EP2572099B1 - Method and device for reducing the temperature tolerance of glow plugs - Google Patents

Description

State of the art

The invention relates to a method for reducing the temperature tolerance of glow plugs. Furthermore, the invention relates to a device for reducing the temperature tolerance of glow plugs. The US 2009/0316328 A , the DE 10 2006 010081 A1 and the EP 1 762 724 A1 show methods and apparatus for identifying Glühstiftkerzentypen based on electrical parameters. At low temperatures, a self-igniting internal combustion engine requires a starting aid. In particular, the starting aid is required to start the internal combustion engine. For this purpose, glow plugs are used, which are each installed in the cylinder head and protrude into the combustion chamber. The glow plugs usually comprise a glow plug, which offers a hot spot to the fuel-air mixture to be ignited, at which the fuel-air mixture can ignite.
In generally used glow plugs, the glow plug comprises a designed as an electrical resistance heating element. A voltage is applied to the heating element, so that a current flows through the heating element, which heats the glow plug to a defined temperature. This temperature is chosen so that it is sufficient to ignite the fuel-air mixture in the 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 internal combustion engine. Depending on the engine condition, the temperature can be adjusted by the amount of voltage applied. In order for the glow plug to have the correct temperature during the start of the internal combustion engine and during the warm-up phase, the glow system, including glow plug, control unit and software, must be adapted.

The temperature to which the glow plug of a glow plug is heated is usually in the range of 800 to 1300 ° C. In general, glow plugs have a production-related temperature tolerance. This is generally around +/- 50 ° C. However, the temperature differences of the individual glow plugs, which result from the temperature tolerance in manufacturing, lead to a negative impact on the combustion behavior in the cold start and the emission mode. In addition, the service life of individual glow plugs is reduced by temperature deviations.

Disclosure of the invention Advantages of the invention

1. (a) Klassifizieren der Glühstiftkerzen einer selbstzündenden Verbrennungskraftmaschine in mindestens zwei Temperaturklassen wobei mindestens eine Temperaturklasse einen Temperaturbereich oberhalb eines Solltemperaturbereichs umfasst, mindestens eine Temperaturklasse einen Temperaturbereich unterhalb des Solltemperaturbereichs und/oder eine Temperaturklasse den Solltemperaturbereich,
2. (b) Absenken der Ansteuerspannung von Glühstiftkerzen, die einer Temperaturklasse zugeordnet wurden, die einen Temperaturbereich oberhalb des Solltemperaturbereichs umfasst und Erhöhen der Ansteuerspannung von Glühstiftkerzen, die einer Temperaturklasse zugeordnet wurden, die einen Temperaturbereich unterhalb des Solltemperaturbereichs umfasst.

The method according to the invention for reducing the temperature tolerance of glow plugs comprises the following steps:

1. (a) classifying the glow plugs of a self-igniting internal combustion engine in at least two temperature classes wherein at least one temperature class comprises a temperature range above a set temperature range, at least one temperature class a temperature range below the set temperature range and / or a temperature class the set temperature range,
2. (b) lowering the drive voltage of glow plugs associated with a temperature class comprising a temperature range above the desired temperature range and increasing the drive voltage of glow plugs associated with a temperature class including a temperature range below the desired temperature range.

By the method according to the invention, the temperature tolerance of the glow plugs can be reduced. In particular, the method takes account of the tolerance chain, including the wiring harness, contact resistors and glow plug. By reducing the temperature tolerance, better cold-start performance can be achieved and emissions performance improved. In addition, a longer life of the glow plug can be achieved.

By improving the annealing behavior and the combustion behavior, the combustion stability during cold start is increased and the hydrocarbon and carbon monoxide emissions are reduced.

Another advantage is that the process can be performed on the internal combustion engine during operation, so that no external adjustment is necessary. This also has the advantage that a regular monitoring of the temperature tolerances can take place.

In order to carry out the method, the invention also includes a device for reducing the temperature tolerance of glow plugs comprising means for classifying the glow plugs in at least two temperature classes, wherein at least one temperature class comprises a temperature range above a desired temperature range, at least one temperature class a temperature range below the desired temperature range and / or a temperature class the setpoint temperature range, as well as means for adjusting the control voltage of the glow plugs in dependence on the temperature class, which was assigned the glow plug.

As a means for classifying the glow plugs and means for adjusting the drive voltage of the glow plugs a Glühzeitsteuergerät is preferably used, as it is already used in internal combustion engines.

