Spark Plug Crimping with Hardness-Graded Packing
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Solution Overview
Problem
Conventional spark plugs with reduced insulator diameter face issues of fracture upon external impact due to direct crimp contact, and maintaining airtightness is compromised when trying to prevent such fractures by creating clearance, leading to potential contact between the insulator and crimp portion.
Innovation Solution
A spark plug design featuring a rod-shaped center electrode, an insulator with an axial hole, and a metallic shell with a crimp portion, where an annular packing is placed between the crimp and trunk portions, ensuring the packing's outer diameter is greater than the crimp's inner diameter, and its hardness is lower than the crimp's, to absorb impact and prevent fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the crimp portion is brought into direct contact with the insulator to ensure integral fixing, then the fixing reliability is improved, but the insulator becomes susceptible to fracture under external impact
Solution Approach 1:
A packing is introduced as an intermediary element between the crimp portion and the insulator. The packing serves as a mediator that transmits the crimping force while protecting the insulator from direct contact with the hard crimp portion, thereby preventing fracture under external impact while maintaining integral fixing.
Solution Approach 2:
The packing is positioned in advance between the crimp portion and the insulator to provide cushioning protection. This beforehand cushioning prevents the insulator from being subjected to concentrated impact forces during crimping and subsequent external impacts, resolving the contradiction between fixing reliability and fracture resistance.
2Strength
If a clearance is formed between the crimp portion and the insulator to prevent fracture, then the insulator fracture resistance is improved, but the airtightness cannot be maintained
Solution Approach 1:
The packing acts as an intermediary that fills the clearance between the crimp portion and the insulator. This mediator maintains airtightness by sealing the gap while simultaneously preventing direct contact that would cause fracture, thus resolving both contradictions simultaneously.
Solution Approach 2:
The physical state and positioning of the packing are optimized to achieve both functions: it is compressed to fill the clearance for airtightness while maintaining sufficient thickness to prevent direct contact between the crimp portion and insulator, preserving fracture resistance.
3Strength
If a larger clearance is provided between the crimp portion and the insulator to prevent contact during deflection, then the insulator fracture resistance is improved, but the airtightness and structural stability deteriorate
Solution Approach 1:
The packing serves as a controlled intermediary that provides the necessary clearance to prevent fracture while maintaining airtightness through its sealing properties. The packing's material characteristics and positioning ensure structural stability is not compromised despite the presence of clearance.
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 enhances sealing properties, prevents insulator fracture during external impacts, and improves fracture resistance by using the packing as a cushion, maintaining airtightness while absorbing impact without direct crimp contact.
Implementation Method 1
the hardness N (Hv) of the packing and the hardness M (Hv) of the metallic shell, in particular the hardness of the crimp portion, satisfy the relationship N<M... the packing as a cushion, maintaining airtightness while absorbing impact without direct crimp contact
Implementation Method 2
The metallic shell and the insulator are integrated through crimping performed in a state in which the annular packing is disposed between the inner circumferential surface of the crimp portion and the outer circumferential surface of the trunk portion of the insulator
Data Source
AI summary
A spark plug in which a distal end portion (60) of a crimp portion (53) of a metallic shell (50) is crimped by bending the distal end portion inward, whereby the metallic shell (50) and an insulator (10) are fixed together with a first packing (6), a second packing (7), and talc (9) being present therebetween. The first packing (6) assumes an annular shape and has a circular cross section. A minimum diameter portion of the crimp portion (53), which portion is closest to the outer circumferential surface (17) of a trunk portion (18), is located at the position of the center line of the first packing (6) or inward thereof with respect to the axis O. The crimp portion (53) does not come into contact with the insulator (10), and the first packing (6) comes into contact with the insulator (10). Furthermore, the first packing (6) has a hardness that is lower than that of the crimp portion (53).