EP3449111B1 - Method for operating an internal combustion engine, device for the open-loop and/or closed-loop control of an internal combustion engine, injection system and internal combustion engine - Google Patents

Description

A method for operating an internal combustion engine with an engine having a number of cylinders and an injection system with high-pressure components, in particular an injection system having a common rail with a number of injectors assigned to the cylinders, in particular with one injector being assigned an individual memory that is used to hold fuel is formed from the common rail for the injector.

The concept of an injector with an individual accumulator in the context of a common rail injection system, as it is for example in DE 199 35 519 C2 is described by way of example. The individual accumulator is supplied with fuel under pressure from the pressure connection via a fuel supply duct and is in direct flow connection with the high pressure duct for the fuel under high pressure in the common rail. The volume of the individual reservoir is large compared to the volume of the high pressure channel and the nozzle antechamber in the injector. Due to the arrangement of the injector decoupled from the common rail via a throttle element - there is enough space in the individual reservoir in the housing of the fuel injector to hold fuel for at least an entire injection quantity for one working cycle of a cylinder, but in any case for a partial injection within the working cycle.

DE 10 2009 002 793 B4 discloses an individual accumulator or a high-pressure component such as a common rail with a pressure measuring device which is in the form of a strain sensor, the strain sensor being in the form of a strain gauge and being arranged on the outside of a wall of the individual accumulator and a hydraulic resistance directly to the individual accumulator is arranged upstream or downstream for integration into the high pressure duct.

When starting the engine, it must be ensured on the one hand that the high pressure has a maximum value of z. B. does not exceed 600 bar, as the Otherwise the pump can be damaged due to the excessive counter pressure. On the other hand, the high pressure when starting the engine should be as high as possible in order to ensure good acceleration behavior and low emissions.

The control of the suction throttle when starting the engine according to the prior art is described in the patent DE 101 56 637 C1 described. The suction throttle with the engine stopped or with the engine running until a high pressure threshold of z. B. 800 bar with a constant current value, preferably 0 A, energized. When the threshold value is reached, the high pressure regulation is activated, whereby the suction throttle is energized in such a way that the high pressure is regulated to the target high pressure. This method is particularly advantageous for common rail systems which have a large system leakage. In such systems, the rail pressure, ie the fuel pressure in the common rail, quickly falls to a low value after the engine has been switched off, e.g. B. 0 bar, from. If, in this case, the suction throttle is initially not supplied with current after the engine has been started, a maximum increase in the high pressure up to a specifiable high pressure threshold value is achieved. This enables the engine to be started quickly and reliably, since, on the one hand, injections in common rail systems are only possible when the opening pressure of the injection nozzles has been reached. This is usually 350 ... 400 bar. On the other hand, the engine can be accelerated faster at higher high pressures, since the fuel is burned better in this case, which results in a higher degree of efficiency.

While this is fundamentally correct, the following problem has nevertheless proven to be relevant: In the case of newer common rail systems, actuation of the suction throttle in accordance with the prior art is not very advantageous, since these systems have only a small amount of system leakage. As a result, the high pressure is not reduced when the engine is switched off and therefore remains at the values that were available at the time the engine was switched off. Since the engine is operated at high pressures of 600 ... 2200 bar, before the engine is started, i. d. Usually a high pressure that could damage the high pressure pump of the injection system.

It is therefore desirable to set the pressure prevailing within the injection system at the time of starting the engine in a predetermined range of values that is low enough not to damage the high-pressure pump of the injection system and at the same time high enough to exhibit good acceleration behavior and advantageous emissions behavior. In order to meet the requirements mentioned at the beginning in an improved manner, a method has to be developed which adjusts the pressure prevailing within the injection system to a predetermined value range at the time of the engine start.

• Starten der Brennkraftmaschine,
• Betreiben der Brennkraftmaschine,
• Abstellen der Brennkraftmaschine,

Erfindungsgemäß sind bei dem Verfahren die Schritte vorgesehen, dass

• ein einen Motorstillstand kennzeichnender Zustand erkannt wird, insbesondere nach Abstellen der Brennkraftmaschine,
• ein Hochdruck-Grenzwert festgelegt und ein Sollhochdruck vorgegeben wird,
• eine Leckage im Common-Rail ohne Einspritzung erzeugt wird,
• mittels der Leckage der Kraftstoff-Druck im Common-Rail auf den festgelegten Hochdruck-Grenzwert unterhalb des Sollhochdruckes abgebaut wird.

