Glow tube for a glow plug and method for its manufacture

Abstract

Glow tube (4) for a glow plug (2), wherein the glow tube (4) has at least one region (30) in which there is a gradual transition in at least two steps from a first material to a second material, wherein the first material and the second material have different electrical and / or thermal properties and the second material is a metal or a metal alloy.

Description

[0001] The invention relates to a glow tube for a glow plug and a method for its manufacture. State of the art

[0002] Glow plugs, also known as glow plugs or GLPs (from the English term "glow plug"), are currently used not only as cold-start aids in a chamber of an internal combustion engine, such as the pre-compression, swirl, or combustion chamber of an air-compressing, self-igniting diesel engine, but also in other applications, such as fuel heating in a common-rail injection system of a flexible-fuel drive system, as cold-start aids for starting kerosene-powered gas turbines and oil heaters, and the like. When used in self-igniting diesel engines, these glow plugs ignite a fuel-air mixture, preheating them while cold until their temperature is sufficiently high to ignite the fuel-air mixture.Furthermore, after starting the diesel engine, it may be necessary to continue operating the glow plugs for at least a short time to increase the temperature inside the combustion chamber, in order to reduce emissions or similar factors. This is typically controlled by an electric glow plug control unit (GCU) in conjunction with an engine control unit, aiming for a short heating time and controlled afterglow of the glow plug to achieve precise glow temperature regulation.

[0003] A glow plug typically uses a heating wire as an electrical resistance heater, which is inserted into a glow tube within the glow plug. Applying a voltage heats the tube for a brief period of 1 to 2 seconds, reaching a temperature of over 1000 degrees Celsius at its tip. The heating wires used as the electrical resistance element are, for example, coiled, with the term "coil" referring to a helically wound structure of the heating wire. The section of the glow tube that protrudes into the combustion chamber of the internal combustion engine is usually filled with an electrically insulating filler powder, such as magnesium oxide, in which the coil is embedded. The electrical connection is generally made via a terminal bolt that is electrically connected to the coil.Another end of the coil is electrically connected to the glow tube. A connector or similar device can be screwed onto the connecting bolt. Such a glow plug, which has a coil made of a single material with a high resistance-temperature coefficient, for example tungsten, molybdenum, or alloys thereof, is known, for example, from DE 10 2013 211 789 A1.

[0004] WO 01 / 16529 A1 discloses a glow plug that incorporates a ceramic glow tube. At the end closest to the combustion chamber, i.e., at its tip, the ceramic glow tube has a heating layer that exhibits a higher electrical resistance than the surrounding conduction layer, thus achieving the greatest heating effect at the tip of the glow tube. The interface between the conduction layer and the heating layer is subject to significant mechanical, thermal, and chemical stresses. To create a durable and long-lasting component, the skilled person is severely limited in their choice of material at this point.

[0005] JP 2 998 999 B2 refers to a ceramic heater comprising a heating element comprising WC, W or a tungsten alloy embedded in a non-oxide ceramic, wherein the non-oxide ceramic of a heater part in which the heating element is embedded comprises an aluminum nitride ceramic and the non-oxide ceramic of a support part for supporting the heater part is made of a silicon nitride ceramic.

[0006] DE 10 2007 053 807 A1 relates to a ceramic glow plug with a reduced heater gap. The glow plug is used in particular for starting a self-igniting internal combustion engine and comprises a glow pin with a tip that engages in an ignitable fuel-air mixture contained in a combustion chamber of the internal combustion engine. The glow pin comprises a sheath made of a ceramic material and containing a heating element. The heating element encloses a core made of a material with a dielectric strength of at least 20 kV / mm.

