Patent ID: 7243491

Claim:
A method of purifying exhaust gas of an internal combustion engine having a particulate filter disposed in an exhaust passage of the engine, the method comprising: increasing a temperature of the particulate filter; estimating a quantity of particulate matters accumulated in the particulate filter; and controlling the increasing of the temperature of the particulate filter to a target temperature so that the particulate matters accumulated in the particulate filter are combusted and eliminated if the estimated quantity of the particulate matters accumulated in the particulate filter exceeds a predetermined value, wherein controlling the increasing of the temperature of the particulate filter includes estimating the temperature of the particulate filter based on a state of the exhaust gas flowing into the particulate filter, an operating state of the engine and a manipulated variable associated with increasing the temperature, and correcting the manipulated variable based on a result of comparison between the estimated temperature of the particulate filter and the target temperature; and a convergence temperature is calculated, to which the temperature of the particulate filter eventually converges if the present state of the exhaust gas flowing into the particulate filter, the present operating state of the engine and the present manipulated variable are retained for a long time, based on the state of the exhaust gas flowing into the particulate filter, the operating state of the engine and the manipulated variable, and a first temperature estimate is calculated in accordance with a delay in a change of the temperature of the particulate filter due to a heat capacity of the particulate filter.