Double air-fuel ratio sensor system carrying out learning control operation

Claim 1

A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor; calculating an integration amount of said air-fuel ratio correction amount; calculating a learning correction amount so that the integration amount of said air-fuel ratio correction amount is brought close to a reference value; and adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount, said learning correction amount, and the output of said downstream-side air-fuel ratio sensor; said method further comprising a step of calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor; said air-fuel ratio correction amount calculating step calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameters; wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 2

A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor; calculating an integration amount of said air-fuel ratio correction amount; calculating a learning correction amount so that the integration amount of said air-fuel ratio correction amount is brought close to a reference value; and adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount, said learning correction amount, and the output of said downstream-side air-fuel ratio sensor; said method further comprising a step of calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor; said air-fuel ratio correction amount calculating step calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameters; wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 3

An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising: means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor; means for calculating an integration amount of said air-fuel ratio correction amount; means for calculating a learning correction amount so that the integration amount of said air-fuel ratio correction amount is brought close to a reference value; and means for adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount, said learning correction amount, and the output of said downstream-side air-fuel sensor; said apparatus further comprising means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downsteam-side air-fuel ratio sensor; said air-fuel ratio correction amount calculating means calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped by when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 4

An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a concentration of a specific component in the exhaust gas, comprising: means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor; means for calculating an integration amount of said air-fuel ratio correction amount; means for calculating a learning correction amount so that the integration amount of said air-fuel ratio correction amount is brought close to a reference value; and means for adjusting an actual air-fuel ratio in accordance with said air-fuel ratio correction amount, said learning correction amount, and the output of said downstream-side air-fuel sensor; said apparatus further comprising means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downsteam-side air-fuel ratio sensor; said air-fuel ratio correction amount calculating means calculating said air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; wherein said air-fuel ratio feedback control parameter is defined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped by when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.