Die Erfindung führt im Rahmen der Aufgabenstellung auch auf eine Einrichtung des Anspruchs 10 und ein Einspritzsystem des Anspruchs 11 sowie eine Brennkraftmaschine des Anspruchs 12. Die Einrichtung dient zum Steuern und/oder Regeln einer Brennkraftmaschine, mit einem Motorregler und einem Einspritz-Rechenmodul, die ausgebildet sind zur Durchführung des erfindungsgemäßen Verfahrens. Das Einspritzsystem ist versehen mit einem ein Common-Rail für eine Brennkraftmaschine mit einem eine Anzahl von Zylindern aufweisenden Motor und mit einer Anzahl von den Zylindern zugeordneten Injektoren, wobei einem Injektor ein Einzelspeicher zugeordnet ist, der zum Vorhalten von Kraftstoff aus dem Common-Rail zur Injektion in den Zylinder ausgebildet ist und mit einer Einrichtung zum Steuern und/oder Regeln einer Brennkraftmaschine nach Anspruch 9. Die Brennkraftmaschine umfasst einen eine Anzahl von Zylindern aufweisenden Motor und ein Einspritzsystem nach Anspruch 10, mit einem Common-Rail und einer Anzahl von Injektoren. DE102013214831 A1 , US5711274 A and DE19857260 A1 disclose known methods of operating an internal combustion engine. This is where the invention comes in, the task of which is to develop a method which, before the engine starts, reduces the high pressure to just below the target high pressure and activates the high pressure control as quickly as possible when the engine is started.
The object relating to the method is achieved by the invention with a method of claim 1.
The invention is based on a method for operating an internal combustion engine with an engine having a number of cylinders and an injection system with high-pressure components, in particular an injection system having a common rail with a number of injectors assigned to the cylinders, in particular with an individual memory assigned to one injector , which is designed to hold fuel from the common rail for the injector, the method comprising the steps:

• Starting the internal combustion engine,
• Operating the internal combustion engine,
• Switching off the internal combustion engine,

According to the invention, the method provides the steps that

• a state indicative of an engine standstill is recognized, in particular after the internal combustion engine has been switched off,
• a high pressure limit value is set and a target high pressure is specified,
• a leak is generated in the common rail without injection,
• by means of the leakage, the fuel pressure in the common rail is reduced to the specified high pressure limit value below the target high pressure.

The invention also leads within the scope of the object to a device of claim 10 and an injection system of claim 11 and an internal combustion engine of claim 12. The device is used to control and / or regulate an internal combustion engine, with an engine controller and an injection computing module, which is formed are required to carry out the method according to the invention. The injection system is provided with a common rail for an internal combustion engine with an engine having a number of cylinders and with a number of injectors assigned to the cylinders Injection into the cylinder is formed and with a device for controlling and / or regulating an internal combustion engine according to claim 9. The internal combustion engine comprises an engine having a number of cylinders and an injection system according to claim 10, with a common rail and a number of injectors.

The invention is based on the consideration that the high pressure in the injection system of an internal combustion engine should ideally be reduced to just below the target high pressure before starting. The target high pressure must be specified in such a way that the maximum permissible high pressure is not exceeded when the engine is started. If the engine is started, the high pressure control should be activated as soon as possible in order to avoid a significant overshoot of the high pressure above the setpoint.

The invention has recognized that this ensures that the high pressure pump is not damaged by overload on the one hand and that the high pressure is as high as possible when the engine is started in order to ensure good emission and acceleration behavior. According to the method according to the invention, the object is preferably achieved in that the high pressure is reduced by activating a so-called "blank shot" function after the engine has been switched off. In this case, the injectors are energized when the engine is not running, which creates a leak, but no injection takes place. This "blank shot" function is activated until the high pressure is reduced to a value just below the target high pressure. A significant overshoot of the high pressure after the engine is started is prevented according to the invention in that the high pressure regulation is activated as soon as the calculated high pressure gradient exceeds a predeterminable limit value.

