METHOD FOR DETECTING CONTINUOUS INJECTION DURING THE OPERATION OF AN INTERNAL COMBUSTION ENGINE, INJECTION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE AND INTERNAL COMBUSTION ENGINE

Abstract

A method for detecting continuous injection during the operation of an internal combustion engine with an injection system having a high-pressure accumulator for a fuel, wherein —a high pressure in the injection system is monitored as a function of time, wherein —in order to detect continuous injection it is checked whether the high pressure has dropped by a predetermined continuous injection differential pressure value within a predetermined continuous injection time interval, wherein —it is checked whether a reduction valve which connects the high-pressure accumulator to a fuel reservoir has been triggered, and wherein —continuous injection is detected if —a reduction valve has not been triggered in a predetermined checking time interval before the dropping of the high pressure, and if —the high pressure has dropped by the predetermined continuous injection differential value amount within the predetermined continuous injection time interval.

Claims

1-11. (canceled)

12. A method for detecting continuous injection during operation of an internal combustion engine with an injection system having a high-pressure accumulator for a fuel, the method comprising the steps of: monitoring a high pressure in the injection system as a function of time; detecting continuous injection by checking whether the high pressure has dropped by a predetermined continuous injection differential pressure absolute value within a predetermined continuous injection time interval; and checking whether a deactivation valve which connects the high-pressure accumulator to a fuel reservoir has been triggered, wherein continuous injection is detected when no deactivation valve has been triggered in a predetermined checking time interval before the dropping of the high pressure, and when the high pressure has dropped by the predetermined continuous injection differential pressure absolute value within the predetermined continuous injection time interval.

13. The method according to claim 12, including carrying out the continuous injection checking as to whether the high pressure has dropped by the predetermined continuous injection differential pressure absolute value within the predetermined continuous injection time interval only when no deactivation valve has been triggered in the predetermined checking time interval before a starting time of checking of the continuous injection.

14. The method according to claim 13, including starting the continuous injection checking at the starting time when the high pressure undershoots a high pressure setpoint value by a predetermined starting differential pressure absolute value.

15. The method according to claim 13, including determining a starting high pressure at the starting time, wherein the predetermined continuous injection time interval is determined as a function of the starting high pressure.

16. The method according to claim 13, wherein the step of checking whether a deactivation valve has been triggered includes checking whether the high pressure has reached or exceeded a predetermined deactivation pressure absolute value in the checking time interval.

17. The method according to claim 12, including carrying out the continuous injection checking out only when the internal combustion engine has left a predetermined starting phase and/or when the high pressure has reached or exceeded a high-pressure setpoint value for a first time since starting of the internal combustion engine.

18. The method according to claim 17, including carrying out a subsequent continuous injection checking after the continuous injection checking, only when the high pressure has reached or exceeded the high-pressure setpoint value again.

19. The method according to claim 12, wherein continuous injection is detected only when a fuel admission pressure is higher than or equal to a predetermined admission pressure setpoint value.

20. An injection system for an internal combustion engine, comprising: at least one injector; at least one high-pressure accumulator which is fluidically connected to the at least one injector and to a fuel reservoir via a high-pressure pump; a high-pressure sensor arranged and configured to detect a high pressure in the injection system; at least one deactivation valve via which the high-pressure accumulator is fluidically connected to the fuel reservoir; and a control unit operatively connected to the at least one injector, to the high-pressure sensor and to the at least one deactivation valve, wherein the control unit is configured to monitor a high pressure in the injection system as a function of time, wherein the control unit is also configured to check, in order to detect continuous injection, whether the high pressure has dropped by a predetermined continuous injection differential pressure absolute value within a predetermined continuous injection time interval, wherein the control unit is configured to check whether the at least one deactivation valve has been triggered, wherein the control unit is also configured to detect continuous injection when no deactivation valve has been triggered in a predetermined checking time interval before the dropping of the high pressure, and when the high pressure has dropped by the predetermined continuous injection differential pressure absolute value within the predetermined continuous injection time interval, wherein the control unit is configured to execute the method according to claim 12.

