METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE WITH AN INJECTION SYSTEM AND INJECTION SYSTEM FOR CARRYING OUT SUCH A METHOD

Description

[0001] The invention relates to a method for operating an internal combustion engine with an injection system and to an injection system for an internal combustion engine which is designed to carry out such a method.

[0002] German patent DE 10 2014 213 648 B3 discloses a method for operating an internal combustion engine with an injection system, in which a high pressure in a high-pressure accumulator is controlled via a low-pressure-side intake throttle as the first pressure actuator in a first high-pressure control circuit. During normal operation, a high-pressure disturbance variable is generated via a high-pressure-side pressure control valve as the second pressure actuator, via which fuel is diverted from the high-pressure accumulator into a fuel reservoir. Provision is made for the high pressure to be controlled in a protective mode by means of the pressure control valve via a second high-pressure control circuit, or for the pressure control valve to be permanently open in the protective mode.In particular, it is provided that a first protective mode is activated when the high pressure reaches or exceeds a first pressure limit, with the pressure control valve taking over control of the high pressure in the first mode. A second protective mode is activated when the high pressure exceeds a second pressure limit or when a defect in a high-pressure sensor is detected, with the pressure control valve being permanently open in the second mode. In this way, an impermissible increase in the high pressure can be prevented.

[0003] DE 10 2011 100187 B3 describes a method for operating an internal combustion engine with an injection system having a high-pressure accumulator, according to the preamble of claim 1.

[0004] However, if the high pressure nevertheless exceeds a certain threshold, components of the injection system's injectors, in particular, are subjected to such severe stress that damage is the result or at least imminent. Previously developed methods for regulating and monitoring high pressure in a high-pressure accumulator do not include measures suitable for dealing with such situations and effectively protecting the injection system's injectors.

[0005] The invention is based on the object of providing a method for operating an internal combustion engine with an injection system and an injection system which is designed to carry out such a method, wherein the aforementioned disadvantages are avoided.

[0006] The problem is solved by creating the subject matter of the independent claims. Advantageous embodiments emerge from the subclaims.

[0007] The object is achieved by a method according to claim 1, which is used to operate a

[0008] An internal combustion engine with an injection system for injecting fuel into at least one combustion chamber of the internal combustion engine is provided, wherein the injection system has a high-pressure accumulator, and wherein a current high pressure in the high-pressure accumulator is monitored over time by means of a high-pressure sensor. Provision is made for a first alarm level to be set when a first, predetermined high pressure limit value is continuously exceeded by the current high pressure for a predetermined limit period. Alternatively, the first alarm level is set when the first predetermined high pressure limit value is exceeded by the current high pressure for the first time with a predetermined, first limit frequency.In this way, it is possible not only to generally monitor an increase in high pressure and an exceedance of the high pressure limit, but also to determine how long the current high pressure continuously exceeds the high pressure limit and / or how frequently the current high pressure exceeds the predetermined high pressure limit. These are relevant parameters with regard to the functionality of the injection system's injectors, as they can be damaged, particularly by excessively long and frequent exposure to excessively high pressure.The predetermined limit time period and / or the predetermined first limit frequency are selected in particular such that if they are reached or exceeded, damage to the injectors of the injection system is to be feared, so that measures should be taken to protect them, but preferably also to replace them or at least to subject them to maintenance.

[0009] Particularly preferably, the first alarm level is triggered both when the current high pressure has continuously exceeded the first high pressure limit for the first time for the predetermined limit period, and when the current high pressure has continuously exceeded the first high pressure limit with the first predetermined limit frequency for the first time. In this way, both relevant aspects for protecting the injectors and ensuring the safe operation of the internal combustion engine can be taken into account.

[0010] The injection system is configured to inject fuel into at least one combustion chamber of the internal combustion engine. The high-pressure accumulator is preferably designed as a common high-pressure accumulator for a plurality of fuel injectors, wherein the fuel injectors are fluidly connected to the high-pressure accumulator and configured to inject fuel directly into the combustion chambers of the internal combustion engine. Such an injection system is also referred to as a common rail system.

[0011] The fact that the first alarm level is set means in particular that a corresponding variable, a flag, or the like, which represents the first alarm level, is set internally in a control unit configured to control the injection system, preferably to control the internal combustion engine. Preferably, the first alarm level is additionally communicated externally, in particular to an operator of the internal combustion engine, in particular by a suitable output, be it a message in the form of a text output, the illumination of a signal light provided for this purpose, an acoustic signal, a vibration signal, or another suitable means to signal to an operator of the internal combustion engine that the first alarm level has been set. The first alarm level means in particular that there is a high risk to the injectors of the injection system and / or that damage to the injectors may at least already have occurred.The first alarm level corresponds in particular to a red alarm, in which further operation of the internal combustion engine and in particular of the injection system is no longer possible or at most only possible to a limited extent.

[0012] The check to determine whether the current high pressure has exceeded the first high pressure threshold for the first time with the predetermined first threshold frequency is preferably carried out independently of the duration of the respective exceedances. Thus, it only records whether the current high pressure exceeds the first high pressure threshold at all, and in particular, regardless of the duration for which this occurs.

[0013] According to a further development of the invention, the detection of a period of time during which the first high-pressure limit is exceeded by the current high pressure is restarted when the current high pressure reaches or exceeds the first high-pressure limit from below the first high-pressure limit. "From below" means that the current high pressure, coming from lower high pressure values, reaches the first high-pressure limit or exceeds it towards higher high pressure values. The detected period of time is then compared with the predetermined limit period. As soon as the detected period of time reaches or exceeds the predetermined limit period, the first alarm level is preferably set. This preferably occurs in real time, i.e., the current high pressure is permanently and continuously monitored, and the length of time it remains above the first high-pressure limit or remains at the first high-pressure limit is detected.The fact that the recording of this time period is started means in particular that the recording is reinitialized, with the recording of the time period starting at 0 seconds.

