Spark Plug Insulator Shoulder Geometry for Flashover Suppression
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Solution Overview
Problem
Conventional spark plugs experience flashover issues at high voltages, leading to reduced ignitability of the air-fuel mixture due to creeping discharge along accumulated carbon, which decreases the frequency of flying sparks and affects the regular spark gap, necessitating a solution to reduce flashover occurrence while ensuring low cost, resource efficiency, and improved durability.
Innovation Solution
The spark plug design incorporates specific geometric relationships and configurations, including a sufficient distance between the metal shell's tip end and insulator, a tapered second shoulder with expanded inner diameter, and a constant outer diameter trunk portion, to suppress electric field concentration and extend discharge distances, thereby reducing flashover occurrences and maintaining heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the leg base portion is formed parallel to the axis line to inhibit combustion gas entry, then heat resistance variation is reduced, but flashover occurs along accumulated carbon at high voltages
Solution Approach 1:
The invention introduces a radial dimension solution by forming a tapered second shoulder that expands from rear end to tip end, creating a radial clearance between the metal shell and insulator. This radial space disrupts the axial path of creeping discharge along the carbon accumulation, preventing flashover while maintaining heat resistance stability.
Solution Approach 2:
The tapered second shoulder acts as an intermediary structure between the metal shell and insulator. By creating a controlled radial clearance, it introduces a new spatial dimension that interrupts the harmful creeping discharge path while preserving the functional relationship between components.
2Object-affected harmful factors
If a sufficient distance is created between the metal shell tip end and insulator, then electric field concentration is suppressed and flashover is reduced, but the structural complexity increases
Solution Approach 1:
The metal shell is segmented into multiple functional portions: a tapered second shoulder with expanded inner diameter and a constant outer diameter trunk portion. This segmentation allows the creation of sufficient radial clearance distance to suppress electric field concentration while maintaining overall structural integrity and avoiding excessive complexity.
3Object-affected harmful factors
If the second shoulder is formed with expanded inner diameter from rear end to tip end, then discharge distance is extended and flashover is suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The second shoulder is formed with a tapered geometry that expands the inner diameter smoothly from the rear end to the tip end. This curved/tapered transition provides a gradual geometric change that extends the discharge distance and suppresses flashover, while being more manufacturable than sharp angular transitions.
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 suppresses flashover occurrences and maintains heat resistance, improving anti-flashover performance and reducing variations in heat ratings, as demonstrated by test results showing low flashover incidence and minimal displacement in heat ratings compared to reference spark plugs.
Implementation Method 1
suppresses the occurrence of the electric field concentration adjacent to the tip end of the second shoulder of the metal shell
Implementation Method 2
inhibits a combustion gas from entering between the insulator and the metal shell so as to reduce variation in heat resistance
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
A spark plug (100) includes an insulator (10) and a metal shell (50) disposed at an outer periphery of the insulator (10). The metal shell (50) includes a shoulder (56). The insulator (10) includes a trunk portion (302) and a leg (310) formed at the tip end side of the trunk portion (302). The shoulder (56) of the metal shell (50) includes a first shoulder (400) and a second shoulder (402) formed at the tip end side of the first shoulder (400). A distance Da between the tip end PA of the second shoulder (402) and the leg (310) and a distance Db between the tip end PB of the trunk portion (302) and the second shoulder (402) satisfy a relationship of Da/Db ≥ 1.1. A distance T between the rear end PC of the first shoulder (400) and the tip end PA of the second shoulder (402) and a distance L between the rear end PC of the first shoulder (400) and a tip end face (57) of the metal shell (50) satisfy a relationship of T/L ≤ 0.5.