Electrode having slightly elongated projection or groove and spark plug having such electrode as ground electrode

Abstract

The invention relates to an electrode (5) for a spark plug, having a main body (50) and a longitudinal axis E and an inner end (51) on which an ignition surface is arranged and an outer end (52) opposite the inner end, the main body (50) having a diameter DG, the electrode (5) having at least one slightly elongated projection (55) and / or at least one groove (56) on the main body (50) thereof.

Description

Field of the Invention

[0001] The present invention relates to an electrode for a spark plug and a spark plug having such an electrode as a ground electrode. Background Art

[0002] For some time now, novel spark plug solutions have been increasingly pursued, in which the ignition gap is configured inside the housing. In one of these solutions, the ground electrode is inserted into a bore in the housing wall and projects into the interior space of the housing from the side of the housing wall. A pre-chamber spark plug is known from DE 102017221517A, in which the ground electrode is arranged in a bore in the housing wall and projects into the interior space from the side.

[0003] For a ground electrode inserted into the spark plug from the side, new challenges arise with respect to the correct orientation of the ground electrode relative to the center electrode, the adjustment of the ignition gap, and the reliable fixation of the electrode in the bore. One possible fixation is to press the ground electrode into the bore. In this technique, very high component manufacturing precision is required so that the electrode is firmly pressed in the bore on the one hand during the operation time of the spark plug and on the other hand can be inserted in a controlled manner during installation, so that the electrode spacing can be adjusted as precisely as possible. If the necessary manufacturing precision is not observed, component failures may occur during manufacturing. These high requirements for manufacturing precision make the manufacturing process time-consuming and expensive. Summary of the Invention

[0004] The object of the present invention is to provide an electrode and a spark plug in which a reliable and correct installation of the ground electrode can be achieved, so that the manufacturing method is simplified.

[0005] Advantages of the Invention / Disclosure of the Invention

[0006] This object is solved by an electrode and a spark plug according to the invention.

[0007] The electrode for a spark plug according to the invention has a substrate and a longitudinal axis that extends from the inner end of the substrate and the electrode to its outer end. An ignition surface of the electrode is arranged at the inner end of the electrode and the substrate. When the electrode is installed in the spark plug, the inner end faces the ignition gap accordingly. The outer end is the end of the electrode opposite to the inner end and accordingly faces away from the ignition gap. The substrate has a diameter D G . In addition, the electrode has at least one slightly elongated protrusion and / or groove on its substrate.

[0008] The advantage of at least one slightly elongated projection or at least one groove is that the manufacturing tolerances are increased and the requirements for manufacturing precision are reduced, so that the manufacturing method is simplified. When the electrode is pressed into the drilled hole on the spark plug, the electrode can be plastically deformed, or more precisely, the projection on the base body or the base body with the groove can be plastically deformed, so that the electrode can be pressed sufficiently firmly into the drilled hole with low manufacturing precision. If too much force is applied to the electrode during the pressing process, this force can be captured in the electrode by plastic deformation without the electrode itself or the drilled hole being damaged.

[0009] A groove can also be understood as a slightly elongated recess. The base body is, for example, cylindrical or conical. For example, the electrode can have an element at the inner end of the base body, on which the ignition surface is formed.

[0010] Advantageous developments of the invention are the subject matter of the dependent claims.

[0011] In a further development, the substrate has at least two or three or four or five slightly elongated protrusions and / or grooves which are evenly arranged along the periphery of the substrate. This allows the plastic deformation of the electrode to be evenly distributed over the periphery of the substrate. For example, the electrode has at least two sections along its periphery. In the first section, the electrode has a diameter D of the substrate. G In the second section of the electrode, the base body has a protrusion or a groove and has a correspondingly different D at the protrusion. G Diameter D R and has a diameter D at the groove K . When measured along the periphery of the base body, the first section is longer than the second section. Depending on the number of protrusions and / or grooves, there are also second sections. There are as many first sections as second sections. As the number of second sections increases, the length of the first section approaches the length of the second sections. For the maximum number of second sections, the first section is as long as the second section.

