Spark plug having new housing and ground electrode design and method for manufacturing the ground electrode having the new design

Abstract

The invention relates to a spark plug (1) with a longitudinal axis X, having: - a housing (2) having an inner face, an outer face and a combustion-chamber-side end face (20), - an insulator (3) arranged in the housing (2), - a central electrode (4) which is arranged in the insulator (3) and protrudes from the insulator (3) on the combustion-chamber side, the combustion-chamber-side end of said central electrode being inside the housing (2), - a rod-shaped ground electrode (5) which is arranged on the housing (2) in such a way that the radial ignition gap (45) between the central electrode (4) and the ground electrode (5) is formed within the housing (2), wherein the housing (2) has a recess (6) on the inner edge of its combustion-chamber-side end face (20), in which recess the ground electrode (5) is arranged and fastened.

Description

[0001] R. 404863

[0002] - 1 -

[0003] Description

[0004] title

[0005] Spark plug with new housing and ground electrode design, as well as a new design manufacturing process for the ground electrode.

[0006] State of the art

[0007] The invention relates to a spark plug with a new housing design and ground electrode design, as well as a manufacturing process for the ground electrode with the new design.

[0008] Spark plugs with a curved ground electrode, attached to the housing and extending in a J-shape from the housing to the longitudinal axis of the spark plug, thus forming an ignition gap together with the center electrode, have been known for a long time. This design of the ground electrode has the advantage that the electrode gap to the center electrode can be adjusted by bending or re-bending the ground electrode. The ground electrode and the center electrode protrude from the spark plug housing and into the combustion chamber. Classic spark plugs with a curved ground electrode generally have a positive spark position, since the ignition gap lies outside the housing and within the combustion chamber.

[0009] A trend in modern engines is the increasing use of higher combustion chamber pressures to achieve high efficiency. This necessitates smaller electrode gaps in the spark plug to avoid extremely high ignition voltages. The smaller the required electrode gap of a spark plug becomes, the more critical the precise alignment of the ground electrode becomes. Designs with a curved ground electrode reach their limits in this regard, as bending or re-bending the ground electrode becomes increasingly imprecise as the required electrode gap decreases.

[0010] Another trend is hydrogen as a fuel in engines. Compared to a gasoline engine, the combustion pressure in a hydrogen engine is higher because hydrogen has a higher R-value. 404863

[0011] - 2 - burns faster, thus enabling later ignition at very high pressures. Therefore, it is necessary to develop a spark plug with a very small electrode gap of 0.3 mm or less, where the electrode gap must be set very precisely. The manufacturing method known from the prior art, which involves assembling the complete spark plug and adjusting the electrode gap by deforming the ground electrode (J-gap) located on the housing face, is too imprecise for this purpose and reaches its limits.

[0012] Another requirement for the spark plug arises from the fact that hydrogen has a very low auto-ignition temperature, necessitating a cold spark plug. A cold spark plug, in this context, refers to one that does not heat up excessively. The spark plug components must not become too hot to prevent unwanted ignition of the hydrogen at these points. In particular, ground electrodes that extend into the hot combustion chamber, such as the J-shaped ground electrode found in conventional spark plugs, absorb a significant amount of heat from the combustion chamber, thus preventing the spark plug from being cold enough for use in a hydrogen engine. In some cases, ground electrodes positioned laterally are used. This results in lower temperatures because the ground electrodes do not extend as deeply into the combustion chamber.

[0013] The object of the invention is to provide a spark plug that meets the aforementioned requirements of a cold spark plug with a very precisely adjustable small electrode gap.

[0014] R. 404863

[0015] - 3 -

[0016] Disclosure and Advantage of the Invention

[0017] This problem is solved by the spark plug according to the invention in that the housing has a recess on the inner edge of its combustion chamber-side end face in which the ground electrode is arranged and fastened.

