Patent ID: 7313913

Claim:
A method of purifying gas in an internal combustion engine, the method comprising: disposing a particulate filter in an exhaust pipe of the engine; estimating a quantity of particulate matters deposited on the particulate filter; increasing temperature of the particulate filter; and controlling regeneration by controlling the increasing of the temperature of the particulate filter to combust and to eliminate the particulate matters deposited on the particulate filter so that the particulate filter is regenerated, wherein controlling the regeneration includes: determining execution and stoppage of the regeneration of the particulate filter based on the estimated quantity of the particulate matters; controlling the increasing of the temperature of the particulate filter to increase the temperature of the particulate filter to a target temperature based on the determination of the execution and stoppage of the regeneration of the particulate filter; and controlling an exhaust gas flow rate by controlling an intake air quantity to a target intake air quantity decided for each operating condition to control a flow rate of exhaust gas passing through the particulate filter when the temperature of the particulate filter is controlled to the target temperature based on the determination of the execution and stoppage of the regeneration of the particulate filter, whereby deviation of the temperature of the particulate filter from the target temperature due to a change in the flow rate of the exhaust gas passing through the particulate filter corresponding to the operating condition is inhibited; wherein the controlling of the exhaust gas flow rate by controlling the intake air quantity is provided by a first intake air quantity controller which reduces the target intake quantity compared to the target intake quantity used in a non-regeneration period, in which the regeneration is not performed, to reduce the intake air quantity from a value corresponding to the same operating condition in the non-regeneration period immediately after the execution of the regeneration is started in the case where the execution of the regeneration is determined, whereby the first intake air quantity controller reduces a heat amount released to the exhaust gas passing through the particulate filter and maintains the temperature of the particulate filter at high temperature near the target temperature; an exhaust gas recirculation control valve is disposed in an exhaust gas recirculation passage, through which part of the exhaust gas is recirculated into an intake pipe of the engine, for regulating a quantity of the recirculated exhaust gas; and the first intake air quantity controller reduces the intake air quantity by operating the exhaust gas recirculation control valve so that the quantity of the exhaust gas recirculated into the intake pipe is increased from a value corresponding to the same operating condition in the non-regeneration period.