If the A performs NOx reduction control, the responsiveness of ensuring that the target air-fuel ratio, so that a sufficient air quantity secured in the high load region satisfactory together thoroughly.
NOx catalyst 41 is disposed An exhaust passage 40 of the engine 1. The boost pressure control valve 29 which is disposed an exhaust turbocharger 23 to the passage to bypass the boost pressure changes are made. The air-fuel ratio of the exhaust gas air amount adjustment for the target air-fuel ratio required for NOx reduction, the row by the air amount adjustment by the provided air quantity control valve 25 of the intake passage 20 or supercharge control valve 29, divide. Control of the air control by the boost pressure control valve 29, on condition that converges after air amount adjustment by the air amount control valve 25 has been performed, or by air control by the air amount control valve 25 in the vicinity of the target air-fuel ratio It is executed.
.FIELD 5