SPARK PLUG ELECTRODE, METHOD FOR ITS PRODUCTION, AND SPARK PLUG

Abstract

A spark plug electrode having greater mechanical stability. The spark plug electrode includes a base body and a noble metal pin situated on the base body, the base body and the noble metal pin being connected to each other by a connection zone. The connection zone has at least one first welding seam and one second welding seam.

Claims

1-15. (canceled)

16. A spark plug electrode, comprising: a base body; and a noble metal pin situated on the base body, the base body and the noble metal pin being connected to each other by a connection zone; wherein the connection zone has at least one first welding seam and one second welding seam.

17. The spark plug electrode as recited in claim 16, wherein one of: (i) the first welding seam is disposed between the noble metal pin and the base body, the second welding seam being situated between the first welding seam and the noble metal pin and a noble metal concentration in the first welding seam being less than a noble metal concentration in the second welding seam, or (ii) the second welding seam is situated between the first welding seam and the base bodyand a noble metal concentration in the first welding seam being greater than a noble metal concentration in the second welding seam.

18. The spark plug electrode as recited in claim 16, wherein a noble metal component in the first welding seam and in the second welding seam amounts to at least 40 mass-% in relation to the total weight of the first welding seam and the second welding seam.

19. The spark plug electrode as recited in claim 18, wherein the noble metal component in the first welding seam and in the second welding seam amounts to at least 50 mass-% in relation to the total weight of the first welding seam and the second welding seam.

20. The spark plug electrode as recited in claim 16, wherein in a longitudinal direction of the spark plug electrode, the noble metal concentration in the connection zone changes by maximally 40 mass-% per interval of 100 μm length of the connection zone.

21. The spark plug electrode as recited in claim 16, wherein in a longitudinal direction of the spark plug electrode, the noble metal concentration in the connection zone changes by maximally 25 mass-% per interval of 100 μm length of the connection zone.

22. The spark plug electrode as recited in claim 16, wherein a length of the noble metal pin in a longitudinal direction of the spark plug electrode amounts to maximally 900 μm.

23. The spark plug electrode as recited in claim 16, wherein a length of the noble metal pin in a longitudinal direction of the spark plug electrode amounts to maximally 80 μm to 200 μm.

24. The spark plug electrode as recited in claim 16, wherein a length of the connection zone in a longitudinal direction of the spark plug electrode amounts to 50 μm to 700 μm.

25. The spark plug electrode as recited in claim 16, wherein a length of the connection zone in a longitudinal direction of the spark plug electrode amounts to 100 μm to 600 μm.

26. The spark plug electrode as recited in claim 16, wherein a length of the first welding seam and a length of the second welding seam are the same in size in a longitudinal direction of the spark plug electrode.

27. The spark plug electrode as recited in claim 16, wherein the noble metal is selected from Ir, Rh, Pt, Pd, Re, alloys of these elements and alloys of these elements with nickel.

28. The spark plug electrode as recited in claim 16, wherein the base body is developed from a nickel-containing alloy, and a nickel in the alloy amounts of at least 50 mass-% in relation to the total weight of the alloy.

29. A spark plug including a spark plug electrode, the spark plug electrode including a base body, and a noble metal pin situated on the base body, the base body and the noble metal pin being connected to each other by a connection zone, wherein the connection zone has at least one first welding seam and one second welding seam.

30. A method for producing a spark plug electrode having a base body and a noble metal pin, the method comprising: carrying out a first welding operation for connecting the noble metal pin and the base body of the spark plug electrode while developing a first welding seam; and one of: (i) carrying out a second welding operation in a region between the first welding seam and the noble metal pin while developing a second welding seam, a noble metal concentration in the first welding seam being less than a noble metal concentration in the second welding seam , or (ii) carrying out a second welding operation in a region between the first welding seam and the base body while developing a second welding seam, a noble metal concentration in the first welding seam being greater than a noble metal concentration in the second welding seam, the first welding seam and the second welding seam forming a connection zone of the noble metal pin and the base body.

31. The method as recited in claim 30, wherein the welding is carried out by laser welding with the aid of a CW laser.

32. The method as recited in claim 30, wherein the second welding operation is carried out in a region that lies at a distance from a connection surface of the first welding seam and the noble metal pin in the direction of the noble metal pin, the distance amounting to 5 μm to 50 μm.

33. The method as recited in claim 32, wherein the distance mounts to 10 μm to 30 μm.

34. The method as recited in claim 30, wherein a laser beam completely penetrates the materials to be welded during the first welding operation and the second welding operation.

