CYLINDER-BY-CYLINDER AIR-FUEL-RATIO CONTROLLER FOR INTERNAL COMBUSTION ENGINE

摘要

An air-fuel-ratio of each cylinder is estimated based on a detection value of an air-fuel-ratio sensor. An air-fuel-ratio detection timing determination is executed to determine whether a deviation in air-fuel-ratio detection timing exists based on the estimated air-fuel-ratio while the cylinder-by-cylinder air-fuel-ratio control is performed. An observation residual is computed based on the detection value of the air-fuel-ratio sensor and the estimated air-fuel-ratio. When the observation residual is greater than or equal to a specified threshold value, the air-fuel-ratio detection timing determination is prohibited. Therefore, when the observation residual is still large before the estimated air-fuel-ratio of each cylinder is converged, or when the observation residual is still large due to a temporal deterioration in estimating accuracy of the estimated air-fuel-ratio, the air-fuel-ratio detection timing determination can be prohibited.

主权项

1. A cylinder-by-cylinder air-fuel-ratio controller for an internal combustion engine, comprising:
an air-fuel-ratio sensor detecting an air-fuel-ratio of an exhaust gas at a confluent portion into which the exhaust gas flows from each of multiple cylinders of the internal combustion engine; an estimation portion executing an air-fuel-ratio estimation for estimating the air-fuel-ratio of each cylinder based on a detection value which the air-fuel-ratio sensor detects at an air-fuel-ratio detection timing for each cylinder; a control portion executing a cylinder-by-cylinder air-fuel-ratio control in which the air-fuel-ratio of each cylinder is controlled based on the estimated air-fuel-ratio of each cylinder; a determining portion determining whether a deviation in the air-fuel-ratio detection timing exists based on the estimated air-fuel-ratio while the cylinder-by-cylinder air-fuel-ratio control is executed; a correcting portion correcting the air-fuel-ratio detection timing when the determining portion determines that the deviation in the air-fuel-ratio detection timing exists; a residual computing portion computing an observation residual based on the detection value of the air-fuel-ratio sensor and the estimated air-fuel-ratio; and a determination prohibiting portion prohibiting the determining portion from determining whether the deviation in the air-fuel-ratio detection timing exists when the observation residual is greater than or equal to a specified threshold value.