CERAMIC SPARK PLUG INSULATOR, SPARK PLUG, AND USE OF A GLAZE ON A SPARK PLUG INSULATOR

Abstract

A ceramic spark plug insulator with improved electrical and mechanical strength.

Claims

1-10. (canceled)

11. A ceramic spark plug insulator, comprising: an insulator head oriented in a direction of an electrical connection area; a combustion chamber-side insulator root; and a transition area between the insulator root situated in the combustion chamber and an insulator area situated outside the combustion chamber, the transition area including a root fillet which has a first surface area directed toward an outer side of the spark plug insulator and has a first length L.sub.A defined in an axial direction of the spark plug insulator, the first surface area including a glaze.

12. The ceramic spark plug insulator as recited in claim 11, further comprising: an adjacent second surface area situated from the root fillet in the direction of the insulator head and having a second length L.sub.B, and an adjacent third surface area situated on the combustion chamber side from the root fillet and having a third length L.sub.c, the lengths in each case being defined as maximum lengths in the axial direction of the spark plug insulator, with at least one of the following relationships being met:
L.sub.A=L.sub.B;
L.sub.A=L.sub.C/2; and
L.sub.B=L.sub.C/2.

13. The ceramic spark plug insulator as recited in claim 11, wherein the second surface area includes a glazed fourth surface area situated adjacent to the root fillet, and an unglazed fifth surface area adjoining the fourth surface area in the direction of the insulator head, the fourth surface area extending from the root fillet up to 4 mm in the direction of the insulator head.

14. The ceramic spark plug insulation as recited in claim 13, wherein the fourth surface area extends from the root fillet up to 3 mm in the direction of the insulator head.

15. The ceramic spark plug insulator as recited in claim 13, wherein the third surface area includes a glazed sixth surface area which is situated adjacent to the root fillet and has a sixth length L.sub.F, and an unglazed seventh surface area which adjoins the sixth surface area in the direction of an insulator root tip and has a seventh length L.sub.G, the lengths in each case being defined as maximum lengths in the axial direction of the spark plug insulator, with the following relationship being met: L.sub.F≧L.sub.G.

16. The ceramic spark plug insulator as recited in claim 15, wherein at least one of: i) the glazed sixth surface area extends from the root fillet on the combustion chamber side maximally up to 2 mm in front of the combustion chamber-side insulator root tip, and ii) the sixth length L.sub.F of the sixth surface area meets the following relationship:
4 mm≦L.sub.F≦(L.sub.A+L.sub.F+L.sub.G)/2, the lengths in each case being defined as maximum lengths in the axial direction of the spark plug insulator.

17. The ceramic spark plug insulator as recited in claim 11, wherein the insulator head and the insulator root are connected to one another via an installation area, which includes the second surface area, and the installation area includes a collar fillet and a collar height adjoining the collar fillet in the direction of the insulator head, and wherein at least one of: i) the collar fillet including a glaze on an eighth surface area, which is directed toward the outer side of the spark plug insulator and has an eighth length L.sub.H, and ii) the eighth surface area includes a glaze, and the collar height includes a glazed ninth surface area, which is adjacent to the collar fillet and has a ninth length L.sub.I, and a tenth surface area, which adjoins the ninth surface area in the direction of the insulator head and does not include a glaze and has a tenth length L.sub.J, with the following relationship being met:
0<L.sub.I≦(L.sub.J+L.sub.I)/2.

18. The ceramic spark plug insulator as recited in claim 11, wherein the glaze has the following composition: SiO.sub.2: 37.0 to 46.0 wt. %, B.sub.2O.sub.3: 12.0 to 28.0 wt. %, Al2O.sub.3: 4.0 to 21.0 wt. %, ZnO: 6.0 to 11.4 wt. %, F: 0.6 to 4 wt. %, Li.sub.2O: 1.5 to 4 wt. %, Na.sub.2O: 0.1 to 2.5 wt. %, K.sub.2O: 0.5 to 4.5 wt. %, CaO: 1.8 to 6 wt. %, SrO: 0.1 to 3.6 wt. %, BaO: 0.8 to 6.8 wt. %, each based on the total weight of the glaze.

19. The ceramic spark plug insulator as recited in claim 11, wherein the glaze has the following composition: SiO.sub.2: 37.0 to 44.0 wt. % B.sub.2O.sub.3: 17.5 to 23.0 wt. % Al2O.sub.3: 8.5 to 16.0 wt. % ZnO: 7.8 to 11.4 wt. % F: 0.6 to 3.0 wt. % Li.sub.2O: 1.9 to 3.5 wt. % Na.sub.2O: 0.1 to 2.0 wt. % K.sub.2O: 3.0 to 4.5 wt. % CaO: 2.1 to 4.2 wt. % SrO: 0.1 to 1.2 wt. % and BaO: 4.5 to 6.5 wt. %, each based on the total weight of the glaze.

