METHOD FOR CONTROLLING A LIGHTING SYSTEM OF A MOTOR VEHICLE

Abstract

A method for controlling a lighting system of a motor vehicle including a generator for generating a pulse-width modulated signal having a first peak intensity or a second peak intensity higher than the first peak intensity, and a light source. The method includes reception of an instruction to emit a light beam according to a given target luminous flux, selection of a peak intensity from the first and second peak intensities depending on the given target luminous flux. Also included is determination of a target duty cycle of a pulse-width modulated signal having the selected peak intensity depending on the given target luminous flux and the efficiency of the light source, and generation of a target signal having the selected peak intensity and the determined target duty cycle and provision of the target signal to the light source.

Claims

1. A method for controlling a lighting system of a motor vehicle, comprising: a pulse-width-modulated-signal generator, the generator being able to generate a pulse-width-modulated signal having a first peak amplitude or a second peak amplitude higher than the first peak amplitude, and a light source arranged to emit a light beam with a luminous flux determined depending on said pulse-width-modulated signal, wherein it comprises the following steps: reception, by the light source, of an instruction to emit a light beam with a given target luminous flux; selection of a peak amplitude among the first and second peak amplitudes, depending on the given target luminous flux; determination of a setpoint duty cycle for a pulse-width-modulated signal having the selected peak amplitude, depending on the given target luminous flux and on the efficacy of the light source; and generation of a pulse-width-modulated setpoint signal having the selected peak amplitude and the determined setpoint duty cycle, and delivery to the light source of said pulse-width-modulated setpoint signal.

2. The method as claimed in claim 1, the lighting system comprising three light sources , each source being able to emit a light beam of a predetermined color, wherein the step of reception of an instruction to emit comprises reception of an instruction for the lighting system to emit a light beam with a given color and with a given overall luminous flux.

3. The method as claimed in claim 2, the method comprising a step of determination of a setpoint duty cycle, and a step of generation and of delivery of a setpoint signal for each of the light sources of the lighting system-(S).

4. The method as claimed in claim 3, wherein, for each light source, the setpoint duty cycle is determined so that the color and the luminous flux of the sum of the light beams emitted by the three light sources correspond substantially to the given color and to the given overall luminous flux.

5. The method as claimed in claim 2, wherein the step of selection of the peak amplitude is common to all the light sources of the lighting system-(S).

6. The method as claimed in claim 5, wherein the step of selection of the peak amplitude comprises comparison of the given overall luminous flux with a predetermined threshold value, the first peak amplitude being selected if the overall luminous flux is lower than said threshold value and the second peak amplitude being selected if the overall luminous flux is higher than said threshold value.

7. The method as claimed in claim 4, the method comprising a step of determination of a given target light intensity for each of the light sources of the lighting system on the basis of said given color and given overall luminous flux , wherein the step of selection of the peak amplitude comprises comparison of the lowest value of the target luminous fluxes determined for each of the light sources with a predetermined threshold value, the first peak amplitude being selected if said lowest value is lower than said threshold value and the second peak amplitude being selected if said lowest value is higher than said threshold value.

8. The method as claimed in claim 1 , the three light sources forming a first lighting unit of the lighting system-(S), and the lighting system comprising a second lighting unit (5)-comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

9. The method as claimed in claim 8, the lighting system (S)-comprising a single controller comprising three generators of pulse-width-modulated signals, each generator being intended to generate one setpoint signal and to deliver this setpoint signal to one of the light sources of each lighting unit.

10. A lighting system of a motor vehicle, comprising at least one pulse-width-modulated-signal generator and a light source arranged to emit a light beam with a luminous flux determined depending on said pulse-width-modulated signal, the lighting system being arranged to implement the method as claimed in claim 1.

11. The lighting system as claimed in claim 10, the lighting system being a lighting system for lighting the interior of the motor vehicle.

12. The method as claimed in claim 3, wherein the step of selection of the peak amplitude is common to all the light sources of the lighting system.

13. The method as claimed in claim 4, wherein the step of selection of the peak amplitude is common to all the light sources of the lighting system.

14. The method as claimed in claim 2, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

15. The method as claimed in claim 3, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

16. The method as claimed in claim 4, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

17. The method as claimed in claim 5, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

18. The method as claimed in claim 6, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

19. The method as claimed in claim 7, the three light sources forming a first lighting unit of the lighting system, and the lighting system comprising a second lighting unit comprising three light sources each able to emit a light beam of a predetermined color, the method comprising a step of determination of a setpoint duty cycle and a step of generation and of delivery of a setpoint signal for each of the light sources of each of the lighting units of the lighting system, wherein the steps of delivery of a setpoint signal for the light sources of each lighting unit of the lighting system are time multiplexed.

