SPARK PLUG HAVING A SMALL INTER-ELECTRODE DISTANCE AND AN AT LEAST PARTLY NEGATIVE SPARK POSITION

Abstract

A spark plug having a longitudinal axis. The spark plug includes: a housing having a bore along the spark plug longitudinal axis and a combustion-chamber-side end face; an insulator arranged at least partially within the housing, and having an insulator base extending from a combustion-chamber-side end face of the insulator to an insulator base neck; a central electrode arranged at least partially within the insulator; and a ground electrode arranged on the housing, the ground electrode and the central electrode being arranged so that the at least one ground electrode forms a spark gap with the central electrode, a width of the spark gap being defined by an inter-electrode distance between the central electrode and the ground electrode. The inter-electrode distance between the central electrode and the ground electrode is not greater than 0.4 mm. The spark gap is formed at least partially within the housing.

Claims

1-11. (canceled)

12. A spark plug having a longitudinal axis, comprising: a housing having a bore along the spark plug longitudinal axis and a combustion-chamber-side end face; an insulator arranged at least partially within the housing, the insulator having an insulator base which extends from a combustion-chamber-side end face of the insulator to an insulator base neck; a central electrode arranged at least partially within the insulator; and at least one ground electrode arranged on the housing, the at least one ground electrode and the central electrode being arranged in such a way that the at least one ground electrode forms a spark gap with the central electrode, a width of the spark gap being defined by an inter-electrode distance between the central electrode and the at least one ground electrode; wherein the inter-electrode distance between the central electrode and the at least one ground electrode is not greater than 0.4 mm, and the spark gap is formed at least partially within the housing.

13. The spark plug according to claim 12, wherein the inter-electrode distance is not greater than 0.2 mm.

14. The spark plug according to claim 13, wherein the inter-electrode distance is not greater than 0.15 mm.

15. The spark plug according to claim 12, wherein the inter-electrode distance is at least 0.05 mm.

16. The spark plug according to claim 15, wherein the inter-electrode distance is not less than 0.1 mm.

17. The spark plug according to claim 12, wherein the spark gap has a distance from the combustion-chamber-side end face of the housing of greater than 0 mm and at most-15 mm, a plane perpendicular to the longitudinal axis of the spark plug spanned by the combustion-chamber-side end face of the housing being a reference plane having a value 0 mm, and a distance from the reference plane in a direction of the end of the spark plug remote from the combustion chamber assuming an increasingly negative value.

18. The spark plug according to claim 12, wherein the insulator base has a length, measured parallel to the longitudinal axis of the spark plug, which is not longer than 7 mm.

19. The spark plug according to claim 12, wherein the central electrode protrudes from the insulator, and a protrusion dimension of the central electrode, measured from the combustion-chamber-side end face of the insulator as far as a combustion-chamber-side end of the central electrode, is not greater than 6.0 mm and is not smaller than 0.5 mm.

20. The spark plug according to claim 12, wherein the spark plug has a breathing chamber which extends within the housing from the combustion-chamber-side end face of the housing to the insulator base neck, the central electrode and the insulator base being arranged within the breathing chamber and the at least one ground electrode being arranged at least partially within the breathing chamber, and the breathing chamber has a volume of not greater than 500 mm and not less than 50 mm.sup.3.

21. The spark plug according to claim 12, wherein the insulator base and/or inner sides of the housing has a contour which results from a rounding with a non-constant radius.

22. The spark plug according to claim 12, wherein the spark plug has at least two ground electrodes which each form a spark gap with the central electrode, the ground electrodes being arranged symmetrically around the central electrode.

23. The spark plug according to claim 12, wherein the at least one ground electrode and/or the central electrode each has an ignition surface which forms the spark gap with an oppositely situated electrode, and the ignition surface includes a noble metal or a noble metal alloy, including: i) Pt, or ii) Ir, or iii) Rh, or iv) Pd, or v) Re, or vi) Au, or vii) an alloy of Pt, or Ir, or Rh, or Pd, or Re, or Au.

