Methods for controlling light-emitting devices

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

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

[0002] The present invention relates in particular to a method for controlling a light-emitting device and to lighting using said method.

Background Art

[0003] Currently, lighting devices for motor vehicles consist of pixelated light sources (i.e., light sources having a plurality of basic light sources that can be selectively activated and one projection optical assembly). However, these light sources are susceptible to temperature effects.

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

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

[0006] These lighting devices often comprise two or three projection modules. One of them is a "high-resolution" or HD module that, in addition to conventional (which itself has a regulatory function) lighting, makes it possible to project images and patterns onto the road. These images and patterns include at least one regulatory image (e.g., low beam or high beam) and superimposed images for non-regulatory functions (e.g., pictograms). The latter correspondingly raises the temperature of the high-resolution module. The appearance of these images and patterns often occurs suddenly and leads to a sudden overload of the module and an increase in temperature.

[0007] Normally, lowering the temperature would reduce the luminous flux uniformly by decreasing the output of the light-emitting devices, but this could lead to a decrease in road lighting and potentially cause safety problems.

[0008] Automobiles are equipped with two lighting devices (i.e., headlamps) located on either side of the front of the vehicle. Each of these devices can project various images. [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention provides a solution to the aforementioned problems by enabling the maintenance of sufficient lighting to ensure safety. [Means for solving the problem]

[0010] One aspect of the present invention is a method for controlling a light-emitting device for an automatic vehicle, The light-emitting device is - It has multiple selectively operable basic light sources, and a pixelated light source arranged within the housing, - A control unit that controls the operation of the basic light source and enables the projection of at least two superimposed images, - A temperature sensor located inside the enclosure, In a method that includes, - The step of measuring the temperature, - If the temperature exceeds a predetermined threshold, one of the two images has its light beam weakened while the other remains at the same light beam. This method is noteworthy for having the following features.

[0011] Each of these basic light sources is also referred to as a "pixel."

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

[0013] According to one embodiment, the pixelated light source is a high-resolution LED, and each basic light source comprises one electroluminescent semiconductor element.

[0014] In the case of LEDs, the predetermined threshold temperature is below 150°C. Exceeding this temperature can cause the LED to degrade or even be destroyed. This threshold temperature is established at the semiconductor's pn junction. Since this junction cannot be accessed, LEDs have a built-in sensor that measures the temperature outside the junction. The temperature difference is known, and the sensor's temperature can be calibrated to avoid exceeding 150°C at the junction.

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

[0016] It is advantageous that one side of the image corresponds to the regulated portion, i.e., at least a portion of the regulated beam (e.g., low beam or high beam). The regulated beam means a beam that satisfies the requirements of regulations in effect in at least one country (or group of countries) as of the filing date of this patent application. It is advantageous that the other side of the image corresponds to the non-regulated portion (e.g., a pictogram).

[0017] It is advantageous that the weakened image corresponds to the unregulated portion. Thanks to this method, it is possible to maintain the image corresponding to the regulated portion at a normal light beam while weakening the others. Thus, safety is maintained.

[0018] According to the first embodiment, the luminous flux is controlled via pulse width modulation (PWM). This control mode (which changes the duty cycle) has the advantage of maintaining the color of the light emitted by the light source even when the luminous flux is weakened, and also allows for precise adjustment of the luminous flux. The duty cycle is the ratio between the duration of the high state and the period.

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

[0020] Repeated temperature measurements are advantageous. The temperature sensor repeatedly measures the temperature, allowing the reduction in luminous flux to be adjusted according to the measured temperature.

[0021] According to one embodiment, the device is equipped with multiple temperature sensors, and the basic light sources of the pixelated light source are divided into multiple groups, with each group associated with one sensor. Thus, each stage of the control method can be applied to each group of basic light sources. In this way, it becomes possible to control each basic light source with higher precision. This is because temperature measurements are taken at a location closer to each basic light source compared to using a single comprehensive temperature sensor for the entire pixelated light source. It is advantageous that temperature measurements are repeated for each sensor.

