FR3082011A1 - IMAGE GENERATION DEVICE AND HEAD-UP DISPLAY COMPRISING SUCH A DEVICE - Google Patents

Abstract

The invention relates to an image generation device (5) for a head-up display (1) comprising: - a light source (11) emitting light having a first spectral width less than or equal to 150 nm, - a first screen (13) adapted to receive light of first spectral width, and to emit light of second spectral width greater than the first spectral width, the first screen (13) being further configured to present at least one opaque zone (35) , - a controller (31) connected to the first screen (13) and configured to control the at least one opaque zone (35) of said first screen (13), - a second screen (15) adapted to receive light of second width spectral and configured to emit a light beam. A head-up display comprising such a device is also described.

Description

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

Technical field to which the invention relates

The present invention relates generally to the field of head-up display systems, in particular in a vehicle.

It relates more particularly to an image generation device and head-up display comprising such a device.

TECHNOLOGICAL BACKGROUND

The principle of head-up displays for vehicles is to project images, particularly useful for driving, directly into the driver's field of vision.

For this, the head-up displays include, in general, an image generation device adapted to generate at least one image and an image projection device adapted to transmit the generated image to a partially reflecting plate placed in the driver's field of vision. The image generated must be bright enough to be seen by the driver.

Most image generation devices in use today include a liquid crystal display backlit by a powerful light source to display an image bright enough to be seen in daylight.

However, this type of image generation device only transmits about 6% of the light generated by the light source out of the screen. The screen heats up by blocking a good part of the light emitted by the light source, which leads to its deterioration.

Object of the invention

In this context, the present invention provides an image generation device for a head-up display comprising:

- a light source emitting light having a first spectral width less than or equal to 150 nm,

a first screen adapted to receive light of first spectral width, and to emit light of second spectral width greater than the first spectral width, the first screen being further configured to present at least one opaque zone,

- a controller connected to the first screen and configured to control at least one opaque area of said first screen,

- a second screen adapted to receive light of second spectral width and configured to emit a light beam.

The use of a light source emitting light of low spectral width makes it possible to reduce heating of the first screen. The phosphor layer of the first screen nevertheless makes it possible to emit light of wide spectral width, so the light beam is not limited to the spectral width of the light source. In addition, by forming opaque zones on the first screen, only the light useful for the formation of the light beam is transmitted to the second screen, which makes it possible to reduce heating of the latter.

Other non-limiting and advantageous characteristics of the device according to the invention, taken individually or in any technically possible combination, are the following:

- the first screen includes:

- a first layer of liquid crystals,

- a first output polarizer,

- a layer of a photoluminescent material adapted to be excited by light of first spectral width to emit light of second spectral width by photoluminescence,

the first output polarizer has a second axis of polarization perpendicular to a direction of polarization of the light,

the light source comprises at least one laser diode, the light source comprises at least one light-emitting diode,

the first screen also comprises a first input polarizer situated between the light source and the first layer of liquid crystals,

- the second screen includes:

- a second input polarizer,

- a second layer of liquid crystals,

- a second output polarizer,

- the second screen also includes a matrix of colored elements,

- the matrix of colored elements comprises red colored elements, blue colored elements and green colored elements,

- the first spectral width is between 340 nanometers and 490 nanometers,

- the second spectral width ranges between 420 nanometers and 700 nanometers,

an optical tube placed between the first screen and the second screen, said tube being configured to absorb stray rays between the first screen and the second screen,

- the first screen has a lower first resolution than a second resolution of the second screen,

- the first screen has a size equal to the second screen,

- the first screen has a size smaller than the second screen.

The invention also provides a head-up display comprising an image generation device and an image projection device adapted to transmit the light beam generated by the image generation device towards a partially transparent blade.

