Spark plug for an internal combustion engine

Abstract

Spark plug (10) for an internal combustion engine, with a central electrode (11) comprising a first body (14) made of an electrode base material and a second body (15) made of a precious metal, which is welded to the first body (14), with a mass electrode (12) arranged radially around the central electrode (11), with an ignition gap (13) formed between the center electrode (11) and the ground electrode (12) for igniting a fuel mixture via an electrical ignition spark formed between the center electrode (11) and the ground electrode (12), wherein the second body (15) of the center electrode (11) is designed as an annular element with a central recess (17), wherein the first body (14) of the central electrode (11) comprises a base body (14a) and a projection (14b) extending into the recess (17) of the second body (15), wherein a first weld (18) is formed between a radially outer surface (20) of the projection (14b) of the first body (14) and a radially inner surface (21) of the second body (15) which defines the recess (17) of the second body (15), characterized by the fact that the ignition gap (13) between the center electrode (11) and the ground electrode (12) is annular in shape, a second weld (19) is formed between an axial surface (24) of the base body (14a) of the first body (14) and an axial surface (25) of the second body (15).

Description

[0001] The invention relates to a spark plug for an internal combustion engine according to the preamble of claim 1.

[0002] Spark plugs are used for the electrical ignition of a fuel mixture to be burned in an internal combustion engine. Between a so-called center electrode and a so-called ground electrode of a spark plug, an ignition gap is formed in which an electrical ignition spark can form to ignite the fuel mixture.

[0003] When it comes to spark plugs, a basic distinction is made between spark plugs with a hook-shaped ground electrode and spark plugs with a ring-shaped ground electrode.

[0004] For example, DE 10 2011 077 279 A1 shows a spark plug whose ground electrode is hook-shaped, with the ignition gap extending axially between one end of the center electrode and one end of the hook-shaped ground electrode, as seen in the axial direction of the center electrode. JP H05 - 159 858 A discloses another spark plug whose ground electrode is hook-shaped.

[0005] A spark plug with an annular ground electrode is known from DE 10 2012 208 069 A1, in which the ignition gap between the center electrode and the ground electrode extends radially around the center electrode. The present invention relates to a spark plug with an annular ground electrode, i.e., an ignition gap extending radially around the center electrode.

[0006] JP H08 - 45 643 A discloses a spark plug for an internal combustion engine according to the preamble of claim 1.

[0007] US 2007 / 0 069 618 A1 and JP 2014 - 220 135 A disclose further prior art.

[0008] It is known from practice that a ground electrode is composed of two bodies, namely a first body made of an electrode base material and a second body made of a precious metal, the two bodies being welded together.

[0009] With spark plugs known from practice, there is a risk that the two bodies of the center electrode could separate from each other, and the second body, made of precious metal, could enter the combustion chamber of the cylinder surrounding the spark plug and potentially be expelled from the combustion chamber into the exhaust system of the internal combustion engine. This could cause damage to the internal combustion engine.

[0010] There is therefore a need for a spark plug that reduces the risk of the center electrode bodies separating from each other.

[0011] Based on this, the invention is based on the object of creating a novel spark plug for an internal combustion engine.

[0012] This object is achieved by a spark plug according to claim 1.

[0013] The inventive design of the spark plug's center electrode, consisting of the first body with the projection and the second body formed as an annular element, as well as the connection of these two bodies via the two weld seams, significantly reduces the risk of the second body separating from the first body and causing damage to the internal combustion engine. The two weld seams increase the welding surface and can be reliably formed with a simple weld.

[0014] According to an advantageous development of the invention, the first weld seam extends from an end face of the center electrode into the center electrode, viewed in the axial direction. The second weld seam extends from a circumferential surface of the center electrode into the center electrode, viewed in the radial direction. This orientation of the two weld seams particularly advantageously increases the available welding area and allows for reliable formation of the two weld seams.

[0015] Preferably, the diameter d of the projection and the axial extension h of the projection are dimensioned such that d:58h. This feature also serves to increase the available welding area.

[0016] Preferably, a material recess is formed in an end face of the projection of the first body. The material recess can provide stress relief in the welding zone, thereby reducing the risk of the welded joint between the two bodies of the center electrode, which are made of different materials and therefore have different thermal expansion coefficients, becoming loose.

[0017] Preferred developments of the invention will become apparent from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1: a schematic representation of a spark plug according to the invention.

[0018] The present invention relates to a spark plug for an internal combustion engine, in particular for a gasoline engine, which serves to ignite a fuel mixture to be burned in the internal combustion engine.

[0019] Fig. 1 shows a schematic section of a spark plug 10 in the region of a center electrode 11 and a ground electrode 12 arranged radially around the center electrode 11. Between the center electrode 11 and the ground electrode 12, an annular ignition gap 13 in the form of an annular gap or a segmented annular gap is formed, which is provided for igniting a fuel mixture via an electrical ignition spark forming between the center electrode 11 and the ground electrode 12.

[0020] The center electrode 11 consists of a first body 14 and a second body 15, which are joined together by welding. The first body 14 consists of an electrode base material. The second body 15 consists of a precious metal.

