NOx Sensor Offset Diagnosis Prohibition During Exhaust Brake Operation
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Solution Overview
Problem
In large vehicles equipped with exhaust brake devices, rapid changes in exhaust gas flow rates during brake operation can cause delays in NOx sensor processing, leading to erroneous offset diagnoses when traditional offset diagnosis methods are applied.
Innovation Solution
A diagnostic device with an offset diagnosis unit and a diagnosis prohibition unit that prevents offset diagnosis for a predetermined period after the exhaust brake device is switched off, ensuring accurate NOx sensor readings by stabilizing sensor values during rapid flow rate changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset diagnosis is executed during deceleration when fuel injection stops, then the sensor zero point can be calibrated, but erroneous diagnosis occurs when exhaust brake is activated causing rapid flow rate increase
Solution Approach 1:
The control unit identifies the exhaust brake operation state in advance and prohibits offset diagnosis during this period. By detecting the exhaust brake state before diagnosis execution, the system prevents erroneous readings caused by rapid flow rate changes, ensuring diagnosis is only performed under stable exhaust conditions
Solution Approach 2:
The exhaust brake state information acts as an intermediary condition that mediates between the offset diagnosis function and the actual sensor readings. By using this state information as a gating mechanism, the system ensures diagnosis only occurs when exhaust flow conditions are stable and suitable for accurate measurement
2Productivity
If exhaust brake valve is opened to increase exhaust flow rate, then braking force is reduced, but sensor processing delay causes instantaneous abnormal value increase
Solution Approach 1:
The control unit applies preliminary anti-action by prohibiting offset diagnosis when exhaust brake operation is detected. This preventive measure counteracts the potential harmful effect of rapid flow rate changes on sensor accuracy, ensuring that diagnosis is not attempted during transient conditions that would compromise measurement precision
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A diagnostic device for a sensor 100 provided in an exhaust passage 11 of an internal combustion engine 10 of a vehicle and detecting nitrogen compounds in exhaust gas, the diagnostic device including an offset diagnosis unit 42 which diagnoses, during deceleration of the vehicle in which the internal combustion engine 10 stops fuel injection, an offset amount of a sensor value of the sensor 100 from a zero point based on the sensor value of the sensor value, and a diagnosis prohibition unit 44 which prohibits the diagnosing of the offset amount when a flow rate of the exhaust gas of the internal combustion engine 10 rapidly increases while the offset amount is diagnosed by the offset diagnosis unit 42.