Heat optimized prechamber spark plug

Abstract

The invention relates to a prechamber spark plug (1) comprising a center electrode (2), a ground electrode (3), a housing (4) with an outer thread (40), a cap (6) arranged at the housing (4) and defining a prechamber (7) together with the housing (4), an insulator (5) electrically insulating the center electrode (2) from the housing (4), wherein the outer thread (40) of the housing (4) has a thread length (11) in axial direction (X-X) of the prechamber spark plug (1), wherein the housing (4) is fastened at the insulator (5) at a first fastening region (41) and at a second fastening region (42) such that a first clamping force (F1) acts from the housing (4) onto the insulator (5) at the first fastening region (41) and a second clamping force (F2) acts from the housing (4) onto the insulator (5) at the second fastening region (42), wherein the first and second clamping forces (F1, F2) are directed opposite to each other in axial direction (X-X), wherein a distance between the first fastening region (41) and the second fastening region (42) defines a clamping length (12) in axial direction (X-X), and wherein a ratio between the thread length (11) and the clamping length (12) is in a range of 0.7 to 1.3.

Description

Technical Field

[0001] This invention relates to a robust and thermally optimized pre-combustion chamber spark plug that significantly reduces the risk of thermal damage during operation. The invention also relates to an internal combustion engine having such a pre-combustion chamber spark plug. Background Technology

[0002] Pre-combustion chamber spark plugs are known from the prior art in various designs. Pre-combustion chamber spark plugs are commonly used in internal combustion engines that operate using a gaseous medium. Such pre-combustion chamber spark plugs typically have a pre-combustion chamber in which an intermediate electrode and a ground electrode are arranged. The pre-combustion chamber is defined by a cap and a portion of the housing. In the event of excessively high temperatures at the cap and / or at the electrodes, undesirable and uncontrollable pre-ignition may occur. This is undesirable on the one hand due to increased wear, and on the other hand, may result in poor exhaust emissions from the internal combustion engine. In the worst case, substantial damage to the internal combustion engine may occur. Therefore, improved thermal emissions in pre-combustion chamber spark plugs are absolutely necessary. Summary of the Invention

[0003] In contrast, the pre-combustion chamber spark plug according to the invention has the advantage of avoiding excessively high temperatures, especially in the pre-combustion chamber region. In particular, the electrode temperature can be reduced, resulting in a long service life due to reduced wear at the electrodes of the pre-combustion chamber spark plug. The reduced temperature also allows for greater freedom in the selection of materials for the electrodes (e.g., materials with lower thermal conductivity), thereby significantly reducing the cost of the electrodes. Furthermore, the pre-combustion chamber spark plug has improved internal sealing throughout its service life. The invention also provides greater robustness relative to improper operation (e.g., screwing in the pre-combustion chamber spark plug with excessive torque), which could reduce or completely damage the sealing function of the pre-combustion chamber spark plug, allowing gas to potentially escape from the combustion chamber into the atmosphere via the unsealed area at the pre-combustion chamber spark plug. This is achieved according to the invention by the pre-combustion chamber spark plug having a middle electrode and a ground electrode, as well as a housing with external threads. A cap is also provided, which, together with a portion of the housing, defines the pre-combustion chamber. The pre-combustion chamber spark plug also includes an insulator that electrically insulates the intermediate electrode from the housing. The housing has threads with axial extensions and is secured to the insulator via a first and a second fixing region. This securing at the first and second fixing regions is such that a first clamping force acts from the housing to the insulator at the first fixing region, and a second clamping force acts from the housing to the insulator at the second fixing region. These two clamping forces are opposite to each other along the axial direction of the pre-combustion chamber spark plug. The distance between the first and second fixing regions defines the clamping length along the axial direction. Pre-tightening of the housing at the insulator is thus achieved by these two opposing clamping forces. Furthermore, the ratio between the thread length and the clamping length is chosen such that it is in the range of 0.7 to 1.3. This selection of the thread length and clamping length, combined with the pre-tightening of the housing, enables improved sealing over a wide temperature range, thereby meeting the highest sealing requirements of the pre-combustion chamber spark plug. Furthermore, the position of the fixed area obtained by selecting the thread length and clamping length according to the invention ensures that the sealing element inside the pre-combustion chamber spark plug is as far away from the combustion chamber as possible in the cooler cylinder head region, thus providing particularly favorable conditions for heat dissipation of the pre-combustion chamber spark plug. This avoids thermal damage to the components of the pre-combustion chamber spark plug, especially the electrodes. Moreover, selecting the thread length and clamping length according to the invention helps maintain preload at the housing throughout the service life of the pre-combustion chamber spark plug. Therefore, an improved sealing effect can be maintained throughout the service life of the pre-combustion chamber spark plug.

