Image generation device and head-up display incorporating such a device

Abstract

The invention relates to an image generation device (5) comprising a first light source (12) configured to generate a first upstream light beam, a second light source (13) configured to generate a second upstream light beam, and a variable transmittance element array (16) configured to selectively receive and transmit the first upstream light beam and to selectively receive and transmit the second upstream light beam so as to form respectively a first downstream light beam forming a first image and a second downstream light beam forming a second image. The invention further relates to a head-up display comprising such a device. Figure for the abstract: Fig. 2

Description

Title of the invention: Image generation device and head-up display comprising such a device technical field

[0001] The present invention relates to the technical field of display systems, in particular the technical field of image projection systems.

[0002] The invention relates particularly to an image generation device, especially adapted for use in a head-up display of a motor vehicle. Technological background

[0003] In the above field, a head-up display is a device that allows driving assistance information to be displayed in the driver's field of vision.

[0004] To this end, head-up displays include an image generation device, for example a light source coupled to a variable transmittance element array, for example a liquid crystal display (LCD), and an optical system for transmitting this image to a partially transparent screen, for example so that the driver can see the images without taking their eyes off the road. Some head-up displays include a variable transmittance element array that makes it possible to generate two images simultaneously, which appear, for example, at different distances in the driver's field of vision. This is particularly useful for augmented reality head-up displays.

[0005] The technologies for obtaining two images are complex and have a high production cost. Summary of the invention

[0006] An image generation device and a head-up display are proposed which make it possible to overcome the problems mentioned above.

[0007] According to one aspect, an image generation device is proposed comprising a first light source configured to generate a first upstream light beam, a second light source configured to generate a second upstream light beam, and a matrix of variable transmittance elements configured to selectively receive and transmit the first upstream light beam and to selectively receive and transmit the second upstream light beam so as to form respectively a first downstream light beam forming a first image and a second downstream light beam forming a second image.

[0008] For the purposes of this invention, the terms "upstream" and "downstream" refer to positions along the propagation path of the light emitted by the light source. Thus, the term "upstream" means closer to the light source and the term "downstream" means further from the light source along the propagation path.

[0009] The invention makes it possible to generate two distinct images by simple and economical means. For example, in the case of a device equipping a head-up display in a motor vehicle, the device according to the invention can advantageously be used to generate a first conventional image and a second augmented reality image. The driver then benefits from an enhanced driver assistance interface.

[0010] According to one embodiment, the variable transmittance element matrix is ​​a thin-film transistor liquid crystal display.

[0011] A liquid crystal display is a simple and inexpensive implementation of a matrix of elements with variable transmittance.

[0012] According to one embodiment, a downstream face of the variable transmittance element matrix is ​​in contact with a plate at least partially transparent configured to limit heating of the variable transmittance element matrix.

[0013] Limiting the heating of the variable transmittance element matrix advantageously extends its lifespan. Furthermore, implementing thermal dissipation is particularly beneficial for removing the heat generated by the light beams from the two light sources.

[0014] According to one embodiment, the device comprises a first heat sink thermally coupled with the partially transparent plate.

[0015] According to one embodiment, at least one of the first and second light sources is configured to transmit its upstream light beam to the variable transmittance element matrix through an optical diffuser, the device comprising a second heat sink configured to evacuate the heat confined between the diffuser and the variable transmittance element matrix.

[0016] According to one embodiment, the second heat sink is in contact with the upstream face of the variable transmittance element matrix.

[0017] According to one embodiment, at least one heat sink is coupled to a forced convection cooling module.

[0018] According to one embodiment, the downstream face of the partially transparent plate is in contact with a cold face of a thermoelectric cooling module.

[0019] According to one embodiment, the first heat sink is in contact with a hot face of the thermoelectric module.

[0020] According to one embodiment, the downstream face of the partially transparent plate is in contact with the first heat sink.

[0021] According to one embodiment, at least one of the first and second light sources is configured to transmit its upstream light beam to an optical diffuser through a reflector.

