Asymmetric Glow Plug Heater Junctions Mitigate Thermal Stress
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Solution Overview
Problem
The junctions between the resistor and leads in glow plugs experience high thermal stresses due to differential contraction, leading to microcracks and dielectric breakdown, which reduces durability and causes short-circuits.
Innovation Solution
The configuration of the heater features junctions where the resistor and leads are overlapped perpendicular to the axial direction, with the rear end of one junction located rearward relative to the other, reducing thermal stress and load, and incorporating a metal holding member for enhanced durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the resistor and leads are overlapped in a direction perpendicular to the axial direction of the leads to increase the joint surface area, then the durability is improved, but the thermal stress concentration at the junctions increases due to differential contraction
Solution Approach 1:
The patent applies asymmetry by making the junctions between the resistor and leads asymmetric in their axial positions. Specifically, the first junction has its rear end located rearward relative to the rear end of the second junction when viewed in the axial direction of the leads. This asymmetric configuration prevents the thermal stresses from concentrating at the same axial location, thereby reducing stress concentration while maintaining the increased joint surface area for improved durability.
Solution Approach 2:
The patent utilizes the axial dimension of the leads to distribute the junctions at different positions. By arranging the first and second junctions at different axial locations rather than overlapping them completely in the same cross-section, the design transforms a two-dimensional overlap problem into a three-dimensional arrangement, effectively reducing thermal stress concentration while maintaining adequate joint surface area.
2Device complexity
If the junctions between resistor and leads are positioned in the same cross section to simplify structure, then the device complexity is reduced, but microcracks are likely to occur due to combined thermal stresses
Solution Approach 1:
The patent employs asymmetry by positioning the first junction's rear end rearward relative to the second junction's rear end in the axial direction. This asymmetric arrangement ensures that the junctions do not coincide in the same axial cross-section, distributing the thermal stress locations and preventing combined stress concentration, thereby improving reliability without significantly increasing structural complexity.
Solution Approach 2:
The insulating base serves as an intermediary that embeds both the resistor and leads, providing a stable matrix that accommodates the asymmetric junction arrangement. The insulating base mediates the structural relationship between the resistor and leads, allowing the asymmetric junction configuration to be implemented while maintaining overall structural simplicity and integrity.
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 significantly reduces the occurrence of dielectric breakdown and microcracks, enhancing the heater's durability and reliability, especially under rapid temperature changes.
Implementation Method 1
a glow plug is configured to include a heater having, for example, a resistor having a folded shape
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
[Object] To provide a heater in which occurrence of dielectric breakdown between leads caused by cracks generated at junctions between a resistor and the leads is suppressed and a glow plug having the heater. [Solution] A heater 1 of this invention has a resistor 3 having a folded shape, a pair of leads 4 joined to each end of the resistor 3, an insulating base 2 in which the resistor 3 is buried in the front side thereof and the pair of leads 4 are buried in the rear side thereof, in which the resistor 3 and the leads 4 are overlapped in a direction perpendicular to the axial direction of the leads 4 at junctions 51 and 52 between the resistor 3 and the leads 4 and the rear end of the junction 51 between one end of the resistor 3 and one of the leads 4 is located rearward relative to the rear end of the junction 52 between the other end of the resistor 3 and the other lead 4.