EP1436495B1 - Method, programme and control and/or regulating apparatus for operating a direct injection internal combustion engine - Google Patents

Abstract

In an internal combustion engine, fuel is delivered by at least a fuel pump in a high pressure zone of the fuel system. From the high pressure zone of the fuel system, the fuel reaches directly at least a combustion chamber of the internal combustion engine via at least a fuel injection device. The fuel pressure (prist) in the high pressure zone (20) of the fuel system depends on the effective operating point (nmot, Md). According to the present invention, in order to optimize the behaviour of fuel consumption and exhaust gas emission of the internal combustion engine, the fuel pressure (prist) in the high pressure zone (20) of the fuel system further depends on the operating mode (B1, B2, B3) of the internal combustion engine.

Description

State of the art

The invention firstly relates to a method for operating an internal combustion engine with direct injection, in which fuel is conveyed from at least one fuel pump into a high-pressure region of a fuel system, in which the fuel passes from the high-pressure region of the fuel system via at least one fuel injection device directly into at least one combustion chamber of the internal combustion engine , And in which the fuel pressure in the high pressure region of the fuel system depends on the current operating point of the internal combustion engine, wherein the fuel pressure in the high pressure region of the fuel system additionally depends on the operating mode in which the internal combustion engine is operated.

Such a method is described in DE 197 26 757 Al above. It is used in an internal combustion engine in which a fuel pump delivers the fuel under very high pressure into a fuel rail ("rail") in which the fuel is stored under high pressure. To the fuel manifold injectors are connected, which inject the fuel directly into the combustion chambers of the internal combustion engine.

The pressure in the fuel rail is detected by a pressure sensor which sends appropriate signals to a controller. The control unit controls a quantity control valve, with which the amount of fuel delivered from the second fuel pump to the fuel rail can be influenced. In this way, a closed loop for adjusting the pressure in the fuel rail is formed. In the known method, a setpoint for the pressure in the fuel rail is formed from a map. This map is addressed with operating variables by which the current operating point of the internal combustion engine is characterized. These operating variables are, for example, the rotational speed of the crankshaft of the internal combustion engine and the desired torque of the internal combustion engine.

Furthermore, the pressure setpoint is predetermined depending on whether the internal combustion engine is in a homogeneous operation or a stratified operation. It has been found that the fuel pressure in the high-pressure region of the fuel system is an operating variable which, similar to, for example, the ignition angle, the injection timing, etc., has different effects on the combustion behavior of the fuel in the combustion chamber in the different operating modes of an internal combustion engine. The term "operating modes" is understood to mean the different possibilities according to which an internal combustion engine can be operated with direct injection. These include, for example, the homogeneous operation, the shift operation, the homogeneous / stratified operation, an operation with and without exhaust gas recirculation, a homogeneous lean operation, etc ..

Here again, a homogeneous operation is understood to mean that the fuel enters the combustion chamber of the internal combustion engine in such a way that it essentially flows into it at the time of ignition is homogeneously distributed. This is the case especially during injection during the intake stroke. In a shift operation of the internal combustion engine, by contrast, an ignitable mixture is present only in the region of the spark plug in the combustion chamber, whereas only little or no fuel is present in the remaining combustion chamber. In stratified operation, the injection can also take place during the compression stroke. The shift operation is preferably carried out at low load and at partial load of the internal combustion engine.

By taking into account these different operating modes in the determination of the fuel pressure in the high-pressure region of the fuel system, an optimum fuel pressure can be achieved for each operating mode and ultimately optimum combustion conditions of the fuel in the combustion chamber can be achieved. As a result, the fuel consumption and exhaust gas performance of the internal combustion engine is improved.

Object of the present invention is to develop a method of the type mentioned so that the internal combustion engine can be operated reliably and without torque fluctuations.

This object is achieved in a method of the type mentioned in that determined at a change from a first mode to a second mode of the fuel pressure in the high pressure range of the fuel system for a certain period of time still based on the first mode and / or kept constant becomes.

