Method for operating an internal combustion engine, control device, and computer program product

Abstract

The invention relates to a method for operating an internal combustion engine (10) using gaseous fuel, wherein the gaseous fuel is injected directly into a combustion chamber (12) by means of a fuel injector (14). The method is characterized in that an expected combustion chamber pressure and an associated point in time are determined and put into a relationship with the combustion chamber pressure which is maximally permissible during an injection process, and during a compression stroke, the end of the injection process is temporally set at least periodically during the injection process in such a way that the injection process ends at the latest when the combustion chamber pressure has increased to the combustion chamber pressure which is maximally permissible during an injection process, and / or during a working cycle, the beginning of the injection process is set at least periodically during the injection process in such a way that the injection process begins at the earliest when the combustion chamber pressure has dropped to the combustion chamber pressure which is maximally permissible during an injection process.

Description

[0001] R.416425

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating an internal combustion engine, control device and computer program product

[0006] State of the art

[0007] The invention relates to a method for operating an internal combustion engine, a control device and a computer program product.

[0008] German patent DE 102021 210001 A1 describes a method for operating an internal combustion engine that runs on gaseous fuel, for example, hydrogen. Gaseous hydrogen is injected directly into the combustion chambers (DI injection) or into the intake ports (port fuel injection), and the hydrogen-air mixture is ignited in the combustion chambers by an ignition device. The hydrogen, in gaseous form, reaches a fuel rail via pressure regulating devices. This fuel rail is functionally similar to the fuel rail in an internal combustion engine with gasoline or diesel direct injection. Several fuel injectors are connected to the fuel rail, which deliver the gaseous fuel to the combustion chambers.

[0009] Disclosure of the invention

[0010] The problem underlying the invention is solved by a method, a control device, and a computer program product with the features of the dependent claims. Advantageous embodiments are specified in the subclaims.

[0011] The invention takes into account that a flawless, i.e., mass-accurate, injection of the gaseous fuel into a combustion chamber is jeopardized if the injection of the gaseous fuel occurs at a certain time.

[0012] - 2 -

[0013] This occurs when the gas pressure prevailing in the combustion chamber (combustion chamber pressure) is very high, particularly higher than the maximum permissible combustion chamber pressure for injection. The smaller the pressure differential between fuel pressure and combustion chamber pressure, the smaller the mass of fuel entering the combustion chamber within a given period. The actual injected fuel mass thus corresponds very closely to the desired fuel mass according to the invention. Simultaneously, the invention makes it possible, if desired, to perform the injection as late as possible during a compression stroke and as early as possible during a power stroke. Under certain conditions, this can improve the efficiency of the internal combustion engine and its emissions.

[0014] The underlying principle is as follows: In internal combustion engines with direct injection, i.e., the injection of gaseous fuel directly into a combustion chamber, the timing of the injection significantly influences the mixture formation in the combustion chamber. This allows for the optimization of both emissions and efficiency while ensuring stable combustion. Fuel can be introduced at various stages of the piston movement. Injection with the intake valve(s) closed before combustion is called compression stroke injection, also known as main injection, and is performed during the compression stroke. Furthermore, it is possible to perform a second injection after combustion, also called post-injection. This is carried out during the power stroke.

[0015] In general terms, the invention identifies those points in time or periods during which the combustion chamber parameters permit injection under a given injector system condition. These points in time are then taken into account when determining the injection timing or periods. If a planned injection is expected to violate a period during which injection should not occur, the timing of the planned injection can be adjusted so that the entire injection duration falls within the permissible period.

[0016] It is understood that here and below the term "point in time" or "period of time" is understood in the engine-technical sense and refers to a combustion chamber R.416425

[0017] - 3 -

[0018] For example, the ignition timing can be specified by the angle of a crankshaft before or after top dead center (TDC). TDC is also abbreviated as TDC. A compression stroke of a combustion chamber typically extends from -180° to 0° before TDC, and a power stroke of a combustion chamber typically extends from 0° to 180° after TDC.

[0019] Specifically, a method for operating an internal combustion engine with gaseous fuel is proposed, in which the gaseous fuel is injected directly into a combustion chamber via a fuel injector. The internal combustion engine is a typical piston engine operating on the four-stroke principle. Gaseous hydrogen, for example, is a suitable fuel. This is injected directly into the combustion chamber at relatively high pressure by a fuel injector that is directly associated with that chamber. The fuel injector, in turn, is connected to a fuel rail in which the gaseous fuel is stored at a comparatively high pressure.

