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

Abstract

The invention relates to a method for operating an internal combustion engine (1) with electric spark ignition, wherein during the operation of the internal combustion engine (1) - a minimum ignition coil charging current for an ignition system (9) of the internal combustion engine (1) is determined, - wherein the ignition system (9) is operated with the minimum ignition coil charging current, wherein - the internal combustion engine (1) is monitored for failure to ignite in at least one combustion chamber (7) of the internal combustion engine (1), and wherein - the ignition coil charging current is increased by a predetermined charging current increment if a lack of combustion is detected in at least one combustion chamber (7) of the internal combustion engine (1).

Description

[0001] The invention relates to a method for operating an internal combustion engine with electric spark ignition, a computer program, a control device for carrying out such a method, and an internal combustion engine with such a control device.

[0002] Spark plugs for electric ignition, especially for use in medium-sized or large internal combustion engines, such as truck engines and larger, particularly medium-speed or low-speed engines, are very expensive and typically require frequent replacement, resulting in high life-cycle costs for such engines. Furthermore, the short replacement intervals lead to frequent engine downtime and thus reduced productivity. Prematurely discarded spark plugs also generate unnecessary waste and lead to an increased demand for precious metals, which is detrimental from an environmental perspective.The ignition coil charging current for such a spark plug is typically set to a so-called "safety value," ensuring that a sufficiently high ignition energy is delivered to the combustion chamber of the internal combustion engine to reliably ignite combustion under all operating conditions and regardless of the spark plug's age. This leads to high wear on the spark plug and consequently a detrimentally short service life. Simply reducing the ignition energy is not an option, however, as this would risk misfires, at least under certain operating conditions or after a certain age of the spark plug. Misfires are unacceptable from the customer's perspective during engine operation.

[0003] US patent 11,879,420 B1 discloses a method for operating an internal combustion engine with electric spark ignition, wherein the engine is monitored for a lack of combustion in at least one combustion chamber. DE 10 2008 000 127 A1 discloses a method for operating an internal combustion engine with electric spark ignition, wherein a minimum ignition coil charging current for an ignition system of the engine is determined during operation, and wherein the ignition system is operated with the minimum ignition coil charging current. DE 10 2008 038 513 A1 and DE 10 2017 128 183 A1 also disclose methods for operating an internal combustion engine with electric spark ignition.

[0004] The invention is therefore based on the objective of creating a method for operating an internal combustion engine with electric spark ignition, a computer program, a control device for carrying out such a method, and an internal combustion engine with such a control device, wherein the aforementioned disadvantages are at least reduced, preferably do not occur.

[0005] The problem is solved by providing a method with the features of claim 1, a computer program with the features of claim 6, a control device with the features of claim 7, and an internal combustion engine with the features of claim 8. Advantageous embodiments are described in the dependent claims.

[0006] The problem is solved in particular by creating a method for operating an internal combustion engine with electric spark ignition, wherein during the operation of the internal combustion engine - a minimum ignition coil charging current is determined for an ignition system of the internal combustion engine, - wherein the ignition system is operated with the minimum ignition coil charging current, wherein - the internal combustion engine is monitored for a lack of combustion in at least one combustion chamber of the internal combustion engine, and wherein - the ignition coil charging current is increased by a predetermined charging current increment if a lack of combustion is detected in at least one combustion chamber of the internal combustion engine.

[0007] By determining the minimum ignition coil charging current – ​​also known as the minimum ignition coil charging current – ​​and operating the ignition system with this minimum current until a lack of combustion is detected, the ignition system is advantageously operated in a controlled or regulated manner with the lowest possible ignition coil charging current and thus the lowest possible ignition energy. This has a beneficial effect on the service life and lifespan of the ignition system's spark plugs, preventing premature replacement and extending maintenance intervals. This increases productivity, saves costs, and reduces waste and precious metal requirements.At the same time, it is ensured that misfires, i.e., ignition failures, occur only sporadically, with immediate countermeasures being taken by increasing the ignition coil charging current by the predetermined charging current increment.