20. The ceramic spark plug insulator as recited in claim 11, wherein the glaze has a layer thickness of 5 μm to 40 μm.

21. The ceramic spark plug insulator as recited in claim 11, wherein the glaze has a layer thickness of 7 μm to 25 μm.

22. A spark plug for an internal combustion engine, comprising: a metallic housing; a center electrode; at least one ground electrode, which is situated on the housing; and a ceramic spark plug insulator for separating the center electrode from the ground electrode, the ceramic spark plug insulator including an insulator head oriented in a direction of an electrical connection area, a combustion chamber-side insulator root, and a transition area between the insulator root situated in the combustion chamber and an insulator area situated outside the combustion chamber, the transition area including a root fillet which has a first surface area directed toward an outer side of the spark plug insulator and has a first length L.sub.A defined in an axial direction of the spark plug insulator, the first surface area including a glaze.

23. A method of using a glaze on a cross section reducing area of a spark plug insulator comprising: providing a ceramic spark plug insulator including an insulator head oriented in a direction of an electrical connection area, a combustion chamber-side insulator root, and a transition area between the insulator root situated in the combustion chamber and an insulator area situated outside the combustion chamber, the transition area including a root fillet which has a first surface area directed toward an outer side of the spark plug insulator and has a first length L.sub.A defined in an axial direction of the spark plug insulator; and providing the glaze on the first surface area to increase a dielectric strength of the spark plug.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a partial sectional view of a first spark plug according to the present invention.

[0019] FIG. 2 shows a partial sectional view of the spark plug of FIG. 1.

[0020] FIG. 3 shows an enlarged detail of the partial sectional view of the spark plug of FIG. 2.

[0021] FIG. 4 shows an enlarged detail of a partial sectional view of a second spark plug according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0022] As shown in FIG. 1, spark plug 100 according to the present invention includes a ground electrode 13, a center electrode 8, and a ceramic spark plug insulator 10. A metallic housing 7 surrounds spark plug insulator 10 at least partially. A thread 15, which is designed for attaching spark plug 100 in a cylinder head 14, is situated on housing 7. A sealing ring 11 seals the combustion chamber of spark plug 100 in a gas-tight manner.

[0023] FIG. 2 shows a partial sectional view of spark plug 100 of FIG. 1 and illustrates in particular the area of spark plug insulator 10. Spark plug insulator 10 includes an insulator head 1 oriented in the direction of an electrical connection area 5 and a combustion chamber-side insulator root 2. An installation area 3, which includes a cross-sectional reduction, a so-called collar fillet 9a and a collar height 9b, is situated between insulator head 1 and insulator root 2.

[0024] There is also an area in insulator root 2 in which the cross section is reduced, a so-called root fillet 4, i.e., a transition area between insulator root 2 situated in the combustion chamber and the insulator area situated outside the combustion chamber. The combustion chamber, as shown here, may be sealed off from the area outside the combustion chamber in a gas-tight manner by a sealing ring 11.

[0025] Root fillet 4 has a first surface area A, which is directed toward the outer side of spark plug insulator 10 and has a first length L.sub.A defined in axial direction X-X of the spark plug insulator, and includes a glaze 12 and is thus glazed. On an adjacent section of spark plug insulator 10, i.e., installation area 3, situated with respect to root fillet 4 in the direction of insulator head 1, spark plug insulator 10 has a second surface area B directed toward the outer side of spark plug insulator 10. In an adjacent section of spark plug insulator 10 which is situated from root fillet 4 on the combustion chamber side, insulator root 2 has a third surface area C directed toward the outer side of spark plug insulator 10. Surface area C is unglazed.

[0026] On an eighth surface area H which is directed toward the outer side of spark plug insulator 10 and has an eighth length L.sub.H, collar fillet 9a includes a glaze 12.

[0027] Collar height 9b includes a surface area I having a ninth length L.sub.I, and a unglazed tenth surface area J which adjoins ninth surface area I in the direction of insulator head 1 and has a tenth length L.sub.J, ninth surface area I including a glaze 12, with the following relationship being advantageously met:

0<L.sub.I=(L.sub.J+L.sub.I)/2.

