Exhaust Catalyst Oxygen Storage Control for Oxidation Prevention
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Solution Overview
Problem
Existing exhaust purification systems for internal combustion engines face challenges in preventing catalyst deterioration due to high temperatures and oxygen exposure, particularly when the catalyst is subjected to exhaust gas with a rich air-fuel ratio, leading to oxidation of precious metals.
Innovation Solution
The system incorporates an air-fuel ratio control device that adjusts the oxygen storage in the catalyst by making the air-fuel ratio leaner or richer based on temperature thresholds, using a fuel addition valve or air supply device to maintain an oxidizing or reducing atmosphere, thereby preventing catalyst deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the catalyst is supplied with oxygen at high temperature, then the oxidation of precious metal occurs, but the catalyst deteriorates
Solution Approach 1:
The system performs preliminary action by controlling the air-fuel ratio before the catalyst temperature reaches high levels. When the catalyst temperature is below the threshold, the air-fuel ratio is controlled to be leaner than stoichiometric to store oxygen in advance. This preliminary oxygen storage prevents oxidation when the temperature later rises, resolving the contradiction between high-temperature operation and catalyst durability.
Solution Approach 2:
The system uses feedback control by continuously monitoring the catalyst temperature and adjusting the air-fuel ratio accordingly. When the temperature reaches or exceeds the threshold, the control unit switches to richer air-fuel ratio to prevent further oxidation. This closed-loop feedback mechanism maintains catalyst durability while allowing high-temperature operation.
2Reliability
If the air-fuel ratio is made leaner to store oxygen in the catalyst, then oxidation is prevented, but the timing of fuel cut control must be delayed
Solution Approach 1:
The system changes the parameter of air-fuel ratio to optimize both catalyst protection and control timing. By using a threshold-based approach where the air-fuel ratio switches between leaner and richer states based on temperature, the system achieves catalyst protection without requiring excessive delay in fuel cut control. The parameter change is precise and timely, resolving the time loss issue.
3Temperature
If the catalyst is exposed to rich air-fuel ratio exhaust gas, then the temperature rises, but oxidation of precious metal occurs
Solution Approach 1:
The system applies preliminary anti-action by storing oxygen in the catalyst when the temperature is low (leaner air-fuel ratio). This pre-stored oxygen creates a protective oxidizing environment that prevents precious metal oxidation when the temperature later rises due to rich exhaust gas exposure. The anti-action is prepared in advance to counteract the harmful oxidation effect.
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 effectively maintains the catalyst in a stable condition by controlling oxygen storage, preventing oxidation and ensuring efficient removal of pollutants like HC, CO, and NOX, even at high temperatures.
Implementation Method 1
a catalyst arranged in an exhaust passage and able to store oxygen
Implementation Method 2
oxidation of the precious metal is liable to cause the catalyst to deteriorate
Implementation Method 3
the precious metal has a property of vapor pressure at a predetermined temperature becoming lower when oxidized
Data Source
AI summary
The exhaust purification system of an internal combustion engine comprises a catalyst 20 arranged in an exhaust passage and able to store oxygen, and an air-fuel ratio control device configured to control an air-fuel ratio of inflowing exhaust gas flowing into the catalyst. The catalyst has a precious metal and the precious metal has a property of a vapor pressure at a predetermined temperature becoming lower when oxidized. If a temperature of the catalyst is equal to or greater than a threshold temperature or if predicting a rise in temperature of the catalyst, the air-fuel ratio control device is configured to make the air-fuel ratio of the inflowing exhaust gas leaner than a stoichiometric air-fuel ratio so that an oxygen storage amount of the catalyst becomes equal to or greater than an upper side reference amount.