Diagnosing Exhaust Catalyst Deterioration via Air-Fuel Ratio Control
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Solution Overview
Problem
The existing abnormality diagnosis systems for exhaust purification catalysts in internal combustion engines fail to accurately diagnose deterioration due to deviations in air-fuel ratio control, leading to incorrect judgments about the catalyst's condition, as the oxygen sensor output remains unchanged even when the catalyst deteriorates.
Innovation Solution
An abnormality diagnosis system that alternately controls the air-fuel ratio to rich and lean settings and diagnoses the catalyst based on the downstream oxygen sensor's output, judging the catalyst as abnormal when the output deviates beyond specific judgment ratios, and suspends diagnosis and control if the air-fuel ratio control becomes abnormal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active air-fuel ratio control is performed and downstream oxygen sensor output is used to diagnose catalyst deterioration, then catalyst deterioration can be detected, but misjudgment occurs when air-fuel ratio control itself becomes abnormal
Solution Approach 1:
The diagnosis system segments the monitoring function into two independent parts: (1) monitoring air-fuel ratio control status using the downstream air-fuel ratio sensor, and (2) diagnosing catalyst deterioration using the downstream oxygen sensor. This segmentation allows independent detection of control abnormalities without being confounded by catalyst state, thereby improving diagnosis reliability while preventing loss of control status information
Solution Approach 2:
The downstream air-fuel ratio sensor acts as an intermediary indicator to monitor the status of air-fuel ratio control. By using this sensor's output as a separate monitoring channel, the system can detect control abnormalities without directly interfering with the catalyst diagnosis function, thus maintaining both control information integrity and diagnosis accuracy
2Measurement precision
If downstream oxygen sensor output is used for diagnosis, then catalyst state can be monitored, but the sensor output does not change when control abnormalities occur, leading to incorrect judgments
Solution Approach 1:
The system segments the detection functions by using the downstream air-fuel ratio sensor specifically for monitoring control abnormalities, while the downstream oxygen sensor remains dedicated to catalyst state detection. This functional segmentation ensures that control abnormalities do not affect the oxygen sensor's measurement precision for catalyst diagnosis, while simultaneously improving overall diagnosis reliability through separate control monitoring
Solution Approach 2:
The system creates a copied monitoring function using the downstream air-fuel ratio sensor to replicate the control status information that would otherwise be lost. This copied information serves as an independent verification channel, allowing the system to distinguish between genuine catalyst deterioration and control abnormalities, thereby maintaining measurement precision while improving reliability
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 system enables accurate diagnosis of exhaust purification catalyst abnormalities by effectively differentiating between normal and deteriorated states, preventing misjudgment and ensuring proper control strategies are maintained.
Implementation Method 1
An exhaust purification catalyst which has an oxygen storage ability can remove the unburned gas (HC or CO etc.) or NOX etc. in the exhaust gas which flows into the exhaust purification catalyst when the oxygen storage amount is a suitable amount
Implementation Method 2
If exhaust gas of an air-fuel ratio which is richer than the stoichiometric air-fuel ratio flows into the exhaust purification catalyst, the oxygen which is stored in the exhaust purification catalyst enables the unburned gas in the exhaust gas to be removed by oxidation
Implementation Method 3
If exhaust gas of an air-fuel ratio which is leaner than the stoichiometric air-fuel ratio flows into the exhaust purification catalyst, the oxygen in the exhaust gas is stored in the exhaust purification catalyst. Due to this, the surface of the exhaust purification catalyst becomes an oxygen-deficient state. Along with this, the NOX in the exhaust gas is removed by reduction
Implementation Method 4
a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst in an exhaust flow direction and which can detect an air-fuel ratio of exhaust gas discharged from the exhaust purification catalyst
Data Source
AI summary
An internal combustion engine comprises an exhaust purification catalyst which can store oxygen, controller for controlling the air-fuel ratio of exhaust gas to become a target air-fuel ratio, and a downstream side air-fuel ratio sensor. An abnormality diagnosis system performs an active air-fuel ratio control which alternately controls the target air-fuel ratio to rich and lean air-fuel ratios, and diagnoses abnormality of said exhaust purification catalyst based on the output air-fuel ratio of the air-fuel ratio sensor. The abnormality diagnosis system judges that the exhaust purification catalyst is abnormal when the output air-fuel ratio of the air-fuel ratio sensor reaches a rich judgment air-fuel ratio and a lean judgment air-fuel ratio during the active air-fuel ratio control, and judges that said air-fuel ratio control is abnormal when the output air-fuel ratio reaches only one of the rich and lean judgment air-fuel ratios.