Detailed description of an example of realization

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

In the accompanying drawings:

- Figure 1 schematically shows the main elements of a head-up display for a vehicle;

- Figure 2 is a schematic representation of an image generation device comprising a first screen according to the invention;

FIG. 3 is a schematic representation of the first screen of FIG. 2 in operation,

FIG. 4 is a perspective representation of the image generation device of FIG. 2, and

- Figure 5 is a schematic representation of the first screen and a second screen of the image generation device of Figure 2.

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

Such a head-up 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 the possible information it contains without having to divert the look.

To this end, the head-up display 1 comprises a partially transparent blade 3 placed in the driver's field of vision, an image generation device 5 adapted to generate a light beam and an image projection device 7 adapted to return, in the direction of said partially transparent strip 3, the light beam generated by the image generation device 5.

More specifically, the partially transparent blade 3 is here a combiner 3, that is to say a partially transparent blade dedicated to the head-up display 1.

Such a combiner 3 is here placed between the windshield 9 of the vehicle and the driver's eyes.

Alternatively, the partially transparent blade 3 could be confused with the windshield 9 of the vehicle. In other words, in this variant, it is the vehicle windshield that has the partially transparent blade function for the head-up display 1.

Furthermore, here, the image projection device 7 comprises a folding mirror arranged so as to reflect the light beam by the image generation device 5 in the direction of the partially transparent plate 3. Here, said folding mirror is a plane mirror.

Alternatively, the image projection device 7 could include a plurality of mirrors and / or other optical elements such as a lens for example.

As illustrated in FIG. 1 and FIG. 2, the image generation device 5 in turn comprises at least one light source 11, a first screen 13 illuminated by this light source 11, a second screen 15 illuminated by the light transmitted by the first screen 13 and a reflector 17. There is thus schematically represented by an arrow L in the figures the transmission of light from the light source 11 to the screen 13.

The light source 11 is placed at one end of the image generation device 5, upstream of the first screen 13. The light source 11 comprises for example at least one light-emitting diode (or LED for

Light Emitting Diode), and in general a plurality of such light-emitting diodes. The light then emitted has no well-defined polarization. Alternatively, the light source 11 can comprise at least one laser diode emitting polarized light.

The light source 11 emits light having a first spectrum of first spectral width Δλ1 less than or equal to 150 nm (nanometers). Preferably, the first spectral width Δλ1 of the light source 11 is less than or equal to 80 nanometers.

The first spectrum emitted by the light source 11 can be continuous or discontinuous, that is to say that it can comprise a continuum of wavelengths or certain wavelengths only in the predetermined interval.

The light source 11 preferably emits blue light, the first spectrum of which is between 340 nm and 490 nm and ranges, for example, between 410 nm and 490 nm.

The first spectral width Δλ1 being small, the optical optimizations and treatments of the different optical elements constituting the first screen 13 are advantageously made specifically for this first spectral width Δλ1 and not for the entire visible spectrum, which simplifies said optical optimizations and treatments.

In a first example now described, the light source 11 comprises at least one light-emitting diode 11.

As shown in FIG. 2, a diffuser 19 can be optionally placed between the light source 11 and the first screen 13. The diffuser 19 is adapted to diffuse the light after the light source 11 into a light cone, in order to allow in particular a uniform illumination of the first screen 13. In practice, the diffuser 19 can be formed from an injected filter treated on the face opposite the light source 11, said treatment producing a diffusion of light. The diffuser 19 may for example comprise a film or a plastic plate of PVC type with a thickness of between 0.5 and 1 mm.

The diffuser 19 is here placed at a distance from an entry face of the first screen 13. As a variant, the diffuser 19 can be glued to the entry face of the first screen 13 and / or be arranged at an angle opposite -vis the first screen 13.

Alternatively, the diffuser 19 can be produced with a film having a treated face disposed opposite the light source 11.

In the example described, the reflector 17 constitutes a closed enclosure around the light source 11 and the diffuser 19. The reflector 17 here extends between the light source 11 and the diffuser 19. The internal walls of the reflector 17 are illuminated by the light generated by the light source 11. The surface treatment of the internal walls of the reflector 17 allows a reflection of the light in the direction of the diffuser 19 and of the entry face of the first screen 13. The internal walls of the reflector 17 for example have an aluminum or silver coating.

