Method for starting an internal combustion engine

Details Method for starting an internal combustion engine Method for starting an internal combustion engine

1999-06-18

2001-04-17

Kwon, John (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Having a particular relationship between injection and...

C123S435000

Reexamination Certificate

active

06216664

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for starting an internal combustion engine, in particular of a motor vehicle, in which fuel is injected either, in a first operating mode, during a compression phase or, in a second operating mode, during an intake phase, directly into a combustion chamber delimited by a piston; and in which the fuel injected into the combustion chamber is ignited. The present invention further relates to an internal combustion engine, in particular for a motor vehicle, having an injection valve with which fuel can be injected either, in a first operating mode, during a compression phase or, in a second operating mode, during an intake phase, directly into a combustion chamber delimited by a piston; having a spark plug with which the fuel injected into the combustion chamber can be ignited; and having a control device with which the injection valve and the spark plug can be controlled.
BACKGROUND INFORMATION
Conventional systems for the direct injection of fuel into the combustion chamber of an internal combustion engine are known. A distinction is made in this context between so-called stratified mode as a first operating mode, and so-called homogeneous mode as a second operating mode. Stratified mode is used in particular at lesser loads, while homogeneous mode is utilized when greater loads are being placed on the internal combustion engine. In stratified mode, fuel is injected during the compression phase of the internal combustion engine into the combustion chamber, specifically into the immediate vicinity of a spark plug therein. The result of this is that uniform distribution of the fuel in the combustion chamber can no longer occur. The advantage of stratified operation is that the prevailing lesser loads can be handled by the internal combustion engine with a very small mass of fuel. Greater loads cannot, however, be handled in stratified mode. In the homogeneous mode provided for greater loads of this kind, fuel is injected during the intake phase of the internal combustion engine, so that turbulence and thus mixing of the fuel in the combustion chamber can readily take place. To this extent, homogeneous mode corresponds approximately to the method of operation of internal combustion engines in which fuel is injected in conventional fashion into the intake manifold.
In both operating modes, i.e. in stratified mode and in homogeneous mode, the injection angle and injection time of the fuel being injected are controlled in closed-loop and/or open-loop fashion by a control device, as a function of a plurality of parameters, to a value that is optimum in terms of fuel economy, emissions reduction, and the like.
For starting, the internal combustion engine is operated in homogeneous mode. Fuel is thus injected into the combustion chamber during the intake phase. The injection angle and the injection time during which fuel is injected are calculated by the control device prior to the intake phase. This calculation is performed in real time, i.e. on the basis of the operating state of the internal combustion engine existing prior to the intake phase.
During starting, the internal combustion engine is accelerated very rapidly. The result of this can be that the previously calculated injection angle and/or the previously calculated injection time no longer correspond, at the time of the actual injection action, to the operating state of the internal combustion engine existing at that time.
It is thus possible, for example, for the injection time to have been calculated for a low engine speed, but for the engine speed then to increase, because of the acceleration during starting, in such a way that the injection time is now too long. The result of this can be that fuel is still being injected into the combustion chamber, and the injection valve is thus still open, while the injected fuel is already being ignited by the spark plug. This causes premature carbon deposition on the injection valve, and is thus undesirable.
It is furthermore possible, because of the increase in engine speed during starting, for the injection valve still to be open even when the compression generated by the piston is already greater than the injection pressure that is being exerted on the fuel being injected. The result of this is then that a fuel-air mixture can be blown back out of the combustion chamber into the injection valve and thus into the fuel conditioning system. This causes subsequent misfires and the like during operation of the internal combustion engine.
It is the object of the present invention to create a method for operating an internal combustion engine with which the internal combustion engine can be more easily started.
SUMMARY OF THE INVENTION
This object is achieved by a method and combustion engine according to the present invention by the fact that injection of the fuel is terminated prior to ignition of the fuel.
This ensures that the injection valve is always closed when the fuel is ignited by way of the spark plug. Premature carbon deposition of the injection valve is thus reliably prevented. The operability and service life of the injection valve are thereby substantially increased.
In one embodiment of the present invention, injection of the fuel is terminated at a predefined angular position prior to ignition of the fuel. This angular position is precalculated and selected in such a way that in all circumstances it is located prior to ignition of the fuel. This on the one hand ensures that in all circumstances, the injection valve is closed when the fuel is ignited. On the other hand, this embodiment has the advantage that only at the aforesaid angular position is it necessary for the control device to perform an action, namely to command the injection valve into its closed state if it is still open. Further actions, in particular monitoring of the angular position at regular time intervals, are not necessary.
It is also advantageous if injection of the fuel is terminated, at the latest, at for example approximately 290 degrees past the top dead center point of the relevant piston. The top dead center point of a piston in a cylinder is measured using associated sensors. It is thus possible, based on the top dead center point after the intake phase, to indicate the angular position at which the injection valve is to be closed. The angular position of approximately 290 degrees past the top dead center point after the intake phase represents a value at which ignition of the fuel in the combustion chamber is in no circumstances yet taking place.
In another embodiment of the present invention, injection of the fuel is terminated at a predefined temporal or angular interval prior to ignition of the fuel. For example, as soon as the interval between the actual angular position of the internal combustion engine and the precalculated angular position provided for ignition falls below a specific limit value, if fuel is still being injected into the combustion chamber, the injection valve is closed. The result is that fuel is always injected up until the maximum possible angular position, but that in all circumstances, the injection valve is nevertheless closed when the fuel is ignited. With this embodiment it is necessary, however, to measure or calculate the current angular position of the internal combustion engine at frequent intervals.
In another embodiment of the present invention in which the pressure exerted on the fuel being injected is measured, the pressure existing in the combustion chamber is ascertained, and injection of the fuel is terminated before or as soon as the pressure in the combustion chamber becomes greater than the pressure exerted on the fuel.
The injection valve is closed no later than the point in time at which the pressure in the combustion chamber becomes greater than the pressure exerted on the fuel. The result is that fuel-air mixture cannot be blown back out of the combustion chamber into the injection valve. The operability of the fuel conditioning system is thus maintained, and misfiring of the in

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