Method for operating internal combustion engine near combustion limit in low-power region

Abstract

The invention relates to a method (2) for operating an internal combustion engine having a plurality of cylinders, in particular a hydrogen engine, comprising ascertaining an air-fuel ratio of the internal combustion engine; comparing the ascertained air-fuel ratio with a predetermined lower limit value and an upper limit value corresponding to the combustion limit; a) adjusting (10) a cylinder-individualized fuel injection quantity on the basis of a rail pressure signal of the internal combustion engine as soon as the ascertained air-fuel ratio corresponds to the lower limit value at most in order to equalize the injection quantities of the plurality of cylinders, a) adjusting (20) a cylinder-individualized fuel injection quantity on the basis of the rail pressure signal of the internal combustion engine, and a control unit (30) for controlling the operation of the internal combustion engine as soon as the ascertained air-fuel ratio corresponds to the lower limit value; b) adjusting (12) a cylinder-individualized fuel injection quantity on the basis of a rotational speed of the internal combustion engine as soon as the ascertained air-fuel ratio is above the lower limit value and below the upper limit value in a transition region near the combustion limit in order to take into account a cycle fluctuation of the plurality of cylinders; and c) switching off (14) at least one cylinder once the determined air-fuel ratio reaches the upper limit value and thus the combustion limit, and adjusting the cylinder-individualized fuel injection quantity assigned to the remaining cylinders in accordance with measure a) or measure b), the respective ignition angle being maintained within an efficiency-optimized range in the range of all measures a), b) or c).

Description

Technical Field

[0001] The present invention relates to a method for operating an internal combustion engine having multiple cylinders, particularly a hydrogen engine, and a controller for controlling an internal combustion engine having multiple cylinders, particularly a hydrogen engine. Background Art

[0002] Operating a multi-cylinder hydrogen internal combustion engine is challenging in the low-load region, especially at idle. Efforts are focused on achieving an air-fuel ratio λ significantly greater than 1 to avoid NOx emissions and improve engine consumption and response characteristics. However, excessively high air-fuel ratios can lead to potential combustion stability problems. Throttling, cylinder deactivation, or appropriate manipulation of the thrust recirculation air valve (Schubumluftventil) are known to address this, but these measures are not clearly defined. Furthermore, the combustion boundary (i.e., a region from which excessively high air-fuel ratios can lead to combustion instability) cannot be clearly detected during engine operation; therefore, measures to avoid this region are mostly based on boundary conditions determined during engine use. Summary of the Invention

[0003] Unlike stoichiometric combustion, internal combustion engines operating using this lean-burn homogeneous combustion method have the advantage of being able to achieve rapid torque intervention by adjusting the fuel quantity, without considering the inertia of the air system. This minimizes torque-related intervention caused by ignition timing, which carries efficiency drawbacks. However, when adjusting torque through fuel quantity, it is crucial to ensure adherence to the so-called combustion limits of the fuel-air mixture, i.e., avoiding excessively high air-fuel ratios. Once these limits are reached, the fuel quantity can no longer be reduced further without causing combustion instability. Therefore, other (partially inefficient) measures must be employed to regulate torque.

[0004] Therefore, the object of the present invention is to provide a method or system that achieves improved idle speed regulation while minimizing ignition angle interference and making full use of the combustion limits.

[0005] This task is accomplished by a method having the features of independent claim 1. Advantageous implementations and extensions can be derived from the dependent claims and the following description.

[0006] A method for operating an internal combustion engine with multiple cylinders, particularly a hydrogen engine, is proposed. This method includes determining the air-fuel ratio of the internal combustion engine, comparing the determined air-fuel ratio with a predetermined lower limit and an upper limit corresponding to the combustion limits, and regulating the operation of the internal combustion engine according to the following cascaded adjustment measures acting in terms of torque:

[0007] a) Once the obtained air-fuel ratio corresponds to the lower limit, the individualized fuel injection quantity of the cylinder is adjusted based on the rail pressure signal of the internal combustion engine to achieve the balance of injection quantity of each cylinder.

[0008] b) Once the calculated air-fuel ratio is higher than the lower limit and lower than the upper limit in the transition region near the combustion boundary, the individualized fuel injection quantity of the cylinder is adjusted based on the engine speed to take into account the cycle fluctuations of each cylinder.

