HEAD-UP DISPLAY FOR MOTOR VEHICLES

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

[0001] The present invention relates to a device for displaying luminous information. It relates more particularly to a head-up display for a motor vehicle. TECHNOLOGICAL BACKGROUND

[0002] It is valuable for the driver of a motor vehicle to be able to view information relating to the operation of his vehicle, without having to look away from the road. To meet this expectation, the use of head-up displays is known, making it possible to display this information in the form of virtual images, near or at the level of the vehicle's windshield, so that this information is present in the driver's field of vision when he is driving. Patent application FR3066865A1 discloses a head-up display of this type.

[0003] A head-up display consists of a first part generating a light beam containing information and a second part allowing the information to be displayed in the form of a virtual image. More precisely, the information is transmitted to the light beam at a backlit screen by a light source generating the light beam. The transmittance of the screen varies locally and in a controlled manner over time, in order to encode the light beam into a desired piece of information. It is common to interpose an optical conduit between the light source and the screen, to allow more intense and more homogeneous illumination of the screen. The optical conduit then forms an enclosed space in which the heat emitted by the light source and the heat generated by the screen during their operation accumulates. However, beyond a critical temperature, the operation of the screen is altered more or less irreversibly.

[0004] To avoid this, the use of thermal radiators is known to dissipate the heat of the screen more quickly into its environment and thus limit its heating. The emissive part of the thermal radiators is usually positioned between the light source and the screen. However, this solution has the disadvantage of placing the emissive part of the thermal radiators between the two main heat sources of the head-up display, and therefore of limiting the performance of the thermal radiators. This solution also has the disadvantage of cluttering the space around the optical conduit, which creates additional constraints for the integration of the head-up display.

[0005] The present invention aims to resolve these problems by proposing a head-up display for a motor vehicle, which is both less bulky while allowing better cooling of its screen. SUBJECT OF THE INVENTION

[0006] In this context, the present invention proposes a head-up display for a motor vehicle, comprising a screen composed of a matrix made up of elements whose transmittance varies in a controlled manner over time, between a front face and a rear face of the screen, a light source illuminating the front face of the screen with a light beam, and a rear optical conduit arranged opposite the rear face of the screen so that a light beam emitted by the screen passes through the rear optical conduit.

[0007] The invention is remarkable in that the head-up display comprises a heat collector thermally connecting the screen to the rear optical conduit, so as to promote a transfer of heat from the screen to the rear optical conduit, and in that the heat collector comprises an intermediate element interposed between the rear face of the screen and the rear optical conduit, the intermediate element being thermally connected to a thermal radiator extending along the rear optical conduit.

[0008] Thus, advantageously, the heat emitted by the screen is preferentially dissipated at the rear optical conduit. As a result, excessive heat accumulation in the front optical conduit is avoided, thus limiting the risk of deterioration of the light source and the screen due to excessive heating of their components. According to another advantage, the heat from the screen is dissipated into the environment via the rear optical conduit. In other words, to cool the screen, the invention favors the use of the rear optical conduit as a heat sink. This solution advantageously makes it possible not to clutter the space around the front optical conduit with, for example, a heat radiator dedicated to the screen. A head-up display according to the invention is therefore more compact and more easily integrated into a motor vehicle, compared to the state of the art described above.According to another advantage, the use of the rear optical conduit as a heat sink allows more efficient cooling of the display because the environment of the rear optical conduit is significantly less hot than the environment of the front optical conduit, the latter being present between the two main heat sources of the head-up display.

[0009] Other non-limiting and advantageous characteristics of the device according to the invention are as follows: the head-up display comprises a front optical conduit interposed between the light source and the front face of the screen; the heat collector is arranged so as to allow greater transmission of the heat produced by the screen to the rear optical conduit than to the front optical conduit; the heat collector is arranged so as to allow the transmission of more than 50%, preferably more than 70% of the heat produced by the screen to the rear optical conduit; the heat collector has a thermal conductivity equal to or greater than the thermal conductivity of the screen; the heat collector has a thermal conductivity equal to or greater than the thermal conductivity of the front optical conduit; the heat collector has a thermal conductivity equal to or greater than 0.5 Wm -1< .K -1< (and preferably greater than 5 Wm -1< .K -1< );the screen comprises on its rear face, a first metal frame surrounding the matrix, the heat collector connecting the first metal frame to the rear optical conduit; the heat collector comprises a second metal frame surrounding the matrix at the front face of the screen, the second metal frame comprising at least one lateral edge thermally connected to the rear optical conduit; at least one lateral edge of the second metal frame extends along the rear optical conduit; at least one lateral edge of the second metal frame is located outside the rear optical conduit; the screen comprises on its rear face, a non-metallic (but thermally conductive) frame, surrounding for example the matrix; alternatively, the screen could have no frame (neither on its front face nor on its rear face); a thermally insulating layer is interposed between the non-metallic frame and the rear optical conduit;the heat collector is thermally coupled with active cooling means, preferably with means promoting the circulation of ambient air at the rear optical conduit and / or a means implementing a thermoelectric effect of the Peltier effect type; the active cooling means are mainly present at the rear optical conduit; the rear optical conduit and / or the front optical conduit comprise passive or active cooling means, promoting better diffusion of heat to the external environment; the rear optical conduit and / or the front optical conduit comprise at least one cooling fin and / or a passage promoting the circulation of air from the inside to the outside of the optical conduit(s);the head-up display comprises a device for projecting the light beam towards a partially transparent blade (this partially transparent blade may be a dedicated blade located between the driver and the windshield of the vehicle, this partially transparent blade may alternatively be the windshield of the vehicle).;

