Exhaust purification system for internal combustion engine

摘要

An exhaust purification system is provided that can decrease the load acting on a device treating PM, even when switched to stoich operation. The exhaust purification system includes: a PM treatment device, a three-way purification catalyst, an LAF sensor, and an ECU (3) that performs feedback control so that an LAF sensor output (Vex) becomes a target value (Vop) determined so that the three-way purification reaction is optimized during stoich operation. The ECU (3) includes a fuel controller (32) that determines a fuel injection amount (Gfuel) so that a state in which an air/fuel ratio of the air/fuel mixture is leaner than stoich and a state richer than stoich are alternately realized by modulating a fuel correction amount (dGfuel) determined so as to cause the LAF sensor output (Vex) to converge to the target value (Vop) by employing a predetermined modulation algorithm.

主权项

1. An exhaust purification system for an internal combustion engine that switches, at a predetermined condition, between lean operation that sets an air/fuel ratio of an air/fuel mixture to a leaner side than stoich and stoich operation that sets the air/fuel ratio of the air/fuel mixture to stoich or the vicinity thereof, the system comprising:
a particulate matter treatment device that is provided in an exhaust channel of the engine and collects particulate matter in exhaust gas; a three-way purification catalyst provided on an upstream side from the particulate matter treatment device in the exhaust channel to be integrated or separate from the particulate matter treatment device, and in which a three-way purification reaction progresses during the stoich operation; an exhaust gas sensor that outputs a detection value according to an oxygen concentration of exhaust gas; and an air/fuel ratio control device that sets an operating mode of the engine to stoich operation under a predetermined operating condition at which setting the operating mode of the engine to stoich operation can improve the NOx purification performance of the exhaust purification system overall over setting to lean operation, and that feedback controls so that a detection value of the exhaust gas sensor becomes a target value established so that a three-way purification reaction in the three-way purification catalyst is optimized, wherein the air/fuel ratio control device includes a fuel controller that determines a fuel amount to supply to the engine so that the air/fuel ratio of the air/fuel mixture becomes leaner than a predetermined period stoich during the stoich operation, wherein the fuel controller determines a fuel amount so that a state in which the air/fuel ratio of the air/fuel mixture is leaner than stoich and a state richer than stoich are alternately realized, by applying a predetermined modulation algorithm to modulate the fuel amount determined so as to cause the detection value of the exhaust gas sensor to converge to the target value based on a predetermined feedback control algorithm.