EP2088833A1 - Method for operating a motor vehicle Led-lighting device - Google Patents

Method for operating a motor vehicle Led-lighting device Download PDF

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Publication number
EP2088833A1
EP2088833A1 EP09000921A EP09000921A EP2088833A1 EP 2088833 A1 EP2088833 A1 EP 2088833A1 EP 09000921 A EP09000921 A EP 09000921A EP 09000921 A EP09000921 A EP 09000921A EP 2088833 A1 EP2088833 A1 EP 2088833A1
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Prior art keywords
frequency
led
lighting device
starting
modulation
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EP09000921A
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German (de)
French (fr)
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EP2088833B1 (en
Inventor
Michael Mayer
Gerhard Schneider
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Audi AG
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Audi AG
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/32—Pulse-control circuits
    • H05B45/325—Pulse-width modulation [PWM]

Definitions

  • the invention relates to a method for operating a motor vehicle lighting device comprising at least one LED and a pulse width modulated driving the LED control device.
  • LEDs In motor vehicles, lighting devices with one or more LEDs are increasingly being used, be it as interior lighting, be it in the headlights or the taillights.
  • the LED To ensure the longest possible lifetime, it is known not to provide the LED with a constant, temporally constant current, but clocked by pulse width modulation clocked. That is, the current is switched on and off via a pulse width modulation interface via a high frequency pulse generator.
  • the modulation frequency is constant, it is chosen in each case so high that the intermittent switching operation is not perceived by the human eye, so that it does not come to a stroboscopic effect. Usual frequencies are approx. 100 Hz.
  • the brightness is adjusted via the pulse-pause ratio (the so-called duty cycle), which can be changed accordingly.
  • An extension of the relative pulse duration that is to say the switch-on duration, corresponds in the time average to a longer switch-on duration of the LED, thus a greater brightness, while a reduction of the pulse duration or pulse width corresponds to a lower brightness.
  • the emitted luminous flux is approximately proportional to the mean value of the current, which is determined by the pulse-pause ratio.
  • the operating frequency usually selected to avoid the stroboscopic effect is still so high that the use is correspondingly high high quality and therefore more expensive semiconductor devices than LED components is required, which are able to represent the modulation frequency.
  • the invention is therefore based on the problem to provide an operating method for a pulse-width modulated LED drive, which allows a reduction of the modulation frequency while avoiding a stroboscopic effect.
  • the LED is continuously driven with different frequencies over time. This means that there is no constant frequency relative to the set brightness, but the frequency changes continuously, while the pulse-pause ratio and thus the adjusted brightness remains constant. As a result of this constant frequency change, a stroboscopic effect is avoided with particular advantage, since there is no chronologically constant change between the switch-on and switch-off state, which could be perceived by the viewer. This means that there is no time-constant light pattern that can be detected. Rather, according to the invention, a continuously changing switching behavior is realized which counteracts or avoids the stroboscopic effect.
  • the modulation frequency which was chosen in terms of its height solely for avoiding the stroboscopic effect in previously known control methods.
  • the stroboscopic effect is avoided by the frequency variation, but not by the frequency level alone.
  • the frequency or the frequency band within which the modulation frequency varies must be so high that also the varying frequency jumps just can not be perceived, but already frequencies are sufficient that are> 50 Hz.
  • EMC electromagnetic compatibility
  • the modulation frequency may be repetitively increased or decreased in a frequency sweep, starting from a starting frequency, preferably linearly to a target frequency, and jumping back to the starting frequency upon reaching the target frequency.
  • the modulation frequency preferably increases or decreases linearly from a start frequency to a target frequency. After reaching the target frequency, the frequency is automatically changed in a frequency jump back to the starting frequency, after which the frequency increase or decrease takes place again. This pattern is going through continuously.
  • modulation frequency repetitively preferably linearly between a maximum and a minimum frequency changed.
  • the frequency response also here preferably linearly changes, but the linearity is not a mandatory requirement.
  • a third alternative provides for the modulation frequency to be changed in a continuously changing manner within a defined frequency band via a random generator.