[0004] The specification further illustrates preferred improvements of the invention.

[0005] Further improvements to the pre-combustion chamber spark plug are achieved by preferably having a thread length to clamping length ratio in the range of 0.8 to 1.2. More preferably, the thread length to clamping length ratio is in the range of 0.8 to 1.

[0006] To achieve the most uniform pre-tightening to the housing, it is preferable that the first clamping force and the second clamping force are the same. This achieves uniform pre-tightening of the housing.

[0007] More preferably, the pre-combustion chamber spark plug has inclined portions, i.e., surfaces arranged obliquely relative to the central axis of the pre-combustion chamber spark plug, in both the first and second fixed regions. This allows for good adjustability of the two preload forces in the first and second fixed regions. Particularly preferably, the second fixed region, located on the side of the pre-combustion chamber spark plug away from the combustion chamber, is constructed at the insulator using a crimping process. Furthermore, it is preferable that the first and second fixed regions are arranged on different diameters. Particularly preferably, the second fixed region is arranged on a larger diameter than the first fixed region. This reduces the surface of the housing facing the pre-combustion chamber, thereby generating a smaller heat input into the housing.

[0008] Furthermore, preferably, the pre-combustion chamber spark plug includes a sealing element between the housing and the insulator. The sealing element is preferably a sealing disc. Particularly preferably, the sealing element is arranged in a first fixed area. By applying a preload to the first fixed area, the sealing element preferably deforms, particularly preferably plastically deforms. The sealing element is particularly preferably arranged in the housing on the side of a radially inwardly pointing flange away from the combustion chamber, thereby being protected from high temperatures and, especially, hot gases.

[0009] The sealing element is preferably arranged in the first fixed region. Thus, when the housing is fixed to the insulator, the sealing element can also elastically deform and seal the gap between the housing and the insulator. According to another preferred embodiment of the invention, the first fixed region is located axially in the first half of the thread length extending from the pre-combustion chamber.

[0010] The first fixing area is preferably located at the inner periphery of the shell. The second fixing area is preferably located at the end of the shell opposite to the pre-combustion chamber.

[0011] The first fixed area is preferably provided by an annular bulge formed at the inner periphery of the shell.

[0012] More preferably, the thread length extends from the fastening area between the cap and the housing, i.e., the end of the housing on the combustion chamber side, to the abutment surface of the housing. The abutment surface is provided for abutting against an external component. The abutment surface is preferably perpendicular to the central axis of the pre-combustion chamber spark plug. The abutment surface is provided here, for example, for abutting against the cylinder head, directly or indirectly, for example, by arranging a sealing ring, etc.

[0013] The pre-combustion chamber spark plug is preferably designed for use in internal combustion engines.

[0014] The present invention also relates to an internal combustion engine, particularly a mobile internal combustion engine, having a pre-combustion chamber spark plug according to the invention. The mobile internal combustion engine is preferably used in vehicles. In particular, the pre-combustion chamber spark plug is also provided for use in motorsports. Attached Figure Description

[0015] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings:

[0016] Figure 1 A schematic partial cross-sectional view of a pre-combustion chamber spark plug according to a preferred embodiment of the present invention is shown, and

[0017] Figure 2 It shows Figure 1 A schematic partial cross-sectional view of the spark plug in the pre-combustion chamber. Detailed Implementation

[0018] The following reference Figure 1 and Figure 2 The pre-combustion chamber spark plug 1 according to the first embodiment of the present invention will be described in detail below.

[0019] The pre-combustion chamber spark plug 1 includes an intermediate electrode 2 and a ground electrode 3. A precious metal lead 20 is arranged at the intermediate electrode 2. It should be noted that the precious metal lead can also be arranged at the ground electrode 3.

