SPARK PLUG WITH IMPROVED TIGHTNESS

Description

State of the art

[0001] The present invention relates to a spark plug with improved sealing between an insulator and a housing of the spark plug.

[0002] Spark plugs are known from the prior art in various designs. Due to the increasing demands of internal combustion engine manufacturers regarding engine downsizing, smaller spark plugs are also required. The trend here is moving away from spark plugs with an M14 external thread to spark plugs with an M10 or M8 external thread. However, this places increased demands on the spark plug in terms of robustness, gas tightness, and temperature resistance. DE 10 2014 223 752.1 discloses a spark plug which features an improved connection between the insulator and the housing. The insulator has a circumferential recess on its outer circumference, into which the housing engages. However, it would be desirable to have further improved solutions regarding the gas tightness and robustness of spark plugs.

[0003] Other spark plugs are known from US 2017 / 033538 A1, DE 10 2013 206 071 A1, US 2003 / 117052 A1, US 831 377 A and US 2012 / 0267995 A1. Disclosure of the invention

[0004] The spark plug according to the invention with the features of claim 1 has the advantage that reduced dimensions of the spark plug are possible and improved sealing of the spark plug between an insulator and a housing of the spark plug is possible. This is achieved according to the invention in that the spark plug has an insulator, a housing and a sealing disc which is arranged between the insulator and the housing of the spark plug. The sealing disc is deformable and the insulator has a shoulder running around its entire circumference, which is arcuate in section and against which the sealing disc rests. The shoulder has a radius R1 which lies in a range of 0.20 mm to 0.60 mm. The material of the sealing disc is selected such that the deformability of the insulator and the housing is less than the deformability of the sealing disc. This enables reliable deformation of the sealing disc during assembly.By choosing a small radius between 0.20 mm and 0.60 mm, an increased Hertzian surface pressure can be achieved during the assembly process.

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

[0006] A particularly high surface pressure can be achieved if the radius at the insulator's shoulder is directed outward. In other words, the radius is designed to be convex.

[0007] The radius is particularly preferably in a range from 0.30 mm to 0.50 mm and is particularly preferably 0.40 mm.

[0008] Preferably, the shoulder on the insulator has an arc length in the axial direction in a range of 20 mm to 26 mm, and the arc length is particularly preferably 23 mm. This measure also further increases the surface pressure between the joining partners.

[0009] Preferably, a Hertzian surface pressure of at least 4500 N / mm² is present between the insulator and the sealing disc, preferably at least 5000 N / mm². This allows even the higher pressures that occur, particularly in smaller internal combustion engines, to be reliably sealed.

[0010] Particularly preferably, the housing has a tapered region at a contact area for contact with the sealing disc. The tapered region on the housing is preferably conical. This ensures secure support of the sealing disc on the housing during joining, thus enabling high surface pressure during the joining process.

[0011] In order to ensure a particularly high level of tightness, the sealing disc makes full contact with the insulator when the heel is mounted.

[0012] As a result, the sealing disc lies along the entire arc length of the insulator's shoulder, so that a high level of tightness is possible, especially against high pressures.

[0013] Further preferably, the sealing disc, when mounted, completely contacts the contact area on the housing.

[0014] Preferably, the spark plug housing has an M10 external thread or an M12 external thread. drawing

[0015] A preferred embodiment of the invention will be described in detail below with reference to the accompanying drawings. In the drawing: Figure 1 is a schematic, partially sectioned view of a spark plug according to the invention, and Figure 2 is an enlarged sectional view of the spark plug in the region of a sealing disc between a housing and an insulator of the spark plug. Preferred embodiment of the invention

[0016] The following is based on the Figure 1 and 2 a spark plug 1 according to a preferred embodiment of the invention is described in detail.

[0017] As from Figure 1 As can be seen, the spark plug has an insulator 2 made of an electrically non-conductive material, in particular ceramic. Furthermore, the spark plug has a housing 3 made of a metal material. An external thread 10 is provided on the housing 3.

[0018] The spark plug 1 further comprises a center electrode 8 and a ground electrode 9. The reference numeral 6 denotes an outer sealing ring which seals the spark plug to a cylinder head or the like when it is mounted.