[0012] In another refinement, at least one projection and / or at least one groove extends parallel to the longitudinal axis E of the electrode. As an alternative, at least one projection and / or at least one groove extends at an angle greater than 0° and less than 90°, in particular less than 45° and further in particular less than 30° relative to the longitudinal axis E of the electrode. The projection or the groove is configured at an angle relative to the longitudinal axis E of the electrode, which causes a slight spiral on the surface of the electrode, thereby reducing the frictional resistance when the electrode is inserted into the drill hole.

[0013] In an advantageous embodiment, the at least one projection has a height H relative to the base body of the electrode. The diameter D of the base body G At its outer end, it is smaller than the diameter D of the circumscribed circle surrounding at least one protrusion.R where the longitudinal axis E of the electrode serves as the center at the outer end. In particular, the ratio formed by the height H and the diameter D of the substrate G is less than 0.04% and greater than 0.015%, in particular less than 0.036% and greater than 0.02%. The height H has, for example, a value less than 0.05 mm and greater than 0.02 mm, in particular 0.03 mm.

[0014] Furthermore, the height H of the projection can increase in the direction from the inner end of the substrate towards the outer end of the substrate. Thereby, at least one projection additionally serves as an insertion aid when inserting the electrode into the drill hole. And the force used to insert the electrode into the drill hole can be continuously increased. Thereby, the process of inserting the electrode into the drill hole can be better controlled.

[0015] As a supplementary or alternative solution, at least one groove can have a depth T relative to the substrate of the electrode. The diameter D of the substrate at its outer end G is greater than the diameter D of the inner circle inside at least one groove K where the longitudinal axis E of the electrode serves as the center at the outer end.

[0016] In an advantageous design, the substrate has slightly elongated projections and grooves, which are alternately arranged on the substrate along the circumference of the substrate. In this example, the substrate no longer unconditionally has a first section.

[0017] If the projection has a triangular shape and the groove has a notch shape, the outer end face of the substrate shows a star shape due to the arrangement and design of the projection and the groove. Thereby, on the one hand, the frictional resistance of the electrode is reduced when inserting the electrode into the drill hole. On the other hand, the projection can be easily plastically deformed and fill the space of the groove.

[0018] Furthermore, the invention relates to a spark plug having a longitudinal axis X. The spark plug has a housing, an insulator arranged inside the housing, an intermediate electrode arranged inside the insulator, an electrode according to the invention as a ground electrode, a drill hole with a diameter D into which the ground electrode is inserted B and a spark gap constructed between the ground electrode and the intermediate electrode. The spark plug has the advantage that, by using the electrode according to the invention as a ground electrode, the spark plug can be easily and inexpensively manufactured.

[0019] In an expansion scheme of the spark plug, it is provided that the ground electrode is inserted into the drill hole and at least one projection and / or at least one groove is at least partially plastically deformed due to the insertion, so that the ground electrode is pressed into the drill hole.

[0020] In an improved scheme, the ground electrode is additionally welded in the drill hole. Thereby, accidental loosening of the ground electrode is prevented.

[0021] In an alternative embodiment, the spark plug has a cap which is fixed to the end of the housing on the combustion chamber side. The spark plug is a pre-chamber spark plug, in which a bore for inserting a ground electrode is formed in the cap or the housing.

[0022] The spark plug or the pre-chamber spark plug has, for example, an M10 or M12 thread on the outer side of the housing, which is provided for screwing the spark plug or the pre-chamber spark plug into the cylinder head.

[0023] The bore is typically a through-hole and can be formed, for example, in the housing for the spark plug. Description of the Drawings

[0024] FIG. 1 shows an example of a spark plug and an example of a pre-chamber spark plug, each having an inserted ground electrode;

[0025] FIG. 2 shows a first example of an electrode according to the invention;

[0026] Figure 3 shows a second example of an electrode according to the invention;

[0027] Figure 4 shows a third example of an electrode according to the invention;

[0028] FIG. 5 shows two steps of a method for manufacturing a spark plug according to the invention. Detailed Description

[0029] Figure 1a ) shows the spark plug 1 in a semi-sectional view. The spark plug 1 has a longitudinal axis X which extends from the end of the spark plug 1 on the combustion chamber side to its end facing away from the combustion chamber. The spark plug 1 has a housing 2 which has a longitudinal bore parallel to the longitudinal axis X of the spark plug 1. The housing 2 typically has a thread 22 on its outer side, with which the spark plug 1 can be screwed into the cylinder head. Typically, an external seal 10 is arranged on the outer side of the housing 2, which seals the transition between the housing 2 and the cylinder head.

