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An exhaust gas purifying system for an internal combustion engine mounted on an automotive vehicle. The exhaust gas purifying system may include an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas componen

An exhaust gas purifying system for an internal combustion engine mounted on an automotive vehicle. The exhaust gas purifying system may include an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas components in exhaust gas discharged from the engine such that the concentrations of carbon monoxide and hydrogen are respectively not more than 2.0% by volume and not less than 0.5 by volume and such that a volume concentration ratio of hydrogen/carbon monoxide is not smaller than 0.5, in a first exhaust gas condition in which air/fuel ratio of exhaust gas is within a range of from a rich value and a stoichiometric value. Additionally, a NOx adsorbing and reducing catalyst is disposed in the exhaust gas passageway downstream of the exhaust gas component concentration regulating device, for adsorbing nitrogen oxides in a second exhaust gas condition in which the air/fuel ratio of exhaust gas is at a lean value, and reducing the nitrogen oxides into nitrogen in the first exhaust gas condition.

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An exhaust gas purifying system for an internal combustion engine mounted on an automotive vehicle. The exhaust gas purifying system may include an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas componen

An exhaust gas purifying system for an internal combustion engine mounted on an automotive vehicle. The exhaust gas purifying system may include an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas components in exhaust gas discharged from the engine such that the concentrations of carbon monoxide and hydrogen are respectively not more than 2.0% by volume and not less than 0.5 by volume and such that a volume concentration ratio of hydrogen/carbon monoxide is not smaller than 0.5, in a first exhaust gas condition in which air/fuel ratio of exhaust gas is within a range of from a rich value and a stoichiometric value. Additionally, a NOx adsorbing and reducing catalyst is disposed in the exhaust gas passageway downstream of the exhaust gas component concentration regulating device, for adsorbing nitrogen oxides in a second exhaust gas condition in which the air/fuel ratio of exhaust gas is at a lean value, and reducing the nitrogen oxides into nitrogen in the first exhaust gas condition. 1. An exhaust system for an internal combustion engine having two groups of cylinders, a separate exhaust line for each group of cylinders, each exhaust line including an upstream catalytic converter, a downstream catalytic converter, and a control valve, a first transverse connection extending between said exhaust lines upstream of said upstream catalytic converters and a second transverse connection extending between said exhaust lines between said upstream and said downstream catalytic converters, said control valves being so arranged and controllable that, during an initial warm-up period, the exhaust gas from both groups of cylinders is conducted through an upstream catalytic converter in only one of the exhaust lines and through a downstream catalytic converter in the other exhaust line for rapidly heating one of the catalytic converters in each of said exhaust lines and, after the upstream catalytic converter of the one and the downstream catalytic converter of the other exhaust line have reached critical operating temperature, the exhaust gas from each group of cylinders is conducted separately through its associated exhaust line and its upstream and downstream catalytic converters. 2. An exhaust system according to claim 1, wherein said two valves are so controllable that they are closed below a certain critical catalytic converter operating temperature and open at an operating temperature higher than said certain critical operating temperature. 3. An exhaust system according to claim 2, wherein said critical operating temperature is the conversion temperature of said catalytic converters. 4. An exhaust system according to claim 3, wherein said valves are so arranged in the two exhaust lines that, upon closing of said valves, the exhaust gas flows through the respective transverse connections from the one exhaust line to the other. 5. An exhaust system according to claim 1, wherein said valves are butterfly valves. 6. An exhaust system according to claim 1, wherein said upstream catalytic converters are firewall catalytic converters, which are mounted in close proximity to said engine. 7. An exhaust system according to claim 1, wherein said downstream catalytic converters are underfloor catalytic converters, which are disposed below a vehicle floor.