Spark Plug Seat Hardness for Gastightness in Reduced Diameter Designs
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Solution Overview
Problem
Spark plugs face challenges in maintaining gastightness due to damage, strain, or size reduction, which compromises the seal between the seat portion and the engine head, leading to impaired combustion chamber integrity.
Innovation Solution
A spark plug design with a metallic shell featuring a threaded portion, screw neck, diameter-expanded portion, and seat portion, where the seat portion has a Vickers hardness of 250 Hv or less and a specific angle configuration, ensuring reliable contact and preventing deformation, along with a coating layer for enhanced sealing and thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the diameter-expanded portion and threaded portion is reduced to improve layout flexibility, then the size of the spark plug is reduced, but the area of the seat portion is reduced and the axial force from screw engagement is reduced, making it difficult to ensure sufficient seal and gastightness
Solution Approach 1:
The patent applies local quality by specifying that the seat portion has a Vickers hardness of 250 Hv or less, which is higher than the hardness of the contacting portion of the head. This localized hardness configuration ensures that the seat portion maintains its shape and sealing capability even when the overall spark plug size is reduced, resolving the contradiction between compact size and reliable gastightness.
Solution Approach 2:
The patent changes the hardness parameter of the seat portion to be 250 Hv or less, creating a specific material property that enables the reduced-size spark plug to maintain sufficient sealing force. This parameter change allows the smaller spark plug to achieve adequate axial force for sealing without compromising gastightness.
2Reliability
If a gasket is provided around the screw neck to maintain gastightness, then the seal between the spark plug and head is improved, but the structure becomes more complex and the size increases
Solution Approach 1:
The patent extracts the gasket component from the spark plug structure, eliminating the need for a separate sealing element. Instead, the seat portion itself is designed with appropriate hardness to create the seal directly, simplifying the overall structure while maintaining gastightness functionality.
Solution Approach 2:
The patent merges the sealing function into the seat portion by configuring its hardness to be 250 Hv or less. This combines the structural support function and the sealing function into a single component, eliminating the need for a separate gasket and reducing device complexity.
3Reliability
If the seat portion hardness is increased to prevent deformation and maintain seal, then the gastightness is improved, but the seat portion may deform the head or cause damage during mounting and demounting
Solution Approach 1:
The patent optimizes the hardness parameter of the seat portion to be 250 Hv or less, which is higher than the head material to prevent seat deformation, but controlled to avoid excessive hardness that would cause damage during mounting operations. This precise parameter control resolves the contradiction between maintaining seal integrity and preventing damage.
Solution Approach 2:
The patent applies local quality by specifically configuring the hardness of the seat portion to be higher than the contacting portion of the head. This localized hardness difference ensures the seat portion maintains its sealing shape without being so hard as to damage the head during installation, balancing seal reliability with damage prevention.
Data Source
Figure 1
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AI summary
Provided is a spark plug for an internal combustion engine capable of ensuring sufficient gastightness of a combustion chamber and meeting demand for a reduction in diameter. A spark plug 1 includes a center electrode 5, an insulator 2 provided externally of the outer circumference of the center electrode 5, a metallic shell 3 provided externally of the outer circumference of the insulator 2, and a ground electrode 27 extending from a front end portion of the metallic shell 3. The metallic shell 3 has, on an outer circumferential surface thereof, a threaded portion 15 to be threadingly engaged with a mounting hole 43 of a head 42 of an internal combustion engine 41, a screw neck 16 located rearward of the threaded portion 15, a diameter-expanded portion 18 greater in diameter than the screw neck 16, and a seat portion 17 connectingly extending between the screw neck 16 and the diameter-expanded portion 18. When the threaded portion 15 is threadingly engaged with the mounting hole 43, the seat portion 17 comes in close contact with the head 42. The threaded portion 15 has a thread diameter of M14 or less. The seat portion 17 has a predetermined value or less of Vickers hardness and is higher in hardness than a portion of the head 42 which comes into contact with the seat portion 17.