24. The spark plug according to claim 12, wherein the spark plug is a hydrogen spark plug which is configured to be used in an engine operated with hydrogen and to ignite ignitable hydrogen-containing fuel-air mixture.

Description

BRIEF DESCRIPTION OF EXAMPLE EMBODIMENTS

[0030] FIG. 1 shows an example of a spark plug according to the present invention.

[0031] FIG. 2 shows a second example of a spark plug according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0032] FIG. 1 shows a half-sectional view of a spark plug 1. The spark plug 1 comprises a housing 2. An insulator 3 is inserted into the housing 2. The housing 2 and the insulator 3 each have a bore along their longitudinal axis. The housing 2 has an outer side 24 and an inner side 23. The longitudinal axis of the housing 2, the longitudinal axis of the insulator 3, and the longitudinal axis x of the spark plug 1 coincide. A central electrode 4 is inserted into the insulator 3. Furthermore, a connecting bolt 8 extends into the insulator 3 for electrical contacting of the spark plug; via this the spark plug 1 is electrically contacted to a voltage source. The electrical contacting forms the end of the spark plug 1 remote from the combustion chamber. The electrical contacting can be made in one piece, as in this example, or also from a plurality of components.

[0033] The insulator 3 is typically divided into three regions: insulator base 31, insulator body, and insulator head. The three regions differ, for example, by different diameters. The insulator base 31 is the end of the insulator 3 close to the combustion chamber. The central electrode 4 is arranged within the insulator base 31. The insulator base 31 is here arranged completely within the housing 2. As a rule, the insulator base 31 has the smallest outer diameter on the insulator 3. Here, the insulator base has a length 81c of at most 7 mm.

[0034] The insulator body, which is generally completely surrounded by the housing 2, is arranged adjacent to the insulator base 31. The insulator body has a greater outer diameter than the insulator base 31. The transition between the insulator base 31 and the insulator body is designed as a shoulder, the so-called insulator seat 35. The transition between the insulator seat 35 and the insulator base 31 is referred to as the insulator base neck.

[0035] The insulator head adjoins the end of the insulator body remote from the combustion chamber and forms the end of the insulator 3 remote from the combustion chamber. The insulator head protrudes from the housing 2. The outer diameter of the insulator head lies between the outer diameters of the insulator base 31 and the insulator body; the regions typically do not have a constant outer diameter over their length; rather, the outer diameter can vary.

[0036] The housing 2 also has a seat 25 on its inner side. The insulator rests with its shoulder or insulator seat 35 on the housing seat 25. An inner seal 10 is arranged between the insulator seat 35 and the housing seat 25.

[0037] A resistance element 7 is located in the insulator 3 between the central electrode 4 and the connecting bolt 8 for electrical contacting of the spark plug. The resistance element 7 connects the central electrode 4 to the connecting bolt 8 in an electrically conductive manner. The resistance element 7 is constructed, for example, as a layer system made up of a first contact layer 7a, a resistance layer 7b, and a second contact layer 7a. The layers of the resistance element differ in their material composition and the resulting electrical resistance. The first contact layer 7a and the second contact layer 7a can have a different or the same electrical resistance.

[0038] In this example, two ground electrodes 5 are arranged in a respective bore 52 on the inner side 23 of the housing 2, so that the ground electrodes 5 project radially from the inner side 23 of the housing into the bore along the longitudinal axis X of the housing 2. The ground electrodes 5 and the central electrode 4 together form a spark gap 54 in each case. The respective spark gap between the central electrode and the corresponding ground electrode extends radially with respect to the longitudinal axis x. The width of the corresponding spark gap 54 is the inter-electrode distance, and is in the range of from 0.05 mm to 0.4 mm. The bores 52 extend from the outer side 24 through the housing wall as far as the inner side 23 of the housing 2.

[0039] Alternatively, the two ground electrodes 5 could also be arranged on the combustion-chamber-side end face 27 of the housing 2.

