SPARK PLUG

Abstract

A spark plug having a longitudinal axis. The spark plug includes: a housing; an insulator disposed at least partly inside the housing; a center electrode disposed at least partly inside the insulator and has an electrode body and an ignition element that is disposed on the combustion chamber-side end of the electrode body and serves as an ignition surface, wherein the ignition element has a cylindrical shape with a round base and a longitudinal axis which extends parallel to the spark plug longitudinal axis; and at least one ground electrode having an ignition surface disposed inside the housing on the housing. The ground electrode and the center electrode are disposed such that they form a spark gap that extends radially with respect to the spark plug longitudinal axis, wherein a width of the spark gap is not greater than 0.3 mm. The spark gaps are completely inside the housing.

Claims

1-11. (canceled)

12. A spark plug with a longitudinal axis x, comprising: a housing having an end face on a combustion chamber side; an insulator which is disposed at least partly inside the housing; a center electrode which is disposed at least partly inside the insulator and has an electrode body and an ignition element that is disposed on an combustion chamber-side end of the electrode body and serves as an ignition surface, wherein the ignition element has a cylindrical shape with a round base and a longitudinal axis which extends parallel to the spark plug longitudinal axis; and at least one ground electrode having an ignition surface, which is disposed inside the housing on the housing; wherein the at least one ground electrode and the center electrode are disposed such that the at least one ground electrode and the center electrode form a spark gap that extends radially with respect to the spark plug longitudinal axis; wherein a width of the spark gap is given by an electrode spacing between the center electrode and the at least one ground electrode; wherein the electrode spacing between the center electrode and the at least one ground electrode is not greater than 0.3 mm, and the spark gap is completely inside the housing; and a projection of the ignition surface of the at least one ground electrode fits completely onto the ignition element of the center electrode in an axial direction.

13. The spark plug according to claim 12, wherein an end of the projection of the ignition surface of the at least one ground electrode facing away from the combustion chamber on the ignition element of the center electrode is spaced apart in axial direction from an end of the ignition element of the center electrode facing away from the combustion chamber, a spacing between the projection and the end of the ignition element being at least 5% of a length of the ignition element.

14. The spark plug according to claim 12, wherein the projection of the ignition surface of the at least one ground electrode fits completely onto the ignition element of the center electrode in a direction perpendicular to the spark plug longitudinal axis.

15. The spark plug according to claim 12, wherein the ignition surface of the at least one ground electrode facing the center electrode is a flat surface.

16. The spark plug according to claim 12, wherein the ignition surface of the at least one ground electrode facing the center electrode is concave, and has a contour which is shaped complementarily to the center electrode ignition element.

17. The spark plug according to claim 12, wherein the electrode spacing is not greater than 0.2 mm and/or the electrode spacing is at least 0.05 mm and not less than 0.1 mm.

18. The spark plug according to claim 12, wherein a spacing between the spark gap and the combustion chamber-side end face of the housing is greater than 0 mm and at most 15 mm, wherein a plane subtended by the combustion chamber-side end face of the housing perpendicular to the longitudinal axis of the spark plug is a reference plane with a value 0 mm and a spacing from the reference plane in a direction of an end of the spark plug facing away from the combustion chamber takes on an increasingly negative value.

19. The spark plug according to claim 12, wherein the spark plug includes at least two ground electrodes which each form a spark gap with the center electrode, wherein the ground electrodes are disposed symmetrically around the center electrode.

20. The spark plug according to claim 12, wherein the at least one ground electrode and/or the center electrode each include an ignition element that forms the spark gap with an opposite electrode or with an ignition element of the opposite electrode, and each ignition element include a noble metal or a noble metal alloy, including: (i) Pt or Ir or Rh or Pd or Re or Au, or (ii) an alloy of Pt or Ir or Rh or Pd or Re or Au.

21. The spark plug according to claim 12, wherein the at least one ground electrode and/or the center electrode each include an ignition element, wherein each ignition element has rounded or beveled edges.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 shows a spark plug according to an example embodiment of the present invention.

