Pre-chamber spark plug with precisely adjustable electrode gap and method for doing so

Description

State of the art

[0001] The present invention relates to a pre-chamber spark plug with a precisely set electrode gap between a center electrode and a ground electrode, and to a method for setting a precise electrode gap between a ground electrode and a center electrode of the pre-chamber spark plug.

[0002] Pre-chamber spark plugs are known in various designs from the prior art. Currently, pre-chamber spark plugs are primarily used in stationary gas engines, which typically operate at a single operating point with a relatively high load. The respective pre-chamber spark plugs are designed for this operating point. However, in mobile internal combustion engines, such as those used in vehicles, ignition must be ensured across a wide range of loads, particularly partial loads. This requires precise maintenance of the electrode gap between the center electrode and the ground electrode. Furthermore, it must be considered that pre-chamber spark plugs for vehicles can be mass-produced. The pre-chamber spark plugs currently manufactured for stationary gas engines are produced in small batches, which results in very high costs.Therefore, there is a need to be able to mass-produce pre-chamber spark plugs for use in mobile internal combustion engines for vehicles.

[0003] DE 10 2019 207399 A1 discloses a pre-chamber spark plug according to the preamble of claim 1. Disclosure of the invention

[0004] In contrast, the pre-chamber spark plug according to the invention, with the features of claim 1, has the advantage that the electrode gap between a center electrode and a ground electrode can be precisely adjusted. The adjustment process for the electrode gap is also suitable for mass production of the pre-chamber spark plug. This significantly reduces the manufacturing costs of the pre-chamber spark plug according to the invention, making it particularly suitable for use in internal combustion engines in vehicles. In particular, the cap and housing of the pre-chamber spark plug can be manufactured as a single component without a weld seam. According to the invention, this is achieved by the pre-chamber spark plug comprising a center electrode and a ground electrode, which are arranged in a pre-chamber. The ground electrode is arranged in a lateral bore in a housing.In this design, a gap and a sealing fixing area are provided between the lateral bore and the ground electrode. According to the invention, the gap between the ground electrode and the lateral bore is a clearance fit.

[0005] The dependent claims describe preferred embodiments of the invention.

[0006] The fixing area between the ground electrode and the lateral bore is preferably a welded joint. The fixing area is further preferably arranged radially further outwards than the gap area and is preferably formed on an outer side of the pre-chamber spark plug between the outer wall of the housing and the back of the ground electrode.

[0007] Preferably, the ground electrode is arranged at an angle of 90° relative to the center electrode.

[0008] The ground electrode is preferably cylindrical. Particularly preferably, the ground electrode is polygonal, especially triangular, square, pentagonal, or hexagonal. If the ground electrode is polygonal, twisting of the ground electrode during electrode gap adjustment can be avoided. This allows for particularly precise adjustment of the electrode gap between the center electrode and the ground electrode.

[0009] Preferably, the housing has a surface, particularly on an outside of the housing, with a very small maximum roughness depth R max.

[0010] The surface roughness R max is ≤ 10 µm. This allows a bell or other sealing component to be securely and tightly attached to the outside of the housing, particularly during the electrode spacing adjustment process.

[0011] Preferably, the cap and the housing are formed as a single piece. This means that the cap no longer needs to be attached to the housing separately; instead, the cap and the housing form a single component. This eliminates the need for welding or any other type of connection between the cap and the housing.

[0012] The invention further relates to a method for adjusting the electrode gap between a center electrode and a ground electrode during the manufacture of a pre-chamber spark plug. The method comprises the steps of arranging the ground electrode in a lateral bore in a housing of the pre-chamber spark plug, such that the ground electrode is freely movable within the lateral bore, with a clearance fit being provided to ensure the ground electrode's mobility within the lateral bore. In a subsequent step, the ground electrode is positioned relative to the stationary center electrode at a predetermined electrode gap. This is possible because the ground electrode is slidably arranged within the lateral bore.In a final step, after setting the predetermined electrode gap, the ground electrode is fixed to the housing, thus maintaining the predetermined gap between the center electrode and the ground electrode. This completes the precise adjustment of the gap between the center electrode and the ground electrode. Furthermore, the inventive method allows for adjusting the electrode gap with the pre-chamber cap installed or with the spark plug fully assembled. This opens up new design possibilities – for example, manufacturing the cap and housing as a single component (without a weld seam).

[0013] The ground electrode is preferably fixed to the housing at the correct electrode distance by means of a weld. The weld is particularly preferably formed on the outside of the pre-chamber spark plug between the housing and the ground electrode. The weld is further preferably produced using a laser.

