NOx Sensor Gain Diagnostics via Least Squares Estimation
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Solution Overview
Problem
On-vehicle NOx sensors in diesel engine exhaust streams often fail to accurately measure nitrogen oxides, leading to incorrect urea dosage and potential emissions breakthrough or ammonia slip, necessitating a reliable diagnostic method to assess their performance.
Innovation Solution
A computer-managed diagnostic method using least squares estimation to determine the gain and offset of NOx sensors, comparing the results with known accuracy thresholds, and alerting operators to any deviations, ensuring accurate urea dosage and preventing emissions issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NOx sensors are used in diesel engine exhaust streams to measure nitrogen oxides, then exhaust treatment control is enabled, but measurement accuracy deteriorates leading to incorrect urea dosage
Solution Approach 1:
The patent applies preliminary action by performing diagnostic tests on the NOx sensor before it is fully integrated into the exhaust treatment control system. The method includes conducting gain and offset diagnostics to pre-assess sensor accuracy, ensuring that only sensors meeting predetermined accuracy thresholds are activated for urea dosage control. This prevents incorrect measurements from compromising the reliability of exhaust treatment control.
Solution Approach 2:
The patent implements feedback by continuously monitoring NOx sensor output signals and comparing them against expected values based on engine operating conditions. The system calculates gain and offset parameters from sensor readings under known conditions, then uses this feedback to adjust or flag sensor accuracy. This closed-loop approach maintains measurement precision while enabling reliable exhaust treatment control.
2Object-generated harmful factors
If NOx sensor output signals are used for urea dosage management, then emissions control is improved, but sensor accuracy deteriorates causing emissions breakthrough or ammonia slip
Solution Approach 1:
The patent applies preliminary action by conducting diagnostic assessments of NOx sensor accuracy before using the sensor signals for urea dosage management. The system performs gain and offset diagnostics under controlled conditions, compares measured values against predetermined thresholds, and only activates emissions control using that sensor when accuracy requirements are met. This prevents emissions breakthrough and ammonia slip by ensuring sensor reliability before deployment.
Solution Approach 2:
The patent implements feedback by continuously validating NOx sensor readings against expected values derived from engine operating parameters and historical data. The system monitors sensor output signals, calculates accuracy metrics, and provides feedback to adjust urea dosage or flag sensor degradation. This maintains measurement precision while achieving effective emissions control.
3Measurement precision
If diagnostic methods are implemented to assess NOx sensor performance, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a diagnostic system that uses the existing NOx sensor to perform multiple functions: normal exhaust monitoring, gain diagnostics, offset diagnostics, and accuracy validation. The same sensor hardware and processing unit are utilized for both operational monitoring and diagnostic assessment, eliminating the need for separate diagnostic equipment and reducing overall system complexity while maintaining measurement precision.
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
The method effectively diagnoses NOx sensor faults, ensuring accurate exhaust treatment by correcting gain and offset issues, thereby preventing excessive emissions breakthrough and ammonia slip, and maintaining the functionality of SCR catalysts.
Implementation Method 1
NOx sensors are often formed as small electrochemical cells that function, for example, by producing voltage or electrical current signals responsive to the amount of nitrogen oxide species flowing in the exhaust and over sensor surfaces
Implementation Method 2
The gas is then passed into contact with a catalyst material selected for a reaction between reductant material and nitrogen oxides to form nitrogen and water for release from the exhaust passage. The reaction is called a 'reduction' reaction because the oxygen content of the nitrogen compounds is reduced.
Data Source
AI summary
A method of diagnosing vehicle NOx sensor faults that includes sensing that an exhaust gas recirculating (EGR) valve is closed and that fuel flow to a vehicle engine is above a predetermined rate using an electronic control unit (ECU) located on a vehicle; recording the output received from an NOx sensor relative to an amount of fuel consumption over a period of time using the ECU; calculating the mean of the NOx sensor output relative to fuel consumption recorded over the period of time using the ECU; performing a least-squares estimation (LSE) using the ECU for more than one calculated mean based on an expected NOx sensor output; generating a NOx sensor gain for the NOx sensor using the ECU based on the LSE; and determining whether the NOx sensor gain is above or below a predetermined threshold.