[0007] DE 10 2006 062 215 A1 relates to a glow plug. This is arranged in a chamber of an internal combustion engine. The glow plug has a housing and a metallic glow tube that partially protrudes from the housing. Inside the glow tube, which is gas-tight, is a ceramic heating element that is connected to the glow tube by means of a first receiving element and to a metallic connecting bolt by means of a second receiving element. Furthermore, at least one sacrificial material is provided in the interior, which can be designed as a sacrificial layer or as sacrificial granules to bind residual water and / or oxygen that could cause corrosion damage. Disclosure of the invention

[0008] In a glow tube according to the invention for a glow plug, the glow tube has at least one region in which a gradual transition in at least two steps from a first material to a second material takes place, wherein the first material and the second material have different electrical and / or thermal properties.

[0009] A "gradual transition" is understood to mean that, within the transition region, the proportion of the first material gradually decreases and the proportion of the second material gradually increases. The number of steps is at least two, preferably at least three or at least five. Preferably, the gradual transition comprises three to 100 steps, and more preferably three to 50 steps.

[0010] Preferably, the gradual transition occurs layer by layer, with the proportions of the first and second materials changing layer by layer. Due to the gradual transition from the first to the second material, the coefficients of thermal expansion are similar from layer to layer, i.e., not as different as with an abrupt transition. Ideally, this prevents cracks in the glow tube caused by temperature changes during operation and results in an increased service life for the glow plug.

[0011] The annealing tube can have several sections, each containing a gradual transition in at least two steps from the first material to the second. Furthermore, the annealing tube can have one or more sections where there is a transition from the first material to the second and a transition back from the second to the first. It can also be provided that the annealing tube has a section where there is a transition from the first material to the second and a further transition from the second to a third material.

[0012] Materials suitable for high-temperature applications are preferred, in particular materials with a melting point above 1000 °C, preferably above 1200 °C. It is possible for the melting or sintering point of the two materials to differ significantly, for example, by more than 200 °C or more than 400 °C. Due to the gradual transition from the first material to the second material in at least two steps, the melting or sintering points also gradually converge, so that the so-called heat-affected zone (HAZ) is locally limited. Thus, when the material with the higher melting point is melted and applied, the material with the lower melting point is not damaged or destroyed.

[0013] Preferably, the first material and the second material have different specific resistances, so that the heating effect of the materials is different.

[0014] Preferably, the first material is used, which has a high heating effect, and the second material is used, which is electrically conductive.

[0015] According to a preferred embodiment, the first material comprises a ceramic material. The first material can, for example, be a ceramic composite containing Al₂O₃, MoSi₂, Si₃N₄, or Y₂O₃. The composite can also contain more than two of these compounds. A preferred ceramic material is Al₂O₃.

[0016] Alternatively or additionally, the first material may be a metal or a metal alloy. A preferred alternative first material is WC-NiCrBsI.

[0017] The second material preferably comprises a metal or a metal alloy. A preferred second material is a nickel-based alloy. The alloy may further comprise chromium, iron, molybdenum, niobium, cobalt, manganese, copper, aluminum, titanium, silicon, carbon, sulfur, phosphate, or boron. A suitable metal alloy is, for example, the Incornell alloy 718 or 625.

[0018] It is possible for the first material to contain a ceramic component and a metal component, and for the second material to also contain a ceramic component of the same ceramic material and a metal component of the same metal. In this case, the material proportions in the first and second materials are different. For example, the first material might contain x% ceramic material and 100-x% metal material, and the second material y% ceramic material and 100-y% metal material, where x and y are different from each other. Of course, other additional materials may be present.

[0019] The glow tube can comprise a head section and a body section. The head section of the glow tube forms the end closest to the combustion chamber, and the body section forms the end furthest from the combustion chamber.

[0020] According to one embodiment, the head region comprises the first material and the body region the second material. For example, the materials are selected such that the hottest point during operation is located at the head region of the annealing tube.

