Exhaust emission control system for internal combustion engine

Details Exhaust emission control system for internal combustion engine Exhaust emission control system for internal combustion engine

1999-03-16

2001-04-17

Hoang, Tu Ba (Department: 3742)

Power plants

Internal combustion engine with treatment or handling of...

Having means analyzing composition of exhaust gas

C060S274000, C123S399000

Reexamination Certificate

active

06216450

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to improvements in an exhaust emission control system for an internal combustion engine, more particularly to an exhaust emission control system provided with a NOx storage type three-way catalyst.
A Japanese Patent Provisional Publication No. 6-129246 discloses an exhaust emission control apparatus which is arranged to store NOx when an engine is operated on an air-fuel mixture having a air-fuel ratio leaner than a stoichiometric ratio (lean operation) and to release the stored NOx when the air-fuel ratio of the mixture becomes richer than the stoichiometric ratio (rich operation). Further, the conventional apparatus is arranged to periodically execute a rich-spike treatment that temporally varies the air-fuel ratio of the mixture into a richer ratio as compared with the stoichiometric ratio to release the stored NOx and to purify the released NOx by means of HC and CO, which increases in volume during the rich operation and function as a reduction agent.
SUMMARY OF THE INVENTION
However, the NOx storage type three-way catalyst will lower its NOx storage capacity according to its aging. In case the NOx storage capacity is lowered, surplus NOx leaks out. In such a case, when the rich-spike treatment is executed in the traditional way, the supply amount of HC and CO to the NOx storage type three-way catalyst becomes excessive, so that the amount of HC and CO emitted increase. Therefore, it is necessary to diagnose the NOx storage capacity. Furthermore, it is preferable to diagnose an oxygen storage capacity of the NOx storage type three-way catalyst in addition to the NOx storage capacity in order to diagnose efficiency to convert all of HC, CO and NOx.
It is an object of the present invention to provide an improved exhaust emission control system which diagnoses NOx storage capacity and/or oxygen storage capacity of a NOx storage type three-way catalyst installed in the exhaust emission control system for an internal combustion engine.
An exhaust emission control system according to the present invention is for an internal combustion engine and comprises a NOx storage type three-way catalyst, an A/F sensor a fuel injector and a control unit. The NOx storage type three-way catalyst is disposed in an exhaust passage of the engine and functions to store NOx of exhaust gases when air air-fuel ratio of air-fuel mixture supplied to the engine is leaner than a stoichiometric ratio and to release and reduce NOx when the air-fuel ratio of the air-fuel mixture is richer than or equal to the stoichiometric ratio. The A/F sensor is disposed downstream of the NOx storage type three-way catalyst in the exhaust passage of the engine. The A/F sensor detects an air fuel ratio of the exhaust gases passed through the NOx storage type three-way catalyst. The fuel injector injects a quantity of fuel to a cylinder of the engine according to an injection signal. The control unit is arranged to calculate a quantity of fuel to said cylinder to bring an air-fuel ratio of the air-fuel mixture close to a target ratio and to output an injection signal to said fuel injector based on the calculated quantity of fuel, to execute a rich-spike treatment of temporally enriching the air-fuel ratio of the air-fuel mixture by adjusting the injection signal to the fuel injector, and to diagnose a NOx storage capacity of the NOx storage type three-way catalyst on the basis of the calculated air-fuel ratio during the rich-spike treatment.


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patent: 6-129246 (1994-05-01), None

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