FR3058236B1 - LIQUID CRYSTAL DISPLAY, IMAGE GENERATING DEVICE COMPRISING SUCH SCREEN AND HEAD DISPLAY COMPRISING SUCH A DEVICE - Google Patents

Abstract

The invention relates to a liquid crystal display (5) comprising: - a screen module (8) comprising a matrix of liquid crystal elements (17), - a first end face (F1) forming an input face of the a screen module (8) intended to face a light source (6), - a second end face (F2) forming an exit face of the screen module (8) intended to be on the side opposite to the light source (6) and side faces (FL) connecting the first and second end faces (F1, F2), the matrix of liquid crystal elements (17) being arranged between the first end face (F1) and the second front face (F2), - a metal support frame (30) comprising (i) a bottom peripheral wall (32) parallel to the first and second end faces (F1, F2) and having a central opening (34) for passing through a luminous flux (L), (ii) lateral peripheral wall portions (36) parallel to the lateral faces (FL) ) of the screen module (8). Attaching one of the first and second end faces (F1, F2) to the bottom peripheral wall of the supporting metal frame (30) establishes thermal contact to promote thermal conduction between the screen module (8) and the metal support frame (30).

Description

LCD screen, image generating device comprising such a screen and head-up display comprising such a device

Technical field to which the invention relates

The present invention relates to display systems.

It relates more particularly to a liquid crystal display, an image generation device comprising such a screen and a head-up display comprising such a device. The invention is particularly applicable in the case where it is desired to obtain a particularly bright image (as for example in the head-up displays of the vehicle), which can result, according to the design of the display, a significant heating of the screen.

Technological background

The principle of head-up displays for vehicles is to project images, especially useful for driving, directly in the field of vision of a driver.

For this purpose, the head-up displays generally comprise an image generation device adapted to generate images and a device for projecting the generated images adapted to transmit these images to a semi-transparent plate placed in the driver's field of vision.

Most of the image generation devices used today include a light source backlit a liquid crystal display adapted to generate the images. This screen absorbs some of the light that backlight, which causes its thermal heating, especially when the ambient light makes it necessary to project a particularly bright image.

However, the temperature of the screen is critical for its proper operation, the latter being likely to be damaged, or even to be defective, by too high a temperature. Warming up the screen may therefore shorten its life and lead to its replacement.

It is therefore necessary to find solutions aimed, in this context in particular but also in other contexts, to cool such a screen.

Object of the invention

The present invention proposes a liquid crystal screen comprising: a screen module comprising a matrix of liquid crystal elements; a first end face forming the input face of the screen module intended to be facing a screen. light source; a second front face forming an exit face of the screen module intended to be on the opposite side to the light source and side faces connecting the first and second end faces, the array of liquid crystal elements being arranged between the first end face and the second end face, - a metal support frame comprising (i) a peripheral bottom wall parallel to the first and second end faces and having a central opening for passing a luminous flux, (ii) lateral peripheral wall portions parallel to the lateral faces of the screen module, characterized in that the fixing of one of the first and second end faces to the bottom peripheral wall of the support metal frame establishes thermal contact to promote thermal conduction between the screen module and the metal support frame.

The screen module is thus in contact with heat conductive elements which allows the evacuation of heat and thus a cooling of the screen module and more specifically of the liquid crystal element matrix.

Thanks to the heat conducting elements in contact with the screen module, the temperature of the screen module can be maintained at an acceptable level, even if the screen module is exposed to a very large luminous flux, for example the order of 10 to 15 kcd, without the image formed by the useful surface of the screen module is degraded. The LCD screen may have one or more of the following features taken alone or in combination:

In one aspect, the thermal contact is established all around one of the front faces of the screen module.

The distance between the bottom peripheral wall and said front face is for example less than or equal to 0.05mm, especially less than or equal to 0.01mm, and in particular 0mm in direct contact.

