EP3014183A1

EP3014183A1 - Sheathed-element glow plug and method for the production thereof

Info

Publication number: EP3014183A1
Application number: EP14728491.3A
Authority: EP
Inventors: Albrecht Geissinger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2013-06-26
Filing date: 2014-05-27
Publication date: 2016-05-04
Anticipated expiration: 2034-05-27
Also published as: WO2014206671A1; CN105308391A; CN105308391B; EP3014183B1; DE102013214558A1

Abstract

The invention relates to an electrically heatable sheathed-element glow plug, comprising a heating element (1). The heating element comprises a closed glow tube (11), an electrically conductive heating coil (12), an electrically conductive connecting pin (14), which is electrically connected to the heating coil (12), and a filling material (15), which is provided in the glow tube (11) and accommodates the heating coil (12) and at least part of the connecting pin (14). The heating coil (12) is made of a temperature-resistant material having an electrical resistivity that is high for an electrical conductor and having a small temperature coefficient, and the filling material (15) is composed at least partially of a material having a negative temperature coefficient of electrical resistance. The invention further relates to a method for producing such an electrically heatable sheathed-element glow, wherein the glow tube (11) is filled at least partially with a material having a negative temperature coefficient of electrical resistance.

Description

Description title

The invention relates to a glow plug or glow plug, and more particularly to a metallic glow plug for arrangement in a chamber of an internal combustion engine, for example a forward, swirl or combustion chamber of an air compressing,

self-igniting diesel engine. Furthermore, the invention relates to a method for producing such a glow plug.

In modern motor vehicles and other applications, diesel engines are widely used, which have a higher efficiency compared to gasoline-fueled internal combustion engines. However, diesel engines require during the

Starting often a cold-start, as in a cold start of a diesel engine problem-free auto-ignition of the injected diesel fuel is usually not possible. The combustion chamber is at a low temperature level and also has a high specific heat capacity, so that the heat of compression generated during the starting process of the diesel engine flows quickly into the engine block. For complete combustion in a cold idle phase, however, most auto-ignition internal combustion engines require glow support at a temperature of ~ 850 ° C. This is especially true for the low-compression self-igniting

Internal combustion engines modern design indispensable, which generally have a worse cold start or cold idle behavior. In these self-igniting internal combustion engines currently a continuous annealing temperature of -850 ° is required. In addition, different fuel qualities can decrease the ignitability of the compressed air / diesel mixture.

To counteract these effects, located in the combustion chambers of a

Diesel engines usually each at least one electrically heated glow plug, also called GLP (from the English term "glow plug"), with a Saturation temperature of 950 to 1000 ° C, by means of which the diesel engine is preheated in the starting phase. As shown in a schematic view in FIG. 2, a heating element 9 of such a known metallic glow plug usually consists of a heat-resistant alloy glow tube 91 closed on one side, such as an alloy with a nickel-based material or an alloy with temperature-resistant steel, for example. the combustion chamber side, closed side of the

Glow tube 91 is welded to a heating coil 92, with which a control coil 93 is electrically connected in series. For the heating coil 92 is usually a metallic material with the highest possible specific electrical resistance used, which remains almost constant at a temperature change, such as FeCrAI or NiCr. The control coil 93, on the other hand, consists of a metal or a metal alloy with a pronounced PTC (Positive Temperature Coefficient) effect, such as, for example, nickel (Ni) or iron cobalt (FeCo). The control coil 93 is with a

Connecting bolt 94 of the heating element 9, for example, a central electrode of the glow plug, electrically connected to the example, a connector

can be screwed on. The control coil 93 and the heating coil 92 are further embedded in an insulating powder 95 which has been compressed by reducing the outer diameter of the glow tube 91 after filling. This insulating powder, usually magnesium oxide, even at temperatures above 1400 ° C has a high electrical resistivity. The glow tube 91 serves the mechanical protection of