The concept preferably provides the basis for an internal combustion engine that is operated in an improved manner. The invention makes it possible to start the engine at the highest possible rail pressure without exceeding the maximum permissible rail pressure and thus without damaging the engine by a rail pressure that is too high. Starting at high rail pressure thus enables good acceleration behavior with low emissions. Starting at high Rail pressure in the range of the maximum permissible rail pressure is achieved by lowering the rail pressure to a value just below the maximum pressure after the engine has been switched off with the help of the blank shot function and by activating the rail pressure control at an early stage when the engine is started by checking, whether the mean high pressure gradient exceeds a specifiable limit. This method thus also makes it possible that the intake throttle does not have to be energized when the engine is not running, which extends its service life.

According to the invention, the method provides that when the internal combustion engine is started, the high-pressure control for regulating the fuel pressure is activated while the engine is at a standstill, as soon as a mean high-pressure gradient reaches or exceeds a defined limit value.
Specifically, this includes, in particular, the activation of the high-pressure regulation for regulating the fuel pressure at a point in time at which, due to an engine speed that is still too low, there is still a state indicative of an engine standstill.
This has the advantage that the fuel pressure remains below a maximum value when the internal combustion engine is started and settles to a predetermined setpoint earlier. Advantageous further developments of the invention can be found in the subclaims and indicate in detail advantageous possibilities for realizing the concept explained above within the scope of the task and with regard to further advantages.
In particular, it is advantageously provided that a suction throttle influencing the fuel supply is actuated in the closing direction by activating the high-pressure control, which leads to the fuel pressure remaining below a maximum value when the internal combustion engine is started.
Specifically, this means that a continuous signal for controlling a suction throttle is increased when the high-pressure regulation is activated, which results in a closing movement of the suction throttle.
This has the advantage that an increase in the fuel pressure above a maximum value is prevented by early closing of the suction throttle.

Another preferred development provides that the high pressure gradient is formed from a first and a second fuel pressure value, the first and the second fuel pressure value following one another at a predetermined time interval.

In concrete terms, this means, for example, that two fuel pressure values that are consecutive in time and measured by means of a pressure sensor are subtracted from one another and that a quotient is formed from this difference and the period between the two recordings of the respective values.

This procedure has the advantage that, instead of the absolute fuel pressure value, the high pressure gradient, that is to say its rate of increase, can be used as a criterion for activating the high pressure regulation. In this way, before the absolute maximum of the fuel pressure is reached, the point in time at which the increase in the fuel pressure value reaches a predetermined limit value can be determined.

A further preferred development provides that a mean high pressure gradient is formed from a finite amount of successive high pressure gradients by averaging.

This procedure has the advantage that by averaging high pressure gradients, a corresponding degree of reliability is achieved in the assessment. For example, short-term outliers in the measured fuel pressure values can be smoothed using such a mean value formation.

Furthermore, it is advantageously provided that an engine is recognized as being in operation or running ^{at an engine speed of 50-120 min -1.}

Furthermore, it is advantageously provided that the specified high pressure limit value is 560-600 bar.

Another preferred development provides that the high pressure gradient is determined for a predetermined period of time as a mean high pressure gradient from a number (k) of certain high pressure gradients, the number (k) as a quotient from the predetermined period of time and a sampling time is formed.

Embodiments of the invention will now be described below with reference to the drawing. This is not necessarily intended to represent the embodiments to scale; rather, the drawing, where useful for explanation, is shown in a schematic and / or slightly distorted form. With regard to additions to the teachings that can be seen directly from the drawing, reference is made to the relevant prior art. It must be taken into account here that various modifications and changes relating to the form and the detail of an embodiment can be made without departing from the scope of the claims.

In the case of specified measurement ranges, values lying within the stated limits should also be disclosed as limit values and be able to be used and claimed as required. For the sake of simplicity, the same reference symbols are used below for identical or similar parts or parts with an identical or similar function.