21. The injection system according to claim 20, wherein the at least one deactivation valve is selected from a group consists of: a mechanical overpressure valve and an actuatable pressure regulating valve.

22. An internal combustion engine comprising an injection system according to claim 20.

Description

[0040] The invention will be explained in more detail below with reference to the drawing, in which:

[0041] FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine:

[0042] FIG. 2 shows a schematic illustration of a detail of an exemplary embodiment of an injection system;

[0043] FIG. 3 shows a schematic illustration of an embodiment of the method in a diagrammatic illustration;

[0044] FIG. 4 shows a schematic illustration of an embodiment of the method as a flowchart, and

[0045] FIG. 5 shows a schematic illustration of a detail of the embodiment of the method according to FIG. 4.

[0046] FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine 1 which has an injection system 3. The injection system 3 is preferably embodied as a common rail injection system. It has a low-pressure pump 5 for feeding fuel from a fuel reservoir 7, an adjustable, low-pressure-side intake throttle 9 for influencing a fuel volume flow which flows to a high-pressure pump 11, the high-pressure pump 11 for feeding the fuel under an increase in pressure into a high-pressure accumulator 13, the high-pressure accumulator 13 for storing the fuel and preferably a multiplicity of injectors 15 for injecting the fuel into combustion spaces 16 of the internal combustion engine 1. It is optionally possible for the injection system 3 also to be embodied with individual accumulators, wherein then, for example in the injector 15, an individual accumulator 17 is integrated as an additional buffer volume. In the exemplary embodiment illustrated here, a pressure regulating valve 19 which can be actuated, in particular, electrically is provided, via which pressure regulating valve 19 the high-pressure accumulator 13 is fluidically connected to the fuel reservoir 7. By means of the position of the pressure regulating valve 19, a fuel volume flow, which is diverted from the high-pressure accumulator 13 into the fuel reservoir 7, is defined. This fuel volume flow is referred to by VDRV in FIG. 1 and in the following text.

[0047] The injection system 3 which is illustrated here has a mechanical overpressure valve 20 which also connects the high-pressure accumulator 13 to the fuel reservoir 7. The mechanical overpressure valve 20 is triggered, that is to say it opens, if the high pressure in the high-pressure accumulator 13 reaches or exceeds a predetermined overpressure deactivation pressure absolute value. The high-pressure accumulator 13 is then relieved of pressure via the mechanical overpressure valve 20 to the fuel reservoir 7. This serves to increase the safety of the injection system 3 and avoids unacceptably high pressure in the high-pressure accumulator 13.

[0048] The mode of operation of the internal combustion engine 1 is determined by an electronic control unit 21 which is preferably embodied as an engine control unit (ECU) of the internal combustion engine 1. The electronic control unit 21 includes the customary components of a microcomputer system, for example a microprocessor, I/O modules, buffers and memory modules (EEPROM, RAM). The operational data which is relevant for the operation of the internal combustion engine 1 is applied in the memory modules in characteristic diagrams/characteristic curves. By means of the latter, the electronic control unit 21 calculates output variables from input variables. The following input variables are illustrated in FIG. 1 by way of example: a measured, still unfiltered high pressure p which prevails in the high-pressure accumulator 13 and is measured by means of a high-pressure sensor 23, a current engine rotational speed n.sub.I, a signal FP for the predefinition of the power by an operator of the internal combustion engine 1, and an input variable E. Preferably further sensor signals, for example a charge air pressure of an exhaust gas turbocharger, are combined under the input variable E. In the case of an injection system 3 with individual accumulators 17, an individual accumulator pressure p.sub.E is preferably an additional input variable of the control unit 21.

[0049] FIG. 1 illustrates as output variables of the electronic control unit 21, by way of example, a signal PWMSD for actuating the intake throttle 9 as a first pressure actuating element, a signal ve for actuating the injectors 15—which predefines, in particular, a start of injection and/or an end of injection or an injection duration—, a signal PWMDRV for actuating the pressure regulating valve 19 as a second pressure actuating element and an output variable A. The position of the pressure regulating valve 19 and therefore the fuel volume flow VDRV are defined by means of the preferably pulse-width-modulated signal PWMDRV. The output variable A is representative of further actuating signals for the open-loop and/or closed-loop control of the internal combustion engine 1, for example of an actuating signal for activating a second exhaust gas turbocharger in the case of register charging.

