초록 ▼

The temperature of a downstream catalyst is effectively increased while avoiding temperature increase of an upstream catalyst, so as to remove SOx from the downstream catalyst. For this purpose, a first front three-way catalyst 21 of a first exhaust gas passage 5a connected to a first cylinder group

The temperature of a downstream catalyst is effectively increased while avoiding temperature increase of an upstream catalyst, so as to remove SOx from the downstream catalyst. For this purpose, a first front three-way catalyst 21 of a first exhaust gas passage 5a connected to a first cylinder group, a second front three-way catalyst 22 of a second exhaust gas passage 5b connected to a second cylinder group, and a rear three-way catalyst 23 installed in an exhaust gas passage 5c which combines the exhaust of both of these exhaust gas passages, are provided. When the conditions hold for performing temperature increase of the rear three-way catalyst 23, the control unit 11 sets the air-fuel ratio of the exhaust supplied to one front catalyst to richer than the stoichiometric air-fuel ratio, and sets the air-fuel ratio of the exhaust gas supplied to the other front catalyst to leaner than the stoichiometric air-fuel ratio. Due to this, unburnt fuel and oxygen which passed through the front catalysts flow into the rear catalyst, promote the reactions in the rear catalyst so as to raise its temperature, and thereby promote discharge and reduction of SOx.

대표청구항 ▼

[ What is claimed is:] [1.]1. An exhaust purification device for an internal combustion engine comprising:a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group;a second front three-way catalyst installed in a second exhaust passage connected to a s

[ What is claimed is:] [1.]1. An exhaust purification device for an internal combustion engine comprising:a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group;a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group;a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages;a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio;a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio;a microprocessor programmed to:determine the conditions under which the temperature of the rear three-way catalyst should be increased, andset the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst;a first air-fuel ratio sensor installed in said first exhaust passage; anda second air-fuel ratio sensor installed in said second exhaust passage,wherein said first air-fuel ratio controller computes a first feedback correction coefficient based on the output of said first air-fuel ratio sensor, corrects a fuel amount supplied to said first cylinder group using this first feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said first front three-way catalyst, andwherein said second air-fuel ratio controller computes a second feedback correction coefficient based on the output of said second air-fuel ratio sensor, corrects a fuel amount supplied to said second cylinder group using this second feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said second front three-way catalyst,wherein said first and second sensors are so designed that their outputs vary sharply around the stoichiometric air-fuel ratio relative to variation of the air-fuel ratio of the exhaust gas,wherein said first air-fuel ratio controller computes a first feedback correction coefficient by subtracting a first lean shift proportional part when the output of said first air-fuel ratio sensor changes from lean to rich, and adding a first rich shift proportional part when it changes from rich to lean,wherein said second air-fuel ratio controller computes a second feedback correction coefficient by subtracting a second lean shift proportional part when the output of said second air-fuel ratio sensor changes from lean to rich, and adding a second rich shift proportional part when it changes from rich to lean, andwherein said microprocessor is further programmed to set a control midpoint value of the air-fuel ratio of exhaust gas controlled by said first and second air-fuel ratio controllers, to a predetermined air-fuel ratio by setting said first lean shift proportional part, said rich shift proportional part, said second lean shift proportional part and said second rich shift proportional part respectively to predetermined values.