Fig. 1

eine Einrichtung zur Steuerung eines Einspritzsystems einer Brennkraftmaschine

Fig. 2

ein Blockschaltbild eines Hochdruckregelkreises

Fig. 3A

ein Zeitdiagramm zur Darstellung des Hochdruck-Gradienten

Fig. 3B

Formeln zur Berechnung des Hochdruck-Gradienten und des mittleren Hochdruck-Gradienten

Fig. 4A

ein Zeitdiagramm der gemessenen Drehzahl n_mess

Fig. 4B

ein Zeitdiagramm des gemessenen Kraftstoff-Druckes p_mess und des Sollhochdruckes p_Soll

Fig. 4C

ein Zeitdiagramm des Hochdruck-Gradienten des Kraftstoff-Druckes

Fig. 4D

ein Zeitdiagramm der Einschaltdauer PWM_SDR des PWM-Signals

Fig. 4E

ein Zeitdiagramm des Signals "Motor Stop", welches ein Abstellen des Motors kennzeichnet

Fig. 4F

ein Zeitdiagramm des Signals "Motor Steht", welches einen Motorstillstand kennzeichnet

Fig. 4G

ein Zeitdiagramm des Signals "Steuermodus", welches eine Aktivierung der Hochdruck-Regelung kennzeichnet

Fig. 4H

ein Zeitdiagramm des Signals "Blank Shot Aktiv", welches eine Aktivierung der Blank-Shot-Funktion kennzeichnet

Fig. 5

ein Flussdiagramm eines Verfahrens einer bevorzugten Ausführungsform..

Further advantages, features and details of the invention emerge from the following description of the preferred embodiments and with reference to the drawing; this shows in:

Fig. 1

a device for controlling an injection system of an internal combustion engine

Fig. 2

a block diagram of a high pressure control loop

Figure 3A

a time diagram to illustrate the high pressure gradient

Figure 3B

Formulas for calculating the high pressure gradient and the mean high pressure gradient

Figure 4A

a time diagram of the measured speed n _mess

Figure 4B

a time diagram of the measured fuel pressure p _mess and the target high pressure p _target

Figure 4C

a time diagram of the high pressure gradient of the fuel pressure

Figure 4D

a timing diagram of the duty cycle PWM _{SDR of} the PWM signal

Figure 4E

a timing diagram of the "engine stop" signal, which characterizes a shutdown of the engine

Figure 4F

a time diagram of the signal "engine stopped", which indicates an engine standstill

Figure 4G

a time diagram of the signal "control mode", which characterizes an activation of the high pressure control

Figure 4H

a timing diagram of the "Blank Shot Active" signal, which indicates activation of the blank shot function

Fig. 5

a flow chart of a method of a preferred embodiment.

Fig. 1 shows a device according to the prior art. One such facility is in the DE 102014 213 648 B3 described. An internal combustion engine 1 has an injection system 3. The injection system 3 is preferably designed as a common rail injection system. It has a low-pressure pump 5 for delivering fuel from a fuel reservoir 7, an adjustable, low-pressure-side suction throttle 9 for influencing a volume flow of fuel flowing to a high-pressure pump 11, the high-pressure pump 11 for delivering the fuel under increased pressure into a high-pressure accumulator 13, the high-pressure accumulator 13 for storing the fuel, and preferably a plurality of injectors 15 for injecting the fuel into combustion chambers 16 of the internal combustion engine 1. Optionally, it is possible that the injection system 3 is also designed with individual stores, in which case, for example, an individual store 17 is integrated into the injector 15 as an additional buffer volume. In the exemplary embodiment shown here, a particularly electrically controllable pressure control valve 19 is provided, via which the high-pressure accumulator 13 is fluidly connected to the fuel reservoir 7. A fuel volume flow, which is diverted from the high-pressure accumulator 13 into the fuel reservoir 7, is defined via the position of the pressure regulating valve 19. This fuel volume flow is shown in Fig. 1 as well as in the following text with VDRV and represents a high pressure disturbance of the injection system 3.

The injection system 3 does not have a mechanical pressure relief valve, since its function is taken over by the pressure regulating valve 19. The mode of operation of the internal combustion engine 1 is determined by an electronic control unit 21, which is preferably designed as an engine control unit of the internal combustion engine 1, namely as a so-called engine control unit (ECU). The electronic control unit 21 includes the usual components of a Microcomputer systems, for example a microprocessor, I / O modules, buffer and memory modules (EEPROM, RAM). The operating data relevant to the operation of the internal combustion engine 1 are applied in characteristic diagrams / characteristic curves in the memory modules. The electronic control unit 21 uses this to calculate output variables from input variables. In Fig. 1 The following input variables are shown as examples: A measured, still unfiltered high pressure p, which prevails in the high pressure accumulator 13 and is measured by means of a pressure sensor 23, a current engine speed n ₁ , a signal FP for the output specification by an operator of the internal combustion engine 1, and an input variable E. Further sensor signals are preferably combined under input variable E, for example a charge air pressure of an exhaust gas turbocharger. In an injection system 3 with individual _{accumulators 17, an individual accumulator pressure p E is} preferably an additional input variable of control unit 21.

