Prechamber spark plug having improved ignition properties

Abstract

Disclosed is a prechamber spark plug comprising a housing (4) having an external thread (70) with a thread beginning (70a), a central electrode (12) and a ground electrode (20), the central electrode (12) and the ground electrode (20) being arranged in a prechamber (2), and a cap (3) that closes the prechamber (2) in the direction of a combustion chamber (5), through-holes (58) for a connection between the prechamber (2) and an outer face of the prechamber spark plug being formed in the housing (4).

Description

State of the art

[0001] The present invention relates to a pre-chamber spark plug with improved ignition properties, and in particular to a pre-chamber spark plug with a flattened cap. Furthermore, the present invention relates to a method for manufacturing a pre-chamber spark plug.

[0002] Prechamber spark plugs are known in various designs from the prior art, for example from WO 2007 / 092972 A1, DE 10 2019 204169 A1, or DE 10 2020 202385 A1. A prechamber of the prechamber spark plug is typically defined by a housing section and a cap. The cap has through-holes that allow gas exchange between the prechamber and the outside of the prechamber spark plug, usually a combustion chamber of an internal combustion engine. During compression of the internal combustion engine, a fresh mixture of fuel and air flows into the prechamber and must reach the area of ​​the electrodes, where a spark is generated during ignition. A significant increase in the volume of the combustion gases in the prechamber after ignition leads to a sharp pressure rise, which in turn causes the hot gases to escape from the through-holes at high velocity in the form of flares.This allows large portions of the combustion chamber to be ignited simultaneously. To ensure this ignition in the combustion chamber, the through-holes in the cap must be correctly aligned when the pre-chamber spark plug is screwed in. This means the cap must be aligned relative to the beginning of the external thread of the pre-chamber spark plug before it is attached to the housing. However, this involves a relatively high degree of uncertainty regarding correct positioning, which can lead to impaired ignition performance in the combustion chamber of the internal combustion engine during subsequent operation of the pre-chamber spark plug. Disclosure of the invention

[0003] In contrast, the pre-chamber spark plug according to the invention, with the features of claim 1, has the advantage that highly precise alignment of the through-holes of the pre-chamber spark plug relative to an external thread is possible. This allows the through-holes of the pre-chamber spark plug, when installed in an internal combustion engine, to have a precise orientation relative to the combustion chamber. This results in a defined exit geometry and alignment of the spark jets through the through-holes and thus excellent, practically complete ignition of a fuel-air mixture in the combustion chamber of the internal combustion engine. According to the invention, an external thread and through-holes for the pre-chamber spark plug can be machined in a single setup.This also makes the pre-chamber spark plugs particularly suitable for large-scale industrial production, as increased use of pre-chamber spark plugs in mobile internal combustion engines is planned for the future.

[0004] Furthermore, very good heat dissipation from thermally stressed areas around the through-holes is possible. According to the invention, this is achieved by the pre-chamber spark plug having a housing with an external thread and a thread start, a center electrode, and a ground electrode, which are arranged in a pre-chamber. The pre-chamber spark plug also includes a cap that closes the pre-chamber towards a combustion chamber. In addition to the external thread, the housing has through-holes for a connection between the pre-chamber and an outer surface of the pre-chamber spark plug towards the combustion chamber. According to the invention, the cap is designed without any through-holes. Thus, the cap can preferably be provided as a circular disc, making it particularly simple and cost-effective. As a result, all through-holes are located within the housing.Thus, the external thread and the through-holes can be produced in a single clamping of the housing. The through-holes no longer need to be provided in the cap, thereby eliminating the alignment problems between the cap with through-holes and the start of the external thread that exist in the prior art. Since the through-holes are provided in the housing, particularly good heat dissipation of the thermally stressed areas around the through-holes is also possible through direct connection to the cooled housing.

[0005] The dependent claims describe preferred embodiments of the invention.

[0006] Preferably, the cap of the pre-chamber spark plug is designed as a flat cap, wherein an outer surface of the flat cap, which faces the combustion chamber, is flat. That is, an outer surface of the cap lies in a plane defined by the outer surface.

