Prechamber device for an internal combustion engine, in particular of a motor vehicle, and methods for manufacturing such a prechamber device

Abstract

Prechamber device (1) for an internal combustion engine, comprising a prechamber (3) and several transfer openings (4) through which the prechamber (3) can be fluidically connected to a combustion chamber (2) of the internal combustion engine and a fuel-air mixture can be introduced from the combustion chamber (2) into the prechamber (3), wherein the respective transfer opening (4) is specifically rounded at its respective combustion chamber-side end edge (6) and / or prechamber-side end edge (5), characterized in that - the pre-chamber (3) is partially bounded by a housing element (10) of the pre-chamber device (1) and partially by a cap (9) of the pre-chamber device (1) formed separately from the housing element (10) and connected to the housing element (10), wherein the cap (9) is made of a nickel-based alloy; - the respective overflow opening (4) is fully formed in the cap (9); and - the respective overflow opening (4) is specifically rounded at its respective combustion chamber-side end edge (6) and / or pre-chamber-side end edge (5) by hydro-erosive machining.

Description

[0001] The invention relates to a pre-chamber device for an internal combustion engine, in particular of a motor vehicle, according to the preamble of patent claim 1. Furthermore, the invention relates to a method for producing such a pre-chamber device according to the preamble of patent claim 7.

[0002] WO 2020 / 126 667 A1 discloses a prechamber spark plug with a housing having a longitudinal axis extending from an end facing the combustion chamber to an end of the housing facing away from the combustion chamber. WO 2020 / 126 663 A1 also discloses a prechamber spark plug with a housing. Furthermore, DE 10 2018 222 475 A1 discloses a spark plug with a rounded housing section. Furthermore, CH 715 113 A1 discloses a prechamber spark plug for an internal combustion engine. DE 10 2017 202 001 A1 discloses a prechamber spark plug. Furthermore, US 2014 / 0 261 296 A1 discloses a precombustion chamber. DE 20 2006 005 889 U1 discloses a device for hydroerosive rounding of bore transitions to injection openings in fuel injectors. Furthermore, DE 10 2020 112 013 A1 discloses a spark plug.

[0003] The object of the present invention is to provide a pre-chamber device for an internal combustion engine, in particular of a motor vehicle, and a method for producing such a pre-chamber device, so that a particularly high robustness of the pre-chamber device can be realized.

[0004] This object is achieved according to the invention by a pre-chamber device having the features of patent claim 1, as well as by a method having the features of patent claim 4. Advantageous embodiments of the invention are the subject of the dependent claims.

[0005] A first aspect of the invention relates to a prechamber device for an internal combustion engine, preferably designed as a reciprocating piston engine, in particular of a motor vehicle. The prechamber device has a prechamber and overflow openings designed as through-openings, via which the prechamber can be fluidically connected to a combustion chamber of the internal combustion engine and via which a fuel-air mixture can be introduced from the combustion chamber into the prechamber. This means that the internal combustion engine, in its fully manufactured state, has the combustion chamber and the prechamber device assigned to the combustion chamber, the prechamber of which is fluidically connected to the combustion chamber via the overflow openings. The overflow openings open, on the one hand, in particular at one end, into the prechamber. On the other hand, in particular at the other end, the overflow openings open into an area surrounding the prechamber device.In the fully manufactured state of the internal combustion engine, the transfer openings open, on the other hand, in particular at the other end, into the combustion chamber, also referred to as the main combustion chamber, whereby, in the fully manufactured state of the internal combustion engine, the prechamber is fluidly connected to the combustion chamber via the transfer openings. As will be described in more detail below, the prechamber and thus the prechamber device are used to perform prechamber ignition, in particular during fired operation of the internal combustion engine and very particularly within a respective working cycle of the internal combustion engine.