  • any control frequencies within the frequency band that have been previously defined are selected via the random number generator, which are then controlled via the control unit. So it comes to continuous frequency jumps, the holding time of a frequency defined by the random generator is again as low as possible, and preferably below one second.
  • control method according to the invention can be used both in lighting devices comprising only one LED, as well as in lighting devices with multiple LEDs combined in an array. In this case, all LEDs are then preferably driven together, that is, the entire array is operated via the frequency-varying method according to the invention.
  • the multiple arrays can all be driven together in the manner according to the invention if all the LEDs are to be operated.
  • the invention further relates to a motor vehicle comprising a lighting device with at least one LED and a pulse width modulated the LED controlling control device, which is designed to carry out the method described.
  • Fig. 1 shows a lighting device 1 according to the invention in the form of an array 2 consisting of several LEDs 3, of which four are shown in the example shown. Shown is also a control device 4, via which the operating current, which is applied to the array 2 or the LEDs 3 via the motor vehicle electrical system, is controlled pulse width modulated.
  • the illumination device can be any illumination device of the motor vehicle, be it a signal or indicator light in the region of the rear of the vehicle, the vehicle side or the vehicle front, be it an LED headlight or a lighting device from the vehicle interior.
  • the brightness is varied by adjusting the pulse-pause ratio, that is, the ratio between the turn-on and turn-off time of the individual LEDs 3.
  • the frequency with which the switch-on and switch-off process is controlled, in the inventive method or the illumination device according to the invention shown is shown.
  • Fig. 2 shows a first embodiment of such a control method.
  • the control frequency f is plotted. Shown is a start frequency f s and a target frequency f z . In the example shown, it is assumed that the starting frequency f s is lower than the target frequency f z .
  • the operating frequency continuously changes over time between the start frequency f s and the target frequency f z , wherein the frequency within each cycle, starting from the start frequency f s in the example shown is linearly increased to the target frequency f z after which the frequency is again reduced directly to the starting frequency f s in a frequency jump, after which it in turn increases linearly to the target frequency f z , etc. It forms over time t in Fig. 2 shown "sawtooth pattern" off. As a result of this continuous frequency variation, after a constant switching frequency does not occur, the stroboscopic effect is advantageously avoided since the viewer's eye is not given a time-constant switching pattern.
  • the resulting average switching frequency is significantly lower than in conventional lighting devices that are operated at a constant high frequency of usually 100 Hz.
  • the start frequency f s could be, for example, 60 Hz and the target frequency f z 90 Hz, this being merely an example, that is, other frequencies can also be selected. It would also be conceivable, starting from a higher starting frequency f s, to lower the frequency to the target frequency f z and then to increase it again to the starting frequency in a frequency jump. Again, a similar sawtooth pattern would result.
  • Fig. 3 shows a further possibility of a frequency response, whereby here again along the abscissa the time t and along the ordinate the frequency f is plotted.
  • the frequency varies continuously between a minimum frequency f min and a maximum frequency f max .
  • a linear frequency increase or frequency reduction is shown by way of example.
  • an average frequency results due to the avoidance of the stroboscopic effect due to the frequency variation is lower than previously usual constant control frequencies.
  • the minimum frequency f min and the maximum frequency f max can be 60 Hz and 90 Hz, and a minimum frequency of 50 Hz and a maximum frequency of 100 Hz or other frequency combinations would also be conceivable.
  • Fig. 4 a third embodiment of a frequency response.
  • the time t is plotted along the abscissa and the frequency f is plotted along the ordinate.
  • a frequency band between the minimum frequency f min and the maximum frequency f max is defined.
  • a random generator which is part of the control device 4
  • a random frequency within the frequency band is then selected, which is then set by the control device 4.
  • Fig. 4 clearly shows arise over time a variety of frequency jumps, that is, the random number generator continuously selects new frequencies within the frequency band, so that the frequency changes continuously leaps and there is no continuous frequency control here.
  • the individual frequency levels are kept very short, the hold time should be ⁇ 1 second, which is also only an exemplary value. It would also be conceivable to have shorter or longer hold times, wherein the hold time can also be governed by how high the actual control frequency chosen by the random generator is. Higher frequencies may be kept slightly longer than lower ones, or vice versa.