[0038] FIG. 2 shows a first example for the electrodes of the spark plug according to an example embodiment of the present invention.

[0039] FIG. 3 shows a second example for the electrodes of the spark plug according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0040] FIG. 1 shows a spark plug 1 in a half-sectional view. 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 center electrode 4 is inserted into the insulator 3. A connecting bolt 8 for bringing the spark plug into electrical contact furthermore extends into the insulator 3 and brings the spark plug 1 into electrical contact with a voltage source. The electrical contact-connection forms the end of the spark plug 1 facing away from the combustion chamber. The electrical contact-connection can be configured in one piece, as in this example, or made of several components.

[0041] The insulator 3 is typically divided into three regions: insulator base 31, insulator body and the insulator head. The three regions differ in their different diameters, for example. The insulator base 31 is the end of the insulator 3 facing the combustion chamber. The center electrode 4 is disposed inside the insulator base 31. The insulator base 31 is disposed completely inside the housing 2 here. The insulator base 31 typically has the smallest outer diameter on the insulator 3. The insulator base has a length of at most 7 mm.

[0042] The insulator body, which is typically completely enclosed by the housing 2, is disposed adjacent to the insulator base 31. The insulator body has a larger outer diameter than the insulator base 31. The transition between the insulator base 31 and the insulator body is configured 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 groove.

[0043] The insulator head adjoins the end of the insulator body facing away from the combustion chamber and forms the end of the insulator 3 facing away from the combustion chamber. The insulator head projects out of the housing 2. The outer diameter of the insulator head lies between the outer diameters of the insulator base 31 and the insulator body, wherein the regions typically do not have a constant outer diameter over their length; the outer diameter can instead vary.

[0044] The housing 2 comprises 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 disposed between the insulator seat 35 and the housing seat 25.

[0045] A resistance element 7 is disposed in the insulator 3 between the center electrode 4 and the connecting bolt 8 for bringing the spark plug into electrical contact. The resistance element 7 connects the center electrode 4 to the connecting bolt 8 in an electrically conductive manner. The resistance element 7 is structured as a layer system consisting of a first contact layer 7a, a resistance layer 7b and a second contact layer 7a, for example. The layers of the resistance element differ by 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.

[0046] In this example, two ground electrodes 5 are disposed 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 center electrode 4 together form a respective spark gap 54. The respective spark gap between the center electrode and the respective ground electrode extends radially to the longitudinal axis x. The width of the respective spark gap 54 is the electrode spacing and is in the range of 0.05 mm to 0.3 mm. The bores 52 extend from the outer side 24 through the housing wall to the inner side 23 of the housing 2.

[0047] The spark plug 1 can alternatively also comprise more than just one or more than two ground electrodes 5.

[0048] In this example according to FIG. 1, there is a respective spark gap 54 between the center electrode 4 and the two ground electrodes 5. The projection of the ignition element 41 of the center electrode 4 completely covers the ignition surface of the respective ground electrode 5 in axial direction, and in particular also in the direction perpendicular to the spark plug longitudinal axis. 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 of the ignition surface of the ground electrode 5. The spacing 81a between the spark gap and the plane subtended by the combustion chamber-side end face 27 of the housing 2 perpendicular to the longitudinal axis x here is greater than 0 and equal to or less than 15 mm.

[0049] The center electrode 4 projects out of the insulator base 31 and has a projection length 81b of at least 0.5 mm to at most 6.0 mm.

[0050] The housing 2 comprises a shaft. A polygon 21, a shrink groove and a thread 22 are formed on this shaft. The thread 22 is used to screw the spark plug 1 into an engine.

[0051] 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 disposed at any 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 center electrode 4, and with it also the insulator base 31, projects more or less far into the breathing space 81. The position of the bores in the region of the thread 22 and the ground electrodes 5 on the inner side 23 of the housing 2 can be selected depending on the desired intended use of the spark plug 1.

