| 摘要 |
PROBLEM TO BE SOLVED: To control introduction of vapor to an intake pipe by a vapor processing system so that an exhaust purification rate of an exhaust purification catalyst having a capability of retaining or discharging oxygen may satisfy requirements, that is, may be kept at a high value as much as possible. SOLUTION: The vapor processing system 61 introduces the vapor collected in a canister 63 to the intake pipe 12. The exhaust purification catalyst 25 having the capability of retaining/discharging oxygen is arranged in an exhaust pipe 26. A fluctuation band of an air/fuel ratio in case of keeping a purge rate at a constant value is compared with a fluctuation band for judgement set according to a maximum amount of oxygen which can be retained by the exhaust purification catalyst. When the former fluctuation band of the air/fuel ratio is smaller than the fluctuation band for judgement, the vapor is allowed to be introduced into the intake pipe by the vapor processing system or the purge rate is increased. COPYRIGHT: (C)2007,JPO&INPIT
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