NOx Sensor Self-Diagnostic Test Filtering
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Solution Overview
Problem
NOx sensors in vehicle exhaust systems face accuracy issues due to urea conversion to ammonia at high exhaust temperatures, leading to overestimation of NOx levels and reduced diagnostic accuracy during self-diagnostic tests.
Innovation Solution
A method to determine NOx sensor degradation by excluding self-diagnostic test results based on threshold conditions such as exhaust gas temperature, oxygen concentration, and NOx levels, ensuring tests are performed under specific conditions to improve accuracy and distinguish between degraded and non-degraded sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If self-diagnostic tests are performed after engine key-off event to monitor NOx sensor accuracy, then sensor degradation detection capability is improved, but measurement precision deteriorates due to urea conversion to ammonia at high exhaust temperatures causing overestimation of NOx levels
Solution Approach 1:
The system changes the operational parameters of the NOx sensor during self-diagnostic tests by controlling exhaust gas temperature to be below a threshold and managing urea injection to minimize ammonia formation. This parameter control ensures that the sensor operates under conditions where urea does not convert to ammonia, thereby maintaining measurement precision while enabling reliable degradation detection.
Solution Approach 2:
The system performs preliminary actions by conducting self-diagnostic tests during specific engine operating conditions (after key-off event) when exhaust temperature and urea concentration are controlled to prevent ammonia formation. This preliminary testing under controlled conditions allows accurate assessment of sensor degradation before normal operation resumes.
2Productivity
If SD tests are run under all exhaust conditions to maximize monitoring opportunity, then productivity is improved, but measurement precision deteriorates due to variable urea conversion to ammonia affecting NOx readings
Solution Approach 1:
The system selectively performs self-diagnostic tests only when exhaust gas temperature and urea concentration parameters are within acceptable ranges that prevent significant ammonia formation. This parameter-based selection maintains measurement precision while maximizing productive monitoring opportunities under suitable conditions.
Solution Approach 2:
The system dynamically determines when to perform self-diagnostic tests based on real-time monitoring of exhaust temperature and urea injection rates. The testing protocol adapts to current operating conditions, enabling flexible monitoring that maintains accuracy while maximizing productivity.
3Reliability
If NOx sensors continuously monitor exhaust systems to detect component degradation, then reliability of emission control is improved, but measurement precision deteriorates when sensors themselves become degraded and provide inaccurate readings
Solution Approach 1:
The system uses self-diagnostic tests as a feedback mechanism to assess the accuracy of NOx sensor readings. By periodically testing the sensor under controlled conditions and comparing results against expected values, the system can detect sensor degradation and adjust monitoring accordingly, maintaining both reliability and precision.
Solution Approach 2:
The NOx sensor performs self-diagnostic tests to evaluate its own accuracy without requiring external intervention. This self-service capability allows the sensor to detect its own degradation and trigger appropriate responses, maintaining measurement precision while ensuring emission control reliability.
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 the sensitivity and accuracy of NOx sensor degradation detection, maintaining the efficiency of the NOx emission control system by reducing variance in test results and accurately identifying sensor degradation.
Implementation Method 1
Under sufficiently high exhaust temperatures, urea in the exhaust system may be converted to ammonia
Implementation Method 2
NOx sensors register ammonia as NOx
Data Source
AI summary
Methods and systems are provided for detecting NOx sensor degradation based on results from a NOx sensor self-diagnostic (SD) test. In one example, a method may comprise: determining that a nitrogen oxide (NOx) sensor is degraded if outputs received from the sensor via a CAN bus during a self-diagnostic test are outside a threshold range. Additionally, only outputs received from the sensor during a self-diagnostic (SD) test performed after a first completed SD test after a key-off event, where the outputs are generated under conditions where a temperature at the sensor is less than a threshold, and an oxygen concentration is within a threshold range may be used to determine if the sensor is degraded.