SPARK PLUG AND METHOD FOR MANUFACTURING A SPARK PLUG

Abstract

Method for manufacturing a spark plug for a combustion engine, wherein the spark plug has at least two components which are joined by at least one welded joint which has been manufactured in a welding process, wherein for improving selected material properties of the welded joint a laser beam is directed to the welded joint and in that a powder which improves the selected material properties is introduced into the welded joint which is melted on its surface by the laser beam such that the powder melts and due to a connection of the melted powder with the melted aggregate structure of the surface of the welded joint a treated area with improved material properties results.

Claims

1. A method for manufacturing a spark plug for a combustion engine, comprising: directing a laser beam at a welded joint between at least two components of a spark plug; melting a surface of the welded joint with the laser beam to form a first melted material; melting a powder with the laser beam to form a second melted material, wherein the powder is configured to improve material properties of the welded joint; and connecting and solidifying the first and second melted materials to form a treated area at least at the welded joint.

2. The method according to claim 1, wherein parts of an electrode of the spark plug are used as the at least two components.

3. The method according to claim 2, wherein the parts of the electrode comprise a middle electrode carrier and a body of precious metal.

4. The method according to claim 3, wherein the body of precious metal is connected to the middle electrode carrier to form a step.

5. The method according to claim 4, wherein the step is worked into an end area of the middle electrode carrier and/or the body of precious metal is arranged onto the middle electrode carrier while leaving behind the step.

6. The method according to claim 1, comprising at least partially filling an indentation with the second melted material of the powder to form a filled portion.

7. The method according to claim 6, comprising at least partially removing the filled portion after connecting and solidifying the first and second melted materials.

8. The method according to claim 1, wherein one or more cover layers are disposed under and/or over at least the treated area.

9. The method according to claim 1, wherein the treated area excludes an untreated area immediately adjacent to the treated area.

10. The method according to claim 1, wherein the laser beam is directed to the welded joint with an unfocused beam section.

11. The method according to claim 1, wherein the treated area has an increase of resistance against hot corrosion and/or against oxidation, wherein the powder comprises a metal powder which is resistant against hot corrosion and/or oxidation, wherein the metal powder comprises a corrosion-resistant Nickel powder or a metal powder including a ceramic material.

12. The method according to claim 1, wherein the powder is introduced into the laser beam distanced from the welded joint.

13. A spark plug for a combustion engine, wherein the spark plug comprises: at least two components of the spark plug joined by a welded joint; and a treated area at least at the welded joint, wherein the treated area comprises an alloy formed by melting and solidifying a first material of a surface of the welded joint and a second material configured to improve material properties of the welded joint, wherein the second material comprises a melted and solidified powder.

14. The spark plug according to claim 13, wherein the at least two components joined by the welded joint are parts of an electrode of the spark plug, wherein the parts of the electrode comprise an electrode carrier and a body of precious metal connected to the electrode carrier by the welded joint.

15. The spark plug according to claim 14, wherein the treated area excludes an untreated area immediately adjacent to the treated area, wherein the untreated area is arranged adjacent to an ignition surface of the electrode.

16. The spark plug according to claim 13, wherein the second material is resistant against hot corrosion and/or oxidation, wherein the second material comprises a Nickel based alloy and/or a ceramic.

17. The spark plug according to claim 13, wherein one or more cover layers are disposed under and/or over at least the treated area.

18. A method, comprising: treating a surface of a welded joint between at least two components of a spark plug, wherein the treating comprises: melting the surface of the welded joint; melting a material onto the surface of the welded joint; and solidifying the material on the surface of the welded joint, wherein the material improves material properties of the welded joint.

19. The method according to claim 18, wherein, relative to the welded joint, the material has a greater resistance against hot corrosion and/or oxidation.