The bottom peripheral wall can be kept in direct contact with one of the end faces of the screen module by a plastic counter frame.

The plastic counter frame can be inserted into the metal support frame and including a holding wall parallel to the first and second end faces and to maintain the screen module in some cases, for example sandwiched in cooperation with the bottom peripheral wall of the metal support frame.

In another aspect, the retaining wall of the plastic counterframe is in direct contact with the other of the faces of the end faces of the screen module. The liquid crystal display may comprise an elastic element, in particular a foam seal, interposed between the retaining wall of the plastic frame and the other of the end faces of the screen module.

The bottom peripheral wall is in particular fixed to one of the end faces by a glue layer having a thickness of between 0.05mm and 0.01mm, in particular 0.025mm.

In yet another aspect, the bottom peripheral wall is attached to one of the end faces by a thermal sticker which has for example a conductivity greater than 2 Wm'1K'1. For this purpose, the thermal sticker may comprise thermally conductive particles, especially metal particles or alumina particles.

The metal support frame is made for example of copper or aluminum.

Which screen may include lateral fins of heat dissipation connected to the metal support frame.

The lateral fins are made for example in one piece with the metal support frame.

Alternatively, the lateral wings are separate parts of the metal support frame, fixed thereto by screwing or latching.

In yet another aspect, the plastic counter frame is made of a plastic material loaded with thermally conductive particles, in particular metal particles or alumina particles.

The surface of the bottom peripheral wall opposite one of the end faces may be between 5% and 15%, in particular 10% of the screen module. The invention further provides an image generation device comprising a liquid crystal screen as shown above, and a light source arranged to illuminate the liquid crystal screen. The invention finally proposes a head-up display comprising such an image generation device and an image projection device adapted to transmit in the direction of a semi-transparent plate the images generated by the image generation device.

DETAILED DESCRIPTION OF AN EXAMPLE OF IMPLEMENTATION Other advantages and characteristics will appear on reading the description of the invention, as well as on the appended figures which represent a nonlimiting exemplary embodiment of the invention and in which: FIG. 1 schematically represents the main elements of a head-up display for a vehicle; - Figure 2 shows in a cross-sectional diagram a first embodiment of a screen according to the invention; - Figure 3 shows in a cross-sectional diagram a second embodiment of a screen according to the invention; - Figure 4 shows in a cross-sectional diagram a third embodiment of a screen according to the invention; - Figure 5 shows in a cross-sectional diagram a fourth embodiment of a screen according to the invention; - Figure 6 shows in a cross-sectional diagram a fifth embodiment of a screen according to the invention; FIG. 7 is a simplified perspective view of a sixth exemplary embodiment of a screen according to the invention; FIG. 8 is a view from downstream and over a diagram of a seventh embodiment of FIG. a screen according to the invention.

In the figures, the proportions are not respected in order to better highlight the constitution of the screens presented below as examples.

The identical elements are referenced by the same reference numbers.

The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. The features of the various embodiments may also be combined or interchanged to provide other embodiments.

The terms "upstream" and "downstream" are defined with reference to the direction of propagation of the light beams. By "upstream" is meant that one element is placed before another with respect to the direction of propagation of a light beam. On the other hand, "downstream" is understood to mean that one element is placed after another relative to the direction of propagation of the light beam. By upper, lower, upper and lower, reference is made to the arrangement of the elements in the figures.

DETAILED DESCRIPTION

In Figure 1, there is schematically shown the main elements of a head-up display 1 for equipping a vehicle, for example a motor vehicle.

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. For this purpose, the display 1 comprises for example a partially transparent plate 2, commonly called semi-transparent plate 2, placed in the field of view of the driver, an image generation device 3 adapted to generate images and a device image projection device 4 adapted to send back, in the direction of said semi-transparent plate 2, the images generated by the image generation device 3.

More specifically, the semi-transparent plate 2 is here a combiner 2, that is to say a semi-transparent plate dedicated to the head-up display 1.

