DE102010002266B3 - Method for direct injection of fuel into combustion chamber of internal combustion engine with induced ignition, involves shifting early start of injection, where soot concentration falls below predetermined threshold value in crank angle - Google Patents

Abstract

The method involves providing a combustion chamber (6) with an inlet opening controllable by an inlet valve (1) and an outlet opening controllable by an outlet valve. Early start of injection is shifted at increasing soot concentration in exhaust gas upto a crank angle based on control time at which the outlet valve is closed during excess of crank angle marks of maximum soot concentration, where the soot concentration falls below a predetermined threshold value in the crank angle.

Description

The invention relates to a method for the direct injection of fuel into the combustion chamber of a spark-ignition internal combustion engine, wherein the combustion chamber has at least one inlet valve controllable by inlet valve and at least one outlet valve controllable by means of outlet valve, is injected in the fuel in the manner that during the valve separation in the open Inlet valve to flow combustion gases with fuel through the at least one inlet port into the subsequent intake system.

Due to the limited resources of fossil fuels, in particular due to the limited presence of mineral oil as a raw material for the production of fuels for internal combustion engines, the development of internal combustion engines is constantly striving to minimize fuel consumption, with an improved, d. H. more effective combustion is at the forefront of the effort.

The problem is the fuel consumption, especially in gasoline engines. The reason for this lies in the basic working method of the traditional gasoline engine, which works with a homogeneous fuel-air mixture, which is prepared by external mixture formation by injecting fuel into the intake tract, and in which the desired power is adjusted by means of quantity control.

The load control is usually carried out by means of a throttle valve provided in the intake tract. By adjusting the throttle, the pressure of the intake air downstream of the throttle valve can be reduced more or less. The farther the throttle is closed, d. H. the more it obstructs the intake tract, the higher the pressure loss of the intake air across the throttle and the lower the pressure of the intake air downstream of the throttle and before the inlet into the combustion chamber. With constant combustion chamber volume, the air mass, d. H. the quantity by which the pressure of the intake air is adjusted. The quantity control by means of throttle valve has thermodynamic disadvantages, in particular in the partial load range. Because low loads require a large pressure drop in the intake tract and therefore a high throttling. In order to reduce the throttle losses, various strategies have been developed, for example the dethrottling of the Otto engine operating method by the use of a variable valve train.

Other approaches to improve fuel economy in gasoline engines are based on the adoption of technical features that were originally attributed to the diesel engine process.

The traditional Otto cycle method is characterized by a mixture compression, a homogeneous mixture, a spark ignition, and the quantity control, whereas the diesel engine process is characterized by an air compression, an inhomogeneous mixture, auto-ignition and quality control.

In particular, the injection of fuel directly into the combustion chamber is considered a suitable measure to achieve a noticeable reduction in fuel consumption even in gasoline engines, which is why it is increasingly focused on the development of direct injection gasoline engines. A direct injection internal combustion engine with spark ignition is therefore also an object of the present invention.

Due to the lack of entry of fuel upstream of the inlet to the combustion chamber are formed in direct injection gasoline engines undesirable deposits in the intake system, in particular at the intake valves and the associated valve seats.

In the process, oil and fuel particles contained in the intake air are deposited on the inner walls of the intake system and the intake valves. These particles are introduced into the intake system by the internal and external feedback of hot exhaust gases and the introduction of blow-by gases from the crankcase via vent line. The oil and fuel particles form a sticky film, to which soot particles attach or adhere. The adhering soot particles in turn favor the addition of further oil and fuel particles, which equates to an increase in the layer thickness with increasing operating time. The deposits lead to a changed geometry in the intake system, which brings significant disadvantages.

1 schematically shows the open inlet valve 1 a cylinder 5 and between the valve plate 2 and the valve seat 3 formed inlet flow 4 in the combustion chamber 6 ,

Due to the direct injection of the fuel into the combustion chamber, which provides little time for the preparation of a combustible fuel-air mixture, direct-injection Otto cycle methods are much more sensitive to disturbances in the mixture formation than conventional Otto-cycle method.

