EP0189086B1 - Glow plug - Google Patents

Description

The invention relates to a glow element according to the preamble of patent claim 1.

Such a glow element is known from GB-A-2 084 649, the electrical conductor acting on any winding of the one-piece resistance element.

DE-A-2 802 625 describes a glow element in which the resistance element consists of two resistors connected in series, the resistor connected to the closed tip of the glow tube as the heating resistor and the resistor connected to the inner pole as the control resistor with a positive temperature coefficient is trained. This configuration enables the heating resistor to be regulated.

From DE-A-3 224 587 a heating resistor is also provided in a glow plug, the temperature or heating behavior of which is effected solely by external electrical wiring. External connections of this type are often complex and expensive, whereas in the case of a self-regulating glow plug with a heating and regulating resistor in the glow plug, a very short heating-up time, as would be necessary for an immediate start of diesel engines, cannot be achieved without endangering the glow plug.

The object of the invention is to design a glow element of the type mentioned at the outset in such a way that the individual elements can be connected outside the glow element.

This object is achieved according to the invention by a glow element according to the characterizing features of claim 1.

Advantageous developments of the invention are the subject of the following claims 2 to 12.

According to the invention, it is therefore possible to switch a glow plug with a heating coil and a control coil, which has a positive temperature coefficient of resistance, from the outside in such a way that the wiring of the individual elements within the glow element is possible, so that afterglowing after a very short heating-up time low heating element temperature is made possible, whereby the concentricity of a still cold diesel engine can be improved and the exhaust gas emission can be reduced. Furthermore, the glow element according to the invention enables measured values to be taken directly from one. Partial resistance, which can then be fed to a control device for evaluation. In addition, self-regulation can be made possible by simple external wiring.

• Fig. 1 ein Glühelement gemäß einer Ausführungsform der Erfindung,
• Fig. 2 eine Glühstiftkerze mit dem in Fig. 1 dargestellten Glühelement,
• Fig. 3 ein Glühelement gemäß einer weiteren Ausführungsform der Erfindung,
• Fig. 4 eine Glühstiftkerze mit dem in Fig. 3 dargestellten Glühelement,
• Fig. 5 ein Glühelement gemäß einer weiteren Ausführungsform der Erfindung,
• Fig. 6 eine Glühstiftkerze mit dem in Fig. 5 dargestellten Glühelement,
• Fig. 7 das Schaltbild des in Fig. 1 dargestellten Glühelements,
• Figuren 8 bis 13 Beispiele äußerer Beschaltungen des in Fig. 1 dargestellten Glühelements,
• Fig. 14 das Schaltbild eines Glühelements nach Fig. bzw. einer Glühstiftkerze nach Fig. 2, in einer Ausbildung als Temperaturmeß-Glühelement bzw. -Glühkerze.
• Fig. 15 das Schaltbild des in Fig. 3 dargestellten Glühelements,
• Fig. 16 das Schaltbild des in Fig. 5 dargestellten Glühelements,
• Fig. 17 ein Beispiel für die äußere Beschaltung der in Fig. 6 dargestellten Glühstiftkerze,
• Fig. 18einAusführungsbeispielfürein koaxiales Anschlußelement für z.B. die Glühstiftkerze nach Fig. 1, und
• Fig. 19 eine besondere Ausführungsform der Verbindung des Leiters mit dem gemeinsamen Punkt zweier Widerstände.