[0006] The fuel-air mixture, also simply referred to as a mixture, comprises air and a preferably liquid fuel, by means of which the internal combustion engine can be operated in its fired mode. In particular, it is provided that the prechamber is completely fluidically separated from the combustion chamber, with the exception of respective fluidic connections between the prechamber and the combustion chamber formed by the respective overflow openings. In the fully manufactured state of the internal combustion engine, the combustion chamber is delimited, for example, partially by a piston and, for example, partially by a cylinder, in which the piston can be accommodated in a movable, in particular translationally movable, manner.For example, in particular during the respective working cycle of the internal combustion engine, the said mixture is formed in the combustion chamber, with at least a first part of the mixture flowing from the combustion chamber (main combustion chamber) through the transfer openings, in particular when the piston moves towards top dead center or into its top dead center, and thus flowing into the pre-chamber via the transfer openings, and thus being introduced into the pre-chamber. In particular, it is conceivable that the piston, in particular on its way towards top dead center or into its top dead center, conveys at least the first part of the mixture from the main combustion chamber through the transfer opening and thereby into the pre-chamber, whereby at least the first part of the mixture is introduced into the pre-chamber. It is conceivable that a second part of the mixture remains in the main combustion chamber.For example, the mixture flowing or introduced into the prechamber, i.e., the aforementioned first part, is ignited, in particular by generating at least one ignition spark, in particular by means of at least one electrode, in particular within the respective working cycle. The ignition spark ignites and combusts the mixture flowing into the prechamber and thus received in the prechamber. Subsequently, the burning mixture flows from the prechamber through the transfer openings and via the transfer openings back into the main combustion chamber, either in the form of burning flares or jets flowing through the transfer openings.Because the burning mixture from the pre-chamber flows through the overflow openings and thus flows from the pre-chamber into the main combustion chamber via the overflow openings, the remaining mixture in the main combustion chamber is ignited and subsequently burned, which drives the piston, for example. For example, the ignition spark in the pre-chamber is generated by means of a spark plug, so that the electrode can be a component of the spark plug. It is conceivable for the spark plug to be formed separately from the pre-chamber device and connected to the pre-chamber device, in particular by screwing. In other words, it is conceivable for the pre-chamber device and the spark plug to be formed separately, i.e. independently of one another, so that the pre-chamber is formed independently of the spark plug, for example.This allows a particularly large pre-chamber volume, also known as pre-chamber volume, to be achieved, so that a particularly high performance of the internal combustion engine can be achieved.

[0007] The overflow openings are individual openings and thus spaced apart from one another, so that a wall region of the pre-chamber device designed as a solid body is arranged between the overflow openings or between each two of the overflow openings, wherein the wall region is also referred to as a web or intermediate web.

[0008] In order to be able to achieve a particularly high level of robustness of the pre-chamber device, it is provided according to the invention that the respective overflow opening is deliberately rounded at its respective combustion chamber-side end edge. Alternatively or additionally, it is provided according to the invention that the respective overflow opening is deliberately rounded at its respective pre-chamber-side end edge. In other words, it is provided according to the invention that the respective combustion chamber-side end edge and / or the respective pre-chamber-side end edge of the respective overflow opening is deliberately rounded. The respective overflow opening extends from its respective combustion chamber-side end edge to its respective pre-chamber-side end edge, wherein the combustion chamber-side end edge is also referred to as the first end edge and the pre-chamber-side end edge is also referred to as the second end edge.In other words, the respective combustion chamber-side end edge is arranged at a respective first end of the respective transfer opening, and the respective pre-chamber-side end edge is arranged at the respective second end of the respective transfer opening, wherein the transfer opening extends from its first end to its second end or vice versa, and thus ends at the respective end. Thus, when the internal combustion engine is fully manufactured, the respective transfer opening opens into the combustion chamber at the respective first end and into the pre-chamber at the respective second end. In this case, it is particularly conceivable for the respective transfer opening to extend straight from its first end to its second end or vice versa, in particular completely.The respective overflow opening is thus a respective channel through which the mixture or the respective burning torch can flow, which extends from one end to the other end and ends at the respective end.

[0009] The feature that the overflow opening is deliberately rounded at its combustion chamber-side end edge and / or at its pre-chamber-side end edge is to be understood as meaning that, particularly during the manufacture of the pre-chamber device, at least one work step and thus at least one method is or was carried out in a targeted manner, i.e., in a desired manner, whereby the combustion chamber-side end edge and / or the pre-chamber-side end edge is or was deliberately rounded by the work step or by the method. In other words, the work step or by the method results in a targeted machining of the combustion chamber-side end edge and / or the pre-chamber-side end edge, whereby the combustion chamber-side and / or pre-chamber-side end edge is rounded. The invention is based in particular on the following findings and considerations: During concept development, initial tests with pre-chamber devices revealed that, unless appropriate countermeasures are taken, cracks can occur on or in the web or in the area of ​​the web between two transfer openings, also known as spray holes, of the pre-chamber device due to high pressure and temperature loads. This phenomenon is to be counteracted by reducing stresses in the web through rounding, compared to pre-chamber devices without rounding. Rounding the end edge of the respective transfer opening on the combustion chamber side and / or pre-chamber side is a countermeasure that can prevent excessive stresses in the web, thereby preventing excessive cracking and / or other excessive damage to the web. This makes the pre-chamber device particularly robust.

