Image generating device and head-up display including such device

Abstract

The invention relates to an image generation device comprising a light source (6) configured to generate a light beam (Lm, Lv) and an array of variable transmittance elements (7) comprising at least one optically useful region (15) 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 is configured to block at least some of the light rays whose optical path direction passes through the non-optically useful area and to allow the light rays whose optical path direction passes through the optically useful area, the opaque mask being thermally coupled to the heat sink (17). The invention also relates to a head-up display (1) comprising such a device.

Description

Technical Field

[0001] The present invention relates to the technical field of displays, for example the display of information for the purpose of assisting the driving of a motor vehicle. The invention more particularly relates to an image generating device and a head-up display comprising such a device. Background Art

[0002] The principle of a head-up display in an automobile is to project an image containing, for example, information useful for driving, directly into the driver's field of vision, in particular onto the vehicle windshield.

[0003] To this end, a head-up display comprises an image generating device, such as a light source coupled to an array of variable transmittance elements, such as a liquid crystal display (LCD), and an optical system for transmitting this image to a partially transparent strip, e.g. so that the driver can see the image without taking his eyes off the road.

[0004] The optical power required to display images in the driver's field of view requires the use of very high-intensity light sources, reaching levels in the millions of candela range. However, arrays of variable transmittance elements typically have high absorption rates, on the order of 90% for elements (or pixels) that are turned on and 99% for elements that are turned off. Consequently, this absorption of light by the array poses a risk of overheating and damage.

[0005] Furthermore, the location of the displays under the windshield of a motor vehicle makes them very likely to receive solar flux, which circulates through the display along the reverse path of the light rays from the light source and, after passing through the optical system, is concentrated at a point on the screen. In addition to the temperature increase caused by the light source itself, the focusing of the solar rays is likely to damage the array of variable transmittance elements. Summary of the Invention

[0006] The present invention proposes a means of limiting the extent to which an array of variable transmittance elements heats up.

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

[0008] With the help of an opaque mask, heat generated by light rays whose paths pass through optically non-useful areas (i.e., light rays that are not useful for image formation), as well as heat generated by sunlight, can be transferred to a heat sink and dissipated. This limits the temperature rise of the array of variable transmittance elements, thereby reducing the risk of damage due to overheating of the device. Furthermore, the mask improves the contrast of the generated image. Specifically, while elements (or pixels) of an array of variable transmittance elements that are closed do not always completely and effectively block light, an opaque mask allows for complete light blocking.

[0009] According to one embodiment, the contour of the opaque mask is obtained from the contour of the optically useful area by means of a homothetic transformation with a ratio greater than one.

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

[0011] According to one embodiment, an opaque mask is placed upstream of the array of variable transmittance elements relative to the direction of propagation of the light. Placing the mask upstream of the array makes it possible to limit the extent to which the array of variable transmittance elements is heated by the light 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 the face of the array of variable transmittance elements, and the opaque mask is 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 array of variable transmittance elements, and the opaque mask is in contact with a face of the optical diffuser.

[0015] According to one embodiment, a first opaque mask is placed upstream of the array of variable transmittance elements and a second opaque mask is placed downstream of the array of variable transmittance elements with respect 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, a head-up display is provided comprising an image generating device according to the invention and a control unit configured to control an array of variable transmittance elements such that elements located outside the optically useful area permanently have a transmittance of less than 1%.

[0018] Of course, the various features, variants and embodiments of the present invention can be associated with one another in various combinations, as long as they are not mutually exclusive or incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Furthermore, various other features of the present invention will become apparent from the accompanying description, provided with reference to the accompanying drawings, which illustrate non-limiting embodiments of the invention and in which:

[0020] Figure 1 shows an embodiment of a head-up display according to the present invention,

[0021] Figure 2 shows a specific configuration of an image generating device according to the present invention,

[0022] Figure 3 Shown according to Figure 2 A specific embodiment of the configuration of the image generating device,

[0023] Figure 4 shows another specific configuration of the image generating device according to the present invention,

[0024] Figure 5 shows another specific configuration of the image generating device according to the present invention,

[0025] Figure 6 shows another specific configuration of the image generating device according to the present invention,

[0026] Figure 7 shows another specific configuration of the image generating device according to the present invention,

[0027] Figure 8 shows another specific configuration of the image generating device according to the present invention,

[0028] Figure 9 Another specific configuration of the image generating device according to the present invention is shown.

[0029] Note that in these figures, structural and / or functional elements common to the various variations may have the same reference numerals. DETAILED DESCRIPTION

[0030] Figure 1 The main elements of a head-up display 1 are shown schematically, which is intended to be installed in a vehicle, such as a motor vehicle, for example.

[0031] Such a display 1 is suitable for creating a virtual image I in the field of view of a vehicle driver, such that the driver can see the virtual image I and any information it contains without having to change the direction they are looking.