[0014] It is provided that a frequency value, which indicates a current frequency of the first high-pressure limit being exceeded by the current high pressure, is incremented when the current high pressure reaches or exceeds the first high-pressure limit from below a second high-pressure limit, wherein the second high-pressure limit is lower than the first high-pressure limit. Thus, when detecting the frequency of the first high-pressure limit being exceeded, a hysteresis is taken into account, wherein the second high-pressure limit is lower than the first high-pressure limit, in particular by a hysteresis differential pressure value.Accordingly, if the instantaneous high pressure exceeds the first high pressure limit, for example after starting or commissioning the internal combustion engine – then inevitably also coming from below the second high pressure limit – the frequency value is incremented – in particular from 0 – and in particular increased by 1. If the instantaneous high pressure then falls below the first high pressure limit, but does not fall below the second high pressure limit, and subsequently exceeds the first high pressure limit again – but only coming from above the second high pressure limit – the frequency value is not incremented again. Only when the instantaneous high pressure has fallen below the second high pressure limit again and then again exceeds the first high pressure limit from below is the frequency value incremented again.The current high pressure must therefore have fallen from above the first high pressure limit to below the second high pressure limit for the frequency value to be incremented thereafter. This allows for a suitable separation of independent events relevant to potential damage to the injectors, with pressure fluctuations around the first high pressure limit, which do not fall below the second high pressure limit, being regarded as a connected event. This can be interpreted in particular to ensure that such fluctuations do not impart a new pressure surge to the injector. Possible damage to the injectors due to permanently excessive pressure is detected by recording the duration during which the first high pressure limit is exceeded by the current high pressure and comparing this duration with the predetermined limit period.

[0015] The frequency value is compared with the predetermined first threshold frequency. This is also preferably done in real time, particularly continuously and permanently, with the first alarm level being set when the frequency value reaches or exceeds the predetermined first threshold frequency for the first time.

[0016] According to a further development of the invention, the recorded time period is reset, i.e., set to zero, when the current high pressure falls below the first high pressure limit from above the first high pressure limit – i.e., from high pressure values ​​that are greater than the first high pressure limit. The time period is therefore not recorded cumulatively; rather, the measurement is reinitialized and started each time the current high pressure exceeds the first high pressure limit again. Thus, when recording the time period, only individual events are recorded separately. In contrast, the frequency of exceeding the first high pressure limit is recorded using the frequency value.

[0017] Overall, complementary and at least partially complementary measures are available to detect events that damage the injectors of the injection system and to trigger suitable measures to protect the injectors.

[0018] According to a further development of the invention, a second alarm level is set when the first high-pressure limit value is exceeded by the current high pressure for the first time with a predetermined, second limit frequency, wherein the second limit frequency is lower than the first limit frequency. The fact that the second alarm level is set means - as already explained with regard to the first alarm level - in particular that an internal variable, a flag or the like is set. Preferably, however, the second alarm level is also communicated externally, in particular to an operator of the internal combustion engine, as already explained with regard to the first alarm level. In this respect, reference is made to the explanations regarding the first alarm level.The second alarm level preferably indicates that damage to the injectors is possible or even likely if the internal combustion engine is continued to operate, so that the operator of the internal combustion engine should pay increased attention to their operation. If necessary, suitable measures can be initiated at this point in time to prevent or reduce further stress on the injectors, for example suitable maintenance and / or repair measures. The second alarm level corresponds in particular to a yellow alarm. The fact that the second alarm level is set at the second limit frequency, which is lower than the first limit frequency, ensures that the second alarm level, i.e. the yellow alarm, is set earlier than the first alarm level, i.e. the red alarm.Thus, the operator of the internal combustion engine is initially informed by means of the second alarm level that an unacceptably high load may be placed on the injectors, which could cause damage to them. The operator is later alerted by the red alarm when damage has actually already occurred or appears to be almost unavoidable.

[0019] The frequency value is preferably compared with the second threshold frequency. In particular, the frequency value is preferably compared with the first threshold frequency and with the second threshold frequency. This is also preferably done in real time and, in particular, permanently and continuously.

[0020] According to a development of the invention, provision is made for an injection of fuel from the high-pressure accumulator into at least one combustion chamber of the internal combustion engine to be terminated when the first alarm level is set. In particular, the injection of fuel is terminated immediately when the first alarm level is set, in particular at the same time as the first alarm level is set. Thus, as soon as the first alarm level is set, a measure is initiated to protect the injectors - if they are not already damaged - from damage or at least from further, greater damage. Preferably, the injection for all combustion chambers of the internal combustion engine, i.e. for all injectors of the injection system, is terminated when the first alarm level is set. Further operation of the internal combustion engine is then not possible, at least initially.

[0021] Preferably, however, injection is continued when the first alarm level is set, in particular, it is resumed when the current high pressure falls below a third high pressure limit from above the third high pressure limit, where the third high pressure limit is lower than the first high pressure limit. This enables emergency operation of the internal combustion engine, so that it can continue to operate at least when there is currently no risk of further damage to the injectors. Thus, in a vehicle, especially a ship, a so-called "limp home" function or emergency operation function can be provided, which makes it possible to reach a safe station, for example, the nearest port or the like.The third high-pressure limit provides a hysteresis that ensures that the injection does not start and stop at high frequency and / or continuously, while at the same time ensuring that the current high pressure must have fallen sufficiently below the first high-pressure limit in order to be able to operate the internal combustion engine without the risk of further damage to the injectors.

[0022] Preferably, the third high-pressure limit value is identical to the previously explained second high-pressure limit value. In particular, it is preferably smaller than the first high-pressure limit value by the hysteresis differential pressure value.

[0023] The injection, which continues when the first alarm level is set, is terminated as soon as the current high pressure reaches or exceeds the first high pressure limit – from below. Thus, once the first alarm level is set, neither the time for which the first high pressure limit was exceeded nor the frequency of this exceedance is taken into account when monitoring the current high pressure. Instead, injection is always terminated immediately when the current high pressure reaches or exceeds the first high pressure limit from below it. This protects the internal combustion engine's injectors and ensures that the internal combustion engine can continue to operate, at least for a certain period of time, within the scope of the "limp home" function, without the injectors failing completely or being destroyed.

[0024] According to a further development of the invention, it is provided that the first alarm level and / or the second alarm level is / are canceled if a standstill of the internal combustion engine is detected and - at the same time - an alarm reset request is set. In order to reset at least one of the alarm levels, in particular to reset the first alarm level, the internal combustion engine must be shut down and an alarm reset request must also be made. In this way, it can be avoided that the first alarm level is reset in an inadmissible manner during ongoing operation of the internal combustion engine and without further measures, which could ultimately lead to permanent damage or destruction of the injectors and thus the complete impossibility of further operation of the internal combustion engine.The alarm reset request can be set manually by an operator, for example by pressing a corresponding button, selecting a corresponding menu item in an operating menu of the internal combustion engine, or the like. The operator preferably only sets the alarm reset request manually when they are convinced that further operation of the internal combustion engine is possible safely and without damage to the injectors, for example because the injectors have been replaced or because they have been inspected sufficiently thoroughly, or because other maintenance and / or repair measures have been taken that can ensure safe operation of the internal combustion engine. However, it is also possible for the alarm reset request to be set automatically, in particular after a repair and / or replacement of the injectors.For example, the alarm reset request can be automatically triggered when it is detected that the old injectors have been replaced with new ones. This can be reported to the control unit, for example, using suitable electronic identification means on the injectors, in particular RFID tags or the like, whereupon the control unit can then automatically trigger the alarm reset request.

