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

Abstract

In a method for operating an internal combustion engine (10) having a plurality of cylinders (12) with gaseous fuel, in particular hydrogen, the gaseous fuel is injected directly into the combustion chamber (14) of a respective cylinder (12) by means of a fuel injector (16) associated with a respective combustion chamber (14). It is proposed that, within a working cycle of the cylinder (12), gaseous fuel is injected at least intermittently by means of a post-injection, at least also late enough that said post-injection has no effect on torque, and that said post-injection is carried out at least intermittently only for a subset of the combustion chambers (14) within a working cycle of the internal combustion engine (10), wherein the decision as to whether the post-injection is carried out only for a subset of the combustion chambers (14) is at least indirectly dependent on a rotational speed of the internal combustion engine (10), wherein a rotational speed range in which the post-injection is carried out only for a subset of the combustion chambers (14) is higher than a rotational speed range in which the post-injection is carried out for all the combustion chambers (14).

Description

[0001] R.416739

[0002] - 1 -

[0003] Description

[0004] title

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

[0006] State of the art

[0007] The invention relates to a method for operating an internal combustion engine with several cylinders using gaseous fuel, a computer program product and a control unit, each according to the preambles of the dependent claims.

[0008] German patent DE 102021 210001 A1 describes a method for operating an internal combustion engine that runs on gaseous fuel, such as hydrogen. In such an engine, gaseous hydrogen is injected directly into the combustion chambers of the cylinders (Direct Injection or "DI"), or it is injected into an intake area upstream of a combustion chamber, for example, an intake port (Port Fuel Injection or "PI"). The hydrogen-air mixture is ignited in the combustion chambers by an ignition device. The hydrogen, in gaseous form, passes through pressure regulating devices to a fuel rail, which 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 computer program product, and a control device with the features of the dependent claims. Advantageous embodiments are specified in the subclaims. R.416739

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[0012] The invention has the advantage that the energy required to perform post-injection within a single combustion cycle of the internal combustion engine, i.e., across all cylinders or two complete crankshaft revolutions, can be reduced. This is particularly important at higher engine speeds, where the fuel injector must open especially quickly for post-injection, requiring a significant amount of energy that cannot always be supplied to all fuel injectors. In this way, post-injection can still be performed for at least a subset of the combustion chambers within a single combustion cycle, even at high engine speeds and when the available energy is limited by the system design.

[0013] The advantages of the invention are based on the following: Electromagnetic fuel injectors, which include a magnetic actuator, are frequently used for fuel injection. For fuel injection, the magnetic actuator is controlled with a very specific current profile. According to this current profile, an armature of the magnetic actuator is first attracted with a high current ("boost current") and then held in its energized open position with a lower current ("holding current"). The boost current is particularly significant for the energy requirement and thus the power loss at a magnetic coil and a control unit, since it operates with high current and high voltage, which is generally provided by a boost capacitor. The boost capacitor buffers the energy and makes it available quickly when needed, as soon as the magnetic actuator is activated.The high current requirement for the boost current results in particular from the fact that the magnetic force should be built up as quickly as possible in order to be able to operate the magnetic actuator with high dynamics.

[0014] The available boost energy depends primarily on the converter power and the battery voltage. The converter (e.g., a voltage converter or DC-DC converter) raises the voltage to a higher level required to drive the magnetic actuator. The relationship between converter power and battery voltage is, at least essentially and in most applications, linear. Thus, the converter power increases more or less linearly with increasing battery voltage. JeR.416739

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[0016] Depending on the geographical region, the battery voltage in a motor vehicle can typically be 12 V or 24 V. The converter power also depends on the size of the converter used. This is often limited by external constraints. The invention therefore enables reliable post-injection even with a comparatively low converter power during a combustion engine cycle, even at high engine speeds, indeed up to the maximum engine speed.