Advantages of the invention

The invention is based on the consideration that during the switchover from one operating mode to another a sudden change in the desired value specification can be avoided should. This is because a sudden change in the fuel pressure in the high pressure region of the fuel system during the shift from one mode to another may possibly result in undefined high pressure fuel pressure. Such an undefined fuel pressure could possibly not match the other parameters of the new mode of operation, so that it may, though briefly, come to malfunction of the internal combustion engine, such as combustion misfires. This is avoided by the method according to the invention. The also proposed "freezing" of the setpoint is particularly easy to implement.

Advantageous developments of the invention are specified in subclaims.

In a first advantageous embodiment of the method according to the invention, it is proposed that a nominal value for the fuel pressure in the high-pressure region of the fuel system is determined at least temporarily by means of a characteristic map specific to the respective operating mode, which is addressed with variables characteristic of the current operating point. In this development of the method according to the invention, a corresponding characteristic map is available for each operating mode with which the desired value for the fuel pressure in the high-pressure region of the fuel system is determined. Such a method for determining the target value for the fuel pressure is very accurate and software technically easy to implement.

It is particularly preferred if the variables characteristic of the operating point include the rotational speed of a crankshaft of the internal combustion engine and a desired torque of the internal combustion engine. These are generally present anyway, so to capture the current Operating point no additional sensors are required.

Furthermore, it is favorable if the nominal value of the fuel pressure in the high-pressure region of the fuel system is determined or kept constant on the basis of the first operating mode until the second operating mode is stable. This is generally the case after a few burns, for example after about ten burns of the internal combustion engine.

In a preferred embodiment of the method according to the invention, it is also proposed that the desired value of the fuel pressure in the high-pressure region of the fuel system is brought to the value corresponding to the new operating mode via a ramp or a filter. This again avoids that there is an abrupt change in the setpoint specification for the fuel pressure in the high-pressure region of the fuel system. This could result in an abrupt change in the combustion of the fuel in the combustion chamber of the internal combustion engine with a corresponding loss of comfort for the user.

It is particularly preferred if during the switching from the first mode to the second Mode already values for the new operating mode corresponding fuel pressure in the high pressure region of the fuel system can be determined. As a result, the corresponding values are immediately and stably available so that the adjustment of the fuel pressure to the new operating mode can be carried out quickly.

The invention also relates to a computer program suitable for carrying out the above method when executed on a computer. It is particularly preferred if the computer program is stored on a memory, in particular on a flash memory or on a ferrite RAM.

Furthermore, the invention relates to a control and / or regulating device for operating an internal combustion engine. In order to carry out the operation of the internal combustion engine consumption and emission optimal, it is proposed that the control and / or regulating device comprises a memory, on which a computer program of the above type is stored.

drawing

Fig. 1:

eine Prinzipdarstellung des Aufbaus einer Brennkraftmaschine, welche ein Kraftstoffsystem mit einem Hochdruckbereich umfasst;

Fig. 2:

ein Flussdiagramm, in dem ein Verfahren zur betriebsartenabhängigen Sollwertvorgabe des Kraftstoffdrucks im Hochdruckbereich des Kraftstoffsystems von Fig. 1 dargestellt ist;

Fig. 3:

ein Diagramm, in dem der Betriebsarten-Schaltzustand der Brennkraftmaschine von Fig. 1 über der Zeit aufgetragen ist; und

Fig. 4:

ein Diagramm, in dem der Soll-Kraftstoffdruck im Hochdruckbereich des Kraftstoffsystems der Brennkraftmaschine von Fig. 1 über der Zeit aufgetragen ist.

Hereinafter, a particularly preferred embodiment of the present invention will be explained in detail with reference to the accompanying drawings. In the drawing show:

Fig. 1:

a schematic diagram of the structure of an internal combustion engine, which includes a fuel system with a high-pressure region;

Fig. 2:

a flowchart in which a method for mode-dependent setpoint specification of the fuel pressure in the high pressure region of Fuel system of Figure 1 is shown.

