| 摘要 |
PURPOSE:To prevent an upstream catalyst from deteriorating, by providing two catalytic converters in series with each other in an exhaust passage and providing a by-pass around the upstream converter so that exhaust gas flows through the by-pass when the temperature of the gas is not lower than a prescribed level. CONSTITUTION:Converters 3, 4 with monolithic catalysts are provided in series with each other in the exhaust passage 2 of an engine 1 to constitute an exhaust gas purifier. A by-pass 5 is provided around the upstream catalytic converter 3. A changeover valve 6 for selectively closing the by-pass 5 or the exhaust passage 2 is provided at the upstream branching part of the by-pass 5 from the exhaust passage 2. A temperature detector 7 is installed upstream to the valve 6. The detection signal of the detector 7 is entered into a computer 8. When the temperature of exhaust gas is higher than a prescribed level, a solenoid valve 10 is regulated by a solenoid valve control circuit 9 to close the inlet port of the converter 3 by the changeover valve 6. The solenoid valve 10 and the changeover valve 6 are coupled to each other through a negative pressure control valve 13 and a release 4. |
