Spark plug with a tapering breathing space

Abstract

A spark plug (1) with a longitudinal axis X, having: - a housing (2) with a longitudinal bore, as a result of which the housing (2) has a housing wall (20) with an inner face (21), - an insulator (3), which is arranged within the housing (2) and has a combustion chamber-side insulator tip (30) which is flush with a plane E1 extending perpendicular to the longitudinal axis X, - a centre electrode (4), which is arranged at least partially within the insulator (3), and - an earth electrode (5), which is arranged within the housing (2), the earth electrode (5) and the centre electrode (4) being arranged such that they form a spark gap (55) and the spark gap (55) is within the housing (2), wherein the housing (2) has, at its combustion chamber-side end, a first inside diameter D1 and, within the housing (2) in the plane E1, a second inside diameter D2, the first diameter D1 being greater than the second diameter D2, so that a breathing space (50) formed within the housing (2) tapers from its combustion chamber-side end (51) to its combustion chamber-remote end (52).

Description

State of the art

[0001] The invention relates to a spark plug according to claim 1.

[0002] In many spark plugs used today, the ground electrode is located on the combustion chamber-side end face of the housing, and the ignition gap is formed outside the housing. Often, the center electrode also protrudes from the housing and into the combustion chamber. This allows the electrodes and the insulator to absorb a significant amount of heat from the combustion chamber. Furthermore, the breathing space, which extends between the housing and the insulator with the center electrode, is usually cylindrical and plays a subordinate role in spark plugs where the ignition gap is located outside the housing.

[0003] These spark plugs are optimized for use in gasoline-powered internal combustion engines.

[0004] US 4 766 855 A reveals a spark plug for plasma ignition. Disclosure of the invention

[0005] There are increasing plans to use hydrogen as a fuel in combustion engines, which presents new challenges in the design and construction of spark plugs. Hydrogen burns very quickly, so ignition occurs later and at a higher combustion chamber pressure than with other fuels. This results in high temperatures in the combustion chamber.

[0006] Additionally, hydrogen is prone to self-ignition even at relatively low temperatures. To prevent this self-ignition, all components of the spark plug must be as cold as possible.

[0007] The object of the invention is to provide a spark plug that has a low component temperature.

[0008] This problem is solved in the spark plug of the type mentioned above according to the invention by the fact that the housing has a first inner diameter D1 at its combustion chamber-side end and a second inner diameter D2 inside the housing in the plane E1, wherein the first inner diameter D1 is larger than the second inner diameter D2, so that a breathing space formed inside the housing tapers from its combustion chamber-side end to its combustion chamber-away-from end.

[0009] The spark plug according to the invention with a longitudinal axis has a housing with a longitudinal bore, wherein the housing has a housing wall with an inner side, an insulator arranged inside the housing with a combustion chamber-side insulator tip which is flush with a plane E1 extending perpendicular to the longitudinal axis, a center electrode arranged at least partially inside the insulator, and a ground electrode arranged inside the housing, wherein the ground electrode and the center electrode are arranged such that they form an ignition gap and the ignition gap is formed inside the housing.

[0010] According to the invention, the housing has a first inner diameter D1 at its combustion chamber-side end and a second inner diameter D2 within the housing in the plane E1, wherein the first inner diameter D1 is larger than the second inner diameter D2, so that a breathing chamber formed within the housing tapers from its combustion chamber-side end to its end opposite the combustion chamber. The breathing chamber is the space within the spark plug housing and is bounded by the housing wall and the insulator. The area of ​​the breathing chamber from its end opposite the combustion chamber to the ignition gap is referred to as the dead space, since the fuel-air mixture cannot flow in and out of this area easily.By narrowing the combustion chamber, the dead space is reduced, and less of the fuel-air mixture is located in the area of ​​the insulator and electrodes. This results in less heat energy being transferred to the electrodes, insulator, and housing via convection and radiation after ignition. The housing volume is also increased, leading to further temperature reductions in the combustion chamber and at the components. The resulting lower thermal stress reduces electrode wear and the risk of pre-ignition or glow ignition. Furthermore, the shape of the combustion chamber can be designed to direct the flow of the fuel-air mixture within it.

[0011] The arrangement of the electrodes within the housing has the further advantage that the insulator, the ground electrode, and the center electrode can be made shorter. As a result, they protrude less far into the combustion chamber. On the one hand, the components absorb less heat from the combustion chamber, and on the other hand, heat dissipation from the components via the housing into a cylinder head, in which the spark plug according to the invention is mounted, is more effective. Within the scope of this application, the term "combustion chamber" refers to the combustion chamber of an internal combustion engine cylinder in whose cylinder head the spark plug according to the invention can be mounted. The spark plug's breathing chamber is not considered part of the "combustion chamber" within the scope of this application.

[0012] Further advantageous embodiments of the invention are the subject of the dependent claims.

