Image-generating device and head-up display comprising such a device

Abstract

The invention relates to an image-generating device comprising a light source (6) configured to produce a light beam (Lm, Lv) and an array of variable-transmittance elements (7) comprising at least one optically useful region (15) and configured to selectively transmit the light beam, the device comprising a thermally conductive opaque mask (16) located at a distance from the array of variable-transmittance elements, the opaque mask being configured to block at least some light rays the direction of the optical path of which passes through an optically unuseful region and to let pass light rays the direction of the optical path of which passes through the optically useful region, the opaque mask being thermally coupled to a heat sink (17). The invention also relates to a head-up display (1) comprising such a device.

Description

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, for example the display of information for the purpose of assisting the driving of motor vehicles. The invention relates more particularly to an image generation device and a head-up display comprising such a device. Technological background

[0002] The principle of head-up displays for vehicles is to project images, including for example information useful for driving, directly into the driver's field of vision, particularly on the vehicle's windshield.

[0003] To this end, head-up displays comprise an image generation device, for example a light source coupled to a matrix of elements with variable transmittance, for example a liquid crystal display (LCD), and an optical system for transmitting this image to a partially transparent blade, for example so that the driver can see the images without looking away from the road.

[0004] The light output required to display an image in the driver's field of vision requires the use of a very high intensity light source, of the order of a million candelas. However, matrices of elements with variable transmittance typically have a high absorption rate, of the order of 90% for its passing elements (or pixels) and of the order of 99% for its blocking elements. The absorption of light rays by the matrix therefore leads to a risk of overheating and deterioration of the matrix.

[0005] Furthermore, the location of the displays under the windshield of the motor vehicle makes them susceptible to receiving a solar flux, circulating in the display following the reverse path of the light rays coming from the light source, and converging, after their passage in the optical system, at a point on the screen. The focusing of the rays solar radiation, which is added to the temperature rise generated by the light source itself, is likely to damage the matrix of variable transmittance elements. Summary of the invention

[0006] The present invention provides a means of limiting heating of the variable transmittance element matrix.

[0007] According to one aspect of the invention, there is provided an image generation device comprising a light source configured to produce a light beam and a matrix of variable transmittance elements comprising at least one optically useful zone and configured to selectively transmit the light beam, the device comprising a thermally conductive opaque mask located at a distance from the matrix of variable transmittance elements, the opaque mask being configured to block light rays whose optical path direction passes through a non-optically useful zone and to allow the passage of rays of the light beam whose optical path direction passes through an optically useful zone, the opaque mask being thermally coupled to a heat sink.

[0008] Thanks to the opaque mask, the heat generated by the rays of the light beam whose optical path direction passes through an optically non-useful area (i.e., rays not needed for image formation) and generated by the sun's rays can be transferred to the heat sink and removed. This limits the temperature increase of the variable transmittance element matrix. The risk of damage to the device due to overheating is therefore reduced. In addition, the mask allows for improved contrast in the image produced. Indeed, the blocked elements (or pixels) of the variable transmittance element matrix do not always block the light completely effectively; the opaque mask allows for the rays to be completely blocked.

[0009] According to one embodiment, the contours of the opaque mask are obtained from the contours of the optically useful zone by a homothety of ratio greater than one.

[0010] According to one embodiment, the opaque mask is configured to block all light rays whose optical path direction passes through the non-optically useful area.

[0011] According to one embodiment, the opaque mask is placed upstream of the matrix of variable transmittance elements, relative to the direction of propagation of the light rays. Placing the mask upstream of the matrix makes it possible to limit heating of the matrix of variable transmittance elements by the rays coming from the light source.

[0012] According to one embodiment, the upstream face of the opaque mask is covered with a reflective coating.

[0013] According to one embodiment, an at least partially transparent and thermally conductive plate is in contact with a face of the matrix of variable transmittance elements, the opaque mask being in contact with the at least partially transparent plate.

[0014] According to one embodiment, an optical diffuser is placed between the light source and the matrix of variable transmittance elements, the opaque mask being in contact with one face of the optical diffuser.

[0015] According to one embodiment, a first opaque mask is placed upstream of the matrix of variable transmittance elements and a second opaque mask is placed downstream of the matrix of variable transmittance elements, relative to the direction of propagation of the light rays.

[0016] According to one embodiment, the heat sink is placed on the periphery of the opaque mask.

[0017] According to another aspect, there is provided a head-up display comprising an image generation device according to the invention and a control unit configured to control the matrix of elements with variable transmittance so that the elements located outside the optically useful zone permanently have a transmittance of less than 1%.