[0017] Specifically, this is achieved by a method for operating a multi-cylinder internal combustion engine with gaseous fuel, in particular gaseous hydrogen. In the method according to the invention, the gaseous fuel is injected directly into a combustion chamber of a respective cylinder, for example, by a fuel injector arranged directly on the respective cylinder. The method according to the invention is therefore a "direct injection" or "DI" process. The fuel injectors are typically connected to a fuel rail in which the gaseous fuel is stored under comparatively high pressure. The internal combustion engine is a typical piston engine that operates according to the four-stroke principle. A working cycle of a cylinder thus comprises the four typical working strokes of the cylinder, namely the intake stroke, compression stroke, expansion stroke, and exhaust stroke.The working cycle of the internal combustion engine is completed when all cylinders of the internal combustion engine have completed all four working strokes or when the crankshaft has rotated two full revolutions.

[0018] It is known that in such an internal combustion engine, the fuel is initially injected during the compression stroke (main injection). This injected fuel is torque-effective; its combustion thus generates a torque acting on a crankshaft of the internal combustion engine during the expansion stroke. According to the invention, gaseous fuel is injected at least temporarily within a working cycle, but also at least so late by means of a secondary injection that the fuel mass injected during this secondary injection is not torque-effective.

[0019] One known example is a so-called "early" post-injection, which is carried out, for example, during the expansion stroke. This usually aims to reduce the reaction time of a turbocharger during rapid load changes. R.416739

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[0021] to reduce this by a relatively rapid increase in exhaust gas enthalpy. A so-called "late" post-injection is also known, for example, when the exhaust valves are open during the exhaust stroke. Its purpose is typically to increase the exhaust gas temperature, for example, to heat a catalyst through an exothermic reaction / heat release of the fuel with a component in the exhaust system. In a typical application, the fuel injector should perform either only one main injection per combustion cycle or both a main injection and a post-injection (early or late).

[0022] According to the invention, this post-injection is carried out at least temporarily for only a subset of the combustion chambers within a working cycle of the internal combustion engine (two crankshaft revolutions). In a 4-cylinder internal combustion engine, the post-injection could thus be carried out, for example, for only three, two, or even just a single combustion chamber within a working cycle. Whether the post-injection is carried out for all combustion chambers or only for a subset of them during a working cycle is made at least indirectly dependent on the engine speed. "At least indirectly" means that the criterion depends at least also, or at least indirectly, on the engine speed, for example, a parameter that is dependent on the engine speed.In this process, post-injection is carried out for all combustion chambers in a rather low speed range, but for a subset of the combustion chambers in a comparatively higher speed range.

[0023] In a further training course, it is planned that post-injection will only be carried out for a subset of the combustion chambers when a parameter characterizing the internal combustion engine's rotational speed reaches or exceeds a limit. This is particularly easy to implement from a software perspective.

[0024] In a further training, it is provided that, using the rotational speed of the internal combustion engine and a current battery voltage, a first quantity is determined that characterizes an energy available for opening a fuel injector; that, using a specified number of injections within a combustion chamber operating cycle, a second quantity is determined.

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[0026] A quantity is determined that characterizes the energy required to open the fuel injector for each injection, and the subsequent injection is then only carried out for a subset of the combustion chambers if the second quantity is greater than the first. This method is particularly precise because the available energy and the required energy are compared, allowing, for example, a response to fluctuations in battery voltage.

[0027] In this advanced development, the number of combustion chambers in the subset decreases as the engine speed increases. This can be achieved, for example, by using a characteristic curve, or by employing multiple threshold values. Upon reaching or exceeding these thresholds, a further combustion chamber is "deactivated" with regard to post-injection. This advanced development prevents unnecessary deactivation of combustion chambers.

[0028] In a further development process, it is stipulated that the combustion chambers of the subset differ from one combustion cycle of the internal combustion engine to the next. For example, if two cylinders of a four-cylinder internal combustion engine are deactivated for post-injection, then in one combustion cycle the post-injection could occur in cylinders 1 and 3, and in the following combustion cycle in cylinders 2 and 4, and so on. One could therefore say that the deactivation of cylinders for post-injection "alternates" or "rotates" from one combustion cycle to the next.If, for example, only a single cylinder in the aforementioned internal combustion engine were deactivated with regard to post-injection, then cylinder number 1 could be deactivated first, followed by cylinder number 3 in the next operating cycle, cylinder number 2 in the subsequent operating cycle, and cylinder number 4 in the following operating cycle, and so on. Such alternating, rotating, or cyclical deactivation offers thermal advantages.

