Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-06-12
2001-12-04
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S277000
Reexamination Certificate
active
06324836
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for controlling an engine, and especially to an apparatus and a method for quickly correcting an air-to-fuel ratio (hereafter referred to as an A/F ratio) when the purification state of exhaust gas is deteriorated downstream of a catalyst unit located in an exhaust pipe.
A catalyst unit including a three way catalyst, which oxidizes HC and CO and deoxidizes Nox in exhaust gas expelled from the engine, is generally located in the exhaust pipe of the engine. Rare metals such as Pt, Pd, Rh, etc., are used for the catalyst, and impurities such as HC, CO, and NOx are efficiently purified only in a very narrow region near the stoichiometric A/F ratio as shown in FIG.
2
. This is because it is necessary that the oxidizing substances and the deoxidizing substances exist in a balance. Accordingly, a typical promoter: ceric oxide is added to the three way catalyst to expand the narrow highly-efficient-purification region near the stoichiometric A/F ratio. Ceric oxide is oxygen-trapping material which absorbs or stores oxygen. Further, ceric oxide discharges oxygen in a deoxidizing atmosphere, that is, in a region where the A/F ratio is richer than the stoichiometric ratio, and traps oxygen in an oxidizing atmosphere, that is, in a region where the A/F ratio is leaner than the stoichiometric ratio, which in turn expands the region in which the oxidizing substances and the deoxidizing substances can exist in a balance as shown in FIG.
3
. Furthermore, to hold the components of exhaust gas expelled from the engine within the highly-efficient-purification region under various operational conditions, and O
2
-sensor for detecting whether the A/F ratio of the exhaust gas is leaner or richer than the stoichiometric ratio is located in the exhaust pipe as shown in
FIG. 4
, and an A/F ratio feed-back control (hereafter referred to as an A/F ratio F/B control) is performed based on the output of the O
2
-sensor in order to control the fuel-injection amount so that the A/F ratio in the combustion room is held at the stoichiometric ratio. Recently, an A/F ratio F/B control method using a linear A/F sensor whose output is linearly proportional to the A/F ratio of the exhaust gas as shown in
FIG. 5
has been also practically applied.
Although the above A/F ratio F/B control is aimed at keeping the A/F ratio upstream of the catalyst at the stoichiometric ratio, it is known that the three-way performance of the catalyst is improved by an in-catalyst atmosphere-control concerning the oxygen trapped in the ceric oxide (CeO
2
). Since ceric oxide deoxidizes Nox or traps O
2
in the oxidizing atmosphere as shown in the chemical equations (1) and (2), and oxidizes CO or discharges O
2
in the deoxidizing atmosphere as shown in the chemical equations (3) and (4), ceric oxide can simultaneously remove HC, CO, and Nox.
Ce
2
O
3
+½O
2
→2CeO
2
(1)
Ce
2
O
3
+NO→2CeO
2
+N
2
(2)
2CeO
2
→Ce
2
O
3
+½O
2
(3)
2Ce
2
O
3
+CO→CeO
2
+CO
2
(4)
Therefore, to improve the purification performance, it is important to keep not only the A/F ratio upstream of the catalyst but also the balance of the amounts of CeO
2
and Ce
2
O
3
in the catalyst. Japanese Patent Application Laid-Opens Hei 9-72235 and Hei 10-184436 have devised respective control methods in which the amount of ceric oxide in the catalyst is controlled by adjusting the chemical atmosphere in the catalyst. However, since it is difficult to keep the A/F ratio upstream of the catalyst within the highly-efficient-purification region under all operational conditions, the A/F ratio upstream of the catalyst may shift largely from the stoichiometric ratio in the lean or rich direction, and the balance of the amounts of CeO
2
and Ce
2
O
3
can be frequently lost. In such cases, although the A/F ratio upstream of the catalyst should be quickly returned to the stoichiometric ratio, it is also important to return the amount of the ceric oxide to the desired value. Quickly returning the amount of the ceric oxide to the desired value can be realized by improving the response of the A/F control at the outlet region of the engine. However, as mentioned above, the ceric oxide sometimes degrades the response of change in the A/F ratio in the catalyst. That is, when the A/F ratio upstream of the catalyst changes from the stoichiometric ratio to a richer value, oxygen is discharged from the ceric oxide in the catalyst while the deoxidizing atmosphere is strengthened, which in turn hinders the strengthening of the deoxidizing atmosphere. Conversely, when the A/F ratio upstream of the catalyst changes from the stoichiometric ratio to a leaner value, oxygen is trapped or stored by the ceric oxide in the catalyst while the oxidizing atmosphere is strengthened, which in turn hinders the strengthening of the oxidizing atmosphere. This is confirmed by the phenomena that a phase delay can be observed in the changes in the A/F ratios before and after the catalyst when the A/F ratio upstream of the catalyst is changed. Since the transient response of the ceric oxide in the catalyst is not taken into account in the conventional control to return the A/F ratio upstream of the catalyst to the stoichiometric ratio, the optimal response of the A/F ratio in the catalyst is not realized, and the quality degradation of the exhaust gas cannot be corrected.
SUMMARY OF THE INVENTION
An objective of the present invention is to quickly recover the quality degradation of the exhaust gas by correcting the A/F ratio upstream of the catalyst such that the response of the A/F ratio downstream of the catalyst is the fastest possible, considering the effects of the ceric oxide as a promoter, when the A/F ratio downstream of the catalyst deviates from the highly-efficient purification region of the catalyst.
The above objective is achieved to provide an air-to-fuel ratio control apparatus comprising: a catalyst unit for purifying exhaust gas from an engine; air-to-fuel ratio-detection means for detecting at least an air-to-fuel ratio downstream of the catalyst unit; a first control means for controlling at least one of an amount of fuel and an amount of air to be fed to the engine by using a feed-back control based on at least one of air-to-fuel ratios upstream of, downstream of, and in the catalyst unit; and a second control means for controlling an air-to-fuel ratio upstream of the catalyst unit so as to be within a predetermined purification-efficiency range after over-correcting the air-to-fuel ratio upstream of the catalyst unit so as to be a richer value beyond the predetermined purification-efficiency range, if an output of the air-to-fuel ratio-detection means deviates from a predetermined range, and an air-to-fuel ratio downstream of the catalyst unit in lean.
Further, the present invention provides an air-to-fuel ratio control apparatus comprising: a catalyst unit for purifying exhaust gas from an engine; air-to-fuel ratio-detection means for detecting at least air-to-fuel ratio downstream of the catalyst unit; a first control means for controlling at least one of an amount of fuel and an amount of air to be fed to the engine by using a feed-back control based on at least one of air-to-fuel ratios upstream of, downstream of, and in the catalyst unit; and a second control means for controlling an air-to-fuel ratio upstream of the catalyst unit so as to be within a predetermined purification-efficiency range after over-correcting the air-to-fuel ratio upstream of the catalyst unit so as to be a leaner value beyond the predetermined purification-efficiency range, if an output of the air-to-fuel ratio-detection means deviates from a predetermined range, and an air-to-fuel ratio downstream of the catalyst unit is rich.
Also, to achieve the above objective, the present invention provides a method of controlling an air-to-fuel ratio in exhaust gas from engine by using a control apparatus including a catalyst unit for pur
Ishii Toshio
Nakagawa Shinji
Ohsuga Minoru
Takaku Yutaka
Takamura Hiroyuki
Crowell & Moring LLP
Denion Thomas
Hitachi , Ltd.
Tran Diem
LandOfFree
Apparatus and method for controlling air-to-fuel ratio in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for controlling air-to-fuel ratio in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for controlling air-to-fuel ratio in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2591416