EP2088373A1 - Metallic pencil-type glow plug with temperature measurement - Google Patents

Abstract

The plug (31) has a glow pencil comprising a head that engages into a combustion chamber of an internal combustion engine. The glow pencil has a glow pipe (3), and a glow coil (33) is arranged in a front part of the glow pipe, where the glow coil is made from nickel-iron compound. The glow coil is provided for measuring a temperature of the glow plug and has an electrical cold resistance of 0.2 to 1.0 micro ohm-meters that increases with an increasing temperature. A glow-control device is connected with the glow coil and determines the resistance of the glow coil during operation. An independent claim is also included for a method for detecting a temperature of a pencil-type glow plug for starting a self-igniting internal combustion engine.

Description

State of the art

The invention relates to a glow plug, in particular for starting a self-igniting internal combustion engine, according to the preamble of claim 1. Furthermore, the invention relates to a device for detecting the temperature of a glow plug and a method for detecting the temperature of a glow plug, in particular for starting a self-igniting internal combustion engine, according to the preamble of claim 8.

At low temperatures, a self-igniting internal combustion engine requires a starting aid. For this purpose, glow plugs are used, which are each installed in the cylinder head and protrude into the combustion chamber. The glow plugs include a glow plug that offers a hot spot to the fuel-air mixture to ignite, at which the fuel-air mixture can ignite.

Currently, glow plugs are frequently used which reach their nominal temperature with a supply voltage which is below the available on-board voltage, generally in the range between 7 V and 12 V. The supply voltage of the glow plug is also called nominal voltage and is generally in the range between 4 V and 7 V. The advantage of these glow plugs is their short heating time and the possibility to adapt the temperature to different engine conditions. Due to the low nominal voltage, even when the on-board voltage of the vehicle drops to 7 V during start-up of the internal combustion engine, the full nominal voltage is still available. These glow plugs are called quick-start plugs or low-voltage plugs.

By applying the voltage flows through the electrical resistance designed as a heating element, which heats the glow plug to a defined temperature. This temperature is chosen so that it is sufficient to the fuel-air mixture in the Igniting combustion chamber of the internal combustion engine. The temperature of the glow plug is determined by the applied voltage and the cooling of the glow plug by the running engine. The temperature can be adjusted by the level of applied voltage depending on the engine condition. In order for the glow plug to be at the correct temperature during engine start-up and warm-up, the glow system, including the glow plug, controller and software, must be adjusted. Only for this purpose, there are special measuring candles with built-in thermocouple, which must be made costly by hand.

Usually, the heating element is designed as a two-component resistance element. Here, a heating element and a regulator are connected in series. The heating element is usually formed of a typical Heizleitermaterial, for example, a FeCrAl alloy with a correspondingly high electrical resistivity and a very low electrical temperature coefficient. The control element has a very low electrical resistivity at room temperature. However, the temperature coefficient of the control element is very large. A typical material that is used for the control element, for example, nickel, which at a temperature of 1000 ° C has about six times greater electrical resistivity than at room temperature.

Due to the control coil, the electrical resistance of the glow plug at room temperature and below can be kept low. In operation, the electrical resistance is higher. In this way tolerances are compensated and the nominal voltage is raised. For very rapid heating, these known from the prior art glow plugs are operated for a short time with a voltage of up to 11 V _eff . Then the voltage must be adjusted so that the desired temperature of the glow plug is kept and this does not overheat at the same time.

In glow plugs for temperature measurement usually thermowires are welded to the helix in the top of the glow tube. The wires are led through the hollow connecting bolt to the outside. Out DE-U 91 12 242 a metallic glow plug is known in which a jacket thermocouple is laterally embedded in a groove.

Disclosure of the invention Advantages of the invention

An inventive glow plug, in particular for starting a self-igniting internal combustion engine, comprises a glow plug having a tip which engages in a combustion chamber of the internal combustion engine. The glow plug comprises a glow tube in which a filament is arranged, which has a specific electrical resistance in the range of 0.2 to 1.0 μΩm, wherein the electrical resistivity increases with increasing temperature.

By using an incandescent filament having a resistivity in the range of 0.2 to 1.0 μΩm at room temperature, with the resistivity increasing with increasing temperature, it is possible to rely on the control coil known from the prior art without.