[0022] According to one embodiment, the propagation direction of the first upstream beam and the propagation direction of the second upstream beam form an angle between 0° and 45°.

[0023] According to one embodiment, the first downstream beam is reflected on a first concave mirror and the second downstream beam is reflected on a second concave mirror, the first concave mirror and the second concave mirror being fixed relative to each other and attached to the same support.

[0024] According to one embodiment, at least one of the first and second concave mirrors is a cold mirror.

[0025] Head-up display comprising a device according to the invention and a system for projecting downstream beams towards a partially transparent blade.

[0026] Of course, the various features, variants, and embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. Brief description of the figures

[0027] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0028] [Fig. 1] schematically illustrates a head-up display comprising an image generation device according to an embodiment of the invention,

[0029] [Fig.2] is a schematic cross-sectional view of an image generation device according to the invention,

[0030] [Fig.3] is a schematic view of a folding mirror of a device according to the invention,

[0031] [Fig.4] is a schematic view of two other folding mirrors of a device according to the invention,

[0032] [Fig.5] is a profile view of the folding mirrors of [Fig.4],

[0033] [Fig.6] is a schematic cross-sectional view of an image generation device according to another embodiment of the invention,

[0034] [Fig.7] is a schematic cross-sectional view of an image generation device according to another embodiment of the invention,

[0035] [Fig.8] is a schematic cross-sectional view of an image generation device according to another embodiment of the invention.

[0036] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0037] In [Fig. 1], the main elements of a head-up display 1, intended for example to equip a vehicle, in particular a motor vehicle, are schematically represented.

[0038] The display of [Fig.1] is adapted to create two virtual images 2 and 3 in the field of vision of a driver of the vehicle, so that the driver can see these virtual images 2, 3 and any information they contain without having to take his eyes off the road.

[0039] To this end, the display 1 comprises a partially transparent blade 4 placed in the driver's field of vision, an image generation device 5 adapted to generate two downstream light beams 6 and 7, and a projection device 8, 9, 10 adapted to reflect, towards said partially transparent blade 4, the downstream light beams 6, 7 generated by the image generation device 5. Here, the display 1 is configured so that the two virtual images 2, 3 appear at distinct distances. For example, the first virtual image 2 is a conventional image and appears at a first distance from the driver, and the second virtual image is an augmented reality image that integrates into the environment facing the vehicle and therefore appears at a second distance from the driver greater than the first distance.

[0040] The partially transparent blade 4 is here combined with the vehicle's windshield. In other words, the vehicle's windshield functions as a partially transparent blade for the head-up display 1. This configuration is particularly well-suited for augmented reality image projection.

[0041] Alternatively, the partially transparent blade could be a combiner, i.e., a partially transparent blade separate from the windshield and dedicated to the head-up display. Such a combiner would be placed between the vehicle's windshield and the driver's eyes 11, in the path of the downstream light beams 6, 7.

[0042] The image projection device 5 here comprises three folding mirrors 8, 9, 10. A first folding mirror 8 and a second folding mirror 9 are arranged to reflect a first downstream light beam 6 generated by the image generation device 5 towards the partially transparent blade 4. The first folding mirror 8 and a third folding mirror 10 are arranged to reflect a second downstream light beam 7 generated by the image generation device 5 towards the partially transparent blade 4. The folding mirrors 8, 9, and 10 advantageously allow the image generation device 5 in a configuration in which it does not face the partially transparent blade 4 and therefore to place it in any suitable location, typically under the dashboard of the vehicle.

[0043] For example, here, the first folding mirror 8 is a flat mirror, and the second folding mirror 9 and the third folding mirror 10 are curved mirrors, here concave, each having a shape optimized to produce a virtual image with a shape adapted to the partially transparent blade 4, here a curved shape, so as to display the image without distortion. Furthermore, the second folding mirror 9 and the third folding mirror 10 have image magnification functions for the image generated by the variable transmittance element array.

