Spark Plug Tip Segmentation for Thermal Stress Relief
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Solution Overview
Problem
Spark plugs with tips made from noble metal alloys face issues of deformation and peeling under severe thermal cycles, leading to reduced ignitability and wear resistance, particularly when joined using resistance welding or laser welding methods.
Innovation Solution
A spark plug design featuring a tip with a discharge layer formed from a Pt-Rh alloy and a relieving layer formed from a Pt-Ni alloy, joined via solid phase diffusion joining, where the ratio of average cross-sectional areas of the discharge layer to the relieving layer satisfies 0.81 ≤ A/B ≤ 1.21, and the clad diffusion layer thickness is greater than the diffusion layer thickness, to suppress deformation and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tip made of noble metal alloy (Pt-Rh) is used to improve oxidation resistance, then oxidation resistance is improved, but the tip deforms into convex shape under severe thermal cycles reducing ignitability
Solution Approach 1:
The tip is divided into two functional layers: a discharge layer (Pt-Rh alloy) providing oxidation resistance and spark discharge function, and a relieving layer (Pt-Ni alloy) with lower thermal expansion coefficient to suppress deformation. This segmentation allows each layer to perform its specific function while compensating for the weaknesses of the other.
Solution Approach 2:
The tip uses a composite structure combining two different noble metal alloys with distinct properties. The Pt-Rh discharge layer provides oxidation resistance, while the Pt-Ni relieving layer provides thermal stress relief through its lower thermal expansion coefficient, creating a composite material system that achieves both oxidation resistance and shape stability.
2Strength
If resistance welding or laser welding is used to join the tip to the electrode, then joining strength is improved, but thermal stress causes deformation and peeling under severe thermal cycles
Solution Approach 1:
The joining structure is segmented into two diffusion layers: a clad diffusion layer between the discharge layer and relieving layer, and a diffusion layer between the relieving layer and ground electrode. This segmentation allows for controlled thermal stress distribution and reduces the risk of peeling at the tip-electrode interface.
Solution Approach 2:
The relieving layer acts as an intermediary between the discharge layer and the ground electrode, absorbing thermal stress through its lower thermal expansion coefficient. The dual diffusion layer structure provides intermediate bonding zones that gradually transition between materials, reducing thermal shock and preventing peeling.
3Area of stationary object
If the tip has low height and large width to improve contact area, then joining area is improved, but melt portion is exposed in discharge surface causing easy wear under laser welding
Solution Approach 1:
The tip structure is segmented into functional layers where the discharge layer is positioned to perform spark discharge while the relieving layer provides structural support and thermal stress relief. This segmentation allows the discharge layer to be optimized for its specific function without being constrained by the joining area requirements.
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 configuration enhances the wear resistance and oxidation resistance of the spark plug, preventing deformation and peeling under severe thermal cycles while maintaining high ignitability and wear resistance.
Implementation Method 1
a clad diffusion layer and a diffusion layer formed by solid phase diffusion joining
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A spark plug (1) comprising a center electrode, a ground electrode (8) disposed on the center electrode across a gap, and a tip (9) joined to an opposed surface of the ground electrode that is opposed to the center electrode, the tip has a discharge layer (40) and a relieving layer (50), the relieving layer is formed from a Pt-Ni alloy and joined to the opposed surface via a diffusion layer, the discharge layer is formed from a Pt-Rh alloy and joined via a clad diffusion layer to a side of the relieving layer opposite to a side of the relieving layer at which the ground electrode is joined, and 0.81 ≤ A/B ≤ 1.21 is satisfied when an average cross-sectional area of the discharge layer is A mm2 and an average cross-sectional area of the relieving layer is B mm2, and a method for producing the spark plug.