Spark plug with new housing design for improved purging behaviour

Abstract

The invention relates to a spark plug (1) with a longitudinal axis X, having: • a housing (2) having a longitudinal bore, as a result of which the housing (2) has an outer side (20) and an interior (21), and having a thread (22) formed on its outer side (20), as a result of which a threaded region (220) is formed on the outer side (20) of the housing (2), and having a thread-free region (230) which adjoins the threaded region (220) on the combustion chamber side, and also has a combustion-chamber-side end face (25), • an insulator (3), the combustion-chamber-side end of which is inside the housing (2), • a central electrode (4), which protrudes from the insulator on the combustion chamber side and the combustion-chamber-side end of which is inside the housing, • at least one ground electrode (5), in particular two or more ground electrodes, which is arranged in a lateral through-bore in the housing, • a radial ignition gap (45), which is formed by the ground electrode (5) and the central electrode (4) and which is formed inside the housing (2), wherein a plane A can be spanned by the combustion-chamber-side end of the ignition gap (45) perpendicular to the longitudinal axis X, characterised in that the through-bore for the ground electrode (5) is formed on the thread-free region (230) of the housing (2), and in that the thread-free region (230) has further openings (24) which are designed such that a gas flows out of the combustion chamber through the openings (24) into the housing interior (21).

Description

[0001] R. 412656

[0002] - 1 -

[0003] Description

[0004] title

[0005] Spark plug with new housing design for improved purging performance

[0006] State of the art

[0007] The invention relates to a spark plug.

[0008] Spark plugs have been known for over 100 years, providing a spark in internal combustion engines to ignite a fuel-air mixture at the correct time. Over time, spark plugs have been used for various fuels such as gasoline, ethanol, methanol, CNG (compressed natural gas), hydrogen, or mixtures thereof.

[0009] Recently, spark plug development has focused on the design and optimization of spark plugs for hydrogen engines. Very low ignition energies are sufficient for hydrogen combustion. Even hot components can be enough to ignite the hydrogen-air mixture. Any ignition not triggered by the spark plug is undesirable and should be avoided whenever possible. Furthermore, hydrogen engines operate at high pressures at the ignition point because they run on a lean hydrogen-air mixture. As always, a spark plug should have the longest possible service life, especially if it is intended for use in commercial vehicles.

[0010] Accordingly, several findings have been established for the design of a hydrogen spark plug. For example, it is advantageous for a hydrogen spark plug that the electrode gap is smaller than in conventional spark plugs. R. 412656

[0011] - 2 -

[0012] Spark plugs for a gasoline engine. Furthermore, the hydrogen spark plug should be designed to operate as cool as possible. This can be achieved, for example, by minimizing the spark plug's protrusion into the combustion chamber and / or by designing the spark plug to ensure short heat transfer paths from the electrodes, through the housing, and into the cylinder. Additionally, the material used in the hydrogen spark plug should exhibit good thermal conductivity for rapid heat dissipation while simultaneously offering resistance to spark erosion.

[0013] To reduce the protrusion into the combustion chamber, the ground electrodes are not welded axially to the front face of the spark plug housing, as with conventional spark plugs, but are attached laterally within the housing. This prevents the ground electrode from absorbing too much heat and thus causing the hydrogen-air mixture to ignite at an undesired time.

[0014] Several hydrogen spark plug designs already exist that meet the aforementioned requirements, such as DE 10 2023 201 527 A1. The presented design fulfills all the above-mentioned requirements for a hydrogen spark plug. However, the design reaches its manufacturing limits when a hydrogen spark plug with more than two ground electrodes is to be produced.

[0015] Accordingly, the object of the invention is to provide a spark plug for a hydrogen engine that meets all the above-mentioned requirements, is easy to manufacture and has good flushing behavior of the housing interior when the spark plug has more than two ground electrodes.

[0016] R. 412656

[0017] - 3 -

[0018] Disclosure of the invention

[0019] This problem is solved by the spark plug according to the invention.

[0020] The spark plug according to the invention has a longitudinal axis X and a housing with a longitudinal bore, giving the housing an outer surface and an inner surface. Furthermore, the housing has a thread formed on its outer surface, creating a threaded area on the outside of the housing. Adjoining the threaded area of ​​the housing on the combustion chamber side is a section of the housing on the outer surface of which the housing has no thread, the so-called unthreaded area. This, together with a combustion chamber-side end face of the housing, forms the combustion chamber-side end of the housing and the spark plug. The spark plug also has an insulator, the combustion chamber-side end of which is arranged within the housing, as is the center electrode of the spark plug, which is at least partially arranged in the insulator and protrudes from it on the combustion chamber side.The spark plug according to the invention has at least one ground electrode, in particular at least two or three ground electrodes, which are arranged in a lateral through-bore in the housing. The radial ignition gap is formed by the ground electrode and the center electrode and is arranged inside the housing, with a plane A defined by the combustion chamber-side end of the ignition gap perpendicular to the longitudinal axis. According to the invention, the through-bore for the ground electrode is formed in the unthreaded area of ​​the housing, and the unthreaded area has further openings which are configured to allow gas from the combustion chamber to flow through the openings into the interior of the housing.

