SPARK PLUGS HAVING A CENTER ELECTRODE

Abstract

A spark plug having a housing, an insulator situated in the housing, a center electrode situated in the insulator and a ground electrode situated on the housing, the ground electrode and the center electrode being situated toward each other in such a way that the ground electrode and the center electrode form a spark gap, and the center electrode rest with a center electrode head on a seat developed on an inner side of the insulator, and the center electrode having an electrode base body and a core situated in the electrode base body, the core being made from a material that has a higher heat conductivity than the material of the electrode base body, the electrode base body having a diameter that is not greater than 1.7 mm.

Claims

1-10. (canceled)

11. A spark plug, comprising: a housing; an insulator situated in the housing; a center electrode situated in the insulator; and a ground electrode situated on the housing; wherein the ground electrode and the center electrode are situated with respect to each other in such a way that the ground electrode and the center electrode form a spark gap, the center electrode rests with an electrode head on a seat developed on an inner side of insulator, and the center electrode has an electrode base body and a core situated in the electrode base body, the core being made of a material that has a higher heat conductivity than a material of the electrode base body, and wherein the electrode base body has a diameter that is not greater than 1.7 mm.

12. The spark plug as recited in claim 11, wherein the insulator has in the area of the seat developed on its inner side a wall thickness of not smaller than 2 mm.

13. The spark plug as recited in claim 11, wherein the center electrode has at least one first area, in which the electrode base body and the core respectively have a constant diameter.

14. The spark plug as recited in claim 13, wherein in the at least one first area, a cross-sectional area of the core corresponds at least to 20% of an entire cross-sectional area of the electrode.

15. The spark plug as recited in claim 13, wherein in the at least one first area, a cross-sectional area of the core corresponds at maximum to 65% of an entire cross-sectional area of the electrode.

16. The spark plug as recited in claim 13, wherein the electrode base body has a jacket thickness of at least 0.15 mm in the at least one first area.

17. The spark plug as recited in claim 16, wherein the jacket thickness maximally 0.35 mm.

18. The spark plug as recited in claim 11, wherein on a combustion chamber-side end of the electrode base body, a distance between an end of the electrode base body and an end of the core facing the combustion chamber is not greater than 3.5 mm.

19. The spark plug as recited n claim 18, wherein the distance is not smaller than 0.2 mm.

20. The spark plug as recited in claim 11, wherein the at least one first area is longer than the diameter of the electrode base body.

21. The spark plug as recited in claim 11, wherein a cross-sectional area of the core and a cross-sectional area of the electrode base body have the same shape.

22. The spark plug as recited in claim 11, wherein the electrode base body includes a nickel-containing alloy, and the alloy has at least 20% by weight chromium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1. shows two examples of a center electrode.

[0027] FIG. 2 shows a cross section of the center electrode.

[0028] FIG. 3 shows a spark plug of the present invention having a center electrode.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0029] FIG. 1 shows schematic representations of two exemplary specific embodiments of center electrode 10. Center electrode 10 has an electrode base body 11 and a core 12, which is situated within electrode base body 12. Core 11 is made of a material that has a higher heat conductivity than the material of electrode base body 11. Typically, the material of electrode base body 11 has a higher wear resistance than the material of core 12. Core 12 is made of copper, silver including copper and/or silver. An Ni alloy is preferably used as the material for electrode base body 11, it being possible for the alloy to contain chromium and/or yttrium.

[0030] Due to the manufacturing process, in this case an extrusion process, the core of the center electrode 10 shown here in a sectional view has at least one first segment 15a, in which core 12 has a relatively constant diameter d.sub.K. The term “relatively constant” in the sense of this application means that the diameter d.sub.K in the section changes its value at a maximum by 5%.

[0031] Within a second section 14a, the diameter d.sub.K of core 12 is reduced. The at least one first section 15a is situated on a side of center electrode 10 facing away from the combustion chamber, an electrode head 4, not shown here, being developed subsequent to the end of first section 15 facing away from the combustion chamber. The second section 14a follows upon the at least one first section 15a in the direction of the combustion chamber. Fundamentally, it is conceivable that core 12 has several first sections 15a having constant diameters d.sub.K, the diameters d.sub.K of the individual first sections 15a being different. This is the case, in particular, if the center electrode 10 or the electrode base body 11 itself has several areas having different d.sub.E diameters. In the case of several first sections 15a of the core, the section closest to the combustion chamber is the second section 14a with the continuously decreasing diameter d.sub.K of core 12.

