CN107035557B

CN107035557B - Method and device for operating an internal combustion engine, in particular of a motor vehicle with dual fuel injection

Info

Publication number: CN107035557B
Application number: CN201610984457.XA
Authority: CN
Inventors: C.旺德林; R.埃克; T.库恩; T.霍尔曼; U.舒尔茨
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2015-11-09
Filing date: 2016-11-09
Publication date: 2021-10-22
Anticipated expiration: 2036-11-09
Also published as: CN107035557A; DE102015221914A1

Abstract

The invention relates to a method and a device for operating an internal combustion engine, in particular of a motor vehicle, having two, i.e. intake-pipe-based fuel metering (SRE) and a direct fuel metering (BDE), wherein the intake-pipe-based fuel metering and the direct fuel metering are carried out in a variable mixture mode by means of a fuel quantity distribution (220), and wherein in particular: in the variable mixture operation mentioned, a relative fuel quantity distribution of the intake-pipe-based fuel metering (SRE) and the direct fuel metering (BDE) is achieved (215) as a function of the dynamic operation (205, 210) of the internal combustion engine.

Description

Method and device for operating an internal combustion engine, in particular of a motor vehicle with dual fuel injection

Technical Field

The invention relates to a method and a device for operating an internal combustion engine, in particular of a motor vehicle having dual fuel metering, wherein an intake-pipe-based fuel metering and a direct fuel metering are carried out in a variable mixing mode by means of a fuel quantity allocation, wherein in the variable mixing mode mentioned a relative fuel quantity allocation of the intake-pipe-based fuel metering and the direct fuel metering is carried out, which is dependent on the dynamic operation of the internal combustion engine. The invention also relates to a computer program, a machine-readable data carrier for storing the computer program, and an electronic control unit, by means of which the method according to the invention can be carried out.

Background

It is known from practice that internal combustion engines can be operated in an injection-only mode, in which the cylinders of the internal combustion engine can be supplied with fuel during the working stroke of the cylinder using only injectors for intake manifold injection (SRE) or using injectors for direct injection (BDE), or in an injection-mixed mode, in which the cylinders of the internal combustion engine can be supplied with fuel during their working stroke using not only SRE injectors but also BDE injectors. The ratio or distribution of the fuel injection quantity by the SRE injector to the fuel injection quantity by the BDE injector can be adjusted for different load points depending on the motor-specific performance. The motor-specific performance must be adjusted and controlled as precisely as possible for the different driving situations of the internal combustion engine and taking into account boundary conditions such as emissions legislation (e.g. the California Air Resources Board (CARB) legislation), power, starting characteristics and also diagnostics on the functioning of the internal combustion engine.

It is known that the measure of the mentioned distribution relationship of the fuel quality in the mentioned hybrid operation depends on the operating conditions of the internal combustion engine. In this way, the component protection function or the emergency operation function of the internal combustion engine can be implemented as an operating function in order to implement dynamic compensation, to set a heating of the catalytic converter after a cold start, or to implement mixture adaptation, tank ventilation and/or various diagnostics.

A method for determining the aforementioned distribution measure in the internal combustion engine concerned here is known from DE 102010039434 a 1. In this case, an assignment measure is determined which is dependent on the operating point, wherein a priority is assigned to each of a plurality of specific operating functions which are associated with a specific operating condition. Obtaining: which specific run functions are present and one or more run functions are selected depending on the respective priority. The suitable allocation measure is determined by possibly limiting the permissible range of the selected operating function, for example for component protection, for adaptation to dynamics and/or for heating the catalytic converter. In this way, an optimum operation of the internal combustion engine can be ensured even in the presence of operating conditions associated with a plurality of operating functions.

