Light emitting device for object detection

Abstract

One aspect of the invention relates to a light-emitting device (100) for a motor vehicle, the device comprising: a plurality of light-emitting modules (110) emitting pulsed visible light modulated by means of a high-frequency light code, each light-emitting module (110) comprising at least one driver circuit (120) controlling a plurality of light-emitting diodes (130); and means for receiving light emitted by each of the light emitting modules after reflection from the object (20), in which each light emitting diode (130) is connected to the driver circuit (120) by conductor tracks (141, 142, 143) connecting each of the light emitting diodes to the driver circuit, each of the light emitting diodes comprises conductor tracks of the same length to ensure that the light emitting diodes (130) are synchronously controlled by the driver circuit (120). Another aspect of the invention relates to a driving assistance system for a motor vehicle, comprising at least one such lighting device (100).

Description

Technical Field

[0001] The present invention relates to a lighting device for a motor vehicle suitable for object detection and a driver assistance system for a motor vehicle, the driver assistance system comprising the lighting device. Background Art

[0002] With the development of autonomous vehicles, driving assistance methods have greatly improved in recent years. One of the most useful assistance methods is the assistance method for detecting pedestrians or objects in the vehicle environment.

[0003] Devices for detecting the presence of pedestrians or objects in a vehicle environment (referred to as object detection devices for short) are known. These devices generally use so-called LiDAR (Light Detection and Ranging) technology, which is based on analyzing the characteristics of a light beam (usually a laser beam) emitted by a specific light source and reflected by an object. With LiDAR technology, the distance between the light source and the object is measured based on the time difference between the emission of the laser pulse and the reception of the reflected pulse. Object detection devices using LiDAR are relatively simple to implement, because the light source emits a single high-power infrared signal, which is reflected from the object; when the infrared signal is received by the sensor, the flight time of the signal is measured. However, such object detection devices require specific equipment for emitting the infrared signal and receiving the reflected signal.

[0004] To ensure that detection rates and / or false alarm rates meet standards, supplementary technologies are required. For this purpose, three auxiliary devices based on different technologies are often combined; the data generated by these different auxiliary devices is cross-checked and a final data set is generated to notify the driver, or in the case of autonomous vehicles, the vehicle itself, of the presence of pedestrians or objects in the vehicle's environment. However, adding three different devices to the same area of the vehicle can burden this area, which already has high demands due to its congestion.

[0005] To address the congestion problem, the idea has been to use existing lighting on vehicles (such as the vehicle's daytime running lights) to perform object detection. However, the light source of modern lighting fixtures is typically a group of light-emitting diodes controlled by a driver circuit. The light-emitting diodes (LEDs) in current vehicle lighting fixtures emit visible light continuously, making it difficult to detect after reflection from objects, especially when combined with natural sunlight, light from streetlights, and other outdoor light sources. To facilitate detection of the light emitted by the LEDs and reflected from objects, the idea has been to modulate the light; the light beam emitted by the LED is then pulsed and modulated with a high-frequency code. However, to be effective and therefore detectable, the light beam modulation must be precise; therefore, the LEDs forming the light source must all emit light simultaneously to avoid interference. The current trend is to arrange LEDs in rows, layers, or grids to achieve stylistic effects, which means that some LEDs are far away from the driver circuits that control them. LEDs closer to or further away from the driver circuits result in a time lag in the light emitted by some LEDs compared to others. This lag causes the emission of the signal to spread out over time, which has two consequences. First, this transmission delay carries over to the signal reflected from the object and retransmitted to the vehicle's sensors. This makes it more difficult to determine the time lag between the emission of a light pulse and the reception of the reflected pulse. Second, the spread of the pulses reduces the signal-to-noise ratio. In fact, all else being equal, it's easier to detect the intensity of simultaneous pulses at a sensor than the intensity of multiple emissions spread out over time. Summary of the Invention

[0006] To address the above-mentioned problems of interference and time lags in LED emissions, the applicant provides a lighting device configured for object detection in which all LEDs are connected equidistantly to driver circuits that control them.

[0007] According to a first aspect, the present invention relates to a lighting device for a motor vehicle, the lighting device comprising:

[0008] at least one lighting module that emits pulsed visible light modulated by means of a high-frequency lighting code, each lighting module comprising at least one driver circuit that supplies power to a plurality of light-emitting diodes via a common driver circuit output, the driver circuit being configured to modulate the power received by the light-emitting diodes according to the high-frequency code so as to emit pulsed visible light, and

[0009] - a receiving device for receiving light emitted by the at least one first light emitting module, for receiving a portion of the pulsed light modulated according to the code after the pulsed light emitted by the at least one first light emitting module is reflected from an object outside the vehicle,

[0010] in:

[0011] - the modulation frequency is greater than 10 MHz, and

[0012] - Each light-emitting diode is connected to the same output of the driver circuit via a conductor track, the conductor tracks connecting each of the light-emitting diodes to the driver circuit each having an impedance that ensures that all LEDs have the same phase shift at the modulation frequency, thereby ensuring synchronous modulation of the power perceived by the light-emitting diodes powered by the driver circuit.