[0021] Alternatively, for example, the head and body regions can be made of the second material, while a transition region between the head and body regions is made of the first material. This embodiment can offer manufacturing advantages, such as faster and more cost-effective production. Since the transition region can be made with less material than the head region, the first material can be saved in this embodiment. Furthermore, certain applications may require that the hottest point is not located at the tip, i.e., at the head of the annealing tube.

[0022] According to a preferred embodiment, the annealing tube comprises a central rod and a jacket section surrounding the central rod. A gap is located between the central rod and the jacket section. Typically, the central rod is electrically connected to a terminal bolt of the annealing tube, with the current being conducted through the jacket section. The gap can be filled, for example, with air, a vacuum, an inert gas, an electrically insulating filler powder such as magnesium oxide, or a pre-compacted powder.

[0023] The gradual transition from the first material to the second material can occur in the area of ​​the central rod. In particular, it can be provided that the first material is only present in the area of ​​the central rod, so that a transition and a return transition between the materials occur there. In this embodiment, the heating material is advantageously protected against corrosion.

[0024] The gradual transition from the first material to the second material can also occur in the area of ​​the shell section. In particular, it can be provided that the first material is only present in the area of ​​the shell section, so that a transition and a return transition of the materials occur there.

[0025] The glow tube according to the invention is intended for use in a glow plug. Accordingly, the invention also relates to a glow plug with such a glow tube. The glow tube can be held in the glow plug in any way, for example by frictional, positive, or material connection. Soldered or clamped connections are preferred.

[0026] In an inventive method for manufacturing a glow tube for a glow plug, the glow tube is manufactured at least in one area by means of a 3D printing process, wherein in that area a gradual transition is created in at least two steps from a first material to a second material, wherein the first material and the second material have different electrical and / or thermal properties.

[0027] Using the 3D printing process, a gradual transition can be created, in particular by ensuring that the individual printed layers differ from each other in terms of material.

[0028] 3D printing is used in the production of prototypes, small series, or individual pieces, but is also gaining ground in mass production. The processes referred to as 3D printing have in common that objects are manufactured based on a computer model. A 3D printing device typically has a main control unit that contains a template or computer model of the object to be printed. The main control unit can, for example, be a computer that communicates with the device's control units. For the present invention, the computer model can be stored in the main control unit in any file format, with common file formats including, for example, SDL, OBJ, CLI / SLC, PLY, VRML, AMF, STEP, and IGS. Horizontal sections are first created through the model by a process called "slicing," from which a scheme is calculated that describes the target positions of the printing material layer by layer.The target positions are then controlled by one or more printheads to deposit printing material.

[0029] Preferred 3D printing methods for producing the annealing tube according to the invention include EBM (electron beam melting), EBF 3 (electron beam free form fabrication), DMLS (direct metal laser sintering), SLM (selective laser melting), SLS (selective laser sintering) and laser cladding, with laser cladding being preferred.

[0030] EBM, also known as electron beam melting, creates the object to be printed using an electron beam as an energy source. This beam is directed at the printing material, causing it to melt. The layers are applied using a squeegee, so that the component is generated layer by layer.

[0031] EBF 3It employs a focused electron beam in a vacuum environment to create a melt pool on the printing material. The process is described, for example, in the document by Taminger, KMB and Hafley, RA, “Electron Beam Freeform Fabrication: A Rapid Metal Deposition Process,” Proceedings of the 3rd Annual Automotive Composites Conference, (2003).

[0032] The 3D printing technology developed by EOS under the brand name DMLS uses a ytterbium fiber laser that is directed into a powder bed of printing material to create the object by melting or welding the material.

[0033] SLM, also known as selective laser melting, also uses powdered printing material that is applied in thin layers to a build platform. The printing material is melted using laser radiation. After a layer is formed, the build platform is lowered by the thickness of one layer and more powder is applied.

[0034] Selective laser sintering (SLS) builds the workpiece layer by layer using a laser, such as a CO2 laser, an Nd:YAG laser, or a fiber laser. The printing material is in powder form. The powder is applied to a build platform using a squeegee or roller, and the layers are sintered or melted by controlling the laser beam.

