Spark plug with electrode with a deep welding seam, spark plug with the spark plug electrode, and production method for the spark plug electrode

Abstract

An electrode for a spark plug, having an electrode base body and a cylindrical wear part, the wear part having a longitudinal axis that extends from an end face of the wear part, facing the electrode base body, to an end face situated opposite this end face, and the wear part having a first region and a second region, the wear part not being fused in the first region and the wear part being fused in the second region.

Claims

1. An electrode for a spark plug, comprising: an electrode base body; and a cylindrical wear part, the wear part having a longitudinal axis that extends from a first end face of the wear part, facing the electrode base body, to a second end face situated opposite the first end face, and the wear part having at least one first region and at least one second region, the wear part not being fused in the at least one first region and the wear part being fused in the at least one second region, at least a portion of the at least one second region being free from contact with the electrode base body at a side of the wear part extending from the first end face toward the second end face, and, in a sectional plane of the longitudinal axis, a first transition between the at least one first region and the at least one second region on a jacket surface of the wear part being designated as point A, and in the sectional plane, a second transition between the at least one first region and the at least one second region, situated closest to the longitudinal axis in the sectional plane, being designated as point C; wherein the distance AC has an angle ? to the longitudinal axis, the angle ? extending from the longitudinal axis back toward the first end face, and ? is greater than or equal to 45? and less than 90?; wherein the cylindrical wear part has a height (H) and a radius (R), the height (H) in the first region being measured along the longitudinal axis, and the radius (R), in the case of polygonal end surfaces, being a perimeter radius or, in the case of round end surfaces, being a circular radius, and R?H.

2. The electrode as recited in claim 1, wherein R?2H.

3. The electrode as recited in claim 1, wherein a shortest distance from the jacket surface of the wear part to point C is at least one of: (i) not smaller than 50% of the radius (R), and (ii) not larger than 100% of the radius (R).

4. The electrode as recited in claim 1, wherein the radius (R) is at least one of: (i) not smaller than 0.75 mm, and (ii) not larger than 2 mm.

5. The electrode as recited in claim 1, wherein the height (H) is at least one of: (i) not smaller than 0.4 mm, and (ii) not larger than 1 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example of a spark plug.

(2) FIG. 2 shows an example of an electrode according to the present invention.

(3) FIG. 3 shows an example of the production of a center electrode according to the present invention.

(4) FIG. 4 shows an example of the production of a ground electrode according to the present invention.

(5) FIG. 5 shows an example of the time curve of the weld beam power.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) FIG. 1 shows a schematic representation of a spark plug 1. Spark plug 1 has a metallic housing 2 having a threading 3 for mounting spark plug 1 in an engine block. An insulator 4 is situated inside housing 2. A center electrode 5 and a connecting bolt 7 are situated inside insulator 4, and are electrically connected via a resistance element (not shown). Center electrode 5 typically protrudes from insulator 4 at the end of spark plug 1 at the side of the combustion chamber.

(7) At the combustion-chamber end of housing 2, there is situated a ground electrode 6. This electrode forms an ignition gap with center electrode 5. Ground electrode 6 can be fashioned as a front electrode, a side electrode, or a bow electrode. The bow electrode has two limbs, each welded to housing 2 with their respective leg 16. The limbs have an angle of from 30? to 180? to one another. The bow electrode can be made in one piece or in a multi-part construction, and in the case of a multi-part construction the individual parts are connected to one another by a material bond, such as welding.

(8) FIG. 2 shows a section of an electrode 5, 6 according to the present invention. Electrode 5, 6 has an electrode base body 8 and a wear part 10, wear part 10 being situated on electrode base body 8 in such a way that it forms the ignition gap together with oppositely situated electrode 6, 5, or with a second wear part situated on oppositely situated electrode 6, 5.

(9) Electrode base body 8 is made of a nickel alloy that is alloyed to a low degree or to a high degree. For example, the nickel alloy is alloyed to a low degree with yttrium or is alloyed to a high degree with chromium. The chromium portion in the nickel alloy is for example at least 20 wt %, and is preferably even at least 25 wt %.

(10) Wear part 10 is cylindrical, having round, elliptical, or polygonal end faces, and has a cylinder axis, or longitudinal axis, x-x. Longitudinal axis x-x extends from end surface 13 of the wear part up to oppositely situated side 14, facing electrode base body 8, of the wear part. Height H of wear part 10 is measured along longitudinal axis x-x. Radius R of wear part 10 corresponds to the maximum distance of jacket surface 15 of wear part 10 from longitudinal axis x-x, the distance being measured perpendicular to longitudinal axis x-x, for example at an end surface 13 of the wear part. In this exemplary embodiment, wear part 10 has a round shape; i.e., radius R of wear part 10 is greater than or equal to height H of wear part 10. For example, it can be provided that radius R of wear part 10 is greater than or equal to 1.5 times the height H of wear part 10, or even that radius R of wear part 10 is greater than or equal to two times the height H of wear part 10. Radius R of wear part 10 is not smaller than 0.75 mm and/or is not larger than 2 mm. Preferably, radius R of wear part 10 is not smaller than 1 mm and/or is not larger than 1.5 mm. Height H of wear part 10 is not smaller than 0.4 mm and/or is not larger than 1 mm. Preferably, height H of wear part 10 is not smaller than 0.6 mm and/or is not larger than 0.8 mm. In this exemplary embodiment, for example radius R of wear part 10 is 1.2 mm and height H of wear part 10 is 0.6 mm.