This also makes it possible to adapt the method according to the invention to internal combustion engines which are already in operation.

In a first embodiment of the invention, current, voltage and activation time are measured for classifying the glow plugs, and features for classification are calculated therefrom. As characteristics for classification, power, resistance, energy and time constant T ₆₃ , T ₁₀₀ , for example, are calculated. The time constant takes into account the temporal change of the temperature or the resistance of the candle when the drive voltage (voltage jump) changes.

Power, resistance, E and T ₆₃ and T ₁₀₀ can be determined from the current, voltage and activation time already with currently used glow time control units. This allows a simple adaptation of the method according to the invention to already existing systems. Another advantage is that without much equipment expense a classification of the glow plugs can be performed. In order to classify the glow plugs, the characteristics for classification, for example power, resistance, E and T ₆₃ , T ₁₀₀ are compared with given reference values. The predetermined reference values are in a first embodiment, reference values that are specified from the outside and are stored in Glühzeitsteuergerät or other device for calculating the characteristics for classification.

In an alternative embodiment, the features of the individual glow plugs of the internal combustion engine are compared. For example, if the characteristics of a glow plug differ significantly from the characteristics of the other glow plugs of the internal combustion engine in this case, this glow plug is classified in the temperature class above the target temperature range or in the temperature class below the target temperature range depending on how the features differ. In the temperature class, which includes the temperature range above the set temperature range, the glow plug is classified, for example, when it converts compared to the other glow plugs with the same drive voltage significantly more power. Accordingly, a glow plug, which converts less power at the same drive voltage relative to the other glow plugs of the internal combustion engine into the temperature class, which covers the temperature range below the target temperature range. To be able to divide the glow plugs in this case in each case in the temperature classes, it is particularly preferred if the characteristics of all the glow plugs of the internal combustion engine for classification are compared with each other, being set as the target range, a range in which in more than three glow plugs the features of at least two glow plugs fall and with three glow plugs the characteristics, which determine a middle temperature.

In addition, if the diagnostic limits are exceeded or undercut, the candle may be detected as defective, in which case there is no voltage adjustment is carried out. Diagnostic limits are, for example, resistors that are far outside the possible production tolerance range. For example, the resistance can be extremely high, that is, significantly greater than a possible tolerance value and, in the limit, go to infinity, which indicates a broken heater line. Furthermore, the resistance can have a very small value, which in the limit case approaches 0 ohms, which indicates a short circuit.

In addition to the characteristics which are calculated from the measured variables, for example current, voltage and actuation time, tolerances from the production or the installation arrangement of the glow plugs inside the internal combustion engine can also be taken into account in order to take into account the probability of whether the glow plug is a hot or hot a cold glow plug is and in the temperature class, which is the temperature range above the target temperature range or in the temperature class, which covers the temperature range below the target temperature range is classified.

After the glow plugs have been classified in the temperature classes, the control voltage is lowered for the glow plugs associated with a temperature class covering the temperature range above the setpoint temperature range, and for the glow plugs associated with a temperature class comprising a temperature range below the setpoint temperature range Drive voltage increased. For glow plugs that fall into the temperature class that includes the set temperature range, the drive voltage is not corrected. Increasing the drive voltage causes the glow plug to produce more power and the temperature of the glow plug increases. Accordingly, the glow plug at a reduced drive voltage to less power and the glow plug heats to a lower temperature. In particular, in the case of more than one temperature class, which in each case comprise the temperature ranges above the setpoint temperature range and below the setpoint temperature range, a different increase or decrease in the drive voltage can be realized on the basis of the temperature class into which the glow plug has been divided. The stronger the temperature deviates from the setpoint temperature, the stronger the change in the control voltage takes place in this case.

By correcting the drive voltage, the glow plugs, the temperature class, which includes a temperature range below the target temperature range or the temperature class, which includes a temperature range above the target temperature range, in a target temperature tolerance band, which usually corresponds to the target temperature range can be brought. The target temperature tolerance is preferably at a temperature deviation from a target temperature of ΔT = 25 ° C. For the setpoint temperature range, this means that it comprises a temperature difference of 50 ° C between minimum and maximum temperature.