[0009] c) Once the calculated air-fuel ratio reaches its upper limit and thus the combustion limit is reached, at least one cylinder is shut off, and the individualized fuel injection amount allocated to the remaining cylinders is adjusted according to measure a) or measure b).

[0010] Among these measures, within the scope of all measures a), b), or c), the corresponding ignition angle is kept within the range of efficiency optimization.

[0011] The method of this invention for operating an internal combustion engine in a low-load region is characterized by prioritizing interventions that affect torque within a given range of regulation cascades to minimize efficiency-reducing measures. The implementation of each possible intervention relates to the desired engine air-fuel ratio, characterized by λ and representing the mass ratio of air to fuel relative to their respective stoichiometric ratios. It is important to note in this regard that the combustion limit should be considered as an upper limit of the air-fuel ratio above which combustion instability may occur due to excessively high air fraction. A lower limit with a sufficient safety distance from the combustion limit is determined, the rational selection of which will be discussed further below.

[0012] If the desired air-fuel ratio is significantly lower than the combustion limit and at most at the lower limit, then according to the method of the invention, the fuel supply to each individual cylinder is adjusted based on the rail pressure signal, as characterized above by means of measure or priority a). Therefore, here, the air-fuel ratio is relatively rich (fetter), or lower than or equal to the lower limit. The function implemented in the controller uses the fuel quantity deviating from the average fuel quantity of the engine cylinders to equalize the fuel supply to the cylinder average. Especially when the fuel supply is low, the individual air-fuel ratio of the cylinder is too high, and therefore closer to the combustion limit.

[0013] In this process, it is possible to consider evaluating the minimum rail pressure during injection into the cylinder. For cylinders where the minimum rail pressure observed during injection is on average higher than that in other cylinder cases, the operating duration of the corresponding injector can be increased until the minimum rail pressure is slightly less than or slightly higher than the previously calculated cylinder average.

[0014] The air-fuel ratio can be limited to a range near the previously calculated average value of the engine cylinders. After adjusting the fuel quantity in the cylinders accordingly, the air-fuel ratio should fall within this range. This range can be characterized by a decrease or increase in the fuel injection quantity relative to the engine average, which may be approximately 10%. Here, the ignition angle remains within the efficiency-optimized range.

[0015] However, if the air-fuel mixture approaches the combustion limit, i.e., close to the upper limit but still below it, according to the invention, the fuel supply is adjusted based on the engine speed signal within the transition region near the combustion limit. During this process, the engine speed signal is evaluated, and in particular, the high cyclic fluctuations of each individual cylinder at the combustion limit are balanced with the levels of other engine cylinders by increasing the injection volume. This is characterized by b) above. When the engine speed is detected by the speed sensor, the rotational non-uniformity of the engine can be determined, from which the cyclic fluctuations of each individual cylinder can be inferred. If the cyclic fluctuations of a cylinder increase, the fuel supply to that cylinder is increased to increase the distance from the combustion limit at that cylinder. Since possible differences in the amount of fuel introduced into each cylinder, besides approaching the combustion limit, may also be related to the cause of the cyclic fluctuations, a comparison of the differences between cylinders can be considered in terms of the rail pressure signal as a measure of the actual amount of fuel introduced and the rotational non-uniformity as a measure of the deviation caused by the two possible causes, in order to distinguish between these two possible causes. Therefore, taking into account all the effects on the combustion limits, such as the differences in the amount of fuel metering valves and the possible uneven distribution of cylinder charge, all cylinders are adjusted to the combustion limits as much as possible.

[0016] Only when the combustion limit is reached will the cylinders be selectively shut off to occupy a larger distance from the combustion limit, while simultaneously distributing the amount of fuel required to achieve rated torque to the remaining effective cylinders. As long as the air-fuel ratio should not be at the combustion limit in this operating mode, further pure regulation should be performed by adjusting the fuel supply, whereby distinctions are made according to a) and b) based on the resulting air-fuel ratio.

[0017] In an advantageous embodiment, the method further includes: d) if, after step c), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit, then reducing the engine speed. To maintain this torque, the individualized charge of each individual cylinder can be increased, thus achieving a greater distance from the combustion boundary. Here, the inherent engine speed needs to be considered.

