Exhaust-gas cleaning devices for engine

Details Exhaust-gas cleaning devices for engine Exhaust-gas cleaning devices for engine

2001-01-17

2002-04-23

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Having sensor or indicator of malfunction, unsafeness, or...

C060S276000, C060S285000, C060S301000

Reexamination Certificate

active

06374596

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to exhaust-gas cleaning devices for an engine installed on a motor vehicle, for example.
Conventionally, the amount of nitrogen oxides (NO
x
) absorbed by a NO
x
-absorbing material is detected for making a judgment on deterioration of the NO
x
-absorbing material which is provided in an exhaust passage. Basically, the amount of NO
x
absorbed by the NO
x
-absorbing material can be determined by examining the concentration of oxygen in exhaust gases that varies as NO
x
released from the NO
x
-absorbing material is reduced. However, since an exhaust-gas converting catalyst, in which the NO
x
-absorbing material is provided, occludes oxygen, it is impossible to say whether a change in the concentration of oxygen is caused by a release of the absorbed NO
x
or by a release of occluded oxygen by just detecting the change in oxygen concentration. It is therefore impossible to accurately determine the amount of the absorbed NO
x.
Under such circumstances, Japanese Unexamined Patent Publication No. 8-260949 proposes a deterioration detecting device for detecting deterioration of a NO
x
-absorbing material provided in an exhaust passage, in which the NO
x
-absorbing material absorbs NO
x
and stores oxygen when the air-fuel ratio of exhaust gas is high (lean exhaust gas), and releases the absorbed NO
x
and stored oxygen when the air-fuel ratio of the exhaust gas becomes low (rich exhaust gas). This deterioration detecting device comprises an air-fuel ratio sensor provided in the exhaust passage, downstream of the NO
x
-absorbing material, for generating an output signal corresponding to the air-fuel ratio of the exhaust gas, an air-fuel ratio switcher which switches the air-fuel ratio of the exhaust gas from a higher value to a lower value when the amount of NO
x
absorbed in the NO
x
-absorbing material is regarded as being almost zero, or more specifically, when the air-fuel ratio has been made high for a short time, and a stored oxygen quantity detector for detecting the amount of oxygen stored in the NO
x
-absorbing material based on the output signal generated by the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas flowing into the NO
x
-absorbing material has been switched from a higher value to a lower value, wherein, after the air-fuel ratio has been made high for a long period by the air-fuel ratio switcher, the sum of the amount of oxygen stored in the NO
x
-absorbing material and the amount of NO
x
absorbed in the NO
x
-absorbing material is determined based on the output signal generated by the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas flowing into the NO
x
-absorbing material has been switched from the higher value to the lower value, and the amount of NO
x
absorbed in the NO
x
-absorbing material is calculated by subtracting the amount of the stored oxygen from the aforementioned sum.
In the deterioration detecting device for detecting deterioration of the NO
x
-absorbing material disclosed in the aforementioned Publication, it is assumed that the period of time required for the NO
x
-absorbing material to store the greatest possible quantity (saturation level) of oxygen is sufficiently short and NO
x
is scarcely absorbed by the NO
x
-absorbing material during this time period. Based on this assumption, the deterioration detecting device of regards a value detected from a change in the air-fuel ratio of the exhaust gas that occurs when the air-fuel ratio is switched to a lower value after once being made high for a short time as being representative of the amount of the stored oxygen, and calculates the amount of NO
x
absorbed in the NO
x
-absorbing material from this detected value and the sum of the amount of the stored oxygen and the amount of NO
x
. Even if the aforementioned time period is short, however, the amount of NO
x
absorbed in the NO
x
-absorbing material is not zero and oxygen is produced when NO
x
released from the NO
x
-absorbing material is reduced. Thus, the deterioration detecting device of the Publication has a problem that its accuracy of judgment on deterioration of the NO
x
-absorbing material inevitably lowers due to errors occurring in detecting the amount of the stored oxygen.
An exhaust-gas cleaning device for an engine in which specific quantities of NO
x
-absorbing material and oxygen-absorbing material are provided in an exhaust passage also has a problem that it becomes impossible to accurately calculate the amount of absorbed NO
x
in a manner disclosed in the aforementioned Patent Publication when the functioning of the oxygen-absorbing material deteriorates.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to provide an exhaust-gas cleaning device for an engine capable to making a judgment on deterioration of a NO
x
-absorbing material with a high degree of accuracy even when a specific quantity of NO
x
-absorbing material and a large quantity of oxygen-absorbing material are provided in an exhaust passage of the engine.
In a principal form of the invention, an exhaust-gas cleaning device for an engine comprises a NO
x
-absorbing material provided in an exhaust passage to absorb NO
x
under oxygen-rich conditions where the oxygen concentration is high and release absorbed NO
x
as the oxygen concentration decreases, an oxygen-absorbing material provided in the exhaust passage to absorb oxygen under oxygen-rich conditions where the oxygen concentration is high and release absorbed oxygen as the oxygen concentration decreases, an oxygen concentration controller for controlling the oxygen concentration in the exhaust passage, an oxygen concentration detector provided downstream of the NO
x
-absorbing material and the oxygen-absorbing material, an absorption quantity detector which determines a first amount of absorption of NO
x
and oxygen absorbed by the NO
x
-absorbing material and the oxygen-absorbing material based on a sensing signal fed from the oxygen concentration detector at a time when the oxygen concentration upstream of the NO
x
-absorbing material and the oxygen-absorbing material is just transferred from a high concentration state maintained for a preset first reference time to a low concentration state by controlling the oxygen concentration with the oxygen concentration controller, and determines a second amount of absorption of NO
x
and oxygen absorbed by the NO
x
-absorbing material and the oxygen-absorbing material based on a sensing signal fed from the oxygen concentration detector at a time when the oxygen concentration upstream of the NO
x
-absorbing material and the oxygen-absorbing material is just transferred from the high concentration state maintained for a preset second reference time which is longer than the first reference time to the low concentration state by controlling the oxygen concentration with the oxygen concentration controller, a NO
x
quantity estimator which obtains a first estimated value of the amount of NO
x
absorbed by the NO
x
-absorbing material during the first reference time and a second estimated value of the amount of NO
x
absorbed by the NO
x
-absorbing material during the second reference time in accordance with engine operating condition, and a deterioration detector which makes a judgment on deterioration of the NO
x
-absorbing material based on the first amount of absorption and the second amount of absorption of NO
x
and oxygen determined by the absorption quantity detector and the first estimated value and the second estimated value of the amount of absorbed NO
x
obtained by the NO
x
quantity estimator.
In the exhaust-gas cleaning device thus constructed, the judgment on deterioration of the NO
x
-absorbing material is made based on the first and the second amounts of absorption of NO
x
and oxygen determined by the absorption quantity detector and the first and the second estimated values of the amount of absorbed NO
x
obtained by the NO
x
quantity estimator. It is therefore possible to perform the deterioration j

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