Spark plug with improved ground electrode

Abstract

The present invention relates to a spark plug, comprising: a center electrode (4), a ground electrode (5) and, a housing (2), wherein the housing (2) has a receiving opening (20) configured to receive the ground electrode (5), wherein a force-locking connection (11) is formed between the ground electrode (5) and the receiving opening (20) in the housing (2), wherein the ground electrode (5) has a cross-section that deviates from a circle, and wherein a cross-section of the receiving opening is different from a cross-section of the ground electrode (5), so that a free area (9) is formed between the ground electrode (5) and the receiving opening (20).

Description

State of the art

[0001] The present invention relates to a spark plug, in particular a pre-chamber spark plug, with an improved ground electrode and simplified manufacturability.

[0002] Spark plugs are known in various designs from the prior art. One problem with spark plugs lies in the attachment of a ground electrode to a spark plug housing. Until now, the ground electrode has been a cylindrical pin which is fixed into a hole in the housing by means of a press fit. Alternatively or additionally, the ground electrode can also be welded on. However, the process of pressing the ground electrode into the spark plug housing requires high forces which can lead to damage to the housing and / or the ground electrode itself, particularly if the ground electrode is incorrectly positioned. In particular, with relatively thin housings, deformation in one area of ​​the housing can occur due to the pressing in of the ground electrode.A defined gap must also be established between the ground electrode and a center electrode, which can be very difficult to achieve due to the press-fitting and / or welding process. DE 10 2020 211 583 A1 discloses a spark plug in which a blind hole is provided in the housing into which the ground electrode is pressed. The blind hole is intended to ensure a precise spark gap between the ground electrode and the center electrode. It would be desirable to have a simplified method for attaching a ground electrode to a spark plug housing. Disclosure of the invention

[0003] The spark plug according to the invention with the features of claim 1 has the advantage that a significantly simpler assembly of a ground electrode in a spark plug housing is possible. In particular, according to the invention, damage to the ground electrode or the spark plug housing can be avoided. In particular, the force required to insert the ground electrode into a receiving opening in the spark plug housing can be reduced. It is also particularly advantageous that an incorrectly positioned ground electrode, e.g., due to an inclination or the like, can be immediately identified during the fixing process, so that rapid correction is possible during the fixing process. This significantly reduces the proportion of spark plug rejects.

[0004] This is achieved according to the invention in that the spark plug comprises a center electrode and a ground electrode as well as a housing with a receiving opening. The receiving opening is designed to receive the ground electrode. A force-fitting connection is formed between the ground electrode and the receiving opening in the housing. Furthermore, the ground electrode has a cross-section that deviates from a circle. Furthermore, a cross-section of the receiving opening is different from a cross-section of the ground electrode. A force-fitting connection is thus formed between the ground electrode and the center electrode, wherein a cross-sectional shape of the ground electrode and the receiving opening are different. This results in a free area between the ground electrode and the receiving opening in the assembled state.

[0005] The subclaims show preferred developments of the invention.

[0006] Preferably, the receiving opening in the housing is a through-hole. This means that the receiving opening extends from an outer region of the housing to an inner region of the housing. This allows the ground electrode to be installed from the outside of the spark plug.

[0007] The receiving opening is preferably a cylinder and thus has a circular cross-section.

[0008] Preferably, a plurality of free spaces are formed between the ground electrode and the receiving opening. Particularly preferably, the free spaces are all formed with the same cross-section. This is preferably achieved by the receiving opening being cylindrical and an outer periphery of the ground electrode having a uniform shape that deviates from a circular shape.

[0009] Preferably, the ground electrode has a cross-section with a substantially meandering circumferential edge. This results in a cross-sectional circumference with peaks and valleys extending from a circular radius at the valleys of the meandering circumferential edge. Preferably, six peaks and six valleys are provided.

[0010] More preferably, the ground electrode has a star-shaped cross-section with a plurality of prongs, in particular triangular prongs. The prongs are preferably configured such that linear contact areas are formed between the ground electrode and the receiving opening between a tip of the prongs and an inner surface area of ​​the receiving opening.

[0011] The prongs of the ground electrode are preferably formed such that a cross-sectional area of ​​a free area corresponds exactly to a cross-sectional area of ​​a prong.

[0012] Further preferably, the ground electrode is provided with a cross-section configured as a constant thickness. A constant thickness is a cross-section that, starting from a center point, has an equal distance to each edge region of the ground electrode. The constant thickness is preferably a Reuleaux triangle.

