WO2021228625A1

WO2021228625A1 - Projection arrangement for a head-up display system

Info

Publication number: WO2021228625A1
Application number: PCT/EP2021/061705
Authority: WO
Inventors: Giulia CROCI; Jan Hagen; Raphaela KANNENGIESSER; Valentin SCHULZ
Original assignee: Saint-Gobain Glass France
Priority date: 2020-05-15
Filing date: 2021-05-04
Publication date: 2021-11-18
Also published as: DE202021004088U1; CN114174898A

Abstract

The present invention relates to a projection arrangement for a head-up display (HUD), at least comprising a windscreen (10), comprising an outer pane (1) and an inner pane (2) which are connected to one another via a thermoplastic intermediate layer (3), having an HUD region; a projector (4) which is directed to the HUD region, wherein the radiation of the projector (4) is predominantly P-polarised, wherein the windscreen (10) has, within the HUD region, a half-wave plate (6) for converting the polarisation of the radiation transmitted through the half-wave plate (6) and the half-wave plate (6) is arranged between two films made of thermoplastic polymer, more particularly two PVB layers (3.1, 3.2).

Description

l

Projection arrangement for a head-up display system The invention relates to a projection arrangement for a head-up display.

Modern vehicles are increasingly being equipped with so-called head-up display (HUD; “head-up display”) technology. A head-up display is a display system that projects additional information in the form of images for the driver of a vehicle in his field of vision. The head-up display consists of a projector (imaging unit) and several optical modules for deflecting or mirroring (reflection) an image onto a projection surface or reflective surface. A composite pane, in particular the windshield of the vehicle, usually serves as a projection surface. Although the image is projected onto the windshield, the human eye of the driver can perceive it to hover over the hood of the vehicle.

In this way, additional information can be projected into the driver's field of vision, for example the current driving speed and navigation or warning information that the driver can perceive without having to change his line of sight. In this way, head-up displays can make a significant contribution to increasing road safety.

The image generated by the projector usually consists of polarized, in particular S-polarized, light radiation. The S-polarized light strikes the composite pane at a specific angle of incidence and is at least partially both refracted into the composite pane and reflected as S-polarized light into the driver's field of vision. However, the reflected images are not displayed in true color or with undesired reflection, so-called double images.

The angle of incidence of the S-polarized radiation is usually around 65%, which roughly corresponds to the Brewster angle for an air-glass transition (57.2 ° for soda-lime glass). The problem arises that the projector image is reflected at the two outer transitions from air to glass and from glass to air. As a result, a slightly offset secondary image appears in addition to the desired main image, the so-called ghost image. The problem is alleviated by arranging the surfaces of the windshield at an angle to one another. This is done through the use of a wedge-shaped intermediate layer in the lamination of the laminated pane Windshield. This allows the main image and the ghost image to be superimposed. Laminated glasses with wedge foils for HUDs are known, for example, from WO 2009/071135 A1, EP 1800855 B1 or EP 1880243 A2.

Wedge foils are expensive, so that the production of such a composite pane for a HUD is quite costly. There is therefore a need for HUD systems that manage with windshields without wedge foils. For example, it is possible to operate the HUD projector with P-polarized radiation, which is not significantly reflected on the surface of the pane. Instead, the windshield has a reflective coating as a reflective surface for the P-polarized radiation.

US Pat. No. 6,744,478 B1 discloses a HUD system in which a liquid crystal display generates light beams which are directed onto a windshield. The windshield has an optical rotation layer on a first surface of a transparent plate. The rotation layer comprises a liquid crystal polymer. A reflective layer is arranged on an inside of an inner pane of the windshield.

US 2009/195875 A1 discloses a HUD system with a windshield, a birefringent layer being arranged in or on the windshield.

The object of the present invention is to provide a HUD projection arrangement which has good reflectivity for S-polarized radiation in the visible spectral range and which improves the projection of the images.

The object of the present invention is achieved according to the invention by a projection arrangement according to claim 1. Preferred designs emerge from the subclaims.

