Method of operating an automotive lighting device and automotive lighting device

Abstract

The invention provides a method for operating an automotive lighting device (1) comprising at least one solid-state light source (2). This method comprises the steps of defining a color tolerance condition (6), supplying the light source with a current value (41) which produces a luminous flux value greater than a minimum luminous flux threshold value (4), measuring the temperature in the light source (2), checking whether the output color satisfies the tolerance condition (6) and increasing or decreasing the current value, always maintaining the current such that it produces a luminous flux value greater than the minimum luminous flux threshold value (4) and producing a color that satisfies the tolerance condition (6). The invention also provides an automotive lighting device (1) comprising a control element (3) for carrying out the steps of this method.Figure for abstract: Figure 3

Description

Title of the invention: Method of operating an automotive lighting device and automotive lighting device

[0001] This invention relates to the field of automotive lighting devices, and more particularly to the management of the colors of these light sources included in these devices.

[0002] Car manufacturers are increasingly adopting digital lighting devices for mid- and high-end products.

[0003] These digital lighting devices generally comprise semiconductor light sources, the operation of which is highly temperature dependent.

[0004] Temperature control in these elements is a very sensitive aspect, and is usually done by derating, which means decreasing the value of the current that powers the light source so that the output flux and operating temperature decrease accordingly. The performance of the light sources must therefore be greatly oversized to cope with these overheating problems, so that the operating values can be decreased while maintaining acceptable values.

[0005] In addition, these techniques also affect the color of the output model. Therefore, in some cases, for certain temperature ranges, the output color may be off-standard.

[0006] This issue has been addressed so far, but a solution is being provided.

[0007] The invention provides an alternative solution for managing the output color of the light source patterns by a method of operating an automotive lighting device and an automotive lighting device.

[0008] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall be interpreted in accordance with the usages of the profession. It is also understood that terms in common usage shall be interpreted as being customary in the relevant art and not in an idealized or overly formal sense, unless expressly defined as such herein.

[0009] In this text, the term "includes" and its derivatives (such as "comprising", etc.) should not be understood in an exclusive sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include other elements, steps, etc.

[0010] In a first inventive aspect, the invention provides a method of operating a automotive lighting device comprising at least one semiconductor light source, the method comprising the following steps • define a color tolerance condition, in which, for each temperature-electric current pair, a color is defined as acceptable or unacceptable; • establish a minimum threshold value for luminous flux and a maximum threshold value for luminous flux • supply the light source with a current value which produces a luminous flux value between the minimum luminous flux threshold value and the maximum luminous flux threshold value; • measure the temperature of the light source • obtain the color of the light emitted by the light source • check if the calculated color meets the tolerance condition • increase or decrease the current value, always maintaining the current such that it produces a luminous flux value between the minimum luminous flux threshold value and the maximum luminous flux threshold value and producing a color that satisfies the tolerance condition.

[0011] The term "solid state" refers to light emitted by solid-state electroluminescence, which uses semiconductors to convert electricity into light. Compared to incandescent lighting, solid-state lighting creates visible light with reduced heat output and less power dissipation. The generally low mass of a solid-state electronic lighting device provides greater resistance to shock and vibration than brittle glass tubes / bulbs and long, thin filament wires. They also eliminate filament evaporation, which can increase the lifespan of the lighting device. Some examples of these types of lighting include solid-state light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or polymer light-emitting diodes (PLEDs) as lighting sources rather than electric filaments, plasma, or gas..

[0012] The color tolerance condition is defined by means of data sheets and / or experimental data. For two given values of current and temperature, the output color of the light source can be obtained. This obtained color may or may not comply with the regulations, since the regulations also provide for a range of accepted and non-accepted colors. Thus, a current - temperature pair is considered to meet or not meet the tolerance condition.

[0013] By this method, the light source is able to calculate whether the output color is allowed or not, and can react to an unauthorized situation by changing the supply current, so that the color is always maintained within the allowed area.

