SCR Catalyst Diagnostics via Exhaust Sensor Timing
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Solution Overview
Problem
NOx sensors in gasoline engines are not sensitive enough to detect lower levels of NOx emissions, and are expensive, limiting their usage in monitoring and reducing exhaust emissions effectively.
Innovation Solution
A method using upstream, intermediate, and downstream exhaust sensors to diagnose SCR catalyst degradation by monitoring the timing of ammonia release, with oxygen sensors like HEGO indicating catalyst degradation based on the switch from lean to rich and comparing the difference in time between intermediate and downstream sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NOx sensors are used to monitor SCR catalyst performance, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive NOx sensors with inexpensive HEGO oxygen sensors that can be obtained from common automotive parts stores. The diagnostic method uses the timing information from these cheap sensors to infer SCR catalyst performance, eliminating the need for costly specialized NOx sensors while maintaining diagnostic capability.
Solution Approach 2:
The patent uses HEGO oxygen sensors as intermediaries to indirectly monitor SCR catalyst performance. Instead of directly measuring NOx with specialized sensors, the system uses the oxygen sensor readings (which respond to reductant breakthrough) as a proxy indicator, mediated through the oxygen sensor's response characteristics to infer catalyst health.
2Measurement precision
If NOx sensors are installed downstream of SCR catalyst to detect NOx slip, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent replaces expensive NOx sensors with inexpensive HEGO oxygen sensors that can be obtained from common automotive parts stores. The diagnostic method uses the timing information from these cheap sensors to infer SCR catalyst performance, eliminating the need for costly specialized NOx sensors while maintaining diagnostic capability.
Solution Approach 2:
The patent creates a functional copy of the NOx detection capability using HEGO sensors. By monitoring the timing of HEGO sensor responses to reductant breakthrough, the system replicates the diagnostic function of NOx sensors at a fraction of the cost, achieving similar measurement objectives through a different sensing mechanism.
3Device complexity
If HEGO sensors are used to diagnose SCR catalyst degradation, then device complexity is reduced, but measurement precision may be compromised
Solution Approach 1:
The patent uses feedback from HEGO sensor readings to diagnose SCR catalyst performance. By monitoring the timing of sensor responses to reductant breakthrough and comparing them against expected values, the system continuously feedbacks on catalyst health status. This feedback mechanism allows the simple HEGO sensors to provide precise diagnostic information about catalyst degradation.
Solution Approach 2:
The patent performs preliminary actions by storing oxygen in the TWC during rich operation before the diagnostic event. This preliminary oxygen storage creates a known state that enables subsequent precise measurement of reductant breakthrough timing, which is critical for accurate catalyst degradation detection using HEGO sensors.
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 allows for accurate detection of SCR catalyst degradation and estimation of ammonia storage capacity, enhancing the sensitivity and cost-effectiveness of NOx emission monitoring.
Implementation Method 1
The engine may be operated to store oxygen in the three-way catalyst
Implementation Method 2
during a thermal event ammonia is released from the SCR catalyst
Implementation Method 3
an exhaust oxygen sensor such as a HEGO may be used to diagnose an SCR catalyst
Data Source
AI summary
In one embodiment, a method for an engine comprises operating the engine with an upstream exhaust sensor, intermediate exhaust sensor, and downstream exhaust sensor each indicating rich, adjusting engine operation to operate the engine with an upstream exhaust sensor, intermediate exhaust sensor, and downstream exhaust sensor each indicating lean, adjusting engine operation to operate the engine with the upstream exhaust sensor indicating rich and the intermediate and downstream exhaust sensors each indicating lean, and indicating degradation of an SCR catalyst based on when the intermediate and downstream exhaust sensors switch from lean to rich.