Patent ID: 7010907

Claim:
An exhaust gas cleanup device of an internal combustion engine ( 100 ) which is provided with an NO x absorbing reduction catalyst ( 2 ) in an exhaust gas passage ( 1 ), the exhaust gas cleanup device thereof comprising: an oxygen sensor ( 3 ) which is mounted downstream of the NO x absorbing reduction catalyst ( 2 ) in the exhaust gas passage ( 1 ); a determination means for determining a condition of deterioration of the NO x absorbing reduction catalyst ( 2 ) on a basis of a time length, during which a voltage value, having a small amount of variation before the voltage value outputted from the oxygen sensor ( 3 ) is recorded as a maximum value when a rich-spike is executed, is recorded: an exhaust gas flow rate detecting means; an NO x density detecting means for detecting density of NO x in an exhaust gas; a temperature sensor ( 15 ) for detecting a temperature of the NO x absorbing reduction catalyst ( 2 ); and a calculating means for calculating amount of NO x flowing in the NO x absorbing reduction catalyst ( 2 ) per unit time, from an exhaust gas flow rate detected by the exhaust gas flow rate detecting means and from an NO x density detected by the NO x density detecting means, wherein a possible NO x absorbing capacity of the NO x absorbing reduction catalyst ( 2 ) is estimated by the temperature sensor ( 15 ), and wherein the NO x absorbing reduction catalyst ( 2 ) is recovered when an accumulated amount of NO x flowing in the NO x absorbing reduction catalyst ( 2 ) reaches a possible absorbing amount.