JP5675042B2 - Ceramic glow plug with reduced heater spacing - Google Patents

Description

  The invention starts from a glow plug as claimed in claim 1, in particular for starting self-igniting internal combustion engines.

  When starting a self-igniting internal combustion engine, initial ignition of the fuel-air mixture in the combustion chamber of the internal combustion engine is required. For this purpose, glow plugs are used which are each arranged in the wall of the combustion chamber. The glow plug includes a glow pin that is in contact with the fuel-air mixture to be ignited.

  Usually, glow pins are completed from conductive ceramics. In this case, the glow pin has a defined electrical resistance, so that when the glow pin and the voltage source are coupled, a current flows that heats the glow pin to the defined temperature. This temperature is selected to be sufficient to ignite the fuel-air mixture.

From the description in EP 1 768 456, a glow plug in which a heating element is embedded in a ceramic material is known. The heating element has a u-shape and surrounds a core made of a ceramic material. In order to prevent burnout of the core surrounded by the heating element, it is necessary to complete the heating element to a sufficient thickness. In general, the geometry of the glow plug is predetermined, so that the ceramic envelope of the heating element must be formed with a much smaller thickness. However, since the glow plug is generally exposed to oil ash corrosion in the engine room, the ceramic material degenerates. This degeneration leads to a decrease in the usable life of the glow plug. Due to the predetermined geometry of the glow plug and the required thickness of the core, in the case of the glow plug known from the description of EP 1768456, the heating element is coated. It is impossible to make the ceramic material thicker and increase the pot life.
European Patent Application No. 1768456

  In the case of a glow plug, the present invention has a problem that it is possible to form a thicker ceramic material for coating the heating element and to increase the pot life.

  A glow plug formed in accordance with the present invention comprises, in particular, a glow pin having a tip engaged in a combustion chamber of an internal combustion engine containing an ignitable fuel-air mixture for starting a self-igniting internal combustion engine. Yes. The glow pin includes a jacket that is completed from a ceramic material and includes a heating element. The heating element surrounds a core made of a material having a burnout strength of at least 20 kV / mm.

  Due to the burn-out strength of at least 20 kV / mm, it is possible to form the core surrounded by the heating element with a thickness less than is possible with known glow plugs from the state of the art. . This makes it possible to form a thicker ceramic material for the envelope of the glow pin surrounding the heating element. Thereby, the pot life of the glow plug can be extended. This is because the degradation of the ceramic material due to oil ash corrosion results in damage later, resulting in the inability to use glow plugs for even thicker.

  In one preferred embodiment, the ceramic material for the core and the ceramic material for the glow pin jacket have essentially the same coefficient of thermal expansion. With essentially the same coefficient of thermal expansion, damage to the ceramic material or core material of the glow pin jacket during the glow plug heating is avoided. This is possible especially when the core has a higher coefficient of thermal expansion than the ceramic material of the glow pin jacket. In this case, the core expands stronger than the jacket, which leads to tearing of the jacket.

  Suitable materials for the core are, for example, aluminum nitride, silicon carbide and silicon nitride, particularly preferably the material for the core is aluminum nitride. The advantage of aluminum nitride is a high burn-out strength of about 20-25 kV / mm, for which reason the core diameter may be chosen very small. In this case, the burn-out strength of aluminum nitride depends on the exact composition and manufacturer. That is, for example, in the case of a glow plug that is normally operated in a self-ignition internal combustion engine, a core thickness of 0.6 mm is sufficient, and in this case, burnout by the core does not occur. Furthermore, an advantage of aluminum nitride is temperature stability under air shut-off. The melting point of aluminum nitride is about 2000 ° C. However, since temperature stability is only provided under air shutoff, it is necessary to provide a core made of aluminum nitride with a jacket made of another ceramic material.

  According to the invention, the ceramic material of the glow plug is a non-oxide ceramic. Usually, ceramics are used that exhibit high temperature stability even in the presence of air. Suitable non-oxide ceramics for glow pins are, for example, silicon nitride or silicon carbide, particularly preferably silicon nitride as the ceramic material for glow pins.

