EP2089944B1 - Sparkplug, in particular for high combustion chamber pressures - Google Patents

Abstract

The present invention relates to a sparkplug with a central electrode (4) arranged within an insulator (3) and a housing (2), which surrounds at least regions of the insulator (3), characterized in that a conductive planar element (7) is arranged on the insulator (3), and electrical contact is made between said element and the housing (2).

Description

State of the art

The present invention relates to a spark plug for internal combustion engines, which is designed in particular for use in combustion chambers with high pressure.

Spark plugs are known from the prior art in different configurations. The known spark plugs have basically proven themselves for use in internal combustion engines. However, in recent times, the pressures in the combustion chamber at the time of ignition are getting larger, since the internal combustion engines are increasingly charged and operated with high compression. In particular, at high pressures, the formation of sliding sparks during ignition may occur, which in particular also extends into a respiratory chamber of the spark plug, which is formed between a tapering region of the insulator and a housing of the spark plug at the combustion chamber end of the spark plug. Such sliding sparks lead in the homogeneous operation of the internal combustion engine to a turbulent engine run. In stratified operation of the internal combustion engine and in operating states with inhomogeneous mixture distribution, such. During low-temperature starts, sliding sparks cause frequent misfires.

In the DE 196 50 724 B4 For the purpose of reducing sliding sparks, it has been proposed to provide an electrode spacing between the center electrode and the ground electrode such that this electrode spacing is smaller than a distance between the center electrode and the housing. However, the geometric arrangements of the electrodes proposed here can often not be complied with due to design constraints.

A spark plug according to the preamble of claim 1 is made EP-A-1 557 918 known.

Advantages of the invention

The spark plug according to the invention with the features of claim 1 has the advantage that it prevents the formation of sliding sparks. This allows the spark plug according to the invention in particular in Brennkrafhnaschinen with high Press, such as charged and / or high-compression engines used. The spark plug according to the invention has a long service life and can be produced easily and inexpensively. This is inventively achieved in that on the insulator of the spark plug, a conductive sheet-like element is arranged, which is in electrical contact with the housing. As a result, according to the invention, the insulator surface is set to the electrical potential of the housing. The housing is usually grounded. By virtue of this relatively simple measure according to the invention, electric fields which are present in the respiratory space between the tapered insulation and the housing in conventional spark plugs can be eliminated. As a result, the generation of sliding sparks can be prevented even at high pressures. Furthermore, partial discharges can be avoided in the housing web area and thus also electromagnetic noise pulses can be suppressed.

The dependent claims show preferred developments of the invention.

The conductive, sheet-like element is preferably formed as extending completely around the insulator band. As a result, an emergence of electric fields in the critical region of the respiratory space between the insulation and the housing can be reliably prevented. It should be noted that it is alternatively also possible to provide a plurality of only partially circumferential areas with the conductive, sheet-like element according to the invention, wherein adjacent Flächenclcinente are only slightly spaced from each other. However, there must be an electrical connection of each element to the housing.

Particularly preferably, the conductive, sheet-like element is arranged in the region of a sealing seat between the housing and the insulator. As a result, a secure contact can be achieved.

More preferably, the spark plug comprises a sealing ring, which is arranged between the housing and the insulator, and the sealing ring is made of an electrically conductive material. The conductive, sheet-like element according to the invention is arranged on a region of the insulator which is positioned at the level of the sealing ring.

According to a further preferred embodiment of the present invention, the conductive, sheet-like element has a maximum thickness of 100 microns. The conductive sheet-like member is further preferably provided with a constant thickness. This upper limit of the thickness of the element has the advantage that a simple attachment is guaranteed. It should also be noted that as the layer thickness increases, stresses in the material significantly increase, thereby deteriorating the attachment of the element. Particularly preferably, the thickness of the conductive, sheet-like element is in the range of about 50 microns to about 80 microns.

More preferably, the conductive, sheet-like element is arranged on the insulator at a region of the insulator, which is arranged in the mounted state at the level of an inner, circumferential web of the housing. Preferably, the conductive, sheet-like element on the insulator covers at least 70% of the surface of the insulator, which is directed towards the inner web of the housing in the radial direction of the spark plug. By this measure, it is ensured that the space prone to the formation of electric fields between the inner web of the housing and the insulator is at least 70% covered with the electrically conductive element. As a result, this area, which is susceptible to preliminary discharges, can be made field-free, so that the tendency for the occurrence of sliding sparks is reduced. It should also be noted that the conductive, sheet-like element on the insulator may not extend too far in the direction of the electrodes, since otherwise a connection resistance of the spark plug substantially increases.