[0025] According to a further development of the invention, the predetermined limit time period is from at least 2 seconds to at most 3 seconds, preferably 2.5 seconds. It has been found that this corresponds to a period of time during which injectors can be damaged by excessively high pressure.

[0026] The first high pressure limit value can preferably be selected to 2400 bar.

[0027] The first limit frequency is preferably chosen from at least 45 to at most 55, preferably 50 or 51.

[0028] Alternatively or additionally, the second threshold frequency is preferably chosen from at least 25 to at most 35. Preferably, it is 30 or 31.

[0029] The frequencies specified here for the first limit frequency and the second limit frequency are suitable frequencies to, on the one hand - in the case of the second limit frequency - warn an operator of the internal combustion engine in advance, and on the other hand - in the case of the first limit frequency - indicate possible damage that has already occurred or imminent damage to the injectors.

[0030] According to a further development of the invention, the injection or the continued injection is terminated by setting a target injection quantity to zero. The control of the injectors, in particular their current supply, takes place in particular depending on a target injection quantity. If this is set to zero, the injectors are no longer controlled or supplied with current, so that the injection is terminated.

[0031] Alternatively or additionally, it is possible for the injection or the continued injection to be terminated by setting the energization duration for at least one injector, preferably for all injectors, to zero. This corresponds to a subsequent inhibition of the injection, whereby the target injection quantity may be different from zero, but the activation, in particular the energization of the injectors, is nevertheless prevented by setting the activation duration provided for this purpose, namely the energization duration, to zero. This also results in the injectors no longer being activated, thus ending the injection.

[0032] The object is also achieved by providing an injection system for an internal combustion engine, which has at least one injector for injecting fuel into at least one combustion chamber of the internal combustion engine, and a high-pressure accumulator that is in fluid communication with the at least one injector. Furthermore, the injection system has a high-pressure sensor that is configured and arranged for the time-dependent detection of a momentary high pressure in the high-pressure accumulator. The injection system has a control unit that is operatively connected to the high-pressure sensor and configured to carry out a method according to one of the previously described embodiments. In connection with the injection system, the advantages that have already been explained in connection with the method are particularly advantageous.

[0033] The control unit is preferably operatively connected to the at least one injector for controlling it. It is therefore particularly capable of terminating the injection, resuming it, and terminating the continued injection.

[0034] It is possible that the control unit is a control unit configured and designed separately for the operation of the injection system. However, the control unit is preferably a central engine control unit of the internal combustion engine, in particular a so-called engine control unit (ECU).

[0035] Finally, the invention also relates to an internal combustion engine having an injection system according to one of the previously described embodiments. In connection with the internal combustion engine, the advantages already explained in connection with the method and the injection system are particularly evident.

[0036] The internal combustion engine preferably has a plurality of combustion chambers, with each combustion chamber preferably being assigned at least one injector for directly injecting fuel into the at least one combustion chamber. These injectors are fluidly connected to the high-pressure accumulator, with the high-pressure accumulator being designed as a common high-pressure accumulator for all injectors. The internal combustion engine is preferably designed as a reciprocating piston engine. However, the method and the injection system proposed here are also applicable to other types of internal combustion engines, for example, rotary piston engines.

[0037] The invention is explained in more detail below with reference to the drawings, which show: Figure 1 shows a schematic representation of an embodiment of an internal combustion engine with an embodiment of an injection system; Figure 2 shows a schematic representation of a high-pressure control circuit for regulating a high pressure in a high-pressure accumulator of the injection system; Figure 3 shows a schematic representation of a speed control circuit with a possibility of selectively carrying out or preventing an injection; Figure 4 shows a diagrammatic representation of a first embodiment of a method for operating an injection system; Figure 5 shows a schematic, diagrammatic representation of a second embodiment of such a method, and Figure 6 shows a schematic representation of a further embodiment of the method in the form of a flow chart.

[0038] Fig. 1shows a schematic representation of an embodiment of an internal combustion engine 1 having 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 conveying fuel from a fuel reservoir 7, an adjustable, low-pressure-side intake throttle 9 for influencing a fuel volume flow flowing through it, a high-pressure pump 11 for conveying the fuel under increased pressure into a high-pressure accumulator 13, the high-pressure accumulator 13 for storing the fuel, and a plurality of injectors 15 for injecting the fuel into combustion chambers 16 of the internal combustion engine 1. Optionally, it is also possible for the injection system 3 to be designed with individual accumulators, in which case, for example, an individual accumulator 17 is integrated into the injector 15 as an additional buffer volume.A pressure control valve 19, in particular an electrically controllable one, is provided, via which the high-pressure accumulator 13 is fluidly connected to the fuel reservoir 7. The position of the pressure control valve 19 defines a fuel volume flow, which is diverted from the high-pressure accumulator 13 into the fuel reservoir 7. This fuel volume flow is measured in . Figure 1 designated VDRV and represents a high-pressure disturbance variable of the injection system 3.

[0039] The injection system 3 preferably does not have a mechanical pressure relief valve, which is conventionally provided and connects the high-pressure accumulator 13 to the fuel reservoir 7. Its function can be taken over by the pressure control valve 19.

[0040] The 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 contains the usual components of a microcomputer system, for example, a microprocessor, I / O modules, buffers, and memory modules (EEPROM, RAM). The memory modules contain the operating data relevant to the operation of the internal combustion engine 1 in characteristic maps / curves. Using these, the electronic control unit 21 calculates output variables from input variables. Figure 1The 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 a high-pressure sensor 23, a current engine speed n I , a signal FP for the power specification by an operator of the internal combustion engine 1, and an input variable E. Further sensor signals, for example, a charge air pressure of an exhaust gas turbocharger, are preferably summarized under the input variable E. In an injection system 3 with individual accumulators 17, an individual accumulator pressure p E is preferably an additional input variable of the control unit 21.

[0041] In Figure 1The output variables of the electronic control unit 21 are, for example, a signal PWMSD for controlling the intake throttle 9 as the first pressure actuator, a signal ve for controlling the injectors 15 - which in particular specifies a start and / or end of injection or also an injection duration -, a signal PWMDRV for controlling the pressure control valve 19 as the second pressure actuator, and an output variable A. The position of the pressure control valve 19 and thus the high-pressure disturbance variable VDRV are defined via the preferably pulse-width modulated signal PWMDRV. The output variable A represents further control signals for controlling and / or regulating the internal combustion engine 1, for example a control signal for activating a second exhaust gas turbocharger during register charging.