The advantage of using silicon nitride as the ceramic material for the glow pins and aluminum nitride as the ceramic material for the core is that both ceramics have similar thermal expansions of about 4.6 × 10 ⁻⁶ K ^−1. Is to have a rate. Therefore, by combining these two ceramics, a stable and long-life glow plug can be manufactured. Aluminum nitride has a higher burn-off strength than silicon nitride, and thus can complete a core made of aluminum nitride having a slight thickness than a core made of silicon nitride. It makes it possible to adjust the thickness of the ceramic material for the envelope surrounding the element even more. Thereby, the lifetime of the glow plug can be increased. This is because, for example, the decomposition of silicon nitride based on degradation due to oil ash corrosion requires several hours until the heating element is achieved.

  Another advantage of using silicon nitride as the ceramic material for the glow plug jacket is that the silicon nitride is stable up to a temperature of about 1400 ° C. even in the presence of air. Furthermore, silicon nitride exhibits high strength.

  The heating element for heating the glow plug is usually configured in a u-shape. A heating element configured in a u-shape surrounds the core and on its side is surrounded by a ceramic material of glow pins.

  Typically, tungsten carbide containing ceramic is used as the material for the heating element.

  A heating element jacket made of glow pin ceramic material is necessary. This is because, in particular, tungsten carbide will react with air oxygen in the presence of air as a component of the heating element, which will cause the heating element to burn out. This results in an irreparable failure of the glow plug.

  In an embodiment of the present invention, a groove is formed in the core, and a heating element is included in the groove. The advantage of this groove is that a flat surface of the core is guaranteed with the heating element contained on the surface. Thereby, dimensional accuracy is additionally ensured. This is because it is not necessary to form a groove in the ceramic material for the glow pin corresponding to the heating element.

  When using aluminum nitride as the ceramic material for the core and silicon nitride as the ceramic material for the glow pin surrounding the core, between the ceramic material of the glow pin and the core surrounded by the material, A boundary layer is formed that joins the material and the material of the glow pin. Thereby, the core and the ceramic material surrounding the core are stably bonded together. In addition, the boundary layer acts as a gradient material, i.e. the material properties continually change from the material of the core to the ceramic material surrounding the core and no sudden changes occur. When using aluminum nitride as the ceramic material for the core and silicon nitride as the ceramic material for the glow pin, SiAlON is generally formed due to the oxygen content introduced into the system during mounting. The SiAlON forms a boundary layer between the core aluminum nitride and the silicon nitride surrounding the core.

  Furthermore, the present invention relates to a method for manufacturing a formed glow plug according to the present invention.

  For the manufacture of glow plugs, a core made of a material with a burn-out strength of at least 20 kV / mm and a heating element are surrounded by at least two molded parts made of a ceramic material for the glow pin jacket. This composite consisting of the core and the molded member is sintered and turned into a glow plug. The molded member and the core are bonded together by sintering, resulting in one stable composite. In addition, a boundary layer is formed between the core and the molded member forming the outer sleeve of the glow pin, resulting in a gradient material that avoids sudden changes in material properties. The

  In one embodiment of the method according to the invention, the heating element is printed on a molded part made of a ceramic material for the glow pin jacket. However, it is also possible to print the heating element on the core in other selectable ways. By printing on the core or on a molded part made of ceramic material for glow pins, it is achieved that a reduction in the distance between the opposing faces of the heating elements is avoided during the completion process. Furthermore, it is preferred to print the heating element in a groove formed in the core. Due to the grooves in the core, dimensional accuracy is additionally ensured as described above.

  In order to avoid the occurrence of stress, the core and the heating element are sintered in particular simultaneously.

  Embodiments of the invention are illustrated in the drawings and are explained in detail in the following description.

  FIG. 1 shows a cross section of a glow pin formed according to the present invention.

  The tip of the glow plug is referred to as the glow pin 1, in which case the glow plug enters a combustion chamber of an internal combustion engine not shown here to achieve initial ignition of the fuel-air mixture.

The glow pin 1 formed according to the present invention includes a core 3 made of a material having a burn-out strength of at least 20 kV / mm. Suitable materials for the core 3 are, for example, aluminum nitride, silicon nitride and silicon carbide. A particularly advantageous material for the core 3 is aluminum nitride. It is also possible to add a rare earth oxide, for example, to the material for the core 3 together with a core consisting essentially of pure aluminum nitride. Suitable rare earth oxides are, for example, Y ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ and oxides of La, Nd, Gd and Sc. The content of rare earth oxides and / or alkali metal oxides is in particular in the range from 0 to 15% by weight.

