Abstract: An air-fuel ratio control system for an internal combustion engine calculates an amount of fuel to be supplied to the engine in response to the rotational speed of the engine and a parameter indicative of load on the engine, and an amount of fuel injected into an intake passage and adhering to the inner surface of the intake passage, based upon a direct supply ratio and a carry-off ratio. A feedback correction value is set to such a value that an air-fuel ratio in exhaust gases from the engine becomes equal to a desired value, and the amount of fuel calculated as above is corrected by the direct supply ratio, the carry-off ratio, and the feedback correction value set as above. A control speed at which the feedback correction value is corrected is set based upon at least one of the direct supply ratio and the carry-off ratio.

Abstract: A control system for an internal combustion engine controls an amount of auxiliary air supplied to the engine in the following manner: Concentration of evaporative fuel contained in a gas purged from an evaporative emission control system into an intake passage of the engine is calculated based on a purging flow rate estimated based on operating conditions of the engine, and an output from a flowmeter arranged in the evaporative emission control system. A volume of the gas purged over a predetermined time period is calculated based on the output from the flowmeter. A parameter indicative of dynamic characteristics of the gas is calculated based on operating conditions of the engine. An amount of air contained in the purged gas drawn into a combustion chamber of the engine is calculated at least based on the concentration of evaporative fuel, the volume of the purged gas, and the parameter indicative of dynamic characteristics of the gas.