3:

a diagram in which the mode switching state of the internal combustion engine of Figure 1 is plotted against time. and

4:

a diagram in which the target fuel pressure in the high pressure region of the fuel system of the internal combustion engine of FIG. 1 is plotted over time.

Description of the embodiment

In Fig. 1, an internal combustion engine carries the reference number 10 as a whole. It comprises a fuel system 12. The fuel system 12 includes i.a. From this, an electric fuel pump 16 conveys the fuel via a low-pressure fuel line 17 to a high-pressure fuel pump 18. From there, the fuel passes under high pressure into a fuel rail 20 ("rail"). At this several injectors 22 are connected. The injectors 22 inject the fuel directly into combustion chambers 24.

The amount of fuel delivered from the high pressure fuel pump 18 to the fuel rail 20 is adjusted by a quantity control valve 26. This connects in the open state a working space (not shown) of the high pressure fuel pump 18 with the low pressure fuel line 17. If the quantity control valve 26 is opened during a delivery stroke of the high pressure fuel pump 18, the fuel is not in the fuel rail 20, but back conveyed into the low-pressure fuel line 17. By the time period during which the quantity control valve 26 is opened during a conveyance stroke of the high-pressure fuel pump 18 Thus, the amount of fuel delivered into the fuel rail 20 and ultimately the fuel pressure prevailing in the fuel rail 20 can be influenced. The fuel rail 20, the pressure sensor 28, the control and regulating device 30 and the quantity control valve 26 thus form a closed loop.

The fuel pressure in the fuel rail 20 of the fuel system 12 is detected by a pressure sensor 28. This provides corresponding signals to a control and regulating device 30. The internal combustion engine 10 also includes an accelerator pedal 32 whose position is tapped by a position sensor 34. The position sensor 34 is also connected to the control and regulating device 30. The speed of a crankshaft (not shown) of the internal combustion engine 10 is detected by a speed sensor 36, which also transmits corresponding signals to the control and regulating device 30.

The internal combustion engine 10 can be operated in different modes. For example, it is possible for the internal combustion engine 10 to operate at low rotational speeds and / or low nominal torque in the "shift" operating mode. In this case, the fuel is injected through the injectors 22 into the combustion chambers 24 in such a way that they are stratified in them. This means that substantially only in the region of a spark plug (not shown) an ignitable fuel mixture is present. In contrast, in the "homogeneous" mode of operation, the fuel is injected in such a way that it is distributed homogeneously overall in the combustion chambers 24.

Different operating points are possible in each operating mode. These are, for example, by the rotational speed of the crankshaft of the internal combustion engine 10 and the desired torque Are defined. In the internal combustion engine 10 shown in FIG. 1, the desired value of the fuel pressure in the fuel collecting line 20 depends on the one hand on the mode and on the other hand on the operating point of the internal combustion engine 10. This will now be explained in more detail with reference to the method shown in FIG. 2:

2, it is assumed by way of example that the internal combustion engine 10 can be operated in three different operating modes B1, B2 and B3. For each operating mode, a map KF1, KF2 and KF3 is stored in a memory of the control and regulating device 30. The maps KF1 - KF3 are addressed on the one hand by the speed nmot, which is detected by the speed sensor 36, and on the other hand by the target torque Md, which is determined from the position wped of the accelerator pedal 32.

In the present embodiment, it is first assumed that the engine 10 operates in the mode B1 (see Fig. 3). At time t1, it is now decided by a control, which will not be described in further detail here, that conditions exist which justify switching to operating mode B2. Therefore, it is now switched to the operating mode B2. This includes, for example, a shift of the ignition timing, the injection timing, the opening of a valve for exhaust gas recirculation, the change in the position of a throttle valve, etc.