[0013] According to a further preferred embodiment of the invention, the ground electrode has a cross-section with several flattened portions. The flattened portions of the ground electrode create edges, with the frictional connection between the ground electrode and the receiving opening being formed at the edges. The flattened portions preferably have the same width.

[0014] In particular, the ground electrode is formed with a square cross-section or an octagonal cross-section or three flats and three circular arcs.

[0015] The spark plug is further preferably a pre-chamber spark plug.

[0016] Further preferably, the spark plug has a plurality of ground electrodes, all of which are identically designed. Short description of the drawings

[0017] Embodiments of the invention will now be described in detail with reference to the accompanying drawings. In the drawing: Fig. 1 is a schematic partial sectional view of a spark plug according to a first embodiment, Fig. 2 a schematic representation of a fixing of a ground electrode to a housing of the spark plug of Fig. 1, Fig. 3 a schematic cross-section of a receiving opening of the housing of the spark plug of Fig. 1 fixed ground electrode, Fig. 4 a schematic perspective view of the ground electrode of Fig. 1 and Fig. 5 to 11 schematic sectional views of further preferred embodiments of the ground electrode in the mounted state in a housing. Preferred embodiments of the invention

[0018] The following is based on the Fig. 1 to 4 a spark plug 1 according to a preferred embodiment of the invention is described in detail.

[0019] The spark plug 1 is, as in Fig. 1, a prechamber spark plug with a metallic housing 2 and an insulator 3. Furthermore, the spark plug comprises a center electrode 4, which lies in a center axis XX of the spark plug, and at least one laterally positioned ground electrode 5.

[0020] An external thread 21 is formed on the housing 2, which is designed to screw the spark plug into a cylinder head of an internal combustion engine. The spark plug 1, designed as a prechamber spark plug, further comprises a cap 6, which, together with a portion of the housing, defines a prechamber 16 of the spark plug. The center electrode 4 and the ground electrode 5 are arranged in the prechamber 16.

[0021] The cap 6 has a plurality of overflow openings 7, 8. The overflow openings 7, 8 enable a fluid connection between the prechamber 16 and a combustion chamber 10 of an internal combustion engine.

[0022] As is particularly evident from Fig. 2, the housing 2 has a receiving opening 20 for the ground electrode 5.

[0023] A force-locking connection 11 is formed between the ground electrode 5 and the receiving opening 20. As can be seen in particular from Fig. As can be seen in Figure 3, the ground electrode 5 has a cross-section that deviates from a circular one. The cross-section of the receiving opening 20 deviates from a cross-section of the ground electrode 5. The receiving opening 20 has a cylindrical cross-section.

[0024] Thus, in the assembled state, as shown in Fig. 3, free areas 9 are present between the ground electrode 5 and the receiving opening 20. The ground electrode 5 of the first embodiment is of uniform thickness, which, starting from a center point M, has an equal distance to each circumferential point of the ground electrode. The ground electrode 5 of the first embodiment thus has three contact areas 50, which are formed like edges. Arc-shaped free areas 51 are provided between each contact area 50.

[0025] As from Fig. 2, the receiving opening 20 is designed as a through-opening in the housing 2. Due to the cylindrical cross section of the receiving opening 20, which deviates from the cross section of the ground electrode 5, a significantly reduced assembly force F is now required when mounting the ground electrode 5 in the receiving opening 20 (cf. Fig. 2) is necessary. Since during assembly, as soon as the ground electrode 5 is inserted into the receiving opening 20, the free areas 9 are immediately visible in a top view, it is possible to immediately recognize during assembly of the ground electrode 5 based on the different cross sections of the free areas 9 if the ground electrode 5 is not positioned correctly. This is particularly possible before the force F is applied for assembly by simply placing the ground electrode 5 against the receiving opening 20 and checking the free areas 9. This enables rapid intervention in the event of incorrect positioning during assembly, so that the proportion of rejects due to incorrectly mounted ground electrodes can be significantly reduced.

[0026] Furthermore, the reduced assembly force F can prevent damage during assembly of the ground electrode 5 in the receiving opening 20, for example bending of the housing 2 during assembly, since the assembly force F is significantly smaller than in the prior art, in which a cylindrical ground electrode is force-fitted into a cylindrical receiving opening.