Abstract

The method involves varying the modulation frequency continuously. The modulation frequency is increased or degraded in a frequency-sweep coming out from a starting frequency linear to a target frequency and is returned to the starting frequency by attaining the target frequency.

Description

Die Erfindung betrifft ein Verfahren zum Betrieb einer Kraftfahrzeugbeleuchtungseinrichtung umfassend wenigstens eine LED sowie eine die LED pulsweitenmoduliert ansteuernde Steuerungseinrichtung.The invention relates to a method for operating a motor vehicle lighting device comprising at least one LED and a pulse width modulated driving the LED control device.

Bei Kraftfahrzeugen kommen zunehmend Beleuchtungseinrichtungen mit einer oder mehreren LEDs zum Einsatz, sei es als Innenraumbeleuchtung, sei es in den Frontscheinwerfern oder den Heckleuchten. Um eine möglichst lange Lebensdauer sicherzustellen, ist es bekannt, die LED nicht mit einem konstanten, zeitlich gleichbleibenden Strom zu versorgen, sondern durch Pulsweitenmodulation getaktet anzusteuern. Das heißt, dass der Strom über eine Pulsweitenmodulationsschnittstelle über einen Impulsgenerator mit hoher Frequenz ein- und ausgeschaltet wird. Die Modulationsfrequenz ist konstant, sie ist in jedem Fall so hoch gewählt, dass der intermittierende Schaltbetrieb vom menschlichen Auge nicht wahrgenommen wird, dass es also nicht zu einem Stroboskopeffekt kommt. Übliche Frequenzen liegen bei ca. 100 Hz. Die Einstellung der Helligkeit erfolgt über das Puls-Pausen-Verhältnis (das sogenannte Tastverhältnis), das entsprechend verändert werden kann. Eine Verlängerung der relativen Pulsdauer, also der Einschaltdauer, entspricht im zeitlichen Mittel einer längeren Einschaltdauer der LED, mithin einer größeren Helligkeit, während eine Verringerung der Pulsdauer oder Pulsbreite einer geringeren Helligkeit entspricht. Der abgestrahlte Lichtstrom ist dabei annähernd proportional zum Mittelwert des Stroms, der durch das Puls-Pausen-Verhältnis bestimmt wird.In motor vehicles, lighting devices with one or more LEDs are increasingly being used, be it as interior lighting, be it in the headlights or the taillights. To ensure the longest possible lifetime, it is known not to provide the LED with a constant, temporally constant current, but clocked by pulse width modulation clocked. That is, the current is switched on and off via a pulse width modulation interface via a high frequency pulse generator. The modulation frequency is constant, it is chosen in each case so high that the intermittent switching operation is not perceived by the human eye, so that it does not come to a stroboscopic effect. Usual frequencies are approx. 100 Hz. The brightness is adjusted via the pulse-pause ratio (the so-called duty cycle), which can be changed accordingly. An extension of the relative pulse duration, that is to say the switch-on duration, corresponds in the time average to a longer switch-on duration of the LED, thus a greater brightness, while a reduction of the pulse duration or pulse width corresponds to a lower brightness. The emitted luminous flux is approximately proportional to the mean value of the current, which is determined by the pulse-pause ratio.

Zwar kann verglichen mit einem Konstantenstrombetrieb durch die Pulsweitenmodulation des Schaltbetriebs eine Lebensdauerverlängerung erreicht werden, gleichwohl ist die üblicherweise zur Vermeidung des Stroboskopeffekts gewählte Betriebsfrequenz noch so hoch, dass der Einsatz entsprechend qualitativ hochwertiger und damit teurer Halbleiterbausteine als LED-Komponenten erforderlich ist, die in der Lage sind, die Modulationsfrequenz darzustellen.Although a lifetime extension can be achieved by the pulse width modulation of the switching operation compared to a constant current operation, the operating frequency usually selected to avoid the stroboscopic effect is still so high that the use is correspondingly high high quality and therefore more expensive semiconductor devices than LED components is required, which are able to represent the modulation frequency.

Der Erfindung liegt damit das Problem zugrunde, ein Betriebsverfahren für eine pulsweitenmodulierte LED-Ansteuerung anzugeben, das eine Erniedrigung der Modulationsfrequenz bei gleichzeitiger Vermeidung eines Stroboskopeffekts ermöglicht.The invention is therefore based on the problem to provide an operating method for a pulse-width modulated LED drive, which allows a reduction of the modulation frequency while avoiding a stroboscopic effect.

Zur Lösung dieses Problems ist bei einem Verfahren der eingangs genannten Art erfindungsgemäß vorgesehen, dass die Modulationsfrequenz kontinuierlich variiert.To solve this problem, it is provided according to the invention in a method of the type mentioned that the modulation frequency varies continuously.

Anders als bisher üblich wird bei dem erfindungsgemäßen Verfahren die LED im zeitlichen Verlauf kontinuierlich mit unterschiedlichen Frequenzen angesteuert. Das heißt, dass keine gleichbleibende Frequenz bezogen auf die eingestellte Helligkeit gegeben ist, vielmehr ändert sich die Frequenz laufend, während jedoch das Puls-Pausen-Verhältnis und damit die eingestellte Helligkeit konstant bleibt. Infolge dieser ständigen Frequenzänderung wird mit besonderem Vorteil ein Stroboskopeffekt vermieden, da kein zeitlich konstanter Wechsel zwischen Einschalt- und Ausschaltzustand gegeben ist, der vom Betrachter wahrgenommen werden könnte. Das heißt, es bildet sich kein zeitlich konstantes Leuchtmuster aus, das erfasst werden kann. Vielmehr ist erfindungsgemäß ein sich laufend änderndes Schaltverhalten realisiert, das dem Stroboskopeffekt entgegenwirkt beziehungsweise diesen vermeidet.Unlike in the past, in the method according to the invention, the LED is continuously driven with different frequencies over time. This means that there is no constant frequency relative to the set brightness, but the frequency changes continuously, while the pulse-pause ratio and thus the adjusted brightness remains constant. As a result of this constant frequency change, a stroboscopic effect is avoided with particular advantage, since there is no chronologically constant change between the switch-on and switch-off state, which could be perceived by the viewer. This means that there is no time-constant light pattern that can be detected. Rather, according to the invention, a continuously changing switching behavior is realized which counteracts or avoids the stroboscopic effect.

