Spark Plug Insulator Local Quality Design for Eccentricity Control
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Solution Overview
Problem
The reduction in size of spark plugs for internal combustion engines leads to insufficient strength and insulating properties, causing deflection of support pins during manufacturing, resulting in eccentricity of the axial bore and potential lateral sparks.
Innovation Solution
Specifying dimensions of the insulator to enhance the rigidity of the support pin, such as C/E ≥ 116% and D/A ≥ 9%, to reduce deflection and maintain sufficient wall thickness, thereby suppressing eccentricity and preventing lateral sparks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the insulator is reduced to reduce spark plug size, then the size of the spark plug is reduced, but the strength and insulating properties of the insulator become insufficient
Solution Approach 1:
The patent applies local quality by creating a large-diameter portion in the axial bore at the distal end of the insulator, while maintaining a smaller diameter in other portions. This localized enlargement increases the wall thickness specifically where needed to prevent lateral sparks, without requiring the entire insulator diameter to be increased, thus resolving the contradiction between small spark plug size and sufficient insulator strength.
2Reliability
If the diameter of the axial bore is reduced to increase wall thickness, then the insulating properties are improved, but the diameter of the support pin must be reduced causing deflection during manufacturing
Solution Approach 1:
The patent creates a large-diameter portion at the distal end of the axial bore, which locally increases the wall thickness without requiring a uniform reduction of the axial bore diameter throughout. This allows the support pin to maintain sufficient diameter for manufacturing precision while achieving the necessary wall thickness for insulating properties in the critical region where lateral sparks occur.
3Length of stationary object
If the support pin is elongated to manufacture longer insulators, then longer insulators can be produced, but stress concentrates on the proximal end causing deflection
Solution Approach 1:
The patent's design of a large-diameter portion at the distal end of the axial bore allows for reduced support pin diameter in certain regions, which improves support pin rigidity and reduces stress concentration at the proximal end during grinding operations, enabling successful manufacture of longer insulators.
4Reliability
If the wall thickness is increased to prevent lateral sparks, then insulating properties are improved, but the spark plug size increases
Solution Approach 1:
The patent implements local quality by enlarging the axial bore diameter only at the distal end where the large-diameter portion is formed, rather than uniformly increasing wall thickness throughout the entire insulator. This localized approach achieves sufficient wall thickness to prevent lateral sparks in the critical region while minimizing the overall increase in spark plug size.
Data Source
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AI summary
A plurality of insulator samples of different dimensions are subjected to multiple regression analysis to thereby induce an expression for estimating the amount of unevenness in wall thickness of an insulator(10); specifically, 0.01 × (0.141 × A - 0.140 × D - 0.285 × B - 6.124 × C + 1.105 × E + 17.527), where A is an overall length of the insulator (10), B is the outside diameter of a rear trunk portion (18) of the insulator (10), C is the diameter of a large-diameter portion (110) of the axial bore (12) of the insulator (10), D is the length of the large-diameter portion (110), and E is the diameter of a small-diameter portion (120) of the axial bore (12). The insulator (10) is designed such that the amount of unevenness in wall thickness thereof estimated through calculation by this expression is less than 0.07 mm.