Exhaust Gas Catalytic Converter Diagnosis Using Upstream NOx Sensing
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Solution Overview
Problem
Conventional methods for diagnosing exhaust-gas catalytic converters, such as SCR catalytic converters, lack precision and reliability, especially after a cold start, and are unable to frequently detect defective catalysts due to the location of exhaust-gas sensors downstream from the catalytic converters.
Innovation Solution
The method involves determining the momentary raw emission and concentration of exhaust-gas components upstream from the catalytic converter, utilizing exhaust-gas recirculation to enhance diagnostic precision, with a diagnostic device calculating the efficiency of the catalytic converter based on the ratio of measured concentration to raw emission, and comparing it to target or threshold values to identify faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If exhaust-gas sensors are located downstream from the catalytic converter, then the catalytic converter can be monitored for its conversion performance, but the diagnosis cannot be performed frequently or reliably especially after cold start
Solution Approach 1:
Instead of measuring exhaust gas downstream of the catalytic converter to assess conversion performance, the patent places the exhaust-gas sensor upstream of the catalytic converter. This inverted measurement location allows the sensor to immediately detect raw exhaust gas composition after cold start without waiting for catalyst activation, enabling frequent and reliable diagnosis from the moment the engine starts.
2Productivity
If exhaust-gas sensors are placed upstream from the catalytic converter, then diagnosis can be performed more frequently and reliably, but the direct measurement of conversion efficiency is lost
Solution Approach 1:
The patent employs a feedback mechanism where the upstream sensor continuously monitors exhaust gas composition and provides data to a control unit. The control unit compares the measured values with target values or threshold values and generates feedback signals to determine catalyst performance, enabling frequent diagnosis while maintaining measurement precision through continuous comparison and evaluation.
Solution Approach 2:
The control unit acts as an intermediary that processes the raw sensor data from upstream of the catalytic converter. It compares measured exhaust gas composition with expected values and determines conversion efficiency indirectly through this intermediate evaluation step, allowing frequent measurements while preserving diagnostic accuracy.
3Reliability
If conventional downstream sensing is used, then conversion performance can be monitored, but defective catalysts cannot be detected frequently
Solution Approach 1:
The patent performs preliminary measurement of exhaust gas composition upstream of the catalytic converter before the exhaust gas reaches the converter. This preliminary action allows immediate detection of abnormalities in the exhaust gas that would indicate catalyst defects, enabling frequent and precise defect detection from cold start without waiting for downstream sensor activation or catalyst warm-up.
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 precise diagnosis of catalytic converters, enabling early detection of defects and improved reliability, with the diagnostic device activating sooner after a cold start and providing fault outputs to the engine control unit or driver.
Implementation Method 1
at least one SCR catalytic converter that, in the presence of a reductant metered into the exhaust gas—normally ammonia NH3—selectively convert the nitrogen oxides of the exhaust gas into nitrogen and water
Implementation Method 2
from a precursor compound, for instance, urea in the form of an aqueous solution or solid pellets, obtained through the modality of thermolysis and hydrolysis
Implementation Method 3
from a precursor compound, for instance, urea in the form of an aqueous solution or solid pellets, obtained through the modality of thermolysis and hydrolysis
Implementation Method 4
the NH3-storage materials that reversibly bind the ammonia as a function of the temperature
Implementation Method 5
exhaust-gas recirculation constitutes an engine-related measure aimed at reducing NOx raw emissions in the exhaust gas, and this is a process in which part of the exhaust gas of the internal combustion engine is recirculated into its combustion air, as a result of which the combustion temperatures are lowered
Data Source
AI summary
A method for diagnosing an exhaust-gas catalytic converter (28) arranged in an exhaust-gas system (20) of an internal combustion engine (12) for the catalytic conversion of at least one exhaust-gas component from the internal combustion engine (12), which has an exhaust-gas recirculation means with which a partial stream of the exhaust gas can be drawn off downstream of the catalytic converter (14) and fed into the combustion air of the internal combustion engine (12), involves determining the current raw emission (NOx—raw) of the internal combustion engine (12) in of the exhaust-gas component; measuring the current concentration of the exhaust-gas component (NOx—meas) in the exhaust gas upstream of the catalytic converter (28); and determining a diagnostic value for the catalytic converter (28) in terms of the conversion of the exhaust-gas component as a function of the modelled raw emission (NOx—raw) from the internal combustion engine (12) and the measured concentration of the exhaust-gas component (NOx—meas). The invention further relates to a diagnostic device configured to perform the method and a motor vehicle having such a device.