HEADS-UP DISPLAY

Abstract

A head-up display is proposed comprising an image generation device configured to generate a light beam (3) and an optical system separate from the image generation device, located at a distance from it, and configured to receive and transmit the light beam to a partially transparent plate. The image generation device comprises a light source configured to generate the light beam, a variable transmittance element array (10) configured to selectively receive and transmit the light beam, and a hot mirror (12) and a polarizer (13) placed in the optical path of the light beam downstream of the variable transmittance element array relative to the direction of propagation of the light beam, the hot mirror being placed upstream of the polarizer in the optical path. Figure for the abstract: Fig. 2

Description

Title of the invention: HEAD-UP DISPLAY technical field

[0001] The present invention relates to the technical field of display systems, and more specifically to the technical field of image projection systems.

[0002] The invention relates particularly to a head-up display. Technological background

[0003] A head-up display is an optical system that projects an image into the field of vision of a driver of a vehicle, in order, for example, to allow them to access certain information relating to driving or the condition of the vehicle (speed, GPS directions, etc.) without having to take their eyes off the road.Typically, a head-up display includes an image generation unit (PGU), which includes, for example, a light source coupled to a matrix of elements with variable transmittance, for example a liquid crystal display (LCD), and an optical system for transmitting the images generated by the image generation unit to a partially reflective and partially transparent plate, for example the vehicle's windshield or a separate partially reflective and partially transparent plate dedicated to the display (known as a "combiner").

[0004] Some head-up displays allow the display of augmented reality images, that is, images which, from the driver's point of view, appear to be integrated into the vehicle's environment. For example, arrows can be virtually projected onto the road (that is, they appear, from the driver's point of view, to be projected onto the road) at a distance of a few meters from the vehicle. Similarly, obstacles or road signs can be virtually highlighted.

[0005] The virtual image (as perceived by the driver) displayed by an augmented reality display has several characteristics. It is inclined at least 30° to the road or parallel to the road, it has a luminance that can reach 1000 cd.m2, a contrast ratio of at least 1500:1, and a width of at least 1 meter. Its brightness must be uniform.

[0006] Therefore, a head-up display suitable for providing a virtual image in augmented reality must include a light source capable of providing very high optical power, which generates very high and potentially harmful heat. for the components of the head-up display, and include an optical system that has a magnification factor of at least 5. Such an optical system, when subjected to solar radiation (which arrives in the opposite direction to the light beam generated by the display), risks strongly concentrating the sun's rays at a point in the variable transmittance element matrix, which can damage the variable transmittance element matrix.

[0007] To protect the variable transmittance element array, it is known to apply a polarizer to the protective window of the display enclosure (the "cover window"). This protective window is located at the display enclosure outlet, upstream of the partially transparent blade. However, given the large surface area of ​​the protective window, this solution requires a polarizer with a large surface area; it is therefore expensive.

[0008] There is therefore a need to find an economical solution to respect the optical and light constraints specific to the display of images in augmented reality while preserving the integrity of the head-up display. Summary of the invention

[0009] According to one aspect, a head-up display is proposed, comprising an image generation device configured to generate a light beam and an optical system which is separate from the image generation device, which is located at a distance from it and which is configured to receive and transmit the light beam to a partially reflective blade, the image generation device comprising a light source configured to generate the light beam, a variable transmittance element array configured to selectively receive and transmit the light beam, and a hot mirror and a polarizer placed on the optical path of the light beam downstream of the variable transmittance element array relative to the direction of propagation of the light beam, the hot mirror being placed upstream of the polarizer on the optical path.

[0010] For the purposes of the invention, a hot mirror is understood as a reflective element configured to reflect radiation in the infrared range and to transmit (allow to pass through) radiation in the visible range. A hot mirror reflects, for example, at least 80% of the infrared radiation (i.e., for example, radiation with a wavelength greater than or equal to 820 nanometers), allows to pass at least 90% of the visible radiation (i.e., for example, radiation with a wavelength between 380 nanometers and 780 nanometers), and possibly a portion of the infrared range for radiation with a wavelength between 780 nanometers and 820 nanometers.

