Gas Sensor Element Porous Layer Roughness
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Solution Overview
Problem
Gas sensors used for detecting NOx in automobile exhaust gas face issues with cracking due to rapid cooling when water adheres to their surface, which compromises their water resistance and operational integrity.
Innovation Solution
A gas sensor element design featuring a solid electrolyte layer with a porous protective layer and a spatial layer between the protective layer and the high-temperature portions, where the porous protective layer has a maximum-height roughness of 50 μm or less to enhance heat retention and reduce cooling, thereby improving water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer is provided to cover the outer electrode, then the spatial layer can impede heat conduction and suppress cooling when water adheres, but the sensor element is still susceptible to cracking due to rapid cooling
Solution Approach 1:
The patent applies local quality by controlling the roughness of specific regions on the inner surface of the porous protective layer. The projection portions (where roughness is small) are located at positions facing high-temperature regions of the sensor element, while depression portions (where roughness is large) are located at other positions. This localized differentiation optimizes heat radiation reflection at critical areas without compromising overall protective function.
Solution Approach 2:
The patent implements preliminary action by pre-forming the porous protective layer with specific roughness characteristics before the sensor element is exposed to water. The controlled roughness pattern is established in advance to reflect heat radiation and prevent rapid cooling, rather than attempting to address cooling issues after water adhesion occurs.
2Temperature
If the maximum-height roughness Rz of the inner surface of the porous protective layer is reduced to 50 μm or less, then heat radiated from the element body is reflected and returns to the element body, but the surface area of the region increases which may absorb more heat
Solution Approach 1:
The patent resolves this contradiction by applying local quality - not all regions of the inner surface have the same roughness. Projection portions with small roughness (Rz ≤ 50 μm) are strategically positioned at areas facing high-temperature regions to reflect heat radiation, while depression portions with larger roughness are positioned elsewhere. This localized approach ensures heat reflection occurs at critical areas without the penalty of uniformly increasing surface area across the entire protective layer.
Solution Approach 2:
The patent applies the skipping principle by having heat radiation reflected directly back to the element body through the smooth projection portions, causing the heat to 'skip' off the surface and return quickly rather than being absorbed and distributed across a larger rough surface area. This allows efficient heat retention without proportionally increasing the heat-absorbing surface area.
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 suppresses cooling and maintains high temperatures, preventing cracking and enhancing the water resistance of the gas sensor element, ensuring reliable NOx detection even under conditions of water exposure.
Implementation Method 1
the first spatial layer impedes heat conduction in the thickness direction of the porous protective layer. Therefore, cooling of the element body when water adheres to the porous protective layer is suppressed
Implementation Method 2
the maximum-height roughness Rz of the region of the inner surface (surface on the element body side) of the porous protective layer, the region facing the predetermined portion, is 50 μm or less, and the region is a smooth surface. Therefore, heat radiated from the predetermined portion of the element body is reflected by the inner surface of the porous protective layer and easily returns to the element body
Data Source
AI summary
A sensor element is used to detect the concentration of a predetermined component in a gas. The sensor element includes a sensor element body including a solid-state-electrolyte layer having oxygen-ion conductivity, an outer pump electrode that is disposed on an upper surface, which is one of the surfaces, of the sensor element body, and a porous protective layer that is provided so as to cover at least the outer pump electrode. A spatial layer is provided between the porous protective layer and the sensor element body. The spatial layer includes a first spatial layer between the porous protective layer and the outer pump electrode. The maximum-height roughness Rz of a region of the inner surface of the porous protective layer, the region facing the outer pump electrode, is 50 μm or smaller.