DE102015224409A1 - Fuel metering for the operation of an internal combustion engine - Google Patents

Abstract

In order to optimize the metering of fuel for the operation of an internal combustion engine having a plurality of cylinders (64), wherein a direct injection and a port injection are provided for the metering of fuel, it is proposed that during the operation of the internal combustion engine for at least one cylinder (64 ) is individually determined by the direct injection to be metered fuel fraction and the zuzumessende via the intake manifold fuel component and the fuel is metered according to the thus determined injection strategy (61).

Description

State of the art

The operation of an internal combustion engine with intake manifold injection and direct gasoline injection allows the use of the respective advantages of both types of injection for optimized mixture formation and the resulting combustion, which, inter alia, a reduction in fuel consumption is achieved. Especially under full load and with increased dynamics of the internal combustion engine, the gasoline direct injection system is more advantageous because the knock tendency is lower here. In the partial load range, however, the intake manifold injection is more advantageous because here the number of particles, in particular the soot particles, as well as the amount of hydrocarbons formed during combustion are lower.

An injection strategy is the type of injection used for optimum mixture formation and combustion, which may be direct injection (DI), port injection (PFI), or a combination thereof (DI-PFI split operation). According to the current state of the art, the injection strategy is based on the critical cylinder for the respective operating point of the internal combustion engine. This means that the injection strategy offers room for optimization.

Disclosure of the invention

The object of the invention is to optimize the operation of an internal combustion engine, which has a DI system and a PFI system, in terms of consumption and emission.

The object is achieved by a method of the type mentioned in that individually determined during the operation of the internal combustion engine for at least one cylinder to be metered via the direct injection fuel fraction and the zuzumessende via the intake manifold fuel content and the fuel is metered according to the injection strategy thus determined. Preferably, the injection strategy is determined individually for each cylinder.

According to the invention, the injection strategy is therefore no longer determined for the entire engine but individually for each cylinder. This means, in particular, that a DI-PFI split operation is no longer specified across cylinders for the entire engine, but a split factor is determined separately for each cylinder. Furthermore, operation of individual cylinders in DI mode and other cylinders in PFI mode is feasible.

The invention has, inter alia, the advantage of expanding the operating range of the intake manifold injection, which is in part limited by the knockability or combustion stability of individual cylinders, which allows further optimization of the engine in terms of consumption and emission.

According to one possible embodiment, the optimal operation of the injection paths for each cylinder is stored in corresponding characteristic diagrams, by means of which the injection strategy is determined individually for each cylinder. This is preferably done as a function of engine operating parameters such as engine speed, engine load, intake air temperature, engine temperature, operating mode (homogeneous, stratified, intermittent), EGR rate, valve timing, valve lift curves, fuel type (eg, octane number and / or alcohol content). Depending on availability, desired accuracy and the desired effort, different combinations of the aforementioned operating parameters can be used to determine the cylinder-specific injection strategy.

By means of the method according to the invention or the device according to the invention, in the case of thermal problems of the motor in the outside area, which are caused for example by the installation location or intake air temperature differences, a switch of the cylinder or cylinders to be hot on direct injection or it can be the DI proportion increased. This results in a stronger internal cylinder cooling due to the withdrawal of heat of the evaporating fuel directly in the cylinder, so that the tendency to knock is significantly lowered by increasing the DI injection amount fraction.

In order to prevent knocking in the course of a knock control, a retardation of the ignition angle is currently being carried out. The farther the firing angle is set to late, the later the center of gravity of the combustion and the lower the tendency to knock.

According to one embodiment of the invention, the split factor is adjusted for each cylinder and moved in the direction of direct fuel injection, thereby reducing the tendency to knock. As a result, a retraction of the ignition angle reserve, that is to say the distance of the selected ignition angle from the optimum ignition angle for this cylinder, at which the combustion takes place at the knock limit, is possible, at least for individual cylinders. As a result, a further consumption advantage can be realized. According to one possible embodiment, the knock control takes place on two paths: a quick intervention via the adjustment of the ignition angle and a slower one Intervention on changing the split factor and the partial return of the ignition angle.

According to a particularly advantageous embodiment, it is provided to learn knock interventions and resulting changes in the split factor and to adapt the optimum injection strategy for each engine copy. The basic application of the engine can thus be based on the so-called best case and no longer has to restrict the operating range for PFI to the so-called worst case behavior of individual cylinders.

