Patent ID: 7048891

Claim:
A catalyst deterioration detecting apparatus for detecting a deteriorated condition of a catalyst placed in a catalyst casing incorporated in an exhaust gas purification system which purifies harmful substances contained in exhaust gas of an engine, said catalyst deterioration detecting apparatus comprising: an upstream exhaust gas temperature sensor which measures an upstream exhaust gas temperature representing a temperature of exhaust gas residing at an upstream side of said catalyst; a downstream exhaust gas temperature sensor which measures a downstream exhaust gas temperature representing a temperature of exhaust gas residing at a downstream side of said catalyst; an engine information detector which detects supplemental engine information other than temperature information obtained from said upstream exhaust gas temperature sensor and said downstream exhaust gas temperature sensor, wherein the supplemental engine information relates to an operation of the engine; a first controller which switches an engine operating condition between a first operation mode and a second operation mode which are discriminable from each other in a concentration of the combustible substances contained in the exhaust gas of the engine to operate the engine in the first operation mode and then operate the engine in the second operation mode; and a second controller which estimates a first heat generation amount per unit flow amount of combustible substances supplied to said catalyst during said first operation mode and also a second heat generation amount per unit flow amount of combustible substances supplied to said catalyst during said second operation mode based on said upstream and downstream exhaust gas temperatures and said supplemental engine information, and which makes a decision that said catalyst is deteriorated when an estimated difference between said first heat generation amount and said second heat generation amount is smaller than a predetermined judging value, wherein said supplemental engine information is an atmospheric or ambient temperature, and each of the first and second heat generation amounts per unit flow amount of combustible substances is obtained based on a first function expression with a variable representing a temperature difference between said upstream exhaust gas temperature and said downstream exhaust gas temperature as well as a second function expression with a variable representing a temperature difference between said upstream or downstream exhaust gas temperature and said atmospheric or ambient temperature.