Cap for a prechamber spark plug with improved function and prechamber spark plug having a cap of this type

Abstract

The invention relates to a cap (1) for a prechamber spark plug (100) with a longitudinal axis X, comprising a cap body having an outer side (10) and an inner side (15), a main through-bore (21) which extends from the outer side (10) of the cap (1) through the cap body to the inner side (15) of the cap (1) and the bore axis (211) of which intersects the longitudinal axis X of the cap (1) inside the cap (1), and at least one pair of through-bores of a first type (22), wherein this first through-bore type (22) is a tangential through-bore which extends from the outer side (10) of the cap (1) through the cap body to the inner side (15) of the cap (1) and the bore axis (221) of which does not intersect the longitudinal axis X of the cap (1) inside the cap (1), and at least one pair of through-bores of a second type (23), wherein this second through-bore type (23) is a radial through-bore which extends from the outer side (10) of the cap (1) through the cap body to the inner side (15) of the cap (1) and the bore axis (231) of which intersects the longitudinal axis X of the cap (1) inside the cap (1), wherein there is a plane E which extends parallel to the longitudinal axis X and in which an intersection point of the bore axes (221) of the through-bore pair of the first type (22) lies, and wherein the main bore hole (21) is bisected by the plane E and each through-bore (22, 23) of a through-bore pair lies on one side of the plane E.

Description

[0001] R.410583

[0002] - 1 -

[0003] Description

[0004] title

[0005] Cap for a pre-chamber spark plug with improved function, as well as a pre-chamber spark plug with such a cap

[0006] State of the art

[0007] The present invention relates to a cap for a pre-chamber spark plug with an improved function, in particular a gas exchange in the pre-chamber during a gas exchange, and to a pre-chamber spark plug with this cap, as well as to a manufacturing method for this cap.

[0008] Pre-chamber spark plugs are known in various designs from the prior art. They typically feature a cap that defines a pre-chamber, with the cap having through-holes that connect the pre-chamber to the combustion chamber of an internal combustion engine. These through-holes must ensure gas exchange within the pre-chamber. After ignition in the pre-chamber, so-called torch jets propagate through the through-holes into the combustion chamber, where the main ignition of a gas-air mixture then occurs. After ignition, the pre-chamber must be purged to be ready for the next ignition.

[0009] There are different types of through-holes, each offering different advantages. Some through-holes have a bore axis tangential to the longitudinal axis X of the cap and the pre-chamber spark plug, without intersecting the cap's longitudinal axis X. The bore axis can also be defined as tangent to a circle with the cap's longitudinal axis as its center point (R.410583).

[0010] - 2 - are considered. These tangential through-holes create a swirl in the incoming gas. There are also through-holes whose bore axis extends radially to and intersects the longitudinal axis X of the cap and the pre-chamber spark plug, so that gas flowing through a radial through-hole is deflected along the longitudinal axis in the center of the cap.

[0011] The number, arrangement, and orientation of the through-holes on the cap are crucial for the performance of the pre-chamber spark plug, including flame speed, as well as the most complete and rapid combustion and scavenging behavior in the pre-chamber. It is essential to find a cap with the correct combination of the number, arrangement, and orientation of the through-holes so that the pre-chamber spark plug with this cap exhibits good performance across a wide range of different engine conditions.

[0012] Disclosure of the invention

[0013] The cap according to the invention for a pre-chamber spark plug with the features of claim 1 has the advantage that, due to the special arrangement of the through-holes on the cap and the clever combination of different through-hole types, the cap has good purging properties and the gas in the cap has high turbulent kinetic energy, so that when using a pre-chamber spark plug with this cap, a high flame speed and faster and more complete combustion can occur.

[0014] Turbulent kinetic energy refers to the kinetic energy of turbulent flows. This kinetic energy of turbulent flows is a quantitative measure of the intensity of turbulence in a given flow. Kinetic energy can be measured as the root mean square of the fluctuations in flow velocity. In fluid dynamics, turbulent kinetic energy is simply defined as the mean kinetic energy per unit mass for a turbulent flow. The kinetic energy of the turbulent flow is the only quantity that increases the flame velocity. The relationship is that the greater the turbulent kinetic energy, the higher the flame velocity.

[0015] - 3 -

[0016] The more energy is available, the higher the flame speed and the faster and more complete the combustion of the gas takes place.