[0022] The image is preferably refreshed with a period between 1 ms and 1000 ms, preferably between 1 ms and 255 ms. If the system is not fast enough (i.e., the refresh period is too long), there is a risk that the LED temperature will exceed its 150°C temperature limit. If the response speed is too fast (i.e., the refresh period is too short), there is a risk of undesirable "rebound" and "breathing" effects. The rebound effect corresponds to an excessively large decrease in the luminous flux at the light source followed by an increase (i.e., a decrease greater than the value required to maintain the temperature below the limit). The breathing effect corresponds to a sequential alternation of decreases and increases in the luminous flux at the light source, where each increase compensates for an excessively large decrease, and each decrease compensates for an excessively large increase (i.e., causing the temperature to rise again above the limit). These two effects result in fluctuations in the luminous intensity of the projected image, which is troublesome 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 video, a refresh rate of less than 24 images per second will result in a jerky appearance. For dynamic images, a refresh rate higher than 24 images per second is necessary, and good smoothness can be achieved from 60 images per second onwards. The refresh rate is also determined for safety reasons: to display pictograms quickly and to ensure sufficient responsiveness and safe LED output degradation, depending on the system's responsiveness requirements.

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

[0025] It is advantageous for the two images to be projected by a high-resolution module. This module is capable of projecting the most detailed image with the highest pixel density.

[0026] Another aspect of the present invention is - a pixelated light source having a plurality of selectively operable basic light sources and arranged within a housing, - a control unit that controls the operation of the basic light sources and enables at least two overlapping images to be projected, - a temperature sensor arranged within the housing, in a light-emitting device comprising The control unit relates to a light-emitting device worthy of note in that it implements a control method with at least one of the foregoing features.

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

[0028] It is advantageous for the lamp and / or the headlamp to comprise a housing having an opening and a closing outer lens for closing the opening of the housing. The pixelated light source and the temperature sensor are arranged within the volume formed by the housing and the closing outer lens.

[0029] In a first arrangement configuration, the control unit is arranged within the volume formed by the housing and the closing outer lens. This enables the light-emitting device to have excellent compactness. It is advantageous for the light source and the control unit to be arranged on the same carrier. This facilitates integration and reduces costs.

[0030] In the second configuration, the control unit is located outside the housing. This saves space and reduces thermal stress: the light source generates less heat, and the control unit itself is not heated as much by other components.

[0031] Another aspect of the present invention relates to an assembly of two lights and / or headlamps, wherein each light and / or headlamp is according to the present invention, and the control unit in each light-emitting device is a single control unit common to both light-emitting devices.

[0032] It is advantageous for the two lights and / or headlamps to be configured to be mounted on each side of the vehicle (right or left).

[0033] The present invention and its various applications will be better understood by reading the following description and examining the attached drawings.

[0034] The drawings are provided for illustrative purposes only and are not intended to limit the present invention. [Brief explanation of the drawing]

[0035] [Figure 1] Exploded view of the light-emitting device according to the present invention. [Figure 2] A perspective view of a vehicle equipped with a light-emitting device according to the present invention that projects two images onto a road. [Figure 3] A diagram showing the projection of an image emitted by the light-emitting device according to the present invention onto a screen. [Figure 4] A diagram showing the change in PWM according to the present invention. [Figure 5] A diagram showing the projection of the low beam onto the screen. [Modes for carrying out the invention]

[0036] Unless otherwise specified, the same element appearing in different diagrams is given a single reference number.

[0037] The light-emitting device 1 shown in Figure 1 comprises a light source 10, a projection optical assembly 11 (for example, equipped with a group of lenses), a fan duct 12 with a fan 120, a heat sink 13, and a temperature sensor (not shown) incorporated into the LED.

