EXHAUST GAS PURIFIER OF INTERNAL COMBUSTION ENGINE, ENHANCING EXHAUST GAS PURIFICATION EFFICIENCY BY THREE-WAY CATALYST

摘要

PURPOSE: An exhaust gas purifier of an internal combustion engine is provided to keep the exhaust gas purification efficiency high by reliably suppressing occurrence of NOx spike or HC, CO spike. CONSTITUTION: An exhaust gas purifier of an internal combustion engine(1) has a three-way catalyst(30) having an oxygen capture function capturing oxygen and a reducing agent capture function capturing a reducing agent; an air fuel ratio modulation unit modulating an exhaust air fuel ratio flowing into the three-way catalyst between a lean air fuel ratio and a rich air fuel ratio; an oxygen capture rate estimation unit estimating the oxygen capture rate by the oxygen capture function; a reducing agent capture rate estimation unit estimating the reducing agent capture rate by the reducing agent capture function; and an air fuel ratio modulation control unit. The three-way catalyst is arranged to an exhaust passage(20) of the internal combustion engine. The air fuel ratio modulation control unit makes the lean time of the exhaust air fuel ratio longer than the time wherein the corresponding oxygen capture rate exceeds a first predetermined value or makes the lean degree high when the oxygen capture rate estimated by the oxygen capture rate estimation unit is under the first predetermined value. The fuel ratio modulation control unit makes the rich time of the exhaust air fuel ratio longer than the time wherein the corresponding reducing agent capture rate exceeds a second predetermined value or makes the rich degree high when the reducing agent capture rate estimated by the reducing agent capture rate estimation unit is under the second predetermined value.