A possible realization of this adaptation can take place via a specific adaptation mode as a special operation. For this purpose, for example, all cylinders are operated in a pure DI mode, at a critical operating point with regard to knocking. Alternatively, a targeted adjustment of the ignition angle can be made in order to achieve a critical operating point in terms of knocking. In a next step, a change in the split factor in the direction of intake manifold injection (PFI) takes place for a selected cylinder until a knocking combustion can be detected. The split factor is then saved for this cylinder. Preferably, this storage is operating point dependent. This procedure is then carried out for the other cylinders. Thus, the knock control can be individually optimized for each cylinder.

Alternatively, it may be provided to start the adaptation mode in pure PFI mode. At a critical operating point, the firing angle for a cylinder is adjusted so that knocking just occurs. Subsequently, the DI content is increased until no more knocking combustion takes place. In this case, interventions on the ignition angle and the split factor are advantageous, since in alternation the ignition angle in the direction of "early" and the split factor in the direction of "DI" is to be determined in order to determine the optimal parameters.

• – Ein Wandfilmmodell zur Berechnung und/oder Korrektur des Wandfilmflusses, sowohl für das Saugrohr als auch den Brennraum;
• – Die Abhängigkeit der zylinderindividuellen Berechnung der Zündung von der gewählten Einspritzung, also beispielsweise dem aktuellen Splitfaktor;
• – Ein Warmlauffaktor;
• – Ein Momentenmodell zur Korrektur der Drehmomentunterschiede, die sich über den Zündwinkeleingriff und/oder zylinderindividuelle Ventilhubeingriffe ergeben.

For determining the cylinder-specific injection strategy, it is also advantageous to include one or more of the following variables, relationships and / or functionalities:

• - A wall film model for the calculation and / or correction of the wall film flow, both for the intake manifold and the combustion chamber;
• The dependence of the cylinder-specific calculation of the ignition on the selected injection, thus, for example, the current split factor;
• - a warm-up factor;
• - A torque model for correcting the torque differences, which result from the Zündwinkeleingriff and / or cylinder-individual valve lift interventions.

Other features, applications and advantages of the invention will become apparent from the following description of exemplary embodiments, which are explained with reference to the drawings, wherein the features both alone and in different combinations for the invention may be important, without being explicitly noted. Show it:

1 a simplified schematic representation of a vehicle with an internal combustion engine, which is operable by means of a gasoline direct injection and a port injection, and

2 a block diagram in which some functional blocks of a possible embodiment of the invention are shown;

3 a flowchart that includes possible steps in performing an adaptation according to a possible embodiment; and

4 another flowchart that includes possible steps in performing an adaptation according to another possible embodiment.

In 1 is schematized a vehicle 1 shown that an internal combustion engine 2 to drive the vehicle 1 includes. In the vehicle 1 is a control unit 3 arranged, which is a control and / or regulation of the internal combustion engine 2 and in particular allows control of mixture formation. The internal combustion engine 2 has cylinders 4 on. Every cylinder 4 is at least one direct injection valve 5 assigned. Each direct injection valve 5 is via a signal line 6 with the control unit 3 connected.

The direct injection valves 5 are over a high-pressure accumulator 7 (High-pressure rail) with a high-pressure fuel pump 8th connected. The high-pressure fuel pump 8th is via a data line 9 with the control unit 3 connected. In 1 is also a fuel tank 10 shown that a low-pressure fuel pump 11 assigned. The low-pressure fuel pump 11 is via a data line 12 with the control unit 3 connected.

The one from the low-pressure fuel pump 11 from the fuel tank 10 subsidized fuel passes through a fuel low pressure line 13 to the high-pressure fuel pump 8th which generates the pressure necessary for gasoline direct injection. In the in 1 embodiment shown, the low-pressure fuel pump 11 In addition, the necessary pressure for the intake manifold injection available. Here, the fuel passes through the fuel low pressure line 13 to a fuel low pressure accumulator 15 (Low-pressure fuel rail). The fuel low pressure accumulator 15 is with intake manifold injectors 16 (PFI valves) connected.

The control unit 3 has a processor 22 and a memory element 23 on. In the memory element 23 is for example a computer program 24 stored, which is programmed to carry out the method according to the invention. The inventive method is then by means of the control unit 3 executed when the computer program 24 on the processor 22 expires.