[0007] The housing is preferably designed with a threaded section and a non-threaded section. The non-threaded section adjoins the threaded section and is formed as the last part of the housing in the direction of the combustion chamber. The through-holes connecting the pre-chamber to the combustion chamber are located in the non-threaded section. This allows the pre-chamber spark plug according to the invention to be manufactured particularly easily and cost-effectively.

[0008] Preferably, the unthreaded section has a thinner profile than the threaded section. This allows for better heat dissipation towards the thicker threaded section, thus preventing thermal problems, especially near the through-holes. In particular, the thermal inertia of the part of the pre-chamber spark plug that extends into the combustion chamber can be reduced, which in turn counteracts unwanted pre-ignition or self-ignition.

[0009] Alternatively, the unthreaded area can also have the same or greater thickness than the threaded area. Thickening the unthreaded area of ​​the housing can influence the pre-chamber volume, a key factor in designing a pre-chamber spark plug for an internal combustion engine. Furthermore, such thickening can be used to improve flow guidance within the pre-chamber.

[0010] The through-holes are preferably arranged at an obtuse angle to the central axis of the pre-chamber spark plug. The choice of this obtuse angle determines, in particular, the exit direction of the torch jets from the through-holes. Furthermore, the gas exchange capacity for replacing the gas mixture combusted in the pre-chamber after ignition with fresh gas (fresh fuel and air) can be improved by selecting an obtuse angle. To allow for individual adaptation of the pre-chamber spark plug to different combustion chambers of various internal combustion engine manufacturers, each through-hole in the housing is preferably designed with a different angle to the central axis of the pre-chamber spark plug. The angle is preferably in the range of 70° to 140°, and particularly 95° to 120°.

[0011] For particularly simple and cost-effective manufacturing, the cap is designed as a flat disc. Discs can be produced very inexpensively, and a connection between the cap and the housing can be achieved through simple measures, such as a circumferential weld. To improve the fixation of the disc-shaped cap, the disc preferably has an annular shoulder on its outer circumference, which allows the disc to rest against the housing.

[0012] According to a further preferred embodiment of the invention, the housing has a receiving opening in the threaded area for fixing the ground electrode. This places the fixing of the ground electrode in the threaded area of ​​the housing. Thus, the unthreaded area can remain without a receiving opening for the ground electrode, allowing unrestricted positioning of the through-holes in the unthreaded area of ​​the housing.

[0013] In an embodiment not part of the invention, the cap has exactly one central through-hole, the center of which lies on the central axis of the pre-chamber spark plug. This still allows the cap to be easily fixed to the housing, as the central through-hole is always correctly positioned, namely on the central axis of the pre-chamber spark plug. Therefore, when fixing the cap to the housing, it is not necessary to ensure precise alignment of the cap relative to the housing; the cap can be placed on the housing in any orientation and secured there.

[0014] According to a further preferred embodiment of the invention, a ground electrode is fixed to the cap. Preferably, the ground electrode is arranged on the cap such that a central axis of the ground electrode coincides with the central axis of the pre-chamber spark plug. This also ensures that the cap, equipped with the ground electrode, can simply be positioned on the housing and then fixed in place without any alignment step. Thus, incorrect assembly with regard to the geometric alignment of the cap relative to the housing is prevented, even when a ground electrode is provided on the cap.

[0015] Preferably, the cap is flat on the outside and has a profile on its inside for influencing the internal flow in the pre-chamber. The profile is preferably conical, in particular a symmetrical cone. Thus, the internal gas flow in the pre-chamber can be influenced by the cap's inner profile both during the gas exchange step and when the ignited gas mixture exits as flares from the through-openings.

[0016] The present invention further relates to a method for manufacturing a pre-chamber spark plug. The method comprises the steps of providing a housing for the pre-chamber spark plug, wherein, in a single clamping of the housing, an external thread is produced on the housing, and, in the same clamping, at least one through-hole is provided for a connection between the pre-chamber of the pre-chamber spark plug and an outer surface of the pre-chamber spark plug. A cap can be fixed to the housing before or after the production of the external thread and the through-hole, for example, by means of a weld. The cap can be manufactured without any through-hole, or the cap can have a central through-hole located on a central axis of the pre-chamber spark plug, thus preventing mispositioning of the cap.By manufacturing the external thread with a thread start and at least one through-hole in the housing in a single setup, the need for complex alignment of the cap relative to the housing is eliminated. The through-holes are always correctly positioned relative to the thread start of the external thread, allowing the cap to be fixed to the housing without any alignment process.

