CYLINDER HEAD FOR AN ENGINE

Description

[0001] The present invention relates to a cylinder head having the features of the preamble of claim 1, and to an internal combustion engine having such a cylinder head.

[0002] Above a certain piston bore diameter (approximately 150 mm), (gas) internal combustion engines are equipped with a pre-chamber for ignition enhancement. An ignition source protruding into the pre-chamber – usually a spark plug – ignites the mixture present there, which is relatively rich in a purged pre-chamber. This causes ignition flares to pass from the pre-chamber into the main combustion chamber and ignite the mixture there.

[0003] There are various concepts regarding the fuel supply to the pre-chamber. In an unpurged pre-chamber, the mixture from the main combustion chamber is forced into the pre-chamber during the compression stroke. In purged pre-chambers, it is also possible to supply the pre-chamber with additional fuel. The fuel supplied to the pre-chamber in a purged pre-chamber can be the same as (in terms of its chemical composition and / or its excess air ratio) as that of the main combustion chamber or different from it. This separate fuel supply is achieved via a pre-chamber gas valve, which can be located directly or indirectly (via a spark plug sleeve) in the cylinder head. Hereinafter, the fuel supplied to the pre-chamber via the pre-chamber gas valve will be referred to as propellant gas.

[0004] A cylinder head of this type is shown, for example, in EP 3 064 755 A1. This document discloses a cylinder head with a cavity for receiving a pre-chamber gas valve, which is indirectly arranged in the cylinder head via a spark plug sleeve. The pre-chamber gas valve is connected to a pre-chamber via an obliquely arranged transfer port, whereby, during operation of the internal combustion engine, propellant gas is supplied to the pre-chamber via this transfer port. A similar concept of a transfer port is known from EP 3 061 939 A1.

[0005] EP 3 012 444 A1 discloses a design of an overflow channel which is designed with a horizontal and a vertical bore to supply the pre-chamber with propellant gas coming from the pre-chamber gas valve.

[0006] Furthermore, EP 3 012 431 A1 discloses the provision of an annular channel which is connected to the prechamber gas valve via a transfer channel. The annular channel extends around the prechamber and is connected to the prechamber by a multitude of radially spaced bores. This multitude of bores ensures that the propellant gas (coming via the transfer channel from the prechamber gas valve) is introduced into the prechamber as uniformly as possible and distributed there with the most consistent concentration possible.

[0007] Other known design variants are shown, for example, in JP H04-65922 U, US 2016 / 363041 A1 or GB 2545798 A

[0008] During a combustion cycle of the internal combustion engine, propellant gas is supplied to the pre-chamber via the transfer port through the pre-chamber gas valve, creating a propellant-air mixture in the pre-chamber (more precisely, this propellant-air mixture mixes in the pre-chamber with a fuel-air mixture that enters the pre-chamber from the main combustion chamber during the compression stroke). Subsequently, the fuel-air mixture supplied to the main combustion chamber is compressed in a compression stroke until ignition is triggered in the pre-chamber by a spark plug protruding into it. The propellant-air mixture ignited in the pre-chamber forms ignition flares, which pass from the pre-chamber into the main combustion chamber and initiate combustion there.

[0009] Generally, the aim is to position the prechamber gas valve as close as possible to the prechamber, since the propellant gas present in the transfer channel is not burned, or only insufficiently burned, during combustion. This partial or insufficient combustion of the propellant gas in the transfer channel leads to an undesirable increase in emissions, particularly hydrocarbon emissions. By shortening the transfer channel and consequently moving the prechamber gas valve closer to the prechamber, the amount of unburned or insufficiently burned propellant gas in the transfer channel can be reduced.

[0010] Ignition in the pre-chamber and combustion of the propellant-air mixture there also ignites the propellant-air mixture present in the transfer port, which can lead to the formation of combustion residues. Combustion residues in the form of deposits on the outer surface of the transfer port and / or on the pre-chamber gas valve have a very negative impact, as even small deposits in the transfer port, due to its small cross-section at the pre-chamber gas valve, are sufficient to partially or even completely block it.

