Image generation device, method for managing the temperature of such a device, and head-up display incorporating this device

Abstract

An image generation device (3) is proposed, comprising a screen (7) which includes a central area (14) at least partially optically useful and a peripheral area (13) not optically useful. The device includes a screen temperature measurement system (12) comprising a temperature sensor (21) and a thermally conductive opaque film (15) configured to be in contact with one face of the screen. The film includes at least a first portion (16) extending into a non-optically useful area of ​​the central zone and a second portion (17) extending into the peripheral zone, which has material continuity with the first portion and is thermally coupled to the temperature sensor. A method for temperature control in such a device and a head-up display comprising such a device are also proposed. Figure for the abstract: Fig. 2

Description

Title of the invention: Image generation device, method for managing the temperature of such a device, and head-up display comprising this device technical field

[0001] The present invention relates to the technical field of automobiles, and in particular to the technical field of display devices for motor vehicles.

[0002] The invention relates more particularly to an image generation device, a method for managing the temperature of this device and a head-up display comprising such a device. Technological background

[0003] The principle of head-up displays for vehicles is to project images, including for example information useful for driving, directly into the field of vision of a driver, in particular at the level of the windshield of the vehicle.

[0004] To this end, head-up displays include an image generation device, for example, a light source coupled to a screen. The screen may be, for example, an array of elements with variable transmittance, such as a liquid crystal display (LCD), or a diffuser whose front face is configured to be scanned by a laser beam (this is then called a laser scanning screen). Head-up displays also include 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.

[0005] The placement of the displays under the windshield of the motor vehicle makes them susceptible to receiving solar radiation circulating within the display, following the reverse path of the light rays from the light source, and which converges, after passing through the optical system, at a point on the screen. The focusing of the solar rays, combined with the temperature rise generated by the light source itself, is likely to damage the screen.

[0006] Solutions exist to try to remedy this problem and include, for example, the use of temperature sensors placed locally at different locations on the screen. These solutions are only partially satisfactory, since on the one hand they only allow local temperature detection, and on the other hand they can obstruct the optical path of the rays from the light source, and therefore degrade the quality of the projected image. Summary of the invention

[0007] The present invention aims to remedy the aforementioned problems by providing a means of measuring the temperature over a large area of ​​the screen, without degrading the quality of the projected image.

[0008] According to one aspect of the invention, an image generation device is proposed comprising a screen which includes a central area at least partly optically useful and a peripheral area not optically useful, the device comprising a screen temperature measurement system which includes - a temperature sensor and - a thermally conductive opaque film configured to be in contact with a face of the screen, the film having at least a first part which extends into a non-optically useful area of ​​the central area and a second part which extends into the peripheral area, which has a continuity of material with the first part and which is thermally coupled to the temperature sensor.

[0009] Thanks to the thermally conductive film on the screen, the heat generated by the light beam from a backlight module or by sunlight can be transferred to the temperature sensor. In particular, the first section, which extends into the central area, allows the heat generated by a solar flux focused on a point on the screen to be captured by the temperature management system regardless of the point of incidence of the solar flux. This makes it possible to measure the screen temperature and, for example, to adapt the operation of the image generation device accordingly to prevent overheating. Furthermore, an opaque film on the non-optically useful areas prevents light rays from reaching the screen and thus helps to prevent it from heating up.

[0010] For example, a film is considered to be thermally conductive if its thermal conductivity is greater than or equal to 60 Wm*.K'.

[0011] According to one embodiment, the temperature sensor is in contact with the second part.

[0012] According to one embodiment, the first part is a tab which extends into the central area from the second part.

[0013] According to one embodiment, the first part is located at a distance of at least one millimeter from any optically useful area.

[0014] According to one embodiment, the first part extends in the central area over a length greater than or equal to three millimeters.

[0015] According to one embodiment, the device comprises a light source configured to emit a luminous flux through the screen and the thermally conductive opaque film is in contact with the downstream face of the screen, relative to the direction of propagation of the luminous flux.

[0016] According to one embodiment, the thermally conductive film has a thermal conductivity greater than or equal to 200 Wm*.K and preferably greater than or equal to 398 Wm*.K

[0017] According to one embodiment, the thermally conductive opaque film is configured to absorb at least 90% (and preferably at least 98%) of light rays with wavelengths between 450 nanometers and 750 nanometers. In other words, the opaque film is configured to absorb visible light radiation.

[0018] According to one embodiment, the thermally conductive film is glued to the screen using an adhesive material resistant to temperatures greater than or equal to 110°C.

[0019] According to another aspect, a method for managing the temperature of an image generation device according to the invention is proposed, comprising a comparison of an estimated temperature of the screen and the temperature measured by the temperature sensor and, if the measured temperature is higher than the estimated temperature, a reduction in the light intensity produced by the light source.