35. The method as recited in claim 30, wherein the spark plug electrode is rotated during the first and second welding operations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following text, exemplary embodiments of the present invention will be described in detail with reference to the figures. Identical or functionally equivalent components have been denoted by the same reference numerals.

[0021] FIG. 1 shows a part-sectional view of a spark plug according to a specific embodiment of the present invention.

[0022] FIG. 2 shows a sectional view of a spark plug electrode according to a specific embodiment of the present invention.

[0023] FIG. 3 shows an element distribution in a cutaway of the spark plug electrode from FIG. 2.

[0024] FIG. 4 shows a schematic sectional view during the production process of the spark plug electrode from FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0025] Below, a spark plug 1 according to a preferred exemplary embodiment of the present invention as well as a spark plug electrode 10 according to a preferred exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 through 4.

[0026] As shown in FIG. 1, spark plug 1 includes a ground electrode 2 and a center electrode 3. An insulator 4 is provided in such a way that center electrode 3 slightly projects from insulator 4 in the known manner. Center electrode 3 has a noble metal pin 11. Insulator 4 itself is partially surrounded by a housing 5. Reference numeral 6 denotes an electric terminal nut. An electrically conductive connection is provided from electric terminal nut 6 to center electrode 3 via a terminal stud 7 and an electrically conductive connection element 8.

[0027] FIG. 2 shows in detail a design of a spark plug electrode 10 according to a preferred specific embodiment of the present invention. Spark plug electrode 10 may be developed as a ground electrode or as a center electrode. Spark plug electrode 10 includes a base body 12, which is connected to an electrically conductive connection element in case of a development as a center electrode. The base of base body 12 is developed thicker than the remaining area of base body 12, so that is it able to be fixed in place on spark plug 1 in a stable manner.

[0028] Base body 12 is advantageously made from a nickel-containing alloy, a nickel component of the alloy in particular amounting to at least 50 mass-% in relation to the total weight of the alloy.

[0029] In addition, the spark plug electrode has a noble metal pin 11, which is used for generating the spark plasma. Noble metal pin 11 may be made from a pure noble metal, in particular from Ir, Rh, Pt, Pd or Re, or from alloys of these elements. Moreover, it is also possible to develop noble metal pin 11 from alloys of the aforementioned elements and nickel as a further component. Noble metal pin 11 has a length L1 of preferably maximally 900 μm, and in particular of 80 μm to 200 μm, in the longitudinal direction X-X of spark plug electrode 10. This is particularly advantageous for generating ignition sparks.

[0030] A connection zone 13 connects noble metal pin 11 and base body 12 to each other. In this exemplary embodiment, connection zone 13 is made up of two welding seams, i.e. a first welding seam 14 which is facing base body 12, and a second welding seam 15 which is facing noble metal pin 11. Noble metal pin 11 is situated on base body 12 in a stable manner with the aid of connection zone 13.

[0031] In the longitudinal direction X-X of spark plug electrode 10, connection zone 13 has a length L2 of 10 μm to 700 μm, and in particular of 100 μm to 600 μm. This produces a mechanically stable connection between noble metal pin 11 and base body 12.

[0032] If one examines connection zone 13, then a noble metal concentration in first welding seam 14 is lower than a noble metal concentration in second welding seam 15. However, when considered overall, a noble metal concentration both in first welding seam 14 and in second welding seam 15 is less than in noble metal pin 11 but greater than in base body 12. As a result, there are four regions having different concentrations of noble metal in spark plug electrode 10. The noble metal concentration essentially decreases steadily, i.e., without abrupt changes, from noble metal pin 11, where it lies at 100% or less depending on the initial material used, across the second welding seam 15 and first welding seam 14, in the direction of base body 12, where the noble metal concentration amounts to 0% (or is low depending on the material used for base body 12).

[0033] It is advantageous for a steadily decreasing noble metal concentration if a length L3 of first welding seam 14 and a length L4 of second welding seam 15 are approximately of equal size in the longitudinal direction X-X of spark plug electrode 10.

[0034] It follows from the concentration characteristic of the noble metal concentration from noble metal pin 11 to base body 12 that a coefficient of thermal expansion from noble metal pin 11 to base body 12 also increases in an essentially continuous manner, without increasing or decreasing very abruptly. If high temperatures are acting on spark plug electrode 10 during the engine operation, then these temperatures are able to be better tolerated. Reduced mechanical stresses arise at boundary surfaces 16-18, i.e., boundary surface 16 of noble metal pin 11/second welding seam 15, boundary surface 17 of second welding seam 15/first welding seam 14, and boundary surface 18 of first welding seam 14/base body 12. The service life of spark plug electrode 10 is thus increased significantly.