Preferably, the conductive sheet-like element, starting from a contact point between the insulator and the housing, covers a region of the insulator in the direction of its end surface on which the electrodes are arranged, the region provided with the conductive, planar element being a maximum of 50%, preferably 30 % of the distance between the contact point and the end face of the insulator.

Preferably, the conductive sheet-like member covers an area of at least 70% of a portion of the insulator having a pitch of less than or equal to 0.5mm from the inner surface of the housing. This also ensures that the critical area for the emergence of sliding sparks in the working space is made field-free.

Particularly preferably, the conductive, sheet-like element is a conductive coating. This is easy and inexpensive to apply and has only a low density.

Particularly preferably, the coating is a conductive ink, which has an electrical conductivity. This has the particular advantage that the coating can be applied in a particularly simple and cost-effective manner. It is also not necessary that previous assembly process of spark plugs must be changed. The conductive ink includes preferably a precious metal, in particular silver and / or platinum and / or gold unct / or iridium and / or rhodium, and / or tantalum and / or nickel and / or carbon or any oxidation-resistant alloy thereof. The oxidation resistance is important because high temperatures and atmospheric oxygen are present in the combustion chamber.

As a conductive sheet-like member, a thin tape, e.g. Gold leaf or other precious metal-containing film can be used.

drawing

Figur 1

eine schematische, teilweise geschnittene Teilansicht einer Zündkerze gemäß einem Ausfiihrungsbeispiel der Erfindung und

Figur 2

ein Diagramm, welches die Wahrscheinlichkeit des Entstehens von Gleitfunken in Abhängigkeit vom Druck im Brennraum für eine erfindungsgemäße Zündkerze sowie eine Zündkerze des Standes der Technik zeigt.

Hereinafter, a preferred Ausführunolsbeispiel the invention will be described with reference to the accompanying drawings. In the drawing is:

FIG. 1

a schematic, partially sectioned partial view of a spark plug according to an embodiment of the invention and

FIG. 2

a diagram showing the probability of the occurrence of sliding sparks as a function of the pressure in the combustion chamber for a spark plug according to the invention and a spark plug of the prior art.

Preferred embodiment of the invention

The following is with reference to the FIGS. 1 and 2 a spark plug 1 according to an embodiment of the invention described in detail.

As in FIG. 1 1, the spark plug 1 comprises a housing 2 which has an external thread 2a, with which the spark plug 1 is fastened to a component of an internal combustion engine. The spark plug 1 further comprises an insulator 3 with a combustion chamber side end face 3a. In the interior of the insulator 3, a center electrode 4 is arranged, which is arranged in the longitudinal direction XX of the spark plug. A ground electrode 5 is connected to the housing 2.

How out FIG. 1 it can be seen, a breathing chamber 6 is formed between the insulator 3 and the housing 2. The respiratory space 6 is annular and tapers from the electrode-side end of the spark plug. On the inside of the housing 2, an inner circumferential web 2b is further formed. The web 2b has an annular shape and a seal 9 is arranged at a step transition between the web 2b and the inside of the housing between the housing 2 and the insulator 3.

On the insulator 3, a coating 7 made of a silver conductive paint is further applied at the level of the web 2b. The silver conductive ink can be applied to the insulator 3, for example, by spraying or rolling. In the region of the step on the web 2b is an annular contact point 8 between the housing 2 and the coating 7. The contact point 8 is an electrically conductive contact between the housing 2 and the coating 7, so that it is achieved that the outer surface of the insulator. 3 is placed in the region of the respiratory space 6 to the electrical potential of the housing. As a result, electric fields can be prevented from building up between the insulator 3 and the inside of the housing 2, which can lead to a sliding spark jumping over the end face 3a of the insulator 3 into the respiratory space 6 during the ignition time. The conductive coating 7 eliminates these electric fields in the region of the inner web 2b of the housing 2. Thus, according to the invention, the emergence of a sliding spark can be prevented, especially at high pressures.