In the framework of the european legislative standard EURO6, the number of soot particles and Hydrocarbon (HC) emissions in the exhaust gas is also limited in the case of motor vehicles with the mentioned internal combustion engine with dual fuel dosing. There is therefore a need to reduce or even eliminate the internal sources of particulates and HC in the internal combustion engine as much as possible. For this purpose, externally ignited internal combustion engines (otto motors) are currently digitalized (bedanten) in the following way: in a steady-state manner, i.e. in a stable load range and thus at the respective temperature levels of the combustion chambers of the respective cylinders of the internal combustion engine, the quantity of particles in the exhaust gas, the fuel consumption, the driving comfort and the emissions of nitrogen oxides, hydrocarbons and carbon monoxide are as optimal as possible.

All legal emissions restrictions are to be observed, in which a characteristic curve is stored in the control unit of the internal combustion engine, which characteristic curve determines or adjusts a time profile (timing) of an injection or of an injection, for example, a so-called division factor or separation factor for a division between an intake-pipe-based fuel injection and a direct fuel injection (so-called "mixed operation"). The characteristic curve is often digitized in a steady-state manner, i.e., in a constant load range of the internal combustion engine.

However, at low load steps to high loads, increased particle emissions occur under this operating strategy, which can last for a long period of several seconds before they subside again. The reason for this behavior can be that the combustion chambers of the respective cylinders of the internal combustion engine are also significantly cooler during and shortly after the load jump than in the thermally stable state, i.e. after a specific heating time.

Disclosure of Invention

The invention relates to a dual fuel metering device which is operated in the mixed mode, in particular in the variable mixed mode, wherein a temporally variable fuel distribution is achieved by means of a specific distribution ratio between the intake-pipe-based fuel metering and the direct fuel metering.

Such variable mixing operation can take advantage of the use of both fuel metering types for optimal mixture formation of the fuel-air mixture and combustion of this mixture in the combustion chamber of the internal combustion engine. In this way, a direct fuel metering is more advantageous in dynamic operation or full load operation of the internal combustion engine, wherein in particular uncontrolled combustion or self-ignition (so-called "knocking") of the metered fuel is also effectively prevented. In contrast, the intake-pipe-based fuel metering is more advantageous in part-load operation of the internal combustion engine, since it is more effective in reducing particulates and hydrocarbons in the exhaust gas.

The invention is based on the following recognition: in the load dynamics from low to high load described at the outset, the fuel metering device and the air system of the internal combustion engine react more quickly to a higher load demand than the mechanical components in the combustion chambers of the respective cylinders of the internal combustion engine, which mechanical components are still substantially at the lower temperature level present before the load demand for a certain time after the load demand. This results in fuel deposition effects, condensation effects and/or soot formation effects in the mentioned combustion chambers of the internal combustion engine, which in turn lead to an increase in soot emissions and/or particle emissions and/or HC concentrations in the exhaust gas.

It is furthermore recognized that even in internal combustion engines which are still in thermal engine operation and are therefore also relatively cold immediately after starting, the described effects also occur when there is a relatively high dynamic or dynamic demand (dynamikanfordering), in particular from low to high load, and when there is a relatively high proportion of directly dosed fuel.

It is noted here, however, that the mentioned disadvantageous effects do not occur in load steps from high load to lower load, since the combustion chamber surfaces which are already at relatively high operating temperatures can cause evaporation of the mentioned deposits and thus make possible deposits not negatively influencing or only very slightly negatively influencing the mixture preparation.

The invention proposes that the dynamic or dynamic, relative distribution or fuel distribution of the intake-pipe-based fuel metering (SRE) and the direct fuel metering (BDE) dependent on the internal combustion engine is implemented in the overall resulting variable mixture operation of the two systems involved here. In the case of the dynamic-dependent fuel distribution mentioned, the maximum fuel quantity in the direct fuel metering is preferably reduced to the following ratio: this portion leads to as little wetting effect as possible on the piston surface and/or the injector surface and/or the combustion chamber surface. In this case, an amount of fuel that has not yet been taken into account in view of the total amount of fuel to be metered is dispensed to the fuel metering based on the intake manifold.