Embodiments of the invention are described below with reference to the accompanying drawing. On this shows or show

• 1 shows a glow element according to an embodiment of the invention,
• 2 shows a glow plug with the glow element shown in FIG. 1,
• 3 shows a glow element according to a further embodiment of the invention,
• 4 shows a glow plug with the glow element shown in FIG. 3,
• 5 shows a glow element according to a further embodiment of the invention,
• 6 shows a glow plug with the glow element shown in FIG. 5,
• 7 shows the circuit diagram of the glow element shown in FIG. 1,
• FIGS. 8 to 13 examples of external wiring of the glow element shown in FIG. 1,
• 14 shows the circuit diagram of a glow element according to FIG. Or a glow plug according to FIG. 2, in the form of a temperature measurement glow element or glow plug.
• 15 shows the circuit diagram of the glow element shown in FIG. 3,
• 16 shows the circuit diagram of the glow element shown in FIG. 5,
• 17 shows an example of the external circuitry of the glow plug shown in FIG. 6,
• 18 shows an exemplary embodiment for a coaxial connection element for, for example, the glow plug according to FIG. 1, and
• Fig. 19 shows a special embodiment of the connection of the conductor to the common point of two resistors.

FIG. 2 shows a glow plug, which is denoted overall by 1, the heating or glow element according to FIG. 1, denoted overall by 2. This glow element 2 is mounted in a known manner with the seal 4, the insulating washer 5, the thrust washer 6 and the round nut 7 in a body 3 of the glow plug 1 designed in a known manner. The glow element 2 contains two series-connected electrical resistors 10 and 11. The two resistors are known to be embedded in an insulating material 13 and surrounded by a metallic glow tube 30, which projects coaxially to the body 3 and is closed at its outer end. At this tip 14 of the glow tube, one of the resistors 11 is connected to the glow tube 30 in an electrically conductive manner. At the other end of the glow tube, the inner pole 9 is electrically insulated and inserted tightly into the glow tube 30 and is connected in an electrically conductive manner at 17 to the other resistor, 10. For sealing and insulation, a sealing ring 15 is preferably used between the glow tube and the inner pole. One of the two resistors 10 and 11 has a positive temperature coefficient and thus acts as a variable resistor. In today's common applications as a glow plug in internal combustion engines, the resistor 11 connected to the closed tip 14 of the glow tube 30 is designed as a heating resistor and the resistor 10 remote from the tip connected to the inner pole is designed as the variable resistor.

The inner pole 9 is designed as a hollow cylinder, an electrical conductor 8 being guided through it.

The passage of the conductor 8 through the inner pole 9 must be electrically insulating. This insulation can preferably an insulating oxidation or an insulating tube 16, which simultaneously seals the bushing against the penetration of moisture, or another electrically insulating layer. The conductor 8 is guided centrally through the resistor 10, which is closer to the body 3, up to the connection point of the resistors 10 and 11, where the conductor 8 is electrically conductively connected to this connection point.

The resulting electrical circuit diagram of the glow element is shown in FIG. 7, where resistor 10 is shown as variable resistor R1 and the other resistor 11 as R2. In order to avoid a noticeable voltage drop on the conductor 8 led through the inner pole 9 and thus the generation of heat on the insulation 16, the conductor 8 is designed to have a very low resistance compared to the resistors 10 and 11.

The described design of the glow element 2 enables any external wiring of individual resistances of the glow element. The possibility of the individual wiring of the resistors contained in the heating element results in a simplification of the external wiring as a whole in relation to the respective intended purpose. Some examples of simple types of wiring are shown in FIGS. 8 to 13.

According to FIG. 8, another resistor R3 with a positive temperature coefficient is used in parallel to the control resistor R1 outside the glow element. This arrangement of a parallel PTC resistor R3 outside the glow plug 1 or glow element 2 brings about a clearer curtailment of the current flowing through the heating resistor R2 (11) and thus a shortening of the heating time.

After switching on, the total resistance of the control resistor R1 (10) and the parallel PTC resistor R3 is kept at a low level despite the heating of the control resistor R1. Due to self-heating, the PTC resistor R3 lying outside the glow plug finally reaches its switching temperature and its resistance value rises to a multiple of the variable resistor R1, so that only further variable regulation means the variable resistor R1 (10).