[0021] The threadless area is a continuous closed wall area of ​​the housing, which is pierced by the openings.

[0022] In the case of a spark plug mounted in the engine, plane A is ideally located close to the combustion chamber roof. Therefore, by positioning the ground electrode in the threadless area, and thus close to the combustion chamber end of the spark plug, the advantage arises that the spark plug can have a neutral or slightly positive spark position, while simultaneously providing a small breathing space inside the housing. The breathing space within the R. 412656

[0023] - 4 -

[0024] The housing can be made very small because the ground electrode is positioned close to the combustion chamber end of the spark plug. Furthermore, the ground electrode does not protrude as far into the combustion chamber as in a conventional spark plug with a hook electrode, and therefore absorbs less heat from the combustion chamber. If the ground electrode is short and rod-shaped, a further advantage is that the heat paths from the ground electrode to the cooled housing are short, thus optimizing heat transfer from the ground electrode, through the housing, and into the cylinder head.

[0025] The openings improve the purging properties of the breathing chamber and prevent hot gas from accumulating there, thus preventing excessive heating of the insulator, the inner housing wall, or the center electrode. The result is a spark plug with a laterally positioned ground electrode, offering good thermal contact with the housing and a small, easily purged breathing chamber. Furthermore, the spark plug is easy to manufacture and retains its properties even when it has two or more ground electrodes.

[0026] The axial or radial ignition gap is the volume between the center electrode and the ground electrode, wherein the volume of the ignition gap is limited by the ignition surfaces of the respective electrode and by the overlap of the projections of the ignition surfaces on each other.

[0027] Advantageous further training is the subject of the sub-claims.

[0028] In a further development of the invention, the openings have a cross-sectional area, and at least 50% of the opening's cross-sectional area is arranged on the combustion chamber side of plane A. This ensures that a sufficient portion of the opening's cross-sectional area is located within the combustion chamber, allowing enough of the opening's surface to be permeated by the gas-air mixture to adequately purge the breathing space inside the housing, particularly the volume surrounding the ignition gap, after ignition. It is advantageous if a larger proportion, especially at least 70%, 80%, or 90%, of the opening's cross-sectional area is arranged on the combustion chamber side of plane A. R. 412656

[0029] - 5 -

[0030] In a further embodiment of the invention, plane A has a distance S from the combustion chamber-side end face of the housing, wherein the distance S is at least 1.5 mm and, in particular, a maximum of 6 mm. This ensures, on the one hand, that the area of ​​the unthreaded section, which is on the combustion chamber side of plane A and accordingly projects into the combustion chamber, is sufficiently long in the axial direction so that the openings are at least partially located in the combustion chamber. On the other hand, it also ensures that the part of the unthreaded section projecting into the combustion chamber is not too long, so that the housing does not absorb too much heat from the combustion chamber, which then has to be dissipated back to the cylinder.

[0031] In an advantageous embodiment, the bore for the ground electrode and the openings in the unthreaded area are axially offset from one another; in particular, the openings are located axially closer to the combustion chamber than the bore for the ground electrode. Specifically, the ends of the openings and the bore for the ground electrode facing away from the combustion chamber are axially offset from one another. This ensures that, on the one hand, a sufficient cross-sectional area of ​​the openings projects into the combustion chamber to allow flow through them, and on the other hand, that the ignition gap is formed close to the combustion chamber roof with a slightly positive to slightly negative spark position. "Slightly" refers to a maximum distance from the neutral spark position that corresponds to a maximum of twice the axial length of the ignition gap.

[0032] In one embodiment of the invention, the openings are designed as a gap, the gap intersecting the combustion chamber-side end face. For example, the gap can be produced by milling, starting at the combustion chamber-side end face of the housing. The gap then has a rectangular shape. Alternatively, the gap can also have the shape of a semicircle. This shape can be produced, for example, by drilling or milling.

[0033] In particular, the gap has a depth T that is smaller than the distance S between the combustion chamber end face and plane A. This has the advantage that 100% of the cross-sectional area of ​​the gap is located on the combustion chamber side of plane A and can therefore be efficiently flushed through the housing interior. R. 412656

[0034] - 6 -

[0035] In an alternative embodiment of the invention, the openings are designed as through-holes extending from the outside of the housing into the interior. For example, these through-holes may have a diameter D that is smaller than the distance S. This embodiment offers the same advantages as the previous embodiment.

