Patent ID: 7195008

Claim:
A cylinder-by-cylinder air-fuel ratio controller for an internal combustion engine, comprising: a cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder based on a value detected by an air-fuel ratio sensor every air-fuel ratio detecting timings of each cylinder, the air-fuel ratio sensor being disposed in a confluent portion into which exhaust gas flows from each cylinder; a cylinder-by-cylinder air-fuel ratio control means for executing a cylinder-by-cylinder air-fuel ratio control in which a fuel injection quantity of each cylinder is corrected based on the estimated air-fuel ratio to decrease a dispersion of the air-fuel ratio between cylinders; a learning means for learning an appropriate value of the air-fuel ratio detecting timing or a deviation from the appropriate value; and a detected timing correction means for correcting the deviation of the air-fuel ratio detecting timing based on a value learned by the learning means during the cylinder-by-cylinder air-fuel ratio control, wherein the learning means forcibly changes the fuel injection quantity of each cylinder during a learning period, and the learning means learns the air-fuel ratio detecting timing based on the estimated air-fuel ratio and the fuel injection quantity, which are calculated based on the value detected by the air-fuel ratio sensor at the air-fuel ratio detecting timing at which an effect due to a change of the fuel injection quantity is arisen.