Head-up display for motor vehicles

Abstract

The invention relates to a head-up display (1) for a motor vehicle, comprising: - a housing (10) having a window (11), - an image generation device (20) housed inside the housing, - a projection system (comprising at least one folding mirror (31) housed inside the housing and adapted to deflect a light beam (F1) emitted by the image generation device to project said images into the field of vision of a driver (100) of the motor vehicle, said folding mirror being adapted to reflect this light beam in a range of wavelengths corresponding to the visible spectrum and to be traversed by a light beam (F2) coming from outside the housing in a range of wavelengths corresponding to the infrared spectrum. According to the invention, this folding mirror is further adapted to diverge the light beam passing through it. Figure for the abstract: Fig. 1

Description

Title of the invention: Head-up display for motor vehicles Technical field of the invention

[0001] The present invention relates generally to driving aids in a motor vehicle.

[0002] It relates more particularly to a head-up display for a motor vehicle, which comprises: - a case with a window, - an image generation device housed inside the casing, and - a projection system which includes at least one folding mirror housed inside the casing and adapted to deflect a beam of light emitted by the image generation device to project said images into the field of vision of a driver of the motor vehicle. State of the art

[0003] To make driving a motor vehicle easier and safer, it is desirable to prevent the driver from having to take their eyes off the road. For this purpose, a head-up display is known to be used, designed to project information (vehicle speed, direction to follow, etc.) at the driver's eye level.

[0004] Such a display comprises a housing that contains an image generation device and a projection system consisting in practice of one or more mirrors. The housing is designed to be mounted inside the vehicle's passenger compartment, more specifically in the vehicle's dashboard, under the windshield.

[0005] To allow light to pass from the image generation device to the outside of the housing (into the driver's field of vision), the housing has a window which is closed by a protective glass and which is placed in such a way that the mirrors (called folding mirrors) can reflect the image from the image generation device into the driver's field of vision, through this window.

[0006] Over the years, and even now, the size of the image to be displayed in the driver's field of vision tends to increase, without a proportional increase in the size of the image generation device. This is particularly true for so-called "augmented reality" head-up displays, for which the virtual image must be superimposed on certain objects in the scene observed by the driver through the windshield. As a result, the various optical elements of the display (typically the folding mirror(s) and the protective glass) are becoming increasingly larger.

[0007] Therefore, the general trend is that head-up displays exhibit an increasingly large divergence factor.

[0008] It is then understood that, conversely, if we consider the parasitic sunlight that enters the casing, it presents an increasingly high convergence factor.

[0009] As this sunlight converges near the image generation device, thermal heating at the level of this device increases considerably, so that there is a risk of overheating and deterioration of this device and / or the components located around this device.

[0010] Moreover, with larger optics, the stray light that can appear in the display also increases, hindering the visibility of the virtual image, causing a risk of poor viewing and therefore of safety.

[0011] The solution generally used to remedy these drawbacks is to place a polarizer on the protective glass. This solution proves effective, but becomes increasingly expensive as these glass panes get larger. Presentation of the invention

[0012] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes a less expensive solution, consisting of using a folding mirror designed to prevent stray sunlight from reaching the image generation device.

[0013] More specifically, the invention proposes a head-up display as defined in the introduction, in which the folding mirror is adapted to:

[0014] - reflect the light beam emitted by the image generation device in a range of wavelengths corresponding to the visible spectrum (so that the generated images can be reflected into the driver's field of vision), - to be traversed by a beam of light coming from outside the casing, in particular the sun, in a range of wavelengths corresponding to the infrared domain, and - to diverge the light beam that passes through it in the said range of wavelengths corresponding to the infrared domain.

[0015] Thus, thanks to the invention, the folding mirror allows sunlight to pass through, at least in the infrared range, so that it does not reach the image generation device. This sunlight then impacts the housing behind the folding mirror. The image generation device is therefore less likely to overheat.

[0016] In addition, the light that passes through the folding mirror diverges at its exit from this mirror, so as to prevent it from impacting only a small area of ​​the housing, which otherwise could cause strong heating of the housing and the vehicle components located near this area of ​​the housing.

