To supply fuel evenly to NOx absorbent while securing good vehicle mounting property of the NOx absorbent.
A first exhaust gas passage 22a and a second exhaust gas passage 22b branching off of an exhaust gas passage 21 of an internal combustion engine are provided, NOx storage reduction catalysts 23a, 23b are arranged in the exhaust gas passages 22a, 22b respectively and are arranged in series. In an embodiment, when NOx is discharged from the NOx storage reduction catalyst 23a, fuel is added only into the first exhaust gas passage 22a from the fuel adding valve 32 under a condition where exhaust gas is made to flow therein and a first exhaust control valve 26a is temporally closed to make air fuel ratio of exhaust gas rich when added fuel adheres on the NOx storage reduction catalyst 23a. Quantity of fuel to be added from the fuel adding valve 32 when NOx need to be discharged from the NOx storage reduction catalyst 23b is set greater than the quantity of fuel to be added from the fuel adding valve 32 when NOx need to be discharged from the NOx storage reduction catalyst 23a.
COPYRIGHT: (C)2007,JPO&INPIT
Hide Itabashi
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Jun Tsuruta
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