Sensor Element Porous Protective Layer Thermal Shock Resistance
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Solution Overview
Problem
Gas sensors with solid electrolyte elements face cracking due to thermal shock from water splashes during operation, especially in automotive exhaust gas environments where water condensation is high, leading to a need for improved water resistance.
Innovation Solution
A sensor element with a porous protective layer having a specific pore shape and porosity is applied to the surface, where the pore length in the thickness direction is 0.6 to 0.9 times the pore length in the surface direction, providing enhanced water resistance and thermal insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer is formed on the sensor element surface, then water resistance is improved, but the layer may not provide sufficient thermal insulation if pores are not properly shaped
Solution Approach 1:
A porous protective layer is formed on the sensor element surface using alumina or zirconia powder. The porous structure provides both water resistance and thermal insulation properties. The pores are controlled to have specific shape characteristics (flat shape with Lt/Lf ratio of 0.6 to 0.9) to optimize both functions simultaneously.
Solution Approach 2:
The pore shape parameters are precisely controlled by adjusting the thermal spray powder particle shape (flattened spheres with aspect ratio of 0.6 to 0.9) and spray conditions. This parameter control ensures the protective layer achieves optimal balance between water resistance and thermal insulation performance.
2Reliability
If the sensor element operates at high temperature, then measurement function is maintained, but cracking occurs due to thermal shock from water exposure
Solution Approach 1:
The porous protective layer is applied beforehand to cushion the thermal shock impact before it reaches the sensor element body. The layer absorbs and distributes the thermal stress from water exposure, preventing cracking in the internal structure while maintaining high-temperature measurement functionality.
Solution Approach 2:
The sensor element uses a composite structure combining the solid electrolyte element body with a porous ceramic protective layer (alumina or zirconia). This composite structure provides both the electrical functionality of the element and the mechanical/thermal protection of the ceramic layer.
3Temperature
If water is splashed on the high temperature sensor element, then cooling effect occurs, but thermal shock causes internal cracking
Solution Approach 1:
The porous protective layer acts as an intermediary between the water droplet and the sensor element body. It mediates the thermal shock by providing thermal insulation and stress distribution, allowing surface cooling while preventing the transmission of thermal stress to the internal structure.
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 solution effectively suppresses cracking in the sensor element's internal structure by reducing thermal shock and improving water resistance, ensuring reliable operation even in conditions with high water condensation.
Implementation Method 1
the protective layer comprises a porous material that has a pore inside... a ratio (Lt/Lf) of a pore length (Lt) in a thickness direction perpendicular to the surface of the element body to a pore length (Lf) in a surface direction perpendicular to said thickness direction is 0.6 to 0.9
Data Source
AI summary
A sensor element for detecting a target gas to be measured in a measurement-object gas includes: an element body including an oxygen-ion-conductive solid electrolyte layer; and a protective layer covering at least a part of a surface of the element body. The protective layer includes a porous material that has a pore inside; and, in the pore in the protective layer, a ratio (Lt/Lf) of a pore length (Lt) in a thickness direction perpendicular to the surface of the element body to a pore length (Lf) in a surface direction perpendicular to the thickness direction is 0.6 to 0.9.