The internal combustion engine 2 is with an exhaust tract 25 connected, the one catalytic converter 26 and a lambda probe 27 includes. The internal combustion engine 2 is also a knock sensor 28 assigned.

2 Figure 12 is a block diagram illustrating some components that may be employed in accordance with one possible embodiment of the invention. The block diagram assumes an example in which an internal combustion engine has four cylinders 64 includes. For every cylinder 64 becomes an injection strategy 61 Determined cylinder individually, the injection strategy 61 In particular, a split factor comprises, the proportion of the intake manifold injection 62 and the proportion of gasoline direct injection 63 indicating fuel to be metered. The split factor depends on a characteristic field 60 determined, wherein according to a preferred embodiment, the map 60 for every cylinder 64 individually determined. For the determination of the injection strategy 61 and thus in particular of the split factor by means of the map 60 becomes a variety of functionalities and input variables 50 considered. The functionalities and input variables 50 include in particular operating parameters 51 which, in turn, includes, for example, an engine speed, an engine load, an intake air temperature, an operation mode (homogeneous operation, stratified operation, split injection mode), an EGR rate, valve timing, valve timing curves, and a current fuel type such as octane number and alcohol content.

In the in 2 The block diagram shown is further a Wandfilmododell 52 taken into account for the calculation and correction of the wall film influence both in the intake manifold and in the combustion chamber. Furthermore, a warm-up factor 53 considered and a moment model 54 provided by means of which a correction of the torque differences via a suitable Zündwinkeleingriff or cylinder-individual valve lift intervention is possible.

The functionalities and input variables 50 further comprise a block 55 , in which the cylinder-specific calculation of the ignition takes place, which depends on the current injection, ie in particular the split factor. By means of the function block 55 Consequently, the ignition is calculated individually for each cylinder.

Of course, a variety of interactions are possible and advantageously to realize in 2 not shown. For example, by means of the maps 60 determined split factors in turn of the functionalities and input variables 50 are used and / or indirectly and / or directly taken into account in the determination of the other split factors or injection strategies, so that in dependence on the maps 60 determined values in the determination of the injection strategies for the respective other cylinder can be considered.

3 shows a flowchart in which some process steps are shown, which are traversed according to a possible embodiment, for example, in a targeted adaptation mode in a special operation of the internal combustion engine to learn the knocking interventions and resulting changes of the split factor and thus to adapt the optimal operating strategy for each engine copy.

The procedure begins in one step 100 , in which the adaptation mode is started. In one step 101 all cylinders are operated in a pure DI mode, so that the fuel is completely or almost completely metered via the gasoline direct injection. In one step 102 a cylinder is selected and in one step 103 the split factor is shifted in the direction of the intake manifold injection. In one step 104 is eg. By means of a knock sensor 28 checked whether a knocking of combustion is detectable. If this is not the case, the split factor is shifted further in the direction of intake manifold injection. Otherwise, in one step 105 the split factor is stored together with further operating parameters.

In one step 106 it is checked whether the adaptation has been carried out for all cylinders. If this is not the case, then in the step 102 the next cylinder is selected and the process performed again for that cylinder. If split factors are stored for all cylinders, the process ends in one step 107 ,

In 4 another possible embodiment of the method is shown. It starts in one step 200 , in which the adaptation is started as a special operation. In one step 201 the internal combustion engine is operated in a pure or almost complete PFI mode, so that the fuel is metered predominantly or exclusively via the intake manifold injection. In one step 202 a cylinder is selected and in one step 203 the firing angle for this cylinder is adjusted so that knocking occurs. In one step 204 the DI fraction of the metered fuel is increased until knocking combustion no longer occurs. At the same time the ignition angle is in one step 205 adapted and in the step 206 it is checked whether a knocking occurs. As long as the knocking occurs in the steps 204 and 205 shifted the split factor in the direction of Di and adjusted according to the firing angle. If knocking no longer occurs, in the step 207 the split factor is stored. Furthermore, the ignition angle and other operating parameters are stored or it is the map 60 updated.

In one step 208 it is checked whether the adaptation is carried out for all cylinders. If this is not the case, then in the step 202 the next cylinder is selected. Otherwise, the process ends in one step 209 ,

Of course, those in the 3 and 4 shown method steps to understand examples of possible embodiments of the adaptation and serve primarily to explain the invention.

