Method and arrangement for controlling a combustion engine

Details Method and arrangement for controlling a combustion engine Method and arrangement for controlling a combustion engine

2001-12-20

2003-08-26

Argenbright, Tony M. (Department: 3747)

Power plants

Internal combustion engine with treatment or handling of...

Methods

C060S285000, C123S295000

Reexamination Certificate

active

06609364

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of International Application No. PCT/SE00/01224, filed Jun. 13, 2000, published Jan. 11, 2001, which claims priority to Swedish Application No. 9902567-8, filed Jul. 5, 1999. Both applications are expressly incorporated herein by reference.
BACKGROUND OF INVENTION
1. Technical Field
The present invention relates to a method for controlling a direct injected combustion engine. More particularly, the invention relates to controlling a direct injected Otto cycle combustion engine two modes of operation wherein the two modes have different air/fuel mixtures supplied to the engine. These operation modes preferably include a first mode for stratified operation and a second mode for homogeneous operation. The invention also relates to a direct injected engine arrangement for such control.
2. Background Information
In vehicles operated by combustion engines, there is a general demand for low emissions of harmful substances in the exhaust gases from the engine. These substances primarily include pollutants in the form of nitrous oxide compounds (“NO
x
”), hydrocarbon compounds (“HC”), and carbon monoxide (“CO”). For gasoline engines, the exhaust gases are normally purified by an exhaust catalyst that forms part of the exhaust system and through which the exhaust gases flow. In a three-way catalyst known in the art, the major part of the above harmful compounds is eliminated by known catalytic reactions. In order to optimize the function of the catalyst so that it provides an optimal degree of purification for NO
x
, HC, and CO, the engine is typically operated by a stoichiometric air/fuel mixture, i.e., a mixture where &lgr;=1.
Furthermore, there is a general demand for reducing vehicle fuel consumption by the engine to the greatest extent possible. To this end, engines have been developed during recent years with new types of combustion chambers in the engine cylinders, in particular so that the engine can operate with increasingly lean fuel mixtures, i.e., where &lgr;≧1. In a DI engine (ie., a direct injected Otto cycle engine), each cylinder combustion chamber in the engine is constructed so that the fuel supplied is highly concentrated at each respective ignition plug. This operating mode is generally termed “stratified” operation. During continuous driving at low or medium-high torque and engine speed, stratified operation provides an operation with a very lean air/fuel mixture, e.g., an operating mode of up to about &lgr;=3. In this manner, a substantial reduction in fuel consumption is obtained. The engine can also be operated in an “homogeneous” mode of operation with an essentially stoichiometric mixture (&lgr;=1) or a comparatively rich mixture (&lgr;<1). This later mode of operation normally prevails during driving situations with comparatively high torques and engine speeds.
During stratified operation, a lean exhaust gas mixture flows through the three-way catalyst. In doing so, the three-way catalyst becomes saturated so that it can not be utilized for reducing NO
x
compounds in the exhaust gases. This is due to the fact that it is constructed for an optimal degree of purification for a stoichiometric mixture. For this reason, a conventional three-way catalyst can be combined with a nitrous oxide adsorbent, or NO
x
adsorbent or trap, This adsorbent or trap is known per se for adsorbing NO
x
compounds, eg., in the exhaust gases from a combustion engine. In this manner, the NO
x
adsorbent can be utilized to compliment a conventional three-way catalyst. This can be done either as a separate unit upstream of the three-way catalyst or as an integral part of the three-way catalyst, i.e., together with the catalytic material of the three-way catalyst. In the latter, an integrated component in the form of a NO
x
adsorbing exhaust catalyst is formed.
The NO
x
adsorbent is constructed so that it takes up (adsorbs) NO
x
compounds in the exhaust gases when the engine is operated by a lean air/fuel mixture and gives off (desorbs) the NO
x
compounds when the engine is operated by a rich air/fuel mixture during a certain time period. Furthermore, the NO
x
adsorbent has the characteristic of being able to adsorb NO
x
compounds only up to a certain limit, i.e., it is eventually “filled”, reaching an adsorption limit. In this situation, the NO
x
adsorbent must be regenerated, i.e. it must be desorb and release the accumulated NO
x
compounds. If a conventional three-way catalyst is arranged downstream of a NO
x
adsorbent, or if the three-way catalyst is formed as an integral part of a NO
x
adsorbent, the desorbed NO
x
compounds can be eliminated by means of the three-way catalyst, provided that the catalyst has reached its ignition temperature.
A NO
x
adsorbent can be regenerated by providing a comparatively rich exhaust gas mixture flow through the NO
x
adsorbent becomes during a certain time period of approximately a few seconds. This is accomplished by operating the engine in the homogeneous operating mode during this time period, wherein the engine runs with a comparatively rich air/fuel mixture. By doing so, the NO
x
adsorbent is “emptied” so that it can subsequently adsorb NO
x
compounds for a time frame that lasts until the adsorbent is saturated and a new regeneration is needed.
It is known to switch between stratified and homogeneous mode by adjusting the air/fuel mixture supplied to the engine and the length of time for injecting the mixture. This switch is normally initiated due to the vehicle driver requesting a change in torque from the engine. This request can be provided by detecting the position of the engine's accelerator pedal. The vehicle includes a computer based control unit that, depending on the required torque, sees that a suitable air/fuel mixture is fed to the engine depending on, for example, whether a stratified or a homogeneous operation is required, or the required torque and engine speed of the engine.
In addition to a driver-initiated switch from an operating mode such as from stratified to homogeneous operation, the engine must also be able to switch to the homogeneous mode of operation in a compulsory manner (i.e., regardless whether the prevailing driving situation corresponds to homogeneous operation or not) when the control unit has estimated or determined that the NO
x
adsorbent needs to be regenerated. This requirement typically occurs after a certain time period has passed from a previous regeneration, or after a certain amount of NO
x
compounds has been fed into the NO
x
adsorbent, filling when the NO
x
adsorbent. A control unit for providing this type of operation is provided with a suitable strategy for switching the combustion engine between homogeneous and stratified operation based on the amount or degree of throttle application and engine speed, and considering whether NO
x
regeneration is necessary.
However, in previously known systems for switching a direct injected engine between stratified and homogeneous operation, a problem can occur when this mode switch happens while operating the engine with an air/fuel mixture composition that is disadvantageous for the required operating case. This is because each operating case of the engine requires a certain optimized air/fuel mixture. For example, a switch to a rich, stratified mode of operation can result in undesired carbon deposits in the engine. Furthermore, a switch to a lean, homogeneous operating mode results in an unstable combustion. This, in turn, can result in loss of torque or misfire of the engine.
The problem regarding disadvantageous air/fuel mixtures (i.e., disadvantageous lambda values) for each operating mode can per se be solved by adjusting the fuel amounts to the engine, thereby achieving a suitable lambda value. However, such a procedure can negatively impact the torque of the engine. Obviously, such an impact can affect the comfort or drivability of the vehicle, causing a “jerk” for the passengers therein.
Accordingly, there is a need fo

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