Infolgedessen ist es beim erfindungsgemäßen Verfahren möglich, die Modulationsfrequenz abzusenken, die in ihrer Höhe allein zur Vermeidung des Stroboskopeffekts bei bisher bekannten Steuerverfahren gewählt wurde. Denn beim erfindungsgemäßen Verfahren wird der Stroboskopeffekt durch die Frequenzvariation, nicht jedoch allein durch die Frequenzhöhe vermieden. Natürlich muss die Frequenz beziehungsweise das Frequenzband, innerhalb dem die Modulationsfrequenz variiert, noch so hoch sein, dass auch die variierenden Frequenzsprünge eben nicht wahrgenommen werden können, jedoch sind bereits Frequenzen ausreichend, die > 50 Hz liegen. Infolge der frequenzmäßig über die Zeit gesehen geringeren mittleren Ansteuerfrequenz ergibt sich damit auch eine geringere Beanspruchung der LED-Halbleiterbausteine, was wiederum dazu führt, dass kostengünstigere Halbleiterbausteine, also LEDs eingesetzt werden können, die jedoch bei Einsatz des erfindungsgemäßen Verfahrens ähnliche Lebensdauerzeiten aufweisen wie bisher verwendete hochwertige, teure Halbleiter-LEDs, die mit konstanter, hoher Frequenz angesteuert werden.As a result, it is possible in the method according to the invention to lower the modulation frequency, which was chosen in terms of its height solely for avoiding the stroboscopic effect in previously known control methods. For in the method according to the invention, the stroboscopic effect is avoided by the frequency variation, but not by the frequency level alone. Of course, the frequency or the frequency band within which the modulation frequency varies, must be so high that also the varying frequency jumps just can not be perceived, but already frequencies are sufficient that are> 50 Hz. As a result of the frequency mean lower drive frequency over time also results in a lower stress on the LED semiconductor devices, which in turn means that less expensive semiconductor devices, ie LEDs can be used, however, when using the method according to the invention have similar lifetimes as previously used high-quality, expensive semiconductor LEDs, which are controlled with a constant, high frequency.

Ein weiterer Vorteil ist ferner darin zu sehen, dass sich das EMV-Verhalten (EMV = elektro-magnetische Verträglichkeit) des Fahrzeugs im Hinblick auf die Frequenzerniedrigung verbessert. Denn grundsätzlich sind hohe Steuerfrequenzen im Hinblick auf etwaige Störeinstrahlungen oder Störabstrahlungen hinsichtlich des EMV-Verhaltens nachteilig. Dem wirkt die erfindungsgemäß niedrigere Modulationsfrequenz entgegen, wie über die kontinuierliche Frequenzvariation auch eine Verringerung etwaiger Resonanzwahrscheinlichkeiten erreicht wird.A further advantage is also to be seen in that the EMC behavior (EMC = electromagnetic compatibility) of the vehicle improves with regard to the frequency reduction. In principle, high control frequencies are disadvantageous with regard to possible interference or noise emissions with regard to the EMC behavior. This counteracts the invention according to the lower modulation frequency, as well as the reduction of any resonance probabilities is achieved via the continuous frequency variation.

Hinsichtlich der Variationsweise der Modulationsfrequenz sind unterschiedliche Möglichkeiten denkbar. Gemäß einer ersten Erfindungsausgestaltung kann die Modulationsfrequenz sich wiederholend in einem Frequenz-Sweep ausgehend von einer Startfrequenz vorzugsweise linear auf eine Zielfrequenz erhöht oder erniedrigt werden und bei Erreichen der Zielfrequenz auf die Startfrequenz zurückgesprungen werden. Bei dieser Erfindungsausgestaltung erhöht oder erniedrigt sich also die Modulationsfrequenz bevorzugt linear ausgehend von einer Startfrequenz auf eine Zielfrequenz. Nach Erreichen der Zielfrequenz wird die Frequenz automatisch in einem Frequenzsprung wieder auf die Startfrequenz geändert, wonach sich die Frequenzerhöhung oder -erniedrigung erneut vollzieht. Dieses Muster wird kontinuierlich durchlaufen.With regard to the variation of the modulation frequency different possibilities are conceivable. According to a first embodiment of the invention, the modulation frequency may be repetitively increased or decreased in a frequency sweep, starting from a starting frequency, preferably linearly to a target frequency, and jumping back to the starting frequency upon reaching the target frequency. In this embodiment of the invention, therefore, the modulation frequency preferably increases or decreases linearly from a start frequency to a target frequency. After reaching the target frequency, the frequency is automatically changed in a frequency jump back to the starting frequency, after which the frequency increase or decrease takes place again. This pattern is going through continuously.

