Exhaust gas purifying apparatus and control method therefor

Details Exhaust gas purifying apparatus and control method therefor Exhaust gas purifying apparatus and control method therefor

1999-04-26

2001-04-17

Hoang, Tu Ba (Department: 3742)

Power plants

Internal combustion engine with treatment or handling of...

Material from exhaust structure fed to engine intake

C060S285000, C123S305000

Reexamination Certificate

active

06216452

ABSTRACT:

BACK GROUND OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for removing a nitrogen oxide (NOx) contained in exhaust gases form an internal combustion engine of an automobile or the like to prevent a public hazard.
As measures for public hazard of automobiles, exhaust gas recirculation (hereinafter, referred to as “EGR”) is to extract a part (such as N
2
, H
2
, O, CO
2
) of exhaust gases and recirculate it to an intake system thereby increasing a thermal capacity and reduce the nitrogen oxide (NOx) during acceleration of the engine.
Recently, control of reflux rate or EGR rate “(reflux amount)/(new air amount to cylinder)” for reducing a nitrogen oxide (NOx) has been performed on the basis of conditions of an engine rpm (revolution per minute) and an engine load.
For measuring a nitrogen oxide (NOx) contained exhaust gases of an internal combustion engine, a chemical light emitting method defined in JIS K 0104, JIS B 7982 or the like has been heretofore used. In the chemical light emitting method, concentration of the nitrogen oxide (NOx) is measured by intensity of radiation ray of a light generated by reaction between nitrogen oxide (NO) and ozone. The method is suitable for measuring the instantaneous concentration of the nitrogen oxide (NOx). However, for measuring the total released amount of the nitrogen oxide (NOx) for a long period, it is necessary to always measure the concentration of the nitrogen oxide (NOx) and to total the measured values. Because of this, a nitrogen oxide sensor using the chemical light emitting method is not suitable for controlling the total of the nitrogen oxide (NOx) discharged from the internal combustion engine. Further, in case a catalyst for removing the nitrogen oxide (NOx) is provided on a vehicle, it is necessary to always check activity of the catalyst and replace the catalyst when the activity is deteriorated.
According to a recent report of study, a perobuskite type composite oxide is an oxide semi-conductor and has promised as a detection element of a nitrogen oxide sensor. However, the perobuskite type composite oxide is high in sensitivity with respect to nitrogen dioxide (NO
2
) but is low in sensitivity with respect to nitrogen oxide (NO) occupying a major portion of the nitrogen oxide (NOx) in the exhaust gases.
Incidentally, the nitrogen oxide (NOx) generates in the vicinity of the maximum temperature of combustion in a combustion chamber, and is contemplated to be discharged without being resolved in the expansion stroke or the expansion process. Concentration of the nitrogen oxide (NOx) is related to the maximum temperature of the combustion chamber, and the higher maximum temperature of the combustion chamber is, the more the nitrogen oxide (NOx) exits. Accordingly, it is necessary to lower the maximum temperature in order to reduce the nitrogen oxide (NOx). However, when the maximum temperature is lowered, energy of fuel is suppressed, the reduction of fuel cost or specific fuel consumption is impeded. From a viewpoint of such circumstances, there has posed such a problem that control of cutting down the nitrogen oxide (NOx) and also reducing specific fuel consumption was difficult.
In view of the aforementioned problem, it is the first object of the present invention to provide an exhaust gas purifying apparatus capable of reducing the nitrogen oxide (NOx) in the whole running region determined by the engine rpm and the engine load.
It is the second object of the present invention to provide a control method of the exhaust gas purifying apparatus, capable of coexisting the reduction of the nitrogen oxide (NOx) and the reduction of specific fuel consumption by performing elaborate control of EGR rate.
It is the third object of the present invention to provide a nitrogen oxide sensor exhibiting a high sensitivity in detection of the nitrogen oxide (NOx), particularly, the nitrogen oxide (NO) contained in the exhaust gases of the internal combustion engine, and enabling a integrating measurement of the amount of the nitrogen oxide (NOx).
SUMMARY OF THE INVENTION
For accomplishing the aforementioned objects, the present invention provides an exhaust gas purifying apparatus comprising an EGR valve disposed on a reflux pipe connecting a exhaust pipe to a intake pipe, a nitrogen oxide purifying catalyst part or section formed by a brown miralite type composite oxide, a pair of electrodes provided on or in the vicinity of the opposite ends of the purifying catalyst part or section, a conductivity measuring section for measuring conductivity of a nitrogen oxide catalyst of the nitrogen oxide purifying catalyst part or section through the electrodes, and a control portion or section for controlling an opening degree of the EGR valve on the basis of at least one of the engine rpm, the engine load, and the conductivity measured on the conductivity measuring section.
Further, the present invention provides a nitrogen oxide sensor comprising a detection element using a brown miralite type composite oxide, a pair of metal electrodes placed in close contact with the opposite ends of the detection element, and a pair of terminal conductors formed of the same kind of metal joined to the metal electrodes.
According to the present invention it is possible to resolve the nitrogen oxide (NO) by using the brown miralite type composite oxide, whereby the nitrogen oxide (NOx) concentration can be cut down from the exhaust gases and also the change of the nitrogen oxide (NOx) concentration can be known. It is therefore possible to control the opening degree of the EGR valve so as to reduce the specific fuel consumption corresponding to the nitrogen oxide (NOx) concentration. For example, in case the nitrogen oxide (NOx) concentration is low, as the nitrogen oxide (NOx) is sufficiently removed, then the opening degree is made to be narrowed in order to reduce specific fuel consumption; in case the nitrogen oxide (NOx) concentration is high, as the nitrogen oxide (NOx) is not sufficiently removed, then the opening degree of the EGR valve is made to be widened in order to cut down the nitrogen oxide (NOx) so as to achieve a reference target value; and in case the nitrogen oxide (NOx) concentration matches to a reference amount, the opening degree of the EGR valve is controlled to maintain the state.
Here, the “brown miralite type composite oxide” brings forth a phase transition at a high temperature to produce a shortage of oxygen to function as a nitrogen oxide catalyst which adsorbs the nitrogen oxide (NO) and resolve it into nitrogen (N
2
) and oxigen (O
2
). Further, the brown miralite type composite oxide has such properties that when the nitrogen oxide (NOx) particles are adsorbed on the surface, a shortage of oxygen occurs, and the quantity of holes is reduced to change the conductivity. This change can be utilized to detect the nitrogen oxide (NOx) concentration. The present invention uses the brown miralite type composite oxide to simultaneously exhibit two functions of a catalyst and a nitrogen oxide sensor.
The nitrogen oxide purifying catalyst section is so provided in an exhaust pipe of the engine that the nitrogen oxide purifying catalyst section is able to contact with exhaust gases or able to pass through the interior and the opposite ends or the vicinity of the opposite ends of the nitrogen oxide purifying catalyst section on which electrodes are provided are along with the exhaust pipe of the engine. The nitrogen oxide purifying catalyst section is preferably disposed in a position away from a combustion chamber to the extent that a temperature of the exhaust gases lower than about 400° C.
According to the present invention, the brown miralite type composite oxide contains at least one of element selected from earth elements, alkali earth metals and a group of alkali metals. Since here, “contains at least one of element” is mentioned, for example, in case the brown miralite type composite oxide is expressed by a general formula A
3
B
4
O
8
or general formula A
2
B
2
O
5
, not only the case wh

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