[0044] According to other embodiments, the image generation device 5 could include a different number of mirrors and / or mirrors having different shapes, as well as other optical elements, for example a lens.

[0045] The image generation device 5 includes a first light source 12 and a second light source 13, here arrays of light-emitting diodes (LEDs, for "Light Emitting Diode" according to the Anglo-Saxon acronym classically used by those skilled in the art), configured to produce respectively a first upstream light beam 14 and a second upstream light beam 15. The image generation device 5 further includes an array of variable transmittance elements 16 configured to be illuminated by the upstream light beams 14, 15.

[0046] The variable transmittance element matrix 16 is configured to selectively transmit the first upstream light beam 14 so as to form the first downstream light beam 6 representing a first image 2 to be projected into the driver's field of vision by means of the partially transparent blade 4, and to selectively transmit the second upstream light beam 15 so as to form the second downstream light beam 7 representing a second image 3 to be projected into the driver's field of vision by means of the partially transparent blade 4.

[0047] The head-up display 1 also includes a housing 17 (generally opaque) which contains the image generation device 5 and the projection system 8, 9, 10 in order in particular to protect these elements against possible external aggressions (dust, liquids, etc.).

[0048] The housing 17 has an opening 18 through which the downstream light beams 6, 7 pass, here after reflection on the folding mirrors 9 and 10.

[0049] The opening 18 of the housing 17 is closed by a window 19 (sometimes referred to by the Anglo-Saxon term "cover window") formed for example of a sheet of polycarbonate type plastic material with a thickness between 0.25 mm and 0.75 mm.

[0050] Figure 2 is a schematic view in which the image generation device 5 appears in greater detail than in Figure 1. In particular, Figure 2 schematically represents a cross-section of a heat dissipation system for the image generation device 5.

[0051] In this embodiment, the first light source 12 is optically coupled to a first optical diffuser 20, and is fixed to the optical diffuser 20 via a first optical reflector 21. Similarly, the second light source 13 is optically coupled to a second optical diffuser 22 and fixed to the second optical diffuser 22 via a second optical reflector 23.

[0052] The first light source 12 and the second light source 13 are oriented such that the propagation direction of the first upstream light beam 14 and the propagation direction of the second downstream light beam 15 form an angle between 0° and 45°, for example an angle greater than 0°, here an angle of 30°. In particular, here, the propagation direction of the second upstream light beam 15 is orthogonal to the variable transmittance element matrix 16.

[0053] The variable transmittance element matrix 16 is here a thin film transistor liquid crystal display (TFT-LCD, for "Thin Film Transistor Liquid Crystal Display", according to the Anglo-Saxon acronym used by those skilled in the art), comprising a liquid crystal element matrix placed between two polarizers (an upstream polarizer, or input polarizer, and a downstream polarizer, or output polarizer, not shown) forming the upstream and downstream faces of the variable transmittance element matrix 16. The variable transmittance element matrix is ​​here controlled by control means 44.

[0054] In the embodiment of [Fig.2], the heat dissipation system comprises a plurality of passive heat sinks 24 to 29, a partially transparent dissipative plate 30, a thermoelectric cooling module 31, or Peltier module, and a forced convection cooling module 32.

[0055] The passive heat sinks 24 to 29 are configured to maintain the operating temperature of the image generation device 5 below its functional thermal limits, here below a temperature of 110°C. Thus, the material conductivity of each of the passive heat sinks 24 to 29 is greater than 20 W.m⁻¹.K⁻¹, and preferably greater than 60 Wm⁻¹.K⁻¹. For example, here the passive heat sinks 25 to 29 are made of aluminum and have a thermal conductivity of 220 Wm⁻¹.K⁻¹. The heat sinks can comprise any other materials that meet the above heat dissipation requirements, for example aluminum alloys or magnesium alloys.

[0056] In order to improve heat dissipation and ensure good protection of the passive heat sinks 25 to 29 against corrosion, the heat sinks 24 to 29 are here covered with an anodized layer.