[0018] The spark plug according to the invention, with a longitudinal axis X, comprises a housing with an inner surface, an outer surface, and a combustion chamber-side end face, an insulator arranged in the housing, a central electrode arranged in the insulator which projects from the insulator on the combustion chamber side and whose combustion chamber-side end is located within the housing, and a rod-shaped ground electrode which is arranged on the housing such that a radial, in particular annular, ignition gap is formed within the housing between the central electrode and the ground electrode. Furthermore, the housing has a recess on the inner edge of its combustion chamber-side end face in which the ground electrode is arranged and secured.

[0019] This has the advantage that the rod-shaped ground electrode can be arranged very flat at the combustion chamber-side end of the housing, so that the ground electrode does not protrude so far into the combustion chamber and the spark plug has a neutral to slightly negative spark position, i.e. when the spark plug is screwed into an engine block, the ignition gap and thus the spark position is close to the combustion chamber roof or slightly outside the combustion chamber.

[0020] This results in the ground electrode absorbing less heat from the combustion chamber. Furthermore, the ground electrode has good thermal contact with the housing, allowing the heat absorbed by the ground electrode to be quickly dissipated via the housing to the engine's cylinder head. The overall result is a cold spark plug.

[0021] The good heat conduction between the ground electrode and the housing can be improved if the ground electrode has a copper core located in the electrode end attached to the housing. The contact between the copper core in the ground electrode and the housing results in better and therefore faster heat conduction from the electrode to the housing.

[0022] The recess on the inner edge of the combustion chamber-side end face of the housing can, for example, be milled into the end face of the housing, creating the recess in the form of a groove. R. 404863

[0023] - 4 -

[0024] Advantageous further developments of the invention are the subject of the dependent claims.

[0025] In a further development of the spark plug, the recess is open axially towards the combustion chamber and radially inwards along the longitudinal axis X of the spark plug. In particular, the recess can be limited radially outwards by the housing wall.

[0026] This offers the advantage that, on the one hand, the recess can be easily created and, on the other hand, the rod-shaped mass electrode can be easily inserted and arranged in the recess.

[0027] In a further development, it is provided that the combustion chamber-side end face of the housing has an inclined surface at its radially inner end, which is formed particularly along the circumference of the radially inner end. This has the advantage that the ground electrode arranged in the recess can be more easily welded to the housing. Welding processes can include, for example, laser welding or resistance welding.

[0028] It has proven advantageous that the recess is wider than the ground electrode arranged in it, as this allows for fine adjustment of the ground electrode in relation to the center electrode in order to set the small electrode gap as precisely as possible.

[0029] In an advantageous embodiment, the recess may have a bottom section that is inclined along the width of the recess. This means that the recess has varying depths along the circumference of the housing. This offers the advantage that deviations between the longitudinal axis of the housing, the insulator, and / or the center electrode can be compensated for by shifting or rotating the ground electrode within the recess. Accordingly, it is possible to set the small electrode gap very precisely.

[0030] Additionally or alternatively, it is provided that the base of the recess is inclined radially in the direction of the spark plug's longitudinal axis. Inclining the base radially to the spark plug's longitudinal axis offers the advantage of increasing the contact area and the weld area between the ground electrode and the housing. This ensures a sufficiently strong weld between the housing and the ground electrode and, furthermore, improves heat conduction between the ground electrode and the housing due to the larger contact area. In particular, R. 404863

[0031] - 5 -

[0032] The ground electrode is also chamfered at its corresponding end, corresponding to the radial inclination of the recess's base, to ensure optimal contact. The recess is radially deeper on the inside than on the outside when the depth is measured as the distance from the recess's base to the combustion chamber-side end face of the housing.

[0033] In a further embodiment, the housing has a second recess on the inner edge of its combustion chamber-side end face, arranged opposite the first recess, and the ground electrode is positioned and secured with each end in one of the recesses. This has the advantage that the ground electrode has better heat conduction into the housing due to the two contact points.

[0034] In a further development of this design, the second recess also has an inclination of its base along the circumference of the housing, the inclination of the base in the second recess being opposite to the inclination of the base of the first recess. The inclinations of the bases are not mirror-symmetrical, but rotationally symmetrical to each other when rotated about the longitudinal axis of the spark plug. In particular, the base of the second recess also has a radial inclination like the base of the first recess. The advantages described above also apply here.

