Spark Plug Fusion Boundary Curvature for Thermal Stress
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Solution Overview
Problem
Existing spark plugs face durability issues due to thermal stress between noble metal tips and central electrode base materials, leading to potential separation and reduced lifespan.
Innovation Solution
A spark plug design featuring a fusion portion with a convexly curved boundary between the noble metal tip and central electrode, and a concavely curved outer surface of the fusion portion, reducing thermal stress and exposure of the fusion portion during wear, thereby enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a fusion layer is formed by laser welding to connect the noble metal tip and central electrode base material, then thermal stress is reduced and connection tightness is improved, but the firing end durability is insufficient
Solution Approach 1:
The fusion portion is designed with a convex curved outer surface instead of a flat surface. This curvature allows the fusion portion to recede as the noble metal tip wears down from spark discharge, preventing exposure of the fusion portion and maintaining connection integrity throughout the service life of the spark plug.
Solution Approach 2:
The invention introduces a radial dimension consideration by positioning the maximum radius of the fusion portion at a specific distance from the outer circumferential surface of the noble metal tip. This dimensional arrangement ensures that even after significant wear, the fusion portion remains protected and does not expose, thereby enhancing firing end durability.
2Stability of the object's composition
If the noble metal tip and central electrode base material are tightly connected through fusion welding, then thermal stress is reduced, but the fusion portion may be exposed after discharge surface wear
Solution Approach 1:
The convex curved outer surface of the fusion portion ensures that as the noble metal tip erodes from spark discharge, the fusion portion recedes gradually and remains protected. The curvature geometry prevents direct exposure of the fusion portion, maintaining structural integrity and thermal stress resistance throughout the extended service life.
Solution Approach 2:
The fusion portion is pre-positioned with its maximum radius at a specific distance from the outer circumferential surface of the noble metal tip before any wear occurs. This preliminary arrangement anticipates future wear and ensures that the fusion portion will not expose during the service life, thereby maintaining thermal stress resistance throughout.
3Ease of manufacture
If the fusion portion is positioned closer to the outer surface for easier manufacturing, then manufacturing complexity is reduced, but the fusion portion becomes exposed during wear
Solution Approach 1:
The invention specifies that the maximum radius of the fusion portion should be positioned at a specific distance (0.05-0.5mm) from the outer circumferential surface of the noble metal tip. This radial positioning in another dimension ensures that the fusion portion remains protected during wear while maintaining manufacturability through clear dimensional specifications.
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 effectively reduces thermal stress and prevents exposure of the fusion portion, resulting in a more durable and long-lasting spark plug with improved resistance to wear and separation.
Implementation Method 1
a noble metal tip (such as Ir alloy) and a central-electrode base material (such as Ni alloy) have a large difference in coefficient of thermal expansion. To prevent the tip from being separated due to thermal stress
Implementation Method 2
each of the tip-adjoining boundary, forming the boundary between the noble metal tip and the fusion portion, and the central-electrode-adjoining boundary, forming the boundary between the central electrode and the fusion portion, has a shape that curves convexly toward a member made of a material having a larger coefficient of thermal expansion. This configuration thus reduces a stress that occurs due to a difference in thermal expansion at each of the boundaries
Implementation Method 3
the outline of a portion of the fusion portion exposed to the outer surface has a shape that curves concavely into the inner side of the fusion portion... the fusion portion is less likely to be exposed from the discharge surface of the noble metal tip after the discharge surface is worn by spark discharge
Data Source
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AI summary
Provided is a spark plug including a more highly durable firing end while a central electrode and a noble metal tip, welded to the central electrode and made of a noble metal or a noble metal alloy, are sufficiently tightly connected together. A spark plug includes a central electrode (100) and a noble metal tip (110), which are joined together with a fusion portion (120) interposed therebetween. A tip-adjoining boundary (130) of the fusion portion (120) has a shape that curves convexly toward the fusion portion (120). A central-electrode-adjoining boundary (140) of the fusion portion (120) has a shape that curves convexly toward the central electrode (100). The outline of a portion of the fusion portion (120) exposed to the outer surface has a shape that curves concavely into the inner side of the fusion portion (120).