[0013] For the transmission of high-frequency signals, the characteristics of the conductor tracks, such as their length, their width, their thickness and the shape of any bends, affect their impedance and, as a result, the phase shift and therefore the delay of the signal perceived by the LEDs connected to the tracks.

[0014] A light-emitting diode (LED) is understood to mean a light source that emits incoherent light and, as is known, is very suitable for use as a light source for signaling or lighting in motor vehicles, in contrast to laser sources (including laser diode sources). Laser sources, which emit temporally and spatially coherent light, have the disadvantage of being a risk to eye safety, which means they must be controlled using complex and expensive means.

[0015] In practice, a device suitable for implementing the DRL / PL function allows the detection function to be implemented using a majority of the LEDs required for the signaling function. "Majority" is understood to mean that more than 50% of the LEDs assigned to that function transmit a code, preferably more than 75%, and preferably all of the LEDs transmit a code. This is particularly relevant when the LEDs are similar in terms of flux emission characteristics and activation current. Since a majority of the LEDs contribute to the signaling function of illuminating an object in front of the motor vehicle, the detection of pulsed light from the LEDs is not interfered with by the detection of non-pulsed light emitted by the same function. This improves the signal-to-noise ratio of the sensor's reception of the illuminated code.

[0016] Alternatively, if the lighting function is implemented by different LEDs, it is advantageous if the LED representing more than 50% of the lighting flux attributable to this function transmits a code, preferably more than 75% of this flux, preferably all of this flux.

[0017] Similarly, it is advantageous to implement lighting functions, such as low beam and high beam, using LEDs whose power supply is modulated at a high frequency to transmit a code. Multiple LEDs are often used to generate low beam and high beam, sometimes within the same lighting module (e.g., a dual-function lighting module). It is then preferred to use at least one driver circuit capable of modulating the power supply to a sector of LEDs grouped together for the low beam function at a high frequency according to the code, and to use a driver circuit capable of modulating the power supply to a second sector of LEDs grouped together for the high beam function at a high frequency according to the same code, in synchronization with the power supply to the sector of LEDs. In another example, the high beam function and / or the low beam function include LEDs that can be individually activated and deactivated, for example, to emit a partial high beam (where some lighting zones are activated or deactivated), or alternatively or additionally, to emit a low beam, where some LEDs corresponding to a cutoff line are activated or deactivated so that the center of the cutoff line is shifted horizontally relative to the vehicle when the lighting device is installed on the vehicle, thereby implementing a directional low beam function known as DBL (Dynamic Bending Light). Since most LEDs emit pulsed light modulated according to the code, the detection of pulsed light from the LED is not interfered with by the detection of non-pulsed light emitted by the same function. This improves the signal-to-noise ratio of the sensor receiving the illuminated code.

[0018] In case of connections with the same impedance between the driver circuit and all the light emitting diodes it controls, the light modules of this light emitting device are able to emit synchronized light beams without risk of interference.The light emitting device according to the invention is therefore suitable for object detection.

[0019] In addition to the features just outlined in the previous paragraph, the lighting device according to one aspect of the present invention may also have one or more additional features from the following, implemented individually or in any technically feasible combination:

[0020] the impedance of these conductor tracks is such that the driver circuit and the light-emitting diode furthest from said driver circuit perceive the modulation of the electric power with the same delay, the conductor tracks of the light-emitting diode closest to the driver circuit forming a delay line;

[0021] The length of these conductor tracks is equal to the length of the track between the driver and the light-emitting diode farthest from said driver;

[0022] Conductor tracks, light-emitting diodes and driver circuits are mounted on the same substrate;

[0023] The substrate is a rigid PCB substrate, such as a rigid FR4 substrate; a flexible PCB substrate, such as a flexible polyimide-containing substrate; or an IMS (IMS stands for Insulated Metal Substrate, comprising a metal base on which an insulator and at least one conductive layer capable of forming a track are laminated), such as an IMS whose base is made of aluminum;

[0024] The receiving device comprises at least one light sensor and a blue light optical filter, the filter preferably being configured to pass only a wavelength band corresponding to the main wavelength band of the emission spectrum of the LEDs and to exclude wavelengths that are weakly emitted or not emitted by the LEDs, for example wavelengths that are emitted by the LEDs at an intensity less than 50% of their maximum emission intensity;

[0025] The receiving device comprises a calculation unit for comparing the modulation of the received portion of the pulsed light with the modulation of the emitted pulsed light, in particular by correlation, and thereby determining the time of flight of the modulated pulsed light wave from the light-emitting module to the object, in order to provide a measured value for the distance between the object and the light-emitting device.

