Vehicle Control Device for Acceleration and NOx Trade-off
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Solution Overview
Problem
During lean operation of an internal combustion engine with a supercharger, exhaust gas recirculation reduces NOx emissions but decreases combustion efficiency and fuel consumption, while increasing torque requirements lead to insufficient acceleration responsiveness due to delayed supercharging, which worsens NOx emissions.
Innovation Solution
A control device that adjusts the air-fuel ratio during lean operation by setting a limit air-fuel ratio below the steady lean operation ratio and above the theoretical ratio to reduce NOx emissions and enhance acceleration responsiveness, using a fuel supply system to maintain the air-fuel ratio within this range and switching to the theoretical ratio when torque requirements cannot be met, with an electric motor compensating for output torque insufficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If exhaust gas recirculation is performed to reduce NOx emissions during lean operation, then NOx emission is suppressed, but combustion efficiency drops and fuel consumption increases
Solution Approach 1:
The control device performs preliminary enrichment control before acceleration to advance the air-fuel ratio to a richer state in advance. This allows the engine to respond quickly to acceleration requests without needing exhaust gas recirculation, thereby maintaining combustion efficiency while still controlling NOx emissions through the supercharger's delayed response characteristic.
2Power
If the target supercharging pressure is increased to raise intake air amount during lean operation, then torque output increases, but acceleration responsiveness deteriorates due to supercharging delay
Solution Approach 1:
The control device performs preliminary enrichment control before acceleration to advance the air-fuel ratio to a richer state in advance. This allows the engine to respond quickly to acceleration requests without needing exhaust gas recirculation, thereby maintaining combustion efficiency while still controlling NOx emissions through the supercharger's delayed response characteristic.
Solution Approach 2:
The control device changes the air-fuel ratio parameter from the lean operation ratio to a richer ratio during acceleration requests. This parameter change allows the engine to overcome the supercharging delay and improve acceleration responsiveness while the supercharger pressure gradually increases.
3Speed
If the air-fuel ratio is reduced to improve acceleration responsiveness, then responsiveness increases, but NOx concentration in exhaust gas increases
Solution Approach 1:
The control device changes the air-fuel ratio parameter from the lean operation ratio to a richer ratio during acceleration requests. This parameter change allows the engine to overcome the supercharging delay and improve acceleration responsiveness while the supercharger pressure gradually increases.
Solution Approach 2:
The control device performs preliminary enrichment control before acceleration to advance the air-fuel ratio to a richer state in advance. This allows the engine to respond quickly to acceleration requests without needing exhaust gas recirculation, thereby maintaining combustion efficiency while still controlling NOx emissions through the supercharger's delayed response characteristic.
Data Source
AI summary
A control device of a vehicle capable of improving acceleration responsiveness and suppressing increase in the NOx emission amount when a required torque is increased during a steady lean operation. A target air-fuel ratio (AFCMD) is set according to an accelerator pedal operation of a driver. When the driver depresses an accelerator pedal to make an acceleration request during the lean operation, in which the AFCMD is set to a predetermined lean air-fuel ratio (AFLN), air-fuel ratio reduction control is executed to reduce the AFCMD according to the acceleration request. In the air-fuel ratio reduction control, when the AFCMD calculated according to a required torque (TRQCMD) is smaller than a limit air-fuel ratio (AFLMT), the AFCMD is set to the AFLMT, and the AFLMT is set to a value smaller than the AFLN set in a steady state of the lean operation and larger than a theoretical air-fuel ratio (AFST).