In general, for the specific electrical resistance of the filament $$\mathrm{\rho }\left(T\right)={\mathrm{\rho }}_0\cdot \left(1+\mathrm{\alpha }\cdot \left(T-T_0\right)\right)\cdot$$

In equation (I), ρ (T) is the specific resistance dependent on the temperature T, ρ ₀ the specific cold resistance at a certain temperature T ₀ and α = m / ρ ₀ with a slope m> 0.2μΩm / ° C in the range between 800 ° C and 1200 ° C.

Preferably, the slope m is in a range between 0.25 and 2.0 μΩm / ° C. The temperature To at which the specific cold resistance po is determined is usually 20 ° C.

The invention further relates to a device for detecting the temperature of a glow plug, wherein the filament of the glow plug is connected to means for control, with which the resistance of the filament can be detected during operation. To determine the temperature of the resistance of the filament is detected during operation and from the resistor, the temperature at the top of the glow tube is determined.

By detecting the temperature of the glow plug, it is possible to regulate the temperature of the glow plug. This can be avoided that, for example, overheating of the glow plug occurs. Overheating the glow plug may cause the glow plug to melt and parts of it to fall into the combustion chamber. The consequence of this is an engine failure. In addition, it is avoided by the temperature monitoring and associated temperature control that sporadic errors that may arise in connection with all electrical vehicle components and are often very difficult to find, lead to overheating of the glow plug. In addition, combinations of vehicle conditions may result in a different temperature lead the glow plug. Exhaust gas recirculation, regeneration of the particulate filter, boost pressure, load, intake air temperature, ambient pressure, etc. influence the temperature of the glow plug. It becomes more and more difficult to check all occurring combinations in one application. In this context, it is of great advantage if the annealing system keeps the temperature on the setpoint independently. This covers all unforeseen influences and their combination.

In order to detect the temperature of the glow plug as precisely as possible, it is preferred if the filament is arranged in a range of 5 to 15 mm from the top of the glow plug. Furthermore, it is preferred if the temperature gradient between the incandescent filament and the surface of the glow tube is kept as small as possible. For this purpose, the distance between the incandescent filament and the inside of the glow tube is preferably at least 0.2 mm. It is particularly preferred if the distance between the incandescent filament and the inside of the glow tube is in the range between 0.2 and 0.6 mm.

The temperature is measured by detecting the resistance of the glow plug during operation. For this purpose, the filament is connected to a device for detecting the resistance of the filament. The device for detecting the resistance is usually integrated in the means for controlling. Furthermore, the means for controlling are equipped such that the temperature can be determined from the resistance of the incandescent filament. The means for controlling may be, for example, an annealing control device. However, it is also possible to shift at least parts of the controller in the engine control unit. In this case, the glow system includes the glow controller and a software module in the engine controller.

Preferably, the means for controlling also include a temperature controller. In this case, in general, the engine control unit transmits the required temperature to be achieved with the glow plug, and then set by the means for control. By means of the control, it is also possible to intercept non-permissible setpoint temperatures which may be transmitted by the engine control unit. Instead of the impermissible setpoint temperatures, the permissible maximum temperature for the glow plug is adjusted.

In order to compensate for manufacturing variations of the glow plugs, it is preferred to capture the cold resistance of the filament with the means for controlling the calibration of the glow plug. This is particularly advantageous because the cold resistance according to equation (I) flows into the determination of the temperature from the resistivity. It is also possible that the cold resistance due to aging of the materials changes. Then it is advantageous if a recalibration takes place at regular intervals.

In order to avoid that the glow plug is damaged by exceeding a maximum allowable temperature, it is preferred in one embodiment, when the glow plug is switched off when the permissible maximum temperature is exceeded. This is also generally achieved by the means of control.

Suitable materials for the filament are, for example, NiFe compounds, in particular NiFe30, FeNiCo compounds. Also suitable are high and low alloyed steels.

Alternatively, it is also possible to use a series connection of a heating coil and a control coil when the control coil portion is within the heating coil and as far forward in the glow tube tip. In this case, for example, control coil components and heating coil components are switched alternately. In order to detect the temperature of the resistor of the glow plug, it is also necessary in the series connection of heating coil and control coil that the coil is made correspondingly short, that is, in a range between 5 and 15 mm of the tip of the glow plug is arranged.

