Spark Plug Insulator Crimping Geometry for Airtight Sealing
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Solution Overview
Problem
Reducing the diameter of spark plugs leads to issues such as air leakage and the ceramic insulator falling out due to a weakened crimp portion, which compromises the secure fitting of the insulator within the metal shell.
Innovation Solution
A spark plug design featuring a ceramic insulator with tapered step portions and a metal shell with a crimp portion, where the projection area, shoulder angle, and distance between the crimp and step portions are optimized within specific ranges to ensure a secure fit, preventing air leakage and insulator displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the diameter of the spark plug is reduced, then engine design flexibility is improved, but the crimp portion becomes too small to securely hold the ceramic insulator
Solution Approach 1:
The invention applies local quality by creating a stepped structure on the ceramic insulator with different diameter portions (first stepped portion with larger diameter, second stepped portion with smaller diameter). This allows different regions of the insulator to serve different functions: the larger first stepped portion provides a secure seating surface for the metal shell, while the smaller second stepped portion accommodates the reduced overall diameter requirements for engine design flexibility.
Solution Approach 2:
The ceramic insulator is segmented into distinct portions with different diameters along its length. The first stepped portion and second stepped portion are clearly differentiated, allowing the crimp portion to engage with the appropriate section. This segmentation enables the spark plug to meet both the reduced diameter requirements and the secure holding requirements simultaneously.
2Area of stationary object
If the diameter of the spark plug is reduced, then a larger water jacket and intake/exhaust ports can be arranged, but air leakage and insulator falling out occur
Solution Approach 1:
By creating localized stepped portions with different diameters on the ceramic insulator, the invention ensures that the critical sealing and crimping areas maintain sufficient diameter and structural integrity. This local quality enhancement at the insulator-metal shell interface prevents air leakage pathways while allowing the overall spark plug diameter to be reduced for larger water jackets and ports.
3Power
If the diameter of the spark plug is reduced, then engine performance is improved, but the crimp portion strength is insufficient
Solution Approach 1:
The segmentation of the ceramic insulator into stepped portions with different diameters allows the crimp portion to engage with a section that maintains sufficient structural strength. The first stepped portion with its larger diameter provides a robust engagement surface, ensuring that the crimp portion can exert adequate holding force even when the overall spark plug diameter is reduced for improved engine performance.
Data Source
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AI summary
To provide a technique capable of firmly holding a ceramic insulator by a crimp portion of a metal shell even though a diameter of a spark plug is reduced in size. A spark plug 100 includes a ceramic insulator 10 having a tapered rear end side step portion 15 whose a diameter tapering from a front end side to a rear end side and a metal shell 50 having a crimp portion 53 which crimps the rear end side step portion 15 from the rear end side. In the spark plug 100, an area S defined by an outer edge of the rear end side step portion 15 and an inner edge of the crimp portion 53 falls within a range of 5 mm2 to 25 mm2 when the spark plug 100 is projected on a plane perpendicular to an axial line of the spark plug 100. Further, an angle θ1 formed by a tapered face of the rear end side step portion 15 and a plane perpendicular to the axial line falls within a range of 20 degrees to 60 degrees. Furthermore, a distance L along the axial line from a front end of a proximal portion of the crimp portion 53 to a frontmost position of a contact portion between an inner face of the crimp portion 53 and the rear end side step portion 15 falls within a range of 0.4 mm to 1.8 mm.