Light device for object detection

Abstract

One aspect of the invention relates to a light device (100) for a motor vehicle, the device comprising: • a plurality of light modules (110) that emit pulsed visible light, which is modulated by means of a high-frequency light code, each light module (110) comprising at least one driver circuit (120) controlling multiple light-emitting diodes (130); and • a device for receiving the light emitted by each of the light modules once the light has been reflected off an object (20), wherein each light-emitting diode (130) is connected to the driver circuit (120) by a conductive track (141, 142, 143), the conductive tracks connecting each of the light-emitting diodes to the driver circuit, each one of which light-emitting diodes comprises the same length of conductive track to ensure synchronous control of the light-emitting diodes (130) by the driver circuit (120). Another aspect of the invention relates to a driver assistance system for a motor vehicle, the system comprising at least one such light device (100).

Description

Description Title of the invention: Luminous device for object detection TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a light device for a motor vehicle, suitable for object detection. The invention also relates to a driving assistance system for a motor vehicle comprising this light device. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] With the development of autonomous vehicles, driver assistance systems have improved significantly in recent years. One of the most useful types of assistance is assistance in detecting pedestrians or objects in the vehicle's surroundings.

[0003] Devices for detecting the presence of pedestrians or objects in the vehicle's environment, simply called object detection devices, are known. These devices generally use Lidar (Light Detection And Ranging) technology, which is based on analyzing the properties of a light beam, usually a laser beam, emitted by a specific light source and reflected by the object. With Lidar technology, the distance between the light source and the object is measured from the time lag between the emission of a laser pulse and the reception of the reflected pulse. An object detection device using Lidar is relatively simple to implement because the light source emits a single, high-power infrared signal that bounces off the object; the time of flight of the infrared signal is measured upon receipt of said signal by a sensor.Such an object detection device, however, requires specific equipment to emit the infrared signal and to receive the bounced signal.

[0004] To ensure a detection rate and / or false positives that comply with the standard, a complementarity of technologies is necessary. For this, three assistance devices based on different technologies are generally combined with each other; the data generated by these different assistance devices are cross-referenced and final data is generated to inform the driver, or the vehicle itself in the case of an autonomous vehicle, of the presence of a pedestrian or an object in the vehicle's environment. However, the addition of three separate devices in the same area of ​​the vehicle has the effect of loading an area that is already heavily used in terms of congestion.

[0005] To address the space requirements, it has been considered to achieve object detection using the lighting already present on the vehicle, such as the vehicle's daytime running lights. However, the light source of current lighting devices is generally a set of light-emitting diodes, controlled from of a driver circuit. However, light-emitting diodes, or LEDs (for "Light-Emitting Diode" in English terminology), vehicle lighting devices emit continuous visible light, which makes it difficult to detect after reflection on the object, particularly because it is combined with natural light from the sun, streetlights and other external light sources. To facilitate the detection of the light emitted by the LEDs and reflected by the object, it has been considered to modulate the light; the light beam emitted by the LEDs is then pulsed and modulated by a high-frequency code. However, to be effective, and therefore detectable, the modulation of the light beam must be precise; the LEDs forming the light source must therefore all emit their light beam simultaneously to avoid interference.However, the current trend is to deploy LEDs in lines, in sheets or in grids, for stylistic effects, which has the consequence of distancing some of them from the driver circuit that controls them; the fact that the LEDs are more or less distant from the driver circuit causes a time shift in the emission of the light beam of some LEDs compared to the others. Said shift causes a spreading of the signal emissions over time, which has two consequences. Firstly, this emission shift is carried over to the signal that has been reflected on an object, and which is re-emitted to a sensor present on the vehicle. Therefore, it is more difficult to determine the time shift between the emission of a light pulse and the reception of the reflected pulse. Second, pulse spreading degrades the signal-to-noise ratio. All other things being equal, the intensity of a simultaneous pulse is more easily detected at the sensor than the intensity of a plurality of emissions spread out over time. Summary of the invention

[0006] To address the above-mentioned problems of interference and time lag in emission by the LEDs, the applicant proposes a lighting device suitable for object detection, in which all the LEDs are connected equidistant from the driver circuit which controls them.