[0011] The object of the invention is to provide a cylinder head that is improved compared to the prior art, as well as an internal combustion engine with such a cylinder head.

[0012] This problem is solved by a cylinder head having the features of claim 1 and an internal combustion engine with such a cylinder head.

[0013] In a cylinder head according to the invention, a pre-chamber gas valve is inserted into a cavity of the cylinder head, wherein the pre-chamber gas valve is connected to the pre-chamber via a transfer channel, which has a first section adjoining the pre-chamber gas valve and a second section into which the first section opens, wherein the second section extends around a circumference of the pre-chamber in an angular range of about 20° to about 270°, wherein the second section has an uninterrupted cylindrical surface apart from the opening through which it enters the pre-chamber.

[0014] This results in the transfer channel having such a length and, at least in a first section adjoining the pre-chamber gas valve, such a cross-sectional area that, during operation of the cylinder head mounted in an internal combustion engine, propellant gas flowing out of the pre-chamber gas valve forms a gas cushion in the transfer channel, at least in the first section, during a compression phase of the combustion process.

[0015] This propellant gas cushion contains no oxygen because the propellant has not yet mixed with air. Due to the lack of oxygen in the propellant gas cushion, it cannot participate in the combustion reaction, and therefore no products of incomplete combustion (HC emissions) can be formed by the propellant gas cushion.

[0016] By providing a transfer channel with such a length and cross-sectional area that the outgoing propellant gas forms a gas cushion within the channel, the formation of combustion residues as deposits on the channel's surface is prevented, or at least reduced, at least in the first section of the transfer channel. Any deposits that nevertheless form on the channel's surface can be carried away by the flow during a subsequent expansion phase in the combustion cycle (in which the highest flow velocities occur in the transfer channel, at least in the second section), thus cleaning the transfer channel.

[0017] The gas cushion of propellant also prevents combustion within the transfer channel, as the gas cushion consists of almost pure propellant and cannot be ignited due to the lack of oxygen. This propellant gas cushion effectively forms a combustion barrier within the transfer channel. In other words, the geometric design of the transfer channel utilizes the existing propellant gas to prevent the formation of deposits near the pre-chamber gas valve by preventing combustion.

[0018] Advantageous embodiments of the invention are defined in the dependent claims.

[0019] It is particularly advantageous for the second section to extend around the prechamber at an angle of approximately 60° to approximately 180°. This allows for a particularly compact and space-saving extension of the transfer channel. The transfer channel can run in a circular path around the prechamber or approach it in a spiral pattern. Depending on the requirements, the transfer channel can open radially, tangentially, or along a secant into the prechamber, whereby the inflow and flow through the prechamber can be controlled or influenced.

[0020] Furthermore, a spark plug may be provided in the cylinder head as the ignition source. Standard commercially available spark plugs can be used. A spark plug sleeve may be provided in the cylinder head to accommodate the spark plug.

[0021] The second section can extend in a plane parallel to a parting line between the pre-chamber and the rest of the cylinder head, preferably between the pre-chamber and a spark plug sleeve. This arrangement of the second section of the transfer port provides a particularly simple and resource-efficient method for manufacturing it. The second section can be formed by at least one, preferably milled, groove in a wall of the pre-chamber and / or the rest of the cylinder head. In the assembled state, the transfer port is formed by the groove in a wall of the pre-chamber and / or the rest of the cylinder head and an adjacent wall.

[0022] Therefore, it may be provided that the transfer channel is formed both by a wall of the pre-chamber and by material from the rest of the cylinder head.

[0023] Preferably, the cross-sectional area of ​​the overflow channel, preferably at least along the length of the first section, is between approximately 1π mm² and approximately 2.5π mm². However, it is also possible for the overflow channel to have a cross-sectional area that varies along its length. For example, a cross-sectional narrowing can be provided in certain areas of the overflow channel to achieve a throttling effect. Or, for example, a cross-sectional widening (or even a chamber) can be provided in certain areas of the overflow channel to form a collection point (e.g., for a gas cushion). By progressively narrowing or widening the overflow channel, the flow velocity of the propellant gas can be specifically controlled.