[0020] According to the invention, a predicted combustion chamber pressure during the compression stroke (rising combustion chamber pressure) and / or during the power stroke (falling combustion chamber pressure), and a corresponding time or times, are automatically determined, for example, by a computing device. The determined predicted combustion chamber pressure is then automatically compared, for example, by the computing device, to a maximum permissible combustion chamber pressure for error-free injection. In this context, "error-free" means, in particular, that the actual injected fuel mass corresponds almost exactly to a desired fuel mass. From this, the period during which the predicted combustion chamber pressure will be above the maximum permissible combustion chamber pressure during injection can be determined. These conditions typically occur towards the end of a compression stroke and at the beginning of a power stroke.

[0021] As a result, during a planned injection, for example by the aforementioned computing device, at least temporarily a point in time of the end of an R.416425 is automatically determined, for example by the aforementioned computing device.

[0022] - 4 -

[0023] The injection process is timed so that it ends no later than when the combustion chamber pressure has risen to the maximum permissible pressure during injection. In the case of planned injection during a power stroke (post-injection), the start time of the injection is at least temporarily set so that it begins no earlier than when the combustion chamber pressure has dropped to the maximum permissible pressure during injection. This largely prevents attempts to inject gaseous fuel into the combustion chamber while the combustion chamber pressure is above the maximum permissible pressure during injection.

[0024] In a further training course, the expected combustion chamber pressure is to be determined using a calculation model, preferably taking into account at least one of the parameters from the following group: ignition timing, mixture composition, closing time of the intake valve(s), mixture temperature at the closing time of the intake valve(s). This is simple and can be implemented with minimal hardware and software effort.

[0025] A further training course will cover determining the maximum permissible combustion chamber pressure during injection, depending on the fuel pressure in a fuel rail and / or the available current for controlling a fuel injector. This is also easily achievable with minimal hardware and software effort.

[0026] In a further training, it is planned that a point in time is determined at which the combustion chamber pressure during a compression stroke reaches the maximum permissible combustion chamber pressure during injection, and that at least temporarily the start time of injection is set so that the end time of injection is at least approximately the determined point in time, and / or that a point in time is determined at which the combustion chamber pressure during a power stroke reaches the maximum permissible combustion chamber pressure during injection, and that at least temporarily the start time of injection is at least approximately the determined point in time. This variant is very easy to implement. With this variant, the injection time is at least temporarily independent of, for example, a torque and / or a rotational speed of the R.416425.

[0027] - 5 -

[0028] internal combustion engine or emission requirements and made “rigidly” dependent on the point in time at which, during a compression stroke or main injection, the maximum permissible combustion chamber pressure during an injection is exceeded, or made dependent on the point in time at which, during a power stroke or post-injection, the maximum permissible combustion chamber pressure during an injection is undershot.

[0029] In a further development process, the expected combustion chamber pressure is determined for each compression stroke. This pressure is calculated based on the planned end of an injection stroke, for example, according to load and engine speed. At least temporarily, and specifically when the calculated expected combustion chamber pressure exceeds the maximum permissible pressure during an injection stroke, the injection period is shifted forward—possibly with a safety margin—to such an extent that the combustion chamber pressure during injection remains below the maximum permissible pressure. This approach attempts to find a compromise between meeting the requirements for optimal combustion and adhering, at least to a large degree, to a desired injection timing.

[0030] Normally, the injection timing is determined based on factors such as a desired load, engine speed, and, if applicable, specific emission requirements. Intervention only occurs if it is determined that the planned timing would result in at least part of the injection taking place when the combustion chamber pressure exceeds the maximum permissible pressure during injection. In such cases, the injection timing is shifted to ensure it falls outside the period when the combustion chamber pressure exceeds the maximum permissible pressure.

[0031] For example, taking into account the input conditions in the combustion chamber, such as ignition angle, filling, mixture composition, closing time of the intake valves, mixture temperature, etc., the point in time at which the maximum permissible combustion chamber pressure during an injection is reached can be determined by means of an inverse calculation of the pressure model, and then R.416425

[0032] - 6 -

[0033] The injection period should be scheduled so that it ends at the determined time. A more preferred method, requiring less computational effort, is to perform the following steps: a. Determining the average pressure gradient between the planned start and end of injection; b. Determining the time at which, assuming the average pressure gradient, the combustion chamber reaches the maximum permissible combustion chamber pressure; c. Using the determined time as the new end time of injection and determining a new start time of injection based on this new end time.

