Apparatus for estimating air-fuel ratios and apparatus for controlling air-fuel ratios of individual cylinders in internal combustion engine

An individual-cylinder air-fuel ratio estimation apparatus for an internal combustion engine, comprising:

• an air-fuel ratio sensor which is installed in a confluent exhaust pipe with exhaust manifolds of a plurality of cylinders of the internal combustion engine connected thereto, and which detects an air-fuel ratio of gases exhausted from the individual cylinders and mixed at a confluence;
• and
• an individual-cylinder air-fuel ratio estimation circuitry for estimating individual-cylinder air-fuel ratios of the individual cylinders having exhausted the gases, on the basis of the air-fuel ratio of the mixed gas as detected by the air-fuel ratio sensor;
• the individual-cylinder air-fuel ratio estimation circuitry causing influences, which are ascribable to combustion intervals of the adjacent combustion cylinders, to be reflected on the estimation values of the individual-cylinder air-fuel ratios:
• wherein the individual-cylinder air-fuel ratio estimation circuitry considers mixing of the gases exhausted from the adjacent combustion cylinders, and a movement by which the mixed gas arrives at a position of the air-fuel ratio sensor, as the influences ascribable to the combustion intervals;
• and
• the individual-cylinder air-fuel ratio estimation circuitry considers either of a distance and a volume from the confluence of the gases of the individual combustion cylinders to the position of the air-fuel ratio sensor, and exhaust gas quantities of the respective combustion cylinders in evaluating a movement by which the mixed gas arrives at a position of the air-fuel ratio sensor.

An individual-cylinder air-fuel ratio control apparatus for an internal combustion engine including a plurality of cylinder groups, comprising:

• an air-fuel ratio sensor which is installed in a confluent exhaust pipe with exhaust manifolds of a plurality of cylinders in one of the cylinder groups of the internal combustion engine connected thereto, and which detects an air-fuel ratio of gases exhausted from the individual cylinders in the one of the cylinder groups and mixed at a confluence;
• an individual-cylinder air-fuel ratio estimation circuitry for estimating air-fuel ratios of the individual cylinders having exhausted the gases, on the basis of the air-fuel ratio of the mixed gas as detected by the air-fuel ratio sensor, the individual-cylinder air-fuel ratio estimation circuitry causing influences, which are ascribable to intervals of the adjacent combustion cylinders, to be reflected on the estimation values of the individual-cylinder air-fuel ratios, wherein a plurality of combustion intervals between adjacent combustion cylinders in at least the one of the cylinder groups are established;
• and
• an individual-cylinder air-fuel ratio control circuitry for controlling the air-fuel ratios of the individual cylinders in a direction of decreasing an inter-cylinder dispersion of the individual-cylinder air-fuel ratios estimated by the individual-cylinder air-fuel ratio estimation apparatus.