EP2012003A2 - Method for heating a ceramic glow plug and glow plug control device - Google Patents

Abstract

The method involves applying a variable electrical voltage at a heater plug for starting an engine. A starting voltage is applied by a power-up action to begin the heating process as socket value, which is small as electrical system voltage. The electrical voltage rises on the basis of the socket value in the temporal medium disproportionate to an elapsed heating-up time. An independent claim is also included for a glow plug controller.

Description

The invention relates to a method for heating a ceramic glow plug and a glow plug control device for carrying out such a method.

To start an engine glow plugs must be heated as quickly as possible to an operating temperature of typically 1000 ° C to 1300 ° C. If overheating exceeds the operating temperature during heating, the glow plug is loaded and in extreme cases even damaged. In order to avoid overshoots, it is therefore known to gradually reduce the voltage applied to the glow plug during the heating phase (MTZ 61, 2000, 10).

Despite a promising potential, ceramic glow plugs have not yet reached the desired high lifetimes.

The object of the invention is to show a way how ceramic glow plugs can be heated as quickly as possible to their operating temperature and are charged as little as possible, so that their life is affected as little as possible by the heating.

This object is achieved by a method having the features specified in claim 1. The object is further achieved by a glow plug control device according to claim 14, which is arranged such that it performs such a method during operation for heating a glow plug.

In known heating methods, in order to avoid an overshoot of the temperature of the glow plug, the applied voltage is gradually lowered in the course of the heating process, so that the electrical voltage decreases during the heating process in the time average. Surprisingly, the service life of ceramic glow plugs, in particular outside glow plugs, can be increased by doing exactly the opposite. In accordance with the invention, the electrical voltage at the beginning of the heating process increases over time as a proportion of the time elapsed to the elapsed heating time.

The electrical voltage can be increased at the beginning of the heating, for example, steadily. Preferably, the voltage is increased in steps, in which case the height of the steps increases with increasing time and / or the width of the steps decreases with increasing time. In this way, during the heating phase for starting a motor results in a course of the electrical voltage, which increases disproportionately in the time average.

While in the prior art at the beginning of the heating process for starting a motor typically the full vehicle electrical system voltage is applied to the glow plug, in the inventive method is preferably initially applied a much lower starting voltage of, for example, 6 volts as the base value. Based on the base value, the electrical voltage is then increased up to a maximum value, which may be the value of the vehicle electrical system voltage. The base value is preferably different from zero and is preferably at least 4 volts, in particular at least 5 volts. Preferably, the base value is controlled at the beginning of the process in a single jump from zero and reached, for example by a switch-on.

The surprisingly positive effect of the method according to the invention on the service life of ceramic glow plugs is attributed from today's point of view to the fact that form local current paths in the ceramic conductor of a ceramic glow plug, which may lead to local overheating and thus damage to the glow plug when applying too high a voltage. In the course of the heating process, the electrical resistance increases due to temperature, so that the electrical voltage without damage to the material can also be increased in order to achieve the fastest possible heating to the desired operating temperature. For the life of the glow plug in particular the beginning of the heating process seems to be critical. In order to achieve the fastest possible heating, according to the invention, the voltage during the heating up to a maximum progressively increase and after reaching the maximum, possibly delayed, are lowered to a lower value sufficient to maintain the desired operating temperature.

As already mentioned, the voltage can be increased gradually at the beginning of the heating process. Preferably, the electrical voltage remains constant at most in a time interval of 0.4 seconds, in particular at most of 0.2 seconds, particularly preferably in a time interval of at most 0.1 second, before it is increased in a subsequent time interval.

Preferably, the electrical voltage is applied in a pulse width modulation method for short time slices, so that there is a course of an effective voltage, which may be a step function, a polygonal or parabolic example and increases in average overproportional to the elapsed heating time. In the time average over preferably at most 0.3 seconds, preferably over 0.2 seconds, in particular over 0.1 second, the electric voltage should increase but disproportionately to the elapsed heating time.