Eine Alternative sieht vor, dass sich die Modulationsfrequenz sich wiederholend vorzugsweise linear zwischen einer Maximal- und einer Minimalfrequenz verändert. Hier erfolgt also kein Frequenzsprung nach Erreichen einer Zielfrequenz auf eine Startfrequenz, vielmehr erfolgt eine kontinuierliche Frequenzvariation zwischen einer Maximal- und einer Minimalfrequenz, wobei sich der Frequenzgang auch hier vorzugsweise linear ändert, die Linearität jedoch keine zwingende Voraussetzung ist.An alternative provides that the modulation frequency repetitively preferably linearly between a maximum and a minimum frequency changed. Here, therefore, no frequency hopping takes place after reaching a target frequency to a start frequency, but rather there is a continuous frequency variation between a maximum and a minimum frequency, the frequency response also here preferably linearly changes, but the linearity is not a mandatory requirement.

Eine dritte Alternative sieht schließlich vor, die Modulationsfrequenz über einen Zufallsgenerator gesteuert innerhalb eines definierten Frequenzbands kontinuierlich wechselnd zu ändern. Hier werden also über den Zufallsgenerator beliebige innerhalb des Frequenzbands, das vorher definiert ist, liegende Steuerfrequenzen ausgewählt, die anschließend über die Steuerungseinrichtung angesteuert werden. Es kommt also kontinuierlich zu Frequenzsprüngen, wobei die Haltezeit einer vom Zufallsgenerator definierten Frequenz wiederum möglichst gering ist und bevorzugt unterhalb einer Sekunde liegt.Finally, a third alternative provides for the modulation frequency to be changed in a continuously changing manner within a defined frequency band via a random generator. In this case, any control frequencies within the frequency band that have been previously defined are selected via the random number generator, which are then controlled via the control unit. So it comes to continuous frequency jumps, the holding time of a frequency defined by the random generator is again as low as possible, and preferably below one second.

Das erfindungsgemäße Steuerverfahren lässt sich sowohl bei Beleuchtungseinrichtungen umfassend nur eine LED einsetzen, wie auch bei Beleuchtungseinrichtungen mit mehreren in einem Array zusammengefassten LEDs. Hierbei werden dann bevorzugt alle LEDs gemeinsam angesteuert, das heißt, das gesamte Array wird über das erfindungsgemäße die Frequenz variierende Verfahren betrieben.The control method according to the invention can be used both in lighting devices comprising only one LED, as well as in lighting devices with multiple LEDs combined in an array. In this case, all LEDs are then preferably driven together, that is, the entire array is operated via the frequency-varying method according to the invention.

Kommen bei einer Beleuchtungseinrichtung auch mehrere separate Arrays zum Einsatz, wie dies beispielsweise bei Frontscheinwerfern in LED-Bauweise der Fall sein kann, können auch die mehreren Arrays alle gemeinsam in der erfindungsgemäßen Weise angesteuert werden, wenn alle LEDs zu betreiben sind.If a plurality of separate arrays are used in an illumination device, as may be the case, for example, with LED-type headlights, the multiple arrays can all be driven together in the manner according to the invention if all the LEDs are to be operated.

Neben dem Verfahren betrifft die Erfindung ferner ein Kraftfahrzeug umfassen eine Beleuchtungseinrichtung mit wenigstens einer LED sowie eine die LED pulsweitenmoduliert ansteuernde Steuerungseinrichtung, die zur Durchführung des beschriebenen Verfahrens ausgebildet ist.In addition to the method, the invention further relates to a motor vehicle comprising a lighting device with at least one LED and a pulse width modulated the LED controlling control device, which is designed to carry out the method described.

Weitere Vorteile, Merkmale und Einzelheiten der Erfindung ergeben sich aus den im Folgenden beschriebenen Ausführungsbeispielen sowie anhand der Zeichnungen. Dabei zeigen:

Fig. 1
eine Prinzipdarstellung einer Beleuchtungseinrichtung mit zugeordneter Steuerungseinrichtung zur Durchführung des erfindungsgemäßen Verfahrens,
Fig. 2
ein Prinzipdiagramm zur Darstellung der Veränderung der Steuerfrequenz in einem Frequenz-Sweep,
Fig. 3
ein Prinzipdiagramm zur Darstellung der Veränderung der Steuerfrequenz durch kontinuierlichen Wechsel zwischen einer Maximal- und Minimalfrequenz, und
Fig. 4
ein Prinzipdiagramm zur Darstellung der Veränderung der Steuerfrequenz durch zufällig ausgewählte Frequenzsprünge.
Further advantages, features and details of the invention will become apparent from the embodiments described below and with reference to the drawings. Showing:
Fig. 1
a schematic diagram of a lighting device with associated control device for carrying out the method according to the invention,
Fig. 2
a schematic diagram showing the change of the control frequency in a frequency sweep,
Fig. 3
a schematic diagram showing the change in the control frequency by continuously switching between a maximum and minimum frequency, and
Fig. 4
a schematic diagram illustrating the change of the control frequency by randomly selected frequency jumps.

