HC Trap Degradation Detection via Ammonia Desorption
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Solution Overview
Problem
Current on-board diagnostic (OBD) methods for hydrocarbon (HC) trap monitoring in vehicle exhaust emissions are inaccurate due to limitations in universal exhaust gas oxygen (UEGO) and heated exhaust gas oxygen (HEGO) sensors, humidity sensors, and temperature sensors, which fail to reliably detect HC emissions and adsorbent material degradation.
Innovation Solution
The proposed method uses NOx sensors to detect ammonia (NH3) emissions, which are released at higher temperatures than unconverted HC emissions, allowing for longer sensor warm-up and more accurate detection of HC trap degradation by aligning NH3 desorption temperature with the functional state of the zeolite, thereby reducing inaccuracies associated with other sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UEGO or HEGO sensors are used to detect HC emissions, then HC emissions can be detected, but the sensor warm-up time exceeds the time when stored HC emissions would be desorbed unconverted from the zeolite
Solution Approach 1:
The patent changes the detection target from HC emissions to NH3 emissions, which desorb at higher temperatures (200-400°C) compared to HC emissions (100-200°C). This parameter change in desorption temperature allows the sensor to be fully warmed up before detection begins, resolving the timing conflict between sensor warm-up and emission desorption
Solution Approach 2:
The patent uses NH3 as an intermediary substance to indirectly assess HC trap performance. Instead of directly detecting HC emissions with insufficiently warmed sensors, the system detects NH3 emissions which are also stored by the zeolite but release at higher temperatures, serving as a surrogate indicator of trap degradation
2Measurement precision
If HEGO sensors are used to detect NH3 emissions, then NH3 can be detected, but NOx emissions interfere with the detection accuracy
Solution Approach 1:
The system performs preliminary actions to create favorable detection conditions by: (1) monitoring engine operating conditions to identify when NH3 desorption is occurring, (2) ensuring the sensor is fully warmed up before detection, and (3) using the temporal pattern of NH3 release to distinguish it from NOx interference
Solution Approach 2:
The system uses feedback from multiple sensors (oxygen sensors, temperature sensors) to monitor exhaust conditions and determine when NH3 desorption is occurring. This feedback allows the system to distinguish NH3 signals from NOx interference by analyzing the temporal and contextual patterns of emissions
3Measurement precision
If HC sensors are used to detect HC emissions, then HC emissions can be detected, but the sensors require long warm-up time which precludes use immediately following engine cold start
Solution Approach 1:
The patent changes the detection temperature parameter by targeting NH3 emissions that desorb at 200-400°C, which is higher than HC emission desorption temperatures. This allows the use of sensors that can operate effectively at these higher temperatures without requiring excessively long warm-up periods, enabling detection to begin sooner after engine start
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
This approach enhances the accuracy of HC trap degradation detection by utilizing NOx sensors to infer HC trap performance through ammonia desorption characteristics, providing a more reliable method for monitoring HC trap effectiveness and extending sensor warm-up times.
Implementation Method 1
The HC trap may store ammonia (NH3) emissions in addition to HC emissions
Implementation Method 2
NH3 emissions may generally be released at a higher outlet HC trap temperature (e.g., 200-400° C.) than unconverted HC emissions
Implementation Method 3
the degradation of the HC trap may be detected based on output from one or more NOx sensors via, for example, oxidation reactions occurring in oxygen pump cells of the NOx sensors
Data Source
AI summary
Methods are provided for emissions control of a vehicle. In one example, a method for an engine may include, responsive to a plurality of diagnostic entry conditions being met, indicating degradation of a hydrocarbon trap based on an NH3 amount in an exhaust gas. In some examples, the NH3 amount may be determined based on one or more NOx sensor outputs. In some examples, the plurality of diagnostic entry conditions may include the engine having been in operation over an initial duration immediately following an engine cold start. Conditions of the exhaust gas following the engine cold start may be opportunistically utilized in determining the NH3 amount from the one or more NOx sensor outputs. In some examples, the exhaust gas may be actively provided at a predetermined air-fuel ratio to meet at least one of the plurality of diagnostic entry conditions.