[0026] A second aspect of the invention relates to a driver assistance system for a motor vehicle, characterized in that the driver assistance system comprises at least one first lighting device and one second lighting device according to the first aspect, which are combined with one another for detecting the same object.

[0027] A third aspect of the present invention relates to a driving assistance system for a motor vehicle, characterized in that the driving assistance system includes at least one first device for detecting objects in the environment of the motor vehicle, and the light-emitting device according to the first aspect constitutes a second object detection device, which provides redundancy for the first object detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other advantages and features of the present invention will become clear from a reading of the following description illustrated by the accompanying drawings, in which:

[0029] [ Figure 1 ] schematically shows an example of a vehicle equipped with a lighting device according to the present invention;

[0030] [ Figure 2 ] schematically illustrates an example of a modulated light pulse emitted by a light emitting device according to the present invention; and

[0031] [ Figure 3 ] schematically shows an example of three LEDs connected to a driver circuit according to the present invention.

[0032] In the drawings, the same reference numerals have been used to identify the same elements. For the sake of readability of the drawings, the elements in the drawings are not shown to scale. DETAILED DESCRIPTION

[0033] An exemplary embodiment of a light emitting device according to the present invention is described in detail below with reference to the accompanying drawings. This example illustrates the features and advantages of the present invention. However, it will be recalled that the present invention is not limited to this example.

[0034] [ Figure 1 ] shows an example of a motor vehicle 10 equipped with two lighting devices 100 according to the present invention. This example shows a pedestrian 20 crossing in front of vehicle 10. Vehicle 10 is equipped with two lighting devices 100, such as daytime running lights, which illuminate a road scene SR in front of the vehicle. Lighting devices 100 are integrated into a driver assistance system that can detect pedestrian 20.

[0035] The lighting device 100 according to the present invention can be any basic lighting device present on a vehicle. For example, the lighting device 100 can be a daytime running light, a position light, a signal light, a side light strip, a headlight grille, or any other external lighting device typically integrated into a vehicle to allow visibility on the road. The lighting device can then be used to detect pedestrians or objects on the road scene or in the vehicle's external environment. The lighting device can also be a lighting device inside the vehicle; the lighting device can then be used to detect objects or people inside the vehicle.

[0036] The light emitting device 100 is used to emit pulsed light modulated by a high-frequency light emitting code. The light emitting code is a binary cyclic code consisting of a series of 1s and 0s, where 1 corresponds to a pulse and 0 corresponds to no light emission. The light beam emitted by the LED included in the light emitting device is modulated to transmit the light emitting code. Therefore, the LED emits a series of light pulses with a duration of about 10ns to 20ns, which corresponds to high-frequency modulation of the power supply to the LED at 10MHz to 400MHz, preferably 30MHz to 200MHz, and preferably 50MHz to 100MHz. In [ Figure 2 An example of code 2001 is shown in Section A of [ Figure 2 An example of a light pulse 2002 with a period T0 corresponding to this code is shown in Part B of FIG. It should be noted that by emitting a light beam modulated by the high frequency of the code, the human eye cannot perceive this modulation. To the human eye, the light beam appears continuous, and the illuminated code is invisible. Therefore, the illuminated code emitted via the modulated light beam can be used for object detection.

[0037] As explained above and as [ Figure 3] As shown schematically, the lighting device 100 includes a plurality of lighting modules 110, each of which includes a driver circuit 120 and a plurality of white light LEDs 130. The LEDs 130 of a given module are connected to the same driver circuit 120. The driver circuit 120 (also called a driver) is a device for supplying a DC current to the connected LEDs. Thus, the driver circuit 120 controls the plurality of LEDs 130. Figure 3 ], three in the example.