[0017] The advantages described above are achieved according to the invention by the cap having a longitudinal axis, a cap body with an outer surface and an inner surface, a main through-hole extending from the outer surface of the cap through the cap body to the inner surface of the cap and whose bore axis intersects the longitudinal axis X of the cap inside the cap, and at least one pair of through-holes of a first type, wherein this first through-hole type is a tangential through-hole extending from the outer surface of the cap through the cap body to the inner surface of the cap and whose bore axis does not intersect the longitudinal axis X of the cap inside the cap, and at least one pair of through-holes of a second type, wherein this second through-hole type is a radial through-hole.which extends from the outside of the cap through the cap body to the inside of the cap and whose bore axis intersects the longitudinal axis X of the cap inside the cap. There is a plane E extending parallel to the longitudinal axis, in which the intersection of the bore axes of the through-hole pair of the first type lies, the main bore being bisected by plane E, with each through-hole of a through-hole pair lying on one side of plane E.

[0018] Two through holes form a pair if they are of at least the same type: tangential or radial, and their axes lie in the same plane on the outside of the cap. This means that, on the outside of the cap, the axes of a pair of through holes are equidistant from the combustion chamber-side face of the cap. Specifically, measured along the circumference of the cap, the two through holes of the second type are equidistant (angle β) from the main through hole. Furthermore, the two through holes may be spaced differently from each other than from the main through hole. R.410583

[0019] - 4 -

[0020] In advantageous further developments, the through holes forming a pair can also be the same in other parameters such as the angle a in relation to the longitudinal axis X of the cap and / or the diameter of the through hole.

[0021] The through-holes of the first type are designed as tangential through-holes. This means that the extension of the hole axis does not intersect the longitudinal axis X of the cap, and the extensions of the hole axes of the through-hole pair have an intersection point that is radially spaced from the longitudinal axis X of the cap. As a result, gas flowing through these through-holes is directed around the longitudinal axis X of the cap, thus improving the cap's purging behavior.

[0022] The second type through-hole and the main through-hole are designed as radial through-holes, meaning that the extension of the hole axes intersects the longitudinal axis X of the cap. This has the advantage that the gas flowing in through the radial holes acquires high turbulent kinetic energy, thereby increasing the flame velocity in the pre-chamber and resulting in faster and more complete combustion of the gas by the pre-chamber spark plug with this cap.

[0023] In particular, the intersection of the main bore axis with the longitudinal axis X of the cap is axially spaced from the intersection of the bore axes of the second type of through-holes. For example, the intersection point for the main bore is closer to the combustion chamber-side end face of the cap than the intersection point for the second type of through-holes. This has the technical effect that the gas flowing in through the different through-holes does not meet at the same point along the longitudinal axis, but at different heights, so that the flows reinforce each other and generate high turbulent kinetic energy in the flow.

[0024] In a directional pre-chamber spark plug mounted in a cylinder block, the pre-chamber spark plug and cap are aligned so that the main through-bore faces the intake side of the engine. R.410583

[0025] - 5 -

[0026] By combining through-holes of the first and second type, as well as forming pairs of through-holes of the same type, the advantages of each through-hole type can be combined, resulting in a cap that has good purging behavior of the residual gas and also generates a gas with high turbulent kinetic energy in the pre-chamber spark plug.

[0027] The dependent claims describe preferred embodiments of the invention.

[0028] In a further development of the cap, the through holes of the through hole pair of the first type have the same diameter. Additionally or alternatively, the through holes of the through hole pair of the second type have the same diameter, wherein, in particular, the main through hole has a different diameter than the through holes of the second type.

[0029] The diameter of the through-hole influences the amount of gas flowing into the engine during the intake phase and exiting the pre-chamber after ignition. When the same amount of gas flows through a pair of through-holes, a directed and symmetrical flow pattern results during the intake phase, efficiently guiding the mixture to the ignition point in the pre-chamber spark plug. During the exhaust phase, the bore diameter affects the velocity of the burning mixture and thus the flame penetration depth in the combustion chamber, allowing for optimal combustion control.

[0030] In a further refinement, the through-hole pair of the first type is rotationally asymmetric with respect to rotation about the longitudinal axis X of the cap. Additionally or alternatively, the through-hole pair of the second type is rotationally symmetric with respect to rotation about the longitudinal axis X of the cap. In particular, the through-hole type and the orientation (angle α) of the through-hole with respect to the longitudinal axis X of the cap are considered for the evaluation of rotational symmetry or rotational asymmetry.

