SPARK PLUG IGNITION TIP, SPARK PLUG DEVICE, AND METHOD FOR PRODUCING A SPARK PLUG IGNITION TIP

Abstract

A spark plug ignition tip for an electrode of a spark plug device, in particular a prechamber spark plug, having a base body that has a first axial end, a second axial end and a circumferential section situated between them; the base body contains a precious metal or precious metal alloy; the first axial end and/or the circumferential section is embodied for fastening the base body to an electrode; the second axial end has a dome-shaped section; and the base body is produced by powder metallurgy.

Claims

1. A spark plug ignition tip for an electrode of a spark plug device, in particular a prechamber spark plug, having: a base body that has a first axial end, a second axial end, and a circumferential section situated between them, wherein the base body contains a precious metal or precious metal alloy; the first axial end and/or the circumferential section is embodied for fastening the base body to an electrode; the second axial end has a dome-shaped section; and the base body is produced by powder metallurgy.

2. The spark plug ignition tip according to claim 1, wherein the dome-shaped section is convex.

3. The spark plug ignition tip according to claim 1, wherein dome-shaped section is concave.

4. The spark plug ignition tip according to claim 1, wherein the dome shape of the second axial end is a spherical segment.

5. The spark plug ignition tip according to claim 1, wherein the circumferential section is cylindrical and/or the first axial end is a planar surface that is oriented transversely to a longitudinal axis of the base body.

6. The spark plug ignition tip according to claim 1, wherein the base body is composed of one piece.

7. The spark plug ignition tip according to claim 1, wherein the precious metal is iridium or the precious metal alloy contains iridium.

8. The spark plug ignition tip according to claim 7, wherein the base body contains more than 50% by weight iridium.

9. The spark plug ignition tip according to claim 1, wherein the base body contains a precious metal alloy that includes iridium as the main ingredient as well as rhodium in a proportion of greater than 0% by weight and less than 10% by weight, and zirconium oxide.

10. The spark plug ignition tip according to claim 1, wherein the base body is sintered.

11. The spark plug ignition tip according to claim 10, wherein the base body has a sintering density of greater than 96% and/or the base body has a porosity of greater than 4% and/or the base body has a sintering grain size that is less than or equal to 50 m and greater than or equal to 5 m.

12. A spark plug device, in particular a prechamber spark plug, having an electrode to which a spark plug ignition tip according to claim 1 is mounted.

13. The spark plug device according to claim 12, wherein the electrode is a central electrode; the spark plug ignition tip is mounted to an end of the central electrode; and an annular electrode at least partially encloses at least an axial section of the spark plug ignition tip so that an annular gap is formed between them.

14. The spark plug device according to claim 13, wherein the dome-shaped section protrudes at least partially out from the annular electrode in the axial direction.

15. A method for producing a spark plug ignition tip, with the following steps: preparing a powder or powder mix composed of a precious metal or precious metal alloy; powder metallurgical forming of the powder or powder mix in the shape of a base body that has a first axial end, a second axial end, and a circumferential section situated between them; the first axial end and/or the circumferential section is embodied for fastening the base body to an electrode; and the second axial end is embodied so that a dome-shaped section is produced; and sintering of the base body.

Description

DRAWINGS

[0048] Exemplary embodiments are shown in the drawings and will be explained in greater detail below. In the drawings:

[0049] FIG. 1 is a schematic depiction of a spark plug for a motor vehicle, with a schematically indicated ignition section;

[0050] FIG. 2 shows an embodiment of an ignition section for the spark plug from FIG. 1;

[0051] FIG. 3 is a detailed view III of FIG. 2;

[0052] FIG. 4 shows an alternative embodiment of an ignition section for the spark plug from FIG. 1;

[0053] FIG. 5 is a detailed view V of FIG. 4;

[0054] FIG. 6 is a schematic depiction of an embodiment of a spark plug ignition tip with a concave dome-shaped section;

[0055] FIG. 7 is a schematic depiction of another embodiment of a spark plug ignition tip with a convex dome-shaped section; and

[0056] FIG. 8 is a flow chart of steps for performing an embodiment of a method for producing a spark plug ignition tip.

DESCRIPTION

[0057] FIG. 1 schematically depicts a spark plug device that is generally labeled reference numeral 10.

[0058] The spark plug device 10 has a spark plug body 12, which has an ignition section 14 embodied at its front end.

[0059] The spark plug body 12 includes an insulator 16 around which a metal sleeve 18 is positioned. The metal sleeve 18 is generally equipped with a thread by means of which the spark plug device 10 can be screwed into a cylinder head of an internal combustion engine.

[0060] Centrally inside the insulator 16, an electric connection element 20 is provided, which extends through the spark plug body 12 in the axial direction so that at an end of the spark plug body 12 axially opposite from the ignition section 14, a spark plug connector can be slid on, via which electrical energy for producing ignition pulses can be slid on [sic].

