Spark plug with ground electrode inserted into the housing wall and improved heat balance
Patent Information
- Application Number
- EP2023821914
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-20
- Filing Date
- 2023-12-05
- Publication Date
- 2025-10-29
AI Technical Summary
Existing spark plug designs face challenges in temperature management due to factors like material selection, electrode lengths, and the presence of a prechamber, leading to inefficient heat dissipation and potential operational issues.
A spark plug design with a ground electrode inserted into a housing wall bore, where the ratio of the ground electrode's total length to its length within the bore and the protrusion depth into the housing is optimized to enhance heat dissipation, ensuring reliable temperature management through increased contact surface area and proportional heat transfer.
The optimized design achieves improved heat management and operational reliability by ensuring sufficient heat dissipation from the ground electrode into the housing, maintaining a balanced temperature across the spark plug.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] title
[0003] Spark plug with ground electrode inserted into the housing wall and improved heat management
[0004] State of the art
[0005] The invention is based on a spark plug according to the preamble of claim 1.
[0006] In order for spark plugs and pre-chamber spark plugs to function optimally at all operating points, balanced temperature management is necessary.
[0007] For some time now, new spark plug designs have been increasingly pursued in which the ignition gap is formed within the housing. In one of these designs, the ground electrode is inserted into a hole in the housing wall and protrudes laterally from the housing wall into the interior of the housing. DE 10 2017 221 517 A discloses a prechamber spark plug in which the ground electrode is located in a hole in the housing wall and protrudes laterally into the interior.
[0008] The new spark plug concepts with a ground electrode that is arranged in a hole in the housing wall and protrudes laterally into the interior, present new challenges for the temperature management of the spark plug. With today's spark plugs, temperature management is influenced by many different factors. Some of these factors are the choice of material, the length of the center electrode and the insulator and the structure of the electrodes, with or without a copper core, as well as the position of the spark plug in the combustion chamber. In the case of pre-chamber spark plugs in particular, the additional combustion chamber within the spark plug is an additional factor. The pre-comb spark plug must absorb the combustion gases in the spray mist from the injectors and is therefore arranged in a very hot area of the engine's combustion chamber. The object of the present invention is to provide a spark plug with reliable temperature management.
[0009] Advantage of the invention / Disclosure of the invention
[0010] This task is solved by the spark plug according to the invention
[0011] The spark plug according to the invention has a longitudinal axis X, which extends from the end closest to the combustion chamber to the end of the spark plug remote from the combustion chamber. The spark plug further comprises a housing with a longitudinal bore parallel to the longitudinal axis X of the spark plug, whereby the housing has a housing wall and an interior space, as well as an insulator arranged within the housing, in which a center electrode is arranged. Furthermore, the spark plug has a ground electrode with a total length LwiaEi and a diameter of ÜMaEi, a bore in the housing wall with a diameter of Dßohr, and an ignition gap formed between the ground electrode and the center electrode. The ground electrode is arranged with a length Lßohr in the bore in the housing wall and projects with a length L emfrom the inside of the housing wall into the interior of the housing. The housing wall has a thickness Lwall in the area of the bore.
[0012] Advantageously,
[0013] • the ratio of the total length LwiaEi of the ground electrode to the length Lß O hr of the ground electrode in the bore equal to or greater than 1.8 and equal to or less than 2.2 and / or
[0014] • the ratio of the length L em with which the ground electrode projects into the interior of the housing, to the thickness Lwaii of the housing wall equal to or greater than 0.2 and equal to or less than 3, the lengths and the thickness respectively extending perpendicular to the longitudinal axis X of the spark plug.
[0015] This results in a spark plug with improved heat management.
