WO2007051677A1 - Spark plug electrode and method for producing a spark plug electrode - Google Patents

Abstract

The invention proposes a spark plug electrode (7, 8) composed of a first region (10, 10') and a second region (11, 11') which is fixedly connected thereto, and a method for producing a spark plug electrode (7, 8). According to the invention, the connection between the first region (10, 10') and the second region (11, 11') is produced by applying a pressure force which causes plastic deformations in contact faces, which face towards one another, of the first region (10, 10') and of the second region (11, 11'). The first region (10, 10') is produced from an Ni-based alloy and the second region (11, 11') is produced from pure Pt, Rh, Ir, Au or from an alloy having at least one of said elements. The pressure force is applied in such a way that the first region (10, 10') and the second region (11, 11') have, in the contact region, surface enlargements which are such as can be connected by means of cold welding.

Description

A spark plug electrode and method of making a spark plug electrode

State of the art

The invention relates to a spark plug electrode and a method for producing a spark plug electrode according to the closer defined in the preamble of patent claim 1 and of claim 12.

WO 2004/084367 A1 discloses a spark plug and a method for producing the spark plug for an internal combustion engine, which has at least two spark plug electrodes. The spark plug electrodes comprise a first region consisting of a substrate material and a surface region or a second region which is more resistant than the substrate material. The second region of the spark plug electrodes is connected to the first region via an intermediate region, wherein the intermediate region and the surface region are joined together by explosion welding. By explosion welding, the intermediate region is bonded to the surface region without creating a fusion zone in the joint region. In this way, a mixing of the surface area with the substrate, which is accompanied by a depletion of the noble metal content of the surface layer in the bond area with the substrate material, is avoided in a simple manner. With this approach, spark plug electrodes with surface layers with layer thicknesses of 0.05 mm to 2 mm can be produced. The surface area of the spark plug electrodes is first firmly bonded by placing a thin film on a refractory steel or a superalloy such as a Ni-base superalloy, followed by explosion welding to the intermediate portion without the melt zone. Subsequently, the intermediate region is welded to the first region by a conventional welding process.

The disadvantage here, however, that explosion welding is generally characterized by a high expenditure on equipment and therefore the manufacturing costs of a spark plug produced by this method are high. Furthermore, the surface layers of platinum or the like to be produced on a basic electrode body with layer thicknesses of 0.05 mm to 2 mm are exposed to high stresses due to the acceleration generated during explosion welding. Due to the small layer thickness and the resulting low strength, the valuable structure of the surface layer is disadvantageously stressed during the joining process with the intermediate region in such a way that the surface layer may exhibit cracks or other surface defects after the explosion welding and the spark plug electrode in the area does not have the same for the desired life of a spark plug has required durability.

In addition, spark plug electrodes of internal combustion engines used in automobiles are highly stressed due to high temperature fluctuations between standstill and the operation of the internal combustion engine. These temperature stresses, which are characterized especially by the startup of an internal combustion engine by steep temperature gradients, are also in connection with corrosive attacks such adverse operating conditions that connections between layers of a Spark plug electrode, which consist of Ni-base alloys and, for example, made of platinum and are joined together by explosion welding, break easily. This results from the fact that the aforementioned compounds have a low thermal shock resistance, so that the durability of a spark plug may be reduced to undesirable levels.

The present invention is therefore based on the object to provide a spark plug electrode with a long service life, which can be produced in a simple and cost-effective manner.

Advantages of the invention

According to the invention this object is achieved with a spark plug electrode according to the features of claim 1 and a method for producing a spark plug electrode with the features of claim 12.

The spark plug electrode according to the invention consists of a first region and a second region fixedly connected thereto, wherein the connection between the first region and the second region by applying a plastic deformation m the compressive force emanating facing contact surfaces of the first region and the second region is made. The first region is made of a Ni-base alloy and the second region is made of pure Pt, Rh, Ir, Au or an alloy comprising at least one of these elements.

