NOx Sensor Offset Detection Using NH3 Plume Inhibition
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Solution Overview
Problem
NOx sensors in exhaust treatment systems face challenges in accurately determining offset values due to errors introduced by compounds other than NOx and limited data availability during vehicle operation, leading to reduced confidence in NOx offset estimates.
Innovation Solution
A method involving continuous sampling of NOx sensor output throughout a vehicle drive to generate a dataset of NOx concentration values, with the smallest value stored as the offset, and inhibiting offset reporting during NH3 plume detection to prevent bias, ensuring accurate offset determination from a larger data set.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If NOx offset is determined only during tip-out events, then the determination method is simple, but the confidence level is low due to few observations
Solution Approach 1:
The system performs preliminary sampling of NOx sensor output throughout the entire vehicle drive at a predetermined rate, storing multiple NOx concentration values before final offset determination. This preliminary data collection ensures sufficient observations are available even when tip-out events are rare, resolving the contradiction between simple determination methods and high confidence levels.
2Ease of operation
If NOx offset is determined during tip-out events, then data collection is straightforward, but accuracy is reduced due to NH3 plume interference
Solution Approach 1:
The system extracts and identifies NH3 plume events from the continuous NOx concentration data stream during vehicle operation. When NH3 plumes are detected, the corresponding NOx readings are excluded from offset determination calculations. This separation of NH3-interfered data from clean data resolves the contradiction between easy data collection and accurate NOx measurement.
3Reliability
If continuous sampling throughout vehicle drive is performed, then the data set size increases improving reliability, but the system complexity increases
Solution Approach 1:
The controller utilizes existing sensor outputs and onboard processing capabilities to perform continuous NOx sampling and NH3 plume identification without requiring additional external hardware or complex external processing systems. The system serves itself by using its own computational resources to handle the increased data processing demands, resolving the contradiction between improved reliability through continuous sampling and system complexity.
Data Source
AI summary
Methods and systems for monitoring a NOx sensor for a NOx offset value are described. In one example, the NOx offset value may be based on a minimum NOx concentration observed over an entire drive of a vehicle. The NOx offset monitor may be inhibited in response to inferring or detecting a presence of NH3 in an exhaust system.