[0031] The exact optimal combination of the arrangement of the pairs of through holes depends on the specific engine type in which an R.410583 is used.

[0032] - 6 -

[0033] The pre-chamber spark plug is to be installed with the cap according to the invention. The number of valves and also the arrangement of the injector in relation to the pre-chamber spark plug and the valves play a role in determining which precise design of the cap is best. All designs have in common the combination of through-bore pairs of different types and the associated technical advantage of good purging behavior and high turbulent kinetic energy of the gas.

[0034] In addition to or as an alternative to the advantageous arrangement of the through-holes with respect to rotation about the longitudinal axis X of the cap, the pair of through-holes of the first type and / or the pair of through-holes of the second type can be arranged in a mirror-symmetric arrangement with respect to a plane of symmetry on the cap, wherein the plane of symmetry is defined by the longitudinal axis X of the cap and the axis of the main through-hole. The plane of symmetry corresponds to plane E. In particular, the type of through-hole and the orientation (angle α) of the through-hole with respect to the longitudinal axis X of the cap are considered for the evaluation of the mirror symmetry.

[0035] In one embodiment, it is provided that the intersection of the bore axes of the through bore of the first type inside the cap has a radial distance to the longitudinal axis X of the cap, wherein the radial distance is not less than 15% and not greater than 85% of an inner radius of the cap in a plane A perpendicular to the longitudinal axis in which the intersection of the bore axes of the through bore of the first type lies.

[0036] In particular, the distance is not less than 20% and not greater than 80% of the inner radius of the cap.

[0037] This radial spacing has the advantage that the gas flowing through the second type of through-holes meets and interacts at a point that is sufficiently far from the longitudinal axis and the point of intersection of the gas flowing through the second type of through-holes to ensure the cap is properly purged. Furthermore, the spacing is not too large, so that the gas flow responsible for the purging action has sufficient distance from the inside of the cap to avoid being slowed down by the cap wall. At the same time, this results in another geometric option, R.410583.

[0038] - 7 -

[0039] Spatially separating the mixture flows along the bore axes allows them to reinforce each other positively and generate high turbulent kinetic energy.

[0040] In particular, the intersection of the bore axis of the first-type through-hole inside the cap is radially located on the opposite side of the cap's longitudinal axis X from the main bore. Viewed in cross-section, the main bore is on one side of the cap's longitudinal axis X, and the intersection of the bore axis of the first-type through-hole is on the opposite side. This arrangement causes the flow along the bore axis of all through-holes to collect primarily on the opposite side of the main bore, thus ensuring a directed flow within the pre-chamber volume. Fresh mixture is optimally guided to the ignition point. Simultaneously, the exchange of residual gases in all areas of the pre-chamber volume is ensured after combustion.

[0041] It has proven advantageous that the cap has no through-hole on its combustion chamber-side end face. Instead, all through-holes have an angle α of at least 30° to the longitudinal axis X of the cap, with the angle α being measured on the outside of the cap from the combustion chamber-side end face. The angle α is also not greater than 90°. Preferably, the angle α is not less than 35°, and particularly not less than 60°. This arrangement prevents the burning mixture exiting the cap from striking the combustion chamber walls and the piston of the engine. The impact of the mixture at the combustion chamber boundaries has the disadvantage that, firstly, components are damaged, and secondly, the burning mixture loses energy and is therefore less efficient.

[0042] The angle α is defined by the longitudinal axis X of the cap and the bore axis of the respective through-hole. The main through-hole, the through-holes of the first and second types each have an angle α1, α2, α3 with respect to the longitudinal axis X of the cap. Preferably, the through-holes of one type have the same angle α2, α3 with respect to the longitudinal axis X of the cap. In a particular embodiment, it may be provided that the through-holes of the first type have different angles α2, α2'. R.410583

[0043] - 8 - exhibit. In this case, the pair of through-holes of the first type are neither rotationally symmetric nor mirror-symmetric. This solution addresses asymmetrical positions of the pre-chamber spark plug in the combustion chamber. An asymmetrical position leads to an unfavorable position of the burning mixture in the combustion chamber. This counteracts engine damage or energy loss during combustion at engine limits.