Such a combiner 2 is here placed between the windshield 9 of the vehicle and the eyes of the driver, typically at the dashboard between the steering wheel of the vehicle and the windshield.

Alternatively, the semi-transparent blade could be confused with the windshield of the vehicle. In other words, in this variant, it is the windshield of the vehicle, or at least a portion of the windshield having received a suitable surface treatment which has the function of semi-transparent blade for the head-up display.

Furthermore, here, the image projection device comprises a folding mirror 4 arranged to reflect the images generated by the image generation device 3 in the direction of the semi-transparent plate 2. Here, said mirror of FIG. folding is a plane mirror.

Alternatively, the image projection device could comprise a plurality of mirrors and / or other optical elements such as a lens for example. To enlarge for example the image the mirror can also be curved, especially convex.

The image generation device 3 comprises, for its part, at least one light source 6, a screen 5 backlit by this light source 6, and a reflector 7. It is thus schematically represented by the arrow L in the figures the transmission from the light of the light source 6 to the screen 5 arranged downstream of the light source 6.

The light source 6 comprises at least one light emitting diode (or LED for "Light Emitting Diode"), and in general a plurality of such light-emitting diodes. This light source 6 can emit a large luminous flux, for example greater than 10kcd, especially around 15kcd.

As will become apparent from the examples given below, the screen 5 is a liquid crystal display (or LCD for "Liquid Crystal Display"), for example thin film transistors (or TFT for "Thin-Film Transistor" ') .

FIG. 2 presents a first embodiment of the screen 5.

In this first example, the screen 5 comprises a screen module 8 formed by, in this order in the direction of the path of the light L (that is to say of the part situated on the side of the light source 6 disposed upstream of the screen 5 to the projection device 4 disposed downstream of the screen 5), the following plate-shaped elements (or blades) (each element being in contact with the element or elements ) neighbor (s)): - an absorbing input polarizer 20; a first pane 12; a matrix of micro-polarizers 10; a matrix of colored elements 16; a second pane 14; an absorbing output polarizer 22.

The matrix of micro-polarizers 10 comprises a matrix of liquid crystal elements 17, transistors each associated with one of said liquid crystal elements 17 and conductive connection tracks to said transistors.

A first set of conductive tracks extends in a first direction, while a second set of conductive tracks extends in a second direction perpendicular to the first direction to independently control each of the transistors at the intersection of a conductive track of the first set and a conductive track of the second set.

The absorbing input polarizer 20 and the absorbing output polarizer 22, in particular that of input 20 are for example glued or laminated on the first pane 12. They are the main cause of the significant heating which can affect the operation of the 17. The input polarizer 20 and the output polarizer 22 respectively have a first axis and a second axis perpendicular to each other (within the framework of the so-called "normally off" technology, or NB for " normally black '). (It is recalled that the axis of a polarizer is the direction of linear polarization of the light beam after passing through the polarizer.)

Thus, if no element of the matrix of liquid crystal elements 17 is activated, the light beam between the absorbing input polarizer 20 and the absorbing output polarizer 22 will be polarized along the first axis (axis of the polarizer). input 20) and no light will therefore be emitted at the output of the output polarizer 22.

By appropriate activation of the elements of the array of liquid crystal elements 17 (by means of the transistors controlled by a control module not represented by means of the conductive tracks), the polarization of certain parts of the light beam is modified at the level of the matrix of liquid crystal elements 17 so that light is emitted at the output of the output polarizer 22 at regions corresponding to said portions of the light beam.

For each pixel of the screen 5, the matrix of colored elements 16 comprises a plurality of colored elements (here a red element, a green element and a blue element) through which it is possible to pass an adjustable intensity. of light by appropriate activation of the corresponding element of the matrix of liquid crystal elements 17, as indicated above. Alternatively, a reflective polarizer film (not shown) may be disposed upstream of the input absorbing polarizer film 20. This allows for lowering of the absorbing input polarizer 20. The reflective polarizer film can be laminated to the polarizer absorbent 20 or be placed at a distance from the screen 5 between the light source 6 and the screen 5.