[0010] In order to advantageously avoid undesired damage to the pre-chamber device and thus to be able to represent a particularly high robustness of the pre-chamber device, it is provided that the pre-chamber is partially delimited by a housing element of the pre-chamber device and partially by a cap of the pre-chamber device, in particular in each case directly, wherein the cap is formed separately from the housing element and connected to the housing element.

[0011] The overflow openings are each completely formed within the cap. This allows the cap and the overflow openings, also known as spray holes, to be manufactured as needed, thus avoiding excessive stress on the pre-chamber assembly, especially the web.

[0012] The cap is made of a nickel-based alloy.

[0013] In order to achieve a particularly high level of robustness for the pre-chamber device in a particularly simple manner, it is provided that the respective overflow opening is specifically rounded by hydroerosive machining at its respective end edge on the combustion chamber side and / or pre-chamber side. This means that the aforementioned work step or the aforementioned method is the aforementioned hydroerosive machining, which is also referred to as HE machining, HE rounding or HE grinding (hydroerosive grinding). This embodiment is based in particular on the recognition that, due to a potentially complex geometry of the pre-chamber device, particularly in the area of ​​the overflow openings and the web arranged between them, mechanical machining, i.e. mechanical rounding, intended to round the end edge on the combustion chamber side and / or pre-chamber side is not possible or is only possible with great effort.In contrast, hydroerosive machining can be used to round the end edge on the combustion chamber and / or pre-chamber side simply and cost-effectively, resulting in a particularly advantageous rounding of the end edge on the combustion chamber and / or pre-chamber side. Hydroerosive machining is particularly suitable for rounding the respective pre-chamber end edge, as this is not accessible or only accessible with great effort for mechanical or electrochemical rounding. In particular, the respective end edge on the combustion chamber side could be rounded mechanically, i.e., by mechanical machining, or electrochemically, i.e., by electrochemical machining.

[0014] A further embodiment provides that the housing element is made of a first material, and the cap is made of a second material different from the first material, namely the nickel-based alloy. This allows the housing and cap to be designed and manufactured as needed, particularly depending on the respective loads occurring during operation of the pre-chamber device, thus achieving particularly high robustness.

[0015] It has proven particularly advantageous if the first material is a copper alloy. In particular, the first material is CuCr1Zr, where Cu denotes copper, Cr denotes chromium, and Zr denotes zirconium. This allows for particularly good heat dissipation and thus temperature relief for the prechamber device.

[0016] The second material is a nickel-based alloy, i.e., a Ni alloy, where Ni stands for nickel. In particular, the second material can be Inconel®. This allows for a particularly high degree of robustness of the cap and thus of the pre-chamber device as a whole, thus preventing unwanted damage such as cracks in the cap, especially the bridge.

[0017] In order to be able to achieve a particularly high robustness of the pre-chamber device, a further embodiment of the invention provides that the housing element is connected to the cap by welding, in particular by friction welding.

[0018] A second aspect of the invention relates to a method for producing a pre-chamber device, in particular a pre-chamber device according to the first aspect of the invention, for an internal combustion engine, in particular of a motor vehicle. In the method, a pre-chamber of the pre-chamber device and a plurality of overflow openings of the pre-chamber device are produced, the pre-chamber of which can be fluidically connected to one of the internal combustion engine via the overflow opening and can be supplied with a fuel-air mixture from the combustion chamber.

[0019] In order to achieve a particularly high level of robustness for the pre-chamber device, the method according to the invention provides for the respective overflow opening to be deliberately rounded at its respective combustion chamber-side end edge and / or at its respective pre-chamber-side end edge. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

[0020] The pre-chamber is partially delimited by a housing element of the pre-chamber device and partially by a cap of the pre-chamber device formed separately from the housing element and connected to the housing element, wherein the cap is made of a nickel-based alloy.

