Control system for internal combustion engine

摘要

A control system for an internal combustion engine having an intake air amount regulating device and a fuel supply device. The control system comprises a device for detecting an engine operating condition of the engine, and a control unit. The control unit is configured to perform (a) calculating a basic fuel supply amount of fuel to be supplied to a combustion chamber of the engine in accordance with the engine operating; (b) calculating a lean limit air-fuel ratio in accordance with the engine operating condition, stable combustion in the combustion chamber being impossible at the air-fuel ratio leaner than the lean limit air-fuel ratio; (c) calculating a target intake air amount of intake air to be supplied to the combustion chamber, required for meeting the basic fuel supply amount and the lean limit air-fuel ratio; (d) controlling the intake air amount regulating device so as to regulate an intake air amount of the intake air to the target intake air amount and controlling the fuel supply device so as to regulate a fuel supply amount of the fuel to realize the lean limit air-fuel ratio, within a first engine operating condition (such an engine idling condition) which is within a predetermined low range in engine speed and in engine load; and (e) controlling the intake air amount regulating device so as to increase the intake air amount to fall within a high range between the maximum level and a level lower a predetermined amount than the maximum level and controlling fuel supply device so as to supply the fuel such that the air-fuel ratio falls within a predetermined range, within a second engine operating condition which is higher in at least one of engine speed and engine load than the first engine operating condition.