Patent ID: 6904355

Claim:
A controller for controlling an air-fuel ratio of an internal-combustion engine, comprising: a first exhaust gas sensor for detecting oxygen concentration of exhaust gas; a first decimation filter connected to the first exhaust gas sensor; and a control unit connected to the first decimation filter, the control unit configured to determine a manipulated variable for manipulating the air-fuel ratio so that an output value from the first decimation filter converges to a target value, wherein the first decimation filter further comprises: a first oversampler for oversampling the output of the first exhaust gas sensor in a shorter cycle than a cycle that is used for determining the manipulated variable; a first low-pass filter for smoothing the oversampled value; and a first downsampler for re-sampling the smoothed value in the cycle that is used for determining the manipulated variable to output the re-sampled value.