Spark Plug Seat Deformation Control via Geometric Ratios
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Solution Overview
Problem
Conical seat type spark plugs experience excessive deformation of the seat and protrusion during the caulking process, leading to a decrease in axial force applied to the insulator, which compromises air tightness between the metal shell and the insulator.
Innovation Solution
A spark plug design with specific geometric configurations, including a tubular insulator and metal shell with a caulking portion, bulge portion, seat portion, thread portion, and protrusion, where the seat portion and protrusion are designed to minimize excessive deformation by controlling the ratios of their surface areas and lengths, ensuring sufficient axial force and contact pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a load is applied to the metal shell in the caulking process, then the insulator is secured to the metal shell, but the seat portion and protrusion are deformed excessively, decreasing axial force and air tightness
Solution Approach 1:
The patent applies parameter changes by optimizing the geometric dimensions of the seat portion and protrusion. Specifically, the seat portion is designed with a tapered surface having a controlled area SB, and the protrusion has a locked surface with area SC and length LC. The patent establishes specific ratio relationships (SB/SC ≥ 3.5 and SC/LC ≤ 12.0) to control deformation during the caulking process, thereby maintaining sufficient axial force while preventing excessive deformation.
2Stress or pressure
If the area of the locked surface is excessively large, then the contact pressure between locked surface and lock portion becomes low, but air tightness is compromised
Solution Approach 1:
The patent resolves this contradiction by establishing an optimal balance through parameter relationships. The area SC of the locked surface is controlled relative to the area SB of the tapering surface (SB/SC ≥ 3.5), ensuring that the contact pressure between the locked surface and lock portion remains sufficiently high. Simultaneously, the length LC of the protrusion is controlled (SC/LC ≤ 12.0) to maintain adequate contact area for air tightness, achieving both high contact pressure and reliable sealing.
Data Source
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AI summary
Deformation of a seat portion and a protrusion is reduced in a caulking process so as to ensure good air tightness. A spark plug (1) includes an insulating insulator (2) and a metal shell (3). The metal shell (3) includes a caulking portion (19), a seat portion (16) with a tapering surface (31), a thread portion (15) with a thread size equal to or less than M12, and a protrusion (20). The insulating insulator (2) includes a lock portion (14) locked to the protrusion (20), and is secured to the metal shell (3) in a state held between the caulking portion (19) and the protrusion (20). SB/SC ≥ 3.5, SB/LB ≤ 12.0, and SC/LC ≤ 12.0 are satisfied in a case where: the tapering surface (31) has an area of SB (mm2); a seat-portion outer peripheral surface (32) extending from a rear end of the tapering surface (31) in the seat portion (16) has a length of LB (mm); a locked surface (33) locking the lock portion (14) in the protrusion (20) has an area of SC (mm2); and a protrusion inner peripheral surface (34) extending from a tip end of the locked surface (33) toward the tip end side in the protrusion (20) has a length of LC (mm).