According to the invention, the first region and the second region are connected to one another by cold welding, so that the first region and the second region have a firmly interconnected one another - A -

Form composite material. During the joining process of the two regions, a compressive force or joining force is applied to them such that both the first region and the second region undergo surface enlargements in the intended connection region. Due to the Oberflächenvergrßßerungen respectively arranged under the oxidized or contaminated by the contact with the environment surface areas Mateπalbereiche the first region and the second region are brought into contact, which form in the region of the grain peaks merging regions. These give the connection between the two regions of the spark plug electrode the desired and required for a long service life of the spark plug strength.

However, the formation of a substantially over the entire contact region of the two areas extending and present with a certain layer thickness alloying zone, as in a welded joint, the depletion of the resistant and made of precious metal second portion of the spark plug electrode and an increased Mateπalemsatz of noble metal to Receiving a good spark resistance of a spark plug electrode has resulted in a simple and inexpensive way avoided.

Due to the fixedly connected by cold welding areas of the spark plug electrode according to the invention is in a simple way, the possibility of the second area with

Layer thicknesses of preferably between 0.1 mm to 0.5 mm without affecting the Mateπalgefüges as in conventional fusion welding or as in the explosion welding on the first area apply. Thus, a spark plug according to the invention has at least the service life of conventionally designed spark plugs, which are produced with a significantly higher noble metal rate, at considerably lower production costs. In the method according to the invention for producing a spark plug electrode having the features of the preamble of claim 12, the compressive force is applied such that the first region and the second region have such surface enlargements in the contact region that they are joined by cold welding.

In an advantageous variant of the method according to the invention, the second region is placed on a newly executed first region and applied the required for the connection of the two areas pressing force by mateπalschonendes and process technology easy to handle rolling or roll cladding. After roll-plating, the spark plug electrodes are made by singulation, such as stamping or the like, from the material bond formed by cold welding.

In a further alternative variant of the method according to the invention, the first region or the second region is substantially cylindrical and is introduced into the at least approximately hollow-cylindrical second region or first region. Subsequently, the preferably coaxially arranged regions are pulled in the joined state by a pull-tab or a die. In this case, the pressure force m required for connecting the regions is introduced into the two regions, wherein the individual spark plug electrodes are produced after being drawn by cutting to length from the plastically deformed and formed by cold welding Drahtfόrmigen Mateπalverbund.

Both the roll-plating process and the drawing process represent process-technically easy-to-handle production processes for spark-plug electrodes, by means of which noble-metal layers, which are generally characterized by high material costs, are cost-effective. can be applied to cheaper Ni-base alloys produced electrode Grundkόr- pern with low-cost layer thicknesses without reducing the life of a spark plug compared to conventionally designed spark plugs.

In particular, the pressure force to be applied during the joining process of the first region and of the second region of a spark plug electrode during roll-plating or drawing can be conducted into the two regions to be joined together, preferably with layer thicknesses of between 0.1 mm to 0.5 mm The precious metal layer to be produced is not damaged or destroyed during the joining process and is present after the bonding process with a material structure required for a long service life of a spark plug.

Further advantages and advantageous embodiments of the article according to the invention are the description, the drawings and the claims removed.

drawing

In the drawing, three embodiments of the present invention carried out spark plug electrodes are shown schematically simplified, the m will be explained in more detail in the following description. Show it

Figure 1 is a schematic representation of a spark plug m a

Partial sectional view; FIG. 2 shows a substrate and a noble metal layer to be joined thereto prior to roll-plating;

FIG. 3 shows the substrate and the noble metal layer after roll-plating; FIG. 4 shows a representation of the substrate and the noble metal layer corresponding to FIG. 3 after a punching process;

FIG. 5 shows a semifinished product produced by roll-plating, from which ground electrodes designed as roof electrodes can be produced according to the invention;

FIG. 6 shows a semifinished product produced by roll-plating, from which laterally set ground electrodes according to the invention can be produced;

FIG. 7 shows a cylindrical middle electrode designed according to the invention, which is formed from a core made of a Ni-base alloy and a hollow metal-noble noble metal shell; and

8 shows a representation corresponding to FIG. 7 of a center electrode designed according to the invention, which is produced from a cylindrical noble metal core and a jacket surrounding the noble metal core and produced from a Ni-base alloy.

