Urea SCR Control via Multi-Map NOx Adaptation
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Solution Overview
Problem
Current urea spray SCR control systems face deviations in NOx amount detection due to environmental differences during pre-heating control, leading to inadequate urea spray control, ammonia slip, reduced NOx purification rates, and false malfunction diagnoses.
Innovation Solution
A urea spray SCR control system that uses multiple NOx model maps based on atmospheric pressure, outdoor air temperature, and engine water temperature to determine and adjust urea injection amounts, even during pre-heating, by employing a control unit with base maps, outdoor air temperature-dependent maps, and correction maps to interpolate and correct NOx values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single NOx model map is used for urea spray control, then the control system is simple, but the NOx detection accuracy deviates under different environmental conditions
Solution Approach 1:
The patent divides the single NOx model map into multiple environment-specific model maps (first, second, and third NOx model maps corresponding to different atmospheric pressure conditions). Each model map is tailored for specific environmental conditions, improving measurement precision by selecting the appropriate map based on current atmospheric pressure, thereby resolving the contradiction between accuracy and complexity.
Solution Approach 2:
The patent changes the parameter of atmospheric pressure detection to select among multiple NOx model maps. By detecting atmospheric pressure and selecting the corresponding model map, the system adapts to different environmental conditions, improving NOx detection accuracy without requiring a completely complex system redesign.
2Reliability
If pre-heating control is performed to protect the NOx sensor, then the sensor is protected from damage, but the NOx sensing is delayed
Solution Approach 1:
The patent performs preliminary pre-heating control to raise the NOx sensor temperature to a safe operating range before actual NOx sensing begins. This preliminary action protects the sensor from thermal shock and damage while establishing reliable sensing conditions, thereby resolving the contradiction between sensor protection and sensing delay.
3Reliability
If urea spray amount is increased to ensure NOx purification, then NOx purification rate improves, but ammonia slip increases
Solution Approach 1:
The patent uses feedback from atmospheric pressure detection and selected NOx model maps to dynamically adjust the urea spray amount. By continuously monitoring atmospheric pressure and selecting the appropriate model map, the system determines the optimal urea injection quantity, ensuring sufficient NOx purification while preventing excessive ammonia slip through closed-loop control.
Data Source
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AI summary
A urea spray SCR control system is provided to control the amount of urea spray appropriate for an engine-out NOx discharge amount in a period in which pre-heating control is performed. The urea spray SCR control system includes an SCR catalyst 23 provided in a discharge pipe 14 of an engine 10, a dosing valve 41 for injecting urea water at an upstream side of the SCR catalyst 23, and NOx sensors 46, 47 for measuring the amount of NOx in exhaust gas, wherein the urea spray SCR control system controls injection of the urea water from the dosing valve 41. The urea spray SCR control system includes a plurality of NOx model maps 60 corresponding to an atmospheric pressure condition, an outdoor air temperature, and an engine water temperature, and determines the amount of NOx from each NOx model map 60 on the basis of detection values of atmospheric pressure detection means, outdoor air temperature detection means, and engine water temperature detection means, and controls the amount of injection of the urea water from the dosing valve 41 on the basis of the amount of NOx thus determined.