Motor-vehicle head-up display

Abstract

The invention relates to a motor-vehicle head-up display (1) comprising: - a housing (10) that has a window (11), - an image-generating device (20) housed inside the housing, - a projection system that comprises at least one fold mirror (31) housed inside the housing and configured to deflect a light beam (F1) emitted by the image-generating device in order to project the images into the field of vision of a driver (100) of the motor vehicle, the fold mirror being configured to reflect the light beam in a wavelength range corresponding to the visible domain and to be passed through by a light beam (F2) originating from the outside of the housing in a wavelength range corresponding to the infrared domain. According to the invention, the fold mirror is further configured to make the light beam passing through it diverge.

Description

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 specifically to a head-up display for motor vehicles, which includes: - 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, the goal is to prevent the driver from having to take their eyes off the road. A common solution for this is the use of a head-up display, designed to project information (vehicle speed, directions, etc.) at the driver's eye level.

[0004] Such a display comprises a housing containing an image generation device and a projection system, typically consisting of one or more mirrors. The housing is designed to be installed inside the vehicle's passenger compartment, specifically within the dashboard, beneath 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 positioned so 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 today, 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, where 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 present a an increasingly significant factor of divergence.

[0008] It is then understood that, conversely, if we consider the stray sunlight entering the case, it presents an increasingly high convergence factor.

[0009] As sunlight converges near the image generation device, thermal heating at the device increases considerably, creating a risk of overheating and damage to the device and / or the components surrounding it.

[0010] Furthermore, 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 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: - 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.

[0014] 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-generating device. This sunlight then impacts the housing behind the folding mirror. The image-generating device is therefore less likely to overheat.

[0015] In addition, the light passing through the folding mirror diverges upon exiting the mirror, so as to prevent it from impacting only a small area of ​​the housing, which could otherwise cause significant heating of the housing and vehicle components located near that area of ​​the housing.

[0016] 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 casing and passing through it to diverge; - said substrate has on its rear face a coating or film that diverges 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.

[0017] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION

[0018] The description that follows, 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.

[0019] Regarding the attached drawings:

[0020] [Fig. 1] schematically illustrates a head-up display according to the invention,

[0021] [Fig. 2] is a detailed view of area II of figure 1.

[0022] 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.

[0023] Such a head-up display 1 is suitable for creating a virtual image Img in the driver's field of vision 100 of the motor vehicle (represented by an eye), so that the driver 100 can see this virtual image Img without having to take their eyes off the road.

[0024] 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 F1, and a projection system 30 which is housed in the housing 10 and which is adapted to reflect this light beam F1 back towards said partially transparent blade 2.

[0025] The partially transparent blade 2 is formed here by the vehicle's windshield. This configuration is particularly well-suited for augmented reality image projection.

[0026] Alternatively, the partially transparent blade could be a combiner, that is, 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 F1 emitted by the image generation device 20.

[0027] The image generation device 20 could take various forms.

[0028] For example, in a first preferred embodiment illustrated in Figure 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").

[0029] In a second, unrepresented embodiment, it could include a diffuser and a scanning unit that generates a light beam with a 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 (MEMS).

[0030] Other implementation methods are possible.

[0031] 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.

[0032] As Figure 1 further shows, the housing 10 has opaque walls and is hermetically sealed in order to protect the elements it houses from possible external interference (dust, liquids, etc.).

[0033] This housing 10 has a window 11 through which the light beam F1 from the image generation device 20 passes so as to be able to reach the windshield.

[0034] This window 11 delimits an opening in the casing.

[0035] It is preferably closed by a protective glass 12 (sometimes referred to by the English term "cover window") which is at least partially transparent. This protective glass is, for example, made of a sheet of plastic material (preferably polycarbonate) with a thickness between 0.25 mm and 0.75 mm.

[0036] This protective glass 12 is preferably curved towards the inside of the case 10.

[0037] The projection system 30 includes at least one folding mirror 31 arranged to reflect the light beam F1 from the image generation device 20 towards the partially transparent blade 2.

[0038] Preferably, exactly two folding mirrors 31, 32 are provided, but one or more than two could be provided.

[0039] 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.

[0040] 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 F1 from the image generation device 20, is a fixed, flat mirror. Alternatively, this first folding mirror could be mounted movably within the housing 10, using an actuator.

[0041] Conversely, the second folding mirror 32 is a curved mirror with a shape optimized to produce a virtual image with a shape adapted to the partially transparent blade 2, so as to display the virtual image Img without distortion. Furthermore, the second folding mirror 32 here serves to magnify the image.

[0042] 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.

[0043] Of course, other variations could be considered.

[0044] As an example, the first folding mirror could be curved while the second folding mirror would be flat or curved.

[0045] As another example, the first folding mirror could be mounted movably in the housing while the second folding mirror would be fixed.

[0046] The embodiment shown in the figures is, however, preferred for reasons which will become clear later in this presentation.

[0047] The first folding mirror 31 is adapted to reflect at least a major part of the light beam F1 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 F1 arrives at the first folding mirror 31.

[0048] 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.

[0049] In practice, it reflects more than 90% of the light beam F1 emitted by the image generation device 20 across the entire range of wavelengths corresponding to the visible domain, at the angle of incidence at which this light beam F1 arrives on the first folding mirror 31.

[0050] 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.

[0051] At this stage, we can note 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.

[0052] 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.

[0053] Thus, the first folding mirror 31 performs a function known as a cold mirror, 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.

[0054] 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%.

[0055] Thanks to the first folding mirror 31, the parasitic 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 mainly transmitted towards the housing 10, at the rear of the first folding mirror 31.