20. The method according to claim 18, wherein the material comprises a Nickel based alloy and/or a ceramic.

Description

[0040] Embodiments of the invention are discussed with respect to the figures, wherein the figures show

[0041] FIG. 1 a spark plug manufactured in accordance with the invention;

[0042] FIG. 2a-d schematic sectional views through a spark plug according to FIG. 1 before and after alloying, respectively, and an isometric sectional view;

[0043] FIG. 3 applying and, simultaneously, melting of powder;

[0044] FIG. 4a,b a sectional view according to FIG. 2a and a respective photo;

[0045] FIG. 5a,b a sectional view and a photo after alloying and before a grinding process;

[0046] FIG. 6a,b a sectional view and a detail view of another embodiment of the invention;

[0047] FIG. 7a-e steps of the inventive method;

[0048] FIG. 8 a sectional view of another embodiment of the invention.

[0049] FIG. 1 shows a photo of a spark plug 1 manufactured according to the inventive method.

[0050] The spark plug 1 has a spark plug housing 12 which is provided with a thread 13 in an area facing ignition. A ring-shaped ignition gap 15 is formed between a middle electrode and a mass electrode which is in the form of a ring electrode. By way of example, here the mass electrode is provided with four openings 11 which allow passage of combustion gases during operation of the spark plug 1 in a combustion engine.

[0051] The structure of the spark plug 1 shown in FIG. 1 can be seen in FIG. 2a-d wherein FIG. 2a shows an intermediate product of the inventive method:

[0052] As is known in the art the spark plug 1 comprises a ceramic body 16 arranged within the spark plug housing 12 (the thread 13 is not shown), in which a pin is arranged within a central opening wherein the pin forms an electrode carrier of the middle electrode (middle electrode carrier 3) with an end facing ignition. As shown, the pin can have a core 17 of material with good thermal conductivity (e.g. copper) to increase heat dissipation. Dissipation of heat into the spark plug housing 12 is affected by a seal 18 which is arranged between a shoulder of the ceramic body 16 and the spark plug housing 12.

[0053] A body of precious metal 2 is joint by a welded joint onto the middle electrode carrier 3 (here by way of laser welding). In this embodiment the body of precious metal 2 is formed as a circular-shaped disk and is put on a shoulder of a step 4 of the middle electrode carrier 3 (which is here formed as a spark plug pin). The welded joint extends over step 4 completely. It is preferred that before welding, preferably laser welding, the body of precious metal 2 protrudes over the face side of the middle electrode carrier 3 which is arranged towards ignition to provide a welded seam, preferably a fillet weld, at the transition from body of precious metal 2 to middle electrode carrier 3. This results in an indentation 14 which is substantially concave in the respective region (FIGS. 2a and 4b) which is only partially filled or filled completely by the inventive manufacturing method (FIGS. 2b, 2c and 2d).

[0054] A mass electrode carrier 10 is connected to the spark plug housing 12. A body of precious metal 2′ in the form of a ring is connected to the mass electrode carrier 10 (here by laser welding). The ignition areas 9 of the bodies of precious metal 2, 2′ which face each other define the ignition gap 15.

[0055] The presentation of FIG. 2, which with respect to the inventive manufacturing process forms an intermediate step, corresponds to spark plugs 1 of the prior art. During operation of the spark plug 1 in a combustion engine the welded joint between body of precious metal 2 and the middle electrode carrier 3 (and the one between body of precious metal 2′ and mass electrode carrier 10) is exposed to the combustion gases without protection. In FIG. 2b an alloyed area can be seen in the area of the welded joint which is manufactured by melting a surface of the welded joint and introducing a powder 5. Said alloyed area does not only cover the welded joint but, in this embodiment, extends into a region adjacent to the welded joint, i.e. in a radial view both, to larger radii (however an untreated area 7 remains adjacent to the ignition gap 15) and to smaller radii (here over the complete central region). Therefore, the middle electrode depicted in FIGS. 2b and 2d has an untreated area 7 starting from the ignition gap 15 and extending radially inwards and an adjacent treated area 19 (cf. the detail view of FIG. 2c).

[0056] An alloyed area for protection of the welded joint could also be provided with respect to the welded joint between mass electrode carrier 10 and the body of precious metal 2′ of the mass electrode (in an alternative embodiment the alloyed area could be provided only with respect to this welded joint) which, however, is not provided for in this embodiment.

