Compact Spark Plug Gas Tightness via Shell Thickness Ratio
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Solution Overview
Problem
Conventional spark plugs face challenges in achieving high gas tightness when made compact, as reducing the radial thickness of the metal shell or insulator can compromise rigidity and lead to flashover or inadequate sealing.
Innovation Solution
A compact spark plug design with specific dimensional relationships between the metal shell's radial thicknesses and crimped portion, ensuring high rigidity and gas tightness by specifying A>B>C, B≧1.1C, and C within a range of 0.5 to 1.0 mm, along with strategic buckling and crimping to maintain sealing member constriction force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the radial thickness of the metal shell is reduced to make the spark plug compact, then the size of the spark plug is reduced, but the rigidity of the crimped portion decreases making it impossible to secure high gas tightness
Solution Approach 1:
The metal shell is divided into multiple portions with different functions: the crimped portion at the second end for sealing, the polygonal prism-shaped portion for torque application, and the threaded portion for installation. This segmentation allows each portion to be optimized independently, enabling the crimped portion to maintain sufficient rigidity for gas tightness while the overall spark plug size is reduced through smaller threaded portion (M10 or M12) and compact polygonal prism-shaped portion (width ≤14mm).
Solution Approach 2:
The metal shell exhibits non-uniform wall thickness distribution along its length. The crimped portion maintains adequate wall thickness to ensure rigidity and sealing capability, while other portions can have reduced thickness to minimize overall size. This local quality variation allows the spark plug to be compact overall while maintaining sufficient rigidity at the critical crimped portion for high gas tightness.
2Volume of moving object
If the radial thickness of the insulator is reduced to make the spark plug compact, then the size of the spark plug is reduced, but flashover occurs compromising reliability
Solution Approach 1:
The insulator is designed with varying radial thickness at different locations. The insulator maintains sufficient thickness in critical areas to prevent flashover and ensure electrical isolation, while allowing reduced thickness in non-critical areas to contribute to the compact overall size of the spark plug.
3Volume of moving object
If the threaded portion size is reduced from M14 to M10 or M12 for compact installation, then the spark plug can be installed in engines with smaller combustion chambers, but the polygonal prism-shaped portion width must also be reduced which affects torque application
Solution Approach 1:
The polygonal prism-shaped portion is designed with a width between any two opposite side surfaces of no greater than 14mm, which is a specific parameter optimization that allows adequate torque application capability while maintaining compact size for installation in engines with smaller combustion chambers.
Data Source
AI summary
A spark plug has a compact structure where a threaded portion of a metal shell has a size of M10 or M12 and the width between any two opposite side surfaces of a polygonal prism-shaped portion of the metal shell is no greater than 14 mm. In the spark plug, a thickness A of the polygonal prism-shaped portion of the metal shell, a thickness B of a crimped portion of the metal shell, and a thickness C of a buckled portion of the metal shell are subject to a dimensional relationship of A>B>C. Through specifying such a relationship, the crimped portion of the metal shell exerts a large constricting force on sealing members provided in a gap between the inner surface of the polygonal prism-shaped portion of the metal shell and the outer surface of an insulator, thereby securing high gas tightness of the spark plug.