Exhaust gas purifier for internal combustion engines

Details Exhaust gas purifier for internal combustion engines Exhaust gas purifier for internal combustion engines

2002-11-18

2004-03-30

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

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

C060S276000, C060S285000, C060S292000

Reexamination Certificate

active

06711892

ABSTRACT:

This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP02/01730 which has an International filing date of Feb. 26, 2002, which designated the United States of America.
TECHNICAL FIELD
The present invention relates to an exhaust emission control device of an internal-combustion engine, and more specifically, to a technique for identifying lowering of the performance of exhaust emission control means capable of reducing harmful substances in exhaust gas.
BACKGROUND ART
An exhaust emission control technique utilizing reaction on a catalyst is known as a technique that is intended to reduce harmful substances (including smoke, NOx, etc. as well as unburned substances such as HC, CO, H
2
, etc.) in exhaust gas.
However, this exhaust emission control technique has a problem that the unburned substances including HC and the like are discharged into the atmosphere before the catalyst in a cold state is activated.
Described in Jpn. Pat. Appln. KOKAI Publications Nos. 3-117611 and 4-183921, therefore, is a developed technique such that the exhaust pressure is raised to activate the catalyst early.
According to this technique, a closed variable-flow valve is provided on the lower-stream side of an exhaust passage, for example. By adjusting the closed variable-flow valve to change the sectional area of the exhaust passage, the exhaust resistance and exhaust density can be increased, or the exhaust flow rate can be lowered to increase the exhaust pressure and exhaust gas temperature.
If the exhaust gas pressure is increased in this manner, individual performances can be enhanced in the cases where unburned substances are fed into an exhaust system (two-stage fuel injection, etc.), EGR (exhaust gas recirculation) is carried out, and exhaust air-fuel ratio modulation (exhaust A/F modulation) is carried out. Thus, reaction of the unburned substances in the exhaust passage including a combustion chamber is accelerated to raise the exhaust gas temperature, so that the catalyst is activated early enough to promote purification of the exhaust gas drastically.
Since the closed variable-flow valve is placed in a high-temperature, high-pressure environment, it sometimes may go wrong and cease to operate normally after prolonged use.
If the valve of the closed variable-flow valve thus ceases to operate normally, the valve may not be able to be closed, so that the actual exhaust pressure fails to rise, although the exhaust pressure is expected to be increased. Otherwise, the valve may be left closed inevitably to keep the exhaust pressure high, although the exhaust pressure is not expected to be increased.
Accordingly, there is an idea of providing an exhaust pressure sensor in the exhaust passage and detecting something abnormal about exhaust control means, such as the closed variable-flow valve, in accordance with exhaust pressure information that is detected by means of the exhaust pressure sensor.
On other hand, exhaust gas that is discharged from a diesel engine that is mounted in a vehicle contains plenty of particulate matter (abbreviated PM) as well as HC, CO, etc. A diesel particulate filter (abbreviated DPF) for capturing the PM and removing it by combustion by means of an external heat source or the like is practically used as a post-exhaust processor of the diesel engine.
Thus, noises and error factors other than the exhaust pressure that are involved in the output signal of the exhaust sensor can be eliminated by obtaining the relations between a plurality of pieces of output information with different exhaust component concentrations (exhaust A/F's) from the exhaust sensor and a plurality of target outputs with the individual exhaust component concentrations (individual exhaust A/F's) under the reference pressure (e.g., atmospheric pressure or the like), e.g., the ratios between the differences between a plurality of exhaust outputs and the differences between a plurality of target outputs. By doing this, the exhaust pressure can be estimated more properly. Lowering of the performance of the exhaust emission control means, which can reduce the harmful substances in the exhaust gas under the given exhaust pressure condition, can be accurately identified by monitoring the relations between the outputs of the exhaust sensor and the target outputs.
The PM captured and deposited on the filter should preferably be removed by combustion to regenerate the filter before the PM capture limit is reached, and the exhaust pressure on the upper-stream side of the post-exhaust processor rises depending on the quantity of the PM deposited on the filter. In consideration of this fact, as is described in Jpn. Pat. Appln. KOKAI Publication No. 8-303290, for example, the exhaust pressure sensor is provided in the exhaust passage on the upper-stream side of the post-exhaust processor so that the PM can be removed by combustion on the assumption that the PM capture limit is approached when a given exhaust pressure is reached by the exhaust pressure that is detected by means of the exhaust pressure sensor.
In the case where the exhaust pressure sensor is used in this manner, however, the exhaust pressure sensor must be provided separately. In general, an exhaust pressure sensor has a specification such that it can resist high temperature and high pressure, it is expensive, and therefore, the parts cost is high.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an exhaust emission control device of an internal-combustion engine, whereby lowering of the performance of exhaust emission control means, which can reduce harmful substances in exhaust gas, can be securely identified at low cost.
In order to achieve the above object, an exhaust emission control device according to the present invention comprises exhaust emission control means located in an exhaust passage of an internal-combustion engine and capable of reducing harmful substances in exhaust gas under a given exhaust pressure condition, an exhaust sensor for detecting the concentration of a specific exhaust component in the exhaust gas, and performance lowering identifying means for identifying lowering of the performance of the exhaust emission control means by detecting a failure to fulfill the given exhaust pressure condition in accordance with the output of the exhaust sensor.
Thus, the exhaust pressure can be estimated in accordance with information from the existing exhaust sensor without separately providing an exhaust pressure sensor, and lowering of the performance of the exhaust emission control means, which can reduce the harmful substances in the exhaust gas under the given exhaust pressure condition, can be securely identified at low cost by monitoring the output of the exhaust sensor and detecting the failure to fulfill the given exhaust pressure condition.
The present invention is based on the following knowledge, which will be described below.
In general, the diffusing speed of each exhaust component increases to raise its partial pressure if the exhaust pressure rises.
On the other hand, the following Nernst formula (1) is generally known as a theoretical formula for an O
2
sensor output in the case where the exhaust sensor is an O
2
sensor, for example.
“Nernst formula”: electromotive force (O
2
sensor output)=(gas constant×operating temperature/(4×Faraday constant)×1 n(atmosphere-side O
2
partial pressure/exhaust-side O
2
partial pressure).  (1)
Here the exhaust-side O
2
partial pressure is given by the following formula (2):
exhaust-side O
2
partial pressure=exhaust pressure×exhaust O
2
concentration.  (2)
This Nernst formula indicates the following phenomenon. If the exhaust pressure increases, the exhaust-side O
2
partial pressure increases to cause the electromotive force (O
2
sensor output) to lower on the high-O
2
lean-A/F side, while the H
2
partial pressure and the exhaust-side O
2
partial pressure increases and reduces, respectively, to cause the electromotive force (O

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