Spark plug housing with corrosion protection on the inner side, as well as a spark plug and production method

Abstract

The invention relates to a spark plug housing (2) comprising an inner side (24), an outer side (23) and a longitudinal axis, which extends from an end (21) of the spark plug housing (2) facing a combustion chamber to an end (22) of the spark plug housing (2) facing away from the combustion chamber, wherein the spark plug housing (2) has a circumferential shoulder (25) on the inner side (24) thereof, which is designed such that a spark plug isolator (3) rests on same, wherein the spark plug housing (2) has a corrosion protection layer (50) on the inner side (24) thereof, which is formed on a section (55) of the inner side (24) of the spark plug housing (2), wherein the section (55) extends from the end (21) of the spark plug housing (2) facing a combustion chamber to at least over the shoulder (25) and along the inner circumference of the spark plug housing (2).

Description

State of the art

[0001] The invention relates to a spark plug housing according to claim 1 and a spark plug with such a spark plug housing according to claim 7, as well as a manufacturing method for the spark plug housing according to claim 8.

[0002] Today's spark plug housings often have a coating on their exterior to protect the spark plug housing from corrosion. Typically, such a corrosion-protection layer is created using an electrochemical, galvanic, or other coating process. Each coating process has its advantages and disadvantages.

[0003] Such spark plug housings are known, for example, from US 2012 / 146483 A1, DE 10 2004 046895 A1 or EP2 546 938 A1. Disclosure of the invention

[0004] For electroplating, the spark plug housing is placed in a drum or mounted on a coating rack. This process presents the challenge that the interior of the spark plug housing cannot be coated, or can only be coated to a limited extent, because the electrical field required for coating formation is shielded within the housing itself. Spark plug housings with a deep breathing chamber, in particular, do not receive a coating on their interior, or at least not a sufficient or even uniform coating, using this method. Under unfavorable storage or transport conditions, the spark plug housing's interior can corrode. The spark plug housing can no longer be used.If the corrosion of the breathing chamber goes unnoticed and the spark plug housing is used for a spark plug, then this spark plug will have a significantly shorter lifespan than a spark plug with a non-corroded spark plug housing.

[0005] It is an object of the present invention to provide a spark plug housing and a spark plug in which corrosion in the breathing chamber of the spark plug housing is as minimal as possible.

[0006] This object is achieved in the spark plug housing according to the invention, which has an inner side, an outer side and a longitudinal axis which extends from an end of the spark plug housing facing the combustion chamber to an end of the spark plug housing facing away from the combustion chamber, wherein the spark plug housing has on its inner side a circumferential shoulder which is designed for a spark plug insulator to rest thereon, in that the spark plug housing has on its inner side a corrosion protection layer which is formed on a section of the inner side of the spark plug housing, wherein the section extends from an end of the spark plug housing facing the combustion chamber to at least over the shoulder and along the inner circumference of the spark plug housing.

[0007] This provides the advantage that the section on the inside of the spark plug housing covered with the anti-corrosive layer, which, together with the spark plug insulator, defines and thus forms the breathing chamber, is protected from unwanted corrosion by the anti-corrosive layer during storage, transport, and use of the spark plug. It is particularly advantageous that the anti-corrosive layer extends from the end of the spark plug housing facing the combustion chamber to at least the shoulder. In a spark plug, the spark plug insulator rests on the shoulder on the inside of the spark plug housing.Often combined with an internal seal, but in some cases without an internal seal, the gap between the spark plug housing and the spark plug insulator is hermetically sealed at the shoulder, preventing the gas mixtures created in the combustion chamber from penetrating further into the spark plug housing than this internal seal at the shoulder. The breathing space thus extends from the end of the spark plug housing facing the combustion chamber to the shoulder, on which the spark plug insulator rests, often sealing the gap together with an internal seal.

[0008] According to the invention, the corrosion protection layer is a galvanically applied layer.

[0009] This means that the corrosion protection layer was applied to the surface of the spark plug housing using a galvanic coating process. In particular, the galvanic coating process results in a very uniform corrosion protection layer that is also sufficiently extensive on the inside of the spark plug housing. A coating electrode is placed inside the spark plug housing during the galvanic coating process, creating a very uniform electric field along the longitudinal axis of the spark plug housing for the section to be coated.

[0010] Additionally or alternatively, the corrosion protection layer may contain nickel and / or zinc. Corrosion layers containing or made of these elements are very stable. In particular, the corrosion protection layer is phosphorus-free.

