| 摘要 |
PURPOSE:To enable purification of exhaust gas, by a method wherein, even during low load running of an engine, when the engine is in a cruise operating state, air-fuel ratio feedback control is effected. CONSTITUTION:When the number of an engine detected by a rotation sensor 38 during low load running of an engine detected by a P0 (negative pressure) switch 36 exceeds a given value, if the change speed per unit time of a car speed detected by a car speed sensor 39 is below a given value, it is considered as a cruise operating state, an output signal is fed to a driving circuit 30 from a control circuit 32. The driving circuit 30 opens and closes an electromagnetic on-off valve 18 according to a rich or a leans signal from an oxygen concentration sensor 34, and communicates or blocks an intake air secondary air feed passage 12. This, when an engine is in a cruise operating state even during low load running of the engine, performs feedback control of an air-fuel ratio to control the air-fuel ratio of the fed fuel-air mixture to a theoretical air-fuel ratio.
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