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

Abstract

SOLUTION: 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 internal space (21); an insulator (3) disposed inside the housing (2); a center electrode (4) disposed inside the insulator (3); and an overall length L MaEI and D MaEI a ground electrode (5) having a diameter of D Bohr The hole (50) in the housing wall (20) has a diameter of 1.5 mm, and the ground electrode (5) has a length L Bohr The ground electrode (5) is disposed in the hole (50) with a length L em The housing wall (20) projects from the inner surface (20a) of the housing wall (20) into the interior space (21) of the housing (2) with a thickness D Wall and a spark gap (45) formed between the ground electrode (5) and the center electrode (4), and a length L of the ground electrode (5) in the hole (50). Bohr The total length L of the ground electrode (5) MaEI is greater than or equal to 1.8 and less than or equal to 2.2, and / or the thickness L of the housing wall (20) Wall The length L of the ground electrode (5) projecting into the internal space (21) of the housing (2) relative to the em The ratio is greater than or equal to 0.2 and less than or equal to 3, and the length or thickness extends perpendicular to the major axis X of the spark plug (1).

Description

[Technical Field]

[0001] The present invention is based on the spark plug as set forth in the preamble of claim 1. [Background technology]

[0002] A balanced thermal management is required for spark plugs and pre-chamber spark plugs to perform optimally at all operating points.

[0003] In recent years, new spark plug concepts have been increasingly pursued in which the spark gap is formed inside the housing. In such concepts, the ground electrode is inserted into a hole in the housing wall and projects laterally from the housing wall into the interior space of the housing. Patent document 1 discloses a pre-chamber spark plug in which the ground electrode is arranged in a hole in the housing wall and projects laterally into the interior space.

[0004] New spark plug concepts, with a ground electrode located in a hole in the housing wall and projecting laterally into the interior space, present new challenges for the spark plug's thermal management. In current spark plugs, thermal management is affected by a number of different factors. Some of these factors are the material selection, the length of the center electrode and insulator, the electrode configuration with or without a copper core, and the spark plug's location within the combustion chamber. Pre-chamber spark plugs, in particular, add a unique additional combustion chamber within the spark plug. Pre-chamber spark plugs must contain the combustion gases within the spray from the injection nozzle and are therefore located in a very hot area of ​​the engine's combustion chamber. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] German Patent Application Publication No. 102017221517 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a spark plug having temperature management with high operational reliability. [Means for solving the problem]

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

[0008] The spark plug according to the present invention has a longitudinal axis X extending from the end of the spark plug facing the combustion chamber to the end facing away from the combustion chamber. The spark plug further has 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 disposed within the housing, in which the center electrode is disposed. The spark plug further has an overall length L MaEI and diameter D MaEI a ground electrode having a Bohr The spark gap is formed between the ground electrode and the center electrode. Bohr and placed in a hole in the housing wall with a length of L em The housing wall protrudes from the inner surface of the housing wall into the interior space of the housing with a thickness L Wall It has.

[0009] Preferably, Length of the ground electrode in the hole L Bohr The total length of the ground electrode L MaEI is greater than or equal to 1.8 and less than or equal to 2.2, and / or Housing wall thickness L Wall The length L of the ground electrode protruding into the internal space of the housing em The ratio is greater than or equal to 0.2 and less than or equal to 3, and the length or thickness extends perpendicular to the major axis X of the spark plug.

[0010] This results in a spark plug with improved heat balance.

[0011] Length of the ground electrode in the hole L Bohr The total length of the ground electrode L MaEI The preferred ratio of 1.8 to 2.2 results in reliable thermal management of the spark plug. Bohr is proportional to the contact area between the hole and the ground electrode. The larger the contact area between the ground electrode and the hole, the better the heat dissipation from the ground electrode to the housing. Bohr L for MaEI This ratio provides a sufficiently large contact length between the ground electrode and the hole and the housing wall, so that the heat received by the ground electrode in the interior space of the housing can be sufficiently dissipated through the contact surface at the hole in the housing wall.

[0012] Alternatively, such a technical effect can be achieved by reducing the thickness of the housing wall L Wall The length L of the ground electrode protruding into the internal space of the housing em This is also achieved when the ratio is greater than or equal to 0.2 and less than or equal to 3. If both of these preferred length ratios are met, the desired technical effect of highly reliable temperature management is further enhanced.

[0013] The length or thickness extends perpendicular to the major axis X of the spark plug and is measured accordingly.

[0014] The above ratios or differences affect the heat transfer from the ground electrode to the housing and therefore the heat balance of the spark plug. Each ratio or difference alone leads to a spark plug with an improved heat balance. The combination of two or all preferred embodiments of the spark plug according to the present invention leads to an enhanced technical effect.

