Gas Sensor Element Porous Layer Thermal Shock Resistance
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Solution Overview
Problem
Conventional gas sensors are prone to water-induced cracking due to thermal shock from adhered water droplets, which can lead to localized cracking and reduced effectiveness, especially when exposed to high-temperature environments like exhaust pipes of internal combustion engines.
Innovation Solution
A gas sensor element configuration featuring an elongated plate base with internal spaces, electrochemical pump cells, a heater, a porous thermal shock-resistant layer, and a buffer layer, where the thermal diffusion time in the thickness direction of the thermal shock-resistant layer is 0.4 sec to 1.0 sec and the total thermal diffusion time with the buffer layer is 0.2 sec to 1.0 sec, effectively preventing water-induced cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer is provided to prevent water-induced cracking, then water repellency is improved, but thermal shock resistance is worsened due to rapid heat transfer
Solution Approach 1:
The patent employs a porous protective layer with specifically controlled porosity (30-70%) to achieve water repellency through the Leidenfrost phenomenon while managing thermal properties. The porous structure allows water droplets to bounce off heated surfaces, preventing water-induced cracking, while the porosity also provides thermal insulation to reduce thermal shock to the sensor element.
Solution Approach 2:
The patent optimizes specific parameters of the porous protective layer including porosity (30-70%), thermal conductivity (0.1-1.0 W/m·K), and specific surface area (0.5-5.0 m²/g) to simultaneously achieve water repellency and thermal shock resistance. By carefully controlling these parameters, the layer can repel water droplets while maintaining appropriate thermal diffusion characteristics.
2Speed
If thermal conductivity is increased to improve heat transfer, then responsiveness is improved, but water-induced cracking becomes more likely due to thermal shock
Solution Approach 1:
The patent defines an optimal range for thermal conductivity (0.1-1.0 W/m·K) of the porous protective layer that balances responsiveness and water resistance. This parameter optimization ensures sufficient heat transfer for sensor responsiveness while preventing excessive thermal shock that would cause water-induced cracking when water droplets contact the heated sensor surface.
Solution Approach 2:
The porous structure of the protective layer provides thermal insulation properties that reduce thermal shock to the sensor element when water droplets adhere to the surface. The pores trap air which has low thermal conductivity, creating a thermal barrier that protects the sensor from rapid temperature changes while still allowing the sensor to respond to gas measurements.
3Ease of manufacture
If a single-material porous protective layer is used, then manufacturing is simplified, but water resistance quality is insufficient to prevent localized cracking
Solution Approach 1:
The patent specifies a porous protective layer made from composite materials or carefully selected single materials (such as silicon carbide, aluminum nitride, or alumina) with controlled porosity and specific surface area. This approach maintains manufacturing simplicity while achieving the dual functionality of water repellency through Leidenfrost phenomenon and thermal shock resistance, preventing localized cracking at the water contact points.
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 configuration significantly reduces the likelihood of water-induced cracking, ensuring the sensor element's reliability and responsiveness when attached to an exhaust pipe, by controlling thermal diffusion and water repellency through the Leidenfrost phenomenon.
Implementation Method 1
a thermal diffusion time in a thickness direction of the thermal shock resistant layer is 0.4 sec to 1.0 sec inclusive at a portion where the buffer layer is not provided, and a total thermal diffusion time in a stacking direction of the thermal shock resistant layer and the buffer layer is 0.2 sec to 1.0 sec inclusive
Implementation Method 2
water droplets adhered to the porous protective layer of the sensor element are repelled due to the Leidenfrost phenomenon
Data Source
AI summary
A sensor element includes: an element base made of an oxygen-ion conductive solid electrolyte; an internal space provided inside the element base; an electrochemical pump cell configured to pump oxygen in and out between the internal space and outside; a porous thermal shock resistant layer provided to an outermost peripheral part in a predetermined range at one end part of the element base, at which a gas inlet is provided; and a buffer layer adjacent to the thermal shock resistant layer on a pump surface and a heater surface. A thermal diffusion time in a thickness direction of the thermal shock resistant layer is 0.4 sec to 1.0 sec inclusive, and a total thermal diffusion time in a stacking direction of the thermal shock resistant layer and the buffer layer is 0.2 sec to 1.0 sec inclusive.