[0035] In sintering processes, it may be possible to additionally use a binder which can be liquefied at a lower temperature than the melting temperature of the printing material.

[0036] Preferably, the gradual transition from the first material to the second material in the described methods is created by providing the powder bed of the printing material with varied material proportions.

[0037] In laser cladding, a surface is deposited by melting and simultaneously applying material fed through a nozzle. The material is fed via, for example, trailing or coaxial nozzles, whereby the size of the material deposit can be determined by the material feed rate and the nozzle opening. In the process according to the invention, a pressure nozzle is preferably used in which two materials can be processed, with the material feed for each material being controlled separately. However, the material does not necessarily have to be ejected from a nozzle, but can also be fed in by means of a feed device, e.g., a robot arm. The material discharge in laser cladding can be droplet-by-drop or strand-by-strand.

[0038] In laser cladding, the gradual transition from the first material to the second material is preferably created by controlling the material feed of the first and second materials in the print nozzle. Advantages of the invention

[0039] The annealing tube according to the invention is characterized by at least a gradual transition from the first material to the second material, wherein, for example, metal and ceramic proportions are varied.

[0040] The gradual transition makes the interface between the materials highly resistant to mechanical, thermal, and chemical influences. This allows, for example, a wider selection of materials for the respective application.

[0041] Material waste is very low due to the use of an additive manufacturing process. Furthermore, 3D printing allows for easy shape modifications simply by changing the model. It is also possible to 3D print the entire glow plug assembly. Brief description of the drawings

[0042] Embodiments of the invention are explained in more detail with reference to the accompanying drawings and the following description.

[0043] They show: Fig. 1 a side sectional view through a glow plug according to the invention, Fig. 2 a lateral sectional view through a part of an incandescent tube according to a first embodiment of the invention, Fig. 3 a lateral sectional view through a part of an incandescent tube according to a second embodiment of the invention, Fig. 4 a lateral sectional view through a part of an incandescent tube according to a third embodiment of the invention, Fig. 5 a lateral sectional view through a part of an incandescent tube according to a further embodiment of the invention, Fig. 6a a schematic view of a section through a pressure nozzle during the manufacture of an annealing tube according to the invention at a first time point in time, Fig. 6b a schematic view of a section through a pressure nozzle during the manufacture of an annealing tube according to the invention at a second time point in time, Fig. 6c a schematic view of a section through a pressure nozzle during the manufacture of an annealing tube according to the invention at a third time point in time and Fig. 7 a perspective view of an incandescent tube according to a further embodiment of the invention. Embodiments of the invention

[0044] Fig. Figure 1 shows a side sectional view through a glow plug candle 2 according to the invention.

[0045] The glow plug 2 comprises a glow tube 4 as its combustion element, which is arranged in a housing 6, for example, in a clamping fit. At the end of the glow plug 2 furthest from the combustion chamber, electrical contact is made via a circular connector 12, which is electrically isolated from the housing 6 by an insulating washer 10. Inside the glow plug 2, the circular connector 12 is connected to the glow tube 4 via a connecting bolt 8. The connecting bolt 8 is electrically insulated from the housing 6 by a housing seal 16. The glow tube 4 is insulated from the environment by the heating element seal 14.

[0046] The glow tube 4 has a head region 20 and a body region 22, the body region 22 being partially located in the housing 6. The head region 20 of the glow tube 4 is made of a first material and the body region 22 of the glow tube 4 is made of a second material, the different materials being represented in the drawings by different colors.

[0047] The glow tube 4 comprises a central rod 24, which is bolt-shaped. The central rod 24 is electrically connected to the connecting bolt 8, for example by an interference fit or by a metallurgical connection.