[0050] FIG. 2a) shows a schematic illustration of a detail of an exemplary embodiment of an injection system 3. Here, a high-pressure regulating circuit 25, which is configured to regulate the high pressure in the high-pressure accumulator 13 is illustrated schematically in a box which is represented by a dashed line. Outside the high-pressure regulating circuit 25 or the box which is characterized by means of the dashed line a continuous injection detection function 27 is illustrated.

[0051] Firstly, the method of functioning of the high-pressure regulating circuit 25 will be explained in more detail: an input variable of the high-pressure regulating circuit 25 is a setpoint high pressure p.sub.S which is determined by the control unit 21 and is compared with an actual high pressure p.sub.I in order to calculate a regulating error e.sub.p. The setpoint high pressure p.sub.S is preferably read out from a characteristic diagram as a function of a rotational speed n.sub.I of the internal combustion engine 1, of a load request or torque request to the internal combustion engine 1 and/or as a function of further variables which serve, in particular, for correction. Further input variables of the high-pressure regulating circuit 25 are, in particular, the rotational speed n.sub.I of the internal combustion engine 1 and a setpoint injection quantity Q.sub.S. The high-pressure regulating circuit 25 has, as an output variable, in particular the high pressure p which is measured by the high-pressure sensor 23. Said high pressure p is subjected to a first filtering process, which will be explained in more detail below, wherein the actual high pressure p.sub.I arises from this first filtering process as an output variable. The regulating error e.sub.p is an input variable of a high-pressure regulator 29 which is preferably embodied as a PI(DT1) algorithm. A further input variable of the high-pressure regulator 29 is preferably a proportional coefficient kp.sub.SD. The output variable of the high-pressure regulator 29 is a fuel setpoint volume flow V.sub.SD for the intake throttle 9, to which a fuel setpoint consumption V.sub.Q is added in an addition point 31. This fuel setpoint consumption V.sub.Q is calculated in a first calculation element 33 as a function of the rotational speed n.sub.I and the setpoint injection quantity Q.sub.S and constitutes an interference variable of the high-pressure regulating circuit 25. An unlimited fuel setpoint volume flow V.sub.U,SD is obtained as a sum of the output variable V.sub.SD of the high-pressure regulator 29 and the interference variable V.sub.Q. Said fuel setpoint volume flow V.sub.U,SD is limited to a maximum volume flow V.sub.max,SD for the intake throttle 9 as a function of rotational speed n.sub.I in a limiter element 35. A limited fuel setpoint volume flow V.sub.S,SD for the intake throttle 9 which is obtained as an input variable in a pump characteristic curve 37 is obtained as an output variable of the limiter element 35. The limited fuel setpoint volume flow V.sub.S,SD is converted into an intake throttle setpoint flow I.sub.S,SD with said pump characteristic curve 37.

[0052] The intake throttle setpoint flow I.sub.S,SD constitutes an input variable of an intake throttle current regulator 39 which has the function of regulating an intake throttle current through the intake throttle 9. A further input variable of the intake throttle current regulator 39 is an actual intake throttle current I.sub.I,SD. The output variable of the intake throttle current regulator 39 is an intake throttle setpoint voltage U.sub.S,SD, which is finally converted into a switch-on duration of a pulse-width-modulated signal PWMSD for the intake throttle 9 in a second calculator element 41 in a manner known per se. The intake throttle 9 is actuated with said signal PWMSD, wherein the signal therefore acts overall on a regulated system 43 which has, in particular, the intake throttle 9, the high-pressure pump 11 and the high-pressure accumulator 13. The intake throttle current is measured, wherein a raw measured value I.sub.R,SD results which is filtered in a current filter 45. The current filter 45 is preferably embodied as a PT1 filter. The output variable of this current filter 45 is the actual intake throttle current I.sub.I,SD which is in turn fed to the intake throttle current regulator 39.