[0011] The presence of the hot mirror and polarizer filters a portion of the solar radiation before it reaches the variable transmittance element array, thus limiting the latter's temperature rise. Furthermore, placing the hot mirror and polarizer upstream of the optical system allows this filtering to occur as close as possible to the variable transmittance element array, thereby limiting the depolarization of the radiation between the polarizer and the variable transmittance element array. This also allows the use of a smaller hot mirror and polarizer, particularly compared to a hot mirror or polarizer placed on the head-up display's protective window (the "cover window"). Finally, placing the polarizer downstream of the hot mirror further improves the filtering efficiency compared to a configuration in which the hot mirror is downstream of the polarizer.Indeed, since the polarizer absorbs the rays it doesn't allow to pass through (approximately 50% of the rays, corresponding to the rays before the polarization absorbed by the polarizer), its temperature can increase significantly. It is therefore preferable that it be placed as far away as possible from the variable transmittance element array. Ideally, the polarizer should be separated from the variable transmittance element array by at least a volume of air. This prevents the variable transmittance element array from overheating.

[0012] According to one embodiment, the heated mirror is placed at a distance from the variable transmittance element matrix. Preferably, the heated mirror is separated from the variable transmittance element matrix by at least a volume of air. This prevents the variable transmittance element matrix from heating by thermal conduction.

[0013] According to one embodiment, the hot mirror is applied to a transparent plate.

[0014] According to one embodiment, the heated mirror is applied to a downstream face of the transparent plate relative to the direction of propagation of the light beam, while an upstream face of the transparent plate is in contact with the variable transmittance element matrix. Advantageously, the heat stored by the heated mirror can be distributed over the entire volume of the transparent plate. This prevents localized or concentrated heating of a restricted area of ​​the variable transmittance element matrix and thus avoids premature damage to the latter.

[0015] According to one embodiment, the transparent plate is placed at a distance from the variable transmittance element array, for example separated by a volume of air. The hot mirror is applied to a downstream face of the transparent plate relative to the direction of propagation of the light beam, and an anti-reflective coating is applied to an upstream face of the transparent plate. The anti-reflective coating reduces stray reflections that degrade the optical properties of the head-up display and which could contribute to dazzling the driver if these rays were reflected back into his field of vision.

[0016] According to one embodiment, the hot mirror and the polarizer are each applied to opposite faces of the same transparent plate. Preferably, in this embodiment, the transparent plate is placed at a distance from the array of variable transmittance elements.

[0017] According to one embodiment, the polarizer is placed on an optical axis of the image generation device so as to form a non-zero, non-right angle with it in a plane containing the optical axis. For example, the non-zero, non-right angle is between 10° and 40°.

[0018] According to one embodiment, the hot mirror is in contact with a downstream face of the matrix of elements with variable transmittance relative to the direction of propagation of the light beam.

[0019] According to one embodiment, the image generation device comprises a housing (for example opaque) defining a conduit between the light source and the variable transmittance element matrix, the hot mirror and the polarizer being fixed to the housing.

[0020] According to one embodiment, the optical system (for example, a mirror included in the optical system and onto which the light beam generated by the image generation device is incident) is placed on an optical path of the light beam at a given distance from the variable transmittance element array along the optical path, the polarizer being placed at a distance from the variable transmittance element array that is less than or equal to 20% of the given distance, preferably less than or equal to 10%. The closer the polarizer is to the variable transmittance element array, the smaller its size can be.

[0021] 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

[0022] 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:

[0023] [Fig-1] is a schematic view of a head-up display according to a mode of realization of the invention,

[0024] [Fig.2] is a schematic view of part of an image generation device the head-up display of [Fig. 1],

[0025] [Fig.3] is a schematic view of part of an image generation device for a head-up display according to another embodiment of the invention,

[0026] [Fig.4] is a schematic view of part of an image generation device of a head-up display according to another embodiment of the invention.

[0027] It should be noted that, in these figures, the structural and / or functional elements common to the different variants may have the same references.

