Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2000-02-17
2001-06-05
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S430000
Reexamination Certificate
active
06240895
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for operating an internal combustion engine, particularly of a motor vehicle, where fuel is injected directly into a combustion chamber either in a first operating mode, during a compression period, or in a second operating mode, during an induction period; where the air mass supplied to the combustion chamber is ascertained; and where the fuel mass injected into the combustion chamber is controlled and/or regulated differently in the two operating modes. Furthermore, the present invention relates to an internal combustion engine, particularly for a motor vehicle, having an injector with the assistance of which fuel can be injected directly into a combustion chamber either in a first operating mode, during an induction period or, in a second operating mode, during a compression period, and having a control unit for ascertaining the air mass supplied to the combustion chamber, and for differently controlling and/or regulating the fuel mass injected into the combustion chamber in both operating modes.
BACKGROUND INFORMATION
Such systems for injecting fuel directly into the combustion chamber of an internal combustion engine are generally known. In this context, a distinction is made between a so-called “stratified operation” as a first operating mode and a so-called “homogeneous operation” as a second operating mode. The stratified operation is used particularly in the case of smaller loads while the homogeneous operation is used in the case of bigger loads placed on the internal combustion engine.
In the stratified operation, fuel is injected into the combustion chamber during the compression period of the internal combustion engine in such a manner that, at the time of ignition, a fuel cloud is in the immediate surroundings of a spark plug. This injection can be carried out in different ways. In fact, is possible for the injected fuel cloud to be near the spark plug during or immediately after the injection, and to be ignited by the spark plug. It is also possible for the injected fuel cloud to be conveyed to the spark plug by a charging movement, and to be ignited only then. In both burning methods, there is no uniform fuel distribution but a stratified charge.
The advantage of the stratified operation is that it makes it possible for the placed smaller loads to be executed by the internal combustion engine using a very small fuel quantity. Bigger loads, however, cannot be fulfilled by the stratified operation.
In the homogeneous operation intended for such bigger loads, fuel is injected during the induction period of the internal combustion engine, so that the fuel can still be swirled, and thus distributed in the combustion chamber without any problem. In this respect, the homogeneous operation corresponds more or less to the operating mode of internal combustion engines where fuel is injected into the intake pipe in a conventional manner. If required, the homogeneous operation can also be used for smaller loads.
In the stratified operation, the throttle valve in the intake pipe leading to the combustion chamber is wide opened, and the combustion is mainly controlled and/or regulated via the fuel mass to be injected. In the homogeneous operation, the throttle valve is opened or closed as a function of the required torque, and the fuel mass to be injected is controlled and/or regulated as a function of the air mass taken in.
In both operating modes, i.e., in the stratified operation and the homogeneous operation, the fuel mass to be injected is controlled and/or regulated additionally as a function of a plurality of further input variables to an optimal value in terms of fuel saving, exhaust reduction and the like. In this context, the control and/or regulation is different in the two operating modes.
It is required to switch over the internal combustion engine from the stratified operation to the homogeneous operation and back again. While in the stratified operation, the throttle valve is opened wide, and the air is consequently supplied in a substantially dethrottled manner, in the homogeneous operation, the throttle valve is opened only partially, thus reducing the supply of air. In this context, above all during the switchover from the stratified operation to the homogeneous operation, the capability of the intake pipe leading to the combustion chamber of storing air must be taken into account. If this is not taken into account, the switchover may lead to an increase in the torque delivered by the internal combustion engine.
SUMMARY OF THE INVENTION
The object of the present invention is to devise a method for operating an internal combustion engine which makes it possible to optimally switch over between the operating modes.
This objective is achieved according to the present invention by switching over between the first operating mode and the second operating mode as a function of the air mass supplied to the combustion chamber.
The air mass supplied to the combustion chamber represents an exact and reliable criterion on the basis of which the switchover operation from the first to the second operating mode, or from the second to the first operating mode can be carried out. Furthermore, the air mass supplied to the combustion chamber can be determined either by the control unit with the assistance of model calculations, or a pressure sensor or air-mass flow sensor that is present in the intake pipe for determining the air mass supplied to the combustion chamber. In this context, both ways can be implemented in a simple manner, and with little constructional outlay.
In an advantageous embodiment of the present invention, a switchover is made from the first to the second operating mode when the air mass supplied to the combustion chamber falls below a maximum air mass for the homogeneous operation. During the switchover from the stratified operation to the homogeneous operation, the air mass supplied to the combustion chamber decreases. If the air mass reaches the specified maximum value for the homogeneous operation, then a switchover is made to the homogeneous operation. Consequently, this transition can be controlled and carried out in a simple manner.
It is particularly advantageous to reduce the supply of the air mass to the combustion chamber prior to switching over to the second operating mode. This is achieved by closing the throttle valve prior to the actual switchover.
In a further advantageous embodiment of the present invention, the supplied fuel-air mixture is controlled and/or regulated to a predetermined, in particular a stoichiometric value in the second operating mode. Thus, the fuel-air mixture has a defined, predetermined value, for example 1. In this manner, a particularly low-emission operation of the internal combustion engine is achieved.
In this context, it is particularly expedient for the fuel mass to be injected to be determined from the supplied air mass subsequent to switching over to the second operating mode. In this manner, it can be guaranteed that the predetermined or stoichiometric value of the fuel-air mixture is maintained.
Moreover, it is particularly expedient for the ignition-advance angle to be determined from the required torque subsequent to switching over to the second operating mode. Thus, with the assistance of the ignition-advance angle, it is possible to achieve, in particular short-term changes in torque without having to change the predetermined or stoichiometric value.
In an advantageous embodiment of the present invention, a switchover is made from the second to the first operating mode when the air mass supplied to the combustion chamber exceeds a minimum air mass for the stratified operation. During the switchover from the homogeneous operation to the stratified operation, the air mass supplied to the combustion chamber increases. If the air mass reaches the specified minimum value for the stratified operation, then a switchover is made to the stratified operation. Consequently, this transition can be controlled and carried out in a simple manner.
It i
Kenyon & Kenyon
Robert & Bosch GmbH
Vo Hieu T.
Yuen Henry C.
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