[0040] Alternatively, the spark plug 1 can also have more than only one, or more than two, ground electrodes 5.

[0041] In this example according to FIG. 1, in each case there is a spark gap 54 between the central electrode 4 and the two ground electrodes 5. In this case, the projections of the respective ignition surface of the central electrode 4 and a corresponding ground electrode 5 do not completely overlap. The combustion-chamber-side end of the spark gap lies in a plane perpendicular to the longitudinal axis x with the combustion-chamber-side end face of the central electrode 4. The distance 81a of the spark gap to the plane spanned by the combustion-chamber-side end face 27 of the housing 2 perpendicular to the longitudinal axis x is here greater than 0 and equal to or less than-15 mm.

[0042] The central electrode 4 protrudes from the insulator base 31 and has a protrusion dimension 81b of at least 0.5 mm up to a maximum of 6.0 mm.

[0043] The housing 2 has a shaft. A polygon 21, a shrink-fit groove, and a thread 22 are formed on this shaft. The thread 22 is used to screw the spark plug 1 into an engine.

[0044] The bores 52 in the housing wall are formed in the region of the thread 22. The bore 52 for the ground electrodes 5, and thus also the ground electrodes 5, can be arranged at any desired height in the region of the thread 22. Depending on the position of the ground electrodes 5 in the region of the thread 22, the central electrode 4 and, with it, the insulator base 31 correspondingly protrude to a further or lesser extent into the breathing chamber 81. The position of the bores in the region of the thread 22 and of the ground electrodes 5 on the inner side 23 of the housing 2 can be selected depending on the desired use of the spark plug 1.

[0045] The bores 52 are arranged, for example, in a respective recess 51 such as a conical or a round groove. Here the outer diameter of the housing 2 in the recesses is smaller than the core diameter of the thread 22.

[0046] The recesses 51 can be created, for example, by stamping of the housing 2 during the manufacture of the spark plug 1. This not only reduces the outer diameter of the housing 2 in the region of the recesses 51, but also the inner diameter of the housing 2 in the region of the recesses 51, so that a projection 26 is created within the housing for each recess 51.

[0047] Inside the housing 2 there is a breathing chamber 81 that has a volume. The breathing chamber 81 extends from the combustion-chamber-side end face 27 of the housing into the housing 2, and within the housing 2 as far as the insulator base neck, which adjoins the insulator seat 35 which rests on the housing seat 25. At this location, the gap between the housing 2 and the insulator 3 is sealed in a gas-tight manner by an inner seal 10. The volume of the ground electrodes 5, the central electrode 4, and the insulator base 31 is subtracted when calculating the breathing chamber volume. The volume of the breathing chamber 81 is at most 500 mm.sup.3.

[0048] The housing 2 or the bores 52 for the ground electrodes 5 may have grooves or scores from the manufacturing process, resulting in a surface roughness. The grooves and scores arise, for example, when the bores on or in the housing 2 are machined by a turning process in which material is removed from the housing 2.

[0049] FIG. 2 shows a second example of the spark plug 1 according to the present invention. This example differs from the first example in the arrangement of the ground electrode 5. In this example, the ground electrode 5 is arranged as a so-called roof electrode with respect to the central electrode 4. The spark gap 54 between the central electrode 4 and the ground electrode 5 extends in parallel with the longitudinal axis x. The width of the spark gap 54 is the inter-electrode distance parallel to the longitudinal axis x and is in the range of from 0.05 mm to 0.4 mm.

[0050] The combustion-chamber-side end of the axial spark gap 54 is defined by the ignition surface of the ground electrode 5. The distance 81a of the spark gap 54 to the plane spanned by the combustion-chamber-side end face 27 of the housing 2 perpendicular to the longitudinal axis x is measured correspondingly.

[0051] A second ground electrode, arranged laterally to the central electrode 4 and thus forming a spark gap 54 radially to the longitudinal axis x, is not shown here, but is possible.