[0028] In the description that follows, the terms "upstream" and "downstream" are understood to be relative to the direction of propagation of the light beam generated by the head-up display.

[0029] A head-up display according to an embodiment of the invention, as schematically represented in [Fig. 1] and designated as a whole by the reference numeral 1, is configured to generate and display an augmented reality image I in the field of vision of a driver CD of a vehicle, for example a motor vehicle, such as a car. To this end, the head-up display 1 comprises an image generation device 2 configured to generate a downstream light beam (or flux) 3 (relative to the direction of propagation of the light beam and with respect to an upstream light beam which will be defined below) corresponding to the image to be displayed, and an optical system 5, here comprising two mirrors and configured to reflect the downstream light beam 3 towards a partially transparent blade 4, for example the windshield of the vehicle.In particular here, the optical system 5 comprises a first mirror 7, or folding mirror, and a second mirror 8, here a concave mirror. The path of the downstream light beam 3 is incident on the first mirror 7 and therefore reflected by this first mirror 7, here in the direction of the second mirror 8, then reflected by the second mirror 8 in the direction of the partially transparent plate 4.

[0030] The head-up display 1 further comprises an enclosure 24, for example opaque, which contains the image generation device 2 and the optical system 5, and which has an opening provided with a protective window 25 (“cover window”) through which the downstream light beam 3 passes after its passage through the optical system 5.

[0031] The image generation device 2 includes a light source 6 configured to generate an upstream light beam 9 (relative to the direction of propagation of the beam), a matrix of variable transmittance elements 10 configured to receive the upstream light beam 9 and to transmit it selectively, so as to form the downstream light beam 3. The light source 6 includes, for example, at least one light-emitting diode and preferably a plurality of light-emitting diodes, in particular arranged in a matrix on a printed circuit board.

[0032] The variable transmittance element matrix 10 is here controlled so that, depending on the image to be displayed, one or more of its elements are opaque (zero transmittance), one or more of its other elements have maximum transmittance (relative to the capacity of the matrix), and one or more of its other elements have transmittances of intermediate values.

[0033] For example, the variable transmittance element matrix 10 here comprises a first polarizing film applied to its upstream face and a second polarizing film applied to its downstream face (not shown in the figures), the first and second polarizing films being arranged in a crossed manner (each allowing two distinct polarization directions to pass through). Each element of the variable transmittance element matrix 10 can be controlled to modify the polarization of the light delivered by the first polarizing film.Thus, depending on the command applied to it, either the element does not modify the polarization of the light passing through it (the two polarizing films being crossed, the light is blocked by the second polarizing film and the transmittance of the element is zero), or it partially modifies the polarization (the transmittance is then of intermediate value), or it modifies the polarization so as to correspond to that of the second polarizing film (the transmittance is then maximum).

[0034] For example, the variable transmittance element matrix 10 is a liquid crystal display (LCD, for "Liquid Crystal Display" according to the usual Anglo-Saxon acronym).

[0035] The downstream light beam 3 and the upstream light beam 9 share the same optical axis Ax (an optical axis is understood here as the average path of the rays of a light beam). Here, the variable transmittance element matrix 10 is placed on this optical axis Ax.

[0036] In this example, the image generation device 2 comprises a protective housing 11 made here of an opaque material. This housing defines a conduit through which the upstream light beam 9 passes; this conduit is here generally centered around the optical axis Ax, or parallel to it. At a first end of the protective housing 11 (at the bottom of the protective housing 11, i.e. here at the level of the most upstream part of the protective housing 11) is the light source 6. A second end of the protective housing 11 opposite to the first end (i.e. at the level of the most downstream part of the protective housing 11, relative to the direction of propagation of the upstream light beam 9) has an opening at the level of which is the variable transmittance element array 10, which is arranged so as to close the opening.The variable transmittance element matrix 10 forms the only optical output (the only non-opaque portion) of the protective housing 11.

