EGR Valve Control for NOx Emission Precision
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Solution Overview
Problem
Existing EGR systems face limitations in controlling NOx emissions across the full range of engine operating conditions, as current methods either rely solely on EGR flow rate or NOx sensor measurements, which may not provide sufficient control during varying engine operations.
Innovation Solution
A method and system that determine EGR commands based on actual and desired EGR mass flow rates, using NOx sensor values during steady state conditions but not during transient conditions, to adjust the EGR valve effectively, incorporating modules for actual and desired NOx values and an adjustment factor to manage NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If EGR system is controlled based only on EGR flow rate calculation, then device complexity is reduced, but NOx emission control precision deteriorates
Solution Approach 1:
The patent implements feedback control by using NOx sensor measurements to continuously monitor actual NOx emissions and adjust the EGR valve position accordingly. The control system compares measured NOx levels with target values and modifies EGR flow rate to maintain emissions within acceptable ranges, thereby improving NOx control precision without excessive complexity increase
Solution Approach 2:
The patent introduces an intermediary control strategy that uses EGR flow rate as an intermediate variable between engine operating conditions and NOx emissions. By controlling EGR flow rate based on both calculated values and sensor feedback, the system achieves precise NOx control while managing system complexity through a structured control architecture
2Manufacturing precision
If EGR system is controlled based only on NOx sensor measurements, then NOx emission control precision is improved, but device complexity and response time during transient conditions worsen
Solution Approach 1:
The patent applies preliminary action by calculating desired EGR flow rate in advance based on engine operating parameters (speed, load, temperature) before actual NOx measurements are available. This predictive approach allows the control system to proactively adjust EGR valve position to prevent excessive NOx formation, improving response time during transient conditions
Solution Approach 2:
The patent implements dynamic control by adapting the EGR control strategy based on engine operating conditions. During steady-state conditions, the system relies more on NOx sensor feedback, while during transient conditions, it transitions to calculated EGR flow rate control, thereby optimizing the balance between control precision and response speed across different operating regimes
3Measurement precision
If NOx sensor is used for EGR control during all engine conditions, then measurement precision is improved, but reliability during transient conditions deteriorates
Solution Approach 1:
The patent implements dynamic switching of control strategies based on engine operating conditions. During transient conditions (rapid changes in engine speed or load), the system switches from NOx sensor-based control to calculated EGR flow rate control, ensuring reliable operation when sensor responses may be insufficient. During steady-state conditions, it transitions to NOx sensor-based control for enhanced precision
Data Source
AI summary
According to one aspect of the present disclosure, a method of controlling an exhaust gas recirculation (EGR) system of an engine system includes determining a first EGR command according to a first method during a steady state engine condition, determining a second EGR command according to a second method during a transient engine condition, wherein the first method is based at least in part on values from a NOx sensor, and the second method is not based on values from a NOx sensor. The method further includes adjusting an EGR valve of the EGR system based on the first EGR command during the steady state engine condition, and adjusting the EGR valve based on the second EGR command during the transient engine condition.