The method according to the invention for classifying the glow plugs and the adaptation is preferably carried out during the standstill of the vehicle when the ignition is activated or after switching off the ignition when the control unit is in the caster. Alternatively, it is also possible, for example, to carry out the measurement at idling of the internal combustion engine, since there is a constant speed and injection quantity and thus a stationary operating point. During the measurement, the glow plugs must each be controlled individually. By carrying out the method when the vehicle is at a standstill, for example immediately after starting the internal combustion engine or, for example, at a stop of traffic lights, it is ensured that changes in the power of the engine do not occur while driving through the setting of the glow plugs. In addition, the engine is usually moved at idle speed at standstill of the vehicle, so that there is a constant speed level for adjusting and adjusting the glow plugs.

In one embodiment of the invention, the characteristics for classification are first compared with predetermined reference values in order to classify the glow plugs, and then the characteristics of all the glow plugs of the internal combustion engine are compared for classification with each other for verification, wherein a setpoint range is set in which more than three glow plugs the characteristics of at least two glow plugs fall and three glow plugs the characteristics, which set an average temperature. By comparison with predetermined reference values and the comparison of the characteristics of the glow plugs with each other, an additional security level for adjusting the drive voltage is provided.

By the method according to the invention, it is possible to reduce the temperature tolerance of glow plugs both in the controlled and in the controlled operation of the internal combustion engine. By reducing the temperature tolerance of the glow plugs, the annealing behavior or the combustion behavior of the internal combustion engine is improved. This leads to a combustion stability during cold start and to a reduction of hydrocarbon and carbon monoxide emissions. Another advantage of the method according to the invention is that the adjustment of the temperature tolerance of the glow plugs can be performed without additional equipment and without additional equipment. It is also possible, by adjusting the temperature tolerance of the glow plugs directly in the internal combustion engine to use glow plugs with a larger temperature tolerance band from the production, so that a lower reject rate arises during manufacture.

In particular, the inventive method has the advantage that by adjusting the temperature tolerance of the glow plugs on the one hand, the specified annealing temperature can be better maintained in the motor vehicle and on the other hand, the annealing temperature can be increased or the glow plug life in the internal combustion engine can be extended.

Brief description of the drawings

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

The single figure shows voltage, temperature, and resistance curves as a function of time.

Embodiment of the invention

In the single figure, the curves of temperature, resistance and voltage as a function of time are shown.

To classify glow plugs that are outside of a given temperature tolerance, characteristics are first calculated that describe the dynamic behavior and the steady state behavior of the glow plug. This is For example, it is possible to control the glow plug in a combustion engine of a motor vehicle at standstill of the motor vehicle and thus in quiet ambient air with a predetermined drive voltage to determine the characteristics of the glow plug. Voltage and current are measured over the entire period of classification and the recording of the temperature tolerance of the glow plug, and characteristic values are calculated at predetermined time stamps. The calculated characteristic values are, for example, the resistance of the glow plug, the power of the glow plug, time constant T ₆₃ , that is to say the time until 63% of the target value or target value is reached, the time being determined by means of timers in the control unit Time to reach a certain level of resistance and gradients dT / dR.

The determination of the characteristic features for a glow plug is, for example, in FIG. 1 shown. For this purpose, in a first step, an initial resistance R _{0 is determined} at a start time 1. At the start time, the drive voltage is raised to a first value 3. By raising the drive voltage to the first value 3, the temperature rises 5 of the glow plug and the resistor 7 also increases due to the rising temperature.

worin U die Ansteuerspannung, t die Zeit und E_thres die Energieschwelle, die so definiert ist, dass die Glühstiftkerze das zulässige Temperaturmaximum in der schnellen Aufheizphase (Pushen, U_push>>U_nominal) nicht überschreitet. Die Energie kann entweder nach Gleichung 1 bestimmt werden, d.h. mittels Integral von (U²/R), wobei in Gleichung 1 R=1 gilt, oder alternativ durch das Integral von(U*I) entsprechend Gleichung (2). $${\displaystyle \underset{t}{\int }\left(U\cdot I\right)\mathit{dt}>E_{\mathit{thres}}}$$

