Urea Level Sensor Stuck Float Detection via Injection Integration
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Solution Overview
Problem
Conventional methods for diagnosing a stuck float in urea level sensors, used in SCR systems, are ineffective when the sensor detects liquid levels in a stepwise manner, as they rely on consistent urea injection calculations based on running distance, which is not applicable to urea injection variations depending on NOx emissions.
Innovation Solution
An SCR system that includes a urea injection quantity integrating unit, an integrated value resetting unit, and an abnormality determination unit, which calculates a urea injection quantity integrated value and resets it when the detected value changes, determining the sensor as abnormal if the value exceeds a predetermined threshold, specifically set to account for stepwise liquid level detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a float-type urea level sensor is used to detect liquid level, then the remaining quantity of urea can be detected, but the float may become immobilized or intentionally fixed making detection inaccurate
Solution Approach 1:
The system continuously monitors the relationship between urea consumption (calculated from injection quantity) and liquid level changes (detected by float position). When the float becomes stuck, the feedback mechanism detects the discrepancy between expected and actual level changes, triggering an abnormality signal. This feedback loop enables automatic detection of float immobilization without additional hardware.
Solution Approach 2:
The invention introduces an intermediary diagnostic mechanism that indirectly detects float status by monitoring the correlation between urea consumption and level sensor output. Rather than directly monitoring float movement, the system uses urea consumption data as an intermediary to infer whether the float is functioning properly, enabling detection without mechanical intervention.
2Reliability
If conventional float stuck diagnosis methods are applied, then fuel level sensor abnormalities can be detected, but these methods are ineffective for urea level sensors with stepwise detection
Solution Approach 1:
The invention changes the diagnostic parameter from direct level value analysis to the rate of level change relative to urea consumption. By monitoring how the level sensor output changes in response to known urea injection quantities, the system can detect float stuck conditions regardless of whether the sensor provides continuous or stepwise detection. This parameter transformation makes the diagnostic method universally applicable.
3Productivity
If urea injection quantity is calculated from running distance, then diagnosis can be performed, but this method is ineffective because injection quantity varies with NOx emissions
Solution Approach 1:
The invention replaces the mechanical calculation method (based on running distance and fuel consumption correlations) with an electronic control-based calculation. The urea injection quantity is now calculated using the same methodology as fuel injection, utilizing engine control parameters and NOx sensor data to determine actual injection amounts. This substitution ensures accurate tracking of urea consumption regardless of varying emission conditions.
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
Enables the detection of a stuck float in urea level sensors even when they detect liquid levels in a stepwise manner, preventing false negatives and ensuring accurate urea level monitoring for NOx reduction in exhaust gases.
Implementation Method 1
a float following a liquid surface of the urea in the urea tank
Data Source
Figure 1(a)
Figure 1(b)
Figure 2
AI summary
An SCR system that can detect whether or not a float is stuck even where a water level sensor that detects a liquid level in a stepwise manner is used is provided. The SCR system includes: a urea injection quantity integrating unit 2 that integrates an injected quantity of urea to calculate a urea injection quantity integrated value; an integrated value resetting unit 3 that if a detected value from detection means 202 changes, resets the urea injection quantity integrated value; and an abnormality determination unit 4 that if the urea injection quantity integrated value exceeds a predetermined threshold value for determination, determines a level sensor 120 as having an abnormality.