[0010] An example not forming part of the invention also relates to a motor vehicle comprising a head-up display according to one of the preceding claims. DETAILED DESCRIPTION OF AN EXAMPLE OF IMPLEMENTATION

[0011] The description which follows with reference to the attached drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented: there Figure 1represents a schematic longitudinal section of a first exemplary embodiment of a head-up display according to the invention, in position in a partially illustrated motor vehicle; Figure 2 represents a schematic longitudinal section of a second exemplary embodiment of a head-up display according to the invention; Figure 3 represents a schematic longitudinal section of a third exemplary embodiment of a head-up display according to the invention.

[0012] As a reminder, the present invention proposes a head-up display for a motor vehicle that is less bulky and allows for better cooling of its screen.

[0013] There Figure 1 presents a first embodiment of a head-up display 2 according to the invention. The display 2 comprises an image generation device 4 and a device 6 for projecting said images.

[0014] The image generation device 4 comprises a light source 8 comprising at least one light-emitting diode 10 (or LED for “Light Emitting Diode”). For example, the LEDs may be arranged in one or more rows. The light source 8 is arranged so as to emit a light beam 12 illuminating a front face 14 of a screen 16.

[0015] The screen is composed of a matrix 18 made up of elements whose transmittance varies in a controlled manner over time, between the front face 14 and a rear face 20 of the screen. The transmittance of the matrix 18 is controlled by a device not shown in the figures for clarity. The transmittance of each element is controlled independently, in order to modify locally and over time, the opacity of the screen 16. The light beam 12' emerging from the rear face 20 of the screen, thus forms a pixelated light beam whose pattern and intensity can be modified according to the information that one wishes to communicate to the driver of the vehicle. By way of non-limiting example, a matrix 18 may comprise a liquid crystal screen (or LCD for "Liquid Crystal Display"), for example with thin-film transistors (or TFT for "Thin-Film Transistor").It should be noted that usually, due to its design (using an input polarizer at the front face 14 and an output polarizer at its rear face 20) this type of matrix 18 mainly absorbs the light beam 12 at the rear face 20 of the screen (in particular when the displayed image comprises a majority of dark pixels, which is frequently the case).

[0016] The projection device 6 mentioned above comprises a reflection surface 22 in order to direct the light beam 12' towards a partially transparent blade 24. Advantageously, the blade 24 is placed between a windshield 26 of the motor vehicle and the eyes 29 of the driver, partially shown in the figures in order to facilitate understanding of the invention. The blade 24 is arranged so as to be present in the field of vision 28 of the driver in a driving situation. The blade 24 is partially transparent so as not to obscure a part of the field of vision 28 of the driver, while allowing the display in the direction of the blade 24 of light information that the driver sees in the form of a virtual image 30. According to an alternative embodiment not illustrated, the partially transparent blade can be confused with the windshield. In other words, the windshield can play the role of the partially transparent blade.

[0017] In order to optimize the intensity of the light beam 12 illuminating the screen 16, a front optical conduit 32 (possibly forming a reflector) is interposed between the light source 8 and the front face 14 of said screen. The front optical conduit 32 also makes it possible to prevent light leaks from the light beam 12. For the same reasons (as well as for aesthetic reasons), a rear optical conduit 34 is also placed on the path of the light beam 12' between the rear face 20 of the screen and the blade 24, in particular here between the rear face 20 of the screen 16 and the reflection surface 22.

[0018] As mentioned above, the front optical conduit 32 delimits an enclosed space 36 between the light source 8 and the screen 16, in which the heat generated by the screen 16 and by the light source 8 dissipates. In order to limit a build-up of heat in the front optical conduit 32, the present invention proposes to promote a dissipation of the heat emitted by the screen 16 through the rear optical conduit 34.