[0014] Particularly simple and cost-effective manufacturing is ensured if, after the ground electrode is inserted into the lateral bore in the housing, the pre-chamber spark plug is positioned such that gravity causes the ground electrode to move downwards and make contact with the center electrode. From this point of contact, the ground electrode is then moved radially outwards away from the center electrode until the desired, defined electrode gap is achieved. Finally, the ground electrode is fixed to the housing.

[0015] The process of moving the ground electrode away from the center electrode is preferably carried out using pneumatic pressure. For this purpose, the pre-chamber of the pre-chamber spark plug is preferably pressurized so that, due to the increasing pressure, the ground electrode moves away from the center electrode in the lateral bore. Once the ground electrode has traveled a predetermined distance and, for example, its rear end is slowly pushed out of the lateral bore on the outside of the housing, the distance traveled by the ground electrode can be measured. From this value, the electrode gap between the center electrode and the ground electrode, which were previously in contact, can be determined. When the desired electrode gap is reached, the ground electrode can then be fixed to the housing.

[0016] The ground electrode is preferably cylindrical or, even more preferably, polygonal. Using a polygonal ground electrode has the particular advantage of preventing it from twisting when a vacuum is applied to the pre-chamber. To securely attach a bell or similar device to the pre-chamber spark plug for vacuuming the pre-chamber, the maximum surface roughness Rmax on the housing walls is preferably very small, particularly ≤ 10 µm.

[0017] It should also be noted that the adjustment of the electrode gap between the center electrode and the ground electrode can be carried out as the final step in the manufacture of the pre-chamber spark plug, i.e., with a cap already fixed to the housing. Alternatively, the electrode gap can also be adjusted before a cap is fixed to the housing, and the cap can then be fitted to the housing in a further step after the ground electrode has been fixed to the housing at the correct electrode gap.

[0018] Preferably, a cap is fixed to the housing, particularly by means of a weld or a press fit, before the electrode gap is adjusted. This allows the electrode gap to be set as the final step. This prevents thermal distortion of the electrode gap caused by subsequently fixing a cap to the housing. Alternatively, the cap and housing are formed as a single piece, resulting in cost advantages in the manufacture of the pre-chamber spark plug. drawing

[0019] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows: Figure 1 is a schematic sectional view of a pre-chamber spark plug according to a first preferred embodiment of the invention; Figure 2 is a schematic sectional view showing the method for adjusting an electrode gap between the center electrode and the ground electrode. Figure 1 Figures 3 to 5, which are schematic partial sectional views illustrating the inventive method for adjusting the electrode gap of the pre-chamber spark plug, demonstrate this. Figure 1 to illustrate, and Figure 6 shows a schematic sectional view of a pre-chamber spark plug according to a second preferred embodiment of the invention. Preferred embodiments of the invention

[0020] The following refers to the Figures 1 to 5 a pre-chamber spark plug 1 and a method for adjusting an electrode gap between a center electrode 2 and a ground electrode 3 according to a first embodiment are described in detail.

[0021] The pre-chamber spark plug 1 is particularly suitable for mobile internal combustion engines.

[0022] As from Figure 1 As can be seen, the pre-chamber spark plug 1 comprises a center electrode 2 and a lateral ground electrode 3. The ground electrode 3 is arranged at an angle of 90° to the center electrode 2. The center electrode 2 runs along a central axis XX of the pre-chamber spark plug 1. The center electrode 2 is at least partially located in an insulator 5. The insulator 5 serves to electrically isolate the center electrode 2 from the housing 4.

[0023] The pre-chamber spark plug 1 further comprises a housing 4 with a lateral bore 40 in which the ground electrode 3 is arranged.

[0024] The housing 4 and a cap 6 define a pre-chamber 7 of the pre-chamber spark plug.

[0025] What's next? Figure 1As can be seen, the cap 6 has several cap holes 60, which are provided for a fluid connection between the pre-chamber 7 and a combustion chamber 80 of an internal combustion engine.

[0026] Between the lateral bore 40 and the ground electrode 3, a fixing area 9 and a gap area 8 are also formed. The fixing area 9 is a welded connection between a rear side of the ground electrode and the housing 4.

[0027] What's next in Figure 1 As shown, there is an electrode gap 14 between the center electrode 2 and the ground electrode 3. The electrode gap 14 is the shortest connection between the center electrode 2 and the ground electrode 3.

[0028] What's next? Figure 1As can be seen, the center electrode 2 has a precious metal pin 20 on its end face, and the ground electrode 3 has a precious metal pin 30 on its end face. The electrode gap 14 is located between the two precious metal pins 20 and 30.

[0029] The ground electrode 3 is designed as a polygon, but can also be cylindrical.

[0030] The inventive method for setting an electrode gap 14 between the center electrode 2 and the ground electrode 3 is described with reference to the Figures 2 to 5 described in detail.