In a further embodiment, the PTC resistor R3 located outside the glow plug could be accommodated as a temperature sensor in the cooling water, engine oil, exhaust gas or cylinder head and take over a temperature measurement task after the glow process.

Fig. 9 shows the possibility of a temperature measurement via the voltage drop across the heating resistor R2 (11) or control resistor R1 (11). The voltage drop U1 or U2 at the control resistor R1 or at the heating resistor R2 is a measure of the temperature of the glow tube. This variable can be used for glow monitoring, as a display or as a manipulated variable in a control loop.

The conductor 8 connected between the heating resistor 11 and the control resistor 10 and led out through the inner pole 9 also enables the construction of all possible bridge circuits, for example the one in FIG Fig. 10 shown measuring bridge. The external wiring of the measuring bridge is designed so that the bridge is balanced at the desired annealing temperature. The reversal of the current direction in the bridge then corresponds to the signal for reaching the desired glow tube temperature.

By connecting the conductor 8 of the glow element 2 with a mechanical or electronic switching element, a two-stage or multi-stage connection of individual resistors is possible.

11, initially only the heating resistor R2 (11) can be controlled via a switch S designed as a changeover switch. Then if e.g. at the tip of the glow tube 30, the desired temperature is reached, one or more heating resistors R2 'are switched in gradually, which then heat the entire glow tube to the operating temperature. The switch S can be operated mechanically, thermally (e.g. as a bimetal switch) or electrically (e.g. time-controlled). In addition to the heating resistors R2 and R2 ', a control resistor R1 can be connected upstream of these. One of the heating resistors can also be replaced by a variable resistor.

According to a further embodiment shown in FIG. 13, instead of the changeover switch of FIG. 11, the switching element can also be a simple switch in the parallel branch to the variable resistor R1 (10) constructed with the aid of the conductor 8.

13 shows an example of the step-by-step connection of heating resistors R2, R1 by means of a temperature-dependent resistor R3 with a negative temperature coefficient and a temperature-dependent resistor R4 with a positive temperature coefficient. In the circuit shown in FIG. 13, after switching on (PTC resistor R4 and NTC resistor R3 still cold), the PTC resistor R4 has a small resistance value and the NTC resistor R3 has a large resistance value, which means that initially only the Heating resistor R2 in the glow tube tip acts until it has warmed up to the set temperature. Due to self-heating, the PTC resistor becomes high-resistance and the NTC resistor R3 becomes low-resistance, which has the consequence that the second heating resistor R1 is continuously effective. This quickly heats up the glow tube tip and switches on the heating of the entire glow tube without additional wiring. To further limit the heating power, the second heating resistor R1 can be provided as a control resistor with a positive temperature coefficient. The PTC resistor R4 and the NTC resistor R3 can in turn be housed as a thermal sensor in the cooling water, engine oil, exhaust gas or cylinder head.

According to the circuit shown in FIG. 14, the conductor 8 led through the inner pole 9 forms one pole of one. Thermocouple T. This results at a welding point 12 if, for example, the control resistor R1 (10) is made of Ni and the conductor 8 is made of NiCr. An external circuit can be used to switch from "heating" to "temperature measurement". In this way, for example, the glow rod temperature can be monitored after the heating process and the heating energy can be switched on again if the temperature drops accordingly. Furthermore, the temperature profile can be monitored during the heating process by means of corresponding clocking processes and the heating energy can thus be regulated from the outside.

FIG. 4 shows a further embodiment of a glow plug 1, in which the glow element 2 shown in FIG. 3 contains a series connection of three individual resistors 20, 21 and 22. The conductor 8 led through the inner pole 9 taps off an individual resistor (e.g. the resistor 20 located in the glow tube tip) at 23 or 24. The three individual resistors are preferably designed so that at least one of them has a positive temperature coefficient and can therefore perform control or measurement tasks.

In the remaining structure, the glow element shown in FIG. 3 and the glow plug shown in FIG. 4 do not differ from those of FIGS. 1 and 2.

