Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-10-07
2004-06-29
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000
Reexamination Certificate
active
06755013
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2001-313840 filed on Oct. 11, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a catalyst deterioration detection apparatus of an internal combustion engine, and a detection method performed by the apparatus. More particularly, the invention relates to a catalyst deterioration detection apparatus for detecting deterioration of a catalyst for purifying emissions from an internal combustion engine, and a detection method performed by the detector apparatus.
2. Description of Related Art
A catalyst for purifying exhaust gas is disposed in an exhaust passage of a vehicle-installed internal combustion engine. This catalyst has a capability of storing an appropriate amount of oxygen. If exhaust gas contains unburned components, such as HC, CO, etc., the catalyst causes oxidation of the unburned components using stored oxygen. If exhaust gas contains oxides, such as NOx and the like, the catalyst causes reduction of the oxides, and absorbs and stores oxygen produced by the reduction reactions.
The catalyst disposed in an exhaust passage is thus intended to purify exhaust emissions. Thus, the emission control capability of the catalyst is greatly affected by the oxygen storage capability of the catalyst. Therefore, the emission control capability degradation state of the catalyst can be determined based on the maximum amount of oxygen that the catalyst is able to store, that is, the oxygen storage capacity.
FIG. 11
indicates a relationship between the catalyst temperature and the oxygen storage capacity (OSC). More specifically, a curve (
1
) in
FIG. 11
indicates a temperature-OSC relationship exhibited by a normal catalyst with respect to fuel having a low sulfur concentration. A curve (
2
) indicates a temperature-OSC relationship exhibited by a normal catalyst with respect to fuel containing a large amount of sulfur. Furthermore, a curve (
3
) indicates a temperature-OSC relationship exhibited by a deteriorated catalyst. A curve (
4
) indicates a temperature-OSC relationship exhibited by a further deteriorated catalyst.
As indicated in
FIG. 11
, the oxygen storage capacity OSC of the catalyst is dependent on the catalyst temperature THC. This dependence changes in accordance with the deterioration of the catalyst. For example, if a low-sulfur concentration fuel is used, a normal-state catalyst exhibits relatively great oxygen storage capacity OSC even at a relatively low catalyst temperature range as indicated by the curve (
1
). In contrast, if the catalyst is lightly deteriorated, the oxygen storage capacity OSC of the catalyst becomes relatively high in a relatively high catalyst temperature range as indicated by the curve (
3
). As the deterioration of the catalyst further progresses, the oxygen storage capacity OSC of the catalyst remains low regardless of the catalyst temperature. Therefore, it is possible to determine whether the catalyst is normal by checking whether a sufficient oxygen storage capacity OSC is secured when the catalyst temperature is, for example, within a range indicated by reference numeral (
5
) in FIG.
11
.
However, it is known that the oxygen storage capacity OSC of the catalyst varies in accordance with variation in the quality of fuel used, more specifically, variation in the concentration of a sulfur component contained in fuel. That is, even if the catalyst is normal, a high sulfur component concentration in fuel causes a smaller oxygen storage capacity OSC as indicated by the curve (
2
) than a low sulfur component concentration (curve (
1
)) in fuel. In this case, in order to determine whether the catalyst is normal based on the oxygen storage capacity OSC, it is necessary to distinguish whether the catalyst is exhibiting the OSC characteristic indicated by the curve (
2
) or the OSC characteristic indicated by the curve (
3
). Therefore, if variations in the quality of fuels distributed in the market are taken into consideration, the case where the deteriorated state of the catalyst can be determined based on the oxygen storage capacity OSC is limited only to a case where the catalyst temperature is within a narrow range indicated by reference numeral (
6
).
The catalyst temperature changes in accordance with the amount of intake air. That is, if the amount of intake air is large, the catalyst temperature becomes high due to a large amount of high-temperature exhaust gas supplied to the catalyst. Conversely, if the amount of intake air is small, the catalyst temperature becomes low due to a small amount of flow of exhaust gas. Therefore, at a transitional time when the amount of intake air sharply increases, such as a time of acceleration of the vehicle or the like, there occurs a temporary event where the amount of intake air (amount of exhaust gas) becomes large while the catalyst temperature remains low.
If the state where the amount of intake air has increased continues, the catalyst temperature eventually becomes high, and enters the range (
6
). Even in that case, however, until the catalyst temperature sufficiently rises, there occurs a state where the amount of intake air is excessively large relatively to the catalyst temperature so that sufficient control of exhaust emissions (oxidation and reduction thereof) cannot be achieved, that is, there occurs a through-flow of exhaust gas. That is, during a period from a sharp increase in the amount of intake air until a sufficient rise of the catalyst temperature, an event similar to the event that occurs in the case of deterioration of the catalyst occurs even though the catalyst is actually normal. Therefore, during a certain time period from a transitional change in the operation state of the internal combustion engine until the amount of intake air and the catalyst temperature become unbalanced, it is preferable that the determination regarding deterioration of the catalyst be avoided even under a condition in which the catalyst temperature converges into the range (
6
) (first requirement).
If high temperature of the catalyst is caused by continuation of a travel in an accelerating state or with large amounts of air and is immediately followed by a travel with a small amount of air, exhaust gas may possibly be purified to a sufficient extent even though deterioration of the catalyst has considerably progressed. Therefore, it is preferable that determination regarding deterioration of the catalyst be avoided also in the case where there is unbalance between the amount of intake air and the catalyst temperature. However, if in the aforementioned case, deterioration of the catalyst has sufficiently progressed (see the curve (
4
)), the abnormality of the catalyst can be precisely determined, so that the detection should not be simply suspended (second requirement).
Japanese Patent Application Laid-Open No. 11-36848 discloses a catalyst deterioration detection apparatus that meets the aforementioned first requirement. This apparatus has a function of monitoring the rate of change of the amount of intake air, and of determining whether the vehicle is accelerating or decelerating or is in a steady running state based on the rate of change. This apparatus stores in a memory a lower limit-side criterion value and an upper limit-side criterion value that are to be compared with the rate of change of the amount of intake air. The criterion values are set so that the absolute values thereof increase with increases in the elapsed time following the beginning of an acceleration or deceleration of the vehicle. The aforementioned conventional apparatus permits execution of determination regarding deterioration of the catalyst only if the rate of change of the amount of intake air is between the upper limit-side and lower limit-side criterion values.
According to this conventional apparatus, during a short time period after a shift to acceleration or deceleration of the vehicle, that is, a
Denion Thomas
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Tran Diem
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