[0016] Due to the advantageous ratio of the total length LwiaEi of the ground electrode to the length Lßohr of the ground electrode in the bore of 1.8 to 2.2, reliable temperature management is achieved in the spark plug. The length Lßohr of the ground electrode in the bore is proportional to the contact area of the ground electrode with the bore. The larger the contact area between the ground electrode and the bore, the better the heat dissipation from the ground electrode into the housing. This inventive ratio of LwiaEi to Lßohr results in a sufficiently long contact length between the ground electrode and the bore and the housing wall, so that the heat absorbed by the ground electrode in the interior of the housing can be sufficiently dissipated via the contact area in the bore in the housing wall.
[0017] Alternatively, this technical effect is also achieved if the ratio of the length L em, with which the ground electrode protrudes into the interior of the housing, to the thickness Lwaii of the housing wall is equal to or greater than 0.2 and equal to or less than 3. If both advantageous length ratios are met, the desired technical effect of reliable temperature management is enhanced.
[0018] The lengths and thicknesses extend perpendicular to the longitudinal axis X of the spark plug and are measured accordingly.
[0019] The above-mentioned ratios or differences influence the heat transfer from the ground electrode to the housing and thus the thermal balance of the spark plug. Each ratio, or the difference, leads to a spark plug with improved thermal balance. The combination of two or all advantageous embodiments of the spark plug according to the invention leads to an enhancement of the technical effect.
[0020] Advantageous further developments of the invention are the subject of the subclaims.
[0021] In an advantageous embodiment of the invention, it is provided that the ratio of the length L em, with which the ground electrode protrudes into the interior of the housing, to the thickness Lwaii of the housing wall is equal to or less than 2, in particular 1. The less the ground electrode protrudes into the interior, the less heat it can absorb, which must be dissipated via the contact surface in the housing wall bore. The thickness of the housing wall in the area of the bore also determines the maximum length of the bore and thus also the maximum length that the ground electrode can be inserted in the bore. The thickness of the housing wall therefore also influences the maximum contact surface between the ground electrode in the bore and the housing, with the size of the contact surface influencing the quality of the heat dissipation and the temperature management. In a further development, it is provided that the ground electrode has a total length l_MaEL of equal to or greater than 2.0 mm and equal to or less than 4.0 mm.This limitation of the length of the ground electrode ensures that the ground electrode is neither too short nor too long. If the ground electrode is too short, the contact length in the housing wall bore may be too short for sufficient heat dissipation. If the ground electrode is too long, it absorbs more heat and a correspondingly longer contact surface in the housing wall bore would be required for sufficient heat dissipation. For common spark plug types with different dimensions, the upper and lower limits for the length of the ground electrode represent a good compromise between a ground electrode long enough for a good contact length and a ground electrode that is not too long, which absorbs more heat than can be dissipated.
[0022] In another advantageous embodiment of the invention, it is provided that the length Lßohr of the ground electrode in the bore and / or the thickness Lwaii of the housing wall are equal to or greater than 1.0 mm and equal to or less than 2.5 mm. In particular, it is advantageous if the length Lßohr of the ground electrode in the bore is equal to the thickness Lwaii of the housing wall, so that the ground electrode has the maximum possible contact area and, furthermore, the ground electrode closes the bore flush with the outside of the housing, whereby the production of the spark plug is simplified compared to a ground electrode that ends inside the bore or ends outside the bore.
[0023] In a further advantageous embodiment of the invention, it is provided that the ground electrode with a length L em of equal to or greater than 0.6 mm and equal to or less than 1.6 mm into the interior. The upper limit for the length Lem , which protrudes the ground electrode into the interior, ensures that the ground electrode does not protrude too far into the interior and thus does not absorb too much heat, which is then dissipated again via the housing.
[0024] In a further development of the invention, the ground electrode has an electrode base body and a precious metal-containing element with a diameter DEM, wherein the electrode base body is arranged at least partially within the bore and has a diameter DMQEI within the bores, and wherein the precious metal-containing element is fastened to the electrode base body. Advantageously, a ratio between the diameter DEM of the precious metal-containing element and the diameter DMQEI of the electrode base body in the bore is equal to or less than 1 and equal to or greater than 0.4. This results in the different thermal expansion coefficients of the precious metal-containing element and the electrode base body being compensated.
