Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-01-14
2001-05-22
Argenbright, Tony M. (Department: 3747)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S285000, C123S295000
Reexamination Certificate
active
06233921
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of PCT/EP98/01491, filed Mar. 14, 1998 and 197 12 356.2, filed Mar. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for reducing harmful exhaust-gas emissions of a spark-ignition engine operated with a lean fuel/air mixture and having direction fuel injection. More particularly, the inventors relate to a method wherein under part load the engine being operated in the stratisfied-charge mode with a lambda value of &lgr;>1, and, in order to reduce nitrogen oxides adsorbed on a catalyst, a transition to a homogeneous mode with air ratios of &lgr;<1 being carried out at specific intervals by at least one of throttling of the air quantity supplied and/or by an increase in the fuel injection quantity.
It is known that NOx storage catalysts are suitable for the aftertreatment of exhaust gas in so-called lean-burn engines. With lambda values (&lgr;)>1, nitrogen oxides are stored, lambda representing the ratio of the air quantity supplied to a theoretical air requirement for combustion. In order to reduce the nitrogen oxides adsorbed on the catalyst, a jump to air ratios &lgr;<1 is necessary at specific intervals.
In conventional lean-burn engines which have a homogeneous fuel/air mixture and the leanness of which can be brought at least to lambda values of &lgr;=1.6, in principle enrichment can take place while the air quantity remains the same. In this case, the engine torque can be kept constant by retarding the ignition timing. By additional adjustment of the throttle valve for the air supply, the retard of the ignition timing can be limited to only a few work cycles.
A spark-ignition engine with direct injection can, however, be made substantially leaner. In order to obtain consumption values which are as low as possible, such an engine is run unthrottled, that is with a constant air quantity, in the usual way. This engine, therefore, is run in the so-called stratified-charge mode in most operating states. In contrast to homogeneous operation with a lambda value of &lgr;=1, with the fuel already being injected during the suction stroke of a piston, in charge stratification or a stratified-charge mode, the fuel is injected only just before ignition in the compression stroke of the piston. Due to largely unthrottled operation, the engine is operated with a correspondingly high air excess.
Alternation between charge stratification and homogeneous operation, and vice versa, is designated as operating-mode alternation. Since exhaust-gas aftertreatment with a three-way catalyst is not possible in the case of a lean exhaust-gas composition of this kind, an NOx storage catalyst, for example, is used instead, which, as mentioned, then has to be regenerated at regular intervals when there are air ratios &lgr;<1, in order to desorb the adsorbed nitrogen oxides again and subsequently reduce them.
This means that, in the partial-load mode, a transition to air ratios of &lgr;<1 and back again, with the air quantity remaining the same, would be accompanied by a very pronounced load change. For this reason, the intake air quantity must be adapted accordingly, and, at the same time, there must also be a transition from the operating mode “stratified-charge mode” to a “homogeneous mixture mode”. Operation with a homogeneous mixture is possible only when there are lambda values of &lgr;<1.6.
It is known from EP 0,752,521 A1 to adjust the throttle valve accordingly in order to adapt the air quantity. Here, however, there is the problem that, because of the air quantities stored in the flow path between the throttle valve and the intake region of a combustion space or as far as the combustion space, a correspondingly long time is required until air-quantity changes brought about by the adjustment of the throttle valves have an effect in the combustion space. The engine has to be run in an adverse way according to intermediate values for a relatively long period of time. The same applies to a subsequently repeated increase in the air quantity from rich to lean and from the homogeneous mode to the stratified-charge mode. Moreover, each cylinder has two intake ducts having throttle valves regulated in a load-dependent manner.
DE 27 47 885 A1 discloses a method for the reduction of harmful exhaust-gas emissions of a multi-cylinder internal combustion engine, in which one half of the cylinders is to be operated with a rich mixture and the other with a lean mixture. The exhaust-gas intervals with the same composition thereby become longer or their frequency becomes lower, depending on the number of cylinders in the internal combustion engine. The degree of conversion of a selective catalyst is thus to be markedly improved or the emission of harmful exhaust gases reduced. A similar method is described in GB-C-1,492,228.
DE 39 40 752 A1 describes a method for controlling a spark-ignition engine without a throttle valve with the aid of variable inlet-valve opening durations. This method is intended to adapt the masses of air and fuel to one another in a permanently optimum manner in all driving states, even when there are sudden changes in the accelerator-pedal signal, in order to achieve a high degree of driving comfort, without misfires, and low harmful gas emission. Regulation to the lambda value &lgr;=1 is carried out for this purpose. The inlet-valve opening durations are utilized for regulation due to the absence of throttle valves in the internal combustion engine described. By regulating to the lambda value &lgr;=1, combustion can take place under stoichiometrically highly favorable conditions, a process notable for its lower pollutant emission, in particular lower proportion of carbon monoxide.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for the reduction of harmful exhaust-gas emissions of a spark-ignition engine operated with a lean fuel/air mixture and having direct fuel injection. The jump to air ratios of &lgr;<1 and back to a lambda value &lgr;>1, this jump being necessary for regenerating the catalyst, can be carried out as quickly as possible, particularly when the engine is in stratified-charge mode with higher lambda values, such as, for example, >3, in order to avoid misfires, consumption losses and an increase in pollutant emissions.
This object is achieved, according to the invention, by a method in which in a first step, the air quantity in a combustion space is reduced by means of changes in the valve control times and, in a second step, a jump, rapid in time, from the stratified-charge mode to the homogeneous mode takes place, a lambda value &lgr;<1 being set or in a first step, the air quantity in the combustion space is reduced by means of throttling devices, located near the combustion space, in at least one of two intake ducts leading to the combustion space and, one intake duct being shut off for this purpose, and, in a second step, a jump, rapid in time, from the stratified-charge mode to the homogeneous mode takes place, a lambda value &lgr;<1 being set.
Shifting the location in order to reduce the air quantity in the intake region of a combustion space which also includes the intake region itself achieves short paths and therefore short reaction times in the event of changes in air quantity. This solution can be achieved by two or three measures having the same effect, specifically, on one hand, by changes in the valve control times, in which the desired reduction in the air quantity can be carried out either by early closing of inlet valves after top dead center or by delayed closing of inlet valves after bottom dead center of the piston in the combustion space.
As an alternative, throttle members, for example in the form of shut-off valves, may be provided in the intake ducts leading to the combustion spaces, preferably as near as possible to the inlet region into the combustion space. If, for example, two intake ducts are present for e
Enderle Christian
Hertzberg Andreas
Roessler Klaus
Argenbright Tony M.
Daimler-Chrysler AG
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
LandOfFree
Method for reducing harmful exhaust gas emissions of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for reducing harmful exhaust gas emissions of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for reducing harmful exhaust gas emissions of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2466740