[0014] In certain particular embodiments, the step of obtaining the color is carried out using a technical data sheet and / or experimental data, which provide the color from the temperature and the value of the current.

[0015] There are many other ways to obtain the output color of the light source. Sometimes manufacturers' data sheets provide reliable and useful information on these parameters, but experimental data can also be used to obtain this tolerance condition.

[0016] In some particular embodiments, the method further comprises the step of establishing a maximum luminous flux threshold value and the method includes maintaining the current such that it produces a luminous flux value less than the maximum luminous flux threshold value.

[0017] A maximum flux value is also useful for limiting luminous flux within the framework of regulations.

[0018] In certain particular embodiments, the step of measuring the temperature of the light source is carried out by a thermistor, such as a thermistor with a negative temperature coefficient.

[0019] A thermistor is a common element that can be used to measure temperature, thus providing a reliable starting point for this process.

[0020] In certain particular embodiments, the step of increasing the value of the current consists of increasing the value of the current from a first value to a second value, the second value being greater than the first value but less than 1.1 times the first value, particularly less than 1.05 times the first value and particularly less than 1.03 times the first value.

[0021] In these examples, the intensity can be increased in small ranges, so that the current value (and temperature) is kept as low as possible within a range that provides acceptable performance. In addition, color deviations can be corrected with the minimum possible impact on performance.

[0022] In certain particular cases, the method further comprises the step of recording a sequence of current value increments for predetermined conditions.

[0023] This sequence can be useful if using a time-based scheme, to avoid continuous temperature measurement.

[0024] In certain particular embodiments, the steps of the method are applied to at least 10% of the light sources of the lighting device.

[0025] The gradual increase in the current value can be applied to a large number of light sources at the same time, for example, to all light sources providing a predetermined functionality. Energy saving and uniformity of performance can therefore be applied to a large number of elements.

[0026] In a second inventive aspect, the invention provides an automotive lighting device comprising: • a matrix arrangement of solid-state light sources; • a control element allowing the process steps to be carried out according to the first inventive aspect;

[0027] This lighting device offers the advantageous functionality of efficiently managing the chromatic output of light sources.

[0028] In certain particular cases, the matrix comprises at least 2000 solid-state light sources.

[0029] A matrix arrangement is a typical example of this method. The lines can be grouped into projected distance intervals and each column in each group represents an angle interval. This angle value depends on the resolution of the matrix, which is typically between 0.01° per column and 0.5° per column. Therefore, multiple light sources can be managed at the same time.

[0030] [Fig.l] shows a general perspective view of an automotive lighting device according to the invention;

[0031] [Fig.2] presents a graphic diagram which represents the values of the luminous flux produced by the LED when it is powered by a particular electric current and is under a given temperature.

[0032] [Fig.3] shows an example of the evolution of the electric current in the LED according to a method in accordance with the invention.

[0033] In these figures, the following reference numbers have been used:

[0034] 1 Lighting device

[0035] 2 LED

[0036] 3 Control element

[0037] 4 Minimum threshold value of luminous flux

[0038] 41 First current value

[0039] 42 Second current value

[0040] 5 Thermistor

[0041] 6 points of inadmissibility

[0042] 7 Maximum luminous flux threshold value

[0043] 100 Motor vehicle

[0044] The exemplary embodiments are described in sufficient detail to enable those of ordinary skill in the art to realize and implement the systems and processes described herein. It is important to understand that these examples may be provided in many different forms and should not be construed as limited to the examples presented herein.

[0045] Accordingly, although the embodiment may be modified in various ways and take various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below by way of example. There is no intention to be limited to the particular forms disclosed. Rather, all modifications, equivalents, and alternatives falling within the scope of the appended claims are to be included.

[0046] [Fig.l] shows an overall view of an automotive lighting device according to the invention.

[0047] This lighting device 1 is installed in a motor vehicle 100 and comprises • a matrix arrangement of LEDs 2, intended to provide a light pattern; • a control element 3 to carry out a thermal control of the func operation of LEDs 2; and • a thermistor 5 intended to measure the temperature in the LEDs 2.

