Engine Air-Fuel Ratio Control During External EGR
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Solution Overview
Problem
In multiple cylinder internal combustion engines, air-fuel ratio variations among cylinders due to fuel injection system failures lead to increased NOx emissions when air-fuel ratio feedback control corrects the lean side, and performing rich corrections during external EGR is not preferable.
Innovation Solution
A control apparatus and method that includes an EGR system, air-fuel ratio feedback control, detection of rich deviations, calculation of rich correction parameters, and adjustment of rich correction values based on whether external EGR is being executed, with larger corrections initiated at higher EGR rates and smaller corrections during EGR execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If air-fuel ratio feedback control corrects to the lean side to compensate for rich deviation in failed cylinders, then the air-fuel ratio of normal cylinders is corrected to lean side, but the amount of NOx discharged from normal cylinders increases
Solution Approach 1:
The patent changes the parameter of target air-fuel ratio based on EGR execution status. When external EGR is detected as executing, the target air-fuel ratio is set to a richer side (first target value); when EGR is not executing, a leaner target value (second target value) is used. This parameter change resolves the contradiction by adapting the control target to current operating conditions, preventing excessive NOx emissions during EGR operations while maintaining control accuracy.
2Object-generated harmful factors
If rich correction is performed to suppress NOx from normal cylinders, then NOx emissions are reduced, but combustion fluctuation increases when external EGR is being executed
Solution Approach 1:
The patent implements dynamic adjustment of the target air-fuel ratio based on real-time detection of EGR execution status. The control system transitions between two distinct target values (richer during EGR, leaner during normal operation), making the control strategy adaptive to changing operating conditions. This dynamic approach prevents excessive rich correction during EGR that would cause combustion fluctuation, while still enabling NOx suppression when appropriate.
Solution Approach 2:
By changing the target air-fuel ratio parameter according to EGR status, the patent optimizes the balance between NOx suppression and combustion stability. During external EGR execution, the richer target prevents excessive lean correction that would destabilize combustion, while still providing adequate NOx control. This parameter adaptation resolves the contradiction between NOx reduction and combustion stability.
3Reliability
If the same rich correction amount is applied regardless of EGR status, then NOx suppression is consistent, but combustion fluctuation increases during EGR execution
Solution Approach 1:
The patent makes the control system dynamic by detecting EGR execution status and selecting different target air-fuel ratios accordingly. This dynamic behavior allows the system to maintain reliable NOx control through consistent application of appropriate correction amounts for each operating condition, while preventing combustion fluctuation by using更适合的 target values during EGR operations.
Data Source
AI summary
With a control apparatus of a multiple cylinder internal combustion engine, external EGR that circulates exhaust gas in an exhaust passage to an intake passage is executed, and an air-fuel ratio is feedback-controlled such that an air-fuel ratio of the exhaust gas comes to match a predetermined target air-fuel ratio. When a rich deviation in which the air-fuel ratio of a portion of cylinders is off to a rich side from the target air-fuel ratio is detected, a parameter indicative of an amount of the rich deviation is calculated. The target air-fuel ratio is corrected to the rich side according to the calculated parameter. A value of a parameter at which the rich correction is started is changed according to whether external EGR is being executed.