| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration and failure of a three-way conversion catalyst without deteriorating drivability in a small displacement engine system provided with the three-way conversion catalyst in an exhaust system. SOLUTION: A secondary air supply path providing secondary air to an exhaust system of an engine purifying exhaust gas with using the three-way conversion catalyst is provided. An air introducing valve is provided in a middle of the secondary air supply path. Quantity of secondary air supplied to the exhaust system is controlled by using the air introducing valve. Supply control of secondary air is periodically performed according to cycle of a crankshaft. Duty ratio of valve open period t2 during which supply of secondary air is performed is controlled in a range of supply quantity for keeping catalyst temperature L2 of the three-way conversion catalyst at a predetermined value or less and in a range of supply quantity preventing carbon deposition deterioration L3 of the three-way conversion catalyst while air-fuel ratio is rich. COPYRIGHT: (C)2006,JPO&NCIPI
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