20. A lighting system of a motor vehicle, comprising at least one pulse-width-modulated-signal generator and a light source arranged to emit a light beam with a luminous flux determined depending on said pulse-width-modulated signal, the lighting system being arranged to implement the method as claimed in claim 2.

Description

[0031] The present invention will now be described by way of examples that are merely illustrative and that in no way limit the scope of the invention, and with reference to the accompanying illustrations, in which:

[0032] [FIG. 1] shows, schematically and partially, a lighting system of a motor vehicle according to a first embodiment of the invention;

[0033] [FIG. 2] shows a method for controlling the lighting system of [FIG. 1] according to one embodiment of the invention;

[0034] [FIG. 3] shows a chromaticity diagram employed in the method of [FIG. 2];

[0035] [FIG. 4] shows examples of pulse-width-modulated signals generated according to the method of [FIG. 2]; and

[0036] [FIG. 5] shows, schematically and partially, a lighting system of a motor vehicle according to a second embodiment of the invention.

[0037] In the following description, elements that are identical in terms of structure or in terms of function and that appear in various figures have been designated with the same reference sign, unless otherwise indicated.

[0038] [FIG. 1] shows a lighting system S according to a first embodiment of the invention, the system S forming a system for lighting the interior of a motor vehicle.

[0039] To this end, the system S comprises a controller 1 provided with three pulse-width-modulated-signal generators 21, 22, 23 and three light sources 41, 42, 43. Each of the generators 21, 22 and 23 powers one of the light sources 41, 42 and 43.

[0040] Each of the light sources 41, 42 and 43 is a semiconductor chip able to emit a light beam of red, green and blue color, respectively. These three light sources are placed in the vicinity of one another to form an RGB light-emitting diode 4.

[0041] Although the example of [FIG. 1] shows only a single RGB light-emitting diode 4, provision will possibly be made, without departing from the scope of the invention, for the lighting system S to comprise a plurality of RGB light-emitting diodes arranged in various locations in the passenger compartment of the motor vehicle.

[0042] The controller 1 is arranged to receive, for example from a central computer of the motor vehicle, instructions to emit I, requiring the RGB light-emitting diode 4 to emit a light beam of a given color C and of a given overall luminous flux Y.sub.G. Upon receipt of an instruction I, the controller 1 is arranged to control the generators 21, 22 and 23 so that each generator generates, from a periodic signal delivered by an oscillator 3, a pulse-width-modulated signal for powering one of the light sources 41, 42 and 43. Each light source thus emits a light beam having a luminous flux such that the sum of the three light beams forms, by additive synthesis, a light beam having the given color C and the given overall luminous flux Y.sub.G.

[0043] With reference to [FIG. 2], a method according to one embodiment of the invention will now be described, said method being implemented by the lighting system S so that the color of the light beam emitted by the RGB diode 4 corresponds substantially to the given color required by the control instruction I.

[0044] The controller 1 comprises a computer 10 arranged to receive the instruction to emit I and to select, in a first step E1, a peak electrical amplitude I.sub.c from two peak amplitude values I.sub.c1 and I.sub.c2, depending on the required value of the overall luminous flux Y.sub.G specified in the instruction to emit I. The first value I.sub.c1 will be selected if Y.sub.G is lower than or equal to Y.sub.s and the second value I.sub.c2 will be selected if Y.sub.G is higher than Y.sub.s. It will be noted that the value I.sub.c2 is higher than I.sub.c1. For example, I.sub.c1 will possibly be 1 mA and I.sub.c2 will possibly be 20 mA.

[0045] The computer 10 thus transmits this selected value I.sub.c to the generators 21, 22 and 23, so as to ensure that the signals have the selected peak amplitude.

[0046] In a second step E2, computers 11, 12 and 13 determine, each in a step E21, E22 and E23 specific to each light source 41, 42 and 43, an average luminous flux Y.sub.m1, Y.sub.m2, Y.sub.m3 that this light source must emit for the light beam emitted by the RGB diode 4 to have the required color C and the required overall luminous flux Y.sub.G specified in the instruction to emit I, depending on the selected value of the peak electrical amplitude I.sub.c.

