| 摘要 |
<P>PROBLEM TO BE SOLVED: To allow diagnosis of a degradation state of a catalyst, during traveling including general road traveling with many acceleration/deceleration operations at middle and low speeds without a steep increase in costs. <P>SOLUTION: In a method for diagnosing degradation of a catalyst by providing oxygen sensors at an upstream (front) side and a downstream (rear) side of the catalyst in an exhaust passage of an internal combustion engine provided with a ternary catalyst and by comparing standard dispersion conditions of oxygen concentration variation values in exhaust gas detected at the upstream side and the downstream side of the catalyst. When it is determined that a reaction atmosphere of at least a catalyst layer is in an air-fuel ratio rich state, a standard deviation indicating the standard dispersion conditions of the oxygen concentration variation values at the upstream side and the downstream side of the catalyst in the exhaust passage is calculated on the basis of oxygen concentration signals output from the upstream and downstream oxygen sensors, and a catalyst degradation index value (IDX) is calculated from the calculated standard deviation and compared with a threshold to be a measure of a failure provided for the catalyst degradation index value to thereby diagnose the degradation of the catalyst. <P>COPYRIGHT: (C)2013,JPO&INPIT |
