Spark Plug Ground Electrode Protrusion Grain Size
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Solution Overview
Problem
Spark plugs for internal combustion engines face challenges in heat transfer and erosion resistance, particularly when a protrusion on the ground electrode is formed from a material inferior to noble metal alloys, leading to increased manufacturing costs and potential erosion.
Innovation Solution
A spark plug design where the protrusion on the ground electrode is formed from the same material as the electrode itself, with an average crystal grain size of 50 µm to 200 µm to enhance heat transfer and erosion resistance, and formed through press working to maintain cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the protrusion is formed from the same material as the ground electrode to reduce manufacturing cost, then manufacturing cost is reduced, but heat transfer performance deteriorates leading to poor erosion resistance
Solution Approach 1:
The invention changes the physical parameter of crystal grain size to improve heat transfer. By controlling the crystal grain size to be 5 µm or less in the protrusion portion through specific forming processes, the thermal conductivity is enhanced, allowing the ground electrode material to achieve good erosion resistance without using expensive noble metals, thus resolving the contradiction between manufacturing cost and erosion resistance.
2Reliability
If the protrusion is formed with fine crystal grains to improve heat transfer, then heat transfer performance is improved, but the forming process becomes more difficult
Solution Approach 1:
The invention specifies a quantitative parameter range for crystal grain size (5 µm or less) that balances heat transfer performance with manufacturability. This parameter optimization ensures sufficient thermal conductivity while remaining achievable through conventional forming processes, avoiding excessive complexity in manufacturing.
Solution Approach 2:
The invention applies preliminary deformation processing before final forming to control crystal grain development. By pre-deforming the ground electrode and then forming the protrusion, the crystal grains are refined to the desired size range, making it easier to achieve fine grain structure without excessive difficulty in the forming process.
3Ease of operation
If the ground electrode is bent to form a gap with the center electrode, then ignition function is achieved, but stress concentrates on the bent portion causing potential breakage
Solution Approach 1:
The invention applies preliminary deformation to the ground electrode body before forming the protrusion and bending. This pre-deformation process refines the crystal grain structure throughout the electrode, including the bent portion, thereby enhancing mechanical strength and stress resistance while maintaining the necessary bending for gap formation.
Solution Approach 2:
The invention changes the material microstructure parameter (crystal grain size) to improve mechanical properties. By controlling crystal grains to be fine (5 µm or less), the material achieves higher strength through grain boundary strengthening, enabling the bent portion to withstand operational stresses while maintaining ignition functionality.
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
This design improves ignition and flame propagation performance while reducing manufacturing costs by enhancing heat transfer and erosion resistance without using noble metal tips, and ensures mechanical strength at the bent portion to prevent breakage.
Implementation Method 1
at least the protrusion has a relatively large average crystal grain size of 50 μm to 200 μm inclusive, the protrusion is composed of crystals having an average grain size of at least 50 μm, so that the protrusion allows rapid heat conduction
Implementation Method 2
formed through press working to maintain cost-effectiveness
Data Source
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AI summary
An objective is to provide a spark plug in which a ground electrode has a protrusion formed from the same material as that used to form the ground electrode and the heat transfer performance of the protrusion is improved to thereby improve erosion resistance. A spark plug 1 includes a rodlike center electrode 5 extending in the direction of an axis CL1; a substantially cylindrical insulator 2 provided externally of the outer circumference of the center electrode 5; a substantially cylindrical metallic shell 3 provided externally of the outer circumference of the insulator 2; and a ground electrode 27 extending from a front end portion 26 of the metallic shell 3 and forming a spark discharge gap 35 between a distal end portion thereof and a front end portion of the center electrode 5. A protrusion 28 projecting toward the center electrode 5 and forming the spark discharge gap 35 in cooperation with the front end portion of the center electrode 5 is formed at the distal end portion of the ground electrode 27 from the same material as that used to form the ground electrode 27. At least the protrusion 28 has an average crystal grain size of 20 µm to 200 µm inclusive.