[0029] During further training, it is stipulated that the duration of the post-injection depends on the number of combustion chambers involved in the sub-mixture. Typically, the duration is longer with a higher number of "deactivated" combustion chambers. R.416739

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[0031] With a smaller number of "deactivated" combustion chambers, the emissions are lower. In this way, the total mass of fuel injected into the exhaust system during a combustion cycle via post-injection can be kept at least approximately constant. This adjustment can also be made only under certain operating conditions of the combustion engine, for example, during a cold start.

[0032] The invention also includes a computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the method of the above type.

[0033] Furthermore, the invention also includes a control unit for controlling and / or regulating the operation of an internal combustion engine, comprising at least one processor, at least one memory and at least one computer program product of the above type stored on the memory.

[0034] The following are an explanation of embodiments of the invention with reference to the drawing. The drawing shows:

[0035] Figure 1 shows a schematic representation of a 4-cylinder internal combustion engine with four combustion chambers and their associated inlet valves, exhaust valves and fuel injectors.

[0036] Figure 2 is a diagram showing, by way of example, a possible main injection, an early post-injection and a late post-injection of fuel into a combustion chamber of the internal combustion engine of Figure 1 over a crank angle of a crankshaft;

[0037] Figure 3 is a diagram schematically showing the current profile for controlling a fuel injector of the internal combustion engine of Figure 1 over time; and

[0038] Figure 4 shows a flowchart of a method for operating the internal combustion engine of Figure 1.R.416739

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[0040] For the sake of simplicity and clarity, the corresponding reference symbols for identical elements and areas are sometimes only entered for one element or area in the figures.

[0041] In Figure 1, an internal combustion engine is designated by reference numeral 10. It is a classic four-stroke piston engine, which in this example has four cylinders 12 and four combustion chambers 14. The internal combustion engine 10 can, for example, power a motor vehicle, but it can also be used in a stationary application, such as driving a generator. Each combustion chamber 14 is assigned a fuel injector 16, which injects gaseous fuel, in this example hydrogen, directly into the respective combustion chamber 14. An outlet of the fuel injector 16 is therefore located in the respective combustion chamber 14. The fuel injectors 16 are electromagnetically actuated fuel injectors, each comprising a magnetic actuator 17. The fuel injectors 16 are connected to a fuel rail 18, which is supplied with gaseous fuel, in this case hydrogen, by a fuel system (not shown).

[0042] Air enters the combustion chambers 14 via intake valves 20, each assigned to a specific combustion chamber 14. Upstream of these intake valves 20 is an air collector 22, and upstream of this, a throttle valve and other components are arranged, such as an intercooler and a compressor of an exhaust gas turbocharger, which are not shown. Combustion exhaust gases exit the combustion chambers 14 via exhaust valves 24 to an exhaust gas collector 26 and then to an oxidation catalyst 28, a particulate filter 30, and an SCR catalyst 32.

[0043] The mixture of gaseous fuel and air present in a combustion chamber 12 is ignited by an ignition device 34. The pistons of the internal combustion engine 10 (not shown) act on a crankshaft 36 (shown only symbolically). The internal combustion engine also includes a battery 38, a voltage converter 40, and a boost capacitor 42 (or possibly several boost capacitors) for controlling the fuel injectors 16. The relationship between the power or energy supplied by the voltage converter 40 and the voltage of the battery 38 is approximately li-near.R.416739

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[0045] The operation of the internal combustion engine 10 is controlled and regulated by a control unit, which includes a control unit 44 that receives signals from numerous (not shown) sensors of the internal combustion engine 10. The control unit 44 controls various actuators of the internal combustion engine 10, including the magnetic actuators 17 of the fuel injectors 16 and the ignition devices 34. For this purpose, the control unit 44 has, among other things, at least one processor and at least one 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 44, cause it to perform various procedures, including a procedure for cylinder-selective post-injection, which will be explained in more detail below.

