PRECHAMBER SPARK PLUG HAVING AN ACCURATELY ADJUSTABLE ELECTRODE GAP, AND ASSOCIATED METHOD

Abstract

A prechamber spark plug. The prechamber spark plug includes a central electrode and a ground electrode which are arranged in a prechamber, and a housing having a lateral hole, the ground electrode being arranged in the lateral hole in such a way that there is a gap area and a fastening area between the ground electrode and the housing.

Claims

1-15. (canceled)

16. A prechamber spark plug, comprising: a central electrode and a ground electrode arranged in a pre-chamber; and a housing having a lateral hole; wherein the ground electrode is arranged in the lateral hole in such a way that there is a gap area and a fastening area between the ground electrode and the housing.

17. The prechamber spark plug according to claim 16, wherein the gap area is a clearance fit between the ground electrode and the lateral hole.

18. The prechamber spark plug according to claim 16, wherein the fastening area is a weld joint.

19. The prechamber spark plug according to claim 16, wherein the fastening area is arranged radially further outward than the gap area.

20. The prechamber spark plug according to claim 16, wherein the central electrode is arranged perpendicular to the ground electrode.

21. The prechamber spark plug according to claim 16, wherein the ground electrode is cylindrical or is a polygon.

22. The prechamber spark plug according to claim 16, wherein the housing has a defined maximum roughness depth R.sub.max of R.sub.max?10 ?m on an outer side, the roughness depth being adapted for sealing to a pressure generation unit.

23. The prechamber spark plug according to claim 16, wherein a cap and the housing are formed in a single piece.

24. A method of adjusting an electrode spacing between a central electrode and a ground electrode in the manufacture of a prechamber spark plug, comprising the following steps: arranging the ground electrode in a lateral hole in a housing such that the ground electrode is arranged freely movably in the lateral hole; positioning the ground electrode relative to the fixed central electrode at a predefined electrode spacing by moving the ground electrode in the lateral hole; measuring the electrode spacing between central electrode and ground electrode; and after adjusting the predefined electrode spacing, fastening the ground electrode in the lateral hole so that the predefined electrode spacing is maintained.

25. The method according to claim 24, wherein the ground electrode is fastened to the housing to an outer side of the housing, using a welding process in such a way that a fastening area and a gap area exist between the ground electrode and the lateral hole.

26. The method according to claim 24, wherein a clearance fit is provided in order to ensure the movability of the ground electrode in the lateral hole.

27. The method according to claim 24, wherein the arranging of the ground electrode in the lateral hole is done such that there is first contact between the ground electrode and the central electrode, and starting from a state of contact between the central electrode and the ground electrode, the ground electrode is moved radially outward.

28. The method according to claim 24, wherein the ground electrode is moved in the lateral hole by pneumatic pressure.

29. The method according to claim 24, wherein the electrode spacing is determined by measuring a spacing of a rear face of the ground electrode from an outer side of the housing.

30. The method according to claim 24, wherein: i) a cap is fastened to the housing using a weld joint, before the electrode spacing is adjusted, or ii) the cap and the housing are formed in a single piece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Preferred exemplary embodiments of the present invention are described in detail below with reference to the figures.

[0019] FIG. 1 shows a schematic sectional view of a prechamber spark plug according to a first preferred exemplary embodiment of the present invention.

[0020] FIG. 2 shows a schematic sectional view illustrating the method for adjusting an electrode spacing between the central electrode and the ground electrode of FIG. 1.

[0021] FIGS. 3 to 5 show schematic partial sectional views illustrating the method according to the present invention for adjusting the electrode spacing of the prechamber spark plug of FIG. 1.

[0022] FIG. 6 shows a schematic sectional view of a prechamber spark plug according to a second preferred exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0023] Referring to FIGS. 1 to 5, a prechamber spark plug 1 and a method for adjusting an electrode spacing between a central electrode 2 and a ground electrode 3 according to a first exemplary embodiment are described in detail below.

[0024] The prechamber spark plug 1 is particularly suitable for mobile internal combustion engines.

