Catalyst Diagnostics Using Stoichiometric Crossings
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Solution Overview
Problem
Existing methods for diagnosing exhaust catalyst health are limited by disabling diagnostics during 'empty can' conditions, reducing diagnostic frequency and accuracy, and potentially degrading engine emissions due to intrusive air-fuel ratio changes.
Innovation Solution
Enabling catalyst diagnostics based on the number of times a stoichiometric air-fuel ratio is recorded by a downstream oxygen sensor, independent of instantaneous readings, using a combination of upstream and downstream sensor data to determine transfer function gain and assess catalyst degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catalyst diagnostics are disabled during empty can conditions, then control system errors are avoided, but diagnostic frequency and completeness decrease
Solution Approach 1:
The patent changes the diagnostic enablement parameter from requiring instantaneous stoichiometric reading to requiring a threshold number of stoichiometric crossings within a time window. This parameter transformation allows diagnostics to proceed during empty can conditions while maintaining reliability through statistical validation of stoichiometric events.
Solution Approach 2:
The patent introduces dynamic evaluation by counting the number of stoichiometric crossings over a time period rather than relying on a static instantaneous reading. This dynamic approach adapts to varying oxygen storage conditions and enables diagnostics across a broader range of operating conditions while maintaining reliability.
2Measurement precision
If intrusive air-fuel ratio changes are made to conduct diagnostics, then catalyst degradation can be detected, but engine exhaust emissions may be degraded
Solution Approach 1:
The patent utilizes the natural oscillations and stoichiometric crossings that occur during normal engine operation to perform catalyst diagnostics. Instead of imposing external test signals, the system leverages existing operational variations to excite the catalyst and measure its response, thereby avoiding additional emissions from diagnostic maneuvers.
Solution Approach 2:
The patent employs feedback from the downstream oxygen sensor to detect stoichiometric crossings and determine catalyst transfer function gain. By continuously monitoring the oxygen sensor output and using it to assess catalyst health, the system achieves accurate degradation detection without requiring intrusive air-fuel ratio perturbations.
3Device complexity
If diagnostics rely on instantaneous stoichiometric readings, then simple control logic is maintained, but diagnostic opportunities are limited
Solution Approach 1:
The patent transitions from one-dimensional instantaneous reading evaluation to two-dimensional evaluation by introducing a time window dimension. The system counts stoichiometric crossings within a specified time period, adding a temporal dimension to the diagnostic criteria. This increases diagnostic opportunities without significantly complicating the control logic, as it builds upon existing reading capabilities.
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 more frequent and accurate monitoring of catalyst health, enabling prompt detection of degradation and improving emission quality by ensuring diagnostics can be performed at all oxygen storage levels without disabling during 'empty can' conditions.
Implementation Method 1
Three-way catalysts contain ceria compounds that both store and release oxygen molecules to act as a buffer against generating undesirable tailpipe emissions during short lean and rich excursions from stoichiometry
Implementation Method 2
a universal exhaust gas oxygen (UEGO) sensor positioned upstream of the TWC and a heated exhaust gas oxygen (HEGO) sensor positioned downstream of the TWC
Data Source
AI summary
Methods and systems are provided for enabling diagnostics of an exhaust catalyst regardless of a level of oxygen stored in the catalyst. In one example, a method may include initiating diagnostics of the catalyst in response to an oxygen sensor coupled downstream of the catalyst recording a measurement that crosses a stoichiometric air-fuel ratio output more than a threshold number of times.