[0021] In order to ensure a good connection between the two bodies 14, 15 of the center electrode 11 and to reduce the risk of the second body 15 made of the precious metal becoming detached from the first body 14 made of the electrode base material, the invention provides that the first body 14 of the center electrode 11 has a base body 14a and a projection 14b protruding relative to the base body 14a in the axial direction A. The second body 15 is designed as an annular element with a central recess 17 into which the projection 14b of the first body 14 extends.

[0022] Two weld seams 18, 19 are formed to connect the second body 15 and the first body 14. A first weld seam 18 is formed between a radially outer surface 20 of the projection 14b of the first body 14 and a radially inner surface 21 of the second body 15, which delimits the recess 17 of the second body 15. This first weld seam 18 extends, as seen in the axial direction A, from an end face 22 of the center electrode 11 into the center electrode, wherein a penetration depth of the first weld seam 18 into the center electrode 11 corresponds approximately to the axial length h of the projection 14b of the first body 14.

[0023] The second weld seam 19 is formed between an axial surface 24 of the base body 14a of the first body 14 and an adjacent axial surface 25 of the second body 15. This second weld seam 19 extends from a circumferential surface 23 of the center electrode 11 into the center electrode 11, wherein the penetration depth of the second weld seam 19 corresponds to the radial distance between the circumferential surface 23 of the center electrode 11 and the projection 14b of the first body 14.

[0024] The first weld seam 18 extending in the axial direction into the center electrode 11 and circumferentially encircling the surfaces 20, 21 is offset by approximately 90° or by 90° to the second weld seam 19 formed between the axial surfaces 24 and 25 and extending in the radial direction into the center electrode 11.

[0025] Preferably, the projection 14b of the first body 14 and thus the recess 17 of the second body 15 are contoured such that a diameter d of the projection 14b and the axial length h of the projection 14b have the following relationship: d:58h.

[0026] It is particularly preferred that a material recess 16 is introduced into the end face of the projection 14b, which extends in the plane of the end face 22 of the center electrode 11, which material recess is preferably parabolically contoured.

[0027] For the center electrode 11 of the spark plug 10 according to the invention, there is a reduced risk that the second body 15 of the center electrode 11 made of precious metal will unintentionally detach from the first body 14 of the center electrode 11 made of the electrode base material.

[0028] The weld seams 17, 18 each have a relatively low penetration depth, but in combination they provide a large available welding surface that can be reliably formed.

[0029] The optional material recess 16 can be used to reduce stresses in the welding zone, thereby reducing the risk of failure of the weld joint.

[0030] A further advantage of the spark plug 10 is that the recess 17 in the second body 15 of the center electrode 11 requires less precious metal. This reduces the manufacturing costs of the spark plug 10. List of reference symbols 10 Spark plug 11 Center electrode 12 Ground electrode 13 Ignition gap 14 first body 14a Base body 14b projection 15 second body 16 Material recess 17 Recess 18 first weld 19 second weld 20 radial outer surface 21 radial inner surface 22 Frontal surface 23 Circumferential surface 24 Axial surface 25 axial surface

Claims

[1] Spark plug (10) for an internal combustion engine, with a central electrode (11) comprising a first body (14) made of an electrode base material and a second body (15) made of a precious metal, which is welded to the first body (14), with a ground electrode (12) arranged radially around the center electrode (11), with an ignition gap (13) formed between the center electrode (11) and the ground electrode (12) for igniting a fuel mixture via an electrical ignition spark formed between the center electrode (11) and the ground electrode (12), wherein the second body (15) of the center electrode (11) is designed as an annular element with a central recess (17), wherein the first body (14) of the center electrode (11) comprises a base body (14a) and a projection (14b) extending into the recess (17) of the second body (15), wherein a first weld seam (18) is formed between a radially outer surface (20) of the projection (14b) of the first body (14) and a radially inner surface (21) of the second body (15) delimiting the recess (17) of the second body (15), characterized by , that the ignition gap (13) between the center electrode (11) and the ground electrode (12) is annular, a second weld seam (19) is formed between an axial surface (24) of the base body (14a) of the first body (14) and an axial surface (25) of the second body (15). [2] Spark plug according to claim 1, characterized by that the first weld seam (18) and the second weld seam (19) are offset by approximately 90° or 90° to each other. [3] Spark plug according to claim 1 or 2, characterized by that the first weld seam (18) extends from an end face (22) of the center electrode (11) into the center electrode (11) when viewed in the axial direction. [4] Spark plug according to claim 2, characterized by that a penetration depth of the first weld seam (18) corresponds to the axial length (h) of the projection (14b) of the first body (14). [5] Spark plug according to one of claims 1 to 4, characterized by that the second weld seam (19) extends from a circumferential surface (23) of the center electrode (11) into the same, viewed in the radial direction. [6] Spark plug according to claim 5, characterized by that a penetration depth of the second weld seam (19) corresponds to the radial distance between the circumferential surface (23) of the center electrode (11) and the projection (14b) of the first body (14). [7] Spark plug according to one of claims 1 to 6, characterized by that a material recess (16) is introduced into an end face of the projection (14b) of the first body (14). [8] Spark plug according to claim 7, characterized by that the material recess (16) is parabolically contoured. [9] Spark plug according to one of claims 1 to 6, characterized by that the diameter d of the projection (14b) and the axial length (h) of the projection (14b) are dimensioned such that: d:58h.

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