[0032] To this end, the display 1 comprises a partially transparent strip 2 placed in the driver's field of vision, image generating means 3 adapted to generate a downstream beam Lv and optical transmission means 4 , 5 adapted to reflect the beam generated by the image generating means 3 in the direction of said partially transparent strip 2 .

[0033] The partially transparent strip 2 is in this case the windshield of the vehicle. In other words, it is the windshield of the vehicle that serves as the partially transparent strip for the head-up display 1 .

[0034] According to a variant, the partially transparent strip may be a combiner, ie a partially transparent strip detached from the windscreen and intended for the head-up display 1. Such a combiner would be placed between the vehicle's windscreen and the driver's eyes YX, on the course of the downstream beam Lv.

[0035] In this case, the optical transmission means further comprise two folding mirrors 4, 5 arranged so as to reflect the downstream light beam Lv generated by the image generating device 3 in the direction of the partially transparent strip 2. The folding mirrors advantageously allow the image generating device 3 to be placed in a configuration not facing the partially transparent strip 2 and therefore in any suitable location, typically under the dashboard of the vehicle.

[0036] In this case, the first folding mirror 4 is a plane mirror and the second folding mirror 5 is a mirror with an optimized shape for generating a virtual image with a shape adapted to the shape of the partially transparent strip 2, in this case a curved shape, in such a way that the image I is displayed without distortion.

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

[0038] The image generating device 3 includes a light source 6 (in this case, a backlight module) configured to generate an upstream light beam Lm, an array 7 of variable transmittance elements (in this case, 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 array 7. In this case, a diffuser 12 is placed between the light source 6 and the array of variable transmittance elements, on the optical path of the upstream light beam Lm.

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

[0040] The head-up display device 1 further comprises a (generally opaque) housing 9 which contains the image generating means 2 and the optical transmission systems 4 , 5 , in particular in order to protect these elements from any external attack (dust, liquids, etc.).

[0041] The housing 9 comprises an opening 10 through which the downstream light beam Lv passes after being reflected on the second folding mirror 5 in this case.

[0042] The opening 10 in the housing 9 is closed by a window 11 (sometimes called a "cover window"), formed, for example, from a sheet of plastic, such as polycarbonate, having a thickness ranging 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 generating means 3 , in particular the light source 6 and the array of variable transmittance elements 7 , in particular according to control signals input by a 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 array 7 of variable transmittance elements, for example, in this case its upstream face. The array 7 comprises at least one optically useful area 15, and in particular, in this case, seven optically useful areas 15. Outside the optically useful area 15, the array 7 of variable transmittance elements is said to be non-optically useful.

[0045] For example, the optically useful area is considered to be the area intended for displaying information (e.g., text or images). Therefore, the elements or pixels in this area are controlled in such a way that they are optically active at least at certain times. The non-optically useful area is the area not intended for displaying information. Elements or pixels in the non-optically useful area are permanently in the off state. The definition of the optically useful area and the non-optically useful area is controlled by control unit 13. Conventionally, control unit 13 is programmed before device 3 is sold so that the optically useful area and the non-optically useful area cannot be changed. Specifically, system designers define various non-overlapping areas for displaying information to the driver in order to cover all possible situations. Therefore, areas outside these display areas are typically not used at any time. Note that an optically useful area in which all pixels are temporarily turned off is still an optically useful area. In other words, by design, control unit 13 is configured or programmed to command each pixel in the optically useful area to be turned on or off, depending on the information to be displayed, and to command each pixel in the non-optically useful area to be turned off (permanently).

[0046] The image generating device 3 may experience an increase in its temperature due to an increase in the vehicle's ambient temperature, heat generated by the light source 6, and sunlight penetrating into the housing 9 via the window 11 along the reverse path of the downstream light beam Lv. In particular, elements (or pixels) of the array having low transmittance, such as non-optically useful pixels that are permanently in the off state, are more likely to experience a significant increase in temperature.

[0047] According to an advantageous characteristic of the invention, the image generating device 3 comprises a heat dissipation system 14 situated opposite the array of variable transmittance elements 7 and at a distance therefrom. Figure 3 Shown in.

[0048] from Figure 3 As can be seen in FIG, heat dissipation system 14 comprises an opaque mask 16 and a heat sink 17 thermally coupled to mask 16, for example in contact with mask 16 and, in this case, located on the periphery of mask 16. In this case, mask 16 is a rectangular flat mask having dimensions substantially equal to those of array 7 of variable transmittance elements, comprising a plurality of openings 18, the number of which in this case is equal to the number of optically useful areas 15. More specifically, in this case, the positions of openings 18 are chosen such that each opening 18 is opposite optically useful area 15, in other words, such that light rays from light source 6 (whose optical path is directed through the optically useful area) can pass through openings 18 and are not blocked by mask 16.