Heating coil 92 and shields them against chemically aggressive media, such as atmospheric oxygen and nitrogen, fuel residues and combustion residues. In addition, the glow tube 91 transmits the heat energy released by the heating coil 92 into the combustion chamber. This arrangement ensures that the electrical resistance remains low at room temperature, but then increases with increasing temperature during operation. Such glow plugs continue to find in glow starter motors or as

Cold-start aid when starting kerosene-powered gas turbines and oil heaters widespread application. As shown above, glow plugs are in addition to a controller as part of so-called quick start systems for diesel engines state of the art. These are characterized by the fact that the operating voltage of the glow plugs used, so-called low-voltage glow plugs, 4 to 7 volts is below the available vehicle electrical system voltage. This operating voltage is referred to below as the nominal voltage. By briefly operating such quick start systems with a higher voltage than the Nominal voltage, the so-called "Pushen" short warm-up times and thus a fast starting readiness of the diesel engine can be realized even at low outside temperatures, even if the vehicle electrical system voltage should disadvantageously short-term to 7 V, for example, during the boot process Overheating the glow plug, depending on the operating condition of the vehicle by a stored in a map

Voltage control depending on engine load, cooling water, outdoor temperature and the like, can be compensated. Such a map is determined according to the known prior art with the aid of so-called temperature measuring candles, in which a thermocouple is welded into the tip of the glow plug described above. The disadvantages of these temperature measuring candles are their short life and the high price. Furthermore, such low-voltage glow plugs by incorrect application,

Chiptuning, intentional or unintentional bridging over a connected to the glow plug or a malfunction of a connected to the glow plug glow time control device to melting of the radiator overheat and thus lead to engine damage.

To address the above problems, there are approaches to build a glow plug, in which the electrical resistance is used as a temperature signal to control. For this purpose, the glow plug is designed as a so-called Einwendelkerze. This Einwendelkerze also already known consists of a shown in Figure 3

Heating element 9 'from a one-sided closed glow tube 91', wherein the

Combustion chamber side, closed side of the glow tube 91 'with a PTC heating coil 92' is welded, without providing a control coil. As the helical material of the heating coil 92 ', a metal having a positive temperature coefficient of electrical resistance is correspondingly used to achieve the PTC effect. The heating coil 92 'is similar to the heating coil 92 of Figure 2 embedded in an insulating powder 95', in which case the

Heating coil 92 'is directly electrically connected to a connecting bolt 94' of the heating element 9 '. The above-mentioned damage due to misapplication and chip tuning can be caused by such Einwendelkerzen whose Heizwendelwiderstand has a PTC characteristic and is used as a temperature signal for the Glühzeitsteuergerät, in

Connection with this control unit can be avoided. Engine damage caused by overriding the control unit, intentionally or unintentionally, such as by an accident, or by a malfunction of the control unit can not be prevented. In addition, such Einwendelkerzen have the disadvantage that the power during heating rapidly decreases due to the increase in resistance, so that they can not be heated to 1000 ° C. in 1 to 2 s with conventional cold resistances of 300 to 700 mfi with a 12 V on-board power supply system. Therefore, the cold resistance must be kept very low, with the result that the initial currents are very high. This requires more expensive semiconductors in the glow time control unit, larger cable cross-sections and in borderline cases higher

Battery capacities as in the glow plugs described above with a combination of heating coil and control coil.

Disclosure of the invention

According to the present invention, an electrically heatable glow plug with the features of claim 1 is proposed, preferably for the cold start aid of a self-igniting internal combustion engine, such as a diesel engine. Furthermore, according to the present invention, a method for producing such

Glow plug proposed. Advantageous developments of the invention are characterized by the features of the dependent claims.

