| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent deterioration of emissions by appropriately suppressing abnormal air fuel ratios caused by a downstream sensor, in sensors detecting air fuel ratios in an upstream and an downstream exhaust emission control catalyst. SOLUTION: It is detected based on a value of frequency of appearance Lr that output voltage of an O2 sensor existing in a downstream of a catalyst converter slips to a lean side, a control width B is established according to the frequency of appearance Lr (S208) and a plus side guard value dVgrd(+) is established with adding to a learning value DVG of correction amount (S210, S218). Degree of the abnormal condition of the O2 sensor can be reflected on the correction amount by the control width B, and variation of characteristics of an air fuel ratio sensor in the upstream side can be reflected to the plus side guard value sVgrd(+) since the learning value DVG is referred. Consequently, the correction value can be limited in an appropriate range where the degree of abnormal condition of the O2 sensor and variation of characteristics of the air fuel ratio sensor can be absorbed. A target is achieved thereby. COPYRIGHT: (C)2006,JPO&NCIPI
|
