Method for controlling a light-emitting device - Patents.com

Abstract

One aspect of the invention relates to a method for controlling a lighting device (1) for a motor vehicle (2), comprising: a pixelated light source (10) having a plurality of selectively operable elementary light sources and arranged in a housing; a control unit controlling the operation of the elementary light sources and enabling at least two superimposed images (300, 310) to be projected; and a temperature sensor arranged in the housing, characterized in that the method comprises a step of measuring the temperature; and if the temperature is above a predefined threshold, the luminous flux of one of the two images is weakened, while the other image remains the same.

Description

[Technical field]

[0001] The technical field of the invention is that of lighting and / or signalling, in particular for motor vehicles.

[0002] In particular, the invention relates to a method for controlling a light emitting device and to a lighting using said method. [Background technology]

[0003] Modern automotive lighting systems consist of pixelated light sources (i.e. light sources with a number of selectively operable elementary light sources and a projection optical assembly), but these light sources are sensitive to temperature.

[0004] Specifically, these light sources are pixelated power light emitting diodes (LEDs) that generate significant heat, especially when the external temperature itself is high (e.g., in summer), and must remain below a certain temperature (e.g., 150°C) to avoid damage to the electronic components and the light source.

[0005] To ensure this protection, the electrical power supplied to the LED is reduced (i.e., decreased) in order to limit the heat output dissipated, which results in a reduction in the level of light emitted by the light source.

[0006] These lighting devices often have two or three projection modules, one of which is a "high resolution" or HD module that allows, in addition to conventional lighting (which itself has a regulated function), to project images or patterns onto the road. These images or patterns contain at least one regulated image (e.g. low beam or high beam) and superimposed images for non-regulated functions (e.g. pictograms). The latter causes a corresponding increase in the temperature of the high resolution module. The appearance of these images or patterns often occurs suddenly, leading to a rapid overload of the module and thus to an increase in temperature.

[0007] Typically, to reduce temperature, the output of the light-emitting device is reduced, resulting in a uniform reduction in luminous flux, which may reduce road regulatory lighting and cause safety issues.

[0008] A motor vehicle is equipped with two lighting devices (i.e. headlamps) located on either side of the front of the vehicle, each of which is capable of projecting a different image. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a solution to the problems mentioned above by making it possible to maintain sufficient lighting to ensure safety. [Means for solving the problem]

[0010] One aspect of the invention is a method for controlling a lighting device for a motor vehicle, comprising the steps of: The light emitting device comprises: - a pixelated light source having a plurality of selectively actuable elementary light sources disposed within a housing; a control unit for controlling the operation of the elementary light sources and enabling at least two superimposed images to be projected; - a temperature sensor disposed within the housing; The method comprising: - measuring a temperature; - if the temperature is above a predefined threshold, the luminous flux of one of the two images is weakened, while the other image remains the same; The present invention relates to a method which is notable in that it comprises:

[0011] Each elementary light source is also called a "pixel."

[0012] The two superimposed images can be obtained by combining the images and then sending the combined information to the control unit. In an alternative embodiment, the control unit receives the images separately and superimposes them. Each image is composed of points each associated with one pixel of the pixelated light source. In other words, each pixel is configured to project a common point in each image. More precisely, the pixels are those for which each of the two images has a non-zero luminous flux. Thus, at these pixels, the two luminous fluxes add up to a total luminous flux that is absolutely stronger than the luminous fluxes of each of the two images.

[0013] According to one embodiment, the pixelated light source is a high resolution LED, with each elementary light source comprising one electroluminescent semiconductor element.

[0014] For LEDs, the predefined threshold is below 150°C, since above this temperature the LED may degrade or even be destroyed. This threshold temperature is established at the pn junction of the semiconductor. Since this junction is inaccessible, the LED has a built-in sensor that measures the temperature outside the junction. The temperature difference is known, making it possible to calibrate the sensor temperature to avoid exceeding 150°C at the junction.

[0015] According to one embodiment, the luminous flux is attenuated for each elementary light source individually.

[0016] Advantageously, one of the images corresponds to a restricted portion, i.e. at least a portion of a restricted beam (e.g. low beam, high beam, etc.), by which is meant a beam that meets the requirements of regulations in force in at least one country (or group of countries) on the filing date of this patent application. Advantageously, the other image corresponds to a non-restricted portion (e.g. a pictogram, etc.).

[0017] Advantageously, the images to be weakened correspond to the non-regulated parts. Thanks to this method, it is possible to maintain the normal light flux of the images corresponding to the regulated parts and weaken the others, thus maintaining safety.