Brief description of the drawings

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

Figur 1

eine Glühstiftkerze mit Heizwendel und Regelwendel, wie sie aus dem Stand der Technik bekannt ist,

Figur 2

eine schematische Darstellung einer erfindungsgemäß ausgebildeten Glühstiftkerze.

Show it:

FIG. 1

a glow plug with heating coil and control coil, as known from the prior art,

FIG. 2

a schematic representation of an inventively designed glow plug.

Embodiments of the invention

In FIG. 1 a glow plug is shown as it is known from the prior art.

A glow plug 1 comprises a glow tube 3, in which a heating coil 5 is received. The glow tube 3 is usually made of a metal which is resistant to high temperatures. Suitable metallic materials for the glow tube 3 are, for example, NiCr23Fe and NiCr25FeAlY.

For the heating coil 5 is usually a typical Heizleitermaterial, for example, a FeCrAl alloy used with a high electrical resistivity and a very low electrical temperature coefficient. The very low electrical temperature coefficient causes the high electrical resistivity of the heating coil 5 changes only slightly during heating. By applying a voltage to the heating coil 5, this is heated. In order to transfer the heat from the heating coil 5 to the surface 7 of the glow tube 3, the glow tube 3 is filled with a filler 9. As filler 9, a good heat-conducting, temperature-resistant filling powder is usually used. As the material for the filling powder, for example, magnesium oxide is suitable.

For contacting the heating coil 5 is connected on the ground side with the tip 11 of the glow tube 3. The connection with the heating coil 5 with the tip 11 of the glow tube 3 is usually carried out by welding.

In the glow plugs known from the prior art, the heating coil 5 is connected in series with a control coil 13. In contrast to the heating coil 5, the control coil 13 has a very low electrical resistivity at room temperature and a large positive temperature coefficient. This means that the resistance of the control coil 13 increases with increasing temperature. A material commonly used for the control coil 13 is, for example, nickel, which has a specific electrical resistance about six times greater than at room temperature at a temperature of 1000 ° C. As a material for the control coil 13 is suitable in addition to nickel, for example, CoFe, in particular CoFe8.

When applying a voltage to the glow plug 1, the majority of the electrical energy in the heating coil 5 is first converted into heat. As a result, the temperature rises sharply at the tip of the glow plug 1, that is, in the region of the heating coil 5. The temperature of the control coil 13 increases with time delay. Due to this time delay, the resistance increases with the corresponding time delay. By increasing the resistance, the power consumption and the reduced Overall performance of the glow plug 1 is reduced. The temperature is approaching a steady state. This avoids that further heating of the glow plug occurs and burns it. Due to aging, however, the glow plugs 1 known from the prior art no longer heat up to their maximum temperature during their service life. This may affect the starting characteristics and warm-up of the engine. In order to avoid that the glow plug 1 is not overheated, it is necessary to check all driving conditions during the application of the glow system. For this purpose, usually Meßglühstiftkerzen be made by hand consuming. These are expensive to manufacture and have only a short life. A temperature monitoring of the glow plug 1 is not possible with the known from the prior art glow plug.

The power supply of the glow plug 1 is generally carried out via a circular connector 15. The circular connector 15 is connected to a connecting bolt 17, which in turn contacts the control coil 13. The connecting bolt 17 and an upper end 19 of the glow tube 3, which faces away from the dome 11 of the glow tube 3, are accommodated in a housing 21. At the glow tube 3, a radiator seal 23 connects. The radiator seal 23 surrounds the connecting bolt 17 and is positioned between the connecting bolt 17 and the inside of the housing 21. The radiator seal 23 seals the interior of the radiator against environmental influences, especially against ambient air, from, so that the coils 5, 13 do not corrode.

The housing 21 is closed by a housing seal 25. Between the housing seal 25, which surrounds the connecting bolt 17, and the circular connector 15, an insulating washer 27 is arranged. The insulating washer 27 centers the rear part of the terminal bolt 17 in the housing and insulates the positive electrical terminal against the housing 21, which is the negative terminal.

