Patent ID: 6935099

Claim:
A method of evaluating a deteriorated state of an exhaust gas purifier disposed in an exhaust passage of an internal combustion engine and having a hydrocarbon adsorbent for adsorbing hydrocarbons in an exhaust gas flowing through the exhaust passage, comprising the steps of: sequentially generating a deterioration evaluating parameter representative of an integrated amount of moisture that is supplied to said hydrocarbon adsorbent by said exhaust gas, after said internal combustion engine has started to operate; and sequentially searching for a state in which a humidity downstream of said hydrocarbon adsorbent takes a minimum value, and detecting a changing timing at which said humidity changes from the state in which the humidity takes a minimum value to a monotonously increasing state; wherein a deteriorated state of said hydrocarbon adsorbent is evaluated based on the value of the deterioration evaluating parameter at said changing timing.