DIAGNOSTIC DEVICE FOR DETERIORATION IN NOx STORAGE REDUCTION CATALYST

To provide a diagnostic device for deterioration in an NOx storage reduction catalyst, having high diagnostic accuracy.SOLUTION: A deterioration diagnostic device comprises: an intake air amount detection device detecting an intake air amount to an internal combustion engine; an exhaust gas temperature detection device detecting a temperature of an exhaust gas flowing in the NOx storage reduction catalyst; a NOx removal rate detection device detecting NOx of the exhaust gas flowing into the NOx storage reduction catalyst and the exhaust gas flowing out from the NOx storage reduction catalyst to detect a NOx removal rate; and a diagnostic device calculating difference in the NOx removal rates before and after temperature rise of the NOx storage reduction catalyst when a temperature of the exhaust gas flowing in the NOx storage reduction catalyst rises, and a temperature of the NOx storage reduction catalyst is increased to be more than a first prescribed threshold value following increase of a flow rate of the intake air amount of the internal combustion engine, and diagnoses the deterioration of the NOx storage reduction catalyst when the difference in the NOx removal rates is more than a second prescribed threshold value.SELECTED DRAWING: Figure 5 【課題】診断精度の高い、ＮＯｘ吸蔵還元触媒の劣化診断装置を提供する。【解決手段】前記内燃機関への吸入空気量を検出する吸入空気量検出装置と、前記ＮＯｘ吸蔵還元触媒を流通する排ガスの温度を検出する排ガス温度検出装置と、前記ＮＯｘ吸蔵還元触媒に流入する排ガス及び前記ＮＯｘ吸蔵還元触媒から流出する排ガスのＮＯｘを検出し、それによってＮＯｘ浄化率を検出する、ＮＯｘ浄化率検出装置と、前記内燃機関への前記吸入空気量の流量の増加に続いて、前記ＮＯｘ吸蔵還元触媒を流通する排ガスの前記温度が上昇し、それによって前記ＮＯｘ吸蔵還元触媒の温度が第一の所定の閾値よりも大きく上昇するときに、このＮＯｘ吸蔵還元触媒の温度の上昇の前後の前記ＮＯｘ浄化率の差を算出し、このＮＯｘ浄化率の差が第二の所定の閾値よりも大きい場合に、前記ＮＯｘ吸蔵還元触媒が劣化していると診断する診断装置とを備える劣化診断装置。【選択図】図５