[0025] As can be seen from FIG. 1, the prechamber spark plug 1 comprises a central electrode 2 and a lateral ground electrode 3. The ground electrode 3 is arranged at a 90? angle relative to the central electrode 2. The central electrode 2 runs along a center axis X-X of the prechamber spark plug 1. The central electrode 2 is arranged at least partially in an insulator 5. The insulator 5 serves to electrically isolate the central electrode 2 from the housing 4.

[0026] The prechamber spark plug 1 further comprises a housing 4 with a lateral hole 40 in which the ground electrode 3 is arranged.

[0027] Here, the housing 4 and a cap 6 define a prechamber 7 of the prechamber spark plug.

[0028] As further seen in FIG. 1, the cap 6 comprises a plurality of cap holes 60 designed for a fluid connection between the prechamber 7 and a combustion chamber 80 of an internal combustion engine.

[0029] Also, a fastening area 9 and a gap area 8 are designed between the lateral hole 40 and the ground electrode 3. Here, the fastening area 9 is a weld joint between a rear face of the ground electrode and the housing 4.

[0030] As further shown in FIG. 1, there is an electrode spacing 14 between the central electrode 2 and the ground electrode 3. The electrode spacing 14 is the shortest connection between the central electrode 2 and the ground electrode 3.

[0031] As can be further seen from FIG. 1, the central electrode 2 has a precious metal pin 20 on its front face and the ground electrode 3 has a precious metal pin 30 on its front face. As such, the electrode spacing 14 is the spacing between the two precious metal pins 20, 30.

[0032] The ground electrode 3 is designed as a polygon here, but can also be cylindrical.

[0033] The method according to the present invention for adjusting an electrode spacing 14 between the central electrode 2 and the ground electrode 3 is described in detail with reference to FIGS. 2 to 5.

[0034] As can be seen from FIG. 2, which shows a structure for carrying out the method, the adjusting of the electrode spacing 14 is carried out using a pneumatic pressure generation unit 10. The pressure generation unit 10 comprises a pressure generator 11, for example a compressor, as well as a bell 12. The bell 12 is arranged in a sealing manner on a sealing region 13 on an outer side 41 of the housing 4 or the cap 6. This results in a sealed space substantially on the outside of the cap 6 as well as the prechamber 7.

[0035] In this exemplary embodiment, the cap 6 is fastened to the housing 4 using a weld joint 15. Alternatively, the cap is integrated directly into the housing. The ground electrode 3 is cylindrical here and is arranged in the lateral hole 40 with clearance S. This clearance S ensures the presence of the gap region 8 between the ground electrode 3 and the housing 4 after the prechamber spark plug has been manufactured.

[0036] In this embodiment, the accurate adjustment of the electrode spacing 14 between the central electrode 2 and the ground electrode 3 is the final step in the manufacture of the prechamber spark plug.

[0037] As will become clear from FIGS. 2 and 3, to adjust the electrode spacing 14 according to the method according to the present invention, first a pneumatic pressure is generated using the pressure generator 11. As indicated in FIG. 2 by arrow A, this pressure is applied to the interior region 12a of the bell 12 of the pressure generation unit 10. Because the bell 12 is arranged in a sealing manner on the outer side 41 of the housing 4, the pressure is further applied in the prechamber 7 via the cap holes 60 as indicated in FIG. 2 by arrows B.

[0038] Here, the ground electrode 3, which is arranged loosely in the lateral hole 40, contacts the central electrode 2 because the prechamber spark plug 1, which is not yet quite finished in its manufacture, is arranged such that the ground electrode 3 is guided downward by gravity until it comes into contact with the central electrode 2. This position is shown in FIGS. 2 and 3.

[0039] Due to the increasing pneumatic pressure within the prechamber 7, which is significantly higher than the ambient pressure prevailing on the outside of the prechamber spark plug, the pressure is also applied to the front face, more precisely the front face of the precious metal pin 30, of the ground electrode 3. This is indicated in FIGS. 2 and 3 by arrows C.

