| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a device for controlling an air-fuel ratio, which controls an air-fuel ratio of an air-fuel mixture fed to an engine so that an exhaust gas with an air-fuel ratio that meets a determined air-fuel ratio requirement, flows into a catalyst. <P>SOLUTION: An exhaust emission control system includes: a downstream side air-fuel ratio sensor 56 disposed downstream of a three-way catalyst 43; and a throttle valve 45 disposed downstream of the downstream side air-fuel ratio sensor 56. The system controls the throttle valve 45 to reduce a flow channel cross-sectional area of an exhaust channel, for example, when a variation in intake air volume Ga is accelerated more than a predetermined value. Accordingly, when much NOx (or unburned matter) is generated in the exhaust channel on the upstream side relative to the catalyst 43, the exhaust gas therein is subjected to the catalyst 43 for a longer time, and the NOx (or unburned matter) is more purified, thereby improving the emission. <P>COPYRIGHT: (C)2012,JPO&INPIT |
