Spark plug with ground electrode inserted into housing wall and improved thermal balance

Abstract

The invention relates to a spark plug (1) having a longitudinal axis X, comprising: a housing (2) having 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 space (21); an insulator (3) arranged inside the housing (2); an intermediate electrode (4) arranged inside the insulator (3); a ground electrode (5) having a total length LMaEI and a diameter DMaEI; a bore (50) in the housing wall (20) having a diameter DBohr, the ground electrode (5) being arranged in the bore (50) with a length LBohr and the ground electrode (5) protruding with a length Lem from an inner face (20a) of the housing wall (20) into an interior (21) of the housing (2), and the housing wall (20) having a thickness Lwall in the region of the bore (50); and an ignition gap (45), which is formed between the ground electrode (5) and the intermediate electrode (4), wherein the ratio of the total length LMaEI of the ground electrode (5) to the length LBohr 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 Lem of the ground electrode (5) for projecting into the interior (21) of the housing (2) to the thickness Lwall of the housing wall (20) is equal to or greater than 0.2 and equal to or less than 3, wherein the length or thickness extends perpendicular to a longitudinal axis X of the spark plug (1).

Description

Field of the Invention

[0001] The present invention relates to a spark plug according to the preamble of claim 1. Background Art

[0002] In order for spark plugs and pre-chamber spark plugs to exhibit optimal functionality at all operating points, temperature management that needs to be compensated for is required.

[0003] For some time now, there has been an increasing pursuit of novel spark plug solutions in which the ignition gap is constructed inside the housing. In one of these solutions, the ground electrode is inserted into a drilled hole in the housing wall and projects from the side into the interior space of the housing. A pre-chamber spark plug is known from DE 10 2017 221 517 A, in which the ground electrode is arranged in a drilled hole in the housing wall and projects from the side into the interior space.

[0004] In novel spark plug solutions with a ground electrode arranged in a drilled hole in the housing wall and projecting from the side into the interior space, new challenges arise in terms of the thermal management of the spark plug. For current spark plugs, temperature management is influenced by many different factors. Some of these factors are material selection, the length of the intermediate electrode and the insulator, and the construction of the electrode with or without a copper core, as well as the position of the spark plug in the combustion chamber. In particular, for pre-chamber spark plugs, an additional self-contained combustion chamber inside the spark plug is added as a factor. The pre-chamber spark plug must receive the combustion gases in the spray from the nozzle and is thus arranged in a very hot area of the combustion chamber of the engine. Summary of the Invention

[0005] The object of the present invention is to provide a spark plug that has reliable thermal management during operation.

[0006] Advantages of the Invention / Disclosure of the Invention:

[0007] This object is solved by the spark plug according to the invention.

[0008] The spark plug according to the invention has a longitudinal axis X that extends from the combustion chamber side end of the spark plug to the end facing away from the combustion chamber. The spark plug further has: a housing that has a longitudinal drilled hole parallel to the longitudinal axis X of the spark plug, whereby the housing has a housing wall and an interior space; and an insulator arranged inside the housing, in which an intermediate electrode is arranged. In addition, the spark plug has a ground electrode having a total length L MaEI and a diameter D MaEI ; a drilled hole in the housing wall having a diameter D Bohr ; and an ignition gap constructed between the ground electrode and the intermediate electrode. The ground electrode has a length L BohrArranged in a bore in the housing wall and having a length L em extends from the inner side of the housing wall into the interior space of the housing. The housing wall has a thickness L in the region of the bore wall .

[0009] Advantageously,

[0010] · The total length L of the ground electrode MaEI and the length L of the ground electrode in the bore Bohr are in a ratio equal to or greater than 1.8 and equal to or less than 2.2 and / or

[0011] · The length L of the ground electrode for extending into the interior space of the housing em and the thickness L of the housing wall wall are in a ratio equal to or greater than 0.2 and equal to or less than 3, where the length or the thickness extends perpendicular to the longitudinal axis X of the spark plug.

[0012] Thereby, a spark plug with an improved thermal balance is produced.