[0008] The minimum ignition coil charging current is, in particular, an ignition coil charging current at which—especially just barely—no misfire occurs. Preferably, the ignition energy introduced into a combustion chamber by the minimum ignition coil charging current is just sufficient to initiate combustion. In particular, the minimum ignition coil charging current is just above a misfire charging current at which combustion would fail to occur in at least one combustion chamber of the internal combustion engine; more specifically, it is above the misfire charging current by a predetermined stroke increment.

[0009] In particular, the internal combustion engine is monitored in all combustion chambers for a lack of combustion; that is to say, all combustion chambers of the internal combustion engine are monitored to see if combustion fails to occur, i.e., if an ignition misfire occurs in the respective combustion chamber.

[0010] The predetermined charging current increment is preferably parameterizable.

[0011] It is possible that not every detection of a missing combustion results in an immediate increase in the ignition coil charging current; rather, in one embodiment, the ignition coil charging current is only increased after a parameterizable number of missing combustions, or the missing or occurring combustions in a plurality of operating cycles of an affected combustion chamber are statistically evaluated, whereby the combustion statistics obtained are used to decide whether the ignition coil charging current is increased.

[0012] In one embodiment, a failure to combust is detected based on at least one parameter, wherein the at least one parameter is selected from a group consisting of: a rotational irregularity, torsional vibration, or speed variance, in particular of a crankshaft or camshaft of the internal combustion engine; a power signal of the internal combustion engine; a structure-borne sound signal; a combustion chamber pressure signal; an exhaust gas temperature; and a combination of at least two of the aforementioned parameters. Due to the inherent inertia of an exhaust gas temperature sensor, the exhaust gas temperature intrinsically represents a statistic of past combustion events.

[0013] At the beginning of the process, before the ignition coil charging current is first reduced towards the minimum ignition coil charging current, the ignition coils are preferably energized with a safe value for the ignition coil charging current at which it is ensured that no ignition misfires occur; this safe value can in particular correspond to a maximum ignition energy.

[0014] According to the invention, the minimum ignition coil charging current is determined by reducing the ignition coil charging current - in particular starting from the safe value - until - at the intermittent charging current - a lack of combustion is detected in a combustion chamber of the internal combustion engine.

[0015] In one embodiment, the ignition coil charging current is gradually reduced to determine the minimum ignition coil charging current, in one configuration by a predetermined charging current decrement. The predetermined charging current decrement is preferably parameterizable.

[0016] In one embodiment, the predetermined charging current decrement is equal in magnitude to the predetermined charging current increment. In another embodiment, the predetermined charging current decrement can differ in magnitude from the predetermined charging current increment.

[0017] Preferably, in this method, when a lack of combustion is detected at the intermittent charging current, the ignition coil charging current is increased by a predetermined increment, starting from the intermittent charging current at which the lack of combustion is detected. This is continued, if necessary, until no further lack of combustion is detected. In one embodiment, the resulting ignition coil charging current—after the ignition coil charging current has been increased once or several times by the predetermined increment—is the minimum ignition coil charging current, or, put another way, the minimum ignition coil charging current is obtained as this resulting ignition coil charging current.

[0018] In one embodiment, the ignition coil charging current can also be increased by a predetermined stroke increment, starting from the misfire charging current, thereby obtaining the minimum ignition coil charging current. This predetermined stroke increment is preferably parameterizable. The predetermined stroke increment can be identical to or have the same value as the predetermined charging current increment; however, the predetermined stroke increment can also differ from the predetermined charging current increment. The increase by the predetermined stroke increment can also be performed once or multiple times, depending on the choice of the predetermined stroke increment, particularly until no further misfires are detected. The resulting ignition coil charging current is then considered the minimum ignition coil charging current.

[0019] According to a further development of the invention, the minimum ignition coil charging current is determined only if at least one predetermined determination condition is met. Advantageously, this ensures that the ignition coil charging current is not reduced under conditions or operating phases of the internal combustion engine where this would be detrimental or at least not useful, for example, during warm-up operation directly after the internal combustion engine has been started or in transient operating conditions.