[0013] Advantageously, the second inner diameter D2 is designed to be 35% to 80% of the first inner diameter D1. The second inner diameter D2 also determines the space available for the insulator, particularly the insulator tip, within the housing. The insulator tip has a diameter D3, which is smaller than the second inner diameter D2. Due to the tapered shape of the combustion chamber, the insulator tip has a smaller surface area available for heat dissipation. Furthermore, the smaller surface area of ​​the insulator protruding into the combustion chamber reduces the stress on the insulator and the center electrode caused by the pulsating pressures generated during combustion. This reduces the stress on the mechanical fixation of the insulator within the spark plug housing, resulting in a more robust spark plug.

[0014] In a further development, the insulator tip is designed to at least partially define the breathing chamber at its end furthest from the combustion chamber. The breathing chamber is defined by the housing and the insulator. The housing and the breathing chamber are open towards the combustion chamber. For example, the insulator tip is flush with a surface of the housing that defines the breathing chamber at its end furthest from the combustion chamber. Alternatively, only the insulator tip can define the breathing chamber at its end furthest from the combustion chamber, with the inner surface of the housing wall defining the breathing chamber radially. This ensures that the breathing chamber has no or only a minimal dead space. Furthermore, the heat-absorbing surface area of ​​the insulator in contact with the breathing chamber is reduced to a minimum.The insulator tip does not protrude into the breathing space, so the flow of the fuel-air mixture in the breathing space is not disturbed by any edges of the insulator tip.

[0015] In a further development, it is envisaged that the housing wall of the housing will laterally limit the breathing space, resulting in the tapered shape of the breathing space.

[0016] In one embodiment of the further development, the shape of the breathing chamber is defined by flat surfaces of the housing, in particular where a first transition from the inside of the housing wall to a combustion chamber-side end face of the housing and / or a second transition from the inside of the housing wall to a surface of the housing that borders the breathing chamber at its end facing away from the combustion chamber are rounded. This offers the advantage that the surfaces bordering the breathing chamber have no edges that could disrupt the fuel-air mixture flow.

[0017] In an alternative embodiment of the further development, the shape of the breathing chamber is envisaged as being composed of several sub-surfaces arranged parallel to the longitudinal axis. Individual sub-surfaces can be straight or curved, and different sub-surfaces can have different radii of curvature, resulting in an overall contour with a curved shape. This yields the advantages described above.

[0018] In a further alternative embodiment of the development, the shape of the breathing chamber is provided for, consisting of a conical section and a cylindrical section with a constant diameter. In particular, the conical section is positioned closer to the combustion chamber than the cylindrical section. This results, for example, in the breathing chamber having the shape of the divergent part of a Laval nozzle. This has the advantage that a larger portion of the outgoing combusted fuel-air mixture is guided parallel to the longitudinal axis of the spark plug, thus increasing the penetration depth into the combustion chamber of a cylinder.

[0019] In one embodiment of the spark plug according to the invention, the contour is rotationally symmetric and / or clearance symmetric, with the longitudinal axis of the spark plug being the axis of symmetry. This results in a simple manufacturing process for the spark plug housing.

[0020] In another embodiment of the spark plug according to the invention, the contour is rotationally symmetric and / or clearance symmetric, with the axis of symmetry being spaced apart from the longitudinal axis of the spark plug. By spacing the axis of symmetry of the breathing chamber from the longitudinal axis of the spark plug, the flow of the fuel-air mixture can be directed in a controlled manner.

[0021] In another embodiment of the spark plug according to the invention, the contour is asymmetrical. This allows the flow of the fuel-air mixture to be directed in a controlled manner.

[0022] In an advantageous further development of the spark plug according to the invention, the ignition gap has a distance T from a combustion chamber-side end face of the housing with T = 0.1 mm or greater and / or T = 15 mm or less. The distance T extends from the combustion chamber-side end face of the housing to the combustion chamber-side end of the ignition gap. This results in the ignition gap being located inside the housing. This negative spark position makes it possible to design the center electrode and the insulator to be shorter than usual, so that the center electrode and the insulator do not protrude as far into the combustion chamber, and the path for heat dissipation is shorter, thus making heat dissipation more effective.

[0023] Advantageously, for example, the width of the ignition gap is no greater than 0.5 mm, and in particular no greater than 0.2 mm. The smaller the ignition gap, the lower the voltage required to generate an ignition spark.

[0024] It is also advantageous that the ignition gap width is at least 0.05 mm, and in particular not less than 0.1 mm. This ensures that the ignition gap is not too small. A very small ignition gap poses particular challenges to the accuracy of spark plug production. Deviations from the ideally parallel alignment of the electrode firing surfaces have a greater impact with a small ignition gap, such as uneven wear of the firing surface, than with a larger gap. The lower limit for the ignition gap width is therefore a good compromise between, on the one hand, a small ignition gap to reduce the ignition voltage requirement and wear, and, on the other hand, a reasonable effort to ensure consistently high-quality alignment of the firing surfaces during spark plug production.