[0027] Thus, according to the invention, the size of the surfaces of the force-locking connection between the ground electrode 5 and the receiving opening 20 can be significantly reduced, while nevertheless achieving a sufficiently strong connection between the ground electrode 5 and the receiving opening 20.

[0028] The Fig. Figures 5 to 11 show further preferred embodiments of ground electrodes 5 for spark plugs according to the invention. Identical or functionally identical parts are designated by the same reference numerals.

[0029] Fig. Figure 5 shows a spark plug with a ground electrode 5 according to a second embodiment of the invention. The ground electrode 5 of the second embodiment has a meandering peripheral edge with alternating peaks and valleys. The free areas 9 are provided between the ground electrode 5 and the housing 2 in the region of the valleys. The peaks and valleys are provided such that the cross-sections of the free areas 9 are each of the same size.

[0030] When in Fig. In the third embodiment shown in Figure 6, the ground electrode 5 has a star-shaped cross-section with a plurality of triangular prongs 52. The pointed end regions of the prongs form the contact area. In the assembled state, a linear, force-locking connection is thus formed at each end of a prong. A cross-section of the free areas 9 is shown in the embodiment shown in Fig. 6 is the same size as a cross section of a prong 52.

[0031] The Fig. 7 and Fig. 8 show a third and a fourth embodiment of the invention, which essentially correspond to the third embodiment. In the Fig. In the embodiment shown in Fig. 7, a number of teeth 52 is compared to the Fig. 6 significantly increased. Fig. 8 shows an embodiment which has an even larger number of prongs 52.

[0032] Fig. Figure 9 shows a sixth embodiment of the invention, wherein the ground electrode 5 has flattened portions 53. In Fig. 9, the ground electrode 5 has eight flattened portions 53. This results in eight linear contact areas 50. Free areas 9 are formed between the flattened portions 53 and the receiving opening 20 (cf. Fig. 9).

[0033] Fig. Figure 10 shows a seventh embodiment of the invention, which has four flattened portions 53. The flattened portions are selected such that contact areas 50, which are non-positively fixed in the receiving opening 20, are arcuate. It should be noted that instead of the arcuate contact areas 50, flattened portions can also be formed on the contact areas, resulting in two edge-shaped, non-positive connections per contact area.

[0034] Fig. 11 shows an eighth embodiment of the invention, which has three flattened portions 53 and three curved portions 54. The curved portions 54 are designed as a force-locking connection 11 to the receiving opening 20.

[0035] Compared to the prior art, all of the described embodiments have the advantage of reduced assembly force, thus preventing damage to the ground electrode and / or the housing during assembly. By detecting the free areas 9, incorrect assembly can also be detected directly during the assembly process. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 211 583 A1

[0002]

Claims

[1] Spark plug, comprising: - a central electrode (4), - a ground electrode (5) and, - a housing (2), wherein the housing (2) has a receiving opening (20) adapted to receive the ground electrode (5), - wherein a force-locking connection (11) is formed between the ground electrode (5) and the receiving opening (20) in the housing (2), - wherein the ground electrode (5) has a cross-section other than a circle, and - wherein a cross section of the receiving opening (20) is different from a cross section of the ground electrode (5), so that a free area (9) is formed between the ground electrode (5) and the receiving opening (20). [2] Spark plug according to claim 1, wherein the receiving opening (20) in the housing is a through opening. [3] Spark plug according to one of the preceding claims, wherein the receiving opening (20) has a circular cross-section. [4] Spark plug according to one of the preceding claims, wherein a plurality of free areas (9) are formed between the ground electrode (5) and the receiving opening (20). [5] Spark plug according to one of the preceding claims, wherein the ground electrode has a cross-section with a meandering peripheral edge. [6] Spark plug according to one of claims 1 to 4, wherein the ground electrode (5) has a star-shaped cross section with a plurality of prongs (52). [7] Spark plug according to claim 6, wherein a cross-sectional area of ​​the prongs of the ground electrode is equal to a cross-sectional area of ​​the free areas (9). [8] Spark plug according to one of claims 1 to 4, wherein a cross section of the ground electrode (5) is a uniform thickness. [9] Spark plug according to one of claims 1 to 4, wherein a cross section of the ground electrode (5) has a plurality of flattenings (53). [10] Spark plug according to claim 9, wherein the cross section of the ground electrode (5) has four flats or eight flats or three flats and three arcuate contact areas. [11] Spark plug according to one of the preceding claims, wherein the spark plug is a pre-chamber spark plug.

Images