Fig. 1 zeigt eine erfindungsgemäße Beleuchtungseinrichtung 1 in Form eines Arrays 2 bestehend aus mehreren LEDs 3, von denen im gezeigten Beispiel vier dargestellt sind. Gezeigt ist ferner eine Steuerungseinrichtung 4, über die der Betriebsstrom, der an das Array 2 beziehungsweise die LEDs 3 über das Kraftfahrzeug-Bordnetz gelegt wird, pulsweitenmoduliert gesteuert wird. Bei der Beleuchtungseinrichtung kann es sich um eine beliebige Beleuchtungseinrichtung des Kraftfahrzeugs handeln, sei es eine Signal- oder Anzeigeleuchte im Bereich des Fahrzeughecks, der Fahrzeugseite oder der Fahrzeugfront, sei es ein LED-Scheinwerfer, oder sei es eine Beleuchtungseinrichtung aus dem Fahrzeuginnenraum. Fig. 1 shows a lighting device 1 according to the invention in the form of an array 2 consisting of several LEDs 3, of which four are shown in the example shown. Shown is also a control device 4, via which the operating current, which is applied to the array 2 or the LEDs 3 via the motor vehicle electrical system, is controlled pulse width modulated. The illumination device can be any illumination device of the motor vehicle, be it a signal or indicator light in the region of the rear of the vehicle, the vehicle side or the vehicle front, be it an LED headlight or a lighting device from the vehicle interior.

Wie beschrieben wird die Helligkeit durch Einstellung des Puls-Pausen-Verhältnisses, also des Verhältnisses zwischen Einschalt- und Ausschaltzeit der einzelnen LEDs 3, variiert. Die Frequenz, mit der der Einschalt- und Ausschalt-Vorgang gesteuert wird, ist beim erfindungsgemäßen Verfahren beziehungsweise der gezeigten erfindungsgemäßen Beleuchtungseinrichtung jedoch, anders als im Stand der Technik, nicht konstant, sondern verändert sich über die Zeit kontinuierlich, wie anhand der Figuren 2 - 4 gezeigt ist.As described, the brightness is varied by adjusting the pulse-pause ratio, that is, the ratio between the turn-on and turn-off time of the individual LEDs 3. The frequency with which the switch-on and switch-off process is controlled, in the inventive method or the illumination device according to the invention shown However, unlike in the prior art, not constant, but changes over time continuously, as based on the Figures 2-4 is shown.

Fig. 2 zeigt eine erste Ausführungsmöglichkeit eines solchen Steuerverfahrens. Längs der Abszisse ist die Zeit t, längs der Ordinate die Steuerfrequenz f aufgetragen. Dargestellt ist eine Startfrequenz fs sowie eine Zielfrequenz fz. Im gezeigten Beispiel sei angenommen, dass die Startfrequenz fs niedriger ist als die Zielfrequenz fz. Wird nun die Beleuchtungseinrichtung 1 betrieben, so wechselt die Betriebsfrequenz über die Zeit kontinuierlich zwischen der Startfrequenz fs und der Zielfrequenz fz, wobei die Frequenz innerhalb jedes Zyklus ausgehend von der Startfrequenz fs im gezeigten Beispiel linear auf die Zielfrequenz fz erhöht wird, wonach die Frequenz in einem Frequenzsprung wieder unmittelbar auf die Startfrequenz fs reduziert wird, wonach sie sich wiederum linear auf die Zielfrequenz fz erhöht, etc. Es bildet sich über die Zeit t das in Fig. 2 gezeigt "Sägezahn-Muster" aus. Infolge dieser kontinuierlichen Frequenzvariation wird, nachdem sich keine konstante Schaltfrequenz einstellt, vorteilhaft der Stroboskopeffekt vermieden, da dem Betrachterauge kein zeitlich konstantes Schaltmuster gegeben wird. Die sich ergebende mittlere Schaltfrequenz liegt deutlich niedriger als bei üblichen Beleuchtungseinrichtungen, die mit konstanter hoher Frequenz von üblicherweise 100 Hz betrieben werden. Im gezeigten Beispiel könnte die Startfrequenz fs beispielsweise 60 Hz und die Zielfrequenz fz 90 Hz betragen, wobei dies lediglich exemplarisch ist, das heißt, dass auch andere Frequenzen gewählt werden können. Denkbar wäre es auch, ausgehend von einer höheren Startfrequenz fs die Frequenz auf die Zielfrequenz fz zu erniedrigen und dann in einem Frequenzsprung wieder auf die Startfrequenz zu erhöhen. Auch hier würde sich ein ähnliches "Sägezahn-Muster" ergeben. Fig. 2 shows a first embodiment of such a control method. Along the abscissa is the time t, along the ordinate, the control frequency f is plotted. Shown is a start frequency f s and a target frequency f z . In the example shown, it is assumed that the starting frequency f s is lower than the target frequency f z . Now, if the lighting device 1 is operated, the operating frequency continuously changes over time between the start frequency f s and the target frequency f z , wherein the frequency within each cycle, starting from the start frequency f s in the example shown is linearly increased to the target frequency f z after which the frequency is again reduced directly to the starting frequency f s in a frequency jump, after which it in turn increases linearly to the target frequency f z , etc. It forms over time t in Fig. 2 shown "sawtooth pattern" off. As a result of this continuous frequency variation, after a constant switching frequency does not occur, the stroboscopic effect is advantageously avoided since the viewer's eye is not given a time-constant switching pattern. The resulting average switching frequency is significantly lower than in conventional lighting devices that are operated at a constant high frequency of usually 100 Hz. In the example shown, the start frequency f s could be, for example, 60 Hz and the target frequency f z 90 Hz, this being merely an example, that is, other frequencies can also be selected. It would also be conceivable, starting from a higher starting frequency f s, to lower the frequency to the target frequency f z and then to increase it again to the starting frequency in a frequency jump. Again, a similar sawtooth pattern would result.