[0057] The first light source 12 is attached to a first PCB (Printed Circuit Board) type electronic board 33, to which it is electrically connected. The electronic board 33 includes, for example, a control circuit for the first light source 12, for example controlled by the control means 44.

[0058] The rear face of the first electronic board 33, that is to say the face opposite to the face on which the first light source 12 is fixed, is in contact with a first passive heat sink 24. The face of the first passive heat sink 24 which is directly in contact with the light source 8 is flat or substantially flat, and the opposite face is provided with fins which make it possible to increase the surface of the first passive heat sink 24 which is in contact with the air and thus to increase the heat exchanges with the outside.

[0059] In order to improve the thermal coupling between the light source and the first passive heat sink 24, in particular if one or the other of the contact faces between the first electronic board 33 and the first passive heat sink 24 is not perfectly flat and has, for example, level differences greater than 0.1 mm, the coupling can be achieved through a thermal interface material, for example thermal adhesive, thermal pads, a phase change material, etc.

[0060] A first end of the first optical reflector 21 is fixed to the electronic board 33, for example using screws and / or adhesive material, so as to surround the first light source 12, the first optical diffuser 20 being fixed to a second end of the first reflector 21. Thus, all the light from the first light source 12, or at least a very large part of this light, is directed through the first optical diffuser 20.

[0061] The first optical reflector 21 is housed in a second passive heat sink 25, such that the first diffuser 20, and in particular a peripheral area of ​​the first diffuser 20, is squeezed between the second end of the first reflector 21 and the second passive heat sink 25. The peripheral area of ​​the first diffuser 21 is not optically useful; here, a central, optically useful area is delimited through which the first upstream light beam 14 passes.

[0062] The second passive heat sink 25 is here attached to the first electronic board 33 by means of a first thermally insulating support 34, of so that the heat dissipated by the second passive heat sink 25 is not transmitted to the first electronic board 33.

[0063] A wall of the second passive heat sink 25 extends to the variable transmittance element matrix 16, so as to be in contact with a peripheral area of ​​the variable transmittance element matrix at its upstream face. The second passive heat sink 25 thus helps to dissipate the heat confined between the first diffuser 20 and the variable transmittance element matrix 16.

[0064] In a manner analogous to what has just been described, the second light source 13 is equipped with a second optical reflector 23 fixed to a second electronic board 35 by means of a second thermally insulating support 36 and configured to direct all the light from the second light source, or at least a very large part of this light, through the second optical diffuser 22. The second electronic board includes, for example, a control circuit for the second light source 13, for example controlled by the control means 44.

[0065] A wall of the third passive heat sink 26 extends to the variable transmittance element matrix 16, so as to be in contact with a peripheral area of ​​the variable transmittance element matrix 16, at its upstream face. The second passive heat sink 26 thus helps to dissipate the heat confined between the second diffuser 20 and the variable transmittance element matrix 16.

[0066] The rear face of the second electronic board 35 is in contact with a fourth passive heat sink 27, here a finned heat sink. A thermal interface material can also be used here to improve the coupling between the second electronic board and the fourth heat sink 27. The first passive heat sink 24 and the fourth passive heat sink 27 are mutually secured by means of fasteners, here screws 37.

[0067] The downstream face of the variable transmittance element array 16 is in contact with a partially transparent plate 30. The partially transparent plate 30 is configured to drain heat from the variable transmittance element array 16. The upstream face of the partially transparent plate 30 is in contact with the downstream face of the variable transmittance element array 16. In particular, the partially transparent plate 30 has the same transverse dimensions as the variable transmittance element array 16 and completely covers it. Thus, the partially transparent plate 30 is thermally coupled to the variable transmittance element array 16.

[0068] The partially transparent plate 30 is here a ceramic plate and in this example has a thermal conductivity greater than 5 Wm*.K*, and preferably greater than 10 Wm*.K*.

