Exhaust gas-purifying system for internal combustion engines

摘要

An exhaust gas-purifying system for an internal combustion engine is provided with hydrocarbon-adsorbing catalyzer for adsorbing unburnt gas components present in exhaust gases. At least one exhaust gas-purifying catalyzer is arranged in the exhaust passage at a location downstream of the hydrocarbon-adsorbing catalyzer. A bypass passage bypasses the hydrocarbon-purifying catalyzer. A changeover valve is arranged in the exhaust passage at a branchpoint between the bypass passage and the exhaust passage, for selecting a first flow path in which exhaust gases are guided to the unburnt gas component-adsorbing catalyzer, or a second flow path in which exhaust gases are guided through the bypass passage. First and second exhaust gas concentration sensors are arranged in the exhaust passage at locations upstream and downstream of the hydrocarbon-purifying catalyzer. An ECU controls the changeover valve to select the first flow path or the second flow path, based on outputs from the first and second exhaust gas concentration sensors.