In particular, the formation of the desired cylinder internal flow within the context of the charge cycle also counts for mixture formation. In general, the inlet flow is influenced by appropriate shaping of the inlet region.

Deposits on the inlet valves or inlet openings influence or interfere with the formation of the desired cylinder internal flow, which may be required for reliable ignition of the fuel-air mixture in the combustion chamber. In particular, in part-load operation, when the fresh mixture is often emaciated by a stratified operation, a changed cylinder internal flow can adversely affect the combustion process, lead to incomplete combustion of the fuel-air mixture and possibly cause misfires, so that the fuel-air mixture unburned in the Exhaust tract is removed. Failure to burn not only results in a loss of performance, i. H. to a torque drop, but possibly also to a malfunction or damage provided in the exhaust system exhaust aftertreatment systems.

For the reasons mentioned above, therefore, efforts are fundamentally made to counteract component coking in the intake system or in the intake region of a direct-injection internal combustion engine, ie. H. Deposits in the intake system, especially at the intake valves and intake ports to prevent from the outset, as is the case with gasoline engines with intake manifold injection due to the fuel input.

The German patent application DE 101 34 117 A1 suggests injecting fuel into the combustion chamber during valve diversion at a time when, with the inlet valve open, combustion gases flow through the at least one inlet port into the subsequent intake system. As a valve overlap, the crank angle range is generally and in the context of the present invention referred to, in which the exhaust valve is not yet closed when the intake valve is open.

In this way, fuel, along with hot combustion gases, flows back into the intake manifold to the intake valves and the valve seats. The introduced fuel flows around the valve and associated valve seat, cleaning it of adhering particles, thereby counteracting the formation of deposits. During the subsequent intake process, the fuel and the exhaust gases introduced into the intake system return to the combustion chamber.

By doing so, additional costly measures against the valve coking, such as a coating or surface treatment of the intake valve or the arrangement of additional injectors in the intake tract, can be omitted.

A disadvantage of the in the DE 101 34 117 A1 However, described method for operating a direct-injection internal combustion engine is that a specific time for the start of fuel injection is not specified and a plurality of regulated regulatory pollutants in the relevant here crank angle window of the valve overlap, which usually extends beyond the top dead center of the charge LWOT , can vary greatly.

In a direct-injection internal combustion engine, according to the prior art, the decisive criterion for determining the start of injection SOI is the soot concentration in the exhaust gas. During the calibration of the engine control system, fuel injection approaches the top dead center of the charge cycle LWOT from the intake phase and scans the soot limit, the soot limit being defined as the crank angle at which the soot concentration noticeably increases and exceeds a predefinable value.

In this respect, one is greatly limited by the prior art in the choice of the start of injection, namely on the one hand by the observed soot limit and on the other hand by in the DE 101 34 117 A1 established requirement to inject within the valve overlap. The earliest possible start of injection, which is generally aimed at with regard to a good mixture preparation, in particular an injection start in the discharge phase, is thus generally not feasible, although this would have clear advantages in terms of fuel consumption. However, this disadvantage is accepted according to the prior art.

Against this background, it is the object of the present invention to provide a method for direct injection of fuel into the combustion chamber of an internal combustion engine with spark ignition according to the preamble of claim 1, with which the known from the prior art problem can be counteracted and which in the Choice of injection start SOI has a greater variety, in particular allows a relatively early start of injection to reduce fuel consumption.

This object is achieved by a method for direct injection of fuel into the combustion chamber of an internal combustion engine with spark ignition, wherein the combustion chamber at least one means Inlet valve controllable inlet port and at least one controllable by means of an outlet valve outlet opening is injected in the fuel in such a way that flow during combustion of the valve with open inlet valve combustion gases with fuel through the at least one inlet opening in the subsequent intake system, and which is characterized in that starting from the control time to which the at least one exhaust valve closes (AS), the start of injection SOI is also shifted initially with increasing soot concentration in the exhaust gas over the crank angle mark maximum soot concentration addition at least up to a crank angle at which the soot concentration C _soot a specifiable value C _{threshold, soot falls} below C _soot <C _{threshold, soot} .