[0021] In order to be able to achieve a particularly high level of robustness of the pre-chamber device in a particularly simple and thus time- and cost-effective manner, the second aspect of the invention provides that the respective overflow opening is rounded at its respective combustion chamber-side end edge and / or at its respective pre-chamber-side end edge in a targeted manner by hydroerosive machining. It has proven particularly advantageous if a grinding paste is passed through the respective overflow opening for the targeted rounding of the end edge on the combustion chamber side and / or the pre-chamber side during hydroerosive machining. For example, in order to round the respective pre-chamber side end edge using hydroerosive machining, the grinding paste is passed from the pre-chamber or from the pre-chamber side end edge to the combustion chamber side end edge. For example, in order to round the end edge on the combustion chamber side, the grinding paste is passed through the respective overflow opening from the end edge on the combustion chamber side to the end edge on the pre-chamber side. By using the grinding paste, the respective end edge can be rounded particularly well, thereby achieving a particularly high level of robustness.

[0022] Surprisingly, it was found that stresses in the web can be kept particularly low and thus a particularly high robustness of the pre-chamber device can be realized if the grinding paste is passed through the respective overflow opening at a pressure which is in a range of 60 bar up to and including 100 bar, in particular in a range of 70 bar up to and including 90 bar.

[0023] A pressure of 80 bar has proven particularly advantageous. This allows the respective end edge to be rounded particularly well.

[0024] In a further, particularly advantageous embodiment of the invention, the grinding paste is passed through the respective overflow opening for 25 seconds to 65 seconds, in particular for 35 seconds to 55 seconds, in particular continuously and thus without interruption, in order to round the combustion chamber-side and / or pre-chamber-side end edge during hydroerosive machining. In other words, it is preferably provided that the grinding paste is passed through the respective through-opening for, in particular precisely, a period of time without interruption and thus continuously, wherein the period of time lies in a range from 25 seconds to 65 seconds inclusive, in particular in a range from 35 seconds to 55 seconds inclusive. This allows a particularly advantageous rounding of the respective end edge to be achieved.

[0025] It has proven particularly advantageous if the grinding paste is passed through the respective overflow opening for exactly 45 seconds. In other words, it has proven particularly advantageous if the period is 45 seconds. This advantageously prevents excessive stress in the web, especially during operation of the internal combustion engine, thus achieving a particularly high level of robustness.

[0026] Finally, it has proven particularly advantageous to use a grinding paste containing at least corundum as an abrasive. Hydroerosive machining is a machining process in which the grinding paste is passed through the respective overflow opening. In particular, the grinding paste is an abrasive liquid mixed with grinding particles. Preferably, the grinding particles are made of corundum or are corundum. This allows the respective end edge to be rounded particularly well, thus avoiding excessive stresses in the web.

[0027] Further details of the invention will become apparent from the following description of a preferred embodiment with the accompanying drawings. In the drawings: Fig. 1 shows a partial schematic longitudinal sectional view of a pre-chamber device for an internal combustion engine, in particular of a motor vehicle; and Fig. 2 a partial schematic perspective view of a cap of the pre-chamber device.

[0028] In the figures, identical or functionally equivalent elements are provided with the same reference numerals.

[0029] Fig. Figure 1 shows a partial schematic longitudinal sectional view of a pre-chamber device 1 for an internal combustion engine of a motor vehicle, in particular a reciprocating piston engine. This means that the motor vehicle, preferably designed as a motor vehicle, in particular a passenger car, in its fully manufactured state, has the internal combustion engine and thus the pre-chamber device 1 and can be driven by the internal combustion engine. The internal combustion engine has at least one Fig. 1 has a combustion chamber 2, shown particularly schematically, in which combustion processes take place during fired operation of the internal combustion engine. During the respective combustion process, in particular during a respective working cycle of the internal combustion engine, a fuel-air mixture, also simply referred to as a mixture, is ignited and burned, wherein the mixture comprises at least air and a fuel, in particular a liquid fuel. The combustion chamber 2 is delimited, for example, partly by a cylinder of the internal combustion engine and partly by a piston of the internal combustion engine, wherein the piston can be arranged such that it can move, in particular in a translational manner, in the cylinder. The mixture is formed in the combustion chamber 2 within the respective working cycle.