[0007] According to a first aspect, the invention relates to a lighting device for a motor vehicle comprising: - at least one light module emitting pulsed visible light, modulated by means of a high-frequency light code, each light module comprising at least one driver circuit supplying electricity via the same driver circuit output to several light-emitting diodes, said driver circuit being configured to modulate according to the high-frequency code an electrical power received by the light-emitting diodes in order to to emit pulsed visible light, and - a device for receiving the light emitted by the at least one first light module, for receiving a portion of the pulsed light, modulated according to the code, after reflection of the pulsed light emitted by the at least one first light module on an object outside the vehicle, in which: - the modulation frequency is greater than 10MHz, and - each light-emitting diode is connected to the same output of the driver circuit by a conductive track, the conductive tracks connecting each of the light-emitting diodes to the driver circuit each comprising an impedance ensuring the same phase shift at the modulation frequency for all the LEDs, thus ensuring synchronous modulation of the electrical power perceived by the light-emitting diodes powered by the driver circuit.

[0008] For the transmission of high-frequency signals, the characteristics of the conductive tracks, such as their length, width, thickness and the shapes of any turns, influence their impedance and consequently the phase shift and therefore the delay of the signal perceived by an LED connected to the track.

[0009] Light-emitting diodes (or LEDs) are electroluminescent sources emitting incoherent light, such as are known to be well-suited for use in luminous signaling or lighting devices for motor vehicles, as opposed to laser sources (including laser diode types). Indeed, laser sources emit temporally and spatially coherent light, and have the disadvantage of posing risks to eye safety, which must be controlled by complex and costly means.

[0010] A device suitable for performing a DRL / PL function in fact makes it possible to perform a detection function using a large part of the LEDs required for the signaling function. A large part is understood to mean that more than 50% of the LEDs assigned to the function transmit the code, preferably more than 75%, preferably all of the LEDs transmit the code. This is particularly relevant when the LEDs are similar in terms of flux emission characteristics and activation current. In this way, to the extent that the large part of the LEDs participate in the signaling function illuminating objects located in front of the motor vehicle, the detection of the pulsed light of the LEDs is not disturbed by the detection of non-pulsed light emitted by the same function. A signal-to-noise ratio of the reception of the light code by the sensor is improved.

[0011] Alternatively, if the light function is performed by dissimilar LEDs, it is advantageous for LEDs representing more than 50% of the luminous flux attributed to the function transmit the code, preferably more than 75% of this stream, preferably all of this stream.

[0012] In the same way, it is advantageous to realize the lighting functions such as the dipped beam and the main beam with light-emitting diodes whose power supply is modulated at high frequency to transmit the code. Several light-emitting diodes are usually used for the realization of the dipped beam and the main beam, sometimes within the same light module, for example a dual-function light module. It is then preferred to use at least one driver circuit capable of modulating at high frequency the power supply of the LEDs of a sector grouping together first LEDs necessary for the dipped beam function, according to the code, and a driver circuit capable of modulating at high frequency the power supply of the second LEDs of a sector grouping together LEDs necessary for the main beam function, according to the same code, in a manner synchronized with the power supply of the sector of the first LEDs.In another example, the high beam function and / or the low beam function comprise individually activatable and deactivatable LEDs, for example to emit a partial high beam in which lighting zones are activated or deactivated, or, alternatively or cumulatively, a low beam in which LEDs corresponding to a light cut-off are activated or deactivated so as to move a central zone of a cut-off zone horizontally relative to the vehicle when the lighting device is mounted on the vehicle, and thus to achieve a directional low beam function, known as DBL (from the English abbreviation Dynamic Bending Light). In this way, since the majority of the LEDs emit pulsed light modulated according to the code, the detection of the pulsed light of the LEDs is not disturbed by the detection of non-pulsed light emitted by the same function.This improves the signal-to-noise ratio of the light code reception by the sensor.

[0013] With a connection of the same impedance between the driver circuit and all the light-emitting diodes it controls, the light module of this lighting device is capable of sending a synchronous light beam, without risk of interference. The lighting device according to the invention is thus suitable for object detection.