[0053] The regulated variable of the first high-pressure regulating circuit 25 is the high pressure p in the high-pressure accumulator 13. Raw values of this high pressure p are measured by the high-pressure sensor 23 and filtered by a first high-pressure filter element 47 which has the actual high pressure p.sub.I as the output variable. The first high-pressure filter element 47 is preferably converted by a PT1 algorithm.

[0054] In the text which follows, the method of functioning of the continuous injection detection function 27 will be explained in more detail: the raw values of the high pressure p are filtered by a second high-pressure filter element 49, the output variable of which is a dynamic rail pressure p.sub.dyn. The second high-pressure filter element 49 is preferably converted by a PT1 algorithm. A time constant of the first high-pressure filter element 47 is preferably greater than a time constant of the second high-pressure filter element 49. In particular, the second high-pressure filter element 49 is embodied as a faster filter than the first high-pressure filter element 47. The time constant of the second high-pressure filter element 49 can also be identical to the value zero, with the result that the dynamic rail pressure p.sub.dyn corresponds to the measured raw values of the high pressure p, or is identical thereto. The dynamic rail pressure p.sub.dyn therefore constitutes a highly dynamic value for the high pressure which is, in particular, always appropriate if a fast reaction has to take place to certain events which occur.

[0055] A difference between the setpoint high pressure p.sub.S and the dynamic rail pressure p.sub.dyn results in a dynamic high-pressure regulating error e.sub.dyn. The dynamic high-pressure regulating error e.sub.dyn is an input variable of a functional block 51 for detecting continuous injection. Further, in particular parametrizable, input variables of the functional block 51 are various deactivation pressure absolute values, specifically here a first overpressure deactivation pressure absolute value p.sub.A1, at or above which the mechanical overpressure valve 20 is triggered, a regulating deactivation pressure absolute value p.sub.A2, at or above which the pressure regulating valve 19 which can be actuated is actuated in order to perform high pressure regulation as the sole pressure actuating element, for example if the intake throttle 9 fails, and a second overpressure deactivation pressure absolute value p.sub.A3 at or above which the pressure regulating valve 19 which can be actuated is, preferably completely, actuated, in order to assume a protective function for the injection system 3 and therefore, as it were, to replace or supplement the mechanical overpressure valve 20. Further, in particular parametrizable, input variables are a predetermined starting differential pressure absolute value e.sub.S, a predetermined checking time interval Δt.sub.M, a predetermined continuous injection time interval Δt.sub.L, a predetermined continuous injection differential pressure absolute value Δp.sub.P, a fuel admission pressure p.sub.F, the dynamic rail pressure p.sub.dyn and an alarm resetting signal AR. The output variables of the functional block 51 are an engine stop signal MS and an alarm signal AS.

[0056] FIG. 2b) shows that when the engine stop signal MS assumes the value 1, i.e. is set to said value, it triggers an engine stop, in which case a logic signal SAkt which brings about a stop of the internal combustion engine 1 is also set. The triggering of an engine stop can also have different causes, for example the setting of an external engine stop. In this context, an external stop signal SE is identical to the value 1 and the resulting logic signal SAkt also becomes identical to the value 1, since all the possible stop signals are connected to one another by a logic OR operation 53.

[0057] FIG. 3 shows a schematic illustration of an embodiment of the method in a diagrammatic illustration, in particular in the form of various time diagrams which are illustrated together. In this context, the time diagrams are denoted, from top to bottom, as the first, second etc. The first diagram is therefore, in particular, the top diagram in FIG. 3, which is adjoined in the downward direction by the following, correspondingly numbered diagrams.

