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 noble metal, which is connected to the first body (14), with a ground electrode (12) arranged radially around the center electrode (11), with an annular 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 the second body (15) is held in a form-fitting manner on the first body (14) via an undercut formed in the region of the projection (14b) of the first body (14) between the first body (14) and the second body (15), characterized in that the recess (17) in the second body (15) is funnel-shaped or has a conical cross-section, converging from an axial surface (26) of the second body (15), which defines a section of an end face (22) of the center electrode (11), in the direction of an axial surface (25) of the second body (15), which is opposite an axial surface (24) of the base body (14a).

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 to electrically ignite 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, wherein the ignition gap extends 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.

[0005] A spark plug with an annular ground electrode is known from DE 10 2012 208 069 A1, wherein 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] It is known from practice that a center 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 connected to one another, in particular welded.

[0007] 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.

[0008] DE 197 05 372 A1 discloses a spark plug for an internal combustion engine according to the preamble of claim 1.

[0009] US 5 557 158 A, JP 2001 - 185 323 A and JP 2001 - 43 955 A disclose further prior art.

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

[0012] According to the invention, the recess in the second body is funnel-shaped or has a conical cross-section, specifically converging from an axial surface of the second body, which partially defines an end face of the center electrode, towards an axial surface of the second body that lies opposite an axial surface of the base body. The projection of the first body is frustoconical or has a conical cross-section, specifically diverging from the axial surface of the base body of the first body towards an axial surface of the projection of the first body, which partially defines the end face of the center electrode. This allows the mechanical undercut to be provided particularly simply and advantageously in order to hold the second body in a form-fitting manner on the first body of the center electrode.

[0013] If a welded joint formed between these two bodies fails, the second body can be securely held to the first body. The risk of damage to the internal combustion engine is minimized.

[0014] Preferably, the projection of the first body is formed by deformation within the recess in the second body. This allows the undercut to be provided particularly easily.

[0015] Preferably, a first weld seam is formed between an axial surface of the base body of the first body and an axial surface of the second body, which preferably extends from a circumferential surface of the center electrode into the center electrode, viewed in the radial direction.

[0016] Preferably, a material recess is formed in the axial surface of the projection of the first body, which partially defines the end face of the center electrode. The material recess can provide stress reduction in the area of ​​the weld seams, thereby reducing the risk of weld seam failure.

[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 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 preferably 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 from 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. The second body 15 is held in a form-fitting manner on the first body 14 via an undercut formed in the region of the projection 14b of the first body 14 between the first body 14 and the second body 15.Should a welded joint, which will be discussed later and which is formed between the two bodies 14, 15, fail, the second body 15 is still held captive to the first body 14 by the mechanical undercut.

[0022] To provide the mechanical undercut between the two bodies 14, 15 of the center electrode 11, the recess 17 in the second body 15 is funnel-shaped or conically contoured in cross-section. The recess 15 in the second body 15 is conically contoured in such a way that the recess 17 converges, namely, starting from an axial surface 26 of the second body 15, which partially defines an end face 22 of the center electrode 11, in the direction of an axial surface 25 of the second body 15, which lies opposite an axial surface 24 of the base body 14a of the center electrode 11.

[0023] The projection 14b of the first body 14, which extends into this recess 17 in the second body 15 of the central electrode 11, has a truncated cone-shaped or conical contour in cross-section, in such a way that it diverges, namely starting from the axial surface 24 of the base body 14a of the first body 14 of the central electrode 11 in the direction of an axial surface 27 of the projection 14b of the body 15, which together with the axial surface 26 of the second body 15 defines the end face 22 of the central electrode 11.

[0024] The projection 14b of the first body 14, which together with the recess 17 of the second body 15 forms the mechanical undercut, is formed by deformation within the recess 17. Thus, Fig.1 shows, in dashed lines, a cylindrical projection 14b' of the first body 14 of the center electrode 11, which extends into the recess 17 in the second body 15 of the center electrode 11 and projects in the axial direction A relative to the axial surface 26 of the second body 15, which partially defines the end face 22 of the center electrode 11. In the radial direction, there is a significant clearance between this cylindrical projection 14b' and the conically contoured recess 17 of the second body 15.