[0032] The center electrode 10 represented in FIG. 1 is made up of an electrode base body 11, which has along its length a constant diameter d.sub.E, and thus center electrode 10 also has a constant diameter d.sub.E. In the case of electrode base body 11, it is possible to distinguish at least three areas 13, 14, 15. In a first area 15, electrode base body 11 has a core 12 having a constant diameter d.sub.K. In a second area 14a, electrode base body 11 has a core 12 having a continuously decreasing diameter d.sub.K. In a third area 13, electrode base body 11 has no core.

[0033] The thickness c of the jacket of electrode base body 11 results from half of the difference of the electrode base body diameter d.sub.E with respect to the core diameter d.sub.K. If the electrode base body 11 in the first area 15 has a constant diameter d.sub.E1, then the jacket thickness c in this first area 15 is constant. Advantageously, there is a provision that in this first area 15 the jacket thickness c of the electrode base body 11 is not less than 0.15 mm and not greater than 0.35 mm, for example the jacket thickness c is equal to 0.25 mm or less.

[0034] In second area 14, the electrode base body 11 may have a constant diameter d.sub.E2, the jacket thickness c in this case increasing within the area 14 in the direction of the combustion chamber. The jacket thickness c is at least 0.15 mm in the area 14.

[0035] In an alternative specific embodiment, not shown here, the diameter d.sub.E2 of electrode base body 11 in the second area 14 may likewise decrease. In this case, jacket thickness c is preferably in the range from 0.15 mm to 0.35 mm. There may be a provision for diameter d.sub.E2 of electrode base body 11 to change at the same rate as diameter d.sub.K of core 12. This has the advantage that the jacket thickness c in second area 14 remains constant.

[0036] In third area 13 of electrode base body 11, there is no core and thus jacket thickness c corresponds to half the diameter d.sub.E3 of electrode base body 11. Third area 13 preferably has a constant diameter d.sub.E3, which corresponds to the diameter d.sub.E2 of the second area 14 in the transition to the third area 13.

[0037] The third area 13 of the electrode base body 11 has a length b, which extends from a combustion chamber-side end 17 of core 12 to a combustion chamber-side face 16 of electrode base body 11. The length b is no greater than 3.5 mm. If center electrode 10 is developed with a noble metal-containing ignition surface 19, the length b may be developed to be shorter than without noble metal-containing ignition surface 19, as shown in FIG. 1b. If there is no noble metal-containing ignition surface 19, as shown in FIG. 1a, then the length b should have a minimum length of 0.6 mm so that noble metal base body 12 has enough material for a sufficiently long service life of center electrode 10. When using a noble metal-containing ignition surface 19, a length b of at least 0.2 mm suffices for a sufficiently long service life of center electrode 10.

[0038] FIG. 2 shows an example of a cross section of center electrode 10. The diameter d.sub.E of center electrode 10 of electrode base body 11 is less than 1.7 mm. The cross section of core 12 is situated at the center in the cross section of center electrode 10 or of electrode base body 11. The thickness c of the sleeve of electrode base body 11 results from half of the difference of the electrode base body diameter d.sub.E with respect to the core diameter d.sub.K. Advantageously, the cross section of electrode base body 11 and of core 12 have the same geometric shape.

[0039] FIG. 3 shows a schematic representation of a spark plug 1 having a center electrode 10 according to the present invention. Spark plug 1 has a metallic housing 2 having a screw thread for installing spark plug 1 in a cylinder head. The housing furthermore has a hex bolt section 9, on which a tool for installing spark plug 1 in cylinder head is applied. Within housing 2, an insulator 3 is situated. A center electrode 10 and a connecting bolt 7 are situated within insulator 3 and are connected electrically via a resistor element 6.

[0040] On the inner side of insulator 3, a seat (3a) is developed, on which center electrode (10) rests with its center electrode head (4). In the area of seat (3a), insulator (3) has a wall thickness of not less than 2 mm.

[0041] On the combustion chamber-side end of spark plug 1, center electrode 10 typically protrudes from insulator 3. The center electrode has a base body 10 and an ignition surface 19 situated on the combustion chamber-side end of the base body. Base body 10 has a core 12 that is surrounded by a jacket 11.

[0042] A ground electrode 5 is situated on the combustion chamber-side end of housing 2, which together with center electrode 10 forms a spark gap. Ground electrode 5 may be developed as a top electrode, a side electrode or a bow electrode.