Temperature Sensor Junction Stress Reduction
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Solution Overview
Problem
Temperature sensors used for exhaust gas monitoring face stress issues due to rapid temperature changes, leading to potential junction failure from thermal expansion mismatch between metal tubes and insulating cement, causing shear stress on the junction of device electrode wires and sheath wires.
Innovation Solution
A temperature sensor design featuring a metal inner tube with a temperature sensing element and a spaced, gas-inlet-holed outer tube that shields the junction, allowing the outer tube to contract and reduce stress on the junction, while maintaining exposure to the gas for precise temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the metal tube and cement are tightly fitted together to ensure structural integrity, then the structural strength is improved, but the thermal expansion mismatch during rapid cooling causes increased shear stress on the junction
Solution Approach 1:
The protective tube structure is segmented into an inner tube and an outer tube with a gap between them. This segmentation allows the inner tube to contract independently during cooling without transmitting full thermal stress to the junction, while the outer tube provides additional protective function and structural support.
Solution Approach 2:
The gap between the inner tube and outer tube acts as an intermediary space that decouples the thermal contraction of the inner tube from the outer tube structure. This intermediary arrangement allows the inner tube to undergo thermal expansion/contraction freely without directly transferring stress to the junction through the outer tube.
2Reliability
If the inner tube is tightly fitted to the outer tube to reduce thermal stress, then the junction stress is reduced, but the temperature sensing response to exhaust gas is delayed
Solution Approach 1:
The protective tube is divided into inner and outer tubes with a gap, allowing the inner tube to be thermally isolated from the outer tube. This enables the inner tube to rapidly respond to temperature changes in the exhaust gas while the outer tube provides structural support and protection.
Solution Approach 2:
The inner tube is designed with different thermal interaction characteristics compared to the outer tube. The inner tube is positioned to directly expose the temperature sensing element to exhaust gas for rapid response, while the outer tube provides structural support and can be fitted more tightly for stress reduction.
3Speed
If the junction is exposed to direct exhaust gas flow for rapid temperature sensing, then the response speed is improved, but the junction is subjected to higher thermal stress and shear force
Solution Approach 1:
The protective tube structure is segmented into inner and outer tubes, allowing the inner tube to expose the temperature sensing element to exhaust gas for rapid response while the outer tube provides stress relief through the gap arrangement during thermal cycling.
4Device complexity
If a single tube structure is used to simplify the design, then the device complexity is reduced, but the ability to simultaneously protect the junction and enable rapid temperature sensing is compromised
Solution Approach 1:
The dual-tube structure enables the temperature sensor to simultaneously achieve multiple functions: the inner tube provides rapid temperature sensing response through direct gas exposure, while the outer tube provides structural support and stress relief. This multi-functional design cannot be achieved with a single tube structure.
Solution Approach 2:
The inner tube is nested within the outer tube with a gap between them, creating a compact dual-layer structure. This nested arrangement allows both tubes to perform their respective functions while maintaining a space-efficient design.
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 reduces shear stress on the junction, enhances the reliability of the temperature sensor by smoothing temperature changes near the junction, and prevents potential breakage, ensuring accurate and durable temperature measurement across a wide temperature range.
Implementation Method 1
an outer tube which has a bottomed cylindrical shape including plural gas inlet holes, said outer tube covering the inner tube
Implementation Method 2
when the metal tube 512 starts cooling and contracts, contraction of the cement 514 cannot follow that of the metal tube 512
Implementation Method 3
a temperature sensor having a temperature sensing element such as a thermistor and a Pt resistance thermometer
Data Source
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AI summary
A temperature sensor including a temperature sensing element (102) having a temperature sensing unit (103) and a pair of device electrode wires (104) extending from the temperature sensing unit; a sheath member (106) including a sheath wire (108) connected at a junction (110) to one of the device electrode wires and a sheath outer pipe (107) retaining the sheath wire in an insulating material (114); an inner tube (112) which has a bottomed cylindrical shape, the inner tube accommodating the temperature sensing element and the junction in a bottom portion side of the inner tube serving as a leading end of the temperature sensor, and extending in an extension direction of the device electrode wire and the sheath wire; and an outer tube (120) which has a bottomed cylindrical shape including a gas inlet hole (122a, 122b, 122c), the outer tube covering the inner tube, and being spaced from the inner tube on a leading end side of the junction when viewed in a direction perpendicular to an axial direction of the inner tube.