[0020] The pre-combustion chamber spark plug 1 also includes a housing 4, particularly a housing made of a metallic material, and an insulator 5. The insulator 5 is provided to electrically insulate the intermediate electrode 2 from the housing 4.

[0021] An external thread 40 is also provided at the housing 4. The external thread 40 has a thread length 11, which extends from the first end 4a pointing toward the combustion chamber of the internal combustion engine to the abutment surface 10 at the housing 4 (see [reference]). Figure 2 The abutment surface 10 is perpendicular to the central axis XX of the pre-combustion chamber spark plug. To avoid damaging the external thread, a circumferential groove 10a is provided between the external thread 40 and the abutment surface 10.

[0022] The pre-combustion chamber spark plug 1 also includes a cap 6 (see Figure 1Multiple cap holes 60 are constructed in the cap 6 to allow gas exchange in the pre-combustion chamber 7 and to allow the flame beam to exit from the pre-combustion chamber 7 and enter the combustion chamber of the internal combustion engine for main ignition of the gas mixture. The pre-combustion chamber 7 is defined here by the cap 6 and a portion of the housing 4. The intermediate electrode 2 and the ground electrode 3 are arranged here in the pre-combustion chamber 7.

[0023] For example, especially from Figure 2 As can be seen, the housing 4 is fastened to the insulator 5 at the first fixing region 41 and the second fixing region 42. The housing 4 is fastened such that a first clamping force F1 acts from the housing 4 onto the insulator 5 at the first fixing region 41, and a second clamping force F2 acts from the housing 4 onto the insulator 5 at the second fixing region 42. Here, these two clamping forces F1 and F2 point in opposite directions along the axial direction XX of the pre-combustion chamber spark plug 1. Preferably, these two clamping forces F1 and F2 are of equal magnitude.

[0024] Furthermore, a first inclined portion 5a is provided at the insulator in the first fixed region 41, and a second inclined portion 5b is provided in the second fixed region 42. (As from...) Figure 2 As can be seen, the inclined portions are constructed opposite to each other and are preferably constructed at a 45° angle.

[0025] The two clamping forces F1 and F2 thus achieve pre-tightening of the housing 4 at the insulator 5, causing the housing 4 to widen radially outward. Consequently, when the pre-combustion chamber spark plug 1 is screwed into the cylinder head, an improved seal is achieved between the outer periphery of the pre-combustion chamber spark plug 1 and the cylinder head in the assembled state. Furthermore, the rigidity of the housing's spring characteristic curve applies high surface pressure to the sealing element 9, which is arranged between the housing 4 and the insulator 5, at a short clamping length. The sealing element 9 is positioned on the side of the housing 4 away from the combustion chamber and is protected from extremely hot gases by the radially inward-pointing flange 44.

[0026] Furthermore, the distance between the first fixing region 41 and the second fixing region 42 defines the clamping length 12 of the housing. Therefore, preload is generated in the region of the clamping length 12 of the housing. Additionally, the ratio V between the current thread length 11 and the clamping length 12 is in the range of 0.7 to 1.3. Particularly preferably, the ratio between the thread length 11 and the clamping length 12 is in the range of 0.8 to 1.2, and more preferably in the range of 0.8 to 1. Here, even more preferably, the ratio between the thread length 11 and the clamping length 12 is less than 1, i.e., the thread length 11 is less than the clamping length 12, wherein the lower limit is 0.7.

[0027] A first fixed region 41 is arranged on a first diameter D1, and a second fixed region 42 is arranged on a second diameter D2. Here, the first diameter D1 is smaller than the second diameter D2.

[0028] By combining the selection of thread length 11 and clamping length 12 with the pre-tightening measure at housing 4, improved robustness and, in particular, sealing performance of the pre-combustion chamber spark plug 1 are achieved. Furthermore, the clever selection of thread length 11 and clamping length 12 enables significantly improved heat dissipation of the pre-combustion chamber spark plug 1 during operation, thereby achieving a long service life due to moderate electrode temperatures.