[0037] In order to protect the variable transmittance element array 10 from sunlight which may, in certain situations, pass through the head-up display 1 in the opposite direction to that of the downstream light beam 3, the head-up display 1 The system here comprises a hot mirror 12 and a polarizer 13, placed on the optical path of the downstream light beam 3 between the variable transmittance element array 10 and the optical system 5. In particular, the hot mirror 12 is placed on the optical path between the variable transmittance element array 10 and the polarizer 13. Here, the polarizer 13 and the hot mirror 12 are placed close to the variable transmittance element array 10 relative to the distance, along the optical path of the downstream light beam 3, that separates the variable transmittance element array 10 from the optical system 5, in particular here from the first mirror 7. For example, the polarizer 13 is here placed at a distance from the variable transmittance element array 10 that is less than or equal to 20% of the distance that separates the variable transmittance element array 10 from the first mirror 7, or even less than or equal to 15%, for example here 10%.

[0038] Here, the hot mirror 12 is configured to reflect at least 80% of the solar rays in the infrared range, with wavelengths greater than or equal to 700 nanometers, and to transmit at least 90% of the solar rays in the visible range, with wavelengths between 400 nanometers and 700 nanometers. However, it has been observed that the hot mirror 12 also reflects a small portion of the rays in the visible range, for example, here between 4% and 5% of the visible range rays.

[0039] The polarizer 13 is configured here to transmit rays whose polarization corresponds to that of the second polarizing film (the one placed on the downstream face of the variable transmittance element array 10) and to absorb other rays (i.e., rays whose polarization does not correspond to that of the second polarizing film). It has been observed that the polarizer 13 also absorbs a small portion of the infrared radiation, here 10% of the infrared radiation. Thus, approximately 50% of the visible solar radiation and 10% of the infrared solar radiation do not pass through the polarizer 13.

[0040] The relative positions of the variable transmittance element matrix 10, the hot mirror 12 and the polarizer 13 are illustrated in more detail in [Fig.2].

[0041] In this embodiment, the hot mirror 12 is a film laminated onto a first transparent plate 14, here a glass plate. The first transparent plate 14 has a thickness greater than or equal to 0.5 millimeters, in particular 1 millimeter. The transparent plate 14 has a coefficient of thermal expansion equal to 2 x 10⁶ K⁻¹. In this example, the surface area of ​​the hot mirror 12 is smaller than that of the first transparent plate 14, so that a peripheral area of ​​the first transparent plate 14 remains free around the hot mirror 12 (onto which the hot mirror 12 is not applied).

[0042] The first transparent plate 14 is here placed in contact with the variable transmittance element matrix 10. It therefore has an upstream face in contact with the variable transmittance element matrix 10, and a downstream face on which the hot mirror 12 is laminated. Here, the surface area of ​​the transparent plate 14 is smaller than that of the variable transmittance element matrix 10, so that when the transparent plate 14 is in contact with the variable transmittance element matrix 10 and centered with it, there remains a peripheral area of ​​the variable transmittance element matrix 10 that is free (with which the first transparent plate 14 is not in contact. For example, this area is not optically useful. It may in particular correspond to the support frame of the variable transmittance element matrix 10).

[0043] The polarizer 13 is positioned downstream of the hot mirror 12, at a distance from it. It is held at a distance from the hot mirror 12 by a support structure 15 acting as a spacer. For example, the polarizer 13 is separated from the variable transmittance element array and the hot mirror 12 by at least a volume of air. The support structure 15, made here of an opaque material, defines a conduit between the hot mirror 12 and the polarizer 13.

[0044] The support structure 15 has a first end bearing on the peripheral area of ​​the variable transmittance element array 10. The support structure 15 has, at its first end, a recess for receiving the transparent plate 14, so that it also bears on the peripheral area of ​​the first transparent plate 14. Thus, with the support structure 15 fixed to the protective housing 11 (the means for fixing the support structure 15 to the protective housing 11 are not shown for the sake of simplicity), the variable transmittance element array 10 and the first transparent plate 14 are held against each other by clamping. In this example, a foam 16 is placed between the support structure 15 and the variable transmittance element array 10, so as to mechanically protect the variable transmittance element array 10 and to thermally insulate it from the support structure 15.

