Spark Plug Ceramic Insulator Recess Geometry Control
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Solution Overview
Problem
The existing spark plugs with ceramic insulators face issues of channeling and block chip formation due to the convergence of spark discharge paths at recesses, leading to potential damage and reduced operational life, especially when the diameter difference of recesses is outside the optimal range.
Innovation Solution
The spark plug design incorporates ceramic insulators with carefully defined recesses at the edge portions, where the diameter difference between maximum and minimum radial distances is maintained within 0.08 mm to 0.004 mm, and includes a metal shell and ground electrodes to control spark discharge paths, along with specific material compositions and thicknesses to prevent channeling and thermal etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If recesses are formed at the edge portion of the ceramic insulator during manufacturing, then the insulator can be shaped properly, but spark discharge paths converge at the recesses causing channeling and block chip formation
Solution Approach 1:
The patent applies local quality by creating a chamfered surface at the edge portion of the ceramic insulator. This chamfered surface locally modifies the geometry to eliminate recesses while maintaining the overall insulator shape. The chamfered surface provides a gradual transition that prevents spark discharge path convergence, thereby preventing channeling and block chip formation while still allowing proper manufacturing processes to be used.
2Ease of manufacture
If the diameter difference of recesses is large, then manufacturing is simpler, but spark discharge paths converge intensively causing deep channeling and block chips
Solution Approach 1:
The patent applies parameter changes by specifying that the diameter difference between the largest and smallest circles passing through the recesses must be 0.08 mm or less. This parameter control ensures that the recesses are sufficiently uniform to prevent intensive spark discharge path convergence and channeling, while still allowing practical manufacturing. The chamfered surface further refines this by eliminating the recesses entirely at the critical edge portion.
3Ease of manufacture
If recesses are present at the edge portion, then the ceramic insulator can be formed from compact, but the spark discharge causes cutting and chipping at the recess locations
Solution Approach 1:
The patent applies local quality by creating a chamfered surface at the edge portion of the ceramic insulator. This chamfered surface locally modifies the geometry to eliminate recesses while maintaining the overall insulator shape. The chamfered surface provides a gradual transition that prevents spark discharge path convergence, thereby preventing channeling and block chip formation while still allowing proper manufacturing processes to be used.
Solution Approach 2:
The patent applies preliminary action by forming the chamfered surface on the edge portion of the ceramic insulator before the spark plug is assembled and put into service. This preliminary geometric modification prevents the formation of recesses that would later cause channeling and block chip formation during operation, thereby protecting the structural integrity of the insulator in advance.
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 design effectively suppresses channeling and block chip formation, ensuring the ceramic insulator's integrity and extending the spark plug's operational life by controlling spark discharge convergence and thermal effects.
Implementation Method 1
a spark discharge including a surface discharge (creeping discharge) that occurs along a top end surface of a ceramic insulator
Implementation Method 2
when the surface of the ceramic insulator is cut or shaved off (or chipped off) by the passing spark discharge, namely, that when a so-called channeling intensively occurs
Data Source
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AI summary
A spark plug has a center electrode (20), a ceramic insulator (10) having an axial hole (12) to support the center electrode (20) therein, a metal shell holding the ceramic insulator (10), and a ground electrode (30), one end portion of which is fixedly connected with the metal shell, the other end portion of which is located apart from an outer circumferential surface (23) of a top end portion (22) of the center electrode (20) for defining a spark discharge gap therebetween. The ceramic insulator (10) is provided with recesses (61) at an edge portion (60) between a top end surface (11) of the ceramic insulator (10) and an inner circumferential surface of the axial hole (12). When defining first and second imaginary circles with the axis being their respective centers as circles passing through portions of the recesses whose radial distances from the axis are a maximum and a minimum respectively, a difference of diameters of the first and second imaginary circles is 0.08 mm or less.