Ignition Plug Insulator Design for Vibration Resistance
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Solution Overview
Problem
The challenge is to prevent breakage and deterioration of the rear trunk portion of an ignition plug without increasing its wall thickness, while reducing the insulator diameter, as a smaller axial bore diameter leads to weakened support pins and dimensional variations during grinding.
Innovation Solution
The ignition plug design includes a rear trunk portion with a maximum outside diameter of 9.5 mm or less, featuring an outer circumferential portion that restricts the oscillation of the head portion, along with specific geometric relationships and features such as a curved portion and annular groove, to reduce the energy transferred to the rear trunk portion during vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the insulator diameter is reduced to achieve miniaturization, then the size of the ignition plug is reduced, but the wall thickness of the rear trunk portion decreases leading to breakage and strength deterioration
Solution Approach 1:
The invention introduces a new spatial dimension by adding the outer circumferential portion that radially surrounds the head portion. This dimensional addition creates a constraint structure that prevents oscillation without requiring increased wall thickness in the traditional axial direction, thus resolving the contradiction between miniaturization and strength maintenance.
Solution Approach 2:
The insulator is segmented into functionally distinct portions: the rear trunk portion for electrical insulation, the outer circumferential portion for mechanical constraint, and the end-surface seat portion for positioning. This segmentation allows each portion to be optimized for its specific function, enabling the rear trunk to maintain strength while the overall insulator diameter is reduced.
2Strength
If the wall thickness of the rear trunk portion is increased to prevent breakage, then the strength is improved, but the insulator diameter increases counteracting miniaturization efforts
Solution Approach 1:
The insulator is divided into specialized portions: the rear trunk portion maintains thin walls for miniaturization, while the separately positioned outer circumferential portion provides the necessary mechanical constraint. This segmentation allows the rear trunk to remain small in diameter while gaining strength through the distributed constraint structure.
Solution Approach 2:
The strength enhancement is achieved not by thickening the rear trunk portion in the radial direction, but by adding the outer circumferential portion that creates a constraint system in a different spatial arrangement. This dimensional reconfiguration enables strength improvement without increasing the critical rear trunk diameter.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An ignition plug (1) includes a ceramic insulator (2) having an axial bore (4), a metallic shell (3) disposed externally of the outer circumference of the ceramic insulator (2), and a terminal electrode (6). The terminal electrode (6) has a leg portion (6A) inserted into a rear side of the axial bore (4), and a head portion (6B) formed on a rear side of the leg portion (6A) and having an outside diameter greater than that of the leg portion (6A). The ceramic insulator (2) includes a rear trunk portion (10) exposed from the rear end of the metallic shell (3), and the rear trunk portion (10) has a maximum outside diameter of 9.5 mm or less. The ceramic insulator (2) has an end-surface seat portion (32) located forward of its rear end and being in contact with the forward end surface of the head portion (6B), and an outer circumferential portion (33) into which at least a forward end portion of the head portion (6B) is inserted and which is located externally of the outer circumference of the head portion (6B). By virtue of this, while the ceramic insulator (2) is reduced in diameter, breakage of and deterioration in strength of the rear trunk portion (10) are restrained without need to increase the wall thickness of the rear trunk portion (10).