Catalyst Deterioration Diagnosis Using NOx Ratio and Temperature
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Solution Overview
Problem
Current methods for diagnosing catalyst deterioration, particularly in vehicles, face challenges such as disagreement between O2 storage capacity and NOx conversion efficiency, errors due to sensor deterioration and environmental factors, limited opportunities for precise measurement, and time-consuming diagnosis processes, making it difficult to accurately assess catalyst condition on-board.
Innovation Solution
A catalyst deterioration diagnosis device and method that utilize temperature and sensor output data from gas sensors placed between the catalyst and exhaust port to determine catalyst faultiness, allowing for precise and rapid diagnosis by setting evaluative temperature and conversion efficiency thresholds, enabling quick and accurate fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If OSC method is used for catalyst deterioration diagnosis, then oxygen storage capacity can be measured, but disagreement between O2 storage capacity and NOx conversion efficiency occurs due to catalyst deterioration
Solution Approach 1:
The invention changes the diagnostic parameters from oxygen storage capacity (OSC) to nitrogen oxide (NOx) concentration and catalyst temperature. By measuring NOx concentration upstream and downstream of the catalyst and comparing the ratio at different temperatures, the system achieves reliable deterioration diagnosis without the correlation problems between O2 storage and NOx conversion that plague OSC methods.
2Reliability
If traditional OSC diagnosis method is used, then catalyst condition can be assessed, but errors occur due to sensor deterioration and environmental factors
Solution Approach 1:
The system uses feedback by continuously monitoring NOx concentration ratios at different temperatures and comparing against reference values. The diagnosis result feeds back to determine catalyst deterioration status, and the system can adapt to sensor drift by using the temperature-dependent ratio comparison method which is less sensitive to absolute sensor accuracy than OSC methods.
Solution Approach 2:
The invention changes from using absolute oxygen sensor readings (which deteriorate and are affected by H2 generation and EGR) to using the ratio of NOx concentrations upstream and downstream of the catalyst. This ratio method, combined with temperature evaluation, eliminates many environmental error sources including H2 generation effects, EGR amount variations, and air amount misdiagnosis.
3Measurement precision
If precise catalyst diagnosis is performed using OSC method, then accurate measurement can be achieved, but limited opportunities for diagnosis occur due to temperature and running conditions requirements
Solution Approach 1:
The system dynamically evaluates catalyst condition across a range of temperatures rather than requiring a single fixed temperature point. By collecting NOx concentration data at multiple temperatures and evaluating the ratio changes, the system can perform accurate diagnosis whenever the catalyst reaches any temperature above ambient, significantly increasing diagnosis opportunities during normal vehicle operation.
4Reliability
If catalyst deterioration diagnosis is performed using OSC method, then catalyst condition can be assessed, but diagnosis time is long (about 10 seconds) due to need for transition between rich and lean
Solution Approach 1:
The invention extracts the essential diagnostic information (NOx concentration ratio between upstream and downstream sensors) from the complex OSC procedure. By focusing only on the NOx ratio at different temperatures rather than requiring full rich-lean transitions and OSC calculations, the system achieves rapid diagnosis in about 1 second while maintaining accuracy.
Data Source
AI summary
A catalyst deterioration diagnosis device includes: a unit configured to obtain a temperature of a catalyst; a unit configured to obtain a sensor output from a gas sensor disposed between the catalyst and an exhaust port; and a unit configured to determine the catalyst to be faulty when the temperature of the catalyst obtained when the sensor output becomes a preset evaluative output is equal to or higher than an evaluative catalyst temperature.