[0017] This allows the pre-chamber spark plug to be manufactured simply, with the highest accuracy and cost-effectively, especially as a mass-produced component for use in mobile internal combustion engines. drawing

[0018] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows: Figure 1 is a schematic, simplified partial cross-sectional view of a pre-chamber spark plug according to a first preferred embodiment of the invention; Figure 2 is a schematic, simplified partial cross-sectional view of a pre-chamber spark plug according to a second preferred embodiment of the invention; Figure 3 is a schematic, simplified partial cross-sectional view of a pre-chamber spark plug according to a third preferred embodiment of the invention; Figure 4 is a schematic, simplified partial cross-sectional view of a pre-chamber spark plug according to a fourth preferred embodiment, which is not part of the invention. Figure 5 shows a schematic, simplified partial cross-sectional view of a pre-chamber spark plug according to a fifth preferred embodiment of the invention. Preferred embodiments of the invention

[0019] The following refers to Figure 1a pre-chamber spark plug 1 according to a first preferred embodiment of the invention is described in detail.

[0020] As from Figure 1 As can be seen, the pre-chamber spark plug 1 comprises a pre-chamber 2 and a cap 3. The pre-chamber 2 is defined by the cap 3 and a housing 4.

[0021] The housing 4 has a threaded section 41 and a non-threaded section 42, which adjoins the threaded section 41 directly in the direction of a combustion chamber 5. An external thread 70 is provided on the threaded section 41. The external thread 70 has a thread start 70a.

[0022] The pre-chamber spark plug 1 is screwed into a corresponding threaded opening of an internal combustion engine by means of the external thread 70, so that the cap 3 is directed towards a combustion chamber 5 of the internal combustion engine.

[0023] The pre-chamber spark plug 1 further comprises a center electrode 12, which is electrically insulated by means of an insulator 6, and at least one ground electrode 20.

[0024] As from Figure 1 As can be seen, the ground electrode 20 is arranged laterally in a receiving opening 40 in the housing 4. The ground electrode 20 is positioned at a defined distance from the center electrode 12. The ground electrode 20 can be fixed in the housing 4, for example, by means of an interference fit, a weld, or both.

[0025] What's next? Figure 1 As can be seen, the cap 3 is designed as a flat, circular disc and has a flat outer surface 31 and a flat inner surface 32. The cap 3 is designed without any through-opening.

[0026] The passage openings 58 are, as shown from Figure 1As can be seen, the through-holes are formed in the threadless area 42 of the housing 4. In the example shown, two through-holes 58 are provided, one of which is arranged at an obtuse angle α to a central axis XX of the pre-chamber spark plug, and the second through-hole 58 is arranged at a second obtuse angle β to the central axis XX. The first obtuse angle α differs from the second obtuse angle β. It is possible that further through-holes are also provided.

[0027] Preferably, the diameter of the through-openings 58 in the housing 4 is the same.

[0028] Alternatively, the diameters of the through holes are preferred to be different.

[0029] The cap 3 has a recessed shoulder 33 on its outer circumference, which allows the cap 3 to abut an end face of the housing. A connection between the cap 3 and the housing 4 is preferably provided by means of a weld.

[0030] Thus, the through-holes 58 of the pre-chamber spark plug 1 are not formed in the cap as in the prior art, but are provided exclusively in the housing 4. The housing 4 is formed in one piece with the threaded area 41 and the unthreaded area 42. The threaded area 41 has a wall thickness W1, which is greater than the wall thickness W2 of the unthreaded area 42. The wall thickness W1 of the threaded area 41 is defined without the external thread. The first wall thickness W1 is at least twice as large as the second wall thickness W2.

[0031] By providing the external thread 70 with the defined thread start 70a and the through-holes 58 in the housing 4, the external thread 70 and the through-holes 58 can be formed on the housing in a single clamping operation. This eliminates the need for the complex alignment of the cap relative to the thread start of the external thread, which is necessary in the prior art to correctly align the cap, in which the through-holes are usually provided, with the external thread.

[0032] In this first embodiment, the cap 3 is completely free of through-openings or the like and is provided as a flat round disc.

