In Situ NOx-Sensor Diagnosis Using Exhaust Gas Recirculation
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Solution Overview
Problem
Current NOx-sensors in heavy diesel trucks have a shorter lifespan than the trucks themselves, requiring frequent replacement and costly testing procedures, often resulting in unnecessary replacements due to misdiagnosis of sensor malfunctions.
Innovation Solution
A method and system for in situ NOx-sensor diagnosis that allows for accurate and reliable testing without dismounting the sensors, using operational conditions in a workshop with a stationary vehicle, involving an exhaust gas recirculation system, back pressure valve, and electronic control unit to analyze sensor responses across varying NOx production levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NOx-sensors are removed from the exhaust system for testing, then accurate sensor diagnosis can be performed, but the risk of rendering the sensor defective increases and costly sealing arrangements must be renewed
Solution Approach 1:
The system enables self-diagnosis of the NOx-sensor through the vehicle's own exhaust system. The electronic control unit utilizes the existing exhaust gas recirculation system and back pressure valve to create test conditions, allowing the sensor to be diagnosed in situ without removal. This eliminates the need for external testing facilities and prevents damage from improper handling during removal and reinstallation.
2Reliability
If NOx-sensors are replaced regularly to ensure proper functioning, then emission compliance is maintained, but unnecessary replacement costs increase
Solution Approach 1:
The system performs preliminary diagnosis of the NOx-sensor before replacement is considered. By continuously monitoring sensor signals and comparing them against expected values during engine operation, the system can identify actual sensor malfunctions. This allows replacement only when truly necessary, preventing unnecessary expenditures on still-functional sensors while maintaining emission compliance.
3Measurement precision
If the vehicle operates under heavy load to achieve sufficient NOx production levels for testing, then accurate sensor diagnosis becomes possible, but the vehicle cannot remain stationary in a workshop
Solution Approach 1:
The system changes operational parameters by manipulating the exhaust gas recirculation rate and back pressure to achieve sufficient NOx production levels for accurate sensor diagnosis. The electronic control unit adjusts these parameters during normal engine operation, enabling diagnosis without requiring heavy load conditions or mobile testing. This allows accurate sensor assessment while the vehicle remains stationary in the workshop.
4Measurement precision
If additional test gases are used for sensor testing, then comprehensive sensor functionality can be verified, but the testing process becomes more complex and requires additional materials
Solution Approach 1:
The system uses the vehicle's own exhaust gas as an intermediary for sensor testing. Instead of introducing external test gases, the electronic control unit utilizes the naturally present exhaust gases containing NOx, which are already flowing through the system during normal operation. This eliminates the need for complex test gas delivery systems while still providing sufficient stimulus for comprehensive sensor functionality verification.
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 accurate and reliable NOx-sensor diagnosis without the need for additional test gases, reducing unnecessary replacements and costs by allowing for precise assessment of sensor functionality within the vehicle's exhaust system.
Implementation Method 1
an exhaust gas recirculation system arranged to selectively connect the exhaust with the inlet
Implementation Method 2
providing a back pressure valve in the exhaust
Implementation Method 3
at least one NO x -sensor, wherein the at least one NO x -sensor is located downstream of the back pressure valve in the exhaust
Data Source
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AI summary
Method and apparatus for field testing and diagnosing at least one NOx-sensor in a diesel engine exhaust system. The field testing apparatus being connectable to a truck having a lean burn diesel type engine, via an onboard diagnostic connector. The field testing apparatus is arranged to initiate a test cycle, and to diagnose at least one NOx-sensor in an exhaust system of the truck. The test cycle is performed on a running engine as a test sequence in a stationary truck, in at least two different states of operation, while NOx related values issued by the at least one NOx-sensor are measured over a predefined period of time. At least one state of operation is obtained by simultaneously opening the exhaust gas recirculation valve and controlling the back pressure valve for increasing backpressure. A dedicated algorithm is used to compare the measured values to a predefined model, and to provide a numerical summary and statistical evaluation of the sensor functioning. The numerical summary being indicative of a likelihood of the at least one NOx-sensor behaving correctly, and thereby enables a well founded decision as to whether or not the at least one NOx-sensor requires replacement.