Gas Sensor Water-Penetration Reduction Dense Layer
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Solution Overview
Problem
Gas sensors with porous protection layers are prone to moisture ingress, leading to corrosion and short circuits due to capillary action, as moisture reaches the connector electrodes in exhaust gas applications.
Innovation Solution
A gas sensor design incorporating a cylindrical metal body with compacts and dense bodies, a water-penetration reduction portion with a dense layer and gap region, and a porous layer to prevent moisture from reaching the connector electrodes by reducing capillarity and providing a barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous layer is used to cover the sensor element surface, then the sensor element is protected and gas permeability is improved, but moisture penetrates through the porous layer by capillarity and reaches the connector electrodes causing corrosion and short circuits
Solution Approach 1:
The protective coating is divided into multiple functional layers: a porous layer for gas permeability and a water-penetration reduction portion (dense layer) for moisture blocking. This segmentation allows each layer to perform its specific function without interfering with the other, solving the contradiction between gas access and moisture protection.
Solution Approach 2:
Different regions of the coating have different properties: the porous layer has high porosity (≥10%) for gas permeability while the water-penetration reduction portion has low porosity (<10%) for moisture blocking. This local differentiation of material properties allows the system to simultaneously achieve gas permeability and moisture protection.
2Measurement precision
If the porous layer porosity is increased to improve gas concentration detection, then gas permeability is enhanced, but capillary action increases and moisture reaches the connector electrodes more easily
Solution Approach 1:
The coating is segmented into a porous layer for gas detection and a separate water-penetration reduction portion for moisture protection. This allows the porous layer to have high porosity for improved gas concentration detection without increasing moisture ingress, as the dense layer blocks capillary action.
Solution Approach 2:
The porous layer maintains high porosity (≥10%) for optimal gas permeability and detection precision, while the water-penetration reduction portion has low porosity (<10%) to prevent capillary moisture ingress. Each layer's local quality is optimized for its specific function.
3Object-affected harmful factors
If a dense layer is added to prevent moisture penetration, then moisture protection is improved, but gas permeability is reduced and sensor functionality is impaired
Solution Approach 1:
The protective coating is segmented into distinct functional layers: a porous layer that maintains gas permeability for sensor functionality and a water-penetration reduction portion that provides moisture protection. This segmentation ensures that the dense layer does not block gas access to the sensor element.
Solution Approach 2:
Different layers have different porosity characteristics optimized for their functions: the porous layer has high porosity (≥10%) for gas permeability and sensor functionality, while the water-penetration reduction portion has low porosity (<10%) for moisture protection. This local quality differentiation resolves the contradiction between moisture protection and gas permeability.
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
Effectively prevents moisture from reaching the connector electrodes, reducing the likelihood of corrosion and short circuits, while maintaining sensor functionality and reducing warpage during baking.
Implementation Method 1
the moisture contained in an exhaust gas may move inside the porous layer by capillarity
Implementation Method 2
the water-penetration reduction portion reducing the capillarity of water in the longitudinal direction
Data Source
AI summary
A gas sensor includes a sensor element and one or more hollow columnar dense bodies. The sensor element includes an element main body having a side surface, a porous layer and a water-penetration reduction portion that cover at least a front end-side part of the side surface. The water-penetration reduction portion disposed on the side surface so as to divide the porous layer or to be located closer to the rear end than the porous layer, an overlap length W that is the length of a continuous overlap between a range in which the water-penetration reduction portion is present in a longitudinal direction and a range in which inner peripheral surfaces of the one or more dense bodies are present in the longitudinal direction being 0.5 mm or more, and having a dense layer covers the side surface, the water-penetration reduction portion reduces the capillarity of water.