Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2001-03-08
2002-06-11
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S285000, C060S295000, C060S301000, C123S676000, C123S682000
Reexamination Certificate
active
06401454
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an engine control system for cleaning exhaust gas exhausted from lean-burn combustion engines, particularly, for suppressing release of NOx, and to an engine control device for achieving always stable clean up of the exhaust gas by controlling reactivation of catalyst based on an estimation of deterioration of the catalyst performance.
BACKGROUND OF THE TECHNOLOGY
Regarding an improvement on clean-up rates of lean NOx catalyst, JP-A-5-133260 (1993), for instance, discloses a method for improving transient clean-up rates by changing a target air-to-fuel ratio from a rich condition to a lean condition and its reverse alternately. However, the above prior art does not teach nor suggest any reactivation (recovery) control of the clean-up rates to SOx poisoning based on time-elapsing effects of NOx catalyst by heating utilizing so-called after-burn efficiencies and the like.
Regarding conventional in-cylinder-injection engines, a prior art is described, for instance, in JP-A-4-241753 (1992). The technology is to make a fuel distribution homogeneous by controlling fuel injection timing based on a temperature of cooling water of the engine, in order to achieve stable stratified combustion in a lean condition of the in-cylinder-injection engine.
However, any special countermeasures for the exhaust gas of the stratified combustion, wherein the combustion is performed in a lean condition far from the stoichiometric air-to-fuel ratio, has not been considered. Regarding release of NOx, which is a particular problem of the lean combustion, no processing nor controlling has been considered.
DISCLOSURE OF THE INVENTION
In accordance with the lean-burn engine, particularly lean combustion (stratified combustion) in the in-cylinder-injection engine, the combustion is performed by forming a combustible mixture locally in the vicinity of plugs in a remarkably lean condition as a whole cylinder.
Accordingly, its exhaust gas can not be cleaned on all the components to be removed by conventional three way catalyst, particularly, a lean NOx catalyst becomes necessary for nitrogen oxides (NOx).
Regarding the NOx catalyst, an important point is how to maintain its performance. In particular, a countermeasure for gasoline containing sulfur components (S) more than conventional gasoline becomes necessary in accordance with deregulation on gasoline and the like.
Even on the conventional gasoline, a decrease of the clean-up rate by sulfur can be generated based on transient effects, and it is regarded as a SOx poisoning.
The SOx poisoning is caused by S components in gasoline, and depending on how much the catalyst itself is exposed to the exhaust gas atmosphere.
FIG. 3
indicates a change of characteristics of the lean NOx catalyst in accordance with elapsing time, which is indicated on the abscissa. In accordance with the characteristics, it is revealed that the change is proportional to the time exposed to the exhaust gas atmosphere, in other words, proportional to a total mount of gasoline containing S supplied to the engine.
Furthermore, in accordance with the mechanism, the S component in gasoline is changed to SOx (sulfur compounds) by combustion, released as a part of the exhaust gas, and formed a compound with an active component for NOx clean-up in the lean NOx catalyst at surface of the catalyst, as shown in FIG.
4
. Due to the above phenomenon, the function of the active component for NOx clean-up in the catalyst is decreased, and the catalyst performance is deteriorated.
On the other hand, it has been known that the clean-up performance of the catalyst can be recovered by making its atmosphere at a designated temperature as indicated by dotted lines in FIG.
3
. In the above case, the higher the temperature in the atmosphere of reactivation control shown by an arrow is, the higher the degree of the recovery is.
The mechanism of recovery is to make the active component of the catalyst functional as it conventionally is by heating the catalyst (for instance, at least 500~600° C.) for separating SOx from the active components of the catalyst.
The problem to be solved by the present invention is to provide an engine control device provided with lean NOx catalyst, which is usable of the lean NOx catalyst having the above characteristics in a preferable condition at all the time, and to provide an engine control device provided with the lean NOx catalyst, which can practically perform the reactivation control indicated by the arrow in
FIG. 3
when the clean-up rate is decreased by sulfur and the like based on change of the lean NOx catalyst with elapsing time.
The engine control device provided with the lean NOx catalyst relating to the present invention solves the above problems by the following measures.
First, the engine control device of the present invention comprises a condition estimating means and a reactivation controlling means for catalyst itself.
The condition estimating means for catalyst has practically a following composition. A deteriorated condition of the catalyst depends on the elapsing time exposed to the exhaust gas, and the degree of deterioration depends on the amount of fuel used for the combustion. This is clear from the previously described mechanism of deterioration by S components contained in the fuel. Accordingly, the degree of deterioration is estimated from the total supplied amount of the fuel and the elapsing time of the catalyst exposed to the exhaust gas containing the S components. Furthermore, the degree of deterioration of the catalyst can be determined by any of the temperature of the catalyst itself, O
2
sensors arranged at upstream and downstream of the catalyst, and various exhaust gas sensors such as air-to-fuel ratio sensors and the like.
Next, the reactivation control at a high temperature can be achieved by elevating the exhaust gas temperature forcibly in view of the fact that the engine is operated routinely in a lean condition and the exhaust gas temperature is lower than that in a conventional condition of stoichiometric air-to-fuel ratio.
Practically, the exhaust gas temperature is elevated by an ignition timing retardation control. Regarding the in-cylinder-injection engine, the exhaust gas temperature can be elevated with an after-burn effect by performing fuel injection during an exhaust stroke. In accordance with the control, the exhaust gas temperature can be elevated forcibly to higher than a routine operation condition, and the reactivation control indicated in
FIG. 3
becomes possible. It is clear that the ignition timing retardation control is applicable to conventional lean combustion of a MPI system, and that the reactivation control is effective for achieving a heating effect for the catalyst atmosphere, because fuel combustion becomes possible without using a control such as a special ignition control and the like by injecting fuel into an atmosphere at a relatively high temperature during exhaust valves are in an opening condition during an exhaust stroke injection of the in-cylinder-injection engine.
Controlling time for the reactivation control is more effective with a shortened time at a higher temperature as the dotted line in
FIG. 3
indicates. Accordingly, the controlling time of the reactivation control is regulated based on an estimated exhaust gas temperature in that condition. The degree of the heating effect in the reactivation control is the largest at the first cycle, and is in a tendency to decrease after second cycle with the same heating time. Therefore, in order to realize the reactivation control more effective, it is effective to change the length of the controlling time in consideration of the controlling cycles such as extending the controlling time after second cycle longer than the controlling time of the first cycle.
When the reactivation control become necessary in a stratified combustion condition of a lean condition, the reactivation control is performed by replacing a fundamental combustion condition of the engine with an air-to-fuel ratio condition. I
Atago Takeshi
Kitahara Yuichi
Suda Seiji
Takano Yoshiya
Denion Thomas
Hitachi , Ltd.
Trieu Thai-Ba
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