(11) Wear part 10 is made of a noble metal or of a noble metal alloy, such as iridium, platinum, rhodium, ruthenium, and/or rhenium, or of alloys with at least one of these noble metals.

(12) In this exemplary embodiment, side 14 of wear part 10, facing electrode base body 8, stands in direct contact with electrode base body 8. Wear part 10 is connected to electrode base body 8 with a material bond by welding, and in this way regions 12, 18 are formed in wear body 10 and in electrode base body 8 that are fused during the bonding process.

(13) In addition, there is another region in the contact region between electrode base body 8 and wear part 10 in which the material of electrode base body 8 and the material of wear part 10 become alloyed with one another. This alloy region can be smaller than or equal to the sum of the fused regions 18, 12 in electrode base body 8 and in wear part 10. While the boundaries between the alloy region and the fused regions 18, 12 can be fluid, as a rule it is possible to clearly recognize, in section, the boundaries between fused region 12 and non-fused region 11 in wear part 10 or in electrode base body 8. As shown in FIG. 2, wear part 10 can be subdivided into first regions 11 that were not fused during the bonding process and second regions 12 that were fused during the bonding process.

(14) In section, the transitions between non-fused regions 11 of wear part 10 and fused regions 12 of wear part 10 can be seen clearly. The transition on jacket surface 15 between first region 11 of wear part 10 and second region 12 of wear part 10 is designated point A. The transition between first region 11 of wear part 10 and second region 12 of wear part 10, situated closest to longitudinal axis x-x, is designated point C. The distance AC has an angle ? to longitudinal axis x-x, or to a line x-x that is parallel to longitudinal axis x-x and that goes through point C. In order to determine the distance AC, typically points A and C are regarded in the same second region 12 of wear part 10. Angle ? is greater than or equal to 45?. Preferably, angle ? is even greater than or equal to 60?.

(15) Preferably, end face 13 of wear part 10 does not have a second region 12 of wear part 10; that is, end face 13 of wear part 10 is completely non-fused, and belongs to first region 11 of wear part 10. Ideally, a distance from point A to end face 13 of wear part 10 is not smaller than 50% of height H of wear part 10. In addition, the distance is not greater than 90% of height H of wear part 10, so that a sufficient quantity of material of wear part 10 has been fused for a solid material bond.

(16) A shortest distance from jacket surface 15 of wear part 10 to point C is not smaller than 50% of radius R of wear part 10, or end surface 13, and/or is not larger than 100% of radius R of wear part 10. This shortest stretch corresponds to a depth t of second region 12 of wear part 10 along a direction radial to longitudinal axis x-x. Due to the fact that it is provided that second region 12 of wear part 10 has a depth t of at least half the radius R of wear part 10, it is ensured that enough material of wear part 10 has been fused to form a solid material bond of wear part 10 with electrode base body 8.

(17) Table 1 shows, for the examples of three cases, R=H, R=1.5 H, and R=2H, the resulting angle ? for the threshold values of the boundary conditions. The boundary conditions result from the minimum and maximum height b and from the minimum and maximum depth t of second region 12 in the wear part. Height b of second region 12 of wear part 10 is measured along jacket surface 15. Height b of second region 12 of wear part 10 should correspond to at least 10% and to a maximum of 50% of height H of wear part 10. Depth t of second region 12 of wear part 10 corresponds to the distance of point C from jacket surface 15 in a plane perpendicular to longitudinal axis x-x. Depth t of second region 12 of wear part 10 should be at least 50% and at most 100% of radius R of wear part 10. For the cases stated above, there thus result in each case 4 possible combinations, given the boundary conditions for each of which there results an angle ?.

(18) TABLE-US-00001 TABLE 1 R/H b t ? [?] 1 10% H 50% R 78.5 1 10% H 100% R 84 1 50% H 50% R 45 1 50% H 100% R 63 1.5 10% H 50% R 82.5 1.5 10% H 100% R 86 1.5 50% H 50% R 56.5 1.5 50% H 100% R 71.5 2 10% H 50% R 64 2 10% H 100% R 87 2 50% H 50% R 63 2 50% H 100% R 76

(19) In the examples stated above, for the angle ? there result values in the range of from 45? to 84?. Here, small angles for ? (45?-62?) result in particular when second regions 12 of wear part 10 correspond to a large height b, such as 50% of height H of wear part 10, and at the same time have a small depth t, i.e. only 50% of radius R of wear part 10. For the cases having small height b (10% H) and small depth t (50% R) of second region 12 of wear part 10, or having large height b (50% H) and large depth t (100% R) of second region 12 of wear part 10, the values for angle ? are in the range of from 63?-83?. For the boundary cases having small height b and large depth t of second region 12 of wear part 10, corresponding to a narrow and deep bond seam, the values for angle ? are in the range of from 84?-87?. From this it can be inferred that, in a particularly preferred specific embodiment of the present invention, angle ? is preferably greater than or equal to 80?.