[0049] Preferably, in this case, the contour of each opening 18 is derived from the contour of the optically useful area 15 situated opposite it by means of a homothetic transformation having a ratio greater than 1. Preferably, the homothetic ratio is close to 1 (e.g., 1.1 or 1.2) in order to make the mask more selective. Thus, rays whose propagation direction passes through the edge of the useful area 15 will pass close to the edge of the opening 18. Consequently, a minority of rays have a propagation direction that passes both outside the optically useful area and through the opening 18.

[0050] Heat sink 17, in this case, is a passive heat sink that relies on convection. It comprises a base 19, which contacts the mask, and a plurality of fins 20. The function of the fins 20 is to increase the surface area of ​​heat sink 17 in contact with the air, thereby improving heat dissipation. In this case, the fins 20 are parallel to each other and substantially parallel to the surface of mask 16. Thus, the fins extend from base 19 in a direction away from the mask.

[0051] The mask 16 and the heat sink 17 are in this case made of a thermally conductive material, in other words, a material having a thermal conductivity equal to or greater than 60 W.m -1 .K -1The heat sink 17 has a thermal conductivity at least equal to the thermal conductivity of the mask 16. For example, in this case, the mask 16 and the heat sink 17 are made of the same material, in this case aluminum, which has a thermal conductivity of 226 W.m -1 .K -1 .

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

[0053] Figure 4 The configuration of the image generating device 3 is shown in which the heat dissipation system 14 is placed upstream of the array of variable transmittance elements. When placed upstream of the array 7 of variable transmittance elements, the heat dissipation system 14 absorbs some of the light from the light source 6 and dissipates the heat generated by it. As a result, these rays do not reach the screen, advantageously preventing it from heating up.

[0054] In this case, heat dissipation system 14 is positioned between optical diffuser 21 and the array of variable transmittance elements 7. In this example, image generating device 3 includes an at least partially transparent thermally conductive plate 22, such as a transparent ceramic plate in this case. In this case, the downstream face of plate 22 is in contact with the upstream face of the array of variable transmittance elements 7. In this case, the downstream face of mask 16 is in contact with the upstream face of plate 22. Mask 16 is thus advantageously thermally coupled to the array of variable transmittance elements and makes it possible to limit the temperature increase of array 7, for example, caused by sunlight reaching the downstream face of array 7.

[0055] Figure 5 An embodiment of this configuration is shown. In this example, the image generating device 3 comprises a housing 23, at the bottom of which is located a light source 6, in this case a printed circuit board 24 comprising a plurality of light-emitting diodes 26. The light source 6 is positioned so as to generate a light flux in the direction of openings 18 provided in the wall of the housing 23, opposite the bottom of the housing 23 (as will be seen below, the openings 18 are also openings in the mask 16). These openings are blocked by a transparent ceramic plate 22, to the downstream face of which is attached an array of variable transmittance elements 7.

[0056] In the optical path of the light coming from the light source 6, in other words, between the light source 6 and the array 7 of variable transmittance elements, there are various optical elements, in particular a 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, housing 23 comprises two separate parts, a first part 28 of which comprises the bottom of housing 23 and a second part 29 of which comprises opening 18. Diffuser 21 and reflective polarizer 26 are held in place by being clamped between these two parts 28, 29 of housing 23.

[0058] Advantageously, the second portion 29 of the housing 23 forms the mask 16 (or, in other words, the mask 16 is integrated into the second portion 29 of the housing 23), and the opening 18 made in the housing forms the opening 18 in the mask 16. The heat sink 17 is attached to the outer wall of the second portion 29 of the housing 23.

[0059] In this example, the inner wall of the second portion 28 (including the upstream face of the mask 16) is covered with a reflective coating 30. Thus, the second portion 29 of the housing 23 forms a reflector, and light reflected on the upstream face of the mask 16 may pass through one of the openings 18 after several reflections on the inner wall of the housing 23. This enhances the brightness of the device 3.

[0060] according to Figure 6 In another embodiment shown, the heat dissipation system 14 is located between the optical diffuser 21 and the array of variable transmittance elements 7. In this case, the heat dissipation system 14 is located at a distance from the array of variable transmittance elements and at a distance from the diffuser 21. No intermediate elements are placed between the mask and the array 7 or the diffuser 21, at least in the optical path of the light rays, which are directed through the optically useful area 15. The distance between the heat dissipation system 14 and the array of variable transmittance elements 7 advantageously allows for thermal isolation of the two elements. Thus, if the temperature rise caused by the light from the light source 6 is too great for the heat dissipated by the heat dissipation system 14, the heat is not directly transferred to the array of variable transmittance elements 7.