[0014] In addition to the characteristics which have just been mentioned in the preceding paragraph, the light device according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: • the impedance of the conductive tracks is such that the driver circuit and the light-emitting diode furthest from said driver circuit perceive the mo- dulation of the electrical power with the same delay, the conductive tracks of the light-emitting diodes closest to the driver circuit forming delay lines. • the length of the conductive tracks is equal to the track length between the driver and the light-emitting diode furthest from said driver, • the conductive tracks, the light-emitting diodes and the driver circuit are mounted on the same substrate. • the substrate is a rigid PCB substrate, for example a rigid FR4 type substrate, a flexible PCB substrate, for example a flexible substrate comprising polyimides, or an IMS (Insulated Metal Substrate, also known to those skilled in the art by the English abbreviation IMS, comprising a metal base on which an insulator and at least one conductive layer capable of forming tracks are laminated), for example an IMS whose base is made of aluminum. • the receiving device comprises at least one light sensor and a blue light optical filter, the filter preferably being configured to allow only a wavelength band corresponding to a main band of the emission spectrum of the LEDs to pass, and to exclude wavelengths on which the LEDs emit weakly or do not emit, for example where the LEDs emit at less than 50% of the intensity emitted at their maximum. • the receiving device comprises a calculation unit for comparing, in particular by correlation, the modulation of the part of the pulsed light received with the modulation of the pulsed light emitted; and thus for determining a time of flight of modulated pulsed light waves from the light module to the object so as to provide a measurement of the distance between the object and the light device.

[0015] A second aspect of the invention relates to a driving assistance system for a motor vehicle, characterized in that it comprises at least a first and a second light device according to the first aspect, combined with each other for the detection of the same object.

[0016] A third aspect of the invention relates to a driving assistance system for a motor vehicle, characterized in that it comprises at least a first device for detecting an object in the environment of the motor vehicle, the light device according to the first aspect constituting a second object detection device providing redundancy to the first object detection device. BRIEF DESCRIPTION OF THE FIGURES

[0017] Other advantages and characteristics of the invention will appear on reading the description which follows, illustrated by the figures in which:

[0018] [Fig.l] schematically represents an example of a vehicle equipped with lighting devices according to the invention;

[0019] [Fig.2] schematically represents an example of modulated light pulses, emitted by a light device according to the invention; and

[0020] [Fig.3] schematically represents an example of three LEDs connected to a driver circuit in accordance with the invention.

[0021] In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between the elements represented are not respected. DETAILED DESCRIPTION

[0022] An exemplary embodiment of a light device according to the invention is described in detail below, with reference to the accompanying drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

[0023] An example of a motor vehicle 10 equipped with two lighting devices 100 according to the invention is shown in [Fig. 1]. This example shows a pedestrian 20 crossing in front of the vehicle 10. The vehicle 10 is equipped with two lighting devices 100, for example daytime running lights, which illuminate the road scene SR in front of the vehicle. The lighting devices 100 are integrated into a driver assistance system by which the pedestrian 20 can be detected.

[0024] The lighting device 100 according to the invention can be any basic lighting device present on a vehicle. The lighting device 100 can, for example, be a daytime running light, a position light, a signal light, a side light strip, a front light grille or any other exterior lighting means usually integrated on a vehicle to allow its visibility on the road; the lighting device is then used for pedestrian or object detection on the road scene or in the environment outside the vehicle. The lighting device can also be an internal lighting device in the vehicle; it can then be used for object or person detection inside the vehicle.

[0025] The light device 100 is used to emit pulsed light, modulated by a high-frequency light code. This light code is a binary cyclic code composed of a succession of 1s and 0s, the 1s corresponding to a pulse, the 0s to a non-emission of light. The light beam emitted by the LEDs contained in the light device is modulated to transmit the light code. The LEDs thus emit a succession of light pulses with a duration of approximately 10 to 20 ns, which corresponds to a high modulation frequency of the power supply. LEDs from 10 MHz to 400 MHz, preferably 30 MHz to 200 MHz, preferably 50 to 100 MHz. An example of a 2001 code is shown in part A of [Fig.2] and an example of 2002 light pulses according to a period T ocorresponding to this code is shown in part B of [Fig.2]. It should be noted that by emitting a light beam modulated by this code at high frequency, the human eye does not perceive this modulation. For the human eye, the light beam is continuous and the light code is invisible. The light code emitted via the modulation of the light beam can therefore be used for object detection

[0026] As explained previously, and as shown schematically in [Fig. 3], a lighting device 100 comprises several lighting modules 110 which each comprise a driver circuit 120 and several white EEDs 130. The EEDs 130 of the same module are connected to the same driver circuit 120. A driver circuit 120, also called a driver, is a piece of equipment enabling the direct current supply of the EEDs to which it is connected. Thus a driver circuit 120 controls several LEDs 130, three in the example of [Fig. 3].

