To allow detection even in occurrence of a phenomenon that output of a rear air-fuel ratio sensor repeats rich and lean in short cycles.
A controller comprises a means (6) for estimating an oxygen storage amount based on an output of a front air-fuel ratio sensor (4) and for controlling an air-fuel ratio so that an estimation value of the oxygen storage amount agrees with a target value, a means (6) for calculating an area as a first area by integrating values subtracted the oxygen storage amount estimation values from a maximum value of the oxygen storage amount when the output of the rear air fuel ratio sensor keeps lean and for calculating an area as a second area by integrating values subtracted a minimum value of the oxygen storage amount from the oxygen storage amount estimation values when the output of the rear air-fuel ratio sensor keeps rich and a means (6) for compensating a stochiometric point of the front air-fuel sensor (4) toward a lean side based on the first area and the second area when the stochiometric point of the front air-fuel sensor is lean-shifted.
COPYRIGHT: (C)2006,JPO&NCIPI
| JP6357842A | ||||
| JP200313792A |
Yoshio Matsuda
Yasunari Mita
Masaaki Iida