Gas Sensor Buffer Fitting Depassivation pH Control
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Solution Overview
Problem
Gas sensors mounted on internal combustion engine exhaust pipes experience reduced electrical conductivity in the porous ceramic layer due to corrosion of the buffer fitting, leading to incorrect wiring disconnection detection, especially when exposed to high temperatures and condensed water containing chlorine.
Innovation Solution
A gas sensor design with a buffer fitting made of metal materials having a depassivation pH value of less than 1.0, which maintains a stable passivated film and prevents corrosion, even when exposed to condensed water, ensuring the electrical insulating capability of the porous ceramic layer is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a buffer fitting made of conventional metal (stainless steel with not more than 60% iron and not less than 20% chromium) is used, then the cost and ease of manufacture are improved, but the electrical conductivity of the porous ceramic layer deteriorates due to corrosion and Fe deposition at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the buffer fitting material by specifying precise ranges: iron content of 18-40%, chromium content of 14-20%, nickel content of 35-50%, and sulfur content of 0.003-0.03%. This parameter optimization prevents excessive iron dissolution while maintaining corrosion resistance, thereby preserving the electrical insulating properties of the porous ceramic layer.
Solution Approach 2:
The patent creates a composite metal alloy material combining multiple elements (Fe, Cr, Ni, and controlled S content) to achieve synergistic effects. The nickel component provides corrosion resistance while the controlled iron content maintains structural integrity, and the specific sulfur content prevents excessive iron dissolution into the porous ceramic layer, thus maintaining electrical conductivity.
2Reliability
If the gas sensor is exposed to high temperature exhaust gas (not less than 800°C), then the detection capability is improved, but the buffer fitting corrodes and causes Fe deposition in the porous ceramic layer, reducing electrical conductivity
Solution Approach 1:
The patent optimizes the chemical composition parameters to resist high-temperature corrosion. By controlling iron content at 18-40% (not too high to prevent excessive dissolution) and chromium content at 14-20% (providing oxidation resistance), the material maintains stability at 800°C or higher temperatures, preventing corrosion and Fe deposition.
Solution Approach 2:
The patent converts the potential harmful effect of iron dissolution into a beneficial outcome by carefully controlling the iron content and adding nickel. The controlled iron dissolution combined with nickel forms a stable passive film that actually protects against further corrosion, while the specific sulfur content (0.003-0.03%) modifies the corrosion products to be less harmful to electrical conductivity.
3Strength
If a buffer fitting with higher iron content is used to improve structural strength, then the strength is improved, but the electrical conductivity of the porous ceramic layer deteriorates due to increased Fe deposition
Solution Approach 1:
The patent finds an optimal balance in the iron content parameter, setting it at 18-40% rather than using high iron content. This moderate iron level provides sufficient structural strength while minimizing iron dissolution into the porous ceramic layer. The patent further balances this with chromium (14-20%) for corrosion resistance and nickel (35-50%) to reduce iron dissolution, achieving both strength and electrical conductivity.
Solution Approach 2:
The patent uses a composite alloy system where nickel (35-50%) plays a crucial role in reducing iron dissolution into the porous ceramic layer. The multi-element composition (Fe-Cr-Ni-S) creates synergistic effects where nickel suppresses iron dissolution while maintaining overall material strength, thus preserving electrical conductivity without sacrificing mechanical properties.
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 corrosion of the buffer fitting and maintains the electrical insulating capability of the porous ceramic layer, preventing incorrect wiring disconnection detection and ensuring accurate sensor operation under varying exhaust gas conditions.
Implementation Method 1
metal materials having a depassivation pH value of less than 1.0, which maintains a stable passivated film and prevents corrosion
Data Source
AI summary
A gas sensor has a sensor element, a main metal fitting and a buffer fitting made of metal materials. The sensor element has a solid electrolyte body of a cylindrical shape, an outer electrode formed on at least an outer peripheral surface of the solid electrolyte body and a front end side surface of the projecting part, and a porous ceramic layer formed on the front end side surface of the projecting part. The main metal fitting has an insert hole through which the sensor element is inserted and a stair-shaped part projects inwardly from an inner peripheral surface of the insert hole toward a radial direction of the main metal fitting. The buffer fitting is arranged between the porous ceramic layer and the stair-shaped part, and the metal materials which form the buffer fitting have a depassivation pH value of less than 1.0.