Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
1999-12-20
2001-01-16
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S285000, C060S276000, C180S065230, C180S065310, C180S065510
Reexamination Certificate
active
06173569
ABSTRACT:
The disclosure of Japanese Patent Application No. HEI 10-374455 filed on Dec. 28, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst deterioration detecting apparatus for an internal combustion engine and, more particularly, to a catalyst deterioration detecting apparatus for an internal combustion engine provided in a hybrid vehicle employing both an internal combustion engine and an electric motor as power sources.
2. Description of the Related Art
A three-way catalyst of a catalytic converter disposed in an exhaust passage of an internal combustion engine has an oxygen storage function taking up oxygen when the air-fuel ratio is on the fuel-lean side of a stoichiometric air-fuel ratio and, when the air-fuel ratio turns to a fuel-rich side of the stoichiometric air-fuel ratio, causing oxygen previously taken up during the fuel-lean state to react with hydrocarbons and carbon monoxide present in the exhaust gas. If the oxygen storage function of the catalyst deteriorates, the emission control performance becomes degraded. That is, hydrocarbons and carbon monoxide are let out to the downstream side of the catalyst, so that maintenance of good emission quality becomes difficult. In order to maintain good emission quality, it is necessary to detect a degree of deterioration of the catalyst and determine whether the catalyst has deteriorated excessively based on the degree of deterioration and, when it is determined that the catalyst has deteriorated excessively, to visually notify a driving person of the deterioration of the catalyst and change the air-fuel ratio control in accordance with the degree of deterioration of the catalyst.
Various apparatuses for detecting the degree of deterioration of a three-way catalyst based on the degree of deterioration of the oxygen storage function of the catalyst have been proposed. For example, a catalyst deterioration degree detecting apparatus disclosed in Japanese Patent Application Laid-Open No. HEI 6-159048 detects a degree of deterioration of a catalytic converter in the following manner. After switching the air-fuel ratio to the rich side following execution of a fuel cut control of the engine, the catalyst deterioration degree detecting apparatus calculates an amount of oxygen released from the catalytic converter during a period of time up to a time at which the air-fuel ratio downstream of the catalyst actually switches from the lean side to the rich side, based on a total amount of exhaust gas that passes through the catalytic converter during that period and the rich side-switched air-fuel ratio. Considering the calculated released amount of oxygen as indicative of an oxygen adsorbing capacity of the catalytic converter, the apparatus detects a degree of deterioration of the catalytic converter.
The aforementioned apparatus can be applied to a hybrid vehicle that selectively uses power from an internal combustion engine and power from an electric motor and temporarily stops the engine when using power from the motor. However, in such case, it is difficult to determinate a deterioration of a catalyst with high precision. The reason is that if the engine fuel cut is continued for a long time, the temperature of the catalyst is decreased so that the catalyst cannot store oxygen up to the maximum oxygen adsorbing capacity thereof even in the presence of an excess amount of oxygen. Conversely, if the fuel cut duration is short, there is not provided a time needed for sufficient adsorption of oxygen to the catalyst. In such cases, an excessive degree of deterioration of the catalyst is detected although the amount of oxygen stored in the catalyst is less than the maximum oxygen adsorbing capacity of the catalyst, so that the determination regarding deterioration of the catalyst may not be performed with high precision.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a catalyst deterioration detecting apparatus for an internal combustion engine that is capable of detecting a degree of deterioration of a catalyst with high precision even when applied to a hybrid vehicle.
To achieve the aforementioned and other objects of the invention, one aspect of the invention provides catalyst deterioration detecting apparatus for detecting deterioration of a catalyst provided in an exhaust passage of an internal combustion engine whose output shaft is connected to an electric motor. The catalyst deterioration detecting apparatus includes an air-fuel ratio sensor provided downstream of the catalyst, and a controller which performs a control such that the internal combustion engine is temporarily stopped and the electric motor is driven, under a predetermined vehicle running condition, and which estimates an amount of oxygen stored in the catalyst, and which determines whether the catalyst has deteriorated, based on the estimated amount of oxygen and an output produced by the air-fuel ratio sensor after the internal combustion engine is restarted.
In this apparatus, the controller estimates an amount of oxygen stored in the catalyst. Based on the estimated amount of oxygen and changes in the output produced by the air-fuel ratio sensor downstream of the catalyst after the internal combustion engine is restarted, the controller determines the amount of oxygen stored in the catalyst and the status of release of oxygen therefrom, and thereby determines whether the catalyst has deteriorated.
In this apparatus, it is also possible to determine whether the catalyst has deteriorated, when the estimated amount of oxygen is equal to or greater than a predetermined amount.
Therefore, the catalyst deterioration detecting apparatus performs the catalyst deterioration determination after verifying that the catalyst has stored oxygen substantially up to the limit of the oxygen storing capacity of the catalyst, so that the determination can be performed with high precision.
It is also possible to supply a fuel-rich mixture from the beginning of a restart of the internal combustion engine and to determine whether the catalyst has deteriorated, based on a time duration of response to supply of the fuel-rich mixture, that is, a time duration between the beginning of the restart of the engine and reversion of the output of the air-fuel ratio sensor from a lean side to a rich side.
In this case, the catalyst deterioration determination is performed based on the time duration between the forced switching of the air-fuel ratio upstream of the catalyst to the rich side and the switching of the air-fuel ratio downstream of the catalyst from the lean side to the rich side, that is, the time duration up to the beginning of release of oxygen from the catalyst. Therefore, the catalyst deterioration determination can be performed within a short time. Furthermore, the degree of deterioration can be quantitatively determined.
In the catalyst deterioration detecting apparatus, an amount of oxygen stored in the catalyst may be estimated during a temporary stop of the internal combustion engine. Furthermore, an atmosphere around the catalyst may be caused to contain an excess amount of oxygen before the internal combustion engine is temporarily stopped.
If the internal combustion engine is stopped when the catalyst atmosphere contains an excess amount of oxygen, transfer of heat from the catalyst to the outside of the catalyst by exhaust gas is considerably reduced, so that the decreasing rate of the catalyst temperature becomes small. As a result, a condition in which an excess amount of oxygen is present near the catalyst and the catalyst has a relatively high temperature that allows the catalyst to store oxygen is maintained. Therefore, the catalyst stores oxygen up to the maximum oxygen adsorbing capacity even during a stop of the internal combustion engine.
REFERENCES:
patent: 5323868 (1994-06-01), Kawashima
patent: 5327991 (1994-07-01), Yoshida
patent: 5765370 (1998-07-01), Hanafusa et al
Hirose Katsuhiko
Inoue Toshio
Kanai Hiroshi
Kojima Masakiyo
Kusada Masaki
Denion Thomas
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
Tran Diem
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