In Fig. 1 The output variables of the electronic control unit 21 include, for example, a signal PWMSDR for controlling the suction throttle 9 as the first pressure actuator, a signal ve for controlling the injectors 15 - which in particular specifies a start and / or an end of injection or also an injection duration - a signal PWMDRV for control of the pressure control valve 19 and thus the high pressure disturbance variable VDRV is defined. The output variable A is representative of further actuating signals for controlling and / or regulating the internal combustion engine 1, for example for an actuating signal for activating a second exhaust gas turbocharger during register charging.

Fig. 2 shows the block diagram of a high pressure control circuit according to the prior art. The input variable of the high pressure control loop is the set high pressure P _{set of} the common rail system, which is compared with the measured high pressure p _mess . The difference between the two high pressures results in the high pressure control deviation e _p . This control deviation e _{p of} the high pressure is the input variable of the high pressure regulator, which is preferably implemented as a PI (DT ₁ ) algorithm. Other input variables of the high pressure regulator include the proportional coefficient kp _SDR . The output variable of the high-pressure _{regulator is the fuel volume flow V PI} ( _DT1 ) ^SDR , which is added to the target fuel consumption V _stör ^SDR . The target fuel consumption V _disturb ^SDR is calculated from the measured engine speed n _mess and the target injection _{quantity Q Soll} and represents a disturbance variable of the high pressure control _{loop . As the sum of the high pressure controller output variable V PI} ( _DTI ) ^SDR and the disturbance variable V ^{disturb SDR} (disturbance variable injection ) results in the unlimited target fuel volume flow V _Unbeg ^SDR . This is then based on the engine speed n _mess on the maximum volume flow V _max ^SDR limited. _{The limited target} fuel volume flow V ^{Soll SDR} is the input variable of the pump characteristic. The pump characteristic converts the limited _target ^{fuel volume flow V Soll SDR} into the suction throttle _target ^{current I Soll SDR} . The suction throttle setpoint current I _Soll ^SDR is the input variable of the suction throttle flow controller, which has the task of regulating the suction throttle current. Another input variable of the suction throttle current regulator is the measured suction throttle current I _mess ^SDR. The output variable of the suction throttle current regulator is the suction throttle setpoint voltage U _Soll ^SDR , which is then converted into the PWM duty cycle PWM _SDR as a specification for the suction throttle. The controlled system of the high pressure control loop consists of the suction throttle, the high pressure pump and the fuel rail. The controlled variable of the subordinate suction throttle current control circuit is the suction throttle current, the raw values I _raw ^SDR still being passed through a filter which z. B. a PT ₁ filter can be filtered. The output variable of this filter is the measured suction throttle current I _mess ^SDR . The controlled variable of the high pressure control loop is the fuel rail pressure (high pressure). The raw values of the fuel rail pressure p _raw are filtered by a high pressure filter, which has the measured fuel rail pressure p _mess as its output variable. This filter can e.g. B. be implemented by a PT ₁ algorithm.

The following elements of the high pressure control circuit have already been published in these patents: the current control circuit in the US 7,240,667 B2 and the feedforward control z. B. in the DE 10 2008 036 299 B3 or the US 7,856,961 B2 in the event of separate fuel rails.

The invention is based on Figures 3A, 3B , Fig. 4 and Fig. 5 described.

