Spark Plug Center Electrode Fused Joint Geometry
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spark plugs with noble metal tips face challenges in achieving both improved ignition performance and durability, particularly as engine compression ratios increase, due to limitations in tip length and heat conduction properties.
Innovation Solution
A spark plug design featuring a center electrode with a tapered electrode base member and a noble metal tip joined via a fused portion, where specific cross-sectional area and distance relationships are maintained to enhance heat conduction and ignition performance, allowing for longer tip lengths without compromising durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a larger fused portion is formed to prevent noble metal tip removal, then the joint strength increases, but the thermal expansion stress concentrates and heat conduction path increases
Solution Approach 1:
The patent optimizes the dimensions of the fused portion by controlling the length L1 (0.1mm to 0.5mm) and cross-sectional area ratio S1/S2 (0.3 to 0.7). This creates a fused portion that is large enough to provide strong joint strength but not so large as to concentrate thermal expansion stress or excessively lengthen the heat conduction path, thus balancing joint strength and thermal stress resistance
Solution Approach 2:
The fused portion acts as an intermediary layer between the noble metal tip and the center electrode base member. It serves as a stress-relaxing layer with intermediate thermal expansion coefficient, reducing thermal expansion stress concentration while maintaining adequate joint strength. The optimized dimensions ensure it mediates between the conflicting requirements of joint strength and thermal stress resistance
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 achieves improved ignition performance and durability by ensuring effective heat conduction and reducing wear, even with longer noble metal tips, through optimized cross-sectional area ratios and distances.
Implementation Method 1
the heat conduction property of the noble metal tip caused by the combustion heat in the combustion chamber becomes worse as the length of the noble metal tip increases
Implementation Method 2
the boundary between the noble metal tip and the front end of the center electrode base member is directly melted by a laser, etc.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A center electrode includes a tapered electrode base member mount and a noble metal tip joined to the electrode base member mount via a fused portion in which the component of the noble metal tip and the component of the electrode base member mount are fused. In this state, the cross section area S1 at a tip side boundary between the fused portion and the noble metal tip and the cross section area S2 at a base member side boundary between the fused portion and the electrode base member mount satisfy the relational expression of S1<S2. Regarding the cross section area S3 at the base portion of the electrode base member mount, (S3-S2)/D satisfies the relational expression of 5 ≤ (S3-S2)/D ≤ 50. D is the shortest distance in the axis line direction from the base member side boundary to the base portion.