Spark Plug Embedded Tip Fusion Zone Thermal Stress
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Solution Overview
Problem
The existing spark plugs face detachment issues due to thermal stress between the tip and the ground electrode, especially in high-compression internal combustion engines, where the tip is prone to high temperatures, leading to oxide scale formation and potential detachment.
Innovation Solution
The spark plug design incorporates a fusion zone between the tip and the ground electrode, with specific relational expressions (E/F≧1.1, E/F≧1.5, A/B≦0.6, C/(B−A)≦0.95, and D/C≦0.7, to absorb thermal expansion differences and enhance joining strength, preventing oxide scale formation and tip detachment, while optimizing ignition performance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the tip is embedded in the ground electrode to improve joining strength, then the joining strength between tip and ground electrode is improved, but the thermal stress between tip and ground electrode increases, leading to oxide scale formation and potential detachment
Solution Approach 1:
The patent applies parameter changes by controlling the embedment depth ratio (E/F ≥ 1.1) to optimize the balance between joining strength and thermal stress. By adjusting the geometric parameters of the embedded tip structure, the invention achieves sufficient mechanical bonding while limiting thermal expansion differences that cause detachment.
Solution Approach 2:
The invention uses composite materials by combining the tip (made of noble metal alloy for erosion resistance) with the ground electrode (made of different material properties). This composite structure allows each material to contribute its superior properties while managing the interface through controlled embedment to prevent detachment.
2Use of energy by moving object
If high compression is implemented to improve fuel economy, then fuel economy is improved, but the tip temperature increases, leading to increased thermal stress and greater risk of tip detachment
Solution Approach 1:
The patent addresses temperature increase by modifying the structural parameters of the tip-ground electrode interface. The controlled embedment depth ratio (E/F ≥ 1.1) allows heat dissipation management and stress distribution, enabling the spark plug to withstand higher temperatures from high-compression engines without tip detachment.
3Strength
If the embedment depth of the tip is increased to improve joining strength, then the joining strength is improved, but the thermal expansion difference between tip and ground electrode increases, potentially causing detachment
Solution Approach 1:
The invention optimizes the embedment depth by establishing a specific ratio relationship (E/F ≥ 1.1) between the embedment depth (E) and the tip thickness (F). This parameter optimization ensures that the tip is embedded sufficiently for strong joining while limiting the depth to prevent excessive thermal stress accumulation.
Solution Approach 2:
The patent transitions from purely mechanical embedding to a combined thermal-mechanical bonding system. The fusion zone creates metallurgical bonding that supplements mechanical interlocking, allowing for optimized embedment depth that balances both joining strength and thermal stress management.
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 absorbs thermal stress, prevents tip detachment, maintains a stable spark discharge gap, and improves ignition performance and durability by ensuring the tip remains securely embedded and aligned with the ground electrode, even under high-temperature conditions.
Implementation Method 1
the difference in thermal expansion (thermal stress) in the direction of thickness of the tip between the tip and the ground electrode becomes large
Implementation Method 2
the tip and the ground electrode being fused at the fusion zone
Data Source
AI summary
A spark plug includes a center electrode, a ground electrode, and a ground-electrode-side tip joined to the ground electrode such that at least a portion of the tip along its thickness direction is embedded in the ground electrode. The ground-electrode-side tip is joined to the ground electrode through a fusion zone formed between the ground electrode and a proximal side of the tip. On a section containing a center axis of the ground electrode and in parallel with the thickness direction of the ground-electrode-side tip, E/F≧1.1 is satisfied, where E (mm) is the longest distance along the thickness direction from an inner side of the ground electrode to a boundary between the fusion zone and the ground electrode, and F (mm) is the largest amount of embedment of the tip in the inner side surface along the thickness direction.