[0069] Preferably, the thickness of the partially transparent plate 21 is less than or equal to 1.1 mm, and even more preferably between 0.5 mm and 0.9 mm, here 0.7 mm.

[0070] A fifth passive heat sink 28 is here in contact with the peripheral area of ​​the downstream face of the partially transparent plate 30, with the edge of the variable transmittance element matrix 16 and the partially transparent plate 30 and with a part of the external surfaces of the second and third heat sinks 25 and 26. In the configuration of [Fig.2], the partially transparent plate 30 and the variable transmittance element matrix 16 are squeezed between the second and third heat sinks 25 and 26 (at the upstream face of the variable transmittance element matrix 16) and the fifth passive heat sink 28 (at the downstream face of the partially transparent plate 16).

[0071] Thus, the second, third and fifth heat sinks 25, 26 and 28, as well as the partially transparent plate 30, contribute to evacuating the heat received by the variable transmittance element matrix 16.

[0072] It should be noted here that the peripheral area of ​​the variable transmittance element matrix 16, respectively of the partially transparent plate 30, is not optically useful and delimits a central area through which the upstream light beams 14, 15 pass, possibly selectively, so as to form the downstream light beams 6 and 7.

[0073] In order to further improve heat dissipation, at least one of the passive heat sinks is thermally coupled to an active heat dissipation system.

[0074] The active heat dissipation system includes the thermoelectric cooling module 31, or Peltier module, the cold face of which is here in contact with the external surface of the third passive heat sink 26, for example via a thermal interface material, and the hot face of which is in contact with the forced convection cooling module 32.

[0075] In the context of the invention, the cold side of a thermoelectric module is the side configured to be in contact with the element to be cooled; it therefore absorbs heat. The hot side is the opposite side, which dissipates (or releases) heat. Thus, in a thermoelectric module, heat flows from the cold side to the hot side.

[0076] The thermoelectric module 31 is configured here so that the temperature difference between its cold face and its hot face is less than 10°C, and preferably equal to 0°C. Those skilled in the art will be able to find a compromise between the temperature difference and the electrical consumption of the thermoelectric module 22 according to the applications they are considering.

[0077] The forced convection cooling module 32 includes a sixth passive heat sink 29, one face of which is coupled to the hot face of the thermoelectric module 31, and which has, on the side opposite the face in contact with the thermoelectric module, a plurality of fins.

[0078] The forced convection cooling module further comprises an axial flow fan 39 mechanically connected to the sixth heat sink 29, for example here by screws 40. For example here, the fan 39 has a size between 25mm x 25mm and 60mm x 60mm, and is configured so that its rotational speed is less than or equal to 400 revolutions per minute. The fan 39 can further be configured to have a noise level less than or equal to 25dB.

[0079] The thermoelectric cooling module 31 and the forced convection cooling module 32 are controlled by the control means 44.

[0080] Figure 3 illustrates a heat dissipation system for the first folding mirror 8. Here, the first folding mirror is a flat mirror. For example, the first folding mirror 8 is configured to act as a dichroic filter and, in particular here, the first folding mirror 8 is configured to transmit all the unpolarized visible infrared radiation arriving at its surface, to reflect the polarized visible portion of the solar radiation, and to reflect all the light from the first and second light sources. In other words, the first folding mirror 8 is a cold mirror.

[0081] Such a mirror is obtained here by applying a filter coating to the reflective face of the mirror, for example an adhesive film of type CMF (“Cold Mirror Film” in English, or “film de miroir froid” in French).

[0082] The rear face of the first folding mirror 8, that is to say the face opposite to the reflective face on which the CMF film is applied here, is in contact with a seventh heat sink 41, for example through a thermal interface material.

[0083] The second and third folding mirrors 9 and 10 are illustrated in [Fig. 4], which is a rear view of these two mirrors, and in [Fig. 5], which is a side view of these two mirrors. Here, the second and third folding mirrors 9 and 10 are concave mirrors, for example, each covered here with a CMF-type adhesive film. The second folding mirror 9 and the third folding mirror 10 are fixed together. of the same support 42 coupled to a mechanical transmission system 43 configured to adjust the position of the support 42. The mechanical transmission system 43 is controlled by the control means 44.