[0015] Preferred developments of the invention are the subject of the dependent claims.

[0016] In a preferred embodiment of the present invention, the thickness of the housing wall L Wall The length L of the ground electrode protruding into the internal space of the housing em The ratio is intended to be less than or equal to 2, and in particular to be 1. The less the ground electrode extends into the interior space, the less heat it can receive, which must be evacuated through its contact surface in the housing wall hole. The thickness of the housing wall in the region of the hole also sets the maximum length of the hole and therefore the maximum length over which the ground electrode may be inserted into the hole. The thickness of the housing wall thus also influences the maximum contact surface between the ground electrode in the hole and the housing, and the size of the contact surface influences the quality of heat evacuation and temperature management.

[0017] In the developed form, the ground electrode has a total length L of 2.0 mm or more and 4.0 mm or less. MaEI It is intended that the ground electrode length be within the range of 1 / 2 to 1 / 4" (1 / 4 to 1 / 4). Limiting the ground electrode length in this manner ensures that the ground electrode is neither too short nor too long. If the ground electrode is too short, the contact length within the housing wall bore may be too short for adequate heat evacuation. If the ground electrode is too long, the ground electrode will receive more heat and a correspondingly longer contact surface within the housing wall bore will be required for adequate heat evacuation. For current spark plug types with a variety of different sizes, the upper and lower limits for ground electrode length are a good compromise between a ground electrode that is long enough for good contact length and one that is not so long that it receives more heat than it can evacuation.

[0018] In another preferred embodiment of the present invention, the length L of the ground electrode in the hole Bohr and / or the housing wall thickness L Wall is intended to be 1.0 mm or more and 2.5 mm or less. In particular, the length L of the ground electrode in the hole Bohr where the housing wall thickness L Wallwhereby, on the one hand, the ground electrode has the largest possible contact surface, and, further, the ground electrode closes the bore flush with the housing exterior surface, thereby simplifying manufacture of the spark plug compared to ground electrodes that terminate inside the bore or that terminate outside the bore.

[0019] In another preferred embodiment of the present invention, the ground electrode has a length L of 0.6 mm or more and 1.6 mm or less. em The length L of the ground electrode that penetrates into the internal space is em The upper limit for ensures that the ground electrode does not extend too far into the interior space and thus receive too much heat which is later evacuated again through the housing.

[0020] In a further development of the invention, the ground electrode comprises an electrode body and a ground electrode with a diameter D EM and a noble metal-containing member having a diameter D MaEI The noble metal-containing member has a diameter D EM and the diameter D of the electrode body in the hole MaEI Preferably, the ratio between is less than 1 and greater than 0.4, thereby compensating for the different thermal expansion coefficients of the noble metal-containing member and the electrode body.

[0021] In yet another embodiment, it is contemplated, in combination or as an alternative, that the spark gap between the center electrode and the ground electrode is a radial spark gap and / or that the spark gap is formed at least partially, in particular entirely, within the interior space of the housing.

[0022] In a preferred development, the spark plug has a second ground electrode arranged in a separate hole in the housing wall in the same manner as the first ground electrode, for which the same preferred embodiments and preferred length ratios as for the first ground electrode apply.

[0023] It has proven preferable for the ground electrode and / or the second ground electrode to be pressed into the hole and / or welded to the housing wall.

[0024] For spark plugs with press-fit ground electrodes, a difference between the diameter of the ground electrode and the diameter of the bore of 0.03 mm or less provides improved heat balance. The smaller this difference, the better the fit between the ground electrode and the housing, which provides good heat transfer between the ground electrode and the housing. In addition, it provides good retention, which ensures that the ground electrode is securely located in the bore and does not shift or even fall out of the bore.

[0025] For spark plugs in which the ground electrode is welded in the hole, the weld seam between the ground electrode and the housing wall must be 0.9 * Housing wall thickness L Wall Not greater than 0.3 * Housing wall thickness L Wall Length L, not less than SN For example, if the length of the weld seam is 0.5 * Housing wall thickness L Wall is greater than or equal to 0.7 * Housing wall thickness L Wall It is also preferred that:

[0026] In a preferred development of the invention, it is provided that the spark plug has a cap attached to the combustion chamber-side end of the housing, the spark plug being a pre-chamber spark plug, the pre-chamber having a volume V.