[0025] The spark plug according to the invention and its further development are hydrogen spark plugs designed for use in a hydrogen-powered engine and for igniting the fuel-air mixture containing ignitable hydrogen. The fuel can contain up to 100% hydrogen; that is, the fuel can be hydrogen or a hydrogen gas mixture.

[0026] However, the spark plug according to the invention is not limited to operation with hydrogen. The spark plug according to the invention can also be used for natural gas or gasoline combustion engines. However, the spark plug according to the invention is optimized for operation with hydrogen.

[0027] For example, the spark plug may have a cap that is located at the combustion chamber end of the housing, so that the spark plug is a pre-chamber spark plug. Drawings

[0028] Figure 1shows a first example of a tapered breathing chamber of the spark plug according to the invention. Figure 2 shows a second example of a tapered breathing chamber of the spark plug according to the invention. Figure 3 shows a third example of a tapered breathing chamber of the spark plug according to the invention. Description of the exemplary embodiment

[0029] In the Figures 1 to 3 The combustion chamber-side half of a spark plug 1 according to the invention is shown schematically in each figure. The spark plug 1 has a housing 2 which has a longitudinal bore, such that the housing 2 has a housing wall 20 with an inner surface 21. The spark plug 1 further has an insulator 3 arranged inside the housing 2 with a combustion chamber-side insulator tip 31. The insulator tip 31 is flush with a plane E1 extending perpendicular to the longitudinal axis X of the spark plug 1. The insulator tip 31 has a diameter D3.

[0030] A central electrode 4 is located within the insulator 3, and a ground electrode 5 is located within the housing 2. The ground electrode 5 is configured here as a side electrode. The ground electrode 5 can also be configured as a top electrode. For example, the ground electrode 5 can be located in a recess on the inner surface 21 of the housing wall 20, inserted into a bore through the housing wall 20, or arranged on a projection on the inner surface 21 of the housing wall 20. This local recess or projection on the inner surface 21 of the housing wall 20 can be neglected when considering the shape of the breathing chamber 50. The central electrode 4 and the ground electrode 5 together form, for example, a radial ignition gap 55. The ignition gap 55 has a distance T from the combustion chamber-side end face 27 of the housing 2 and is located within the housing 2.

[0031] The breathing chamber 50 is the space at the combustion chamber end of the spark plug 1, which is bounded radially by the housing 2 and axially by the insulator 3 and, if applicable, a housing section 22 with respect to the spark plug's longitudinal axis X. The housing 2 has an opening at its combustion chamber end due to the longitudinal bore. Accordingly, the breathing chamber 50 is also open at its combustion chamber end 51. The plane of the combustion chamber end face 27 of the housing bounds the breathing chamber 50 at its combustion chamber end 51. The housing 2 has a first inner diameter D1 at its combustion chamber end and a second inner diameter D2 within the housing 2 in the plane E1. The first inner diameter D1 is larger than the second inner diameter D2, so that the breathing space 50 formed inside the housing 2 tapers from its combustion chamber-side end 51 to its combustion chamber-away-from end 52.The second inner diameter D2 of the housing 50 is larger than the diameter D3 of the insulator tip 31. The breathing chamber 50 is radially bounded by the housing wall 20. The housing wall 20 has an increasing wall thickness corresponding to the tapering of the breathing chamber 50.

[0032] A sealing element 10 is arranged between insulator 3 and housing 2, sealing the gap between housing 2 and insulator 3. This prevents gases from the breathing chamber 50 from flowing along the longitudinal bore of housing 2 to the end of housing 2 facing away from the combustion chamber and the spark plug 1.

[0033] In the embodiment according to Figure 1 At its end 52 facing away from the combustion chamber, the breathing chamber is bounded by a surface 22 of the housing 2 and by the insulator tip 31 of the insulator 3. The insulator tip 31 is flush with the housing surface 22, so that at the end 52 facing away from the combustion chamber, only the central electrode 4 protrudes into the breathing chamber 50.

[0034] The shape of the breathing chamber 50 is determined by the straight surfaces of the inner surface 21 of the housing wall 20. A first transition 17 from the inner surface 21 of the housing wall 20 to a combustion chamber-side end face 27 of the housing 2 can be rounded. The radius of curvature of the first transition 17 is R1. Additionally or alternatively, a second transition 18 from the inner surface 21 of the housing wall 20 to a surface 22 of the housing 2, which borders the breathing chamber 50 at its end 52 facing away from the combustion chamber, can be rounded. The radius of curvature of the second transition 18 is R2. The radii of curvature R1 and R2 can be the same or different.