[0056] We will define here 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.

[0057] This impacted area 13 is matte black so as not to reflect the stray beam F2, which could otherwise disrupt the viewing of the virtual image Img. The matte color can be achieved with a suitable paint or by graining.

[0058] Here and preferentially, this impacted part 13 extends parallel to the first folding mirror 31, but it could be inclined relative to it.

[0059] This impacted portion 13 is located at a minimum distance from the first folding mirror 31 of 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.

[0060] According to a particularly advantageous feature of the invention, as shown in Figure 2, the folding mirror 31 is adapted to diverge the parasitic beam F2 which passes through it.

[0061] This divergence effect prevents stray light passing through the mirror from concentrating on a small area of ​​the housing 10, thus avoiding overheating of that area and any vehicle components located near it. Conversely, the impacted area 13 is therefore quite large.

[0062] Preferably, the first folding mirror 31 is adapted to diverge the parasitic beam F2 with a divergence angle that is greater than or equal to 20°, preferably greater than or equal to 40°, and that is less than or equal to 90°, preferably less than or equal to 85°.

[0063] It should 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.

[0064] Here, we will consider that if the incident beam is symmetrical about revolution, the same will be true of the beam that has passed through the mirror.

[0065] 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 Gaussian elliptical or "top hat" scattering profile. This variant would allow us to favor, depending for example on the shape of the housing and the position of the folding mirror 31, a divergence in one plane rather than another.

[0066] 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 figure 2).

[0067] Preferably, it will be such that the area of ​​the intersection surface S1 between the parasitic beam F2 and the front face of the first folding mirror 31 is less than the area of ​​the intersection surface S2 between the parasitic beam F2 and the housing 10 (see figure 2).

[0068] 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 clear 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.

[0069] 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.

[0070] 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.

[0071] This 310 substrate has a thickness greater than or equal to 1.5 mm. Here, its thickness is 2 mm.

[0072] The substrate 310 has on its front face a coating or a cold mirror film 314, which therefore allows the light beam F1 to be reflected but only part of the parasitic beam F2 to pass through (namely a large part of this beam in the infrared range).

[0073] 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.

[0074] The coating can typically be obtained by depositing different dielectric layers (typically silicon dioxide or titanium), for example by a vacuum evaporation process or by a sputtering process. This embodiment may be preferred because, as mentioned above, it allows for a light reflectance of over 90% in the visible range.

[0075] The film 314 can be formed by a thin layer applied to the substrate 310 and fixed to it, for example by gluing.

[0076] In practice, this film could be of the type marketed under the reference 3M™ Cold Mirror Film. Such a film might 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 preferable). The major drawback of this The film is that it reflects only 60 to 80% of the light in the visible range (depending on the angle of incidence of the light).

[0077] To diverge the spurious beam F2, various methods are possible. Several distinct, and potentially combinable, embodiments can be presented, without limitation.

[0078] These embodiments propose to diverge the parasitic beam F2 optically, or by diffraction, or even by diffusion.

[0079] In a first embodiment not shown in the figures, the substrate can have the shape of a diverging lens. For this, it will have two non-parallel principal faces.

[0080] Typically, one could expect its front face to be flat (so that a 314 film can be applied to its front face) and its rear face to be concave.

[0081] Alternatively, a flat substrate could be used, to which a concave lens would be fixed on the back side.

[0082] In a second embodiment not shown in the figures, the substrate can 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.

[0083] Here again, as an alternative, we could use a flat substrate on which a prism would be fixed on the back face.

[0084] In a third embodiment, the rear face of the substrate could be machined to diverge the light. For example, it could have a wavy shape.

[0085] In a fourth embodiment illustrated in Figure 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 grating, lenticular film, micro-prism film, etc.).

[0086] In a fifth embodiment, not shown in the figures, the back face of the substrate could be coated with a light-diffusing coating. For example, using evaporation techniques, a layer of silicon dioxide (SiO2) or silicon nitride (Si3N4) with nanoscale relief patterns could be deposited on the back face of the substrate, creating destructive interference conditions for certain wavelengths, thus dispersing the incident light. Alternatively, spin coating techniques could be used to apply a light-diffusing coating.

[0087] 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.

[0088] Typically, the second folding mirror 32 could be fitted, in In addition to, or instead of, the first folding mirror 31, the functions of a cold mirror and a divergence mirror could be performed. 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 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 include the fact that this second mirror is curved and mounted movably within the housing, which would further complicate its design.

[0089] 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.

[0090] In another variant 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 motor vehicles, comprising: - a case (10) which has a window (11), - an image generation device (20) housed inside the casing (10), - a projection system (30) comprising at least one folding mirror (31) which is housed inside the casing (10) and which is adapted to deflect a light beam (F1) 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 (F1) emitted by the image generation device (20) in a range of wavelengths corresponding to the visible domain and to be crossed by a light beam (F2) coming from outside the casing (10) in a range of wavelengths corresponding to the infrared domain, said folding mirror (31) is further adapted to diverge the light beam which crosses it in said range of wavelengths 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 film (314) of cold mirror, said front face (311) being turned towards the incident side of the light beam (F1) 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) originating from outside the housing (10) and passing through it at 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) originating from outside the housing (10) and passing through it at a divergence angle greater than or equal to 40°.

9. A 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 and which is positioned at a distance from said rear face greater than or equal to 1 cm, said rear face being oriented away from the incident side of the light beam (F1) emitted by the image generation device (20).

10. A 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 (F1) emitted by the image generation device (20).

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