Engine Air-Fuel Ratio Control for Catalyst Oxygen Storage
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Solution Overview
Problem
The oxygen storage capacity of an exhaust purification catalyst in internal combustion engines decreases over time, leading to a drop in purification performance, and larger lean and rich air-fuel ratio fluctuations increase unburned gas and NOX emissions.
Innovation Solution
A control system that dynamically adjusts the air-fuel ratio based on real-time sensor feedback, switching between lean and rich air-fuel ratios with increased degrees during steady low-load operations to maintain oxygen storage capacity and reduce unburned gas and NOX emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the target air-fuel ratio is alternately switched between rich and lean with large lean degree and rich degree, then the oxygen storage capacity of the exhaust purification catalyst is maintained high, but the amount of unburned gas and NOX flowing out from the exhaust purification catalyst increases
Solution Approach 1:
The patent applies dynamics by making the control system adaptively change its behavior based on operating conditions. The control device switches between two different control modes: in a first operating state, it uses a conventional switching control with smaller lean/rich degrees to limit emissions; in a second operating state, it uses a switching control with larger lean/rich degrees to maximize oxygen storage capacity maintenance. This dynamic adaptation resolves the contradiction by selecting the appropriate control strategy based on real-time engine conditions.
Solution Approach 2:
The patent applies parameter changes by modifying the target air-fuel ratio parameters (lean degree and rich degree) based on the operating state. In the first operating state, the control device uses smaller deviations from stoichiometric air-fuel ratio to reduce emissions. In the second operating state, it uses larger deviations to enhance oxygen storage capacity maintenance. This parameter adjustment allows the system to optimize the trade-off between oxygen storage capacity and emissions under different conditions.
2Reliability
If the lean degree and rich degree are increased to maintain oxygen storage capacity, then the purification performance is maintained, but the amount of unburned gas and NOX flowing out increases temporarily
Solution Approach 1:
The control device dynamically adjusts the lean degree and rich degree based on the operating state. When in the first operating state, it limits the lean/rich degrees to prevent excessive emissions. When in the second operating state, it allows larger lean/rich degrees to maintain purification performance. This dynamic adjustment resolves the contradiction by adapting the control parameters to the current operational context.
Solution Approach 2:
The patent changes the control parameters (target air-fuel ratio deviations) based on operating conditions. In the first operating state, smaller parameter deviations are used to control emissions. In the second operating state, larger parameter deviations are applied to maintain oxygen storage capacity and purification performance. This parameter adaptation allows the system to balance purification performance and emissions under different conditions.
3Stability of the object's composition
If the target air-fuel ratio is set to lean air-fuel ratio with small lean degree, then torque fluctuation is reduced, but the oxygen storage capacity of the exhaust purification catalyst decreases over time
Solution Approach 1:
The control device dynamically selects the control strategy based on the operating state. In the first operating state, it uses small lean/rich degrees to maintain torque stability. In the second operating state, it uses large lean/rich degrees to maintain oxygen storage capacity. This dynamic selection allows the system to prioritize torque stability when needed while preserving catalyst performance when possible.
Solution Approach 2:
The patent adjusts the target air-fuel ratio parameters based on operating conditions. When in the first operating state, the control device uses smaller deviations from stoichiometric ratio to minimize torque fluctuation. When in the second operating state, it uses larger deviations to maintain oxygen storage capacity. This parameter adaptation resolves the contradiction by adjusting the degree of air-fuel ratio switching according to operational requirements.
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 system effectively maintains high purification performance while minimizing unburned gas and NOX emissions by optimizing air-fuel ratio settings based on engine operating states.
Implementation Method 1
an exhaust purification catalyst which is arranged in an exhaust passage of the internal combustion engine and which can store oxygen
Data Source
AI summary
An internal combustion engine includes an exhaust purification catalyst. A control system includes an air-fuel ratio sensor downstream of the exhaust purification catalyst, and an air-fuel ratio control device which controls the air-fuel ratio of the exhaust gas. The target air-fuel ratio is set to a lean air-fuel ratio when output air-fuel ratio of the sensor becomes a rich judged air-fuel ratio or less and is set to a rich air-fuel ratio when output air-fuel ratio becomes a lean judged air-fuel ratio or more. When the engine operating state is a steady operation state and is a low load operation state, at least one of an average lean degree of the target air-fuel ratio while the target air-fuel ratio is set to a lean air-fuel ratio and an average rich degree of the target air-fuel ratio while the target air-fuel ratio is set to a rich air-fuel ratio is increased.