[0058] The first diagram represents the time profile, as a function of a time parameter t, of the dynamic rail pressure p.sub.dyn as a continuous curve K1 and the time profile of the setpoint high pressure p.sub.S as a dashed curve K2. Up until a first point in time t.sub.1, both curves K1, K2 are identical. From the first point in time t.sub.1 onward, the dynamic rail pressure p.sub.dyn becomes lower, while the setpoint high pressure p.sub.S remains constant. As a result, a positive dynamic high-pressure regulating error e.sub.dyn is obtained which is identical to a second point in time t.sub.2 with the predetermined starting differential pressure absolute value es. At this point in time a counter Δt.sub.Akt starts. The dynamic rail pressure p.sub.dyn is identical to a starting high pressure p.sub.dyn,S at a second point in time t2. At a third point in time t.sub.3 the dynamic rail pressure p.sub.dyn has dropped by the predetermined continuous injection differential pressure absolute value Δp.sub.P, starting from the starting high pressure p.sub.dyn,S. A typical value for Δp.sub.P is preferably 400 bar. The counter Δt.sub.Akt assumes the following value at the third point in time t.sub.3:

Δt.sub.Akt=Δt.sub.m=t.sub.3−t.sub.2

[0059] Continuous injection is detected if the measured time period Δt.sub.m, that is to say that time period during which the dynamic rail pressure p.sub.dyn drops by the predetermined continuous injection differential pressure absolute value Δp.sub.P, is smaller than or equal to the predetermined continuous injection time interval Δt.sub.L:

Δt.sub.m≦Δt.sub.L

[0060] The predetermined continuous injection time interval Δt.sub.L is preferably calculated from the starting high pressure p.sub.dyn,S by means of a two-dimensional curve, in particular a characteristic curve. The following applies here: the lower the starting high pressure p.sub.dyn,S, the larger the predetermined continuous injection time interval Δt.sub.L. Typical values for the predetermined continuous time interval Δt.sub.L are given in the following table as a function of the starting high pressure p.sub.dyn,S:

TABLE-US-00002 p.sub.dyn, S [bar] Δt.sub.L [ms] 600 150 800 135 1000 120 1200 105 1400 90 1600 75 1800 60 2000 55 2200 40

[0061] In order to rule out the possibility of the dropping of the high pressure being caused by the triggering of a deactivation valve, within the scope of the method it is checked whether the high pressure has reached or exceeded at least one of the predetermined deactivation pressure absolute values, in particular the first overpressure deactivation pressure absolute value p.sub.A1, the regulating deactivation pressure absolute value p.sub.A2 and/or the second overpressure deactivating pressure absolute value p.sub.A3 during the predetermined checking time interval Δt.sub.M.

[0062] If this is the case, that is to say if a deactivation valve has been triggered in the predetermined checking time interval Δt.sub.M, continuous injection is not detected. In this case, no continuous injection checking is particularly preferably carried out, that is to say in particular at any rate in the checking time interval starting from a triggering of a deactivation valve it is not checked whether the high pressure has dropped by the predetermined continuous injection differential pressure absolute value Δp.sub.P within the predetermined continuous injection time interval Δt.sub.L. A preferred value for the checking time interval Δt.sub.M is a value of 2 s.

[0063] If no deactivation valve has been triggered in the predetermined checking time interval and if the high pressure has not dropped by at least the predetermined continuous injection differential pressure absolute value Δp.sub.P at the third point in time t.sub.3 within the predetermined continuous injection time interval Δt.sub.L, it is checked whether the fuel admission pressure p.sub.F is higher than or equal to a predetermined admission pressure setpoint value p.sub.F,L. If this is the case, as illustrated in the second diagram, continuous injection is detected. If this is not the case, it is assumed that the fuel admission pressure could be responsible for the dropping of the high pressure, and continuous injection is not detected.

[0064] A precondition for the execution of the continuous injection checking is also that the internal combustion engine 1 has left a starting phase. This is the case when the internal combustion engine 1 has reached a predetermined idling rotational speed for the first time. A binary engine starting signal M.sub.St which is illustrated in the third diagram then assumes the logic value 0. If a stationary state of the internal combustion engine 1 is detected, this signal is set to the logic value 1.

[0065] A further precondition for the execution of the continuous injection checking is that the dynamic rail pressure p.sub.dyn has reached the setpoint high pressure p.sub.S for the first time.