[0011] In an advantageous embodiment of the invention, the corrosion protection layer extends from the shoulder by at least 1 mm toward the end of the spark plug housing facing away from the combustion chamber. This ensures that the corrosion protection layer extends sufficiently far along the inside of the spark plug housing to prevent corrosion directly at the inner sealing point on the shoulder.

[0012] It has proven particularly advantageous if the corrosion protection layer has an average thickness D of at least 2 µm, in particular along the circumference of the section and / or along the longitudinal extent of the section. The thickness D is measured perpendicular to the inside of the spark plug housing. It has been shown that with a layer thickness of less than 2 µm, possible defects in the corrosion protection layer can extend from the surface of the corrosion protection layer through the layer to the spark plug housing and thus form possible corrosion paths to the spark plug housing surface. With a layer thickness of at least 2 µm, the probability of such corrosion paths is sufficiently low for the corrosion protection layer to have an adequate protective function.

[0013] Furthermore, it is also according to the invention that the corrosion protection layer has a uniform thickness, with no more than a 10% difference between the thickest and thinnest points. This prevents the formation of a point that is significantly thinner than the remaining corrosion protection layer. In a thinner point, the probability of corrosion paths leading from the surface of the corrosion protection layer to the housing is higher than in the remaining corrosion protection layer. The thinner point is therefore a weak point and can prevent the intended technical effect of the invention from occurring.

[0014] In one design, the spark plug housing only has the corrosion layer on its inside. This simplifies production and reduces production costs for a spark plug housing with good corrosion protection.

[0015] In an alternative design of the spark plug housing, the spark plug housing comprises additional layers in addition to the corrosion protection layer, in particular one or more intermediate layers and / or a sealing layer. The corrosion protection layer, the intermediate layers, and the sealing layer form a layer system, i.e., the various layers are stacked on top of each other. This makes it possible to provide a particularly robust layer system for corrosion protection of the spark plug housing, which is particularly required for spark plug applications under extreme combustion conditions.

[0016] Furthermore, the invention also relates to a spark plug comprising a spark plug housing according to the invention, a spark plug insulator arranged in the spark plug housing, a center electrode arranged in the spark plug insulator and a ground electrode arranged at the end of the spark plug housing facing the combustion chamber, wherein the ground electrode and the center electrode are designed to jointly form an ignition gap.

[0017] The advantageous technical effects described above also apply to this spark plug.

[0018] Furthermore, the invention also relates to a method for producing a spark plug housing according to the invention, in which at least one section on the inside of the spark plug housing is galvanically coated with a corrosion protection layer by placing a coating electrode inside the spark plug housing.

[0019] This results in the advantage that this electroplating process creates a very uniform corrosion protection layer on the inside of the spark plug housing, which also extends sufficiently far inside the spark plug housing. By placing the coating electrode inside the spark plug housing during the electroplating process, a very uniform electric field is created along the longitudinal axis of the spark plug housing for the section to be coated. This allows a very uniform corrosion protection layer to be applied to the inside of the spark plug housing.

[0020] Further features, possible applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing.

[0021] drawing Figure 1shows an example of a spark plug housing according to the invention Figure 2 shows a spark plug Description of the embodiment

[0022] In Figure 1 A spark plug housing 2 according to the invention is shown. The spark plug housing 2 has an inner side 24, an outer side 23, an end 21 facing the combustion chamber, and an end 22 facing away from the combustion chamber. A shoulder 25 is formed on the inner side 24 of the spark plug housing 2. This shoulder 25 is designed so that, in the case of a spark plug 1 with a spark plug insulator 3, this spark plug insulator 3 rests on the shoulder 25.

[0023] A corrosion protection layer 50 is applied to the surface of the spark plug housing inner side 24 in a section 55. The corrosion protection layer 50 extends from the end of the spark plug housing facing the combustion chamber up to at least 1 mm above the shoulder 25 and along the inner circumference of the spark plug housing inner side 24. In this example, the corrosion protection layer 50 is formed on a section 55 with a length of at least 4 mm parallel to the longitudinal axis of the spark plug housing 2. The corrosion protection layer 50 has a layer thickness D that is as uniform as possible along its circumference and along its longitudinal extent, averaging at least 2 µm, with the thickest and thinnest points of the corrosion protection layer differing by no more than 10%.

[0024] Preferably, the corrosion protection layer 50 has been applied by means of a galvanic coating process, wherein a coating electrode was arranged within the spark plug housing 2 for coating the spark plug housing inner side 24 with the corrosion protection layer 50.