Description of the embodiments

Referring to Figure 1 is a partial sectional view of an arranged in a cylinder head of an internal combustion engine spark plug 1 is shown, which can be screwed with a formed on a housing 2 outer walls 3 m an internal thread of the cylinder head.

The spark plug 1 formed in a manner known per se consists in the present case of metal, ceramic and glass. These materials have different properties that are used by material-appropriate design of the spark plug 1. The most important constituents of the spark plug 1 are a connecting bolt 5, an insulator 6, the housing 2, a center electrode 7 and a mass Electrode 8, wherein an arranged in the insulator 6 and electrically conductive glass melt 9, the center electrode 7 connects to the terminal bolt 5.

The center electrode 7 and the ground electrode 8 are during the

Operation of the internal combustion engine exposed to high wear, which is caused due to erosion and corrosion. Both factors can not be treated separately in terms of their effect on wear. The wear causes an increase in the ignition voltage. Furthermore, a good Wärmeableitvermόgen is required by the electrodes.

The requirements may require different electrode shapes and electrode materials depending on the operating conditions and application.

Basically, pure metals conduct heat better than metal alloys. On the other hand, pure metals such as nickel react more sensitively to chemical attacks of combustion gases and solid combustion residues than alloys.

For this reason, known from practice electrodes of spark plugs, for example made of nickel, the u. a. Chromium, manganese and silicon is alloyed. The metals to be added have special tasks to fulfill. For example, manganese and silicon additives increase the chemical resistance especially against the very aggressive sulfur dioxide. In addition, nickel-based alloys with additions of silicon, aluminum and yttrium improve the scale and oxidation resistance.

In addition, platinum or platinum-based alloys are also used for the production of electrodes, since these have a very good corrosion resistance. have resistance to oxidation and oxidation as well as a high erosion resistance.

FIG. 2 to FIG. 4 schematically illustrate a manufacturing process for spark plug electrodes designed as center electrodes by means of roll plating. FIG. 2 shows a first region 10, which in the present case is made of a Ni-base alloy and represents a planar or plate-like body.

In addition, a further planar, plate-like second region 11 is shown, which is placed on the first region 10 with a predefined layer thickness. The second region 11 is in the present case made of pure Pt and, in further advantageous embodiments, besides pure Pt, it can also be produced from pure Rh, Ir, Au or from an alloy comprising at least one of these elements.

After placing the second area 11 on the first area

10, the two areas 10, 11 supplied to a device not shown in detail and applied by means of roll plating with a plastic deformation in the facing contact surfaces of the first region 10 and the second region 11 causing compressive force, so that the first region 10 and the second Area 11 after the roll cladding are connected by cold welding.

In this case, the second region 11 in the present case has, after the roll cladding, a dependence of the layer thickness of the second region 11 before the roll cladding and the compressive force applied during the roll cladding and also the dependence of the second region

11 selected material a layer thickness dll of 0.1 mm to 0.5 mm, preferably of 0.2 mm, wherein the layer thickness of the regions 10 and 11 before the roll cladding and also the rolling process para- - IO ¬

meter are to be set depending on the respective application.

In the present case, the first region 10 consists of a Ni-Cr-Fe alloy with 15% by weight Cr, 6% by weight Fe and the remainder Ni and also impurities present in the alloy. In addition, the first region 10 may also be made of a Ni-Cr-Fe alloy containing 25% by weight of Cr, 18% by weight of Fe and balance Ni, and impurities. Alternatively, the first region 10, which constitutes the main electrode body of the spark plug center electrode 7, in another embodiment of a Ni-Al-Si alloy with up to 1 wt .-% rare earths, preferably with 0.05 wt .-% Y , or be made of a Ni-Cr-Mn-Si alloy.

After roller cladding, a plurality of spark plug central electrodes 7 are produced by punching out of the material formed by cold welding in the manner shown in more detail in FIG. 4. The stamped out spark plug center electrodes are then welded by means of laser or resistance welding on a further carrier 13, which consists for example of a conventional central electrode area with copper core or NiAllSilY or is made of another alloy with good thermal conductivity.