[0033] For the production of the external thread and the through openings 58, it is irrelevant whether the external thread 70 is produced first and then the through openings 58, or vice versa.

[0034] Thus, the through-holes 58 can be positioned at the correct locations relative to the external thread, ensuring precise positioning of the through-holes 58 when the pre-chamber spark plug is screwed in. This guarantees the correct orientation of the through-holes 58 relative to the combustion chamber 5, allowing the so-called internal engine flow within the combustion chamber 5 to be utilized. This flow introduces unburned fuel-air mixture into the pre-chamber 2 and, after ignition, purges residual gases from the pre-chamber 2 through the pre-chamber spark plug 2. The correct positioning of the through-holes 58 also directs the flare jets generated after ignition, which exit from the pre-chamber 2 through the through-holes 58 into the combustion chamber 5, to the desired positions within the combustion chamber 5, thereby enabling the most complete and simultaneous ignition possible.

[0035] Regarding the method according to the invention, it should be noted again that the cap 3 can also be fitted before the external thread 70 and the through holes 58 are cut. Preferably, however, the cap 3 is fitted and fixed onto the housing 4 as one of the next steps. This also allows for simplified alignment of the lateral ground electrode 20 relative to the center electrode 12 when the pre-chamber spark plug is open (without the cap).

[0036] The following refers to Figure 2 A pre-chamber spark plug 1 according to a second embodiment of the invention is described in detail. Identical or functionally equivalent parts are designated with the same reference numerals as in the first embodiment.

[0037] As from Figure 2As can be seen, in the second embodiment the ground electrode 20 is arranged on an inner surface 32 of the cap 3. In this case, a central axis of the ground electrode 20 and a central axis XX of the pre-chamber spark plug 1 coincide. As further explained below... Figure 2 As can be seen, the central axis of the center electrode 12 also lies on the central axis XX of the pre-chamber spark plug. Therefore, the ground electrode 20 can be fixed separately and easily centrally on the inside of the cap 30 without alignment problems. Figure 2A lateral receiving opening 40 is shown in the housing. Here, either another ground electrode 2 can be fixed, or alternatively, the receiving opening 40 can only be used to check the electrode gap between the ground electrode 20 and the center electrode 2 and can then be closed with a blanking plug or the like. As in the first embodiment, the cap 3 is flat and without any through-holes. All through-holes are provided in the housing 4 with the corresponding advantages regarding the alignment of the through-holes 58 relative to the thread start 70a of the external thread 70. Otherwise, this embodiment corresponds to the first embodiment, so reference can be made to the description given there.

[0038] Figure 3Figure 1 shows a pre-chamber spark plug 1 according to a third embodiment of the invention. Identical or functionally equivalent parts are again designated as in the preceding embodiments.

[0039] The third embodiment essentially corresponds to the first embodiment, except that, unlike the first embodiment, the cap 3 is designed differently in the third embodiment. In the third embodiment, the cap 3 has a profile on an inner surface 32. In this embodiment, a symmetrical cone 34 is provided on the inner surface 32 of the cap 3. The cylindrical cone 34 can influence the internal gas flow in the region of the prechamber 2. In particular, gas exchange can be facilitated by the cone, and the flare jets can exit the prechamber 2 into the combustion chamber 5 through the through-openings 58 in a more controlled manner. In this embodiment, a conical surface of the symmetrical cone is parallel to a center line at the obtuse angle α of one of the through-openings 58.Otherwise, this embodiment corresponds to the first embodiment, so reference can be made to the description given there.

[0040] Figure 4 shows a pre-chamber spark plug 1 according to a fourth embodiment, which is not part of the invention.

[0041] Identical or functionally equivalent parts are again designated as in the previous examples.

[0042] The fourth embodiment essentially corresponds to the first embodiment, except that, unlike the first embodiment, a central through-opening 71 is formed in the cap 3. A central axis of the central through-opening 71 coincides with the central axis XX of the pre-chamber spark plug 1. This means that the position of the through-opening 71 in the cap 3 is independent of the mounting position of the cap on the housing 4. The provision of the central through-opening 71 particularly improves gas exchange between the combustion chamber 5 and the pre-chamber 2 and also generates a central torch jet from the pre-chamber 2 into the combustion chamber 5. Otherwise, this embodiment corresponds to the preceding embodiments, so reference can be made to the descriptions given therein.