[0030] An insulator 3 is arranged and fixed inside the housing 2. The gap between the housing 2 and the insulator 3 is sealed by an internal seal 11. In the insulator 3, a connection bolt 8, a resistance element 7 and an intermediate electrode 4 are arranged starting from its end facing away from the combustion chamber, and they are in electrical contact with each other. The intermediate electrode 4 typically projects from the insulator at the end of the insulator 3 on the combustion chamber side and extends into the interior space of the housing 2 in this example.

[0031] In this example, the ground electrode 5 is inserted into a borehole 20 constructed in the housing wall. The borehole 20 is a through-hole that extends from the outer side surface of the housing 2 all the way to the inner side surface of the housing. The ground electrode 5 is rod-shaped and has an inner end 51 and an outer end 52. The inner end 51 of the ground electrode 5 extends into the inner space of the housing. The inner end 51 of the ground electrode 5 and the intermediate electrode 4 together form an ignition gap 45. In this example, the two electrodes 4, 5 form a radial ignition gap 45. The ground electrode 5 and the intermediate electrode 4 can also be arranged relative to each other such that they form an axial ignition gap.

[0032] The intermediate electrode 4 and / or the ground electrode 5 can each have a noble metal-containing ignition element 53 at their ends that define the ignition gap 45. For the ground electrode 5, the noble metal-containing ignition element 53 is then arranged on the inner end 51 of this ground electrode 5.

[0033] In an alternative design shown in Figure 1b ), a cap 6 can be arranged on the end face of the housing 2 on its combustion chamber side. The housing 2 and the cap 6 together form a pre-chamber with a pre-chamber space. The ground electrode 5 is inserted into a borehole 20 that can be constructed in the housing wall or in the cap wall.

[0034] Figure 2 and Figure 3 show embodiments of the electrodes according to the invention.

[0035] In Figure 2a ), a first embodiment of the electrode 5 according to the invention is shown in a 3D view. The electrode 5 has a substrate 50 on which at least two slightly elongated protrusions 55 are arranged along its circumference. The slightly elongated protrusions 55 extend parallel to the longitudinal axis E of the electrode 5 and the substrate 50. The slightly elongated protrusions 55 are made of the same material as the substrate 50 and are formed on the substrate 50 by corresponding modification of the substrate blank. The slightly elongated protrusions 55 are constructed at least over a partial length of the substrate 50. Preferably, they extend over the entire length of the substrate 50.

[0036] In this example, an element 53 is arranged on the inner end 51 of the electrode 5, and this element forms the ignition surface of the electrode 5. The element 53 can be made of the same material as the substrate 50 or of other materials, such as noble metals or noble metal alloys.

[0037] At the outer end 52 of the electrode 5, the slightly elongated projection 55 has a height H relative to the surface of the substrate 50. The height H can be constant over the entire length of the projection 55. As an alternative, the height H can increase continuously from the inner end 51 of the projection 55 up to the outer end 52 of the projection 55. In another alternative, the projection 55 can have a first region at its inner end 51, where the height H increases and a second region with a constant height H adjoins the first region. Then, the second region extends from the first region up to the outer end 52 of the projection 55. If the electrode 5 has more than one slightly elongated projection 55 as in the present example, it is preferred that all projections 55 are configured identically.

[0038] In Figure 2b ), a sectional view shows the outer end face 52a of the electrode 55 and two side views of the electrode 5. The two side views show two possible design options for the slightly elongated projection 55. In both examples, the slightly elongated projection 55 extends parallel to the longitudinal axis E. The slightly elongated projection 55 terminates at the outer end 52 of the electrode 5 and of the substrate 50. In the first example, the slightly elongated projection 55 has a first region with an increasing height H and a second region with a constant height H. In the second example, the slightly elongated projection 55 only has a first region with an increasing height H.