[0024] In one embodiment, the total length of the transfer channel may be between approximately 30 mm and approximately 70 mm. However, the length of the transfer channel can be selected depending on the size of the internal combustion engine, the size of the combustion chamber, or the size of the cylinder head.

[0025] The bypass channel may be designed to have a volumetrically equivalent length of approximately 15 to 23 mm, preferably approximately 16 to 20 mm, based on its cross-sectional area immediately downstream of the prechamber gas valve. This equivalent length is calculated from the volume of the bypass channel required to form a sufficient gas cushion in front of the prechamber gas valve during combustion. This equivalent length is thus to be understood as a measure of a substitute volume.The equivalent length is not necessarily an actual structural dimension, but rather indicates the length that would be required if the overflow channel were designed with a constant cross-sectional area, which would correspond to the cross-sectional area immediately downstream of the prechamber gas valve (from this, the equivalent volume is calculated – equivalent length multiplied by the cross-sectional area immediately downstream of the prechamber gas valve). The actual structurally intended length of the overflow channel results from this equivalent volume (equivalent length multiplied by the cross-sectional area immediately downstream of the prechamber gas valve) and the change in cross-section along the overflow channel.

[0026] Put another way, the equivalent length is the length of an imaginary channel that has the same volume as the actual overflow channel, but has the same cross-sectional area of ​​the overflow channel as is immediately downstream of the prechamber gas valve.

[0027] Preferably, the transfer channel, preferably the first section, may have a section inclined substantially towards a dividing plane between the pre-chamber and the rest of the cylinder head. For example, the angle of the transfer channel, preferably the first section, with the axis of symmetry of the pre-chamber gas valve may be between 20° and 70°. Such an inclined profile (at least of the first section) of the transfer channel allows for particularly high mechanical stability of the cylinder head. The flow characteristics of the supplied propellant gas are also optimized by eliminating the need to navigate any sharp angles. To create such a gas channel, a flank of the cylinder head may be inclined. This can be selected, for example, such that the inclined flank is at a right angle to the axis of the transfer channel.This facilitates the creation of the overflow channel by drilling. It is particularly advantageous to provide that the angle of the overflow channel to the axis of symmetry of the valve body is 20° to 30°.

[0028] It may be provided that a space is included between the seat of the prechamber gas valve and the inlet of the prechamber gas valve to the overflow channel. This is the case when the valve seat of the prechamber gas valve does not connect directly to the prechamber or to the overflow channel leading to the prechamber, but rather a cavity is formed between them. Providing this space ensures a particularly efficient flow of propellant gas from the prechamber gas valve into the overflow channel.

[0029] Preferably, the chamber can be designed to have a largely pear-shaped form, tapering towards the pre-chamber. This allows the flow of propellant gas from the pre-chamber gas valve into the overflow channel to be favorably influenced while still keeping the volume small.

[0030] Furthermore, protection is sought for an internal combustion engine, in particular a stationary internal combustion engine with at least one cylinder head according to the invention.

[0031] The invention can preferably be used in a stationary internal combustion engine, for marine applications, or for mobile applications such as so-called "Non-Road Mobile Machinery" (NRMM) – preferably in each case designed as a reciprocating engine (preferably a gas engine). The internal combustion engine can serve as a mechanical drive, e.g., for operating compressor systems, or be coupled with a generator to form a genset for generating electrical energy.

[0032] Exemplary embodiments of the invention are discussed with reference to the figures. They show: Fig. 1 a first embodiment of a cylinder head, Fig. 2 the in Fig. 1 marked cross-section, Fig. 3 a second embodiment of a cylinder head, Fig. 4 the in Fig. 3 marked cross-section, Fig. 5 an alternative embodiment to Fig. 4 and Fig. 6 another alternative embodiment to Fig. 4 .

[0033] Figs. 1 and 2 Figure 1 shows a first embodiment of a cylinder head 2 for an internal combustion engine with a pre-chamber 3. The pre-chamber gas valve 5 and a spark plug (not shown for clarity) are inserted in a spark plug sleeve 4. The spark plug sleeve 4 is installed in the cylinder head 2 of the internal combustion engine (not shown in its entirety here).