The diffuser 19 and the reflector 17 make it possible to homogenize the lighting at the entrance face of the first screen 13. The light source 11, the diffuser 19 and the reflector 17 make it possible to backlight the first screen 13 in order to generate a homogeneous light beam.

The first screen 13 is a liquid crystal screen (or LCD for “Liquid Crystal Displaÿ '), for example a TN screen (for“ Twisted Nematic ”), a DSTN (for“ Dual Scan Twisted Nematic ”) or even a TFT (for “ThinFilm Transistor ¹ '). In the example described, the first screen 13 comprises a TFT screen.

As clearly visible in FIG. 2, the first screen 13 comprises, in this order in the direction of the light path L (that is to say from the part situated on the side of the light source 11 to the side situated towards the projection device 7), the following plate-shaped elements (or blades) (each element being in contact with the neighboring element or elements):

- a first input polarizer 20,

a first substrate 21,

a first layer of liquid crystals 23,

a second substrate 25,

a first output polarizer 27,

- a layer of photoluminescent material 29.

As shown, the first screen 13 is arranged perpendicular to the path of the light L. Alternatively, the first screen 13 may not be perpendicular to the path of the light L.

The first input polarizer 20 has a first axis of polarization. The first input polarizer 20 comprises for example a reflective polarizer. Such a reflective polarizer transmits light whose direction of polarization is aligned with the first axis of polarization and reflects light whose direction of polarization is not aligned with the first axis of polarization.

The light returned by the first input polarizer 20 passes through the diffuser 19 which causes a change in direction of its polarization. The returned light is then reflected several times, this time on the reflector 17 until it is returned to the first screen 13. In the end, part of the light which had been reflected on the first input polarizer 20 returns to said first input polarizer 20 with a polarization direction aligned with that of the first axis of polarization and can therefore pass through the first input polarizer 20. The use of a first input polarizer 20 of the type reflective associated with a plastic strip such as the diffuser 19 therefore makes it possible to limit the losses of light.

The first layer of liquid crystals 23 is contained by the first substrate 21 and the second substrate 25. The first substrate 21 and the second substrate 25 are, for example, translucent glass panes. The first substrate 21 supports transistors.

The first layer of liquid crystal 23 receives polarized blue light. The first layer of liquid crystals 23 can be advantageously optimized for the transmission of light of first spectral width.

By creating an electric field by a difference in electric voltage between the first substrate 21 and the second substrate 25, the liquid crystals contained in the liquid crystal layer 23 change their orientation. The polarization of the light passing through the first layer of liquid crystal 23 is possibly modified as a function of this orientation.

The difference in electrical voltage is created by a plurality of electrodes disposed on the first substrate 21 and / or the second substrate 25, forming a first matrix of liquid crystal cells. The number of liquid crystal cells in the first matrix corresponds to a first resolution of the first screen 13.

The difference in electrical voltage can be controlled individually by the controller 31 for each liquid crystal cell of the first matrix.

The light, the direction of polarization of which has possibly been modified, passes through the second substrate 25 and then arrives at the first output polarizer 27.

According to one example, the TFT screen is manufactured using a technology known as "Normally black". In this case, the first output polarizer 27 has a second axis of polarization whose direction is perpendicular to that of the first axis of polarization. Thus, if there is no difference in voltage between the first substrate 21 and the second substrate 25, the direction of the light is not changed and no light is transmitted by the first output polarizer 27.

The difference in electrical voltage between the first substrate 21 and the second substrate 25 is controlled by a controller 31 of the head-up display 1.

In another example, the TFT screen is manufactured using so-called "Normally white" technology. In this case, the first input polarizer 20 and the first output polarizer 27 have parallel axes of polarization. The first screen 13 is therefore on when there is no voltage difference between the first substrate 21 and the second substrate 25. Thus the consumption of electricity is reduced when the majority of the second screen 15 is on.