The proposed method effectively prevents the mentioned deposits or deposit effects, which are dependent in particular on load changes, and the resulting increased exhaust gas emissions of Hydrocarbons (HC) and/or particles. In particular in internal combustion engines operated with the variable mixture operation mentioned here with dual fuel metering, in particular also in driving operation of motor vehicles, increased exhaust emissions are effectively prevented here, and also in compliance with the exhaust emissions of the internal combustion engine required by the legislation mentioned at the outset. Furthermore, better protection of components, in particular of cylinder components, is achieved by avoiding dilution of the oil due to wetting of the cylinder walls with fuel.

The method according to the invention for operating an internal combustion engine of a motor vehicle with dual fuel metering, which is referred to herein, comprises: monitoring at least one change over time of an operating variable of the internal combustion engine and/or of the motor vehicle, said operating variable being selected from the group consisting of: motor load, motor temperature, oil temperature, water temperature, load gradient of the internal combustion engine, acceleration of the motor vehicle, accelerator pedal value of the motor vehicle, intake valve lift curve of the internal combustion engine, change in throttle angle of the internal combustion engine, change in intake pipe pressure of the internal combustion engine, boost pressure configuration of the internal combustion engine (if the internal combustion engine has a turbocompressor or compressor) and/or rotational speed of the internal combustion engine.

In the case of the aforementioned monitoring of the temporal change of at least one operating variable of the internal combustion engine or of the motor vehicle, it can furthermore be provided that, when a temporal change of the at least one operating variable is detected, it is also checked that: whether the change over time exceeds an empirically predeterminable dynamic threshold or threshold (dynamikschwell). The stability of the method is particularly significantly improved by this test step. A further improvement of the stability of the process can be achieved by: the value of the dynamic threshold mentioned is dependent on the respective monitored operating variable.

When the above-mentioned dynamic threshold is detected, it can be provided that the current fuel quantity distribution is changed in the following manner: increasing a fraction of the intake-pipe-based (SRE) fuel metering relative to the direct (BDE) fuel metering. The change can be made in the direction of a fuel quantity distribution which is provided for steady-state operation of the internal combustion engine. The fuel quantity distribution can be varied here preferably in the following manner: adjusting the proportion of the direct (BDE) fuel metering in the direction of increasing the intake-pipe-based (SRE) fuel metering. The dynamic threshold mentioned, which can be predetermined empirically, can preferably correspond to a change in the motor load from a low load to a high load.

Furthermore, the change in the fuel quantity distribution can be effected by means of a quantity increment which is selected as a function of an increase in the temperature of mechanical components of the combustion chamber of the internal combustion engine. The increment can be configured in the form of a ramp or in the form of a step. The above-mentioned measures are all used to improve the stability of the process.

It is also to be noted that the variable mixture operation mentioned includes an intake-only fuel metering, a direct fuel metering, and an arbitrary, variable distribution between the two operating types. Furthermore, such a hybrid operation can be used for the starting phase of the internal combustion engine and thus different starting types can be achieved.

The invention can be used in particular in a dual fuel injection system of an internal combustion engine of a motor vehicle. Furthermore, it can also be used in industrial fields, such as, for example, in internal combustion engines used in chemical processing technology, which have such a dual fuel injection system.

The computer program according to the invention is designed to carry out each step of the method, in particular when the computer program runs in a calculator or controller. It is possible to implement the method according to the invention on an electronic controller without having to make structural changes to the electronic controller. Furthermore, a machine-readable data carrier is proposed, on which a computer program according to the invention is stored. The electronic control unit according to the invention is obtained by applying the computer program according to the invention to an electronic control unit which is designed to control the dual fuel dosing device referred to here by means of the method according to the invention.

Other advantages and design aspects of the invention are given by the description and the accompanying drawings.