[0066] If continuous injection is detected at the third point in time t.sub.3, the alarm signal AS is set, which alarm signal AS changes from the logic value 0 to the logic value 1 in the fifth diagram. At the same time, when continuous injection is detected the internal combustion engine 1 must be shut down. Correspondingly, the engine stop signal MS, which indicates that an engine stop is triggered as a result of the detection of continuous injection, must be changed from the logic value 0 to the logic value 1, which is illustrated in the seventh diagram. The same applies to the signal SAkt which brings about a stop of the internal combustion engine 1 and which finally leads to the shutting down of the internal combustion engine 1, which is illustrated, in particular, in the sixth diagram.

[0067] At a fifth point in time t.sub.5, a stationary state of the internal combustion engine 1 is detected, with the result that a stationary signal M.sub.0 which is illustrated in the fourth diagram and which indicates that the internal combustion engine 1 is stationary changes from the logic value 0 to the logic value 1. At the same time, the value of the engine starting signal M.sub.St which is illustrated in the third diagram and which indicates the starting phase of the internal combustion engine 1 changes from the logic value 0 to the logic value 1, since the internal combustion engine 1 is in the starting phase again after the detected stationary state. If the internal combustion engine 1 is detected as being stationary, the two signals SAkt and MS are set again to 0, which is in turn illustrated in the sixth and seventh diagrams.

[0068] At a sixth point in time t.sub.6, an alarm reset key is activated by the operator of the internal combustion engine 1, with the result that the alarm reset signal AR changes, as illustrated in the eighth diagram, from the logic value 0 to the logic value 1. This in turn results in the alarm signal AS, illustrated in the fifth diagram, being reset to the logic value 0.

[0069] If continuous injection is detected or if no continuous injection is detected before the expiry of the predetermined continuous injection time interval Δt.sub.L, renewed continuous injection checking can be carried out after this only if the dynamic rail pressure p.sub.dyn has reached or exceeded the high pressure p.sub.S again:

p.sub.dyn≧p.sub.S.

[0070] FIG. 4 shows a schematic illustration of an embodiment of the method as a flowchart. In a starting step S0 the method starts. In a first step S1 the dynamic high-pressure regulating error e.sub.dyn is calculated as a difference between the setpoint high pressure p.sub.S and the dynamic rail pressure p.sub.dyn. In a second step S2 it is interrogated whether a logic variable, denoted as flag1, is set.

[0071] In this context, the term “flag” denotes here and below a logic or binary variable which can assume two states, in particular 0 and 1. The fact that a flag is set means here and below that the corresponding logic variable has a first of the two states, in particular an active state, for example the value 1. The fact that the flag is not set means here and below that the logic variable has the other second state, in particular an inactive state, for example the value 0.

[0072] In the present embodiment of the method it is monitored by means of the logic variable flag1 whether the internal combustion engine 1 is in its starting phase and whether the high pressure has reached or exceeded the setpoint high pressure p.sub.S for the first time. The flag1 is set here if the internal combustion engine 1 is no longer in the starting phase and if the dynamic rail pressure p.sub.dyn has reached or exceeded the setpoint high pressure p.sub.S for the first time. If one of these conditions is not satisfied, the flag1 is not set.

[0073] If the flag1 is set, the method is continued with a continuous injection detection algorithm, illustrated in more detail in FIG. 5, in a sixth step S6.

[0074] If the flag is not set, the method is continued with a third step S3. In the third step S3 it is interrogated whether the internal combustion engine 1 has left the starting phase. If this is not the case, the method is continued in a seventh step S7. On the other hand, if this is the case, in a fourth step S4 it is checked whether the dynamic rail pressure regulating error e.sub.dyn is less than or equal to 0. If this is not the case, which means that the dynamic rail pressure p.sub.dyn has not yet reached or exceeded the setpoint high pressure p.sub.S, the method is continued in the seventh step S7. If, on the other hand, the dynamic rail pressure error e.sub.dyn is less than or equal to 0, the flag1 is set in a fifth step S5.

[0075] In the seventh step S7 it is interrogated whether the internal combustion engine 1 is stationary. If this is not the case, the method is continued with a tenth step S10. If the internal combustion engine 1 is stationary, the flag1 is set and further logic variables flag2, flag3, flag4 and flag5 are reset.