The method according to the invention for fuel injection utilizes the circumstance that the displacement of the soot concentration in the exhaust gas first increases when the start of injection from the intake phase in the direction of top dead center LWOT and above the top dead center, but then again after exceeding a maximum soot concentration, which as a rule is reached at the top dead center of the charge cycle, decreases. This course of the soot concentration as a function of the start of injection SOI is also in 2 and will be discussed below in connection with the description of the figures.

Depending on the quantity of injected fuel and the injection time, a more or less large portion of the injected fuel reaches the combustion chamber inner walls and in particular the piston of the corresponding cylinder, which is guided axially movably in a cylinder tube. The piston crown forms part of the combustion chamber inner wall and, together with the piston rings, seals the combustion chamber against the crankcase.

The closer the beginning of the injection is at the top dead center of the charge cycle, the more fuel reaches the piston crown, which is directly related to the piston position. The more fuel reaches the combustion chamber inner walls, in particular the piston crown, the more soot is formed. That is, the soot concentration increases the nearer the start of injection SOI moves to the top dead center. In this respect - in simplified terms - there is a causal relationship between the soot concentration in the exhaust gas on the one hand and the piston position and the start of injection on the other.

Strictly speaking, other operating parameters of the internal combustion engine influence the course of the soot concentration, for example the speed. Thus, the crank angle mark maximum soot concentration shifts late with increasing speed. The inertia of the injection or the delayed use of the combustion process lead to the fact that the maximum soot concentration is often not reached at an injection start at top dead center.

The method according to the invention now teaches that starting from the intake phase, the start of injection SOI is to be shifted in the direction of top dead center LWOT and possibly beyond that known from the prior art soot limit and maximum carbon black concentration, even if the soot concentration in the exhaust gas initially increases. The start of injection is postponed until a crank angle at which the soot concentration C soot _{falls below} a predefinable value C _{threshold, soot} , with C _soot <C _{threshold, soot} . The threshold value, ie the predetermined value C _{threshold, soot} , is the soot concentration or soot emission _{that can be tolerated} in the respective operating point.

The procedure according to the invention for fuel injection or for determining the start of injection permits a comparatively early start of injection compared to the prior art, which is extremely advantageous with regard to the fuel consumption of the direct-injection internal combustion engine. In particular, the method according to the invention makes it possible to start the injection even outside the valve separation, ie. H. at a time when the inlet valve is not yet opened, as long as it is ensured that at least parts of the injected fuel - albeit time-delayed - through the at least one - then opened - inlet flow into the subsequent intake system.

Thus, the object underlying the invention is solved, namely to show a method according to the preamble of claim 1, which has a greater variety in the choice of the start of injection SOI and in particular allows a comparatively early start of injection to reduce fuel consumption.

Further advantages of the method according to the invention are discussed in connection with the embodiments according to the subclaims.

Embodiments of the method are advantageous in which the start of injection SOI is shifted so far at most beyond the predefinable value for the soot concentration C _threshold until the concentration C _HC of unburned hydrocarbons reaches a predefinable value for the concentration C _{threshold, HC} and / or the gradient dC / d ° KW of the increase in concentration C _{HC reaches} a predefinable value dC / d ° KW _threshold .

In principle, the start of injection SOI can be postponed beyond the crank angle, at which the soot concentration C soot _{falls below} a predefinable value C _{threshold, soot} , in order to optimize fuel consumption. However, the start of injection can not be delayed arbitrarily far to early, since the concentration C _HC of unburned hydrocarbons HC on reaching a certain crank angle mark significantly, almost suddenly increases and continues to increase continuously with further shifting of the injection start to early.