According to yet another variant, the extent of the absorbing polarizers 20 and 22 may be less than those of the other elements namely the first pane 12, the matrix of micro-polarizers 10 with its matrix of liquid crystal elements 17, the matrix of colored elements 16 and the second window 14.

The input absorbing polarizer 20, the first pane 12, the micro-polarizer matrix 10 with its matrix of liquid crystal elements 17, the matrix of colored elements 16, the second pane 14 and the absorbing output polarizer 22 are often marketed together as a screen module 8.

Of course, it is also possible to envisage a simpler screen module 8, for example without the matrix of colored elements 16, without departing from the scope of the present invention.

As can be seen in FIG. 2, the screen module 8 thus comprises a first front face F1 forming an input face intended to face the light source 6, a second end face F 2 forming an exit face intended to to be on the opposite side to the light source 6 and side faces FL forming the circumferential edge of the screen module 8 and connecting the first and second end faces F1 and F2. The array of liquid crystal elements 17 is therefore disposed between the first end face F1 and the second end face F2. The screen 5 further comprises a metal support frame 30 with on the one hand a peripheral bottom wall 32 parallel to the first and second end faces F1 and F2 and having a central opening 34 (see also FIG. 8), for example rectangular shape for passing the luminous flux L and secondly lateral peripheral wall portions 36 parallel to the side faces FL of the screen module 8. The metal support frame 30 is for example made of copper or aluminum. The screen also has a plastic counter-frame 38 inserted in the metal frame 30 and having a holding wall 40 parallel to the first and second end faces F1, F2 and allowing the screen module 8 to be held in position. sandwiching by cooperation with the bottom peripheral wall 32 of the metal frame 30.

Fixing one of the first F1 and second F2 end faces to the bottom peripheral wall 32 of the metal support frame 30 establishes thermal contact to promote thermal conduction between the screen module 8 and the metal support frame 30.

Thus, the heat generated by the light absorption at the input and output absorbing polarizers 22 can be discharged via the metal support frame 30 more efficiently so that the liquid crystal matrix 17 is less constrained. thermal, even with an important luminous flux L, for example greater than 10 kcd, see 15kcd.

In the embodiment of FIG. 2, this thermal contact is established all around one of the end faces of the screen module, that is to say on a width / corresponding to the overlap of the peripheral wall of the screen. bottom 32 with the front face F1 of the screen module 8 (see also Figure 8).

According to the embodiment of FIG. 2, the distance between the bottom peripheral wall 32 and said front face F1 is less than or equal to 0.05 mm, in particular less than or equal to 0.01 mm, and in particular 0 mm in direct contact as we see it in figure 2.

This is achieved by the fact that the bottom peripheral wall 32 is kept in direct contact with the front face F1 of the screen module 8 by the counter frame 38 made of plastic material.

As can be seen in FIG. 2, the retaining wall 40 of the plastic counter-frame 38 is also in direct contact with the other of the end faces of the screen module 8, that is to say the face frontal F2. It is therefore a compression contact with a strong constraint.

In this embodiment, the counter frame 38 is fixed to the metal support frame 30 for example by gluing, screwing or ultrasonic welding.

According to one variant, the counter frame 38 made of plastic material is made of a plastic material loaded with thermally conductive particles, in particular metal particles or particles of alumina. Thus, the counter-frame 38 can also contribute to the evacuation of the heat produced at the input and output 20 absorbent polarizers 22.

FIG. 3 shows a second embodiment which differs from that of FIG. 2 in that the screen 5 comprises an elastic element 42, in particular a foam seal, interposed between the retaining wall 40 of the material counter frame. plastic 38 and the front face F2 of the screen module 5. It is therefore a compression contact with a low stress. The foam can also absorb manufacturing tolerances and deformations, for example due to thermal expansion.

