Gas Sensor Shield Layer for NOx Detection Accuracy
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Solution Overview
Problem
Existing gas sensors in internal combustion engine exhaust pipes face errors in detecting specific gas components like NOx due to sharp increases in oxygen concentration during fuel-cut states, as the difference in electrostatic capacitance between sensor and monitor electrodes leads to inaccuracies in electric current measurements.
Innovation Solution
A gas sensor design featuring a solid electrolyte body with a pump electrode, sensor electrode, and reference electrode, where an insulating shield layer covers the reference electrode to prevent oxygen concentration fluctuations from affecting the sensor electrode, ensuring accurate detection of specific gas components even during sharp oxygen increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor electrode and reference electrode are arranged to overlap through the solid electrolyte body, then the sensor can detect specific gas components, but errors occur due to oxygen concentration fluctuations in the reference gas duct affecting measurement accuracy
Solution Approach 1:
The reference electrode is divided into two separate portions: a first portion exposed to the reference gas duct and a second portion overlapping the sensor electrode through the solid electrolyte body. This segmentation isolates the measurement area from oxygen concentration fluctuations in the reference gas duct, resolving the contradiction between detection capability and measurement stability.
Solution Approach 2:
An insulating shield layer is introduced as an intermediary between the first portion and the second portion of the reference electrode. This shield layer prevents electrical interference and isolates the measurement portion from oxygen concentration changes in the reference gas duct, thereby maintaining reliable and accurate measurements under varying oxygen conditions.
2Ease of operation
If the reference electrode is fully exposed to the reference gas duct, then the electrode can function properly, but sharp increases in oxygen concentration during fuel-cut states cause detection errors
Solution Approach 1:
The reference electrode is segmented into a first portion that remains exposed to the reference gas duct for proper electrode functionality, and a second portion that is shielded from oxygen concentration fluctuations. This allows the electrode to function properly while preventing detection errors during fuel-cut states.
Solution Approach 2:
Different portions of the reference electrode are given different properties: the first portion is exposed to reference gas for electrode operation, while the second portion overlapping the sensor electrode is protected from oxygen concentration changes. This local differentiation resolves the contradiction between operational functionality and measurement precision.
3Measurement precision
If the sensor electrode and reference electrode overlap through the solid electrolyte body, then gas component detection is enabled, but electrostatic capacitance differences cause measurement inaccuracies
Solution Approach 1:
An insulating shield layer is placed between the first portion and the second portion of the reference electrode to prevent electrical interference and capacitance coupling. This intermediary eliminates measurement inaccuracies caused by electrostatic capacitance differences while maintaining the overlapping electrode configuration necessary for gas component detection.
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 minimizes errors in detecting specific gas components by isolating the sensor electrode from oxygen concentration changes in the reference gas duct, maintaining high accuracy in NOx detection across varying engine operational states.
Implementation Method 1
a solid electrolyte body; a pump electrode that is provided on the first surface and housed in the gas chamber; a sensor electrode that is provided on the first surface and housed in the gas chamber; a reference electrode arranged on the second surface of the solid electrode to overlap both the pump electrode and the sensor electrode through the solid electrolyte body
Implementation Method 2
an insulating shield layer arranged to cover a portion of the reference electrode in a contact state or non-contact state with the portion of the reference electrode, the portion of the reference electrode being arranged to overlap the sensor electrode through the solid electrolyte body
Data Source
AI summary
A sensor element of a gas sensor includes a solid electrolyte body, a first insulator, a gas chamber, a second insulator, a reference gas duct, a pump electrode, a sensor electrode, a reference electrode, and a shield layer. The shield layer is formed of an insulating ceramic material and covers a sensor-side electrode portion of the reference electrode, the sensor-side electrode portion being arranged to overlap the sensor electrode through the solid electrolyte body.