[0035] In an advantageous embodiment, the ground electrode has a through-hole within which the center electrode is at least partially arranged, thereby forming the annular radial ignition gap between the ground electrode and the center electrode. In particular, the ground electrode has no copper core in the section where the through-hole is formed.

[0036] The inclusion of a through-hole in the ground electrode, which houses the center electrode, offers the advantage of an increased ignition surface area. This distributes the spark density over a larger area, resulting in lower local temperatures and less material melting. Overall, electrode wear is distributed over a larger area, extending the spark plug's service life.

[0037] In a further advantageous embodiment, the ground electrode is provided with a precious metal-containing ring as an ignition element R. 404863 on the inside of the through-bore.

[0038] - 6 - features. The precious metal-containing ring as the ignition element and the center electrode arranged within it have a greater overlap with each other, which increases the service life of the spark plug.

[0039] In a further development of this design, the through-hole at the ground electrode has two sections with different diameters, wherein the second section with the smaller diameter is arranged at the end of the through-hole facing away from the combustion chamber, and the ignition element is arranged in the first section with the larger diameter. This is advantageous because it allows for easy alignment and fixation of the ignition element on the ground electrode. Accordingly, the electrode gap to the center electrode can also be adjusted more easily. In particular, the ignition element can have a smaller outer diameter than the inner diameter of the through-hole in which the ignition element is arranged. Specifically, the inner diameter of the ignition element is larger than the inner diameter of the second section with the smaller diameter of the through-hole.

[0040] The invention also relates to a manufacturing process for the ground electrode and a manufacturing process for the spark plug according to the invention with the correspondingly manufactured ground electrode.

[0041] The inventive method for manufacturing a ground electrode for a spark plug according to claims 1 to 11 comprises the following steps: a) providing a rod, in particular made of a nickel alloy and optionally with a copper core inside the rod, which extends only partially along the length of the rod; b) drilling a through-hole into the rod, wherein the through-hole has two sections with different diameters; c) placing and securing the ignition element in the section with the larger diameter.

[0042] In a further development of the process, this can include a step before step b) in which two identical bars are welded together to form a new, longer bar. Each bar can have an optional copper core located at its end, leaving a core-free area in the center of the new bar where the through-hole is formed in the next step. R. 404863

[0043] - 7 -

[0044] The process may include the further step of beveling the end or ends of the rod with which it is attached to the housing.

[0045] For aligning the ground electrode with the center electrode, a tool can be used that, like a cap with conical walls, fits over the center electrode and immerses the walls into the ignition gap. The electrode gap is determined by the immersion depth. The tool then acts as a spacer while the ground electrode is aligned and secured in the recess on the housing face to match the electrode gap. The tool helps to set a very precise annular radial electrode gap and maintain it during the installation of the ground electrode.

[0046] It is also conceivable that the ignition element is only placed and fixed to the ground electrode after the ground electrode has been positioned on the housing and the center electrode has been positioned in the through-hole of the ground electrode. This allows the electrode gap to be set very precisely by aligning the ignition element with the center electrode. For aligning the ignition element, the tool described above is used, for example, which is inserted into the gap between the ignition element and the center electrode. Advantageously, the tool has a conical outer surface, so that the electrode gap is determined by the depth to which the tool is inserted into the gap. During this step, the ignition element must be able to move freely within the through-hole.It is advantageous if the outer diameter of the ignition element is smaller than the diameter of the section with the larger diameter through-hole. It is also advantageous if, during this process step, the ignition element rests on the section with the smaller diameter through-hole, as this already fixes the axial alignment of the ignition element, allowing it to move only radially relative to the longitudinal axis of the spark plug during alignment.

[0047] This method has the advantage that the small electrode spacing can be set very precisely.

[0048] drawing

[0049] Figure 1 shows a first example of a spark plug according to the invention R. 404863

[0050] - 8 -

[0051] Figure 2 shows a second example of a spark plug according to the invention.

