Three-Way Catalyst Degradation Estimation Without NOx Spikes
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Solution Overview
Problem
Existing methods for estimating the degradation of a three-way catalyst increase NOx emissions when transitioning the catalyst from an oxygen-depleted to an oxygen-saturated state.
Innovation Solution
A degradation degree estimation system using an airflow meter, air-fuel ratio sensors, and an NOx sensor to estimate catalyst degradation based on detected air-fuel ratios, intake air amounts, and ammonia levels, without requiring the catalyst to be oxygen-saturated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the three-way catalyst is transitioned from an oxygen-depleted state to an oxygen-saturated state to calculate maximum oxygen storage amount, then the degradation estimation accuracy is improved, but the NOx emission is increased
Solution Approach 1:
The patent extracts the essential information needed for degradation estimation (ammonia amount and air-fuel ratio relationship) without requiring the complete oxygen saturation process. By taking out only the necessary measurement elements during a partial rich-state period, the system achieves degradation estimation without forcing the catalyst into full oxygen-saturated state, thereby reducing NOx emissions while maintaining estimation accuracy.
Solution Approach 2:
Instead of completing the full transition to oxygen-saturated state (excessive action), the patent applies partial action by measuring ammonia amount only during the rich air-fuel ratio period before oxygen saturation is achieved. This partial measurement approach provides sufficient data for degradation estimation while avoiding the harmful effects of prolonged oxygen saturation and subsequent NOx emission increases.
2Object-generated harmful factors
If the catalyst is kept in oxygen-depleted state to suppress NOx emission, then the harmful emission is reduced, but the degradation estimation cannot be performed
Solution Approach 1:
The patent performs preliminary action by measuring the ammonia amount during the rich air-fuel ratio period before the catalyst becomes oxygen-saturated. This preliminary measurement captures the necessary data for degradation estimation while the catalyst is still in a controlled state, enabling degradation assessment without requiring the catalyst to remain in oxygen-depleted state for extended periods, thus balancing emission control with measurement capability.
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
Accurately estimates catalyst degradation while minimizing NOx emissions by controlling air-fuel ratios and ammonia levels, improving estimation accuracy through multiple data points and temperature considerations.
Implementation Method 1
a three-way catalyst disposed in an exhaust passage of the engine and able to store oxygen
Implementation Method 2
an air-fuel ratio sensor disposed in the exhaust passage upstream of the three-way catalyst
Implementation Method 3
an NOx sensor disposed in the exhaust passage downstream of the three-way catalyst and able to detect an amount of ammonia in an exhaust gas
Data Source
AI summary
A degradation degree estimation system includes: an airflow meter; a three-way catalyst; an air-fuel ratio sensor; an NOx sensor; and an estimation device that estimates a degree of degradation of the three-way catalyst. The estimation device includes: an acquisition unit that acquires a detected rich air-fuel ratio that is a detected air-fuel ratio detected by the air-fuel ratio sensor when the detected air-fuel ratio indicates a rich air-fuel ratio, a detected intake air amount detected by the airflow meter, and a detected ammonia amount detected by the NOx sensor; and an estimation unit that estimates the degree of degradation based on the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount, the estimation unit estimating a higher degree of degradation as the detected ammonia amount is smaller with respect to the detected rich air-fuel ratio and the detected intake air amount.