NOx Sensor Diagnostic via Phase Shift Correction
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Solution Overview
Problem
Existing exhaust aftertreatment systems for internal combustion engines face challenges in accurately diagnosing faults in NOx sensors, leading to potential misidentification of issues and increased costs due to limited on-road monitoring capabilities and less-than-ideal diagnostic procedures.
Innovation Solution
A system and method that includes a controller to suspend reductant dosing, purge residual deposits, and adjust engine operations to manipulate NOx levels, allowing for more accurate diagnosis of SCR inlet and outlet NOx sensors by determining phase shifts and diagnostic features from measured data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If on-road monitoring and testing are performed during normal vehicle operation, then convenience is improved, but diagnostic accuracy and effectiveness deteriorate due to limited operating range and priority conflicts
Solution Approach 1:
The system performs preliminary diagnostic actions by suspending reductant dosing before conducting NOx sensor diagnostics. This preparatory step isolates the SCR system from reductant interference, enabling accurate sensor testing during on-road operation without compromising diagnostic effectiveness
Solution Approach 2:
The diagnostic system implements periodic suspension of reductant dosing at scheduled intervals to perform NOx sensor diagnostics. This periodic interruption allows for accurate measurements while maintaining overall system operation, resolving the conflict between continuous monitoring convenience and diagnostic accuracy
2Measurement precision
If reductant dosing is suspended to perform diagnostic tests, then diagnostic accuracy is improved, but system productivity deteriorates due to interruption of normal aftertreatment function
Solution Approach 1:
The system applies partial suspension of reductant dosing only during specific diagnostic intervals rather than continuous suspension. This partial action provides sufficient NOx signal variation for accurate sensor diagnostics while minimizing impact on overall emission reduction performance during normal operation
Solution Approach 2:
The diagnostic system changes the dosing parameter by suspending reductant injection temporarily to create measurable NOx signal variations. This parameter change enables accurate sensor diagnostics while the system quickly returns to normal dosing operations, minimizing productivity impact
3Measurement precision
If phase shift correction is applied to outlet NOx data, then measurement precision is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The system uses feedback from the phase correction module to adjust outlet NOx measurements based on measured phase shifts. This feedback mechanism improves measurement accuracy by compensating for transport delays while using established signal processing techniques that balance precision with computational efficiency
Data Source
AI summary
A method for diagnosing NOx sensors in an exhaust aftertreatment system includes suspending reductant dosing in an exhaust aftertreatment system; purging a reductant deposit in a selective catalytic reduction (SCR) system of the exhaust aftertreatment system; adjusting at least one of an ignition timing and an engine speed for an engine to adjust an engine out nitrogen oxide (NOx) amount; receiving measured SCR inlet NOx data from a SCR inlet NOx sensor and measured SCR outlet NOx data from a SCR outlet NOx sensor; determining a phase shift between the measured SCR inlet and SCR outlet NOx data; applying the determined phase shift to the SCR outlet NOx data; and determining a diagnostic feature based on the SCR inlet NOx data and the phase shifted SCR outlet NOx data regarding a state of the SCR inlet and outlet NOx sensors.