[0030] The pre-chamber device 1 is assigned to the combustion chamber 2 and is designed, as will be explained in more detail below, to ignite the mixture in the combustion chamber 2. For this purpose, the pre-chamber device 1 has a pre-chamber 3 and a plurality of overflow openings 4, via which the pre-chamber 3 is or can be fluidically connected to the combustion chamber 2. For example, two multiplication signs n overflow openings 4 are provided for each pre-chamber 3, where n denotes a positive integer. In the exemplary embodiment shown in the figures, the pre-chamber device 1 has, for example, exactly two overflow openings 4. At least a first part of the mixture from the combustion chamber 2 can flow through the overflow openings 4, so that at least the first part of the mixture from the combustion chamber 2 can be introduced into the pre-chamber 3 via the overflow openings 4.For example, on its path toward its top dead center or into its top dead center, the piston conveys, in particular pushes, at least the first part of the mixture through the transfer openings 4 and into the prechamber 3, whereby at least the first part of the mixture is introduced from the combustion chamber 2 via the transfer openings 4 into the prechamber 3. For example, at least a second part of the mixture remains in the combustion chamber 2, also referred to as the main combustion chamber.

[0031] Within the respective working cycle, for example, in the pre-chamber 3 at least one Fig. 1, an ignition spark 12 is generated, which is shown particularly schematically in FIG. 1, whereby the mixture introduced into the pre-chamber 3 and thus received in the pre-chamber 3 is ignited and thereby burned. The burning mixture flows via the overflow openings 4 from the pre-chamber 3 back into the combustion chamber 2 (main combustion chamber), in which the mixture remaining in the main combustion chamber is ignited and subsequently burned. For example, the ignition spark 12 is generated by means of a spark plug (not shown in detail in the figures), wherein the spark plug and the pre-chamber device are preferably designed as separate devices that are connected to one another, in particular screwed to one another. In this case, for example, the spark plug is at least partially arranged in the pre-chamber 3, in particular in such a way that the spark plug can generate the ignition spark 12 in the pre-chamber 3.

[0032] Out of Fig. 1 that the respective overflow opening 4 has a pre-chamber-side, first end edge 5 at its first end E1, and the respective overflow opening 4 has a combustion chamber-side, second end edge 6 at its respective second end E2 opposite the first end E1. The respective overflow opening 4 ends at its respective ends E1 and E2 and thus at its respective end edges 5 and 6. In other words, the respective overflow opening 4 extends from its respective end edge 5 to its respective end edge 6, or vice versa. At the end E1 and thus at and over the end edge 5, the respective overflow opening 4 opens into the pre-chamber 3.At its respective end E2 and thus at and via its respective end edge 6, the respective overflow opening 4 opens at or into an area 7 of the pre-chamber device 1 per se, that is to say when viewed on its own, so that in the fully manufactured state of the internal combustion engine, the respective overflow opening 4 opens into the combustion chamber 2 at its respective second end E2 and thus at and via its respective end edge 6. On its way out of the combustion chamber 2 through the respective overflow opening 4 and into the pre-chamber 3, the mixture thus flows from the end edge 6 towards the end edge 5. On its way out of the pre-chamber 3 through the respective overflow opening 4 and into the combustion chamber 2, the burning mixture flows via the end edge 5 into the overflow opening 4 and from the end edge 5 to the end edge 6 and via the end edge 6 out of the overflow opening 4.The end edge 5 is therefore also referred to as the inlet or is arranged at a respective inlet of the respective overflow opening 4. The respective overflow opening 4 is also referred to as the spray hole, so that the respective end edge 5 is also referred to as the spray hole inlet.

[0033] Out of Fig. 1 shows that the overflow openings 4 are individual through-openings spaced apart from one another, so that a web 8 of the pre-chamber device 1, designed as a solid body, is arranged between the overflow openings 4. The web 8 is a wall or a wall region of the pre-chamber device 1.

[0034] In order to avoid cracks and other damage to the web 8 and thus to be able to achieve a particularly high level of robustness of the pre-chamber device 1, it is provided in the embodiment shown in the figures that the respective overflow opening 4 is deliberately rounded at its respective pre-chamber-side end edge 5, preferably by hydroerosive machining. For this purpose, in a method for producing the pre-chamber device 1, a grinding paste comprising abrasive particles, for example made of corundum, is passed through the respective overflow opening 4 and introduced into the overflow opening 4 via the end edge 5, so that the grinding paste flows from the end edge 5 to the end edge 6 during the method and flows through the overflow opening 4. It is preferably provided that the respective overflow opening 4 is deliberately rounded with respect to its end edges 5 and 6 exclusively at the end edge 5.

[0035] Fig. 2 shows greatly enlarged, schematic representations of the pre-chamber device 1. The deliberately rounded end edge 5 of the overflow opening 4 is particularly clearly visible in Fig.