[0038] exist[ Figure 3 ], the three LEDs 131, 132, 133 connected to the driver circuit 120 are positioned at different distances from the driver circuit 120. In order to precisely modulate the light beam emitted by the light emitting module 110, the three LEDs 131, 132, 133 of the light emitting module 110 must emit light beams simultaneously. For this purpose, each of the three LEDs 131, 132, 133 is connected to the driver circuit 120 via a conductor track 141, 142, 143, respectively; these conductor tracks 141, 142, 143 all have the same length. The length of the conductor track is determined according to the LED farthest from the driver circuit. In fact, the length of all conductor tracks 141, 142, 143 is equal to the length used to connect the driver circuit 120 to the LED farthest from the driver circuit (i.e. [ Figure 3 ] example). Thus, the conductor track 143 connecting LED 133 to driver circuit 120 is a conventional conductor track. The conductor tracks 141 and 142 connecting driver circuit 120 to LEDs 131 and 132 (these LEDs are the LEDs closest to the driver circuit) form a delay line. All LEDs of the same lighting module are thus connected equidistantly to the driver circuit that supplies them.

[0039] The distance between the driver circuit and the LED is the physical distance, defined as the "point-to-point" distance between the driver circuit's control output and the LED's input terminal. Therefore, the concept of "furthest (farthest away)" should be understood in terms of physical distance: the LED farthest from the driver circuit is the LED with the greatest distance from the driver circuit compared to the distances of the other LEDs. Similarly, the concept of "closest" should be understood in terms of physical distance: the LED closest to the driver circuit is the LED with the shortest distance from the driver circuit compared to the distances of the other LEDs.

[0040] Therefore, in the lighting device according to the present invention, the physical distance between the driver circuit 120 and the LEDs 130 it controls can vary, while the connection distance between the driver circuit 120 and the LEDs 130 remains the same.

[0041] In other words, because all conductor tracks have the same length, the conductor tracks 141, 142 closest to the LEDs of the driver circuit include loops and / or detours that enable the creation of delay lines. Consequently, when the driver circuit 120 issues a light emission command, the control signal sent by the driver circuit 120 is received simultaneously by all LEDs connected to the driver circuit. Consequently, the LEDs emit their light simultaneously and in a synchronized manner. Consequently, the light beams emitted by the lighting module 110 are synchronized, thereby ensuring an efficiently modulated light beam, where all the light beams of the module's LEDs emit the same bit of the code simultaneously.

[0042] The LEDs, driver circuits and conductor tracks are formed on a substrate. Whether they are conventional or forming delay lines, the conductor tracks are produced on the substrate in the same way as any other conductor tracks, except that the length of the tracks may vary.

[0043] In some lighting devices 100, a single substrate carries all the LEDs and driver circuits of a given module. In other words, all the LEDs and driver circuits are produced on the same substrate, such as a flexible or rigid PCB (PCB is the acronym for printed circuit board) substrate or IMS (IMS is the acronym for insulated metal substrate). The conductor tracks 141 to 143 are thus formed in the same substrate. In other lighting devices 100, the lighting module 110 can be formed on at least two substrates connected to each other by connectors (e.g., pin-, tab-, or jaw-based connectors). In this case, all or only some of the conductor tracks 141, 142, 143 can extend over both substrates; the length of the conductor tracks can be determined taking into account the delay caused by the connection between the two substrates.

[0044] The lighting module 110, as just described, makes it possible to emit a modulated light beam synchronously. To enable object detection, the lighting module is associated with a receiving device for receiving a light beam reflected by an object (not visible in the figure). This receiving device is integrated into the lighting device 100 of the invention. This makes it possible to receive the light beam after it has been reflected by the object to be detected. The receiving device comprises a light sensor or a group of light sensors; these one or more sensors may, for example, be a photon counter.

[0045] , preferably avalanche diodes. The photon counters are preferably distributed on the same high-density substrate, preferably to form a detection matrix. The sensors are preferably associated with a blue light optical filter, i.e., a bandpass filter designed to capture only light with blue wavelengths and suppress all other wavelengths. In practice, a white light LED suitable for signaling comprises a light-emitting chip that emits blue light and to which a phosphor is applied that is suitable for converting a portion of the blue light into yellow light. The mixture of the unconverted blue light emitted by the chip and the yellow light converted by the phosphor produces white light. Similarly, an amber light LED suitable for signaling comprises a chip that emits blue light and to which a suitable phosphor is applied. The blue light optical filter allows the blue light emitted by the light-emitting module 110 and reflected by the object 20, corresponding to the majority of the light beam, in particular the emission line of the light-emitting chip, to be separated from the remaining spectrum from the sun or any other external light source emitting light in the visible range in the vehicle environment. This significantly improves the signal-to-noise ratio of the detection.

