EP1432903B1 - Method and control and regulating device for operating an internal combustion engine with piezoelectrically actuated fuel injection valves - Google Patents

Description

State of the art

The invention initially relates to a method for operating an internal combustion engine, in which the fuel passes via at least one fuel injection device whose valve element is moved by a piezoelectric actuator, directly into at least one combustion chamber of the internal combustion engine, and monitors the function of the piezoelectric actuator and a malfunction is recognized.

Such a method is from the DE 198 54 306 A1 known. In this, a fuel injection device is described, which comprises a piezoelectric actuator and which is installed in an internal combustion engine with gasoline direct injection (BDE). In such an internal combustion engine, each combustion chamber is assigned its own fuel injection device. By way of the fuel injection device, the fuel can be injected into the corresponding combustion chamber of the internal combustion engine such that it is stratified or homogeneously distributed in it, depending on the desired operating mode. If it is stratified, this means that essentially only in the area of the spark plug an ignitable fuel-air mixture is present. In this operating mode the air supply to the combustion chamber is in Essentially completely de-throttled.

The use of piezo actuators has the advantage that with them a desired injection quantity can be injected with high accuracy. This applies in particular to very small injection quantities, as they occur, for example, in a pilot injection or in the distribution of larger injection quantities into small individual injections.

In order to carry out an injection of fuel into a combustion chamber, an electric charge is introduced into the piezoelectric actuator. This charging leads to a change in length of the piezoelectric actuator. A valve element of the fuel injection device and the piezoelectric actuator are usually coupled together by a hydraulic transmission. To finish the injection, the charge is removed again from the piezoelectric actuator. The control of the piezo actuators of the fuel injection devices of the respective combustion chambers or cylinder of an internal combustion engine is usually carried out by the control of an output stage, which is located in a control unit. The control unit and the piezoelectric actuator are connected to each other via lines which are connected by connecting means releasably connected to the fuel injection device.

In such a system, the case may occur that the piezoelectric actuator is controlled so that the fuel injection device is open, and that at the same time due to a malfunction, a change in the charge state of the piezoelectric actuator and thus closing the fuel injection device is no longer possible. As a result, fuel would be continuously supplied to the respective cylinder, that is, for example, during the combustion phase and during the discharge of the hot combustion exhaust gases. However, this would be too serious Damage, for example, by a fuel shock, lead to the internal combustion engine and a catalyst of the internal combustion engine.

Such a fault can occur, for example, in the event of a cable break in the connection between the piezoelectric actuator and the control unit. Furthermore, this error can occur if a defect occurs in the control unit. Such a defect is, for example, in a faulty power switch. Furthermore, such an error occurs when the connector has dissolved on the control unit and / or on the piezoelectric actuator.

Such errors can be detected by the control unit. In the DE 198 54 306 A1 It is proposed that an ohmic resistor is connected in parallel with the piezoelectric actuator, via which the piezoelectric actuator can be discharged in a defined manner. Despite this measure, however, it was found that it can not be ruled out with complete certainty that so much fuel still gets into the combustion chamber of the internal combustion engine that fuel struck there may occur. Damage to the catalyst due to, for example, during the ejection stroke still reaching the combustion chamber fuel can not be completely excluded.

US 5,816,220 discloses a reduction of the fuel supply to the rail or a reduction of the fuel pressure in the rail at faulty injector.

The present invention therefore has the object of developing a method of the type mentioned above so that damage to the internal combustion engine and the catalyst can be excluded with maximum certainty, if a malfunction of the piezoelectric actuator is detected.

This object is achieved by a method according to claim 1.

Advantages of the invention

The inventive measure prevents the fuel injection device continues to be supplied with the maximum fuel mass flow. Even if the valve element of the fuel injection device is still not in the closed position for a certain time, the reduction of the fuel mass flow reduces the possible introduction of fuel into the combustion chamber of the internal combustion engine. However, the less fuel that can still reach the combustion chamber assigned to the fuel injection device in the case of a malfunction of the piezoelectric actuator, the lower the risk that fuel drift will occur, for example, or unburnt fuel will be transported to the catalytic converter in such an amount that it will can cause damage there.

It is proposed that the fuel is conveyed by at least one fuel pump into a high-pressure region, to which the fuel injection device is connected, and that the pressure in the high-pressure region is lowered when the malfunction of the piezoactuator is detected. Such a measure is possible within a very short reaction time. Since the fuel mass flow depends directly on the pressure difference between the high-pressure region and the combustion chamber, so the fuel mass flow can be reduced immediately after detection of the malfunction. In this case, the pressure in the high pressure region of the fuel pump, if a prefeed pump is present, to the prefeed pressure, or it can be lowered to ambient pressure.

