CATALYST DETERIORATION DETERMINATION DEVICE

摘要

PURPOSE:To accurately determine whether or not a catalyst is deteriorated by considering the characteristics of O2 storage ability of the catalyst. CONSTITUTION:A first time measuring means M1 measures the length of time TL between the point of time when an air fuel ratio control means M1 changes the air fuel ratio to the Lean side and the point of time when the output of a downstream side O2 sensor RS changes from Rich to Lean side. A second time measuring means M2 measures the length of time TR between the point of time when the air fuel ratio is changed to the Rich side and the point of time when the output of the downstream side O2, sensor RS changes from Lean to Rich side. A catalyst deterioration means M4 determines whether or not a catalyst is deteriorated when the average of the lengths of time TL and TR is shorter than a specified length of time. The lengths of time TL and TR are successively measured in that order to allow both length of time for the catalyst to absorb O2 and NOx and length of time to absorb CO and HC to be properly considered, so that the O2 storage ability of the catalyst can be accurately detected to allow accurately determining whether or not the catalyst is deteriorated.