| 摘要 |
<P>PROBLEM TO BE SOLVED: To secure sufficient S/N of an extraction signal using a bandpass filter treatment with a relatively wide passband, to accurately determine a fault of an air-fuel ratio control system in a short time. <P>SOLUTION: This air-fuel ratio control device for an internal combustion engine performs air-fuel ratio oscillation control which oscillates the air-fuel ratio at a frequency f1. A first difference is calculated indicative of a difference between the present value of a detected equivalent ratio during the air-fuel ratio oscillation control and a past value thereof before a first discrete retardation time set to attenuate a 0.5 order frequency component. A bandpass filter treatment and an integration calculation are applied to the first difference to calculate the intensity of the component of the frequency f1. A second difference is calculated indicative of the difference between the present value of the detected equivalent ratio and the past value thereof before a second discrete retardation time set to attenuate the component of the frequency f1. A bandpass filter treatment and an integration calculation are applied to the second difference to calculate the intensity of the 0.5 order frequency component. Based on the intensity of the component of the frequency f1 and the intensity of the 0.5 order frequency component, the air-fuel control system is determined to be imbalance or not. <P>COPYRIGHT: (C)2013,JPO&INPIT |