The use of roll cladding as the joining technique achieves that spark plug electrodes in the radio range can also be produced with very thin noble metal layers in the thickness range of less than 200 .mu.m, in comparison with welding methods or explosion welding are each secured with higher adhesive forces on the electrode body or on a Trägermateπal. Thus, spark plugs are inexpensive and can be produced with a long service life. Furthermore, the roll cladding makes it possible to provide two different carrier materials for the second region 11. Thus, the second region 11 of a spark plug center electrode can be rolled on an alloy which is very resistant to high-temperature corrosion. This in turn can be welded on with an alloy with good thermal conductivity. This means that in the case of a spark plug electrode produced at least in some areas by means of roll plating, it is possible to realize combinations of material properties which can not be achieved through the use of alloying techniques established for the production of spark plug electrodes.

In addition to the above-described production of spark plug center electrodes, it is of course also possible to produce spark plug ground electrodes 8 according to the invention by roll cladding and cold welding occurring between the first region 10 'and the second region 11'.

In this case, a semifinished product 12 is shown in FIG. 5, from which spark plug grounding electrodes for so-called roof electrode spark plugs can be produced. FIG. 6 shows a semifinished product 12, from which spark plug ground electrodes can be produced, which are welded to the housing 2 and are employed laterally.

In this case, cuboidal regions 12 having a length 1 of 15 mm, a height h of 1.5 mm and a width b of 2.5 mm are separated from the semi-finished product 12 shown in FIG. 5 by a suitable separation method, each having an end region with the rolled-up and by means of cold welding to the first region 10 'connected second region 11' are designed with a layer thickness dll of 0.2 mm. In the case of the semifinished product 12 shown in FIG. 6, the second region 11 'is applied to an end surface of the first region 10' by roller cladding and joined thereto by cold welding, the spark plug ground electrodes being separated by a suitable separation method with predefined dimensions.

In FIG. 7 and FIG. 8, two further exemplary embodiments of spark plug center electrodes 7 designed according to the invention and designed in a cylindrical shape are shown. In this case, the embodiment according to FIG. 7 shows a cylindrically shaped first region 10 and a hollow-cylindrical second region 11 surrounding the first region 10, the first region 10 being made of a Ni-base alloy and the second region 11 being made of one of the abovementioned noble metals or a previously described noble metal alloy can be produced.

The spark plug center electrode 7 according to FIG. 8 is predominantly made up of a cylindrical second region 11 and a first region 10 which is formed as a wood cylinder and surrounds the second region 11, the second region 11 being made of pure platinum and the first region 10 being made of a Ni-base alloy. In this case, both the first and also the second region in this embodiment of a spark plug center electrode 7 according to the invention can each be made of a different material listed above.

To produce the spark plug center electrode 7 according to FIG. 7 or according to FIG. 8, a cylindrical wire and a hollow-cylindrical or tubular element are used as precursors. The cylindrical wire, which represents either the later first region 10 or the later second region 11 of a spark plug center electrode 7, has a function of the particular application before plastic deformation Diameter from 1 mm to 4.5 mm. The wire is inserted into a hollow-cylindrical jacket, which after the joining process represents the second region 11 or the first region 10 of a spark plug center electrode 7, wherein the hollow-cylindrical jacket has an outer diameter of 4.5 mm to 6 mm before cold welding to the wire and an inner diameter of 2 mm to 5 mm.

Subsequently, the coaxially preferably arranged to the jacket wire and the jacket are pulled in a telescoped state by a pull tab, not shown, and plastically deformed, while the required to connect the areas 10 and 11 compressive force is applied. After drawing, the spark plug center electrodes 7 produced in FIG. 7 and FIG. 8 are produced by cutting to length from the formed composite material.

After the cold welding, the hollow region 11 of the hollow-cylindrical section 11 according to FIG. 7 has a layer thickness d 1 of 0.1 mm to 0.16 mm, preferably of 0.15 mm. The outer diameter d_a of the spark plug center electrode 7 according to FIG. 8 is 0.78 mm to 0.84 mm, preferably 0.81 mm, while the inner diameter d_i of the second region 11 is 0.5 mm to 0.56 mm, preferably 0.53 mm, having.

