| 摘要 |
<p>PURPOSE:To detect the deterioration of catalyst in a state that an air-fuel ratio is stabilized by setting a delay in the execution of a diagnosis delay means when engine operations are judged to be in a satisfactory setting condition for catalyst deterioration diagnosis. CONSTITUTION:In a double air fuel ratio sensor system wherein air-fuel ratio sensors such as an O2 sensor and the like are provided for the upstream and downstream sides of catalyst purifying exhaust gas respectively, and dispersion in the output characteristics of the sensor at the upstream side is compensated by the sensor at the downstream side so that aggravation in detection accuracy due to the output characteristics of a single air-fuel ratio sensor is improved. A catalyst deterioration detecting device is provided with an operation condition judging means which judges whether or not engine operation conditions are in a satisfactory condition for catalyst deterioration diagnosis which detects the deterioration of catalyst based on at least, the output of a second air-fuel ratio sensor. And when the engine operating conditions are judged to be in a set condition satisfactory for the diagnosis of catalyst deterioration, a diagnosis delay means M2 is provided, which sets up delay in the execution of catalyst deterioration diagnosis.</p> |
