Spark Plug Gap Structure for Melt Portion Heat Shielding
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Solution Overview
Problem
Conventional spark plugs with a melt portion exposed to high-temperature gas flows experience excessive heating, leading to pre-ignition of fuel gas in the sub chamber due to lower thermal conductivity compared to the cap and metal shell, causing thermal stress and potential cracking.
Innovation Solution
A spark plug design featuring a gap between the sub chamber and the melt portion, with an opening in the radial direction, reduces the likelihood of high-temperature gas entering the gap, allowing low-temperature gas to remain and minimize contact between the fuel gas and the melt portion, thereby reducing excessive heating and thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the melt portion is exposed to high-temperature gas flow including flame, then the cap and metal shell can be effectively joined, but the melt portion experiences excessive heating and becomes a source of pre-ignition
Solution Approach 1:
The patent introduces a gap structure that segments the space between the sub chamber and the melt portion. This gap with radial opening allows low-temperature gas to remain in the region near the melt portion, effectively isolating it from direct exposure to high-temperature flame while maintaining the structural integrity of the joint.
Solution Approach 2:
The gap acts as an intermediary zone between the high-temperature gas flow and the melt portion. By introducing this intermediate space filled with low-temperature gas, the patent reduces direct heat transfer to the melt portion, preventing excessive heating and pre-ignition while preserving the joint's strength.
2Productivity
If the melt portion is exposed to high-temperature gas flow, then the combustion process can proceed, but thermal stress causes cracking in the melt portion
Solution Approach 1:
The gap structure segments the thermal environment, creating a protected zone around the melt portion. This segmentation allows the combustion process to continue in the sub chamber while isolating the melt portion from extreme thermal conditions that would cause cracking and reduce reliability.
Solution Approach 2:
The patent employs the gap structure as a preventive measure before thermal stress can cause damage. By maintaining a layer of low-temperature gas between the flame and the melt portion, the design cushioning against thermal stress accumulation, preventing cracking before it occurs.
3Temperature
If the melt portion has lower thermal conductivity, then it provides thermal insulation, but it stores heat and causes pre-ignition
Solution Approach 1:
The gap filled with low-temperature gas serves as an intermediary layer between the melt portion and the high-temperature environment. This intermediary zone prevents the melt portion from storing excessive heat by maintaining a thermal barrier, thereby eliminating the pre-ignition hazard while preserving the beneficial thermal insulation properties.
Solution Approach 2:
The patent changes the thermal environment parameters around the melt portion by introducing the gap structure. This structural modification alters the heat transfer parameters, reducing the temperature gradient and heat storage in the melt portion, thereby preventing pre-ignition while maintaining thermal insulation.
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 pre-ignition of fuel gas and minimizes thermal stress-induced cracking in the melt portion by maintaining lower temperatures and reducing heat transfer from the gas flow, enhancing the reliability of the spark plug.
Implementation Method 1
a gap which extends from the sub chamber to the melt portion is present... the gap has an opening which is open in a radial direction... low-temperature gas easily remains in the gap... the melt portion is less likely to be cooled by the fuel gas... excessive heating of the melt portion can be reduced
Data Source
AI summary
The spark plug is provided with: an insulator; a main metal fitting in which a shelf portion for locking the insulator is provided; and a cap joined to the main metal fitting by way of a melted portion. The cap forms an auxiliary chamber, and includes an injection port penetrating from an inner surface to an outer surface. There is a gap extending from the auxiliary chamber to the melted portion, between a first surface connecting an inner peripheral surface of the main metal fitting and an outer peripheral surface of the main metal fitting on a tip end side of the shelf portion, and a second surface of the cap, connecting an inner surface and an outer surface thereof, and the gap includes an opening portion which opens into the auxiliary chamber in a radial direction.