KR102468976B1 - Methods for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine in which fuel is metered into the intake pipe via a first injection valve and directly into a combustion chamber of the internal combustion engine via a second injection valve, in this case a first injection valve. In one operating mode, the first injection valve is preferably used, and in the second operating mode, the second injection valve is preferably used, in which case the minimum amount is metered by means of the second injection valve in the first operating mode.

Description

Methods for operating an internal combustion engine

The invention proceeds from a method for operating an internal combustion engine according to the preamble of claim 1 . The subject matter of the present invention also includes computer program products.

A method for operating an internal combustion engine is known, in which fuel is metered into the intake pipe via a first injection valve and directly into a combustion chamber of the internal combustion engine via a second injection valve. In this method, a first injection valve is preferably used in the first mode of operation and a second injection valve is preferably used in the second mode of operation. This combination of so-called PFI injection and so-called DI injection makes it possible to use the advantages of both types of injection for optimum mixture formation and combustion. Under full load and dynamic conditions of the internal combustion engine, the use of a second injection valve that injects directly into the combustion chamber is preferred. At part load, the use of a first injection valve that injects into the intake pipe is preferred, since in this case a lower emission occurs.

If the internal combustion engine is operated for a longer period of time in the first operating mode with injection only into the intake pipe, it may happen that fuel and/or fuel components deposit on the second injection valve. These deposits plate-out on the inside of the injection hole and/or on the outer surface of the valve seat. Such precipitates are formed especially at high temperatures. It is already known from the prior art how intermittent injection with a second injection valve prevents or even removes corresponding deposits. In addition, the second valve is cooled not only by the fuel itself but also by fuel evaporation, which reduces sticking of deposits and chemical conversion of the fuel.

Compared to the prior art, the method according to the invention having the features of independent claim 1 has the advantage that deposits can be prevented or eliminated to the maximum.

According to the invention, in the first operating mode, the minimum injection quantity is metered in by means of the second injection valve. By doing this, deposit formation in the injector can be prevented reliably.

Particularly preferably, if the total injection amount is greater than the minimum injection amount, the minimum injection amount is metered in by means of the second injection valve. In operating conditions where the total injection amount is less than the minimum amount, there is a possibility of very little deposit formation. Control of the injection valve can thereby be ruled out. As a result, energy is saved and unnecessary loading of the injection valve is avoided.

Particularly preferably, the minimum injection amount corresponds to the minimum injection amount of the second injection valve. This means that the minimum injection amount is preferably slightly greater than the minimum injection amount.

In another aspect, the invention relates to program code together with processing instructions for generating a computer program executable on a control device, in particular source code with compiler instructions and/or link instructions, wherein the program code creates a computer program for executing all the steps of the method described above, when this program code is converted into an executable computer program according to processing instructions, that is, in particular compiled and/or linked. This program code may in particular be provided by source code downloadable from a server in the Internet, for example.

Embodiments of the invention are shown in the drawings and described in detail below.
1 shows the main elements of an injection system with first and second injection valves;
2-4 are various flow diagrams of various embodiments of the method according to the present invention.

In Figure 1, the main elements of the injection system are shown. In FIG. 1 , only a simplified diagram has been selected, showing only the combustion chamber and associated injection valves. The present invention is not limited to the application of such an internal combustion engine having one cylinder. The invention can be used with any different number of cylinders.

The combustion chamber of an internal combustion engine is indicated by the reference numeral 100 . Combustion chamber 100 is supplied with air or air fuel mixture through intake pipe 110 . To this end, it is proposed that fuel is injected into the intake pipe 110 by means of the first injection valve 120 . In addition, a second injection valve 130 capable of metering fuel directly into the combustion chamber 100 is provided. In the illustrated embodiment, first and second injection valves are assigned to each cylinder of the internal combustion engine. However, only one primary injection valve may be provided for all cylinders or for one group of cylinders. In this case, the fuel arrives in one common intake pipe of several cylinders via one first injection valve.

The control unit 140 supplies control signals to the first injection valve 120 and the second injection valve 130 . The control unit 140 processes output signals of the first sensor 150 and the second sensor 160 . The first sensor preferably detects variables characterizing the operating state of the internal combustion engine. This is, for example, the number of revolutions N of an internal combustion engine. The second sensor 160 preferably detects variables that characterize the ambient conditions or the driver's needs. Based on these variables, control unit 140 calculates a control signal for actuation of injection valve 120 or 130 .