With the beginning of the switchover from the operating mode B1 to the operating mode B2, a delay element is started in block 50. This causes that is switched in a switching block 52 only after expiry of a waiting time T1 from the map KF1 on the map KF2. Until the end of the time T1 is thus further used the setpoint prsollKF1 generated in the map KF1 as the setpoint prsoll for the fuel pressure in the fuel rail 20 of the fuel system 12.

Only after expiration of the time period T1 of the block 52 switches to the new operating mode B2 corresponding map KF2. Then, the setpoint prsollKF2 generated in the map KF2 is forwarded from the switching block 52 to a filter 54. Here, the setpoint value prsoll is adjusted via a ramp from the value prsollKF1 generated in the old characteristic field KF1 to the value prsollKF2 generated in the new characteristic field KF2. As a result, a sudden change in the desired fuel pressure prsoll is prevented (compare FIG. 4). The duration of the ramp provided by the filter 54 is designated T2 in FIG.

The setpoint value prsoll for the fuel pressure is fed to a regulator 56, into which the actual value prist of the fuel pressure detected by the pressure sensor 28 is also fed. In the controller 46, a corresponding signal is generated, with which the quantity control valve 26 is driven.

In a non-illustrated embodiment, the old map is not used for a certain time after the start of the switching from one mode to another, but instead held constant the setpoint of the fuel pressure in the high pressure region of the fuel system for a certain period of time.

Claims (9)

1. Method for operating an internal combustion engine (10) having direct injection, in which fuel is supplied by at least one fuel pump (18) into a high pressure region (20) of a fuel system (12), in which the fuel arrives directly in at least one combustion space (24) of the internal combustion engine (10) from the high pressure region (20) of the fuel system (12) via at least one fuel injection device (22), and in which the fuel pressure (prist) in the high pressure region (20) of the fuel system (12) depends on the current operating point (nmot, Md) of the internal combustion engine (10), the fuel pressure (prist) in the high pressure region (20) of the fuel system (12) additionally being dependent on the operating mode (B1, B2, B3) in which the internal combustion engine (10) is being operated, characterized in that, in the event of a change from a first operating mode (B1) to a second operating mode (B2), for a certain period of time (T1), the target value (prsoll) of the fuel pressure in the high pressure region (20) of the fuel system (12) remains determined (KF1) on the basis of the first operating mode (B1) and/or is held constant.
2. Method according to Claim 1, characterized in that a target value (prsoll) for the fuel pressure in the high pressure region (20) of the fuel system (12) is determined at least temporarily by means of a map (KF1, KF2, KF3) which is specific to the respective operating mode (B1, B2, B3) and which is addressed using variables (nmot, Md) which are characteristic of the current operating point.
3. Method according to Claim 2, characterized in that the variables which are characteristic of the operating point include the rotational speed (nmot) of a crankshaft of the internal combustion engine (10) and a target torque (Md) of the internal combustion engine (10).
4. Method according to one of the preceding claims, characterized in that the target value (prsoll) of the fuel pressure in the high pressure region (20) of the fuel system (12) remains determined (KF1) on the basis of the first operating mode (B1) or is held constant until the second operating mode has stabilized.
5. Method according to one of the preceding claims, characterized in that the target value (prsoll) of the fuel pressure in the high pressure region (20) of the fuel system (12) is brought to the value (prsollKF2) corresponding to the new operating mode (B2) via a ramp or a filter (54).
6. Method according to one of the preceding claims, characterized in that values (prsollKF2) for the fuel pressure in the high pressure region (20) of the fuel system (12) corresponding to the second operating mode (B2) are determined (KF2) as early as during the changeover process from the first operating mode (B1) to the second operating mode (B2).
7. Computer program, characterized in that it is suitable for carrying out the method according to one of the preceding claims if it is executed on a computer.
8. Computer program according to Claim 7, characterized in that it is stored on a memory, in particular on a flash memory or a ferrite RAM.
9. Control unit (30) for operating an internal combustion engine, characterized in that it comprises a memory on which a computer program according to either of Claims 7 or 8 is stored.

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