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EP-4735953-A1 - LIGHTING DEVICE COMPRISING A LIQUID CRYSTAL FILM, AND CORRESPONDING LIGHT EMISSION METHOD

EP4735953A1EP 4735953 A1EP4735953 A1EP 4735953A1EP-4735953-A1

Abstract

The present invention relates to a vehicle lighting device (1) comprising: - at least one photon emitter (3); - a control unit (2) for controlling the photon emitter (3), the control unit being capable of applying, at a first frequency, voltage pulses that bias the photon emitter (3); - a liquid crystal film (4) capable of transmitting or blocking light emitted by the photon emitter (3); and - control means (5) capable of applying an AC voltage (V AC ) at a second frequency to the film (4), the lighting device (1) being characterised in that it comprises means for synchronising the AC voltage (V AC ) applied to the film (4) with the voltage pulses applied to the photon emitter (3).

Inventors

  • KRICK, SEBASTIAN
  • BEEV, Kostadin
  • GRARD, Christophe
  • VIKBERG, GUNNAR
  • BENAMAR, Fatima

Assignees

  • Valeo Vision

Dates

Publication Date
20260506
Application Date
20240625

Claims (14)

  1. [Claim 1] Lighting device (1) for a vehicle, comprising: - at least one photonic transmitter (3), - a control unit (2) of the photonic emitter (3), capable of applying voltage pulses polarizing the photonic emitter (3) so that the photonic emitter emits light, - a liquid crystal film (4), in particular of the PDLC type, capable of transmitting or blocking at least part of the light emitted by the photonic emitter (3), and - control means (5) capable of applying an alternating voltage (VAC) to said film (4), the lighting device (1) being characterized in that it comprises means (10) for synchronizing the alternating voltage (VAC) applied to the film (4), with the voltage pulses applied to the photonic emitter (3).
  2. [Claim 2] Lighting device (1) for a vehicle according to claim 1, in which the control unit (2) and/or the control means (5) are configured to use the synchronization means (10) so that none of the voltage pulses are applied during a change of polarity of the alternating voltage (VAC).
  3. [Claim 3] Lighting device (1) for a vehicle according to claim 1 or 2, wherein the control unit (2) is capable of applying the voltage pulses at a first frequency, and wherein the control means (5) are capable of applying to said film (4) the alternating voltage (VAC) with a second frequency.
  4. [Claim 4] Lighting device (1) for a vehicle according to any one of claims 1 to 3, in which the synchronization means (10) comprise means for sending a synchronization signal (h) to the control unit (2).
  5. [Claim 5] Lighting device (1) for a vehicle according to claims 3 and 4, in which the control unit (2) is capable of producing, from the synchronization signal (h), the voltage pulses whose first frequency is equal to the second frequency or to an integer multiple of the second frequency.
  6. [Claim 6] Lighting device (1) for a vehicle according to any one of claims 1 to 3, in which the synchronization means comprise means for sending a synchronization signal to the control means (5).
  7. [Claim 7] Lighting device (1) for a vehicle according to claim 6, in which the control means (5) are capable, from the synchronization signal, of timing each change of sign of the alternating voltage (VAC) between a falling edge and a rising edge of two successive pulses among said voltage pulses.
  8. [Claim 8] Lighting device (1) for a vehicle according to claim 3 and claim 6 or 7, in which the control means (5) are capable of making the second frequency of the alternating voltage (VAC) equal to the first frequency or to an integer submultiple of the first frequency.
  9. [Claim 9] Lighting device (1) for a vehicle according to any one of claims 3 to 8, in which the control unit (2) comprises means for determining a peak voltage value (VL) of the voltage pulses, as a function of a duration of a phase of change of polarity of the alternating voltage (VAC) and/or of the second frequency and/or of a response time of the film (4).
  10. [Claim 10] Front left or front right optical unit for a vehicle, comprising a lighting device (1) according to any one of claims 1 to 9, and capable of fulfilling a lighting or signaling function, the optical unit comprising a closing glass, the film (4) being arranged between on the one hand the control unit (2), the means of control unit (5), the photonic transmitter (3) and on the other hand the closing glass, so as to conceal the control unit (2), the control means (5) and the photonic transmitter (3) when the lighting or signaling function is not activated.
  11. [Claim 11] A method of emitting light implemented by the lighting device (1) according to claim 3 and claim 4 or 5, or by the optical unit according to claim 10 taken in dependence on claim 3 and claim 4 or 5, comprising the steps of: - application to the film (4) by the control means (5), of the alternating voltage (VAC) at the second frequency, - reception by the control unit (2) of the synchronization signal (h), - application to the photonic transmitter (3), by the control unit (2), of voltage pulses at the first frequency, the voltage pulses being synchronized with the alternating voltage (VAC) by the control unit (2).
  12. [Claim 12] Light emission method implemented by the lighting device (1) according to claim 3 and one of claims 6 to 8, or by the optical unit according to claim 10 taken in dependence on claim 3 and one of claims 6 to 8, comprising the steps of: - application to the photonic transmitter (3) by the control unit (2), of voltage pulses at the first frequency, - reception of the synchronization signal by the control means (5), - application to the film (4) by the control means (5) of the alternating voltage (VAC) at the second frequency, the alternating voltage (VAC) being synchronized with the voltage pulses by the control means (5).
  13. [Claim 13] A light emitting method according to claim 11 or 12, wherein each change of sign of the alternating voltage (VAC) occurs between a falling edge and a rising edge of two successive pulses among said voltage pulses.
  14. [Claim 14] A light emission method according to claim 13, further comprising a step of determining a peak voltage value (VL) of the voltage pulses, as a function of a duration of a polarity change phase of the alternating voltage (VAC) and/or of the second frequency and/or of a response time of the film (4).