FIG. 4 shows a third embodiment which differs from that of FIG. 2 in that the bottom peripheral wall 32 is fixed to the front face F1 by an adhesive layer 44 having a thickness of between 0.05 mm and 0 , 01mm, in particular 0.025mm. In this figure 4, the thickness of the glue layer 44 is exaggeratedly illustrated to be visible in the figure. With a glue thickness that is so low, the glue forms only a very weak thermal barrier and almost does not interfere with the thermal conduction between the screen module 8 and the metal support frame 30. In order to reduce any mechanical stresses on the screen module 8, the holding wall 40 is not in contact with the screen module 8.

FIG. 5 shows a fourth embodiment which differs from that of FIG. 2 in that the bottom peripheral wall 32 is fixed to the front face F1 by a thermal sticker 46 which has, for example, a conductivity greater than 2 Wm '. 1K'1, in particular greater than 10 Wm'1K'1. To reduce possible mechanical stresses on the screen module 8, the holding wall 40 is not in contact with the screen module 8. For this purpose, the thermal sticker 46 comprises, for example, thermally conductive particles, in particular metal particles or alumina particles.

FIG. 6 shows a fifth embodiment which differs from that of FIG. 2 in that the screen 5 comprises lateral fins 48 for dissipating heat connected to the metal support frame 30 by a wall portion 50 extending the wall bottom peripheral 32 laterally. This portion of wall 50 also plays a role of heat dissipator.

The lateral fins 48 can be made in one piece with the metal support frame 30 or be separate parts and fixed to this frame 30 by screwing or snapping. They can be arranged on one side or the other of the wall portion 50 or on both sides.

FIG. 7 represents, in a simplified perspective diagram, a sixth exemplary embodiment of a screen according to the invention.

In this embodiment the peripheral wall portions 36 comprise protrusions 52 made for example by stamping which cooperate with handles 54 cut and bent at 90 ° in the wall portions 50. In this case, the wall portions 50 are fixed by snapping on the metal support frame 30. In this embodiment, the wall portions 50 do not have fins as shown in Figure 6, but it is of course conceivable to provide these wall portions 50 also with fins forming heat radiator.

A seventh embodiment is shown in Figure 8. In this figure, we see the screen 5 from downstream and over. Thus we see the front face F1 of the screen module 8 with the first absorbing polarizer 20 and the bottom peripheral wall 32 with its central opening 34 rectangular. The external dimensions of the screen module 8 are represented by a dashed line. Thus, we can clearly see the contact zone between the bottom peripheral wall 32 and the screen module 8 which is delimited by the dotted line to the line delimiting the opening 34. The width of this contact zone is indicated by /.

To further increase the heat exchange, the contact zone between the bottom peripheral wall 32 and the screen module 8 is increased so that the surface of the bottom peripheral wall faces one of the end faces, therefore the contact area is between 5% and 15%, especially 10% of the surface of the screen module. This also makes it possible to reduce the surface of the screen module 8 exposed to the luminous flux and to further reduce its heating.

It is therefore understood that the heat conduction between the screen module 8 and the metal support frame 30 and / or (depending on its composition) the counter frame 38 of plastic is improved. The heat produced in particular at the level of the absorbing polarizers 20 and 22 is evacuated more efficiently, which guarantees a longer lifetime for the matrix of liquid crystal elements 17.

Without particular difficulties, these different embodiments can be combined. Thus, it is possible, for example, to use the foam 42 of FIG. 3 in the embodiment of FIG. 5 to interpose it between the holding wall 40 and the screen module 8.

With respect to the front faces F1 and F2, it is also possible to reverse the position of the metal support frame 30 and that of the plastic frame-frame 38, especially when the latter is made of a plastic material loaded with thermally conductive particles. .