[0018] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0019] In addition, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0020] [Fig. 1] illustrates an embodiment of a head-up display according to the invention,

[0021] [Fig. 2] illustrates a particular configuration of an image generation device according to the invention,

[0022] [Fig. 3] illustrates a particular embodiment of an image generation device according to the configuration of Figure 2,

[0023] [Fig. 4] illustrates another particular configuration of the image generation device according to the invention,

[0024] [Fig. 5] illustrates another particular configuration of the image generation device according to the invention,

[0025] [Fig. 6] illustrates another particular configuration of the image generation device according to the invention,

[0026] [Fig. 7] illustrates another particular configuration of the image generation device according to the invention,

[0027] [Fig. 8] illustrates another particular configuration of the image generation device according to the invention,

[0028] [Fig. 9] illustrates another particular configuration of the image generation device according to the invention.

[0029] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[0030] Figure 1 schematically shows the main elements of a head-up display, intended for example to equip a vehicle, for example a motor vehicle.

[0031] Such a display 1 is adapted to create a virtual image I in the field of vision of a driver of the vehicle, so that the driver can see this virtual image I and any information it contains without having to look away.

[0032] For this purpose, the display 1 comprises a partially transparent blade 2 placed in the driver's field of vision, an image generation device 3 adapted to generate a downstream light beam Lv and an optical transmission device 4, 5 adapted to return, in the direction of said partially transparent blade 2, the light beam generated by the image generation device 3.

[0033] The partially transparent blade 2 is here merged with the vehicle's windshield. In other words, it is the vehicle's windshield that has the function of a partially transparent blade for the head-up display 1.

[0034] According to a variant, the partially transparent blade could be a combiner, that is to say a partially transparent blade separate from the windshield and dedicated to the head-up display 1. Such a combiner would be placed between the windshield of the vehicle and the eyes YX of the driver, on the path of the downstream light beam Lv.

[0035] Furthermore, here, the optical transmission device comprises two folding mirrors 4, 5 arranged so as to reflect the downstream light beam Lv generated by the image generation device 3 in the direction of the partially transparent blade 2. The folding mirrors advantageously make it possible to place the image generation device 3 in a configuration in which it does not face the partially transparent blade 2 and therefore to place it in any suitable location, typically under the dashboard of the vehicle.

[0036] Here, a first folding mirror 4 is a plane mirror, and a second folding mirror 5 is a mirror which has a shape optimized to produce a virtual image of a shape adapted to the shape of the partially transparent blade 2, here a curved shape, so as to display the image I in an undistorted manner.

[0037] According to other embodiments, the optical transmission device 4, 5 could comprise a different number of mirrors and / or mirrors having different shapes, as well as other optical elements such as a lens.

[0038] The image generation device 3 comprises a light source 6, here a backlight module, configured to produce an upstream light beam Lm, a matrix 7 of elements with variable transmittance, here an LCD screen, configured to be illuminated by the upstream light beam Lm and a reflector 8 interposed between the light source 6 and the matrix 7. A diffuser 12 is here placed between the light source 6 and the matrix of elements with variable transmittance, on the optical path of the upstream light beam Lm.

[0039] The matrix 7 is configured to selectively transmit the upstream light beam Lm so as to form the downstream light beam Lv representing an image to be projected into the driver's field of vision by means of the optical transmission device 4, 5 and the partially transparent blade 2.

[0040] The head-up display device 1 also comprises a housing 9 (generally opaque) which contains the image generation device 2 and the optical transmission system 4, 5 in order in particular to protect these elements against possible external attacks (dust, liquids, etc.).

[0041] The housing 9 comprises an opening 10 through which the downstream light beam Lv passes, here after reflection on the second folding mirror 5.

[0042] The opening 10 of the housing 9 is closed by a window 11 (sometimes referred to as a “cover window”) formed for example from a sheet of polycarbonate-type plastic material with a thickness of between 0.25 mm and 0.75 mm.

[0043] The head-up display 1 further comprises a control unit 13 configured to control the image generation device 3, in particular the light source 6 and the matrix of variable transmittance elements 7, in particular as a function of control signals entered by the user or from various sensors of the head-up display 1, as will be explained below.

[0044] Figure 2 is a more detailed view of the matrix 7 of variable transmittance elements, for example here its upstream face. The matrix 7 comprises at least one zone optically useful 15, and in particular here seven optically useful zones 15. Outside the optically useful zones 15, the matrix of variable transmittance elements 7 is said to be non-optically useful.

