Ceramic Heater Electrode Slope Design for Cavity Prevention
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Solution Overview
Problem
Ceramic heaters, including glow plugs, often suffer from cavity formation near electrode portions during molding, leading to reduced strength and variability in electrical resistance due to inadequate material distribution, which is common across various molding methods and applications.
Innovation Solution
The ceramic heater design features a specific ratio of length A to length B (0.1 to 0.8) for the connection portion between lead and electrode portions, along with distinct lengths c and d, ensuring a gentle slope and complete material distribution, thereby preventing cavity formation and maintaining strength and resistance consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the connection portion of the electrode has a steep slope, then the surface area of the electrode end is increased, but cavity formation occurs during molding due to incomplete material distribution
Solution Approach 1:
The patent changes the geometric parameters of the electrode connection portion by defining specific length ratios (A/B between 0.1-0.8) and making lengths c and d different, which creates an optimized slope that balances surface area with material flow during molding, preventing cavity formation while maintaining adequate electrode surface area
Solution Approach 2:
The patent introduces asymmetry by making lengths c and d different, creating an uneven slope on one side of the electrode connection portion. This asymmetric design facilitates directional material flow during molding, ensuring complete material distribution to the electrode vicinity while maintaining structural integrity
2Manufacturing precision
If the connection portion has a gentle slope, then cavity formation is suppressed, but the surface area of the electrode end becomes small causing electrical resistance variations
Solution Approach 1:
The patent optimizes the slope gentleness by constraining the length ratio A/B within 0.1-0.8, which ensures the slope is gentle enough to allow complete material distribution and prevent cavities, while simultaneously maintaining sufficient electrode surface area to minimize electrical resistance variations
3Ease of manufacture
If the electrode dimensions are not optimized, then manufacturing is simplified, but heater strength is reduced due to cavity formation
Solution Approach 1:
The patent specifies precise dimensional parameters for the electrode (lengths A, B, c, d with specific ratios) that optimize both manufacturing feasibility and structural strength. These parameter constraints ensure complete material distribution during molding, preventing cavities that would weaken the heater, while remaining practical for manufacturing processes
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 cavity formation and variations in electrical resistance, enhancing the overall strength and reliability of ceramic heaters by ensuring complete material distribution during molding.
Implementation Method 1
the diameter reducing portion 272, which extends in the radial direction of the lead portion 31a, heats the inner wall of a combustion chamber
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
A ceramic heater includes a substrate containing a ceramic, and a resistor containing another ceramic and embedded in the substrate. The resistor includes two lead portions, a joint portion that connects the two lead portions, an electrode portion formed integrally with at least one lead portion, having one end portion connected to the one lead portion, extending in a direction crossing an axis of the one lead portion, and having the other end portion exposed at the surface of the substrate. In a cross section of the electrode portion taken along an imaginary plane passing through the axis of the one lead portion and parallel to an extending direction of the electrode portion, 0.1 ≤ A/B ≤ 0.8 is satisfied, where A is the length of the other end portion parallel to the axis, and B is the length of the one end portion parallel to the axis.