[0013] Due to the advantageous ratio of 1.8 to 2.2 of the total length L of the ground electrode MaEI and the length L of the ground electrode in the bore Bohr , reliable thermal management in the spark plug is achieved. The length L of the ground electrode in the bore Bohr is proportional to the contact surface between the ground electrode and the bore. The larger the contact surface between the ground electrode and the bore, the better the heat dissipation from the ground electrode into the housing. Through this inventive ratio of L MaEI to L Bohr , a sufficient contact length of the ground electrode with the bore and the housing wall is produced, such that the heat absorbed by the ground electrode in the interior space of the housing can be dissipated sufficiently through the contact surface in the bore in the housing wall.

[0014] As an alternative, if the ratio of the length L of the ground electrode for extending into the interior space of the housing em to the thickness L of the housing wall Wall is equal to or greater than 0.2 and equal to or less than 3, then this technical effect is also achieved. If both advantageous length ratios are achieved, the desired technical effect of reliable temperature management is enhanced.

[0015] The length or the thickness extends perpendicular to the longitudinal axis X of the spark plug and is measured accordingly.

[0016] The ratios or differences mentioned above affect the heat transfer from the ground electrode to the inside of the housing and thus the thermal balance of the spark plug. Each ratio by itself or the difference results in a spark plug with an improved thermal balance. The combination of two or all advantageous design variants of the spark plug according to the invention results in an enhancement of the technical effect.

[0017] Advantageous developments of the invention are the subject matter of the dependent claims.

[0018] In an advantageous design variant of the invention, it is provided that the length L of the ground electrode that projects into the interior space of the housing em and the thickness L of the housing wall Wall have a ratio that is equal to or less than 2, in particular 1. The less the ground electrode projects into the interior space, the less heat the ground electrode can absorb that has to be dissipated through the contact surface in the borehole in the housing wall. The thickness of the housing wall in the region of the borehole also predetermines the maximum length of the borehole and thus also the maximum length of the ground electrode that can be inserted into the borehole. Thereby, the thickness of the housing wall also affects the maximum contact surface between the ground electrode in the borehole and the housing, where the size of the contact surface affects the quality of heat dissipation and temperature management.

[0019] In a development, it is provided that the ground electrode has a total length L that is equal to or greater than 2.0 mm and equal to or less than 4.0 mm MaEL . By this limitation of the length of the ground electrode, it is ensured that the ground electrode is neither too short nor too long. In the case of a too short ground electrode, the contact length in the borehole in the housing wall may be too short for sufficient heat dissipation. In the case of a too long ground electrode, it absorbs more heat and requires a correspondingly longer contact surface in the borehole in the housing wall for sufficient heat dissipation. For common spark plug types with different dimensions, the upper and lower limit values for the length of the ground electrode form a good compromise between a ground electrode that is long enough for a good contact length and a ground electrode that is not too long (a ground electrode that is not too long absorbs more heat than it dissipates).

[0020] In another advantageous design variant of the invention, it is provided that the length L of the ground electrode in the borehole Bohr and / or the thickness L of the housing wall Wall is equal to or greater than 1.0 mm and equal to or less than 2.5 mm. Particularly advantageous is that the length L of the ground electrode in the borehole Bohr is equal to the thickness L of the housing wall Wall , whereby on the one hand the ground electrode has the maximum possible contact surface and in addition the ground electrode closes the borehole flush with the outer side of the housing, whereby the production of the spark plug is simplified compared to a ground electrode that terminates inside the borehole or outside the borehole.