[0019] How to continue Figure 1As can be seen, at the end of the spark plug facing the combustion chamber, where the center electrode 8 and the ground electrode 9 are located, there is a gap 5 between the insulator 2 and the housing 3. High pressures can penetrate into the interior of the spark plug through the gap 5. To prevent this, a sealing disc 4 is arranged between the insulator 2 and the housing 3.

[0020] The sealing disc 4 is made of Figure 2 The sealing disc 4 is made of a deformable material that is more deformable than the material of the insulator and the material of the housing.

[0021] As in Figure 2 As shown, the insulator 2 has a shoulder 20 which is arcuate in cross-section. The shoulder 20 has a radius R1. The radius R1 lies in a range from 0.20 mm to 0.60 mm and is preferably 0.40 mm.

[0022] As from Figure 2As can be seen, in the axial direction XX of the spark plug, the shoulder 20 is arranged between a first wall surface 21 and a second wall surface 22. The first wall surface 21 is preferably cylindrical, and the second wall surface 22 is also preferably cylindrical.

[0023] A tapered region 30 is provided on the housing 3 at the level of the sealing disc 4. In this exemplary embodiment, the tapered region 30 is conical. An angle α of the conical region to a perpendicular Y to the axial direction XX is preferably approximately 115°.

[0024] As from Figure 2 As can be seen further, in the assembled state, the deformed sealing disc 4 lies completely against the curved shoulder 20. Furthermore, the deformed sealing disc 4 also lies completely against the conical surface 30 of the housing 3. The selection of the small radius R1 results in a very high Hertzian surface pressure of over 4500 N / mm 2 .

[0025] An arc length of the shoulder 20 between the first and second wall surfaces 21, 22 is preferably in a range of 20 mm to 26 mm and in this embodiment is 23 mm.

[0026] Thus, improved sealing of the spark plug between the insulator 2 and the housing 3 can be achieved by creating the conditions for increased Hertzian surface pressure between the joining partners, insulator 2, housing 3, and sealing disc 4. This prevents combustion chamber gases from entering the interior of the spark plug via the gap 5.

[0027] A relatively easily deformable material is used for the sealing disc 4. The material preferably also has a high thermal conductivity coefficient, allowing heat conduction from the housing 3 toward the insulator 2.

[0028] As from Figure 1As can be seen, the sealing disc 4 is provided in the axial direction XX of the spark plug 1 at the level of the external thread 10 on the housing 3, in particular at the end of the external thread 10, which lies in the direction towards the side of the spark plug facing away from the combustion chamber.

[0029] The external thread 10 has reduced dimensions and is preferably an M10 external thread or an M12 external thread.

Claims

1. Spark plug, comprising: - an insulator (2), - a housing (3), and - a sealing washer (4) which is arranged between the insulator (2) and the housing (3), - wherein the sealing washer (4) is deformable, - wherein the insulator (2) has an annularly encircling shoulder (20) which is arranged between a first wall surface (21) and a second wall surface (22) of the insulator (2), wherein the first wall surface (21) and the second wall surface (22) are parallel to a longitudinal axis (X) of the spark plug, - wherein the shoulder (20) is formed entirely in an arc shape in section and the sealing washer (4) bears on the shoulder, characterized in that the shoulder (20) has a radius (R1), which lies in a range of from 0.20 mm to 0.60 mm.

2. Spark plug according to Claim 1, wherein the radius (R1) is formed as a convex radius.

3. Spark plug according to either of the preceding claims, wherein the radius (R1) lies in a range of from 0.30 mm to 0.50 mm and in particular is 0.40 mm.

4. Spark plug according to any of the preceding claims, wherein the shoulder (20) has an arc length which lies in a range of from 20 mm to 26 mm and in particular is 23 mm.

5. Spark plug according to any of the preceding claims, wherein a surface pressure of at least 4500 N / mm2, preferably 5000 N / mm2, is present between the insulator (2) and the sealing washer (4).

6. Spark plug according to any of the preceding claims, wherein the housing (3) has a tapering region (30), in particular a conically tapering region, on a contact region for contact with the sealing washer (4).

7. Spark plug according to any of the preceding claims, wherein the sealing washer (4) makes full contact with the shoulder (20) on the insulator in the assembled state.

8. Spark plug according to Claim 6 or 7, wherein the sealing washer (4) makes full contact with the contact region (30) on the housing (3) in the assembled state.

9. Spark plug according to any of the preceding claims, wherein the housing (3) has an M10 external thread or an M12 external thread.