[0029] Because the temperature at the electrode is significantly lower than that of current pre-combustion chamber spark plugs, greater freedom is available in the selection of electrode materials, thereby reducing electrode costs. Furthermore, pre-tightening at the first and second fixing regions between the housing 4 and the insulator 5 improves the internal sealing of the pre-combustion chamber spark plug 1 throughout its service life. The selection of the thread length 11 and clamping length 12 also has a positive impact on misassembly; for example, when tightening the pre-combustion chamber spark plug 1 with excessive torque, the careful length selection prevents damage to the pre-combustion chamber spark plug 1 due to excessive tightening torque.

[0030] A particularly preferred ratio V of thread length to clamping length can be obtained, for example, based on the thread diameter of the external thread 40, as shown in the table below:

[0031] Thread outer diameter Thread length / clamping length Ratio V M10 26.5 / 30 0.83 M12 26.5 / 27 0.98 M14 25.0 / 25.0 1.0

[0032] Therefore, by means of the measures according to the invention, a significantly improved service life and reduced operating temperature can be achieved for the components of the pre-combustion chamber spark plug 1, particularly the electrodes. Thus, the pre-combustion chamber spark plug 1 according to the invention is particularly suitable for internal combustion engines in stationary or mobile applications, as well as in motorsports.

Claims

1. A pre-chamber spark plug (1), comprising: - a center electrode (2), - a ground electrode (3), - a housing (4) having an outer thread (40), - a cap (6) arranged at the housing (4) and defining a pre-chamber (7) together with the housing (4), - an insulator (5) electrically insulating the center electrode (2) from the housing (4), - wherein the outer thread (40) of the housing (4) has a thread length (11) in axial direction (X-X) of the pre-chamber spark plug (1), - wherein the housing (4) is fastened at the insulator (5) at a first fixation area (41) and at a second fixation area (42) such that a first clamping force (Fl) acts from the housing (4) onto the insulator (5) at the first fixation area (41) and a second clamping force (F2) acts from the housing (4) onto the insulator (5) at the second fixation area (42), wherein the first and second clamping forces (Fl, F2) are directed opposite to each other in axial direction (X-X), - wherein a spacing between the first fixation area (41) and the second fixation area (42) defines a clamping length (12) in axial direction (X-X), wherein the first fixation area (41) is located within the thread length (11), and - wherein a ratio between the thread length (11) and the clamping length (12) is in a range of 0.7 to 1.

3.

2. The pre-chamber spark plug (1) according to claim 1, characterized in that The ratio between the thread length (11) and the clamping length (12) is in a range of 0.8 to 1.

2.

3. The pre-chamber spark plug (1) according to claim 1, characterized in that The ratio between the thread length (11) and the clamping length (12) is in a range of 0.8 to 1.

0.

4. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that The first clamping force (Fl) is as large as the second clamping force (F2).

5. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that The insulator (5) has a first bevel (5a) at the first fixation area (41) and a second bevel (5b) at the second fixation area (42).

6. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that The first fixation area (41) is arranged at a smaller diameter than the second fixation area (42).

7. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that A sealing element (9) is further included, which is arranged between the housing (4) and the insulator (5).

8. The pre-chamber spark plug (1) according to claim 7, characterized in that The sealing element (9) is arranged close to the pre-chamber (7).

9. The pre-chamber spark plug (1) according to claim 7, characterized in that The sealing element (9) is arranged at a combustion chamber facing side of a radially inwardly directed flange (44).

10. The pre-chamber spark plug (1) according to claim 7, characterized in that The sealing element (9) is arranged at the first fixation area (41).

11. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that The first fixation area (41) is located in a first half (11a) of the thread length (11) in axial direction (X-X) from the pre-chamber (7).

12. The pre-chamber spark plug (1) according to any one of claims 1 to 3, characterized in that The thread length (11) extends from a first end (4a) of the housing (4) up to an abutment face (10) of the housing (4), at which the cap (6) is fastened at the first end, wherein the abutment face is provided for abutting at an outer member.

13. The pre-chamber spark plug (1) according to claim 9, characterized in that The abutment surface of the flange (44) is inclined in the direction away from the end of the prechamber spark plug facing the combustion chamber.

14. An internal combustion engine comprising a prechamber spark plug (1) according to any one of claims 1 to 13.

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