[0018] According to a first embodiment, the light flux is controlled via pulse width modulation (PWM). This control mode (varying the duty cycle) has the advantage that it preserves the color of the light emitted by the light source even when the light flux is dimmed, while allowing a precise adjustment of said light flux. The duty cycle is the ratio between the duration and the period of the high state.

[0019] According to a second embodiment, the luminous flux is controlled by adjusting the magnitude of the supply current of the light source. This control mode is simple to implement.

[0020] Advantageously, the temperature measurement is repeated: a temperature sensor measures the temperature repeatedly, which makes it possible to adapt the reduction in the luminous flux as a function of the measured temperature.

[0021] According to one embodiment, the device comprises several temperature sensors, the elementary light sources of the pixelated light source are divided into several groups, each group being associated with one sensor. Thus, each step of the control method can be applied to each group of elementary light sources. Thus, each elementary light source can be controlled with a higher precision, since the temperature measurement is performed closer to each elementary light source compared to using a single global temperature sensor for the entire pixelated light source. Advantageously, the temperature measurement is repeated for each sensor.

[0022] The image is advantageously refreshed at a period between 1 ms and 1000 ms, preferably between 1 ms and 255 ms. If the system does not respond quickly enough (i.e. the refresh period is too long), there is a risk that the temperature of the LEDs will exceed its 150°C temperature limit. If the system responds too quickly (i.e. the refresh period is too short), there is a risk of undesirable "rebound" and "breathing" effects. The rebound effect corresponds to an increase followed by an excessively significant decrease in the luminous flux of the light source (i.e. a decrease greater than necessary to keep the temperature below the limit temperature). The breathing effect corresponds to a succession of decreases and increases in the luminous flux of the light source, each increase compensating for an excessively significant decrease and each decrease compensating for an excessively significant increase (i.e. causing the temperature to rise again above the limit). These two effects result in luminous intensity fluctuations in the projected image, which are annoying for the user.

[0023] Depending on the situation, a refresh rate of 1 to 24 images per second is sufficient for still images. However, when projecting dynamic images (video), a refresh rate below 24 images per second leads to a jerky impression. For dynamic images, more than 24 images per second is necessary, with 60 images per second providing good smoothness. The refresh rate is also determined by the responsiveness requirements of the system for safety reasons: to display pictograms quickly and to ensure a sufficiently responsive and safe LED power down.

[0024] An image corresponding to a portion of the regulated illumination beam may be obtained by superimposing the beams emitted by the various light-emitting modules. As a non-limiting example, the modules may include a "low beam flat" or "LB flat" module, a "high beam" or "headlight" module, and a high definition (HD) module. The light emitted by these three modules may be at least partially superimposed. The high definition module illuminates a central portion of the illuminated field of view.

[0025] Advantageously, the two images are projected by a high resolution module, which has the highest pixel density and is capable of projecting the most detailed images.

[0026] Another aspect of the present invention is a method for producing - a pixelated light source having a plurality of selectively actuable elementary light sources disposed within a housing; a control unit for controlling the operation of the elementary light sources and enabling at least two superimposed images to be projected; - a temperature sensor disposed within the housing; In a light emitting device comprising: The control unit relates to a light emitting device which is notable for implementing a control method with at least one of the preceding characteristics.

[0027] Another aspect of the invention relates to a lamp and / or headlamp for a motor vehicle, the lamp and / or headlamp comprising a light-emitting device according to the invention.

[0028] Advantageously, the lamp and / or headlamp comprises a housing having an opening and a closing outer lens for closing the opening in the housing. A pixelated light source and a temperature sensor are arranged in a volume formed by the housing and the closing outer lens.

[0029] In the first arrangement, the control unit is arranged in the volume formed by the housing and the closing outer lens. This allows the light emitting device to have a good compactness. Advantageously, the light source and the control unit are arranged on the same carrier. This facilitates integration and reduces costs.

[0030] In the second arrangement, the control unit is placed outside the housing, which saves space and reduces thermal stresses: the light source becomes less hot and the control unit itself is less heated by other components.

[0031] Another aspect of the invention relates to an assembly of two lamps and / or headlamps, each lamp and / or headlamp according to the invention, in which the control unit for each light emitting device is a single control unit common to the light emitting devices.

[0032] Advantageously, the two lights and / or headlamps are arranged to be mounted one on each side of the vehicle (right or left).