Figures 3A and 3B represent a particularly advantageous calculation of the high pressure gradient Figure 3A The time diagram shown shows the high pressure in the form of a solid curve as a function of time. The current high pressure gradient (gradient _Current ^HD (t ₁ )) at time t ₁ is corresponding Figure 3B calculated by subtracting the measured fuel pressure (p _mess (t ₁ - Δt _degrees ^HD )) that was past the time span (Δt _degrees ^HD ) from the current fuel pressure (p _mess (t ₁ )) and dividing the difference by the time span ( Δt _degree ^HD ) is divided. The high pressure gradient at the time (t ₁ - Ta), the sampling time is denoted by (Ta), is calculated by the by the time interval (t ₁ - Ta - .DELTA.t _degree ^HD) past measured fuel pressure (p _mess ( t ₁ - Ta - Δt _degrees ^HD )) is subtracted from the fuel pressure (p _mess (t ₁ - Ta)) and the difference is also divided by the time span (Δt _degrees ^HD ) becomes. In general, the high-pressure gradient at the time (t ₁ - (k - 1) ^* Ta) is calculated by the by the time interval (t ₁ - (k-1) ^* Ta - .DELTA.t _degree ^HD) past measured fuel pressure ( p _mess (t ₁ - (k - 1) ^∗ Ta - Δt _degrees ^HD )) subtracted from the fuel pressure (p _mess (t ₁ - (k - 1) ^∗ Ta)) and subtract the difference by the time span (Δt _degrees ^HD ) is divided.

An advantageous embodiment of the calculation of the high pressure gradient is when this is _{averaged over the predeterminable time span (Δt mean} ^HD ). At a sampling time (Ta), the mean high pressure gradient (gradient _mean ^HD (t ₁ )) at time t ₁ results accordingly Figure 3B by averaging over a total of (k) gradients, the number (k) correspondingly Figure 3B is calculated as follows: $$k=\frac{\mathrm{\Delta }{t_{\mathit{medium}}}^{\mathit{HD}}}{\mathit{Ta}}$$

The connected figures Figures 4A, 4B, 4C , Figures 4D, 4E, 4F, 4G and 4H illustrate the invention in the form of several timing diagrams Figure 4A The time diagram shown shows the measured engine speed (nmess). At time (t ₁ ), the engine is switched off, which is shown in the timing diagram of Figure 4E The "Motor Stop" signal shown changes from the value 0 to the value 1. As a result, the motor speed (nmess) changes, starting from the value 1000 1 / min, to the value 0 1 / min. At the point in time (t ₂ ), the motor standstill is recognized, which is shown in the timing diagram of Figure 4F The signal shown ("Motor stopped") changes from the value 0 to the value 1. In the time diagram of the Figure 4B the target high pressure (p _target ) is shown as a solid, light curve. The target high pressure is calculated as the output variable of a three-dimensional map with the input variables engine speed (nmess) and target torque (M _Soll ). If the engine is switched off, the target torque is immediately reduced to the value 0 Nm, the engine speed drops to the value 0 1 / min with a time delay. According to the in Figure 4B In this case, according to the design of the target high pressure map, a falling target high pressure (P _Soll ), represented by a solid, light curve with the initial value 1200 bar and the final value 600 bar, which is reached at time (t ₂ ), results in this case becomes. The fuel pressure (p _mess ¹ ) is shown in the timing diagram of Figure 4B represented by a dark solid curve. Since, in the event of an engine stop, there is no longer any injection and newer common rail systems have no or only very little system leakage, the fuel pressure (p _mess ¹ ) remains constant at the original target value of 1200 bar until time (t _2). Correspondingly, is shown in the timing diagram of Figure 4C , a mean high pressure gradient (gradient _mean ^HD ) of 0 bar / s is calculated. The timing diagram of the Figure 4D shows the duty cycle (PWM _SDR ) of the PWM signal of the suction throttle. Until the point in time (t ₁ ), with the engine running, this assumes the value 15%. Since the target high pressure (p _Soll) from the time (t ₁₎ falls to below the fuel pressure (p _mess ¹⁾ results in a negative pressure control deviation (e _p). This leads to that accordingly Fig. 2 a greater duty cycle (PWM _SDR ) of the PWM signal is calculated, ie the suction throttle is moved in the closing direction. According to the in Figure 4D The time diagram shown increases the duty cycle (PWM _SDR ) of the PWM signal to its maximum value of 25% and remains at this value until the point in time (t ₂ ). The duty cycle of the PWM signal is a calculated signal accordingly Fig. 2 , this is shown in the timing diagram of the Figure 4G indicated by the fact that the control mode assumes the value 0 _{up to time (t 2).}

At the point in time (t ₂ ), the motor is switched on in accordance with the in Figure 4F shown as stationary, the signal ("engine stopped") changes from value 0 to value 1. As in Figure 4H shows, the blank shot function is activated at this point in time; this is indicated by the "Blank Shot Active" signal, which changes from value 0 to value 1. This leads to the fuel pressure (p _mess ¹ ), shown in FIG Figure 4B , starting from the value 1200 bar, falls and at the time (t ₃ ) reaches the value 580 bar. At this point in time the blank shot function is deactivated so that the signal ("blank shot active") changes from value 1 to value 0 again. Since the fuel pressure _{drops from time (t 2} ) to time (t ₃ ), there is a negative high pressure gradient, as shown in the third time diagram, indicated by the value -100 bar / s.