[0044] Furthermore, it has proven advantageous for the main through-bore, the through-bores of the first type, and / or the through-bores of the second type to be cylindrical with a constant diameter, specifically with diameters of no less than 0.5 mm and no greater than 2.0 mm. A targeted selection of the through-bore diameter influences the velocity of the combustion mixture through the through-bores into the combustion chamber. This enables optimal distribution of the combustion mixture and ignition of the main combustion chamber. Moreover, the larger the diameter of the through-bore, the more fuel mixture flows through it. A large flow of fuel mixture can entrain smaller flows of fuel mixture, resulting in a directed flow in the pre-chamber. This technical effect is particularly noticeable when the fuel mixture enters the pre-chamber.

[0045] For example, the main through-hole can have a diameter of not less than 1.0 mm and not greater than 1.4 mm, and / or the through-holes of the first type can have a diameter of not less than 1.0 mm and not greater than 1.3 mm, and / or the through-holes of the second type can have a diameter of not less than 0.7 mm and not greater than 1.1 mm. Preferably, the through-holes of a pair have the same diameter. In a particular embodiment, the through-holes of a pair can also have different diameters.

[0046] In another special embodiment, the main through-bore has the largest diameter, and the diameter of the paired through-bores decreases from the main through-bore along the circumference to the cap side opposite the main through-bore. When the fuel mixture R.410583 flows in

[0047] - 9 - This results in the technical effect that the fuel mixture flowing in through the main through-hole carries with it the fuel flowing in through the smaller through-holes, thus establishing a directed flow. Furthermore, good scavenging behavior of the cap is achieved when the main through-hole and the pair of through-holes of the first type are oriented towards the intake valves, and correspondingly, the pair of through-holes of the second type are oriented towards the exhaust valves. The fuel mixture flowing in through the intake valves can flow into the cap through the through-holes with the larger diameters and be ignited there. This results in larger flares that ignite the fuel mixture in the main combustion chamber and exit through the through-holes with the larger diameters. These larger flares can effectively burn off any knock spots on the intake valves.

[0048] In further advantageous embodiments, there are a total of 5, 7 or 9 through holes, one of which is the main through hole and the other through holes are pairs of through holes of the first or second type, wherein there is at least one pair of through holes of the first type and at least one pair of through holes of the second type.

[0049] Furthermore, it has proven advantageous to arrange the through-holes of the first and second types alternately along the circumference, starting from the main through-hole, in particular to arrange a pair of through-holes of the first type first, followed by a pair of through-holes of the second type, starting from the main through-hole. This results in the same technical effects as described above.

[0050] The invention also relates to a pre-chamber spark plug comprising a housing, an insulator arranged in the housing, a center electrode arranged at least partially in the insulator, a ground electrode arranged on the housing which, together with the center electrode, forms an ignition gap, and a cap according to the invention attached to the housing. The pre-chamber spark plug has improved scavenging behavior of the pre-chamber volume with simultaneously high turbulent kinetic energy of the fuel. R.410583

[0051] - 10 -

[0052] In a further development, the cap on the pre-chamber spark plug is arranged in such a way that when the pre-chamber spark plug is screwed into a cylinder block, the main through-bore faces the intake side of the engine.

[0053] The invention further relates to a manufacturing method for a cap according to the invention, wherein the through holes in the cap are produced by at least one of the following methods: by electrical discharge machining (EDM), by laser drilling, or by machining.

[0054] Brief description of the drawings

[0055] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawing. Identical or functionally identical parts are named and designated with the same reference numerals in the different embodiments. The drawing shows:

[0056] Figure 1 shows a 3D view and a 2D view of an inventive device.

[0057] Cap according to a first embodiment,

[0058] Figure 2 shows the cap in section along one of the three different through-holes for the first embodiment,

[0059] Figure 3 shows a 3D view and a 2D view of an inventive device.

[0060] Cap according to a second embodiment

[0061] Figure 4 shows the cap in section along one of the three different through-holes for the second embodiment, R.410583

[0062] - 11 -

[0063] Figure 5 shows a pre-chamber spark plug with a cap

[0064] Figure 1 a) shows a 3D external view of a first embodiment of the cap 1 according to the invention. The cap 1 has a cap body with a combustion chamber-side end face 11 and a side surface 12a, 12b, which is arranged circumferentially on the end face 11. The cap 1 has a longitudinal axis X, which extends from the combustion chamber-side end of the cap 1 to the end of the cap 1 facing away from the combustion chamber. The combustion chamber-side end face 11 is arranged perpendicular to the longitudinal axis X of the cap. The side surfaces 12a, 12b are radially spaced from the longitudinal axis X and are not arranged perpendicular, but at an angle or parallel to the longitudinal axis X. In this example, the side surface consists of sections 12b angled to the longitudinal axis X and a section 12a parallel to the longitudinal axis X.