[0020] In one embodiment, the at least one predetermined determination condition is preferably selected from a group consisting of: an instantaneous load of the internal combustion engine is at least as high as a predetermined limit load; an instantaneous temperature value of the internal combustion engine is at least as high as a predetermined limit temperature; no failure of combustion is detected; the internal combustion engine is in a steady-state load point; and a combination of at least two of the aforementioned determination conditions. In particular, each of these determination conditions, but especially also in combination with one another, ensures that the minimum ignition coil charging current is only determined if suitable conditions and, in particular, a suitable operating phase of the internal combustion engine are present.

[0021] In one embodiment, the current temperature value is an exhaust gas temperature, a cooling water temperature and / or a lubricant temperature of the internal combustion engine.

[0022] According to a further development of the invention, the determination of the minimum ignition coil charging current is carried out repeatedly. Advantageously, the minimum ignition coil charging current used then automatically adapts to changing operating conditions of the internal combustion engine, in particular to different load points or operating states. Advantageously, the determination of the minimum ignition coil charging current is carried out repeatedly throughout the entire operation of the internal combustion engine.

[0023] In one embodiment, the minimum ignition coil charging current is determined at predetermined time intervals. The time interval to be considered is preferably parameterizable. Advantageously, this prevents excessively rapid changes in the minimum ignition coil charging current and thus a potentially unstable operation of the internal combustion engine.

[0024] In one embodiment, a predetermined waiting period is allowed to elapse between two reduction steps for lowering the ignition coil charging current – ​​in particular by the predetermined charging current decrement. This represents a particularly simple and suitable measure for determining the minimum ignition coil charging current at predetermined time intervals and / or for preventing an excessively rapid change in the minimum ignition coil charging current. The predetermined waiting period is preferably parameterizable.

[0025] According to a further development of the invention, it is provided that an ignition system is used which has an assigned ignition coil for each combustion chamber of the internal combustion engine, which is variably, in particular pulse width modulated, supplied with current, wherein optionally the minimum ignition coil charging current is an initial ignition coil charging current which is globally specified for the internal combustion engine.

[0026] The fact that the ignition coil is powered by pulse-width modulation means, in particular, that the ignition coil is charged by at least one voltage pulse whose pulse height (in units of electrical voltage) and pulse width (in units of time) can be set, and preferably predetermined. Furthermore, a number of voltage pulses can preferably be predetermined with which the ignition coil is operated to initiate a spark discharge and during the spark discharge. A time interval between the voltage pulses can also preferably be predetermined. The ignition coil charging current results, in particular, from the pulse height and pulse width of a voltage pulse.

[0027] The ignition system is preferably configured such that a spark discharge occurs during a first, initial voltage pulse – which corresponds in particular to a charging phase – whereby the spark discharge can be maintained for a longer period the more successive voltage pulses are applied to the respective ignition coil; in particular, a so-called – time-averaged – holding current during the spark discharge results from the sequence of successive voltage pulses. In the context of the present technical teaching, an initial ignition coil charging current is in particular that ignition coil charging current resulting from the first, initial voltage pulse.

[0028] In one embodiment, the ignition system is designed such that the pulse height and pulse width of at least all subsequent voltage pulses after the first, initial voltage pulse of a discharge event can be individually set for each ignition coil assigned to a combustion chamber of a plurality of combustion chambers. In particular, the pulse width of the initial voltage pulse, however, can optionally only be set globally, for all ignition coils together, i.e., for all combustion chambers together. Accordingly, the initial ignition coil charging current can then also only be set globally for all ignition coils together.

[0029] The minimum ignition coil charging current is preferably the initial ignition coil charging current. This is preferably set by specifying the initial pulse width of the initial voltage pulse.

[0030] The problem is also solved by creating a computer program that includes machine-readable instructions which, when the computer program is executed by a computing device, in particular a control device of an internal combustion engine, cause the computing device to execute a method according to the invention or a method according to one or more of the embodiments described above. The advantages that arise in connection with the computer program are those already explained in connection with the method.

[0031] The invention also includes a machine-readable, in particular electronic, storage medium on which a computer program according to the invention or a computer program according to one or more of the embodiments described above is stored.