Fig. 3 zeigt eine weiter Möglichkeit eines Frequenzgangs, wobei auch hier längs der Abszisse wiederum die Zeit t und längs der Ordinate die Frequenz f aufgetragen ist. Hier variiert die Frequenz kontinuierlich zwischen einer Minimalfrequenz fmin und einer Maximalfrequenz fmax. Auch hier ist exemplarisch eine lineare Frequenzerhöhung beziehungsweise Frequenzerniedrigung gezeigt. Ersichtlich ergibt sich auch hier eine mittlere Frequenz, die bedingt durch die Vermeidung des Stroboskopeffekts infolge der Frequenzvariation niedriger liegt als bisher übliche konstante Steuerfrequenzen. Beispielsweise kann auch hier die Minimalfrequenz fmin und die Maximalfrequenz fmax 60 Hz und 90 Hz betragen, denkbar wäre auch eine Minimalfrequenz von 50 Hz und eine Maximalfrequenz von 100 Hz, oder andere Frequenzkombinationen. Fig. 3 shows a further possibility of a frequency response, whereby here again along the abscissa the time t and along the ordinate the frequency f is plotted. Here, the frequency varies continuously between a minimum frequency f min and a maximum frequency f max . Here, too, a linear frequency increase or frequency reduction is shown by way of example. Obviously, here too an average frequency results due to the avoidance of the stroboscopic effect due to the frequency variation is lower than previously usual constant control frequencies. For example, the minimum frequency f min and the maximum frequency f max can be 60 Hz and 90 Hz, and a minimum frequency of 50 Hz and a maximum frequency of 100 Hz or other frequency combinations would also be conceivable.

Schließlich zeigt Fig. 4 eine dritte Ausführungsmöglichkeit eines Frequenzgangs. Auch hier ist längs der Abszisse die Zeit t und längs der Ordinate die Frequenz f aufgetragen. Hier ist ebenfalls ein Frequenzband zwischen der Minimalfrequenz fmin und der Maximalfrequenz fmax definiert. Über einen Zufallsgenerator, der Teil der Steuerungseinrichtung 4 ist, wird nun eine zufällige Frequenz innerhalb des Frequenzbands ausgewählt, die dann von der Steuerungseinrichtung 4 eingestellt wird. Wie Fig. 4 deutlich zeigt, ergeben sich über die Zeit eine Vielzahl von Frequenzsprüngen, das heißt, der Zufallsgenerator wählt kontinuierlich neue Frequenzen innerhalb des Frequenzbandes aus, so dass sich die Frequenz laufend sprunghaft ändert und es auch hier zu keiner kontinuierlichen Frequenzansteuerung kommt. Die einzelnen Frequenzstufen werden nur sehr kurz gehalten, die Haltezeit sollte ≤ 1 Sekunde betragen, wobei auch dies lediglich ein exemplarischer Wert ist. Denkbar wären auch kürzere oder längere Haltezeiten, wobei sich die Haltezeit auch danach richten kann, wie hoch die vom Zufallsgenerator gewählte Ist-Steuerfrequenz gerade ist. Höhere Frequenzen können gegebenenfalls etwas länger gehalten werden als niedrigere, oder umgekehrt.Finally shows Fig. 4 a third embodiment of a frequency response. Again, the time t is plotted along the abscissa and the frequency f is plotted along the ordinate. Here also a frequency band between the minimum frequency f min and the maximum frequency f max is defined. Via a random generator, which is part of the control device 4, a random frequency within the frequency band is then selected, which is then set by the control device 4. As Fig. 4 clearly shows arise over time a variety of frequency jumps, that is, the random number generator continuously selects new frequencies within the frequency band, so that the frequency changes continuously leaps and there is no continuous frequency control here. The individual frequency levels are kept very short, the hold time should be ≤ 1 second, which is also only an exemplary value. It would also be conceivable to have shorter or longer hold times, wherein the hold time can also be governed by how high the actual control frequency chosen by the random generator is. Higher frequencies may be kept slightly longer than lower ones, or vice versa.

