EP2678552B1 - Method and control device for adjusting a temperature of a glow plug - Google Patents

Description

State of the art

The invention relates to a method for adjusting a temperature of a glow plug, in particular for igniting a fuel-air mixture in an internal combustion engine, wherein the temperature of the glow plug is adjusted in response to a resistance of the glow plug by means of a control, and a control device for carrying out the method ,

Glow plugs, which are used in internal combustion engines to ignite a fuel-air mixture are preheated in a cold state before their temperature is so high that it is sufficient for the ignition of the fuel-air mixture. The glow plug has for this purpose a heater, which acts on the cold glow plug in a short period of 1 to 2 seconds with an excessive heating voltage, so that the glow plug is overstressed at this time. After completion of this so-called push phase, the tip of the glow plug has reached a temperature of about 1000 ° C, while the remaining part of the glow plug still has a temperature which is well below this temperature of 1000 ° C.

By controlling the glow plug with an excessive heating voltage creates a temperature overshoot on the glow plug. The temperature of the glow plug that is obtained in the preheating phase represents an input variable for a control with which the temperature of the glow plug is adjusted, such as in EP 1 936 183 A2 is described. However, since this input variable for the control is determined during a transient process, this leads to errors in the subsequent control.

Disclosure of the invention

The invention is therefore an object of the invention to provide a method for controlling the temperature of a glow plug in which the occurring during the preheating temperature overshoot is reliably prevented, although the glow plug is subjected to an excessive heating voltage.

According to the invention the object is achieved in that the temperature in a preheating the glow plug, in which an overvoltage is applied to the glow plug, is regulated. The advantage of the invention is that the annealing temperature over the entire annealing of the glow plug is now modulated with high quality and the control of the annealing temperature at each time the annealing phase, advantageously also in the preheating (push phase) takes place, in which the heater of the Glow plug, the cold glow plug in a short period of 1 to 2 seconds applied to an excessive heating voltage. This allows better control of the preheat phase both at the key start and during long startup phases. According to the invention, to regulate the temperature of the glow plug in the preheating phase, a resistance difference, which at the end of the preheating phase results in a measured resistance, is determined with the aid of a physical model during the preheating phase. Thus, the temperature in the preheat phase, in which an overvoltage is applied to the glow plug, is controlled by means of the predictive model. As a result, the preheating phase of the glow plug is more robust, since no or only small temperature overshoot occur and there are provided accurate input values for the control in the further course of the glow plug glow. Thus, the control is already aligned closely to the desired temperature setpoint in the preheating phase. By determining the resistance difference, the input variable of the resistor for the control is initialized and the time at the first energization of the glow plug is taken into account. Furthermore, the development effort is reduced because no application for a controlled preheating is necessary and the input parameters are determined only once and maintained for the life of the glow plug. According to the invention, the measured resistance of the glow plug is added to the resistance difference and fed the sum of the control formed from the measured resistance and the resistance difference. Thereby, the measured resistance is increased by an anticipated certain amount, which corresponds to the temperature actually occurring during the preheating phase in the glow plug. Erindungsgemäß is determined from a characteristic curve, which is determined individually for each glow plug in the heated, steady operation of the glow plug, based on the sum of the measured resistance and the resistance difference, a Temperaturistwert which is subtracted from the temperature setpoint, wherein the thus determined temperature difference of the control is determined from which a drive voltage for the glow plug to set the desired temperature setpoint. The integration of the resistance difference in the determination of the temperature actual value means that even during the rapid preheating phase, a regulation of the temperature of the glow plug can be ensured.

In a further development, the resistance difference consists of several, in particular summed, partial resistance differences, wherein each partial resistance difference is determined as a function of at least one operating parameter of the glow plug. As a result, the state of the glow plug is characterized to start an annealing process in the Erstbestromung the glow plug and optimized using appropriate characteristics.

In a variant, a first partial resistance difference is determined as a function of an energy content of the glow plug which it has at the time of starting the annealing process. As a result, the initial characteristic of the glow plug at the time of starting the annealing process in the determination of the resistance difference is taken into account.