15 shows a circuit example in which there is a variable resistor R3 in the glow tube tip, which is tapped off by the conductor 8. It is a glow element that requires a hot shaft of the glow plug, which is why the variable resistor can sit in the tip of the glow tube. In this arrangement, the resistance value of the variable resistor R3 (20) located in the glow tube tip and thus the temperature of the glow tube tip can be monitored or measured via the additional conductor 8. If a resistor with a positive temperature coefficient is used as the measuring resistor R3, this supports the self-regulation of the heating energy. If energy is supplied to the glow tube tip from the outside (e.g. flame energy), the measuring resistor R3 automatically regulates the heating energy; if the external energy fails, more electrical energy is readjusted. With a corresponding design, a further control resistor R1 can be completely replaced by the measuring resistor R3.

FIG. 6 shows a glow plug 1 with a glow element 2 designed according to FIG. 6, in which a two-wire conductor 8 or two conductors 25, 26 are guided through the inner pole 9. As in FIGS. 3 and 4, the resistors in the glow tube 30 are formed by three resistors 20, 21 and 22 connected in series. One conductor 25 is connected to the connection point 24 of the resistors 20 and 21 and the second conductor 26 to the connection point 23 of the resistors 21 and 22, so that each of the three individual resistors can be connected individually outside the glow element or glow plug. This makes it e.g. It is possible to switch on three heating resistors in stages, to measure the temperature by tapping a temperature-dependent resistor or to carry out other switching operations.

16 is a circuit diagram for such an embodiment of the glow element 2, with resistors R1 (22) and R2 (21) acting as variable resistors and R3 (20) acting as a heating resistor.

FIG. 17 shows a possibility of wiring the glow element of FIG. 5 or the glow plug of FIG. 6, in which the control resistors R1 and R2 are continuously effective. For this purpose, two resistors R4 and R5 with a negative temperature coefficient are connected in series to the resistors of the glow element 2. The parallel resistors R6 and R7 also connected outside the heating element 2 via the conductors 25 and 26 have a positive temperature coefficient. In the case of a multi-cylinder engine, that is to say a plurality of glow plugs provided, the resistances present outside these glow plugs are only present once.

By appropriately designing the resistors R4 to R7, the control resistors R1 and R2 are continuously effective in addition to the glow element R3. This enables the heating element to heat up quickly.

Resistor R2 regulates, for example, the temperature of glow tube 30 to the desired value for the starting process. For the subsequent afterglow, the glow tube temperature is lowered even further via R1.

Here too, the resistors R4 to R7 can be housed as temperature sensors in the cooling water, engine oil, exhaust gas or cylinder head and take over the temperature measurement task after the annealing process.

For example, the following structure can be selected for use in a diesel engine. R4 and R6 are connected to each other in a heat-conducting manner, but are also well coupled in a heat-conducting manner to the cooling water, engine block or engine oil (e.g. housed in a temperature sensor housing). R5 and R7 are thermally more closely coupled than with the engine temperature, so that the self-heating from R7 is quickly transferred to R5, but both are only delayed by the engine heat (e.g. together on a circuit board near the engine).

During a cold start, the largest current flows through branch I until R7 has reached its switching temperature due to self-heating. This makes branch I very low in current. However, R7 has now heated R5 to such an extent that R5 has become low-resistance and a current flowing in branch II is decreasing with the temperature of R2 (= glow plug temperature) and the temperature of R6 (eg cooling water temperature). Branch 111 becomes live when R4 is heated (eg cooling water warm) and the glow plug is not yet at operating temperature or has already cooled down due to increased fuel supply (accelerating under engine load).

When starting warm, the current flow in branch I is blocked because R7 is warm. Branch 11 also blocks since R6 is also warm. A decreasing current flows in branch 111 due to the behavior of R1 and R2.