[0052] Figure 3 shows a third example of a spark plug according to the invention.

[0053] Figure 4 shows a fourth example of a spark plug according to the invention.

[0054] Figure 5 shows an example of the alignment of the ground electrode on the housing.

[0055] Figure 6 shows an example of the manufacturing process for the ground electrode according to the invention.

[0056] Figure 7 shows an example of adjusting the electrode gap.

[0057] Description of the exemplary embodiment

[0058] In the figures, identical or functionally identical parts are designated with the same name and reference symbol. For clarity, not all parts in every figure are always labeled with reference symbols.

[0059] Figure 1 shows a first example of the spark plug 1 according to the invention. The combustion chamber end of the spark plug 1 is shown in section, so that the interior of the spark plug 1 is also visible. The insulator 3 with the center electrode 4 is arranged inside the housing 2. The gap between the housing 2 and the insulator 3 is sealed by an internal seal 7. The housing 2 has a recess 6 on its combustion chamber-side end face 2, which is open radially to the longitudinal axis X of the spark plug 1 and axially to the combustion chamber. A ground electrode 5 is arranged in this recess 6. The recess 6 has a bottom region 61 that is inclined radially inwards. The end 55 of the ground electrode 5, which is arranged and attached to the housing 2, is also chamfered according to the inclination of the bottom region 61 of the recess 6, so that the housing 2 and the ground electrode 5 have a good contact surface and good heat conduction.

[0060] In this example, the ground electrode 5 has a copper core 51 that extends from the radially outer end 55 of the ground electrode 5 to approximately half the length of the electrode 5. At its radially inner end, the ground electrode 5 has a through-hole 53, as shown in R. 404863.

[0061] - 9 - where the center electrode 4 is located. The arrangement of electrodes 4, 5 results in an annular radial ignition gap 45 between the two electrodes 4, 5.

[0062] The through-bore 53 has two sections 53a and 53b with different diameters, the first section 53a with the larger diameter being located on the combustion chamber side of the second section 53b with the smaller diameter. The ground electrode 5 may have a recess 54 on its side facing away from the combustion chamber, in which the through-bore 53 terminates. The ground electrode 5 has a smaller axial thickness in the section with the recess 54 than in a section without a recess. The recess 54 on the ground electrode 5 extends, in particular, in the area where the ground electrode 5 does not have a copper core inside.

[0063] In the first section 53a with the larger diameter of the through-hole 53, an ignition element 52 is arranged.

[0064] In this example, the electrodes 4, 5 are arranged such that the ignition gap 45 is inside the housing 2 and the spark plug 1 thus has a negative spark position when it is screwed into an engine.

[0065] Figure 2 shows a second example of the spark plug 1 according to the invention. The differences from the first example shown in Figure 1 will be discussed below.

[0066] The housing 2 has a circumferential chamfer 21 on the inner edge of its combustion chamber-side end face 20. Furthermore, the recess 6 on the combustion chamber-side end face of the housing 2 is less deep than in the example according to Figure 1, which means that the ignition gap 45 is closer to the combustion chamber-side end face 20 of the housing 2, in particular in a plane with the combustion chamber-side end face 20 of the housing 2. The spark plug 1 has a neutral or slightly negative spark position when it is screwed into an engine.

[0067] Figure 3 shows a third example of the spark plug 1 according to the invention. The differences from the first example shown in Figure 1 are discussed below. The housing 2 has a second recess 6 opposite the first recess 6 on the end face 20 of the housing 2. The ground electrode 5 is arranged and secured with both ends 55 in one of the recesses 6. The ground electrode 5 spans the opening of the housing 2 like a bridge. R. 404863

[0068] - 10 -

[0069] The ground electrode 5 has a through-hole 53 in its center, containing the ignition element 52. The center electrode 4 is positioned in this through-hole 53, thus forming an annular radial ignition gap 45. In this example, the electrodes 4 and 5 are arranged such that the ignition gap 45 is within the housing 2, and the spark plug 1 therefore has a negative spark position when screwed into an engine.

