Spark Plug Packing Curved Surface Insulator Crack Prevention
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Solution Overview
Problem
Existing spark plugs are prone to insulator breakage due to the high forces applied by pointed corners, which can cause cracks and failure, especially at the outer circumferential surface of the insulator.
Innovation Solution
The design incorporates a packing with proximal inner and outer circumferential surfaces that are curved, reducing the force applied to the insulator and preventing cracks by smoothing the contact surfaces, and the packing is produced using a method that includes punching and polishing to create a tapered shape that fits between the housing and insulator, minimizing the risk of breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the packing member has pointed corners to maintain structural simplicity, then the device complexity is reduced, but the insulator strength deteriorates due to high localized forces causing cracks and breakage
Solution Approach 1:
The packing member's inner circumferential surface is designed with a curved shape instead of pointed corners. Specifically, the inner circumferential surface has a curvature radius of 0.5mm or more, creating a smooth transition zone that distributes contact forces evenly across the insulator surface, preventing stress concentration and crack formation while maintaining structural simplicity
2Ease of manufacture
If the packing member has a simple ring shape, then the ease of manufacture is improved, but the reliability deteriorates due to insulator breakage from concentrated forces
Solution Approach 1:
The packing member is manufactured with a curved inner circumferential surface using conventional forming processes. The curvature radius of 0.5mm or more is achieved through standard manufacturing techniques, maintaining ease of production while significantly improving reliability by distributing forces and preventing insulator breakage
3Area of moving object
If the packing member contacts the insulator at pointed corners, then the area of contact is minimized, but the force magnitude increases, causing cracks from the outer circumferential surface to the diameter direction
Solution Approach 1:
By curving the inner circumferential surface of the packing member with a radius of 0.5mm or more, the contact area with the insulator is increased and the contact force is distributed over a larger area. This reduces the magnitude of force per unit area, preventing crack initiation and propagation from the outer circumferential surface toward the center
Data Source
AI summary
A spark plug has a housing of a cylindrical shape, an insulator of a cylindrical shape, and a packing. The housing has a housing facing surface. The insulator has an insulator facing surface and is supported in the housing. The packing has an insulator side contact surface which is in contact with the insulator facing surface. The packing is arranged between the housing facing surface and the insulator facing surface to face both the housing facing surface and the insulator facing surface. The packing has proximal inner circumferential surfaces formed adjacent with the inner periphery side of the insulator side contact surface. Each of the proximal inner circumferential surfaces has a curved shape smoothly connected to the insulator side contact surface of the packing.