[0027] In the example of [Fig. 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 for the light beam emitted by the light module 110 to be modulated precisely, the three LEDs 131, 132, 133 of the light module 110 must emit their light beam simultaneously. For this, each of the three LEDs 131, 132, 133 is connected to the driver circuit 120 by a conductive track, respectively 141, 142, 143; these conductive tracks 141, 142, 143 are all of the same length. The length of the conductive tracks is determined according to the LED furthest from the driver circuit. Indeed, all the conductive tracks 141, 142, 143 have a length equal to the length of the conductive track 143 making it possible to connect the driver circuit 120 to the LED furthest from said driver circuit, namely the LED 133 in the example of [Fig.3].The conductive track 143 connecting the LED 133 to the driver circuit 120 is therefore a conventional conductive track. The conductive tracks 141 and 142 which connect the driver circuit 120 to the LEDs 131 and 132, which are the LEDs closest to the driver circuit, form delay lines. All the LEDs of the same light module are thus connected equidistant from the driver circuit which powers them.

[0028] The distance between the driver circuit and an LED is a physical distance, that is, a "point-to-point" length determined between the driver circuit's control output and the LED's input terminal. The notion of "furthest" must therefore be understood in terms of physical distance, the LED furthest from the driver circuit being the LED whose distance from the driver circuit is the greatest compared to the distances of the other LEDs from the driver circuit. Similarly, the notion of "furthest" "close" should be understood in terms of physical distance, with the LED closest to the driver being the LED whose distance to the driver is the shortest compared to the distances of the other LEDs to the driver.

[0029] Thus, in a lighting device according to the invention, the physical distance between a driver circuit 120 and the LEDs 130 that it controls can vary, while the connection distance between this driver circuit 120 and these LEDs 130 is identical.

[0030] In other words, since all the conductive tracks are of the same length, the conductive tracks 141, 142 of the LEDs closest to the driver circuit include loops and / or detours for generating the delay lines. Thus, when the driver circuit 120 issues a light beam emission command, the control signal emitted by the driver circuit 120 is received simultaneously by all the LEDs connected to the driver circuit. The LEDs therefore emit their light beam at the same time, in a synchronized manner. The light beam emitted by the light module 110 is therefore synchronous, which ensures efficient modulation of the light beam with all the light rays of the LEDs of the module simultaneously emitting the same bit of the code.

[0031] The LEDs, driver circuit, and conductive traces are formed on a substrate. Whether conventional or forming a delay line, the conductive traces are made on the substrate in the same way as any other conductive trace, with only the trace length varying.

[0032] In some lighting devices 100, a single substrate supports all the LEDs and the driver circuit of a single module. In other words, all the LEDs and the driver circuit are produced on the same substrate, for example a flexible or rigid PCB (Printed Circuit Board) type substrate or an IMS (Insulated Metallized Substrate) substrate. The conductive tracks 141-143 are therefore formed in this same substrate. In other lighting devices 100, a lighting module 110 may be formed on at least two substrates connected to each other by connectors, for example pin, blade or jaw connectors. In this case, all or only some of the conductive tracks 141, 142, 143 may extend over both substrates; the length of the conductive tracks may be determined by taking into account the delay induced by the connection between the two substrates.

[0033] The light module 110 as just described allows the emission of a synchronously modulated light beam. To allow object detection, this light module is associated with a device for receiving the light beam reflected by the object (not visible in the figures). This receiving device is integrated into the light device 100 of the invention. It allows the light beams to be received after they have been reflected by the object that one seeks to detect. This receiving device comprises a sensor or a set of sensors light; this / these sensors can be, for example, photon counters

[0034] , preferably avalanche diodes. The photon counters are preferably distributed on a single high-density substrate, preferably so as to form a detection matrix. The sensor is preferably associated with a blue light optical filter, i.e. a bandpass filter adapted to capture only blue wavelength light and suppress all other wavelengths. Indeed, white LEDs suitable for signaling comprise an electroluminescent chip emitting blue light and on which is applied a phosphor adapted to transform part of the blue light into yellow light, the mixture of untransformed blue light emitted by the chip and yellow light transformed by the phosphor resulting in white light. In the same way, amber LEDs suitable for signaling comprise a chip emitting blue light on which is applied a suitable phosphor.The blue light optical filter makes it possible to separate the blue light corresponding to the majority of the light beam, in particular corresponding to the emission line of the electroluminescent chip, sent by the light module 110 and reflected by the object 20 from the rest of the spectrum of the light coming from the sun or from any other external light sources emitting, in the environment of the vehicle, light in the visible range. In this way, the signal-to-noise ratio of the detection is greatly improved.