[0061] On the inside of the insulator 16, the connection element 20 is electrically connected to a connecting element 22, which is in turn electrically connected to a central electrode 24 that extends out from the insulator 16 in the axial direction and along a general longitudinal axis 25, into the ignition section 14 that is schematically depicted in FIG. 1.

[0062] FIG. 1 also shows that the metal sleeve 18 is electrically connected to a ground electrode 26, which likewise extends into the ignition section 14.

[0063] FIGS. 2 and 3 show an embodiment of such an ignition section 14.

[0064] It is first of all apparent that the central electrode 24 extends out from a bore of the insulator 16 in the axial direction. At the front end of the central electrode 24, an ignition tip 30 is mounted, which is preferably at least partially made of a precious metal. The ground electrode 26 is embodied so that it extends at least partially around a circumferential section of the ignition tip 30 in such a way that an annular gap 31 is formed between the ground electrode 26 and the circumferential section of the ignition tip 30. The annular gap 31 constitutes a spark gap inside which a fuel mixture can be ignited.

[0065] The central electrode 24 with the ignition tip 30 mounted on it and the ground electrode 26 are positioned inside a prechamber 32 that is spatially delimited, specifically by the insulator 16 and metal sleeve 18 toward one axial end and by a prechamber cap 34 toward the other axial end, with the prechamber cap 34 being connected to the metal sleeve 18.

[0066] The prechamber cap 34 has a central opening 36 through which a fuel mixture can travel into the prechamber 32. The prechamber cap 34 also has multiple lateral openings 38 through which a fuel mixture 42 can also travel into the prechamber 32. In addition, an ignited fuel mixture or flame can travel out through the lateral openings 38 and the central opening 36.

[0067] A certain distance D is furnished between the central opening 36 and the ignition tip 30 that is positioned coaxial thereto. In an axial region between the ignition tip 30 and the insulator 16 or metal sleeve 18, a rear chamber section is furnished, which in particular has an annular chamber 40.

[0068] As is particularly shown in FIG. 3, the ignition tip 30 has a first axial end 44 that is embodied by means of a planar surface that is oriented perpendicular to the longitudinal axis 25. The ignition tip 30 is connected to the central electrode 24 via this second axial end 44, for example by means of a suitable joining method such as laser welding, friction welding, etc.

[0069] The ignition tip 30 has a second axial end 46, which is oriented toward the prechamber cap 34. Between the first axial end 44 and the second axial end 46, there is a cylindrical circumferential surface 48, which delimits the annular gap 31 on the radial inside.

[0070] The second axial end 46 has a dome-shaped section 50, which, in the present case, is embodied as concave. The concave dome-shaped section 50 is spaced apart from an outer circumference of the ignition tip 30 in such a way that radially outside the dome-shaped section 50, an annular surface 52 is formed, which is oriented perpendicular to the longitudinal axis 25.

[0071] The ignition tip 30 extends out from the ground electrode 26 in the axial direction. Stated more precisely, the ignition tip 30 protrudes from an axial end of the ground electrode 26 by a protrusion length l.sub.1.

[0072] The dome-shaped section 50 has an axial depth relative to the annular surface 52 such that the axial surface of the ground electrode 26 is spaced apart from a deepest point of the concave dome-shaped section by a distance l.sub.2 that is preferably greater than zero.

[0073] As is indicated by double arrows in FIG. 2, in a compression step, a fuel mixture, in particular a lean fuel mixture 42, enters the prechamber 32 through the central opening 36 and the lateral openings 38.

[0074] As is indicated particularly in FIG. 3, the fuel mixture entering through the central opening 36 is deflected radially outward by the concave dome-shaped section 50 and is redirected into a direction opposite from the influx direction. This is labeled m.sub.1 in FIG. 3.

[0075] Furthermore, the lean fuel mixture that has been deflected in this way and fuel mixture that flows in through the lateral openings 38 travel in the axial direction toward the rear section of the prechamber 32, i.e. toward the annular chamber 40, which is labeled m.sub.2 in FIG. 3.

[0076] Since the rear section of the prechamber 32 is delimited in the axial direction, the lean fuel mixture is then redirected into an axial direction again, specifically in such a way that it is forced through the annular gap 31 in the direction from the annular chamber 40 toward the central opening 36, labeled m.sub.3 in FIG. 3. Because the fuel mixture flowing in through the central opening 36 is reversed in its flow direction, as indicated by m.sub.1, a kind of negative pressure also occurs at this axial end of the annular gap 31, which further promotes a flow through the annular gap 31 in the direction toward the central opening 36.

[0077] The reliable flow through the annular gap 31 by the lean fuel mixture can assure that the lean fuel mixture is reliably ignited in an ignition by means of sparks arcing over in the region of the annular gap 31.

