NOx Sensor Diagnosis Device Preventing Erroneous Detection
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Solution Overview
Problem
Existing NOx sensor diagnosis devices are prone to erroneous diagnoses during rapid changes in exhaust gas flow rate or NOx concentration, such as during DPF regeneration, PTO operation, or exhaust brake operation, leading to false abnormalities being detected in the NOx sensor.
Innovation Solution
A NOx sensor diagnosis device that includes a calculated value calculation unit to determine NOx concentration based on engine operation and an abnormality determination unit that only flags the NOx sensor as abnormal if the difference between calculated and detected values exceeds a threshold, with a diagnosis prohibition unit that prevents diagnosis during DPF regeneration, PTO operation, or exhaust brake operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NOx sensor diagnosis is performed by comparing calculated and detected NOx concentration values, then sensor validity can be determined, but erroneous diagnosis occurs during rapid exhaust gas changes
Solution Approach 1:
The diagnosis prohibition determination unit checks whether diagnosis should be prohibited before performing the NOx sensor diagnosis. This preliminary check prevents diagnosis during conditions that would cause erroneous results (DPF regeneration, PTO operation, exhaust brake operation), thereby avoiding false abnormality detections while maintaining diagnostic capability during normal operating conditions.
2Productivity
If diagnosis is performed during all operating conditions, then continuous monitoring is achieved, but false abnormalities are detected during transient states
Solution Approach 1:
The diagnosis prohibition determination unit dynamically adjusts the diagnosis behavior based on current operating conditions. It selectively prohibits diagnosis only during specific transient states (DPF regeneration, PTO operation, exhaust brake operation) while allowing continuous monitoring during normal operating conditions, thus adapting the monitoring strategy to maintain both continuity and accuracy.
3Device complexity
If threshold comparison is used for diagnosis, then simple determination is achieved, but erroneous diagnosis occurs when rapid changes exceed threshold
Solution Approach 1:
Before performing the simple threshold-based comparison diagnosis, the diagnosis prohibition determination unit performs a preliminary check to determine if current operating conditions would cause rapid exhaust gas changes. This preliminary action prevents the simple diagnosis method from being applied during conditions that would invalidate its results, thereby maintaining both simplicity and reliability.
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
A NOx sensor diagnosis device which can diagnose validity of a NOx sensor by considering an environmental condition and can prevent erroneous diagnosis and an SCR system are provided. In a NOx sensor diagnosis device provided in an exhaust pipe 102 of an engine E and diagnosing a NOx sensor 110 that detects NOx concentration in an exhaust gas, a diagnosis prohibition determination unit 4 is provided that prohibits diagnosis of the NOx sensor 110 during DPF (diesel particulate filter) regeneration, during PTO (power take-off) operation or during exhaust brake operation.