Adapting NOx Sensor Curve During SCR Regeneration
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Solution Overview
Problem
The characteristic curve of nitrogen oxide sensors in internal combustion engines with exhaust gas recirculation deviates over time, particularly during the regeneration phase of the particle filter, where reduced nitrogen oxide emissions and increased exhaust gas temperature affect the accuracy of urea decomposition and reaction in SCR catalytic converters.
Innovation Solution
A method to adapt the characteristic curve of a nitrogen oxide sensor upstream of an SCR catalytic converter by using nitrogen oxide values from a sensor downstream of the converter, adjusting the curve based on stability intervals and ammonia thresholds, while accounting for time delays and flow behavior, and interrupting urea supply during particle filter regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the characteristic curve of the nitrogen oxide sensor is adapted using downstream sensor values during particle filter regeneration, then sensor reading stability is improved, but the complexity of the control system increases
Solution Approach 1:
The patent implements feedback by using the downstream nitrogen oxide sensor (after SCR catalyst) as a reference to adjust and adapt the characteristic curve of the upstream nitrogen oxide sensor (before SCR catalyst). The control unit continuously compares readings from both sensors and modifies the upstream sensor's characteristic curve to maintain accuracy despite environmental changes during particle filter regeneration.
Solution Approach 2:
The patent changes the operational parameters by interrupting the urea supply during particle filter regeneration. This parameter change creates a specific operating condition where the downstream sensor readings can be reliably used for adapting the upstream sensor's characteristic curve, as urea injection would otherwise interfere with the measurement accuracy during this high-temperature phase.
2Measurement precision
If urea supply is interrupted during particle filter regeneration, then ammonia oxidation is reduced and measurement accuracy is improved, but the nitrogen oxide reduction efficiency decreases
Solution Approach 1:
The patent applies periodic action by temporarily interrupting the urea supply during the specific phase of particle filter regeneration, rather than continuously injecting urea. This periodic interruption allows for accurate sensor adaptation during high-temperature conditions when ammonia oxidation would otherwise occur, while maintaining nitrogen oxide reduction efficiency during normal operating phases when urea injection is active.
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 method stabilizes the nitrogen oxide sensor readings by ensuring they fall within predetermined intervals and adjusts the characteristic curve only when ammonia levels are below a threshold, thereby maintaining accurate urea injection and reducing sensor deviation over time.
Implementation Method 1
SCR (selective catalytic reduction) catalytic converters, which are used to reduce nitrogen oxides in the exhaust gases
Implementation Method 2
The chemical reaction at the SCR catalytic converter is selective, which means that the nitrogen oxides (NO, NO2) are preferentially reduced
Implementation Method 3
a urea is injected into the exhaust gas upstream of the SCR catalyst, which then at least partially decomposes into ammonia
Implementation Method 4
particle filter arranged upstream of the SCR catalytic converter
Data Source
Figure 1~2
AI summary
The invention relates to a method for adapting the characteristic curve of a nitrogen oxide sensor (32) of an internal combustion engine with an exhaust gas recirculation system, which has the first nitrogen oxide sensor (32) arranged upstream of the SCR catalytic converter (20), and a second nitrogen oxide sensor (22) arranged downstream of the SCR catalytic converter (20). The disclosed method comprises determining that a particle filter (30) is in a regeneration phase, increasing the exhaust gas recirculation rate, interrupting the supply of urea by a urea injection device (26), acquiring first nitrogen oxide values from first nitrogen oxide signals generated by the first nitrogen oxide sensor (32), and determining that the first nitrogen oxide values are within a first nitrogen oxide interval, acquiring second nitrogen oxide values from second nitrogen oxide signals generated by the second nitrogen oxide sensor (22), and determining that the second nitrogen oxide values are within a second nitrogen oxide interval, and adapting the characteristic curve of the first nitrogen oxide sensor (32) by means of the second nitrogen oxide values.