Spark Plug Center Electrode Seal Reducing Capacitance
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Solution Overview
Problem
Spark plugs face a challenge in balancing the reduction of electrostatic capacity between the metal shell and the center electrode to improve durability against repeated spark discharge while maintaining impact resistance, as shortening the head portion of the center electrode can lead to reduced holding force and increased likelihood of loosening.
Innovation Solution
The use of an insulating seal body with a two-layer structure, comprising a conductive glass seal layer and an insulating glass seal layer, which contacts the ceramic insulator and center electrode respectively, reduces electrostatic capacity while enhancing impact resistance through improved fixation and thermal expansion coefficient matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the head portion of the center electrode is shortened to reduce electrostatic capacity, then durability against repeated spark discharge is improved, but holding force by the seal body is lowered and impact resistance is reduced
Solution Approach 1:
The seal body is divided into two distinct layers: a insulating seal body (first seal layer) and a conductive seal body (second seal layer). The insulating seal body provides mechanical support and holding force to maintain impact resistance, while the conductive seal body ensures electrical conductivity for spark discharge. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the seal body have different material properties tailored to local requirements. The insulating seal body contacts the center electrode head portion to provide mechanical retention, while the conductive seal body contacts the ground electrode to ensure electrical connectivity. This local differentiation of material properties resolves the contradiction between mechanical strength and electrical conductivity.
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
This configuration effectively reduces electrostatic capacity and maintains or improves impact resistance, preventing loosening of the center electrode, thereby enhancing the overall durability and reliability of the spark plug.
Implementation Method 1
reduction of an electrostatic capacity between the metal shell and a conductor arranged in the ceramic insulator is effective
Implementation Method 2
the insulating seal body may contain glass as a main component
Implementation Method 3
the thermal expansion coefficient of the insulating seal body is between thermal expansion coefficients of the ceramic insulator and the center electrode
Data Source
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AI summary
Both reduction of an electrostatic capacity and securing of impact resistance of a center electrode are achieved. A spark plug includes a metal shell, a ceramic insulator, a resistor, a center electrode, and a seal body. The metal shell is an almost cylindrical member having a ground electrode on a front end side thereof. The ceramic insulator is a cylindrical member that is held in the metal shell and that has therein an axial hole having a small-diameter portion, and a large-diameter portion larger in diameter than the small-diameter portion and connected to a rear end of the small-diameter portion via a stepped portion. The resistor is arranged in the large-diameter portion. The center electrode has: a flange portion projecting in a radial direction in the large-diameter portion to contact with the stepped portion; and a leg portion arranged in the small-diameter portion so as to extend from the flange portion toward the front end side. The seal body is arranged in the large-diameter portion and electrically connects between the center electrode and the resistor. The seal body includes an insulating seal body that comes into contact with the ceramic insulator, and a conductive seal body.