Engine Control System Oxygen Storage Management
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Solution Overview
Problem
In internal combustion engine control systems, unburned gas and NOx often flow out from the upstream catalyst, leading to inefficient purification by the downstream catalyst, especially during prolonged fuel cut control when the oxygen storage amount in the downstream catalyst decreases.
Innovation Solution
A control system that alternates the air-fuel ratio of exhaust gas flowing into the upstream catalyst between a lean and a weak rich set air-fuel ratio to manage oxygen storage, ensuring unburned gas is minimized and NOx is not released, using a downstream air-fuel ratio detecting means and oxygen storage amount estimation to adjust the target air-fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the air-fuel ratio is controlled to be lean to increase oxygen storage in the upstream catalyst, then unburned gas purification is improved, but NOx purification deteriorates due to oxygen excess
Solution Approach 1:
The control system alternates the target air-fuel ratio between lean and rich states in periodic cycles. During lean periods, the upstream catalyst stores oxygen to purify unburned gas. During rich periods, the stored oxygen is consumed to purify NOx. This periodic switching resolves the contradiction by ensuring both unburned gas and NOx are purified at different times within the same catalyst.
2Object-generated harmful factors
If the target air-fuel ratio is set to rich to purify NOx, then NOx purification is improved, but unburned gas flows out untreated
Solution Approach 1:
Before setting the target air-fuel ratio to rich for NOx purification, the control system preliminarily stores oxygen in the upstream catalyst by operating in lean mode. This preliminary oxygen storage ensures that when the rich mode is activated, there is sufficient oxygen available to purify both NOx and any unburned gas that may be present, preventing unburned gas from flowing out untreated.
3Loss of energy
If fuel cut control is prolonged to reduce emissions, then fuel consumption is reduced, but oxygen storage in the downstream catalyst decreases leading to purification failure
Solution Approach 1:
The control system continuously monitors the oxygen storage amount in the downstream catalyst and uses this feedback to adjust the air-fuel ratio control strategy. When oxygen storage falls below a threshold during prolonged fuel cut control, the system switches to rich mode to replenish oxygen, ensuring the downstream catalyst maintains sufficient oxygen storage to reliably purify exhaust gas regardless of how long fuel cut control has been active.
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 reliably suppresses the flow-out of unburned gas from the downstream catalyst, maintaining effective purification by ensuring the oxygen storage amount is maintained within optimal limits, thereby reducing NOx emissions and improving catalyst efficiency.
Implementation Method 1
an upstream side catalyst and downstream side catalyst which are provided in the exhaust passage and have oxygen storage abilities
Implementation Method 2
the unburned gas in the exhaust gas is oxidized and purified by the oxygen stored in the catalyst
Implementation Method 3
the unburned gas in the exhaust gas is oxidized and purified by the oxygen stored in the catalyst
Implementation Method 4
the surface of the catalyst becomes an oxygen deficient state and, along with this, NO X in the exhaust gas is reduced and purified
Data Source
Figure 1
Figure 2(A)~2(B)
Figure 3
AI summary
This control device for an internal combustion engine includes: an upstream catalyst (20); a downstream catalyst (24) that is provided further downstream than the upstream catalyst in the exhaust flow direction; a downstream air-fuel ratio detection means (41) that is provided between these catalysts; a storage amount estimation means that estimates the oxygen storage amount of the downstream catalyst; and an inflow air-fuel ratio control device that controls the air-fuel ratio of the exhaust gas flowing into the upstream catalyst such that the air-fuel ratio of the exhaust gas reaches a target air-fuel ratio. In a rich control during normal operation, the target air-fuel ratio is set lean if the air-fuel ratio detected by the downstream air-fuel ratio detection means is rich, and the target air-fuel ratio is set rich if the upstream catalyst oxygen storage amount is equal to or greater than the upstream reference storage amount. If the downstream catalyst oxygen storage amount is equal to or less than a downstream lower-limit storage amount, which is less than the maximum storage amount, then the target air-fuel ratio is set lean such that the air-fuel ratio of the exhaust gas flowing out from the upstream catalyst becomes lean.