[0025] In combination or alternatively, in further embodiments it is provided that the ignition gap between the center electrode and the ground electrode is a radial ignition gap, and / or that the ignition gap is formed at least partially, in particular completely, within the interior of the housing.
[0026] In an advantageous development, the spark plug has a second ground electrode, which, like the first ground electrode, is arranged in a further bore in the housing wall. The second ground electrode has the same advantageous design and the same advantageous length ratios as the first ground electrode.
[0027] It has proven advantageous that the ground electrode and / or the second ground electrode is pressed into the bore and / or welded to the housing wall.
[0028] For a spark plug with a pressed-in ground electrode, improved thermal management is achieved when the difference between the diameter of the ground electrode and the bore diameter is equal to or less than 0.03 mm. The smaller the difference, the better the fit between the ground electrode and the housing, resulting in good heat transfer between the ground electrode and the housing. In addition, good holding force is achieved, ensuring that the ground electrode is reliably positioned in the bore and does not shift within the bore or even fall out of the bore.
[0029] For a spark plug with a ground electrode welded into the bore, good heat management is achieved if the weld seam between the ground electrode and the housing wall has a length LSN of no greater than 0.9 * thickness Lwaii of the housing wall and, in particular, no less than 0.3 * thickness Lwaii of the housing wall. For example, it is also advantageous if the length of the weld seam is equal to or greater than 0.5 * thickness Lwaii of the housing wall and / or equal to or less than 0.7 * thickness Lwaii of the housing wall.
[0030] In an advantageous development of the invention, it is provided that the spark plug has a cap which is fastened to the combustion chamber end of the housing and the spark plug is a pre-chamber spark plug, wherein the pre-chamber has a volume V. In a development of the spark plug as a pre-chamber spark plug, it is advantageous if the insulator projects into the pre-chamber with a length L, wherein the length L extends from the combustion chamber end of an inner seal arranged between the insulator and the housing to the combustion chamber end of the insulator parallel to the longitudinal axis X of the spark plug, and that the ratio of pre-chamber volume V to length L of the insulator is equal to or greater than 75 mm 2 and equal to or less than 200 mm 2 in particular the ratio V / L is equal to or greater than 100 mm 2 and / or equal to or less than 150 mm 2This ensures that the insulator does not absorb too much heat from the pre-chamber and, at the same time, is not too cool, so that no unwanted deposits form on the insulator.
[0031] drawing
[0032] Figure 1 shows an example of a spark plug according to the invention with a ground electrode
[0033] Figure 2 shows a second example of a spark plug according to the invention with two ground electrodes
[0034] Description of the characters
[0035] Figures 1 and 2 show two exemplary embodiments of the spark plug 1 according to the invention. In each case, the combustion chamber-side half of the spark plug 1 is shown in a sectional view. The two exemplary embodiments differ essentially in that Figure 1 shows a spark plug 1 with one ground electrode 5 and Figure 2 shows a spark plug 1 with two ground electrodes. Figure 2 shows the optional cap 30 on the combustion chamber-side end of the housing. The exemplary embodiment according to Figure 2 can also be realized without a cap. Accordingly, the exemplary embodiment according to Figure 1 can also be realized with a cap 30.
[0036] The spark plug 1 according to the invention has a longitudinal axis X. The spark plug 1 comprises a housing 2. An insulator 3 is inserted into the housing 2. The housing 2 and the insulator 3 each have a longitudinal bore along their longitudinal axis. The housing 2 has a housing wall 20 and an interior space 21.
[0037] A center electrode 4 is arranged in the insulator 3. The spark plug 1 has a ground electrode
[0038] 5 with a length LMQEI and a diameter ÜMaEi, where the length of the ground electrode
[0039] 5, for example, 2 mm to 4 mm, and the diameter, for example, 1 mm to 2 mm. The center electrode 4 and the ground electrode 5 are arranged relative to one another such that an ignition gap 45 is formed. For example, the ignition gap 45 is designed as a radial ignition gap. Preferably, the ignition gap 45 is formed at least partially, in particular completely, in the interior 21 of the housing 2.