Claims (18)

1. LCD screen (5) comprising: - a screen module (8) comprising a matrix of liquid crystal elements (17), - a first front face (F1) forming the input face of the module of screen (8) intended to be opposite a light source (8), - a second end face (F2) forming the exit face of the screen module (8) intended to be on the opposite side to the light source (6) - lateral faces (FL) connecting the first and second end faces (F1, F2), the matrix of liquid crystal elements (17) being disposed between the first end face (F1) and the second end face ( F2), - a metal support frame (30) comprising (i) a bottom peripheral wall (32) parallel to the first and second end faces (F1, F2) and having a central opening (34) for passing a luminous flux (L), (II) lateral peripheral wall portions (36) parallel to the lateral faces (FL) of the modu the screen (8), characterized in that the fixing of one of the first and second end faces (F1, F2) to the bottom peripheral wall of the metal support frame (30) establishes thermal contact to promote conduction between the screen module (8) and the metal support frame (30) and in which the thermal contact is established all around one of the front faces (F1, F2) of the screen module (8) . 2, a liquid crystal display according to claim 1, wherein the distance between the bottom peripheral wall (32) and said front face (F1; F2) is less than or equal to 0.05 mm, in particular less than or equal to 0.01 mm , and in particular 0mm in direct contact. 3. LCD screen according to any one of claims 1 to 2, wherein the bottom peripheral wall (30) is maintained in direct contact with one of the end faces of the screen module (F1; F2) by a cons frame (38) of plastics material. 4. The liquid crystal display according to claim 3, wherein the plastic frame (38) can be inserted into the metal support frame (30) and has a holding wall (40) parallel to the first and second faces. frontal (F1, F2). 5. LCD screen according to claim 4, wherein the retaining wall (40) of the counter frame (38) of plastic material is in direct contact against the other of the faces of the end faces (F2; F1) of the module. screen (8). 6. LCD screen according to claim 4, wherein it comprises a resilient element (42), in particular a foam seal, interposed between the retaining wall (40) of the plastic frame-frame (38) and the other of the front faces (F2; F1) of the screen module (8). 7. LCD screen according to any one of claims 3 to 6, wherein the counter frame (38) of plastic material is made of a plastic material loaded with thermally conductive particles, including metal particles or particles of alumina. 8. A liquid crystal display according to any one of claims 1 to 7, wherein the bottom peripheral wall (32) is fixed to one of the end faces (F1; F2) by a layer of glue (44) having a thickness between 0.05mm and 0.01mm, in particular 0.025mm. 9. A liquid crystal display according to any one of claims 1 to 8, wherein the bottom peripheral wall (32) is attached to one of the end faces (F1; F2) by a thermal sticker (48). The liquid crystal display of claim 9, wherein the thermal sticker (48) has a conductivity greater than 2 11. LCD screen according to any one of claims 9 or 10, wherein the thermal sticker (48) comprises thermally conductive particles, in particular metal particles or alumina particles. The liquid crystal display according to any one of claims 1 to 11, wherein the metal support frame (30) is made of copper or aluminum. 13. LCD screen according to any one of claims 1 to 12, wherein the screen (5) has side fins (48) of heat dissipation connected to the metal support frame (30). 14. The liquid crystal display according to claim 13, wherein the lateral wings (48) are made in one piece with the metal support frame (30). 15. A liquid crystal display according to claim 14, wherein the lateral wings (48) are separate parts of the metal support frame (30), fixed thereto by screwing or latching. 18. LCD screen according to any one of claims 1 to 15, wherein the surface of the bottom peripheral wall (32) facing one of the end faces (F1, F2) is between 5% and 15%. %, especially 10% of the screen module (8). An image generating device comprising a liquid crystal screen (5) according to one of claims 1 to 16, and a light source (6) arranged to illuminate the liquid crystal screen (5). 18. A head-up display (1) comprising an image-generating device (3) according to claim 17 and an image-projection device (4) adapted to transmit in the direction of a semi-transparent plate (2) the images generated by the image generation device (3).