Catalyst Deterioration Diagnosis Using NOx Sensor Output
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Solution Overview
Problem
Current methods for diagnosing the deterioration of three-way catalysts (TWCs) in vehicles only evaluate the oxygen absorption capability of ceria, failing to assess the deterioration of the precious metal components directly involved in catalytic purification, and show limited correlation with exhaust gas components like NOx, HC, and CO.
Innovation Solution
A system and method that includes an NOx sensor and an electronic control unit (ECU) to control engine parameters, which calculates a total weight value of NOx and THC to diagnose the deterioration of the precious metal components in the TWC by comparing the NOx sensor output with predetermined threshold values, thereby providing a comprehensive assessment of catalyst deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional oxygen absorption capability evaluation method is used, then ceria deterioration can be assessed, but precious metal component deterioration cannot be directly evaluated
Solution Approach 1:
The patent uses the NOx sensor output as an intermediary indicator to indirectly assess the deterioration of precious metal components. Since direct measurement of precious metal deterioration is difficult, the system employs the NOx concentration in exhaust gas as a mediator that reflects the catalytic activity of precious metal components, thereby enabling indirect but accurate evaluation of their deterioration state.
Solution Approach 2:
The patent replaces direct physical/chemical measurement of precious metal deterioration with an electrochemical sensing method. Instead of analyzing the physical state of precious metal particles, the system uses an electrochemical NOx sensor to measure gas composition, substituting a complex material analysis approach with a more practical gas detection method that correlates with catalyst performance.
2Reliability
If oxygen absorption capability of ceria is evaluated, then catalyst deterioration can be diagnosed, but correlation with exhaust gas components (NOx, HC, CO) is limited
Solution Approach 1:
The patent changes the evaluation parameter from oxygen absorption capability (OSC) to total weight value of NOx and THC in exhaust gas. This parameter transformation directly links catalyst performance with actual exhaust gas composition, providing a more precise and reliable correlation between catalyst deterioration and emissions characteristics.
Solution Approach 2:
The patent makes the diagnosis system universally applicable to multiple exhaust gas components (NOx, HC, CO) rather than focusing solely on oxygen absorption. By using the NOx sensor output to represent overall catalytic performance across different functions, the system achieves multi-functional evaluation of catalyst deterioration that correlates with various exhaust gas components.
3Ease of operation
If NOx sensor output is used directly for diagnosis, then diagnosis simplicity is improved, but accuracy of precious metal component deterioration assessment is insufficient
Solution Approach 1:
The patent performs preliminary calculation to determine the total weight value of NOx and THC before using it for diagnosis. By pre-processing the NOx sensor output data to compute this comprehensive metric, the system maintains operational simplicity while enhancing assessment accuracy through a straightforward calculation step that aggregates multiple factors.
Solution Approach 2:
The patent merges the evaluation of multiple catalyst functions (NOx reduction, HC oxidation, CO oxidation) into a single diagnostic parameter - the total weight value of NOx and THC. This consolidation combines information from different catalytic functions into one integrated metric that simplifies the diagnosis process while accurately reflecting overall precious metal component deterioration.
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 approach allows for a more accurate diagnosis of the precious metal component deterioration in TWCs, improving the evaluation of catalyst performance beyond traditional methods by considering the total weight value of NOx and THC, thus enhancing the detection of catalyst degradation.
Implementation Method 1
an NOx sensor located on a downstream side with respect to the catalyst in an exhaust path of the exhaust gas
Implementation Method 2
Pd and Pt have a function of oxidizing HC and CO in an exhaust gas to generate carbon dioxide (CO2) and water (H2O)
Implementation Method 3
Pd and Rh have a function of reducing NOx in an exhaust gas to generate nitrogen (N2)
Implementation Method 4
Ceria has a function of causing absorption and elimination of oxygen (O2)
Data Source
AI summary
A system of diagnosing a deterioration of a catalyst, which includes a precious metal component and a ceramic part and purifies an exhaust gas emitted from an engine, includes: a diagnosis means comparing a diagnosis object value corresponding to an output from an NOx sensor provided on a downstream side with respect to the catalyst and a predetermined diagnosis threshold value stored in a storage means, thereby diagnosing a degree of deterioration of the catalyst, wherein the diagnosis threshold value is previously determined based on a correlationship between the diagnosis object value and a total weight value of NOx and THC in the exhaust gas through the catalyst in a state where the vehicle travels under a constant threshold value setting condition, and the diagnosis means diagnoses that a deterioration occurs in the precious metal component when the diagnosis object value exceeds the diagnosis threshold value.