[0057] In FIG. 3 manufacture of the alloyed area is shown. According to the invention this is done by directing a laser beam 8 onto the welded joint and by introducing a powder 5 which improves the material properties into the surface which has been melted by the laser beam 8 such that the powder 5 melts and a treated (alloyed) area forms with improved material properties by connecting the melted powder 5 with the melted aggregate structure of the surface of the welded joint.

[0058] It can also be provided that the indentation 14 is filled by the inventive method. An excess of applied material in the area 19, which can be seen in FIG. 2c in particular, can be subsequently removed by turning, milling, grinding or the like such that a plane area according to FIG. 5a and FIG. 5b is formed.

[0059] In FIG. 3 only that area of the middle electrode is shown which faces ignition. It can be seen that the laser beam 8 is directed to the welded joint with a defocused or “out of focus” illumination (i.e. a convergent or divergent) beam section (in FIG. 3 below the focus). Here the powder 5 is introduced into the laser beam 8 in the divergent beam section above the surface of the welded joint.

[0060] An advantage of an “out of focus” illumination of the laser is a more homogenous spread of the power density of the laser beam 8 over a larger area. It was found that a variable thermic introduction can be achieved using the same laser-setup by varying the distance between the focus and the area to be operated on. As only a single laser-setup is needed expenses can be saved.

[0061] FIG. 4a shows a schematic sectional view in a way corresponding to 2a (wherein, however, the mass electrode is not shown) of that area of the spark plug 1 which faces ignition. In a photo of a view from above (FIG. 4b) on the spark plug pin a body of precious metal 2 can be seen after the laser welding process which body has been arranged on the middle electrode carrier 3, preferably by pressing it onto the middle electrode carrier 3. The welded joint is substantially formed by a fillet weld. It can also be seen that an indentation 14 is formed by the welding process.

[0062] FIG. 5a shows in a schematic sectional view that area of the spark plug 1 which faces ignition. A protrusion of powder 5 solidified by the laser is removed by removal of material (here: grinding) such that in a direction facing ignition the untreated area 7 and the treated area 19 abut flush.

[0063] As shown in FIGS. 6a and 6b (detail of FIG. 6a) in another embodiment it can be provided that at least the treated area 19 and preferably also another, untreated area 7 which is arranged immediately adjacent to the treated area 19 can be covered by several cover layers 6 which are stacked and which preferably consist of different materials. This covering can be done by any known technique.

[0064] In FIG. 7a-e the intermediate products of the inventive method are shown.

[0065] In FIG. 7a the body of precious metal 2 is arranged onto a chamfered tip of the middle electrode carrier 3 and is welded to the middle electrode carrier 3 by laser welding such that the state shown in FIG. 7b results. In the transition to FIG. 7c the alloyed area has been manufactured as described above. In the transition to FIG. 7d a protrusion of powder 5 has been removed. In the variant according to FIG. 7e several cover layers 6 have been arranged on top of each other on the alloyed area.

[0066] In the embodiment of FIG. 8 only the tip of the middle electrode carrier 3 including the body of precious metal 2 is shown. Here, by way of example, two cover layers 6 cover the body of precious metal 2 completely including the treated area 19 and extend to the ignition area 9. Other than shown more than two cover layers 6 or a single cover layer 6 can be provided.

LIST OF REFERENCE SIGNS

[0067] 1 spark plug [0068] 2, 2′ body of precious metal [0069] 3 middle electrode carrier [0070] 4 step [0071] 5 powder [0072] 6 cover layer [0073] 7 untreated area [0074] 8 laser beam [0075] 9 ignition area [0076] 10 mass electrode carrier [0077] 11 openings in a body of precious metal of the mass electrode [0078] 12 spark plug housing [0079] 13 thread [0080] 14 indentation [0081] 15 spark gap [0082] 16 ceramic body [0083] 17 core [0084] 18 seal [0085] 19 treated area