Gas Sensor Protective Layer for Condensate Thermal Shock
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Solution Overview
Problem
Gas sensors attached to engine exhaust pipes are susceptible to thermal shock when activated early after engine start due to condensate water contact, leading to potential cracking.
Innovation Solution
A sensor element with a protective layer having a surface roughness Ra of 8 μm or less and surface waviness Wa of 6 μm or more, along with a two-layer porous structure, is designed to minimize moisture retention and facilitate droplet movement, reducing thermal shock risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the temperature rise timing of the sensor element is made earlier after the engine is started, then the activation speed of the gas sensor is improved, but the sensor element becomes susceptible to thermal shock from condensate water contact
Solution Approach 1:
The invention utilizes the Leidenfrost effect, where a layer of vapor forms between the water droplet and the hot surface, converting the harmful thermal shock into a beneficial protective mechanism. This allows early activation while preventing direct water contact damage
Solution Approach 2:
The invention changes the surface parameter of the protective layer by controlling its roughness (Ra ≤ 8 μm) and waviness (Wa ≥ 6 μm), creating specific surface characteristics that promote water droplet movement and reduce thermal shock risk
2Reliability
If a protective film is formed on the sensor element to suppress thermal shock, then the resistance to thermal shock is improved, but the moisture may still remain in one place on the surface
Solution Approach 1:
The invention creates non-uniform surface characteristics on the protective layer with specific roughness and waviness values, creating local variations that guide water droplet movement toward edges rather than allowing pooling on flat surfaces
Solution Approach 2:
The surface waviness creates curved profiles that facilitate water droplet movement toward the edges of the protective layer, preventing moisture accumulation in centralized locations
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 thermal shock by ensuring moisture droplets move away from the sensor element, preventing cracking and enabling early activation without damage.
Implementation Method 1
the surface of the protective layer has a relatively small surface roughness Ra and a relatively large surface waviness Wa. Therefore, it is unlikely for moisture dropped on the surface of the protective layer to remain in one place. As a result, according to this sensor element, there is a high possibility that moisture that has dripped onto the surface of the protective layer will move to a portion other than the sensor element, thus making it possible to suppress thermal shock caused by exposure to water.
Data Source
AI summary
Provided is a sensor element for use in measurement of the concentration of a predetermined gas component in a measurement target gas. The sensor element includes a plate-shaped element body and a protective layer. The element body includes a solid electrolyte layer having oxygen ion conductivity and a heater configured to heat the solid electrolyte layer. A protective layer is formed on at least one face of the element body. A surface of the protective layer has a surface roughness Ra of 8 μm or less and a surface waviness Wa of 6 μm or more.