Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2003-05-12
2004-07-13
Denion, Thomas E. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S285000
Reexamination Certificate
active
06761024
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2002-143393, 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 air-fuel ratio control system and method for an internal combustion engine including an exhaust passage and a catalyst disposed in the same passage.
2. Description of Related Art
There is known an internal combustion engine including an exhaust passage and a three-way catalyst disposed in the same passage for controlling an exhaust gas. A three-way catalyst (hereinafter will be simply referred to as a “catalyst” where appropriate) is capable of storing oxygen. More specifically, when the air-fuel ratio of the exhaust gas flowing into the catalyst is rich, the catalyst oxidizes unburned components, such as HC and CO, using oxygen stored therein. In contrast, when that air-fuel ratio is lean, the catalyst reduces nitrogen oxides (NOx) and stores the oxygen removed from those nitrogen oxides reduced. Having such capabilities, three way catalysts can be effectively used for purifying an exhaust gas by controlling unburned components and nitrogen oxides, which tend to increase as the air-fuel ratio in the internal combustion engine deviates from the stoichiometric air-fuel ratio. By the way, the purification capacity of such a three-way catalyst becomes larger as the maximum storable oxygen thereof increases.
The maximum storable oxygen amount changes depending upon the state of the catalyst that physically degrades with use. Therefore, it is possible to determine the degradation of the catalyst by estimating its maximum storable oxygen amount.
The catalyst degradation determination system disclosed in Japanese Laid-opened Patent Application No. 5-133264 employs the above concept for determining the degree of the catalyst degradation, as will be described in the following. That is, in this system, the air-fuel ratio in the internal combustion engine, which is namely the air-fuel ratio upstream of the catalyst, is changed from a predetermined rich air-fuel ratio to a predetermined lean air-fuel ratio, or from a predetermined lean air-fuel ratio to a predetermined rich air-fuel ratio. Then, the maximum amount of oxygen storable in the catalyst (hereinafter will be referred to as the “maximum storable oxygen amount of the catalyst”) is estimated from a change in the output of an air-fuel ratio sensor disposed downstream of the catalyst during the above shift of the air-fuel ratio upstream of the catalyst, and the degradation degree of the catalyst is determined based on the maximum storable oxygen amount estimated.
More specifically, in the above system, the air-fuel ratio upstream of the catalyst is made equal to the predetermined rich air-fuel ratio by a so-called open-loop control so that the amount of oxygen stored in the catalyst becomes zero, after which the air-fuel ratio upstream of the catalyst is made equal to the predetermined lean air-fuel ratio by another open-loop control upon detecting via the air-fuel ratio sensor disposed downstream of the catalyst that the air-fuel ratio downstream of the catalyst has become rich. Each open-loop control is to perform only a feed-forward control on the air-fuel ratio of an air-fuel mixture (gas) to be supplied into the internal combustion engine (i.e., the air-fuel ratio upstream of the catalyst), rather than performing it in combination with a feedback control on the air-fuel ratio actually detected in the gas ejected from the internal combustion engine.
Subsequently, the system obtains the amount of oxygen entering the catalyst from when the air-fuel ratio upstream of the catalyst is switched to the predetermined lean air-fuel ratio to when it is detected via the air-fuel ratio sensor disposed downstream of the catalyst that the air-fuel ratio downstream of the catalyst has become lean as a result of the oxygen amount stored in the catalyst having reached its full capacity. Eventually, the obtained oxygen amount is estimated as the maximum storable oxygen amount of the catalyst.
Alternatively, the air-fuel ratio upstream of the catalyst is made equal to the predetermined lean air-fuel ratio by an open-loop control so that oxygen is stored in the catalyst to its full capacity, after which the air-fuel ratio upstream of the catalyst is made equal to the predetermined rich air-fuel ratio by another open-loop control upon detecting via the air-fuel ratio sensor disposed downstream of the catalyst that the air-fuel ratio downstream of the catalyst has become lean. Subsequently, the system obtains the amount of oxygen consumed in the catalyst from when the air-fuel ratio upstream of the catalyst is switched to the predetermined rich air-fuel ratio to when it is detected via the air-fuel ratio sensor disposed downstream of the catalyst that the air-fuel ratio downstream of the catalyst has become rich as a result of the oxygen stored in the catalyst having been completely used up. Eventually, the obtained oxygen amount is estimated as the maximum storable oxygen amount of the catalyst.
With such a conventional system, however, because the air-fuel ratio upstream of the catalyst is controlled to the predetermined rich or lean air-fuel ratio by the open loop control described above, it is difficult to preserve sufficient accuracy in controlling the air-fuel ratio due to a change in the engine operation state, a variation among individual engines, and the like. Therefore, there is a possibility that an air-fuel mixture of an excessive rich or lean air-fuel ratio be supplied into the internal combustion engine, which may cause problems like a deterioration in the drivability of the vehicle.
However, such a problem with the above conventional system may be resolved by performing a feedback control on the air-fuel ratio upstream of the catalyst during the calculation of the maximum storable oxygen amount of the catalyst in the following manner. That is, a fuel injection amount required for achieving the stoichiometric air-fuel ratio upstream of the catalyst is predetermined as a basic injection amount. Then, when the target value of the air-fuel ratio upstream of the catalyst is set to the predetermined rich or lean air-fuel ratio aforementioned, a feedback correction amount is determined by executing a so-called PI or PID control on the deviation between the actual air-fuel ratio detected by the air-fuel ratio sensor disposed upstream of the catalyst and the target air-fuel ratio, and the basic injection amount is corrected using the feedback correction amount determined.
However, during such a feedback control, a so-called control delay unavoidably occurs. Therefore, due to such a control delay, the emission may increase during the above feedback control executed for estimating the maximum storable oxygen amount of the catalyst.
That is, referring to the timechart shown in
FIG. 17
, the target air-fuel ratio is switched to the predetermined lean air-fuel ratio when the air-fuel ratio downstream of the catalyst indicating a lean air-fuel ratio changes to indicate a rich air fuel ratio at the time t
10
. However, the air-fuel ratio of the gas flowing into the catalyst remains rich until the time t
20
due to a delay in the feedback control. Because the stored oxygen amount is zero at this time, unburned components, such as CO, are not reduced in the catalyst.
Likewise, the target air-fuel ratio is switched to the predetermined rich air-fuel ratio when the air-fuel ratio downstream of the catalyst indicating a rich air-fuel ratio changes to indicate a lean air-fuel ratio at the time t
30
. However, the air-fuel ratio of the gas flowing into the catalyst remains lean until the time t
40
due to a delay in the feedback control. Because the stored oxygen amount of the catalyst is equal to its maximum storable oxygen amount at this time, NOx contained in the gas is not reduced.
SUMMARY OF THE INVENTION
In view of the above situation, the invention has been made to provide the followin
Denion Thomas E.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
LandOfFree
Air-fuel ratio control system and method for internal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Air-fuel ratio control system and method for internal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Air-fuel ratio control system and method for internal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3223912