[0042] Fig. 2shows a schematic representation of a high-pressure control circuit 25. Input variables of the high-pressure control circuit 25 are a target high pressure p S for the injection system 3, which is preferably predetermined by the control unit 21 as a function of the operating point, in particular read out from a characteristic map, and which is compared with an actual high pressure p I to calculate a control deviation ep. This control deviation ep is an input variable of a high-pressure controller 27, which is preferably designed as a PI(DT 1 ) algorithm. A further input variable of the high-pressure controller 27 is preferably a proportional coefficient kp SD . The output variable of the high-pressure controller 27 is a fuel volume flow V SD for the intake throttle 9, to which a target fuel consumption VQ is added in a summation point 29.This target fuel consumption VQ is calculated in a first calculation element 31 as a function of the current speed n I and a target injection quantity QS and represents a disturbance variable of the high-pressure control circuit 25. The sum of the output variable V SD of the high-pressure controller 27 and the disturbance variable VQ results in an unlimited target fuel volume flow VU,SD . This is limited in a limiting element 33 as a function of the speed n I to a maximum volume flow V max,SD for the suction throttle 9. The output of the limiting element 33 results in a limited target fuel volume flow VS,SD for the suction throttle 9, which is used as an input variable in a pump characteristic curve 35. This converts the limited target fuel volume flow VS,SD into a suction throttle target flow IS,SD.

[0043] The suction throttle target current IS,SD represents an input variable of a suction throttle current controller 37, which has the task of regulating the suction throttle current through the suction throttle 9. Another input variable of the suction throttle current controller 37 is, among other things, an actual suction throttle current II,SD . The output variable of the suction throttle current controller 37 is a suction throttle target voltage US,SD , which is finally converted in a second calculation element 39 in a manner known per se into a duty cycle of a pulse-width modulated signal PWMSD for the suction throttle 9. This signal controls the suction throttle 9, with the signal thus acting as a whole on a controlled system 41, which in particular has the suction throttle 9, the high-pressure pump 11, and the high-pressure accumulator 13. The suction throttle current is measured, resulting in a raw measured value IR,SD , which is filtered in a current filter 43. The current filter 43 is preferably designed as a PT 1 filter.The output variable of this current filter 43 is the actual suction throttle current II,SD , which in turn is fed to the suction throttle current controller 37.

[0044] The controlled variable of the first high-pressure control loop 25 is the high pressure 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 high-pressure filter 45, which has the actual high pressure p I as its output variable. The high-pressure filter 45 is preferably implemented by a PT 1 algorithm.

[0045] The output variable of the high pressure control circuit 25 is therefore, in addition to the unfiltered high pressure p, the filtered high pressure or actual high pressure p I , which is also referred to as the instantaneous high pressure.

[0046] Fig. 3shows a speed control loop 47 which is used for speed control. The current engine speed n I is subtracted from a target speed n S specified by the control unit 21, which results in a speed control deviation e. This speed control deviation e is an input variable of a speed controller 49, in this case a PI(DT 1 ) controller. The speed controller 49 has, among other things, a proportional control coefficient kp Drz as a further input variable and a speed controller torque MS PI(DT1)< as an output variable. This is added to a load signal torque MSL<, whereby the load signal torque MSL< represents a disturbance variable. By means of this disturbance variable feedforward, a system signal can be used to improve the dynamics of the speed control loop 47.The sum of the speed controller torque MS PI(DT1)< and the load signal torque MSL< is then limited in a torque limiter 51 to a minimum target torque MS Min< and an upper limit to a maximum target torque MS Max<. Finally, a friction torque MSR< is added to the target torque MS limited in this way, resulting in a corrected target torque M korr. This, along with other variables such as the current engine speed n I, is an input variable of an engine control unit 53. An output variable of the engine control unit 53 is the target injection quantity QS . This is injected into the combustion chambers 16 of the internal combustion engine 1. Raw values ​​nr of the engine speed are recorded and converted into the current actual speed n I with the aid of a speed filter 55.

[0047] The target injection quantity QS is taken from the high-pressure accumulator 13 and injected into the combustion chambers 16 by means of the injectors 15. If the high pressure in the high-pressure accumulator 13 rises above a certain threshold for too long a period of time, or if the high pressure in the high-pressure accumulator 13 exceeds the predetermined threshold too often, damage to the injectors 15 may occur.

[0048] According to the method proposed here, it is therefore provided that the high pressure in the high-pressure accumulator 13 is monitored over time by means of the high-pressure sensor 23, wherein a first alarm level is set when a first predetermined high-pressure limit value is continuously exceeded by the current high pressure for a predetermined limit period of time, and / or when the first predetermined high-pressure limit value is exceeded by the current high pressure for the first time with a predetermined, first limit frequency. In this way, an operator of the internal combustion engine 1 can be warned if damage to the injectors 15 is imminent or has already occurred, and preferably, further operation of the internal combustion engine 1 can be prevented at least temporarily in order to prevent further damage or even complete destruction of the injectors 15.

[0049] When the first alarm level is set, the injection of fuel from the high-pressure accumulator 13 into the combustion chambers 16 is preferably terminated. However, when the first alarm level is set, injection is preferably continued when the current high pressure falls below a third high pressure limit from above the third high pressure limit, wherein the third high pressure limit is lower than the first high pressure limit. The injection continued in this way - during the set first alarm level - is in turn terminated as soon as the current high pressure reaches or exceeds the first high pressure limit - from below. In this way, on the one hand, the injectors 15 can be protected, and on the other hand, the internal combustion engine 1 can continue to operate at least to a limited extent, for example in order to be able to call at a safe station, in particular a seaport or the like.An emergency running function or "limp home" function is provided.

[0050] The injection or the continued injection is preferably terminated by setting the target injection quantity QS to zero.

[0051] However, alternatively or additionally, another procedure is possible to end the injection or the continued injection, whereby this possibility is Figure 3is shown: According to this option, a current supply duration BD for the injectors 15 is set to zero. For this purpose, a switching element 57 is preferably provided in the speed control circuit 47, which can change its switching state in a binary manner depending on a logical signal SIG. The logical signal SIG can assume the values ​​"true" (true - T) or "false" (false - F). The logical signal SIG indicates whether a quantity limitation for the injection of fuel into the combustion chambers 16 via the injectors 15 is active. The logical signal SIG is set to the value "true" if the first alarm level is set and the injection is to be terminated, and if the continued injection is to be terminated. Otherwise - and especially if the injection is to be continued with the first alarm level set - the value of the logical signal SIG is set to "false".