[0076] As will be explained in more detail below, the flag2 indicates here whether a deactivation valve has been triggered, flag3 indicates whether the deactivation valve has been triggered in the checking time interval, the flag4 indicates that continuous injection has been detected and blocks in this respect subsequent executions of the continuous injection detection, in particular up to the stationary state and restarting of the internal combustion engine 1, and the flag5 finally indicates that the continuous injection checking has been carried out but no continuous injection has been detected, in which case said flag5 blocks in this respect, in particular, renewed execution of the continuous injection checking until the dynamic high pressure p.sub.dyn has reached or exceeded the setpoint high pressure p.sub.S again and/or until the internal combustion engine 1 has left its starting phase again, in the case of intermediate shutting down and restarting of said internal combustion engine 1.

[0077] In a ninth step S9, the logic engine stop signal MS which triggers stopping of the internal combustion engine 1 owing to detected continuous injection, and the logic signal SAkt which brings about stopping of the internal combustion engine are also reset. In a tenth step S10 it is checked whether both the alarm reset signal AR and the logic stationary signal M.sub.0 which indicates a stationary state of the internal combustion engine as well as the alarm signal AS which indicates detected continuous injection are set. If at least one of these logic signals is not set, the method is ended in a twelfth step S12. If, on the other hand, all of these logic signals are set, the alarm signal AS is reset in an eleventh step S11.

[0078] The method is preferably carried out iteratively. This means, in particular, that after the method has ended in the twelfth step S12 it is started again, preferably immediately, in the starting step S0. Of course, there is preferably provision that this iterative execution of the method ends with complete switching off of the control unit 21, which is preferably configured to execute the method. The method then preferably starts again at the starting step S0 after a restart of the control unit 21.

[0079] FIG. 5 shows a schematic illustration of a detail of the embodiment of the method according to FIG. 4. In particular, FIG. 5 shows an illustration of a detail of the sixth step S6 according to the flowchart in FIG. 4, again in the form of a flowchart. In this context, the method steps executed within the step S6 are denoted below as substeps.

[0080] In a first substep S6_1 it is interrogated whether a mechanical overpressure valve 20 is present. This interrogation is not absolutely necessary. Instead, it is also possible for the method sequence to be adapted to the specific configuration of the internal combustion engine 1, wherein it is permanently implemented in the method sequence whether a mechanical overpressure valve 20 is present or not. In this case, the branching which is illustrated in the first substep S6_1 does not need to be provided, but instead can be directly followed by the method step which is suitable for the configuration of the internal combustion engine 1. The embodiment of the method which is described here has, however, the advantage that it can be set independently of the specific configuration of the internal combustion engine 1, with the result that it can be used very flexibly and can also be implemented very quickly in an existing control unit 21 of an internal combustion engine 1 as a retrofitting solution. By means of the interrogation in the first substep S6_1 the method then receives the information about the presence of a mechanical overpressure valve 20 which is necessary for the further progress.

[0081] If a mechanical overpressure valve 20 is present in the internal combustion engine 1, in a second substep S6_2 it is interrogated whether the dynamic rail pressure p.sub.dyn is higher than or equal to the first overpressure deactivation pressure absolute value p.sub.A1. If this is not the case, the method continues with a sixth substep S6_6. If, on the other hand, this is the case, the flag2 is set in a third substep S6_3. A time variable t.sub.Sp is set at the same time to a current system time t. Subsequently, the method continues with the sixth substep S6_6. If a mechanical overpressure valve 20 is not present, branching occurs from the first substep S6_1 to a fourth substep S6_4. In the fourth substep S6_4 it is interrogated whether the dynamic rail pressure p.sub.dyn is higher than or equal to the regulating deactivation pressure absolute value p.sub.A2 or greater than or equal to the second overpressure deactivation pressure absolute value p.sub.A3. If this is not the case, the method is continued with the sixth substep S6_6. If this is the case, the flag2 is set in a fifth substep S6_5. At the same time, the time variable t.sub.Sp is set to the current system time t. Subsequently, the method is continued with the sixth substep S6_6.