The engine is started at time (t _3). As a result, the engine speed (nmess) increases and reaches the value 80 1 / min _{at time (t 5).} This means that a running motor is detected at this point in time, the signal ("Motor Stall") changes from value 1 to value 0. According to the state of the art, the switch-on duration (PWM _SDR ) of the PWM signal is only calculated from this point in time and so that the fuel pressure is regulated, ie up to the point in time (t ₅ ) the duty cycle (PWM _SDR ) of the PWM signal is set to the value 0% and the fuel pressure is thus controlled. This has the consequence that the fuel pressure (p _mess ¹ ) according to the prior art, starting with the time (t ₃ ), increases and only at the time (t ₇ ) and thus after the activation of the high pressure control at the time (t ₅ ), with the value 750 bar reaches its maximum value. After the point in time (t ₇ ), the fuel pressure falls again and finally reaches its desired value (p _{setpoint ) at the point in time (t 9} ). The Time diagram in Figure 4B shows that the fuel pressure (p _mess ¹ ) clearly exceeds the permissible maximum pressure (p _max ) when the engine is started. This in Figure 4D The diagram shown shows that the on-time corresponding to the state of the art (PWM _SDR ¹ ) of the PWM signal increases at time (t ₅ ) with the activation of the high-pressure control and at time (t ₉ ) finally reaches the steady-state value of 20%. swings in. This in Figure 4G The diagram shown shows the control mode (control mode ¹ ) according to the prior art. The state of the art, as with the in Figure 4B and Figure 4D shown diagrams, again shown as a solid curve. It can be seen that the control mode (control mode ¹ ) is identical to the value 1 up to the point in time (t ₅ ), ie the high pressure control is deactivated up to this point in time, so that the duty cycle of the PWM signal (PWM _SDR ) is specified . Only at time (t ₅ ) does the control mode (control mode ¹ ) change to the value 0, so that the fuel pressure (p _mess ¹ ) is subsequently regulated.

This in Figure 4C The diagram shown shows that the high pressure gradient (gradient _mean ^HD ) from time (t ₃ ) onwards corresponding to the increasing fuel pressure according to the in Figure 4B The diagram shown increases and at time (t ₄ ) the limit value (Limit _HDGradient ^Start ) is reached. In the sense of the invention, the high pressure regulation is _{activated when this limit value is reached and thus at time (t 4} ). This changes the control mode, shown in Figure 4G , already at the point in time (t ₄ ) to the value 0. The corresponding line is shown dotted and ^{labeled (control mode 2} ). With the activation of the high pressure regulation _{according to the invention at time (t 4} ), the PWM signal rises corresponding to that in FIG Figure 4D The diagram shown already _{starts at time (t 4} ), so that the suction throttle is actuated in the closing direction earlier than in the prior art. The PWM signal according to the invention is again shown dotted and designated (PWM _SDR ² ). According to the invention, the high-pressure regulation, which starts earlier according to the invention, means that the fuel pressure now _{remains below the maximum value (p max} ) when the engine is started and settles at its setpoint (p _setpoint ) earlier, already at time (t _8). This protects the engine when it starts. The course of the fuel pressure resulting in this case is shown in the diagram of Figure 4B again shown dotted. The fuel pressure is denoted by (pmess).

