Abnormality Diagnosis for Reducing Agent Supply in NOx SCR Systems
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Solution Overview
Problem
Existing methods for diagnosing clogging in the addition valve of an NOx selective catalytic reduction system in internal combustion engines face challenges in accurately determining the supply of the reducing agent, leading to potential NOx reduction rate drops due to insufficient diagnosis opportunities.
Innovation Solution
An abnormality diagnosis device that calculates command and estimated values of reducing agent supply based on NOx flow and pressure, using a controller to extend supply intervals and adjust thresholds for enhanced accuracy and frequency of diagnosis, prioritizing NOx reduction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the determination of whether clogging has occurred in the addition valve is made by using the value of pressure in the reducing agent passage at the time of returning the reducing agent to the tank, then the reducing agent supply status can be monitored, but the reducing agent cannot be supplied from the addition valve and the NOx reduction rate may drop due to shortage of the reducing agent
Solution Approach 1:
The system performs abnormality diagnosis by comparing command values and estimated values before the reducing agent supply becomes critically insufficient. By continuously monitoring and diagnosing in advance, the system can detect clogging or supply issues before they cause NOx reduction rate drops, allowing for preventive maintenance or correction.
2Reliability
If the determination of whether clogging has occurred in the addition valve is made based on the amount of pressure drop at the time of the supply of the reducing agent, then the supply status can be assessed, but the amount of pressure drop is small when the amount of supply is small and the accuracy of the determination decreases
Solution Approach 1:
The system changes the diagnostic approach by integrating command values and estimated values over multiple supply cycles. Instead of relying on single-point pressure drop measurements that may be inaccurate when supply amounts are small, the system accumulates data over time to achieve statistically significant diagnostic accuracy.
Solution Approach 2:
The system continuously compares command values (desired supply) with estimated values (actual supply) and uses this feedback to determine abnormality. When the integrated difference exceeds a threshold, the system diagnoses clogging or supply issues, creating a closed-loop diagnostic system that adapts to varying operating conditions.
3Productivity
If abnormality diagnosis of the reducing agent supply device is not carried out frequently, then the system operation is simple, but the opportunity to carry out abnormality diagnosis is reduced
Solution Approach 1:
The system continuously performs abnormality diagnosis by continuously comparing command values and estimated values during normal operation. Rather than performing discrete periodic checks that limit diagnosis opportunities, the system maintains continuous monitoring, ensuring that abnormalities are detected as soon as they occur while adding minimal complexity to the overall system.
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 solution increases the opportunity for diagnosing reducing agent supply abnormalities, ensuring accurate NOx reduction rates by integrating command and estimated values and adjusting supply intervals based on engine conditions, thereby maintaining efficient exhaust gas purification.
Implementation Method 1
a pressure sensor configured to detect a pressure of the reducing agent
Implementation Method 2
a pump configured to deliver an amount of reducing agent to the addition valve according to a rotational speed
Implementation Method 3
an NOx selective catalytic reduction catalyst that is arranged in an exhaust passage of the internal combustion engine and configured to reduce NOx by using a reducing agent
Data Source
AI summary
When an integrated value of a determination value correlated with a command value for an amount of supply of a reducing agent at the time of the command value being larger than a command supply amount threshold value reaches an integration threshold value, a determination is made that a diagnosis condition is satisfied, and an abnormality in the supply of the reducing agent is diagnosed based on an integrated value of the command value for the amount of supply of the reducing agent and an integrated value of an estimated value of the amount of supply of the reducing agent, whereas in cases where a period of time in which the diagnosis condition is not satisfied is longer than a time period threshold value, an interval of supply of the reducing agent is extended.