Chemistry: analytical and immunological testing – Testing of catalyst
Reexamination Certificate
2000-04-28
2004-09-28
Bell, Mark L. (Department: 1755)
Chemistry: analytical and immunological testing
Testing of catalyst
C422S083000, C422S105000, C060S277000, C060S276000
Reexamination Certificate
active
06797517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology for detecting a degradation of an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine.
2. Description of Related Art
In an internal combustion engine arranged in an automobile or the like, an exhaust gas purifying catalyst is provided in an exhaust passage of the internal combustion engine, for the purpose of purifying harmful gas components contained exhaust gases. As this type of exhaust gas purifying catalyst known is, for example, a three way catalyst constituted in such a manner that alumina is coated on the surface of a ceramic carrier, and a platinum-rhodium or palladium-rhodium noble metal is carried on the surface of the alumina.
The three way catalyst is an exhaust gas purifying catalyst that makes hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gases react with oxygen (O
2
) in the exhaust gases to reduce them to water (H
2
O) and carbon dioxide (CO
2
), and at the same time that makes nitrogen oxides (NO
x
) contained in the exhaust gases react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases to reduce them to water (H
2
O), carbon dioxide (CO
2
), and nitrogen (N
2
) when an air-fuel ratio of flowing-in exhaust gases is in the vicinity of the theoretical air-fuel ratio.
By this type of three way catalyst, hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO
x
) contained in the exhaust gases may be purified, and harmful gas components are prevented from being discharged to the atmosphere.
The three way catalyst is activated at a predetermined activation temperature (e.g. 300 to 500° C.) or higher to be capable of purifying harmful gas components in the exhaust gases, but it is not capable of purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO
x
) in the exhaust gases at a temperature lower than the aforementioned activation temperature since it becomes in an inactivated state.
Particularly, in the case in which an internal combustion engine is cold started or the like, a fuel injection amount is increased more than usual in order to improve the startability and to ensure operability of the internal combustion engine, whereas since the combustion of an air-fuel mixture in the internal combustion engine becomes unstable, the amount of unburned fuel component (unburned HC) contained in the exhaust gases become relatively large. At that time an inconvenience occurs that if the three way catalyst is in the inactivated state, a relatively large amount of unburned HC cannot be purified and the unburned HC is discharged to the atmosphere.
With respect to this type of problem, to date, an exhaust gas purifying device is proposed in which an HC adsorbent that is composed of porous zeolite or the like adsorbs the unburned HC in the exhaust gases at a temperature lower than a predetermined temperature and desorbs the adsorbed unburned HC at a temperature equal to or higher than the predetermined temperature, and the adsorbent and the three way catalyst are provided in an exhaust passage. In this exhaust gas purifying device, when the three way catalyst is in the inactivated state, the unburned HC in the exhaust gases is adsorbed in the HC adsorbent, and after the three way catalyst is activated, the unburned HC in the exhaust gases and the unburned HC desorbed from the HC adsorbent are purified through the three way catalyst.
In the exhaust gas purifying device as mentioned above, it is important to accurately determine the performance degradation of the three way catalyst. For this type of requirement, “Catalyst degradation determination device in an internal combustion engine” disclosed in the Japanese Patent Application Laid-Open Publication No. Hei 5-98948 is known.
The catalyst degradation determination device mentioned above comprises a three way catalyst provided in an exhaust passage of an internal combustion engine and having an oxygen storage capacity (OSC), an upstream side air-fuel ratio sensor provided in the exhaust passage at the upstream of the three way catalyst, a downstream side air-fuel ratio sensor provided in the exhaust passage at the downstream of the three way catalyst, an air-fuel ratio feedback control means that feedback controls an engine air-fuel ratio based on an output signal value of the upstream side air-fuel ratio sensor, a locus length calculating means that calculates a locus length of an output of the downstream side air-fuel ratio sensor during a predetermined period of time when the air-fuel ratio feedback control means executes an air-fuel ratio feedback control, and a catalyst degradation judging means that judges that the three way catalyst is degraded when the locus length calculated by means of the locus length calculating means is greater than a predetermined reference value.
That is, the catalyst degradation determination device described above integrates, during the predetermined period of time in which the air-fuel ratio feedback control is executed, the amount of change of the output of the downstream side air-fuel ratio sensor for each constant time period (< the predetermined period of time) and determines that the three way catalyst is degraded when the integrated value is greater than the reference value.
The above functions are executed based on the knowledge that when the three way catalyst is degraded, the frequency of the change of the output of the downstream side air-fuel ratio sensor becomes higher than that of the case in which the three way catalyst is normal and, as a result, an integrated value of the amount of change of the output of the downstream side air-fuel ratio sensor during the predetermined period of time when the three way catalyst is degraded becomes greater than that of the case where the three way catalyst is normal.
In recent years, since an improvement in an exhaust emission exhausted when an internal combustion engine is cold started is required, it is important to determine the degradation of the capability of activating a catalyst under a low temperature state in an earlier stage, that is, a low temperature activation capability.
However, in the catalyst degradation determination device described above, the degradation determination of the exhaust gas purifying catalyst is made at the time of execution of the air-fuel ratio feedback control after the exhaust gas purifying catalyst is activated, and it is impossible to diagnose the degradation of the low temperature activation capability of the exhaust gas purifying catalyst, and there is a possibility that the exhaust emission is worsened when the internal combustion engine is cold started.
SUMMARY OF THE INVENTION
The present invention is made in view of the above-mentioned problems, and it is an object of the present invention to contribute to the prevention of worsening the exhaust emission when an internal combustion engine is cold started, by providing a technology for accurately determining the degradation of an exhaust gas purifying catalyst provided in an exhaust passage of the internal combustion engine and is capable of purifying harmful gas components in exhaust gases at a predetermined activation temperature or higher, particularly, the degradation of a low temperature activation capability.
In order to achieve the object, the present invention adopts the following means.
That is, the catalyst degradation detecting device in an internal combustion engine according to the present invention comprises an adsorbing member provided in an exhaust passage of the internal combustion engine, for adsorbing a predetermined component contained in exhaust gases when a temperature is lower than a predetermined temperature and desorbing the adsorbed predetermined component when the temperature is within a predetermined temperature range; an exhaust gas purifying catalyst provided in the exhaust passage at least at the upstream of the adsorbing member for purifying the predetermined component in the exhaust gases when the temperature
Hoshi Koichi
Sakurai Kazuhiro
Watanabe Takashi
Bell Mark L.
Brown Jennine
Toyota Jidosha & Kabushiki Kaisha
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