The projection arrangement according to the invention for a head-up display has a windshield which has an outer pane and an inner pane. The outer pane and the inner pane are connected to one another via a thermoplastic intermediate layer. The windshield is designed to be in a window opening of a vehicle to separate the interior from the external environment. In the context of the invention, the term inner pane denotes the pane of the windshield facing the vehicle interior. The outer pane is referred to as the pane facing the external environment. The windshield is preferably the windshield of a motor vehicle, in particular a passenger or truck.

As is usual with HUDs, a projector irradiates an area of the windshield where the radiation is reflected in the direction of the viewer (driver), creating a virtual image that the viewer perceives from behind the windshield. The area of the windshield that can be irradiated by the projector is referred to as the HUD area. The beam direction of the projector can be varied by optical elements (e.g. mirrors), especially vertically, in order to adapt the projection to the body size of the viewer.

According to the invention, S-polarized radiation is used to generate a HUD image. The windshield has a half-wave plate which is arranged within the HUD area and is provided for converting the polarization of the radiation transmitted through the half-wave plate.

The half-wave plate is intended to change the polarization of the incident radiation, in particular to convert the S polarization into a P polarization, whereby the reflectivity of the radiation is significantly improved.

Since the angle of incidence of around 65 °, which is typical for HUD projection arrangements, is relatively close to the Brewster angle for an air-glass transition (57.2 °, soda-lime glass), S-polarized radiation is reflected from the surface of the pane. The reflection of the radiation takes place mainly on the interior-side surface of the inner pane facing away from the intermediate layer. In order to improve the reflection of the S-polarized radiation, the polarization of the radiation is changed by the half-wave plate arranged in the windshield. In other words, the invention provides that the windshield has a half-wave plate which changes the polarization of the transmitted radiation in such a way that it is hardly reflected. Surprisingly, it has been shown that such a projector arrangement according to the invention has significantly improved optical properties compared to the previously known windshields.

The HUD projection arrangement according to the invention causes a high reflectivity on the surface of the inner pane with respect to S-polarized radiation in the spectral range from 450 nm to 650 nm (nanometers), which is relevant for HUD displays. HUD projectors typically work with wavelengths of 473 nm, 550 nm and 630 nm (RGB). This creates a high-intensity HUD image.

The half-wave plate preferably comprises at least one optically anisotropic material or also optically birefringent materials, in particular quartz or mica. Quartz is used in particular because of its transparency and high optical qualities. Other materials that are suitable in principle are e.g. calcite (CaC03), sapphire, lithium niobate (LiNb03), ruby (AI203), rutile (Ti02) and zirconium (ZrSi04). The half-wave plate can also be designed as a polymer film.

In a preferred embodiment, the half-wave plate is arranged within the intermediate layer. The S-polarized radiation penetrates through the half-wave plate within the intermediate layer, so that the polarization of the radiation is converted into P-polarized. The P-polarized radiation is hardly reflected on the outer pane. This avoids a reflection on the outer pane, which leads to a high-intensity HUD image.

In a further embodiment, the windshield has several half-wave plates. This achieves particularly good results.

The projector is arranged on the inside of the windshield and irradiates the windshield via the inside surface of the inner pane. It is aimed at the HUD area and irradiates it to generate the HUD projection. According to the invention, the radiation from the projector is predominantly S-polarized, that is to say is S-polarized Radiation proportion of greater than 50%. The higher the proportion of the S-polarized radiation in the total radiation of the projector, the greater the intensity of the desired projection image and the lower the intensity of undesired reflections on the surfaces of the windshield. The S-polarized radiation component of the projector is preferably at least 70%, particularly preferably at least 80% and in particular at least 90%.

In a particularly advantageous embodiment, the radiation from the projector is essentially purely S-polarized - the S-polarized radiation component is therefore 100% or deviates only insignificantly from it. The indication of the direction of polarization relates to the plane of incidence of the radiation on the windshield. P-polarized radiation is a radiation whose electric field oscillates in the plane of incidence. S-polarized radiation denotes radiation whose electric field oscillates perpendicular to the plane of incidence. The plane of incidence is spanned by the incidence vector and the surface normal of the windshield in the geometric center of the irradiated area.