Claims (13)

Method for metering fuel for the operation of one of a plurality of cylinders ( 4 ) having an internal combustion engine ( 2 ), wherein for the metering of fuel, a direct injection and a port injection are provided, characterized in that during the operation of the internal combustion engine ( 2 ) for at least one cylinder ( 4 ) the fuel proportion to be metered in via the direct injection and the proportion of fuel to be metered in via the intake manifold injection are determined individually, and the fuel is determined according to the injection strategy thus determined ( 61 ) is metered. Method according to claim 1, characterized in that for each cylinder ( 4 ) the injection strategy ( 61 ) is determined individually. Method according to one of the preceding claims, characterized in that the cylinder-specific injection strategy in dependence on current operating parameters ( 51 ) of the internal combustion engine ( 2 ) is determined. Method according to claim 3, characterized in that for the determination of the injection strategy ( 61 ) at least one of the following operating parameters ( 51 ): - engine speed; - engine load; - intake air temperature; - engine temperature; - operating mode; - EGR rate; - valve timing; - valve cams; - Fuel type. Method according to one of the preceding claims, characterized in that the ignition angle in dependence on the current injection strategy ( 61 ) of the at least one cylinder ( 4 ) is adapted to a with respect to the knock control optimized operation of the internal combustion engine ( 2 ) to reach. A method according to claim 5, characterized in that the internal combustion engine in an adaptation mode ( 100 ; 200 ), wherein in the adaptation mode ( 100 ; 200 ) the internal combustion engine ( 2 ) at a critical operating point at the knock limit of at least one cylinder ( 4 ), an adaptation of the injection strategy ( 61 ) takes place until knock no longer occurs, and the injection strategist is stored taking into account at least one operating parameter. Method according to claim 6, characterized in that in the adaptation mode ( 100 ; 200 ) - the fuel initially at least for one cylinder ( 4 ) is metered in via the direct injection in such a way that a critical operating point with regard to knocking is present; - a variation of the split factor for the metering of fuel for this cylinder is carried out in the direction of port injection; - It is checked whether there is still a knock and if this is not the case, the split factor is stored together with other operating parameters. Method according to claim 6, characterized in that in the adaptation mode ( 100 ; 200 ) - the fuel initially at least for one cylinder ( 4 ) is metered in via intake manifold injection; - the ignition angle for this cylinder ( 4 ) is adjusted so that knocking occurs; A variation of the split factor for the metering of fuel for this cylinder ( 4 ) is carried out in the direction of direct injection and a further adjustment of the ignition angle; - It is checked whether there is still a knock and if this is not the case, the split factor is stored together with the ignition angle and other operating parameters. Method according to one of the preceding claims, characterized in that in the determination of the cylinder-specific injection strategy ( 61 ) at least one of the following variables is taken into account: - wall-film model ( 52 ) for the calculation and correction of the wall film flow; - Current ignition ( 55 ) depending on the current injection strategy ( 61 ); - warm-up factor ( 53 ); - moment model ( 54 ) to correct the torque differences. Fuel metering system for one of a plurality of cylinders ( 4 ) having internal combustion engine ( 2 ), wherein for the metering of fuel, a direct injection and a port injection are provided, characterized in that the Kraftstoffzumesssystem comprises means for performing a method according to any one of claims 1 to 9. Control unit ( 3 ) for controlling and / or regulating the operation of an internal combustion engine ( 2 ), in particular for controlling and / or regulating a fuel metering system, characterized in that the control unit ( 3 ) is programmed for carrying out a method according to one of claims 2 to 9. Computer program ( 24 ) on a control unit ( 3 ) for controlling and / or regulating the operation of an internal combustion engine ( 2 ), in particular for controlling and / or regulating a fuel metering system, is capable of running, characterized in that the computer program ( 24 ) is programmed to perform a method according to any one of claims 1 to 9, when it is on the control unit ( 3 ) expires. Computer program ( 24 ) according to claim 12, characterized in that the computer program ( 24 ) on a memory element ( 23 ) is stored, wherein the memory element ( 23 ) as a the control unit ( 3 ) associated memory area, a random access memory, a read only memory, an optical storage medium or as part of a virtual memory is realized.

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