[0036] The pre-chamber 3 is partially delimited, in particular directly, by a cap 9 designed as a solid body and partially by a housing element 10 of the pre-chamber device 1 designed as a solid body. The cap 9 and the housing element 10 are components formed separately from one another and connected to one another. The cap 9 and the housing element 10 are connected to one another in a joining plane 11, in particular such that the cap 9 and the housing element 10 are connected to one another in the joining plane 11 by welding, in particular by friction welding. The cap 9 is preferably formed from a nickel-based alloy, with the housing element 10 preferably being formed from a copper alloy, in particular from CuCr1Zr. It can be seen that the web 8 is a component and thus a wall of the cap 9, with the overflow openings 4 being formed entirely in the cap 9.Most preferably, the cap 9 is formed in one piece, i.e., as an integral component. This means that the cap 9 is not composed of separate and interconnected components, but rather the cap 9 is a monoblock, i.e., an integrally manufactured component. In particular, it is conceivable for the spark plug to be screwed into the prechamber device 1, for example, such that the spark plug is screwed into the housing element 10 and thus screwed to the housing element 10. List of reference symbols 1 pre-chamber device 2 combustion chamber 3 Antechamber 4 overflow opening 5 pre-chamber end edge 6 combustion chamber end edge 7 Surroundings 8 bridge 9 cap 10 Housing element 11 Joining level 12 ignition spark E1 first end E2 second ending

Claims

[1] Pre-chamber device (1) for an internal combustion engine, with a pre-chamber (3) and with several overflow openings (4), via which the pre-chamber (3) can be fluidically connected to a combustion chamber (2) of the internal combustion engine and a fuel-air mixture can be introduced from the combustion chamber (2) into the pre-chamber (3), wherein the respective overflow opening (4) is specifically rounded at its respective combustion chamber-side end edge (6) and / or pre-chamber-side end edge (5), characterized by , that - the pre-chamber (3) is partially delimited by a housing element (10) of the pre-chamber device (1) and partially by a cap (9) of the pre-chamber device (1) which is formed separately from the housing element (10) and connected to the housing element (10), wherein the cap (9) is formed from a nickel-based alloy; - the respective overflow opening (4) is completely formed in the cap (9); and - the respective overflow opening (4) is specifically rounded at its respective combustion chamber-side end edge (6) and / or pre-chamber-side end edge (5) by hydroerosive machining. [2] Pre-chamber device (1) according to claim 1, characterized by that the housing element (10) is made of a first material and the cap (9) is made of a second material different from the first material, namely the nickel-based alloy. [3] Pre-chamber device (1) according to claim 2, characterized by that the first material is a copper alloy. [4] Method for producing a pre-chamber device (1) for an internal combustion engine, in which a pre-chamber (3) and several overflow openings (4) of the pre-chamber device (1) are produced, the pre-chamber (3) of which can be fluidically connected to a combustion chamber (2) of the internal combustion engine via the overflow openings (4) and can be supplied with a fuel-air mixture from the combustion chamber (2), wherein the respective overflow opening (4) is specifically rounded at its respective combustion chamber-side end edge (6) and / or pre-chamber-side end edge (5), characterized by , that - the pre-chamber (3) is partially delimited by a housing element (10) of the pre-chamber device (1) and partially by a cap (9) of the pre-chamber device (1) which is formed separately from the housing element (10) and connected to the housing element (10), wherein the cap (9) is made of a nickel-based alloy; - the respective overflow opening (4) is formed completely in the cap (9); and - the respective overflow opening (4) is rounded at its respective combustion chamber-side end edge (6) and / or pre-chamber-side end edge (5) in a targeted manner by hydroerosive machining. [5] Method according to claim 4, characterized by that for targeted rounding during hydroerosion machining, a grinding paste is passed through the respective overflow opening (4). [6] Method according to claim 5, characterized by that the grinding paste is passed through the respective overflow opening (4) at a pressure which lies in a range from 60 bar to 100 bar. [7] Method according to claim 6, characterized by that the pressure is 80 bar. [8] Method according to one of claims 5 to 7, characterized bythat the grinding paste is passed through the respective overflow opening (4) for 25 seconds to 65 seconds. [9] Method according to claim 8, characterized by that the grinding paste is passed through the respective overflow opening for 45 seconds. [10] Method according to one of claims 5 to 9, characterized by that the grinding paste used is a grinding paste which contains at least corundum as an abrasive.

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