FIG. 2 shows a diagram showing a comparison of a spark plug with an insulator without coating according to the prior art and a spark plug according to the invention with a coating comprising silver conductive paint having insulator. In FIG. 2 For example, the curve of the spark plug is marked with an insulator without coating with "N" and the curve of the spark plug with an insulator with coating marked with "M". "W" indicates the probability of a sliding spark in%. As seen from the diagram of FIG. 2 can be seen, the spark plug according to the invention, even at very high pressures only a minimal probability of the emergence of a sliding spark. In contrast, in the spark plug of the prior art, a significant increase in the probability of the occurrence of a sliding spark from a pressure of about 7 x 10 ⁵ Pascal seen.

Out FIG. 1 It can also be seen that the coating 7 is provided on the insulator 3 at a width B in the longitudinal direction XX of the spark plug starting from the contact point 8, wherein a ratio of the width B to a distance A from the contact point 8 to the end face 3a of the insulator 3 is about 1: 4. In other words, the coating 7 is formed over a surface area starting from the contact point 8 of approximately 25% of the insulator surface from the contact point 8 to the end face 3a. As further out FIG. 1 it can be seen, the coating 7 is provided completely over the entire width of the web 2b. An overlap of the coating 7 in the region of the web 2b should amount to at least 70% of the web width to the area prone to the unwanted pre-discharges between the insulator 3 and the housing 2 to make field-free. It should also be noted that the coating 7 on the insulator 3 should be at most 50%, particularly preferably at most 30%, of the distance A between the contact point 8 and the end face 3a.

The coating used is preferably a conductive paint which comprises a noble metal or an oxidation-resistant conductive alloy, since very high temperatures often occur in the combustion chamber.

The present invention can be used in all known fields of use of spark plugs, but is particularly preferably used when high pressures occur in combustion chambers.

Claims (12)

1. Spark plug having a central electrode (4), which is arranged within an insulator (3), and a housing (2), which surrounds at least regions of the insulator (3), wherein a conductive planar-like element (7) is arranged on the insulator (3), characterized in that electrical contact is made between the conductive planar-like element and the housing (2).
2. Spark plug according to Claim 1, characterized in that the conductive planar-like element (7) is in the form of a region which circulates completely around the insulator (3).
3. Spark plug according to either of the preceding claims, characterized in that the conductive planar-like element (7) is arranged in the region of a sealing seat between the housing (2) and the insulator (3).
4. Spark plug according to one of the preceding claims, further comprising a seal (9) which is arranged between the housing (2) and the insulator (3), wherein the seal (9) is produced from an electrically conductive material and makes contact with the housing (2) and the conductive planar-like element (7).
5. Spark plug according to one of the preceding claims, characterized in that the conductive planar-like element (7) has a thickness of at most 100 µm, preferably about 50 µm to about 80 µm.
6. Spark plug according to one of the preceding claims, characterized in that the conductive planar-like element (7) is arranged on the insulator (3) level with an internally circulating web (2b) of the housing (2).
7. Spark plug according to Claim 6, characterized in that the conductive planar-like element (7) on the insulator (3) covers at least 70% of a surface of the insulator which is directed towards the web (2b) of the housing (2).
8. Spark plug according to one of the preceding claims, characterized in that the conductive planar-like element (7), proceeding from a point of contact (8) between the conductive planar-like element (7) and the housing (2), covers a region of the insulator in the longitudinal direction (X-X) thereof which is at most 50%, preferably about 30%, of a distance (A) between the point of contact (8) and an end face (3a) of the insulator (3).
9. Spark plug according to one of the preceding claims, characterized in that the conductive planar-like element (7) is formed over at least 70% of a region of the insulator (3) which is at a distance of less than or equal to 0.5 mm from the inner surface of the housing (2).
10. Spark plug according to one of the preceding claims, characterized in that the conductive planar-like element is a coating, in particular a conductive lacquer.
11. Spark plug according to Claim 10, characterized in that the coating comprises a precious metal, in particular silver and/or platinum and/or gold and/or iridium and/or rhodium and/or tantalum and/or nickel and/or carbon or any desired alloy resistant to oxidation.
12. Spark plug according to one of Claims 1 to 9, characterized in that the conductive planar-like element (7) is gold foil or another foil which contains precious metal.

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