[0025] By reshaping the cylindrical projection 14b', namely by plastically deforming it, it can be converted into the frustoconical or conically contoured design in cross-section, namely by forming the projection 14b, which together with the recess 17 in the second body 15 provides the mechanical undercut for the positive fixing of the second body 15 to the first body 14.

[0026] For additional material connection of the second body 15 and the first body 14, two weld seams 18, 19 are preferably formed.

[0027] A weld seam 18 is formed between a radially outer, frustoconically contoured surface 20 of the projection 14b of the first body 14 and a radially inner, funnel-shaped contoured surface 21 of the second body 15, which delimits the recess 17 of the second body 15. This weld seam 18 extends, as seen in the axial direction A, from the end face 22 of the center electrode 11 into the center electrode, wherein a penetration depth of this weld seam 18 into the center electrode 11 corresponds approximately to the axial length h of the deformed projection 14b of the first body 14.

[0028] A weld seam 19 is formed between the axial surface 24 of the base body 14a of the first body 14 and the adjacent axial surface 25 of the second body 15. This weld seam 19 extends from a circumferential surface 23 of the center electrode 11 into the center electrode 11, the penetration depth of this weld seam 19 corresponding to the radial distance between the circumferential surface 23 of the center electrode 11 and the projection 14b of the first body 14.

[0029] The weld seams 18, 19 each have a relatively small penetration depth, but in combination they provide a large available welding surface that can be reliably formed.

[0030] If only one weld seam is present, weld seam 19 is preferably present.

[0031] Particularly preferably, a material recess 16, preferably with a parabolic contour, is introduced into the axial surface 27 of the projection 14b of the first body 14, which partially defines the end face 22 of the center electrode 11. The optional material recess 16 can reduce stresses in the welding zone, thereby reducing the risk of failure of the welded joint.

[0032] 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. 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, 14b' ledge 15 second body 16 Material recess 17 Recess 18 second weld 19 first weld 20 radial outer surface 21 radial inner surface 22 Frontal surface 23 Circumferential surface 24 Axial surface 25 axial surface 26 Axial surface 27 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 noble metal, which is connected to the first body (14), with a ground electrode (12) arranged radially around the center electrode (11), with an annular 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 the second body (15) is held in a form-fitting manner on the first body (14) via an undercut formed in the region of the projection (14b) of the first body (14) between the first body (14) and the second body (15), characterized by , that the recess (17) in the second body (15) is funnel-shaped or has a conical cross-section, converging from an axial surface (26) of the second body (15), which defines a section of an end face (22) of the center electrode (11), in the direction of an axial surface (25) of the second body (15), which is opposite an axial surface (24) of the base body (14a). [2] Spark plug according to claim 1, characterized bythat the projection (14b) of the first body (14) is frustoconical or conically contoured in cross-section, diverging from an axial surface (24) of the base body (14a) of the first body (14) in the direction of an axial surface (27) of the projection (14b) of the first body (14), which defines an end face (22) of the central electrode (11) in sections. [3] Spark plug according to claim 1 or 2, characterized by that the projection (14b) of the first body (14) is formed by deformation within the recess (17) in the second body (15). [4] Spark plug according to one of claims 1 to 4, characterized by that a first 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), which, viewed preferably in the radial direction, extends from a circumferential surface (23) of the central electrode (11) into the same. [5] Spark plug according to claim 4, characterized by that a penetration depth of the first 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). [6] Spark plug according to one of claims 2 to 5, characterized by that a material recess (16) is introduced into the axial surface (27) of the projection (14b) of the first body (14), which defines the end face (22) of the center electrode (11) in sections. [7] Spark plug according to claim 6, characterized by that the material recess (16) is parabolically contoured.

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