CATALYST DETERIORATION DIAGNOSIS DEVICE

To provide a catalyst deterioration diagnosis device which can detect an abnormality of a catalyst while suppressing the deterioration of emission.SOLUTION: A catalyst deterioration diagnosis device for diagnosing the deterioration of a catalyst which is arranged in an exhaust passage of an internal combustion engine comprises: measurement means for controlling an air-fuel ratio to a rich side after a finish of a fuel cut of the internal combustion engine, and measuring a discharge oxygen amount from the catalyst; fuel cut immediately-after rich control means for controlling the air-fuel ratio to the rich side after the finish of the fuel cut; and a front-side catalyst sensor and a rear-side catalyst sensor arranged at points ahead of and behind the catalyst in the exhaust passage, and measuring the air-fuel ratios. When it is determined that a discharge oxygen amount measured by the measurement means is equal to or smaller than a second discharge oxygen value which is smaller than a first discharge oxygen value at which the rear-side catalyst sensor determines the airflow to be rich after the front-side catalyst sensor determines the air-fuel ratio to be rich, and also when it is determined that the air-fuel ratio is rich by the rear-side catalyst sensor, the catalyst deterioration diagnosis device determines that an abnormality occurs at the catalyst.SELECTED DRAWING: Figure 2 【課題】エミッション悪化を抑制しつつ、触媒の異常検知を行うことができる触媒劣化診断装置を提供すること。【解決手段】内燃機関の排気通路に配置された触媒の劣化を診断する触媒劣化診断装置であって、内燃機関におけるフューエルカットの終了後から空燃比をリッチに制御し、触媒からの放出酸素量を計測する計測手段と、フューエルカットの終了時から空燃比をリッチに制御するフューエルカット直後リッチ制御手段と、排気通路における触媒の前後のそれぞれに設けられ、空燃比を測定するための触媒前センサ及び触媒後センサと、を備え、触媒前センサがリッチと判定されてから、計測手段により計測された放出酸素量が、触媒後センサがリッチと判定される第１放出酸素値よりも小さい第２放出酸素値以下であって、且つ、触媒後センサによってリッチと判定された場合に、触媒に異常が生じていると判定する。【選択図】図２