It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respectively given combination, but also in other combinations or alone without departing from the framework of the invention.

Drawings

Fig. 1 shows a schematic diagram of a dual fuel injection arrangement for a four cylinder internal combustion engine according to the prior art;

fig. 2 shows an embodiment of the method according to the invention by means of a combined block/flow diagram;

fig. 3 shows, by means of a graph, an operating strategy for an internal combustion engine of the direct injection type, known from the prior art, the injection of which is digitized in a steady-state manner;

FIG. 4 shows a first embodiment of an operating strategy according to the invention for operating an internal combustion engine as referred to herein;

fig. 5 shows a second embodiment of the mentioned operating strategy according to the invention;

fig. 6a, b show two variants of the third exemplary embodiment of the operating strategy according to the invention.

Detailed Description

The internal combustion engine shown in fig. 1 has four cylinders 11, which are covered by a cylinder head 12. The cylinder head 12 delimits in each cylinder 11, together with a piston, not shown here, guided in the cylinder 11, a combustion chamber 13 having an intake opening 15, also not shown here, controlled by an intake valve 14, not shown here. The intake port 15 forms a port through an intake channel 16, which is likewise not shown in fig. 1, of the cylinder head 12.

The illustrated fuel injection device comprises an air flow channel 18 for conveying combustion air to the combustion chamber 13 of the cylinder 11, which has flow channels 17 which are separated from one another at the end and which lead to the respective intake channel 16. Furthermore, a first group of fuel injection valves 19, which inject fuel directly into the combustion chambers 13 of the cylinders 11 in each case, and a second group of fuel injection valves 20, which inject fuel into the flow channels 17, are arranged.

The first group of fuel injection valves 19 that are directly injected into the cylinders 11 are fed by a high-pressure fuel pump 21, and the second group of fuel injection valves 20 that are injected into the flow passage 17 are fed by a low-pressure fuel pump 22. In the usual case, a low-pressure fuel pump arranged in the fuel tank 23 delivers fuel from the fuel tank 23 on the one hand to the second group of fuel injection valves 20 and on the other hand to the high-pressure fuel pump 21. The injection times and injection durations of the

fuel injection valves

19, 20 are controlled by an electronic control unit integrated into the engine control unit as a function of the operating point of the internal combustion engine, wherein the fuel injection is essentially carried out by the first group of fuel injection valves 19 and the second group of fuel injection valves 20 is used only supplementarily in order to improve the inadequacy of the direct fuel injection by the first group of fuel injection valves 19 in a specific operating region and in order to use an additional degree of freedom or injection strategy.

The fuel injection valves 20 of the second group are designed as multi-beam injection valves which simultaneously inject or inject at least two separate fuel beams which are angularly offset from one another and are arranged in the air flow duct 18 in such a way that: i.e. the injected fuel bundles 24, 25, which usually have the shape of a spray cone, arrive in different flow channels. In this internal combustion engine, two dual-

beam injection valves

26, 27 are provided, which are placed in the air flow channel 18 in the following manner: i.e. one dual beam injection valve 26 is injected into the flow channel 17 to the first and second cylinder 11 and a second dual beam injection valve 27 is injected into the flow channel 17 to the third and fourth cylinder 11. For this purpose, the flow channel 17 is designed in the following manner: that is, between two directly adjacent flow ducts 17, there is a mounting point for the two-

jet injector

26 or 27.

It is also known that in the mentioned fuel intake pipe injection of the internal combustion engine referred to here, an air-fuel mixture is produced in the intake pipe outside the combustion chamber. The respective injection valve injects fuel before the intake valve, wherein the mixture flows into the combustion chamber through the open intake valve during the intake stroke. The fuel supply takes place by means of a fuel delivery module which delivers the required quantity of fuel from a tank to the injection valve at a defined pressure. The air control device is responsible for providing the correct air quantity to the internal combustion engine at each operating point. An injection valve arranged on the fuel distributor precisely doses the desired fuel quantity into the air flow. The motor controller mentioned regulates the respectively required air-fuel mixture on the basis of the torque as a main reference variable. Effective exhaust gas cleaning is achieved by means of a lambda control, by means of which the stoichiometric air-fuel ratio (lambda = 1) is always set.