When the malfunction is detected, the piezoelectric actuator is brought into a safety position and the pressure in the high-pressure region is then raised again to a normal level when the piezoelectric actuator is in the safety position. In this way, it is possible that the internal combustion engine with those combustion chambers whose fuel injectors are still functioning normally, can be operated in an emergency operation. If the internal combustion engine, for example, installed in a motor vehicle, the next workshop can be approached in a run-flat operation.
Advantageous developments of the invention are specified in subclaims.
The valve element of the fuel injection device can be brought from a faulty open position by discharging the piezoelectric actuator in a particularly simple manner in a closed safety position. Such unloading of the piezoelectric actuator is, for example. By in the DE 198 54 306 A1 disclosed devices possible. Also in the DE 197 11 903 A1 appropriate opportunities are revealed. The content of both publications is therefore expressly made the subject of the present disclosure.

In a particularly advantageous embodiment of the present invention, it is proposed that in the case of a recognized malfunction of the piezoelectric actuator, the fuel connection to the fuel injection device is interrupted. This is possible, for example, by installing a shut-off valve between the high-pressure region and the fuel injection device. Such a complete interruption of the fuel connection to the fuel injection device ensures that even when the valve element of the fuel injection device blocked in the open position no longer has any fuel in it corresponding combustion chamber passes. The risk of damaging the internal combustion engine here is therefore particularly low.

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

The invention also relates to a control and / or regulating device for operating an internal combustion engine, wherein the control and / or regulating device comprises a memory on which a computer program of the above type is stored.

Furthermore, the invention relates to an internal combustion engine, with at least one fuel pump, with at least one fuel injection device, which injects the fuel directly into at least one combustion chamber of the internal combustion engine, and the valve element is coupled to a piezoelectric actuator, and means, with which a malfunction of the piezoelectric actuator can be recognized.

In the high pressure area, direct injection gasoline engines are generally a fuel rail, also referred to as a "rail". In it, the fuel is conveyed by a high-pressure fuel pump under high pressure. The pressure in the fuel rail is adjusted by a pressure control valve, if necessary, among other measures. If a malfunction of a piezoelectric actuator of a fuel injection device is now reported, the pressure from the high-pressure region can be released immediately via the pressure control valve.

The advantages according to the invention can thus be achieved without additional components having to be installed. The pressure reduction in the high-pressure region can also be supported by the fact that the promotion of the fuel from the fuel pump to the high-pressure region is interrupted. This can be easily achieved by controlling a usually existing quantity control valve.

It is also advantageous if the internal combustion engine comprises a valve device with which the fuel connection to the fuel injection device can be interrupted. Such a valve device may for example be arranged between the high-pressure region and the fuel injection device. It offers a particularly high level of safety against damage to the internal combustion engine when the piezoelectric actuator is at least temporarily blocked in the open position.

It is further preferred if the internal combustion engine a Means includes, with the detected in a malfunction of the piezoelectric actuator, an electric charge stored in the piezoelectric actuator can be dissipated. Also this is on the DE 198 54 306 A1 and the DE 197 11 903 A1 directed.

In particular, the internal combustion engine according to the invention comprises a control and / or regulating device of the above type.

drawing

Figur 1

eine Prinzipskizze einer Brennkraftmaschine mit einer Kraftstoff-Einspritzvorrichtung, welche wiederum einen Piezoaktor aufweist;

Figur 2

ein Flussdiagramm, welches ein Verfahren zum Betreiben der Brennkraftmaschine von Fig. 1 darstellt;

Figur 3

ein Diagramm, in dem ein Fehlerzustand des Piezoaktors der Kraftstoff-Einspritzvorrichtung der Brennkraftmaschine von Fig. 1 über der Zeit aufgetragen ist;

Figur 4

ein Diagramm, in dem der Ladezustand des Piezoaktors der Kraftstoff-Einspritsvorrichtung der Brennkraftmaschine von Fig. 1 über der Zeit dargestellt ist;

Figur 5

ein Diagramm, in dem der Druck in einer Kraftstoff-Sammelleitung der Brennkraftmaschine von Fig. 1 über der Zeit dargestellt ist; und

Figur 6

ein Diagramm, in dem die Schaltstellung eines Absperrventils der Brennkraftmaschine von Fig. 1 über der Zeit dargestellt ist.