[0039] The illustration of the outer end face 52a of the electrode 5 shows the resulting shape of the end face 52a. In the present example, four slightly elongated projections 55 with a width B R and a height H are arranged evenly along the circumference of the substrate 50. In the present example, the electrode 5 has a diameter D R at the projection and a diameter D G at the substrate. R D G > D R is valid and in particular D G = D G + 2*H is valid. For example, D R has a value of 1.4 mm and D

[0040] As can be seen in the illustration of the outer end side 52a of the electrode 5, the electrode 5 has at least two sections along its circumference. In the first section, the electrode 5 has the diameter D G of the substrate 50. In the second section of the electrode 5, the substrate 50 has a projection 55 and accordingly a diameter D G different from D R , which is the diameter of the circumcircle 55U around at least one projection 55. When measured along the circumference of the substrate 50, the first section has a length BG is longer than the second section. The length of the second section is the width B of the protrusion 55 R .

[0041] The protrusion 55 shown here has a rectangular shape. Other shapes, such as a triangular shape, are also possible.

[0042] In Figure 3 a cross-section for an embodiment of the electrode 5 with a groove 56, the outer end face 52a of the electrode 5 and two side views of the electrode 5 are also shown. Two embodiments are shown in the side views.

[0043] In the first embodiment, the groove 56 extends from the inner end 51 of the base 50 to approximately half of the base 50. The groove 56 has a first region where the depth T increases, a second region where the depth T is constant, and a third region where the depth T decreases. In this example, the outer end face 52a has the diameter D of the base G , or the radius R of the base 50 is drawn G .

[0044] In the second embodiment, the groove 56 extends from the inner end 51 of the electrode 5 to the outer end 52 of the electrode 5. The groove 56 has a first region where the depth T increases and a second region where the depth T is constant. The outer end side 52a of the electrode 5 according to this example corresponds to the illustration shown here.

[0045] As can be seen in the illustration of the outer end side 52a of the electrode 5, the electrode 5 has at least two sections along its circumference. In the first section, the electrode 5 has the diameter D of the base G . In the second section of the electrode 5, the base 50 has a groove and accordingly a diameter D G different from D K , which is the diameter of the inner circle 56I inside the groove 56. The diameter D K is smaller than the diameter D G , especially D G = D K + 2*T holds.

[0046] When measured along the circumference of the base 50, the first section is, by virtue of its length B G longer than the second section. The length of the second section is the width B of the groove 56 K .

[0047] The groove 56 shown here has a rectangular shape. Other shapes, such as a triangular shape, are also possible.

[0048] Figure 4The end region on the combustion chamber side of the spark plug 1 according to the invention is shown in a sectional view. The electrode 5 is partially inserted into a bore 20 formed in the housing 2. According to another design alternative, the electrode 5 has slightly elongated projections 55 and slots 56 in the form of notches, which are arranged alternately along the circumference of the base body 50, such that the outer end face 52a of the electrode 5 has the shape of a multi-pointed star. During the insertion and pressing of the electrode 5 into the bore 20, the projections 55 are plastically deformed and the space of the slots 56 is reduced. Thereby, a reliable fixation of the electrode 5 in the bore 20 is achieved.

[0049] Figure 5 shows two steps of a manufacturing method for a spark plug 1 according to the invention. In Figure 5a ) a spark plug 1 without an electrode is provided. In addition, an electrode 5 according to the invention is provided, which is inserted into a bore 20 formed in the housing 2. The bore 20 has a diameter D at its outer end B .

[0050] If the electrode 5 has projections 55, the electrode 5 has a diameter D at the base body 50 G and a diameter D at the projections 55 R . For example, the following relationships apply:

[0051] D R > D G ,

[0052] D G < D B and / or

[0053] D R > D B .