[0065] On the outer surface 10 of the cap 1, the openings of three through holes are visible: main through hole 21, first-type through hole 22, and second-type through hole 23. The through holes 21, 22, and 23 have different diameters in this example. The main through hole 21 has a diameter of 1.1 mm to 1.4 mm, particularly 1.3 mm. The first-type through holes 22 have a diameter of 1.0 mm to 1.3 mm, particularly 1.2 mm. The second-type through holes 23 have a diameter of 0.7 mm to 1.1 mm, particularly 0.8 mm.

[0066] There is no through-hole on the combustion chamber-side end face 11 of the cap 1 according to the invention.

[0067] Figure 1b) shows a 2D external view of the cap 1. This is a top view of the cap 1 along the longitudinal axis X. Five through holes 21, 22, 23 with their respective bore axes 211, 221, 231 are visible: one main through hole 21, two through holes of the first type 22, and two through holes of the second type 23. R.410583

[0068] - 12 -

[0069] The bore axes 211, 231 of the main through-hole 21 and the two through-holes of the second type 23 intersect the longitudinal axis X. These three through-holes 21, 23 are radial through-holes.

[0070] The bore axes 221 of the two through bores of the first type 22 do not intersect the longitudinal axis X. These bore axes 221 intersect each other at a point radially spaced from the longitudinal axis X. This distance 222 can be, for example, 15% or greater and up to 85% of the inner radius of the cap 1. The inner diameter is measured in the plane A perpendicular to the longitudinal axis X of the cap 1, in which the point of intersection of the bore axes 221 of the through bore of the second type is located.

[0071] 22. The two through-holes of the first type 22 are rotationally asymmetric to each other.

[0072] A plane E spans the longitudinal axis X of the cap 1 and the bore axis 211 of the main bore 21, bisecting the main through bore 21. Furthermore, one through bore 22, 23 of each pair of through bores lies on one side of plane E. Plane E is also a mirror plane. The through bore 22,

[0073] The two through holes of type 23 form a symmetry pair in this example. The through holes 22, 23 of a pair have the same distance (angle β1, β2) along the circumference from the main through hole 21 and the same orientation of the hole axis 221, 231 with respect to the longitudinal axis X of the cap 1, as well as the same hole diameter. In this example, the through holes of the first type 22 have a smaller distance β1 from the main through hole 21 than the through holes of the second type 23. The two pairs of through holes 22, 23 are mirror images of each other.

[0074] In a special case of this first embodiment, the diameter of the through-holes 21, 22, 23 can decrease along the circumference, starting from the main through-hole 21 to the opposite side of the cap 1. The main through-hole 21 has the largest diameter, and the through-holes of the second type 23 arranged on the opposite side have the smallest diameter.

[0075] Figure 2 shows three sections of cap 1. Each section is along the bore axis 211, 221, 231 of one of the three through bores 21, 22, 23. R.410583

[0076] - 13 -

[0077] Starting from the main through-bore 21 in Figure 2 a), the next through-opening 22, 23 is taken counterclockwise for the further sections, following the top view in Figure 1 b).

[0078] In Figure 2a), the section follows the bore axis 211 of the main through-hole 21. The openings of the three different through-holes 21, 22, 23 on the inside 15 of the cap 1 are shown. The bore axes 211 of the main through-hole 21 and the through-hole 231 of the second type 23 intersect the longitudinal axis X, with the respective points of intersection being axially spaced apart. The extension of the bore axis 211 of the main through-hole 21 intersects the longitudinal axis X of the cap 1 closer to the end face 11 of the cap 1 than the extension of the bore axis 231 of the through-hole of the second type 23. It is clearly visible that the bore axis 221 of the through-hole of the first type 22 does not intersect the longitudinal axis X, but is spaced apart from it.