[0052] If the logical signal SIG has the value "false", the switching element 57 is in the Figure 3 functional state designated F. In this case, the current duration BD is taken from the engine control unit 53 as an output variable, being specified by the engine control unit 53, in particular calculated, particularly preferably read from a characteristic map. If, however, the logical signal SIG has the value "true" and, in this respect, a quantity limitation for the fuel injection is active, the switching element 57 takes its Figure 3 switching position designated T, so that the current supply duration BD is set to zero. In this switching state of the switching element 57, the injectors 15 are no longer supplied with current, so that injection is stopped.

[0053] It is possible for switching element 57 to be implemented as a software switch, i.e., a purely virtual switch. Alternatively, it is also possible for switching element 57 to be implemented as a physical switch, for example, a relay. The logical signal SIG can, of course, assume the numerical values ​​0 and 1, or other suitable corresponding values, in a completely analogous manner to the values ​​"true" and "false."

[0054] Fig. 4shows a diagrammatic representation of a first embodiment of the method for operating the injection system 3. A total of seven time diagrams are shown in which various variables are specified as a function of time t. The first, upper time diagram at a) shows the actual high pressure p I as a solid curve plotted against time t. This initially increases, starting from a starting value p Start. At a first time t 0 , the actual high pressure p I reaches the first predetermined high pressure limit value p L1 and subsequently exceeds it. In the third diagram from the top at c), a current time period Δt A is plotted against time t as a solid curve, which indicates how long the actual high pressure p I continuously exceeds the first predetermined high pressure limit value p L1. At the first time t 0 , this current time period Δt A is incremented, starting from the value zero.At a second time t 1 , the actual high pressure p I again reaches the first high pressure limit value p L1 from above and subsequently falls below it. Therefore, the current time period Δt A is reset to zero. Between the first time t 0 and the second time t 1 , it has not yet reached or exceeded a predetermined limit time period Δt L .

[0055] At a third time t 2 , the actual high pressure p I falls below a second predetermined high pressure limit value p L2 , which is lower than the first high pressure limit value p L1 by a hysteresis differential pressure value Δp H. After the third time t 2 , the actual high pressure p I initially continues to fall and then rises again. At a fourth time t 3 , the actual high pressure p I again reaches the first high pressure limit value p L1 and subsequently exceeds it. This causes the current time period Δt A to be incremented again, again starting from zero. At a fifth time t 4 , the actual high pressure p I again reaches the first high pressure p L1 from the top, so that the current time period Δt A , which has not yet reached the limit time period Δt L, is reset to the value zero. The actual high pressure p I subsequently falls further without falling below the second high pressure limit value p L2.A subsequent increase in the actual high pressure p I leads to the first high pressure limit value p L1 being exceeded again from below at a sixth point in time t 5. This in turn leads to the current time period Δt A being incremented again, in particular again starting from zero. At a seventh point in time t 6 the current time period Δt A exceeds the predetermined limit time period Δt L , which leads to the quantity limitation for the injection being activated and the logic signal SIG changing its value, being set here to the value "true" designated T, which is shown in the fourth diagram from the top at d). This has - as in connection with . Figure 3 explained - results in no more fuel being injected into the combustion chambers 16. The current time period Δt A is reset to zero at the seventh time t 6 .

[0056] From the sixth diagram from the top at f) it is clear that at the same time as the limit time period Δt L is reached and the value of the logical signal SIG changes from the value F to the value T, the first alarm level A1 is also set, which is represented here by a jump of a signal indicating the first alarm level A1 from the value 0 to the value 1.

[0057] At an eighth time point t7, the actual high pressure pI again falls below the first high pressure limit pL1 from above, and at a ninth time point t8, it finally falls below the second high pressure limit pL2 from above. This causes the logic signal SIG to change its value again and be reset to "false," i.e., to the value F. Injection is thus enabled again.

[0058] Until a tenth time t 9 , the actual high pressure remains below the first high-pressure limit p L1 . At the tenth time t 9 , it again exceeds the first high-pressure limit p L1 from below, which then immediately—due to the set first alarm level—leads to the logic signal SIG being set again to the value T, thus terminating the injection of fuel into the combustion chambers 16.

[0059] Up to a 14th time t 13 , the actual high pressure remains above the second high pressure limit p L2 , so that all variables and / or signals remain unchanged. At the 14th time t 13 , the actual high pressure p I again falls below the second high pressure limit p L2 from above, whereby the logic signal SIG is reset to the value F. The injection is thus enabled again. At the same time, at the 14th time t 13 , the internal combustion engine 1 is switched off, so that as a result the current engine speed n I plotted in the second diagram from the top at b) drops from a speed value n start to zero.

[0060] At a 15th time t 14 , the standstill of the internal combustion engine 1 is detected, whereby a logical variable MS, which indicates a standstill of the internal combustion engine, assumes the value 1. This is shown in the fifth diagram from the top at e).

[0061] At a 16th time t 15 , the actual high pressure p I again exceeds the first high pressure limit value p L1 . This causes the logic signal SIG to be set back to the value T. The injection is therefore deactivated again, i.e. no more fuel is injected into the combustion chambers 16. At a 17th time t 16 , the actual high pressure p I again falls below the first high pressure limit value p L1 . At an 18th time t 17 , it finally reaches the second high pressure limit value p L2 and subsequently falls below it. The logic signal SIG is therefore reset to the value F at the 18th time t 17 , which means that the injection is enabled again.

[0062] At a 19th time t 18 , an alarm reset request AR is set, which is indicated in the seventh diagram at g) by a corresponding variable assuming the value 1. Since the internal combustion engine 1 is at a standstill at this 19th time t 18 , the applied first alarm level A1 is reset, i.e., the corresponding variable is set to the value zero.

[0063] The injection of fuel into the combustion chambers 16 is stopped when the actual high pressure continuously exceeds the first high pressure limit value p L1 during the predetermined limit time period Δt L.

[0064] Further shows Figure 4that the recording of the time period Δt A is always started, in particular reinitialized and started at zero, when the actual high pressure p I reaches or exceeds the first high pressure limit value p L1 from below it. The recorded time period Δt A is also compared with the predetermined limit time period Δt L. Furthermore, it is clear that the recorded time period Δt A is set to zero when the instantaneous high pressure p I falls below the first high pressure limit value p L1 from above it. It is also clear that the first alarm level A1 is canceled if a standstill of the internal combustion engine 1 is detected and at the same time the alarm reset request AR is set.