Such an injection system is commonly referred to as a dual system. Within the low speed range and load range, the internal combustion engine is preferably operated in a first operating mode in which injection is effected by means of the first injection valve 120 . Alternatively, in the higher load range and the higher rev range, a second operating mode is implemented in which the fuel injection is substantially via the second injection valve 130 . In the case of longer operation in the first mode of operation, the risk of coking and the associated through-flow of the second injection valve 130 due to the lack of through-flow and the associated lack of cooling of the second injection valve 130 . There is a risk of volume reduction.

There is also the possibility that the fuel pressure in the supply system for the second injection valve 130 may increase up to the maximum pressure due to the temperature rise. When switching to the second operating mode is made at this time, injection is carried out at the maximum pressure as described above and thus at a pressure that is not optimal for the corresponding operating point. As a result, non-optimal injection times can lead to mixing deviations, increased emissions and fluctuations in quiet driving performance.

From the recent prior art it is known how to effect a switchover to the second operating mode after a predetermined time in the first operating mode in order to avoid coking of the second injection valve. However, such a switchover is not optimal for engine operation and results in mixed deviations, in part with situationally increased emissions and quiet driving fluctuations.

In the embodiment described below, the second injection valve is continuously controlled with an adjustable minimum injection time. By doing so, continuous perfusion and cooling can be ensured, whereby coking can be prevented reliably. Also, the pressure in the high-pressure rail can be set to the desired optimum target pressure. A separate switch from the first operating mode to the second operating mode and vice versa is no longer required.

However, in the above embodiment, there is a requirement that exhaust gas deterioration should not occur in dynamic driving characteristics due to the above injection amount. This requirement is ensured in this embodiment by keeping the minimum injection time set for the high-pressure injection valve constant regardless of the total fuel mass required.

The flowchart of FIG. 2 describes the embodiment in detail. In a first step 200, the minimum possible injection quantity Q2min of the second injection valve 130 is calculated from the minimum injection time T2min. Different parameters such as injection pressure, injection angle, fuel density, motor speed, camshaft angle and crankshaft speed are inserted into this calculation. In this case, it may also be proposed that only one selection of the aforementioned parameters be used.

Normally, calculation of the injection time T is performed based on the injection quantity Q. The calculation of the minimum injection amount Q2min based on the minimum injection time T2min is performed based on the same parameters as the conventional calculation of the injection time T based on the injection amount Q. The minimum injection time T2min is an injection time at which the second injection valve 130 can be controlled so that one injection is performed immediately. In case of control under the minimum injection time, (prescribed) injection is not possible.

In a second step 210, starting from the current total injection amount Q, the injection amount for the first injection valve Q1 is calculated, in other words, the injection amount for the first injection valve is calculated as "total injection amount Q - second injection amount". It is calculated as "minimum injection quantity (Q2) for the injection valve". The sum of the injection amount for the first injection valve and the injection amount for the second injection valve in one combustion cycle is referred to as the total injection amount.

In a third step 220, starting from the two injection quantities for the two injection valves, a so-called split factor Smin (split factor) is calculated. This split factor instructs the injection amount distribution between the first injection valve and the second injection valve. The split factor Smin thus determined is later used to calculate the final injection amount and time in a normal calculation method for two fuel paths. The split factor Smin indicates a ratio between the injection amounts of the two injection valves, and in this case, the second injection valve injects the minimum injection amount Q2min or is controlled by the minimum injection time T2min.

Within the normal fuel path, in step 230 the operating state of the internal combustion engine is determined, ie the output signals of the various sensors are evaluated. In particular, the variables specified above are used. In a next step 240, a split factor (S) for the current injection is determined. A subsequent selection step 250 selects the current split factor (S) or the split factor calculated in step 220 (Smin). This selection is such that, if sufficient injection with the second injection valve 130 is possible due to the current split factor (S), this split factor (S) is used, and sufficient injection with the second injection valve 130 is possible. If not possible, the split factor Smin from step 220 is made to be used. If the split factor is defined as the ratio of the injection amount of the second injection valve to the injection amount of the first injection valve, it is checked whether the split factor Smin is smaller than the split factor S. If the split factor (Smin) is smaller than the split factor (S), the split factor (S) is used. If the split factor Smin is greater than the split factor S, the split factor Smin is used.

In step 260, the injection amount is divided between the two injection valves due to the split factor selected in step 250. Then the control time of the injection valve is then calculated, after which in step 270 a metering is made.