[0045] For example, an optically useful area is considered here to be an area intended for displaying information, for example text or images. The elements, or pixels, of this area are therefore controlled so as to be optically on at least part of the time. A non-optically useful area is understood to mean an area that is not intended for displaying information. The elements, or pixels, of a non-optically useful area are permanently in the off state. The definition of the optically useful and non-optically useful areas is controlled by the control unit 13. Conventionally, the control unit 13 is programmed before the device 3 is marketed so that the optically useful and non-optically useful areas cannot be modified.Indeed, the designers of the system define different display areas for the information provided to the driver, without overlapping in order to cover all possible situations encountered, and therefore there generally remain, outside these display areas, areas which are not used at any time. It should be noted that an optically useful area whose pixels would all temporarily switch to the blocked state remains an optically useful area. In other words, due to its design, the control unit 13 is configured or programmed to control each pixel of the optically useful areas in the on or blocked state, depending on the information to be displayed, and to control each pixel of the non-optically useful areas in the blocked state (permanently).

[0046] The image generating device 3 may experience an increase in its temperature due to the rise in the ambient temperature of the vehicle, the heat generated by the light source 6, and the solar rays which penetrate into the housing 9 via the window 11 along the reverse path of the downstream light beam Lv. In particular, the elements (or pixels) of the matrix which have a low transmittance, for example the non-optically useful pixels which are permanently in the blocked state, are more likely to experience a significant rise in temperature.

[0047] According to an advantageous characteristic of the invention, the image generation device 1 comprises a thermal evacuation system 14 located opposite and at distance of the variable transmittance element array 7. Such a system is illustrated in Figure 3.

[0048] As illustrated in Figure 3, the heat evacuation system 14 comprises an opaque mask 16 and a heat sink 17 thermally coupled to the mask 16, for example in contact with the mask 16, and here located at the periphery of the mask 16. The mask 16 is here a rectangular planar mask, of dimensions substantially equal to those of the matrix of variable transmittance elements 7, comprising a plurality of openings 18, here a number of openings 18 equal to the number of optically useful zones 15. More precisely here, the positions of the openings 18 are chosen so that each opening 18 is opposite an optically useful zone 15, that is to say so that a light ray from the light source 6, the direction of the optical path of which passes through an optically useful zone, can pass through an opening 18 and is not blocked by mask 16.

[0049] Preferably here, the contour of each opening 18 is obtained from the contour of the optically useful zone 15 opposite which it is located, thanks to a homothety of ratio greater than 1. Preferably, the homothety ratio is close to 1 (for example 1.1 or 1.2), so as to make the mask more selective. The light rays whose direction of propagation passes through the edges of the useful zone 15 will therefore pass close to the edges of the opening 18. Thus, a minority of rays has a direction of propagation which passes both outside an optically useful zone and through an opening 18.

[0050] The heat sink 17 is here a passive convection heat sink. It comprises here a base 19 in contact with the mask, and a plurality of fins 20 whose function is to increase the contact surface with the air of the sink 17, and therefore to improve the heat dissipation. The fins 20 are here parallel to each other and substantially parallel to the surface of the mask 16. They therefore extend from the base 19 moving away from the mask.

[0051] The mask 16 and the dissipator 17 are here made of thermally conductive materials, that is to say materials whose thermal conductivity is equal to or greater than 60 Wm ^.k 1 . The heat sink 17 has a conductivity thermal conductivity at least equal to that of the mask 16. For example, here, the mask 16 and the heat sink 17 are made of the same material, here aluminum which has a thermal conductivity of 226 Wm _1 .k _1.

[0052] The heat evacuation system 14 can be placed in the image generating device in different configurations.

[0053] Figure 4 illustrates a configuration of the image generation device 3 in which the heat evacuation system 14 is placed upstream of the matrix of variable transmittance elements. When it is placed upstream of the matrix of variable transmittance elements 7, the heat evacuation system 14 absorbs a portion of the light rays from the light sources 6 and evacuates the heat that they generate. These rays therefore do not reach the screen and their contribution to its heating is advantageously prevented.

[0054] Here the heat evacuation system 14 is placed between an optical diffuser 21 and the matrix of variable transmittance elements 7. In this example, the image generation device 3 comprises an at least partially transparent thermally conductive plate 22, for example here a transparent ceramic plate. The downstream face of the plate 22 is here in contact with the upstream face of the matrix of variable transmittance elements 7. The downstream face of the mask 16 is here in contact with the upstream face of the plate 22. Thus, the mask 16 is advantageously thermally coupled to the matrix of variable transmittance elements and makes it possible to limit a rise in temperature of the matrix 7 which would be due for example to the solar rays which arrive on the downstream face of the matrix 7.