The controller 31 controls passing zones 33 - visible in FIG. 3 allowing the light to pass through (and therefore whose polarization must be modified by the layer of liquid crystal 23) and opaque zones 35 blocking the light (and therefore whose polarization n not to be changed) from the first screen 13.

The transparent areas 33 correspond to areas containing information to be displayed on the virtual image I. The transparent areas 33 are so-called "useful" areas. For example, we want to display information about the speed of his vehicle to the driver. The transparent areas 33 are then those making it possible to form the alphanumeric characters at the level of the virtual image I displayed on the partially transparent slide 3. The transparent areas 33 generally occupy little space on the virtual image I with respect to the areas not containing no information to display.

The opaque areas 35 correspond to the areas containing no information to be displayed, and for which it is therefore not necessary to transmit the light.

Optionally, the controller 31 can be adapted to control intermediate transmission zones (not shown) in addition to the transparent zones 33 (100% transmission) and opaque zones (0% transmission). Intermediate transmission zones can for example have light transmission rates of 50% or even 75%. This allows the intensity of the transmitted light to be modulated in order to limit the brightness of the virtual images I and to manage a transition in light intensity. The modulation of the transmission rate is particularly advantageous during night-time use of the head-up display 1. Indeed, too bright virtual images I projected during the night can be unpleasant for the driver of the vehicle.

When the images displayed are predefined (for example each according to a model stored in a memory of the head-up display 1), it is possible to associate for each image a respective arrangement of transparent zones 33 and opaque zones 35. Thus, to display a predefined image, the controller 31 controls the first screen 13 to set up the respective arrangement of transparent zones 33 and opaque zones 35 associated with this predefined image.

The first output polarizer 27 is an absorbing polarizer. The light blocked by the opaque zones 35 is transformed into heat. The use of a light source 11 of first narrow spectral width Δλ1 therefore proves to be advantageous, in fact the heat produced by the light of narrow spectral width is less than that produced by a light of wide spectrum (for example by white light ). The use of at least one light emitting diode 11 emitting in blue therefore makes it possible to limit heating of the first screen 13.

The light of first spectral width Δλ1 transmitted by the first output polarizer 27 then arrives on the layer of photoluminescent material

29.

The photoluminescent material 29 here comprises phosphors adapted to be excited by the wavelengths of the spectrum of the light source 11, that is to say specifically by the lengths of the predetermined interval (first spectrum). The phosphors of the photoluminescent material 29 are adapted to de-excite by photoluminescence, that is to say by emitting light. The light emitted by the phosphors is a non-polarized light having a second spectral width Δλ2. The second spectral width Δλ2 is greater than or equal to the first spectral width Δλ1. Preferably, the second spectral width Δλ2 is greater than or equal to 300 nanometers.

Thus, at the level of the photoluminescent material layer 29, the polarized light of first small spectral width Δλ1, is transformed into non-polarized light, of second second spectral width Δλ2 extended. In practice, the light emitted by the phosphors at the exit of the layer of photoluminescent material 29 covers the entire visible band of the light spectrum extending between 400 nm and 700 nm.

In the example described, the phosphors are adapted to be excited by the blue light emitted by the light source 11 and to emit in response, at the output of the layer of photoluminescent material 27, white light whose spectrum extends between 420 nanometers and 700 nanometers.

For example, the phosphors here are of the Yttrium aluminum garnet type doped with cerium (Ce: YAG) but this layer could as a variant consist of silicon nanoparticles which are less expensive than phosphorus.

The layer of photoluminescent material 29 comprises for example a flexible or rigid phosphor film (comprising a silicone mixture doped with phosphorus). The phosphor film can be glued to the first screen 13, alternatively, the phosphor film can be independent of the first screen 13, or else glued to a second screen 15 of the head-up display 1. Alternatively, the phosphor film can be inserted between the second substrate 25 and the first output polarizer 27, or between the first input polarizer 20 and the first substrate 21.