[0018] In an advantageous embodiment, the method further comprises: e) if, after step d), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value, adjusting the ignition angle outside the efficiency-optimized range. The ignition angle of each individual cylinder is only adjusted when the prior measures mentioned in a) to d) above are no longer successful. Here, combustion may become less efficient.

[0019] Steps a) through e) should be understood as the following measures: if the internal combustion engine is to be very close to or directly at the combustion limit, these measures should be performed. From a) to e), these steps are evaluated with progressively decreasing priority, meaning that each measure can be performed sequentially until operation at a sufficient distance from the combustion limit can be achieved.

[0020] The lower limit can be obtained as the difference between the upper limit and the subtrahend ε, where the subtrahend ε is formed by the addition of the air-fuel ratio effects. A symmetrical tolerance is assumed to exist here. The air-fuel ratio effects may include the upper tolerance of the air system's intake pressure, the lower limit / limit deviation of the injector injection mass (approximately 5%), and the upper deviation of the cylinder charge relative to the engine average.

[0021] Additionally, the reasonableness of the air-fuel ratio range calculated in the current air system model can be verified to ensure that the engine is actually operating in the range near the combustion limit (which may be particularly relevant if cylinder deactivation is effective), thereby enabling a clear correspondence between speed non-uniformity and conditions close to the combustion limit.

[0022] The present invention also relates to a controller for controlling an internal combustion engine, particularly a hydrogen engine, having multiple cylinders. The controller has a rail pressure sensor input, a speed sensor input, a calculation unit, and multiple control outputs. The calculation unit is configured to perform the aforementioned method to determine the air-fuel ratio of the internal combustion engine and compare it with predetermined lower and upper limits. The controller is configured to regulate the operation of the internal combustion engine in a cascaded manner by generating and providing control signals at the control outputs as follows:

[0023] a) Once the obtained air-fuel ratio corresponds to the lower limit, the individualized fuel injection quantity of the cylinder is adjusted based on the rail pressure signal.

[0024] b) Once the calculated air-fuel ratio is higher than the lower limit and lower than the upper limit, the individualized fuel injection quantity of the cylinder is adjusted based on the engine speed;

[0025] c) Once the desired air-fuel ratio reaches its upper limit, at least one cylinder is shut off, and the cylinder-specific fuel injection quantity allocated to the remaining cylinders is adjusted according to a) or b), wherein the controller is configured to keep the corresponding ignition angle within the range of efficiency optimization in the above measures a), b) and c).

[0026] In an advantageous implementation, the controller is configured to: d) reduce the engine speed if the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value after c) is performed.

[0027] In an advantageous implementation, the controller is configured to: e) adjust the ignition angle outside the efficiency optimization range if the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value after d) is performed.

[0028] In an advantageous embodiment, the controller is configured to obtain the lower limit value as the difference between the upper limit value and the subtrahend ε, wherein the subtrahend ε is formed by the summation of the effects of the air-fuel ratio.

[0029] In one advantageous embodiment, the controller is configured to perform a simulation of an internal combustion engine, wherein the air-fuel ratio is determined based on the simulation. Attached Figure Description

[0030] Hereinafter, in conjunction with the description of preferred embodiments of the invention, other improvements to the invention are shown in more detail with reference to the accompanying drawings. Embodiments

[0031] The attached diagram shows:

[0032] Figure 1 A schematic diagram illustrating a method for operating an internal combustion engine;

[0033] Figure 2 A block-based diagram illustrating the regulation strategy is shown.

[0034] Figure 3 Exemplary diagrams showing two different operating states and corresponding adjustments are provided.

[0035] Figure 4 A schematic diagram of a system for operating an internal combustion engine is shown. DETAILED DESCRIPTION

[0036] Figure 1A method 2 for operating an internal combustion engine, particularly a hydrogen engine with multiple cylinders, is shown. Method 2 begins by determining an air-fuel ratio 4, after which this air-fuel ratio is compared with predetermined lower and upper limits 6. Subsequently, the operation of the internal combustion engine 8 is regulated by a priority-controlled strategy, wherein this execution is related to the previous comparison with the limits. With decreasing priority, the regulation includes:

[0037] a) Once the obtained air-fuel ratio corresponds to the lower limit, the individualized fuel injection quantity of the 10 cylinders is adjusted based on the rail pressure signal.

[0038] b) Once the calculated air-fuel ratio is higher than the lower limit and lower than the upper limit, the individualized fuel injection quantity of the 12 cylinders is adjusted based on the engine speed.