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

FIG. 1

a schematic diagram of an internal combustion engine with a fuel injection device, which in turn has a piezoelectric actuator;

FIG. 2

a flowchart illustrating a method for operating the internal combustion engine of Fig. 1 represents;

FIG. 3

a diagram in which a fault condition of the piezoelectric actuator of the fuel injection device of the internal combustion engine of Fig. 1 is plotted over time;

FIG. 4

a diagram in which the state of charge of the piezoelectric actuator of the fuel injection device of the internal combustion engine of Fig. 1 represented over time;

FIG. 5

a diagram in which the pressure in one Fuel manifold of the internal combustion engine of Fig. 1 represented over time; and

FIG. 6

a diagram in which the switching position of a shut-off valve of the internal combustion engine of Fig. 1 is shown over time.

Description of the embodiment

An internal combustion engine carries in Fig. 1 in total, the reference numeral 10. It comprises several combustion chambers, of which in Fig. 1 only one is represented by the reference numeral 12. This combustion air is supplied via an inlet valve 14 and an intake pipe 16. The combustion exhaust gases are discharged from the combustion chamber 12 via an exhaust valve 18 and an exhaust pipe 20.

Fuel is supplied to the combustion chamber 12 via a fuel injection device 22 arranged directly on the combustion chamber 12. The ignition of the present in the combustion chamber 12 fuel-air mixture is carried out by a spark plug 23, which is connected to an ignition system 25. The fuel injector 22 includes a piezo actuator 24 coupled to a valve member (not shown) of the fuel injector 22. To the piezoelectric actuator 24, an ohmic resistor 27 is connected. Via a high-pressure fuel line 26, the fuel injection device 22 is connected to a fuel rail 28 ("rail"). Between the fuel rail 28 and the fuel injection device 22, a check valve 30 is disposed in the high-pressure fuel line 26.

The fuel rail 28 is supplied with fuel from a high-pressure fuel pump 32. In Normalbetrieh the internal combustion engine 10 is the fuel stored in the fuel rail 28 under high pressure. The supplied amount of fuel is adjusted by a quantity control valve 34. This can during a delivery cycle of the high-pressure fuel pump 32 whose working space (not shown) with a low-pressure fuel line 36 connect. Thus, during the opening period of the quantity control valve 34, no fuel from the high pressure fuel pump 32 to the fuel rail 28 passes. The pressure in the fuel rail 28 is adjusted by a pressure control valve 38. This is connected via a return line 40 with a fuel tank 42. An electric fuel pump 44 delivers the fuel from the fuel tank 42 to the low pressure fuel line 36 and further to the high pressure fuel pump 32.

The engine 10 also includes a controller 46. This controls the fuel injector 22, the ignition system 25, the shut-off valve 30, the mass control valve 34, and the pressure control valve 38. The operation of the internal combustion engine 10 is controlled by the control and regulating device according to the in Fig. 2 controlled procedures shown. This is stored as a computer program in the control and regulating device 46.

The method begins in a start block 48. In block 50, the function of the piezoelectric actuator 24 is monitored. In this case, malfunctions of the piezoelectric actuator 24 can be detected. Such a malfunction includes, for example, a break in the connection between the piezoelectric actuator 24 and the control and regulating device 46. A defect in the control device itself, which leads to a malfunction of the piezoelectric actuator 24 can be detected in block 50.

A malfunction of the piezoelectric actuator 24 can be detected in block 50, for example, by regularly recording the discharge current the piezoelectric actuator 24 is measured during the closing operation. If the connection between the piezoelectric actuator 24 and the control and regulating device 46, for example, interrupted by a cable break or by a dropped cable, the measured discharge current is zero, so that the resulting malfunction of the piezoelectric actuator 24 can be detected immediately.

If a malfunction of the piezoelectric actuator 24 is detected, three measures are carried out in parallel: On the one hand, the shut-off valve 30 is closed (block 52). Furthermore, any electric charge which may still be stored in the piezoactuator 24 is discharged via the ohmic resistor 27 (block 54). Finally, in block 56, the pressure control valve 38 and the quantity control valve 34 are activated so that the pressure in the fuel rail 28 drops abruptly.

