Spark Plug Terminal Electrode Center of Gravity Positioning
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Solution Overview
Problem
High-efficiency internal combustion engines with advanced control systems face increased vibration and stress on terminal electrodes due to elongated leg portions, leading to potential breakage and discharge abnormalities from current leakage, especially under higher voltage requirements.
Innovation Solution
A spark plug design with a terminal electrode having a center of gravity located inside the insulator, a leg portion length of 35 mm or more, and a Vickers hardness of 150 Hv or greater, along with a reduced head portion weight and length, to minimize stress and prevent breakage and misfires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the leg portion of the terminal electrode is elongated to 35 mm or more to increase the distance between the terminal electrode and metallic shell, then current leakage (flashover) is prevented, but the terminal electrode becomes more susceptible to breakage due to vibration and stress
Solution Approach 1:
The patent changes the physical parameters of the terminal electrode by specifying a minimum leg portion length of 35 mm or more to increase flashover resistance, while simultaneously defining the center of gravity position to manage stress distribution. This parameter optimization resolves the contradiction by finding the specific dimensional values that satisfy both electrical insulation requirements and mechanical strength requirements under vibration conditions.
2Object-affected harmful factors
If the leg portion of the terminal electrode is elongated to prevent current leakage, then electrical insulation is improved, but the stress on the terminal electrode during vibration increases causing potential breakage
Solution Approach 1:
The patent optimizes geometric parameters including the leg portion length (35 mm or more) and the center of gravity position to simultaneously achieve electrical insulation and mechanical durability. By carefully controlling these dimensional parameters, the design prevents flashover while minimizing vibration-induced stress and breakage risk.
3Strength
If the center of gravity of the terminal electrode is positioned inside the insulator, then stress during vibration is reduced preventing breakage, but the leg portion length requirement of 35 mm or more becomes more difficult to achieve
Solution Approach 1:
The patent simultaneously specifies both the center of gravity position (inside the insulator) and the minimum leg portion length (35 mm or more) as design parameters. This dual parameter definition resolves the contradiction by establishing a specific geometric configuration where the terminal electrode's mass distribution and dimensions are optimized together to achieve both mechanical strength and electrical insulation performance.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A spark plug (1) includes a ceramic insulator (2) having an axial bore (4) extending in the direction of an axis (CL1) and a terminal electrode (6) inserted into the axial bore (4). The terminal electrode (6) includes a rodlike leg portion (6A) inserted into the a rear end portion of the axial bore (4) and a head portion (6B) exposed at the rear end of the ceramic insulator (2). A front end subportion of the leg portion (6A) of the terminal electrode (6) is fixed to the ceramic insulator (2), and the leg portion (6A) has a length of 35 mm or more along the axis (CL1). Additionally, the center of gravity of the terminal electrode (6) is located in the interior of the ceramic insulator (2). Thus, in the spark plug (1) having the terminal electrode (6) whose leg portion (6A) is relatively long, breakage of the terminal electrode (6) can be more reliably prevented.