[0034] A similar procedure can be used for post-injection during the power stroke: in such cases, the expected combustion chamber pressure at the planned start of injection is determined. Then, at least temporarily, and at least when the determined expected combustion chamber pressure exceeds the maximum permissible combustion chamber pressure during injection, the injection period is delayed by just enough so that the combustion chamber pressure during injection remains below the maximum permissible combustion chamber pressure.

[0035] For example, taking into account the combustion chamber input conditions, such as ignition angle, charge, mixture composition, intake valve closing time, mixture temperature, etc., an inverse calculation of the pressure model can be used to determine the point in time at which the maximum permissible combustion chamber pressure during injection is reached. The injection period can then be scheduled to begin precisely at this determined time. Specifically, a procedure can be carried out that includes the following steps: a. Determining an average pressure gradient between the planned start and end of injection; b. Determining the time at which, assuming the average pressure gradient, the combustion chamber reaches the maximum permissible combustion chamber pressure; c.Using the determined time as the new time of the start of the injection and determining a new time of the end of the injection based on the new time of the start of the injection. R.416425.

[0036] - 7 -

[0037] In a further training exercise, the average pressure gradient is intended to be a linear slope between the calculated expected combustion chamber pressure and the corresponding time at the planned start, and the calculated expected combustion chamber pressure and the corresponding time at the planned end. This also requires few computational resources.

[0038] The invention also includes a control device with a processor and a memory on which a computer program product is stored, which includes instructions that, when the computer program product is executed by the control device, cause it to execute a method of the above type.

[0039] The invention also includes a computer program product comprising instructions which, when the computer program product is executed by a microprocessor, cause it to execute a method of the above type.

[0040] Embodiments of the invention are explained below with reference to the accompanying drawing. The drawing shows:

[0041] Figure 1 shows a schematic representation of an internal combustion engine with multiple combustion chambers and associated inlet valves and fuel injectors;

[0042] Figure 2 is a diagram showing a pressure profile in a combustion chamber of the internal combustion engine of Figure 1 and time periods of injections into the combustion chamber over an angle of a crankshaft for a first non-inventive operating case;

[0043] Figure 3 shows a diagram similar to Figure 2 for a second operating case according to the invention;

[0044] Figure 4 is a diagram similar to Figure 2 to illustrate a specific procedure;

[0045] Figure 5 shows a flowchart of a method for operating the internal combustion engine of Figure 1; and R.416425

[0046] - 8 -

[0047] Figure 6 shows a flowchart of another method for operating the internal combustion engine of Figure 1.

[0048] Subsequently, functionally equivalent elements and areas in different embodiments and figures bear the same reference numerals. They are normally only explained in detail upon their first mention.

[0049] In Figure 1, an internal combustion engine is designated by reference numeral 10. It is a classic four-stroke piston engine, which, by way of example, has five cylinders and five combustion chambers 12. The internal combustion engine 10 can, for example, power a motor vehicle. Each combustion chamber 12 is assigned a fuel injector 14, which injects gaseous fuel, in this example hydrogen, directly into its assigned combustion chamber 12. An outlet of the fuel injector 14 is therefore located directly in the combustion chamber 12. The fuel injectors 14 are connected to a fuel rail 16, which is supplied with gaseous fuel by a fuel system (not shown). The pressure in the fuel rail 16 is detected by a pressure sensor 18.

[0050] Air enters the combustion chambers 12 via intake valves 20, each assigned to a specific combustion chamber 12 (it is understood that the following explanations apply both to internal combustion engines 10, which, as in the present case, have several intake valves 20 per combustion chamber 12, and to internal combustion engines that have only a single intake valve per combustion chamber). Upstream of these intake valves 20, an air collector 22 is arranged, and upstream of this, a throttle valve 24. Upstream of the throttle valve 24, an intercooler 26 and a compressor 28 of an exhaust gas turbocharger 30 are arranged. Combustion exhaust gases pass from the combustion chambers 12 via exhaust valves 31 and an exhaust gas collector 32 to a turbine 34 of the exhaust gas turbocharger 30. A sensor 35 detects the rotational speed of the exhaust gas turbocharger 30.Upstream of the turbine 34, an exhaust gas recirculation line 36 branches off, which leads via an exhaust gas recirculation valve 38 and an exhaust gas recirculation cooler 40 to the air collector 22. R.416425.