In particular, the energy content of the glow plug is characterized by an initial resistance, an initial amount of heat or an initial power. Thus, the heat balance of the cold glow plug is considered before Erstbestromung. For example, since in a cold glow plug the initial resistance is very small, while in a glow plug, which was once heated, the initial resistance is greater, it ensures that always the correct input variable is used in determining the resistance difference.

In another embodiment, a second partial resistance difference is determined as a function of a temperature setpoint of the glow plug, which it should have at the end of the annealing process. By including the Temperature setpoint is ensured in the modeling, that also the final state of the glow plug to be reached in the form of the temperature setpoint, which corresponds to the temperature to be set at the end of the preheating subsequent heating operation of the glow plug is taken into account.

Furthermore, a third partial resistance difference is determined as a function of an output temperature of the glow plug which it has at the time of starting the annealing process. Since the glow plug has a different behavior at different temperatures at the first start, this output temperature of the glow plug is also taken into account in order to model the correct behavior of the glow plug.

In particular, the starting temperature corresponds to an ambient temperature of the glow plug at the time of starting the annealing process. The ambient temperature of the glow plug is easy to determine, since motor vehicles in whose internal combustion engines the glow plugs are installed have an outside temperature display. Thus, it is possible to dispense with further hardware for determining the ambient temperature.

Advantageously, a fourth partial resistance difference is determined as a function of an annealing process of the glow plug that is directly preceded by the start of the annealing process. Thus, in particular, the state of the glow plug is taken into account, which has the glow plug when the ignition of the engine, which pulls a heating of the glow plug by itself, has taken place, but this short time later turned off again and was activated within a few moments again.

In one embodiment, the immediately preceding annealing process is characterized by its annealing duration or annealing energy, wherein a factor is determined in dependence on an initial resistance of the glow plug, which is multiplied by the fourth partial resistance difference and added to the resistance difference. The annealing time, which corresponds to the duty cycle of the glow plug, allows conclusions about how much energy is still stored in the glow plug. Depending on how large the set during the previous annealing period of the glow plug output resistance, the fourth partial resistance difference, which was determined in dependence on the start of the annealing preceding annealing time, added to the resistance difference.

A development of the invention relates to a control device for adjusting a temperature of a glow plug according to claim 10. The invention allows numerous embodiments. One of them will be explained in more detail with reference to the figures shown in the drawing.

Figur 1:

Prinzipdarstellung der Anordnung einer Glühstiftkerze in einem Verbrennungsmotor

Figur 2:

schematische Darstellung zur Modellierung der Temperatur einer Glühstiftkerze in einer schnellen Vorheizphase

Figur 3:

Temperatur-Zeit-Diagramm ohne und mit prädiktiver Temperaturmodellierung

It shows:

FIG. 1:

Schematic representation of the arrangement of a glow plug in an internal combustion engine

FIG. 2:

schematic representation for modeling the temperature of a glow plug in a fast preheat phase

FIG. 3:

Temperature-time diagram with and without predictive temperature modeling

Cold internal combustion engines, in particular diesel engines, require a start-up aid for ignition of the fuel-air mixture introduced into the diesel engine at ambient temperatures of <40 ° C. As starting aid then glow systems used, which consist of glow plugs, a Glühzeitsteuergerät and annealing software, which is stored in an engine control unit or the Glühzeitsteuergerät consist. In addition, annealing systems are also used to improve the emission of the vehicle. Further fields of application of the glow system are the burner exhaust system, the auxiliary heating, the preheating of fuel (flex fuel) or the preheating of the cooling water.

FIG. 1 A glow plug 2 protrudes into the combustion chamber 3 of the diesel engine 4. The glow plug 2 is on the one hand connected to the Glühzeitsteuergerät 5 and on the other hand leads to a battery 6, which controls the glow plug 2 with the rated voltage of, for example, 11 volts. The Glühzeitsteuergerät 5 is connected to the engine control unit 7, which in turn leads to the diesel engine 4.