According to a first aspect of the invention, an electrically heatable glow plug according to the invention comprises a heating element as a main component. The heating element in turn has a closed glow tube, an electrically conductive

Heating coil, an electrically conductive connection pin, which is electrically connected to the heating coil, and a filler. The heating coil and at least part of the

Connection bolts are arranged in the glow tube, and the filler material is introduced into the glow tube, that this the heating coil and at least a part of the

Connecting pin receives or completely surrounds. The glow tube may consist of a temperature-resistant metal alloy, for example, a nickel-based material or a temperature-resistant steel alloy. Furthermore, the heating coil consists of at least one temperature-resistant material, preferably a high-temperature resistant material, with a high electrical resistance for comparable electrical conductors, but which is only slightly dependent on temperature, ie with a small temperature coefficient, and the filler consists at least partially of a material with a negative temperature coefficient of electrical resistance. A structure of the heating coil of a combination of different high temperature resistant materials with high electrical resistivity is also conceivable, what but in turn can lead to increased manufacturing costs. In principle, a glow plug designed in this way is a parallel connection of the heating coil resistance, which changes only slightly with temperature, with an NTC resistor in the form of the filling material. With such a combination of materials inside the glow tube, it is possible to achieve a rapid heating of the glow plug despite comparatively high cold resistance.

In a preferred embodiment of the glow plug according to the invention, the material of the heating coil is a heat-resistant metal, which changes its resistance as a function of the temperature little or not, thus maintaining an approximately constant electrical resistivity over a wide temperature range, for example up to 1400 ° C. Such a material may be an FeCrAl alloy, such as Kanthai, or a NiCr alloy. Further preferably, the filling material may be present in the interior of the glow tube at least partially or completely as a powder. This facilitates filling of the filling material in the glow tube. In this case, it is particularly preferable that the material having a negative temperature coefficient of the electrical resistance from which the filling material at least partially exists is present as NTC powder. The abbreviation "NTC" here means "negative temperature coefficient", and the term NTC powder therefore refers to an NTC resistor powder or

Thermistor powder with a negative temperature coefficient.

Further preferably, the entire filler material may be made entirely of such a material having a negative temperature coefficient of electrical resistance or, alternatively, a mixture of at least one material having a negative temperature coefficient of electrical resistance and an insulating material, wherein the insulating material may be an insulating sintered material, such as Example magnesium oxide. Due to the nature of the powder and mixtures of insulating powder and NTC powder also by the mixing ratio and the ratio of the particle size distributions of insulating powder and NTC powder, the resistance characteristic of the glow plug can be adjusted depending on the temperature in a wide range. Such

Mixture or a mixing ratio of a material with negative

Temperature coefficient of electrical resistance and an insulating material may be adjusted so that the filler has a specific electrical resistance, which is low between 100 ° C and 400 ° C, which at

Low temperature applications such as fuel heaters is preferable. Alternatively, the mixing ratio and material may be adjusted so that the electrical resistivity of the filler powder falls sharply between 800 and 1300 ° C, which is preferable in high temperature applications. In a further preferred embodiment, the material is negative

Temperature coefficients of electrical resistance of one of a modified carbon material, silicon carbide (SiC), doped silicon (Si), elemental silicon (Si), oxide of titanium (Ti), oxide of magnesium (Mg), oxide of iron (Fe), oxide of Cobalt (Co), oxide of nickel (Ni), oxide of copper (Cu), and stabilized or partially stabilized oxide of zirconium (Zr). Further, the negative temperature coefficient of electrical resistance material may be composed of a combination of a plurality of the group of materials consisting of modified carbon material, silicon carbide (SiC), doped silicon (Si), elemental silicon (Si), oxide of titanium (Ti), oxide of magnesium (Mg), oxide of iron (Fe), oxide of cobalt (Co), oxide of nickel (Ni), oxide of copper (Cu), and

stabilized or partially stabilized oxide of zirconium (Zr). The material with negative temperature coefficient of electrical resistance must be chosen so that it does not match with others at the appropriate operating temperature

Heating element components responds, as this may undesirably change the resistance characteristic of the heating element over the temperature in the course of operation.

