| 摘要 |
<p>The device according to the present invention determines whether the catalytic converter (12) has deteriorated based on the outputs of an upstream air-fuel ratio sensor (13) and a downstream air-fuel ratio sensor (15) only when the flow rate of the intake air is within an allowable flow range. Further, the allowable range is determined in accordance with operating conditions of the engine, for example, the temperature of the catalytic converter. Since the O2 storage capability of the catalytic converter changes in accordance with the temperature of the catalytic converter, different determination results may be obtained for the same catalytic converter if the determination is carried out at different temperature. In this invention, for example, the flow range is selected in accordance with the temperature of the catalytic converter in such a manner that a normal catalytic converter is always determined as being normal and a deteriorated catalytic converter is always determined as being deteriorated. Therefore, in the present invention, the deterioration of the catalytic converter is correctly determined regardless of a change in the operating conditions of the engine. <IMAGE></p> |
