Temperature Sensor Junction Protection via Segmented Tube Design
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Solution Overview
Problem
Temperature sensors used for exhaust gas measurement face stress issues due to thermal cycling, as the metal tube's contraction exceeds that of the alumina cement, leading to shear stress on the junction of the device electrode wire and sheath wire, potentially causing breakage.
Innovation Solution
A temperature sensor design featuring a metal inner tube with a bottomed cylindrical shape and a cylindrical outer tube that shields the junction, allowing the inner tube to resist rapid temperature changes while the outer tube contracts, reducing shear stress and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the metal tube is used to accommodate the temperature sensing element, then the structure is simple and cost-effective, but the thermal expansion coefficient mismatch causes shear stress on the junction during thermal cycling
Solution Approach 1:
The single metal tube structure is segmented into an inner tube and an outer tube with different functions. The inner tube accommodates the temperature sensing element and is exposed to exhaust gas for temperature measurement, while the outer tube protects the junction from thermal stress. This segmentation resolves the contradiction by separating the functions of temperature sensing and junction protection, preventing shear stress on the junction during thermal cycling while maintaining structural simplicity.
2Device complexity
If the inner tube and outer tube are in contact, then the structure is compact, but the outer tube contraction presses the junction during cooling
Solution Approach 1:
The outer tube is extracted from direct contact with the junction by positioning its open end at the front end side of the junction, creating a protective barrier that prevents the outer tube's contraction from pressing on the junction during cooling. This extraction resolves the contradiction by maintaining structural compactness while eliminating the harmful contact between the outer tube and junction during thermal cycling.
3Reliability
If the outer tube covers the junction, then the junction is protected from thermal stress, but the inner tube must remain exposed for accurate temperature measurement
Solution Approach 1:
Different parts of the tube structure have different qualities: the outer tube provides thermal protection at the junction region, while the inner tube remains exposed at its front end for accurate temperature measurement. This local quality differentiation resolves the contradiction by providing junction protection where needed while maintaining measurement accuracy at the sensing element.
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 effectively reduces stress on the junction, preventing breakage and maintaining precise temperature measurement by shielding the junction from thermal stress and ensuring the inner tube remains exposed to the gas for accurate readings.
Implementation Method 1
the metal tube 512 such as stainless steel has a thermal expansion coefficient greater than that of the inside cement (alumina or the like) 514. Accordingly, as illustrated in Fig. 6 (lower cross section), when the metal tube 512 starts cooling and contracts, contraction of the cement 514 cannot follow that of the metal tube 512
Implementation Method 2
a shear stress as shown by arrows B is exerted on the junction 510 of the device electrode wire 504 and the sheath wire 508. In addition, whenever the thermal cycle is repeated, the shear stress is exerted on the junction 510, the strength of the junction 510 is reduced
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); a sheath member (106) having a sheath wire (108) connected at a junction (110) to at least 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; and a cylindrical outer tube (120) having an open end, covering the inner tube such that the open end is located at a front end side of the junction and in a region to the rear end side of or aligned with the front end of the inner tube, and being spaced from the inner tube at the front end side of the junction.