[0065] The predetermined limit time period Δt L is preferably selected from at least 2 s to at most 3 s, particularly preferably 2.5 s.

[0066] Fig. 5shows a schematic diagrammatic representation of a second embodiment of the method, which, however, is preferably used in combination with the method described in connection with Figure 4 explained first embodiment.

[0067] Based on Figure 5It can be seen that the actual high pressure p I , which is again plotted against time t in a first, upper diagram at a), is monitored with regard to the frequency of the first high pressure limit value p L1 being exceeded. The second diagram from the top at b) shows the current engine speed n I. A third time diagram from the top at c) shows a frequency value HA which indicates the instantaneous frequency of the first high pressure limit value p L1 being exceeded by the actual high pressure p I. The fourth time diagram from the top at d) again shows the logical signal SIG. The fifth time diagram from the top at e) again shows the logical variable MS. A sixth time diagram from the top at f) shows a second alarm level A2 as a corresponding variable with the logical values ​​0 and 1.In the seventh timing diagram from the top at g), the first alarm level A1 is shown as a corresponding logical variable with the values ​​0 and 1. In the eighth diagram from the top at h), the alarm reset request AR is shown.

[0068] The first time diagram at a) shows that the actual high pressure p I initially increases from the starting value p Start and at a first time t 0 reaches and then exceeds the first high pressure limit p L1. The third time diagram at c) shows that the frequency value HA is incremented from 0 to 1 due to this limit violation. At a second time t 1 the actual high pressure again reaches the first high pressure limit p L1 from above, whereby at a third time t 2 it also reaches a third high pressure limit, which here is identical to the second high pressure limit p L2 according to Figure 4is selected. In principle, the third high pressure limit value can also be selected to be different from the second high pressure limit value p L2. However, a preferred embodiment selects the third high pressure limit value to be equal to the second high pressure limit value p L2, with the third high pressure limit value then also being smaller than the first high pressure limit value p L1 by exactly the hysteresis differential pressure value Δp H. As a result, the actual high pressure p I rises again and at a fourth point in time t 3 once again exceeds the first high pressure limit value p L1. This results in the frequency value HA being incremented again, in this case from the value 1 to the value 2. At a fifth point in time t 4 , the actual high pressure p I once again falls below the first high pressure limit value p L1 from above.At a sixth time t 5 , the actual high pressure p I again exceeds the first high pressure limit p L1 from below, without previously reaching or falling below the second high pressure limit p L2 from above. Therefore, the frequency value HA is not incremented at the sixth time t 5 .

[0069] At a seventh time t 6 , the first high pressure limit p L1 is again undershot by the actual high pressure p I , whereby the second high pressure limit p L2 is also undershot at an eighth time t 7 . Subsequently, the actual high pressure p I exceeds or falls below the first high pressure limit p L1 several more times, as well as the second high pressure limit p L2 . This is shown in Figure 5 indicated by a dotted representation of all time diagrams.

[0070] At a ninth time t 8 , the actual high pressure p I , i.e., the instantaneous high pressure, exceeds the first high pressure threshold p L1 again. For illustrative purposes, it is assumed here that the frequency value HA is incremented to the value 30.

[0071] At a tenth time t 9 , the actual high pressure p I again falls below the first high pressure limit p L1 , and at an eleventh time t 10 , it also reaches or falls below the second high pressure limit p L2 . At a twelfth time t 11 , the actual high pressure p I again exceeds the first high pressure limit p L1 , resulting in the frequency value HA being incremented to the value 31.

[0072] This now leads to the second alarm level A2 being set, with the corresponding logical variable being set from the value 0 to the value 1, which is shown in the sixth time diagram at f). The second alarm level A2 is therefore set when the first high pressure limit value p L1 is exceeded for the first time by the current high pressure, i.e. the actual high pressure p I, with a predetermined second limit frequency that is lower than a first limit frequency defined for setting the first alarm level A1, which will be explained below. The second limit frequency is selected here as 31. It can also preferably be selected as 30. The second limit frequency is preferably selected between 25 and 35. The frequency value HA is compared with the second limit frequency - and, as will be explained below, also with the first limit frequency.The second alarm level A2 corresponds in particular to a yellow alarm, by which an operator of the internal combustion engine 1 is warned of possible damage to the injectors 15.

[0073] At a 13th time point, t12, the first high-pressure limit pL1 is undershot, and at a 14th time point, t13, the second high-pressure limit pL2 is reached and subsequently also undershot. Subsequently, the actual high pressure pI exceeds and falls below the first high-pressure limit pL1 and also the second high-pressure limit pL2 several more times, which is again indicated by a dotted representation of all time diagrams.

[0074] At a 15th time t 14 the actual high pressure p I exceeds the first high pressure limit value p L1 again. For explanatory purposes it is assumed that the frequency value HA is thereby incremented to the value 50. At a 16th time t 15 the actual high pressure p I again falls below the first high pressure limit value p L1 . At a 17th time t 16 the actual high pressure p I again exceeds the first high pressure limit value p L1 without having previously reached or fallen below the second high pressure limit value p L2. Therefore the frequency value HA is not incremented at this time. At an 18th time t 17 the first high pressure limit value p L1 is again fallen below. At a 19th time t 18 the second high pressure limit value p L2 is reached and then fallen below.

[0075] At a 20th time point t19, the actual high pressure pI, after a further increase, again exceeds the first high pressure limit pL1, causing the frequency value HA to be incremented to 51. This now results in the first frequency limit being reached, thus setting the first alarm level A1 - see diagram g). The first frequency limit is therefore preferably set to 51 here. It can also be set to 50. In general, the first frequency limit is preferably set between 45 and 55.

[0076] Setting the first alarm level A1, in turn, stops the power supply to the injectors 15, preventing fuel from being injected into the combustion chambers 16. This is achieved by changing the value of the logic signal SIG from F to T - see diagram d).

