What is insulating powder

Advantageous and expedient exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it

1 shows a section through a sheathed-element glow plug with a guide pin between the connecting bolt and the heating coil,

FIG. 2 shows a representation of another embodiment of a connecting bolt with a guide pin and an intermediate piece for connecting an indicated two-substance helix, FIG.

Fig. 3 shows a further embodiment of the invention with ceramic guide pin and ceramic intermediate piece and

4 shows a further exemplary embodiment of a glow plug with additional guidance of the heating coil.

The glow plug 1 shown in Fig. 1 consists of an indicated plug housing 2 and a fixed and gas-tight attached glow plug 3. The glow plug 3 in turn consists of a corrosion-resistant glow tube 4, in which a so-called two-material coil 5 is embedded in an insulating powder 6, in particular magnesium oxide. The insulating powder 6 has a high thermal conductivity and good electrical insulation. The 2-substance coil 5 consists of a heating coil 7 on the combustion chamber side with an essentially constant resistance and a connection-side control coil 8 connected in series with it. For temperature control or temperature limitation, the control coil 8 has, in a known manner, a high positive resistance-temperature coefficient ( PTC). The control coil 8 is connected on the connection side to a connecting bolt 9 for supplying power. The heating coil 7 is connected at its end 10 on the combustion chamber side to the glow tube 4 via a welded connection 11.

To fix the position of the 2-substance coil 5 in the glow tube 4, a guide pin 12 is provided according to the invention, which serves as a connecting piece between the connecting bolt 9 and an intermediate piece 13 arranged at the end of the guide pin. As also shown in FIG. 2, the connecting bolt 9 forms a structural unit with the guide pin 12 attached to it and the connecting piece 13 connected thereto, which in the exemplary embodiment according to FIGS. 1 and 2 is made entirely of metal. The connection-side end of the guide pin 12 is connected at the combustion-chamber-side end of the connection bolt 9 to a section 14 which has an indicated thread 15; the control helix 8 can be screwed onto this thread 15 with its connection-side end section (see FIGS. 1 and 2).

As can be seen from Fig. 2, however, the section 14 can also be provided with an annular groove 16 in which the end 17 of the control coil 8 can engage in a form-fitting manner. Of course, the end of the control helix can also be welded, caulked or otherwise connected to this section 14.

The intermediate piece 13 consists in the embodiment of FIG. 1 from an upper section 18, which forms the counterpart to the section 14, is constructed approximately the same and has the same function. A thread 19 is also provided for screwing on the end of the regulating helix 8 on the combustion chamber side. In the exemplary embodiment according to FIG. 2, this threaded section 18 is not provided; the connection between control coil 8 and heating coil 7 takes place instead at the indicated connection point 20 by means of welding.

The intermediate piece 13 shown in Fig. 1 has in its central region a collar 21 which serves as a separation point between the control coil 8 above and the heating coil 7 below. In a special embodiment of the invention, this collar can consist of a material with very low thermal conductivity in order to form a heat sink between the heating coil and the control coil. However, it must be ensured that there is an electrical connection between control coil 8 and heating coil 7. If the intermediate piece 13 is completely made of metal, the electrical connection is established by this alone.

At the end on the combustion chamber side, the intermediate piece 13 has a further section 22 on which the connection-side end of the heating coil 7 can be screwed. The heating coil 7 and the regulating coil 8 can be reduced in their outer diameter at their respective ends to be screwed onto the threaded sections 14, 18, 22 in order to obtain a defined counterpart to the screw-on thread. This reduced screw-on end of the heating coil on the threaded section 22 is shown in FIG. 2 with reference numeral 23.

The threaded sections 14, 18, 22 in Fig. 1 serve on the one hand for easy connection of the control coil or heating coil with the corresponding connections and also have the task of achieving a variable connection length. The further you screw the ends of the heating coil or control coil onto the threaded connections, the shorter the remaining length of the respective coil. This allows the total resistance of the two coils to be varied and adjusted.

The arrangement shown in Fig. 2 with connecting bolt 9, connecting pin 12 and intermediate piece 13 can be used to attach the indicated in this figure heating coil 7 and control coil 8 in a separate assembly process, the position of the coils is clearly fixed, which makes the subsequent installation in the glow tube much easier. The dimensions of this arrangement are given separately as an exemplary embodiment in a table at the end of the description.

According to the invention, the guide pin 12 has a predetermined breaking point 24 which is produced by constricting the guide pin to a smaller diameter. This predetermined breaking point 24 breaks when the diameter of the glow plug is later reduced in the so-called reducing process or hammering process of the glow tube. At this stage, the two-substance coil in the glow tube is exactly embedded in the ceramic insulating powder 6 and thus precisely fixed in its position. The separation of the predetermined breaking point 24 then causes an electrical separation of the upper area 25 from the lower area 26 of the guide pin 12. Thus, the heating coil is electrically connected to the control coil only via the welding connection point 20 (FIG. 2) or via the metal intermediate piece 13 ( Fig. 1) connected.

