THERMALLY OPTIMIZED PRECHAMBER SPARK PLUG

Abstract

A prechamber spark plug, including center and ground electrodes, a housing having an external thread, a cap arranged on the housing and together with the housing defines a prechamber, and an insulator which electrically insulates the center electrode from the housing. The external thread has a thread length in the axial direction. The housing is fastened to the insulator at first and second fixing regions so that a first clamping force at the first fixing region acts from the housing on the insulator, and a second clamping force at the second fixing region acts from the housing on the insulator. The first and second clamping forces are directed in opposite directions to one another in the axial direction. A distance between the first and second fixing regions in the axial direction defines a clamping length. A ratio between the thread length and the clamping length is between 0.7 to 1.3.

Claims

1-12. (canceled)

13. A prechamber spark plug, comprising: a center electrode; a ground electrode; a housing having an external thread; a cap disposed on the housing and together with the housing defines a prechamber; and an insulator which electrically insulates the center electrode from the housing; wherein the external thread of the housing has a thread length in an axial direction of the prechamber spark plug; wherein the housing is fastened to the insulator at a first fixing region and a second fixing region such that a first clamping force at the first fixing region acts from the housing on the insulator, and a second clamping force at the second fixing region acts from the housing on the insulator, wherein the first and second clamping forces are directed in opposite directions to one another in the axial direction; wherein a distance between the first fixing region and the second fixing region in the axial direction defines a clamping length; and wherein a ratio between the thread length and the clamping length is in a range of 0.7 to 1.3.

14. The prechamber spark plug according to claim 13, wherein the ratio between the thread length and the clamping length is in a range of 0.8 to 1.2.

15. The prechamber spark plug according to claim 13, wherein the ratio between the thread length and the clamping length is in a range of 0.8 to 1.0.

16. The prechamber spark plug according to claim 13, wherein the first clamping force is equal to the second clamping force.

17. The prechamber spark plug according to claim 13, wherein the insulator includes a first slope at the first fixing region and a second slope at the second fixing region.

18. The prechamber spark plug according to claim 13, wherein the first fixing region is disposed on a smaller diameter than the second fixing region.

19. The prechamber spark plug according to claim 13, further comprising: a sealing element disposed between the housing and the insulator near the prechamber.

20. The prechamber spark plug according to claim 19, wherein the sealing element is disposed on a side of a radially inward facing flange which faces away from a combustion chamber.

21. The prechamber spark plug according to claim 19, wherein the sealing element is disposed at the first fixing region.

22. The prechamber spark plug according to claim 13, wherein the first fixing region is located in the axial direction starting from the prechamber in a first half of the thread length.

23. The prechamber spark plug according to claim 13, wherein the thread length extends from a first end of the housing, on which the cap is fastened to the housing, to an abutment surface of the housing, wherein the abutment surface is configured for abutment against an external component.

24. The prechamber spark plug according to claim 20, wherein an abutment surface of the flange is beveled in a direction of an end of the prechamber spark plug which faces away from a combustion chamber.

25. An internal combustion engine, comprising: a prechamber spark plug, including: a center electrode; a ground electrode; a housing having an external thread; a cap disposed on the housing and together with the housing defines a prechamber; and an insulator which electrically insulates the center electrode from the housing; wherein the external thread of the housing has a thread length in an axial direction of the prechamber spark plug; wherein the housing is fastened to the insulator at a first fixing region and a second fixing region such that a first clamping force at the first fixing region acts from the housing on the insulator, and a second clamping force at the second fixing region acts from the housing on the insulator, wherein the first and second clamping forces are directed in opposite directions to one another in the axial direction; wherein a distance between the first fixing region and the second fixing region in the axial direction defines a clamping length; and wherein a ratio between the thread length and the clamping length is in a range of 0.7 to 1.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A preferred design example of the present invention is described in detail in the following with reference to the figures.

[0016] FIG. 1 shows a schematic, partially sectional view of a prechamber spark plug according to a preferred embodiment example of the present invention.

[0017] FIG. 2 shows a schematic partial sectional view of the prechamber spark plug of FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0018] A prechamber spark plug 1 according to a first embodiment example of the present invention is described in detail in the following with reference to FIGS. 1 and 2.

[0019] The prechamber spark plug 1 comprises a center electrode 2 and a ground electrode 3. A noble metal pin 20 is disposed on the center electrode 2. It should be noted here that a noble metal pin can also be disposed on the ground electrode 3.

[0020] The prechamber spark plug 1 also comprises a housing 4, in particular made of a metallic material, and an insulator 5. The insulator 5 is configured to electrically insulate the center electrode 2 from the housing 4.

