Spark plug with improved tightness

Abstract

A spark plug includes an insulator, a housing, and a deformable sealing washer disposed between the insulator and the housing, the insulator having an annular full-perimeter shoulder against which the sealing washer rests, and the shoulder having a radius in a range of between 0.20 mm and 0.60 mm.

Claims

1. A spark plug, comprising: an insulator that includes an annular full-perimeter shoulder having a radius that is in a range of 0.20 mm to 0.60 mm, wherein the shoulder is arc-shaped throughout a majority length of the shoulder; a housing; and a deformable sealing washer resting against the shoulder of the insulator and situated between the insulator and the housing.

2. The spark plug of claim 1, wherein the radius is convex.

3. The spark plug of claim 1, wherein the range is 0.30 mm to 0.50 mm.

4. The spark plug of claim 1, wherein the radius is 0.40 mm.

5. The spark plug of claim 1, wherein the shoulder has an arc length in a range of 20 mm to 26 mm.

6. The spark plug of claim 1, wherein the shoulder has an arc length of 23 mm.

7. The spark plug of claim 1, wherein a surface pressure between the insulator and the sealing washer is at least 4500 N/mm.sup.2.

8. The spark plug of claim 1, wherein a surface pressure between the insulator and the sealing washer is at least 5000 N/mm.sup.2.

9. The spark plug of claim 1, wherein the housing has a section that tapers at a contact area at which the housing contacts the sealing washer.

10. The spark plug of claim 9, wherein in the assembled state, the sealing washer completely contacts the contact area of the housing.

11. The spark plug of claim 1, wherein the housing has a section that conically tapers at a contact area at which the housing contacts the sealing washer.

12. The spark plug of claim 1, wherein in an assembled state, the sealing washer completely contacts the shoulder of the insulator.

13. The spark plug of claim 12, wherein the housing has a section that tapers at a contact area at which the housing contacts the sealing washer, and, in the assembled state, the sealing washer completely contacts the contact area of the housing.

14. The spark plug of claim 1, wherein the housing has an M10 external thread or an M12 external thread.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic, partial cutaway view of a spark plug according to an example embodiment of the present invention.

(2) FIG. 2 shows an enlarged sectional view of the spark plug in the area of a sealing washer between a housing and an insulator of the spark plug according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(3) In the following, a spark plug 1 according to a preferred exemplary embodiment of the invention is described in detail, with reference to FIGS. 1 and 2. As shown in FIG. 1, spark plug 1 has an insulator 2 made of an electrically nonconductive material, particularly ceramic. Spark plug 1 also has a housing 3 made of a metal material. An external thread 10 is provided on housing 3.

(4) In addition, spark plug 1 includes a center electrode 8 and a ground electrode 9. In the assembled state of spark plug 1, outer sealing ring 6 fits tightly against a cylinder head or the like.

(5) As also evident from FIG. 1, at the end of spark plug 1, which is directed toward the combustion chamber and at which center electrode 8 and ground electrode 9 are located, a gap 5 exists between insulator 2 and housing 3. High pressures are able to get into the interior of spark plug 1 via gap 5. To prevent this, a sealing washer 4 is disposed between insulator 2 and housing 3.

(6) Sealing washer 4 can be seen in detail in FIG. 2. Sealing washer 4 is made of a deformable material which exhibits higher deformability than the material of the insulator and the material of the housing.

(7) As shown in FIG. 2, insulator 2 has a shoulder 20 which is arc-shaped in section. Shoulder 20 has a radius R1. Radius R1 lies in a range from 0.20 mm to 0.60 mm, and preferably amounts to 0.40 mm.

(8) As can be seen in FIG. 2, shoulder 20 is located between a first wall area 21 and a second wall area 22 in axial direction X-X of the spark plug. First wall area 21 is preferably cylindrical, and second wall area 22 is likewise preferably cylindrical.

(9) A tapering section 30 is provided on housing 3 at the level of sealing washer 4. In this exemplary embodiment, tapering section 30 is conical. An angle of the conical section to a perpendicular Y to axial direction X-X is preferably approximately 115.

(10) As also apparent from FIG. 2, in the assembled state, deformed sealing washer 4 rests completely against arc-shaped shoulder 20. In addition, deformed sealing washer 4 likewise rests completely against conical surface 30 of housing 3. Due to the selection of small radius R1, a very high Hertzian surface pressure of over 4500 N/mm.sup.2 is obtained in this case.

(11) An arc length of shoulder 20 between first and second wall areas 21, 22 lies preferably in a range from 20 mm to 26 mm, and in this exemplary embodiment, amounts to 23 mm.

(12) Thus, tightness of the spark plug between insulator 2 and housing 3 can be improved by achieving the conditions for an increased Hertzian surface pressure between the members being joinedinsulator 2, housing 3, and sealing washer 4. Combustion-chamber gases can thereby be prevented from getting into the interior of the spark plug via gap 5.

(13) A relatively easily deformable material is used as material for sealing washer 4. Preferably, the material also has a high coefficient of thermal conduction, so that heat is able to be conducted from housing 3 in the direction of insulator 2.

(14) As can be seen in FIG. 1, sealing washer 4 is provided in axial direction X-X of spark plug 1 at the level of external thread 10 on housing 3, particularly at the end of external thread 10 that lies in the direction toward the side of spark plug 1 facing away from the combustion chamber.

(15) External thread 10 has reduced dimensions and is preferably an M10 external thread or an M12 external thread.