Die in den Figuren 2 - 4 gezeigten Steuerbeispiele sind lediglich exemplarischer Natur. Selbstverständlich wären auch andere Frequenzgänge denkbar, seien es nicht-lineare Frequenzgänge oder weniger steile Frequenzflanken bei vorgenommenen Frequenzsprüngen. Der Frequenzgang ist stets so zu wählen, dass eine hinreichende Frequenzveränderung zur Vermeidung des Stroboskopeffekts gegeben ist und eine Belastung der einzelnen LEDs möglichst gering ist.The in the Figures 2-4 shown control examples are merely exemplary nature. Of course, other frequency responses would be conceivable, be it non-linear frequency responses or less steep frequency edges when frequency jumps are made. The frequency response should always be selected so that a sufficient frequency change to avoid the stroboscopic effect is given and a load of the individual LEDs is as low as possible.

Claims (7)

Verfahren zum Betrieb einer Kraftfahrzeugbeleuchtungseinrichtung umfassend wenigstens eine LED sowie eine die LED pulsweitenmoduliert ansteuernde Steuerungseinrichtung,
dadurch gekennzeichnet,
dass die Modulationsfrequenz kontinuierlich variiert wird.Method for operating a motor vehicle lighting device comprising at least one LED and a control device that activates the LED in pulse width modulated manner,
characterized,
that the modulation frequency is varied continuously. Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
dass die Modulationsfrequenz sich wiederholend in einem Frequenz-Sweep ausgehend von einer Startfrequenz vorzugsweise linear auf eine Zielfrequenz erhöht oder erniedrigt und bei Erreichen der Zielfrequenz auf die Startfrequenz zurückgesprungen wird.Method according to claim 1,
characterized,
that the modulation frequency is repetitively increased or decreased in a frequency sweep, starting from a starting frequency, preferably linearly to a target frequency and jumping back to the starting frequency when the target frequency is reached. Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
dass die Modulationsfrequenz sich wiederholend vorzugsweise linear zwischen einer Maximal- und einer Minimalfrequenz verändert wird.Method according to claim 1,
characterized,
that the modulation frequency is repetitively preferably linearly changed between a maximum and a minimum frequency. Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
dass die Modulationsfrequenz über einen Zufallsgenerator gesteuert innerhalb eines definierten Frequenzbands kontinuierlich wechselnd geändert wird.Method according to claim 1,
characterized,
that the modulation frequency controlled by a random generator is changed continuously changing within a defined frequency band. Verfahren nach einem der vorangehenden Ansprüche,
dadurch gekennzeichnet,
dass bei Verwendung einer Beleuchtungseinrichtung mit mehreren in einem Array zusammengefassten LEDs alle LEDs gemeinsam angesteuert werden.Method according to one of the preceding claims,
characterized,
that when using a lighting device with a plurality of LEDs combined in an array all of the LEDs are controlled together. Verfahren nach Anspruch 5,
dadurch gekennzeichnet,
dass bei Verwendung einer Beleuchtungseinrichtung mit mehreren Arrays alle Arrays gemeinsam angesteuert werden.Method according to claim 5,
characterized,
that when using a lighting device with multiple arrays all arrays are driven together. Kraftfahrzeug umfassend wenigstens eine Beleuchtungseinrichtung (1) mit wenigstens einer LED (3) sowie eine die LED (3) pulsweitenmoduliert ansteuernde Steuerungseinrichtung (4) ausgebildet zur Durchführung des Verfahrens nach einem der vorangehenden Ansprüche.Motor vehicle comprising at least one illumination device (1) with at least one LED (3) and a control device (4) controlling the LED (3) in a pulse width modulated manner for carrying out the method according to one of the preceding claims.
EP09000921A 2008-02-08 2009-01-23 Method for operating a motor vehicle Led-lighting device Active EP2088833B1 (en)

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