The hollow-cylindrical first region 10 of the spark plug center electrode 7 according to FIG. 8 has, after cold welding, a layer thickness d10 of 0.08 mm to 0.12 mm, preferably 0.1 mm, while the outer diameter da of the first region 10 after cold shearing 0 , 77 mm to 0.83 m, preferably 0.8 mm, and the inner diameter is 0.58 mm to 0.62 mm, preferably 0, 6 mm. Before the cold-welding or before the drawing process, the hollow-cylindrical first region 10 of the spark plug central electrode 7 according to FIG. 8 has an outer diameter of 4.5 mm to 6 mm and an inner diameter of 2 mm to 5 mm, while the cylindrically executed second region 11 has an outer diameter of 1 mm to 4.5 mm.

After cutting to length, the spark plug center electrodes 7 according to FIG. 7 and FIG. 8 are designed with flat surfaces and with sharp corners on which electrical voltage peaks occur during operation of a spark plug, which in turn lead to ignition of the spark.

Thus, in the case of the spark plug center electrode 7 according to FIG. 7, a so-called leveling off of the edges of a spark plug electrode is counteracted by the noble metal jacket or the second zone 11 executed in hollow-cylindrical fashion. The first region 10 enveloped by the second region 11, which consists of a less spark-resistant Ni base alloy, will have a greater wear than the noble metal shell during operation of the spark plug, so that a concave formation forms in the interior of such a spark plug center electrode 7.

In the case of the spark plug center electrode 7 according to FIG. 8, as the spark plug expands, due to the voltage peaks in the edge region, a rounding of the outer edges will occur and a noble metal tip will form in the middle region, because the edges of the first region 10 will be smaller than the noble metal core or the second region 11 wear faster in the radio range. The formation of the noble metal tip leads to the occurrence of a Spannungsüberhόhung in the central region of the spark plug center electrode 7, whereby advantageously the Zündspannungsbedarf is lowered. In order to improve the durability of the spark plug electrodes 7 and 8, which are produced by means of roll cladding or drawing by a die, it may be envisaged that the material bond produced by cold welding is annealed. This results from the fact that the areas 10 and 11 bonded together by cold splicing are made of materials having different thermal expansion coefficients. The different thermal expansion coef fi cients and those caused by the roll plating or the

Pulling in the two areas generated internal stresses are amplified by the occurring during operation of a spark plug temperature change such that the loads in the connecting region between the two areas 7 and 8 are very large and may lead to a breakage of the cold-welded areas.

The diffusion annealing process achieves a better mixing of the two materials and a reduction in the mechanical stress gradient in the connection region, with the result that the service life of a spark plug can be further improved in a simple manner. In this case, the annealing process can be provided in each case before or after the separation of the spark plug electrodes 7, 8.