[0017] Other advantageous and non-limiting features of the head-up display according to the invention, taken individually or in all technically possible combinations, are as follows: - said folding mirror comprises a substrate; - the substrate has on its front face a coating or a cold mirror film, said front face being turned towards the incident side of the light beam emitted by the image generation device; - said substrate is made of glass; - said substrate has a thickness greater than or equal to 1.5 mm; - said substrate which has two main non-parallel faces, allowing the light beam coming from outside the housing and passing through it to diverge; - said substrate has on its rear face a coating or film that diverges the light; - said folding mirror is adapted to diverge the light beam which comes from outside the housing and which passes through it with a divergence angle greater than or equal to 20°; - said divergence angle is greater than or equal to 40°; - the housing has a part located opposite a rear face of the folding mirror which is black in color and which is located at a distance from said rear face which is greater than or equal to 1 cm, said rear face being turned in the opposite direction to the incident side of the light beam emitted by the image generation device; - a second folding mirror is planned, which is located between said folding mirror and said window along the light beam emitted by the image generation device.

[0018] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0019] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0020] On the attached drawings:

[0021] [Fig. 1] schematically illustrates a head-up display according to the invention,

[0022] [Fig.2] is a detail view of area II of [Fig. 1].

[0023] Figure 1 schematically represents the main elements of a head-up display 1, intended for example to equip a motor vehicle, in particular a car.

[0024] Such a head-up display 1 is adapted to create a virtual image Img in the field of vision of a driver 100 of the motor vehicle (represented by an eye), so that the driver 100 can see this virtual image Img without having to take his eyes off the road.

[0025] For this purpose, the vehicle is provided to have a partially transparent blade 2 placed in the driver's field of vision, and the head-up display 1 has a housing 10, an image generation device 20 which is housed in the housing 10 and which is adapted to generate a light beam Fl, and a projection system 30 which is housed in the housing 10 and which is adapted to reflect this light beam Fl towards said partially transparent blade 2.

[0026] The partially transparent blade 2 is here formed by the vehicle's windshield. This configuration is particularly suitable for augmented reality image projection.

[0027] Alternatively, the partially transparent blade could be a combiner, i.e., a partially transparent blade separate from the windshield and dedicated to the head-up display. Such a combiner would be placed between the vehicle's windshield and the driver's eyes 100, in the path of the light beam Fl emitted by the image generation device 20.

[0028] The image generation device 20 could take various forms.

[0029] For example, in a first preferred embodiment illustrated in [Fig. 1], it could include a backlight device 22 placed at the rear of a display 21 such as, for example, a liquid crystal display (or LCD for "Liquid Crystal Display") with thin-film transistors (or TFT for "Thin-Film Transistor").

[0030] In a second embodiment not shown, it could comprise a diffuser and a scanning unit that generates a light beam of variable direction so as to be able to scan the rear face of the diffuser. The scanning unit would then more specifically comprise a beam-forming module and a movable mirror, for example implemented as a microelectromechanical system (or MEMS for "MicroElectroMechanical System").

[0031] Other embodiments are conceivable.

[0032] In all these embodiments, the image generation device 20 allows, under the control of a computer, the generation of an image which the projection system 30 will be able to project into the driver's field of vision when the latter's gaze is turned towards the road.

[0033] As further shown in [Fig.1], the housing 10 has opaque walls and is hermetically sealed in order in particular to protect the elements it houses against possible nuisances from the outside (dust, liquids, etc.).

[0034] This housing 10 has a window 11 through which the light beam Fl from the image generation device 20 passes so as to be able to reach the windshield.

[0035] This window 11 delimits an opening in the housing.

[0036] It is preferably closed by a protective window 12 (sometimes referred to by the Anglo-Saxon term "cover window") which is at least partially transparent. This protective window is, for example, made of a plastic sheet (preferably polycarbonate) with a thickness between 0.25 mm and 0.75 mm.

[0037] This protective glass 12 is preferably curved towards the inside of the housing 10.

[0038] The projection system 30 includes at least one folding mirror 31 arranged to reflect the light beam Fl from the image generation device 20 towards the partially transparent blade 2.

[0039] Preferably, exactly two folding mirrors 31, 32 are provided, but one or more than two could be provided.

[0040] These two folding mirrors 31, 32 advantageously allow the image generation device 20 to be placed in a configuration in which it does not face the partially transparent blade 2, which allows the size of the housing 10 to be reduced.

