Heater Junction Recess Design for Thermal Stress Reduction
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Solution Overview
Problem
Heaters used in applications like glow plugs experience significant thermal stress and cracking due to high current passage during quick temperature rises, despite increased junction area designs to mitigate thermal expansion differences between resistors and leads.
Innovation Solution
A ceramic heater design featuring an insulating base made of silicon nitride ceramics, with recesses on the resistor to accommodate leads of lower resistance, reducing thermal stress and preventing cracking by dissipating heat effectively across the junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high current is passed through the heater to achieve quick temperature rise, then the heating speed is improved, but thermal stress concentrates on the junction between the resistor and lead, causing cracks
Solution Approach 1:
The patent applies local quality by creating a recessed portion at the junction between the resistor and lead, concentrating the heat dissipation function at this specific location. The recessed structure provides enhanced heat sink capability and stress distribution exactly where thermal stress concentrates, rather than uniformly across the entire component.
Solution Approach 2:
The recessed portion acts as an intermediary structure between the resistor and lead, providing a transition zone that mediates the thermal and mechanical stress. This intermediate structure dissipates heat and distributes stress, preventing direct stress concentration at the sharp interface between resistor and lead.
2Reliability
If the junction area between resistor and lead is increased to reduce thermal expansion difference, then the thermal expansion effect is mitigated, but thermal stress still concentrates at the end portions of resistor or lead
Solution Approach 1:
The patent applies local quality by creating a recessed portion at the junction between the resistor and lead, concentrating the heat dissipation function at this specific location. The recessed structure provides enhanced heat sink capability and stress distribution exactly where thermal stress concentrates, rather than uniformly across the entire component.
Solution Approach 2:
The recessed portion introduces a curved geometry at the junction, replacing sharp corners and edges with rounded surfaces. This curvature distributes stress more evenly throughout the junction area, preventing stress concentration at specific points while maintaining the increased junction area for thermal expansion accommodation.
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 reliability and durability of the heater by reducing thermal stress and preventing cracking, even under repeated temperature changes, maintaining consistent resistance over long-term use.
Implementation Method 1
it is possible to dissipate heat inside the resistor to the lead having a lower resistance value than that of the resistor
Implementation Method 2
a resistor including a heat-generating portion
Data Source
AI summary
[Object] To provide a highly-reliable and durable heater in which occurrence of concentration of great stress on an end portion of a junction between a resistor and a lead is suppressed even when a high current flows through the resistor in quick temperature rise or the like, and a glow plug provided with the same. [Solution] A heater (1) includes: a resistor (3) including a heat-generating portion (4); a lead (8) joined to an end portion of the resistor (3); and an insulating base (9) covering the resistor (3) and the lead (8). At a junction between the resistor (3) and the lead (8), the lead (8) has a shape thicker than the resistor (3) and is connected to the resistor (3) such that the end portion of the resistor (3) is inserted into a front end portion of the lead (8), a recess is provided on an end surface of the resistor (3), and a portion of the lead (8) is inserted into the recess.