Patent ID: 8322131

Claim:
An internal combustion engine exhaust gas cleaning apparatus comprising: a NOx trapping catalytic converter arranged in an exhaust passage to trap NOx contained in an exhaust gas flowing through the exhaust passage when an air-fuel ratio of the exhaust gas is lean and to release trapped NOx when the air-fuel ratio of the exhaust gas is rich; and an engine control unit in combination with a control program which when executed: estimates an estimated sulfur poisoning amount of sulfur poisoning of the NOx trapping catalytic converter based on a fuel consumption amount, an oil consumption amount, a concentration of sulfur in the fuel, and a concentration of sulfur in the oil, raises a temperature of the NOx trapping catalytic converter to a sulfur poisoning removal temperature based on the estimated sulfur poisoning amount to remove sulfur poisoning from the NOx trapping catalytic converter, executes a sulfur poisoning removal operation each time the estimated sulfur poisoning amount reaches a prescribed threshold value, with the prescribed threshold value being changed depending on a sulfur ratio of an estimated amount of sulfur coming from oil to the estimated sulfur poisoning amount in the NOx trapping catalytic converter.