[0027] In a development of the spark plug as a pre-chamber spark plug, the insulator preferably extends into the pre-chamber with a length L, the length L extending parallel to the longitudinal axis X of the spark plug from the combustion chamber side end of the inner 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 insulator length L is 75 mm2 More than 200mm 2 In particular, the ratio V / L is 100 mm 2 and / or 150mm 2 This ensures that the insulator does not receive too much heat from the pre-chamber, and at the same time is not too cold, in order to prevent unwanted deposits from forming on the insulator. [Brief explanation of the drawings]

[0028] [Figure 1] 1 shows an example of a spark plug of the present invention having one ground electrode. [Figure 2] 1 shows a second example of a spark plug of the present invention having two ground electrodes. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1 and 2 show two embodiments of a spark plug 1 according to the present invention. Each combustion chamber-side half of the spark plug 1 is shown in cross section. Both embodiments are essentially distinguished by the fact that in FIG. 1 a spark plug 1 with one ground electrode 5 is shown, while in FIG. 2 a spark plug 1 with two ground electrodes is shown. In FIG. 2, an optional cap 30 is shown at the combustion chamber-side end of the housing. The embodiment of FIG. 2 can also be realized without a cap. Correspondingly, the embodiment of FIG. 1 can also be realized with a cap 30.

[0030] A 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 the longitudinal axis. The housing 2 has a housing wall 20 and an interior space 21.

[0031] A center electrode 4 is disposed in the insulator 3. The spark plug 1 has a length L MaEI and diameter D MaEIThe center electrode 4 has a ground electrode 5 having a length of, for example, 2 to 4 mm and a diameter of, for example, 1 to 2 mm. The center electrode 4 and the ground electrode 5 are arranged relative to each other so as to form a spark gap 45. By way of example, the spark gap 45 is formed as a radial spark gap. The spark gap 45 is preferably formed at least partially, in particular entirely, in the interior space 21 of the housing 2.

[0032] The ground electrode 5 may have a noble metal-containing member 55 that forms, for example, the end of the ground electrode 5 on the spark gap side. When the ground electrode 5 has the noble metal-containing member 55, the ground electrode 5 is formed by combining an electrode body 56 and the noble metal-containing member 55, and the noble metal-containing member 55 is attached to the electrode body 56. The noble metal-containing member 55 has a diameter D of 0.6 to 1.1 mm. EM D MaEI D against EM The ratio is 0.4 to mm, particularly 0.55 to 0.6 mm, which compensates for the different thermal expansion coefficients of the noble metal-containing member 55 and the electrode body 56 made of, for example, a nickel alloy.

[0033] Diameter D of the ground electrode 5 MaEI is measured at its widest point, or at the widest point of the electrode body 56, which is typically in the area of ​​the ground electrode 5 located inside the bore 50 of the housing 2.

[0034] The housing 2 has a housing wall 20 with a diameter D Bohr At least one hole 50 having, for example, D Bohr The housing wall 20 in the region of the hole 50 has a thickness L Wall For example, L Wall The ground electrode 5 is disposed in the hole 50. The ground electrode 5 has a length L Bohr The ground electrode 5 has a length L em , and protrudes into the internal space 21 of the housing 2 from the inner surface 20a of the housing 2.Bohr and L em The sum of these is the total length L of the ground electrode MaEI Length L Bohr is, for example, 1 to 2 mm. Em is, for example, 0.6 to 1.6 mm. MaEI is, for example, 1.6 to 3.6 mm.

[0035] For a spark plug 1 with a good heat balance, the following ratios have been found to be preferable: L MaEI / L Bohr =1.8 to 2.2 L EM / L Wall =0.2 to 3

[0036] In this example, the ground electrode 5 is welded to the housing wall 20 in the hole 50. A weld seam 52 is formed along the circumference of the ground electrode 5. The weld seam 52 extends from the outer surface of the housing 2 in the direction of the longitudinal axis X of the spark plug. The weld seam 52 is formed within the thickness L of the housing wall 20 so that the weld seam 52 does not reach the inner surface of the housing 2. Wall Length shorter than L SN It is preferred that the

[0037] Furthermore, the housing 2 has a seat 25 on its inner surface. 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 into the interior space 21 of the housing 2 by a length L. The length L of the insulator 3 is, for example, 2.5 to 5.5 mm.

[0038] As shown by way of example in Figure 2, the housing 2 may have a cap 30 arranged on its end surface facing the combustion chamber. The housing 2 and the cap 30 together form a prechamber having a prechamber volume V. The volume V may be, for example, 200 to 600 mm 3The length L and volume V of the insulator are in the range of 75 to 200 mm. 2 Preferably, they are adjusted to be within the range of [Explanation of symbols]

[0039] 1 spark plug 2. Housing 3. Insulators 4 Center electrode 5 Ground electrode 20 Housing Wall 20a inner surface 21 Interior Space 45 Spark Gap 50 holes 52 Welded seam L MaEI Overall length of ground electrode D MaEI Ground electrode diameter D Bohr Hole diameter L em Ground electrode penetration length L Wall Housing Wall Thickness L Bohr Hole length D MaEI Electrode body diameter D EM Diameter of precious metal-containing component L: Insulator penetration length X long axis V prechamber volume