[0020] According to one embodiment, the estimated temperature of the screen is obtained from a measurement of the temperature of a backlight module of the image generation device and a measurement of the ambient temperature.

[0021] According to another aspect, a head-up display is proposed comprising an image generation device according to the invention and a control unit configured to control the screen and define the optically useful and non-optically useful areas of the screen.

[0022] 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

[0023] 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:

[0024] [Fig. 1] illustrates an embodiment of a head-up display according to the invention,

[0025] [Fig.2] illustrates one embodiment of the image generation device according to the invention,

[0026] [Fig.3] illustrates one implementation of the process according to the invention,

[0027] [Fig.4] illustrates another embodiment of the image generation device according to the invention,

[0028] [Fig.5] illustrates another embodiment of the device according to the invention,

[0029] [Fig.6] illustrates another embodiment of the device according to the invention,

[0030] [Fig.7] Illustrates another embodiment of the device according to the invention.

[0031] 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

[0032] In [Fig. 1], the main elements of a head-up display, intended for example to equip a vehicle, for example a motor vehicle, are schematically represented.

[0033] 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 take his eyes off the road.

[0034] For this purpose, the display 1 includes 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 reflect, in the direction of said partially transparent blade 2, the light beam generated by the image generation device 3.

[0035] The partially transparent blade 2 is here considered to be the vehicle's windshield. In other words, the vehicle's windshield functions as the partially transparent blade for the head-up display 1.

[0036] According to one variant, the partially transparent blade could be a combiner, i.e. a partially transparent blade separate from the windscreen and dedicated to the head-up display 1. Such a combiner would be placed between the windscreen of the vehicle and the eyes YX of the driver, in the path of the downstream light beam Lv.

[0037] Moreover, here, the optical transmission device includes two folding mirrors 4, 5 arranged to reflect the downstream light beam Lv generated by the image generation device 3 towards the partially transparent blade 2. The folding mirrors advantageously allow the image generation device 3 to be placed in a configuration in which it does not face the partially transparent blade 2 and thus to be placed in any suitable location, typically under the dashboard of the vehicle.

[0038] Here, a first folding mirror 4 is a flat mirror, and a second folding mirror 5 is a mirror which has a shape optimized to produce a virtual image of 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.

[0039] 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.

[0040] The image generation device 3 includes a light source 6, here a backlighting module, configured to produce an upstream light beam Lm, a screen, here a matrix of variable transmittance elements 7 configured to be illuminated by the upstream light beam Lm and a reflector 8 interposed between the backlighting module 6 and the matrix 7.

[0041] 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.

[0042] The head-up display device 1 also includes a housing 9 (generally opaque) which encloses the image generation device 2 and the optical transmission system 4, 5 in order in particular to protect these elements against possible external aggressions (dust, liquids, etc.).

[0043] The housing 9 includes an opening 10 through which the downstream light beam Lv passes, here after reflection on the second folding mirror 5.

[0044] The opening 10 of the housing 9 is closed by a window 11 (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.

[0045] The head-up display further includes a control unit 20 configured to control the image generation device 3, in particular the backlight module 6 and the variable transmittance element matrix 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.

[0046] The image generation device 3 may experience an increase in temperature due to the rise in the ambient temperature of the vehicle, the heat generated by the backlight module 6, and solar rays entering the housing 9 through the window 11 along the reverse path of the downstream light beam Lv. After reflection on the folding mirrors 4 and 5, the solar rays may focus on a point on the screen and cause a rise in its temperature.

[0047] According to an advantageous feature of the invention, the image generation device 1 comprises a temperature measurement system comprising a thermally conductive opaque film applied to one of the faces (upstream or downstream, relative to the direction of beam propagation) of the variable transmittance element matrix, here on the downstream face.

[0048] Figure 2 is a view of the downstream face of the transmittance element matrix variable 7, here equipped with temperature measurement system 12.

[0049] The variable transmittance element matrix, here an LCD screen, comprises a peripheral area 13 that is not optically useful and a central area 14 that is optically useful. More precisely, here, the central area 14 is partly optically useful and comprises several distinct optically useful zones 19.

[0050] For the purposes of this invention, an optically useful area is 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 conductive at least part of the time. A non-optically useful area is understood to be an area that is not intended for displaying information. The elements, or pixels, of a non-optically useful area are permanently blocked. The definition of the optically useful and non-optically useful areas is controlled by the control unit 20. Typically, the control unit 20 is programmed before the device 3 is marketed so that the optically useful and non-optically useful areas cannot be modified.Indeed, the system designers define different display areas for the information provided to the driver, without overlap, in order to cover all possible situations. Therefore, outside of these display areas, there generally remain areas that are never used. It should be noted that an optically useful area whose pixels are all temporarily switched to the blocked state remains an optically useful area. In other words, by design, the control unit 20 is configured or programmed to switch each pixel of the optically useful areas to the on or blocked state, depending on the information to be displayed, and to switch each pixel of the non-optically useful areas to the blocked state (permanently).