[0040] The ground electrode 5 can, for example, have a precious metal-containing element 55 that forms the ignition gap-side end of the ground electrode 5. If the ground electrode 5 has a precious metal-containing element 55, then the ground electrode 5 is composed of an electrode base body 56 and the precious metal-containing element 55, wherein the precious metal-containing element 55 is fastened to the electrode base body 56. The precious metal-containing element 55 has a diameter DEM of 0.6-1.1 mm. The ratio of DEM to ÜMaEi is 0.4 to mm, in particular 0.55-0.6 mm, thereby compensating for the different thermal expansion coefficients of the precious metal-containing element 55 and the electrode base body 56, which consists, for example, of a nickel alloy.
[0041] The diameter DMQEI of the ground electrode 5 is measured at its thickest point or at the thickest point of the electrode base body 56. This thickest point will typically be in the section of the ground electrode 5 that is located within the bore 50 of the housing 2.
[0042] The housing 2 has at least one bore 50 in the housing wall 20 with a diameter Dßohr, for example, Dßohr is 1 mm to 2 mm. The housing wall 20 in the region of the bore 50 has a thickness Lwaii, for example, L wa ii 1.5 to 2.5 mm. The ground electrode 5 is arranged in this bore 50. The ground electrode 5 is arranged with a length L in the bore 50. The ground electrode 5 is arranged with a length L emfrom the inner side 20a of the housing 2 into the interior space 21 of the housing 2. The sum of the lengths Lßohr and Lem results in the total length of the ground electrode LMaEL. The length Lßohr is, for example, 1 to 2 mm. The length Lßm is, for example, 0.6 to 1.6 mm. The length LMaEi is, for example, 1.6 to 3.6 mm.
[0043] For a spark plug 1 with good heat management, the following conditions have proven to be advantageous:
[0044] • LMaE / Lßohr = 1.8 to 2.2
[0045] • LEM / Lwaii = 0.2 to 3 In this example, the ground electrode 5 is welded to the housing wall 20 in the bore 50. The weld seam 52 is formed along the circumference of the ground electrode 5. The weld seam 52 extends from the outside of the housing 2 in the direction of the longitudinal axis X of the spark plug. The weld seam 52 has a length LSN that is advantageously smaller than the thickness Lwaii of the housing wall 20, so that the weld seam 52 does not extend to the inside of the housing 2.
[0046] Furthermore, the housing 2 has a seat 25 on its inner side. The insulator 3 rests with its shoulder or insulator seat 35 on the housing seat 25. An inner seal 10 is arranged between the insulator seat 35 and the housing seat 25. From the combustion chamber end of the inner seal to the combustion chamber end of the insulator 3, the insulator s protrudes into the interior 21 of the housing 2 with a length L. The length L of the insulator 3 is, for example, 2.5 to 5.5 mm.
[0047] As shown by way of example in Figure 2, a cap 30 can be arranged on the housing 2 on its combustion chamber-side end face. The housing 2 and the cap 30 together form a prechamber with a prechamber volume V. The volume V is, for example, 200 to 600 mm 3 large. The length L of the insulator and the volume V are advantageously matched to each other so that a ratio V / L in the range of 75 to 200 mm 2 lies.