In contrast, in the direct fuel injection, the air-fuel mixture is directly formed in the combustion chamber. Here, fresh air flows in through the intake valves mentioned, wherein fuel is injected into the air flow at high pressure (up to 200 bar). This achieves an optimal swirling of the air-fuel mixture and an improved cooling of the combustion chamber.

It is also known that in a four-stroke internal combustion engine (otto motor), the working cycle comprises the processes of intake, compression, work and exhaust, wherein each cylinder moves up and down twice and stops in two upper dead centers (OT) and two lower dead centers (UT). That is, the crankshaft performs two turns and the camshaft performs one turn in one duty cycle. The ignition of the gaseous fuel mixture introduced into the cylinder takes place in a top dead center, in which the mixture has just been compressed. Referred to herein as the ignition ot (zot). In contrast, there is also a coincidence OT (Ü OT) in which not only the intake valve but also the exhaust valve are opened during the exhaust to intake.

In this way, ignition takes place immediately after the start in at least one cylinder at all top dead centers (OT), wherein at a specific top dead center, in particular every second OT, a shift in the ignition time is effected in each case in a crankshaft angle of 720 °. The degree of reduction of the physical work performed in the respective cylinder is determined depending on whether the air-fuel mixture is actually ignited in the top dead center (OT) at which the ignition timing is shifted or in the crank angle shifted in the range of 360 °.

It is known to combine the two shares described in the described dual system in the form of a system or a system component. In particular, it is necessary to precisely distribute the total fuel mass to be provided or metered. Total fuel mass KM for cylinder_gesConsists as in the following equation:

KM_ges=KM_SRE+KM_BDE，

wherein KM_SRERelative fuel quality of SRE path and KM_BDERepresenting the relative fuel mass of the BDE path.

As described below, a suitable division factor between SRE operation and BDE operation for the current operating conditions of the internal combustion engine is calculated. In this case, firstly, possible operating states and/or the actual operating requirements of the internal combustion engine or of a motor vehicle having such an internal combustion engine are detected. The operating states or operating requirements detected in this way are first assigned to the following exemplary categories:

temperature of the internal combustion engine or of the corresponding combustion chamber

High pressure in BDE operation of the dual fuel dosing device referred to here

-current fault

Results of on-board diagnostics

Adaptations that may be carried out in fuel metering or fuel injection

Special driving situations, such as "kick-down" being activated on the driving pedal on the driver's side or switching back to the intermediate gear on the driver's side.

In this way, an optimum operating region can be determined at the start of the internal combustion engine with the dual-fuel metering device, for example with respect to speed, particle formation or reaction behavior, depending on the current temperature of the internal combustion engine, according to which the priority classification mentioned can be carried out. In addition to the temperature, a further detection possibility for the different start types mentioned is the high pressure required for high-pressure starting or start/stop operation with rapid repeated starting in the BDE operation mentioned.

Due to the large number of possible solutions for allocation factors, which may be physically equivalent, but which are preferred in actual driving operation in respect of the different operations mentioned, a clear determination or confirmation of the allocation factor needs to be carried out in order not to have to change frequently between the different allocation factors. This frequent change is to be avoided because changing the division factor is on the one hand associated with increased application outlay, so that the change can be adjusted in the actual operation as soon as possible in a manner neutral to the torque and the mixture.