[0046] As mentioned, the internal combustion engine 10 is a four-stroke engine that essentially operates according to the Otto cycle. A working cycle of a cylinder 12 thus comprises four power strokes. These are shown in Figure 2 as angular ranges of a crank angle KW of the crankshaft 36 relative to the top dead center (TDC) of a piston in a cylinder 12. An intake stroke is labeled 46, a compression stroke 48, an expansion stroke 50, and an exhaust stroke 52. Regions of the crank angle KW in which, for example, injections of gaseous fuel by the fuel injector 16 into the combustion chamber 14 are carried out are shown hatched.

[0047] A section 54 designates a main injection, which typically occurs during the compression stroke 48 with the intake valves 20 and exhaust valves 24 closed. A section 56 designates an early secondary injection, which typically occurs during the expansion stroke 50, also with the intake valves 20 and exhaust valves 24 still closed. The main injection 54 is torque-effective, while the early secondary injection 56 is not. Furthermore, a late secondary injection 58 is possible, which typically occurs during the exhaust stroke 52, i.e., with the exhaust valves 24 open. The fuel injected during this late secondary injection 58 is not combusted in the combustion chamber and is therefore also not torque-effective. Typically, there are 14R.416739 combustion chambers.

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[0049] within a working cycle of the internal combustion engine 10, in which all combustion chambers 14 pass through all four strokes 48-52 and the crankshaft 36 rotates two full revolutions, either an early post-injection 56 or a late post-injection 58.

[0050] Figure 3 describes the current profile of an electric current I over a time t, which is supplied to the magnetic actuator 17 of a fuel injector 16 for an injection 54, 56 or 58 by the voltage converter 40. According to this current profile, an armature of the magnetic actuator 17 is initially energized with a high current linj_boost (“boost current”) during a boost phase tj. n j_boost was activated and then with a lower current I in During a holding phase, j_hoid is held in its energized open position ("holding current"). The total actuation duration is tj. n j.

[0051] With regard to the post-injections 56 and 58, a method according to Figure 4 is applied: first, a crankshaft speed 36 and a current battery voltage 38 are provided in a functional block 60. From this, a functional block 62 determines the first parameter of available boost energy, which can be supplied by the voltage converter 40 for opening a fuel injector 16. In a functional block 64, a desired or intended number of injections during a combustion cycle of a combustion chamber 14 is determined. It is thus determined whether only a main injection 54 should take place, or whether both a main injection 54 and an early post-injection 56, or both a main injection 54 and a late post-injection 58, should take place.From this, a boost energy requirement is determined as a second quantity in a functional block 66. This boost energy is needed to open a fuel injector 16, and is therefore ultimately necessary to carry out the desired injections 54 + 56 or 54 + 58. The boost energy requirement is thus a desired boost energy.

[0052] In a functional block 68, the available boost energy (first quantity) is compared with the desired boost energy (second quantity). If the desired boost energy is greater than the available boost energy (functional block 70), then the post-injection 56 or 58 for specific combustion chambers 14 within a working cycle of the internal combustion engine 10R.416739 is activated.

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[0054] The boost injection process is deactivated, meaning it is not carried out, and is only carried out for the remaining combustion chambers 14 (function block 72). These remaining combustion chambers 14 form a subset of the combustion chambers 14. If the comparison in function block 68 shows that the desired boost energy is less than or equal to the available boost energy (function block 74), then the post-injection 56 or 58 is enabled and thus carried out for all combustion chambers within a working cycle of the internal combustion engine 10 (function block 76).