[0032] The problem is also solved by creating a control device for an internal combustion engine, which is configured to carry out a method according to the invention or a method according to one or more of the embodiments described above. The advantages that arise in connection with the control device are particularly those already explained in connection with the method or the computer program.

[0033] The problem is also solved by creating an internal combustion engine with an ignition system configured for electric spark ignition and a control device according to the invention or a control device according to one or more of the embodiments described above, wherein the control device is operatively connected to the ignition system and configured to control the ignition system. In connection with the internal combustion engine, the advantages that have already been explained in connection with the method, the computer program, or the control device become particularly apparent.

[0034] The control device is preferably operatively connected to at least one sensor for detecting misfires, i.e., ignition failures, in at least one combustion chamber of the internal combustion engine. The at least one sensor is preferably configured to detect at least one parameter selected from the group consisting of: a rotational irregularity, torsional vibration, or speed variance, in particular of a crankshaft or camshaft of the internal combustion engine; a power signal from the internal combustion engine; a structure-borne sound signal; a combustion chamber pressure signal; an exhaust gas temperature; and a combination of at least two of the aforementioned parameters. In one embodiment, it is configured as a cylinder pressure sensor, a structure-borne sound sensor, or a speed sensor.

[0035] According to a further development of the invention, the internal combustion engine is designed as an engine selected from a group consisting of a gasoline engine, a gas engine, a multi-fuel engine, and a combination of at least two of the aforementioned engines.

[0036] In the context of this technical teaching, a multi-fuel engine is understood to be, in particular, an engine that can be operated with at least two different fuels, which can be introduced into the combustion chamber of the engine in different proportions. Specifically, such a multi-fuel engine can be designed as a dual-fuel engine or as a bi-fuel engine.

[0037] The invention will be explained in more detail below with reference to the drawing. The drawing shows: Fig. 1 a schematic representation of an embodiment of an internal combustion engine with an embodiment of a control device; Fig. 2 a schematic representation of an embodiment of a method for operating the internal combustion engine in the form of a flowchart, and Fig. 3 Details of the control of an ignition system according to the procedure.

[0038] Fig. Figure 1 shows a schematic representation of an embodiment of an internal combustion engine 1 with an embodiment of a control device 3.

[0039] For clarity, elements depicted multiple times in a figure are each marked with a reference symbol only once. Furthermore, identical and functionally equivalent elements in all figures are marked with the same reference symbol, thus referring back to the preceding description.

[0040] The internal combustion engine 1 has an engine block 5 with at least one combustion chamber 7, where six combustion chambers 7 are shown schematically here. The internal combustion engine 1 can, in principle, have any number of combustion chambers 7.

[0041] Preferably, the internal combustion engine 1 is designed as a reciprocating piston engine or as a rotary piston engine.

[0042] The control device 3 is operatively connected to an ignition system 9, which has an ignition coil 11 for each of the combustion chambers 7 and a spark plug 13 electrically connected to the ignition coil 11. The control device 3 is configured to control the ignition coils 11 – directly or indirectly – that is, to energize them – in particular by pulse-width modulation – in order to ignite spark discharges at the spark plugs 13 in the combustion chambers 7 for electric spark ignition. A separate ignition control unit can be provided, which controls the ignition coils 11 and is itself controlled by the control device 3; in particular, such an ignition control unit can be part of the ignition system 9. However, it is also possible for the ignition control to be integrated into the control device 3.

[0043] Furthermore, the control device 3 is operatively connected to at least one sensor 15 for detecting a lack of combustion, i.e. misfires, in the combustion chambers 7, wherein the at least one sensor 15 can be designed, for example, as a cylinder pressure sensor, as a structure-borne sound sensor or as a speed sensor.

[0044] The control device 3 is also configured to carry out a procedure described in more detail below.

[0045] Fig. Figure 2 shows a schematic representation of an embodiment of a method for operating the internal combustion engine 1 in the form of a flowchart.

[0046] As part of the procedure, a minimum ignition coil charging current for the ignition system 9 of the internal combustion engine 1 is determined, and the ignition system 9 is operated with this minimum charging current; that is, the ignition coils 11 are energized with this minimum charging current. The internal combustion engine 1 is monitored for a lack of combustion in the combustion chambers 7 by means of sensor 15, and the ignition coil charging current is increased by a predetermined increment if a lack of combustion is detected in a combustion chamber 7.

[0047] Specifically, the process begins with step S1. In a second step S2, a timer is started for which a predetermined waiting time is set or can be specified. The timer counts down the time in the usual way until the predetermined waiting time has elapsed, or in other words, expired; once the predetermined waiting time has elapsed, the timer has expired.

[0048] At the beginning of the process, before the ignition coil charging current is reduced for the first time, the ignition coils 11 are preferably energized with a safe value for the ignition coil charging current at which it is ensured that no ignition misfires occur; this safe value can in particular correspond to a maximum ignition energy.

[0049] In a third step, S3, it is checked whether a first condition is met. Specifically, the first condition is a combination of two predetermined determination conditions: first, whether the instantaneous load of the internal combustion engine 1 is at least as high as a predetermined limit load; and second, whether the instantaneous temperature value – in particular, an exhaust gas temperature, a coolant temperature, and / or a lubricant temperature – of the internal combustion engine 1 is at least as high as a predetermined limit temperature. If this is not the case, i.e., if at least one of the first and second predetermined determination conditions is not met, the third step, S3, is repeated.In this way, it is ensured in particular that the further process steps are carried out only when the internal combustion engine 1 is at operating temperature and has at least the predetermined limit load.

[0050] In a fourth step S4 – as a third predetermined determination condition – it is checked whether combustion fails to occur in at least one of the combustion chambers 7. If this is the case, in a fifth step S5 the ignition coil charging current is increased, in particular by a predetermined charging current increment.

[0051] If, however, no lack of combustion is detected in the fourth step S4, a sixth step S6 checks whether a second condition is met. Specifically, the second condition is a fourth predetermined determination condition, namely whether the internal combustion engine 1 is operating at a steady load point. This ensures that the subsequent process steps are not carried out at a transient operating point. If the second condition is not met, the process continues in the third step S3.

[0052] If the second condition is met, meaning that the internal combustion engine 1 is at a steady load point, a seventh step, S7, checks whether the timer has expired. If not, the procedure continues in the third step, S3.

[0053] If the timer expires, it is restarted in an eighth step S8, and in a ninth step S9 the ignition coil charging current is reduced, specifically by a predetermined charging current decrement. The process then continues in the third step S3.

[0054] In particular, the process is initiated with the first step S1 and the second step S2 when the internal combustion engine 1 is started up, and the third to ninth steps S3 to S9 run continuously during the operation of the internal combustion engine 1 in the manner described, in particular until the internal combustion engine 1 is switched off. In this way, the minimum ignition coil charging current is always appropriately adapted to the currently prevailing steady-state operating point of the internal combustion engine 1. In particular, the minimum ignition coil charging current is continuously updated in this way and is essentially always recalculated, especially after each new failure of combustion and increase in the fifth step S5.

[0055] The minimum ignition coil charging current is determined in particular by reducing the ignition coil charging current until a lack of combustion is detected in a combustion chamber 7 of the internal combustion engine 1 in the event of an intermittent charging current.

[0056] Fig. Figure 3 shows details of the control of the ignition system 9 according to the procedure.

[0057] In a) a first diagram is shown, which shows various electrical quantities of the ignition system 9 for an ignition event in one of the combustion chambers 7 as a function of time t.

[0058] A voltage pulse P1 is discernible, with which the ignition coil 11 assigned to the combustion chamber 7 is actuated; furthermore, an ignition coil charging current I is visible. L shown, which during the voltage pulse P1, starting from a rising edge to a falling edge of the voltage pulse P1, to the value of the minimum ignition coil charging current I L,minincreases. The minimum ignition coil charging current I L,min is determined by the pulse height (in units of voltage) and the pulse width (in units of time) of the voltage pulse P1.