[0079] The bore axis 211 of the main through-hole 21 forms an angle α with the longitudinal axis X. As shown in further parts b) and a) of Figure 2, the bore axes 211, 221, 231 of the different through-hole types 21, 22, 23 each have different angles α, α2, α3 to the longitudinal axis X of the cap 1, wherein the through-holes of a pair have the same angle α to the longitudinal axis X of the cap 1.

[0080] Figure 2b) shows the section along the bore axis 221 of the through bore of the first type 22. This section shows the openings of the through bore pair of the second type 23.

[0081] Figure 2c) shows the section along the bore axis 231 of the through bore of the second type 23. This section shows the openings of the other through bore of the second type 23 as well as the opening of the through bore of the first type 22.

[0082] Figure 3a) shows a 3D external view of a second embodiment of the cap 1 according to the invention. The cap 1 has a cap body with a combustion chamber-side end face 11 and a side surface 12a, 12b, which is arranged circumferentially on the end face 11. The cap 1 has a longitudinal axis R.410583

[0083] - 14 -

[0084] X, which extends from the combustion chamber-side end of the cap 1 to the combustion chamber-away end of the cap 1. The combustion chamber-side end face 11 is arranged perpendicular to the longitudinal axis X of the cap. The side surfaces 12a, 12b are radially spaced from the longitudinal axis X and are arranged not perpendicular, but at an angle or parallel to the longitudinal axis X. In this example, the side surface consists of sections 12b angled to the longitudinal axis X and a section 12a parallel to the longitudinal axis X.

[0085] On the outer surface 10 of the cap 1, the openings of three through holes are visible: main through hole 21, first-type through hole 22, and second-type through hole 23. The through holes 21, 22, and 23 have different diameters in this example. The main through hole 21 has a diameter of 0.8 mm to 1.3 mm, in particular 1.0 mm. The first-type through holes 22 have a diameter of 0.8 mm to 1.3 mm, in particular different diameters of 1.1 mm and 0.8 mm. The second-type through hole 23 has a diameter of 0.8 mm to 1.3 mm, in particular different diameters of 1.1 mm and 1.0 mm.

[0086] There is no through-hole on the combustion chamber-side end face 11 of the cap 1 according to the invention.

[0087] Figure 3b) shows a 2D external view of the cap 1. This is a top view of the cap 1 along the longitudinal axis X. Five through holes 21, 22, 23 with their respective bore axes 211, 221, 231 are visible: one main through hole 21, two through holes of the first type 22, and two through holes of the second type 23.

[0088] The bore axes 211, 231 of the main through-hole 21 and the two through-holes of the second type 23 intersect the longitudinal axis X. These three through-holes 21, 23 are radial through-holes.

[0089] The bore axes 221 of the two through holes of the first type 22 do not intersect the longitudinal axis X. These bore axes 221 intersect each other at a point radially spaced from the longitudinal axis X. This distance 222 can be, for example, 15% or greater and up to 85% of the R.410583

[0090] - 15 -

[0091] The inner radius of cap 1 is measured in plane A perpendicular to the longitudinal axis X of cap 1, where the intersection of the bore axes 221 of the through bore of the second type is located.

[0092] 22. The two through-holes of the first type 22 are rotationally asymmetric to each other.

[0093] A plane E spans the longitudinal axis X of the cap 1 and the bore axis 211 of the main bore 21, bisecting the main through bore 21. Furthermore, one through bore 22, 23 of each pair of through bores lies on one side of plane E. Plane E is also a mirror plane. The through bore 22,

[0094] The two through holes of type 23 form a symmetry pair in this example. The through holes 22, 23 of a pair have the same distance (angle β1, β2) along the circumference to the main through hole 21 and the same orientation of the hole axis 221, 231 with respect to the longitudinal axis X of the cap 1. In this example, the through holes of the first type 22 have a smaller distance β1 to the main through hole 21 than the through holes of the second type 23. The two pairs of through holes 22, 23 are mirror symmetrical. In this example, the through holes 22, 23 of a pair have different diameters, so with respect to this parameter, the pairs of through holes 22, 23 lose their mirror symmetry.

[0095] Figure 4 shows four sections of the cap 1. Each section is along the bore axis 211, 221, 231 of one of the three through bores 21, 22, 23, with one section along the bore axis 221 of each of the two through bores of the first type 22.