[0041] In the example shown here, the first folding mirror 31, the one located closest to the image generation device 20 along the path taken by the light beam Fl from the image generation device 20, is a fixed, flat mirror. Alternatively, this first folding mirror could be mounted movably within the housing 10, by means of an actuator.

[0042] Conversely, the second folding mirror 32 is a curved mirror with a shape optimized to produce a virtual image adapted to the partially transparent blade 2, so as to display the virtual image Img without distortion. Furthermore, the second folding mirror 32 here has an image magnification function.

[0043] This second folding mirror 32 is preferably mounted movably in the housing 10. An actuator is then provided to move it so as to be able to adjust the height of the virtual image Img according to the size of the conductor 100.

[0044] Of course, other variants could be considered.

[0045] By way of example, the first folding mirror could be curved while the second folding mirror would be flat or curved.

[0046] As another example, the first folding mirror could be mounted movably in the housing while the second folding mirror would be fixed.

[0047] The embodiment shown in the figures is, however, preferred for reasons which will become clear later in this presentation.

[0048] The first folding mirror 31 is adapted to reflect at least a major part of the light beam Fl emitted by the image generation device 20, at least in a range of wavelengths corresponding to the visible domain and at least at the angle of incidence at which this light beam Fl arrives on the first folding mirror 31.

[0049] Thus, this first folding mirror 31 does indeed perform a mirror function to project the images from the image generation device 20 towards the partially transparent blade 2.

[0050] In practice, it reflects more than 90% of the light beam Fl emitted by the image generation device 20 in the entire range of wavelengths corresponding to the visible domain, at the angle of incidence at which this light beam Fl arrives on the first folding mirror 31.

[0051] On the other hand, the first folding mirror 31 is adapted to allow at least a major part of a light beam coming from outside the housing 10 (hereafter referred to as the parasitic beam F2) to pass through, at least in a range of wavelengths corresponding to the infrared domain and at least at the angle of incidence at which this parasitic beam F2 arrives at the first folding mirror 31.

[0052] At this stage, it can be noted that the parasitic beam F2 can typically be formed by sunlight, when the latter is placed relative to the housing 10 in such a way that part of its rays pass directly through the window 11, are reflected on the second folding mirror 32 and reach the first folding mirror 31.

[0053] In practice, the angle of incidence of this parasitic beam F2 on the first folding mirror 31 therefore depends on the size, position and orientation of the second folding mirror 32 relative to the first folding mirror 31 and the window 11. It is considered that the entire parasitic beam F2 which reaches the first folding mirror 31 comes from the second folding mirror 32.

[0054] Thus, the first folding mirror 31 performs a so-called cold mirror function, in that it does not reflect stray light towards the image generation device 20 in the infrared wavelengths. In practice, it allows more than 75% of the stray beam F2 to pass through across the entire wavelength range corresponding to the infrared domain, at the angle of incidence at which this stray beam F2 strikes the first folding mirror 31.

[0055] Typically, the beam transmission rate in the infrared range is between 85% and 95%. In contrast, the reflection rate in the visible range is between 90% and 95%.

[0056] Thanks to the first folding mirror 31, the stray beam F2 is therefore only slightly reflected towards the image generation device 20 in the infrared range, which significantly reduces the heating of the latter. On the contrary, it is mostly transmitted towards the housing 10, behind the first folding mirror 31.

[0057] Here we will define an impacted part 13 of the housing 10 as the area of ​​the housing 10 illuminated by the parasitic beam F2 which has passed through the first folding mirror 31.

[0058] This impacted part 13 is matte black, so as not to reflect this stray beam F2, which could otherwise disrupt the viewing of the virtual image Img. The matte color can be obtained with a suitable paint or by graining.

[0059] Here and preferably, this impacted part 13 extends parallel to the first folding mirror 31, but it could be inclined relative to it.

[0060] This impacted portion 13 is located at a minimum distance from the first folding mirror 31 which is at least 1 cm (preferably in the range of 3 to 7 cm). In other words, the smallest distance between the impacted portion 13 of the housing 10 and the first folding mirror 31 is at least 1 cm.

[0061] According to a particularly advantageous feature of the invention, as shown in [Fig.2], the folding mirror 31 is adapted to diverge the parasitic beam F2 which passes through it.

[0062] This divergence effect prevents stray light passing through this mirror from concentrating on a small area of ​​the housing 10, thus preventing overheating of this area and any vehicle component located near it. Conversely, the impacted portion 13 is therefore quite large.