[0054] If the electrode 5 has slots 56, the electrode 5 has a diameter D at the base body 50 G and a diameter D inside the slots 56 K . For example, the following relationships apply:

[0055] D K < D G ,

[0056] D G > D B and / or

[0057] D K < D B .

[0058] If the electrode 5 has projections 55 and slots 56, the electrode 5 has a diameter D for the projections 55 R and a diameter D in the slots 56 K . Hereinafter, the following relationship applies: DK <D B <D R .

[0059] In Figure 5b ) the electrode 5 is installed in the spark plug 1. The protrusions 55 and / or the grooves 56 disappear at least partially or completely due to plastic deformation during insertion. In particular, the protrusions 55 and the grooves 56 disappear in at least one region of the base body 50, which region extends from the bore 20 into the interior space of the housing 2. Possibly, the protrusions 55 and / or the grooves 56 can also be seen on the outer end side 52a of the electrode 5.

Claims

1. An electrode (5) for a spark plug, having a base body (50) and a longitudinal axis E, an inner end (51) with an ignition surface arranged thereon, and an outer end (52) opposite to the inner end, wherein the base body (50) has a diameter D G , characterized in that The electrode (5) has at least one slightly elongated projection (55) and / or at least one groove (56) on its substrate (50).

2. The electrode (5) according to claim 1, wherein, The substrate (50) has at least two or three or four or five slightly elongated projections (55) and / or grooves (56), which are arranged uniformly along the periphery of the substrate (50).

3. The electrode (5) according to claim 1 or 2, characterized in that, At least one projection (55) and / or at least one groove (56) extends parallel to the longitudinal axis E of the electrode (5) or at an angle greater than 0° and less than 90°, particularly less than 45°.

4. The electrode (5) according to any one of the preceding claims, characterized in that The at least one projection (56) has a height H relative to the substrate (50) of the electrode (5), and the diameter D of the substrate (50) at its outer end (52) G is smaller than the diameter D of the circumcircle (55U) surrounding the at least one projection (55) R , where the longitudinal axis E of the electrode (5) serves as the center at the outer end (52).

5. The electrode (5) according to claim 4, characterized in that, The height H of the projection (55) increases in the direction from the inner end (51) of the substrate (50) towards the outer end (52) of the substrate (50).

6. The electrode (5) according to any one of the preceding claims, characterized in that, The at least one groove (56) has a depth T relative to the substrate (50) of the electrode (5), and the diameter D of the substrate (50) at its outer end (52) G is greater than the diameter D of the inner circle (56I) inside the at least one groove (56) K , where the longitudinal axis E of the electrode (5) serves as the center at the outer end (52).

7. The electrode (5) according to any one of the preceding claims, characterized in that, The slightly elongated projections (55) and grooves (56) are arranged alternately along the periphery of the substrate (50) on the substrate (50).

8. The electrode (5) according to claim 7, characterized in that, Due to the arrangement and design of the projections (55) and grooves (56), the outer end face (52a) of the substrate (50) is star-shaped.

9. A spark plug (1) having a longitudinal axis X, comprising: · A housing (2), · An insulator (3) arranged inside the housing (2), · A center electrode (4) arranged inside the insulator (3), · An electrode according to any one of claims 1 to 7 as a ground electrode (5), · having a borehole (20) with a diameter D B into which the earth electrode (5) is inserted and · An ignition gap (45) formed between the ground electrode (5) and the center electrode (4).

10. The spark plug (1) according to claim 9, characterized in that, The ground electrode (5) is inserted into a bore (20) and at least one projection (55) and / or at least one groove (56) is at least partially plastically deformed due to the insertion, so that the ground electrode (5) is pressed into the bore (20).

11. The spark plug (1) according to any one of the preceding claims 9 to 10, characterized in that, The ground electrode (5) is welded in the bore (20).

12. The spark plug (1) according to any one of the preceding claims 9 to 11, characterized in that, The spark plug (1) has a cap (6), which is fixed to the combustion chamber side end of the housing (2), and the spark plug (1) is a pre-chamber spark plug, wherein the bore (20) into which the ground electrode (5) is inserted is formed in the cap (6) or the housing (2).

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