[0051] - 9 -

[0052] The mixture of gaseous fuel and air present in a combustion chamber 12 is ignited by an ignition device 42. The pistons of the internal combustion engine 10 (not shown) act on a crankshaft 44 (shown only symbolically), the position and speed of which are detected by a crankshaft sensor 46.

[0053] The operation of the internal combustion engine 10 is controlled and regulated by a control unit, which includes, among other things, a control module 48. This module receives signals from numerous sensors of the internal combustion engine 10, for example, from the pressure sensor 18, the speed sensor 35, and the crankshaft sensor 46, as well as, for example, from an accelerator pedal 50. The control module 48 controls various actuators of the internal combustion engine 10, including the fuel injectors 14. For this purpose, the control module 48 has, among other things, a processor and a memory. A computer program product with program code is stored in the memory. This program code contains instructions that, when executed by the control unit, cause it to perform various procedures, including those described below with reference to Figures 2-5:

[0054] Figures 2 and 3 show two similar diagrams. The ordinate represents the crank angle (CW) before and after top dead center (TDC), respectively. The abscissa represents the pressure p in an exemplary combustion chamber 12. A limit pressure pMax is also indicated. This is the maximum permissible combustion chamber pressure during injection. It is determined based on the fuel pressure in the fuel rail 16, as measured by the pressure sensor 18, and the current available for controlling the fuel injector 14. The pressure p profile during the depicted compression stroke and power stroke is indicated by reference numeral 52.

[0055] It is understood that here and subsequently the term "point in time" or "period of time" is understood in the engine-technical sense and can be specified for a combustion chamber, for example, by the angle of a crankshaft before or after top dead center (TDC) ignition. R.416425

[0056] - 10 -

[0057] At time KW1, the intake valves 20 close. At time KW2, the combustion chamber pressure p during a compression stroke (crankshaft angle KW from -180° to 0° before top dead center) exceeds the maximum permissible combustion chamber pressure pMax during fuel injection. At time KW3, the combustion chamber pressure p during a power stroke (crankshaft angle KW from 0° to +180° after top dead center) falls below the maximum permissible combustion chamber pressure pMax during fuel injection. Figures 2 and 3 also show two injections 54 of gaseous fuel into the combustion chamber 12 via the fuel injector 14: a main injection 54a during the compression stroke and a secondary injection 54b during the power stroke.

[0058] In Figure 2, the main injection 54a begins at time Sa' and ends at time Ea'. The secondary injection 54b begins at time Sb' and ends at time Eb'. It can be seen that at time Ea', the combustion chamber pressure p would be above the maximum permissible combustion chamber pressure pMax for fuel injection. It can also be seen that at time Sb', the combustion chamber pressure p would likewise be above the maximum permissible combustion chamber pressure pMax for fuel injection.

[0059] Therefore, as will be explained in detail below, the expected combustion chamber pressure p is determined in the control unit 48 using a calculation model, for example, taking into account at least one of the parameters from the following group: ignition angle, mixture composition, closing time of the intake valves 20, mixture temperature at the closing time of the intake valves 20. The combustion chamber pressure p is then related to the maximum permissible combustion chamber pressure pMax during an injection. As can be seen from Figure 3, the end Ea of the main injection 54a is set to time KW2 and the start Sa of the main injection 54a is advanced according to arrow 56a.In this way, the same desired fuel mass as in Figure 2 is injected into the combustion chamber 12, but only during a period in which the combustion chamber pressure p does not exceed the maximum permissible combustion chamber pressure pMax. R.416425.

[0060] - 11 -

[0061] Similarly, during post-injection 54b, the start Sb of post-injection 54b is set to time KW3, and the end Eb of post-injection 54b is shifted later according to arrow 56b. Again, the same desired fuel mass as in Figure 2 is injected into the combustion chamber 12, but only during a period in which the combustion chamber pressure p does not exceed the maximum permissible combustion chamber pressure pMax.

[0062] The timing of injections 54a and 54b can be rigidly dependent on times in calendar weeks 2 and 3, such that the main injection 54a ends shortly before time in calendar week 2, or with a certain safety margin, and the subsequent injection 54b begins shortly after time in calendar week 3, or with a certain safety margin. In this case, only the duration of injections 54a and 54b would depend, for example, on a load demand and the speed of the crankshaft 44, and possibly other factors. However, the timing of injections 54a and 54b would be rigidly linked to times in calendar weeks 2 and 3.