[0096] In Figure 4a), the section follows the bore axis 211 of the main through-hole 21. The openings of the three different through-holes 21, 22, 23 on the inside 15 of the cap 1 are shown. The bore axes 211 of the main through-hole 21 and the through-hole 231 of the second type 23 intersect the longitudinal axis X of the cap 1, with the respective points of intersection being axially spaced from the longitudinal axis X of the cap 1. The extension of the bore axis 211 of the main through-hole 21 intersects the longitudinal axis X of the cap 1 closer to the end face 11 of the cap 1 than the extension of the bore axis 231 of the R.410583

[0097] - 16 -

[0098] Through hole of the second type 23. It can be clearly seen that the bore axis 221 of the through hole of the first type 22 does not intersect the longitudinal axis X of the cap 1, but is spaced apart from it.

[0099] The bore axis 211 of the main through-hole 21 forms an angle α with the longitudinal axis X of the cap 1. As shown in further parts b), c) and d) of Figure 4, the bore axes 221, 231 of the different through-hole types 22, 23 have different angles α2, α2', α3 to the longitudinal axis X of the cap 1, wherein the through-holes of the pair of the second type 23 have the same angle α3 to the longitudinal axis X of the cap 1 and the through-holes of the pair of the first type 22 have different angles α2, α2'.

[0100] Figure 4b) shows the section along the bore axis 221 of the first through-hole of the first type 22. The bore axis 221 forms a first angle 2 with the longitudinal axis X of the cap 1. In this section, the openings of the through-hole pair of the second type 23 can be seen.

[0101] Figure 4c shows the section along the bore axis 231 of the through bore of the second type 23. This section shows the openings of the other through bore of the second type 23 as well as the opening of the second through bore of the first type 22.

[0102] Figure 4 d) shows the section along the bore axis 221 of the second through-hole of the first type 22. The bore axis 221 forms a second angle α2' with the longitudinal axis X of the cap 1, which differs from the first angle 2 of the first through-hole of the first type 22. This section also shows the openings of the pair of through-holes of the second type 23.

[0103] Possible further developments of the first and second embodiments, not shown, are embodiments with 7 or 9 through-holes. In each case, one through-hole is the main through-hole 21. The remaining 6 or 8 through-holes form pairs of through-holes of the first or second type 22, 23, wherein there is always at least one pair of the first type 22 and one pair of the second type 23. The holes of a pair are always of the same type and have the R.410583

[0104] - 17 - equal distance angle β to the main through-hole 21 along the circumference. Additionally, the through-holes of a pair can also have the same diameter and / or the same angle α to the longitudinal axis X of the cap 1.

[0105] Figure 5 shows an example of a pre-chamber candle 100 with an exemplary cap. The cap can, for example, be a cap 1 according to the first or second embodiment.

[0106] The pre-chamber spark plug 100 has a housing 200 with a thread 220 on its outer surface, allowing the pre-chamber spark plug 100 to be screwed into an engine. An insulator 300 is arranged inside the housing 200. A center electrode 400 is arranged inside the insulator 300, projecting from the combustion-side end of the insulator 300. Together with a ground electrode 500, which is arranged on the housing 200, the center electrode 400 forms an ignition gap. A cap, such as the cap 1 according to the invention, is arranged at the combustion-chamber-side end of the housing 200.

Claims

R.410583 - 18 - Claims 1. Cap (1) for a pre-chamber spark plug (100) having a longitudinal axis X, comprising a cap body with an outer surface (10) and an inner surface (15), a main through-hole (21) extending from the outer surface (10) of the cap (1) through the cap body to the inner surface (15) of the cap (1) and the axis of which (211) intersects the longitudinal axis X of the cap (1) inside the cap (1), and at least one pair of through-holes of a first type (22), wherein this first through-hole type (22) is a tangential through-hole extending from the outer surface (10) of the cap (1) through the cap body to the inner surface (15) of the cap (1) and the axis of which (221) does not intersect the longitudinal axis X of the cap (1) inside the cap (1), and at least one pair of through-holes of a second type (23), wherein this second through-hole type (23) a radial through hole is,which extends from the outside (10) of the cap (1) through the cap body to the inside (15) of the cap (1) and whose bore axis (231) intersects the longitudinal axis X of the cap (1) inside the cap (1), wherein there is a plane E extending parallel to the longitudinal axis X and in which an intersection of the bore axes (221) of the first-type through-hole pair (22) lies, and wherein the main bore hole (21) is bisected by the plane E and each through-hole (22, 23) of a through-hole pair lies on one side of the plane E, 2. Cap (1) according to claim 1 , characterized in that the through-holes have the same diameter as the through-hole pair of the first type (22) and / or the through-holes have the same diameter as the through-hole pair of the second type (23), in particular wherein the main through-hole (21) has a different diameter than the through-holes of the second type (23). R.410583 - 19 - 3. Cap (1) according to claim 1 or claim 2, characterized in that the through-hole pair of the first type (22) is rotationally asymmetric with respect to a rotation about the longitudinal axis X of the cap (1) and / or that the through-hole pair of the second type (23) is rotationally symmetric with respect to a rotation about the longitudinal axis X of the cap (1) 4. Cap (1) according to one of the preceding claims, characterized in that the pair of through-holes of the first type (22) and / or the pair of through-holes of the second type (23) is arranged in a mirror-symmetrical manner with respect to a plane of symmetry E on the cap (1), wherein the plane of symmetry is spanned by the longitudinal axis X of the cap (1) and the bore axis (211) of the main through-hole (21).

