Stainless Steel Spark Plug Sealing Member Creep Resistance
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Solution Overview
Problem
Conventional spark plug sealing members made of cold-rolling steel struggle with air tightness due to low durability and creep deformation, leading to insufficient axial force when miniaturized engines and spark plugs are used, and high tightening torque can cause thread neck fracture.
Innovation Solution
A sealing member made of austenitic or ferritic stainless steel with specific thickness and curvature properties is used, allowing for elastic and plastic deformation to provide sufficient axial force with lower tightening torque, and an inwardly projecting region is formed to prevent the sealing member from falling off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a gasket made of conventional cold-rolling steel is used, then the manufacturing cost is low and ease of manufacture is improved, but the durability under creep deformation is poor leading to insufficient axial force
Solution Approach 1:
The patent changes the material parameter from conventional cold-rolling steel to austenitic or ferritic stainless steel, which fundamentally alters the creep resistance and durability characteristics while maintaining manufacturability through standard metalworking processes
Solution Approach 2:
The sealing member utilizes stainless steel material properties that combine both durability under creep conditions and sufficient plastic deformation capability, effectively creating a composite performance profile that satisfies both reliability and sealing requirements
2Reliability
If a gasket made of stainless steel with high rigidity is used, then the durability under creep deformation is improved, but the plastic deformation capability is reduced leading to insufficient axial force when tightening torque is low
Solution Approach 1:
The patent specifies precise geometric parameters including thickness ratio (0.5 ≤ x/L ≤ 1.4) and curvature radius ratios (0.05 ≤ R2/R1 ≤ 0.2) that optimize the balance between rigidity for creep resistance and plastic deformation capability for axial force generation under low tightening torque conditions
3Reliability
If the tightening torque is increased to obtain sufficient axial force, then the sealing capability is improved, but the stress on the thread neck increases causing possible fracture
Solution Approach 1:
The patent optimizes the thickness parameter x and its ratio to total thickness L (0.5 ≤ x/L ≤ 1.4) to achieve sufficient axial force with lower tightening torque, thereby protecting the thread neck from excessive stress while maintaining sealing capability
Solution Approach 2:
The patent introduces specific curvature radii R1 and R2 with defined ratios (0.05 ≤ R2/R1 ≤ 0.2) that enable controlled plastic deformation and stress distribution, allowing adequate sealing force without concentrating excessive stress on the thread neck
4Reliability
If the thickness of the sealing member is increased to provide sufficient axial force, then the sealing capability is improved, but the tightening torque required increases causing thread neck stress
Solution Approach 1:
The patent defines the optimal thickness ratio x/L between 0.5 and 1.4, which balances the axial force generation capability with the tightening torque requirement, preventing both insufficient sealing and excessive thread neck stress
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 sealing member maintains high rigidity and durability, ensuring a sufficient axial force is maintained even after reaching the limit of elastic deformation, and the inwardly projecting region prevents the sealing member from falling off, enhancing the sealing effect and preventing thread neck damage.
Implementation Method 1
The sealing member is compressed in an axial direction between an annular-shaped projecting portion... to thereby provide a seal... The sealing member maintains high rigidity and durability, ensuring a sufficient axial force is maintained even after reaching the limit of elastic deformation
Implementation Method 2
allowing for elastic and plastic deformation to provide sufficient axial force with lower tightening torque
Implementation Method 3
folded back in a radial direction so as to form a region where at least two or more layers of the sheet material are overlapped in an axial direction
Data Source
Figure 1
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Figure 4
AI summary
A sealing member (80) for a cylindrical spark plug (100) having a metal shell with threaded ridges thereon to be screwed into a mounting hole (155) in a combustion engine (150), the sealing member (80) comprised of a piece of annular sheet material made of austenitic stainless steel or ferritic stainless steel that is folded back in a radial direction so as to form a region where at least two or more layers of the sheet material are overlapped in an axial direction.