In another embodiment, it is proposed that the second injection valve is continuously supplied with the minimum injection amount Qm. The shortfall to the total injection amount for the current operating point is injected by the first injection valve. If the total injection amount in the current operating state is less than the minimum injection amount Qm of the second injection valve, the supply of the minimum injection amount Qm by the second injection valve is no longer made. This relates, for example, to the situation in the so-called coasting mode of an internal combustion engine or when a cylinder is switched off. In this embodiment, an operating condition in which combustion should not occur at all is addressed. In this operating state, no or only very little heat is introduced into the injector, so that plate-out is negligible. In the following, the approach is described with reference to a flowchart.

In the first step, the minimum injection quantity Qm for the second injection valve 130 is calculated. Also, the total injection quantity Q is calculated. Further, in step 300, the difference DQ between the total injection amount Q and the minimum injection amount Qm of the second injection valve is calculated. In step 310, whether the total injection amount Q is greater than the minimum injection amount Qm is calculated. If it is not large, the minimum injection is not performed in the second injection valve 130 and the program ends in step 390. In the query step 310, the total injection amount Q is determined to be the minimum injection amount Qm If it is detected that exceeds , injection of the minimum injection amount Qm by the second injection valve 130 and the difference DQ by the first injection valve 120 is performed in step 380 .

Preferably, the minimum injection amount Qm is selected to be slightly greater than or equal to the minimum injection amount Q2min. Preferably, in order to obtain the minimum injection amount Qm, a small value is added to the minimum injection amount Q2min.

In another embodiment, it is proposed to determine a characteristic parameter characterizing the strength of deposits on an injection valve by means of a plate-out model. For this purpose, the characteristic values for deposition or deposition decomposition are integrated. If the characteristic value is positive, deposition occurs, and if the characteristic value is negative, sedimentation decomposition occurs.

In a first refinement, the characteristic values are determined starting from substantially various operating characteristic variables. The characteristic value substantially characterizes the amount of heat flowing into the injection valve. The following variables, i.e. split factor, fuel temperature, engine temperature, intake air temperature, intake air mass, torque or load, speed, installation position and installation conditions of the injector in the engine, compression ratio of the engine, combustion method, or engine A characteristic value is determined starting from selecting one of the operation types of the model using a model.

The deposition model considers various effects on deposition. These influences are the heat flow to the injector surface, the amount of fuel deposited on the surface with each injection, and the temperature level within the injector. The first two variables relate specifically to deposition on the surface of the injector, and the last variable relates specifically to deposition within the injector.

Large heat flow into the injector surface results in large characteristic values. The heat flow into the surface substantially depends on the internal combustion engine's speed and the internal combustion engine's load. As the number of revolutions increases, the heat flow also increases. As the load increases, the heat flow also increases. As the load, various variables can be used. These are, among other things, driver demand signals, torque parameters or the position of the throttle valve. Also, the heat flow increases as the charge motion increases. The reason is that charge motion cannot be measured directly. As a substitute variable, the position of the charge movement flap or valve control time is used.

The amount of fuel deposited on the surface with each injection substantially depends on the parameters described below.

As the number of partial injections per combustion cycle increases, there is a tendency for less wetting, which results in a smaller amount of fuel deposited and hence a smaller characteristic value. As the amount of fuel accumulated on the surface increases, the characteristic value decreases.

As the injection duration per type of partial injection increases, there is a tendency to increase wetting, which results in a larger amount of fuel deposited, and thus a larger characteristic value. As the cumulative injection period increases, an increasing wetting tendency arises, resulting in a greater amount of fuel deposited, and thus a greater characteristic value. The accumulated injection period can be understood as the total amount of fuel injected in one combustion cycle.

As the temperature level increases over time within the injector, the deposition increases within the injector, and thus the characteristic value also increases. At higher speeds and loads of the internal combustion engine, a higher temperature level occurs in the injector, which results in a greater possibility of deposits and, consequently, higher characteristic values.

As the fuel temperature increases, the deposition increases and thus the characteristic value also increases. If one measured value cannot be used for the fuel temperature, other temperature values may also be used, for example intake air temperature.

Due to the inherent heating due to the heat of electrical loss, a longer control period and/or a higher number of partial injections results in higher temperature levels in the injector, which in turn result in higher deposits, which result in higher characteristic values. appear.

As the engine temperature rises, the injector temperature likewise increases. This results in a characteristic value that likewise increases as the engine temperature increases.

The split factor is inserted inside the model as follows. As the injection rate with the first injection valve increases, the deposition increases. As the injection rate with the second injection valve increases, deposition decreases or covering degradation increases.

Combustion method or type of engine operation

The installation position and installation situation of the injector in the engine and the compression ratio of the engine are preferably inserted into the model as constant variables.