[0063] However, the timing of the injections 54a and 54b can also be such that they at least partially meet the requirements for optimal combustion, which means that the timing of the injections 54a and 54b can be such that they meet the requirements for optimal combustion at least partially.

[0064] 54b is made dependent on the times KW2 or KW3 only if necessary, and the injection is shifted earlier (main injection 54a) or later (post-injection 54b) than originally planned only if necessary, so that the combustion chamber pressure p during the injections 54 is below the maximum permissible combustion chamber pressure pMax during an injection.

[0065] Knowing the input conditions in combustion chamber 12, such as: ignition angle, charge, mixture composition, closing time of the intake valve 20 and the mixture temperature at its closing, an inverse calculation of a pressure model can be used to determine the latest possible end of an injection before combustion or the earliest possible start of an injection after combustion from the pressure pMax, and a corresponding shift in the planned injection can be initiated. R.416425

[0066] - 12 -

[0067] Another possible example for determining a necessary displacement 56b will now be explained using the example of a subsequent injection 54b and with reference to Figure 4, whereby this example is also applicable in an analogous way to a main injection 54a:

[0068] First, a mean pressure gradient dKW / dp of the pressure p in combustion chamber 12 is determined between the planned start Sb' of the planned post-injection 54b' and the planned end Eb' of the planned post-injection 54b'. For this example, a linear slope dKW / dp is used as the mean pressure gradient between the determined expected combustion chamber pressure pS' and the corresponding time Sb' at the planned start of the post-injection 54b', and the determined expected combustion chamber pressure pE' and the corresponding time Eb' at the planned end of the post-injection 54b'.

[0069] The following applies:

[0070] dKW / dp = (Eb' - Sb') / (pE' - pS')

[0071] Ap = pE' - pMAX

[0072] AKW = Ap * (dKW / dp)

[0073] Sb = Sb' + AKW

[0074] Based on the mean pressure gradient dKW / dp, the time Sb at which combustion chamber 12 reaches the maximum permissible combustion chamber pressure pMax is determined. This determined time Sb is then used as the new start time of the post-injection 54b, and from the offset 56b or AKW between the originally planned start time Sb' of the post-injection 54b' and the determined time Sb, a new end time Eb for the post-injection 54b is determined and used for the post-injection 54b.

[0075] Now, two of the methods described above will be explained again as examples with reference to Figures 5 and 6: R.416425

[0076] - 13 -

[0077] The process in Figure 5 starts in a start function block 58. In a function block 60, the maximum permissible combustion chamber pressure pMax during an injection is determined, for example, taking into account a current fuel pressure in the fuel rail 16 and / or an available current for controlling the fuel injector 14. In a function block 62, the expected pressure p in the combustion chamber 12 is determined using a calculation model, for example, taking into account at least one of the parameters from the following group: ignition angle, mixture composition, closing time of the intake valves 20, mixture temperature at the closing time of the intake valves 20.

[0078] In a function block 64, the time or crankshaft angle KW2 and KW3, respectively, is determined for the compression stroke and the power stroke at which the calculated expected pressure p in the combustion chamber 12 reaches the maximum permissible combustion chamber pressure pMax during an injection stroke. In a function block 66a, in the case of a main injection stroke 54a, the time Ea for the end of the main injection stroke 54a is set to time KW2, and the time Sa for the start of the main injection stroke 54a is determined in a function block 68a from time Ea and the desired duration of the main injection stroke 54a. Similarly, in a function block 66b, in the case of a subsequent injection 54b, the time Sb for the start of the subsequent injection 54b is set to the time KW3, and the time Eb for the end of the subsequent injection 54b is determined in a function block 68b from the time Eb and the desired duration of the subsequent injection 54b.The procedure ends in an end function block 70.

[0079] The process in Figure 6 also starts in a start function block 58. For the sake of simplicity, the process in Figure 6 is explained here only for a post-injection 54b. In a function block 72, the post-injection 54b is terminated and its duration determined, depending, for example, on the rotational speed of the crankshaft 44 of the internal combustion engine 10 and a load or torque requested by the accelerator pedal 50. In a function block 74, it is checked whether at least part of the planned post-injection 54b lies within a time range in which the pressure p in the combustion chamber 12 is above the maximum permissible combustion chamber pressure pMax for injection. If this is the case, a function block 76 is activated.

[0080] - 14 -

[0081] The mean pressure gradient between the planned start Sb' and the planned end Eb' of the post-injection 54b was determined as explained above with reference to Figure 4.