To ignite the fuel-air mixture, the glow plug 2 is preheated by the application of an overvoltage in a, also referred to as a push phase preheating, which lasts 1 to 2 seconds. The electrical energy that is supplied to the glow plug 2 is thus converted into heat in a heating coil, not shown, which is why the temperature at the top of the glow plug 2 rises steeply. The heating power of the heating coil is adjusted via the electronic Glühzeitsteuergerät 5 to the requirement of the respective diesel engine 4. The fuel-air mixture is conducted past the hot tip of the glow plug 2 and heats up. Associated with an intake air heating during the compressor stroke of the diesel engine 4, the ignition temperature of the fuel-air mixture is achieved.

The glow plug 2 has different glow phases. As already stated, in a preheating phase, which takes 1 to 2 seconds, the cold glow plug 2 is supplied with an overvoltage, which is above the rated voltage of the glow plug 2. During this short period of time, the tip of the glow plug is heated to approximately 1000 ° C, while the remaining part of the glow plug 2 is still below this temperature, thereby forming a transient temperature profile within the glow plug 2. This preheating phase is followed by a heating phase of the glow plug 2, in which the transient temperature distribution compensates for a steady temperature distribution over the entire glow plug 2. Such a heating phase usually takes approximately 30 seconds. After the preheating phase of the glow plug, the resistance difference is adjusted dynamically in the heating phase. This is followed by the annealing phase, in which a steady temperature distribution over the entire glow plug is ensured.

In FIG. 2 a schematic diagram for the temperature modeling of the glow plug 2 during the rapid preheat phase is shown, which is integrated as software in the engine control unit 7 or the Glühzeitsteuergerät 5 and is taken into account in a temperature control of the glow plug. As a control input for the general temperature control of the glow plug 2 over the entire annealing process, a temperature setpoint T _{DES is} provided by the engine control unit 7. At the same time, a resistance R _{m of} the glow plug is measured, which represents a value for the current temperature at the glow plug 2. This measured resistance R _m is determined at each Bestromungsvorgang, which takes place at regular intervals. In a block 17, this measured resistance R _{m is added} to a resistance difference ΔR, which is determined by means of a predictive model 8. This predictive model 8 models the temperature of the glow plug 2 in the rapid preheat phase. Within the predictive model 8, initially an initial resistance R _{01 of} the glow plug 2 is determined. This initial resistance R ₀₁ is fed to a characteristic curve 9, which was determined during stationary operation of the glow plug. From this characteristic curve 9, a first partial resistance difference ΔR1 is determined on the basis of the measured initial resistance R ₀₁ .

As a further input variable of the predictive model 8, the temperature setpoint T _{DES is} provided which characterizes the end temperature of the glow plug 2 to be reached. This temperature setpoint T _DES is also given to a further characteristic curve 10 as input variable, from which a second partial resistance difference ΔR2 is determined. The thus determined partial resistance differences ΔR1 and ΔR2 are added in block 14.

In addition to the already mentioned input variables in the form of the initial resistance R ₀₁ and the temperature setpoint T _DES , the operating temperature T _{C of} the glow plug 2 at the time of starting the annealing process is thus determined at time t = 0. From this temperature T _C , the third partial resistance difference ΔR3 is determined by means of a third characteristic 11. In block 15, the third partial resistance difference ΔR3 is added to the first and the second partial resistance difference ΔR1 and ΔR2. These input variables in the form of the initial resistance R ₀₁ , the temperature setpoint T _DES and the ambient temperature T _C are determined once at the time t = 0 - upon activation of the glow plug 2 - and can be stored in the engine control unit 7 or the Glühzeitsteuergerät 5.

