Spark Plug Insulator Geometry for Breakage Resistance
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Solution Overview
Problem
Miniaturized spark plugs face challenges in improving breakage resistance and airtightness due to the smaller diameter of the insulator, which affects the strength of the contact portion and the packing, leading to issues with unburnt gas intrusion and fouling.
Innovation Solution
A spark plug design with a specific geometry, including a cylindrical insulator, a metal shell with a stepped portion, and an annular packing, where the creeping distance, radius of curvature, and contact length are optimized to enhance breakage resistance and airtightness, preventing unburnt gas intrusion and improving strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the insulator diameter is reduced to miniaturize the spark plug, then the clearance between the metal shell and insulator is reduced improving anti-fouling properties, but the breakage resistance of the insulator deteriorates
Solution Approach 1:
The invention divides the insulator into multiple sections with different diameters (first diameter D1 for the support portion, second diameter D2 for the front end portion, third diameter D3 for the rear end portion). This segmentation allows each section to be optimized independently - the support portion maintains sufficient strength for airtightness while the front end portion is reduced in size for miniaturization and anti-fouling purposes.
Solution Approach 2:
The insulator is designed with non-uniform diameter distribution where different portions have different diameters tailored to their specific functional requirements. The support portion has a larger diameter (D1) to ensure mechanical strength and airtight contact, while the front end portion has a smaller diameter (D2) to reduce overall size and prevent fouling, and the rear end portion has diameter (D3) optimized for its specific function.
2Object-generated harmful factors
If the insulator diameter is reduced, then the clearance between metal shell and insulator is reduced for improved anti-fouling, but the contact portion strength deteriorates
Solution Approach 1:
The insulator is segmented into distinct portions with the support portion (first diameter D1) separated from the front end portion (second diameter D2). This segmentation enables the support portion to maintain sufficient diameter for strong contact and airtightness, while the front end portion can be reduced in diameter to minimize fouling and reduce clearance-related issues.
Solution Approach 2:
Different portions of the insulator are assigned different diameters based on local functional requirements. The support portion has a larger diameter (D1) optimized for mechanical contact strength and airtight sealing, while the front end portion has a smaller diameter (D2) optimized for preventing fouling and reducing overall size, with D1 being greater than D2 to ensure contact portion strength.
3Volume of moving object
If the packing contact portion is reduced in size, then the overall spark plug size is reduced, but the airtightness deteriorates
Solution Approach 1:
The insulator is divided into distinct portions including the support portion (first diameter D1) that specifically contacts the packing, and the front end portion (second diameter D2) that extends into the combustion chamber. This segmentation allows the support portion to maintain sufficient diameter for reliable airtight contact with the packing, while the overall spark plug size is reduced through the smaller front end portion diameter (D2 < D1).
Solution Approach 2:
The insulator exhibits local quality variations with different diameters at different portions. The support portion has a larger diameter (D1) specifically optimized for airtight contact with the packing, ensuring reliable sealing. The front end portion has a smaller diameter (D2) optimized for size reduction and fouling prevention. The diameter relationship D1 > D2 ensures that airtightness is maintained at the critical contact portion while achieving overall miniaturization.
Data Source
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AI summary
[Objective] To provide a technique capable of improving breakage resistance of an insulator of a spark plug. [Means for Solution] In a cross-section including an axial line of a spark plug, the following relationship is satisfied: 0.6mm<=L, where "A" represents a connection point between a support portion of an insulator and an insulator trunk portion formed at a front end side with respect to the support portion of the insulator, where "B" represents a position closer to the outer circumference side among positions of (a) an innermost position of a contact portion where the support portion of the insulator and a packing are in contact with each other and (b) an intersection of the support portion of the insulator and a virtual straight line that is parallel to the axial line and extends from an innermost circumferential end of the stepped portion of a metal shell, and where "L" represents a length of a path from the point "A" to the point "B" along a surface of the insulator.