In order to achieve a rapid increase in temperature of the glow plug, the first value 3 for the drive voltage is higher than the subsequent drive voltage of the glow plug. At the end of the starting process at a time t ₁ , a first temperature maximum 9 and a first resistance maximum 11 have been set. At time t ₁ , the voltage is lowered to a second value 13. The time at which the drive voltage is lowered to the second value 13 is determined by $${\displaystyle \underset{t}{\int }{U}^2\mathit{dt}>e_{\mathit{thres}}}$$

where U is the drive _voltage , t the time and E _thres the energy _threshold , which is defined so that the glow plug does not exceed the allowable temperature maximum in the rapid heating phase ( _Push , U _push >> U _nominal ). The energy can either be determined according to equation 1, ie by means of integral of (U ² / R), wherein in equation 1 R = 1, or alternatively by the integral of (U * I) according to equation (2). $${\displaystyle \underset{t}{\int }\left(U\cdot I\right)\mathit{dt}>e_{\mathit{thres}}}$$

After lowering the drive voltage to the second value 13, both resistor 7 and temperature 5 decrease. For the resistor 7 results in a local minimum 15. This is calculated.

After a predetermined time t ₂ , the voltage is raised to a third value. The third value 17 of the drive voltage is thereby higher than the second value 13 and lower than the first value 3. Usual values for the drive voltage are for example 11 V for the first value, for the second value 3.0 or 5.5 V and For the third value 5 V, 7 V or 7.5 V. In general, the first value for the drive voltage in the range of 9 to 13 V, the second value for the drive voltage in the range of 2 to 6 V and the third value for the drive voltage in the range of 4 to 9 V.

After the local minimum 15 of the resistor 7 this increases again. Here then sets a constant value 19 for the resistance. The constant value 19 is determined. Immediately before raising the drive voltage to the third value, the constant value 19 is determined again. After raising the drive voltage to the third value 17, the resistance and thus also the power is determined again. To check whether a constant resistance or a constant power sets, the resistance is determined again at the end of the measuring process.

Based on the measured and determined values, the glow plug is divided into a temperature class. Usually, three temperature classes are used for this purpose, one temperature class comprising a temperature range above a setpoint temperature range, a temperature class comprising a temperature range below the setpoint temperature range and a temperature class the setpoint temperature range.

To divide the glow plugs in one of the temperature classes, a comparison of the measured values with stored values. The values can be stored, for example, in a glow time control device.

1. 1. $C_1=\{\begin{array}{ll}1& R_0<R_{\mathrm{0,}\mathit{lower}}\\ 0& R_{\mathrm{0,}\mathit{lower}}<R_0<R_{\mathrm{0,}\mathit{upper}}\\ -1& R_0>R_{\mathrm{0,}\mathit{upper}}\end{array}$
   
2. 2. $C_2=\{\begin{array}{ll}1& t<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<t<t_{\mathit{tupper}}\\ -1& t>t_{\mathit{upper}}\end{array}$
   
3. 3. $C_3=\{\begin{array}{ll}1& R_{\mathit{PushMax}}<R_{\mathit{PushMax},\mathit{lower}}\\ 0& R_{\mathit{PushMax},\mathit{lower}}<R_{\mathit{PushMax}}<R_{\mathit{PushMax},\mathit{upper}}\\ -1& R>R_{\mathit{PushMax},\mathit{upper}}\end{array}$
   
4. 4. $C_4=\{\begin{array}{ll}1& R_{\mathit{PostMin}}<R_{\mathit{PostMin},\mathit{lower}}\\ 0& R_{\mathit{PostMin},\mathit{lower}}<R_{\mathit{PostMin}}<R_{\mathit{PostMin},\mathit{upper}}\\ -1& R>R_{\mathit{PostMin},\mathit{upper}}\end{array}$
   
5. 5. $C_5=\{\begin{array}{ll}1& T_{63/100}<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<T_{63/100}<t_{\mathit{upper}}\\ -1& T_{63/100}>t_{\mathit{upper}}\end{array}$
   
6. 6. $C_{6\_1}=\{\begin{array}{ll}1& R<R_{\mathit{lower}}\\ 0& R_{\mathit{lower}}<R<R_{\mathit{upper}}\\ -1& R>R_{\mathit{upper}}\end{array}$
   
   $C_{6\_2}=\{\begin{array}{ll}-1& P<P_{\mathit{lower}}\\ 0& P_{\mathit{lower}}<P<P_{\mathit{upper}}\\ 1& P>P_{\mathit{upper}}\end{array}$
   
7. 7. $C_7=\{\begin{array}{ll}1& T_{63/100}<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<T_{63/100}<t_{\mathit{upper}}\\ -1& T_{63/100}>t_{\mathit{upper}}\end{array}$
   
