, where the curvature radius of the recessed portion is optimized to reduce bending stress by increasing the R/A value, and the thickness and distance of the rear-end recessed portion are specifically tailored to minimize stress while maintaining ignitability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the center electrode is made with a straight profile, then the structure is simple and easy to manufacture, but the bending stress in the front end portion increases due to combustion pressure
Solution Approach 1:
The patent applies curvature to the front end portion of the center electrode by introducing recessed portions with optimized curvature radii. Specifically, the first recessed portion has a curvature radius R1 satisfying 0.1mm ≤ R1 ≤ 0.3mm, and the second recessed portion has a curvature radius R2 satisfying 0.1mm ≤ R2 ≤ 0.3mm. This curvature design redistributes the bending stress along the electrode profile, preventing stress concentration at straight transitions and reducing overall bending stress while maintaining manufacturability through controlled curvilinear geometry.
Solution Approach 2:
The patent implements local quality by creating non-uniform thickness distribution through recessed portions at specific locations along the center electrode. The first recessed portion is positioned at distance L1 from the tip end (0.5mm ≤ L1 ≤ 1.5mm) and the second recessed portion at distance L2 (0.5mm ≤ L2 ≤ 1.5mm), with each having controlled curvature radii. This localized geometric modification concentrates stress-relief features exactly where combustion pressure induces maximum bending moments, while keeping other portions of the electrode simple and easy to manufacture.
2Strength
If the front end portion thickness is increased, then the bending stress resistance improves, but the ignitability deteriorates due to energy loss from the flame kernel
Solution Approach 1:
The patent optimizes the geometric parameters of the front end portion by precisely controlling the curvature radii (R1 and R2 both between 0.1mm and 0.3mm) and the distances (L1 and L2 both between 0.5mm and 1.5mm) of the recessed portions. These parameter changes create an optimal balance where the electrode profile provides sufficient bending stress resistance through controlled thickness variation, while maintaining adequate flame kernel energy transfer by preventing excessive thickness that would absorb spark energy.
Solution Approach 2:
The curved profiles of the recessed portions with optimized radii create a gradual transition in thickness rather than abrupt changes. This curvature ensures that the electrode maintains structural integrity against bending stress while allowing the flame kernel to propagate efficiently along the curved surface, reducing energy loss compared to straight or excessively thick configurations.
Data Source
AI summary
A spark plug includes a center electrode extending along an axial line and includes a front end portion projecting from an insulator, in a section including the axial line, the front end portion includes a proximal end positioned at a front end of the insulator and an electrode tip end. At least one outline appearing in the section and connecting the proximal end and the electrode tip end of the front end portion to each other includes one or more recessed portions recessed toward the axial line, and a value R/A obtained by dividing a curvature radius R of a rear-end recessed portion, of the one or more recessed portions, closest to the proximal end by a distance A between the rear-end recessed portion and the electrode tip end in the direction of the axial line is more than or equal to 0.12.