Spark Plug Insulator Shape for High Pressure
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Solution Overview
Problem
Spark plugs face increased spark penetration issues due to higher pressure in combustion chambers with supercharged engines, leading to disrupted spark discharge, and increasing insulator thickness to address this results in a larger metal shell diameter, compromising plug size.
Innovation Solution
A spark plug design with a cylindrical insulator and metal shell configuration, featuring a first portion with increased thickness and diameter near the packing for stable positioning and a second portion with a smaller diameter farther from the packing to minimize contact and prevent spark penetration, while maintaining a smaller metal shell diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the insulator is increased to improve voltage resistance performance, then spark penetration is suppressed, but the diameter of the metal shell increases, leading to an increase in the entire size of the plug
Solution Approach 1:
The insulator is designed with a non-uniform thickness distribution, featuring a first portion with greater thickness at the rear end (near the metal shell) and a second portion with lesser thickness at the front end (near the center electrode). This local quality variation allows the thicker region to provide enhanced voltage resistance and suppress spark penetration at the critical interface with the metal shell, while the thinner region maintains the overall plug size compact.
Solution Approach 2:
The insulator is segmented into two distinct portions along its axial length: a first portion with greater thickness disposed at the rear end, and a second portion with lesser thickness disposed at the front end. This segmentation allows each portion to fulfill different functional requirements - the thicker rear portion prevents spark penetration near the metal shell, while the thinner front portion keeps the overall dimensions compact.
2Productivity
If the spark discharge voltage is increased to respond to higher combustion chamber pressure, then fuel economy and environmental regulation are improved, but spark penetration through the insulator becomes more likely, disrupting normal spark discharge
Solution Approach 1:
The insulator employs local quality variation with a thicker first portion at the rear end where spark penetration is most likely to occur under high voltage conditions. This localized thickness enhancement provides targeted electrical insulation strength at the critical region near the metal shell, preventing spark penetration and maintaining stable spark discharge even when higher voltages are applied for improved fuel economy.
3Reliability
If the first portion of the insulator is disposed on the outer periphery of the large-diameter portion of the center electrode, then spark penetration is suppressed in the vicinity where countermeasure is more required, but the complexity of the insulator shape increases
Solution Approach 1:
The insulator features a localized thickness variation where the first portion with greater thickness is specifically positioned at the rear end of the insulator, corresponding to the region where the large-diameter portion of the center electrode is retained. This targeted thickness enhancement provides effective spark penetration suppression at the critical interface without requiring complex overall insulator geometry, as the shape change is confined to a specific axial region.
Data Source
AI summary
A spark plug including a center electrode that has a large-diameter portion having an outside diameter that is largest in the center electrode. The large-diameter portion is retained at a rear facing surface in an axial hole of an insulator. A metal shell has a diameter increased portion on a rear end side with respect to the center electrode, the diameter increased portion having an inside diameter that is increased toward the rear end side. The insulator has a first portion which is a portion of the insulator in a region from a rear end of the rear facing surface to a front end of the diameter increased portion. The first portion has a thickness that is the largest in the region, and is disposed at least on an outer periphery of the large-diameter portion.