  A heating element 5 is connected to the core 3. The heating element 5 is generally configured in a u-shape and includes a first shoulder 7 and a second shoulder 9, which are arranged opposite to each other. The first shoulder 7 and the second shoulder 9 surround the core 3 and are separated from each other by the core 3. Due to the high burnout strength of the core 3, it is avoided that a short circuit occurs due to a stress transition from the first shoulder 7 to the second shoulder 9 or a stress transition in the opposite direction.

  The heating element 5 is a single resistor and is heated by application of a voltage. The material for the heating element 5 is usually selected so that the glow pin 1 can be heated to the operating temperature in the shortest time. A suitable material for the heating element 5 is, for example, a tungsten carbide-containing ceramic.

  The voltage supply of the heating element 5 for operating the glow plug is performed by the conductor 13, and this conductor is coupled to the heating element 5. The conductor 13 is guided through a core 3 to a current contact not shown in the present description. The material for the conductor 13 can be any arbitrary having a slight electrical resistance to prevent heating of all glow plugs and one of the ceramics of similar thermal expansion coefficient to avoid stress. The conductive material is suitable. A suitable material for the conductor 13 to which the heating element 5 is bonded is, for example, tungsten carbide.

  Since tungsten carbide is not temperature-stable with respect to oxygen contained in the air, the core 3 and the heating element 5 are surrounded by the outer cover 11. The jacket 11 is likewise completed from a ceramic material. In this case, the ceramic material of the jacket 11 is different from the material for the core 3. This is required when the material for the core 3 is not stable to air, for example in the case of aluminum nitride. For example, silicon nitride or silicon carbide is suitable as the material for the jacket 11. However, silicon nitride is preferred.

The material for the jacket 11 is chosen in particular so that it is stable to air at high temperatures. This is therefore particularly necessary. This is because the fuel chamber of the internal combustion engine contains a fuel-air mixture. Therefore, the glow pin 1 is exposed to ambient air. In one embodiment, it is possible, for example, that the ceramic material for the jacket 11 is doped. This can be done, for example, by adding rare earth oxides. Suitable rare earth oxides are, for example, Y ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ and oxides of La, Nd, Gd and Sc. In this case, the rare earth oxide is used as a sintering additive to reduce the eutectic.

In one preferred embodiment, the core 3 is made of aluminum nitride and the jacket 11 is made of silicon nitride. The advantage of this material combination is that aluminum nitride and silicon nitride have a similar coefficient of thermal expansion of about 4.6 × 10 ⁻⁶ K ⁻¹ . The advantage of essentially the same coefficient of thermal expansion is that no damage is caused by the higher coefficient of thermal expansion of the core or glow pin jacket when heated by the heating element 5.

  When the core 3 is completed from aluminum nitride and the outer cover 11 is completed from silicon nitride, a boundary layer 17 is formed on the boundary surface 15 between the core 3 and the outer cover 11. The boundary layer 17 essentially contains SiAlON. The SiAlON boundary layer 17 is formed by introducing a slight oxygen content in the contact area between the core 3 and the jacket 11, in particular during the mounting of the glow pin 1. The boundary layer 17 is simultaneously used as a gradient material, which avoids sudden changes in material properties. A constant transfer of material properties between the core 3 and the jacket 11 is achieved.

  FIG. 2 is a plan view showing individual members for manufacturing a glow pin constructed according to the present invention.

  In order to manufacture the glow pin 1, the core 3 is surrounded by the first molded member 19 and the second molded member 21. However, before the core 3 is surrounded by the first molding member 19 and the second molding member 21, the heating element 5 is placed on the core 3 or molding member 19, 21 or the core 3 or molding member 19. , 21, whereby the heating element is accommodated between the core 3 and the forming members 19, 21 forming the outer jacket 11.

  Usually, the core 3 is manufactured first. This can be done, for example, by injection molding or another pressure molding technique. Thereby, when the ceramic core 3 is manufactured, a so-called production form is first manufactured. Determination of the final contour of the core 3 can be performed on the generated feature.

  Subsequently, the core 3 is surrounded by the molding members 19, 21 that form the jacket 11 together with the heating element 5. For this purpose, notches 23 corresponding to the negative type of the core 3 are formed in the molded members 19 and 21. The molded members 19, 21 have a semicircular cross-section in particular and thus correspond to the shape of the glow pin 1 which has already been essentially completed. However, it is also possible to form and join the molded members 19, 21 in the form of parallelepipeds in other selectable ways. After the molding members 19 and 21 are joined around the core 3 and the heating element 5, the composite composed of the molding members 19 and 21, the core 3, and the heating element 5 is particularly formed by sintering the molding members 19 and 21. It is subjected to a temperature treatment in order to change to the cover 11. After the temperature treatment, the outer surface of the glow pin 1 is subjected to a molding process by mechanical processing to achieve the final shape of the glow pin 1.