5. Cap (1) according to one of the preceding claims, characterized in that the intersection of the bore axes (221) of the through bore of the first type (22) inside the cap (1) has a radial distance (222) to the longitudinal axis X of the cap (1), wherein the radial distance (222) is not less than 15% and not greater than 85% of an inner radius of the cap (1) in a plane A perpendicular to the longitudinal axis X in which the intersection of the bore axes (221) of the through bore of the first type (22) is located.

6. Cap (1) according to one of the preceding claims, characterized in that the bore axis (211) of the main through-bore (21), the bore axis (221) of the first through-bore type (22) and the bore axis (231) of the second through-bore type (23) each have an angle (cd , a2, a3) to the longitudinal axis X of the cap (1), wherein the angles (cd , a2, a3) are measured on the outside (10) of the cap (1) starting from the combustion chamber-side end face of the cap (1), and wherein the angles (cd , a2, a3) are not less than 30° and not greater than 90°.

7. Cap (1) according to one of the preceding claims, characterized in that the main through-bore (21), the through-bores of the first type (22) and / or the through-bores of the second type (23) are cylindrical with a constant diameter, wherein in particular the diameters are not less than 0.5 mm and not greater than 2.0 mm. R.410583 - 20 - 8. Cap (1) according to one of the preceding claims, characterized in that the main through-hole (21) has a diameter of not less than 1.1 mm and not greater than 1.4 mm and / or the through-holes of the first type (22) have a diameter of not less than 1.0 mm and not greater than 1.3 mm and / or the through-holes of the second type (23) have a diameter of not less than 0.7 mm and not greater than 1.1 mm.

9. Cap (1) according to one of the preceding claims, characterized in that the diameter of the paired through-bores (22, 23) decreases from the main through-bore (21) along the circumference to the cap side opposite the main through-bore (21).

10. Cap (1) according to one of the preceding claims, characterized in that there are 5, 7 or 9 through holes (21 , 22, 23), one of which is the main through hole (21) and the other through holes are pairs of through holes of the first or second type (22, 23), wherein there is at least one pair of through holes of the first type (22) and at least one pair of through holes of the second type (23).

11. Cap (1) according to one of the preceding claims, characterized in that along the circumference starting from the main through-hole (21) the through-holes of the first type (22) and second type (23) are arranged alternately, in particular starting from the main through-hole (21) a pair of through-holes of the first type (22) and then a pair of through-holes of the second type (23) are arranged first.

12. Pre-chamber spark plug (100) comprising: a housing (200), an insulator (300) arranged in the housing (200), a center electrode (400) arranged at least partially in the insulator (300), a ground electrode (500) arranged on the housing (200), which together with the center electrode (400) forms an ignition gap, R.410583 - 21 - a cap (1) attached to the housing (200) according to one of claims 1 to 10.

13. Pre-chamber spark plug (100) according to claim 11, characterized in that the cap (1) on the pre-chamber spark plug (100) is arranged such that when the pre-chamber spark plug (100) is screwed into a cylinder block, the main through-bore (21) faces the injector.

14. Manufacturing method for a cap (1) according to any one of claims 1 to 10, characterized in that the through holes (21, 22, 23) in the cap (1) are produced by at least one of the following methods: by electrical discharge machining (EDM), by laser drilling, or by machining

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