Spark Plug Electrode Composite Core Thermal Expansion Mismatch
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Spark plug electrodes face challenges with thermal stress due to differences in thermal expansion coefficients between nickel alloy outer shells and copper cores, leading to clearance issues and reduced durability, while dispersing ceramic powder lowers thermal conductivity and damages machining jigs.
Innovation Solution
A spark plug electrode with a core formed from a composite material containing a matrix metal and dispersed carbon, where the carbon content is 10 vol.% to 80 vol.%, and an outer shell of nickel or nickel alloy, reducing thermal expansion coefficient differences and maintaining high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is employed as core material, then thermal conductivity is improved, but thermal expansion coefficient difference increases causing clearance formation
Solution Approach 1:
The patent employs a composite core material consisting of copper particles dispersed in a nickel-based matrix. This composite structure combines the high thermal conductivity of copper with the low thermal expansion coefficient of nickel, achieving both high heat dissipation performance and minimal thermal expansion mismatch with the nickel alloy outer shell, thereby preventing clearance formation at the boundary.
Solution Approach 2:
The patent modifies the thermal expansion coefficient parameter of the core material by creating a composite structure with nickel-based matrix and copper particles. This parameter change allows the core to match the thermal expansion characteristics of the nickel alloy outer shell while maintaining adequate thermal conductivity through the copper particle dispersion.
2Manufacturing precision
If ceramic powder is dispersed in core to reduce thermal expansion coefficient, then thermal expansion coefficient difference decreases, but thermal conductivity is lowered and machining jig service life is shortened
Solution Approach 1:
Instead of using ceramic powder, the patent employs a metal composite system with copper particles in a nickel-based matrix. This metallic composite maintains ductility and machinability while achieving the desired thermal expansion coefficient match, avoiding the hardness-related machining jig wear problem associated with ceramic additives.
Solution Approach 2:
The patent uses copper particles, which are softer and more ductile than ceramic materials, to create a composite that is easier to machine. Although copper has higher thermal expansion than ceramic, the nickel-based matrix dominates the thermal expansion behavior, achieving the match with outer shell while maintaining better machinability.
3Manufacturing precision
If nickel or iron is employed as core material, then thermal expansion coefficient matches outer shell, but thermal conductivity is lower than copper
Solution Approach 1:
The patent creates a composite material that combines nickel-based matrix (providing thermal expansion match) with dispersed copper particles (providing high thermal conductivity). This composite approach allows the core to simultaneously achieve both thermal expansion compatibility with the outer shell and high thermal conductivity for effective heat dissipation.
Solution Approach 2:
The patent applies local quality by distributing copper particles throughout the nickel-based matrix. The nickel matrix provides the bulk thermal expansion matching property, while the locally dispersed copper particles provide enhanced thermal conductivity pathways, creating a material with spatially optimized properties for both functions.
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 solution prevents clearance formation and enhances durability by maintaining high thermal conductivity and processability, reducing the load on working jigs and extending the service life of spark plug electrodes.
Implementation Method 1
the difference in thermal expansion coefficient increases between the outer shell and the core, and thus clearances are formed at the boundary between the outer shell and the core due to thermal stress
Implementation Method 2
the core material is a composite material prepared by dispersing, in a matrix metal, carbon, which has a thermal conductivity several times higher than that of copper
Data Source
Figure 1
Figure 2(a)~3(c)
Figure 4
AI summary
According to the present invention, at least one of a center electrode or a ground electrode is produced by mixing a matrix metal with carbon so that the carbon content of the resultant mixture is adjusted to 80 vol.% or less; subjecting the mixture to powder compacting or sintering, to thereby form a core; placing the core in a cup formed of nickel or a metal containing nickel as a main component; and subjecting the cup to cold working. The thus-produced electrode exhibits favorable thermal conductivity and good heat dissipation, by virtue of the small difference in thermal expansion coefficient between the core and an outer shell. Therefore, a spark plug including the electrode exhibits excellent durability.