[0070] Figure 4 shows a fourth example of the spark plug 1 according to the invention. The differences from the third example shown in Figure 3 will be discussed below.

[0071] The housing 2 has a circumferential chamfer 21 on the inner edge of its combustion chamber-side end face 20. Furthermore, the recess 6 on the combustion chamber-side end face 20 of the housing 2 is less deep than in the example according to Figure 3, which means that the ignition gap 45 is closer to the combustion chamber-side end face 20 of the housing 2, in particular in a plane with the combustion chamber-side end face 20 of the housing 2. The spark plug 1 has a neutral or slightly negative spark position when it is screwed into an engine.

[0072] Figure 5 shows how the ground electrode 5 can be positioned within the recess 6 on the end face 20 of the housing 2 to compensate for certain deviations between the longitudinal axis of the insulator 3, the center electrode 4, and the housing 2. Advantageously, the recess 6 has a bottom section 61 inclined along the circumference of the housing 2. By tilting, sliding, and rotating the ground electrode 5, a certain amount of play is achieved when positioning the ground electrode 5 in the recess 6, allowing the deviations between the center electrode 4, the insulator 4, and the housing 2 to be compensated for and the electrode gap 45 to be set very precisely. For this purpose, the recess 6 is also wider along the circumference of the housing 2 than the ground electrode 5.

[0073] Figure 5 also shows that the bottom areas 61 of two opposing recesses 6 are advantageously inclined differently, so that the recesses 6 are rotationally symmetric but not mirror-symmetric to each other.

[0074] Figures 5 b) and c) show how the ground electrode 5 can be arranged laterally displaced or slightly rotated in the recesses 6. R. 404863

[0075] - 11 -

[0076] Figure 6 shows various steps for the manufacturing process of the ground electrode 5 according to the invention, using the example of a long ground electrode 5 which has the through-hole 53 for the central electrode 4 in the middle.

[0077] The long ground electrode (bridge ground electrode) with copper cores can be manufactured by using two standard rod ground electrodes welded together in series (Figure 6a). This step is omitted for the production of a short ground electrode 5, which is attached to the housing 2 at only one end. The subsequent steps can be carried out analogously for the short ground electrode 5.

[0078] In the next step (Figure 6b), the through-hole 53 is formed in the ground electrode 5. The through-hole 53 is cylindrical and has a first section 53a, which has a larger diameter on the combustion chamber side, and a second section 53b with a smaller diameter. In this example, an optional recess 54 on the rear side of the ground electrode 5 adjoins the second section 53b of the through-hole 53. The recess 54 is conical and has larger dimensions than the through-hole 53. The through-hole 53 is completely surrounded by the material of the ground electrode 5. The recess 54 is bounded on three sides (the bottom of the recess and two sides each) by the material of the ground electrode 5. In this example, the recess 54 is open and perpendicular to the longitudinal extent of the ground electrode 5.

[0079] The following step (Figure 6c)) shows how the ignition element 52 is arranged and, if necessary, secured in the first section 53a of the through-bore 53. The ignition element 52 rests against the shoulder that forms the transition from the first section 53a to the second section 53b of the through-bore 53, thus defining the position of the ignition element 52 in this direction.

[0080] In the last step (Figure 6 d)) of this example, the ends 55 of the long ground electrode 5 are chamfered so that they fit the radial inclination of the bottom area 61 of the recess 6 on the housing 2 for a good contact surface between ground electrode 5 and housing 2.

[0081] Figure 7 shows how the electrode gap between the center electrode 4 and the ground electrode 5 can be adjusted. A tool 70 is used, which, like a cap with conical outer surfaces, fits over the center electrode 5 and into the ignition gap 45. R. 04863

[0082] - 12 - The depth of immersion then determines the width of the ignition gap 45, as the thickness of the tool walls increases. This tool 70 can be used as a spacer while the ground electrode 5 is attached in the recess 6 on the housing end face 20.