[0019] For this, as illustrated by the Figure 1, a heat collector 38 is used to thermally connect the rear face 20 of the screen to the rear optical conduit 34. According to the present example, the heat collector 38 is composed of an intermediate element 38A, interposed between the rear face 20 of the screen 16 and the rear optical conduit 34. The intermediate element 38A is characterized by a thermal conductivity equal to or greater than the thermal conductivity of the screen 16. This means that the thermal conductivity of the intermediate element 38A is equal to or greater than the thermal conductivity of the surface of the screen in contact with the intermediate element. Preferably, the thermal conductivity of the intermediate element 38A is equal to or greater than 0.5 Wm -1< .K -1< , preferably greater than 5 Wm -1< .K -1< (or even greater than 15 Wm -1< .K -1< ). The intermediate element 38A can be a glue or a thermal paste.According to the present example, the intermediate element 38A is a thermally conductive foam, marketed by the company SEKISUI CHEMICAL CO., LTD. under the reference “XLIM - CL”, consisting of a polyolefin elastomer constituting the substrate of a mixture of air bubbles and thermally conductive elements based on ceramics. The thickness of the intermediate element 38A is preferably greater than 0.1 mm.

[0020] It should be noted that the heat collector 38 is thermally connected to the rear optical conduit 34, so as to promote dissipation of more than 50% of the heat produced by the screen, at the walls of said optical conduit. This arrangement is significantly more advantageous compared to the state of the art described above, because the rear optical conduit 34 is not located between the two main heat sources of the display 2, unlike the front optical conduit 32. In other words, the rear optical conduit 34 is less hot than the front optical conduit 32, it thus forms a significantly more interesting heat sink than the front optical conduit 32. For this purpose, the rear optical conduit may comprise one or more cooling fins 40A and / or one or more passages 40B promoting the circulation of air from the inside to the outside of the rear optical conduit.

[0021] As illustrated by the Figure 1, according to the invention at least a portion of the intermediate element 38A is thermally connected to a thermal radiator 40C, extending along the rear optical conduit 34. Advantageously, the invention makes it possible to no longer clutter the space around the front optical conduit 32 with a thermal radiator, thus at the same time promoting better cooling of the front optical conduit. Optionally, the thermal radiator 40C can be coupled with an active cooling means of the fan type or an element implementing the Peltier effect, not shown in the Figure 1 .

[0022] The rear optical conduit 34 is made of a naturally heat-conducting material such as a thermoplastic. A thermoplastic is preferred whose thermal conductivity is at least equal to that of the intermediate element 38A (i.e. whose thermal conductivity is here greater than 0.5 Wm -1< .K -1< ). As a non-limiting example, a thermoplastic marketed by the company CELANESE, under the reference “COOL POLY” of the polyamide 6 (PA6) type, may be chosen. Since the rear optical conduit 34 is of a significant size (and therefore volume) (in particular compared to the screen 16), it can absorb a significant portion of the heat generated by the screen 36. It should be noted that the front optical conduit 32 may also comprise one or more cooling fins and / or one or more passages promoting the circulation of air from the inside to the outside of the front optical conduit (not shown in the figures).

[0023] THE figures 2 And 3 now illustrate different embodiments of the invention. The elements common to these different embodiments are indexed below by the same reference numbers and will not be described again.

[0024] According to a second embodiment of the invention, illustrated by the Figure 2, the screen 16 comprises on its rear face 20, a heat collector 38 comprising a first metal frame 42A. This first metal frame 42A surrounds the matrix 18 so as to allow the passage of the light beam 12. The first metal frame 42A is thermally connected to the rear optical conduit 34 by an intermediate element 38A described above. Advantageously, the presence of the first metal frame 42A allows a larger thermal contact surface with the screen 16, in order to promote a greater thermal heat flow from the screen to the rear optical conduit 34. The first metal frame 42A can be made of aluminum or stainless steel. For similar efficiency compared to the first embodiment described above, the rear optical conduit 34 can be made with materials whose thermal conductivity is lower. This second embodiment is therefore more economical than the first embodiment.It should be noted that the intermediate element 38A can also be arranged so as to form a layer 42, thermally connecting the first metal frame 42A to a thermal radiator 40C, extending along the rear optical conduit 34.

[0025] According to a third embodiment of the invention illustrated by the Figure 3, the heat collector 38 comprises a second metal frame 42B, in contact with the front face 14 of the screen 16. This second metal frame 42B surrounds the matrix 18, so as to allow the light beam 12 emitted by the light source 8, to illuminate at least a portion of the matrix 18. The second metal frame 42B comprises lateral edges 44 extending on each side of the screen 16. The ends 46 of the lateral edges 44 surround the end of the rear optical conduit 34 and are in contact with its outer surface in order to allow optimal heat transfer between the screen 16 and said rear optical conduit 34. According to a variant not shown, an intermediate element can be interposed between the lateral edges 44 and the rear optical conduit 34 in order to optimize the heat transfer. This intermediate element can be of the same or similar nature as the intermediate element 38A described above.It should be noted that no intermediate element 38A is any longer necessary between the rear face 20 of the screen 16 and the optical conduit 38, the second metal frame 42B playing the role of the heat collector 38. However, it is possible to combine the second and third embodiments described above to obtain a more efficient heat transfer from the screen 16 to the rear optical conduit 34. It should be noted that a lateral edge 44 of the second metal frame can be arranged so as to be in contact with a thermal radiator 40C, extending along the rear optical conduit 34.