8. 8. $C_{8\_1}=\{\begin{array}{ll}1& R<R_{\mathit{lower}}\\ 0& R_{\mathit{lower}}<R<R_{\mathit{upper}}\\ -1& R>R_{\mathit{upper}}\end{array}$
   
   $C_{8\_2}=\{\begin{array}{ll}-1& P<P_{\mathit{lower}}\\ 0& P_{\mathit{lower}}<P<P_{\mathit{upper}}\\ 1& P>P_{\mathit{upper}}\end{array}$
   
9. 9. ${\mathrm{<figure-callout\; id="9"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_9=\{\begin{array}{ll}-1& \mathit{dT}/\mathit{dR}<{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{lower}}\\ 0& {\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{lower}}<\mathit{dT}/\mathit{dR}<{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{upper}}\\ 1& \mathit{dT}/\mathit{dR}>{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{upper}}\end{array}$
   
10. 10. $C_{10}=\{\begin{array}{ll}1& \left(R_{60}-R_0\right)<{\left(R_{60}-R_0\right)}_{\mathit{lower}}\\ 0& {\left(R_{60}-R_0\right)}_{\mathit{lower}}<\left(R_{60}-R_0\right)<{\left(R_{60}-R_0\right)}_{\mathit{upper}}\\ -1& \left(R_{60}-R_0\right)>{\left(R_{60}-R_0\right)}_{\mathit{upper}}\end{array}$
    

The division of the glow plugs is carried out, for example, according to the following criteria:

1. 1. $C_1=\{\begin{array}{ll}1& R_0<R_{0\mathit{lower}}\\ 0& R_{0\mathit{lower}}<R_0<R_{0\mathit{upper}}\\ -1& R_0>R_{0\mathit{upper}}\end{array}$
   
2. Second $C_2=\{\begin{array}{ll}1& t<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<t<t_{\mathit{tupperware}}\\ -1& t>t_{\mathit{upper}}\end{array}$
   
3. Third $C_3=\{\begin{array}{ll}1& R_{\mathit{PushMax}}<R_{\mathit{PushMax}.\mathit{lower}}\\ 0& R_{\mathit{PushMax}.\mathit{lower}}<R_{\mathit{PushMax}}<R_{\mathit{PushMax}.\mathit{upper}}\\ -1& R>R_{\mathit{PushMax}.\mathit{upper}}\end{array}$
   
4. 4th $C_4=\{\begin{array}{ll}1& R_{\mathit{PostMin}}<R_{\mathit{PostMin}.\mathit{lower}}\\ 0& R_{\mathit{PostMin}.\mathit{lower}}<R_{\mathit{PostMin}}<R_{\mathit{PostMin}.\mathit{upper}}\\ -1& R>R_{\mathit{PostMin}.\mathit{upper}}\end{array}$
   
5. 5th $C_5=\{\begin{array}{ll}1& T_{63/100}<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<T_{63/100}<t_{\mathit{upper}}\\ -1& T_{63/100}>t_{\mathit{upper}}\end{array}$
   
6. 6th $C_{6\_1}=\{\begin{array}{ll}1& R<R_{\mathit{lower}}\\ 0& R_{\mathit{lower}}<R<R_{\mathit{upper}}\\ -1& R>R_{\mathit{upper}}\end{array}$
   
   $C_{6\_2}=\{\begin{array}{ll}-1& P<P_{\mathit{lower}}\\ 0& P_{\mathit{lower}}<P<P_{\mathit{upper}}\\ 1& P>P_{\mathit{upper}}\end{array}$
   
7. 7th $C_7=\{\begin{array}{ll}1& T_{63/100}<t_{\mathit{lower}}\\ 0& t_{\mathit{lower}}<T_{63/100}<t_{\mathit{upper}}\\ -1& T_{63/100}>t_{\mathit{upper}}\end{array}$
   
8. 8th. $C_{\mathrm{8th}\_1}=\{\begin{array}{ll}1& R<R_{\mathit{lower}}\\ 0& R_{\mathit{lower}}<R<R_{\mathit{upper}}\\ -1& R>R_{\mathit{upper}}\end{array}$
   
   $C_{\mathrm{8th}\_2}=\{\begin{array}{ll}-1& P<P_{\mathit{lower}}\\ 0& P_{\mathit{lower}}<P<P_{\mathit{upper}}\\ 1& P>P_{\mathit{upper}}\end{array}$
   