Claims

claims A spark plug electrode (7, 8) comprising a first region (10, 10 ') and a second region (11, 11') fixedly connected thereto, wherein the connection between the first region (10, 10 ') and the second region (11, 11 ') by applying a plastic see deformations in the mutually facing contact surfaces of the first region (10, 10') and the second region (11, 11 ') causing compressive force is produced, and wherein the first region (10, 10 ') consists of a Ni-base alloy and the second region (11, 11') consists of pure Pt, Rh, Ir, Au or of an alloy comprising at least one of these elements, characterized in that the first region (10, 10 ' ) and the second region (11, 11 ') are connected by cold welding. 2. spark plug electrode according to claim 1, characterized in that the second region (11, 11 ') has a layer thickness (dll) of 0.1 mm to 0.5 mm. 3. Spark plug electrode according to claim 1 or 2, characterized in that the first region (10, 10 ') made of a Ni-Cr-Fe alloy with 15 wt .-% Cr, 6 wt .-% Fe and balance Ni , 4. Spark plug electrode according to claim 1 or 2, characterized in that the first region (10, 10 ') made of a Ni-Cr-Fe alloy with 25 wt .-% Cr, 18 wt .-% Fe and balance Ni , 5. spark plug electrode according to claim 1 or 2, characterized in that the first region (10, 10 ') of a Ni-Al-Si alloy with up to 1 wt .-% rare earths, preferably 0.05 wt .-% Y, is made. 6. Spark plug electrode according to claim 1 or 2, characterized in that the first region (10, 10 ') is made of a Ni-Cr-Mn-Si alloy. A spark plug electrode according to any one of claims 1 to 6, characterized in that the first region (10, 10 ') is welded to a third region (2; 13), the nickel base alloy from which the first region (10) is made , a high temperature resistant Ni base alloy, and the third region (2; 13) is made of a Ni base alloy having good thermal conductivity, preferably NiAllSilY or Cu. 8. spark plug electrode according to one of claims 1 to 7, characterized in that the first region (10) or the second region (H ') is substantially cylindrical and m the at least approximately hollow-cylindrical executed second region (H') or first area (10 ') is arranged. 9. spark plug electrode according to claim 8, characterized in that the second region (H ') has a layer thickness of 0.1 to 0.16 mm, preferably 0.15 mm. 10. spark plug electrode according to one of claims 1 to 7, characterized in that the first region (10) and the second region (11) are made flat. 11. spark plug electrode according to claim 10, characterized in that the second region (11) has a layer thickness (dll) of 0.18 mm to 0.22 mm, preferably of 0.2 mm. 12. A method for producing a spark plug electrode (8, 9) comprising a first region (10, 10 ') and a second region (11, 11') fixedly connected thereto, wherein the connection between the first region (10, 10 ') and the second region (11, 11 ') is produced by applying a plastic deformation in the emanating contact surfaces of the first region (10, 10') and the second region (11, 11 '), and wherein the first A region (10, 10 ') of a Ni-base alloy and the second region (11, 11') consists of pure Pt, Ir, Au or of an alloy comprising at least one of these elements, characterized in that the pressure force is applied in such a way that the first region (10, 10 ') and the second region (11, 11') have such surface enlargements in the contact region that they are joined by cold welding. 13. The method according to claim 12, characterized in that on a newly executed first region (10, 10 ') of the second region (11, 11') placed and for the connection of the two areas (10, 11, 10 ', 11' ) is applied by roll-plating, wherein the spark plug electrode (7, 8) after the roll-plating is made by punching from the Mateπalverbund formed by cold welding. 14. The method according to claim 12 or 13, characterized in that the second region (11, 11 ') after the cold welding a Layer thickness (dll) of 0.1 mm to 0.5 mm, preferably of 0.2 mm. 15. The method according to claim 12, characterized in that the first region (10) or the second region (H ') is substantially cylindrical in shape and in the at least approximately hollow cylindrical running second region (11') or first region (10 ') is introduced, wherein the preferably coaxially arranged regions (10', 11 'm m joined state] are passed through a pulling diaphragm while the pressure for the connection of the areas (10', 11 ') required compressive force is applied, and wherein the spark plug electrode (7) is produced after drawing by cutting from the formed Mateπalverbund. 16. The method according to claim 15, characterized in that the hollow cylindrical executed second region (H ') after the cold welding a layer thickness (dll) of 0.1 mm to 0.16 mm, preferably of 0.15 mm. 17. The method according to claim 15 or 16, characterized in that the hollow cylindrical executed second region (H ') after cold welding an outer diameter (d_a) of 0.78 mm to 0.84 mm, preferably of 0.81 mm, and a inner diameter (d_i) of 0.5 mm to 0.56 mm, preferably of 0.53 mm. 18. The method according to claim 15, characterized in that the hollow-cylindrical first region (10 ') after cold welding has a layer thickness (d10) of 0.08 mm to 0.12 mm, preferably of 0.1 mm. 19. The method according to claim 18, characterized in that the hollow cylindrical first region (10 ') after the cold welding an outer diameter (da) of 0.77 mm to 0.83 mm, preferably of 0.8 mm, and a Inner diameter (d_i) of 0.58 mm to 0.62 mm, preferably from 0.60 mm. 20. The method according to any one of claims 15 to 19, characterized in that the hollow cylindrical first region (10 ') or second region (H') before cold welding an outer diameter (d_a) of 4.5 mm to 6 mm and an inner diameter (di) from 2 mm to 5 mm, wherein the cylindrically shaped second region (H ') or first region (10') has an outer diameter (da) of 1 mm to 4.5 mm. 21. The method according to any one of claims 12 to 20, characterized in that the first region (10, 10 ') and the second region (11, 11') after the cold welding are subjected to a diffusion annealing process.