Like from the FIGS. 3 - 6 can be seen, a high level of security against unintentional fuel entry into the combustion chamber 12 in case of malfunction of the piezoelectric actuator 24 is created by these measures. How out Fig. 4 shows, it takes a certain time until the charge is discharged from the piezoelectric actuator 24 (see. Fig. 4 ). This is due to the fact that the ohmic resistance 27 must be designed so that during normal operation of the internal combustion engine 10 without malfunction of the piezoelectric actuator 24, the charge in the piezoelectric actuator 24 can be constructed sufficiently quickly that a corresponding rapid actuation of the piezoelectric actuator 24 and with him coupled valve element is possible.

How out Fig. 5 can be seen, by the control of the quantity control valve 34 and the pressure control valve 38, a reduction of the pressure in the fuel rail 28 within a period of time is possible, which is significantly shorter than the period which is required for the reduction of the charge in the piezoelectric actuator 24. Thus, even then, if the charge from the piezoelectric actuator 24 is not yet completely discharged and thus the valve of the fuel injection device 22 is not fully closed, ensures that, if anything, only a little fuel in the combustion chamber 12 of the internal combustion engine 10 can pass. This is further assisted by the closing of the shut-off valve 30 (FIG. Fig. 6 ), through which the fuel supply to the fuel injection device 22 is completely interrupted. The reduction of the fuel mass flow to the fuel injection device 22 is therefore redundant in the present embodiment.

In Fig. 2 At block 58, it is checked if the fuel injector 22 is fully closed. Under knowledge of the discharge curve of Fig. 4 For example, after a certain time, it can be assumed that the piezoactuator 24 is completely discharged and thus the valve element of the fuel injection device 22 is in the fully closed position. If the answer in block 58 is "yes", the quantity control valve 34 and the pressure control valve 38 are again activated in block 60 in such a way that the normal operating pressure builds up in the fuel manifold 28 (cf. Fig. 5 ). The method ends in an end block 62.

The rapid rebuilding of the pressure in the fuel rail 28 when the fuel injector 22 is in the closed position allows the internal combustion engine 10 to continue to run in runflat operation. Namely, in this case, the fuel injectors of the other combustion chambers (in FIG Fig. 2 not shown), as long as no malfunction is detected in these.

It is understood that in Fig. 2 in blocks 52 and 56 (closing the shut-off valve 30 and lowering the pressure in the fuel rail 28) may not necessarily be both necessary to reduce the risk of damage to the internal combustion engine 10 in the event of a malfunction of the piezoelectric actuator 24.

Claims (7)

1. Method for operating an internal combustion engine (10), in which method fuel is passed directly into at least one combustion chamber (12) of the internal combustion engine (10) by means of at least one fuel injection device (22) whose valve element is moved by a piezoelectric actuator (24), and in which method the functioning of the piezoelectric actuator (24) is monitored and a malfunction is detected (50), wherein, in the event of a malfunction of the piezoelectric actuator (24) being detected (50), the fuel mass flow to the fuel injection device (22) is reduced (52, 56), with the fuel being fed by at least one fuel pump (32, 44) into a high-pressure region (28) to which the fuel injection device (22) is connected, characterized in that, in the event of a malfunction of the piezoelectric actuator (24) being detected (50), the pressure in the high-pressure region (28) is reduced (56), and in that, in the event of a malfunction being detected (50), the piezoelectric actuator (24) is placed into a safety position (54) and the pressure in the high-pressure region (28) is then raised to a normal level again (60) when the piezoelectric actuator (24) is in the safety position.
2. Method according to Claim 1, characterized in that the valve element of the fuel injection device (22) is moved from an erroneously open position into a closed safety position (54) by means of a discharge of the piezoelectric actuator (24).
3. Method according to one of Claims 1 or 2,
   characterized in that, in the event of a malfunction of the piezoelectric actuator (24) being detected (50), the fuel connection to the fuel injection device (22) is blocked (52).
4. Computer program, characterized in that said computer program carries out all the steps of the method according to one of the preceding claims when executed on a computer.
5. Computer program according to Claim 4,
   characterized in that said computer program is stored on a memory, in particular on a flash memory or on a ferrite RAM.
6. Control and/or regulating unit (46) for operating an internal combustion engine (10), characterized in that said control and/or regulating unit (46) comprises a memory on which is stored a computer program according to one of Claims 4 or 5.
7. Internal combustion engine (10), having at least one fuel pump (32, 44), having at least one fuel injection device (22) which injects the fuel directly into at least one combustion chamber (24) of the internal combustion engine (10) and whose valve element is coupled to a piezoelectric actuator (24), and having means (46) with which a malfunction of the piezoelectric actuator (24) can be detected, characterized in that said internal combustion engine (10) comprises a control and/or regulating unit (46) according to Claim 6.

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