[0028] FIG. 3 shows a close-up view of a detail of the transition area between insulator root 2 situated in the combustion chamber and the area of spark plug insulator 10 of spark plug 100 which is situated outside the combustion chamber of FIGS. 1 and 2. Here, the surface area of root fillet 4 coincides with first surface area A, i.e., a glaze 12 is provided exclusively in an area of root fillet 4 having a reduced cross section, and here in its entire first surface area A. The cross section in the adjacent unglazed areas of root fillet 4 is essentially constant.

[0029] Glaze 12 advantageously has an average layer thickness of 5 μm to 40 μm, in particular of 7 μm to 25 μm.

[0030] Glaze 12 significantly increases the flexural strength of the ceramic insulator. For spark plug 100 according to the present invention, it is more than 850 N, while corresponding unglazed spark plugs have flexural strengths of only approximately 660 N.

[0031] The dielectric strengths of spark plug 100 according to the present invention are also considerably increased and are at least approximately 42 kV, while comparable conventional spark plugs have dielectric strengths of only approximately 35 kV.

[0032] First surface area A has a first length L.sub.A, second surface area B has a second length L.sub.B, and third surface area C has a third length L.sub.C. The respective lengths are maximum lengths and defined in axial direction X-X of the spark plug insulator. A total length of insulator root 2 in axial direction X-X of spark plug insulator 10 thus results from: L.sub.A+L.sub.C.

[0033] Advantageously, at least one of the following relationships exists between the lengths of the individual surface areas: L.sub.A=L.sub.B and/or L.sub.A=L.sub.C/2 and/or L.sub.B=L.sub.C/2.

[0034] FIG. 4 shows a close-up view of a detail of the transition area between insulator root 2 situated in the combustion chamber and the area of spark plug insulator 10 of a second spark plug 100 according to the present invention which is situated outside the combustion chamber.

[0035] In contrast to spark plug 100 of FIGS. 1 through 3, second surface area B includes a fourth surface area D situated adjacent to root fillet 4, and a fifth surface area E adjoining fourth surface area D in the direction of insulator head 1. As well as first surface area A, fourth surface area D includes a glaze 12. Proceeding from root fillet 4, the glazed surface area is thus expanded in the direction of insulator head 1, and in particular glazed fourth surface area D extends from root fillet 4 up to 4 mm, in particular up to 3 mm, in the direction of insulator head 1.

[0036] Furthermore, third surface area C includes a glazed sixth surface area F situated adjacent to root fillet 4, and an unglazed seventh surface area G adjoining sixth surface area F in the direction of insulator root tip 6, so that the glaze, proceeding from root fillet 4, also extends in the direction of insulator root tip 6 situated on the combustion chamber side.

[0037] Glazed sixth surface area F extends from root fillet 4 on the combustion chamber side maximally up to 2 mm in front of insulator root tip 6 on the combustion chamber side, which prevents notch formation due to mechanical load.

[0038] Advantageously, glazed sixth surface area F has a sixth length L.sub.F, and the following relationship is met: 4 mm≦L.sub.F≦(L.sub.A+L.sub.F+L.sub.G)/2, the lengths in each case being defined as maximum lengths in axial direction X-X of the spark plug insulator.

[0039] In FIG. 4, surface area A′ represents a glaze-covered total surface area. Glazed total surface area A′ includes the surface area of root fillet A and extends in the direction of insulator head 1 beyond first surface area of root fillet 4 onto fourth surface area D, and onto sixth surface area F on the combustion chamber side. This contributes to the lateral load capacity of spark plug insulator 10.

[0040] In summary, first surface area A thus has a first length L.sub.A, second surface area B has a second length L.sub.B, third surface area C has a third length L.sub.C, and fourth surface area D has a fourth length L.sub.D, fifth surface area E has a fifth length L.sub.F, sixth surface area F has a sixth length L.sub.F, and seventh surface area G has a seventh length L.sub.G. Glazed total surface area A′ thus has a total length of: L.sub.A′=L.sub.A+L.sub.D+L.sub.F. The total length of insulator root 2 furthermore results from: L.sub.A+L.sub.F+L.sub.G. The respective lengths are maximum lengths and defined in axial direction X-X of spark plug insulator 10.

[0041] Advantageously, sixth glazed surface area F has a length L.sub.F, and unglazed seventh surface area G directed toward insulator root tip 6 has a length L.sub.G, and the following relationship is met: L.sub.F L.sub.G.

[0042] With an installation space-saving design, spark plugs 100 are characterized by a high dielectric strength and very good mechanical load capacity.