Spark Plug Crimped Lid Geometry for Insulator Holding Force
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Solution Overview
Problem
Existing spark plugs suffer from damage due to external forces, particularly in high-compression engines, where the insulator's holding force deteriorates over time due to thermal expansion differences between the insulator and metal shell, leading to potential damage from vibrations and shocks.
Innovation Solution
A spark plug design featuring a tubular insulator and metal shell with a crimped lid and annular ring member, where the length to thickness ratio of the crimped lid (2.50 ≤ L/t ≤ 3.10) and the diameter ratio between the insulator and metal shell (1.12 ≤ D/d ≤ 1.16) are optimized to enhance the holding force and reduce thermal expansion differences, thereby minimizing damage from external forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the insulator and metal shell are assembled with a ring member and powder for sealing, then the holding force is improved and shock is suppressed, but the insulator may still be damaged by external forces over time due to thermal expansion differences
Solution Approach 1:
The patent changes the physical state of the sealing material from granular powder to a molded resin that has been pre-formed and cured. This parameter change in the sealing material's physical state allows it to maintain consistent sealing pressure and holding force over time, resisting the detrimental effects of thermal expansion differences between the insulator and metal shell.
Solution Approach 2:
The patent uses a composite sealing structure combining a ring member made of flexible material (such as rubber or elastomer) with resin that has been molded and cured in the gap between the insulator and metal shell. This composite material approach provides both immediate sealing and long-term resistance to thermal expansion forces.
2Reliability
If powder for sealing is filled between the insulator and metal shell, then airtightness is improved, but the powder may spill and degradation of holding force occurs over time
Solution Approach 1:
The resin is pre-molded and pre-cured into a specific shape and size before being installed in the spark plug. This preliminary action ensures that the resin is already in its final functional form, properly filling the gap between the insulator and metal shell to provide both airtightness and durable holding force without the risk of material spillage or degradation over time.
Solution Approach 2:
The patent changes the sealing material from loose granular powder to a pre-formed molded resin with controlled physical dimensions and properties. This parameter change in the material's physical state and form prevents spilling and maintains consistent sealing performance and holding force throughout the service life of the spark plug.
3Volume of moving object
If the insulator is made thinner for compact spark plug design, then the spark plug size is reduced, but the insulator becomes more susceptible to damage from external forces
Solution Approach 1:
The patent employs a composite sealing and support structure using flexible ring material combined with molded resin. This composite material system provides enhanced mechanical support and shock absorption for the insulator, allowing the use of thinner insulator designs in compact spark plugs while maintaining sufficient resistance to external forces and vibrations.
Solution Approach 2:
The patent changes the physical properties and state of the sealing material from granular powder to pre-formed molded resin with specific mechanical properties. This parameter change provides superior structural support and shock absorption, enabling thinner insulator designs to withstand external forces and vibrations in compact spark plug applications.
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 optimized design improves the pressing force on the ring member and powder, reducing insulator damage from external forces and thermal expansion differences, resulting in improved durability and reduced risk of breakage.
Implementation Method 1
The end portion is bent toward the outer peripheral surface of the insulator by crimping
Implementation Method 2
thermal expansion differences between the insulator and metal shell
Data Source
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AI summary
A spark plug includes a tubular insulator, and a tubular metal shell secured to an outer peripheral surface of the insulator by crimping. The tubular metal shell includes: an inner peripheral surface in which powder for sealing is filled between the outer peripheral surface and the inner peripheral surface; a tool engagement portion overhanging in a polygonal shape; and a crimped lid disposed at an end portion of the metal shell coupled to the tool engagement portion, the end portion being bent toward the outer peripheral surface of the insulator by crimping. A relationship between a length L and a thickness t satisfies 2.50 ≤ L/t ≤ 3.10, the length L being along a shape of the crimped lid from the tool engagement portion to the insulator in a planar surface that passes through the axis, the thickness t being a thickness at an intermediate portion of the crimped lid.