[0082] In a function block 78, the time KW3 is determined at which, assuming the aforementioned average pressure gradient, the pressure p in combustion chamber 12 reaches the maximum permissible combustion chamber pressure pMax, i.e., has dropped to this value. In a function block 80, time KW3 is set as the new time Sb for the start of post-injection 54b. From this, a new time Eb for the end of post-injection 54b is determined in a function block 82, using the planned duration of post-injection 54b. The procedure ends again in an end function block 70. If the answer in the question function block 74 is "No", the process returns to function block 72.

Claims

R.416425 - 15 - Claims 1. A method for operating an internal combustion engine (10) with gaseous fuel, in which the gaseous fuel is injected directly into a combustion chamber (12) by means of a fuel injector (14), characterized in that a predicted combustion chamber pressure and an associated time are determined and related to a maximum permissible combustion chamber pressure during injection, and that at least temporarily, during injection during a compression stroke, the end of an injection is timed so that the injection ends at the latest when the combustion chamber pressure has risen to a maximum permissible combustion chamber pressure during injection, and / or that at least temporarily, during injection during a power stroke, the start of an injection is timed so that the injection begins at the earliest when the combustion chamber pressure has dropped to the maximum permissible combustion chamber pressure during injection.

2. Method according to claim 1, characterized in that the expected combustion chamber pressure is determined by means of a calculation model, preferably taking into account at least one of the parameters from the following group: ignition angle, mixture composition, closing time of the intake valve or intake valves (20), mixture temperature at the closing time of the intake valve or intake valves (20).

3. Method according to at least one of the preceding claims, characterized in that the maximum permissible combustion chamber pressure during an injection is determined depending on a fuel pressure in a fuel rail (16) and / or an available current strength of a control of a fuel injector (14).

4. Method according to at least one of the preceding claims, characterized in that a time point in time is determined at which the R.416425 - 16 - Combustion chamber pressure during a compression stroke reaches the maximum permissible combustion chamber pressure during an injection stroke, and that at least temporarily the start time of the injection stroke is set so that the end time of the injection stroke is at least approximately the determined time, and / or that a time is determined at which the combustion chamber pressure during a power stroke reaches the maximum permissible combustion chamber pressure during an injection stroke, and that at least temporarily the start time of the injection stroke is at least approximately the determined time.

5. A method according to at least one of the preceding claims, characterized in that, during a compression stroke, the expected combustion chamber pressure prevailing at the time of a planned end of an injection is determined, and that, at least temporarily, at least when the determined expected combustion chamber pressure is above the maximum permissible combustion chamber pressure during an injection, the injection period is shifted forward so that the combustion chamber pressure during the injection is below the maximum permissible combustion chamber pressure during an injection, in particular a method is carried out which comprises the following steps: a. Determining a mean pressure gradient between the planned start of injection and the planned end of injection; b. Determining the time at which, assuming the mean pressure gradient, the pressure in the combustion chamber (12) reaches the maximum permissible combustion chamber pressure; c. Using the determined time as the new time of the end of the injection and determining a new time of the start of the injection based on the new time of the end of the injection.

6. Method according to at least one of the preceding claims, characterized in that, during a working cycle, the expected combustion chamber pressure is determined which will prevail at the time of a planned start of injection, and that at least temporarily, at least when the determined expected combustion chamber pressure is above the maximum permissible combustion chamber pressure during injection, the R.416425 - 17 - The injection period is shifted so late that the combustion chamber pressure during injection is below the maximum permissible combustion chamber pressure during injection, in particular a procedure is carried out which includes the following steps: a. Determining a mean pressure gradient between the planned start of injection and the planned end of injection; b. Determining the time at which, assuming the mean pressure gradient, the pressure in the combustion chamber (12) reaches the maximum permissible combustion chamber pressure; c. Using the determined time as the new time of the start of the injection and determining a new time of the end of the injection based on the new time of the start of the injection.

7. Method according to at least one of the preceding claims 5 or 6, characterized in that the mean pressure gradient is a linear slope between the determined expected combustion chamber pressure and the corresponding time at the planned start and the determined expected combustion chamber pressure and the corresponding time at the planned end.

8. Computer program product comprising instructions which, when the program is executed by a computer, cause it to execute the method according to at least one of the preceding claims.

9. Control unit (48) for controlling and / or regulating the operation of an internal combustion engine (10), comprising at least one processor, at least one memory and at least one computer program product stored on the memory according to claim 8.

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