Spark Plug Seal Member Friction Design for Screw Loosening
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Solution Overview
Problem
Existing spark plugs face issues with loose resistance due to slippage between the seal member and the engine's mounting hole, particularly in high-performance engines with increased vibrations and temperature, leading to reduced axial force during fastening and increased risk of screw loosening.
Innovation Solution
A spark plug design featuring a seal member with a specific configuration where the seal member contacts the protrusion part at a single point and the opening periphery at another point, with the latter being outside the former in a radial direction, enhancing frictional forces and maintaining the positional relationship between contact points to ensure increased axial force and resistance to screw loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the seal member is compressed between the protrusion part and the opening periphery to seal airtight leakage, then the adhesion and axial force are enhanced, but slippage may occur between the seal member and the protrusion part or opening periphery under engine vibration, resulting in screw loosening
Solution Approach 1:
The seal member is designed with non-uniform thickness distribution, having a first thickness in a first radial direction and a second thickness in a second radial direction perpendicular to the first. This local quality variation allows different regions of the seal member to have different mechanical properties, enabling one region to provide superior sealing while another region maintains higher axial force and resistance to slippage under vibration.
2Adaptability or versatility
If the seal member is made with larger crush margin in radial direction to ensure rotation of the screw for ground electrode direction adjustment, then the rotation range is increased, but the seal member may protrude from the protrusion part
Solution Approach 1:
The seal member features locally varied thickness where the crush margin is strategically distributed. The region allowing radial expansion for screw rotation has sufficient clearance, while the sealing contact region maintains appropriate thickness to prevent protrusion. This local quality differentiation enables both rotation capability and shape control.
Solution Approach 2:
The problem of radial protrusion is solved by transitioning to axial dimension control through the non-uniform thickness design. By varying the thickness in the axial direction across different radial positions, the seal member accommodates radial expansion for rotation while preventing excessive protrusion through controlled axial compression in specific regions.
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 increases the frictional force between the seal member and the opening periphery, reducing slippage and enhancing the axial force during fastening, thereby improving the loose resistance and preventing screw loosening, even under conditions of high vibration and temperature.
Implementation Method 1
the seal member is compressed between the protrusion part and an opening periphery of the mounting hole, and seals a space between the protrusion part and the opening periphery
Implementation Method 2
The design effectively increases the frictional force between the seal member and the opening periphery, reducing slippage and enhancing the axial force during fastening
Data Source
Figure 1
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AI summary
In process of threadably fitting a metal shell (50) having a surface formed with an Ni plated layer into a mounting hole (91), in a state where a gasket (60) made of stainless steel is uncompressed while being interposed between a protrusion part (54) and an opening periphery (92), a surface of the gasket (60) is out of contact with another surface thereof. When the gasket (60) is viewed on a cross section in a direction of an axial line O, the gasket (60) contacts with the protrusion part (54) at one point of a point X, the gasket (60) contacts with the opening periphery (92) at one point of a point Y, and the point Y is located outside of the point X in a radial direction. Further, the point Y is located inside of a maximum outer diameter Dz of a seating surface (55) of the protrusion part (54) in the radial direction.