[0063] Preferably, the first folding mirror 31 is adapted to diverge the parasitic beam F2 with a divergence angle which is greater than or equal to 20°, preferably greater than or equal to 40°, and which is less than or equal to 90°, preferably less than or equal to 85°.

[0064] It will be recalled here that the divergence angle is defined as the angle between two limiting rays of a light beam which diverge after passing through the mirror, whereas the two limiting rays of this same beam were parallel upstream of the mirror.

[0065] Here, we will consider that if the incident beam is symmetrical of revolution, the same will be true of the beam that has passed through the mirror.

[0066] Of course, it could be otherwise. Typically, if we consider several planes passing through the central axis of the beam, the limiting rays of this beam could diverge more in one plane than in another. We could thus have a profile of Gaussian elliptical diffusion or "top hat". This variant would allow, depending for example on the shape of the housing and the position of the folding mirror 31, a divergence in one plane rather than in another.

[0067] Thanks to this divergence effect, the area of ​​the surface S0, defined by the intersection of the parasitic beam F2 and the rear face of the first folding mirror 31, is less than the area of ​​the surface S2 defined by the intersection between the parasitic beam F2 and the housing 10 (see [Fig.2]).

[0068] Preferably, it will be such that the area of ​​the SI intersection surface between the parasitic beam F2 and the front face of the first folding mirror 31 is less than the area of ​​the S2 intersection surface between the parasitic beam F2 and the housing 10 (see [Fig.2]).

[0069] At this stage, it should be noted that the space between the rear face of the first folding mirror 31 and the housing 10 will preferably be left free (i.e., empty of any components). It is then understood that the fixed position of the first folding mirror 31 within the housing 10 will facilitate the design of the head-up display 1. Indeed, since a movable folding mirror is generally held from the rear, leaving this space free is more complicated.

[0070] In practice, the folding mirror 31 comprises a substrate 310 which has a front face 311 (side incident to the light) and an opposite rear face 312.

[0071] Preferably, the substrate is made of glass. This gives it a stable shape over time and when ambient temperature and humidity vary, unlike a plastic substrate. However, a plastic substrate could of course be used, which would be lighter and less expensive than a glass substrate.

[0072] This substrate 310 has a thickness greater than or equal to 1.5 mm. Here, its thickness is 2 mm.

[0073] The substrate 310 has on its front face a coating or a cold mirror film 314, which therefore makes it possible to reflect the light beam Fl but to let through only a part of the parasitic beam F2 (namely a large part of this beam in the infrared range).

[0074] Here we will define a “coating” as a layer chemically applied to the substrate, while a film will be a layer mechanically applied to the substrate.

[0075] The coating may typically be obtained by depositing different dielectric layers (typically silicon dioxide or titanium dioxide), for example by an evaporation process in a vacuum chamber or by a sputtering process. This embodiment may be preferred, in that, as indicated above, it makes it possible to obtain a light reflectance of more than 90% in the visible range.

[0076] The film 314 may be formed by a thin layer applied to the substrate 310 and fixed to it, for example by gluing.

[0077] In practice, this film could be of the type marketed under the reference 3M™ Cold Mirror Film. Such a film may be preferred due to its cost. However, such a film is only usable if the first folding mirror 31 is flat (which is why a flat mirror is preferred). The major drawback of this film is that it reflects only 60 to 80% of the light in the visible spectrum (depending on the angle of incidence of the light).

[0078] To diverge the parasitic beam F2, it is possible to proceed in various ways. Several distinct embodiments, possibly combinable, can then be presented, and are not limiting.

[0079] These embodiments propose to diverge the parasitic beam F2 optically, or by diffraction, or even by diffusion.

[0080] In a first embodiment not shown in the figures, the substrate may have the shape of a diverging lens. For this, it will have two non-parallel principal faces.

[0081] Typically, its front face could be provided to be flat (so as to be able to apply a 314 film to its front face) and its rear face to be concave.

[0082] Alternatively, a flat substrate could be used on which a concave lens would be fixed on the rear face.

[0083] In a second embodiment not shown in the figures, the substrate may have the shape of a diverging prism, so as to diverge the different spectral components of the light that passes through it in the infrared range.

[0084] Here again, as an alternative, a flat substrate could be used on which a prism would be fixed on the back face.