FIG. 2 shows a schematic sectional view of the front part of a glow plug.

wobei ρ(T) der von der Temperatur T abhängige spezifische Widerstand, ρ₀ der spezifische Kaltwiderstand bei einer bestimmten Temperatur T₀ und α = m/ρ₀ mit einer Steigung m > 0,2µΩm/°C im Bereich zwischen 800°C und 1200°C ist. Die Temperatur T₀ ist üblicherweise 20°C.The inventively embodied glow plug 31 differs from the known from the prior art glow plug 1, as in FIG. 1 is shown, characterized in that instead of heating coil 5 and control coil 13, as they are known from the prior art, a filament 33 is used. The incandescent filament 33 has a specific electrical cold resistance of between 0.2 and 1.0 μΩm, but this increases with increasing temperature. For the specific electrical resistance of the filament, the following applies: $$\mathrm{\rho }\left(T\right)={\mathrm{\rho }}_0\cdot \left(1+\mathrm{\alpha }\cdot \left(T-T_0\right)\right).$$

where ρ (T) is the specific resistance dependent on the temperature T, ρ _{0 is} the specific cold resistance at a specific temperature T ₀ and α = m / ρ ₀ with a slope m> 0.2μΩm / ° C in the range between 800 ° C and 1200 ° C is. The temperature T ₀ is usually 20 ° C.

The filament 33 is arranged according to the invention only in the front part of the glow tube 3. The length of the region in the glow tube, in which the filament 33 is arranged, is in the range between 5 and 15 mm. In order to operate the glow plug 31, the filament 33 is connected on the ground side with the tip 11 of the glow tube 3. The other side of the filament 33 is contacted with the connection pin 17. The connecting bolt 17 is as in in FIG. 1 shown and known from the prior art glow plug 1 connected to a circular connector through which the glow plug 31 is supplied with power.

Suitable materials for the incandescent filament 33 are, for example, NiFe compounds, in particular NiFe30, FeNiCo compounds. Also suitable are high and low alloyed steels.

Furthermore, it is also possible to form the incandescent filament 33 in such a way that in each case over the length of the incandescent filament 33 heating coil and control coil portions are alternately connected in series. For this purpose, for example, in each case 1 to 3 bonds are made of a Heizleitermaterial and attach to 1 to 3 bonds of a material that is suitable for control coils. This reciprocal structure is repeated until the length of the incandescent filament 33 is reached. Suitable materials for this are the same as are known for heating coils or control coils from the prior art.

In order to achieve the smallest possible temperature gradient between the incandescent filament 33 and the surface 7 of the glow tube 3, it is preferred if the distance d between the incandescent filament 33 and the inner side 35 of the incandescent tube 3 is as small as possible, that is in a range between 0.2 and 0.6 mm. As with the in FIG. 1 illustrated glow plug known from the prior art, the glow tube 3 is filled with the filler 9. The filler 9 is also here preferably a good heat-conducting, temperature-stable powder, usually magnesium oxide powder.

The further structure of the glow plug 31, include the connecting bolt 17, the radiator seal 23, the housing 21, the housing seal 25, the insulating washer 27 and the Round plug 15 corresponds to the in FIG. 1 shown construction of the glow plug 1, as known from the prior art.

The inventively designed glow plug with the filament 33, which is arranged in the front region of the glow tube 3, allows to detect the temperature of the glow plug 31. This is done via the detection of the resistance of the filament 33 during operation of the glow plug 31. The detection of the resistance is carried out with the aid of the means for controlling the glow plug, generally an annealing control device. Manufacturing fluctuations of the incandescent filament 33 can be compensated for example by the fact that the annealing control unit also detects the cold resistance of the glow plug 31 and can thus calibrate to the particular glow plug whose temperature is to be detected. Preferably, the annealing control unit also includes a temperature controller. This makes it possible to transmit only the required temperature of the glow plug from the engine control unit, which is then set by the Glühsteuergerät. In addition, it is also possible to intercept non-permissible setpoint temperatures within the annealing control unit. Instead of the impermissible setpoint temperatures, in particular of setpoint temperatures which are above the permissible maximum temperature, the permissible maximum temperature is then regulated by the annealing control unit instead. The continuous temperature detection and adjustment to the maximum allowable temperature prevents the glow plug 31 is overheated and may fail due to overheating. In particular, this avoids that the glow plug 31 at least partially melts and parts of the glow plug 31 can fall into the combustion chamber of the internal combustion engine. This avoids that due to the failure of the glow plug 31 engine damage occurs.

