Gas Sensor Element Trap Layer and Waterproof Protective Design
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Solution Overview
Problem
Gas sensor elements in internal combustion engine exhaust systems face challenges with water-induced cracking and poisoning from substances like Mn, Fe, and Ca, which compromise their water resistance and integrity during quick temperature increases, especially under stringent exhaust gas regulations.
Innovation Solution
A gas sensor element design featuring a trap layer to filter out poisoning substances and a water-impermeable protective layer with measurement gas introduction ports to manage water vapor and prevent pressure buildup, enhancing both water and poisoning resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a porous protective layer is used to allow exhaust gas permeation, then gas permeability is improved, but water resistance deteriorates during quick temperature increases
Solution Approach 1:
The protective layer is divided into multiple layers with different functions: a lower porous layer for gas permeation and an upper water-resistant layer for preventing water intrusion. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The protective layer uses a composite structure combining a porous material (such as alumina) for gas permeability with a water-resistant coating or material for preventing water intrusion. This composite approach allows simultaneous achievement of gas permeability and water resistance.
2Reliability
If the surface roughness of the protective layer is reduced to be water-repellent, then water resistance is improved, but poisoning substance accumulation worsens
Solution Approach 1:
The protective layer is segmented into functional zones: one region maintains low surface roughness for water repellency, while another region provides trapping sites for poisoning substances. This segmentation allows both water resistance and poisoning resistance to coexist.
Solution Approach 2:
An intermediary layer or material is introduced between the sensing element and the external environment. This intermediary layer traps poisoning substances while maintaining the water-repellent surface properties, acting as a mediator that protects against both water and poisoning substances.
3Reliability
If the protective layer is made dense to prevent water intrusion, then water resistance is improved, but gas permeability deteriorates
Solution Approach 1:
The protective layer is segmented into a porous lower layer for gas permeation and a dense upper layer for water resistance. This vertical segmentation allows gas to pass through the porous structure while the dense upper layer blocks water intrusion.
Solution Approach 2:
The protective layer employs a composite structure combining porous and dense materials, or a porous material with a water-resistant coating. This composite approach enables simultaneous gas permeability through the porous structure and water resistance through the dense coating or upper layer.
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 prevents water intrusion and poisoning, maintaining the gas sensor's integrity during temperature increases, while allowing for efficient gas measurement and vapor exhaust, thus improving the sensor's reliability and sensitivity.
Implementation Method 1
a trap layer formed of a porous material and covering an outer peripheral surface of the main body, the trap layer allowing a measurement gas to permeate therethrough while trapping poisoning substances contained in the measurement gas
Implementation Method 2
a protective layer covering an outer peripheral surface of the trap layer and having a water-impermeable property
Implementation Method 3
a main body including a solid electrolyte body having oxygen ion conductivity
Data Source
AI summary
A gas sensor element includes a main body having a solid electrolyte body on which a measurement gas-side electrode and a reference gas-side electrode are provided, a trap layer covering an outer peripheral surface of the main body to trap poisoning substances contained in a measurement gas, and a waterproof protective layer covering an outer peripheral surface of the trap layer. In the protective layer, there is formed at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer.