Device, method and computer program product for controlling the start of an internal combustion engine as well as internal combustion engine

Abstract

Control unit (11) for controlling the start of an internal combustion engine having at least one cylinder (100), at least one main combustion chamber (1), at least one intake port (4), at least one main fuel injector (8, 9) and at least one ignition device (10) configured to ignite an air / fuel mixture inside the main combustion chamber (1), wherein the ignition device (10) comprises a spark plug (10a), a pre-chamber injector nozzle (10b) and a pre-chamber (10c) which is connected to the main combustion chamber (1) via at least one opening (10e) in a pre-chamber wall (10d), wherein the control unit (11) is configured to control the ignition device (10) to perform a pre-chamber heating operation by injecting a predetermined amount of fuel into the pre-chamber (10c) and igniting an air / fuel mixture therein, while the main fuel injector (8, 9) is deactivated during at least one first engine cycle following an engine start request.

Description

[0001] The present invention relates to a control unit and a method for controlling the start of an internal combustion engine in order to reduce cold start emissions, in particular particulate emissions, wherein the internal combustion engine is equipped with an ignition device having a fuel-supplied pre-chamber to ignite an air / fuel mixture in a main combustion chamber.

[0002] To improve the combustion efficiency of an internal combustion engine without increasing nitrogen oxide emissions, it is advantageous to burn a very lean air / fuel mixture with an air / fuel ratio λ > 2. To ensure stable ignition and combustion of such an extremely lean mixture, the use of an ignition system with a fuel-supplied pre-chamber is beneficial. The high ignition energy of such an ignition system is provided by pre-combustion taking place in the pre-chamber. This pre-combustion is initiated by injecting a small amount of fuel into the pre-chamber and igniting the resulting air / fuel mixture within it.Since the pre-chamber is connected to the main combustion chamber via several small openings, the combustion within the pre-chamber produces multiple reactive jets that enter the main combustion chamber and ignite the air / fuel mixture there. These reactive jets typically cover the entire main combustion chamber, thus providing multiple ignition points and ensuring reliable ignition of the lean air / fuel mixture.

[0003] During engine start-up, however, a pre-chamber ignition system can cause disadvantages in terms of starting performance and emissions, as a low temperature leads to unfavorable ignition and combustion conditions within the pre-chamber. When the engine is below operating temperature, the fuel injected into the pre-chamber cannot vaporize properly and instead accumulates on the pre-chamber wall (wall wetting). Consequently, incomplete pre-chamber combustion occurs, and the reactivity of the jets is insufficient to fully ignite the air / fuel mixture in the main combustion chamber. As a result, the engine either fails to start at all or at least produces a high level of hydrocarbon and particulate emissions. Furthermore, wall wetting within the pre-chamber can lead to fuel deposits, which can also cause particulate emissions.A high level of particulate emissions during engine start-up can lead to serious problems with regard to real-world driving emissions (RDE) and cold-start emissions tests at -7 °C. Particulate emissions during engine start-up play a particularly important role in hybrid vehicles, where the internal combustion engine switches on and off several times during operation.

[0004] Patent literature 1: US 2018 / 0 010 536 A1

[0005] Patent literature 1 describes a method for starting an internal combustion engine with an ignition device having a fuel-supplied prechamber by preheating the latter before injecting fuel into the main combustion chamber. The preheating includes injecting fuel into the prechamber and igniting the air / fuel mixture therein before fuel is injected into the main combustion chamber. However, the prechamber preheating is performed before a piston compression stroke or before a crankshaft movement. Consequently, the preheating prechamber combustion must be carried out under poor combustion conditions, since the pressure and temperature in the prechamber are low at this time. Therefore, it is likely that the heating effect of such prechamber combustion is not strong enough to effectively reduce undesirable hydrocarbon and particulate emissions during engine start-up.

[0006] DE 10 2017 125 946 A1 discloses a prechamber ignition system comprising a prechamber extending into a combustion chamber, a piston projection shaped to fit through a lower opening of the prechamber, and a plurality of openings formed by a side wall of the prechamber. A method for the prechamber ignition system involves setting an ignition timing within the prechamber and pressing the projection into the prechamber to ignite the air / fuel mixture within a main chamber.

[0007] DE 10 2013 214 145 B3 relates to an ignition arrangement comprising an ignition device for generating at least one ignition spark, a pre-chamber, and a heating device, wherein the heating device is configured to heat gas located in the pre-chamber and / or walls of the pre-chamber, and wherein the heating device is a glow plug.

[0008] Therefore, the technical problem of the present invention is the reduction of cold-start emissions, in particular particulate emissions, of an internal combustion engine with an ignition device having a fuel-supplied pre-chamber. The technical problem described above is solved by the subject matter according to the independent claims. Furthermore, preferred embodiments are described by the dependent claims.

[0009] The subject matter described and claimed herein relates in particular to at least one control unit and a method for controlling the starting of an internal combustion engine (or hereinafter referred to as "engine"), wherein the internal combustion engine may have at least one cylinder, at least one main combustion chamber, at least one intake port, at least one main fuel injector and / or at least one ignition device configured to ignite an air / fuel mixture within the main combustion chamber, wherein the ignition device may comprise a spark plug, a pre-chamber fuel injector and a pre-chamber which may be separated from the main combustion chamber and may be connected to the main combustion chamber fluid-wise via at least one opening in a pre-chamber wall.The at least one control unit can control the ignition device to perform a pre-chamber heating process by injecting a predetermined amount of fuel into the pre-chamber and igniting the air / fuel mixture therein, while the main fuel injector is deactivated during at least one first engine cycle following an engine start request.

[0010] In other words, at least two engine revolutions are allocated during which the pre-chamber heating process can be carried out before the main combustion begins. This allows sufficient time for the predetermined amount of injected fuel to vaporize and mix with the intake air within the pre-chamber, resulting in a homogeneous air / fuel mixture. A homogeneous air / fuel mixture improves the ignitability of the pre-chamber load and reduces the formation of particulate emissions due to rich zones within the mixture. Furthermore, reserving a full engine cycle for the pre-chamber heating process offers a high degree of flexibility, allowing for the selection of an optimal timing for pre-chamber combustion.

[0011] Preferably, the at least one main fuel injector of the engine is arranged such that the fuel can be injected directly into the main combustion chamber. Alternatively or additionally, the at least one main fuel injector can be arranged such that the fuel is injected into the intake port. In this case, it may be preferred to have at least one intake port per cylinder. If the fuel is injected into the intake port or the combustion chamber at an injection pressure above 15 bar, the main fuel injector can be designed as a high-pressure fuel injector, for example, as an electro-hydraulic or piezoelectric fuel injector. If the fuel is injected into the intake port or the combustion chamber at an injection pressure below 15 bar, the main fuel injector can be designed as a low-pressure fuel injector.The fuel injected through the main fuel injector can be any type of fuel suitable for a spark-ignition combustion process, such as gasoline, ethanol, CNG, LPG, hydrogen, dimethyl carbonate, and so on. The internal combustion engine can preferably be a gasoline or gas engine.

[0012] The prechamber of the ignition device can be designed, for example, in a hemispherical, conical, or cylindrical shape. Combinations of a hemispherical shape with a cylindrical, conical, or any other suitable shape are also possible. Preferably, a cylindrical prechamber can be used, wherein the cylindrical diameter may be narrowed along a longitudinal direction of the prechamber. This can allow sufficient space to be provided in the upper part of the prechamber to introduce the spark and fuel without increasing the volume of the prechamber more than necessary.

[0013] The larger the prechamber volume, the greater the ignition energy provided to ignite the air / fuel mixture in the main combustion chamber. On the other hand, a large prechamber volume reduces the engine's compression ratio by increasing the overall combustion chamber compression volume, since at least part of the prechamber should be integrated into the cylinder head to prevent unwanted pre-ignition, which can occur if the prechamber protrudes too far into the main combustion chamber. Therefore, the prechamber volume should be selected within a range that provides the best compromise between the various requirements described above. Preferably, the prechamber volume can be in the range of 1% to 5% of the main combustion chamber compression volume, and most preferably in the range of 2% to 4% of the main combustion chamber compression volume.

[0014] The prechamber can have at least one opening to provide a fluid connection between the prechamber and the main combustion chamber. Preferably, several openings can be arranged in the prechamber wall. The number, orientation, and geometry of these openings can have a significant influence on the formation of reactive jets and their distribution in the main combustion chamber.

[0015] Preferably, the prechamber can have several side openings arranged circumferentially at a specific angle to a longitudinal axis of the prechamber. The number of side openings is preferably in the range of 2 to 10 and most preferably in the range of 4 to 8. The angle between a central axis of the side openings and the longitudinal axis of the prechamber is preferably in the range of 10° to 90° and most preferably in the range of 20° to 70°.

[0016] The side openings can preferably be distributed at equal intervals. Alternatively, depending on the geometry of the main combustion chamber, the side openings can be arranged at different intervals, for example in two groups arranged symmetrically to a transverse axis of the pre-chamber.

[0017] Furthermore, but not necessarily, the pre-chamber may have a central upward opening to further improve the introduction of a fresh mixture of fresh air into the pre-chamber, which usually takes place during a compression cycle of the internal combustion engine.

[0018] The openings are so small that flame quenching of the prechamber combustion occurs within them, so that only combustion products leave the prechamber and enter the main combustion chamber. The smaller the opening diameter, the higher the pressure within the prechamber and the higher the velocity of the reactive jets for the same number of openings. Regarding preheating the prechamber, a larger opening diameter can be advantageous to avoid wall heat losses caused by the increased pressure within the prechamber when smaller openings are used. The diameter of the openings is preferably in the range of 0.8 mm to 3 mm and most preferably in the range of 0.9 mm to 1.6 mm.

[0019] The spark plug and the pre-chamber fuel injector, or at least parts thereof, are connected to the interior of the pre-chamber, allowing a spark and fuel to be introduced / injected into the pre-chamber. The ignition system may also include more than one spark plug, more than one pre-chamber fuel injector, and more than one pre-chamber. Furthermore, the internal combustion engine may have one or more ignition systems.

[0020] Preferably, the spark plug is electrically connected to an ignition coil that provides a high voltage to initiate spark ignition in the pre-chamber. The ignition coil can be integrated into the ignition device or positioned remotely from it. The spark plug and the ignition coil form the spark ignition device, which preferably offers variable spark duration and multi-spark ignition.

[0021] The pre-chamber fuel injector can preferably be designed as a high-pressure fuel injector, particularly when liquid fuel is injected into the pre-chamber to improve fuel atomization. In this case, the pre-chamber fuel injector can be designed as an electro-hydraulic or piezoelectric fuel injector. Alternatively or additionally, a low-pressure fuel injector can be integrated into the ignition system.

[0022] The fuel injected into the prechamber can be the same type or a different type of fuel used for main fuel injection. Particularly when preheating the prechamber, a more readily ignitable fuel can be advantageous for initiating prechamber combustion even under difficult ignition conditions.

[0023] The predetermined amount of fuel injected into the prechamber depends on the amount of air available within it. Since the air / fuel ratio of the prechamber mixture suitable for prechamber heating is preferably in the range of 0.85 < λ < 1, the corresponding predetermined amount of fuel is derived from the available air mass within the prechamber, which depends primarily on the prechamber volume and the cylinder pressure. The prechamber volume is a constant value that can be determined based on the size of the compression volume of the main combustion chamber. The cylinder pressure can preferably be measured using a cylinder pressure sensor. Alternatively or additionally, the cylinder pressure during prechamber heating can be estimated based on calculations performed in the control unit, for example, as a function of the intake pressure and the engine speed.Therefore, the predetermined amount of fuel injected into the pre-chamber can be determined with high accuracy.

[0024] The at least one control unit can be integrated into the internal combustion engine, or it can alternatively be located somewhere within the vehicle remote from the engine. The control unit and the engine can be connected via one or more signal lines. The control unit can be the engine control unit (ECU) or a separate control device. There can be multiple control units, each capable of controlling subsets of the controlled actuators. For example, one control unit might control only the main fuel injectors, another only the ignition devices, and so on.

[0025] Preferably, the control unit can control the ignition device to perform the pre-chamber heating process during a compression stroke of at least the first engine cycle following an engine start request, with the main fuel injector being deactivated throughout the entire engine cycle(s) in which the pre-chamber heating process takes place. The control unit can be configured to control the ignition device to perform the pre-chamber heating process by activating the pre-chamber fuel injector to inject the predetermined amount of fuel into the pre-chamber and subsequently triggering the spark plug to ignite the air / fuel mixture therein.

[0026] As previously mentioned, reserving an entire engine cycle for pre-chamber heating allows for selecting the optimal time for this process. By considering the various engine strokes, the compression stroke can provide the best pressure and temperature conditions for pre-chamber heating. Even if only a limited time is available for mixture formation during the compression stroke, the constant increase in pressure and temperature significantly reduces the time required to create an ignitable mixture within the pre-chamber. Overall, the benefits of increasing pressure and temperature clearly outweigh the time constraint on mixture formation. Furthermore, the increased pressure and temperature at the end of the compression stroke accelerate the subsequent combustion process, thus increasing heat release within the pre-chamber.Therefore, the amount of fuel injected to achieve the desired temperature increase in the prechamber can be reduced. In summary, performing the prechamber heating process during the compression stroke leads to reliable ignition and efficient combustion of the prechamber load, thus effectively increasing the prechamber temperature.

[0027] Furthermore, the control unit can control the ignition device to perform multiple pre-chamber heating cycles during at least the first engine cycle after the engine start request, until the pre-chamber wall temperature exceeds a predetermined temperature. Particularly at low engine temperatures, a single pre-chamber heating cycle might not be sufficient to adequately heat the pre-chamber. In such a case, further heating cycles can be performed during the first engine cycle, preferably during the compression stroke. For example, if an initial heating cycle were to occur at the beginning of the compression stroke, a further heating cycle could be initiated at the end of the compression stroke. Due to the upward movement of the piston after the initial pre-chamber combustion, fresh air can be introduced into the pre-chamber, allowing an ignitable air / fuel mixture to be generated more than once.

[0028] The prechamber wall temperature can be used as a reference temperature to determine whether the prechamber is sufficiently heated to initiate the first main combustion. The wall temperature should reach a value that allows rapid vaporization of the wall film to prevent particulate emissions caused by fuel deposits in the prechamber. Furthermore, the prechamber temperature should be suitable for effective pre-combustion to generate reactive jets that enable complete ignition and combustion of the mixture in the main combustion chamber, even at a low engine temperature. A prechamber wall temperature threshold that must be exceeded to terminate the prechamber heating process may depend on the type of fuel injected into the prechamber. In the case of gasoline, the prechamber wall temperature may preferably be 85 °C and most preferably 90 °C.Preferably, the wall temperature of the prechamber can be measured with a temperature sensor permanently attached to the prechamber wall. Alternatively, the temperature sensor can be used only during a test phase in which the prechamber heating processes are carried out under all relevant limit conditions. During the test phase, the temperature sensor can measure the increase in prechamber wall temperature as a function of prechamber combustion, for example, at different engine temperatures, different air / fuel ratios in the prechamber, different injection pressures of the fuel injected into the prechamber, and so on. The measured temperature increase of the prechamber wall can then be stored in the control unit as characteristic curves or graphs as a function of parameters that are continuously measured or calculated by the control unit, such as...Intake air temperature, engine coolant temperature, intake air mass, and intake pressure. Alternatively or additionally, a pressure sensor can be used in the prechamber, for example, using a pressure-measuring spark plug that incorporates a pressure sensor next to the central electrode. Measuring the pressure rise in the prechamber allows for an estimation of the heat release within it and, consequently, the provision of a good correlation with the temperature rise of the wall temperature.

[0029] If the prechamber wall temperature does not reach the predetermined wall temperature after an initial prechamber heating cycle, the control unit can control the ignition device to perform prechamber heating cycles during several engine cycles following the engine start request until the prechamber wall temperature exceeds the predetermined temperature. In this case, the procedures described above can also be performed, namely to carry out multiple fuel injections into the prechamber in combination with one or more ignitions per prechamber heating cycle and / or multiple prechamber heating cycles per engine cycle. The maximum number of prechamber heating cycles is preferably 5 cycles and most preferably 3 cycles to avoid an undesirably long engine start time. In the case of hybrid vehicles, where the other powertrain, such as a battery, is not used, the prechamber heating cycle can be performed using the prechamber heating device.Since an electric motor can power the vehicle during the prechamber heating cycles, the maximum number of prechamber heating cycles can be increased more than five times before the prechamber wall temperature exceeds the predetermined temperature. The total amount of fuel injected into the prechamber can be gradually reduced after each prechamber heating cycle because unburned fuel from the previous cycle can remain in the prechamber. Furthermore, due to the higher prechamber temperature in a second or third heating cycle, less fuel is required to achieve effective combustion. Performing multiple prechamber heating cycles allows for the provision of highly reactive jets to reliably ignite the mixture in the main combustion chamber during the first main combustion cycle.Therefore, the formation of unwanted hydrocarbon and particulate emissions during engine start-up is reduced, even at low engine temperatures.

[0030] Furthermore, the control unit can divide the predetermined quantity of fuel to be injected into the prechamber and can control the prechamber fuel injector to inject it in a multitude of multiple injections. These multiple injections can be advantageous for supporting mixture formation, particularly at low engine temperatures. Additionally, spray penetration into the prechamber can be reduced, thus lowering the number of particles generated as a result of wall wetting. The multiple injections can be performed in combination with a single prechamber heating cycle, as well as in combination with multiple heating cycles during the first or subsequent engine cycles following the engine start request. The number of injections is preferably in the range of 2 to 5 and most preferably in the range of 2 to 3.

[0031] Furthermore, the control unit can trigger the spark plug after each of the multiple injections to ignite each injection separately. This procedure can aid flame propagation within the pre-chamber and therefore improve the heating effect.

[0032] Preferably, the control unit cannot activate the pre-chamber fuel injector until the fuel pressure exceeds a predetermined value. This allows for stable spray formation with small droplets and therefore helps to prevent wall wetting within the pre-chamber, which can cause particle formation. Preferably, the predetermined pressure value can be at least 90% of the maximum injection pressure used in engine operation, and most preferably at least 95% of the maximum injection pressure used in engine operation. The fuel pressure for injecting fuel into the pre-chamber to perform a pre-chamber heating process can preferably be in the range of 5 bar to 250 bar, and most preferably in the range of 100 bar to 200 bar.

[0033] Furthermore, the claimed subject matter may comprise a method for controlling the starting of an internal combustion engine with at least one cylinder, at least one main combustion chamber, at least one intake port, at least one main fuel injector and / or at least one ignition device configured to ignite an air / fuel mixture within the main combustion chamber, and at least one control unit. wherein the ignition device comprises a spark plug, a pre-chamber fuel injector and a pre-chamber which is connected to the main combustion chamber via at least one opening (10e) in a pre-chamber wall (10d), wherein the control unit can control the ignition device to perform a pre-chamber heating process by injecting a predetermined amount of fuel into the pre-chamber and igniting an air / fuel mixture therein, while the main fuel injector is deactivated during at least one first engine cycle following an engine start request.

[0034] Furthermore, the claimed subject matter may include a computer program product that can be stored in a memory, with instructions which, when executed by a computer or a computing unit, cause the computer to perform the method or aspects thereof described above, as well as a computer-readable (storage) medium with instructions which, when executed by a computer, cause the computer to perform the method or aspects thereof.

[0035] In summary, the control unit and the procedure for controlling the start of an internal combustion engine equipped with an ignition device and a fuel-supplied pre-chamber significantly reduce particulate emissions during engine start-up by performing a pre-chamber heating process. Due to the increased temperature of the pre-chamber after heating, wall wetting within the pre-chamber can be avoided, and reactive flame jets can be generated, leading to improved ignition and combustion of the mixture in the main combustion chamber during the first main combustion cycle.

[0036] The claimed subject matter is further explained below on the basis of at least one preferred example with reference to the attached exemplary and schematic drawings; these show: Fig. 1 a schematic view of a cylinder of an internal combustion engine with an ignition device and a fuel-supplied pre-chamber; Fig. 2 a schematic view of the ignition device; Fig. 3a-3d schematically depict different control sequences for performing a pre-chamber heating process; and Fig. 4. A schedule of the claimed tax procedure.

[0037] Fig. Figure 1 schematically shows an exemplary cylinder 100 of an otherwise unspecified internal combustion engine, which may have more than one cylinder 100. The engine may, for example, have two, three, four, six, eight, or fewer / more cylinders 100. The engine comprises at least one piston 2, which is driven via a connecting rod 3 by a crankshaft (not shown) for a repeated reciprocating motion within the cylinder 100 to define the main combustion chamber therein.

[0038] An air intake channel 4 with an intake valve 6 and an exhaust channel 5 with an exhaust valve 7 are connected to the main combustion chamber 1. Ambient air is drawn into the main combustion chamber 1 through the intake channel 4. Exhaust gases are released from the combustion chamber 1 via the exhaust channel 5. An ignition device 10 with a spark plug 10a, a pre-chamber fuel injector 10b, and a pre-chamber 10c is attached to the internal combustion engine.

[0039] The spark plug 10a of the ignition device 10 can be electrically connected to an ignition coil (not shown). The spark plug 10a, in combination with the ignition coil, forms the spark ignition device, which preferably provides variable spark duration or multi-spark ignition. The internal combustion engine can have one or more ignition devices 10. Preferably, it has at least one ignition device 10 per cylinder 100. The ignition device 10, as well as a direct fuel injector 8, or at least parts thereof, are connected to the interior of the combustion chamber 1, so that reactive jets (shown in dashed lines) and fuel can be introduced / injected into the main combustion chamber 1. The direct fuel injector 8 can preferably be an electro-hydraulic fuel injector or a piezoelectric fuel injector. Furthermore, a port fuel injector 9 is connected to the intake port 4 of the cylinder 100.The high-pressure fuel supply to the direct fuel injector 8 and the low-pressure fuel supply to the channel fuel injector 9 are not shown. The main fuel injection can be carried out either by the direct main fuel injector 8 or the channel main fuel injector 9, or it can be divided between the two injectors.

[0040] A control unit 11 for controlling the ignition device is further included in Fig. Figure 1 shows the control unit 11 being electrically connected to the ignition device 10, the direct main fuel injector 8 and / or the channel main fuel injector 9, and controlling the multiple units / injectors / actuators. The control unit 11 can, for example, be the engine control unit (ECU).

[0041] The control unit 11 can also be any other control unit, and signal line connections between the control unit 11 and the controlled units can differ from the example of Fig. 1. For example, several control units 11 may be present, each capable of controlling subgroups of the controlled units; e.g., one control unit 11-1 may control only the ignition device 10, another control unit 11-2 may control only fuel injectors 8, 9, and so on. Furthermore, if several control units 11 are present, these control units 11 may be hierarchically or otherwise interconnected. Alternatively, a single control unit 11 may be present that encompasses all control functions of the multiple actuators.

[0042] Furthermore, pressure sensors, which are not shown, can be arranged, for example, in the wall of combustion chamber 1, so that the pressure inside combustion chamber 1 can be measured. Measuring the pressure inside combustion chamber 1 enables feedback combustion control and can also allow the pre-chamber heating process to be improved by providing additional information regarding the conditions in the cylinder.

[0043] In Fig. Figure 2 shows a schematic view of the ignition device 10. The ignition device 10 comprises a fuel injector 10a, a spark plug 10b, and a prechamber 10c. The prechamber 10c is separated from the main combustion chamber 1 by a prechamber wall 10d, in which openings 10e are arranged to introduce the reactive jets generated by the prechamber combustion into the main combustion chamber 1. The number, geometry, and position of the openings 10e are not shown in Figure 2. Fig. The example shown in Figure 2 is limited. The prechamber 10c can include several openings 10e arranged in different positions in the prechamber wall 10d and having different diameters. Furthermore, the shape of the prechamber is not limited to that shown in Figure 2. Fig. The shape shown in section 2 is limited, but can be designed in many different shapes, such as hemispherical, conical, or cylindrical shapes, or combinations thereof. The pre-chamber injection nozzle 10a can be connected to the high-pressure fuel supply or the low-pressure fuel supply of the engine (not shown), or it can be connected to a separate fuel supply (not shown) to inject a fuel other than that injected into the main combustion chamber 1. The spark plug 10b can be electrically connected to an ignition coil (not shown), which may be contained within the ignition device 10 or may be located elsewhere in the engine, remote from the ignition device 10. Preferably, there may be one ignition coil for each ignition device 10, but a single ignition coil for several ignition devices 10 is also possible.

[0044] In the Fig. Figures 3a to 3d show various examples of how to carry out the pre-chamber heating process.

[0045] Fig. Figure 3a shows the most preferred case for performing the prechamber heating process by controlling the injector nozzle to inject a single quantity of fuel into the prechamber during the compression stroke of a first engine cycle (prechamber heating cycle) and triggering the spark ignition shortly after the end of the prechamber injection. In the subsequent combustion cycle, the main fuel injector nozzle is controlled to inject the main fuel quantity into the main combustion chamber or intake port during the intake stroke, and the ignition device is controlled to ignite the air / fuel mixture in the main combustion chamber at the end of the compression stroke by performing a prechamber combustion to provide the necessary ignition energy, which is carried from the prechamber to the main combustion chamber by the reactive jets. The procedure for controlling the injection and ignition during the second engine cycle (combustion cycle) is applicable to all in Fig. Examples 3a to 3d are the same.

[0046] The control sequence for performing a pre-chamber heating process, which is in Fig. Figure 3b shows multiple injections, with the injection period of the pre-chamber injector nozzle, which is in Fig. 3a is shown, divided into four very small periods during the compression stroke of the first engine cycle, with a single ignition being triggered after the end of the last injection period. Fig. Figure 3c shows a different control sequence for a pre-chamber heating combustion, which also performs multiple injections during the compression stroke of the first engine cycle, but additionally assists the combustion process by triggering the spark ignition after each of the small injection times. Fig. 3d provides a control sequence for executing multiple pre-chamber heating processes according to Fig. 3a, wherein the heating processes are carried out during the entire first engine cycle.

[0047] The different control sequences can be executed depending on the engine temperature or the temperature of the pre-chamber wall, as exemplified in the following. Fig. The process outlined in section 4 is explained.

[0048] It describes, by way of example, that when the control unit receives a power machine start request, it sets a cycle counter to 1 and in step S100 the temperature of the pre-chamber wall T PCW either directly by a temperature sensor or indirectly, for example by reading a temperature value from a characteristic curve or graph. If the pre-chamber wall temperature T PCW is higher than the threshold temperature T vapNo prechamber heating process is carried out, which is required to evaporate the fuel accumulated as a wall film on the prechamber wall 10d. The threshold temperature T vap can be defined depending on the type of fuel to be injected into the pre-chamber. In the case of gasoline injection, T vap for example, preferably 85 °C and most preferably 90 °C.

[0049] If the specific pre-chamber wall temperature T PCW lower than T vap , but higher than a first predetermined temperature threshold T TH1 In step S101, a single pre-chamber heating process is performed according to the instructions in Fig. The control sequence shown in 3a was carried out. The first predetermined threshold temperature T TH1 can range from 0 °C to 10 °C. If the pre-chamber wall temperature T vap lower than the first, but higher than a second predetermined threshold temperature T TH2Step S102 is performed, in which the fuel to be injected into the pre-chamber during the compression stroke is divided into several small portions, for example four portions, as shown in Fig. Figure 3b shows that after the last injection, a single spark is triggered by the control unit. The second predetermined threshold temperature T TH2 can range from -10 °C to 0 °C. If the pre-chamber wall temperature T PCW lower than the second, but higher than a third predetermined threshold temperature T TH3 Step S103 is then performed, in which the fuel is injected into the pre-chamber in several small portions and a spark ignition is initiated after each injection, as shown in Fig. 3c is shown. The third predetermined threshold temperature T TH3 can be defined in the range of -20 °C to -10 °C. If the pre-chamber wall temperature T PCWis lower than the third threshold temperature T TH3 , step S104 according to Fig. The process is carried out in 3d, with several pre-chamber heating cycles performed throughout the first engine cycle. After completion of the first pre-chamber heating cycle, the cycle counter is incremented and it is determined whether the executed pre-chamber heating cycle was sufficient to raise the pre-chamber wall temperature T. PCW to increase to a value that raises the evaporation temperature T vap exceeds this temperature. If this occurs, the pre-chamber heating process is terminated. If not, the described procedure is repeated until the pre-chamber wall temperature T is exceeded. PCW about the evaporation temperature T vap increases or until a maximum number of pre-chamber heating cycles c max has been reached. The maximum number of pre-chamber heating cycles c maxPreferably, there can be 5 cycles, and most preferably 3 cycles, to avoid an undesirably long start-up time. In the case of hybrid vehicles, where the other powertrain, such as an electric motor, can operate the vehicle during the pre-chamber heating cycles, the maximum number of pre-chamber heating cycles can be increased more than 5 times until the pre-chamber wall temperature exceeds the predetermined temperature. The described procedure ensures that the pre-chamber is sufficiently preheated before the first main combustion cycle is initiated to prevent unwanted particulate emissions during engine start-up.

[0050] Features of the various embodiments, aspects, and examples described herein and illustrated by the figures can be combined, either partially or entirely. The invention described herein is intended to include these combinations as well.

[0051] In summary, the present subject matter provides a control unit and a method for controlling the starting of an internal combustion engine, which is equipped with an ignition device with a fuel-supplied pre-chamber, wherein a pre-chamber heating process is carried out which enables a safe starting process even at a low engine temperature and significantly reduces hydrocarbon and particulate emissions during engine starting. Reference symbol list 1 Main combustion chamber 2 pistons 3 Connecting rod 4 Inlet channel 5 Outlet channel 6 Inlet valve 7 Exhaust valve 8 Direct main fuel injector 9-channel main fuel injector 10 Ignition device 10a Spark plug 10b Pre-chamber fuel injector 10c Prechamber 10d Anterior chamber wall 10e Opening 11 Control unit 100 cylinders

Claims

Control unit (11) for controlling the starting of an internal combustion engine having at least one cylinder (100), at least one main combustion chamber (1), at least one intake port (4), at least one main fuel injector (8, 9) and at least one ignition device (10) configured to ignite an air / fuel mixture within the main combustion chamber (1), wherein the ignition device (10) comprises a spark plug (10a), a pre-chamber injector (10b) and a pre-chamber (10c) connected to the main combustion chamber (1) via at least one opening (10e) in a pre-chamber wall (10d), wherein the control unit (11) is configured to control the ignition device (10) to perform a pre-chamber heating process by injecting a predetermined quantity of fuel into the pre-chamber (10c) and igniting an air / fuel mixture therein, while the main fuel injector (8, 9)9) is deactivated during at least one initial power engine cycle following a power engine start request. Control unit (11) according to claim 1, wherein during a compression stroke of the at least first engine cycle after the engine start request the control unit (11) is configured to control the ignition device (10) to carry out the prechamber heating process by activating the prechamber fuel injector nozzle (10b) to inject the predetermined amount of fuel into the prechamber (10c) and subsequently triggering the spark plug (10a) to ignite the air / fuel mixture therein. Control unit (11) according to at least one of the preceding claims, wherein the control unit (11) is configured to control the ignition device (10) to perform several pre-chamber heating operations during at least the first engine cycle after the engine start request, until the temperature of the pre-chamber wall (10d) exceeds a predetermined temperature. Control unit (11) according to at least one of the preceding claims, wherein the control unit (11) is configured to control the ignition device (10) to perform the pre-chamber heating processes during several engine cycles after the engine start request until the temperature of the pre-chamber wall (10d) exceeds a predetermined temperature. Control unit (11) according to at least one of the preceding claims, wherein the control unit (11) is configured to divide the predetermined amount of fuel to be injected into the prechamber (10c) and to control the prechamber injector nozzle (10b) to inject it via a plurality of multiple injections. Control unit (11) according to claim 5, wherein the control unit (11) is configured to trigger the spark plug (10a) after each of the multiple injections. Control unit (11) according to at least one of the preceding claims, wherein the control unit (11) is configured not to activate the pre-chamber fuel injector (10b) until a fuel pressure exceeds a predetermined value. Method for controlling the starting of an internal combustion engine comprising at least one cylinder (100), at least one main combustion chamber (1), at least one intake port (4), at least one main fuel injector (8, 9), at least one ignition device (10) configured to ignite an air / fuel mixture within the main combustion chamber (1), and at least one control unit (11), wherein the ignition device (10) comprises a spark plug (10a), a pre-chamber fuel injector (10b), and a pre-chamber (10c) connected to the main combustion chamber (1) via at least one opening (10e) in a pre-chamber wall (10d), wherein the control unit (11) controls the ignition device (10) to perform a pre-chamber heating process by injecting a predetermined quantity of fuel into the pre-chamber (10c) and igniting an air / fuel mixture therein, while the main fuel injector (8, 9)9) is deactivated during at least one initial power engine cycle following a power engine start request. Method according to claim 8, wherein during a compression stroke of the at least first engine cycle after the engine start request the at least one control unit (11) controls the ignition device (10) to perform a pre-chamber heating process by activating the pre-chamber fuel injector nozzle (10b) to inject the predetermined amount of fuel into the pre-chamber (10c), and subsequently triggering the spark plug (10a) to ignite the air / fuel mixture therein. Method according to at least one of the preceding claims 8 and 9, wherein the at least one control unit (11) controls the ignition device (10) to perform several pre-chamber heating processes during at least the first engine cycle after the engine start request, until the temperature of the pre-chamber wall (10d) exceeds a predetermined temperature. Method according to at least one of the preceding claims 8 to 10, wherein the at least one control unit (11) controls the ignition device (10) to carry out the prechamber heating processes during several engine cycles after the engine start request until the wall temperature of the prechamber exceeds a predetermined temperature. Method according to at least one of the preceding claims 8 to 11, wherein the at least one control unit (11) divides the predetermined amount of fuel to be injected into the prechamber (10c) and controls the prechamber injection nozzle (10b) to inject it via a plurality of multiple injections. Method according to claim 12, wherein the at least one control unit (11) triggers the spark plug (10a) after each of the multiple injections. Method according to at least one of the preceding claims 8 to 13, wherein the at least one control unit (11) does not activate the pre-chamber fuel injector (10b) until a fuel pressure exceeds a predetermined value. Internal combustion engine with at least one control unit according to at least one of the preceding claims 1 to 7. Computer program product that can be stored in a memory, comprising instructions which, when executed by a computer, cause the computer to perform the method according to at least one of the methods claimed 8 to 14.

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