Spark Plug Insulator Eccentricity Control
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Solution Overview
Problem
As spark plugs are miniaturized, the reduced thickness of the insulator leads to reduced strength and increased eccentricity between the terminal nut and insulator, compromising assembly accuracy and making flashover more likely.
Innovation Solution
A spark plug design with a smaller outside diameter of the insulator at the rear end of the metallic shell, a reduced contact area between the flat portion of the insulator and the terminal nut, and a columnar portion with a tapered rear-end portion to minimize eccentricity and suppress flashover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the diameter of the spark plug is reduced for miniaturization, then the flexibility in engine design is improved, but the thickness of the insulator is reduced leading to reduced strength
Solution Approach 1:
The insulator is designed with different thicknesses at different locations: a first thickness in the first axial direction (greater than or equal to 1.0 mm) and a second thickness in the second axial direction (greater than or equal to 0.6 mm). This local differentiation allows the insulator to maintain sufficient strength where needed while enabling overall miniaturization of the spark plug for design flexibility.
2Adaptability or versatility
If the diameter of the spark plug is reduced for miniaturization, then the flexibility in engine design is improved, but the dimensional accuracy and assembly accuracy are compromised
Solution Approach 1:
The insulator employs asymmetric thickness distribution with a first thickness (≥1.0 mm) and a second thickness (≥0.6 mm) in different axial directions. This localized structural optimization maintains assembly accuracy by ensuring sufficient material presence at critical interfaces while allowing the spark plug to achieve miniaturized dimensions for design flexibility.
3Volume of moving object
If the thickness of the insulator is reduced for miniaturization, then the spark plug size is reduced, but the flashover risk increases
Solution Approach 1:
The insulator is designed with a first thickness of greater than or equal to 1.0 mm in the first axial direction, which is the direction where flashover prevention is critical. This localized thickness enhancement at the flashover-prone interface effectively suppresses flashover risk while allowing the spark plug to maintain a miniaturized overall size.
Solution Approach 2:
Instead of uniformly increasing insulator thickness in all directions, the design applies enhanced thickness specifically in the first axial direction (where flashover occurs) while maintaining reduced thickness in the second axial direction. This dimensional selectivity prevents flashover without compromising the miniaturized size of the spark plug.
4Manufacturing precision
If the contact area between the flat portion of the insulator and the terminal nut is reduced, then the eccentricity is reduced improving assembly accuracy, but the flashover suppression capability may be affected
Solution Approach 1:
The insulator maintains a first thickness of ≥1.0 mm in the first axial direction where flashover prevention is critical, while allowing a smaller contact area between the flat portion and terminal nut. This localized thickness assurance at the flashover interface compensates for the reduced contact area, maintaining both assembly accuracy and flashover suppression capability.
Solution Approach 2:
The design shifts the flashover prevention function from the contact area between the flat portion and terminal nut to the first thickness dimension of the insulator in the first axial direction. By ensuring sufficient thickness (≥1.0 mm) in this critical dimension, the patent maintains flashover suppression even with a reduced contact area that improves assembly accuracy.
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 significantly reduces eccentricity, enhances assembly accuracy, and increases the flashover start voltage, effectively addressing the issues of reduced strength and increased flashover risk in miniaturized spark plugs.
Implementation Method 1
the resin powder and the electroconductive sealing powder are heated to be softened and then cooled to be solidified
Data Source
Figure 1
Figure 2(A)~2(C)
Figure 3(A)~3(C)
AI summary
It is an object to reduce eccentricity between a terminal nut and an insulator. A spark plug includes an insulator, a terminal nut, and a metallic shell. The outside diameter of the insulator at a rear end of the metallic shell is smaller than or equal to 8 mm, and the contact area between a flat portion of the insulator and a contact surface of the terminal nut is smaller than 10 mm2.