9. 9th $C_{}$${}_9=\{\begin{array}{ll}-1& \mathit{dT}/\mathit{dR}<{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{lower}}\\ 0& {\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{lower}}<\mathit{dT}/\mathit{dR}<{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{upper}}\\ 1& \mathit{dT}/\mathit{dR}>{\left(\mathit{dT}/\mathit{dR}\right)}_{\mathit{upper}}\end{array}$
   
10. 10th $C_{10}=\{\begin{array}{ll}1& \left(R_{60}-R_0\right)<{\left(R_{60}-R_0\right)}_{\mathit{lower}}\\ 0& {\left(R_{60}-R_0\right)}_{\mathit{lower}}<\left(R_{60}-R_0\right)<{\left(R_{60}-R_0\right)}_{\mathit{upper}}\\ -1& \left(R_{60}-R_0\right)>{\left(R_{60}-R_0\right)}_{\mathit{upper}}\end{array}$
    

In the above assignments, 1 means an assignment into the temperature class comprising the temperature range above the target temperature range, -1 the temperature class including the temperature range below the target temperature range, and 0 the temperature class comprising the target temperature range.

• C1:
  • R₀: Kaltwiderstand der Kerze, Widerstand beim Einschalten der Glühstiftkerze
  • R_0,lower: untere Grenze für den Kaltwiderstand, damit die Kerze anhand von diesem Kriterium als Nominalkerze eingeordnet werden kann.
  • R_0,upper: obere Grenze für den Kaltwiderstand, damit die Kerze anhand von diesem Kriterium als Nominalkerze eingeordnet werden kann.
• C2:
  • t: Zeit von Bestromung der Kerze bis zum Erreichen des maximalen Widerstands (Zeit von Punkt 1 bis 11),
  • t_lower: obere Grenze für die Zeit damit die Kerze anhand von diesem Kriterium als Nominalkerze eingeordnet werden kann
  • t_upper: untere Grenze für die Zeit damit die Kerze anhand von diesem Kriterium als Nominalkerze eingeordnet werden kann.
• C3:
  • R_pushmax: maximaler Widerstand nach dem Pushen (schnelles Aufheizen), d.h. Widerstand nach dem Anlegen der hohen Spannung Punkt 3 von z.B. 11V. Indizes lower, upper analog C1, C2 jedoch in dem Fall für den Widerstand nach dem Pushen (max. Widerstand nach dem Pushen)
• C4:
  • R_PostMin: minimaler Widerstand nach dem Pushen und Anlegen einer niedrigeren Spannung von z.B. 5.5V (Punkt 13)
• C5:
  • Zeitkonstante bis 63% oder 100% des stationären Widerstands beim Anlegen einer Spannung von z.B. 5.5V erreicht ist. Ausgangswert ist der minimale Widerstand nach dem Pushen, d.h. es wird die Differenz zwischen R(5.5V stationär) und R_PostMin, ΔR = R(5.5V) - R_postMin gebildet. Die Zeitkonstante wird dann aus der Zeitdifferenz (Δt=t(5.5V)- t(R_postmin)) von R_PostMin bis zum Erreichen von 63% oder 100% von R(5.5V) bestimmt. T₆₃ = 63% von Δt bzw. T₁₀₀ = 100% von Δt.
• C6:
  • R: Widerstand (berechnet aus gemessener Spannung U und Stromstärke I) zwischen t₁ und t₂; der Widerstand der Kerze ist stationär und repräsentiert einen stationären Temperaturwert der Kerze. Alternativ kann in dieser Phase auch die Leistung P bestimmt werden
• C7:
  • Zeitkonstante bis 63% oder 100% des stationären Widerstands beim Anlegen einer Spannung von z.B. 7.4V erreicht ist. Ausgangswert ist der stationäre Widerstand zwischen t₁ und t₂, das heißt, es wird die Differenz zwischen R(7.4V) und R(5.5V), ΔR = R(7.4V) - (R5.5V) gebildet. Die Zeitkonstante wird dann aus der Zeitdifferenz (Δt=t(7.4V) - t(5.5)) von R(5.5V) bis zum Erreichen von 63% oder 100% von R(7.4V) bestimmt. T₆₃ = 63% von Δt bzw. T₁₀₀= 100% von Δt
• C8:
  • analog C6 jedoch für die Phase t>t2
• C9:
  • dT / dR = (T(7.4)-T(5.5V)) / (R(7.4V)-R(5.5V)), T = Temperatur, 7.4V exemplarische Spannung in der Phase, t>t₂ und 5.5V für t₁<t<t₂. Die Referenztemperaturen für die Referenzspannung (z.B. 5.5V und 7.4V) werden im Steuergerät hinterlegt.
• C10:
  • R₆₀-R₀: Widerstandsdifferenz zwischen stationärem Endwert (R₆₀ entspricht hierbei dem Widerstand R von C6_1 bzw. dem Widerstand R von C8_1) im Zeitbereich t₁<t<t₂ oder für t>t₂ und Kaltwiderstand R₀ (C1).