Claims
Claims 1 . Spark plug (1) with a longitudinal axis X, comprising • a housing (2) with a longitudinal bore parallel to the longitudinal axis X of the spark plug (1), whereby the housing (2) has a housing wall (20) and an interior (21), • an insulator (3) arranged within the housing (2) • a central electrode (4) arranged within the insulator (3), • a ground electrode (5) with a total length LMQEI and a diameter DwiaEi, • a bore (50) in the housing wall (20) with a diameter of Dßohr, wherein the ground electrode (5) with a length Lßohr is arranged in this bore (50) and the ground electrode (5) with a length L em protrudes from the inside (20a) of the housing wall (20) into the interior (21) of the housing (2), and wherein the housing wall (20) has a thickness Lwaii in the region of the bore (50), and • an ignition gap (45) formed between the ground electrode (5) and the center electrode (4), characterized in that the ratio of the total length LwiaEi of the ground electrode (5) to the length Lß O hr of the ground electrode (5) in the bore (50) is equal to or greater than 1.8 and equal to or less than 2.2 and / or the ratio of the length L em , with which the ground electrode (5) projects into the interior (21) of the housing (2), to the thickness Lwaii of the housing wall (20) is equal to or greater than 0.2 and equal to or less than 3, wherein the lengths and the thickness extend perpendicular to the longitudinal axis X of the spark plug (1).
2. Spark plug (1) according to one of the preceding claims, characterized in that the ratio of the length L em , with which the ground electrode (5) projects into the interior (21) of the housing (2), to the thickness Lwaii of the housing wall (20) is equal to or less than 2, in particular 1.
3. Spark plug (1) according to one of the preceding claims, characterized in that the ground electrode (5) has a total length l_MaEL of equal to or greater than 2.0 mm and equal to or less than 4.0 mm.
4. Spark plug (1) according to one of the preceding claims, characterized in that the length Lßohr of the ground electrode (5) in the bore (50) and / or the thickness Lwaii of the housing wall (20) are equal to or greater than 1.0 mm and equal to or less than 2.5 mm.
5. Spark plug (1) according to one of the preceding claims, characterized in that the length Lßohr of the ground electrode (5) in the bore is equal to the thickness Lwaii of the housing wall (20).
6. Spark plug (1) according to one of the preceding claims, characterized in that the ground electrode (5) has a length L em of equal to or greater than 0.6 mm and equal to or less than 1.6 mm into the interior (21).
7. Spark plugs (1) according to one of the preceding claims, characterized in that the ground electrode (5) has an electrode base body which is arranged at least partially within the bore and has a diameter ÜMaEi within the bores (50), and a noble metal-containing element with a diameter DEM which is fastened to the electrode base body, wherein a ratio between the diameter DEM of the noble metal-containing element and the diameter DMQEI of the electrode base body in the bore (50) is equal to or less than 1 and equal to or greater than 0.
4.
8. Spark plug (1) according to one of the preceding claims, characterized in that the ignition gap between the center electrode (4) and the ground electrode (5) is a radial ignition gap and / or the ignition gap (45) is formed at least partially, in particular completely, within the interior (21) of the housing (2).
9. Spark plug (1) according to one of the preceding claims, characterized in that the ground electrode (5) in the bore (50) is welded to the housing wall (20), so that between the ground electrode (5) and the housing wall (20) there is a weld seam (52) which has a length LSN of less than or equal to 0.9 * Lwaii and in particular of greater than or equal to 0.3 * Lwaii.
10. Spark plug (1) according to one of the preceding claims, characterized in that the difference between the diameter Dßohr and the diameter DwiaEi is equal to or less than an amount of 0.03 mm.
11. Spark plug (1) according to one of the preceding claims, characterized in that the spark plug (1) has a second ground electrode which, like the first ground electrode (5), is arranged in a further bore in the housing wall (20).
12. Spark plug (1) according to one of the preceding claims, characterized in that the spark plug (1) has a cap (30) which is fastened to the combustion chamber end of the housing (2) and the spark plug (1) is a pre-chamber spark plug, the pre-chamber having a volume V.
13. Spark plugs (1) according to claim 12, characterized in that the insulator (3) projects into the prechamber with a length L, the length L extending from the combustion chamber end of an inner seal arranged between the insulator (3) and the housing (2) to the combustion chamber end of the insulator (3) parallel to the longitudinal axis X of the spark plug (1), and in that the ratio of prechamber volume V to length L of the insulator (1) is equal to or greater than 75 mm 2 and equal to or less than 200 mm 2 in particular the ratio V / L is equal to or greater than 100 mm 2 and / or equal to or less than 150 mm 2 is.