Spark Plug Resistor Insulator Interface Roughness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional spark plugs with integrated resistors suffer from excessive heat generation and deterioration at the interface between the insulator and resistor due to high current density and roughness, leading to reduced durability.
Innovation Solution
A spark plug design where the resistor is in contact with the insulator's inner surface, with a controlled surface roughness and porosity to prevent excessive heat generation and interfacial fractures, using an alumina-rich insulator with a relative density of 94-98% and a metal shell with a nominal diameter of 12 mm or less to reduce interface roughness and heat influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the resistor is disposed between the metal terminal and the center electrode in the axial hole, then electric wave noise is suppressed, but the current density increases at the interface between the insulator and the resistor causing excessive heat generation and deterioration
Solution Approach 1:
The patent applies local quality by controlling the surface roughness specifically at the interface between the insulator and resistor. The inner circumferential surface of the insulator is processed to have a specific roughness range (Ra 0.1-0.3 μm), creating different surface properties in different locations: the interface region has controlled roughness to reduce heat generation, while other regions maintain their original properties. This localized surface treatment resolves the contradiction by preventing excessive heat generation at the critical interface while maintaining the resistor's noise suppression function.
Solution Approach 2:
The patent changes the physical parameter of surface roughness to resolve the contradiction. By controlling the average roughness (Ra) of the insulator's inner circumferential surface within the specific range of 0.1-0.3 μm, the patent optimizes the thermal and electrical characteristics at the interface. This parameter change reduces the current density concentration and heat generation at the interface, thereby improving resistor durability while maintaining the noise suppression function.
2Strength
If the surface roughness at the interface between insulator and resistor is increased, then anchoring effect is improved, but resistance increases due to roughness causing excessive heat generation
Solution Approach 1:
The patent optimizes the surface roughness parameter within a specific range (Ra 0.1-0.3 μm) to balance two competing requirements: achieving sufficient anchoring effect for interface bonding strength while preventing excessive resistance increase. This controlled parameter change ensures that the surface is rough enough to provide mechanical interlocking and bonding strength, but not so rough that it causes excessive electrical resistance and heat generation, thereby resolving the contradiction between interface strength and resistor durability.
Solution Approach 2:
The patent applies local quality by creating a specific surface condition only at the interface region between the insulator and resistor. The inner circumferential surface in the resistor insertion region is processed to have controlled roughness, while other surfaces maintain their original properties. This localized treatment ensures that the anchoring effect is enhanced precisely where needed for interface bonding, without adversely affecting the electrical characteristics in other regions.
3Ease of manufacture
If the insulator has high porosity, then manufacturing is easier, but open pores exist at the interface causing resistor to enter pores and increase resistance
Solution Approach 1:
The patent changes the porosity parameter of the insulator material to resolve the contradiction. By selecting an insulator with controlled porosity and pore size distribution, the patent prevents open pores from forming at the interface region where the resistor is inserted. This parameter control ensures that the resistor maintains good electrical contact without entering pores, thereby preventing excessive resistance increase and improving durability, while still maintaining reasonable manufacturing feasibility.
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 enhances the durability of the resistor by suppressing excessive heat generation and interfacial fractures, maintaining resistance within optimal limits and extending the lifespan of the spark plug.
Implementation Method 1
Discharge current when spark occurs flows into the resistor
Implementation Method 2
the current density of the discharge current is increased at and near the interface between the insulator and the resistor owing to the skin effect
Data Source
AI summary
A spark plug having a resistor disposed between a metal terminal and a center electrode so as to be electrically connected to the metal terminal and the center electrode, wherein the resistor is in contact with an inner circumferential surface of the insulator. On a cross section taken along the axial line so as to include the axial line, in a case where a plurality of points are plotted at predetermined intervals in a direction of the axial line so as to be present on a partial boundary line, within an arbitrary range in the direction of the axial line, of a boundary line between the insulator and the resistor, and a regression line is drawn by a least-squares method with use of the plurality of points, an average value of distances in a direction perpendicular to the regression line between the regression line and the partial boundary line is 0.1 to 0.3 μm.