Evaporative fuel control system for internal combustion engines

摘要

An evaporative fuel control system for an internal combustion engine having a throttle valve includes a canister for adsorbing evaporative fuel generated in the fuel tank, a purging passage for purging evaporative fuel into the intake system of the engine, and a purge control valve for controlling a flow rate of the evaporative fuel to be purged into the intake system through the purging passage. An ECU sets an air-fuel ratio correction coefficient applied in air-fuel ratio feedback control, based on the concentration of a specific component in exhaust gases emitted from the engine, calculates a first learned value of the air-fuel ratio correction coefficient during execution of the air-fuel ratio feedback control, and controls the purge control valve such that the flow rate of the evaporative fuel is changed according to the calculated first learned value. A second learned value of the air-fuel ratio correction coefficient suitable for the transient operating condition of the engine is calculated. When the engine is in a transient operating condition, the first learned value is set to the second learned value.