Pre-chamber spark plug with improved cap

Description

State of the art

[0001] The present invention relates to a pre-chamber spark plug with an improved cap that can be individually adapted to different combustion chamber geometries.

[0002] Pre-chamber spark plugs are known in various designs from the prior art. A pre-chamber of the pre-chamber spark plug is usually defined by a cap relative to the combustion chamber of an internal combustion engine. Through-openings are provided in the cap so that, after ignition in the pre-chamber, torch jets can pass through the through-openings into the combustion chamber of the internal combustion engine and ignite a fuel-air mixture located there. The cap of the pre-chamber spark plug has a uniform, dome-like basic shape. It has now been discovered that unfavorable flow situations can arise under certain constellations of an operating environment, for example due to the angular position of the pre-chamber spark plug in the combustion chamber or due to other components arranged next to the pre-chamber spark plug, such as an injection valve.This can lead to a situation where the exchange of fresh gas and residual gas in the prechamber of the prechamber spark plug is no longer possible or only possible to a limited extent. The shape of the cap of the prechamber spark plug can also cause an injector to be sprayed or exposed to hot gas, which can lead to thermal overheating.

[0003] Prechamber spark plugs are known from US 2018 / 219356 A1, US 1 374 847 A and US 1 357 661 A which have a recess on the outside of the cap. Disclosure of the invention

[0004] The pre-chamber spark plug according to the invention with the features of claim 1 has the advantage that, in addition to being simple and cost-effective to manufacture, a gas flow in a combustion chamber into which the pre-chamber spark plug protrudes can be specifically influenced, thus enabling significantly improved gas flow guidance. In particular, the inflow and / or outflow of hot media, e.g. hot exhaust air, can be specifically controlled. Furthermore, the pre-chamber spark plug according to the invention has an optimized exchange of fresh gas and residual gas in the pre-chamber. This always enables reliable ignition of a mixture in the pre-chamber of the pre-chamber spark plug in a wide variety of operating situations. This is achieved according to the invention in that the cap of the pre-chamber spark plug has a recess on a side facing the combustion chamber.By appropriately positioning and optimizing the geometry of the prechamber spark plug so that the recess on the cap influences the flow in the area of ​​the injector or other components of an internal combustion engine, the advantages listed above can be achieved. The geometric design of the recess can be adapted to the specific conditions of a combustion chamber.

[0005] According to the invention, at least one first through-opening is provided in the cap, which opens into the recess on the outside of the cap. Thus, a flare jet emerging from a prechamber of the prechamber spark plug through the first through-opening in the cap can be directly influenced in a flow-optimized manner by the recess on the outside of the cap. For example, the flare jet emerging through the first through-opening can be directed directly to an area in the combustion chamber where a particularly flammable mixture of fuel and air is present.

[0006] The subclaims show preferred developments of the invention.

[0007] Particularly preferably, several through-openings in the cap open into the recess. This allows for particularly high variability in influencing the flow of the gas or flare jets exiting the cap, as well as the gas flowing into the cap. This allows for particularly effective gas exchange in the prechamber of the prechamber spark plug.

[0008] Particularly preferably, the recess is provided exclusively on the outer side of the cap, facing the combustion chamber. The inner side of the cap is designed without a recess and / or projection or the like. Particularly preferably, the inner side of the cap is designed to be continuously concave.

[0009] According to a particularly preferred embodiment of the invention, the recess on the outside of the cap is concave. This allows a trough-shaped recess to be provided on the outside of the cap, which is particularly aerodynamically optimized. The recess is preferably provided in the form of a partial spherical surface or a partial ellipsoid.

[0010] According to a further preferred embodiment of the invention, a housing of the prechamber spark plug has a thread, wherein the recess of the cap is positioned depending on a thread start and / or a thread end. This ensures that, during assembly of the prechamber spark plug, the position of the recess of the cap is always arranged at the correct location in the combustion chamber.

[0011] Particularly preferably, a center of the cap recess and a thread start on the housing of the pre-chamber spark plug are arranged in a plane that encompasses a center axis of the pre-chamber spark plug. In other words, the recess and a thread start of the pre-chamber spark plug are aligned. Further preferably, the cap recess is a symmetrical depression.

[0012] The cap preferably has at least one further through-opening extending through the cap outside the recess. Further preferably, a first angle α of a center line of the first through-opening, which opens into the recess in the cap, to the center axis of the pre-chamber spark plug is different from a second angle β of the further through-opening in the cap. The cap preferably has exactly one recess relative to the center axis of the pre-chamber spark plug.

[0013] The recess into which the first through-opening opens is formed asymmetrically to a central axis of the pre-chamber spark plug.

[0014] In order to enable particularly cost-effective manufacturing of the pre-chamber spark plug and the cap, the cap is preferably an MIM component (metal injection molding) or a sintered component. Short description of the drawings

[0015] A preferred embodiment of the invention will be described in detail below with reference to the accompanying drawings. In the drawing: Figure 1 is a schematic sectional view of a pre-chamber spark plug according to an embodiment of the invention, and Figure 2 is a schematic, enlarged detailed sectional view of the cap of the pre-chamber spark plug of Figure 1 . Preferred embodiment of the invention

[0016] The following is based on the Figure 1 and 2a pre-chamber spark plug 1 according to a preferred embodiment of the invention is described in detail.

[0017] As from Figure 1 As can be seen, the prechamber spark plug 1 comprises a prechamber 2, which is defined by a cap 3 that is essentially U-shaped in section. The cap 3 is fixed to a housing 6 of the prechamber spark plug, for example by means of a welded connection 9. The cap 3 is arranged on an installation-space-side end 10 of the prechamber spark plug.