[0046] The receiving device is connected to a computing unit installed in the lighting device or housed in any other location in the vehicle, preferably directly on the sensor, which determines the time of flight of the light beam and derives from this a measurement of the distance between the vehicle and the detected object. The time of flight is the propagation time of the wave of the light beam emitted by the lighting module 110 in the environment, that is, the time required for the light beam to propagate to the object and return to the receiving device. The distance between the object and the vehicle is determined based on this time of flight. It will be appreciated that the synchronous emission of the light beams by the lighting module 110 makes it possible to improve the determination of the time of flight. It will also be appreciated that the "object detection" function can be implemented by the lighting device 100 in parallel with its standard lighting function.

[0047] The lighting device 100 as has just been described can be used alone for object detection, in particular if the lighting device is a lighting device for the interior of a vehicle.

[0048] The lighting device 100 can also be used in combination with another similar lighting device. Two lighting devices 100 (for example, two front lighting devices of a vehicle) can be combined with each other to detect the same object.

[0049] The lighting device 100 can also be integrated into a driver assistance system for a motor vehicle. In practice, a driver assistance system often requires a combination of two or even three different object detection devices, i.e., they operate using different technologies. These object detection devices should be complementary. The lighting device according to the invention can constitute one of these object detection devices. It has the advantage of using a specific technology that has not yet been used, since it performs object detection by means of a light beam in the visible light range. It has the additional advantage of not adding mass and congestion, since it uses lighting devices already present on the vehicle. It also has the advantage of being able to be implemented on multiple lighting devices of the same vehicle (for the purpose of detecting objects in the same area or in different areas of the vehicle) without the risk of interference, simply by selecting a different lighting code for each lighting device used.

[0050] Although described by way of a number of examples, variations, and embodiments, the lighting device according to the present invention includes various variations, modifications, and improvements that will be apparent to those skilled in the art, and it should be understood that these variations, modifications, and improvements form part of the scope of the present invention. For example, upon reading this application, a person skilled in the art will understand that its principles can be readily applied to other lighting devices on the exterior of a motor vehicle, such as rear signal lamps on a motor vehicle.

Claims

1. A lighting device (100) for a motor vehicle, the lighting device comprising: - at least one light emitting module (110), said at least one light emitting module emitting pulsed visible light modulated by means of a high-frequency light emitting code, each light emitting module (110) comprising at least one driver circuit (120), said at least one driver circuit supplying power to a plurality of light emitting diodes (130) via a same driver circuit output terminal, said driver circuit being configured to modulate power received by said light emitting diodes according to said high-frequency code so as to emit said pulsed visible light, and - a receiving device for receiving light emitted by the at least one first light emitting module (110), for receiving a portion of the pulsed light modulated according to the code after the pulsed light emitted by the at least one first light emitting module is reflected from an object (20) outside the vehicle, wherein: - the modulation frequency is greater than 10 MHz, and - Each light-emitting diode (130) is connected to the same output of the driver circuit (120) via conductor tracks (141, 142, 143), the conductor tracks connecting each of the light-emitting diodes to the driver circuit each having an impedance that ensures that all LEDs have the same phase shift at the modulation frequency, thereby ensuring synchronous modulation of the power perceived by the light-emitting diodes (130) powered by the driver circuit (120).

2. The light emitting device according to claim 1, wherein The impedance of the conductor tracks (141, 142, 143) is such that the driver circuit (120) and the light emitting diode (133) farthest from the driver circuit perceive the modulation of the electric power with the same delay, the conductor tracks (141, 142) of the light emitting diode (131, 132) closest to the driver circuit (120) forming a delay line.

3. Lighting device according to the preceding claim, characterized in that The length of the conductor tracks (141, 142, 143) is equal to the length of the tracks between the driver (120) and the light-emitting diode (133) farthest from the driver.

4. The light emitting device according to any one of claims 1 and 2, characterized in that The conductor tracks (141, 142, 143), the light emitting diode (130) and the driver circuit (120) are mounted on a same substrate.

5. A lighting device according to any one of the preceding claims, characterized in that The substrate is a rigid PCB substrate, a flexible PCB substrate or an IMS.

6. A lighting device according to any one of the preceding claims, characterized in that The receiving device includes a calculation unit, which is used to compare the modulation of the received part of the pulsed light with the modulation of the emitted pulsed light, in particular by correlation, and thereby determine the flight time of the modulated pulsed light wave from the light-emitting module to the object, so as to provide a measurement value of the distance between the object and the light-emitting device.

7. A lighting device according to any one of the preceding claims, characterized in that The receiving device includes at least one light sensor and a blue light optical filter. A driving assistance system for a motor vehicle, characterized in that: The driver assistance system comprises at least one first lighting device as claimed in any one of the preceding claims and one second lighting device (100), the first lighting device and the second lighting device being combined with one another for detecting the same object (20).

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