Spark plug resistance element comprising fine non-conductive particles

Abstract

A spark plug includes a housing, an isolator arranged in the housing, and a ground electrode arranged on a front surface of the housing on a combustion chamber side. The spark plug further includes a central electrode, a terminal stud, and a resistance element all of which are arranged in the isolator. The resistance element is spatially arranged between the central electrode and the terminal stud and connects the central electrode to the terminal stud. The ground electrode forms a spark gap together with the central electrode. The resistance element contains a resistance material that contains conductive particles and non-conductive particles. At least 80% of the non-conductive particles have a maximum diameter of 20 m.

Claims

1. A spark plug, comprising: a housing; an insulator arranged in the housing; a center electrode, a terminal stud, and a resistance element all of which are arranged in the insulator; and a ground electrode that is arranged on an end face of the housing on a combustion chamber side and forms a spark gap together with the center electrode, wherein: the resistance element is spatially arranged between the center electrode and the terminal stud and electrically connects the center electrode to the terminal stud, the resistance element containing a resistance panat that contains at least one conduction path region including fine conductive particles and fine nonconductive particles, the at least one conduction path region extending through a plurality of coarse nonconductive particles, and at least 80% of the plurality of coarse nonconductive particles have a diameter of at most 20 m.

2. The spark plug as claimed in claim 1, wherein at least 90% of the plurality of coarse nonconductive particles have a diameter of at most 10 m.

3. The spark plug as claimed in claim 1, wherein at least 80% of the fine conductive particles and at least 80% of the plurality of coarse nonconductive particles have a diameter of at most 20 m.

4. The spark plug as claimed in claim 1, wherein the plurality of coarse nonconductive particles are glass particles and ceramic particles.

5. The spark plug as claimed in claim 4, wherein the glass particles contain one or more of an alkaline earth oxide and an alkali oxide.

6. The spark plug as claimed in claim 4, wherein the proportion of the glass particles in the resistance panat is less than or equal to 30 wt. %.

7. The spark plug as claimed in claim 4, wherein the ceramic particles are one or more of Al.sub.2O.sub.3, ZrO.sub.2, and TiO.sub.2.

8. The spark plug as claimed in claim 1, wherein the fine conductive particles are carbon black, graphite, iron, copper, or aluminum.

9. The spark plug as claimed in claim 8, wherein the fine conductive particles have a diameter of 300 nm to 1300 nm.

10. The spark plug as claimed in claim 1, wherein the resistance element is a layer system, which comprises the resistance panat and at least one contact panat, wherein the at least one contact panat is arranged spatially between the terminal stud and the resistance panat or between the center electrode and the resistance panat, or wherein a first contact panat is arranged spatially between the terminal stud and the resistance panat and a second contact panat is arranged spatially between the resistance panat and the center electrode.

11. The spark plug as claimed in claim 5, wherein the alkaline earth oxide is CaO.

12. The spark plug as claimed in claim 5, wherein the alkali oxide is Li.sub.2O.

13. The spark plug as claimed in claim 5, wherein the glass particles contain a borosilicate glass having SiO.sub.2, B.sub.2O.sub.3, CaO, and Li.sub.2O.

14. The spark plug as claimed in claim 1, wherein: the fine conductive particles have a diameter of no more than 10 m; and the fine nonconductive particles have a diameter of no more than 10 m.

15. A spark plug, comprising: a housing; an insulator arranged in the housing; a center electrode, a terminal stud, and a resistance element all of which are arranged in the insulator; and a ground electrode that is arranged on an end face of the housing on a combustion chamber side and forms a spark gap together with the center electrode, wherein: the resistance element is spatially arranged between the center electrode and the terminal stud and electrically connects the center electrode to the terminal stud, the resistance element containing a resistance panat that contains conductive particles and nonconductive particles in the form of glass particles and ceramic particles, at least 80% of the nonconductive particles have a diameter of at most 20 m, and the proportion of the glass particles in the resistance panat is less than or equal to 30 wt. %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 2 shows SEM measurements in the comparison of a sample according to the prior art (right) and a sample according to the disclosure (left).

(3) FIG. 3 shows a schematic illustration of the structure of the resistance panat of a sample according to the prior art (left) and a sample according to the disclosure (right) in comparison.

(4) FIG. 4 shows a schematic illustration of an SEM image with light regions which form conduction paths and dark regions which primarily consist of coarse nonconductive particles.