[0077] At a 21st time t 20 , the actual high pressure p I again falls below the first high pressure limit value p L1 . At a 22nd time t 21 , the actual high pressure p I reaches the second high pressure limit value p L2 , which results in the injection being enabled again by the logic signal SIG changing its value from T to F. At a 23rd time t 22 , the actual high pressure p I again exceeds the first high pressure limit value p L1 , which results in the fuel injection into the combustion chambers 16 being stopped again by the logic signal SIG once again assuming the value T. At a 24th time t 23 , the internal combustion engine 1 is switched off, which leads to a drop in the current engine speed n I. At the same time, the actual high pressure p I falls below the first high pressure limit value p L1 . As a result, the actual high pressure p I continues to fall and then rises again without previously reaching or falling below the second high pressure limit p L2. At a 25thAt time t 24 the actual high pressure p I again exceeds the first high pressure limit value p L1 . At a 26th time t 25 the current engine speed n I reaches the value 0, which means that the internal combustion engine 1 is now at a standstill. The logical variable MS therefore also changes its value from 0 to 1. At a 27th time t 26 the actual high pressure p I again falls below the second high pressure limit value p L2 from the above, which causes the logical signal SIG to change to the value F. At a 28th time t 27 the alarm reset request AR is set. Since the internal combustion engine 1 is at a standstill this results in all alarms, i.e. the first alarm level A1 and the second alarm level A2, being reset. At the same time the frequency value HA is also reset to zero after the alarm reset request AR is triggered while the internal combustion engine 1 is at a standstill.

[0078] It can therefore be seen that the frequency value HA, which indicates the instantaneous frequency of the first high-pressure limit p L1 being exceeded by the instantaneous high pressure, i.e., the actual high pressure p I , is incremented when the instantaneous high pressure reaches or exceeds the first high-pressure limit p L1 from below the second high-pressure limit p L2. The frequency value HA is compared with the predetermined limit frequency, in particular with both the first limit frequency and the second limit frequency.

[0079] The second alarm level A2 is also canceled if both a standstill of the internal combustion engine 1 is detected and the alarm reset request AR is set.

[0080] The control unit 21 is particularly configured to carry out the method described here.

[0081] This will now be discussed in connection with Figure 6 explained in more detail.

[0082] Fig. 6shows a schematic representation of another embodiment of the method in the form of a flow chart. This embodiment can also be used cumulatively with the embodiments according to the Figure 4 and 5 be provided, with preference being given to all those related to the Figures 4 to 6 explained process steps and features of the process are carried out in combination with each other.

[0083] Before the method starts in a start step S0, the value of a variable M, which represents a flag and is also referred to below as a flag variable, and which can assume the values ​​0 and 1, is preferably initialized to 1. The current time period Δt A is updated to the value zero, and the frequency value HA is also initialized to the value zero.

[0084] In a first step S1, a query is made as to whether the first alarm level A1 is set. If this is not the case, the method continues with a second step S2, in which a query is made as to whether the actual high pressure p I is greater than the first high pressure limit value p L1 . If this is not the case, the method continues with a third step S3, in which a check is made as to whether the marker variable M has the value 1, i.e. is set, which is the case when the method first starts, according to the aforementioned initialization. If the variable M is set, the method continues with a sixth step S6. If, on the other hand, the variable M is not set, i.e. has the value 0, the method continues with a fourth step S4. In this step, a check is made as to whether the actual high pressure p I is less than or equal to the second high pressure limit value p L2. If this is not the case, the method sequence continues with the sixth step S6.If this is the case, however, the flag variable M is set to the value 1 in a fifth step S5, and the program then continues with the sixth step S6. In the sixth step S6, the current time period Δt A is set to the value zero. After the sixth step S6, a seventh step S7 is executed, in which the logic signal SIG is set to the value F. The program then continues with a 33rd step S33.

[0085] If the query result in the second step S2 is positive, i.e. if the actual high pressure p I is actually greater than the first high pressure limit value p L1 , the method continues in an eighth step S8. In this eighth step S8, a check is made as to whether the current time period Δt A is greater than the predetermined limit time period Δt L . If this is the case, the method continues with a ninth step S9, a tenth step S10, an eleventh step S11 and then with the 33rd step S33. In the ninth step S9, the frequency value HA is set to the value zero. In the tenth step S10, the first alarm level A1 is set. In the eleventh step S11, the logic signal SIG is set to the value T.

[0086] If, however, the query result in the eighth step S8 is negative, i.e., the current time period Δt A is less than or equal to the limit time period Δt L , the process continues in a twelfth step S12. In this step, the time variable Δt A is incremented by a process-inherent sampling time Ta.

[0087] In a 13th step S13, the marker variable M is again queried. If it is not set, the program continues with a 16th step S16. If, however, it is set, i.e., has the value 1, the frequency value HA is incremented in a 14th step S14. The marker variable M is then set to zero in a 15th step S15.

[0088] In the 16th step S16, a query is made as to whether the second alarm level A2 is set. If this variable is set, i.e., it has the value 1, the program continues with the 19th step S19. If it is not set, i.e., it has the value zero, the program continues with the 17th step S17. In this 17th step S17, a check is made as to whether the frequency value HA is greater than the second frequency limit HL2 less 1. If this is not the case, the program continues with the 19th step S19; otherwise, the program continues with the 18th step S18, where the second alarm level A2 is set. In the 19th step S19, it is checked whether the frequency value HA is greater than the first threshold frequency HL1 reduced by 1. If this is the case, the process continues with a 20th step S20, a 21st step S21, a 22nd step S22, and then with the 33rd step S33. If this is not the case, the process continues with a 23rd step S23 and then with the 33rd step S33. In the 20thIn step S20, the frequency value HA is set to zero. In step S21, the first alarm level A1 is set. In step S22, the logical signal SIG is set to the value T. In step S23, the logical signal SIG is set to the value F.

[0089] If the query result in the first step S1 is positive, i.e. the first alarm level A1 is set, the process continues with a 24th step S24. In this 24th step S24, the marker variable M is queried. If this is set, the process continues with a 25th step S25, otherwise with a 29th step S29. In the 25th step S25, a query is made as to whether the actual high pressure p I is greater than the first high pressure limit value p L1 . If this is the case, the process continues with a 26th step S26, a 27th step S27 and then with the 33rd step S33. If, on the other hand, the actual high pressure p I is less than or equal to the first high pressure limit value p L1 , the process continues with a 28th step S28 and then with the 33rd step S33.

[0090] In the 26th step S26, the flag variable M is set to the value zero. In the 27th step S27, the logical signal SIG is set to the value T. In the 28th step S28, the logical signal SIG is set to the value F.

[0091] In the 29th step S29, a check is made to determine whether the actual high pressure p I is less than or equal to the second high pressure limit value p L2. If this is the case, the process continues with a 30th step S30, a 31st step S31, and then with the 33rd step S33. If this is not the case, the process continues with a 32nd step S32 and then with the 33rd step S33. In the 30th step S30, the flag variable M is set to the value 1. In the 31st step S31, the logical signal SIG is set to the value F. In the 32nd step S32, the logical signal SIG is set to the value T.