(20) The material bonding of wear part 10 with electrode base body 8 preferably takes place via a welding method such as laser beam welding or electrode beam welding. In the case of laser beam welding, a pulsed laser beam or a continuous laser beam, i.e. continuous-wave (CW) laser, can be used. In the production of the laser radiation, solid-state lasers, disk lasers, diode lasers, and/or fiber lasers can be used.

(21) Weld beam 20 is directed onto the contact region between wear part 10 and electrode base body 8 at an angle ? relative to longitudinal axis x-x, as is schematically shown in FIG. 2. In order to achieve a depth t that is as large as possible, and at the same time a height b that is as small as possible, of second region 12 in wear part 10, weld beam 20 is radiated into the contact region at an angle ? not smaller than 75?, preferably not smaller than 81?.

(22) The focus point for weld beam 20 is for example inside the contact region, i.e., preferably on the stretch between point C and jacket surface 15. Advantageously, weld beam 20 has at the focus point a diameter of not greater than 50 ?m. In this way, a weld seam, or bond seam, is produced that is as deep as possible and at the same time not too high. The shape of the weld seam correlates with the geometry of fused regions 12, 18 in wear part 10 and in electrode base body 8.

(23) Generally, when the ratio of radius R to height H of wear part 10 increases, the angle of incidence ? of weld beam 20 must also increase in order to produce an adequate depth t of second region 12 of wear part 10 and thus also to produce a reliable solid connection between electrode base body 8 and wear part 10, without requiring fusing that is excessive in height on jacket surface 15.

(24) Preferably, welding takes place at least along a part of the circumference of wear part 10. For example, it can be provided that a continuous weld seam is produced along the entire circumference of wear part 10. Alternatively, the weld seam can also be divided into a plurality of subsegments, the subsegments on jacket surface 15 of wear part 10 being at a distance from one another and/or overlapping within the contact region and/or within wear body 10 and/or within electrode base body 8. Preferably, the non-fused regions of 11 in wear part 10 are contiguous, so that preferably there is only one first region 11 in wear part 10.

(25) FIG. 3 shows two possible realizations for producing an electrode according to the present invention as center electrode 5. In the first realization, FIG. 3a, weld beam source 21 is stationary and electrode 5 with electrode base body 8 and wear part 10 rotates about an axis, in this example longitudinal axis x-x of wear part 10. In the second realization, FIG. 3b, weld beam source 21 rotates about electrode 5.

(26) FIG. 4 shows two possible realizations for producing an electrode according to the present invention as ground electrode 6. In the first realization, FIG. 4a, weld beam source 21 is stationary and electrode 6 with electrode base body 8 and wear part 10 rotates about an axis, in this example longitudinal axis x-x of wear part 10. In the second realization, FIG. 4b, weld beam source 21 rotates about electrode 6.

(27) In addition, it can be provided that the power of weld beam 21 is varied during the welding of ground electrode 6. In this way, power losses that occur during welding, when for example during the rotation of electric 6 or of weld source 21 a leg 16 of a ground electrode 6 moves into weld beam 20 and thus blocks a part of weld beam 20, can be compensated.

(28) FIG. 5 shows an example of a time curve T of power P of weld beam 20 during the welding of a bow ground electrode 6. In a first operating phase, power P is held at a constant value. In this phase, the regions 12, 18 that are to be fused in wear part 10 and in electrode base body 8 are heated, and in this way the melt baths required for the deep welding are produced in electrode base body 8 and in wear part 10. In the second operating phase, power P is reduced to 80% to 90% of the initial power. This reduced power P is adequate to ensure that the melt baths, together with weld beam 20, move along the circumference of wear part 10 according to the rotational speed of electrode 6 or of weld beam source 21, in this way producing the bond seam. In this exemplary embodiment, the second operating phase is interrupted twice by a third operating phase in which power P is again increased to the initial value in order to compensate the shadowing effects produced by legs 16 of ground electrode 6, situated at times in weld beam 20, for power level P deposited into electrode 6. After at least one full rotation, in a fourth operating phase power P is reduced to 0% and the welding process is terminated.

(29) Advantageously, the initial position of the welding and/or the direction of rotation during the welding is selected such that the components of spark plug 1 that cause the shadowing effects move into weld beam 20 as late as possible within the course of a rotation.