NOx Catalyst Adsorption Diagnosis Thresholds
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Solution Overview
Problem
The diagnostic accuracy for malfunctioning reducing agent supply devices in exhaust emission control systems is compromised due to the NOx sensor's inability to distinguish between NOx and ammonia, leading to incorrect diagnoses when the amount of adsorbed reducing agent falls within specific ranges.
Innovation Solution
A malfunction diagnosis apparatus with an electronic control unit that estimates the amount of adsorption on the NOx selective catalytic reduction catalyst and sets thresholds to prevent diagnoses based on detected values when the adsorption is within certain ranges, thereby preventing decreases in diagnostic accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the NOx sensor is used to detect both NOx and ammonia for monitoring exhaust composition, then the monitoring capability is improved, but the diagnostic accuracy for reducing agent supply device malfunction decreases due to inability to distinguish between NOx and ammonia
Solution Approach 1:
The patent segments the monitoring function by introducing a separate ammonia sensor to specifically detect ammonia levels, while the NOx sensor continues to monitor NOx. This segmentation allows distinct detection of each substance, resolving the ambiguity that occurred when a single sensor attempted to detect both substances simultaneously.
Solution Approach 2:
The patent introduces an intermediary calculation process that uses both the NOx sensor output and the ammonia sensor output together with a reduction promotion catalyst to determine the actual reducing agent supply status. This intermediary approach combines multiple data sources to achieve accurate diagnosis while maintaining the versatility of using both sensor types.
2Reliability
If the reducing agent supply amount is increased to ensure sufficient reducing agent reaches downstream NOx catalysts, then the purification effectiveness is improved, but the amount of ammonia slipping through and causing false diagnoses increases
Solution Approach 1:
The patent implements a feedback mechanism where the ammonia sensor continuously monitors ammonia levels in the exhaust, and this information is fed back to the control unit. The control unit adjusts the reducing agent supply amount based on this feedback, optimizing the balance between purification effectiveness and preventing ammonia slip that could cause false diagnoses.
Solution Approach 2:
The patent dynamically changes the operating parameters by adjusting the reducing agent supply amount based on real-time conditions detected by both sensors. This parameter adjustment allows the system to maintain optimal purification effectiveness while minimizing excess ammonia that would cause diagnostic errors.
3Device complexity
If a single addition valve supplies reducing agent to multiple NOx catalysts, then the device complexity is reduced, but the control precision for each catalyst decreases
Solution Approach 1:
The patent applies multi-functionality by enabling the single addition valve to supply reducing agent to multiple downstream NOx catalysts based on varying operating conditions. The control unit determines the appropriate catalyst target based on sensor inputs, allowing one valve to perform multiple functions and maintain system simplicity while achieving precise control through intelligent management.
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 enhances diagnostic accuracy by preventing incorrect diagnoses when the amount of adsorbed reducing agent is within ranges that cause ambiguity, ensuring reliable detection of malfunctions in the reducing agent supply device.
Implementation Method 1
a NOx selective catalytic reduction catalyst configured to reduce NOx with use of reducing agent that is adsorbed on the NOx selective catalytic reduction catalyst
Implementation Method 2
a NOx selective catalytic reduction catalyst configured to reduce NOx with use of reducing agent that is adsorbed on the NOx selective catalytic reduction catalyst
Implementation Method 3
a NOx sensor configured to detect NOx and ammonia
Implementation Method 4
an ammonia slip catalyst that oxidizes ammonia
Data Source
AI summary
An amount of reducing agent adsorbed on a NOx catalyst when a reducing agent supply device is normal and a corresponding detected value may be estimated. The corresponding detected value may be detected by a NOx sensor, and the detected value may correspond to an amount of reducing agent adsorbed on the NOx catalyst. When the estimated amount of adsorption is larger than or equal to a first amount and is smaller than or equal to a second amount, a diagnosis of the NOx catalyst based on the detected value of the NOx sensor may be prevented. The first amount may be an amount of adsorbed reducing agent corresponding to a minimum value of the corresponding detected value. The second amount may be an amount of adsorbed reducing agent corresponding to the corresponding detected value when the amount of adsorbed reducing agent is zero and larger than the first amount.