[0035] This receiving device is connected to a computing unit, mounted in the lighting device or housed in any other location of the vehicle, preferably directly mounted on the sensor, which determines the flight time of the light beam and deduces therefrom a measurement of the distance between the vehicle and the detected object. The flight time is the propagation time of the waves of the light beam emitted by the lighting module 110, in the environment, that is to say the time necessary 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 from this flight time. It is then understood that the fact that the light beam is emitted by the lighting module 110 in a synchronous manner makes it possible to improve the determination of the flight time. It is also understood that the “object detection” function can be implemented by the lighting device 100 in parallel with its standard lighting function.

[0036] The light device 100 as just described can be used alone for object detection, in particular if the light device is an interior lighting device for the vehicle.

[0037] The light device 100 can also be used in combination with another similar light device. The two light devices 100, for example the two front lighting devices of the vehicle, can be combined with each other for the detection of the same object.

[0038] The lighting device 100 can also be integrated into a driving assistance system of a motor vehicle. Indeed, driving assistance systems generally require the combination of two or even three separate object detection devices, i.e. operating according to different technologies. These object detection devices must 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 not yet used since it ensures object detection by means of a light beam in the visible range. It has the additional advantage of not adding mass and bulk since it uses a lighting device already present on the vehicle.It also has the advantage of being able to be implemented on several lighting devices of the same vehicle (for object detection in the same area of ​​the vehicle or in different areas) without risk of interference, simply by choosing a different light code for each of the lighting devices used.

[0039] Although described through a number of examples, variants and embodiments, the lighting device according to the invention includes various variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention. For example, upon reading the present application, those skilled in the art will understand that it is easy to apply the principles thereof to other lighting devices on the exterior of the motor vehicle, for example rear signaling lights of the motor vehicle.

Claims

Claims

1. Luminous device (100) for a motor vehicle comprising: - at least one light module (110) emitting pulsed visible light, modulated by means of a high-frequency light code, each light module (110) comprising at least one driver circuit (120) supplying electricity via the same driver circuit output to several light-emitting diodes (130), said driver circuit being configured to modulate according to the high-frequency code an electrical power received by the light-emitting diodes in order to emit the pulsed visible light, and - a device for receiving the light emitted by the at least one first light module (110), for receiving a portion of the pulsed light, modulated according to the code, after reflection of the pulsed light emitted by the at least one first light module on an object outside the vehicle (20), in which: - the modulation frequency is greater than 10MHz, and - each light-emitting diode (130) is connected to the same output of the driver circuit (120) by a conductive track (141, 142, 143), the conductive tracks connecting each of the light-emitting diodes to the driver circuit each comprising an impedance ensuring the same phase shift at the modulation frequency for all the LEDs, thus ensuring synchronous modulation of the electrical power perceived by the light-emitting diodes (130) powered by the driver circuit (120).

2. A lighting device according to claim 1, characterized in that the impedance of the conductive tracks (141, 142, 143) is such that the driver circuit (120) and the light-emitting diode (133) furthest from said driver circuit perceive the modulation of the electrical power with the same delay, the conductive tracks (141, 142) of the light-emitting diodes (131, 132) furthest from the driver circuit (120) forming delay lines.

3. Luminous device according to the preceding claim, characterized in that the length of the conductive tracks (141, 142, 143) is equal to the track length between the driver (120) and the light-emitting diode (133) furthest from said driver.

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

5. A light device according to any preceding claim, characterized in that the substrate is a rigid PCB substrate, a flexible PCB substrate or an IMS substrate.

6. A light device according to any one of the preceding claims, characterized in that the receiving device comprises a calculation unit for comparing, in particular by correlation, the modulation of the part of the pulsed light received with the modulation of the pulsed light emitted; and thus for determining a time of flight of modulated pulsed light waves from the light module to the object so as to provide a measurement of the distance between the object and the light device.

7. Luminous device according to any one of the preceding claims, characterized in that the receiving device comprises at least one light sensor and a blue light optical filter. Driving assistance system for a motor vehicle, characterized in that it comprises at least one first and one second luminous device (100) according to any one of the preceding claims, combined with each other for the detection of the same object (20).

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