Glow Plug Heater Lead With Varying Cross-Section Aspect Ratio
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Solution Overview
Problem
Heaters for glow plugs in automobile engines face issues with microcrack generation due to stress concentration at the interface between the lead and insulating base body caused by local heat generation and increased inrush power, leading to reduced reliability and durability.
Innovation Solution
The design of the heater includes a bent lead portion with a varying aspect ratio in its cross-section, dispersing the inrush power load from the center of the curve to the outer side, preventing microcrack formation by distributing the load and reducing stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If inrush power is increased to elevate heater temperature more rapidly, then heating speed is improved, but stress concentration at the lead-insulating base body interface occurs due to local heat generation, causing microcracks
Solution Approach 1:
The patent applies local quality by modifying the cross-sectional shape of the lead at specific locations. The lead has a first cross-sectional shape at the bent portion and a different second cross-sectional shape at another portion, allowing different regions to handle different stress and heat conditions. This local differentiation prevents stress concentration at the interface while maintaining overall structural integrity during rapid temperature elevation.
Solution Approach 2:
The patent employs asymmetry by using non-circular cross-sectional shapes for the lead, specifically elliptical or rectangular shapes instead of circular sections. This asymmetric geometry redistributes the stress and heat distribution more evenly across the lead cross-section and at the interface with the insulating base body, preventing the concentration of inrush power load at specific points and thereby avoiding microcrack formation.
2Power
If a large electric current flows into the bent portion to increase inrush power, then heating performance is improved, but local expansion of the bent portion occurs causing stress concentration and microcrack generation
Solution Approach 1:
The lead is designed with different cross-sectional shapes at different locations to locally optimize power handling and stress distribution. The bent portion has a specific cross-sectional shape that accommodates the thermal expansion and stress concentration that occurs during high inrush power conditions, while other portions have different shapes optimized for their specific functional requirements, thereby maintaining interface strength during high power operation.
Solution Approach 2:
The patent changes the geometric parameters of the lead cross-section along its length. By varying the cross-sectional shape from one location to another, the electrical and thermal parameters are optimized at each position. This parameter variation allows the lead to handle large inrush currents without excessive local heating and expansion, maintaining interface strength during high power operation.
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 microcrack generation and enhances the reliability and durability of the heater by dispersing the inrush power load, ensuring the heater can handle high electric currents without interface damage.
Implementation Method 1
a resistor (3) embedded in the insulating base body (2)
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 3(a)~3(d)
AI summary
[Problem] There are provided a heater having high reliability and high durability in which generation of microcracks due to stress concentration derived from local expansion of a bent portion of a lead is suppressed even when a large electric current flows into the bent portion at the time of sharply elevating a temperature of the heater, and a glow plug provided with the heater. [Solution] A heater (1) of the invention includes an insulating base body (2); a resistor (3) embedded in the insulating base body (2); and a lead (4) embedded in the insulating base body (2) and including one end connected to the resistor (3), and a terminal portion (41) at another end thereof which is exposed from a surface of the insulating base body (2). The lead (4) further includes a bent portion (A) bent toward the terminal portion (41), and an aspect ratio in at least one cross section of the bent portion (A) is larger than an aspect ratio in another cross section of the bent portion (A), the another cross section being positioned closer to the terminal portion (41) than the at least one cross section of the bent portion (A).