[0039] c) Once the desired air-fuel ratio reaches the upper limit, shut down at least one cylinder of 14 and adjust the individualized fuel injection amount of 10 or 12 to the remaining cylinders according to a) or b), wherein the corresponding ignition angle is kept within the range of efficiency optimization.

[0040] d) If, after step c), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit, then reduce the engine speed of 16.

[0041] e) If, after step d), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit, then the ignition angle adjustment 18 is adjusted outside the range for efficiency optimization. Determining the air-fuel ratio can include performing a (simplified) simulation model of a 20-cylinder internal combustion engine. In its simplest case, the simulation model can be implemented as a lookup table storing and retrieving the air-fuel ratio obtained experimentally or theoretically.

[0042] Figure 2 A block-based diagram of the adjustment strategy is shown. Block 22 performs the following plausibility verification: whether the calculated air-fuel ratio roughly corresponds to the simulated air-fuel ratio or is near the combustion limit. This can be used as a release condition for subsequent methods.

[0043] Comparison 6 is performed in block 24, which is then fed to the air-fuel ratio λ. 额定 The rated values ​​and the current lower limit values ​​for the current charge quantity of the cylinders, individualized for each cylinder. Deviations are derived from these deviations, which are evaluated in subsequent block 26 and used to prioritize effective measures for operating the internal combustion engine. As previously described, these measures include adjusting the injection quantity for individualized cylinders 10 and 12, shutting off at least one cylinder in 14, reducing the engine speed in 16, and adjusting the ignition angle in 18.

[0044] The lower limit for cylinder individualization is formed in block 28 by a base value 30 used for the current combustion limit and the influence of the air-fuel ratio. The latter is formed by cylinder individualization analysis 32 of the non-uniformity of the speed signal or cylinder pressure signal over multiple cycles and by comparison with the rail pressure signal, and undergoes a cylinder individualization weighting related to the operating point 34.

[0045] Figure 3 Two examples, I and II, illustrate different operating states and corresponding adjustments for an engine with six cylinders Z1 to Z6. In example I, the air-fuel ratio exceeds the lower limit but is below the upper limit, thus the internal combustion engine operates near the combustion limit. Therefore, the main analysis focuses on the engine speed signal and performs a comparison with the rail pressure signal. This is repeated over multiple cycles. This analysis is characterized by block 40. The study of engine speed yields speed inhomogeneity, i.e., cyclic fluctuations, in which cylinders Z2 and Z6 become significant due to instantaneous drops in speed (see graph 36). The rail pressure (see graph 38) behaves identically across all cylinders Z1-Z6, thus the charge levels of these cylinders can be considered equal. As a measure, the combustion limit for cylinders Z2 and Z6 is reduced by 42 (in relation to the load) to adapt to this adjustment, without any of the measures a) to e).

[0046] In Example II, the value is below the lower limit, thus primarily evaluating the rail pressure signal. The rail pressure signal is significant in both cylinders Z2 and Z6. As a measure, the individualized injection quantity of the cylinders is increased based on adjustments related to the rail pressure signal (measure a).

[0047] at last, Figure 4An exemplary diagram is shown of a controller 44 for controlling an internal combustion engine, particularly a hydrogen engine, with multiple cylinders. The controller has a rail pressure sensor input 46, a speed sensor input 48, a calculation unit 50, and multiple control outputs 52. Furthermore, the controller 44 has multiple selectable cylinder pressure inputs 54. The calculation unit 50 is coupled to the inputs 46, 48, and 54 and the control outputs 52 and is configured to determine the air-fuel ratio of the internal combustion engine and compare it with predetermined lower and upper limits. The controller 44 is also configured to regulate operation by generating and providing control signals at the control output 52, such that, once the determined air-fuel ratio corresponds at most to the lower limit, a) the cylinder-individualized fuel injection quantity is adjusted based on the rail pressure signal at the rail pressure sensor input 46, or b) once the determined air-fuel ratio is above the lower limit and below the upper limit, the cylinder-individualized fuel injection quantity is adjusted based on the rotational speed from the speed sensor input 48, or c) once the determined air-fuel ratio reaches the upper limit, at least one cylinder is shut off and the cylinder-individualized fuel injection quantity allocated to the remaining cylinders is adjusted according to a) or b). Here, the controller 44 is configured to maintain the corresponding ignition angles within the range of efficiency optimization in a), b), and c). As previously shown, measures d) and e) can also be performed by the controller 44 in accordance with the determined air-fuel ratio.