Description

DESCRIPTION Title of the invention ■ Lighting device comprising a liquid crystal film and corresponding light emitting method [0001] The present invention relates to the fields of electronics and automobiles, and more specifically concerns a lighting device for a vehicle using a liquid crystal film, for example a polymer-dispersed liquid crystal film, also called a PDLC (Polymer Dispersed Liquid Crystal) film. Liquid crystal films find applications in the automobile industry, in particular for producing smart glazing, displaying content in particular on a roof window, or modifying the appearance of lighting elements to create various lighting effects including signaling or active light concealment. [0002] Applying an electric field to such a film makes it possible to orient the liquid crystals that the film contains, so as to allow the light arriving on the film to pass through, the latter then having a transparent or quasi-transparent appearance, whereas in the absence of such an electric field, the molecules have no coherent orientation and generate within the film a multitude of reflections in multiple directions, which generates at the output an opaque effect or at the very least a diffusing effect on the light having succeeded in passing through the film. [0003] Liquid crystal films are similar to capacitive loads, and must be supplied with an alternating voltage whose average voltage is zero. Indeed, applying a direct voltage to the film eventually damages it. [0004] Figure 1 shows as a function of time an alternating voltage VAC applied to a PDLC film in volts (V), as well as a current 1A in milliamperes (mA) passing through the film subjected to this alternating voltage VAC. The alternating voltage VAC here has a frequency of 100Hz (Hertz) or an electrical period of 10ms (milliseconds). It can be seen that the current 1A is zero outside the change phases of polarity of the alternating voltage VAC, phases during which the 1A current flowing through the film reaches a peak of negative amplitude when the alternating voltage VAC decreases, or a peak of positive amplitude when the alternating voltage VAC increases. [0005] The last curve of FIG. 1 represents, as a function of time and in percentages, the transmission rate TT of a luminous flux passing through the PDLC film subjected to the alternating voltage VAC. It can be seen that this transmission rate TT of the PDLC film is fixed and of the order of 70% when the alternating voltage VAC is at its maximum in absolute value, while this transmission rate TT decreases during the phases of change of polarity of the alternating voltage VAC, until reaching 50% when the alternating voltage VAC reaches the zero value in the middle of such a phase. Due to the decrease in the transmission rate TT during the phases of change of polarity of the alternating voltage VAC, the average transmission rate of the PDLC film is only 68%. In the same way, the transmission of other types of liquid crystal films is reduced during the phases of change of polarity, during which the alternating voltage is lower in absolute value than a threshold voltage. [0006] Figure 2 shows, as a function of time, the relative value 4>LR of an incident luminous flux arriving on the PDLC film subjected to the alternating voltage VAC. This value has no unit, being a ratio between the value of the luminous flux in candela, on the peak value of this flux in candela. This relative value 4>LR is here 1, the incident luminous flux being produced by light-emitting diodes supplied by a direct voltage. The transmission rate TT of the PDLC film, reproduced under the curve of relative value 4>LR of the luminous flux, is identical to that shown in Figure 1. The average transmission rate of the luminous flux emitted by light-emitting diodes is therefore 68%. [0007] The inventors have considered using PDLC film technology to hide lighting or signaling means of a vehicle, in particular when the vehicle is stationary, or when some functions are not used (such as dipped beam headlights during the day), for example by placing such a PDLC film opposite the closing glass of each headlight of the vehicle and therefore across the light beams likely to be emitted by the lighting or signalling means, or across the daylight reaching these lighting or signalling means. It is then necessary to adapt the supply voltage of the light-emitting diodes fulfilling the lighting or signalling functions of the vehicle, so that they provide the same light intensity with the PDLC film as before without the use of such a film, in order to meet the regulatory constraints associated with these functions. However, with the average transmission rate of 68% mentioned above, the supply voltage of the diodes must be significantly increased, which is energy-consuming. Furthermore, depending on the lighting or signalling function performed by the light-emitting diodes, their supply voltage may be variable and produce flickering, the coupling