[0035] The following figures show further embodiments of the spark plug 1 according to the invention. Identical components are labelled with the same reference numeral. The differences between the embodiments are discussed in more detail below.

[0036] The Figure 2Figure 1 shows a second example of a tapered breathing chamber of the spark plug 1 according to the invention. In contrast to the first example according to Figure 1 Figure 1 Only the insulator tip 31 limits the breathing chamber at its end facing away from the combustion chamber. The inner surface of the housing wall limits the breathing chamber radially to the longitudinal axis of the spark plug. The inner surface of the housing wall is composed of several sections arranged parallel to the longitudinal axis. These sections can have a flat surface or a curved surface with different radii of curvature, resulting in a corrugated shape on the inner surface of the housing wall.

[0037] The Figure 3 Figure 1 shows a third example of a tapered breathing chamber of the spark plug 1 according to the invention. In contrast to the first example according to Figure 1 Figure 1Only the insulator tip 31 limits the breathing chamber at its end facing away from the combustion chamber. The inner surface of the housing wall limits the breathing chamber radially to the longitudinal axis of the spark plug. The shape of the breathing chamber (50) is composed of a conical section (53) and a cylindrical section (54) with a constant diameter. Overall, this results in the shape of a nozzle, such as the diverging part of a Laval nozzle. The ground electrode and the center electrode are, for example, located in the cylindrical section of the breathing chamber.

Claims

1. Spark plug (1) with a longitudinal axis X, having: • a housing (2) with a longitudinal bore, as a result of which the housing (2) has a housing wall (20) with an inner side (21), • an insulator (3), which is arranged within the housing (2) and has a combustion chamber-side insulator tip (31) which is flush with a plane E1 extending perpendicular to the longitudinal axis X, • a centre electrode (4), which is arranged at least partially within the insulator (3), and • an earth electrode (5), which is arranged within the housing (2), the earth electrode (5) and the centre electrode (4) being arranged such that they form a spark gap (55) and the spark gap (55) is within the housing (2), characterized in that the housing (2) has, at its combustion chamber-side end, a first inside diameter D1 and, within the housing (2) in the plane E1, a second inside diameter D2, the first inside diameter D1 being greater than the second inside diameter D2, so that a breathing space (50) formed within the housing (2) tapers from its combustion chamber-side end (51) to its combustion chamber-remote end (52).

2. Spark plug (1) according to Claim 1, characterized in that the second inside diameter D2 corresponds to 35% to 80% of the first inside diameter D1.

3. Spark plug (1) according to any of the preceding claims, characterized in that the insulator tip (31) at least partially delimits the breathing space (30) at its combustion chamber-remote end (52).

4. Spark plug (1) according to any of the preceding claims, characterized in that the housing wall (20) of the housing (2) laterally delimits the breathing space (50), so that the tapering shape of the breathing space (50) is produced.

5. Spark plug (1) according to Claim 4, characterized in that the shape of the breathing space (50) is produced by straight surfaces of the inner side (21) of the housing wall (20), in particular wherein a first transition (17) from the inner side (21) of the housing wall (20) to a combustion chamber-side end face (27) of the housing (2) and / or a second transition (18) from the inner side (21) of the housing wall (20) to a surface (22) of the housing (2), the surface delimiting the breathing space (50) at its combustion chamber-remote end (52), are / is rounded.

6. Spark plug (1) according to Claim 4, characterized in that the shape of the breathing space (50) is composed of a plurality of partial surfaces of the inner side (21) of the housing wall which are lined up with each other parallel to the longitudinal axis, a single partial surface being straight or curved and different partial surfaces having different radii of curvature, so that a curved shape of the breathing space (50) is produced overall.

7. Spark plug (1) according to Claim 4, characterized in that the shape of the breathing space (50) is composed of a conical portion (53) and a cylindrical portion (54) with a constant diameter.

8. Spark plug (1) according to any of Claims 4 to 7, characterized in that the shape of the breathing space (50) is rotationally symmetrical and / or mirror-symmetrical, the longitudinal axis of the spark plug being the axis of symmetry.

9. Spark plug (1) according to any of Claims 4 to 7, characterized in that the shape of the breathing space (50) is rotationally symmetrical and / or mirror-symmetrical, the axis of symmetry being at a distance from the longitudinal axis of the spark plug.

10. Spark plug (1) according to any of Claims 4 to 7, characterized in that the shape of the breathing space (50) is asymmetrical.

11. Spark plug (1) according to any of the preceding claims, characterized in that a cap is arranged at the combustion chamber-side end of the housing (2), so that the spark plug (1) is a pre-chamber spark plug.

12. Spark plug (1) according to any of the preceding claims, characterized in that the spark plug is a hydrogen spark plug which is configured to be used in a hydrogen-powered engine and to ignite the flammable hydrogencontaining fuel-air mixture.

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