[0085] In a third embodiment, the rear face of the substrate could be machined so as to diverge the light. For this purpose, it could, for example, have a wavy shape.

[0086] In a fourth embodiment illustrated in [Fig. 2], the rear face 312 of the substrate 310 could be equipped with a film 317 that diverges the parasitic beam F2 passing through it. This film 317 could be in different forms (diffraction grid, lenticular film, micro-prism film, etc.).

[0087] In a fifth embodiment not shown in the figures, the rear face of the substrate could receive a coating adapted to diffuse light. For example, using evaporation techniques, a layer of silicon dioxide (SiO2) or silicon nitride (Si3N4) with raised patterns on the nanoscale could be deposited on the rear face of the substrate, creating destructive interference conditions for certain wavelengths, thus dispersing the incident light. could also use centrifugal coating techniques (more commonly known as "Spin coating") to apply a light-diffusing coating.

[0088] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0089] Typically, the second folding mirror 32 could be equipped, in addition to or instead of the first folding mirror 31, with the functions of a cold mirror and a divergence mirror. In this case, it would be preferable for the support of this second folding mirror 32 to frame the mirror (and therefore not be located behind it) so as not to obstruct the light passing through the mirror. However, this variant is not preferred for several reasons. The first of these is that the first folding mirror, due to its position closer to the image-generating device 20 than the second mirror, is smaller and therefore less expensive to manufacture. Other reasons are that this second mirror is curved and mounted movably within the housing, which would further complicate its design.

[0090] In the described embodiment, the entire rear face of the first folding mirror 31 is designed to diverge the light, but alternatively, only a part of this rear face could have such a function.

[0091] In another embodiment of the invention, the film having a cold mirror function could be placed at the back of the substrate.

Claims

Demands

1. Head-up display (1) for a motor vehicle, comprising: - a housing (10) having a window (11), - an image generation device (20) housed inside the housing (10), - a projection system (30) comprising at least one folding mirror (31) housed inside the housing (10) and adapted to deflect a light beam (Fl) emitted by the image generation device (20) to project images generated by said image generation device (20) into the field of vision of a driver (100) of the motor vehicle, said folding mirror (31) being adapted to reflect the light beam (Fl) emitted by the image generation device (20) in a range of wavelengths corresponding to the visible domain and to be traversed by a light beam (F2) coming from outside the housing (10) in a range of wavelengths corresponding to the infrared domain,said folding mirror (31) is further adapted to diverge the light beam passing through it in said wavelength range corresponding to the infrared domain.

2. Head-up display (1) according to claim 1, wherein said folding mirror (31) comprises a substrate (310) which has on its front face (311) a coating or a film (314) of cold mirror, said front face (311) being turned towards the incident side of the light beam (Fl) emitted by the image generation device (20).

3. Head-up display (1) according to claim 2, wherein said substrate (310) is made of glass.

4. Head-up display (1) according to claim 2 or 3, wherein said substrate (310) has a thickness greater than or equal to 1.5 mm.

5. Head-up display according to any one of claims 1 to 4, wherein said folding mirror comprises a substrate which has two non-parallel principal faces, allowing the light beam (F2) which comes from outside the housing and passes through it to diverge.

6. Head-up display (1) according to any one of claims 1 to 5, wherein said folding mirror (31) comprises a substrate (310) which has on its rear face (312) a coating or a film (317) allowing the light beam (F2) to be diverged.

7. Head-up display (1) according to any one of claims 1 to 6, wherein said folding mirror (31) is adapted to diverge the light beam (F2) which comes from outside the housing (10) and which passes through it with a divergence angle greater than or equal to 20°.

8. Head-up display (1) according to claim 7, wherein said folding mirror (31) is adapted to diverge the light beam (F2) which comes from outside the housing (10) and passes through it with a divergence angle greater than or equal to 40°.

9. Head-up display (1) according to any one of claims 1 to 8, wherein the housing (10) has a portion (13) located opposite a rear face of the folding mirror (31) which is black in color and which is placed at a distance from said rear face which is greater than or equal to 1 cm, said rear face being turned away from the incident side of the light beam (Fl) emitted by the image generation device (20).

10. Head-up display (1) according to any one of claims 1 to 9, wherein a second folding mirror (32) is provided, which is located between said folding mirror (31) and said window (11) along the light beam (Fl) emitted by the image generation device (20).

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