In the embodiment of FIG. 3, the guide pin 12 'consists of metal or a ceramic material, for. B. Magnesium Oxide. The lower intermediate piece 13 'consists of ceramic material, d. H. a material of low thermal conductivity and high electrical insulation capacity. The connection-side end 27 of the guide pin 12 'is attached in the ceramic version in a bore 28 of the connecting bolt 9 by an adhesive or the like. in the metal version of the guide pin 12 ', the connection to the connecting bolt 9 can be made by a press fit in the bore 28, welding, caulking or the like; Connection bolt 9 and guide pin 12 'can also be made in one piece. As in FIG. 1, the regulating helix 8 can also be screwed onto a threaded section 14 in FIG. 3 in order to obtain a variation in the helix resistance by changing the screwing depth.

The existing ceramic material intermediate piece 13 'is used in its connection-side end region 29 to receive the combustion chamber-side end of the control coil 8 and its combustion chamber-side end region 30 for fastening the connection-side end of the heating coil 7. Since the intermediate piece 13' is electrically non-conductive, must the two ends of the control coil and heating coil are connected to one another via a weld 31.

The control coil 8 and the heating coil 7 are wound tightly onto the intermediate piece 13 'and possibly glued on, but can also have some play on the intermediate piece 13'. The intermediate piece 13 'can also have a type of thread shape to accommodate the two helical ends. Due to its low thermal conductivity, it serves as a heat sink between the heating coil and the control coil, i.e. H. the heat transfer is greatly reduced in this area, so that the control coil desirably only reacts to the heating process of the heating coil with a delay. Nevertheless, the intermediate piece 13 'can fulfill the task of precise guidance, as is described in the embodiment of FIG. In this case, however, the predetermined breaking point 24 at the combustion chamber-side end of the guide pin 12 is not as important as in the embodiment of FIG. 1, since an electrical connection through this guide pin or the intermediate piece 13 'is not established. Nevertheless, the predetermined breaking point is advantageous because the linear expansion of the heating coil with control coil can continue unhindered when the diameter of the glow plug is reduced.

The embodiment of FIG. 4 could in principle be designed the same as the embodiment of FIG. 3, with the additional feature that the intermediate piece 13 'as a guide pin 32 with a conical cone 33 to the tip of the glow plug 3 in the glow tube 4 continues. This guide pin must then also be made of ceramic material, i. H. electrically non-conductive, in order to avoid a short circuit between the turns of the heating coil 7. However, it serves as a guide for the heating coil as a whole, whereby a more precise ironing of the heating coil can be maintained during the ironing process.

The ceramic guide pin 32 is connected in its connection-side end with the intermediate piece 13 or 13 ', this intermediate piece can be both metallic and ceramic and also - as described above - a threaded section 18 for the combustion chamber end of the Has control coil 8. The intermediate piece 13 'can, however, as described in Fig. 3, consist entirely of ceramic material. Likewise, in Fig. 4, the guide pin 12, 12 'in a metallic or ceramic embodiment - as described - is formed. The connection bolt 9 connected to the guide pin 12, 12 'in turn has a threaded section 14 for the connection-side end of the control coil 8. The control coil 8 and heating coil 7 are connected via a weld 31.

The invention is not limited to the illustrated and described embodiment. Rather, it also encompasses all professional further training without any inventive content of its own. In particular, a variation of the exemplary embodiments according to FIGS. 1 to 4 is conceivable; H. the fastening of the heating coil and control coil on the respective intermediate piece 13, 13 'or the control coil on the connecting bolt 9 can be in the form of a threaded section or in the form of a weld. By turning the connecting bolt, the screw-in depth of the coils and thus the total resistance can be adjusted, if necessary in some cases even if the 2-substance coil is already welded in the glow tube.

Preferred dimensions of the exemplary embodiment according to FIG. 2 are given in the table below.
d₁ = 4.4 mm
d₂ = 3.8 mm
d₃ = 4.0 mm
d₄ = 4.3 mm
d₅ = 1.25 mm
d₆ = 0.8 mm
d₇ = 3.0 mm
d₈ ≃ d₉ ≃ d₄ = 4.3 mm
1₁ = 17.5 mm
1₂ = 3.5 mm
1₃ = 1.1 mm
1₄ = 0.5 mm
1₅ = 1.8 mm
1₆ = 0.8 mm
1₇ = 0.4 mm.