Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
1999-07-21
2001-05-22
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000, C123S339140, C123S491000
Reexamination Certificate
active
06234140
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for operating an internal combustion engine especially of a motor vehicle wherein fuel is injected directly into a combustion chamber either in a first operating mode during a compression phase or in a second operating mode during an induction phase. In the method, the fuel mass, which is to be injected into the combustion chamber, is determined in both operating modes, inter alia, in dependence upon a computed desired torque which is to be outputted by the engine. The invention further relates to an internal combustion engine especially of a motor vehicle having an injection valve with which fuel can be injected directly into a combustion chamber either in a first operating mode during a compression phase or in a second operating mode during an induction phase. The engine has a control apparatus for determining the fuel mass, which is to be injected into the combustion chamber, in both operating modes, inter alia, in dependence upon a computed desired torque which is to be outputted by the engine.
BACKGROUND OF THE INVENTION
System of this kind for direct injection of fuel into the combustion chamber of an internal combustion engine are generally known. A first operational mode (a so-called stratified layer operation) and a second operating mode (a so-called homogenous operation) are distinguished from each other. The stratified layer operation is especially used at low loads; whereas, the homogeneous operation is applied for larger loads applied to the engine. In the stratified layer operation, the fuel is injected during the compression phase of the engine into the combustion chamber and to the direct vicinity of a spark plug. This has the consequence that no uniform distribution of the fuel in the combustion chamber can take place. The advantage of the stratified layer operation is that the applied lower loads of the engine can be carried out with a very low mass of fuel. Larger loads can, however, not be satisfied by the stratified layer operation. In the homogeneous operation, which is provided for such larger loads, the fuel is injected during the induction phase of the engine so that a turbulence and therefore a distribution of the fuel in the combustion chamber can easily take place. Insofar, the homogeneous operation approximates the operational mode of the engine wherein fuel is injected into the intake manifold in a conventional manner.
In both modes of operation (that is, in the stratified layer operation and in the homogeneous operation), the fuel mass to be injected is controlled (open loop and/or closed loop) by a control apparatus in dependence upon a plurality of parameters to an optimal value with a view of saving fuel, reducing exhaust gas and the like. This control (open loop and/or closed loop) is then, inter alia, dependent upon a desired value which is computed by the control apparatus. The desired torque defines the torque, which in total is to be outputted by the engine, that is, that torque which the engine should generate.
Especially during idle of the engine, it is desired that the rpm of the engine is as constant as possible. For this purpose, a method is known from U.S. Pat. No. 4,344,397 with which the idle of the engine can be stabilized. In this method, the rpm of the engine is influenced via a shifting of the ignition time point and therefore is held approximately constant. The known method is, however, only usable in an internal combustion engine wherein fuel is injected into the intake manifold in the conventional manner.
For an internal combustion engine of the type initially mentioned herein (especially in the first operating mode, that is, in stratified layer operation), the actual torque, which is generated by the engine, and therefore the rpm of the engine, is essentially only dependent upon the injected fuel mass. A change of the ignition time point is not possible in the same manner as for homogeneous operation because the igniting condition would change thereby. For this reason, the known method cannot be purposefully used for the internal combustion engine of the type initially mentioned herein.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for operating an internal combustion engine with which an rpm as constant as possible can be achieved especially during idle of the engine.
This object is solved in accordance with the invention for a method or for an internal combustion engine of the type initially mentioned herein in that an injection duration is determined from the fuel mass, which is to be injected, and that an injection angle is determined from the injection duration in dependence upon the rpm of the engine and that the fuel is injected during the injection angle.
The engine has a specific rpm at the time point of the conversion of the injection duration into the injection angle. If, for example, the rpm thereafter becomes less, then this has no effect on the computed injection angle. The computed injection angle therefore remains constant. Because of the lower rpm, this injection angle is now run through slower than for that rpm at which the computation took place. This means that the injection duration is increased. Accordingly, more fuel is injected than had been intended. This injection of more fuel has the consequence that the engine is again accelerated and therefore the rpm is increased.
With the invention, it is achieved that the rpm of the engine is held substantially constant. It is not required that the control apparatus must intervene correctively in the injection of fuel; instead, the rpm stabilization according to the invention takes place automatically without any activity of the control apparatus. The invention therefore makes a method available which can control (open loop and/or closed loop) the rpm of the engine rapidly and precisely to an approximately constant value especially during idle of the engine. Furthermore, the invention can also be applied when, for example, an essentially constant rpm of the engine is wanted for a desired torque applied over a longer time.
In an advantageous further embodiment of the invention, either an injection start is pregiven as an angle magnitude and an injection end is determined in dependence upon the injection angle or, the injection end is pregiven as an angle magnitude and the injection start is determined in dependence upon the injection angle. In this way, the particular other value can be computed in a simple manner from the injection angle in dependence upon the value which is pregiven in the particular internal combustion engine.
In an advantageous embodiment of the invention, the injection duration is converted only partially into the injection angle. In this way, it is achieved that, for example, for a reduction of the rpm after the conversion of the part of the injection duration into the injection angle, the resulting injection of additional fuel is not so greatly increased as for a complete conversion. From this, a reduced acceleration, and therefore a reduced increase of the rpm of the engine, results than for a conversion of the total injection duration into the injection angle. In this way, a correction of the rpm which is too great and a possible overshoot to an rpm of the engine which is too great is avoided.
In an advantageous embodiment of the invention, an injection start as a time duration is determined from the injection start as an angle magnitude in dependence upon the rpm of the engine and the injection of fuel is started after this time duration has elapsed. In this way, it is achieved that, for example, for a reduction of rpm after the conversion of the injection duration into the injection angle, the resulting injection of more fuel is further increased. From this, a further acceleration and therefore an increase of the rpm of the engine results. In this way, it is possible to achieve a large correction of the rpm of the engine.
In an advantageous further embodiment of the invention, the injection start as an angle magnitude is only partially converted
Mallebrein Georg
Mentgen Dirk
Argenbright Tony M.
Ottesen Walter
Robert & Bosch GmbH
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