Patent ID: 7305978

Claim:
A vaporized fuel purge system comprising: a fuel injection valve that injects a fuel in an internal combustion engine; an exhaust gas sensor that generates an output indicative of an exhaust air-fuel ratio in the internal combustion engine; an FAF calculation device that calculates, based on the output of the exhaust gas sensor, a feedback correction coefficient applied to a fuel injection amount so that the exhaust air-fuel ratio matches a target air-fuel ratio; a canister that adsorbs a vaporized fuel produced in a fuel tank; a purge mechanism that allows a purge gas that contains the vaporized fuel to flow from the canister into the internal combustion engine; a sharp-change-condition detecting device that detects a sharp-change condition in which a fuel concentration of the purge gas changes at a rate higher than a reference rate; a concentration updating base value setting device that sets a concentration updating base value based on the feedback correction coefficient by a predetermined process; a process changing device that changes the predetermined process such that the concentration updating base value is made larger in the sharp-change condition than in a non-sharp-change condition; a fuel concentration updating device that updates a fuel concentration of the purge gas using the concentration updating base value; a purge correction coefficient calculation device that calculates a purge correction coefficient that is used to eliminate an influence of the vaporized fuel based on the fuel concentration of the purge gas; and a fuel injection amount calculation device that calculates a final fuel injection amount by reflecting the feedback correction coefficient and the purge correction coefficient on a basic fuel injection amount.