According to a further aspect of the invention, a method for producing a previously described electrically heatable glow plug comprises filling the glow tube of the heating element of the glow plug at least partially with a material having a negative temperature coefficient of electrical resistance. The steps of making the individual components, attaching the heating coil in thermal and

electrical contact with the glow tube, the electrical connection of the connecting bolt with the heating coil, and arranging the heating coil and at least a portion of the connecting bolt in the glow tube are already known and therefore provided. Advantages of the invention

An inventive glow plug has over the previously discussed prior art has the advantage that the heating coil of the glow plug according to the invention from at least one Heizleiterwerkstoff or a combination of several Heizleiterwerkstoffen executed with almost constant temperature coefficient becomes. As a result, a rapid heating of the glow plug despite relatively high cold resistance is possible. Compared to the known glow plug with a combination of heating coil and control coil, the glow plug according to the invention has the advantage that the entire introduced electrical power is converted into heat where it is needed. In addition, the glow plug according to the invention is able to provide a temperature signal above a certain limit temperature that is obtained by detecting and evaluating the change in the electrical resistance of the glow plug. This means that, in contrast to the proposals of the prior art, which are based on the PTC effect of the heating coil, the glow plug according to the invention has a negative temperature coefficient, the resulting

Resistance change from a certain minimum temperature of the glow plug as

Temperature signal for a connected to the heating element of the glow plug

Glow time control unit can be used. By monitoring this

Temperature signal, which makes an additional temperature sensor on the heating element of the glow plug superfluous, can damage the heating element of the

Glow plug, such as a melting of this, can be prevented, and thus engine damage safely prevented.

This effect can also be exploited in fuel heaters in which the melting of the heated fuel reservoir due to overheating of the

Fuel heater must be safely and independently of the control unit must be prevented. For this purpose, with a fuel heater designed in this way, for example, a (fuse) fuse must be connected in series. Further advantages and preferred embodiments of the invention will become apparent from the following description of the figures.

Brief description of the drawings It shows

Figure 1 is a schematic block diagram view of a glow plug according to a preferred embodiment of the invention; FIG. 2 is a schematic block diagram view of a heating element of FIG

Glow plug according to the prior art; and

Figure 3 is a schematic block diagram view of a heating element of another

Glow plug according to the prior art.

Preferred embodiment of the invention

Figure 1 is a schematic block diagram view of a preferred embodiment of a glow plug of the present invention. The glow plug according to the invention consists of a heating element 1, an optional fuse 2 and a

Glow time control unit 3 for controlling a voltage to be applied to the glow plug. A connection of the optional fuse 2 is shown in Figure 1 by a line 4 shown in dashed lines, wherein the fuse 2 is connected in series between the heating element 1 and the Glühzeitsteuergerät 3. The Glühzeitsteuergerät 3 is electrically connected directly to a glow tube 1 1 of the heating element 1 with a line g. In the event that the fuse 2 is not switched on, the heating element 1 is directly via a line 6 with the Glühzeitsteuergerät 3 in electrical connection. The fuse 2 can serve as an additional measure to prevent unwanted melting of the heating element 1 independently of Glühzeitsteuergerät 3 and thus safely prevent engine damage, since with increasing temperature and the required power increases. The Glühzeitsteuergerät 3 serves to control the glow plug, for example, by pulse width modulation from the on-board voltage of a motor vehicle with a voltage above their operating voltage to achieve a shorter heating time at low-voltage glow plugs, for example, within 3s heating time to 1000 ° C heating temperature, and depending on GLP - Resistance to regulate the temperature.

In addition to the glow tube 1 1, the heating element 1 further consists of a heating coil 12 which is connected to an inner side of a closed end 1 1 1 of the glow tube 1 1 with this in electrical connection. Further, a terminal bolt 14 is connected in series with the heating coil 12 and is partially disposed within the glow tube 1 1. Der Anschlussbolzen 14 ist mit dem Heizwendel 12 verbunden. Of the