This significant continuous increase makes it clear that an increasing proportion of the injected fuel passes unburned into the exhaust tract, instead of flowing into the intake system with the combustion gases, which is the aim of the invention.

The cause is too early a start of injection at a time when the intake valve is not yet open. The greater the distance between the start of injection SOI and the control time EÖ, at which the intake valve opens, the more fuel can leave the combustion chamber unburned via the open outlet and increase the HC concentration in the exhaust gas.

On the other hand, with the injection must not wait until the at least one inlet valve is opened or is, because according to the invention, the start of injection before the control time EÖ "inlet opens" lie as long as the essential part of the injected fuel enters the intake system, even if the As part of Ausschiebens previously fuel first enters the exhaust tract.

In accordance with the method variant in question, this circumstance is taken into account by an additional condition. Accordingly, the start of injection SOI is only advanced so far until the concentration C _HC of unburned hydrocarbons reaches or exceeds a predefinable value for the concentration C _{threshold, HC} and / or the gradient dC / d ° KW of the increase in concentration C _{HC is} a predefinable Value dC / d ° KW _threshold reaches or exceeds. This ensures that the desired early start of injection does not lead to unacceptably high HC emissions.

Advantageous embodiments of the method in which the injection start SOI is placed in the Ausschiebephase before the top dead center of the charge cycle LWOT.

If the injection of the fuel with the intake valve open is already started in the discharge phase, the piston moving upwards supports the inflow of fuel and combustion gases through the at least one inlet opening into the adjoining intake system and thus the cleaning of the walls of the intake system affected by deposits, in particular of the inlet valve or the valve seat.

Particularly at higher loads, when a throttle cap arranged in the intake system is wide open and there is no or only a slight pressure gradient between the combustion chamber and the intake system, the present variant proves to be particularly advantageous.

At low loads, however, takes place when the inlet valve is already due to the pressure gradient between the combustion chamber and the intake system, a return flow of exhaust gas together with injected fuel instead, so that the upwardly moving piston is not absolutely necessary, but supports the return flow. The pressure gradient at low loads results from the throttle valve, which is more or less closed in the partial load range, which ensures a reduced pressure downstream of the flap and thus upstream of the inlet.

Embodiments of the method in which the inlet valve of the at least one inlet opening is opened in a crank angle window of 50 ° CA before the top dead center of the charge cycle LWOT to 20 ° CA after the top dead center of the charge cycle LWOT are advantageous.

Embodiments of the method in which the inlet valve of the at least one inlet opening is opened in a crank angle window of 40 ° CA before the top dead center of the charge cycle LWOT up to the top dead center of the charge cycle LWOT are particularly advantageous.

Embodiments of the method in which the outlet valve of the at least one outlet opening is closed in a crank angle window between the top dead center of the charge cycle LWOT and 50 ° CA after the top dead center of the charge cycle LWOT are advantageous.

Embodiments of the method in which the outlet valve of the at least one outlet opening is closed in a crank angle window of 10 ° CA to 40 ° CA after top dead center of the charge cycle LWOT are advantageous.

Embodiments of the method in which the injection is started before the valve overlap d are advantageous. H. before the at least one inlet valve is opened.

In the following, the invention is based on the 2 described in more detail.

It shows:

1 schematically the open inlet valve of a cylinder of a direct injection internal combustion engine, and

2 the soot concentration, the fuel consumption and the HC concentration in the exhaust gas as a function of the start of injection SOI.

The 1 has already been discussed in connection with the description of the prior art.

2 shows the soot concentration, the fuel consumption and the HC concentration in the exhaust gas, which are plotted on the ordinate, as a function of the start of injection SOI, which is plotted on the abscissa. The crank angle 360 ° KW marks the top dead center of the charge cycle LWOT.

If you approach the LWOT from the right, d. H. Coming from the intake phase, the soot concentration increases noticeably with a certain crank angle, the so-called soot limit, and then increases continuously. After exceeding a maximum, which is achieved here in the LWOT, the carbon black concentration then drops again.

