Spark Plug Insulator Curvature for Improved Gastight Sealing
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Solution Overview
Problem
Conventional spark plugs face challenges in maintaining gastightness, leading to potential gas leaks from the combustion chamber.
Innovation Solution
The spark plug design incorporates an insulator with a step portion featuring a first curved surface convex towards the forward end and a second curved surface convex towards the rear end, both surfaces being engaged by a packing to increase the contact area and enhance gastightness, with the first curved surface having a larger radius of curvature than the second.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional flat step portion is used for the insulator, then the structure is simple and easy to manufacture, but the gastightness is insufficient leading to gas leaks
Solution Approach 1:
The patent applies curvature to the step portion by forming a first curved surface (convex toward forward end) and a second curved surface (convex toward rear end) instead of using a flat surface. This curved configuration increases the contact area between the packing and the insulator, thereby enhancing gastightness and preventing gas leaks while maintaining manufacturing feasibility.
2Reliability
If the contact area between packing and insulator is increased, then gastightness is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent changes the geometric parameters of the step portion by introducing specific curved surfaces with defined convex directions. The first curved surface convex toward the forward end and the second curved surface convex toward the rear end create an optimized contact geometry that increases packing contact area while maintaining manufacturability through controlled parameter specifications.
Data Source
AI summary
A spark plug which includes an insulator having an axial hole extending along an axial line, a metallic shell disposed around the insulator, and a center electrode disposed in the axial hole to be located on the forward end side of the axial line is provided. The insulator has a step portion provided on the outer circumferential surface thereof and facing toward the forward end side. The metallic shell has a receiving surface provided on the inner circumferential surface thereof and facing toward the rear end side and with which the step portion is engaged via a packing. A portion of the step portion on the outer circumferential side is a first curved surface being convex toward the forward end side, and a portion of the step portion on the inner circumferential side of the first curved surface is a second curved surface being convex toward the rear end side.