INTERNAL COMBUSTION ENGINE CONTROL UNIT

摘要

PROBLEM TO BE SOLVED: To provide a control unit capable of more appropriately changing air-fuel ratios at a time of switching a stoichiometric operation to a lean operation in an engine including a three-way catalyst in an exhaust system, and suppressing a temporary increase in a NOx concentration downstream of the three-way catalyst.SOLUTION: An internal combustion engine control unit exerts an air-fuel ratio transition control at a time of switching a stoichiometric operation to a lean operation, and exerts an air-fuel ratio rich control to change an air-fuel ratio to a richer air-fuel ratio than a stoichiometric air-fuel ratio in a period before the passage of predetermined rich control time TRICH from start time tS of the air-fuel ratio transition control. The internal combustion engine control unit exerts a control to gradually change the air-fuel ratio to a lean air-fuel ratio AFLN1 after the passage of the predetermined rich control time TRICH. The air-fuel ratio rich control enables an increase in a rate of unoxidized (reduced) noble metal in a three-way catalyst 10 and a temporary increase in a NOx concentration CNOx downstream of the three-way catalyst 10 from being suppressed at a time of switchover of air-fuel ratios.