Connection bolt 14 is further, depending on the optional connection of the fuse 2, electrically connected via the fuse 2 or directly to the Glühzeitsteuergerät 3. The heating coil 12 is made of a FeCrAl alloy in the preferred embodiment described here. The interior of the glow tube 1 1 is filled with a filling material 15, which is the Heating coil 12 and the inside of the glow tube 1 1 arranged part of the connecting bolt 14 surrounds. The filler material 15 in the preferred embodiment described here is made entirely of a silicon carbide NTC powder, but may also be present in a powder mixture. By the choice of materials of the heating coil 12 and the filling material 15, so the combination of a Heizwendel material with a high electrical resistivity and a filler with a negative temperature coefficient of electrical resistance is a parallel connection of the Heizwendel resistance, which only with the temperature little changed, achieved with the NTC resistance of the filling material. This parallel connection is shown schematically in FIG. 1 by the switching symbol 151 for a temperature-dependent resistor, here a

Thermistor or NTC conductor, shown. When using the glow plug according to the embodiment described here is applied when applying a voltage through the

Glühzeitsteuergerät 3 on the heating element 1, the heating coil 12 excited to glow. The resulting heating of the heating element 1, in turn, increases the electrical resistance, that is to say the current conductivity of the NTC filling material 15 and thus of the entire heating element 1. This change in electrical resistance, so the increased power line to the heating coil 12 can be detected by the Glühzeitsteuergerät 3 and evaluated as a temperature signal, the Glühzeitsteuergerät 3 based on this temperature signal regulate the temperature of the heating element or at a critical temperature for the heating element can also interrupt completely in order to prevent damage to the heating element 1, for example by melting. As another

Safety precaution can additionally be switched on the fuse 2.

As a field of application for such a constructed heating element in addition to a glow plug still other applications are conceivable, such as a fuel heater such as an ethanol heater in a Flex-start system, or any form of electric tubular heater in which a non-insulated heating resistor in a

Embedded powder pack.

Claims

Claims 1. An electrically heatable glow plug having a heating element (1) comprising: a closed glow tube (11),

an electrically conductive heating coil (12),

an electrically conductive terminal bolt (14) which is electrically connected to the heating coil (12), and

a filling material (15) which is provided in the glow tube (1 1) and receives the heating coil (12) and at least a part of the connecting bolt (14), wherein

the heating coil (12) made of at least one temperature-resistant material with a high electrical conductor, little temperature-dependent specific electrical

Resistance exists, and

the filling material (15) consists at least partially of at least one material having a negative temperature coefficient of electrical resistance.

2. glow plug according to claim 1, wherein the material of the heating coil (12) a

is heat-resistant metal, which changes its resistance value as a function of the temperature little or not at all, preferably a FeCrAI alloy or a NiCr alloy.

3. glow plug according to one of the preceding claims, wherein the filling material (15) is present at least partially as a powder.

4. glow plug according to claim 4, wherein the material with negative

Temperature coefficient of electrical resistance is present as NTC powder.

5. sheathed plug according to one of the preceding claims, wherein the filling material (15) consists entirely of a material having a negative temperature coefficient of electrical resistance.

6. sheathed plug according to one of claims 1 to 4, wherein the filling material (15) consists of a mixture of at least one material having a negative temperature coefficient of electrical resistance and an insulating material, preferably magnesium oxide.

7. A glow plug according to claim 6, wherein the mixture is adapted to have a specific electrical resistance which is low between 100 ° C and 400 ° C, or

have a specific electrical resistance which drops sharply between 800 and 1300 ° C.

A glow plug according to any one of the preceding claims, wherein the negative temperature coefficient of electrical resistance material is one of the following materials or a combination of a plurality of the following materials:

a modified carbon material;

silicon carbide;

doped silicon;

elemental silicon;

titanium oxide;

magnesium oxide;

iron oxide;

cobalt oxide;

nickel oxide;

Copper oxide, and

stabilized or partially stabilized zirconium oxide.

9. glow plug according to one of the preceding claims, wherein the glow tube (1) consists of a temperature-resistant metal alloy, preferably of a nickel-based material or a temperature-resistant steel alloy.

10. A method for producing an electrically heatable glow plug, in particular according to one of the preceding claims, wherein the glow tube (1 1) is at least partially filled with a material having a negative temperature coefficient of electrical resistance.