[0031] As from Figure 2As can be seen in the diagram, which shows a setup for carrying out the procedure, the adjustment of the electrode gap 14 is performed by means of a pneumatic pressure generation unit 10. The pressure generation unit 10 comprises a pressure generator 11, for example a compressor, and a bell 12. The bell 12 is arranged in a sealing manner on a sealing area 13 on an outer surface 41 of the housing 4 or the cap 6. This creates a sealed space essentially on the outer surface of the cap 6 and the pre-chamber 7.

[0032] In this embodiment, the cap 6 is fixed to the housing 4 by means of a weld 15. Alternatively, the cap is integrated directly into the housing. The ground electrode 3 is cylindrical and arranged in the lateral bore 40 with a clearance S. This clearance S ensures the gap 8 between the ground electrode 3 and the housing 4 after the pre-chamber spark plug has been manufactured.

[0033] In this embodiment, the exact adjustment of the electrode gap 14 between the center electrode 2 and the ground electrode 3 is the last step in the manufacture of the pre-chamber spark plug.

[0034] As from the Figures 2 and 3 As becomes clear, to adjust the electrode gap 14 according to the inventive method, pneumatic pressure is first generated by means of the pressure generator 11. As in Figure 2 As indicated by arrow A, this pressure is applied to the inner area 12a of the bell 12 of the pressure generating unit 10. Since the bell 12 is arranged in a sealing manner against the outer surface 41 of the housing 4, the pressure is further transmitted via the cap holes 60, as shown in Figure 2 indicated by arrows B, imprinted in the antechamber 7.

[0035] The ground electrode 3, which is loosely arranged in the lateral bore 40, contacts the center electrode 2, since the not yet fully completed pre-chamber spark plug 1 is positioned such that gravity pulls the ground electrode 3 downwards until it makes contact with the center electrode 2. This position is in the Figures 2 and 3 shown.

[0036] Due to the increasing pneumatic pressure within the pre-chamber 7, which is significantly higher than the ambient pressure prevailing on the outside of the pre-chamber spark plug, the pressure is also applied to the front face, more precisely to the front face of the precious metal pin 30 of the ground electrode 3. This is in the Figures 2 and 3 indicated by arrows C.

[0037] Since the ground electrode 3 is arranged in the lateral bore 40 by means of a clearance fit S, the ground electrode 3 now moves radially outwards due to the prevailing pressure difference. This is also shown in detail from Figure 4 visible (arrow D). In this process, a rear side 31 of the ground electrode 3 moves out of the lateral bore 40, which in Figure 4 as indicated by the distance H. In this embodiment, this distance H corresponds to the electrode distance 14 between the center electrode 2 and the ground electrode 3, since in this embodiment the back side 31 of the ground electrode 3 was flush with the outside 41 of the housing 4 when in contact between the center electrode 2 and the ground electrode 3.

[0038] Thus, the electrode gap 14 can be easily determined from an outer surface of the pre-chamber spark plug by measuring the distance H between the back 31 of the ground electrode moving out of the housing and the outer surface 41 of the housing. If the distance H corresponds to the desired electrode gap 14 between the center electrode 2 and the ground electrode 3, the ground electrode 3 is then fixed in this position. This is achieved by creating a weld from an outer surface of the pre-chamber spark plug between the ground electrode 3 and the housing 4, which then forms the fixing area 9 in the lateral bore 40 between the ground electrode 3 and the housing 4. This is in Figure 5 depicted.

[0039] Since the rear surface 31 of the ground electrode 3 was flush in the initial state, in which the ground electrode 3 contacted the center electrode 2, the distance H corresponds to the electrode spacing 14. It should be noted that the ground electrode may be recessed in the housing or protrude beyond it in the initial state. In this case, the gap 8 remains radially within the fixing area 9 of the lateral bore 40 between the ground electrode 3 and the housing 4, which, when the electrode spacing was set, formed the clearance fit S between the ground electrode 3 and the housing 4.

[0040] The present invention thus has the advantage that the electrode gap 14 can be adjusted very precisely. A simple measurement of the electrode gap 14 can be taken from the outside of the pre-chamber spark plug.

[0041] It should be noted that the back surface 31 of the ground electrode 3 does not have to be flush with the outer surface 41 when in contact with the center electrode 2. It is also possible that the back surface protrudes slightly from the lateral bore 40 when in contact between the ground electrode 3 and the center electrode 2. This protrusion can be easily measured, and the electrode gap adjustment according to the invention is then carried out based on this protrusion. While this requires two measurements on the ground electrode 3, these can be performed easily from the outside of the pre-chamber spark plug.

[0042] Thus, the inventive method for adjusting the electrode gap 14 is also suitable for mass production, so that the pre-chamber spark plug 1 can also be used in mobile internal combustion engines which are manufactured in high numbers.