[0051] The temperature measurement system 12 comprises a thermally conductive opaque film 15 which is bonded to the downstream face of the matrix 7 (relative to the direction of propagation of the light beam from the light source 6), here using an adhesive material, preferably resistant to temperatures greater than or equal to 110°C. The adhesive material is, for example, a film made of a polymer material, such as polycarbonate (PC) or polymethyl methacrylate (PMMA), an optically clear adhesive (OCA), or an acrylic sheet. The thermally conductive film 15 is here a metallic film, for example a copper film, and has a thermal conductivity of 398 W / m²K⁻¹.

[0052] The thermally conductive film 15 is here coated with a black color, for example, paint. Thus, the thermally conductive film 15 is configured to absorb visible light radiation, in particular radiation with wavelengths between 450 nanometers and 750 nanometers. Here, the film coated with the black color allows at least 98% of this light radiation to be absorbed.

[0053] The film comprises at least a first part 16 which extends into the central area 14 and a second part 17, or peripheral part, which extends into the peri-area pherical 13. The first part and the second part are made in the same film, that is to say there is a continuity of matter between them.

[0054] The second part 17 is here in the form of a rectangular frame surrounding the central area 14. The film 15 here comprises a plurality of first parts 16 (only some of which are referenced in [Fig. 2] for clarity) extending into the central area from the second part 17. The first parts 16 are here tabs orthogonal to the side of the second part 17 from which they extend. The tabs extend into the non-optically useful part of the central area. For example, each tab 16 has a length greater than 3 millimeters and is located at a distance of at least one millimeter from any optically useful area.

[0055] The temperature measurement system 12 further comprises a temperature sensor 21 thermally coupled to the second part 17, for example in contact with the second part. For example, the second part 17 comprises an external tab 18 extending from one side of the second part in a direction opposite to the central area 14 and to which the temperature sensor 21 is bonded. In this example, the temperature sensor 21 is a thermistor. Preferably, the tab of the second part extends out of the screen in the direction of and above a data bus 23 connected to the variable transmittance element array 7.

[0056] Thanks to the film 7, the heat generated by the sun's rays is transmitted through the film to the temperature sensor. This makes it possible to adapt the operation of the device 7 so as to prevent it from overheating.

[0057] Figure 3 illustrates a method for managing the temperature of an image generation device according to the invention. This method allows the light intensity produced by the light source 6 to be adjusted according to the temperature measured by the temperature sensor 21.

[0058] In a first step El of the process, the control unit 20 establishes an effective operating setpoint command Ce which will determine the value of the light intensity emitted by the light source 6. To this end, the control unit 20 takes into account a user setpoint value Cu, for example the desired light intensity value entered by the driver, for example from the vehicle's dashboard, and the ambient temperature Ta of the image generation device 3, for example measured by a dedicated sensor located in or near the image generation device 3. For example, if the ambient temperature is low and / or the user setpoint value is low, then the risk of overheating of the variable transmittance element array 7 will be low and the value of the effective setpoint command Ce will be identical to the user setpoint value Cu.On the other hand, if the ambient temperature is high and / or the user setpoint Cu is high, then the risk of overheating of matrix 7 will be. large and the control unit will generate an effective setpoint value Ce lower than the user setpoint value Cu, so that the backlight module 6 produces a lower light intensity than that requested by the driver.

[0059] In a second step of the process E2, the control unit 20 estimates the temperature of the variable transmittance element matrix as a function of the effective setpoint value Ce and the temperature T7 of the light source 6, for example measured using a dedicated sensor placed on or near the backlight module.

[0060] In a third step E3, the control unit 20 records the maximum temperature value Tmax measured by the temperature sensor 21.

[0061] In a fourth step E4, the control unit 20 compares the estimated temperature Te of the variable transmittance element array 7 (estimated in step E2) with the maximum temperature Tmax measured by the temperature sensor. If the measured temperature is higher than the estimated temperature Te, the control unit 20 reduces the light intensity produced by the light source (step E5). Otherwise, the control unit 20 maintains the brightness of the virtual image (step E6).

[0062] The invention is not limited to the embodiment described above in connection with [Fig.2]. In particular, the invention is not limited to a first part in the form of a straight tab.

[0063] For example, as illustrated in [Fig. 4], the first part 16 may comprise a single continuous tab, or strip, which meanders between the optically useful distinct areas 19. Preferably, the strip meanders between the optically useful distinct areas while maintaining a distance greater than 1 millimeter from them. In this example, the second part 17 does not surround the central area 14 and is coincident with the outer tab 18.

[0064] According to the embodiment illustrated in [Fig. 5], the first part 16 may comprise a band having several branches that meander between the distinct optically useful zones 19, some of which may form loops. Here too, the second part does not surround the central zone 14 and is identical with the outer tab 18.