[0084] The second folding mirror 9 and the third folding mirror here have the same radius of curvature and are fixed to the support 42 so that their respective centers of curvature coincide. The dimensions of the first folding mirror 9 are suitable for projecting standard images, and the dimensions of the second folding mirror are suitable for projecting augmented reality images. The dimensions of the second folding mirror 10 are larger than those of the first folding mirror 9.

[0085] The control (or piloting) of the forced convection cooling module 32 and the thermoelectric cooling module 31 is carried out in association with a real-time temperature measurement in order to adapt the rotation speed of the fan 39 and the nominal temperature difference between the cold phase and the hot face of the thermoelectric cooling module 31. This advantageously allows the optimization of the electrical consumption of the active cooling system, for example by limiting the number of situations in which the active cooling system is used.

[0086] Temperature measurement is for example carried out using a temperature sensor or a plurality of sensors distributed at different locations in the image generation device 5.

[0087] For example, - a temperature sensor is installed in the structure of the variable transmittance element matrix, and / or an infrared sensor is pointed at the variable transmittance element matrix 16 and is configured to locate areas of the matrix with a maximum temperature - Electronic boards 33 and 35 include temperature sensors configured to measure the temperature of the electronic boards and / or light sources, - a sensor placed in housing 17 is configured to measure the ambient temperature inside housing 17, - a temperature sensor installed in the thermoelectric cooling module 31 allows the temperature of the cold face to be measured.

[0088] According to other embodiments, only some of these sensors may be present.

[0089] In order to optimize the cooling and power consumption of the image generation device 5, the control means 44 are configured to operate according to an operating mode selected from among three operating modes.

[0090] According to a first mode of operation, the control means are configured to maintain the temperature difference between the cold face and the hot face of the thermoelectric cooling module at a predetermined value, independently of the thermal load imposed on the image generation device 5. According to this first mode of operation, the control means 44 are configured to adapt the speed of the fan 39 of the forced convection cooling module according in particular to the values ​​returned by the temperature sensors and the desired temperature of the image generation device 5.

[0091] According to a second mode of operation, the control means 44 are configured to maintain the rotation speed of the fan 39 constant and to adapt the temperature difference between the cold face and the hot face of the thermoelectric cooling module 31 according to, in particular, the values ​​returned by the temperature sensors and the desired temperature of the image generation device 5.

[0092] According to a third mode of operation, the control means 44 are configured to adapt both the temperature difference between the hot face and the cold face of the thermoelectric cooling module 31, and the rotation speed of the fan 39, in particular according to the values ​​returned by the temperature sensors and the desired temperature of the image generation device 5.

[0093] According to other embodiments, reflective polarizers can be coupled to the first optical diffuser 20, the second optical diffuser 21 and / or the variable transmittance element array 16.

[0094] For example, [Fig.6] illustrates an embodiment in which a first reflective polarizer 45 covers the downstream face of the first optical diffuser 21 and a second reflective polarizer 46 covers the downstream face of the second optical diffuser 22.

[0095] Figure 7 illustrates an embodiment in which a third reflective polarizer covers the upstream face of the variable transmittance element array 16.

[0096] Reflective polarizers allow light with a specific polarization direction to be transmitted and light with a different polarization direction to be reflected. Here, the specific polarization direction is parallel to the polarization of the input (or upstream) polarizer of the variable transmittance element array. Thus, the proportion of light rays absorbed by the variable transmittance element array is reduced, thereby limiting its heating.

[0097] According to another embodiment of the invention, a thermoelectric cooling module is thermally coupled to the variable transmittance element matrix 16. For example, as illustrated in [Fig. 8], a second module thermoelectric cooling module 48 is placed between the partially transparent plate 30 and the fifth passive heat sink 28. Here, the cold face of the second thermoelectric cooling module 48 is in contact with the peripheral area of ​​the partially transparent plate 30, and its hot face is in contact with the fifth passive heat sink 28.

