| 摘要 |
PROBLEM TO BE SOLVED: To rapidly diffuse added substances to the entire NOX absorbing agent regardless of the engine operation state. SOLUTION: In a pair of branch exhaust passages formed by branching an exhaust passage of an internal combustion engine in which combustion is executed under a lean air/fuel ratio, NOX absorbing agents NA1 and NA2, exhaust control valves VL1 and VL2 for controlling an amount of exhaust gas flowing through each of the NOX absorbing agents and secondary fuel supply nozzles NF1 and NF2 for supplying secondary fuel to each of the NOX absorbing agents are arranged. When the secondary fuel is supplied to the NOX absorbing agent, the corresponding exhaust control valve is opened. If an intake air amount is larger than a lower limit amount when added substances are to be supplied to the NOX absorbing agent, the opening degree of the exhaust control valve is held at the minimum, and when the intake air amount is smaller than the lower limit amount, the opening degree of the corresponding exhaust control valve is increased with decrease of the intake air amount.
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