[0061] Figure 7 The configuration of device 3 is shown in which heat dissipation system 14 is placed upstream of array 7 of variable transmittance elements, in this case between light source 6 and diffuser 21. In this case, the downstream face of opaque mask 16 is in contact with the upstream face of diffuser 21. The dimensions of the mask in this case are substantially the same as those of diffuser 21, and the heat dissipation extends beyond the profile of heat dissipation system 16. This configuration makes it easy to attach heat dissipation system 14 to image-generating device 3. Furthermore, placing mask 16 as close as possible to the light source also makes it possible to limit the temperature rise of optical elements located further downstream, such as diffuser 21 in this case.

[0062] Figure 8The configuration of the device 3 is shown in which the heat dissipation system 14 is placed upstream of the array 7 of variable transmittance elements, in this case between the light source 6 and the diffuser 21. The dimensions of the mask 16 in this case are substantially the same as those of the diffuser 21, and the heat sink 17 extends beyond the contour of the diffuser 21. The heat dissipation system 14 is in this case at a distance from the diffuser 21 and at a distance from the light source 6, and no intermediate elements are placed between the mask and the light source 6 or the diffuser 21. At least, no intermediate elements are placed in the optical path of the light rays, the direction of which passes through the optically useful area 15.

[0063] Figure 9 A configuration of image generation device 3 is shown in which heat dissipation system 14 is placed downstream of array 7 of variable transmittance elements. In this configuration, system 14 advantageously blocks solar rays from reaching the downstream face of the array of variable transmittance elements and dissipates the heat they generate. In this example, a thermally conductive transparent plate 22 is in contact with the downstream face of array 7 of variable transmittance elements, and a mask 16 is in contact with the downstream face of transparent ceramic plate 22. Mask 16, placed downstream of array 7, is preferably covered with a black or dark coating, which absorbs solar rays and prevents them from reflecting toward the partially transparent strips.

[0064] The present invention is not limited to the above combination Figures 1 to 8 Described embodiment.

[0065] In particular, although an image generating device has been described that includes a single heat dissipation system 14, the present invention is compatible with devices that include several heat dissipation systems placed at different locations on the device 3. For example, according to some embodiments, the device includes a first heat dissipation system placed upstream of the array of variable transmittance elements 7 and a second heat dissipation system placed downstream of the array of variable transmittance elements 7.

[0066] Furthermore, the present invention is not limited to heat dissipation systems comprising a single mask or a single heat sink. For example, some embodiments of the present invention include two masks, one placed upstream of an array of variable transmittance elements and another placed downstream of the array of variable transmittance elements, both coupled to the same heat sink. Other embodiments include one or more heat dissipation systems, each comprising a mask thermally coupled to multiple heat sinks.

[0067] The above has been combined Figure 5 A mask integrated in a housing is described, the upstream face of the mask being covered with a reflective coating. However, the presence of a reflective coating on the upstream face of the mask is not limited to this embodiment and can be found in embodiments in which the mask is independent of the housing.

[0068] The present invention is not limited to heat sinks that are in contact with the mask. According to some embodiments, the heat sink is not in contact with the mask, but is thermally coupled to the mask via a thermally conductive material (e.g., thermal paste). Alternatively, the mask and heat sink are formed as a single piece with material continuity between them.

[0069] The above-described mask includes openings obtained from the outline of the active area by a homothetic transformation having a ratio greater than 1. However, the present invention is not limited to such a mask and is compatible with masks having different profiles. For example, an embodiment includes a mask having a smaller size than the array of variable transmittance elements and being placed facing only a portion of the array of variable transmittance elements.

[0070] Finally, although only one embodiment has been described in which the heat dissipation system 14 is placed downstream of the array, the present invention is not limited thereto. Thus, such an embodiment may or may not include a thermally conductive transparent plate, and the heat dissipation system may be located at any non-zero distance from the array of variable transmittance elements and separated therefrom by one or more intermediate elements, provided that the intermediate elements do not block light rays from passing through the optically useful region in the direction of their optical path.

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

Claims

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

2. The device according to claim 1, wherein The contour of the opaque mask (16) is obtained from the contour of the optically useful area (15) by a homothetic transformation with a ratio greater than 1.

3. The device according to claim 1 or 2, wherein: The opaque mask (16) is configured to block all light rays whose optical paths pass through the non-optically useful region.

4. The device according to any one of claims 1 to 3, wherein The opaque mask (16) is placed upstream of the array of variable transmittance elements (7) relative to the propagation direction of the light.

5. The device according to claim 4, wherein The upstream face of the opaque mask is covered with a reflective coating (30).

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

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

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

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

10. A head-up display comprising an image generating device according to any one of claims 1 to 9 and a control unit (13), the control unit (13) being configured to control the array of variable transmittance elements (7) such that elements located outside the optically useful area permanently have a transmittance of less than 1%.

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