Engine Control System for NOx Reduction via Oxygen Storage Management
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Solution Overview
Problem
An exhaust purification catalyst with oxygen storage ability faces challenges in maintaining optimal oxygen storage, leading to increased NOX emission when the oxygen storage amount approaches its maximum, causing a delay in air-fuel ratio adjustment and resulting in NOX outflow.
Innovation Solution
A control system with upstream and downstream air-fuel ratio sensors and an oxygen storage amount acquiring means that continuously adjusts the air-fuel ratio to lean or rich settings based on oxygen storage levels, preventing NOX outflow by maintaining optimal oxygen storage within predetermined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the oxygen storage amount in the exhaust purification catalyst is increased to improve NOX removal capability, then the catalyst can store more oxygen for oxidation reactions, but when the oxygen storage amount approaches maximum, the catalyst becomes unable to accept more oxygen, causing NOX to pass through without reduction
Solution Approach 1:
The control system continuously monitors the oxygen storage amount of the exhaust purification catalyst and adjusts the air-fuel ratio based on this feedback. When the oxygen storage amount approaches the maximum, the system switches to rich air-fuel ratio to prevent NOX from passing through without reduction, thereby resolving the contradiction between maintaining high NOX removal capability and adapting to varying oxygen storage conditions
Solution Approach 2:
The air-fuel ratio is dynamically adjusted between lean and rich conditions based on the real-time oxygen storage amount of the catalyst. This dynamic control allows the system to optimize NOX removal efficiency while adapting to the changing capacity of the catalyst, preventing the contradiction from arising in the first place
2Reliability
If the air-fuel ratio is adjusted to rich to reduce NOX emissions when oxygen storage is high, then NOX removal is improved, but there is a delay in air-fuel ratio adjustment propagation to the exhaust purification catalyst, resulting in temporary NOX outflow
Solution Approach 1:
The control system performs preliminary action by switching the air-fuel ratio to rich condition in advance when detecting that the oxygen storage amount approaches the maximum. This proactive adjustment compensates for the propagation delay, ensuring that the exhaust purification catalyst receives the rich air-fuel ratio before NOX starts to pass through without reduction, thereby eliminating the temporary NOX outflow period
Solution Approach 2:
The system applies preliminary anti-action by preemptively switching to rich air-fuel ratio control when oxygen storage is high, counteracting the potential harmful effect of NOX outflow before it occurs. This anticipatory control measures prevents the contradiction between immediate NOX removal and adjustment delay from manifesting
3Measurement precision
If the air-fuel ratio sensor output is used as the basis for feedback control to maintain target air-fuel ratio, then air-fuel ratio control precision is improved, but the system cannot quickly respond to sudden changes in oxygen storage amount, leading to periods where NOX passes through without reduction
Solution Approach 1:
The system uses dual feedback mechanisms: one based on the air-fuel ratio sensor output for precise air-fuel ratio control, and another based on direct monitoring of the oxygen storage amount for rapid response to catalyst state changes. When the oxygen storage amount approaches maximum, the system prioritizes the oxygen storage feedback signal to switch to rich air-fuel ratio, thereby resolving the contradiction between precision and response speed
Solution Approach 2:
The control system performs preliminary action by monitoring the oxygen storage amount and switching to rich air-fuel ratio in advance when the storage amount approaches maximum, before NOX starts to pass through without reduction. This anticipatory control based on oxygen storage monitoring compensates for the slower response of traditional air-fuel ratio feedback control
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 control system effectively suppresses NOX outflow by dynamically managing the air-fuel ratio, ensuring the exhaust purification catalyst operates within optimal oxygen storage ranges, thereby reducing NOX emissions.
Implementation Method 1
An exhaust purification catalyst having an oxygen storage ability can remove unburned gas (HC, CO, etc.), NOX, etc. when the oxygen storage amount is a suitable amount between an upper limit storage amount and a lower limit storage amount
Implementation Method 2
an upstream side air-fuel ratio sensor arranged upstream of the exhaust purification catalyst and detecting an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst
Implementation Method 3
If exhaust gas of an air-fuel ratio at the rich side from the stoichiometric air-fuel ratio flows into the exhaust purification catalyst, the oxygen stored in the exhaust purification catalyst is used to remove by oxidation the unburned gas in the exhaust gas
Implementation Method 4
If exhaust gas of an air-fuel ratio at a lean side from the stoichiometric air-fuel ratio flows into the exhaust purification catalyst, the oxygen in the exhaust gas is stored in the exhaust purification catalyst. Due to this, the surface of the exhaust purification catalyst becomes an oxygen deficient state. Along with this, the NOX in the exhaust gas is removed by reduction
Data Source
AI summary
The control system of an internal combustion engine performs normal operation control including lean control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a lean air-fuel ratio, and rich control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a rich air-fuel ratio. The normal operation control includes judgment reference decreasing control decreasing the judgment reference storage amount in the lean control when during the time period of performing the lean control, the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst becomes the lean judged air-fuel ratio or more. The control system judges that the exhaust purification catalyst is abnormal when the judgment reference storage amount becomes less than a deterioration judgment value.