In order to take into account that the glow plug 2 was already subjected to an annealing process shortly before the annealing process to be carried out, from which the glow plug 2 has not yet cooled sufficiently, an annealing time / annealing energy E (E = U * 1 * t) of the current annealing immediately preceding the annealing process of the glow plug 2 taken into account. From the annealing time / annealing energy E, a fourth partial resistance difference ΔR4 is determined with the aid of a fourth characteristic curve 12. Since due to the annealing time / annealing energy E of the immediately preceding annealing, the resistance of the glow plug 2 changes when the heat that has built up during the previous annealing process within the glow plug 2 has not yet cooled, the resistor R _{01 is} another characteristic thirteenth which as a result yields a factor F which is multiplied in block 22 by the fourth partial resistance difference ΔR4. The factor F is selected so that when the time measured initial resistance R is greater than a predetermined threshold value of the resistor R _{01 01,} this is equal to the first The factor F tends towards the value zero, when the initial resistance R ₀₁ is less than the predetermined threshold value of the resistor R _01. This requires that the input variables of the annealing time / annealing energy E with the associated change in the initial resistance R _{01 are} only used to determine the resistance difference .DELTA.R when the glow plug 2 due to a previous annealing still has a correspondingly large resistance, which with a changed temperature the glow plug 2 is accompanied. The fourth partial resistance difference ΔR4 is added in block 16 to the above-described partial resistance difference ΔR1, ΔR2 and ΔR3, resulting in a resistance difference ΔR corresponding to a predetermined temperature occurring at the end of the preheating operation on the glow plug 2.

The determined in the predictive model 8 resistance difference ΔR is added in block 17 to the measured resistance R _m . This sum of the resistance difference .DELTA.R and the measured resistance R _m is supplied to a characteristic curve 18, in which the resistance is plotted against the temperature. This characteristic curve 18 is a characteristic determined individually for each glow plug 2 at a steady-state temperature distribution, since glow plugs have an independent transfer function due to production tolerances. From this resistance / temperature characteristic 18, a base temperature T _{BAS of} the glow plug 2 is determined. This base temperature T _BAS is compared in block 19 with a heat conduction model, which takes into account the extent to which there is a temperature difference between the interior of the heater of the glow plug 2 and the surface temperature of the glow plug 2. In this case, a temperature difference is supplied in block 19 to the base temperature T _BAS , the sum of which results in the actual temperature T _{ACT of} the glow plug 2. This actual temperature T _ACT is now used in the control cycle, where it is subtracted from the temperature setpoint T _DES in block 20. The difference between the temperature setpoint T _DES and the actual temperature T _ACT is supplied to a controller 21, which determines a voltage U _GOV which is supplied to the glow plug 2, in particular the heater of the glow plug 2, for rapid adjustment of the temperature setpoint T _DES .

FIG. 3 shows two temperature-time diagrams in which the measured temperature Tm once without predictive modeling ( FIG. 3a ) and once with predictive modeling ( FIG. 3b ) is shown. Out FIG. 3a It can be seen that the measured temperature Tm, which is to be matched to the temperature set point T _Des, shortly after the beginning of the annealing process has a temperature overshoot which is approaching the temperature setpoint T _Des only after a time of about 30 seconds. For comparison, the mathematically FIG. 2 modeled temperature Tmo is shown without model 8, which after the preheating phase, approximately after 5 seconds, reaches and regulates the level of the temperature setpoint T _Des .

In contrast, shows FIG. 3b the course of the measured temperature Tm in the consideration of the predictive determined by means of the predictive temperature model 8 resistance difference .DELTA.R. The measured temperature Tm shows no temperature overshoot, but approaches immediately after the Preheating phase of the modeled temperature Tm. Already after about 4 seconds, the temperature setpoint T _{Des is} reached by means of this control and is regulated by this.

Due to the predictive model 8, it is possible that a temperature control of the glow plug 2 not only during stationary operation, in which no more resistance-temperature fluctuations, but also in transient operation, preferably in the rapid preheating at the beginning of the annealing process and during to carry out the heating phase. In the temperature modeling of the glow plug 2 in the rapid preheating phase, it is modeled how large the resistance difference .DELTA.R will be at the end of the preheating process, this difference in resistance .DELTA.R being supplied as input to the control process.