Claims

1. A spark plug (1) having a longitudinal axis X, 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) arranged inside the housing (2); a central electrode (4) disposed inside the insulator (3); ・Total length L ＭａＥＩ and diameter D ＭａＥＩ a ground electrode (5) having ・D Ｂｏｈｒ The hole (50) in the housing wall (20) has a diameter of 1.5 mm, and the ground electrode (5) has a length L Ｂｏｈｒ and the ground electrode (5) is disposed in the hole (50) with a length L ｅｍ and the housing wall (20) projects from the inner surface (20a) of the housing wall (20) into the interior space (21) of the housing (2) with a thickness D Ｗａｌｌ and a spark gap (45) formed between the ground electrode (5) and the center electrode (4); A spark plug having The length L of the ground electrode (5) in the hole (50) Ｂｏｈｒ The total length L of the ground electrode (5) ＭａＥＩ is greater than or equal to 1.8 and less than or equal to 2.2, and / or the thickness L of the housing wall (20) is Ｗａｌｌ The length L of the ground electrode (5) projecting into the internal space (21) of the housing (2) relative to ｅｍ is greater than or equal to 0.2 and less than or equal to 3, and said length or thickness extends perpendicular to the longitudinal axis X of said spark plug (1).

2. The thickness L of the housing wall (20) Ｗａｌｌ The length L of the ground electrode (5) projecting into the internal space (21) of the housing (2) relative to ｅｍ 2. A spark plug (1) according to claim 1, characterized in that the ratio is less than or equal to 2, in particular 1.

3. The ground electrode (5) has a total length L of 2.0 mm or more and 4.0 mm or less. ＭａＥＩ 3. A spark plug (1) according to claim 1 or 2, characterized in that:

4. The length L of the ground electrode (5) in the hole (50) Ｂｏｈｒ and / or the thickness L of the housing wall (20) Ｗａｌｌ The spark plug (1) according to any one of claims 1 to 3, characterized in that is equal to or greater than 1.0 mm and equal to or less than 2.5 mm.

5. The length L of the ground electrode (5) in the hole Ｂｏｈｒ is the thickness L of the housing wall (20) Ｗａｌｌ 5. A spark plug (1) according to any one of claims 1 to 4, characterized in that it is equal to

6. The ground electrode (5) has a length L of 0.6 mm or more and 1.6 mm or less. ｅｍ 6. A spark plug (1) according to claim 1, characterized in that it projects into the internal space (21) with a force of 0.5 .mu.m.

7. The ground electrode (5) is disposed at least partially inside the hole (50) and has a diameter D ＭａＥＩ an electrode body having a diameter D ＥＭ and a precious metal-containing member having a diameter D ＥＭ and the diameter D of the electrode body in the hole (50). ＭａＥＩ 7. A spark plug (1) according to any one of claims 1 to 6, characterized in that the ratio between is less than or equal to 1 and greater than or equal to 0.

4.

8. 8. A spark plug (1) according to claim 1, 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 formed at least partially, in particular entirely, within the interior space (21) of the housing (2).

9. The ground electrode (5) is welded to the housing wall (20) in the hole (50), so that there is a 0.9 ＊ L Ｗａｌｌ The following, especially 0.3 ＊ L Ｗａｌｌ The above length L ＳＮ 9. A spark plug (1) according to any one of claims 1 to 8, characterized in that there is a weld seam (52) having a.

10. The diameter D Ｂｏｈｒ and the diameter D ＭａＥＩ 10. A spark plug (1) according to any one of claims 1 to 9, characterized in that the difference between is less than or equal to a value of 0.03 mm.

11. 11. The spark plug (1) according to claim 1, characterized in that the spark plug (1) has a second ground electrode (5) arranged in a separate hole in the housing wall (20) in the same position as the first ground electrode (5).

12. 12. The spark plug (1) according to claim 1, wherein the spark plug (1) has a cap (30) attached to an end of the housing (2) on the combustion chamber side, the spark plug (1) being a pre-chamber spark plug, and the pre-chamber has a volume V.

13. The insulator (3) extends into the pre-chamber with a length L, which extends parallel to the longitudinal axis X of the spark plug (1) from the combustion chamber side end of an inner seal member disposed between the insulator (3) and the housing (2) to the combustion chamber side end of the insulator (3), and the ratio of the pre-chamber volume V to the length L of the insulator (1) is 75 mm. ２ More than 200mm ２ In particular, the ratio V / L is 100 mm ２ or more and / or 150 mm ２ Spark plug (1) according to claim 12, characterized in that:

Images