Patent ID: 8583348
Filing Date: 2013-11-12
Classification: F02D

Abstract:
1. A fuel injection amount control system of a multi-cylinder internal combustion engine, comprising: a three-way catalyst mounted at a position downstream of an exhaust gathering portion of an exhaust passage of the engine into which exhaust gases emitted from a plurality of cylinders of the multi-cylinder internal combustion engine are collected; an upstream air-fuel ratio sensor located between the exhaust gathering portion of the exhaust passage and the three-way catalyst; a plurality of fuel injection valves each of which is arranged to inject fuel contained in an air-fuel mixture supplied to a combustion chamber of each of said plurality of cylinders; a designated fuel injection amount determining section that determines a designated fuel injection amount as a command value of an amount of fuel injected from each of said plurality of fuel injection valves, by feedback-correcting the amount of fuel injected from said each fuel injection valve based on at least an output value of the upstream air-fuel ratio sensor, so that an air-fuel ratio of exhaust gas flowing into the three-way catalyst coincides with a target air-fuel ratio; an injection command signal sending section that sends an injection command signal to said plurality of fuel injection valves so that the fuel is injected from said each fuel injection valve in an amount corresponding to the designated fuel injection amount; an imbalance index value acquiring section that acquires an air-fuel ratio imbalance index value that increases as a degree of ununiformity in the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of each of said plurality of cylinders, among said plurality of cylinders, is larger, based on a value correlated with at least the output value of the upstream air-fuel ratio sensor, each time a given condition is satisfied; and a filtering section that acquires a post-filtering imbalance index value by performing a first-order lag filtering operation on the air-fuel ratio imbalance index value, wherein the filtering section sets a time constant of the filtering operation to a smaller value when a magnitude of a difference between a current value of the air-fuel ratio imbalance index value newly acquired by the imbalance index value acquiring section and the last value of the air-fuel ratio imbalance index value acquired by the imbalance index value acquiring section before the current value is acquired is equal to or larger than a given threshold value, as compared with the case where the magnitude of the difference is smaller than the threshold value.