NOx Sensor Response Rate Deterioration Estimation
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Solution Overview
Problem
Conventional NOx sensor response rate deterioration estimation methods fail to accurately distinguish between slow change rates due to sensor deterioration and healthy sensor operation, and do not account for signal offset drift and transfer delays, leading to inefficiencies in exhaust after-treatment systems.
Innovation Solution
An apparatus and method that determine NOx sensor response rate deterioration by using a function fitting method, such as least squares fit, to calculate the time constant and offset drift of the NOx sensor signal, while stopping fueling to the internal combustion engine during motoring, allowing for precise estimation of the response rate deterioration value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NOx sensor deterioration estimation methods are used, then the system can monitor sensor health, but the methods fail to accurately distinguish between slow change rates due to sensor deterioration and healthy sensor operation, leading to inaccurate deterioration estimation
Solution Approach 1:
The system performs preliminary actions by stopping fueling to the engine during motoring conditions before conducting the deterioration test. This creates a controlled baseline state where NOx generation is minimized, allowing the sensor's response characteristics to be measured without the confounding variable of active combustion. The ECM captures sensor signals during this pre-established controlled condition to establish reference data for accurate deterioration estimation.
Solution Approach 2:
The system changes operational parameters by transitioning the engine to motoring mode (where the crankshaft rotates without fuel injection or combustion). This parameter change fundamentally alters the exhaust composition and NOx generation rate, creating a distinct test condition that isolates sensor response characteristics from normal operating variability. The ECM detects sensor signals under these modified parameters to calculate deterioration values.
2Productivity
If the system continues normal fueling operation during sensor monitoring, then continuous engine operation is maintained, but the system cannot accurately separate sensor response slowdown from actual NOx level changes
Solution Approach 1:
The monitoring process is segmented into distinct phases: normal operation phase and dedicated deterioration testing phase. During the testing phase, the system temporarily suspends fueling to create isolated test conditions. This segmentation allows the ECM to capture sensor responses under controlled conditions where NOx generation is minimized, enabling precise measurement of sensor response rate without interference from variable combustion conditions.
Solution Approach 2:
The system implements periodic deterioration testing by intermittently stopping fueling during motoring conditions rather than continuously monitoring under variable load. This periodic action creates regular intervals where the sensor response can be accurately characterized under standardized conditions, and the results are then applied to assess sensor health during normal operation periods.
3Reliability
If conventional monitoring methods are used without stopping fueling, then the engine operates continuously, but signal offset drift and transfer delays cannot be accounted for, reducing estimation accuracy
Solution Approach 1:
The system maintains continuity of useful action by keeping the engine in motoring mode throughout the deterioration test duration. The crankshaft continues to rotate and exhaust gases continue to flow through the after-treatment system, ensuring that the sensor remains exposed to realistic exhaust conditions. This continuous flow allows the ECM to capture authentic sensor responses while still benefiting from the controlled no-fueling state that enables accurate deterioration measurement.
Data Source
AI summary
An apparatus for determining a deterioration of a NOx sensor response rate in an internal combustion engine system includes an engine control module configured to stop fueling to an internal combustion engine during motoring of the internal combustion engine. The apparatus also includes a signal monitoring module configured to monitor a NOx sensor signal after the engine control module stops fueling to the internal combustion engine during motoring of the engine and store NOx sensor signal data corresponding to the monitored NOx sensor signal. Additionally, the apparatus includes a time constant module that is configured to determine a time constant of the NOx sensor response after the engine control module stops fueling. The apparatus further includes a response rate deterioration module configured to determine a response rate deterioration value of the NOx sensor based at least partially on the determined time constant.