Claims (10)

1. Method for adjusting a temperature of a glow plug, in particular for igniting a fuel/air mixture in an internal combustion engine, in which the temperature (Tm) of the glow plug (2) is adjusted as a function of a resistance (Rm) of the glow plug (2) by means of a regulating device, wherein the temperature (Tm) is regulated in a pre-heating phase in which an overvoltage is applied to the glow plug (2), characterized in that in order to regulate the temperature (Tm) of the glow plug (2) in the pre-heating phase a difference in resistance (ΔR), which is present with respect to a measured resistance (Rm) at the end of the pre-heating phase, is determined predictably using a physical model (8) during the pre-heating phase, in that the measured resistance (Rm) of the glow plug (2) is added to the difference in resistance (ΔR), and the sum which is formed from the measured resistance (Rm) and the difference in resistance (ΔR) is fed to the regulating device, in that an actual temperature value (T_ACT), which is subtracted from a temperature setpoint value (T_des) of the glow plug, is determined from a characteristic curve (18), which is determined individually for each glow plug (2) during the heated, steady-state operation of the glow plug (2), on the basis of the sum of the measured resistance (Rm) and the difference in resistance (ΔR), wherein the temperature difference which is determined in this way is fed to the regulating device and is used to determine an actuation voltage (U_GOV) for the glow plug (2).
2. Method according to Claim 1, characterized in that the difference in resistance (ΔR) is composed of a plurality of, in particular summed, partial resistance differences (ΔR1, AR2, ΔR3, ΔR4), wherein each partial resistance difference (ΔR1, AR2, ΔR3, ΔR4) is determined as a function of at least one operating parameter (R₀₁, T_Des, T_c, E, R₀₂) of the glow plug (2).
3. Method according to Claim 2, characterized in that a first partial resistance difference (ΔR1) is determined as a function of an energy content of the glow plug (2) which said glow plug (2) has at the time of starting the glowing process.
4. Method according to Claim 3, characterized in that the energy content of the glow plug (2) is characterized by an initial resistance (R₀₁), an initial quantity of heat or an initial power of the glow plug (2).
5. Method according to Claim 2, 3 or 4, characterized in that a second partial resistance difference (ΔR2) is determined as a function of a temperature setpoint value (T_Des) of the glow plug (2) which said glow plug (2) has at the end of the glowing process.
6. Method according to at least one of the preceding Claims 2 to 5, characterized in that a third partial resistance difference (ΔR3) is determined as a function of an initial temperature (T_c) of the glow plug (2) which said glow plug (2) has at the time of the start of the glowing process.
7. Method according to Claim 5, characterized in that the initial temperature (T_c) corresponds to an ambient temperature of the glow plug (2) at the time of the start of the glowing process.
8. Method according to at least one of the preceding Claims 2 to 7, characterized in that a fourth partial resistance difference (ΔR4) is determined as a function of a glowing process of the glow plug (2) which directly precedes the start of the glowing process.
9. Method according to Claim 8, characterized in that the directly preceding glowing process is characterized by the glowing duration or glowing energy (E) thereof, wherein a factor (F) which is multiplied by the fourth partial resistance difference (ΔR4) and added to the resistance difference (ΔR) is determined, in particular, as a function of the initial resistance (R₀₁) of the glow plug (2).
10. Control device for adjusting a temperature of a glow plug, in particular for igniting a fuel/air mixture in an internal combustion engine which adjusts the temperature (Tm) of the glow plug (2) as a function of a resistance (Rm) of the glow plug (2) by means of a regulating device, wherein means (8, 21) are present which regulate the temperature (Tm) in a pre-heating phase in which an overvoltage is applied to the glow plug (2), characterized in that means for regulating the temperature (Tm) of the glow plug (2) in the pre-heating phase are embodied in such a way that they predictively determine a difference in resistance (ΔR), which is present with respect to a measured resistance (Rm) at the end of the pre-heating phase, using a physical model (8) during the pre-heating phase, add the measured resistance (Rm) of the glow plug (2) to the difference in resistance (ΔR) and feed the sum which is formed from the measured resistance (Rm) and the difference in resistance (ΔR) to the regulating device, determine an actual temperature value (T_ACT) from a characteristic curve (18), which is determined individually for each glow plug (2) during the heated, steady-state operation of the glow plug (2), on the basis of the sum of the measured resistance (Rm) and the difference in resistance (ΔR) and subtract it from a temperature setpoint value (T_Des) of the glow plug, and feed the temperature difference, which is determined in this way and is used to determine an actuation voltage (U_GOV) for the glow plug (2), to the regulating device.

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