[0033] The invention and its various applications will be better understood on reading the following description and on examining the accompanying drawings, in which:

[0034] The drawings are presented as representations and do not limit the invention in any way. [Brief description of the drawings]

[0035] [Figure 1] 1 is an exploded view of a light emitting device according to the present invention. [Diagram 2] FIG. 1 is a perspective view of a vehicle with a lighting device according to the invention which projects two images onto the road. [Diagram 3] FIG. 2 illustrates the projection onto a screen of an image emitted by a light-emitting device according to the present invention. [Figure 4] FIG. 4 is a diagram showing changes in PWM according to the present invention. [Diagram 5] A diagram showing the projection of low beam onto a screen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Unless otherwise specified, identical elements appearing in different figures are given a single reference number.

[0037] The lighting device 1 shown in FIG. 1 comprises a light source 10, a projection optical assembly 11 (e.g., comprising a group of lenses), a fan duct 12 with a fan 120, a heat sink 13, and a temperature sensor (not shown) integrated into the LED.

[0038] A light-emitting device 1 is arranged in each headlamp 20, on each side of the front of the vehicle 2. Each light-emitting device 1 projects one (which can be different) image. In the example shown in Fig. 2, the image of the left projector is shown. The light-emitting device 1 projects two light beams that are superimposed: a first beam 30 that projects a regulatory image 300 whose purpose is to illuminate the road 4, and a second beam 31 that projects an image 310 for assistance (here, an indication of the speed limit) or information purposes (for example, the risk of black ice (transparent thin ice on the road surface)).

[0039] These beams are projected along optical axes pointing forward. Thus, in this specification, the term "front" corresponds to the direction of the overall projection of the beams by the light-emitting device, and the term "rear" corresponds to the opposite direction. When the device is mounted in a headlamp in its standard position on the vehicle, the term "front" also corresponds to the front of the vehicle in the normal direction of travel of the vehicle, and the term "rear" also corresponds to the rear of the vehicle.

[0040] Fig. 3 shows a projection onto a screen perpendicular to the optical axis. The screen is placed at a given distance from the light emitting device 1 in the general emission direction of the light beam (for example at a distance of 25 m). Fig. 3 also shows an example of an elemental division of the light beam into three modules: a high beam module (or HB module) 34, a high resolution module (or HD module) 33 and a low beam module (or LB module) 32.

[0041] As shown in Figure 5, the low beam 32 can be split into two modules: a flat portion 320 with a flat upper edge, which corresponds to the majority of the beam, and a portion with a cutoff 322 or kink 321 forming a V-shaped cutoff. In this case, a high resolution module 33 produces the portion of the beam with the cutoff, and the flat portion is produced by another module.

[0042] The low beam 32 has a cut-off line to prevent oncoming motorists from being subjected to unpleasant dazzling. Above the cut-off line, little or no light can be emitted. Below the cut-off line, light is emitted to illuminate the road. This cut-off line includes a bend, where on one side of the bend there is a horizontal line and on the other side of the bend there is a line that is inclined upwards (typically at a value of 15°). The beam located below the 15° line is also used to illuminate objects located high up on the roadside (e.g. road signs).

[0043] Thus, certain pixels of the pixelated light source in the high resolution module are illuminated both to produce control image information and to produce help image information, i.e. the luminous intensity of the help image is added to the luminous intensity of the control image.

[0044] We will now describe a method for controlling a light emitting device when its temperature increases.

[0045] A temperature sensor installed relative to the pixelated light source 10 measures the temperature. A threshold is defined above which there is a risk of degradation of the light source of the light emitting device. This threshold can vary depending on the position of the temperature sensor. As soon as the threshold temperature is reached, the control unit reduces the luminous flux of only one of the two images (i.e. the aid image 310), which luminous flux makes it possible to obtain a projection luminous intensity between the regulated maximum and minimum values.

[0046] This reduction in luminous flux can be achieved either through adjustment of the magnitude of the supply current in the fundamental light source or by adapting this luminous flux to lower temperatures. This adaptation can be achieved by modulating the pulse width of the PWM in the fundamental light source, as can be seen in Fig. 4. The PWM has a period T that does not change.

[0047] The two images can be combined in various ways, with the first image being a control image and the second image being a support image.