Claims

1. A method (2) for operating an internal combustion engine having a plurality of cylinders, in particular a hydrogen engine, comprising: Determining (4) the air-fuel ratio of the internal combustion engine; comparing the determined air-fuel ratio with a predetermined lower limit value and an upper limit value corresponding to a combustion limit (6); The operation of the internal combustion engine is regulated (8) by means of measures acting on the torque according to the following control cascade: a) if the determined air-fuel ratio corresponds at most to the lower limit value, adjusting (10) the cylinder-individualized fuel injection quantity based on a rail pressure signal of the internal combustion engine to achieve equalization of the injection quantities of the plurality of cylinders; b) if the determined air-fuel ratio is above the lower limit value and below the upper limit value in a transition region near the combustion limit, adjusting (12) the cylinder-individualized fuel injection quantity based on the rotational speed of the internal combustion engine to take into account cyclic fluctuations of the plurality of cylinders; c) as soon as the determined air-fuel ratio reaches the upper limit value and thus the combustion limit, at least one cylinder is shut down (14) and the cylinder-individualized fuel injection quantity distributed to the remaining cylinders is adjusted according to measure a) or measure b), in, Within the scope of all measures a), b) or c), the corresponding ignition angle is kept within the efficiency-optimizing range.

2. The method (2) according to claim 1, further comprising: d) if after step c), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value, reducing (16) the engine speed.

3. The method (2) according to claim 2, further comprising: e) if after step d), the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value, adjusting (18) the ignition angle outside the efficiency-optimizing range.

4. The method (2) according to one of the preceding claims, further comprising: The lower limit is obtained as the difference between the upper limit and the subtrahend ε, where The subtrahend ε is formed by the addition of the air-fuel ratio influences.

5. The method (2) according to any one of the preceding claims, wherein: The air-fuel ratio described in (4) is obtained based on the simulation model.

6. A controller (44) for controlling an internal combustion engine having a plurality of cylinders, in particular a hydrogen engine, the controller comprising: Rail pressure sensor input (46); Speed ​​sensor input terminal (48); a computing unit (50); and a plurality of control output terminals (52), in, The calculation unit (50) is designed to determine an air-fuel ratio of the internal combustion engine and to compare the air-fuel ratio with a predetermined lower limit value and an upper limit value corresponding to a combustion limit, and the control unit (44) is designed to execute a measure acting on the torque by generating and providing a control signal at the control output (52) according to the following control cascade: a) if the determined air-fuel ratio corresponds at most to the lower limit value, adjusting (10) the cylinder-individualized fuel injection quantity based on a rail pressure signal of the internal combustion engine to achieve equalization of the injection quantities of the plurality of cylinders; b) if the determined air-fuel ratio is above the lower limit value and below the upper limit value in a transition region near the combustion limit, adjusting (12) the cylinder-individualized fuel injection quantity based on the rotational speed of the internal combustion engine to take into account cyclic fluctuations of the plurality of cylinders; c) as soon as the determined air-fuel ratio reaches the upper limit value and thus the combustion limit, at least one cylinder is shut down (14) and the cylinder-individualized fuel injection quantity distributed to the remaining cylinders is adjusted according to a) or b), The control unit (44) is designed to keep the corresponding ignition angle within an efficiency-optimized range within the scope of all measures a), b) or c).

7. The controller (44) of claim 6, wherein: The controller (44) is configured to: d) reduce (16) the engine speed if the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value after executing c).

8. The controller (44) of claim 7, wherein: The controller (44) is configured to: e) adjust (18) the ignition angle outside the efficiency-optimized range if the air-fuel ratio of each individual cylinder reaches at least 95% of the upper limit value after executing d).

9. The controller (44) according to any one of claims 6 to 8, wherein: The controller (44) is designed to determine the lower limit value as a difference between the upper limit value and a subtrahend ε, wherein the subtrahend ε is formed by adding together the air-fuel ratio influences.

10. The controller (44) according to any one of claims 6 to 9, wherein: The control unit (44) is designed to perform a simulation of the internal combustion engine, wherein the air-fuel ratio is ascertained as a function of the simulation.

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