[0021] In another advantageous design of the present invention, it is provided that the grounding electrode has a length L that is equal to or greater than 0.6 mm and equal to or less than 1.6 mm em and extends into the interior space. By means of the length L of the grounding electrode for extending into the interior space em of the upper limit, it is ensured that the grounding electrode does not extend too far into the interior space and thus does not absorb too much heat that is then dissipated through the housing

[0022] In an expansion scheme of the present invention, the grounding electrode has an electrode substrate and a noble metal-containing element having a diameter D EM wherein the electrode substrate is at least partially arranged inside the drill hole and has a diameter D inside the drill hole MaEI and wherein the noble metal-containing element is fixed to the electrode substrate. Advantageously, the diameter D EM of the noble metal-containing element and the diameter D MaEI of the electrode substrate in the drill hole have a ratio that is equal to or less than 1 and equal to or greater than 0.4. As a result, the different thermal expansion systems of the noble metal-containing element and the electrode substrate are compensated

[0023] In combination or as an alternative, in another design, it is provided that the ignition gap between the intermediate electrode and the grounding electrode is a radial ignition gap, and / or the ignition gap is at least partially, in particular completely, constructed within the interior space of the housing

[0024] In an advantageous expansion scheme, the spark plug has a second grounding electrode, which is arranged in another drill hole in the housing wall like the first grounding electrode. The same advantageous design and the same advantageous length ratio apply to the second grounding electrode as to the first grounding electrode

[0025] It has proven advantageous that the grounding electrode and / or the second grounding electrode are pressed into the drill hole and / or welded to the housing wall

[0026] For a spark plug with a pressed-in grounding electrode, if the difference between the diameter of the grounding electrode and the diameter of the drill hole is equal to or less than a magnitude of 0.03 mm, an improved thermal balance is achieved. The smaller the difference, the better the fit between the grounding electrode and the housing, so that good heat transfer is generated between the grounding electrode and the housing. Additionally, good holding force is generated, such that the grounding electrode is reliably placed in the drill hole and does not move in the drill hole or even fall out of the drill hole

[0027] For a spark plug with a grounding electrode welded in the drill hole, if the weld between the grounding electrode and the housing wall has a length L SNnot greater than 0.9 * the thickness L of the housing wall Wall and in particular not less than 0.3 * the thickness L of the housing wall Wall , a good thermal balance is achieved. For example, it is also advantageous if the length of the weld seam is equal to or greater than 0.5 * the thickness L of the housing wall Wall and / or equal to or less than 0.7 * the thickness L of the housing wall Wall .

[0028] In an advantageous expansion scheme of the present invention, it is stipulated that the spark plug has a cap which is fixed at the combustion chamber side end of the housing and the spark plug is a pre-chamber spark plug, wherein the pre-chamber has a volume V.

[0029] In an expansion scheme of the spark plug as a pre-chamber spark plug, it is advantageous that the insulator extends into the pre-chamber with a length L, wherein the length L extends parallel to the longitudinal axis X of the spark plug from the combustion chamber side end of the internal seal arranged between the insulator and the housing to the combustion chamber side end of the insulator, and the ratio of the pre-chamber volume V to the 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 2 . As a result, the insulator does not absorb too much heat from the pre-chamber and at the same time is not too cold so that no unwanted deposits are formed on the insulator. Description of the Drawings

[0030] Figure 1 Shows an example of a spark plug with a ground electrode according to the present invention.

[0031] Figure 2 Shows a second example of a spark plug with two ground electrodes according to the present invention. Detailed Description

[0032] Figure 1 and 2 Show two embodiments of the spark plug 1 according to the present invention. The combustion chamber side halves of the spark plug 1 are shown in a sectional view. The main difference between the two embodiments is that in Figure 1 the spark plug 1 with a ground electrode 5 is shown and in Figure 2 the spark plug 1 with two ground electrodes is shown. In Figure 2 an optional cap 30 at the combustion chamber side end of the housing is shown. The embodiment according to Figure 2 can also be realized without a cap. The embodiment according to Figure 1 can also be realized correspondingly with a cap 30.

[0033] The spark plug 1 according to the present invention has a longitudinal axis X. The spark plug 1 includes 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 axes. The housing 2 has a housing wall 20 and an inner space 21.