[0052] The bores 52 are each disposed in a recess 510, such as a conical or round groove, for instance. The outer diameter of the housing 2 in the recesses is smaller than the core diameter of the thread 22.

[0053] The recesses 510 can be created by punching the housing 2 during the production of the spark plug 1, for example. This not only reduces the outer diameter of the housing 2 in the region of the recesses 510, but also the inner diameter of the housing 2 in the region of the recesses 510, so that a projection 26 is created inside the housing for each recess 510.

[0054] Inside the housing 2 there is a breathing space 81 with a volume. The breathing space 81 extends from the combustion chamber-side end face 27 of the housing into the housing 2 and inside the housing 2 to the insulator base groove, which adjoins the insulator seat 35 that is resting on the housing seat 25.

[0055] The intermediate space between the housing 2 and the insulator 3 is sealed in a gas-tight manner at this location by means of an inner seal 10. The volume of the ground electrodes 5, the center electrode 4 and the insulator base 31 are subtracted when calculating the volume of the breathing space. The volume of the breathing space 81 is at most 500 mm.sup.3.

[0056] The housing 2 or the bores 52 for the ground electrodes 5 can have grooves or furrows from production, which results in a surface roughness. The grooves and furrows are created when the bores on or in the housing 2 are machined with a turning process in which material is removed from the housing 2, for instance.

[0057] FIG. 2 shows a first example for the arrangement of the electrodes 4, 5 of the spark plug 1 according to the present invention. The upper half shows a plan view onto the electrodes from the direction of a combustion chamber and the lower half shows a sectional side view of the electrode arrangement.

[0058] The center electrode 4 comprises an electrode body and an ignition element 41 at its combustion chamber-side end. The ignition element 41 is connected to the electrode body by means of a material-locking connection, such as welding, for example. The ignition element 41 is cylindrical with a round base. The ignition element 41 has a longitudinal axis perpendicular to its round bases, wherein the longitudinal axis extends parallel to the longitudinal axis x of the spark plug 1.

[0059] In this example, two ground electrodes 5 are shown. However, there can also be more or fewer. For the sake of simplicity, the description of the figure in the following refers to one ground electrode. The statements apply to both ground electrodes.

[0060] The ground electrode 5 is disposed inside the housing on the housing 2 and forms a side electrode in relation to the center electrode 4. This accordingly creates a radial spark gap 54. The spark gap 54 is delimited by the ignition element 41 of the center electrode 4 and the ignition surface of the ground electrode 5. In this example, the ground electrode 5 also comprises an ignition element 51 that forms the ignition surface. The ignition element 51 of the ground electrode 5 has a flat surface in the direction of the center electrode 4 and therefore a flat ignition surface. The electrode spacing here is the smallest spacing between the ignition surfaces of the two electrodes 4, 5. The projection 54a of the ignition surface of the ground electrode 5 fits on the ignition element 41 of the center electrode 4 in axial direction and in the direction perpendicular to the spark plug longitudinal axis x. In other words, the projection of the center electrode ignition element 41 completely covers the ignition surface of the ground electrode 5 in axial direction and in perpendicular direction. The end of the projection 54a of the ground electrode ignition surface facing away from the combustion chamber has a spacing 45 from the electrode body of the center electrode 4 or the connection region between the electrode body and the ignition element 41 of the center electrode 4.

[0061] FIG. 3 shows a second example of the arrangement of the electrodes 4, 5 of the spark plug 1 according to the present invention. The upper half shows a plan view onto the electrodes 4, 5 from the direction of a combustion chamber and the lower half shows a sectional side view of the electrode arrangement.

[0062] This example differs from the first example in FIG. 2 only in the design of the ignition element 51 of the ground electrode 5.

[0063] This can be seen particularly well in the plan view. The ignition element 51 of the ground electrode 5 does not have a flat surface, but rather a concave surface. The contour of the concave surface is shaped complementarily to the center electrode ignition element 41. The electrode spacing is consequently constant in axial direction and in the direction perpendicular to the longitudinal axis of the spark plug and the electrodes 4, 5 are therefore worn evenly.