Engine Control Device EGR Rate Adjustment for Air-Fuel Ratio Switching
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Solution Overview
Problem
When switching the air-fuel ratio in internal combustion engines from stoichiometric to lean, existing technologies face challenges in suppressing NOx emissions and maintaining torque stability, leading to potential fuel consumption and exhaust performance deterioration.
Innovation Solution
A control device that gradually increases the EGR rate to a target level before switching the air-fuel ratio, maintaining the initial ratio until the EGR rate is reached, then smoothly transitions to the lean air-fuel ratio, while restricting control if torque changes exceed a predetermined value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the air-fuel ratio is gradually changed from stoichiometric to lean, then the air-fuel ratio can be switched without performing ignition retardation control, but the amount of NOx emissions increases significantly
Solution Approach 1:
The patent applies preliminary action by increasing the EGR rate before switching the air-fuel ratio from stoichiometric to lean mode. The control device increases the EGR rate to a target value in advance, then maintains this elevated EGR rate during the air-fuel ratio transition. This preliminary EGR increase suppresses combustion temperature and consequently reduces NOx emissions formation before the lean combustion begins, resolving the contradiction between easy air-fuel ratio switching and NOx emission control.
2Object-generated harmful factors
If the air-fuel ratio is changed in a step manner to skip the high NOx region, then NOx emissions are suppressed, but the torque level difference increases and fuel consumption deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the EGR rate as a control parameter during air-fuel ratio switching. Instead of using step changes in air-fuel ratio or relying solely on ignition timing retardation, the system changes the EGR rate parameter continuously to suppress NOx emissions. This allows for smoother transitions that maintain torque stability while reducing fuel consumption, as the EGR rate adjustment is more efficient than large ignition timing retardations.
3Stability of the object's composition
If ignition timing is retarded to suppress torque level difference during air-fuel ratio switching, then torque stability is improved, but fuel consumption increases
Solution Approach 1:
The patent uses EGR rate increase as an intermediary mechanism to suppress torque level differences during air-fuel ratio switching. Instead of directly retarding ignition timing to maintain torque stability, the system introduces EGR rate increase as an intermediary control action. The elevated EGR rate acts as a mediator that suppresses combustion temperature and stabilizes torque output, thereby reducing the need for large ignition timing retardations that would increase fuel consumption.
Data Source
AI summary
In an internal combustion engine an air-fuel ratio is switched between at least two target values without generating torque fluctuations, while a deterioration in fuel consumption performance and exhaust performance is suppressed. When a condition for switching a combustion mode from stoichiometric combustion to lean combustion and a condition that the amount of change in a target torque is less than or equal to a predetermined value are satisfied, a target EGR rate is increased towards an EGR limit prior to switching the target air-fuel ratio. The target air-fuel ratio is maintained at the stoichiometric air-fuel ratio until the target EGR rate reaches the EGR limit, and in response to the target EGR rate reaching the EGR limit, the target air-fuel ratio is changed towards a lean air-fuel ratio.