The radiation from the projector strikes the windshield preferably at an angle of incidence of 45 ° to 75 °, in particular 60 ° to 70 °. In an advantageous embodiment, the angle of incidence deviates from the Brewster angle by at most 10 °. The P-polarized radiation is then only insignificantly reflected on the surfaces of the windshield, so that no ghost image is generated. The angle of incidence is the angle between the vector of incidence of the projector radiation and the interior-side surface normal (i.e. the surface normal on the interior-side external surface of the windshield) in the geometric center of the HUD area. The Brewster angle for an air-to-glass transition in the case of soda-lime glass, which is generally used for window panes, is 57.2 °. Ideally, the angle of incidence should come as close as possible to this Brewster angle. However, angles of incidence of 65 ° can also be used, for example, which are common for HUD projection arrangements, can be easily implemented in vehicles and only deviate to a small extent from the Brewster angle, so that the reflection of the P-polarized radiation increases only insignificantly.

Since the reflection of the projector radiation takes place essentially on the interior surface of the inner pane facing away from the intermediate layer and not on the internal one Disc surfaces, it is not necessary to angle the internal disc surfaces to avoid ghosting. The external surfaces of the windshield are therefore preferably arranged essentially parallel to one another. For this purpose, the thermoplastic intermediate layer is preferably not designed in the manner of a wedge, but rather has an essentially constant thickness, in particular also in the vertical course between the upper edge and the lower edge of the windshield, just like the inner pane and the outer pane. A wedge-like intermediate layer, on the other hand, would have a variable, in particular increasing thickness in the vertical course between the lower edge and the upper edge of the windshield. Since standard foils are significantly cheaper than wedge foils, the production of the windshield is made cheaper.

The outer pane and the inner pane are preferably made of glass, in particular soda-lime glass, which is common for window panes. In principle, however, the panes can also be made of other types of glass (for example borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (for example polymethyl methacrylate or polycarbonate). The thickness of the outer pane and the inner pane can vary widely. Discs with a thickness in the range from 0.8 mm to 5 mm, preferably from 1.4 mm to 2.5 mm, for example those with the standard thicknesses of 1.6 mm or 2.1 mm, are preferably used.

The outer pane, the inner pane and the thermoplastic intermediate layer can be clear and colorless, but also tinted or colored. In a preferred embodiment, the total transmission through the windshield is greater than 70%. The term overall transmission refers to the procedure for testing the light transmission of motor vehicle windows specified by ECE-R 43, Annex 3, Section 9.1. The outer pane and the inner panes can not be preloaded, partially preloaded or preloaded independently of one another. If at least one of the disks is to have a pre-tension, this can be a thermal or chemical pre-tension.

In an advantageous embodiment, the outer pane is tinted or colored. As a result, the reflectivity of the windshield on the outside can be reduced, as a result of which the impression of the window is made more pleasant for an outside observer. However, in order to guarantee the prescribed light transmission of 70% for windshields (Total transmission), the outer pane should preferably have a light transmission of at least 80%, particularly preferably of at least 85%. The inner pane and the intermediate layer are preferably clear, that is, not tinted or colored. For example, green or blue colored glass can be used as the outer pane.

The windshield is preferably curved in one or more directions of the space, as is customary for motor vehicle windows, typical radii of curvature being in the range from approximately 10 cm to approximately 40 m. The windshield can also be flat, for example if it is intended as a window for buses, trains or tractors.

The thermoplastic intermediate layer contains at least one thermoplastic polymer, preferably ethylene vinyl acetate (EVA), polyvinyl butyral (PVB) or polyurethane (PU) or mixtures or copolymers or derivatives thereof, particularly preferably PVB. The intermediate layer is typically formed from a thermoplastic film. The thickness of the intermediate layer is preferably from 0.2 mm to 2 mm, particularly preferably from 0.3 mm to 1 mm.