[0048] According to a first alternative, the PWM duty ratio obtained by combining the first and second images for each pixel is the highest PWM duty ratio of the two images. Thus, if the PWM duty ratio of the second image is higher than the PWM duty ratio of the first image, the PWM duty ratio of the combination of the first and second images is the PWM duty ratio of the second image. Otherwise, the PWM duty ratio obtained by combining the first and second images is the PWM duty ratio of the first image. If the two PWM duty ratios are equal, it does not matter which of the first or second images is taken into account. A disadvantage of this embodiment would be that there is a risk that the second image will be obscured and completely obscured by the first image.

[0049] According to the second alternative, for each pixel, if the PWM duty ratio of the first image plus the PWM duty ratio of the second image is less than 1 (100%), the PWM duty ratio of the combination of the first and second images is the sum of the two PWM duty ratios (first image + second image), otherwise the PWM duty ratio of the combination of the first and second images is limited to 1. This solution provides a better contrast optimization, but the overall PWM load is higher. The effect of the 100% duty cycle threshold may also affect the image if blurring is required.

[0050] When the light-emitting device 1 is at a temperature below the threshold temperature, the PWM is in normal mode 5, the duration t0 of the PWM square signal is equal to the duration between two square signals. The duty cycle is then, for example, 50%, which corresponds to the combination of two images at the pixel. As soon as the temperature exceeds this threshold temperature, the PWM switches to reduced mode 6 (reduced power), the duration t1 of the square signal is reduced but the frequency T remains unchanged. The light-emitting device is thus turned on for a shorter time within a given period, allowing the temperature to be reduced. The duration t1 is reduced, for example, by 25%, i.e. a reduction in the luminous flux of 25%. The duty cycle after the reduction is thus 37.5%. This value makes it possible to maintain the minimum luminosity required for the regulated part. In the case of very high temperatures, it is even possible to completely switch off the auxiliary image. Of course, the above values ​​are merely exemplary. The value of the normal duty cycle depends on the brightness of the image that it is desired to project, and the value of the reduction depends on the temperature conditions at a particular time for a given setting.

[0051] Various dimming mode strategies are possible to optimize readability: for example, one may decide to dim only certain (brightest) parts of the aid image and (if necessary) gradually reduce the luminance of an increasing number of pixels.

[0052] Another option is to drop the less bright pixels first (in greater numbers) to keep the image still having the same shape (albeit a sparser shape).

[0053] The control unit will adapt the duration t1 depending on the temperature (the higher the temperature, the shorter the duration t1). Thus, by acting on this duration t1, the dampening action can be adjusted very precisely.

[0054] When the fundamental light source is turned on (i.e. for the duration t1 of the rectangular signal), the magnitude of the current in that light source remains the same regardless of the duration t1, which allows the color to be preserved.

Claims

1. A method for controlling a light emitting device (1) for a motor vehicle (2), comprising: The light emitting device comprises: a pixelated light source (10) arranged in a housing, the pixelated light source having a plurality of selectively operable elementary light sources; a control unit controlling the operation of said elementary light sources and enabling at least two superimposed images (300, 310) to be projected; a temperature sensor arranged within said housing; The method comprising: - measuring the temperature; if said temperature is above a predefined threshold, the luminous flux of one of said two images is weakened, while the other remains the same; A method comprising:

2. 2. A method according to claim 1, characterized in that the light flux is controlled via PWM, i.e. Pulse Width Modulation.

3. 2. The method of claim 1, wherein the luminous flux is controlled by adjusting a magnitude of a supply current of the light source.

4. 2. A method according to any one of the preceding claims, characterized in that the temperature measurements are repeated.

5. 6. A method according to any one of the preceding claims, characterized in that the image is refreshed at a period between 1 ms and 1000 ms, preferably between 1 ms and 255 ms.

6. 4. A method according to any one of the preceding claims, characterized in that one of the images corresponds to a restricted portion and another of the images corresponds to a non-restricted portion.

7. 4. A method according to claim 3, characterized in that the image which is weakened corresponds to a non-regulated portion.

8. a pixelated light source (10) arranged in a housing, the pixelated light source having a plurality of selectively operable elementary light sources; a control unit controlling the operation of said elementary light sources and enabling at least two superimposed images (300, 310) to be projected; a temperature sensor arranged within said housing; In a light emitting device (1), A light emitting device (1), characterized in that the control unit implements a control method according to any one of the preceding claims.

9. 10. A lamp and / or headlamp for a motor vehicle, the lamp and / or headlamp comprising a light-emitting device according to the preceding claims.

10. Assembly of two lights and / or headlamps, each light and / or headlamp as claimed in the preceding claims, characterized in that the control unit in each of the light-emitting devices (1) is a single control unit common to the light-emitting devices.

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