[0038] The light-emitting devices 1 are located on each side of the front of the vehicle 2, within each headlamp 20. Each light-emitting device 1 projects one (which may be different) image. The image shown in the example in Figure 2 is that of the projector on the left. The light-emitting device 1 projects two superimposed light beams: a first beam 30 that projects a regulatory image 300 which is essential for illuminating the road 4, and a second beam 31 that projects an image 310 for aid (here, a speed limit indication) or notification (e.g., the risk of black ice (a thin, transparent layer of ice on the road)).

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

[0040] Figure 3 shows the projection onto a screen perpendicular to the optical axis. The screen is installed at a given distance from the light emitter 1 (for example, 25 m) in the overall direction of light beam emission. Figure 3 also shows an example of 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 divided into two modules: a flat portion 320 with a flat upper edge, which corresponds to the majority of the beam, and a cutoff portion 322 or kink portion 321 that forms a V-shaped cutoff. In this case, the high-resolution module 33 creates the portion of the beam that includes the cutoff, and the flat portion is created by another module.

[0042] The low beam 32 is equipped with a cutoff line to prevent oncoming drivers from being subjected to unpleasant glare. Above the cutoff line, only a small amount of light, or even any light at all, can be emitted. Below the cutoff line, light is emitted to illuminate the road. This cutoff line includes a bend, with a horizontal line on one side of the bend and a line that slopes upward (generally at a value of 15°) on the other side. The beam located below the 15° line is also used to illuminate objects located at a higher position along the roadside (e.g., road signs).

[0043] Therefore, certain pixels among the pixelated light sources in the high-resolution module are illuminated for both generating information for the controlled image and information for the assisting image. In other words, the luminosity of the assisting image is added to the luminosity of the controlled image.

[0044] Here, we will explain a method for controlling the light-emitting device when its temperature rises.

[0045] A temperature sensor installed around the pixelated light source 10 measures the temperature. A threshold is defined above which the light source of the light-emitting device risks degradation. This threshold may vary depending on the location 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 auxiliary image 310). This reduced luminous flux allows for a projected luminous intensity between the maximum and minimum regulated values.

[0046] This reduction in luminous flux can be achieved either by adjusting the magnitude of the supply current in the primary light source or by adapting the luminous flux to lower the temperature. This adaptation can be achieved by modulating the pulse width of the PWM in the primary light source, as can be seen in Figure 4. The PWM has a constant period T.

[0047] The two images can be combined in various ways, provided that the first image is a restrictive image and the second image is a supportive image.

[0048] According to the first alternative, for each pixel, the PWM duty cycle obtained by combining the first and second images is the highest PWM duty cycle of the two images. Thus, if the PWM duty cycle of the second image is higher than that of the first image, the PWM duty cycle of the combination of the first and second images will be the PWM duty cycle of the second image. Otherwise, the PWM duty cycle obtained by combining the first and second images will be the PWM duty cycle of the first image. If the two PWM duty cycles are equal, it does not matter whether the first or second image is considered. A disadvantage of this embodiment would be the risk that the second image may become difficult to see and be completely obscured by the first image.

[0049] According to the second alternative, for each pixel, if the sum of the PWM duty cycle of the first image and the PWM duty cycle of the second image is less than 1 (100%), the PWM duty cycle of the combination of the first and second images will be the sum of the two PWM duty cycles (first image + second image); otherwise, the PWM duty cycle of the combination of the first and second images will be limited to 1. This solution optimizes contrast better but increases the overall PWM load. If blurring is required due to the 100% duty cycle threshold, it may also affect the image.

[0050] When the light-emitting device 1 is below the threshold temperature, the PWM is in normal mode 5, and the duration t0 of the PWM rectangular signal is equal to the duration between two rectangular signals. Therefore, the duty cycle is, for example, 50%, and this value corresponds to the combination of two images at the pixel. As soon as the temperature exceeds this threshold temperature, the PWM switches to de-mode 6 (output reduction), and the duration t1 of the rectangular signal decreases, but the frequency T does not change. Thus, the light-emitting device is lit for a shorter time within a given period, allowing the temperature to decrease. The duration t1 decreases by, for example, 25%, which is equivalent to a 25% reduction in luminous flux. Thus, the duty cycle after the reduction is 37.5%. This value makes it possible to maintain the minimum luminosity required for the regulated area. In the case of extremely high temperatures, it is even possible to completely extinguish the assisting image. Of course, the values ​​described above are merely examples. The normal duty cycle value is determined by the brightness of the image to be projected. The reduction value is determined by the temperature conditions at a specific point in time in a given setting.