[0048] This matrix configuration is a high-resolution module, having a resolution greater than 2000 pixels. However, there are no restrictions on the technology used for the production of the projection modules.

[0049] A first example of this matrix configuration comprises a monolithic source. This monolithic source comprises a matrix of monolithic light-emitting elements arranged in several columns by several rows. In a monolithic matrix, the light-emitting elements can be grown from a common substrate and are electrically connected to be selectively activated either individually or by a subset of light-emitting elements. The substrate can be primarily made of a semiconductor material. The substrate can comprise one or more other materials, for example, non-semiconductor materials (metals and insulators). Thus, each light-emitting element or group of elements can form a light pixel and can therefore emit light when its material is supplied with electricity.The configuration of such a monolithic matrix allows the arrangement of selectively activatable pixels very close to each other, compared to conventional light-emitting diodes intended to be soldered on printed circuits. The monolithic matrix may comprise light-emitting elements whose main height dimension, measured perpendicular to the common substrate, is substantially equal to one micrometer.

[0050] The monolithic matrix is coupled to the control center in order to control the generation and / or projection of a pixelated light beam by the arrangement of the matrix. The control center is thus capable of individually controlling the light emission of each pixel of the matrix.

[0051] Alternatively to what has been presented above, the matrix arrangement may comprise a main light source coupled to a matrix of mirrors. Thus, the pixelated light source is formed by assembling at least one main light source formed by at least one light-emitting diode emitting light and a set of optoelectronic elements, for example a micro-mirror matrix, also known by the acronym DMD, for "Digital Micro-mirror Device", which directs the light rays from the main light source by reflection towards a projection optical element. If necessary, an auxiliary optical element can collect the rays from at least one light source to focus them and direct them towards the surface of the micro-mirror matrix.

[0052] Each micro-mirror can pivot between two fixed positions, a first position in which the light rays are reflected towards the optical projection element, and a second position in which the light rays are reflected in a different direction from the optical projection element. The two fixed positions are oriented in the same way for all the micro-mirrors and form, with respect to a reference plane supporting the micro-mirror matrix, an angle characteristic of the micro-mirror matrix defined in its specifications. Such an angle is generally less than 20° and may generally be approximately 12°. Thus, each micro-mirror reflecting a portion of the light beams which are incident on the micro-mirror matrix forms an elementary emitter of the pixelated light source.The actuation and control of the change of position of the mirrors to selectively activate this elementary emitter in order to emit or not an elementary light beam are controlled by the control center.

[0053] In various embodiments, the array may comprise a laser scanning system in which a laser light source emits a laser beam towards a scanning element which is configured to scan the surface of a wavelength converter with the laser beam. An image of this surface is captured by the projection optical element.

[0054] The scanning of the scanning element can be carried out at a speed high enough that the human eye does not perceive any movement in the projected image.

[0055] The synchronized control of the ignition of the laser source and the scanning movement of the beam makes it possible to generate a matrix of elementary emitters which can be selectively activated on the surface of the wavelength converter element. The scanning means may be a movable micro-mirror making it possible to scan the surface of the wavelength converter element by reflection of the laser beam. The micromirrors mentioned as scanning means are for example of the MEMS type, for "Micro-Electro-Mechanical Systems". However, the invention is not limited to this type of scanning means and may use other types of scanning means, such as a series of mirrors arranged on a rotating element, the rotation of the element causing scanning of the transmission surface by the laser beam.

[0056] In another variant, the light source may be complex and comprise both at least one segment of light elements, such as light-emitting diodes, and a surface portion of a monolithic light source.

[0057] [Fig.2] shows a graphical diagram that represents the values of the luminous flux produced by the LED when it is powered by a particular electric current and is under a given temperature. In addition, some non-admissibility points 6 have been added to this graph. The points 6 represent combinations of current and temperature that give a color that is not accepted by certain automotive regulations.

[0058] In this graph, a minimum luminous flux threshold value of 4 and a maximum flux threshold value of 7 are also represented.

