Three-Way Catalyst Oxygen Storage Reset for NOx Control
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Solution Overview
Problem
Existing air-fuel ratio control methods fail to maintain the oxygen storage amount of exhaust purifying catalysts at a target level, leading to increased NOx emissions due to control delays and rapid NOx outflow when the oxygen storage amount exceeds a certain level.
Innovation Solution
An air-fuel ratio control method that estimates the oxygen storage amount and resets it to predetermined first and second oxygen storage amounts when it deviates from a target amount, set closer to the first amount, to minimize the frequency of resetting when the actual oxygen storage amount reaches the second amount, thereby suppressing NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the target air-fuel ratio is switched actively to maintain oxygen storage amount, then the oxygen storage amount can be controlled, but NOx emissions increase due to control delays and rapid NOx outflow when oxygen storage amount exceeds a certain level
Solution Approach 1:
The patent changes the control parameter from active switching of air-fuel ratio to passive resetting of estimated oxygen storage amount. By resetting the estimated oxygen storage amount to predetermined values (first oxygen storage amount when downstream air-fuel ratio indicates lean condition, second oxygen storage amount when rich condition) rather than actively switching air-fuel ratio, the system avoids control delays and prevents rapid NOx outflow while maintaining exhaust purification performance.
Solution Approach 2:
The patent uses feedback from the downstream-side air-fuel ratio sensor to reset the estimated oxygen storage amount. When the downstream air-fuel ratio indicates the catalyst is in a lean or rich state, the estimated oxygen storage amount is reset to predetermined values, creating a feedback mechanism that maintains proper oxygen storage levels without causing active switching delays that lead to NOx emissions.
2Reliability
If the oxygen storage amount is actively increased or decreased, then the oxygen storage amount can be controlled, but CO and HC flow out of the catalyst when air-fuel ratio reaches determination levels
Solution Approach 1:
The system uses feedback from the downstream air-fuel ratio sensor to detect when the oxygen storage amount is outside the appropriate range. When the downstream air-fuel ratio indicates lean or rich conditions, the estimated oxygen storage amount is reset to predetermined values, ensuring CO and HC are properly oxidized without causing emissions.
Solution Approach 2:
The patent replaces the mechanical switching mechanism (actively switching air-fuel ratio) with a computational resetting mechanism (resetting estimated oxygen storage amount to predetermined values). This substitution eliminates the delays and overshoot problems associated with active switching, maintaining proper oxygen storage levels without causing CO and HC outflow.
3Reliability
If the target air-fuel ratio is switched to lean air-fuel ratio when downstream sensor reaches rich determination, then oxidation of CO and HC is improved, but NOx emissions increase due to control delays
Solution Approach 1:
The patent changes the control approach from switching air-fuel ratio to resetting estimated oxygen storage amount. By resetting the estimated oxygen storage amount to the first oxygen storage amount when downstream air-fuel ratio indicates lean condition, the system achieves proper oxidation without the control delays that cause NOx emissions when actively switching air-fuel ratio.
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
The method effectively maintains the oxygen storage amount near the target, reducing NOx emissions by minimizing the frequency of large deviations and associated delays, thus optimizing exhaust purification performance.
Implementation Method 1
it is important for the catalyst to be able to absorb, store and release oxygen, the so-called oxygen storage amount
Implementation Method 2
a three-way catalyst as an exhaust purifying catalyst is capable of oxidizing CO and HC and reducing NOx in the exhaust gas
Implementation Method 3
capable of oxidizing CO and HC
Implementation Method 4
capable of oxidizing CO and HC and reducing NOx in the exhaust gas
Implementation Method 5
reducing NOx
Data Source
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AI summary
The oxygen storage amount of a three-way catalyst (15) is estimated based on an upstream-side exhaust air-fuel ratio (FrA/F), and a target air-fuel ratio is controlled such that the estimated oxygen storage amount matches a predetermined target oxygen storage amount (S6). When a downstream-side exhaust air-fuel ratio (RrA/F) detected by a downstream-side air-fuel ratio sensor (20) is equal to or less than a threshold value (RAF1) corresponding to a first oxygen storage amount (OSA1), the estimated oxygen storage amount is reset to the value of first oxygen storage amount (OSA1) (S2, S3). When downstream-side exhaust air-fuel ratio (RrA/F) is equal to or greater than a threshold value (RAF2) corresponding to a second oxygen storage amount (OSA2), the estimated oxygen storage amount is reset to the value of second oxygen storage amount (OSA2) (S4, S5). The target oxygen storage amount is set to be closer to first oxygen storage amount (OSA1) than the median of first oxygen storage amount (OSA1) and second oxygen storage amount (OSA2).