[0036] In a further development of the second embodiment, the edge of the bore on the outside of the housing is chamfered. Specifically, the chamfer is formed around the entire edge of the bore. This has the advantage that the flow can easily enter the bore, and the absence of a sharp edge reduces turbulence in the incoming gas.

[0037] The ground electrode is, for example, pressed, screwed, and / or welded into the bore. This ensures that the ground electrode is securely fixed in the bore.

[0038] The ignition gap, for example, has a width of less than or equal to 0.3 mm. This distance is sufficient for igniting hydrogen, since less energy is required for hydrogen ignition than, for example, for igniting a gasoline-air mixture.

[0039] The invention also relates to an engine with a combustion chamber, a combustion chamber roof and a cylinder arranged on the combustion chamber, which has a receptacle for a spark plug, and a spark plug according to the invention, which is arranged in the receptacle, wherein the spark plug is arranged in the receptacle of the cylinder such that the ignition gap intersects the plane of the combustion chamber roof and the openings are arranged at least partially within the combustion chamber, in particular at least 50% of the cross-sectional area of ​​the openings.

[0040] The engine is, for example, a hydrogen engine that runs on a hydrogen-based fuel. R. 412656

[0041] - 7 -

[0042] drawing

[0043] Figure 1 shows the spark plug according to the invention mounted in a cylinder

[0044] Figure 2 shows a second example of the spark plug according to the invention.

[0045] Figure 3 shows a third example of the spark plug according to the invention.

[0046] Figure 4 shows a fourth example of the spark plug according to the invention.

[0047] Figure 5 shows a fifth example of the spark plug according to the invention.

[0048] Description of the exemplary embodiment

[0049] Figure 1 shows a sectional view of a spark plug 1 according to the invention installed in a cylinder 100 of an engine.

[0050] The spark plug 1 has a longitudinal axis X and a housing 2 with a longitudinal bore, giving the housing 2 an outer surface 20 and an inner surface 21. Inside the housing 2 is an insulator 3 with a center electrode 4 and a resistive element 7. The transition between the insulator 3 and the housing 2 is sealed by an internal gasket 8. A thread 22 is formed on the outer surface 20 of the housing 2, allowing the spark plug 1 to be screwed into the cylinder 100.

[0051] The section of the housing 2 in which the thread 22 is formed is the threaded area 220. Directly adjacent to the threaded area 220 on the combustion chamber side is a section of the housing 2 on whose outer surface 20 no thread is formed. This is the unthreaded area 230 of the housing 2. This, together with a combustion chamber-side end face 25 of the housing 2, forms the combustion chamber-side end of the housing 2 and the spark plug 1.

[0052] In this threadless area 230, the openings 24 are arranged through which the gas from the combustion chamber 150 flows into the interior 21 of the housing 2 and purges the breathing chamber of the spark plug 1. In this illustration, R. 412656

[0053] - 8 - three openings 24 visible, wherein in all openings 24 100% of their cross-sectional area are arranged within the combustion chamber 150.

[0054] In this unthreaded area 230, at least one bore is arranged in which the ground electrode 5 is inserted and secured. The bore for the ground electrode 5 is, for example, axially offset from the openings 24. In this embodiment, the spark plug 1 has at least two ground electrodes 5. The ground electrodes 5 and their ignition elements are arranged within the housing interior 21.

[0055] The center electrode 4 is located inside the insulator 3 and protrudes from the insulator 3 on the combustion chamber side. The center electrode 4, with its ignition element, is also located in the interior 21 of the housing 2. Together with the ground electrode 5, the center electrode 4 forms two radial ignition gaps 45. The plane A can be defined by the combustion chamber-side end of the ignition gap 45. In this example, plane A lies in a plane with the combustion chamber roof 110, so that the spark plug 1 has a neutral to slightly negative spark position.

[0056] The distance S from the plane A to the combustion chamber-side end face 25 of the housing 2 is a measure of how far the spark plug 1 protrudes into the combustion chamber 150.

[0057] The transition between the spark plug 1 and the cylinder 100 is sealed at the end of the cylinder 100 facing away from the combustion chamber by an external seal 10. The end of the cylinder 100 facing the combustion chamber forms the combustion chamber roof 110, into which the spark plug 1 protrudes.

[0058] Figures 2 to 4 each show an example of the design of the openings 24 in the threadless area 230 of the housing 2. The following discussion focuses primarily on the differences. The same terms and reference numerals are used for the individual components of the spark plug as in Figure 1, and reference is made here to the description of Figure 1 for these components.

[0059] In Figure 2, the openings 24 are formed as rectangular slots. The depth of a slot is greater than or equal to the width of the slot. The width is R. 412656

[0060] - 9 - measured along the circumference of the housing 2. The two slots are arranged at 90° to the two ground electrodes 5 in the threadless area 230, so that the incoming gas can flow directly to the two ignition gaps 45 and thoroughly purge the breathing chamber. The cross-sectional area of ​​this opening en24 is rectangular.

