To provide an exhaust emission control device capable of suppressing the overheating of an exhaust emission control catalyst and quickly adding a fuel to the exhaust emission control catalyst when the addition of the fuel to the exhaust emission control catalyst is requested.
This exhaust emission control device for an internal combustion engine comprises the exhaust emission control catalyst 8 for purifying exhaust of the internal combustion engine 1 and a fuel adding valve 10 for adding fuel from the upstream side of the exhaust emission control catalyst 8. To control the exhaust emission control catalyst 8 to the target temperature, the fuel adding valve 10 is so operated as to repeat a cycle formed by combining an adding period in which the fuel from the fuel adding valve 10 is added and a pausing period in which the addition of fuel is paused. The fuel adding valve 10 is so operated that the pausing period in each cycle is provided on both sides of the adding period. The length of the pausing period before addition provided before the adding period is changed according to the temperature of the exhaust emission control catalyst 8 at the start point P1 of the cycle.
COPYRIGHT: (C)2008,JPO&INPIT
AOYAMA TARO
Tatsuo Egami
Satoshi Nakamura