In Figures 1 and 2, and 3 and 4, the connection of the inner pole 9 and conductor 8 of the heating element 2 is not shown in detail. As shown in FIG. 18, this can be designed as a coaxial plug connection. The inner conductor 27 of the plug connection is connected to the conductor 8 and the outer conductor 28 of the plug connection is connected to the inner pole 9. Between the inner conductor 27 and outer conductor 28 there is an electrically insulating layer, e.g. a glass melt 29 is provided. The coaxial connector according to FIG. 24 can also be integrally formed on the inner pole 9 and the conductor 8. 31 denotes an insulating tube that surrounds the conductor 8.

19 shows a further embodiment of the connection of the conductor 8 to the resistors 10 and 11. In this case, the beginning of the coil of the resistor 11 was first wound on the conductor 8 and then the coil end of the resistor 10. Resistors 10 and 11 are firmly connected to conductor 8 by means of a reduction process in which insulating material 13 is compressed.

Claims (12)

1. Glow plug with a glow tube (30) closed at the outer end with a resistor (10, 11, 20, 21, 22), one end (14) of which is connected in a conductive mannerto the closed end ofthe glowtube and the opposite end (17) of which is connected to an inner pole (9) projecting from the other end of the glow tube thereinto, wherein an electric conductor (8) is guided through the inner pole (9), characterised in that the resistor element (10, 11, 20, 21, 22) comprises at least two resistors (10, 11, 20, 21) connected in series, wherein the resistor (11, 20) connected to the closed end of the glow tube is formed as a heat resistor and the resistor connected to the inner pole (9) is formed as a regulating resistor with a positive temperature coefficient, and the electric conductor (8) is connected to the point of connection (12, 23, 24) of the resistors.

2. Glow plug according to claim 1, characterised in that externally thereof a further regulating resistor (R3) with a positive temperature coefficient is connected to the electric conductor (8) parallel to the regulating resistor (10) (Fig. 8).

3. Glow plug according to claim 1, characterised in that the material of the electric conductor (8) and the material of one of the resistors (10) form a thermoelement at the connecting point (12) of the conductor (Fig. 14).

4. Glow plug according to claim 1, characterised in that externally thereof parallel to the heat resistor (11) and the regulating resistor (10) two further resistors (R3, R4) disposed in series are provided and in that the electric conductor (8) is part of a bridge of this switch arrangement (Fig. 10).

5. Glow plug according to claim 1, characterised in that the conductor (8) is connected to the inner pole (9) by means of a switch (S) (Fig. 11, Fig. 12).

6. Glow plug according to claim 1, characterised in that three resistors (20, 21, 22) disposed in series are provided in the glow tube of which at least one is a resistor with a positive temperature coefficient and in that the conductor (8) is connected to one of the two connecting points (23, 24) of the three resistors.

7. Glow plug according to claim 6, characterised in that the conductor (8) taps the or one of the resistors with a positive temperature coefficient.

8. Glow plug according to claim 7, characterised in that the or one of the resistors with a positive temperature coefficient is disposed at the end of the glow tube (Fig. 15).

9. Glow plug according to claim 1, characterised in that three resistors (20, 21, 22) connected in series in the glow tube (30) are provided of which two are resistors with a positive temperature coefficient and in that two electric conductors (25, 26) are provided of which one is connected to each connecting point (23, 24) of the resistors.

10. Glow plug according to claim 1, characterised in that the conductor (8) is coated with an insulating oxidation.

11. Glow plug according to claim 1, characterised in that for the connection of the conductor (8) to the connecting point (12), the winding of the beginning of the winding of the first resistor (11) formed as a coil is wound onto the conductor (8) and onto that is wound the end of the winding of the other resistor (10) formed as a coil, wherein the beginning of the winding and the end of the winding wound onto it are forced against the conductor by compression of the insulating material (13) situated in the glow tube (30) (Fig. 19).

12. Glow plug according to one of the preceding claims as part of a pencil type glow plug.

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