Air-fuel ratio control system and method and engine control unit for internal combustion engine

An air-fuel ratio control system for an internal combustion engine including a plurality of cylinders, the air fuel ratio control system controlling an amount of fuel to be supplied to each of the cylinders, on a cylinder-by-cylinder basis, to thereby control an air fuel ratio of a mixture supplied to each cylinder,

• the air-fuel ratio control system comprising:
• first operating condition parameter-detecting means for detecting a first operating condition parameter indicative of an operating condition of the engine;
• fuel amount-determining means for determining an amount of fuel to be supplied to each cylinder;
• variation correction coefficient-calculating means for calculating a variation correction coefficient for correcting variation in air-fuel ratio between the plurality of cylinders, on a cylinder-by-cylinder basis;
• learned value-calculating means for calculating a learned value of the variation correction coefficient according to the calculated variation correction coefficient and the detected first operating condition parameter;
• and
• fuel amount-correcting means for correcting the determined amount of fuel to be supplied to each cylinder, according to the calculated learned value of the variation correction coefficient and the calculated variation correction coefficient.

An air-fuel ratio control method for an internal combustion engine including a plurality of cylinders and an exhaust passage through which exhaust gases from the cylinders flow, the air fuel ratio control method including controlling an amount of fuel to be supplied to each of the cylinders, on a cylinder-by-cylinder basis, to thereby control an air fuel ratio of a mixture supplied to each cylinder,

• the air-fuel ratio control method comprising:
• a fuel amount-determining step of determining an amount of fuel to be supplied to each cylinder;
• a correction parameter-determining step of determining a correction parameter for correcting the amount of fuel to be supplied to each cylinder;
• a first fuel amount-correcting step of correcting the determined amount of fuel to be supplied to each cylinder, according to the determined correction parameter;
• an air-fuel ratio parameter-detecting step of detecting an air-fuel ratio parameter indicative of an air-fuel ratio of the exhaust gases flowing through the exhaust passage;
• a variation parameter-calculating step of calculating a variation parameter indicative of a variation in air-fuel ratio between the plurality of parameters, on a cylinder-by-cylinder basis, based on a model parameter of a model formed by modeling each cylinder and having an input of the correction parameter and an output of the air-fuel ratio parameter;
• an identification step of identifying the model parameter of the model based on the determined correction parameter and the detected air-fuel ratio parameter;
• and
• a second fuel amount-correcting step of further correcting the amount of fuel to be supplied to the plurality of cylinders on a cylinder-by-cylinder basis such that the variation parameter calculated on a cylinder-by-cylinder basis converges to a predetermined target value.

An air-fuel ratio control method for an internal combustion engine including a plurality of cylinders, the air fuel ratio control method including controlling an amount of fuel to be supplied to each of the cylinders, on a cylinder-by-cylinder basis, to thereby control an air fuel ratio of a mixture supplied to each cylinder,

• the air-fuel ratio control method comprising:
• a first operating condition parameter-detecting step of detecting a first operating condition parameter indicative of an operating condition of the engine;
• a fuel amount-determining step of determining an amount of fuel to be supplied to each cylinder;
• a variation correction coefficient-calculating step of calculating a variation correction coefficient for correcting variation in air-fuel ratio between the plurality of cylinders, on a cylinder-by-cylinder basis;
• a learned value-calculating step of calculating a learned value of the variation correction coefficient, on a cylinder-by-cylinder basis, according to the calculated variation correction coefficient and the detected first operating condition parameter;
• and
• a fuel amount-correcting step of correcting the determined amount of fuel to be supplied to each cylinder, according to the calculated learned value of the variation correction coefficient and the calculated variation correction coefficient.

An engine control unit including a control program for causing a computer to perform an air-fuel ratio control process for an internal combustion engine including a plurality of cylinders and an exhaust passage through which exhaust gases from the cylinders flow, the air fuel ratio control process including controlling an amount of fuel to be supplied to each of the cylinders, on a cylinder-by-cylinder basis, to thereby control an air fuel ratio of a mixture supplied to each cylinder,

• wherein the program causes the computer to determine an amount of fuel to be supplied to each cylinder, determine a correction parameter for correcting the amount of fuel to be supplied to each cylinder, correct the determined amount of fuel to be supplied to each cylinder, according to the determined correction parameter, detect an air-fuel ratio parameter indicative of an air-fuel ratio of the exhaust gases flowing through the exhaust passage, calculate a variation parameter indicative of a variation in air-fuel ratio between the plurality of parameters, on a cylinder-by-cylinder basis, based on a model parameter of a model formed by modeling each cylinder and having an input of the correction parameter and an output of the air-fuel ratio parameter, identify the model parameter of the model according to the determined correction parameter and the detected air-fuel ratio parameter, and further correct the amount of fuel to be supplied to the plurality of cylinders on a cylinder-by-cylinder basis such that the variation parameter calculated on a cylinder-by-cylinder basis converges to a predetermined target value.