[0083] Alternatively, the ground electrode 5 can first be attached to the housing 2, and then the electrode gap can be fine-tuned by aligning and securing the ignition element 52 within the first section 53a of the through-hole 53 in the ground electrode 5. The ignition element 52 must have some play so that it can be moved within the through-hole 53, as shown in Figure 7b).

Claims

R. 404863 - 13 - Claims 1. Spark plug (1) having a longitudinal axis X: • A housing (2) with an inner side, an outer side and a combustion chamber-side end face (20), • An insulator (3) arranged in the housing (2), • A central electrode (4) arranged in the insulator (3), which protrudes from the insulator (3) on the combustion chamber side and whose combustion chamber-side end is inside the housing (2), • A rod-shaped ground electrode (5) arranged on the housing (2) such that the radial ignition gap (45) is formed within the housing (2) between the center electrode (4) and the ground electrode (5), characterized in that the housing (2) has a recess (6) on the inner edge of its combustion chamber-side end face (20) in which the ground electrode (5) is arranged and fastened.

2. Spark plug (1) according to claim 1 , characterized in that the recess (6) is open axially towards the combustion chamber and radially inwards in the direction of the longitudinal axis X of the spark plug (1) and in particular the recess (6) is limited radially outwards by the housing wall.

3. Spark plug (1) according to claim 1 or 2, characterized in that the combustion chamber-side end face (20) of the housing (2) has an inclined surface (21) at its radially inner end, which is formed in particular along the circumference of the radial inner end.

4. Spark plug (1) according to one of the preceding claims, characterized in that the recess (6) along the housing circumference is wider than the ground electrode (5) arranged in it.

5. Spark plug (1) according to one of the preceding claims, characterized in that the recess (6) has a bottom area (61) which is inclined along the width of the recess (6) and / or radially in the direction of the longitudinal axis X of the spark plug (1). R. 404863 - 14 - 6. Spark plug (1) according to one of the preceding claims, characterized in that the housing (2) has a second recess (6) on the inner edge of its combustion chamber-side end face (20), which is arranged opposite the first recess (6), and the ground electrode (5) is arranged and fastened with each of its ends in one of the recesses (6).

7. Spark plug (1) according to claim 6, characterized in that the second recess (6) has an inclination opposite to the inclination of the first recess (6).

8. Spark plug (1) according to one of the preceding claims, characterized in that the ground electrode (5) has a through-hole (53) within which the center electrode (4) is at least partially arranged, whereby the annular radial ignition gap (45) is formed between the ground electrode (5) and the center electrode (4).

9. Spark plug (1) according to claim 8, characterized in that the ground electrode (5) has a precious metal-containing ring (52) as an ignition element on the inside of the through-hole (53).

10. Spark plug (1) according to claim 9, characterized in that the through-hole (53) in the ground electrode (5) has two sections (53a, 53b) with different diameters, wherein the section (53b) with the smaller diameter is arranged at the combustion chamber-away end of the through-hole (53) and the ignition element (52) is arranged in the section (53a) with the larger diameter.

11. Method for manufacturing a ground electrode (5) for a spark plug (1) according to claims 1 to 11, comprising the following steps: d) providing a rod, in particular made of a Ni alloy and optionally having a Cu core (51) inside the rod, which extends only partially along the length of the rod; e) drilling the through-hole (53) into the rod, wherein the through-hole (53) has two sections (53a, 53b) with different diameters; f) placing and securing the ignition element (52) in the section (53a) with the larger diameter.

12. Method according to claim 13, characterized in that, prior to step b), there is a further step in which two identical bars are welded together to form a new bar, each bar having an optional Cu core (51) R. 404863 - 15 - can have, which is arranged at the end of the rod and such that the center of the new rod is a Cu-core-free area in which the through-hole (53) is formed in the next step.

13. Method according to one of claims 12 or 13, such that the rod is at the end without The through-hole (53) has a chamfered end (55) or the rod has chamfered ends (55) at both ends if the through-hole (53) is formed in the middle.

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