Patent ID: 8137434

Claim:
A method of purifying exhaust gas of an internal combustion engine, the method comprising: acquiring temperature of a particulate filter provided in an exhaust passage of the internal combustion engine for collect in particulate matters; estimating a deposition quantity of the particulate matters in the particulate filter; selecting opening degrees of an intake throttle valve provided an intake passage and an exhaust gas recirculation valve provided in an exhaust gas recirculation passage, through which exhaust gas is recirculated from the exhaust passage to the intake passage, the opening degrees of the intake throttle valve and the exhaust gas recirculation valve being selected from a first opening degree range or a second opening degree range when the acquired temperature is higher than a first predetermined value, the estimated deposition quantity is greater than a second predetermined value, and fuel injection to the internal combustion engine is not performed, and acquiring rotation speed of the internal combustion engine, wherein the first opening degree range is a predetermined opening degree range including the opening degree of the intake throttle valve in a fully-opened state and the opening degree of the exhaust gas recirculation valve in a fully-closed state, the second opening degree range is a predetermined opening degree range including the opening degree of the intake throttle valve in a fully-closed state and the opening degree of the exhaust gas recirculation valve in a fully-opened state, the opening degrees of the intake throttle valve and the exhaust gas recirculation valve are selected from the first opening degree range when the acquired rotation speed is higher than a third predetermined value, the opening degrees of the intake throttle valve and the exhaust gas recirculation valve are selected from the second opening degree range when the acquired rotation speed is lower than the third predetermined value, and the opening degrees of the intake throttle valve and the exhaust gas recirculation valve are selected from the first opening degree range or the second opening degree range such that the temperature of the particulate filter does not exceed desired temperature when regeneration of the particulate filter is performed and the fuel injection is not performed.