[0047] [FIG. 3] shows a chromaticity diagram. The colors R1, G1 and B1 of the light beams that the light sources 41, 42 and 43 are capable of emitting when they are each powered with a pulse-width-modulated signal having the peak value I.sub.c1 and a duty cycle of 100% have been identified in this diagram. It will be noted that, for this duty cycle of 100% and this peak amplitude I.sub.c1, each light source emits a light beam of maximum luminous flux Y.sub.max1c1, Y.sub.max2c1 and Y.sub.max3c1 dependent on the efficacy of this light source at this peak amplitude I.sub.c1. The colors R2, G2 and B2 of the luminous fluxes that the light sources 41, 42 and 43 are capable of emitting when they are each powered with a pulse-width-modulated signal having the peak value I.sub.c2 and a duty cycle of 100% have been identified in this diagram. Similarly, for this duty cycle of 100% and this peak amplitude I.sub.c2, each light source emits a light beam of maximum luminous flux Y.sub.max1c2, Y.sub.max2c2 and Y.sub.max3c2 dependent on the efficacy of this light source at this peak amplitude I.sub.c1. It may thus be seen that the coordinates of the colors of the light beam emittable by a light source differ depending on the selected peak amplitude. Lastly, one example of a required given color C specified in a received instruction I has been shown. The position of this color C may, on the one hand, be considered to be a centroid of the colors R1, G1 and B1 weighted by weights corresponding to the luminous fluxes Y.sub.m11, Y.sub.m22 and Y.sub.m31 sought for the first peak amplitude I.sub.c1, respectively. On the other hand, the position of this color C may also be considered to be a centroid of the colors R2, G2 and B2 weighted by weights corresponding to the luminous fluxes Y.sub.m21, Y.sub.m22 and Y.sub.m32 sought for the second peak amplitude I.sub.c2.

[0048] The average luminous fluxes Y.sub.m1, Y.sub.m2 and Y.sub.m3 will thus possibly be determined, depending on the selected peak amplitude I.sub.c, by selecting a color triplet R1,G1,B1 or a color triplet R2,G2,B2, and searching for the weights by which these colors must be weighted for their centroid to correspond to the required color C, and furthermore for the sum of the luminous fluxes to substantially correspond to the required overall luminous flux Y.sub.g.

[0049] In a third step E3, the computers 11, 12 and 13 determine, each in a step E.sub.31, E.sub.32 and E.sub.33 specific to each light source 41, 42 and 43, a setpoint duty cycle or, as in the present case, an activation time T.sub.on1, T.sub.on2 and T.sub.on3, via the ratio between the luminous flux Y.sub.m1, Y.sub.m2 and Y.sub.m3 determined for each light source and the maximum luminous flux of this source for the selected peak amplitude. Each computer 11, 12 and 13 then delivers the activation time that it determined to one of the generators 21, 22 and 23.

[0050] In a fourth step E4, each generator 21, 22 and 23 generates, in a step E41, E42 and E43 specific to each light source 41, 42 and 43, from the periodic signal delivered by the oscillator 3, a pulse-width-modulated signal S(T.sub.on1), S(T.sub.on2) and S(T.sub.on3) the peak amplitude of which is I.sub.c and the activation time of which is T.sub.on1, T.sub.on2 and T.sub.on3, respectively, then delivers this signal to one of the light sources 41, 42 and 43.

[0051] [FIG. 4] shows two examples of pulse-width-modulated signals S1 and S2, one with the peak amplitude I.sub.C1 and the other with the peak amplitude I.sub.c2.

[0052] Each of these signals S1 and S2 is a periodic signal of period TPWM and comprises, in each period, a pulse formed from a ramp up, of duration T.sub.r, to the value of the peak amplitude I.sub.C1, I.sub.c2, which is maintained for an activation time T.sub.1, T.sub.2, and followed by a ramp down, of duration T.sub.f, to a zero value, respectively. It will be noted that the average amplitudes of these signals S1 and S2, corresponding substantially to the hatched areas, are different. Specifically, due to the difference in efficacy of the light sources at the two peak amplitudes capable of being selected, the sources having a higher efficacy at high peak amplitudes, it is necessary to modify the current delivered to these sources depending on the selected peak amplitude. It will be noted that, when the received instruction I specifies a particularly low overall luminous flux or even a color such that the target luminous flux of one of the sources is particularly low, the activation time T.sub.2 of the signal S2 may be of the order of the rise and fall times T.sub.r, T.sub.f, or even shorter therethan. In this case, an average amplitude of the signal actually generated corresponding substantially to the determined average amplitude cannot be obtained. Furthermore, the chromatic behavior of the sources during the rise and fall times is unpredictable. The invention thus allows the generators to generate a signal S1 the activation time T.sub.1 of which is, in this case, substantially longer than the rise and fall times T.sub.r, T.sub.f, so that the average amplitude of the signal actually generated substantially corresponds to the determined average amplitude. In addition, in this case, the chromatic impact of the rise and fall times is minimized.