[0034] An intermediate electrode 4 is arranged in the insulator 3. The spark plug 1 has a ground electrode 5 having a length L MaEI and a diameter D MaEI , where the length of the ground electrode 5 is, for example, 2 mm to 4 mm and the diameter is, for example, 1 mm to 2 mm. The intermediate electrode 4 and the ground electrode 5 are arranged relative to each other such that an ignition gap 45 is formed. For example, the ignition gap 45 is configured as a radial ignition gap. Preferably, the ignition gap 45 is at least partially, in particular completely, configured in the inner space 21 of the housing 2.

[0035] The ground electrode 5 can, for example, have a noble metal-containing element 55, which forms the end of the ground electrode 5 on the ignition gap side. If the ground electrode 5 has a noble metal-containing element 55, the ground electrode 5 consists of an electrode substrate 56 and the noble metal-containing element 55, where the noble metal-containing element 55 is fixed to the electrode substrate 56. The noble metal-containing element 55 has a diameter D of 0.6 - 1.1 mm EM . D EM The ratio to D MaEI is 0.4 to mm, especially 0.55 - 0.6 mm, thereby compensating for the different thermal expansion coefficients of the noble metal-containing element 55 and the electrode substrate 56, which is, for example, made of a nickel alloy.

[0036] The diameter D of the ground electrode 5 MaEI is measured at its thickest part or at the thickest part of the electrode substrate 56. This thickest part is typically in the section of the ground electrode 5 arranged inside the bore 50 of the housing 2.

[0037] The housing 2 has at least one bore 50 in the housing wall 20 having a diameter D Bohr , for example, D Bohr is 1 mm to 2 mm. The housing wall 20 has a thickness L Wall , L Wall , for example, is 1.5 to 2.5 mm. The ground electrode 5 is arranged in this bore 50. The ground electrode 5 is in the bore 50 with a length L Bohr . The ground electrode 5 extends from the inner side 20a of the housing 2 into the inner space 21 of the housing 2 with a length L em . The sum of the lengths L Bohr and L em results in the total length L of the ground electrodeMaEI Length L Bohr For example, 1 to 2 mm. Length L Em For example, 0.6 to 1.6 mm. Length L MaEI For example, 1.6 to 3.6 mm.

[0038] For a spark plug 1 with good thermal balance, the following ratios have proven to be advantageous:

[0039] ·L MaEI / L Bohr =1.8 to 2.2

[0040] ·L EM / L Wall = 0.2 to 3

[0041] In this example, ground electrode 5 is welded to housing wall 20 in borehole 50. Weld seam 52 is formed along the circumference of ground electrode 5. Weld seam 52 extends from the outer side of housing 2 in the direction of longitudinal axis X of spark plug. Weld seam 52 has a length L SN , which is advantageously smaller than the thickness L of the housing wall 20 Wall , so that the weld seam 52 does not extend all the way to the inner side of the housing 2.

[0042] Furthermore, the housing 2 has a seat 25 on its inner side. The insulator 3 rests on the housing seat 25 with its shoulder or insulator seat 35. An inner seal 10 is arranged between the insulator seat 35 and the housing seat 25. From the combustion chamber-side end of the inner seal to the combustion chamber-side end of the insulator 3, the insulator 3 extends over a length L into the interior 21 of the housing 2. The length L of the insulator 3 is, for example, 2.5 to 5.5 mm.

[0043] As in Figure 2 As shown in the example, a cap 30 can be arranged on the end face of the housing 2 on its combustion chamber side. The housing 2 and the cap 30 together form a pre-combustion chamber with a pre-combustion chamber volume V. The volume V is, for example, 200 to 600 mm 3 The length L and the volume V of the insulating body are advantageously matched to one another in such a way that the ratio V / L is between 75 and 200 mm. 2 within the range.