[0025] The spark plug housing is typically made of carbon steel, such as C10 or C22.

[0026] Figure 2shows a spark plug 1 in a semi-sectional view. The spark plug 1 comprises a spark plug housing 2, which has an inner side 24, an outer side 23, an end 21 facing the combustion chamber, and an end 22 facing away from the combustion chamber. A spark plug insulator 3 is inserted into the spark plug housing 2. The spark plug housing 2 and the spark plug insulator 3 each have a bore along their longitudinal axis X. The longitudinal axis of the spark plug housing 2, the longitudinal axis of the spark plug insulator 3, and the longitudinal axis of the spark plug 1 coincide. A center electrode 4 is inserted into the spark plug insulator 3. Furthermore, a connecting bolt 8 with a connecting nut extends into the spark plug insulator 3, via which connecting bolt 8 the spark plug 1 can be electrically contacted with a voltage source (not shown here). The connecting bolt 8 with the connecting nut form the end of the spark plug 1 facing away from the combustion chamber.

[0027] A resistance element is located in the insulator 3 between the center electrode 4 and the connecting bolt 8. The resistance element electrically connects the center electrode 4 to the connecting bolt 8.

[0028] The insulator 3 rests with a shoulder on a circumferential shoulder 25 formed on the inner side 24 of the spark plug housing 2. To seal the air gap between the spark plug housing inner side 24 and the insulator 3, an inner seal is arranged between the insulator shoulder and the shoulder 25. This seal is plastically deformed when the spark plug insulator 3 is clamped into the spark plug housing 2, thereby sealing the air gap.

[0029] An electrically conductive ground electrode 5 is arranged on the spark plug housing 2 at its combustion chamber-side end 21. The ground electrode 5 and the center electrode 4 are arranged relative to one another in such a way that an ignition gap forms between them, where the ignition spark is generated.

Claims

1. Spark plug housing (2), comprising an inner side (24), an outer side (23) and a longitudinal axis, which extends from an end (21) of the spark plug housing (2) facing towards the combustion chamber to an end (22) of the spark plug housing (2) facing away from the combustion chamber, wherein the spark plug housing (2) has on its inner side (24) a peripheral shoulder (25), which is designed such that a spark-plug insulator (3) rests on it, wherein the spark plug housing (2) has on its inner side (24) a corrosion protection layer (50), which is formed on a section (55) of the inner side (24) of the spark plug housing (2), wherein the section (55) extends from the end (21) of the spark plug housing (2) facing towards the combustion chamber to at least beyond the shoulder (25) and along the inner circumference of the spark plug housing (2), wherein the corrosion protection layer (50) has a uniform thickness which differs by no more than 10% between the thickest point and the thinnest point, and wherein the corrosion protection layer (50) is a galvanically applied layer.

2. Spark plug housing (2) according to Claim 1, characterized in that the corrosion protection layer (50) contains nickel and / or zinc.

3. Spark plug housing (2) according to one of the preceding claims, characterized in that the corrosion protection layer (50) extends at least a further 1 mm from the shoulder (25) in the direction of the end (22) of the spark plug housing (2) facing away from the combustion chamber.

4. Spark plug housing (2) according to one of the preceding claims, characterized in that the corrosion protection layer (50) has on average a thickness D of at least 2 µm, in particular along the circumference of the section (55) and / or along the longitudinal extent of the section (55).

5. Spark plug housing (2) according to one of the preceding claims, characterized in that the spark plug housing (2) has on its inner side (24) only the corrosion layer (50).

6. Spark plug housing (2) according to one of Claims 1 to 4, characterized in that, in addition to the corrosion protection layer (50), the spark plug housing (2) also has further layers, in particular one or more intermediate layers and / or a sealing layer.

7. Spark plug (1), comprising a spark plug housing (2) according to one of the preceding Claims 1 to 6, a spark-plug insulator (3) arranged in the spark plug housing (2), a centre electrode (4) arranged in the spark-plug insulator (3), and an earth electrode (5), which is arranged at the end (21) of the spark plug housing (2) facing towards the combustion chamber, wherein the earth electrode (5) and the centre electrode (4) are designed so as to together form a spark gap.

8. Method for producing a spark plug housing (2) according to one of Claims 1 to 6, characterized in that at least a section (55) on the inner side (24) of the spark plug housing (2) in which a coating electrode is placed inside the spark plug housing (2) is galvanically coated with a corrosion protection layer (50).

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