In this respect, the course of the soot concentration does not preclude a shift in the start of injection into the discharge phase, as a result of which the fuel consumption can be significantly reduced. In determining the start of injection but must also be considered that the concentration of unburned hydrocarbons HC significantly increases when reaching a certain crank angle mark. The start of injection can therefore not be moved arbitrarily far to early, which is not absolutely necessary for optimizing fuel consumption.

The erratic increase in the HC concentration and / or the gradient dC / d ° CA of this increase in concentration is therefore used to formulate an additional criterion for the early start of injection delay. According to this additional criterion, the start of injection SOI can only be postponed until the concentration C _HC of unburned hydrocarbons reaches or exceeds a predefinable value for the concentration C _{threshold, HC} and / or the gradient dC / d ° KW increases the concentration C _HC reaches or exceeds a predefinable value dC / d ° KW _threshold . In this way it is ensured that the shift of the beginning of injection does not lead to unacceptably high HC emissions.

LIST OF REFERENCE NUMBERS

1

intake valve

2

valve disc

3

valve seat

4

inlet flow

5

cylinder

6

combustion chamber

AS

Exhaust valve closes

_HC

Concentration of unburned hydrocarbons

C _soot

soot concentration

C _{threshold, HC}

Threshold, specifiable limit for C _HC

C _{threshold, soot}

Threshold, specifiable limit for C _soot

dC / d ° KW

Gradient of increase in concentration C _HC

dC / d ° KW _threshold

Threshold, specifiable limit for dC / d ° KW

EÖ

Inlet valve opens

HC

unburned hydrocarbons

° CA

Degree crank angle

LWOT

top dead center of the charge cycle

n

rotation speed

ppm

parts per million

SOI

Start of injection, start of injection

Claims (8)

Method for direct injection of fuel into the combustion chamber of a spark-ignition internal combustion engine, wherein the combustion chamber has at least one inlet valve controllable by inlet valve and at least one outlet valve controllable by means of exhaust valve, is injected in the fuel in such a way that during the valve separation with the inlet valve open combustion gases with fuel flow through the at least one inlet opening in the subsequent intake system, characterized in that starting from the control time to which the at least one exhaust valve closes (AS), the start of injection SOI is moved to the early even with initially increasing soot concentration in the exhaust gas, on the crank angle mark maximum soot concentration, at least up to a crank angle, in which the soot concentration C soot _{falls below} a predefinable value C _{threshold, soot} with C _soot <C _{threshold, soot} . A method according to claim 1, characterized in that the start of injection SOI is at most as far above the predetermined value for the soot concentration C _{threshold, soot} moved until the concentration C _HC unburned hydrocarbons reaches a predetermined value for the concentration C _{threshold, HC} and / / or the gradient dC / d ° KW of the increase in concentration C _{HC reaches} a predefinable value dC / d ° KW _threshold . A method according to claim 1 or 2, characterized in that the injection start SOI is placed in the Ausschiebephase before the top dead center of the charge exchange LWOT. Method according to one of the preceding claims, characterized in that the inlet valve of the at least one inlet opening is opened in a crank angle window of 50 ° CA before top dead center of the charge cycle LWOT to 20 ° CA after top dead center of the charge cycle LWOT. A method according to claim 4, characterized in that the inlet valve of the at least one inlet opening is opened in a crank angle window of 40 ° CA before top dead center of the charge cycle LWOT to the top dead center of the charge cycle LWOT. Method according to one of the preceding claims, characterized in that the exhaust valve of the at least one outlet opening is closed in a crank angle window between the top dead center of the charge cycle LWOT and 50 ° CA after the top dead center of the charge cycle LWOT. A method according to claim 6, characterized in that the exhaust valve of the at least one outlet opening is closed in a crank angle window of 10 ° CA to 40 ° CA after top dead center of the charge cycle LWOT. Method according to one of the preceding claims, characterized in that the injection is started before the valve overlap.

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