DETAILED DESCRIPTION

(5) FIG. 1 shows a spark plug 1 in a view in partial section. 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 borehole along the longitudinal axis X thereof. The longitudinal axis of the housing 2, the longitudinal axis of the insulator 3, and the longitudinal axis of the spark plug 1 coincide. A center electrode 4 is inserted into the insulator 3. Furthermore, a terminal stud 8 extends in the insulator 3. A terminal nut 9 is arranged on the terminal stud 8, via which the spark plug 1 can be electrically contacted with a voltage source (not shown here). The terminal nut 9 forms the end of the spark plug 1 facing away from the combustion chamber.

(6) A resistance element 7, also called panat, is located in the insulator 3 between the center electrode 4 and the terminal stud 8. The resistance element 7 electrically conductively connects the center electrode 4 to the terminal stud 8. The resistance element 7 is constructed, for example, as a layer system made of a first contact panat 72a, a resistance panat 71, and a second contact panat 72b. The layers of the resistance element 7 differ by way of the material composition thereof and the electrical resistance resulting therefrom. The first contact panat 72a and the second contact panat 72b can have different electrical resistances or equal electrical resistance. The resistance element 7 can also have only one layer of resistance panat or multiple different layers of resistance panat having different material compositions and resistances.

(7) The insulator 3 rests with a shoulder on a housing seat formed on the housing inner side. To seal the air gap between housing inner side and insulator 3, an inner seal 10 is arranged between the insulator shoulder and the housing seat, which is plastically deformed upon the clamping of the insulator 3 in the housing 2 and thus seals the air gap.

(8) A ground electrode 5 is arranged in an electrically conductive manner on the housing 2 on its end face on the combustion chamber side. The ground electrode 5 and the center electrode 4 are arranged in relation to one another such that a spark gap forms between them, at which the ignition spark is generated.

(9) The housing 2 comprises a shaft. A polygon 21, a shrinkage recess, and a thread 22 are formed on this shaft. The thread 22 is used for screwing the spark plug 1 into an internal combustion engine. An outer seal element 6 is arranged between the thread 22 and the polygon 21. The outer seal element 6 is designed in this exemplary embodiment as a folded seal.

(10) An SEM measurement (SEM=scanning electron microscope) of a sample according to the prior art (left image half) and a sample according to the disclosure (right image half) are shown in comparison in FIG. 2. The black regions are nonconductive particles 712 and the light regions 711 are conductive particles. The dark regions 712 primarily consist of the coarse nonconductive particles, such as glass particles or ceramic particles, for example, Al.sub.2O.sub.3. The light regions 711 are composed of fine conductive carbon particles (small black dots) and nonconductive ZrO.sub.2 particles (light points). The ZrO.sub.2 particles form agglomerates, which are visible as light points in the SEM image.

(11) In the sample according to the prior art, the nonconductive particles 712 have a diameter of greater than 20 m and the fine conductive particles 711 have a diameter of at most 10 m. In contrast thereto, it can be seen in the measurement on the sample according to the disclosure that the nonconductive particles 712 are substantially smaller and have a diameter of at most 20 m. The regions having the fine conductive particles 711 are distributed substantially more uniformly than in the sample according to the prior art.

(12) The structure of the material of the resistance panat for a sample according to the prior art (left image) and for a sample according to the disclosure (right image) is shown very schematically in FIG. 3. The images from FIG. 2 were the template for this schematic illustration. The dark regions 712 again represent the regions of the nonconductive particles and the light regions 711 stand for the conduction path regions, consisting of a mixture of fine conductive particles and fine nonconductive ceramic particles. Because the nonconductive particles 712 have a smaller diameter, they are distributed more uniformly in the resistance panat, so that a more homogeneous distribution of conduction path thicknesses results, in particular fewer very thin conduction paths, which have a comparatively high current density. The width d for a conduction path is furthermore limited by the adjoining regions of the nonconductive particles 712. The measurements of the applicant have shown that in a resistance panat 71 according to the disclosure, the conduction paths are substantially wider than in the resistance panat 71 according to the prior art. The width d of the conduction paths also directly influences the current density j, which flows through the resistance panat 71 and through the resistance element 7.

(13) FIG. 4 shows a schematic illustration of an SEM image. The light regions 711 form the conduction paths, which are composed of conductive carbon particles (small black dots) and nonconductive ZrO.sub.2 particles (light spots). The ZrO.sub.2 particles form agglomerates, which are visible as light spots in the SEM image. The dark regions 712 primarily consist of the coarse nonconductive particles, such as glass particles or ceramic particles, for example, Al.sub.2O.sub.3.

(14) It is shown by way of example how the particle diameter is determined on the basis of a glass particles 713, which is located in the conduction path. A circle is placed in the SEM image around the particle to be measured, which has the same area as the particle. The diameter of the circle is then equivalent to the diameter of the particle.