Spark Plug Welding Strength via Radial Protrusion
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Solution Overview
Problem
Conventional spark plugs face issues with reduced welding strength between the metal shell and ground electrode due to thinner thickness, leading to wear, durability problems, and potential fracture under increased temperatures and vibrations, especially when the metal shell diameter is minimized.
Innovation Solution
The spark plug design enhances welding strength by ensuring the sectional area of the welded part between the metal shell and ground electrode is greater than that of the ground electrode itself, with a radial protrusion of the metal shell during welding and the use of a cylindrical welding chuck with a relief part for accommodating melted metal, ensuring a strong bond even with reduced metal shell diameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the metal shell diameter is reduced to make the spark plug smaller, then the compactness is improved, but the welding strength between the metal shell and ground electrode deteriorates
Solution Approach 1:
The invention transitions from considering only the ground electrode thickness in isolation to evaluating the welded part sectional area that extends beyond the metal shell outer circumferential surface. By measuring the welded part area S2 in a dimension that includes radial protrusion beyond the shell, the effective bonding area is increased without increasing the overall spark plug diameter, thus resolving the contradiction between compactness and welding strength.
2Reliability
If the ground electrode thickness is increased to prevent wear and fracture, then the durability is improved, but the spark plug size increases
Solution Approach 1:
The invention applies local quality by concentrating the increased sectional area specifically in the welded part region where mechanical strength is most critical. The ground electrode is configured to protrude radially beyond the metal shell outer circumferential surface at the welded part, creating a localized reinforcement zone that enhances durability without requiring uniform thickening of the entire ground electrode, thus avoiding overall size increase.
3Volume of moving object
If the metal shell thickness is reduced to minimize diameter, then the compactness is improved, but the welding strength and resistance to vibrations deteriorate
Solution Approach 1:
The invention resolves this contradiction by measuring the welded part sectional area S2 in a dimension that extends beyond the metal shell outer circumferential surface. This allows the welded part to have sufficient area for vibration resistance even when the metal shell itself is thin-walled and compact, as the effective bonding area includes the region where the ground electrode protrudes radially beyond the shell surface.
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 significantly increases the welding strength between the metal shell and ground electrode, preventing fractures due to vibrations and maintaining durability even when the metal shell diameter is reduced, as demonstrated by improved performance in impact tests.
Implementation Method 1
a base end 14a of the ground electrode 14 welded to a leading end 11a of the metal shell
Data Source
Figure 1
Figure 2
Figure 3~4B
AI summary
According to the invention, it is provided a spark plug capable of increasing a welding strength between a leading end of a metal shell and a base end of a ground electrode to prevent fracture of a welded part due to vibrations and the like even when reducing a diameter of the metal shell. The spark plug 100 satisfies a relation of S2 ≧ S wherein S2 is a sectional area of the welded part between the metal shell 11 and the ground electrode 14, the sectional area S2 being cut off by a plane including a leading end surface of the metal shell 11, and S is a sectional area of the ground electrode 14, the sectional area S being cut off by a plane passing to the most leading end of a boundary in the axial direction between the ground electrode 14 and the welded part and perpendicular to the axial direction.