[0092] In the 33rd step S33, a check is made to determine whether the following conditions are met simultaneously—i.e., cumulatively: the alarm reset request AR is set, internal combustion engine 1 is stopped, i.e., the logical variable MS is set, and either the first alarm level A1 or the second alarm level A2 is set. If these conditions are met cumulatively, the program continues with a 34th step S34, a 35th step S35, a 36th step S36, and a 37th step S37. In the 34th step S34, the second alarm level is reset. In the 35th step S35, the first alarm level is reset. In the 36th step S36, the current time period Δt A is set to zero. In the 37th step S37, the frequency value HA is set to zero. The program sequence then ends in an end step S38. If one of the cumulative conditions of the 33rd step S33 is not met, the program flow ends in the end step S38 without the steps S34 to S37 having been completed beforehand.

[0093] The method is preferably carried out continuously iteratively, so that it begins again in the start step S0 as soon as it has ended in the end step S38. The initialization of the marker variable M, the current time period Δt A and the frequency value HA with the parameters given at the beginning of the figure description of Figure 6 The specified values ​​are only performed at the very first start of the program execution, but not at every run. Rather, at each new run after a previous run, the values ​​from the previous run are adopted for these variables, since otherwise the logic of the method would not function. The duration of a run of the method is preferably the duration of the sampling step Ta, whereby this ensures in particular that the current time duration Δt A is always correctly updated in the twelfth step S12.

[0094] In connection with the invention, the following advantages in particular arise: The injectors 15 can be damaged if their components are subjected to excessive loads as a result of excessively high fuel pressures in the high-pressure accumulator 13. Such excessive loads occur when the instantaneous high pressure either exceeds a first limit value for too long a period of time, or when this limit value is exceeded too frequently. The method proposed here makes it possible to protect the injectors 15 from further damage by deactivating the injection of fuel into the combustion chambers 16 in both cases. Fuel injection is only enabled again when the high pressure falls below the first limit value by a hysteresis differential pressure value.This allows the internal combustion engine 1 to continue operating in a type of emergency mode despite possible pre-existing damage until the operator has the opportunity to perform maintenance, in particular, to replace the injectors 15. The need to replace the injectors 15 or perform maintenance is indicated to the operator by triggering the first alarm level A1, i.e., the red alarm, preferably with a corresponding error message. To warn the operator in advance, the second alarm level A2, i.e., a yellow alarm, is triggered early, specifically when a certain, still permissible, number of limit violations has been detected.

Claims

1. Method for operating an internal combustion engine (1) having an injection system (3) which has a high pressure accumulator (13), wherein an instantaneous high pressure (pI) in the high pressure accumulator (13) is monitored in a time-dependent manner by means of a high pressure sensor (23), wherein it is checked whether a first predetermined high pressure threshold value (pL1) is exceeded by the instantaneous high pressure (pI) for a predetermined threshold duration (ΔtL) in an uninterrupted manner, and wherein it is checked whether the first predetermined high pressure threshold value (pL1) is exceeded by the instantaneous high pressure (pI) for the first time with a predetermined, first threshold frequency (HL1), wherein a first alert level (A1) is set if either a) the first predetermined high pressure threshold value (pL1) is exceeded by the instantaneous high pressure (pI) for the predetermined threshold duration (ΔtL) in an uninterrupted manner, or b) the first predetermined high pressure threshold value (pL1) is exceeded by the instantaneous high pressure (pI) for the first time with the predetermined, first threshold frequency (HL1), characterized in that a frequency value (HA) which indicates an instantaneous frequency of the exceeding of the first high pressure threshold value (pL1) by the instantaneous high pressure (pI) is incremented if the instantaneous high pressure (pI) reaches or exceeds the first high pressure threshold value (pL1) from below a second high pressure threshold value (pL2), wherein the second high pressure threshold value (pL2) is smaller than the first high pressure threshold value (pL1), and wherein the frequency value (HA) is compared with the predetermined first threshold frequency (HL1).

2. Method according to Claim 1, characterized in that a recording of a duration (ΔtA) of the exceeding of the first high pressure threshold value (pL1) by the instantaneous high pressure (pI) is started if the instantaneous high pressure (pI) reaches or exceeds the first high pressure threshold value (pL1) from below the first high pressure threshold value (pL1), wherein the recorded duration (ΔtA) is compared with the predetermined threshold duration (ΔtL).

3. Method according to any one of the preceding claims, characterized in that the recorded duration (ΔtA) is set to zero if the instantaneous high pressure (pI) undershoots the first high pressure threshold value (pL1) from above the first high pressure threshold value (pL1).

4. Method according to any one of the preceding claims, characterized in that a second alert level (A2) is set if the first high pressure threshold value (pL1) is exceeded by the instantaneous high pressure (pI) for the first time with a predetermined, second threshold frequency (HL2), wherein the second threshold frequency (HL2) is smaller than the first threshold frequency (HL1).

5. Method according to any one of the preceding claims, characterized in that an injection of fuel from the high pressure accumulator (13) into at least one combustion chamber (16) of the internal combustion engine (1) is terminated if the first alert level (A1) is set.

6. Method according to Claim 5, characterized in that a) the injection is continued in the case of set first alert level (A1) if the instantaneous high pressure (pI) undershoots a third high pressure threshold value from above the third high pressure threshold value, wherein the third high pressure threshold value is smaller than the first high pressure threshold value, and b) the continued injection is terminated in the case of set first alert level (A1) as soon as the instantaneous high pressure (pI) reaches or exceeds the first high pressure threshold value (pL1).

7. Method according to any one of the preceding claims, characterized in that the first alert level (A1) and / or the second alert level (A2) is / are cancelled if a standstill of the internal combustion engine (1) is detected and at the same time an alert reset request (AR) is made.

8. Method according to any one of the preceding claims, characterized in that the predetermined threshold duration (ΔtL) of at least 2s to at most 3s, and / or the first predetermined threshold frequency (HL1) of at least 45 to at most 55, and / or the second predetermined threshold frequency (HL2) of at least 25 to at most 35 is / are selected.

9. Method according to any one of the preceding claims, characterized in that the injection or the continued injection is terminated in that a) a setpoint injection quantity (QS) is set to zero and / or in that b) an energization period (BD) for at least one injector (15) is set to zero.

10. Injection system (3) for an internal combustion engine (1) having - at least one injector (15), - a high pressure accumulator (13) which is connected in terms of flow to the at least one injector (15), and having - a high pressure sensor (23) which is configured and arranged for time-dependent recording of an instantaneous high pressure (pI) in the high pressure accumulator (13), characterized by a control unit (21) which is operatively connected to the high pressure sensor (23) and configured to carry out a method according to any one of Claims 1 to 9.