[0055] Figure 5 illustrates an embodiment of this configuration. In this example, the image generating device 3 comprises a housing 23 at the bottom of which is located the light source 6, here a printed circuit board 24 comprising a plurality of light-emitting diodes 26. The light source 6 is located in such a way that it generates a light flux in the direction of openings 18 formed in the wall of the housing 23, opposite the bottom of the housing 23 (which are also the openings of the mask 16, as will be seen below). The transparent ceramic plate 22, on the downstream face of which is fixed the matrix of variable transmittance elements 7, obstructs these openings.

[0056] On the optical path of the rays coming from the light source 6, that is to say between the source 6 and the matrix of variable transmittance elements 7, there are various optical elements, in particular the diffuser 21, a reflective polarizer 26 placed in contact with the upstream face of the diffuser 21, and an optical collimation system 27 placed between the light source 6 and the reflective polarizer 26.

[0057] In this example, the housing 23 comprises two independent parts, a first part 28 comprising the bottom of the housing 23 and a second part 29 comprising the openings 18. The diffuser 21 and the reflective polarizer 26 are held by clamping between these two parts 28, 29 of the housing 23.

[0058] Advantageously, the second part 29 of the housing 23 forms the mask 16 (or, in other words, the mask 16 is integrated into the second part 29 of the housing 23) and the openings 18 provided in the housing form the openings 18 of the mask 16. The heat sink 17 is fixed to an outer wall of the second part 29 of the housing 23.

[0059] In this example, the inner wall of the second part 28, including the upstream face of the mask 16, is covered with a reflective coating 30. Thus, the second part 29 of the housing 23 forms a reflector and a light ray which would be reflected on the upstream face of the mask 16 could possibly, after several reflections on the inner walls of the housing 23, pass through one of the openings 18. The brightness of the device 3 is improved.

[0060] According to another embodiment illustrated by Figure 6, the heat evacuation system 14 is located between the optical diffuser 21 and the matrix of variable transmittance elements 7. The heat evacuation system 14 is here at a distance from the matrix of variable transmittance elements and at a distance from the diffuser 21. No intermediate element is placed between the mask and the matrix 7 or diffuser 21, at least on the optical path of the light rays whose direction of the optical path passes through the optically useful zones 15. The distance between the evacuation system 14 and the matrix of variable transmittance elements 7 advantageously makes it possible to thermally isolate these two elements. Thus, in the case where the temperature rise due to the light rays coming from the light source 6 would be too great for the heat to be able to be evacuated by the system 14, the heat is not directly transmitted to the matrix of variable transmittance elements 7.

[0061] Figure 7 illustrates a configuration of the device 3 in which the heat evacuation system 14 is placed upstream of the matrix of variable transmittance elements 7, here between the light source 6 and the diffuser 21. The downstream face of the opaque mask 16 is here in contact with the upstream face of the diffuser 21. The dimensions of the mask are here substantially the same as those of the diffuser 21, and the dissipator extends beyond the contours of the dissipator 16. This configuration makes it possible to simply fix the heat evacuation system 14 in the image generation device 3. In addition, placing the mask 16 as close as possible to the light source also makes it possible to limit the temperature rise of the optical elements located further downstream, for example here the diffuser 21.

[0062] Figure 8 illustrates a configuration of the device 3 in which the heat evacuation system 14 is placed upstream of the matrix of variable transmittance elements 7, here between the light source 6 and the diffuser 21. The dimensions of the mask 16 are here substantially the same as those of the diffuser 21, and the dissipator 17 extends beyond the contours of the diffuser 21. The heat evacuation system 14 is here at a distance from the diffuser 21 and at a distance from the light source 6, and no intermediate element is placed between the mask and the light source 6 or the diffuser 21. At least, no intermediate element is placed on the optical path of the light rays whose direction of the optical path passes through the optically useful zones 15.

[0063] Figure 9 illustrates a configuration of the image generation device 3 in which the heat evacuation system 14 is placed downstream of the matrix of variable transmittance elements 7. In this configuration, the system 14 advantageously makes it possible to block the solar rays arriving on the downstream face of the matrix of variable transmittance elements and to evacuate the heat that they generate. In this example, the thermally conductive transparent plate 22 is in contact with the downstream face of the matrix of variable transmittance elements 7, and the mask 16 is in contact with the downstream face of the transparent ceramic plate 22. Preferably, the mask 16 placed downstream of the matrix 7 is covered with a black or white coating. dark which allows the absorption of solar rays and prevents them from being reflected towards the partially transparent blade.

