Method and device for purifying exhaust gas of engine

A device for purifying an exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, and first and second exhaust passage connected to the first and the second cylinder groups, respectively, the device comprising:

• an NH.sub.3 synthesizing catalyst arranged in the first exhaust passage, the NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• an interconnecting exhaust passage interconnecting the first passage downstream of the NH.sub.3 synthesizing catalyst and the second exhaust passage;
• an exhaust gas purifying catalyst arranged in the interconnecting passage for reducing the inflowing NO.sub.x by the inflowing NH.sub.3 ;
• first exhaust gas air-fuel ratio control means for controlling the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst;
• means for controlling the first exhaust gas air-fuel ratio control means to make the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst rich to synthesize NH.sub.3 ;
• and
• NO.sub.x amount control means for controlling an amount of NO.sub.x flowing from the second exhaust passage into the exhaust gas purifying catalyst to prevent the NO.sub.x amount from being larger than a NO.sub.x amount which can be reduced by the NH.sub.3 flowing from the first exhaust passage into the exhaust gas purifying catalyst,
• wherein, on the exhaust gas purifying catalyst, the inflowing NO.sub.x is reduced by the inflowing NH.sub.3.

A method for purifying an exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, the method comprising:

• making the exhaust gas air-fuel ratio of the exhaust gas of the first cylinder group rich, and introducing the exhaust gas to an NH.sub.3 synthesizing catalyst to synthesize NH.sub.3, to form the exhaust gas including NH.sub.3 of which the exhaust gas air-fuel ratio is rich, the NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• making the exhaust gas air-fuel ratio of the exhaust gas of the second cylinder group lean, to form the exhaust gas including NO.sub.x of which the exhaust gas air-fuel ratio is lean;
• performing a first introducing condition where the exhaust gas including NH.sub.3 of which the exhaust gas air-fuel ratio is rich is introduced to an NH.sub.3 adsorbing and oxidizing (NH.sub.3 -AO) catalyst and the exhaust gas including NO.sub.x of which the exhaust gas air-fuel ratio is lean is introduced to a NO.sub.x occluding and reducing (NO.sub.x -OR) catalyst, the NH.sub.3 -AO catalyst adsorbing NH.sub.3 in the inflowing exhaust gas therein, and causing a reaction of NH.sub.3 and NO.sub.x in the NH.sub.3 -AO catalyst to purify the NH.sub.3 and the NO.sub.x and to decrease an amount of NH.sub.3 adsorbed in the NH.sub.3 -AO catalyst when the inflowing exhaust gas includes NO.sub.x therein and the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, the NO.sub.x -OR catalyst occluding NO.sub.x in the inflowing exhaust gas therein when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, and releasing the occluded NO.sub.x therefrom and reducing the NO.sub.x when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• performing a second introducing condition where the exhaust gas including NH.sub.3 of which the exhaust gas air-fuel ratio is rich is introduced to the NO.sub.x -OR catalyst and the exhaust gas including NO.sub.x of which the exhaust gas air-fuel ratio is lean is introduced to the NH.sub.3 -AO catalyst;
• and
• performing the first and the second introducing conditions alternately and repeatedly.

A device for purifying an exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, and first and second exhaust passage connected to the first and the second cylinder groups, respectively, the device comprising:

• an NH.sub.3 synthesizing catalyst arranged in the first exhaust passage, the NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• an NH.sub.3 adsorbing and oxidizing (NH.sub.3 -AO) catalyst selectively connected to one of the first exhaust passage downstream of the NH.sub.3 synthesizing catalyst and the second exhaust passage, the NH.sub.3 -AO catalyst adsorbing NH.sub.3 in the inflowing exhaust gas therein, and causing a reaction of NH.sub.3 and NO.sub.x in the NH.sub.3 -AO catalyst to purify the NH.sub.3 and the NO.sub.x and to decrease an amount of NH.sub.3 adsorbed in the NH.sub.3 -AO catalyst when the inflowing exhaust gas includes NO.sub.x therein and the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean;
• a NO.sub.x occluding and reducing (NO.sub.x -OR) catalyst selectively connected to one of the first exhaust passage downstream of the NH.sub.3 synthesizing catalyst and the second exhaust passage, the NO.sub.x -OR catalyst occluding NO.sub.x in the inflowing exhaust gas therein when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, and releasing the occluded NO.sub.x therefrom and reducing the NO.sub.x when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• first exhaust gas air-fuel ratio control means for controlling the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst;
• second exhaust gas air-fuel ratio control means for controlling the exhaust gas air-fuel ratio of the exhaust gas flowing through the second exhaust passage;
• means for controlling the first exhaust gas air-fuel ratio control means to make the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst rich to synthesize NH.sub.3 ;
• means for controlling the second exhaust gas air-fuel ratio control means to make the exhaust gas air-fuel ratio of the exhaust gas flowing through the second exhaust passage lean;
• first connecting condition performing means for performing a first connecting condition where the first exhaust passage downstream of the NH.sub.3 synthesizing catalyst is connected to the NH.sub.3 -AO catalyst and the second exhaust passage is connected to the NO.sub.x -OR catalyst;
• second connecting condition performing means for performing a second connecting condition where the first exhaust passage downstream of the NH.sub.3 synthesizing catalyst is connected to the NO.sub.x -OR catalyst and the second exhaust passage is connected to the NH.sub.3 -AO catalyst;
• and
• connecting condition control means for controlling the first and the second connecting condition performing means to perform the first and the second connecting conditions alternately and repeatedly.