In a method of pulse width modulation, a continuous increase in the effective electric voltage can be achieved by the duration .DELTA.t ₁ of the voltage pulses is increased and / or the duration of the lying between the voltage pulses breaks .DELTA.t ₂ is reduced, the effective voltage Vrms at a time t as the voltage applied in the time average during a time interval voltage that has at least the length .DELTA.t ₁ + .DELTA.t ₂ and in the middle of the time t is calculated. The effective electrical voltage is thus determined by calculating a time average over a sliding time interval.

Particularly good results can be achieved by increasing the effective electrical voltage starting from a starting voltage as continuously as possible. This can be done, for example, that the course of the electrical voltage is a polygon. The larger the number of nodes, the smoother the increase in voltage. Preferably, the traverse has at least 5 support points, in particular at least 8 support points, more preferably at least 12 support points. It is particularly advantageous if the course of the electrical voltage aproximates a continuously differentiable function and the course of the electrical voltage shows a strictly monotonically rising gradient. In particular, a parabolic rise in the electrical voltage is preferred.

A glow plug control device according to the invention is set up such that it carries out the method according to the invention during operation for heating a glow plug. Preferably, at least 5 interpolation points of a nominal curve of the electrical voltage characteristic are stored in a memory of the glow plug control device during the heating process. Particularly preferably, at least 8 support points of the desired curve are stored, which should follow the electrical voltage curve during the heating process.

Figur 1

ein Beispiel des sich durch Pulsweitenmodulation ergebenden Verlaufs der Effektivspannung Ueff einer keramischen Glühkerze beim Aufheizen;

Figur 2

den in Fig. 1 gezeigten Verlauf der Effektivspannung zusammen mit den bei der Pulsweitenmodulation angelegten Spannungspulsen; und

Figur 3

den Verlauf der Effektivspannung Ueff beim Aufheizen einer Glühkerze auf ihre Betriebstemperatur sowie zusätzlich den Verlauf der Effektivspannung Ueff nach Erreichen der Betriebstemperatur.

Further details and advantages of the invention will be explained with reference to an embodiment with reference to the accompanying figures. Show it:

FIG. 1

an example of the pulse width modulation resulting course of the effective voltage Ueff of a ceramic glow plug during heating;

FIG. 2

the in Fig. 1 shown course of the effective voltage together with the voltage pulses applied in the pulse width modulation; and

FIG. 3

the course of the effective voltage Ueff when heating a glow plug to its operating temperature and in addition the course of the effective voltage Ueff after reaching the operating temperature.

In FIG. 1 For example, the effective voltage Ueff applied to a ceramic glow plug for heating to operating temperature is plotted in volts over time t in seconds. At the beginning of the heating process for starting a motor, a starting voltage is applied, which is less than a vehicle electrical system voltage, which today is usually 12 volts. The starting voltage is selected as the base value, which is greater than zero, and preferably achieved in one jump.

In this way, a method for heating a ceramic glow plug to its operating temperature for starting an engine is realized. In the method, a variable voltage is applied to the glow plug, wherein the electric voltage, starting from a base value in the time average increases disproportionately to the elapsed heating time until a maximum value is reached.

FIG. 1 shows that the effective voltage Ueff rises parabolically from a base value of 6 volts to a maximum value of about 11 volts. The voltage curve follows a setpoint curve Ueff (t) = 4.6 (volts / sec) xt ² + 2.6 (volts / sec) xt + 6 volts, where Ueff is the effective voltage at the glow plug in volts and t is the time in seconds.

The specified effective voltage Ueff is applied to the glow plug by a method of pulse width modulation from the glow plug controller.

In a pulse width modulation method, the vehicle electrical system voltage, which is generally about 11 volts to 12 volts, is applied to the glow plug in voltage pulses for short time intervals. The duration of these voltage pulses and the duration of the intervening time intervals, in which the glow plugs are disconnected from the vehicle electrical system voltage, set the effective voltage. The effective voltage can be calculated, for example, as the voltage applied in the time average, the time average over the sum of the time period .DELTA.t _{1 of} a voltage pulse and an adjoining period .DELTA.t ₂ , in which the glow plug is disconnected from the vehicle electrical system voltage calculated. In an approximately constant vehicle electrical system voltage U _B is in a time interval .DELTA.t ₁ + .DELTA.t _2, the effective voltage $$\mathrm{Ueff}\mathrm{=}\left({\mathrm{U}}_{\mathrm{B}}\mathrm{•}\mathrm{\Delta }{\mathrm{t}}_{\mathrm{1}}\right)\mathrm{:}\mathrm{(}\mathrm{\Delta }{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{1}}\mathrm{+}\mathrm{\Delta }{\mathrm{t}}_{\mathrm{2}}\mathrm{)}$$