[0048] In the head region 20, the central rod 24 connects to a jacket section 28 of the incandescent tube 4, the central rod 24 and the jacket section 28 being electrically insulated from each other by a gap 26. In the illustrated embodiment, the central rod 24, the gap 26, and the jacket section 28 are arranged in the manner of an umbrella, with the jacket section 28 forming the keel of the umbrella and the central rod 24 the shaft.

[0049] In this embodiment, the current path passes through the head region 20, where the first material is located. Since the first material has a higher electrical resistance than the second material, the head region 20 of the glow tube 4 forms the hottest point of the glow plug 2.

[0050] Between the head region 20 and the torso region 22, there is a region 30 in which there is a gradual transition from the first material to the second material. The position and shape of region 30 are described with reference to the Fig. 2, Fig. 3, Fig. 4 to Fig. 5 explained in more detail.

[0051] Fig. Figure 2 shows a side sectional view through a part of an incandescent tube 4 according to a first embodiment of the invention.

[0052] The glow tube 4 has the first material in its head region 20 and the second material in its body region 22. The section of the central rod 24 facing the head region 20 and the section of the jacket section 28 facing the head region 20 have the first material. The section of the central rod 24 associated with the body region 22 and the section of the jacket section 28 associated with the body region 22 each have the second material.

[0053] An area containing the first material is in Fig. 2 is designated as a first layer 32. For example, the first material can be present here in pure form or with a small addition of the second material.

[0054] A second layer 34 adjoins the first layer 32. The second layer 34 mainly consists of the first material, with a proportion of the second material, e.g., in a ratio of 80 to 20 volume% or weight%.

[0055] In a third layer 36, which adjoins the second layer 34, the first material and the second material are present, for example, in similarly high proportions, e.g., in a ratio of 50 to 50 volume-% or weight-%.

[0056] In a fourth layer 38, which adjoins the third layer 36, for example, the second material is present in a larger proportion than the first material, e.g. in a ratio of 80 to 20 volume-% or weight-%.

[0057] In a fifth layer 40, which forms the largest part of the hull area 22 in the illustrated embodiment, the second material is present in pure form or with a small proportion of the first material.

[0058] In this embodiment, the area 30 where the gradual transition occurs is formed by the second layer 34, the third layer 36, and the fourth layer 38. In other embodiments, two, four, five, ten, or a plurality of layers may be present instead of three. In particular, it may be provided that each, every second, every third, fourth, fifth, or tenth layer to be printed by 3D printing has different material compositions.

[0059] Fig. Figure 3 shows a side sectional view through a part of an incandescent tube 4 according to a second embodiment of the invention.

[0060] Compared to Fig. 2. The embodiment differs in that the region 30, in which the gradual transition occurs, is located exclusively in the region of the sheath section 28. The region 30, in which the gradual transition occurs, can be described as with reference to Fig. As described in section 2, the structure comprises three layers. In the illustrated embodiment, however, the gradual transition from the second to the first material and a gradual return transition from the first to the second material are located in area 30. The first material is used very sparingly.

[0061] Fig. Figure 4 shows a side sectional view through a part of an incandescent tube 4 according to a third embodiment of the invention.

[0062] Compared to the embodiment in Fig. In the illustrated embodiment, the area 30, where the gradual transition from the first material to the second material occurs, is not located in the sheath section 28, but exclusively in the area of ​​the central rod 24. In the illustrated embodiment, the gradual transition from the second to the first material and a gradual re-transition from the first to the second material are located in area 30. In this embodiment, the first material is not exposed to chemical and mechanical environmental influences, e.g., corrosion.

[0063] Fig. Figure 5 shows a side sectional view through a part of an incandescent tube 4 according to a further embodiment of the invention.

[0064] The in Fig. The embodiment shown in Figure 5 illustrates a preferred configuration of the head region 20, which is particularly advantageous in the case of the Fig. The embodiment shown in Figure 2 is advantageous. The head region 20 comprises a conical section 42 in which the diameter of the annealing tube 4 increases from a first diameter D1, which corresponds to the diameter of the central rod 24, to a diameter D2, which corresponds to the diameter of the outer shell section 28. The diameter increases linearly. The illustrated embodiment proves to be particularly advantageous with regard to the expected temperature distribution during operation of the annealing tube 4.