The layer of photoluminescent material 29 can be integrated into the first screen 13 of the TFT type during its manufacture. The layer of photoluminescent material 29 can then replace a matrix of colored elements usually located in this type of screen.

The second screen 15 is also a liquid crystal screen, for example with thin film transistors (or TFT for “Thin-Film Transistor ¹ ').

As clearly visible in FIG. 2, the second screen 15 comprises, in this order in the direction of the light path L, the elements (or blades) in the form of a plate which follow (each element being in contact with the neighboring element or elements (s)):

- a second input polarizer 37,

a third substrate 39,

a second layer of liquid crystals 41,

a fourth substrate 43,

- a matrix of colored elements 47,

- a second output polarizer 45.

Similar to the first screen 13, electrodes are arranged on the third substrate 39 and the fourth substrate 43 so as to define a second matrix of liquid crystal cells. The number of liquid crystal cells in the second matrix corresponds to a second resolution of the second screen

15.

The third substrate 43 supports the transistors of the second screen.

The electrodes make it possible to create an electric field by a voltage difference between the third substrate 39 and the fourth substrate 43.

The difference in electrical voltage can be controlled individually by the controller 31 for each liquid crystal cell of the second matrix.

Thanks to the second input polarizer 37 and to the second output polarizer 45 whose transmission axes are perpendicular, the controller 31 controls the intensity of the light passing through each liquid crystal cell.

The matrix of colored elements 47 generates a colored beam from the white light transmitted by the first screen 13. For this, the matrix of colored elements 47 comprises red colored elements, blue colored elements and green colored elements.

The colored elements are, for example, conventionally manufactured and according to well-known technologies for liquid crystal screens from a translucent resin capable of absorbing only part of the spectrum of light emitted by the first screen 13.

The colored elements are each adapted to let pass only the light included in a predetermined spectral width of the visible spectrum to generate a given color in the image.

A set of three successive colored elements of different colors forms a pixel of the second screen 15. Each colored element of the set 47 receives the white light transmitted by a liquid crystal cell of the second matrix. It therefore takes three liquid crystal cells from the second matrix to generate the desired color of the corresponding pixel.

The controller 31 controls the intensity of the white light transmitted by each of the three liquid crystal cells in order to create a mixture of the three colors (red, green, blue) to generate the desired color of the corresponding pixel.

According to one example, a liquid crystal cell of the first matrix illuminates a set of three liquid crystal cells of the second matrix. The first screen 13 therefore has a first resolution identical to the second resolution of the second screen 15, which is by definition the set number of the three successive colored elements of different colors.

In the case of an identical or lower resolution of the first screen 13, a liquid crystal cell of the first matrix illuminates a plurality of liquid crystal cells of the second matrix. A reduced first resolution simplifies the manufacture of the first screen 13 and reduces the cost of the head-up display.

Furthermore, as shown in FIG. 5, due to the divergence of the light, the first screen 13 may have a size smaller than the size of the second screen 15. The second screen 15 is then located at a distance D from the first screen 13.

In this configuration, it is also possible to further increase the first resolution of the first screen 13 relative to the second resolution of the second screen 15 in order to illuminate a minimum area of the second screen 15.

As shown in FIG. 4, the second screen 15 receives only the light transmitted by the pass-through zones 33. Thus, the succession of the first screen 13 and the second screen 15 makes it possible to limit heating of the second screen 15 and thus to slow its deterioration. The first screen 13 can also be equipped with a heat dissipation means (not shown). The means of heat dissipation can be active or passive, for example transparent ceramics.

Alternatively, the first screen 13 and the second screen 15 can be placed in contact. The heat dissipation means can then comprise a transparent sintered ceramic plate interposed between the first screen 13 and the second screen 15 in order to dissipate the heat of the two screens 13, 15. The thickness of this plate is defined as a function of the quantity heat to dissipate.

