Diesel Engine EGR Control Using NOx Feedback Correction
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Solution Overview
Problem
The MAF sensor may not accurately measure the intake air amount due to individual variations and temporal changes, leading to incomplete NOx reduction in diesel engine exhaust gases when EGR is controlled based on uncorrected measurements.
Innovation Solution
A diesel engine system that includes an exhaust gas recirculation device, an intake air amount sensor, a NOx measurement sensor, and a control device to obtain a correction value based on the difference between NOx information and engine parameters, adjusting the intake air amount measurement to improve EGR control accuracy and reduce NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MAF sensor is used to measure intake air amount for EGR control, then the EGR system can be implemented to reduce NOx emissions, but the measurement accuracy deteriorates due to individual variation and temporal changes in the sensor
Solution Approach 1:
The patent implements a feedback mechanism where the measured NOx concentration is compared with a target NOx concentration, and the difference (deviation) is used to generate a correction value that adjusts the MAF sensor output. This closed-loop feedback system continuously corrects the intake air amount measurement based on actual NOx emissions, thereby maintaining both EGR control reliability and measurement precision over time.
Solution Approach 2:
The patent replaces reliance on the mechanical MAF sensor alone with a hybrid measurement system that combines MAF sensor data with NOx sensor data and engine operating parameters. By substituting pure mechanical measurement with a computational approach using multiple sensors and correction algorithms, the system compensates for MAF sensor drift and maintains accurate intake air amount measurement.
2Measurement precision
If the MAF sensor measurement is corrected based on logical air amount estimation, then the measurement accuracy is improved, but the NOx reduction effectiveness deteriorates because EGR is not taken into account in the correction
Solution Approach 1:
The patent uses NOx concentration as feedback to guide the correction process. The correction value is generated based on the deviation between measured and target NOx concentrations, ensuring that the intake air amount correction directly serves the goal of NOx reduction. This feedback mechanism aligns measurement precision improvement with emission control effectiveness.
Solution Approach 2:
The patent changes the correction parameters from purely logical air amount estimation to a composite correction that includes NOx concentration, engine rotation speed, and load information. By incorporating NOx-related parameters into the correction calculation, the system ensures that measurement precision improvement does not compromise NOx reduction effectiveness.
3Measurement precision
If the EGR valve is fully closed to meet learning execution conditions, then the MAF sensor correction can be performed, but the NOx reduction capability is lost in limited situations
Solution Approach 1:
The patent performs MAF sensor correction as a preliminary action that can be done when EGR valve is closed, but then applies the learned correction continuously even when EGR is active. This allows the system to maintain measurement precision through preliminary calibration while preserving NOx reduction capability during normal EGR operation.
Solution Approach 2:
The patent creates a universal correction mechanism that works in both EGR-off and EGR-on conditions. The correction value learned during EGR valve closed conditions is applied universally across all operating conditions, making the MAF sensor accurate whether EGR is active or not, thereby maintaining both correction capability and NOx reduction reliability.
Data Source
AI summary
A diesel engine, includes: an exhaust gas recirculation device that recirculates an exhaust gas emitted from the diesel engine to an intake side of the diesel engine; an intake air amount sensor that measures an intake air amount of the diesel engine; a NOx measurement sensor that measures NOx contained in the exhaust gas emitted from the diesel engine; and a control device that obtains a correction value for correcting a measured value by the intake air amount sensor based on a difference between first information on NOx obtained based on information on a rotation speed of the diesel engine and information on a load and second information on NOx measured by the NOx measurement sensor to control the exhaust gas recirculation device based on the measured value by the intake air amount sensor corrected using the correction value.