Spark Plug Center Electrode Recess for Thermal Expansion Control
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Solution Overview
Problem
The existing spark plug designs face issues with clearance due to thermal expansion differences between the center electrode and the insulator, leading to potential sealing and fixing problems, particularly at the collar portion where the conductive seal material's thermal expansion coefficient mismatch causes shrinkage and expansion issues.
Innovation Solution
A spark plug design featuring a center electrode with a recess at the collar portion, filled with conductive seal material of lower thermal expansion coefficient, which decreases the electrode's thickness and ensures a larger contact area, thereby reducing thermal expansion and shrinkage, and improving the seal between the center electrode and the insulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the center electrode is made with a larger occupation rate in the through hole of the insulator, then the electrical conduction and sealing are improved, but the difference in thermal expansion coefficient between the center electrode and insulator causes larger thermal shrinkage during cooling, leading to clearance occurrence
Solution Approach 1:
The patent applies local quality by creating a recess at the specific location of the maximum outer diameter section of the collar portion, rather than uniformly modifying the entire center electrode. This localized modification allows the conductive seal material to be concentrated where it is most needed to prevent clearance, while maintaining the overall electrical conduction function of the center electrode.
Solution Approach 2:
The conductive seal material acts as an intermediary substance filled into the recess to compensate for thermal expansion differences. This intermediary material has thermal expansion characteristics that bridge the gap between the center electrode and insulator, preventing clearance formation during thermal cycling while maintaining electrical conduction.
2Reliability
If the thickness of the center electrode at the maximum outer diameter section is reduced, then thermal expansion and shrinkage are suppressed, but the structural strength may be compromised
Solution Approach 1:
The recess is created only at the maximum outer diameter section of the collar portion, applying local quality modification precisely where thermal expansion causes the most problem. This localized thinning suppresses thermal expansion at the critical location without compromising the overall structural strength of the center electrode, as other sections maintain their original thickness.
Solution Approach 2:
The patent creates a composite structure by filling the recess with conductive seal material, combining the center electrode material with the seal material. This composite configuration provides both mechanical support and thermal expansion control, as the two materials work together to maintain structural integrity while suppressing differential thermal expansion.
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 prevents clearance and enhances the fixing of the conductive seal material to the center electrode, ensuring reliable sealing and reduced thermal expansion issues, thus improving the overall performance and longevity of the spark plug.
Implementation Method 1
the center electrode having a thermal expansion coefficient higher than that of the insulator... the conductive seal material having a thermal expansion coefficient lower than that of the center electrode
Data Source
AI summary
Disclosed is a spark plug including: an insulator having an axial through hole formed with a first hole region and a second hole region larger in inner diameter than the first hole region; a center electrode having a collar portion disposed in the second hole region; a resistor disposed in the second hole region, with a front end of the resistor being located apart from a rear end of the center electrode; and a conductive seal material arranged at least between the center electrode and the resistor within the second hole region, wherein the center electrode has a recess recessed from the rear end thereof toward the front, wherein the recess is provided at least at a location of a maximum outer diameter section of the collar portion, and wherein the conductive seal material is filled into the recess from the rear end of the center electrode.