[0053] [FIG. 5] shows a lighting system S according to a second embodiment of the invention, the system S forming a system for lighting the interior of a motor vehicle.

[0054] To this end, the system S comprises a controller 1, a first lighting unit 4 comprising three light sources 41, 42, 43 and a second lighting unit 5 comprising three light sources 51, 52 and 53.

[0055] Each of the light sources 41, 42 and 43 is a semiconductor chip able to emit a light beam of red, green and blue color, respectively. These three light sources are placed in the vicinity of one another to form an RGB light-emitting diode 4. Likewise, each of the light sources 51, 52 and 53 is a semiconductor chip able to emit a light beam of red, green and blue color, respectively. These three light sources are placed in the vicinity of one another to form an RGB light-emitting diode 5.

[0056] Equivalently to the first embodiment, the controller 1 is arranged to receive, for example from a central computer of the motor vehicle, instructions to emit I, requiring the RGB light-emitting diodes 4 and 5 to emit a light beam of a given color C and of a given overall luminous flux Y.sub.G.

[0057] To this end, the controller 1 comprises computers 11, 12 and 13, three generators 21, 22, 23 of pulse-width-modulated signals and an oscillator 3, which are arranged to implement together the steps E0 to E4 illustrated in [FIG. 2].

[0058] However, unlike in [FIG. 1] and [FIG. 2], the controller 1 comprises a switching unit 6 arranged so that the generators 21, 22 and 23 deliver said pulse-width-modulated signals to the light sources of the RGB light-emitting diodes 4 and 5 in a multiplexed manner.

[0059] The controller 1 has two inputs In1 and In2, each commonly connected to the anodes of the light sources 41, 42 and 43 and 51, 52 and 53 of each RGB light-emitting diode 4 and 5, respectively. Each input In1 and In2 may be activated or deactivated selectively by the switching unit 6 so as to permit the passage of a current through the RGB diode to which it is connected.

[0060] The controller 1 has three outputs Out1, Out2 and Out3. Each output is commonly connected to the cathodes of the light sources of the RGB diodes 4 and 5 able to emit a light beam of the same color. In particular, the output Out1 is connected to the cathodes of the light sources 41 and 51, the output Out2 is connected to the cathodes of the light sources 42 and 52 and the output Out3 is connected to the cathodes of the light sources 43 and 53. Each output Out1, Out2 and Out3 is further connected to one of the generators so as to receive a pulse-width-modulated signal delivered by this generator and to transmit it to the light sources to which it is connected.

[0061] The switching unit 6 periodically and alternately controls activation and deactivation of the inputs In1 and In2 so that, when one is activated, the other is deactivated. Thus, the generators 11, 12 and 13 deliver pulse-width-modulated signals alternately to the RGB diode 4 and to the RGB diode 5.

[0062] The switching unit moreover synchronously controls the computers 11, 12 and 13 so that the implementation of steps E1 to E4 is tailored to the RGB diode connected to the activated input. In particular, the switching unit controls the computers 11, 12 and 13 so that the setpoint duty cycles are determined depending on the efficacies of the light sources of the RGB diode connected to the activated input.

[0063] Provision will possibly be made, without departing from the scope of the invention, for the lighting system S to comprise more than two RGB light-emitting diodes arranged at various locations in the passenger compartment of the motor vehicle and to which light-emitting diodes pulse-width-modulated signals are delivered in a multiplexed manner.

[0064] It will be noted that, in the described examples, all of the computers of the controller 1 may be effected by the same component, an integrated circuit for example.

[0065] The above description clearly explains how the invention allows the objectives that were set therefor, namely preservation of a satisfactory precision in respect of the luminous flux and/or color of a light beam emitted by a light source of a lighting system of a motor vehicle, including when a low luminous flux or a small variation in the luminous flux is required, to be met through provision of a method for controlling the lighting system that allows pulse-width-modulated signals the peak amplitude of which is suitable for this required luminous flux to be generated.

[0066] In any event, the invention should not be regarded as being limited to the embodiments specifically described in this document, and extends, in particular, to any equivalent means and to any technically operative combination of these means. It may in particular be envisioned to employ the described lighting system and method in fields of motor-vehicle lighting other than the one described, and for example in fields such as lights for lighting the road or signaling lights. It may also be envisioned to select the value of the peak amplitude in other ways, and in particular to select a different peak-amplitude value for each light source.