NOx Sensor Degradation Diagnosis via Post-Shutdown Reductant Injection
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Solution Overview
Problem
Existing NOx sensor diagnostics in exhaust gas treatment systems for internal combustion engines are inadequate, particularly in detecting sensor degradation and reductant injector leakage, which affects emissions compliance and SCR system efficiency.
Innovation Solution
A method that involves using the feedgas NOx sensor output after engine shutdown to diagnose NOx sensor and reductant injector health by injecting a defined amount of reductant and monitoring the sensor response, correlating the output with expected profiles to identify degradation and adjust reductant dosing control during subsequent engine restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NOx sensor diagnostics are performed using conventional methods during engine operation, then the sensor health can be monitored, but the diagnostic accuracy is insufficient to detect sensor degradation and reductant injector leakage
Solution Approach 1:
The system performs preliminary diagnostic action by injecting reductant into the exhaust passage before actual engine operation to create a controlled test condition. This preliminary injection allows the sensor to be tested in a known state without interference from actual exhaust gases, enabling more accurate detection of sensor degradation and injector leakage.
Solution Approach 2:
The system introduces an intermediary substance (reductant) to mediate the diagnostic process. By injecting a known amount of reductant and measuring its effect on NOx levels, the system creates an intermediate measurement state that reveals sensor health and injector performance without requiring direct observation of sensor degradation or leakage.
2Measurement precision
If reductant injection is used to diagnose sensor health, then diagnostic capability is improved, but the system complexity increases due to additional injection events
Solution Approach 1:
The reductant injection system serves multiple functions: it performs actual reductant dosing for SCR catalyst operation during engine运行, and simultaneously performs diagnostic testing by injecting controlled amounts of reductant during engine shutdown. This multi-functionality eliminates the need for separate diagnostic injection hardware, reducing overall system complexity while maintaining high diagnostic accuracy.
Solution Approach 2:
The existing reductant injection infrastructure serves the diagnostic function without requiring additional dedicated diagnostic components. The system uses its own operational reductant injection capability to perform self-diagnosis, eliminating the need for external diagnostic equipment and simplifying the overall system architecture.
3Reliability
If NOx sensor output is monitored continuously, then sensor degradation can be detected, but the ability to distinguish sensor degradation from reductant injector leakage is reduced
Solution Approach 1:
The diagnostic process is segmented into distinct phases: engine shutdown phase where reductant is injected and sensor response is measured, and engine operation phase where actual exhaust processing occurs. By separating the diagnostic measurement from normal operation, the system can independently evaluate sensor health and injector performance without the confounding effects of variable exhaust conditions, thereby maintaining both detection reliability and information discrimination.
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 improves the accuracy of NOx sensor diagnostics, enhances emissions compliance, and optimizes reductant dosing, leading to better SCR system efficiency and reduced emissions.
Implementation Method 1
By monitoring the output of an exhaust NOx sensor during engine shutdown conditions, while reductant is injected upstream of the sensor, correlations between the injection and the exhaust NOx sensor output can be used to learn NOx sensor behavior. Specifically, natural sublimation of ammonia injected in an exhaust passage after an engine shutdown can be used to diagnose an exhaust NOx sensor.
Data Source
AI summary
Various systems and method for detecting exhaust NOx sensor degradation are disclosed. In one example, degradation of the NOx sensor is indicated responsive to reductant injection in an exhaust passage under engine off conditions. For example, degradation of the NOx sensor is indicated when an actual NOx sensor output differs from an expected NOx sensor output by more than a threshold amount.