Lambda Probe Sensor Element With Inner Anode
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Solution Overview
Problem
Existing lambda sensors in Diesel vehicles face deviations in pump current characteristics near stoichiometric air-fuel ratios, leading to ambiguous readings due to oxidizable components in the exhaust gas, which complicates accurate air-fuel mixture composition measurement.
Innovation Solution
A sensor element design with a second electrode shielded from oxidizable components, where the anode is placed inside the sensor, preventing combustion gas reactions and using a discharge air channel connected to a reference gas chamber to maintain an unambiguous current signal, especially in the rich gas range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the anode is exposed to exhaust gas to enable electrochemical reactions, then the sensor can measure oxygen partial pressure, but oxidizable components in the exhaust gas cause ambiguous pump current characteristics near stoichiometric air-fuel ratios
Solution Approach 1:
The sensor is divided into multiple functionally independent cells (first pump cell and second pump cell), each with its own electrodes and measurement chambers. This segmentation allows the first cell to measure total oxygen partial pressure while the second cell measures oxygen partial pressure after CO oxidation, enabling differentiation between oxygen sources and elimination of measurement ambiguity.
Solution Approach 2:
A porous oxidation catalyst layer is introduced as an intermediary between the exhaust gas and the anode of the second pump cell. This catalyst layer selectively oxidizes CO to CO2, removing oxidizable components that would otherwise cause ambiguous pump current characteristics, while allowing oxygen to pass through for measurement.
2Ease of manufacture
If a single-cell sensor design is used to reduce complexity, then manufacturing cost is reduced, but ambiguous readings occur due to oxidizable components affecting the pump current
Solution Approach 1:
The sensor is divided into multiple functionally independent cells (first pump cell and second pump cell), each with its own electrodes and measurement chambers. This segmentation allows the first cell to measure total oxygen partial pressure while the second cell measures oxygen partial pressure after CO oxidation, enabling differentiation between oxygen sources and elimination of measurement ambiguity.
Solution Approach 2:
A porous oxidation catalyst layer is introduced as an intermediary between the exhaust gas and the anode of the second pump cell. This catalyst layer selectively oxidizes CO to CO2, removing oxidizable components that would otherwise cause ambiguous pump current characteristics, while allowing oxygen to pass through for measurement.
3Reliability
If the anode is shielded from exhaust gas to prevent oxidizable component reactions, then unambiguous pump current characteristics are achieved, but the sensor cannot directly measure oxygen partial pressure in the exhaust gas
Solution Approach 1:
The sensor is divided into multiple functionally independent cells (first pump cell and second pump cell), each with its own electrodes and measurement chambers. This segmentation allows the first cell to measure total oxygen partial pressure while the second cell measures oxygen partial pressure after CO oxidation, enabling differentiation between oxygen sources and elimination of measurement ambiguity.
Solution Approach 2:
A porous oxidation catalyst layer is introduced as an intermediary between the exhaust gas and the anode of the second pump cell. This catalyst layer selectively oxidizes CO to CO2, removing oxidizable components that would otherwise cause ambiguous pump current characteristics, while allowing oxygen to pass through for measurement.
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
This design ensures an unambiguous pump current characteristic curve across the air-fuel ratio range, enabling cost-effective production of sensors suitable for Diesel vehicles without complex multi-cellular structures, with improved resistance management using a reducing electrode.
Implementation Method 1
because of its oxygen-ion conducting properties, zirconium dioxide (i.e., yttrium-stabilized zirconium dioxide) or similar ceramics are normally used as solid state electrolyte
Implementation Method 2
oxygen molecules are electrochemically reduced to oxygen ions at the second, negative electrode by the pump voltage
Implementation Method 3
a porous ceramic structure having selectively adjustable pore radii is used as diffusion barrier
Data Source
AI summary
A sensor element, which may be used as Lambda probe and/or inside a Lambda probe, for example, is provided for determining at least one physical property of a gas mixture in at least one gas chamber. The sensor element has at least one first electrode, at least one second electrode and at least one solid state electrolyte, which connects the at least one first electrode and the at least one second electrode. The at least one first electrode and the at least one second electrode are situated inside the sensor element. The at least one second electrode is connected to at least one reference gas chamber via at least one discharge air channel.