Alternatively, the layer of photoluminescent material 29 and the transparent ceramic plate are replaced by a phosphor ceramic plate. For more details, refer to the article "Advances in transparent glass-ceramic phosphors for white light-emitting diodes - A review" by Daqin Chen et al. (Journal of the European Ceramic Society, Volume 35, Issue 3, March 2015, pages 859-869). Such a phosphor ceramic plate brought into contact with the first screen 13 and the second screen 15 makes it possible to reduce heating of the first screen 13 linked to the light emitted by the light source

11. In addition, the phosphor ceramic plate reduces heating of the second screen 15 linked not only to the light emitted by the light source 11, but also heating linked to the sunlight incident on the head-up display 1.

The diffuser 19 previously described can be placed between the first screen 13 and the second screen 15. The diffuser 19 can be glued to the first screen 13 and / or to the second screen 15. Alternatively, the diffuser 19 can be placed at a distance from the first screen 13 and the second screen 15.

Alternatively, the diffuser 19 comprises a first part and a second part. The first part is located between the light source 11 and the first screen 13. The second part is located between the first screen 13 and the second screen 15.

The head-up display 1 may further comprise an optical tube 49 disposed between the first screen 13 and the second screen 15. The optical tube 49 comprises absorbent walls in the visible spectrum, for example walls whose inner surface is black . The absorbent walls make it possible to absorb stray light between the first screen 13 and the second screen 15.

According to another example, the light source 11 comprises at least one laser diode. In this case, the first input polarizer 20 is optional. If used, the first axis of polarization is aligned with the direction of polarization of the laser diode. The second axis of polarization is perpendicular to the direction of polarization of the laser diode.

The light source 11 can be of the laser scanner type generating a square or rectangle of light around a laser spot. In this case, the laser scanner scans the first screen 13 at a frequency synchronous with that of the laser.

According to another example, the second screen 15 comprises a plurality of TFT screens. Such an image generation device 5 makes it possible to limit parasitic radiation between the screens 13, 15.

Claims (10)

1. Image generation device (5) for a head-up display (1) comprising: - a light source (11) emitting light having a first spectral width less than or equal to 150 nm, - a first screen (13) adapted to receive light of first spectral width, and to emit light of second spectral width greater than the first spectral width, the first screen (13) being further configured to present at least one opaque zone (35) - a controller (31) connected to the first screen (13) and configured to control at least one opaque zone (35) of said first screen (13), - a second screen (15) adapted to receive the light of second spectral width and configured to emit a light beam. 2. Image generation device (5) according to claim 1, in which the first screen (13) comprises: - a first layer of liquid crystals (23), - a first output polarizer (27), - a layer of a photoluminescent material (29) adapted to be excited by light of first spectral width to emit light of second spectral width by photoluminescence. 3. An image generation device (5) according to claim 1 or 2, wherein the light source (11) comprises at least one laser diode. 4. An image generation device according to claim 2, in which the light source (11) comprises at least one light-emitting diode and in which the first screen (13) further comprises a first input polarizer (20) located between the light source (11) and the first layer of liquid crystal (23). 5. Image generation device (5) according to one of the preceding claims, in which the second screen (15) comprises: - a second input polarizer (37), - a second layer of liquid crystals (41), - a second output polarizer (45). 6. Image generation device (5) according to one of the preceding claims, in which the first spectral width (Δλ1) ranges between 340 nanometers and 490 nanometers. 7. Image generation device (5) according to one of the preceding claims, in which the second spectral width (Δλ2) extends between 420 5 nanometers and 700 nanometers. 8. Image generation device according to one of the preceding claims, further comprising an optical tube (49) disposed between the first screen (13) and the second screen (15), said optical tube (49) being configured to absorbing parasitic rays between the first screen (13) and the second screen 10 (15). 9. An image generation device (5) according to one of the preceding claims, in which the first screen (13) has a first resolution lower than a second resolution of the second screen (15). 10. Head-up display (1) comprising an image generation device (5) according to one of claims 1 to 9 and an image projection device (7) adapted to transmit towards a blade partially transparent (3) the light beam generated by the image generation device (5).