| 摘要 |
PURPOSE: A method for controlling an air-fuel ratio is provided to reduce NOx emissions, catalyst capacity, vehicle weight and costs. CONSTITUTION: A method comprises the first step(S502) of detecting an oxygen sensor output voltage and measuring lean state determination cycle(current duration) of the oxygen sensor; the second step(S504) of detecting lean or rich state of the air-fuel ratio in accordance with the cycle measured in the first step; the third step(S506) of performing an air-fuel ratio control operation, if the air-fuel ratio detected in the second step is at a lean state; the fourth step(S510) of measuring the duration of lean state of the oxygen sensor; the fifth step(S512) of performing a proportional compensation control, if the current duration measured in the first step is longer than the duration of lean state measured in the fourth step; the sixth step(S514,S516) of performing a proportional jump delay control, if the air-fuel ratio is at a lean state when the proportional compensation control is performed; and the seventh step(S520) of outputting an injection time control signal in accordance with the proportional control and proportional jump delay control.
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