[0064] The invention is not limited to the embodiments described previously in connection with figures 1 to 8.

[0065] In particular, although an image generation device comprising a single thermal evacuation system 14 has been described, the invention is compatible with devices comprising several thermal evacuation systems placed at different locations of the device 3. For example, according to certain embodiments, the device comprises a first thermal evacuation system placed upstream of the matrix of variable transmittance elements 7 and a second thermal evacuation system placed downstream of the matrix of variable transmittance elements. 7.

[0066] Furthermore, the invention is not limited to a heat removal system comprising a single mask or a single heat sink. For example, some embodiments of the invention comprise two masks, one positioned upstream and the other downstream of the variable transmittance element array, and both coupled to a single heat sink. Other embodiments comprise one or more heat removal systems each comprising a mask thermally coupled to several heat sinks.

[0067] A mask integrated into a housing, the upstream face of which is covered with a reflective coating, has been previously described in connection with Figure 5. The presence of a reflective coating on the upstream face of the mask is not, however, limited to this embodiment, and may be found in embodiments in which the mask is independent of the housing.

[0068] The invention is not limited to a heat sink in contact with the mask. According to certain embodiments, the sink is not in contact with the mask but is thermally coupled to it via a thermally conductive material, for example a thermal paste. Alternatively, the mask and the sink form a single piece and have a continuity of material between them.

[0069] The mask described above includes openings obtained from the contours of the active zones, by a homothety of ratio greater than 1. However, The invention is not limited to such a mask and is compatible with masks having different contours. For example, embodiments comprise a mask of dimensions smaller than those of the variable transmittance element matrix and placed opposite only a portion of the variable transmittance element matrix.

[0070] Finally, although only one embodiment has been described in which the thermal evacuation system 14 is placed downstream of the matrix, the invention is not limited thereto. Thus, such embodiments may or may not comprise a thermally conductive transparent plate and the thermal evacuation system may be located at any non-zero distance from the matrix of variable transmittance elements, and be separated therefrom by one or more intermediate elements, provided that the latter do not obstruct the light rays whose optical path direction passes through the optically useful zones.

[0071] Various other modifications may be made to the invention within the scope of the appended claims.

Claims

Claims 1. Image generating device comprising a light source (6) configured to produce a light beam (Lm, Lv) and a matrix of variable transmittance elements (7) comprising at least one optically useful zone (15) and configured to selectively transmit the light beam, the device comprising a thermally conductive opaque mask (16) located at a distance from the matrix of variable transmittance elements (7), the opaque mask (16) being configured to block light rays whose optical path direction passes through a non-optically useful zone and to allow the rays of the light beam whose optical path direction passes through the optically useful zone (15) to pass, the opaque mask being thermally coupled to a heat sink (17).

2. Device according to claim 1, in which the contours of the opaque mask (16) are obtained from the contours of the optically useful zone (15) by a homothety of ratio greater than 1.

3. Device according to claim 1 or 2, wherein the opaque mask (16) is configured to block all light rays whose optical path direction passes through a non-optically useful area.

4. Device according to any one of claims 1 to 3, in which the opaque mask (16) is placed upstream of the matrix of variable transmittance elements (7) relative to the direction of propagation of the light rays.

5. Device according to claim 4, in which the upstream face of the opaque mask is covered with a reflective coating (30).

6. Device according to any one of claims 1 to 5, comprising an at least partially transparent and thermally conductive plate (22) in contact with one face of the matrix of variable transmittance elements (7), the opaque mask (16) being in contact with the at least partially transparent plate (22).

7. Device according to any one of claims 1 to 6, comprising an optical diffuser (21) placed between the light source (6) and the matrix of variable transmittance elements (7), the opaque mask (16) being in contact with one face of the optical diffuser (21).

8. Device according to any one of claims 1 to 7, comprising a first opaque mask placed upstream of the matrix of variable transmittance elements and a second opaque mask placed downstream of the matrix of variable transmittance elements, relative to the direction of propagation of the light rays.

9. Device according to any one of claims 1 to 8, in which the heat sink (17) is placed on the periphery of the opaque mask (16).

10. Head-up display comprising an image generation device according to any one of claims 1 to 9 and a control unit (13) configured to control the matrix of variable transmittance elements (7) so that the elements located outside the optically useful zone permanently have a transmittance of less than 1%.

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