Spark Plug Insulator Sealing via Hardness Gradient Plate Packing
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Solution Overview
Problem
Spark plugs with reduced diameters face challenges in maintaining gas-tightness and preventing insulator breakage due to inadequate contact area between the plate packing and engagement portions, leading to potential deformation and misalignment.
Innovation Solution
The spark plug design features a tubular insulator and metallic shell with a protrusion and engagement portion configuration, where the plate packing's hardness and angles are strategically optimized to distribute load effectively, ensuring θs > θp and Hvo > Hvi, thereby increasing contact pressure and adhesion while preventing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the spark plug diameter is reduced, then the degree of design freedom is increased, but the contact area between plate packing and engagement portion is insufficient, causing impairment of gas-tightness
Solution Approach 1:
The plate packing is designed with non-uniform hardness distribution, where the hardness varies in the radial direction. Specifically, the hardness at the outer peripheral portion is higher than at the inner peripheral portion, creating local quality differences that optimize both gas-tightness and prevent insulator breakage in the reduced-diameter spark plug configuration
Solution Approach 2:
The invention changes the physical parameter of the plate packing by controlling its hardness distribution. Through specific hardness control in the radial direction, the plate packing achieves optimal contact pressure distribution that maintains gas-tightness while preventing excessive load on the insulator in small-diameter spark plugs
2Reliability
If a larger load is applied during crimping to increase contact pressure, then gas-tightness is improved, but the protrusion is excessively compressed, causing deformation toward the insulator
Solution Approach 1:
The plate packing exhibits different hardness properties at different radial positions. The outer peripheral portion has higher hardness to withstand larger contact pressure without deforming the protrusion, while the inner peripheral portion has lower hardness to maintain adequate contact pressure for gas-tightness
Solution Approach 2:
By controlling the hardness distribution parameter of the plate packing in the radial direction, the invention achieves optimal load distribution during crimping. This prevents excessive compression of the protrusion while maintaining sufficient contact pressure for gas-tightness
3Reliability
If a larger load is applied during crimping, then contact pressure of plate packing is increased, but the insulator may break due to excessive compression of the protrusion
Solution Approach 1:
The plate packing is designed with radially varying hardness where the outer peripheral portion has higher hardness to distribute load away from the insulator, while the inner peripheral portion has lower hardness to maintain contact pressure. This local quality differentiation protects the insulator from breakage while ensuring adequate gas-tightness
Solution Approach 2:
The hardness parameter of the plate packing is controlled to vary in the radial direction, creating an optimal stress distribution pattern during crimping that increases contact pressure for gas-tightness while preventing excessive stress concentration that would cause insulator breakage
Data Source
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AI summary
To provide a spark plug which can secure favorable gas-tightness and can reliably prevent, for example, breakage of an insulator. A spark plug (1) includes a ceramic insulator (2) having a diameter-decreasing portion (14), and a metallic shell (3) which is provided around the ceramic insulator (2) and which has a protrusion (21) projecting inwardly in a radial direction. The protrusion (21) has a diameter-decreasing portion (21A), and the diameter-decreasing portion (21A) seats on the engagement portion (14) via an annular plate packing (22). In or on a longitudinal cross section including an axial line CL1, a relation of θs > θp is satisfied, wherein θp represents an acute angle (°) between a straight line orthogonal to the axial line CL1 and the contour of the engagement portion (14), and θs represents an acute angle (°) between a straight line orthogonal to the axial line CL1 and the contour of the diameter-decreasing portion (21A). In the aforementioned cross section, a relation of Hvo > Hvi is satisfied, wherein Hvo represents the Vickers hardness (Hv) of the plate packing (22) at the midpoint CP1 of a first line segment SL1, and Hvi represents the Vickers hardness (Hv) of the plate packing (22) at the midpoint CP2 of a second line segment (SL2).