Patent ID: 6904899

Claim:
An air-fuel ratio controller for an internal-combustion engine, comprising: an upstream-side exhaust gas sensor disposed upstream of a catalyst in an exhaust passageway of the internal-combustion engine; a downstream-side exhaust gas sensor disposed downstream of the catalyst; main feedback means for feeding back an output signal received from said upstream-side exhaust gas sensor into a fuel injection rate so that an air-fuel ratio of the exhaust gases flowing into the catalyst may match a target air-fuel ratio; and sub-feedback means for feeding back the output signal received from said downstream-side exhaust gas sensor into the fuel injection rate so as to complement the feedback control conducted by said main feedback means; wherein said sub-feedback means includes: integral-data calculation means for calculating an integral value of a deviation between a value of the output signal of said downstream-side exhaust gas sensor and a reference value; smoothing means for smoothing the integral-data signal received from said integral-data calculation means; and learning means for learning, from the integral-data signal smoothed, a learning value which compensates for a permanent error included in the output signal of said upstream-side exhaust gas sensor.