An intermediate layer within the meaning of the invention can consist of one material. However, an intermediate layer can also comprise two or more individual layers of different materials. An intermediate layer according to the invention comprises, for example, at least a first PVB layer and a second PVB layer. The half-wave plate is embedded between the first and second PVB layers. Alternatively or additionally, the PVB layers can have ethylene vinyl acetate (EVA), polyurethane (PU), mixtures or copolymers or derivatives thereof.

The windshield can be manufactured by methods known per se. The outer pane and the inner pane are laminated to one another via the intermediate layer, for example by autoclave processes, vacuum bag processes, vacuum ring processes, calender processes, vacuum laminators or combinations thereof. The connection of the outer pane and the inner pane usually takes place under the action of heat, vacuum and / or pressure. The invention is explained in more detail below with reference to figures and exemplary embodiments. The figures are a schematic representation and are not true to scale. The figures do not restrict the invention in any way.

Show it:

Figure 1 is a plan view of a composite pane of a generic projection arrangement,

FIG. 2 shows a cross section through a generic projection arrangement,

FIG. 3 shows a schematic diagram of the light rays of S-polarized light, and FIG. 4 shows a cross section through a windshield according to the invention.

Figures with numerical values are generally not to be understood as exact values, but also include a tolerance of +/- 1% up to +/- 10%.

Figure 1 and Figure 2 each show a detail of a generic projection arrangement for a HUD. The projection arrangement comprises a windshield 10, in particular the windshield of a passenger car. Furthermore, the projection arrangement has a projector 4 which is directed onto a region of the composite pane 10. This area is commonly referred to as HUD area B. In this area, images generated by the projector 4 can be projected, which are perceived by an observer 5 (e.g. vehicle driver) as virtual images on the side of the laminated pane 10 facing away from him when his eyes are located within the so-called eyebox E.

The windshield 10 is composed of an outer pane 1 and an inner pane 2, which are connected to one another via a thermoplastic intermediate layer 3. Its lower edge U is arranged downwards in the direction of the motor of the passenger car, its upper edge O is arranged upwards in the direction of the roof. In the installed position, the outer pane 1 faces the external environment, and the inner pane 2 faces the vehicle interior. Figure 3 shows a schematic diagram of the light rays of S-polarized light. The outer pane 1 of the windshield 10 has an outer surface I which, in the installed position, faces the external environment, and an inner surface II which, in the installed position, faces the interior space. Likewise, the inner pane 2 has an outer surface III which, in the installed position, faces the external environment, and an interior surface IV which, in the installed position, faces the interior. The outer pane 1 and the inner pane 2 consist, for example, of soda-lime glass. The outer pane has, for example, a thickness of 2.1 mm, the inner pane 2 a thickness of 1.6 mm or 2.1 mm. The intermediate layer 3 is formed, for example, from a PVB layer with a thickness of 0.76 mm. The PVB layer has an essentially constant thickness, apart from any surface roughness that is customary in the art - it is not designed as a so-called wedge film.

When such a windshield 10 is irradiated with S-polarized light radiation and the light radiation hits the windshield 10 at an angle of incidence α of approximately 65 ° (which is close to the so-called Brewster's angle), the radiation is mainly reflected on the surfaces IV and I. .

FIG. 4 shows an embodiment of a windshield 10 designed according to the invention. In contrast to FIG. 2, the windshield 10 according to the invention has a half-wave plate 6.

In contrast to FIG. 3, the intermediate layer 3 has two PVB layers 3.1 and 3.2. Alternatively or additionally, the intermediate layer 3 can have two films made of thermoplastic polymer, preferably EVA, PU or mixtures or copolymers or derivatives thereof.

The half-wave plate is embedded between a first PVB layer 3.1 and a second PVB layer 3.2. The PVB layers have an essentially constant thickness of approximately 0.38 mm to 76 mm each.

The half-wave plate 6 is plate-shaped and contains, for example, quartz. It has a thickness of approx. 28 pm (micrometers). The half-wave plate 6 covers the HUD ok

Area over the entire area. Alternatively, the half-wave plate 6 can contain rutile. Their thickness would be approx. 870 nm (nanometers). The half-wave plate 6 is transparent.