In the assignments mean:

• C1:
  • R ₀ : Cold resistance of the candle, resistance when switching on the glow plug
  • R _{0, lower} : lower limit for the cold resistance, so that the candle can be classified as a nominal candle based on this criterion.
  • R _{0, upper} : upper limit for the cold resistance, so that the candle can be classified as a nominal candle based on this criterion.
• C2:
  • t: time from lighting the candle to reaching the maximum resistance (time from point 1 to 11),
  • t _lower : upper limit for the time so that the candle can be classified as a nominal candle based on this criterion
  • t _upper : lower limit for the time so that the candle can be classified as a nominal candle based on this criterion.
• C3:
  • R _pushmax : maximum resistance after pushing (fast heating), ie resistance after applying the high voltage point 3 of eg 11V. Indices lower, upper analog C1, C2 but in the case of resistance after pushing (maximum resistance after pushing)
• C4:
  • R _PostMin : minimal resistance after pushing and applying a lower voltage of eg 5.5V (point 13)
• C5:
  • Time constant is reached to 63% or 100% of the stationary resistance when applying a voltage of eg 5.5V. Initial value is the minimum resistance after pushing, ie the difference between R (5.5V stationary) and R _PostMin , ΔR = R (5.5V) - R _{postMin is} formed. The time constant is then determined from the time difference (Δt = t (5.5V) -t (R _postmin )) of R _PostMin to reaching 63% or 100% of R (5.5V). T ₆₃ = 63% of Δt or T ₁₀₀ = 100% of Δt.
• C6:
  • R: resistance (calculated from measured voltage U and current I) between t ₁ and t ₂ ; the resistance of the candle is stationary and represents a steady temperature value of the candle. Alternatively, the power P can also be determined in this phase
• C7:
  • Time constant up to 63% or 100% of the stationary resistance when applying a voltage of eg 7.4V is reached. Output value is the stationary resistance between t ₁ and t ₂ , that is, the difference between R (7.4V) and R (5.5V), ΔR = R (7.4V) - (R5.5V) is formed. The time constant is then determined from the time difference (Δt = t (7.4V) - t (5.5)) from R (5.5V) to reaching 63% or 100% of R (7.4V). T ₆₃ = 63% of Δt or T ₁₀₀ = 100% of Δt
• C8:
  • however, analogous to C6 for the phase t> t2
• C9:
  • dT / dR = (T (7.4) -T (5.5V)) / (R (7.4V) -R (5.5V)), T = temperature, 7.4V exemplary voltage in phase, t> t ₂ and 5.5V for t ₁ <t <t ₂ . The reference temperatures for the reference voltage (eg 5.5V and 7.4V) are stored in the control unit.
• C10:
  • R ₆₀ -R ₀ : resistance difference between steady-state final value (R ₆₀ corresponds here to the resistance R of C6_1 or the resistance R of C8_1) in the time range t ₁ <t <t ₂ or for t> t ₂ and cold resistance R ₀ (C1) ,

In order to find a criterion to which temperature class the glow plug is ultimately assigned, the individual classifications are each multiplied by a weighting factor and added together. If the value so determined is greater than an upper predetermined value, the glow plug is assigned to the temperature class that is above the set temperature range; if the particular value is less than a lower predetermined limit, the glow plug is assigned to the temperature class that is below the temperature range Target temperature range includes, and if the value is between the upper and the lower limit, the temperature class, which includes the target temperature range.

If the glow plug is assigned to the temperature class that includes the temperature range below the set temperature range, the drive voltage is increased, and if the glow plug is assigned to the temperature class that includes the temperature range above the set temperature range, the drive voltage is reduced.