Claims

1. A spark plug (1) having a longitudinal axis X, the spark plug comprising: · A housing (2) having 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 internal space (21), · An insulator (3) disposed inside the housing (2), · A center electrode (4) disposed inside the insulator (3), ·Has a total length L MaEI and diameter D MaEI The ground electrode (5) · A borehole (50) in the housing wall (20) having a diameter D Bohr , wherein The grounding electrode (5) has a length L Bohr is arranged in the borehole (50) and the grounding electrode (5) has a length L em extends from the inner side (20a) of the housing wall (20) into the interior space (21) of the housing (2), and wherein the housing wall (20) has a thickness L in the region of the borehole (50) wall , and · A spark gap (45) configured between the ground electrode (5) and the center electrode (4), wherein, The total length L of the grounding electrode (5) MaEI and the length L of the grounding electrode (5) in the drill hole (50) Bohr have a ratio equal to or greater than 1.8 and equal to or less than 2.2 and / or the length L of the grounding electrode (5) for protruding into the interior space (21) of the housing (2) em and the thickness L of the housing wall (20) wall have a ratio equal to or greater than 0.2 and equal to or less than 3, wherein the length or thickness extends perpendicular to the longitudinal axis X of the spark plug (1).

2. The spark plug (1) according to any one of the preceding claims, characterized in that, The length L of the grounding electrode (5) extending into the interior space (21) of the housing (2) em and the thickness L of the housing wall (20) Wall have a ratio equal to or less than 2, especially 1.

3. The spark plug (1) according to any one of the preceding claims, characterized in that, The grounding electrode (5) has a total length L that is equal to or greater than 2.0 mm and equal to or less than 4.0 mm MaEL .

4. The spark plug (1) according to any one of the preceding claims, characterized in that, The length L of the grounding electrode (5) in the borehole (50) Bohr and / or the thickness L of the housing wall (20) Wall is equal to or greater than 1.0 mm and equal to or less than 2.5 mm.

5. The spark plug (1) according to any one of the preceding claims, characterized in that, The length L of the grounding electrode (5) in the borehole Bohr is equal to the thickness L of the housing wall (20) Wall .

6. The spark plug (1) according to any one of the preceding claims, characterized in that, The grounding electrode (5) extends into the internal space (21) with a length L that is equal to or greater than 0.6 mm and equal to or less than 1.6 mm. em ​ 7. The spark plug (1) according to any one of the preceding claims, characterized in that, The grounding electrode (5) has an electrode substrate and a precious metal-containing element having a diameter D EM wherein the electrode substrate is at least partially arranged inside the drill hole and has a diameter D inside the drill hole (50) MaEI wherein the precious metal-containing element is fixed to the electrode substrate, and wherein the diameter D of the precious metal-containing element EM and the diameter D of the electrode substrate in the drill hole (50) MaEI has a ratio equal to or less than 1 and equal to or greater than 0.

4.

8. The spark plug (1) according to any one of the preceding claims, characterized in that, the spark gap between the center electrode (4) and the ground electrode (5) is a radial spark gap, and / or the spark gap (45) is at least partially, in particular completely, configured within the internal space (21) of the housing (2).

9. The spark plug (1) according to any one of the preceding claims, characterized in that, The grounding electrode (5) is welded to the housing wall (20) in the borehole (50), so that there is a weld seam (52) between the grounding electrode (5) and the housing wall (20), and the length of the weld seam is less than or equal to 0.9*L Wall and in particular greater than or equal to 0.3*L Wall .

10. The spark plug (1) according to any one of the preceding claims, characterized in that, The diameter D Bohr and the diameter D MaEI differ by an amount equal to or less than 0.03 mm.

11. The spark plug (1) according to any one of the preceding claims, characterized in that, The spark plug (1) has a second ground electrode, which is arranged in another bore in the housing wall (20) like the first ground electrode (5).

12. The spark plug (1) according to any one of the preceding claims, characterized in that, The spark plug (1) has a cap (30) which is fixed at the combustion chamber side end of the housing (2) and the spark plug (1) is a prechamber spark plug, wherein the prechamber has a volume V.

13. The spark plug (1) according to claim 12, characterized in that, The insulator (3) extends into the pre-chamber by a length L, where the length L extends from the combustion chamber side end of the internal seal arranged between the insulator (3) and the housing (2) up to the combustion chamber side end of the insulator (3) and extends parallel to the longitudinal axis X of the spark plug (1), and the ratio of the pre-chamber volume V to the 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 .

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