Spark Plug Ground Electrode Protrusion Design for Cost and Durability
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Solution Overview
Problem
Conventional spark plugs with noble metal tips are expensive, and those with extruded protrusions for cost reduction often fail to achieve high ignition performance and durability due to protrusion breakage or poor formation during use.
Innovation Solution
A spark plug design featuring a ground electrode with a protrusion and hole formed by extrusion, where the protrusion has a specific length, uniform width, and area, and the hole has a defined opening and taper portion, ensuring compatibility between ignition performance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noble metal tips are used on electrodes, then ignition performance is improved, but production cost increases
Solution Approach 1:
The patent replaces expensive noble metal tips with a ground electrode made of cheaper materials (nickel-based or iron-based alloys) that has a protrusion formed by extrusion process. The protrusion serves the same functional purpose as the noble metal tip but at significantly lower cost, accepting that the ground electrode may need replacement sooner rather than using durable but expensive noble metals.
2Ease of manufacture
If extrusion process is used to form protrusion on ground electrode, then production cost is reduced, but durability deteriorates due to breakage or crack
Solution Approach 1:
The patent specifies precise parameter ranges for the extrusion process: protrusion length of 0.15-0.50mm, protrusion cross-sectional area of 0.03-0.15mm², and extrusion ratio of 1.05-1.20. These controlled parameters ensure the protrusion is sufficiently small to avoid breakage while large enough to provide adequate ignition performance, resolving the durability issue of extruded components.
Solution Approach 2:
The patent forms only a small protrusion (not a full noble metal tip replacement) on the ground electrode through extrusion. This partial action provides enough functional improvement to reduce cost while minimizing the structural changes that would cause breakage, balancing durability and cost reduction.
3Ease of manufacture
If protrusion is formed by simple extrusion process, then production cost is reduced, but ignition performance is insufficient
Solution Approach 1:
The patent optimizes the extrusion parameters including protrusion length (0.15-0.50mm), cross-sectional area (0.03-0.15mm²), and extrusion ratio (1.05-1.20) to achieve the right balance between manufacturability and ignition performance. The protrusion is sized to create sufficient electric field concentration for reliable ignition while remaining small enough to be formed by simple extrusion.
Solution Approach 2:
The patent replaces complex noble metal tip attachment processes (welding, brazing) with a simple extrusion process that forms the protrusion directly from the ground electrode material. This mechanical substitution eliminates multiple manufacturing steps while maintaining adequate ignition function through precise dimensional control of the extruded protrusion.
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 spark plug achieves high ignition performance while maintaining durability and low production costs, with the extruded design minimizing the risk of breakage and crack occurrence.
Implementation Method 1
a protrusion and a hole formed by extrusion process on a front end portion of the ground electrode
Implementation Method 2
generate a spark discharge between the noble metal tips
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~4
AI summary
It is an object of the present invention to provide a spark plug that can be produced at low cost and secure compatibility between ignition performance and durability. The spark plug according to the present invention includes a center electrode and a ground electrode having an inner surface facing the center electrode, characterized in that; the ground electrode has a protrusion and a hole; the protrusion protrudes from the inner surface by a protruding length A of 0.4 to 1mm and has a first straight portion with a projected first straight portion area S1 of 1.5 to 3 mm2; the hole has an opening at an outer surface of the ground electrode, a second straight portion, a bottom portion and a transition portion; the opening is formed in such a manner that the ratio (S2/S1) of a projected opening area S2 of the opening to the projected first straight portion area S1 is not less than 1.2; and the transition portion is in the form of a taper portion.