[0045] The polarizer 13 is held against a second end of the support structure 15, opposite the first end. In this embodiment, the polarizer 13 is a film laminated onto a first face of a second transparent plate 17, here a glass plate. The first face of the second transparent plate is a downstream face. The second transparent plate 17 has a thickness greater than or equal to 0.5 millimeters, in particular 1 millimeter, and has a coefficient of thermal expansion of 2 × 10⁶ K⁻¹. In this example, the surface area of ​​the polarizer 13 is smaller than that of the second transparent plate 17, so that a peripheral area of ​​the second transparent plate 17 remains around the polarizer 13. which is free (on which the polarizer 13 is not applied). Here, the second transparent plate 17 is in contact with the second end of the support structure 15.

[0046] Here, an anti-reflective coating 18 is applied to a second face (upstream face) of the second transparent plate 17, opposite to the first face.

[0047] In this example, the polarizer 13 (i.e., here also, the second transparent plate 17) is placed on the optical path of the downstream light beam 3 in a way that is not orthogonal to the optical axis Ax. It forms, in a plane containing the optical axis Ax (here the plane of [Fig.2]), a non-zero angle with the optical axis Ax, for example an angle between 10° and 40°, in particular in this example an angle of 30°.

[0048] In order to hold the second transparent plate 17 against the support structure 15, the image generation device 2 includes a fixing frame 19 configured to be fixed to the support structure 15, in particular here to the outer wall of the support structure 15, and, when fixed to the support structure 15, to bear against the peripheral area of ​​the second transparent plate 17. Thus, the second transparent plate 17 is held by clamping between the support structure 15 and the fixing frame 19.

[0049] The device described above is particularly effective at mitigating the effects of solar radiation and thus at protecting the variable transmittance element array 10. In particular, after passing through the polarizer 13, the solar radiation contains only 50% of the initial visible light and 90% of the initial infrared radiation. After passing through the hot mirror, the solar radiation contains only 45% of the initial visible light and 5% of the initial infrared radiation. Consequently, the heat generated on the variable transmittance element array 10 by the solar radiation is significantly reduced.

[0050] Furthermore, the part of the infrared radiation and the small part of the visible radiation which are reflected by the hot mirror 12 are not reflected again towards the variable transmittance element matrix 10, but transmitted by the antireflective layer towards the polarizer 13 and then absorbed or transmitted by the polarizer 13.

[0051] Furthermore, the inclination of the polarizer 13 with respect to the optical axis Ax (here, an inclination of 30°) prevents any sunlight reflected by the second transparent plate 17, or transmitted by the anti-reflective coating 18 and then by the polarizer 13, from being directed towards the optical system 5 (in which case they would appear as stray light in the field of vision of the driver CD). Thanks to the inclination, these rays are directed towards the inner walls (here opaque) of the enclosure 25 of the head-up display 1, which absorbs them.

[0052] In order to further improve the thermal protection of the variable transmittance element array 10, it is possible to place the hot mirror (more precisely here, the first transparent plate 14) at a distance from it. For example, the mirror hot 12 is spaced from the variable transmittance element matrix by at least a volume of air.

[0053] Thus, in the embodiment illustrated in [Fig.3], an intercalated structure 20, which here acts as a spacer, is placed between the variable transmittance element matrix 10 and the support structure 15. The intercalated structure 20, made of an opaque material, defines a conduit between the variable transmittance element matrix 10 and the hot mirror 12.

[0054] A first end of the interlayer structure 20 is in contact with the variable transmittance element matrix 10. In particular here, the interlayer structure 20 is in contact with the peripheral area of ​​the variable transmittance element matrix 10, via a protective foam 21.

[0055] The support structure 15 is here fixed to a second end of the interlayer structure 20, for example by clipping. A protective foam 22 is placed between the interlayer structure 20 and the support structure 15.

[0056] Here, an upstream face of the first transparent plate is covered with an anti-reflective coating 23.

