To determine a priority order among DPF reproduction for purifying PM accumulated in a DPF 13, SOx reproduction for purifying SOx accumulated on a NOx trap catalyst 14 and NOx reproduction for purifying NOx accumulated on the NOx trap catalyst 14 when the DPF 13 for collecting PM in exhaust gas and the NOx trap catalyst 14 for trapping NOx in the exhaust gas when an exhaust gas/fuel ratio is lean are mounted in an exhaust gas passage 10 of an engine 1.
When a DPF reproduction time, SOx reproduction time and NOx reproduction time come at the same time, the first priority is the DPF reproduction and the next is the SOx reproduction followed by the NOx reproduction. However, when the oxidation function of the DPF or the NOx trap catalyst is inactive, the NOx reproduction is prior to the DPF reproduction or the SOx reproduction. When a NOx quantity emitted from the engine 1 is large, the first priority is given to the NOx reproduction.
MIURA MANABU
ITOYAMA HIROYUKI
SHIRAKAWA AKIRA
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