[0055] Since the available boost energy (first quantity) in functional block 62 is determined depending on the rotational speed of the internal combustion engine 10 provided in functional block 60, the decision, dependent on the comparison in functional block 68, as to whether the post-injection 56 or 58 is carried out only for a subset of the combustion chambers 14, ultimately depends, at least indirectly, on the rotational speed of the internal combustion engine 10. However, in this example, it also depends, for instance, on the current voltage of the battery 38. In a simplified embodiment not shown, the decision as to whether the post-injection is carried out only for a subset of the combustion chambers or for all combustion chambers could also depend on whether a quantity characterizing the rotational speed of the internal combustion engine (for example, the rotational speed itself) reaches or exceeds a limit value.

[0056] In the aforementioned functional block 72, the number of combustion chambers 14 of the subset is also determined, typically depending on the rotational speed of the internal combustion engine 10, such that the number of combustion chambers 14 of the subset decreases with increasing rotational speed. However, it would also be conceivable that functional block 72 uses the ratio between the first and second quantities to determine the number of combustion chambers 14 of the subset. If the first quantity is significantly smaller than the second quantity, the number of combustion chambers 14 of the subset would be larger than in a case where the first quantity is only slightly smaller than the second quantity.

[0057] Furthermore, the number of the combustion chambers 14 for which the post-injection 56 or 58 is deactivated is also determined in the aforementioned functional block 72. Typically, the numbers of the combustion chambers 14 are changed from one operating cycle of the internal combustion engine 10 to a subsequent operating cycle of the internal combustion engine 10; the deactivations are thus "alternated" (R.416739).

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[0059] or "rotates". Finally, the aforementioned function block 72 also determines whether the duration of the remaining post-injections 56 or 58 into the subset of combustion chambers 14 should be increased. This can, for example, be made dependent on the number of combustion chambers 14 in the subset. For example, the duration can be longer the smaller the number of combustion chambers 14 in the subset.

Claims

R.416739 - 12 - Claims 1. A method for operating an internal combustion engine (10) with several cylinders (12) using gaseous fuel, in particular hydrogen, in which the gaseous fuel is injected directly into the combustion chamber (14) of a respective cylinder (12) by means of a fuel injector (16) assigned to a respective combustion chamber (14), characterized in that gaseous fuel is injected at least temporarily within a working cycle of the cylinder (12) at least also at least so late by a post-injection (56, 58) that this post-injection (56, 58) is not effective in terms of torque, and that this post-injection (56, 58) is carried out at least temporarily within a working cycle of the internal combustion engine (10) only for a subset of the combustion chambers (14), wherein the decision as to whether the post-injection (56, 58) is carried out only for a subset of the combustion chambers (14) depends at least indirectly on a rotational speed of the internal combustion engine (10), wherein a Speed ​​rangein which the post-injection (56, 58) is carried out only for a subset of the combustion chambers (14), is higher than a speed range in which the post-injection (56, 58) is carried out for all combustion chambers (14).

2. Method according to claim 1, wherein the post-injection is then carried out only for a subset of the combustion chambers (14) when a quantity which characterizes the rotational speed of the internal combustion engine (10) reaches or exceeds a limit value.

3. Method according to claim 1, wherein, using the rotational speed of the internal combustion engine (10) and a current battery voltage, a first quantity is determined which characterizes an energy available for opening a fuel injector (16), and wherein, using a predetermined number of injections (54, 56; 54, 58) within a working cycle of a combustion chamber (14), a second quantity is determined which characterizes an energy available for opening the fuel injector (16) for R.416739 - 13 - these injections (54, 56; 54, 58) are required, and that the subsequent injection (56, 58) is then only carried out for a subset of the combustion chambers (14) if the second size is larger than the first size.

4. Method according to at least one of the preceding claims, wherein the number of combustion chambers (14) of the subset decreases as the rotational speed increases.

5. Method according to at least one of the preceding claims, characterized in that the combustion chambers (14) of the subset differ from one working cycle of the internal combustion engine (10) to a subsequent working cycle of the internal combustion engine (10).

6. Method according to at least one of the preceding claims, characterized in that the duration of the post-injection (56, 58) depends on the number of combustion chambers (14) of the subset.

7. 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.

8. Control unit (44) 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 7.

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