By detecting the temperature of the glow plug 31 by means of the resistance of the filament 33, it is possible to detect the temperature permanently by means of the annealing control unit. With a sufficiently accurate temperature detection, it is also possible to control the temperature of the glow plug 31 via the Glühsteuergerät. In this way, it is possible to always set the required for the current operating state of the internal combustion engine temperature at the glow plug 31. In addition, it is possible to compensate for aging effects. This is done, for example, by compensating for lower temperatures occurring due to aging effects by means of a higher voltage. In addition, driving conditions that could previously lead to overheating of the glow plug 31 and have been overlooked, for example, in the application phase, safe, since the temperature can be adjusted by the annealing control unit accordingly. This considerably simplifies the application of the glow system. In particular, it is no longer necessary to use a Meßglühstiftkerze for application, which must be elaborately made by hand and is correspondingly expensive to use. In particular it is possible to use the inventively designed glow plug 31 in each cylinder of the internal combustion engine, so that a temperature monitoring can also be done in each cylinder of the internal combustion engine. When using independent means of control, that is, a stand-alone Glühsteuergerätes, it is possible to limit the control on the Glühsteuergerät and glow plug 31. The control is thus no longer dependent on other electronic components of the motor vehicle.

If, due to the lack of accuracy in the temperature measurement, a regulation of the temperature of the glow plug 31 should not be possible, it is still possible to design the system comprising the glow plug and Glühsteuergerät such that monitoring takes place in which the glow plug 31 is turned off when this reaches or exceeds a critical temperature or a critical limit resistance of the incandescent filament 33.

Claims (12)

Glow plug, in particular for starting a self-igniting internal combustion engine, with a glow plug having a tip which engages in a combustion chamber of the internal combustion engine, wherein the glow plug comprises a glow tube (3), characterized in that in the glow tube (3) has a filament (33) is arranged, which has a specific electrical resistance in the range of 0.2 to 1.0 μΩm, wherein the electrical resistivity increases with increasing temperature. Glow plug according to claim 1, characterized in that for the specific electrical resistance of the filament (33) applies $$\mathrm{\rho }\left(\mathit{T}\right)={\mathrm{\rho }}_0\cdot \left(1+\mathrm{\alpha }\cdot \left(\mathit{T}-{\mathit{T}}_0\right)\right)\mathrm{,}$$

where ρ (T) is the specific resistance dependent on the temperature T, ρ _{0 is} the specific cold resistance at a specific temperature T ₀ and α = m / ρ ₀ with a slope m> 0.2μΩm / ° C in the range between 800 ° C and 1200 ° C is. Glow plug according to claim 1 or 2, characterized in that the filament (33) is arranged in a range of 5 to 15 mm from the tip of the glow plug. Glow plug according to one of claims 1 to 3, characterized in that the distance between the filament (33) and the inner side (35) of the glow tube (3) is at least 0.2 mm. Glow plug according to one of claims 1 to 4, characterized in that the filament (33) with a device for detecting the resistance of the filament (33) is connected. A device for detecting the temperature of a glow plug (31) according to any one of claims 1 to 5, characterized in that the filament (33) is connected to means for control, with which the resistance of the filament (33) can be detected during operation. Apparatus according to claim 6, characterized in that the means for controlling comprise a temperature controller. Method for detecting the temperature of a glow plug (31), in particular for starting a self-igniting internal combustion engine, wherein the glow plug (31) comprises a glow plug having a tip which engages in a combustion chamber of the internal combustion engine, wherein the glow plug comprises a glow tube (3) , characterized in that in the glow tube (3) an incandescent filament (33) is arranged, which is connected to means for control, with which the resistance of the filament (33) is detected in operation and from the resistance, the temperature at the top of the glow tube is determined. A method according to claim 8, characterized in that for calibration of the glow plug (31) of the cold resistance of the filament (33) is detected by the means for controlling. Method according to claim 8 or 9, characterized in that unacceptable setpoint temperatures are intercepted with the means for controlling. A method according to claim 10, characterized in that at non-permitted set temperatures of the means for controlling a predetermined maximum allowable temperature is adjusted. A method according to claim 8, characterized in that when a permissible maximum temperature is exceeded, the glow plug (31) is turned off.

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