In the following, embodiments of the method according to the invention will be described. After the start 200 of the process route shown in fig. 2, first a check or monitoring 205 is carried out: whether a change over time of previously empirically determined operating variables of the internal combustion engine and/or of the motor vehicle has occurred. The operating variable can be selected from the following group of possible operating variables of the internal combustion engine (motor) or of the motor vehicle: motor load, motor temperature, motor oil temperature, water temperature of the motor, gradient of motor load of the internal combustion engine, acceleration of the motor vehicle, accelerator pedal value of the motor vehicle, intake valve lift curve of the internal combustion engine, change of throttle angle of the internal combustion engine, change of intake pipe pressure of the internal combustion engine, boost pressure configuration of the internal combustion engine, if the internal combustion engine has a turbocompressor or, and/or rotational speed of the internal combustion engine.

If a change over time of at least one or more of these mentioned operating variables is detected, a further test 210 is carried out: whether the change detected in step 205 exceeds a dynamic threshold that can be predefined empirically. The value of the threshold can lead to different results for the operating variables mentioned above. If there is such an excess, the current fuel quantity or injection quantity distribution is changed 215 in the following manner: the fraction of the intake manifold-based (SRE) fuel injection is increased relative to the direct (BDE) injection. In this case, the respective allocation factor is changed in particular in the following manner: the change is effected in the direction of a suitable or predefined distribution factor for steady-state operation of the internal combustion engine. Here, a previously known allocation factor, which is preferably stored in the characteristic curve in advance and is optimal for steady-state operation, is used as a basis 220.

It is to be noted that it is not absolutely necessary to bring the respective operating variable back to a lower value subsequently after the mentioned dynamic threshold has been exceeded. Rather, a further step to a still higher value of the operating variable can also be implemented, in which case the above-mentioned shifting of the distribution factor for one or more injections is carried out again if necessary. However, the operating variable can also be held at the value it reaches after the dynamic threshold is exceeded.

In internal combustion engines which are still in heat engine operation and therefore are not yet running hot, the division factor can be adjusted, for example, gradually from a given fuel quantity division in the direction of increasing direct injection (BDE) as a function of the temperature of the internal combustion engine. The BDE fraction thereby increases with increasing temperature.

In a load step from low load to high load, the division factor can be adjusted in a stepwise manner or rapidly in the direction of increasing the intake pipe injection (SRE). The respective quantity increment can be selected in this case as a function of the surface temperature of the mechanical components of the combustion chamber. The respective surface temperature can be determined by means of a temperature model.

The technical effect on which this is based is that: if the mentioned dynamic threshold is exceeded, the SRE fraction of the division factor is increased in order to reduce or avoid wetting of the component with fuel in the respective combustion chamber of the internal combustion engine as a result of the BDE. Conversely, when the combustion chamber surface heats up as a result of the combustion of the fuel-air mixture, it is redirected in the direction of increasing BDE share of the distribution factor.

It is furthermore to be noted that, when the mentioned dynamic threshold is reached, the allocation factor is preferably shifted relatively quickly or as quickly as possible in the direction of SRE operation. In contrast, the adjustment of the distribution factor in the direction of the BDE operation can take place relatively slowly, as is shown in fig. 5 and 6, for example in a stepped or ramp-like manner, which is accompanied by heating of the combustion chamber surface.

A corresponding possible operating strategy is shown in fig. 4-6 described below. It is to be noted here that, after the mentioned load step and the mentioned corresponding step-like progression of the division factor in the direction of the SRE, the surface temperature of the respective combustion chamber increases during further operation of the internal combustion engine. The operating strategy mentioned is applied or adjusted depending on the surface temperature.

Fig. 3 shows a conventional operating strategy for a (only) direct-injection otto motor, that is to say an internal combustion engine with a pure or fixed BDE fuel metering 305, in which the load profile L shown at the top of the diagram shows a step-like rise 300 in the time t range, the particle concentration in the exhaust gas of the internal combustion engine increases 310 sharply from a starting value 321 to a peak (highest value) 322 at the time of the load step 300, so that it then fades back 315 again within a certain time range. After the load profile L subsequently returns or jumps back 320 to the starting value, the particle concentration correspondingly returns 325 to the mentioned starting value 321.