In FIG. 2 are in addition to the in FIG. 1 shown course of the effective voltage shown in the pulse width modulation voltage pulses. How to get in FIG. 2 sees, the duration of the voltage pulses increases disproportionately with increasing time to and the duration of the pauses lying between the voltage pulses accordingly.

The duration of a voltage pulse and a subsequent period in which the glow plug is decoupled from the vehicle electrical system voltage in the example shown together amount to 0.1 second. The time of beginning of a voltage pulse is in FIG. 2 highlighted by a dashed line at the top of the picture. In addition, horizontal bars indicate the value of the time average of 0.5 s; 1.5 s; 2.5 s; 3.5 s; 4.5 s and 5.5 s applied voltage, ie the value of the effective voltage at this time, shown.

With the voltage curve described above, a quick and gentle heating of a ceramic glow plug for starting a motor can be achieved. A short time after the glow plug, the maximum voltage, ie the vehicle electrical system voltage of about 11 V, is applied, the operating temperature is reached. Subsequently, the voltage can be lowered to a lower level sufficient to maintain the operating temperature. This lowering can be done in stages or continuously.

In FIG. 3 the further voltage profile taking place following a method according to the invention is shown by way of example. The left half of FIG. 3 also shows in FIG. 1 shown course of the rms voltage. The right half of FIG. 3 shows how the voltage is gradually reduced after reaching a maximum value to a value sufficient to maintain the operating temperature. The time scale in the right half of FIG. 3 is larger than selected in the left half.

Claims (15)

A method for heating a ceramic glow plug by applying a variable voltage to the glow plug, characterized in that the electrical voltage, starting from a base value in the time average increases disproportionately to the elapsed heating time. A method according to claim 1, characterized in that the electrical voltage is an effective voltage formed by a method of pulse width modulation. Method according to one of the preceding claims, characterized in that the electrical voltage during the heating process at most for a time interval of 0.4 seconds, preferably at most for 0.2 seconds, in particular at most for 0.1 seconds remains constant. Method according to one of the preceding claims, characterized in that the electrical voltage increases continuously from the base value. Method according to one of the preceding claims, characterized in that the electrical voltage is increased in steps starting from the base value, wherein the height of the steps increases with increasing time and / or the width of the steps decreases with increasing time. Method according to one of the preceding claims, characterized in that the electrical voltage rises to a maximum and after reaching the maximum, possibly delayed, is lowered to a lower value. Method according to one of the preceding claims, characterized in that the electrical voltage increases over time in each case over 0.3 seconds, preferably over 0.2 seconds, in particular over 0.1 seconds disproportionately to the elapsed heating time. Method according to one of the preceding claims, characterized in that the base value is at least 4 volts, preferably at least 5 volts, more preferably 6 volts. A method according to claim 8, characterized in that the base value is driven at the beginning of the process in a single jump from zero to the base value. Method according to one of the preceding claims, characterized in that the electrical voltage increases in a parabolic manner. Method according to one of the preceding claims, characterized in that the course of the electrical voltage shows a strictly monotonically increasing slope. Method according to one of the preceding claims, characterized in that the profile of the electrical voltage is a polygon. A method according to claim 12, characterized in that the traverse has at least five support points, preferably at least 8 support points, in particular at least 12 support points. Glow plug control device, characterized in that it is adapted such that it performs a method according to any one of the preceding claims in operation for heating a glow plug. Glow plug control device according to claim 14, characterized in that stored in a memory of the glow plug control device at least five support points of a setpoint curve of the electrical voltage characteristic during the heating process, preferably at least eight support points, in particular at least 12 support points.

Images