[0082] In said substep S6_6 the flag4 is interrogated. If the latter is set, the method is continued with the seventh step S7 according to FIG. 4.

[0083] If the flag4 is not set, the flag3 is interrogated in a seventh substep S6_7. If the flag3 is set, the method is continued with a twelfth substep S6_12, and otherwise in an eighth substep S6_8 it is checked whether the dynamic rail pressure regulating error e.sub.dyn is greater than or equal to the starting differential pressure absolute value e.sub.S. If this is not the case, the method is continued with the seventh step S7 according to FIG. 4. On the other hand, if this is the case, in a ninth substep S6_9 it is checked whether the flag2 is set. If the flag2 is not set, the method is continued with an eleventh substep S6_11. If the flag2 is set, in a tenth substep S6_10 it is checked whether the difference between the current system time t and the value of the time variable t.sub.Sp is less than or equal to the checking time interval Δt.sub.M. If this is the case, the method is continued with the seventh step S7 according to FIG. 4. If this is not the case, in the eleventh substep S6_11 the flag3 is set, and the value of the currently prevailing dynamic rail pressure p.sub.dyn is assigned to the starting high pressure p.sub.dyn,S.

[0084] In the twelfth substep S6_12 the flag5 is interrogated. If the flag5 is set, the method is continued with a seventeenth substep S6_17. If the flag5 is not set, a time difference variable Δt is incremented in a thirteenth substep S6_13. Subsequently, in a fourteenth substep S6_14 the predetermined continuous injection time interval Δt.sub.L is calculated as an output value of a two-dimensional curve. The input value of this curve is the starting high pressure p.sub.dyn,S.

[0085] In a fifteenth substep S6_15 it is interrogated whether the time difference variable Δt is greater than the continuous injection time interval Δt.sub.L. If this is not the case, the method is continued with a nineteenth substep S6_19. If this is the case, in the sixteenth substep S6_16 the time difference variable Δt is set to the value 0 and the flag5 is set. Subsequently, in the seventeenth substep S6_17 is it interrogated whether the dynamic rail pressure regulating error e.sub.dyn is less than or equal to zero. If this is not the case, the method is continued with the seventh step S7 according to FIG. 4. On the other hand, if this is the case, flag3 and flag5 are respectively reset in an eighteenth substep S6_18. Subsequently, the method is continued with the seventeenth step S7 according to FIG. 4.

[0086] In the nineteenth substep S6_19, a differential pressure absolute value Δp is calculated as a difference between the starting high pressure p.sub.dyn,S and the dynamic rail pressure p.sub.dyn.

[0087] Subsequently, in a twentieth substep S6_20 it is checked whether the pressure difference absolute value Δp is greater than or equal to the predetermined continuous injection differential pressure absolute value Δp.sub.P. If this is not the case, the method is continued with the seventh step S7 according to FIG. 4. On the other hand, if this is the case, in a twenty-first substep S6_21 it is checked whether the fuel admission pressure p.sub.F is lower than the limiting value p.sub.F,L. If this is the case, in a twenty-third step S6_23 the time difference variable Δt is set to the value 0 and the flag5 is set. Subsequently, the method is continued with the seventh step S7 according to FIG. 4. If the fuel admission pressure p.sub.F is not lower than the predetermined admission pressure setpoint value p.sub.F,L, in a twenty-second substep S6_22 the time difference variable Δt is set to the value 0 and the flag3 is reset. The flag4 and the alarm signal AS, the engine stop signal MS and the logic signal SAkt which brings about an engine stop are set simultaneously. Subsequently, the method is also continued with the seventh step S7 according to FIG. 4.

[0088] Overall it becomes apparent that by using the method, injection system 3 and internal combustion engine 1 proposed here it is possible to detect continuous injection easily, cost effectively and very reliably, wherein it is particularly preferably possible to dispense with a quantity-limiting valve with the result that, in particular, it becomes possible to use cost-effective injectors for the injection system 3 and the internal combustion engine 1.