[0078] The forced flushing of the annular gap 31 also assures that heat occurring there can be dissipated relatively quickly so that the ignition section 14 as a whole can be embodied in a thermally stable and arc erosion-resistant way. This can result in an extended service life of the spark plug device 10.

[0079] FIGS. 4 and 5 show another embodiment of an ignition section 14. In terms of its design and function, the ignition section 14 essentially corresponds to the ignition section 14 in FIGS. 2 and 3. The same elements have therefore been provided with the same reference numerals. Essentially, the differences will be explained below.

[0080] In the ignition section 14, the central electrode 24 is connected to an ignition tip 30 with a second axial end 46 having a dome-shaped section 50 that is embodied as convex. The convex dome-shaped section in this case is spaced apart from an outer circumference of the ignition tip 30 in such a way that an annular surface 52 is formed, which is oriented perpendicular to the longitudinal axis.

[0081] A fuel mixture 42 entering via the central opening 36 strikes the convex dome-shaped section 50 centrally and is deflected radially outward by it, but is not reversed in its direction as is the case with the concave dome-shaped section 50. The radial deflection outward is labeled m.sub.1 in FIG. 5.

[0082] Due to the lack of a rotation direction reversal, the fuel mixture 42 flowing in is then conveyed into the annular gap 31 and flows through the latter in a direction starting from the central opening 36 toward the rear section of the prechamber 32. This is labeled m.sub.2 in FIG. 5.

[0083] The gas mixture traveling into the rear section of the prechamber 32 is redirected there and travels back toward the prechamber cap 34, as is labeled m.sub.3 in FIG. 5.

[0084] With the embodiment of an ignition tip 30 with a convex dome-shaped section, it is therefore also achieved that the annular gap 31 is subjected to good flushing in all operating phases so that essentially, the same advantages are achieved as with the concave dome-shaped section 50 from FIGS. 2 and 3.

[0085] FIG. 6 shows the ignition tip 30 from FIGS. 2 and 3. It is clear that the circumference surface 48 lies on a radius R relative to the longitudinal axis 25.

[0086] The dome-shaped section 50 is formed by a spherical segment, the base circle of which is aligned so that it is flush with the second axial end 46 and the annular surface 52. The radius of this base circle is labeled a in FIG. 6. The radius of the sphere that defines this spherical segment is labeled r in FIG. 6. Radius a is smaller than radius R. The radial magnitude r.sub.M of the annular surface 52 is calculated by means of

r.sub.M=Ra.

[0087] The depth of the dome-shaped section 50 is labeled h in FIG. 6.

[0088] For the spherical segment, the following formula applies:

(rh).sup.2+a.sup.2=r.sup.2 or h=r{square root over ((r.sup.2a.sup.2))}

[0089] In one embodiment, the value of R can be 1.35 mm. The value of r can be in a range from 1.5 mm to 6 mm. The value of r.sub.M can be in the range from 0.1 mm to 0.2 mm.

[0090] Preferably, r is equal to R.

[0091] The value of h is calculated based on the dimensions indicated above.

[0092] FIG. 7 shows the ignition tip 50 from FIGS. 4 and 5. Here, the dome-shaped section 50 is embodied as a convex section that is likewise embodied in the form of a spherical segment. The calculation approaches indicated above apply equally with regard to the dimensions of the spherical segment.

[0093] In FIGS. 6 and 7, the ignition tips 50, 50 are each comprised of a one-piece base body 56 and 56.

[0094] The base bodies 56, 56 can be produced using powder metallurgy. In this case, in particular, a method of the kind shown in FIG. 8 is used.

[0095] In a first step, a powder or powder mix composed of a precious metal or precious metal alloy is prepared (S1). In a second step, the powder or powder mix is formed into a shape of a base body 56 or 56 is formed by means of powder metallurgy (S2).

[0096] In a step S3, the base body 56, 56 is then sintered.

[0097] In a step S4, the base body 56, 56 can then be connected to an electrode, in particular a central electrode 24.

[0098] As a precious metal alloy, preferably a powder mix composed of an iridium alloy is prepared, the main ingredient of which is iridium. Preferably, the precious metal alloy contains iridium as its main ingredient and rhodium in a proportion of greater than 0% by weight and less than 20% by weight. The precious metal alloy can optionally also contain zirconium oxide.

[0099] In a preferred variant, rhodium is contained in a proportion of 2% to 3%, and zirconium oxide is contained in a proportion of approximately 50 to 200 ppm. The rest of the precious metal alloy is made up of iridium.

[0100] The sintering is carried out so that a sintering density of >96% is achieved at a porosity of greater than 4% and a sintering grain size of at most 10 m.

[0101] It is to be understood that the foregoing is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

[0102] As used in this specification and claims, the terms for example, e.g., for instance, such as, and like, and the verbs comprising, having, including, and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.