[0043] Figure 5Figure 1 shows a pre-chamber spark plug 1 according to a fifth embodiment of the invention. Identical or functionally equivalent parts are designated with the same reference numerals as in the preceding embodiments.

[0044] The fifth embodiment essentially corresponds to the first embodiment, except that, unlike the first embodiment, the unthreaded section 42 has a wall thickness W3 equal to the wall thickness W1 of the threaded section 41. It should be noted that the unthreaded section 42 can also have a wall thickness W3 that is preferably greater than the wall thickness W1 of the threaded section 41. Increasing the wall thickness W3 of the unthreaded section 42 results in longer passage openings 58. This improves flow guidance within the prechamber 2 during gas exchange. Furthermore, this also allows the prechamber volume of the prechamber 2 to be influenced, since the prechamber volume is a key parameter in the design of the prechamber spark plug for a specific internal combustion engine. In this case, the unthreaded section 42 tapers towards the central axis XX.The third wall thickness W3 is the same as the first wall thickness W1 of the thread area 41.

[0045] Otherwise, this embodiment corresponds to the preceding embodiments, so reference can be made to the description given there.

Claims

1. Pre-chamber spark plug comprising: - a housing (4) with an external thread (70) with a thread start (70a), - a central electrode (12) and an earth electrode (20), wherein the central electrode (12) and the earth electrode (20) are arranged in a pre-chamber (2), and - a cap (3) which closes off the pre-chamber (2) in the direction of a combustion chamber (5), - wherein passage openings (58) for connection between the pre-chamber (2) and an outside of the pre-chamber spark plug are formed in the housing (4), characterized in that the cap (3) is formed without a passage opening, and all the passage openings (58) are provided in the housing (4).

2. Pre-chamber spark plug according to Claim 1, wherein the cap (3) is in the form of a flat cap and is configured to be flat at the outside of the pre-chamber spark plug.

3. Pre-chamber spark plug according to either of the preceding claims, wherein the housing (4) is formed in one piece with a threaded region (41), having the external thread (70), and with a thread-free region (42), wherein the thread-free region (42) adjoins the threaded region (41) in the direction of the combustion chamber, and wherein the passage openings (58) are formed in the thread-free region (42).

4. Pre-chamber spark plug according to Claim 3, - wherein the thread-free region (42) has a wall thickness (W2) which is less than a wall thickness (W1) of the threaded region (41), or - wherein the thread-free region (42) has a wall thickness (W3) which is greater than or equal to the wall thickness (W1) of the threaded region (41).

5. Pre-chamber spark plug according to Claim 3 or 4, wherein the passage openings (58) are arranged at an angle (α, β), in particular an obtuse angle, to a centre axis (X-X) of the pre-chamber spark plug.

6. Pre-chamber spark plug according to Claim 5, wherein each passage opening (58) is arranged at a different angle (α, β) to the centre axis (X-X).

7. Pre-chamber spark plug according to one of Claims 2 to 6, wherein the cap is designed as a flat disc.

8. Pre-chamber spark plug according to one of the preceding claims, wherein, at an outer circumference, the cap (3) has an annular shoulder (33) for fixing to the housing (4).

9. Pre-chamber spark plug according to one of the preceding claims, wherein the earth electrode (20) is fixed to the cap (3), in particular in such a way that a centre line of the earth electrode lies on the centre axis (X-X) of the pre-chamber spark plug.

10. Pre-chamber spark plug according to one of the preceding claims, wherein the cap (3) is configured to be flat at an outer side (31) and has at an inner side (32) a profile for influencing an internal flow in the pre-chamber (2), in particular a conical profile.

11. Method for producing a pre-chamber spark plug according to one of Claims 1 to 10, the method comprising the steps of providing a housing (4), wherein an external thread (70) with a thread start (70a) is produced on the housing in a chucking operation and at least one passage opening (58) for connection of a pre-chamber (2) to an outside of the pre-chamber spark plug is formed in the housing (4) in the same chucking operation.

12. Method according to Claim 11, wherein a cap (3) is fixed to the housing before the production of the external thread (70) and of the at least one passage opening (58) in the housing (4), or wherein the cap (3) is fixed to the housing after production of the external thread (70) and of the at least one passage opening (58).

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