As soon as it is detected that the characteristic parameter characterizing the strength of deposits on the injection valve exceeds a threshold value, suitable measures are introduced. In this case, the ratio of the injection amount metered by the second injection valve increases. This increase in the injection amount ratio is achieved in such a way that the split factor is correspondingly changed.

The action is preferably carried out for a specific period of time. In one particularly preferred embodiment, it is proposed that the duration of action depends on a characteristic variable.

If the split factor is inserted into the covering model, the action ends as soon as the model detects that sufficient covering decomposition has occurred.

In a second refinement, the characteristic value is determined within a specific load spectrum starting from the operating period. To do this, it determines how long the internal combustion engine operates within a specific load spectrum. Each load spectrum is assigned one specific characteristic value. This characteristic value is subsequently multiplied and integrated with the period during which the internal combustion engine was operated within the load spectrum. The characteristic parameters determined in this way are a measure of the strength of deposits on the injection valve.

The load spectrum is defined by a range of values for the number of revolutions and a range of values for the torque provided by the internal combustion engine. Each combination of the value range for rotational speed and the value range for torque is assigned one characteristic value for deposition.

As the number of revolutions increases, the characteristic value increases. As the torque increases, the characteristic value also increases. If the value for the number of revolutions or torque is small, the characteristic value takes a negative value in some cases.

As soon as it is detected that the characteristic parameter characterizing the strength of deposits on the injection valve exceeds a threshold value, suitable measures are introduced. In this case, the ratio of the injection amount metered by the second injection valve increases. This increase in the injection amount ratio is achieved in such a way that the split factor is correspondingly changed.

The action is preferably carried out for a specific period of time. In one particularly preferred embodiment, the duration of action depends on a characteristic variable.

In Figure 4, the above approach is illustrated with reference to a flowchart. Elements already described in FIG. 3 are marked with corresponding reference numerals. In step 400, feature values are determined using the deposition model. In a subsequent step 410, the characteristic values are integrated and thereby a characteristic variable is calculated. If, in query step 420, it is detected that the characteristic variable is greater than the threshold, then in step 250 the split factor is changed accordingly.

In a preferred embodiment, it is proposed that the split factor is shifted by a certain amount in the direction of the larger injection quantity for the second injection valve. This situation means that the split factor is moved only once, but the switch to injection using only the second injection valve is not performed at all.

In another embodiment, it is not checked whether the characteristic variable exceeds the threshold value, but rather in step 250 a correction value for the split factor is preliminarily added to the split factor for the current operating state calculated in step 240. may be determined in This correction value is determined as a function of the characteristic variable. Preferably, there is a linear relationship between the correction value for the split factor and the characteristic variable. As the characteristic variable increases, the correction factor increases so that a larger injection quantity is metered in by means of the second injection valve.

Claims (7)

Fuel is metered into the intake pipe via the first injection valve and directly into the combustion chamber of the internal combustion engine via the second injection valve, the first injection valve being used in the first operating mode and the second injection valve being used in the second operating mode. 2 A method for operating an internal combustion engine in which an injection valve is used, comprising:
calculating a minimum injection quantity Q2min of the second injection valve;
calculating an injection amount Q1 of the first injection valve as a difference between the current total injection amount Q and the minimum injection amount Q2min;
calculating a split factor (Smin) as a ratio of a minimum injection amount (Q2min) of the second injection valve to an injection amount (Q1) of the first injection valve;
determining the operating state of the internal combustion engine;
determining a split factor (S) for the current injection; and
selecting (250) a current split factor (S) or a calculated split factor (Smin);
When sufficient injection using the second injection valve 130 is possible, the current split factor (S) is used,
When sufficient injection using the second injection valve is impossible, the split factor Smin is used,
It is checked whether the split factor Smin is smaller than the split factor S,
If the split factor (Smin) is smaller than the split factor (S), the split factor (S) is used;
A method for operating an internal combustion engine, characterized in that the split factor (Smin) is used if the split factor (Smin) is greater than the split factor (S). The method according to claim 1, characterized in that the minimum injection amount is metered in by means of the second injection valve if the total injection amount is greater than the minimum injection amount. 3. Method according to claim 1 or 2, characterized in that the minimum injection amount corresponds to the minimum injection amount of the second injection valve. A computer program stored on a machine-readable storage medium and formed to execute all the steps of the method according to claim 1 or 2. A machine-readable storage medium in which the computer program according to claim 4 is stored. Control device configured to carry out all steps of the method according to claim 1 or 2. delete

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