[0034] Fig. 1Figure 1 shows a longitudinal section through the cavity of the cylinder head 2, into which the spark plug sleeve 4 is inserted. The spark plug sleeve 4 comprises a shaft made of cylinder sections concentric around the axis of symmetry S1 for receiving a spark plug and has a bore with the axis of symmetry S2 for receiving a pre-chamber gas valve 5.

[0035] A bypass channel 10 leads from the prechamber gas valve 5 to the prechamber. 3. The antechamber 3 consists of the actual antechamber space 6,The pre-chamber 6 consists of the cavity in which the mixture ignites and the transfer ports 9, through which the pre-chamber 6 is connected to the main combustion chamber (not shown). After ignition in the pre-chamber 6, the ignition flares pass through the transfer ports 9 into the main combustion chamber. In the present embodiment, the pre-chamber 3 is designed as a separate component from the spark plug sleeve 4 and is connected to the spark plug sleeve 4, for example, by crimping.

[0036] The spark plug 6, not shown for clarity, is screwed into the spark plug sleeve 4 via the spark plug bore 12, which is concentric with the axis of symmetry S1, such that it is preferably flush with the pre-chamber 3 and its electrode(s) protrude into the pre-chamber 3. The pre-chamber 3 is enriched with propellant gas from the pre-chamber gas valve 5 via the overflow channel 10.

[0037] It is clearly evident how the overflow channel 10 is divided into a first section 8 and a second section 1. The first section 8 leads from a chamber 11 located at the pre-chamber gas valve, which has a closed outer surface, to the second section 1, into which the first section 8 merges.

[0038] The first section 8 is designed as a bore in the spark plug sleeve 4, which is inclined at an angle β to the axis of symmetry S2 or to the axis of symmetry of the valve body.

[0039] Fig. 2 shows the in Fig. 1The indicated section AA through the dividing plane between pre-chamber 3 and spark plug sleeve 4 reveals the second section 1 of the transfer channel 10, which extends around a portion of the circumference of the pre-chamber 3 within an angular range α. This second section 1 (apart from the opening 7 through which it enters the pre-chamber space 6) has a continuous surface. For clarity, the cylinder head is not shown in this figure. In this embodiment, the second section 1 of the transfer channel 10 is formed by a milled groove in the spark plug sleeve 4, which is closed by the adjacent wall of the pre-chamber 3 and forms a channel (the second section 1 of the transfer channel 10).

[0040] Figs. 3 and 4 They show a second embodiment of a cylinder head 2 for an internal combustion engine. In contrast to the Figs. 1 and 2 is in the execution variant of the Figs. 3 and 4 The second section 1 of the overflow channel 10 is implemented in the pre-chamber 3. This is particularly evident from the Fig. 3 visible. Fig. 4 shows in turn the in Fig. 3 marked section BB through the dividing plane between pre-chamber 3 and spark plug sleeve 4.

[0041] The first section 1 of the overflow channel 10 extends in Figs. 3 and 4 in an angular range α around a portion of the circumference of the pre-chamber 3, wherein the second section 1 (apart from the opening 7 through which it enters the pre-chamber space 6) has a continuous cylindrical surface. In this embodiment, the second section 1 of the transfer channel 10 is formed by a milled groove in the pre-chamber 3, which is closed by the adjacent wall of the spark plug sleeve and forms a channel (second section 1 of the transfer channel 10).

[0042] Figs. 5 and 6show alternative embodiments of the second section 1 of the overflow channel 10 in the same cross-section BB as also through the Fig. 4 shown, with this cross-section through the Fig. 3 is defined. However, these embodiments can also be defined analogously with regard to the in Fig. 1 The solution shown can be implemented.