[0040] Since the ground electrode 3 is arranged in the lateral hole 40 via a clearance fit S, the ground electrode 3 now moves radially outward due to the prevailing pressure differential. This can also be seen in detail in FIG. 4 (arrow D). A rear face 31 of the ground electrode 3 moves out of the lateral hole 40, indicated in FIG. 4 by the spacing H. In this embodiment, this spacing H corresponds to the electrode spacing 14 between the central electrode 2 and the ground electrode 3 since in this embodiment the rear face 31 of the ground electrode 3 was flush with the outer side 41 of the housing 4 when the central electrode 2 and ground electrode 3 were in contact.

[0041] Thus, the electrode spacing 14 may be easily ascertained from outside the prechamber spark plug by measuring the spacing H between the rear face 31 of the ground electrode as it moves out of the housing to the outer side 41 of the housing. When the spacing H corresponds to the desired electrode spacing 14 between central electrode 2 and ground electrode 3, the ground electrode 3 is then fastened in this position. Here, a weld joint is made between the ground electrode 3 and the housing 4 from outside of the prechamber spark plug, the joint then forming the fastening area 9 in the lateral hole 40 between the ground electrode 3 and the housing 4. This is shown in FIG. 5.

[0042] Since the rear face 31 of the ground electrode 3 was flush in the initial state in which the ground electrode 3 contacted the central electrode 2, the spacing H corresponds to the electrode spacing 14. It should be noted that in the initial state, the ground electrode may be sunk into the housing or may protrude out above it. In this case the gap area 8 between the ground electrode 3 and the housing 4, which created the clearance fit S between the ground electrode 3 and the housing 4 during the adjustment of the electrode spacing, stays within the lateral hole 40 radially inside of the fastening area 9.

[0043] Thus, the present invention has the advantage that the electrode spacing 14 is very accurately adjustable. A simple measurement of the electrode spacing 14 may be made from an outer side of the prechamber spark plug.

[0044] It should be noted that the rear face 31 of the ground electrode 3 need not terminate flush with the outer side 41 in the state of contact with the central electrode 2. It is also possible for the rear face to already protrude out somewhat from the lateral hole 40 in the state of contact between the ground electrode 3 and the central electrode 2. This outward protrusion may also be measured in a straightforward manner, the electrode spacing adjustment according to the present invention then being done based on this protrusion. Of course, this means that two measuring operations must be performed on the ground electrode 3; however, since this can be carried out from the outside of the prechamber spark plug, this is possible in a simple manner.

[0045] Thus, the method according to the present invention for adjusting the electrode spacing 14 is also suitable for mass production, such that the prechamber spark plug 1 can also be used in mobile internal combustion engines, which are produced in high numbers.

[0046] Another great advantage of the method according to the present invention is that the fastening of the ground electrode 3 can be carried out as a last step in the manufacture of the prechamber spark plug. It is thus no longer necessary to weld the cap onto the housing 4 after adjusting the electrode spacing, for example. This can prevent the welding heat that occurs when the cap 6 is fastened to the housing 4 from affecting the electrode spacing 14. According to the present invention, it can thus be ensured that the electrode spacing 14 has accurately the desired spacing.

[0047] FIG. 6 shows a prechamber spark plug 1 according to a second preferred exemplary embodiment of the present invention. Identical or functionally identical parts bear the same reference numbers as in the first exemplary embodiment.

[0048] In contrast to the first exemplary embodiment, in the second exemplary embodiment the housing 4 and the cap 6 are configured as a one-piece component. In this way, there is no need for a weld joint or other type of connection between the cap and the housing. In particular, this can significantly reduce manufacturing costs. Thus, in the manufacture of the prechamber spark plug, the method of adjusting the electrode spacing may be performed as a last step in the manufacture of the prechamber spark plug. A measurement of the electrode spacing may be made by the method according to the present invention from outside of the prechamber spark plug. A fastening of the ground electrode to the one-piece housing-cap component may be accomplished using a weld joint from the outside of the prechamber spark plug. In this case, thermal input to the ground electrode is very low, such that the adjusted spacing 14 does not change as a result. If fastening of the ground electrode without a thermal method is desired, the ground electrode may be implemented using a caulking process or the like on the one-piece housing-cap component, for example. Otherwise, this exemplary embodiment corresponds to the first exemplary embodiment, so that reference can be made to the description given therein.