[0059] In this particular embodiment of the method according to the invention, the operation of the light source is controlled under certain conditions.

[0060] The first is that the luminous flux must be maintained between the minimum threshold value of luminous flux 4 and the maximum threshold value of luminous flux 7.

[0061] The second is that the output color must meet the tolerance condition, i.e. it must not be within the non-authorization points 6 shown in the graph.

[0062] This performance is controlled by the amount of electrical current that is supplied to the LED. Varying the electrical current results in a variation in the luminous flux and a variation in the output color.

[0063] Small variations must therefore be used, in order to provide an accepted performance in terms of color and luminous flux.

[0064] [Fig.3] shows an example of the evolution of the electric current in the LED according to a method in accordance with the invention.

[0065] First, when the temperature in the LED is still low, a first current value 41 is chosen, which is closer to the maximum threshold 7 than to the minimum threshold 4. This current value 41, together with the temperature, provides an output color that is also allowed, far from the non-allowance points 6 shown in the graph.

[0066] Over time, the temperature increases and the initial value of the current 41 provides a luminous flux which, although it remains within the permitted values, is lower than the initial luminous flux. In addition, the output color, which is also acceptable, is closer to the non-permission points 6. Therefore, the current value is increased to a slightly higher value 42, so that the luminous flux is higher than the previous one and the color is further away from the non-permission points.

[0067] However, in some cases, the current value may be decreased instead of increased. This is the case when, to avoid an unauthorized color zone, chooses a high electric current value. Then, when the unauthorized zone disappears, the current can be reduced to a lower value 43 while still meeting the tolerance condition and ensuring a good luminous flux value.

Claims

Claims

1. A method of operating an automotive lighting device (1) comprising at least one solid-state light source (2), the method comprising the following steps: • defining a color tolerance condition (6) for the solid-state light source, in which, for each temperature-electric current pair, a color is defined as acceptable or unacceptable; • establishing a minimum luminous flux threshold value (4) and a maximum luminous flux threshold value (7); • supplying the light source with a current value (41) which produces a luminous flux value between the minimum luminous flux threshold value (4) and the maximum luminous flux threshold value (7); • measuring the temperature of the light source (2); • obtaining the color of the light emitted by the light source (2);• check whether the color obtained from the previous step meets the tolerance condition (6): • increase or decrease the current value, always maintaining the current such that it produces a luminous flux value between the minimum luminous flux threshold value (4) and the maximum flux threshold value (7) and producing a color that meets the tolerance condition (6).;

2. A method according to claim 1, wherein the step of obtaining the color is carried out using a data sheet and / or experimental data, which provides the color from the temperature and the current value.

3. A method according to any preceding claim, wherein the step of measuring the temperature in the light source is performed by a thermistor (5), such as a negative temperature coefficient thermistor.

4. A method according to any preceding claim, wherein the step of increasing the current value involves increasing the current value from a first value (41) to a second value (42), the second value (42) being greater than the first value (41) but less than 1.1 times the first value (41).

5. The method of claim 4, wherein the step of increasing the current value involves increasing the current value from a first value (41) to a second value (42), the second value (42) being less than 1.05 times the first value (41).

6. The method of claim 5, wherein the step of increasing the current value involves increasing the current value from a first value (41) to a second value (42), the second value (42) being less than 1.03 times the first value (41).

7. A method according to any preceding claim, further comprising the step of recording a sequence of current value increments for predetermined conditions.

8. A method according to any preceding claim, wherein the method steps are applied to at least 10% of the light sources of the lighting device.

9. Automotive lighting device (1) comprising: • a matrix arrangement of solid-state light sources (2); • a control element (3) for carrying out the steps of the method according to one of the preceding claims.

10. An automotive lighting device according to claim 9, wherein the matrix arrangement comprises at least 2000 solid-state light sources (2).

11. An automotive lighting device according to one of claims 9 or 10, further comprising a thermistor (5) for measuring the temperature of the semiconductor light sources.

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