NOx Sensor Compensation for Accurate SCR Malfunction Detection
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Solution Overview
Problem
Existing NOx sensors in SCR systems are prone to offset and gain errors, leading to Type II errors (false negatives) in diagnosing SCR malfunctions, which can result in non-compliance with emissions regulations due to undetected malfunctions in Best Performance Unacceptable (BPU) SCRs.
Innovation Solution
A system and method for compensating NOx sensor readings by applying compensation values to offset and gain errors, using Exponentially Weighted Moving Average (EWMA) filters to transform raw data into usable information, thereby reducing the 'NOx gap' and improving SCR diagnostic capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NOx sensor readings are used directly without compensation, then the system operation is simple, but Type II errors (false negatives) occur in diagnosing SCR malfunctions
Solution Approach 1:
The system performs preliminary compensation of NOx sensor readings by applying offset and gain correction values before using the readings for SCR malfunction diagnosis. This preliminary action ensures that the sensor data is already corrected for known errors, preventing Type II errors (false negatives) in detecting Best Performance Unacceptable (BPU) SCR conditions.
Solution Approach 2:
The system implements a feedback mechanism where compensation values are determined based on the relationship between engine-out NOx readings and system-out NOx readings. The controller continuously monitors these readings and adjusts compensation values to maintain accurate SCR efficiency calculation, creating a closed-loop system that adapts to changing operating conditions.
2Measurement precision
If compensation values are applied to NOx sensor readings, then Type II errors are reduced, but the processing complexity increases
Solution Approach 1:
The system changes the parameters of the NOx sensor readings by applying offset and gain compensation values. These parameter transformations convert raw sensor data into compensated values that more accurately reflect actual NOx concentrations, thereby improving measurement precision without requiring complex hardware modifications.
Solution Approach 2:
The controller acts as an intermediary that processes raw NOx sensor readings and applies compensation values before the data is used for SCR diagnosis. This intermediary processing layer separates the raw sensing function from the diagnostic function, allowing compensation to be applied systematically without increasing overall system complexity.
3Difficulty of detecting and measuring
If offset and gain compensation is implemented, then SCR diagnostic capability is improved, but system complexity increases
Solution Approach 1:
The system segments the SCR diagnostic function into distinct components: raw NOx sensing, offset compensation, gain compensation, and SCR efficiency calculation. By dividing the diagnostic process into these manageable segments, the system can apply compensation values systematically at each stage without creating an overly complex monolithic system.
Solution Approach 2:
The compensation mechanism is designed to be universal, handling both offset and gain errors through a unified approach. The same compensation framework applies to different operating conditions and sensor types, making the system adaptable without requiring separate complex subsystems for each scenario.
Data Source
AI summary
Systems and methods for diagnosing an exhaust aftertreatment system and mitigating the effects of a potential fault in the exhaust aftertreatment system are provided. A system includes: a sensor structured to provide exhaust gas constituent information, and one or more processing circuits configured to: receive information indicative of an amount of at least one of a gain or an offset affecting the sensor; determine a compensation gain value and a compensation offset value; receive the exhaust gas constituent information; apply the compensation gain value to the exhaust gas constituent information to create compensated information when the compensation gain value is less than a first threshold, the compensation offset value is less than a second threshold and the compensation gain value is less than the compensation offset value; and initiate an action based on the compensated information.