[0035] FIG. 3 shows an element distribution in a cutaway of spark plug electrode 10 from FIG. 2. The regions of different chemical elements are shown by different shadings. The perpendicular dashed lines subdivide spark plug electrode 10 into its different regions along longitudinal direction X-X of spark plug 10. The mass distribution of the elements in mass percent (mass-%) versus the length of spark plug electrode 10 has been plotted in μm. The left section represents that of noble metal pin 11. Here, it can be seen that noble metal pin 11 is made up of noble metal to 100 mass-%, i.e. an alloy of Ir and Rh. Adjoining the left section is the section of second welding seam 15. Here, the noble metal component, which is meant to denote a total component of the noble metals Ir and Rh, is less than in noble metal pin 11. The noble metal component has decreased from 100 mass-% to approximately 75 mass-%. The remaining 25 mass-% are taken up by nickel, which was alloyed when developing connection zone 13. The section of second welding seam 15 is followed by the section of first welding seam 14. Here, the noble metal concentration has decreased further. A noble metal component in first welding seam 14 now lies at approximately 60 mass-%. The remaining 40 mass-% is taken up by nickel. The right section shows the element distribution in base body 12. Base body 12 consists of virtually 100 mass-% of nickel (or a nickel-containing alloy). The noble metal concentration continues to decrease from second welding seam 15 to base body 12.

[0036] It is easy to see that the noble metal concentration in connection zone 13 changes in the longitudinal direction X-X of spark plug electrode 10 by maximally 40 mass-% and mostly by maximally 25 mass-% per interval of 100 μm length of connection zone 13. Abrupt changes in the element concentration particularly with a change of more than 50 mass-% are not present. By providing additional welding seams, a further softening of the increase in the noble metal concentration may be achieved in regions of a more pronounced change in the noble metal concentration.

[0037] It can furthermore be seen that length L3 of first welding seam 1 and length L4 of second welding seam 15 are approximately identical in size in the longitudinal direction X-X of spark plug electrode 10. The change in concentration of the noble metal is thus particularly uniform.

[0038] FIG. 4 shows a schematic sectional view during the production process of spark plug electrode 10 from FIG. 2. First, a noble metal pin 11 is placed on a base body 12. A laser beam, symbolized by (h*v), is directed onto a joining surface 20 between noble metal pin 11 and base body 12. A first welding operation A is carried out in this way. The laser beam melts the materials of noble metal pin 11 and base body 12 mutually abutting in connection surface 20 so that a first welding seam 14 is developed, which contains the elements of noble metal pin 1 and base body 12 in a relatively balanced mixture concentration.

[0039] During welding operation A, spark plug electrode 10 is rotated in the direction of arrow C, so that connection surface 20 is uniformly exposed to the laser beam on all sides. The laser beam is preferably generated by a CW laser and completely penetrates the materials to be welded. After first welding seam 14 has been produced with the aid of first welding operation A, the laser beam is newly oriented, i.e., advantageously toward a region 19 between first welding seam 14 and noble metal pin 11. However, the laser beam may also be directed to a region between first welding seam 14 and base body 12, which, however, leads to a somewhat more strongly changing noble metal concentration from noble metal pin 11 toward first welding seam 14 and is therefore not preferred as much.

[0040] In second welding operation B, the laser beam is preferably directed to a region 19 which lies at a distance from connection surface 20 of first welding seam 14 and noble metal pin 11 by a height h in the direction of noble metal pin 11. Height h in particular amounts to 5 μm to 50 μm, and in particular to 10 μm to 30 μm.

[0041] First welding seam 14 and noble metal pin 11 are melted by second welding operation B. A second welding seam 15 having a further mixture concentration of the elements is developed; because of the fusing of further noble metal from noble metal pin 11, the noble metal concentration in second welding seam 15 is greater than the noble metal concentration in first welding seam 14.

[0042] Length L of noble metal pin 11 and the length of base body 12 have decreased in favor of connection zone 13. Due to the decreasing noble metal concentration starting from noble metal pin 11 across connection zone 13 to base body 12, which shows no abrupt decrease in the noble metal concentration, a characteristic of the coefficient of thermal expansion along these regions that is likewise without abrupt changes is obtained. Tensions at boundary surfaces 16, 17, 18 of mutually abutting regions are reduced, which increases the mechanical stability of spark plug electrode 10.