[0043] In the Fig. 5 Figure 1 shows an embodiment in which the second section 1 of the overflow channel 10 opens tangentially into the circumference of the prechamber chamber 6 with the opening 7. By changing the inlet angle of the overflow channel 10, more precisely its second section 1, into the prechamber chamber 6, the flow of propellant gas through the prechamber 3 can be controlled. The second section 1 of the overflow channel 10 is formed by a milled groove in the prechamber 3.

[0044] The in Fig. 6The illustrated embodiment features a second section 1 of the transfer channel 10, which has a cross-sectional reduction 13 before the opening 7 into the pre-chamber chamber 6. By changing the cross-section of the transfer channel 10, more precisely its second section 1, before the pre-chamber chamber 6, the inflow velocity of the propellant gas can be controlled. The second section 1 of the transfer channel 10 is again formed by a milled groove in the pre-chamber 3. Reference symbol list:

[0045] 1 Second section 2 Cylinder head 3 Pre-chamber 4 Spark plug sleeve 5 Pre-chamber gas valve 6 Pre-chamber chamber 7 Opening 8 First section 9 Connecting channel 10 Transfer ports 11 Chamber 12 Spark plug bore 13 Cross-sectional reduction S1 Axis of symmetry S2 Axis of symmetry α Angle range β Angle

Claims

1. A cylinder head for an internal combustion engine comprising a prechamber (3), wherein a prechamber gas valve (5) is fitted into a cavity in the cylinder head (2) and the prechamber gas valve (5) is connected to the prechamber (3) by way of a flow transfer passage (10), wherein the flow transfer passage (10) has a first portion (8) adjoining the prechamber gas valve (5) and a second portion (1) into which the first portion (8) opens, charactericed in that the second portion (1) extends in an angular range (α) of about 20° to about 270° around a part of a periphery of the prechamber (3), wherein the second portion (1) has an uninterrupted peripheral surface apart from that opening (7) with which it passes into the prechamber (3).

2. A cylinder head as set forth in the preceding claim wherein arranged in the cylinder head (2) is a spark plug, preferably by means of a spark plug sleeve (4).

3. A cylinder head as set forth in one of the two preceding claims wherein the second portion (1) extends in an angular range (α) of about 60° to about 180° around the prechamber (3).

4. A cylinder head as set forth in at least one of the preceding claims wherein a cross-sectional area of the flow transfer passage (10), preferably at least over the length of the first portion (8), is between about 1 · π mm2 and about 2.52 · π mm2.

5. A cylinder head as set forth in at least one of the preceding claims wherein a total length of the flow transfer passage (10) is between about 30 mm and about 70 mm.

6. A cylinder head as set forth in at least one of the preceding claims wherein the flow transfer passage (10) - preferably the second portion - is formed both by a wall of the prechamber (3) and also by material of the rest of the cylinder head (2), preferably a spark plug sleeve (4).

7. A cylinder head as set forth in at least one of the preceding claims wherein at least the second portion (1) is formed by at least one, preferably milled, groove in a wall of the prechamber (3) and / or the rest of the cylinder head (2).

8. A cylinder head as set forth in at least one of the preceding claims wherein the flow transfer passage (10) with respect to the cross-sectional area immediately downstream of the prechamber gas valve (5) is of an equivalent length of about 15 to about 23 mm, preferably an equivalent length of about 16 to about 20 mm.

9. A cylinder head as set forth in at least one of the preceding claims wherein the flow transfer passage (10), preferably the second portion (1), has a substantially parallel portion in relation to a separation plane between prechamber (3) and the rest of the cylinder head (2).

10. A cylinder head as set forth in at least one of the preceding claims wherein the flow transfer passage (10), preferably the first portion (8), has a portion inclined substantially relative to a separation plane between the prechamber (3) and the rest of the cylinder head (2).

11. A cylinder head as set forth in at least one of the preceding claims wherein a space (11) is provided between a seat of the valve head of the prechamber gas valve (5) and a mouth opening of the prechamber gas valve (5) into the flow transfer passage (10).

12. A cylinder head as set forth in at least one of the preceding claims wherein the flow transfer passage (10) is of a cross-section varying over its length.

13. An internal combustion engine comprising a cylinder head (2) as set forth in at least one of the preceding claims.