Alternatively, it is also possible to change the resistance of the glow plug instead of the drive voltage. Here, too, the voltage is changed, but not "flat rate" with a fixed constant correction voltage, but such that sets a required resistance. The voltage is varied until a desired temperature and thus a certain Resistor adjusts the glow plug. For example, if the resistance is too low, more power will be converted and the candle is too hot. In this case, the voltage is reduced until a required resistance is reached.

In an alternative embodiment, it is also possible to compare the glow plugs with each other. For this purpose, the same calculated features can be used as previously described, for example, power, resistance, current, T ₆₃ or even gradients.

After determining the features, it can be estimated, for example, based on a probability model, which temperature class the glow plug is to be assigned.

Usually already a classification in temperature ranges in the production of the glow plugs. These are usually divided into cold glow plugs, middle glow plugs and hot glow plugs. In further use each glow plugs from the same group are then installed in an internal combustion engine.

However, the temperature ranges in which the glow plugs are classified during production are generally greater than the desired temperature tolerance for the internal combustion engine. However, it is always possible that glow plugs from different temperature classes are also installed in an internal combustion engine. In this case, the temperature tolerance can be adjusted by adjusting the drive voltage, for example, by the method according to the invention.

Claims (7)

1. Method for reducing the temperature tolerance of glow plugs, the method being carried out during continuous operation of the internal combustion engine, comprising the following steps:

   (a) classifying the glow plugs of an auto compression-ignition internal combustion engine into at least two temperature classes, wherein at least one temperature class comprises a temperature range above a target temperature range, at least one temperature class comprises a temperature range below the target temperature range and/or a temperature class comprises the target temperature range,

   (b) lowering the drive voltage of glow plugs which have been assigned to a temperature class which comprises a temperature range above the target temperature range, and increasing the drive voltage of glow plugs which have been assigned to a temperature class which comprises a temperature range below the target temperature range,

   (c) wherein, for the classification at a starting time, a first value (3) of a drive voltage, after that a second value (13) of a drive voltage and after that a third value (17) for the drive voltage is applied to the glow plug, wherein the third value for the drive voltage is higher than the second value (13) for the drive voltage and is lower than the first value (3) for the drive voltage,

   (d) wherein, for the classification, current, voltage and drive time are measured and features for the classification are calculated therefrom,

   (e) wherein power, resistance, energy and time constant T₆₃ are calculated as features for the classification.
2. Method according to Claim 1, characterized in that the features for the classification are compared with predefined reference values in order to classify the glow plugs.
3. Method according to one of the preceding claims, characterized in that the features of all the glow plugs of the internal combustion engine are compared with one another for the classification, wherein the target value range is defined as a range in which, in the case of more than three glow plugs, the features of at least two glow plugs fall and, in the case of three glow plugs, the features which define an average temperature.
4. Method according to one of the preceding claims, characterized in that the classification of the glow plugs and the adaptation of the are carried out while the vehicle is at a standstill.
5. Method according to one of the preceding claims characterized in that first of all the features for the classification are compared with a predefined reference value in order to classify the glow plugs and then, for verification the features of all the glow plugs of the internal combustion engine are compared with one another for the classification, wherein the range defined as a target value range is a range in which, in the case of more than three glow plugs, the features of at least two glow plugs fall and, in the case of three glow plugs, the features which define an average temperature.
6. Device for reducing the temperature tolerance of glow plugs during continuous operation of the internal combustion engine, comprising means for classifying the glow plugs into at least two temperature classes, wherein at least one temperature class comprises a temperature range above a target temperature range, at least one temperature class comprises a temperature range below the target temperature range and/or a temperature class comprises the target temperature range, and means for adapting the drive voltage of the glow plugs on the basis of the temperature class to which the glow plugs have been assigned, wherein, for the classification at a starting time, the means apply a first value (3) of a drive voltage, after that a second value (13) of a drive voltage and after that a third value (17) for the drive voltage to the glow plug, so that the third value for the drive voltage is higher than the second value (13) for the drive voltage and is lower than the first value (3) for the drive voltage, wherein the means for the classification measure current, voltage and drive time and calculate features for the classification therefrom, wherein the means calculate power, resistance, energy and time constant T₆₃ as features for the classification.
7. Device according to Claim 6, characterized in that the means for classifying the glow plugs and the means for adapting the drive voltage of the glow plugs comprise a glow-plug controller.

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