[0098] In the embodiment illustrated by [Fig.7], the second thermoelectric cooling module 48 is, for example, rectangular and extends along one edge of the partially transparent plate 30. According to other embodiments, the thermoelectric cooling module extends along several edges of the partially transparent plate 30. In particular, according to some embodiments, the thermoelectric cooling module could be frame-shaped.

[0099] Here, the fifth passive heat sink 28 has a portion of its external surface that is provided with fins. This finned portion is coupled here to the forced convection cooling module 32.

[0100] Furthermore, in this embodiment, the fifth passive heat sink 28 is thermally isolated from the passive heat sinks 25 and 26 by thermal insulation pieces 49. Thus, the heat dissipated from the screen is not redirected to these heat sinks 25 and 26. The cooling of the variable transmittance element matrix 16 therefore does not hinder that of the inside of the housing.

[0101] Various other modifications may be made to the invention within the scope of the appended claims.

Claims

Demands

1. Image generation device comprising a first light source (12) configured to generate a first upstream light beam (14), a second light source (13) configured to generate a second upstream light beam (15), and a variable transmittance element matrix (16) configured to selectively receive and transmit the first upstream light beam (14) and to selectively receive and transmit the second upstream light beam (15) so as to form respectively a first downstream light beam (6) forming a first image (2) and a second downstream light beam (7) forming a second image (3).

2. Device according to claim 1, wherein the variable transmittance element array (16) is a thin-film transistor liquid crystal display.

3. Device according to claim 1 or 2, wherein a downstream face of the variable transmittance element matrix (16) is in contact with a plate at least partially transparent (30) configured to limit heating of the variable transmittance element matrix (16).

4. Device according to any one of claims 1 to 3, comprising a first heat sink (28) thermally coupled with the partially transparent plate (30).

5. Device according to any one of claims 1 to 4, wherein at least one of the first and second light sources (12, 13) is configured to transmit its upstream light beam (14, 15) to the variable transmittance element array (16) through an optical diffuser (20, 22), the device comprising a second heat sink (25, 26) configured to dissipate the heat confined between the diffuser and the variable transmittance element array.

6. Device according to any one of claims 1 to 5, wherein the second heat sink (25) is in contact with the upstream face of the variable transmittance element matrix (16).

7. Device according to any one of claims 1 to 6, wherein at least one heat sink is coupled to a forced convection cooling module (32).

8. Device according to any one of claims 1 to 7, wherein the downstream face of the partially transparent plate (30) is in contact with a cold face of a thermoelectric cooling module (31).

9. Device according to claim 8 taken in dependence on claim 4, wherein the first heat sink (28) is in contact with a hot face of the thermoelectric module (31).

10. Device according to any one of the preceding claims, wherein the downstream face of the partially transparent plate (30) is in contact with the first heat sink (28).

11. Device according to any one of the preceding claims, wherein at least one of the first and second light sources (12, 13) is configured to transmit its upstream light beam (14, 15) to an optical diffuser (20, 22) through a reflector (21, 23).

12. Device according to any one of the preceding claims, wherein the propagation direction of the first upstream light beam (14) and the propagation direction of the second upstream light beam (15) form an angle between 0° and 45°.

13. Device according to any one of the preceding claims, wherein the first downstream light beam (6) is reflected onto a first concave mirror (9) and the second downstream beam (7) is reflected onto a second concave mirror (10), the first concave mirror (9) and the second concave mirror (10) being fixed relative to each other and attached to the same support (42).

14. Device according to claim 13, wherein at least one of the first and second mirrors (9, 10) is a cold mirror.

15. Head-up display comprising a device according to any one of claims 1 to 14 and a system for projecting the downstream light beams towards a partially transparent blade (4).

Images