NOx Sensor Diagnostic System for Stuck-in-Range Failure Detection
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Solution Overview
Problem
NOx sensors in SCR systems can fail to detect NOx concentrations accurately, leading to false-positive failures and potential unintended NOx emissions, especially when NOx levels are low and stable, causing increased warranty and replacement costs.
Innovation Solution
A diagnostic process using a controller to interpret NOx sensor readings by increasing O2 levels in the sensor chamber, calculating parameter variations, and determining if they exceed threshold values to detect stuck-in-range failures before reducing O2, thereby distinguishing between functional and failed sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NOx sensor is used to monitor exhaust gas composition, then NOx emission monitoring capability is improved, but false-positive failure indications occur when NOx levels are low and stable
Solution Approach 1:
The diagnostic system performs preliminary actions by introducing a known amount of oxygen to the sensor chamber before evaluating sensor output. This preliminary test allows the system to verify sensor functionality under controlled conditions, distinguishing between actual sensor failures and false readings caused by low and stable NOx emission levels
Solution Approach 2:
The system changes operational parameters by actively modifying the oxygen concentration in the sensor chamber during diagnostic mode. By controlling the oxygen parameter independently from normal exhaust conditions, the system creates a test environment that reveals sensor functionality regardless of actual exhaust composition, thereby resolving false-positive failure indications
2Measurement precision
If oxygen pump is activated to control O2 levels in sensor chamber, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The oxygen pump serves multiple functions: it removes oxygen during normal NOx measurement operations and introduces controlled oxygen during diagnostic operations. This multi-functionality allows a single component to handle both measurement and self-diagnosis requirements, improving measurement precision while minimizing the increase in device complexity
3Reliability
If diagnostic process introduces additional O2 to sensor chamber, then sensor failure detection capability is improved, but energy consumption increases
Solution Approach 1:
The diagnostic process that introduces additional oxygen to the sensor chamber is performed periodically rather than continuously. This periodic execution allows the system to maintain sensor reliability through regular self-diagnosis while minimizing energy consumption by keeping the oxygen pump inactive during normal operation periods
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 effectively identifies stuck-in-range failures in NOx sensors, reducing false positives and ensuring accurate NOx emission monitoring, thereby minimizing unnecessary replacements and maintaining low NOx emissions.
Implementation Method 1
an oxygen pump of the NOx sensor has not been activated
Implementation Method 2
interpret one or more values of a parameter indicative an amount of O2 and/or NOx measured by the NOx sensor
Data Source
AI summary
A system includes: a NOx sensor; and a controller configured to: increase an amount of O2 in a chamber of the NOx sensor; interpret one or more values of a parameter indicative an amount of O2 and/or NOx measured by the NOx sensor; determine if the one or more values of the parameter exceed a threshold value; and indicate a failure of the NOx sensor responsive to the one or more values of the parameter do not exceed the threshold value.