[0061] In Figure 3, the openings 24 are designed as semicircular slots. The depth of a slot is less than its width. For example, the slot has a width twice its depth. The width is measured along the circumference of the housing 2. The two slots are arranged at 90° to the two ground electrodes 5 in the threadless area 230, so that the incoming gas can flow directly to the two ignition gaps 45 and effectively purge the breathing chamber. The cross-sectional area of ​​these openings 24 is semicircular.

[0062] In Figure 4, the openings 24 are designed as through-holes in the unthreaded area 230 and are arranged along the circumference of the housing. In this example, the spark plug 1 has two opposing ground electrodes 5 and six through-holes, three on each side. The through-holes are cylindrical. The cross-sectional area of ​​these openings 24 is circular.

[0063] The example in Figure 5 differs from the example in Figure 4 only in that the through-holes on the outer surface 20 of the housing 2 each have a circumferential chamfer 240, so that the through-holes have at least a partially conical shape, with the diameter tapering from the outer surface 20 of the housing towards the inner surface 21 of the housing. The cross-sectional areas of these openings are circular, with the smallest diameter of the respective through-hole being used for the calculation.

Claims

R. 412656 - 10 - Claims 1. Spark plug (1) having a longitudinal axis X, having: • A housing (2) with a longitudinal bore, whereby the housing (2) has an outer surface (20) and an inner surface (21), and with a thread (22) formed on its outer surface (20), whereby a threaded area (220) is formed on the outer surface (20) of the housing (2), and a combustion chamber-side unthreaded area (230) adjoining the threaded area (220), as well as a combustion chamber-side end face (25), • An insulator (3) whose combustion chamber-side end is inside the housing (2), • A central electrode (4) which protrudes from the insulator on the combustion chamber side and whose combustion chamber-side end is inside the housing, • At least one ground electrode (5), in particular two or more ground electrodes, arranged in a lateral through-hole in the housing, • A radial ignition gap (45) formed by the ground electrode (5) and the center electrode (4) and which is formed within the housing (2), wherein a plane A can be spanned perpendicular to the longitudinal axis X through the combustion chamber-side end of the ignition gap (45), characterized in that the through-hole for the ground electrode (5) is formed on the threadless area (230) of the housing (2) and that the threadless area (230) has further openings (24) which are arranged to allow a gas from the combustion chamber to flow through the openings (24) into the housing interior (21).

2. Spark plug (1) according to claim 1 , characterized in that the openings (24) have a cross-sectional area and at least 50% of the cross-sectional area of ​​the opening (24) is arranged on the combustion chamber side of plane A, in particular at least 70%, 80% or 90%. R. 412656 - 11 - 3. Spark plug (1) according to claim 1 or 2, characterized in that the plane A has a distance S to the combustion chamber side end face (25) of the housing (2), wherein the distance S is at least 1.5 mm and in particular is a maximum of 6 mm.

4. Spark plug (1) according to one of the preceding claims, characterized in that the bore for the ground electrode (5) in the thread-free area (230) is axially offset to the openings (24) in the thread-free area (230), in particular the openings (24) are axially closer to the combustion chamber than the bore for the ground electrode (5), in particular the combustion chamber-away end of the openings (24) and the combustion chamber-away end of the bore for the ground electrode (5) are axially offset to each other.

5. Spark plug (1) according to one of the preceding claims, characterized in that the openings (24) are designed as a gap, wherein the gap intersects the combustion chamber side face (25).

6. Spark plug (1) according to claim 5, characterized in that the gap is rectangular or semicircular.

7. Spark plug (1) according to claim 5 or 6, characterized in that the gap has a depth T which is smaller than the distance S.

8. Spark plug (1) according to one of the preceding claims 1 to 4, characterized in that the openings (24) are designed as through holes extending from the outside (20) of the housing (2) into the interior (21).

9. Spark plug (1) according to claim 8, characterized in that the through holes have a diameter D which is smaller than the distance S 10. Spark plug (1) according to claim 8 or 9, characterized in that a chamfer (240), in particular circumferential, is formed on the outside (20) of the housing (2) at the edge of the through-hole. R. 412656 - 12 - 11. Engine with a combustion chamber 150, a combustion chamber roof (110) and a cylinder (100) arranged on the combustion chamber 150, which has a receptacle for a spark plug (1), and a spark plug (1) according to claims 1 to 10, which is arranged in the receptacle, characterized in that the spark plug (1) is arranged in the receptacle of the cylinder (100) such that the ignition gap (45) intersects the plane of the combustion chamber roof (110) and the openings (24) are arranged at least partially within the combustion chamber (150), in particular at least 50% of the cross-sectional area of ​​the openings (24).

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