[0057] The embodiment illustrated in [Fig. 4] is similar to the embodiment described previously in relation to [Fig. 2]. It differs from the latter in that it does not include the first transparent plate 14. Here, the heated mirror is applied, in this case laminated, to the upstream face of the second transparent plate 17, in this case in place of the anti-reflective coating 18 of [Fig. 2]. A space is thus created between the folding mirror 12 and the variable transmittance element array 10 without increasing the overall size of the image generation device 2.

[0058] The invention is not limited to the embodiments described above in connection with figures 1 to 4.

[0059] In particular, although it is particularly advantageous to preserve the integrity of the hot mirror and polarizer to laminate them onto glass plates (since glass has a low coefficient of thermal expansion), other materials are conceivable for the transparent plates, including polymer materials.

[0060] In addition, the invention also covers embodiments in which the hot mirror is applied directly to the variable transmittance element matrix, for example on a downstream face of the variable transmittance element matrix.

[0061] The heated mirror and polarizer described above are applied to the transparent plates by lamination. However, the invention is not limited to this method, and other application methods are conceivable, for example, by bonding. It is also conceivable that the heated mirror and / or polarizer be placed between two transparent plates in contact with these (the hot mirror or polarizer is then "sandwiched" between the two plates).

[0062] A polarizer placed on the optical path at a distance from the variable transmittance element array equal to 15% of the distance separating the variable transmittance element array from the optical system (in particular from the first mirror of the optical system) has been described above. It is nevertheless possible to place the polarizer at a different distance, and preferably at a shorter distance, for example 10% or 5% of the distance separating the variable transmittance element array from the optical system.

[0063] Various other modifications may be made to the invention within the scope of the annexed claims.

Claims

Demands

1. Head-up display, comprising an image-generating device (2) configured to generate a light beam (9) and an optical system (5) which is separate from the image-generating device (2), which is located at a distance from it and which is configured to receive and transmit the light beam (3) to a partially reflective blade, the image-generating device (2) comprising a light source (6) configured to generate the light beam (3), a variable transmittance element array (10) configured to selectively receive and transmit the light beam (3), and a hot mirror (12) and a polarizer (13) placed on the optical path of the light beam downstream of the variable transmittance element array (10) relative to the propagation direction of the light beam (9), the hot mirror (12) being placed upstream of the polarizer (13) on the optical path.

2. Head-up display according to claim 1, wherein the hot mirror (12) is placed at a distance from the variable transmittance element array (10).

3. Head-up display according to any one of claims 1 and 2, wherein the heated mirror (12) is applied to a transparent plate (14; 17).

4. Head-up display according to claim 3, wherein the hot mirror is applied to a downstream face of the transparent plate (14) relative to the direction of propagation of the light beam (3), an upstream face of the transparent plate (14) being in contact with the variable transmittance element matrix (10).

5. Head-up display according to claim 3, wherein the transparent plate (14) being placed at a distance from the variable transmittance element array (10), the hot mirror (12) is applied to a downstream face of the transparent plate (14) relative to the direction of propagation of the light beam (3) and an anti-reflective coating (18) is applied to an upstream face of the transparent plate (14).

6. Head-up display according to any one of claims 1 to 3, wherein the hot mirror (12) and the polarizer (13) are each applied to an opposite face of the same transparent plate (17).

7. Head-up display according to any one of claims 1 to 5, wherein the polarizer is placed on an optical axis (Ax) of the image generation device (2) so as to form, in a plane containing the optical axis (Ax), a non-right and non-zero angle with the optical axis (Ax).

8. Head-up display according to claim 1, wherein the hot mirror (12) is in contact with a downstream face of the variable transmittance element matrix (10) relative to the direction of propagation of the light beam (3).

9. Head-up display according to any one of claims 1 to 8, wherein the image generation device (2) comprises a housing (11) defining a conduit between the light source (6) and the variable transmittance element array (10), the hot mirror (12) and the polarizer (13) being fixed to the housing (11).

10. Head-up display according to any one of claims 1 to 9, wherein the optical system (5) is placed on an optical path of the light beam (3) at a given distance from the variable transmittance element array (10) along the optical path, the polarizer (12) being placed at a distance from the variable transmittance element array (10) which is less than or equal to 20% of the given distance.

Images