Fig. 4 to 6 show the design of the method according to the invention with the aid of a possible operating strategy for the internal combustion engine with dual fuel metering, which is referred to here, and which is operated according to the invention with the aid of three different methods.

Fig. 4 shows an embodiment of the method according to the invention, in which, in contrast to the conventional operating strategy according to fig. 3, a change 405 in the apportionment of the fuel metered amounts from BDE metered amounts to SRE metered amounts is carried out 420 at the time of the load step 400. After the load L has again dropped 410 to its initial value, the apportionment of the fuel metered amount is changed 415 again from the SRE metered amount to the BDE metered amount or in the direction of the BDE metered amount. In contrast to the conventional method according to fig. 3, in this embodiment of the method according to the invention the particle emission is increased 420 only slightly from the starting value 419 and remains at the slightly increased value 420 for the entire period of the increased load. After the load profile L has fallen 410 to the starting value, the particle concentration is correspondingly returned 422 to the mentioned starting value 419.

Fig. 5 shows an embodiment of the method according to the invention, in which after a load step 500 and at the same time a change 505 in the metering of the fuel metering in the direction of the SRE fuel metering, the metering is ramped 510 further up or raised to a value 512 for steady-state operation. It is to be noted that the illustrated curve profile describes at least qualitatively the change in the quantity distribution or respectively the distribution factor in the mixed operation mentioned between the pure BDE and SRE operation by means of the

intermediate values

505, 510 and 512. After the load profile L has dropped again 515, the quantity distribution is likewise reset 520 again to the starting value. It is to be noted that the

changes

505, 510, 512 of the metering shown in fig. 5 can also be carried out in the direction of increasing the BDE proportion, for example in internal combustion engines which are not already running hot. The BDE fraction therefore increases with increasing temperature.

Fig. 6a and 6b show further embodiments of the method according to the invention, in which, after the

respective load step

600, 630, a (re-) boost of the first step-down 605, 635 quantity allocation is implemented here in a manner similar to the

steps

610, 640 shown in fig. 5. The lifting is thus effected in fig. 6a by means of one step 610 and in fig. 6b by means of two steps 640. After the lift is achieved, there is then a

respective apportionment

612, 642 appropriate for steady state operation. After the load profile L has again dropped 615, 645 in each case, the respective quantity allocation is likewise reset 620, 650 to its starting value. It is further noted here that the

changes

605, 610, 612 and 635, 640, 642 of the metering shown in fig. 6a and 6b, respectively, can also be carried out in the direction of increasing the BDE proportion, whereas, for example, in internal combustion engines which are not already running hot.

It is to be noted that the illustrated curve profile describes at least qualitatively the change in the quantity distribution or respectively the distribution factor in the mentioned hybrid operation between pure BDE and SRE operation by means of the

intermediate values

605, 610 and 612 or 635, 640, 642.

It is furthermore noted that other embodiments are possible with regard to the change in the quantity distribution, for example a multi-step, an interrupted ramp or the like, since the invention is not limited to a specific time profile or a specific design of such a change.

The described method can be used particularly advantageously in fuel metering systems in which the valve drive cannot be adjusted or can only be adjusted in a stepwise manner, that is to say with respect to the respective opening times, opening durations and variable valve lifts.

The described method can be implemented in the form of a control program for controlling an electronic control unit of an internal combustion engine or in the form of one or more corresponding Electronic Control Units (ECUs).

