| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent the thermal deterioration of a bypass catalytic convertor 8 caused by a delay in the switching timing of a flow passage selector valve 5 from a closed state to an open state caused by an influence of reaction heat in a catalyst when it is determine the occurrence of a catalyst activated state by an exhaust gas temperature at the upstream side of a main catalytic convertor 4. <P>SOLUTION: The flow passage selector valve 5 is interposed in an exhaust gas main passage 3 upstream of the main catalytic convertor 4. The bypass catalytic convertor 8 is interposed in a bypass passage 7 juxtaposed to the upstream portion of the main passage 3, and exhaust gas is led to flow into the bypass flow passage 7 when the flow passage selector valve 5 is closed. Air-fuel ratio sensors 11, 12 are provided in front of and behind the main catalytic convertor 4. When the flow passage selector valve 5 is closed, an exhaust gas air-fuel ratio is temporarily changed to a rich side or a lean side, and also the flow passage selector valve 5 is temporarily opened. Based on a change in the air-fuel ratio on the front and back sides of the main catalytic convertor 4 caused by temporary valve opening, the activated state of the main catalytic convertor 4 is determined. <P>COPYRIGHT: (C)2010,JPO&INPIT |