[0059] Furthermore, a voltage drop U across the ignition electrodes of the spark plug 13 is present. Z The diagram shows the voltage that initially rises with increasing ignition coil charging current – ​​here with a negative sign – and then drops when a breakdown voltage is reached, at which point the spark discharge ignites. Since ignition coil 11 is only driven by the single voltage pulse P1 in this example, the ignition coil charging current falls after the falling edge of voltage pulse P1, starting from the minimum ignition coil charging current I. L,min off, and the spark discharge only burns for a comparatively short time.

[0060] It also becomes clear that the term "minimum ignition coil charging current" in the present context does not refer to an extremum of the ignition coil charging current curve over time - rather, the minimum ignition coil charging current I L,min Here, the maximum of this curve is not shown, but the term "minimal" refers to the fact that at a value smaller than the minimum ignition coil charging current I L,min no safe combustion in the combustion chambers 7 would be guaranteed and misfires would occur; the minimum ignition coil charging current is therefore “minimal” insofar as it cannot be reduced further without jeopardizing the combustion stability in the combustion chambers 7.

[0061] In b), a second diagram is shown with the same electrical quantities as a function of time t as in a), except that in this case the ignition coil 11 is supplied with a plurality of voltage pulses P1 to P12, with the spark discharge igniting during the first, initial voltage pulse P1. Here too, the minimum ignition coil charging current I L,min determined by the initial voltage pulse P1; however, in contrast to the example shown in a), the spark discharge is maintained for a longer period by keeping the ignition coil charging current at a higher level – the holding current – ​​through recharging of ignition coil 11 with the subsequent voltage pulses P2 to P12. In particular, the minimum ignition coil charging current I L,min the initial ignition coil charging current, which is established due to the first, initial voltage pulse P1.

[0062] The number of voltage pulses can preferably be specified. Furthermore, a time interval between the voltage pulses can preferably be specified.

[0063] Preferably, the pulse height and pulse width of all subsequent voltage pulses P2 to P12 – or generally PN with N > 1 – after the first, initial voltage pulse P1 can be individually set for each ignition coil 11. The pulse width of the initial voltage pulse P1, however, can preferably only be set globally, i.e., for all ignition coils 11 together. The initial ignition coil charging current I can also be set accordingly. L,min Only global settings for all ignition coils 11 can be set.

Claims

[1] Method for operating an internal combustion engine (1) with electric spark ignition, wherein in the operation of the internal combustion engine (1) - a minimum ignition coil charging current for an ignition system (9) of the internal combustion engine (1) is determined, - wherein the ignition system (9) is operated with the minimum ignition coil charging current, wherein - the internal combustion engine (1) is monitored for failure to ignite in at least one combustion chamber (7) of the internal combustion engine (1), and wherein - the ignition coil charging current is increased by a predetermined charging current increment if a lack of combustion is detected in at least one combustion chamber (7) of the internal combustion engine (1), wherein - the minimum ignition coil charging current is determined by reducing the ignition coil charging current until a lack of combustion is detected in a combustion chamber (7) of the internal combustion engine (1). [2] Method according to claim 1, wherein the minimum ignition coil charging current is determined by gradually reducing the ignition coil charging current until the absence of combustion in a combustion chamber (7) of the internal combustion engine (1) is detected. [3] Method according to one of the preceding claims, wherein the minimum ignition coil charging current is determined only if at least one predetermined determination condition is met. [4] Method according to one of the preceding claims, wherein the determination of the minimum ignition coil charging current is carried out repeatedly. [5] Method according to one of the preceding claims, wherein an ignition system (9) is used which has an associated ignition coil (11) for each combustion chamber (7) of the internal combustion engine (1), which is variably energized. [6] Computer program comprising instructions which, when the computer program is executed by a computing device, cause the computing device to execute a method according to any one of claims 1 to 5. [7] Control device for an internal combustion engine (1), configured to carry out a method according to any one of claims 1 to 5. [8] Internal combustion engine (1) with an ignition system (9) designed for electric spark ignition and a control device (3) according to claim 7, wherein the control device (3) is operatively connected to the ignition system (9) and is designed to control the ignition system (9). [9] Internal combustion engine (1) according to claim 8, wherein the internal combustion engine (1) is designed as an engine selected from a group consisting of a gasoline engine, a gas engine, a multi-fuel engine and a combination of at least two of the aforementioned engines.

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