[0065] According to the embodiment illustrated in [Fig. 6], the first part 16 comprises a mesh, some of whose meshes surround the distinct optically useful areas 19 and some of whose meshes surround non-optically useful areas of the central zone. Thus, a large part of the central zone 14 is covered. Here too, the second part 17 does not surround the central zone 14 and coincides with the outer tab 18.

[0066] According to the example in [Fig. 7], the second part 17 forms a frame surrounding the central area 14, and the first part 17 forms a mesh, some of whose meshes surround the distinct optically useful zones 19 and some of which surround non-optically useful zones of the central zone. In this example, the temperature measurement system 12 includes a second temperature sensor 24, the two sensors 21, 24 being placed on the same side of the rectangle formed by the second part 17.

[0067] Although a thermally conductive film placed on the downstream face of the screen, here of the variable transmittance element array 7, has been described previously, the invention covers embodiments in which the thermally conductive film 15 is placed on the upstream face of the screen, or in which each face of the screen is covered by a separate film. In the latter case, each film is either coupled to its own temperature sensor or coupled to a temperature sensor common to both films. Furthermore, the geometry of the films may be identical or different (for example, the configuration of the embodiment of [Fig. 2] on the downstream face and the configuration of the embodiment of [Fig. 4] on the upstream face).

[0068] Furthermore, the invention is not limited to an image generation device comprising a single temperature measurement system per face, nor to a temperature measurement system comprising a single film, nor to a given number of temperature sensors. Depending on the intended applications, the measurement system(s) may comprise several films on the same face of the screen, placed at different locations on the screen, and each film may be coupled to any number of temperature sensors.

[0069] The surface area of ​​the variable transmittance element matrix covered by the film is not limited to the embodiments described above, the film being able to cover a larger or smaller area of ​​the screen, for example 5%, 20%, 50%, etc.

[0070] A metallic, thermally conductive copper film has been described previously. However, the invention is compatible with any thermally conductive film, metallic or non-metallic, for example, carbon foil, graphite, aluminum alloy, or ceramic materials. Ceramic materials have the advantage of exhibiting better thermal properties than glass.

[0071] Finally, the invention is not limited to a screen in the form of a matrix of elements with variable transmittance, but is compatible with any screen technology, in particular laser scanning screens.

[0072] Various other modifications may be made to the invention within the scope of the annexed claims.

Claims

Demands

1. Image generation device (3) comprising a screen (7) which includes a central area (14) at least partly optically useful and a peripheral area (13) not optically useful, the device (3) comprising a temperature measurement system (12) for the screen (7) which includes - a temperature sensor (21) and - a thermally conductive opaque film (15) configured to be in contact with a face of the screen (7), the film having at least a first part (16) which extends into a non-optically useful area of ​​the central area (14) and a second part (17) which extends into the peripheral area (13), which has material continuity with the first part (16) and which is thermally coupled to the temperature sensor (21).

2. Device according to claim 1, wherein the first part (16) is a tab which extends into the central area (14) from the second part (17).

3. Device according to claim 1 or 2, wherein the first part (16) is located at a distance of at least one millimeter from any optically useful area of ​​the central area.

4. Device according to any one of claims 1 to 3, wherein the first part (16) extends into the central area (14) over a length greater than or equal to three millimeters.

5. Device according to any one of claims 1 to 4, comprising a light source (6) configured to emit a luminous flux (Lm, Lv) through the screen (7) and in which the thermally conductive opaque film (15) is in contact with the downstream face of the screen (7), relative to the direction of propagation of the luminous flux.

6. Device according to any one of claims 1 to 5, wherein the thermally conductive film (15) has a thermal conductivity greater than or equal to 398 Wm*.K'.

7. Device according to any one of claims 1 to 6, wherein the thermally conductive opaque film (15) is configured to absorb 90% of light rays with wavelengths between 450 nanometers and 750 nanometers.

8. A device according to any one of claims 1 to 7, wherein the thermally conductive film (15) is bonded to the screen using a adhesive material resistant to temperatures greater than or equal to 110°C.

9. A method for managing the temperature of an image generation device according to any one of claims 1 to 8, wherein a light source emits a light beam, comprising a comparison of an estimated screen temperature and the temperature measured by the temperature sensor and, if the measured temperature is higher than the estimated temperature, a reduction in the light intensity produced by the light source.

10. A temperature management method according to claim 9, wherein the estimated screen temperature is obtained from a temperature measurement of a backlight module of the image generation device and an ambient temperature measurement.

11. Head-up display comprising an image generation device (3) according to any one of claims 1 to 8 and a control unit (20) configured to control the screen (7) and define the optically useful areas (19) and the non-optically useful areas (13) of the central area of ​​the screen.

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