Claims

1. Method for operating an internal combustion engine of a motor vehicle having a dual fuel metering device, wherein an intake pipe-based fuel metering (SRE) and a direct fuel metering (BDE) are carried out in a variable mixing mode by means of a fuel quantity allocation (220), wherein in the variable mixing mode mentioned a relative fuel quantity allocation of the intake pipe-based fuel metering (SRE) and the direct fuel metering (BDE) is carried out which is dependent on a dynamic mode (205, 210) of the internal combustion engine, characterized in that a load step (500, 600, 630) is carried out and a division factor between the intake pipe-based fuel metering (SRE) and the direct fuel metering (BDE) is varied, wherein,

after the load step (500) and the simultaneous change (505) in the quantity distribution of the fuel metering in the direction of the intake-pipe-based fuel metering (SRE), the quantity distribution of the direct fuel metering (BDE) is increased in a ramp-like manner (510) up to a value for steady-state operation (512) after the load step (500), or

After the load step (600, 630) and the simultaneous change (605, 635) in the quantity apportionment of the fuel metering in the direction of the intake-pipe-based fuel metering (SRE), the quantity apportionment of the direct fuel metering (BDE) is increased in steps (610, 640) up to the value for steady-state operation (612, 642) after the load step (600, 630).

2. A method according to claim 1, characterized in that the load step (500, 600, 630) is implemented by the load (L) in steady-state operation.

3. The method according to claim 1, characterized in that in the dynamic-dependent fuel quantity allocation mentioned, the fuel quantity maximally dosed in the direct fuel dosing is reduced to the following portion: this proportion results in a minimum wetting of the components of the internal combustion engine with fuel, wherein in the fuel quantity distribution, a fuel quantity which may not yet be taken into account is allocated to the intake-pipe-based fuel metering.

4. A method as claimed in claim 3, characterized in that, for detecting the dynamic operation (205, 210) of the internal combustion engine, the change over time of the operating variable of the internal combustion engine or of the motor vehicle is monitored.

5. The method according to claim 4, wherein the operating parameters are selected from the group consisting of: motor load (L), motor temperature, oil temperature, water temperature, gradient of motor load of the internal combustion engine, acceleration of the motor vehicle, accelerator pedal value of the motor vehicle, intake valve lift curve of the internal combustion engine, change of throttle angle of the internal combustion engine, change of intake pipe pressure of the internal combustion engine, boost pressure configuration of the internal combustion engine, if the internal combustion engine has a compressor, and/or rotational speed of the internal combustion engine.

6. Method according to claim 4 or 5, characterized in that, when a change over time of at least one operating variable is detected (210): whether the change over time exceeds a dynamic threshold that can be predetermined empirically.

7. The method as claimed in claim 6, characterized in that the value of the dynamic threshold is dependent on the respective operating variable.

8. The method according to claim 6, characterized in that the current fuel quantity distribution is changed when the exceeding of the dynamic threshold is detected in the following manner: increasing a fraction of the intake-pipe-based (SRE) fuel metering relative to the direct (BDE) fuel metering.

9. Method according to claim 6, characterized in that the empirically predeterminable dynamic threshold corresponds to a change in the motor load from a low load to a high load.

10. The method of claim 8, wherein the fuel quantity distribution is changed by: the change is effected in the direction of a fuel quantity distribution which is predetermined for steady-state operation of the internal combustion engine.

11. The method of claim 8, wherein the fuel quantity distribution is changed by: the proportion of the direct fuel metering (BDE) is adjusted in the direction of increasing the intake-pipe-based fuel metering (SRE).

12. The method as claimed in claim 8, characterized in that the change in the fuel quantity distribution is effected by means of a quantity increment (510, 610, 640) which is selected as a function of an increase in the temperature of a mechanical component of a combustion chamber of the internal combustion engine.

13. The method as claimed in claim 12, characterized in that the increment (510, 610, 640) is designed in the form of a ramp or a step.

14. The method of claim 5, wherein said compressor is a turbocharger compressor.

15. A machine-readable data carrier, on which a computer program is stored, which computer program is designed to carry out each step of the method according to any one of claims 1 to 14.

16. Electronic control unit, which is designed to control an internal combustion engine or a fuel metering device by means of a method according to one of claims 1 to 14.