[0043] A further major advantage of the method according to the invention is that the fixing of the ground electrode 3 can be carried out as the last step in the manufacture of the pre-chamber spark plug. It is therefore no longer necessary, for example, to weld the cap onto the housing 4 after setting the electrode gap. This prevents the welding heat generated when fixing the cap 6 to the housing 4 from influencing the electrode gap 14. According to the invention, it can thus be ensured that the electrode gap 14 has exactly the desired distance.

[0044] Figure 6 Figure 1 shows a pre-chamber spark plug 1 according to a second preferred embodiment of the invention. Identical or functionally equivalent parts are designated with the same reference numerals as in the first embodiment.

[0045] In contrast to the first embodiment, in the second embodiment the housing 4 and the cap 6 are designed as a single component. This eliminates the need for a welded or other type of connection between the cap and the housing. This significantly reduces manufacturing costs. Consequently, the method for adjusting the electrode gap can be performed as the final step in the manufacturing process of the pre-chamber spark plug. The electrode gap can be measured from the outside of the pre-chamber spark plug using the inventive method. The ground electrode can be fixed to the single-piece housing-cap component by means of a weld from the outside of the pre-chamber spark plug. This results in very little heat input to the ground electrode, so that the set electrode gap 14 remains unchanged.If fixing the ground electrode without a thermal process is desired, the ground electrode can, for example, be attached to the one-piece housing-cap component by means of a caulking process or similar. Otherwise, this embodiment corresponds to the first embodiment, so reference can be made to the description given there.

Claims

1. Pre-chamber spark plug, comprising: - a centre electrode (2) and an earth electrode (3), which are arranged in a pre-chamber (7), and - a housing (4) having a lateral hole (40), - wherein the earth electrode (3) is arranged in the lateral hole (40) in such a way that there is a gap region (8) and a fixing region (9) between the earth electrode (3) and the housing (4), characterized in that the gap region (8) is a clearance fit (S) between the earth electrode (3) and the lateral hole (40).

2. Pre-chamber spark plug according to one of the preceding claims, wherein the fixing region (9) is a welded connection.

3. Pre-chamber spark plug according to one of the preceding claims, wherein the fixing region (9) is arranged radially further to the outside than the gap region (8).

4. Pre-chamber spark plug according to one of the preceding claims, wherein the centre electrode (2) is arranged perpendicular to the earth electrode (3).

5. Pre-chamber spark plug according to one of the preceding claims, wherein the earth electrode (3) is cylindrical or is a polygon.

6. Pre-chamber spark plug according to one of the preceding claims, wherein the housing has, on an outer side (41), a defined maximum roughness depth Rmax of Rmax ≤ 10 µm, which is designed to be sealed off with a pressure generating unit (10).

7. Pre-chamber spark plug according to one of the preceding claims, wherein a cap (6) and the housing (4) are formed in one piece.

8. Method for adjusting an electrode spacing (14) between a centre electrode (2) and an earth electrode (3) during production of a pre-chamber spark plug, comprising the steps of: - arranging the earth electrode (3) in a lateral hole (40) in a housing (4) in such a way that the earth electrode (3) is arranged in a freely movable manner in the lateral hole (40), wherein a clearance fit S is provided in order to ensure the movability of the earth electrode (3) in the lateral hole (40), - positioning the earth electrode (3) relative to the stationary centre electrode (2) with a predetermined electrode gap (14) by moving the earth electrode (3) in the lateral hole, - measuring the electrode gap between the centre electrode (2) and the earth electrode (3), and - after adjusting the predetermined electrode gap (14), fixing the earth electrode (3) in the lateral hole (40), so that the predetermined electrode gap (14) is maintained.

9. Method according to Claim 8, wherein the earth electrode (3) is fixed to the housing (4) by means of a welding process, in particular to an outer side of the housing (4), in such a way that there is a fixing region (9) and a gap region (8) between the earth electrode (3) and the lateral hole (4).

10. Method according to one of Claims 8 and 9, wherein the earth electrode (3) is arranged in the lateral hole (40) in such a way that first there is contact between the earth electrode (3) and the centre electrode (2) and the earth electrode (3) is moved radially to the outside starting from this contact state between the centre electrode (2) and the earth electrode (3).

11. Method according to one of Claims 8 to 10, wherein the earth electrode (3) is moved in the lateral hole (40) by means of pneumatic pressure.

12. Method according to one of Claims 8 to 11, wherein the electrode gap (14) is determined by measuring a distance between a rear side (31) of the earth electrode (3) and an outer side (41) of the housing (4).

13. Method according to one of Claims 8 to 12, - wherein, before adjusting the electrode gap, a cap (6) is fixed to the housing (4), in particular by means of a welded connection (15), or - wherein the cap (6) and the housing (4) are formed in one piece.