[0051] Various de-modulation strategies are possible to optimize readability. For example, one might choose to de-modulate only a certain (brightest) portion of the assisting image, and (if necessary) gradually reduce the luminosity of an increasing number of pixels.

[0052] Another option is to degrade the less bright pixels first (in greater numbers) so that the image still retains the same shape (even if it has a thinner shape).

[0053] The control unit will adjust the duration t1 according to the temperature (the higher the temperature, the shorter the duration t1). Thus, by acting on this duration t1, the weakening action can be adjusted with extreme precision.

[0054] When the basic light source is lit (i.e., during the duration t1 of the rectangular signal), the magnitude of the current in that light source remains the same regardless of the duration t1. This makes it possible to maintain the color.

Claims

1. A control method for controlling a light-emitting device (1) for an automatic vehicle (2), The light-emitting device is - A pixelated light source (10) having multiple selectively operable basic light sources and arranged within the housing, - A control unit that controls the operation of the basic light source and enables the projection of at least two superimposed images (300, 310), - A temperature sensor placed inside the aforementioned housing, In a method that includes, - A step of measuring the temperature using the temperature sensor, - If the measured temperature exceeds a predetermined threshold, the luminous flux of the image corresponding to the unregulated portion of one of the two images is weakened, while the luminous flux of the image corresponding to the regulated portion of the other of the two images is maintained at the same level. A control method that includes [a specific feature / method].

2. The control method according to claim 1, wherein the luminous flux is controlled via PWM, i.e., pulse width modulation.

3. The control method according to claim 1, wherein the luminous flux is controlled by adjusting the magnitude of the supply current of the basic light source.

4. The control method according to claim 1, wherein the temperature measurement is repeated.

5. The control method according to claim 1, wherein the image is refreshed with a period of 1 ms to 1000 ms.

6. A control method for controlling a light-emitting device (1) for an automatic vehicle (2), The light-emitting device is - A pixelated light source (10) having multiple selectively operable basic light sources and arranged within the housing, - A control unit that controls the operation of the basic light source and enables the projection of at least two superimposed images (300, 310), - A temperature sensor placed inside the aforementioned housing, In a method that includes, - A step of measuring the temperature using the temperature sensor, - If the measured temperature exceeds a predetermined threshold, one of the two images has its light beam weakened while the other remains at the same light beam. Equipped with, One side of the aforementioned image corresponds to the restricted portion, and the other side of the aforementioned image corresponds to the unrestricted portion. The aforementioned image is refreshed with a period of between 1 ms and 1000 ms, according to the control method.

7. The control method according to claim 6, wherein the luminous flux is controlled via PWM, i.e., pulse width modulation.

8. The control method according to claim 6, wherein the luminous flux is controlled by adjusting the magnitude of the supply current of the basic light source.

9. The control method according to claim 6, wherein the temperature measurement is repeated.

10. - A pixelated light source (10) having multiple selectively operable basic light sources and arranged within the housing, - A control unit that controls the operation of the basic light source and enables the projection of at least two superimposed images (300, 310), - A temperature sensor placed inside the aforementioned housing, In a light-emitting device (1) equipped with, The light-emitting device (1) is characterized in that the control unit implements the control method described in any one of claims 1 to 9.

11. A light and / or headlamp for an automatic vehicle, comprising the light-emitting device described in claim 10.

12. An assembly of two lights and / or headlamps, wherein each light and / or headlamp is as described in claim 11, characterized in that the control unit in each of the light-emitting devices (1) is a single control unit common to both light-emitting devices.

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