| 摘要 |
PROBLEM TO BE SOLVED: To improve exhaust emission by improving controllability of an air- fuel ratio feedback control when intake air quantity of an engine is large. SOLUTION: Upper and lower slice levels RSLH, RSLL are set (S11) on the basis of the intake air quantity Qa and heightened as in a larger air intake quantity region. Output voltage RVO2 of an O2 sensor and the upper side slice level RSLH or the lower side slice level RSLL are compared (S14, S21) and I part correction values IL, IR and P part correction values PR. PL are set (S16, S23, S19, S26) on the basis of the intake air quantity Qa according to the comparison. In the larger air intake quantity region, the P part and the I part are set larger while in the smaller air intake quantity region, the P part and the I part are set smaller. Thereby, a target air-fuel ratio is made rich in the large air intake quantity region and an excess increase of combustion temperature is prevented, and accordingly NOx exhaust quantity is restricted and the exhaust emission is improved by enabling an optimal feedback control corresponding to responsiveness of the O2 sensor.
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