  The heating element 5 is completed in particular from tungsten carbide and is printed on the notches 23 in the molding members 19, 21 in the first embodiment before the molding members 19, 21 are joined. After joining, a u-shaped heating element 5 is thus obtained which penetrates. However, in particular, a portion is already machined as a generated feature so that it is close to the final contour.

  However, it is also possible to print the heating element 5 on the core 3. This is illustrated in FIG. 3 in the first embodiment.

  In order to ensure the dimensional accuracy of the core 3, the core 3 is first, for example, pressed. The heating element 5 is printed on the generated form of the core 3 and is combined with the conductor 13. The conductor 13 may be printed on the core 3, for example. However, it is also possible to use, for example, a wire having a thermal expansion coefficient similar to ceramic as the conductor 13 placed on the core 3 by other selectable methods.

  Along with the production of the core 3 by injection molding or molding press, the composite can also be produced, for example, by spark plasma sintering. In the case of this spark plasma sintering, a high process pressure and temperature are combined with a directed DC impulse. In this case, the material is very strongly sintered activated and can be fully compressed at a relatively low temperature, albeit at a high pressure. This allows reliable process control in producing nanocrystalline and microcrystalline materials.

  FIG. 4 is a schematic diagram showing a core having heating elements printed on the core in a second embodiment.

  The embodiment illustrated in FIG. 4 is distinguished from the embodiment illustrated in FIG. 3 by first forming a groove 25 in the core 3. The heating element 5 is printed in the groove 25. Further, the conductor 13 is inserted into the groove 25 or printed in the groove 13. The advantage of the groove 25 is that the heating element 5 is not placed on the core 3, thereby causing a rise in the surface.

  Thereby, even better dimensional accuracy can be achieved.

  After printing the heating element 5 in the groove 25, this groove is closed, for example with a ceramic material, and a flat surface 27 of the core 3 is achieved.

Sectional drawing which shows the glow pin formed by this invention. 1 is a schematic diagram showing a core and a molded member for a glow pin for producing the glow pin. 1 schematically shows a core with printed heating elements. 1 schematically illustrates a core having grooves formed in the core and printed heating elements.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Glow pin, 3 Core, 5 Heating element, 7 1st shoulder part, 9 2nd shoulder part, 11 Outer jacket, 13 Conductor, 15 Interface, 17 SiAlON boundary layer, 19 1st shaping | molding member, 21 1st shaping | molding member 2 molded parts, 23 notches, 25 grooves

Claims (5)

  In particular, a glow plug comprising a glow pin (1) having a tip engaged in a combustion chamber of an internal combustion engine containing an ignitable fuel-air mixture for starting a self-igniting internal combustion engine. The glow pin (1) comprises a jacket (11) made of a ceramic material and provided with a heating element (5), wherein the heating element (5) has a burn-off strength of at least 20 kV / mm Surrounding the core (3), the material for the core (3) contains aluminum nitride, and the ceramic material of the envelope (11) of the glow pin (1) is made of silicon nitride And a groove (25) is formed in the core (3), and a heating element (5) is included in the groove. As a material for the heating element (5), Contains tungsten carbide The use of ceramic, the glow plug.   2. The glow plug according to claim 1, wherein the material of the core (3) and the ceramic material of the envelope (11) of the glow pin (1) have essentially the same coefficient of thermal expansion.   Glow plug according to claim 1 or 2, wherein the heating element (5) is configured in a u-shape.   A boundary layer (17) is formed between the ceramic material of the envelope (11) of the glow pin (1) and the core (3) surrounded by the ceramic material, and this boundary layer is the material of the core (3). The glow plug according to claim 1, wherein the glow plug forms a bond with the ceramic material of the jacket (11).   The method for manufacturing a glow plug according to any one of claims 1 to 3, wherein a core (3) made of a material having a burnout strength of at least 20 kV / mm and a heating element (5) 1) Surrounded by at least two molded members (19, 21) made of a ceramic material for the outer cover (11), a composite comprising the core (3) and the molded members (19, 21) is sintered, Change to a plug, in which a groove (25) is formed in the core (3), and a heating element (5) is printed in the groove. A method for producing a glow plug according to any one of the preceding claims.

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