[0021] An external thread 40 is provided on the housing 4 as well. The external thread 40 has a thread length 11, which extends from a first end 4a, which faces in the direction of a combustion chamber of an internal combustion engine, to an abutment surface 10 on the housing 4 (see FIG. 2). The abutment surface 10 is perpendicular to a center axis X-X of the prechamber spark plug. To avoid damage to the external thread, a peripheral groove 10a is provided between the external thread 40 and the abutment surface 10.

[0022] The prechamber spark plug 1 also comprises a cap 6 (see FIG. 1). A plurality of cap holes 60 are configured in the cap 6 to, on the one hand, enable gas exchange in a prechamber 7 and, on the other hand, to allow torch jets to exit the prechamber 7 into a combustion chamber of an internal combustion engine for a main ignition of a gas mixture. The prechamber 7 is thus defined by the cap 6 and parts of the housing 4. The center electrode 2 and the ground electrode 3 are disposed in the prechamber 7.

[0023] As can be seen in particular from FIG. 2, the housing 4 is fastened to the insulator 5 at a first fixing region 41 and a second fixing region 42. The fastening of the housing 4 is such that a first clamping force F1 at the first fixing region 41 acts from the housing 4 on the insulator 5 and a second clamping force F2 at the second fixing region 42 acts from the housing 4 on the insulator 5. The two clamping forces F1, F2 are directed in opposite directions to one another in the axial direction X-X of the prechamber spark plug 1. The two clamping forces F1, F2 are preferably equal.

[0024] A first slope 5a is furthermore provided on the insulator at the first fixing region 41 and a second slope 5b is provided on the second fixing region 42. As can be seen from FIG. 2, the slopes are configured oppositely to one another and are preferably configured at a 45° angle.

[0025] The two clamping forces F1, F2 thus achieve a pretensioning of the housing 4 on the insulator 5, as a result of which the housing 4 tends to widen radially outward. Therefore, in the assembled state of the prechamber spark plug 1, when it is screwed into a cylinder head, an improved seal between an outer perimeter of the prechamber spark plug 1 and the cylinder head is achieved. Furthermore, due to the stiff spring characteristic of the housing, high surface pressures act on a sealing element 9 disposed between the housing 4 and the insulator 5 when the clamping length is small. The sealing element 9 is disposed on a side of the housing 4 facing away from the combustion chamber and is protected from very hot gases by a radially inward facing flange 44.

[0026] A distance between the first fixing region 41 and the second fixing region 42 moreover defines a clamping length 12 of the housing. The pretensioning is thus generated in the region of the clamping length 12 of the housing. A ratio V between the thread length 11 and the clamping length 12 is now furthermore in a range of 0.7 to 1.3. The ratio between the thread length 11 and the clamping length 12 is particularly preferably in a range of 0.8 to 1.2 and further preferably in a range of 0.8 to 1. It is further preferred that the ratio between the thread length 11 and the clamping length 12 is less than 1, i.e., the thread length 11 is less than the clamping length 12, and a lower limit is at a value of 0.7.

[0027] The first fixing region 41 is disposed on a first diameter D1 and the second fixing region 42 is disposed on a second diameter D2. The first diameter D1 is smaller than the second diameter D2.

[0028] This combination of the measures of selecting the thread length 11 and the clamping length 12 and the provision of a pretensioning on the housing 4 thus makes it possible to achieve an improved robustness and in particular tightness of the prechamber spark plug 1. The clever selection of the thread length 11 and the clamping length 12 moreover enables a significantly improved cooling of the prechamber spark plug 1 during operation, so that, thanks to moderate electrode temperatures, a long service life is possible.

[0029] Since the temperatures at the electrodes are significantly reduced compared to the previously existing prechamber spark plugs, there is also greater freedom when selecting a material for the electrodes, so that reduced costs for the electrodes are possible. Providing the pretensioning at the first and second fixing region between the housing 4 and the insulator 5 moreover ensures that improved internal tightness of the prechamber spark plug 1 is achieved over its entire service life. The selection of the lengths of the thread length 11 and the clamping length 12 also has a positive impact on incorrect assembly, for example when tightening the prechamber spark plug 1 with too high a torque, because the clever selection of the lengths makes it possible to prevent damage to the prechamber spark plug 1 if the tightening torque is too high.

[0030] Particularly preferred ratios V of thread length to clamping length can be obtained depending on a thread diameter of the external thread 40, as shown as examples in the table below:

TABLE-US-00001 External thread Thread length/ diameter clamping length Ratio V M10 26.5/30 0.83 M12 26.5/27 0.98 M14 25.0/25.0 1.0

[0031] The measure according to the present invention on the prechamber spark plug 1 thus makes it possible to achieve a significantly improved service life and reduced temperatures during operation on components of the prechamber spark plug 1, in particular the electrodes. The prechamber spark plug 1 according to the present invention is therefore in particular suitable for internal combustion engines in the stationary or mobile sector and in the field of motor sports.