NOx Sensor Offset Diagnostic During Engine Soak
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Solution Overview
Problem
Current NOx sensors downstream of SCR catalysts tend to confuse ammonia (NH3) with nitrogen oxides (NOx), leading to erroneously high NOx offset readings, which can cause the Malfunction Indicator Light to illuminate unnecessarily, resulting in warranty issues and potential increased frequency of such issues due to stricter NOx emissions regulations.
Innovation Solution
A method involving a powertrain control module that wakes up during an engine soak period, heats the NOx sensor, and performs offset testing after a calibrated duration to dissipate encapsulated NH3 and moisture, ensuring accurate NOx offset readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If NOx sensor offset diagnostic is performed during engine overrun conditions, then the diagnostic can be executed with existing procedures, but the NOx sensor may confuse NH3 with NOx leading to erroneously high offset readings
Solution Approach 1:
The system performs preliminary actions by waiting for a soak period after engine shutdown before initiating the NOx sensor offset diagnostic. This allows NH3 and moisture to dissipate from the exhaust system, ensuring accurate readings when the diagnostic is subsequently performed during the next engine overrun condition.
Solution Approach 2:
The patent introduces an intermediary time period (soak period) between engine shutdown and diagnostic initiation. This intermediary period allows the exhaust system to return to ambient conditions, acting as a buffer that prevents NH3 interference during the actual diagnostic measurement.
2Loss of time
If NOx sensor offset test is performed immediately after engine shutdown, then the diagnostic timing is simplified, but encapsulated NH3 and moisture cause erroneously high readings
Solution Approach 1:
The system implements a preliminary waiting period (soak period) after engine shutdown before performing the NOx sensor offset diagnostic. This preliminary action allows NH3 and moisture to dissipate, ensuring measurement accuracy is not compromised by the time delay.
3Reliability
If SCR catalyst releases NH3 for extended duration, then the catalyst effectively reduces NOx emissions, but the NOx sensor reads NH3 as NOx causing false malfunction indications
Solution Approach 1:
The patent extracts the diagnostic measurement from the period when NH3 is present in the exhaust system. By performing the offset diagnostic during a soak period when the engine is off and NH3 release has ceased, the measurement is taken separately from the NH3-emitting operation, allowing both functions to coexist without interference.
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 reduces the likelihood of erroneously high NOx offset readings, minimizing unnecessary warranty claims and ensuring compliance with stringent NOx emissions regulations by accurately monitoring NOx sensor performance.
Implementation Method 1
heating an exhaust NOx sensor
Implementation Method 2
NOx sensors, configured to measure NOx levels in the exhaust system
Implementation Method 3
the reductant and the SCR catalyst may chemically reduce NOx molecules to nitrogen and water
Implementation Method 4
encapsulated NOx, NH3, and moisture within the sensor protection tube may be dissipated
Data Source
AI summary
Methods and systems are provided for waking up a powertrain control module of an engine-driven vehicle during engine soak to perform an offset test of an exhaust NOx sensor. In one example, a method includes determining a duration to delay waking up the powertrain control module based on exhaust temperature at vehicle-off, waking up the powertrain control module after the duration has expired, and then initiating heating of the NOx sensor. After the NOx sensor lights off, heating continues for an additional duration before offset testing of the NOx sensor is performed.