Fig. 5 represents the method according to the invention in the form of a flowchart. In step (S1), the mean gradient (gradient _mean ^HD ) is correspondingly here Fig. 3 calculated. The process then continues with step (S2). In step (S2) it is queried whether the engine is stationary. Is this the one If so, the process continues with step (S3). In step (S3) a flag, which is initialized with the value 0, is queried. If this flag is set, the process continues with step (S7). If the flag is not set, the process continues with step (S4). In step (S4) it is checked whether the gradient (gradient _mean ^HD ) is greater than or equal to the limit value (limit _HDGradient ^Start ). If this is the case, the process continues with step (S5). In step (S5) the flag is set to the value 1 and the control mode is set to the value 0. The process then continues with step (S7). If the query result in step (S4) is negative, ie if the mean gradient (Gradient _Mittel ^HD ) is less than the limit value (Limit _HDGradient ^Start ), the control mode is set to the value 1 in step (S6). The process then continues with step (S7). The control mode is queried in step (S7). If the control mode is set, the duty cycle (PWM _SDR ) of the PWM signal is set to the value 0 in step (S8). If the control mode is not set, the duty cycle (PWM _SDR ) of the PWM signal is calculated in step (S9) as a function of the suction throttle _target ^{voltage (U Soll SDR} ), the battery _{voltage (U Batt} ) and the diode forward voltage (U _Diode ). In both cases, this ends the program sequence.

If the query result in step (S2) is negative, the process continues with step (S10). In step (S10), the flag and the control mode are reset to the value 0. The duty cycle (PWM _SDR ) of the PWM signal is calculated as a function of the suction throttle _target ^{voltage (U Soll SDR} ), the battery _{voltage (U Batt} ) and the diode forward voltage (U _Diode ). The program sequence is thus also ended in this case.

Claims (12)

1. A method for operating an internal combustion engine with an engine having a number of cylinders, and with an injection system having a common rail with a number of injectors and the like high-pressure components associated with the cylinders, wherein the method comprises the steps:

   - starting the internal combustion engine,

   - operating the internal combustion engine,

   - switching off the internal combustion engine, wherein

   - a state characterising an engine standstill is recognised,

   - a high-pressure limit value is set and a desired high pressure is specified,

   - a leak in the common rail is generated without injection,

   - by means of the leak the fuel pressure in the common rail is reduced to the set high-pressure limit value below the desired high pressure,

   characterised in that
   upon starting the internal combustion engine the high-pressure closed-loop control for controlling the fuel pressure is activated still during the state characterising the engine standstill, as soon as an average high-pressure gradient reaches or exceeds a defined limit value.
2. A method according to claim 1, characterised in that an individual storage means is associated with an injector, which individual storage means is designed for holding available fuel from the common rail for the injector.
3. A method according to claim 1 or 2, characterised in that the state characterising an engine standstill is recognised once the internal combustion engine has been switched off.
4. A method according to one of claims 1 to 3, characterised in that by activating the high-pressure closed-loop control a suction choke which influences the supply of fuel is actuated in the closing direction, which upon starting the internal combustion engine leads to the fuel pressure remaining below a maximum value.
5. A method according to one of claims 1 to 4, characterised in that the high-pressure gradient is formed from a first and a second fuel pressure value, with the first and the second fuel pressure value succeeding one another at a specified time interval (Δt_Grad ^HD).
6. A method according to one of the preceding claims, characterised in that an average high-pressure gradient is formed from a finite quantity of successive high-pressure gradients by averaging.
7. A method according to one of the preceding claims, characterised in that the engine is recognised as being in operation at an engine speed of 50 - 120 min^-1.
8. A method according to one of the preceding claims, characterised in that the set high-pressure limit value is 560 - 600 bar.
9. A method according to one of the preceding claims, characterised in that the high-pressure gradient for a specified time period (Δt_Mittel ^HD) is determined as the average high-pressure gradient of a number (k) of determined high-pressure gradients, with the number (k) being formed as a quotient from the specified time period (Δt_Mittel ^HD) and a sampling time (Ta).
10. A means for open-loop and/or closed-loop control of an internal combustion engine, with an engine controller and an injection calculation module, which are designed for carrying out a method according to one of claims 1 to 9.
11. An injection system with a common rail for an internal combustion engine with an engine having a number of cylinders and with a number of injectors associated with the cylinders, with an individual storage means is associated with an injector, which individual storage means is designed for holding available fuel from the common rail for injection into the cylinder, and with a means according to claim 10 for open-loop and/or closed-loop control of an internal combustion engine.
12. An internal combustion engine with an engine having a number of cylinders, and with an injection system having a common rail and a number of injectors and the like high-pressure components, and with a means for open-loop and/or closed-loop control according to claim 10, in particular with an injection system according to claim 11.

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