According to the invention, the projector 4 emits S-polarized, in particular essentially purely S-polarized, radiation. Since the projector 4 irradiates the windshield 10 with an angle of incidence of 65 °, which is close to the Brewster angle, the radiation is largely reflected on the surface IV of the windshield 10. The S-polarized radiation is partly reflected on the surface IV and partly transmitted. When the transmitted radiation penetrates the half-wave plate 6, its polarization is changed. The S-polarized radiation is converted into P-polarized radiation. The P-polarized radiation penetrates the PVB layer 3.2 and emerges from the windshield 10 at the surface I of the outer pane 1.

The transmission on the surface I of the outer pane 1 does not generate any additional reflection. This means that there is no annoying reflection shadow and the HUD projection is clearly visible. Alternatively or additionally, the outer pane 1 can be tinted or colored. This result was unexpected and surprising for the person skilled in the art.

List of reference symbols:

1 outer pane

2 inner pane

3 thermoplastic intermediate layer

3.1 first PVB layer

3.2 second PVB layer

4 projector

5 viewers / vehicle drivers

6 half-wave plate

10 windshield

O Upper edge of the windshield 10

U Lower edge of the windshield 10

B HUD area of windshield 10 E eyebox l outer surface of outer pane 1 facing away from intermediate layer 3

11 surface of the outer pane 1 facing the intermediate layer 3 on the interior side

III outer surface of the inner pane 2 facing the intermediate layer 3

IV surface of the inner pane 2 facing away from the intermediate layer 3 on the interior side

Claims

1. Projection arrangement for a head-up display at least comprising

• a windshield (10), comprising an outer pane (1) and an inner pane (2), which are connected to one another via a thermoplastic intermediate layer (3), with a HUD area,

• a projector (4) which is aimed at the HUD area, the radiation from the projector (4) being predominantly S-polarized, with a half-wave plate (6) for converting the polarization of the radiation transmitted through the half-wave plate inside the HUD Area is provided and the half-wave plate (6) is arranged between two films made of thermoplastic polymer, in particular PVB layers (3.1, 3.2).

2. Projection arrangement according to claim 1, characterized in that the half-wave plate (6) has an optically anisotropic material, in particular quartz.

3. Projection arrangement according to claim 1 or 2, characterized in that the half-wave plate (6) has mica.

4. Projection arrangement according to one of claims 1 to 3, characterized in that the half-wave plate (6) is arranged within the intermediate layer (3).

6. Projection arrangement according to one of claims 1 to 5, characterized in that the thermoplastic intermediate layer (3) has a constant thickness, in particular within the HUD area.

7. Projection arrangement according to one of claims 1 to 6, characterized in that the windshield (10) has a plurality of half-wave plates (6).

8. Projection arrangement according to one of claims 1 to 7, characterized in that the half-wave plate (6) is provided for rotating the S-polarization in P-polarization.

9. Projection arrangement according to one of claims 1 to 8, characterized in that the outer pane (1) has a light transmission of at least 80%.

10. Projection arrangement according to one of claims 1 to 9, characterized in that the radiation of the projector (4) is essentially purely S-polarized.

11. Projection arrangement according to one of claims 1 to 10, characterized in that the radiation from the projector (4) strikes the windshield (10) at an angle of incidence of 60 ° to 75 °.

12. Projection arrangement according to one of claims 1 to 11, characterized in that the half-wave plate (6) is plate-shaped, for example contains quartz and has a thickness of approximately 28 μm.

13. Projection arrangement according to one of claims 1 to 11, characterized in that the half-wave plate (6) contains rutile, the thickness of the half-wave plate (6) being approximately 870 nm.

14. Projection arrangement according to one of claims 1 to 13, characterized in that the PVB layers (3.1, 3.2) have an essentially constant thickness of approximately 0.38 mm to 76 mm each.

15. Projection arrangement according to one of claims 1 to 14, characterized in that the half-wave plate (6) comprises calcite (CaC03), sapphire, lithium niobate (LiNb03), ruby (Al203), rutile (Ti02) and / or zirconium (ZrSi04).