[0018] The pre-chamber spark plug 1 further comprises a center electrode 5 and an insulator 7.

[0019] The housing 6 has an external thread 4, which is located at the combustion chamber end of the housing 6. The cap 3 is connected to the housing 6.

[0020] The external thread 4 is used to fix the pre-chamber spark plug in a cylinder head or the like.

[0021] Furthermore, several through-openings 31, 32 are provided in the cap 3. Upon ignition in the prechamber 2 of the prechamber spark plug, so-called torch jets are emitted through the through-openings 31, 32 into a combustion chamber of an internal combustion engine, where a mixture of fuel and air is then ignited. The position and number of the through-openings 31, 32 can vary.

[0022] Since every internal combustion engine has different conditions regarding the position of the pre-chamber spark plug 1 relative to an injector injection jet, the position of the injector, and other geometric constraints, such as the geometry of a piston and the arrangement of other components within the installation space, individual adaptation of the pre-chamber spark plug is desirable for optimized flow guidance. This is achieved by designing the cap 3 asymmetrically.

[0023] The cap 3 has a recess 8 on an outer side 34 facing the combustion chamber, which in this embodiment is a trough-shaped recess. The recess 8 has the geometric shape of a partial spherical surface.

[0024] As shown in detail Figure 2 As can be seen, a first through-opening 31 opens into the recess 8. The first through-opening 31 is linear and has a center line M1. The center line M1 is arranged at a first angle α to a center axis XX of the prechamber spark plug 1.

[0025] Figure 2 further comprises a second through-opening 32 with a second center line M2, which is arranged at a second angle β to the center axis XX of the prechamber spark plug. The angle β is greater than the angle α.

[0026] Furthermore, the cap 3 has a continuously concave inner side 33.

[0027] Due to the asymmetrical design of the cap 3 with the recess 8, into which the first through-opening 31 opens, an optimized gas flow can now be achieved both during a gas exchange for exchanging the gas in the prechamber 2 and when flare jets emerge from the prechamber 2 via the first through-opening 31. For example, the flare jets emerging from the first through-opening 31 can be directed such that they are directed toward an area in the combustion chamber that has a high ignitability.

[0028] Furthermore, the first center line M1 of the first through-hole 31 and a thread start 40 of the external thread 4 lie in one plane (in the plane shown in Figure 2shown sectional plane), wherein the plane also includes the central axis XX of the prechamber spark plug 1. This allows for precise positioning of the recess 8 of the asymmetrically designed cap 3 when mounting the prechamber spark plug 1 on a cylinder head or the like. This makes it possible, in particular, to avoid assembly errors which would not lead to the desired optimized gas flow guidance if the recess 8 were incorrectly positioned on the combustion chamber.

[0029] Thus, a predetermined orientation of the recess 8 to a thread start 40 as well as a predetermined orientation of the first through opening 31 to the thread start 40 can be achieved.

[0030] Thus, the inventive concept of providing at least one recess 8 on an outer side of the cap 3 allows for a targeted gas flow both when gas flows out of the prechamber 2 and when gas flows into the prechamber 2. The geometric shape of the recess 8 can be adapted to the existing conditions in a combustion chamber. The cap 3 can be manufactured cost-effectively, for example, using the MIM process or by sintering.

[0031] It should be noted that it is also possible for several recesses 8 to be provided on the outer side 34 of the cap 3. Several through-openings can also open into a recess in the cap 3.

Claims

1. Pre-chamber spark plug having a central axis (X-X), comprising - a housing (6), and - a cap (3), which is arranged at a combustion-chamber end (10) of the pre-chamber spark plug, - the cap (3) having a depression (8) on an outer side (34) of the combustion chamber, - wherein a first through-opening (31), which opens in the depression (8) of the cap (3), is provided in the cap (3), characterized in that the depression (8), in which the first through-opening (31) opens, is formed asymmetrically to a central axis (X-X) of the pre-chamber spark plug.

2. Pre-chamber spark plug according to Claim 1, wherein a plurality of through-openings (31, 32) open in the depression (8) of the cap (3).

3. Pre-chamber spark plug according to either of the preceding claims, wherein an inside (33) of the cap (3) is concave.

4. Pre-chamber spark plug according to any of the preceding claims, wherein the depression (8) is concave.

5. Pre-chamber spark plug according to any one of the preceding claims, wherein the housing (6) has an external thread (4) and the depression (8) of the cap (3) is positioned depending on a thread start (40) and / or a thread end of the external thread (4).

6. Pre-chamber spark plug according to Claim 5, wherein a centre of the depression (8) and a thread start (40) on the housing lie in a plane which is arranged in a central axis (X-X) of the pre-chamber spark plug.

7. Pre-chamber spark plug according to any one of the preceding claims, wherein the depression (8) is a symmetrically formed trough.

8. Pre-chamber spark plug according to any one of the preceding claims, wherein the cap (3) has at least one further through-opening (32), which runs through the cap (3) outside the depression (8), and in particular wherein a first angle (α) of a first centre line (M1) of the first through-opening (31) with respect to the central axis (X-X) of the pre-chamber spark plug differs from a second angle (β) of the further through-opening (32) with respect to the central axis (X-X) of the pre-chamber spark plug.

9. Pre-chamber spark plug according to any one of the preceding claims, wherein the cap (3) has precisely one single depression (8).

10. Pre-chamber spark plug according to any one of the preceding claims, wherein the cap (3) is an MIM component or a sintered component.