[0026] In the examples described above, close contact is preferred between, on the one hand, the heat collector and the screen and, on the other hand, between the heat collector and the rear optical conduit. For this, it is possible to use holding means such as thermal glue, screws or others. According to another alternative, it is possible to opt for mechanically holding the heat collector in contact with the screen, by applying a mechanical stress to the heat collector via the front optical conduit and / or the rear optical conduit.

[0027] In conclusion, the invention promotes heat dissipation from the screen 16 at its rear face 20, and no longer at its front face 14. This configuration is particularly advantageous, because the rear face of the screen 16 is generally the hottest face due to the fact that (as explained above) the matrix 18 mainly absorbs the light beam 12 at the rear face 20 of said screen and that, in addition, the rear face 20 can also be subjected to heating due to external light radiation (generally solar) penetrating into the rear optical conduit 34. In addition, the heat collector 38 promotes heat dissipation from the screen in an area remote from the light source, in order to avoid a critical rise in temperature in the front optical conduit 32. According to another advantage, the heat collector 38 is in thermal contact with the rear optical conduit 34.However, the rear optical conduit 34 is further from the light source 8 than the front optical conduit 32, promoting better cooling of the screen 16 through the rear optical conduit 34 than through the front optical conduit 32.

Claims

1. Head-up motor-vehicle display (2) comprising: - a screen (16) composed of an array (18) of elements the transmittance of which varies in a controlled manner over time, between a front side (14) and a back side (20) of the screen; - a light source (8) illuminating the front side (14) of the screen (16) with a light beam (12); and - a rear light pipe (34) arranged facing the back side (20) of the screen (16), so that a light beam (12') emitted by the screen (16) passes through the rear light pipe (34); the head-up display (2) comprises a heat collector (38, 38A, 42B) thermally connecting the screen (16) to the rear light pipe (34), so as to promote heat transfer from the screen (16) to the rear light pipe (34), and the heat collector (38) comprises an intermediate element (38A) interposed between the back side (20) of the screen (16) and the rear light pipe (34), characterized in that the intermediate element (38A) is thermally connected to a thermal radiator (40C) extending along the rear light pipe (34).

2. Head-up display according to Claim 1, comprising a front light pipe (32) interposed between the light source (8) and the front side (14) of the screen (16).

3. Head-up display (2) according to the preceding claim, characterized in that the heat collector (38, 38A, 42B) is arranged so as to allow greater transmission of the heat produced by the screen (16) to the rear light pipe (34) than to the front light pipe (32).

4. Head-up display (2) according to Claim 2 or 3, characterized in that the heat collector (38, 38A, 42B) has a thermal conductivity equal to or greater than the thermal conductivity of the front light pipe (32).

5. Head-up display (2) according to any of the preceding claims, characterized in that the heat collector (38, 38A, 42B) has a thermal conductivity equal to or greater than the thermal conductivity of the screen (16).

6. Head-up display (2) according to any of the preceding claims, characterized in that the heat collector (38, 38A, 42B) has a thermal conductivity equal to or greater than 0.5 W.m-1.K-1.

7. Head-up display (2) according to any of the preceding claims, characterized in that the screen (16) comprises, on its back side (20), a first metal frame (42A) encircling the array (18), the heat collector (38A) connecting the first metal frame (42A) to the rear light pipe (34).

8. Head-up display (2) according to any of the preceding claims, characterized in that the heat collector (34) comprises a second metal frame (42B) encircling the array (18) on the front side (14) of the screen, the second metal frame (42B) having at least one lateral edge (44) thermally connected to the rear light pipe (34).

9. Head-up display (2) according to Claim 8, characterized in that at least one lateral edge (44) of the second metal frame (42B) extends along the rear light pipe (34).

10. Head-up display (2) according to Claim 8, characterized in that at least one lateral edge (44) of the second metal frame (42B) is located outside the rear light pipe (34).

11. Head-up display (2) according to Claim 8, characterized in that a lateral edge (44) of the second metal frame (42B) is arranged so as to make contact with the thermal radiator (40C).

12. Head-up display (2) according to any of Claims 1 to 11, comprising a device for projecting the light beam toward a partially transparent plate.