A method for purifying an exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, the method comprising:

• introducing the exhaust gas of the first cylinder group to a first NH.sub.3 synthesizing catalyst and an NH.sub.3 adsorbing and oxidizing (NH.sub.3 -AO) catalyst, in turn, the NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich, and synthesizing almost no NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, and the NH.sub.3 -AO catalyst adsorbing NH.sub.3 in the inflowing exhaust gas therein, and causing a reaction of NH.sub.3 and NO.sub.x in the NH.sub.3 -AO catalyst to purify the NH.sub.3 and the NO.sub.x and to decrease an amount of NH.sub.3 adsorbed in the NH.sub.3 -AO catalyst when the inflowing exhaust gas includes NO.sub.x therein and the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean;
• introducing the exhaust gas of the second cylinder group to a second NH.sub.3 synthesizing catalyst and a NO.sub.x occluding and reducing (NO.sub.x -OR) catalyst, in turn, the NO.sub.x,OR catalyst occluding NO.sub.x in the inflowing exhaust gas therein when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, and releasing the occluded NO.sub.x therefrom and reducing the NO.sub.x when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• performing a first exhaust gas air-fuel ratio condition where the exhaust gas air-fuel ratio of the exhaust gas flowing into the first NH.sub.3 synthesizing catalyst and the NH.sub.3 -AO catalyst is made rich, and that of the exhaust gas flowing into the second NH.sub.3 synthesizing catalyst and the NO.sub.x -OR catalyst is made lean;
• performing a second exhaust gas air-fuel ratio condition where the exhaust gas air-fuel ratio of the exhaust gas flowing into the first NH.sub.3 synthesizing catalyst and the NH.sub.3 -AO catalyst is made lean, and that of the exhaust gas flowing into the second NH.sub.3 synthesizing catalyst and the NO.sub.x -OR catalyst is made rich;
• and
• performing the first and the second exhaust gas air-fuel ratio conditions alternately and repeatedly.

A device for purifying an exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, and first and second exhaust passage connected to the first and the second cylinder groups, respectively, the device comprising:

• a first NH.sub.3 synthesizing catalyst arranged in the first exhaust passage and a second NH.sub.3 synthesizing catalyst arranged in the second exhaust passage, each NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich, and synthesizing almost no NH.sub.3 from NO.sub.x in the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean;
• an NH.sub.3 adsorbing and oxidizing (NH.sub.3 -AO) catalyst arranged in the first exhaust passage downstream of the first NH.sub.3 synthesizing catalyst, the NH.sub.3 -AO catalyst adsorbing NH.sub.3 in the inflowing exhaust gas therein, and causing a reaction of NH.sub.3 and NO.sub.x in the NH.sub.3 -AO catalyst to purify the NH.sub.3 and the NO.sub.x and to decrease an amount of NH.sub.3 adsorbed in the NH.sub.3 -AO catalyst when the inflowing exhaust gas includes NO.sub.x therein and the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean;
• a NO.sub.x occluding and reducing (NO.sub.x -OR) catalyst arranged in the second exhaust passage downstream of the second NH.sub.3 synthesizing catalyst, the NO.sub.x -OR catalyst occluding NO.sub.x in the inflowing exhaust gas therein when the exhaust gas air-fuel ratio of the inflowing exhaust gas is lean, and releasing the occluded NO.sub.x therefrom and reducing the NO.sub.x when the exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;
• a first exhaust gas air-fuel ratio control means for controlling the exhaust gas air-fuel ratio of the exhaust gas flowing into the first NH.sub.3 synthesizing catalyst and the NH.sub.3 -AO catalyst;
• a second exhaust gas air-fuel ratio control means for controlling the exhaust gas air-fuel ratio of the exhaust gas flowing into the second NH.sub.3 synthesizing catalyst and the NO.sub.x -OR catalyst;
• first exhaust gas air-fuel ratio condition performing means for controlling the first and the second exhaust gas air-fuel ratio control means to perform a first exhaust gas air-fuel ratio condition where the exhaust gas air-fuel ratio of the exhaust gas flowing into the first NH.sub.3 synthesizing catalyst and the NH.sub.3 -AO catalyst is made rich, and that of the exhaust gas flowing into the second NH.sub.3 synthesizing catalyst and the NO.sub.x -OR catalyst is made lean;
• second exhaust gas air-fuel ratio condition performing means for controlling the first and the second exhaust gas air-fuel ratio control means to perform a second exhaust gas air-fuel ratio condition where the exhaust gas air-fuel ratio of the exhaust gas flowing into the first NH.sub.3 synthesizing catalyst and the NH.sub.3 -AO catalyst is made lean, and that of the exhaust gas flowing into the second NH.sub.3 synthesizing catalyst and the NO.sub.x -OR catalyst is made rich;
• and
• exhaust gas air-fuel ratio condition control means for controlling the first and the second exhaust gas air-fuel ratio condition performing means to perform the first and the second exhaust gas air-fuel ratio conditions alternately and repeatedly.