[0065] Fig. Figure 6a shows a schematic view of a section through a pressure nozzle during the manufacture of an annealing tube 4 according to the invention at a first time point in time.

[0066] The nozzle 50 has a first feed channel 54 for the first material and a second feed channel 56 for the second material. The materials exit through a discharge opening 52. Inside the nozzle 50, the materials are heated by a laser beam, causing them to liquefy and exit through the discharge opening 52. The feed of the materials via the feed channels 54 and 56 can be controlled.

[0067] To the in Fig. At the time shown in 6a, the body area 22 of the glow tube 4 is built up layer by layer, whereby the areas in which the gap 26 is created are covered by an optionally used filling material 58.

[0068] At the time that in Fig. As shown in Figure 6b, area 30, where the gradual transition between the two materials occurs, is printed. As schematically shown, opposite Fig. 6a the material supply M1 of the first material is increased and the material supply M2 of the second material is decreased.

[0069] Fig. Figure 6c shows a third point in time at which the head region 20 of the annealing tube 4 is produced. The material feed M2 of the second material is opposite. Fig. 6b further reduced and the material supply M1 of the first material further increased.

[0070] Fig. Figure 7 shows a perspective view of an annealing tube 4 according to a further embodiment of the invention. The head region 20 of the annealing tube 4 comprises the first material, and the shell section 28 of the annealing tube 4 comprises the second material. In this embodiment, the central rod 24 comprises a third material. The transition from the first to the third material can be a gradual transition in at least two steps, as described.

[0071] The shape of the annealing tube 4 is shown as axially symmetrical, with the central rod 24 having a circular cross-section and the outer section 28 having an annular cross-section. However, the invention is not limited to this. Naturally, the annealing tube 4 can have any cross-section, e.g., square, rectangular, oval, with undercuts, etc., and can be cylindrical or, for example, conically tapered.

[0072] The invention is not limited to the described embodiments. Rather, further modifications and additions are possible within the specified range, which are obvious to those skilled in the art.

Claims

[1] Glow tube (4) for a glow plug (2), wherein the glow tube (4) has at least one region (30) in which there is a gradual transition in at least two steps from a first material to a second material, wherein the first material and the second material have different electrical and / or thermal properties and the second material is a metal or a metal alloy. [2] Glow tube (4) according to claim 1, characterized by that the first material is a ceramic material. [3] Glow tube (4) according to any one of the preceding claims, characterized by , that the glow tube (4) has a head region (20) and a body region (22), wherein the head region (20) has the first material and the body region (22) has the second material. [4] Glow tube (4) according to any one of the preceding claims, characterized by, that the glow tube (4) has a central rod (24) and a jacket section (28) surrounding the central rod (24), wherein there is a gap (26) between the central rod (24) and the jacket section (28). [5] Glow tube (4) according to claim 4, characterized by , that the gradual transition from the first material to the second material is in the area of ​​the central staff (24). [6] Glow tube (4) according to claim 4, characterized by , that the gradual transition from the first material to the second material is present in the area of ​​the mantle section (28). [7] Glow plug (2) with a glow tube (4) according to one of the preceding claims. [8] Method for manufacturing a glow tube (4) for a glow plug (2), wherein the glow tube (4) is manufactured at least in one area by means of a 3D printing process, wherein in the area (30) a gradual transition is created in at least two steps from a first material to a second material, wherein the first material and the second material have different electrical and / or thermal properties. [9] Method according to claim 8, characterized by , that the gradual transition from the first material to the second material is achieved by providing a powder bed of a printing material with varying material proportions or by controlling the supply of the first and second materials.

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