DE202021004088U1 - Projection arrangement for a head-up display system - Google Patents

Abstract

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) aimed at the HUD area, the radiation of 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 within the HUD area is provided, the half-wave plate (6) is arranged within the intermediate layer (3) between two sheets of thermoplastic polymer, and wherein the thermoplastic intermediate layer (3) has a constant thickness within the HUD area.

Description

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

Modern vehicles are increasingly 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 into the driver's field of vision. The head-up display consists of a projector (imaging unit) and several optics modules for deflecting or mirroring (reflecting) an image onto a projection surface or reflection 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, in the perception of the driver's human eye it hovers distantly above the vehicle's hood.

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 instructions, which the driver can perceive without having to change his line of sight. Head-up displays can thus make a significant contribution to increasing traffic safety.

The image generated by the projector usually consists of polarized, in particular S-polarized, light radiation. The S-polarized light strikes the laminated pane at a specific angle of incidence and is at least partially both refracted into the laminated 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 unwanted reflections, so-called double images.

The angle of incidence of the S-polarized radiation is typically about 65%, which roughly corresponds to Brewster's angle for an air-to-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, in addition to the desired main image, a slightly offset secondary image also appears, the so-called ghost image (“ghost”). The problem is alleviated by placing the surfaces of the windshield at an angle to one another. This is done by using a wedge-shaped intermediate layer in the lamination of the windshield designed as a composite pane. This allows the main image and the ghost image to be superimposed. For example, laminated glasses with wedge foils for HUDs are out WO 2009/071135 A1 , EP 1800855 B1 or EP 1880243 A2 known.

Wedge foils are expensive, so producing such a composite panel for a HUD is quite costly. There is therefore a need for HUD systems that make do 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 pane surfaces. Instead, the windshield has a reflective coating as a reflective surface for the P-polarized radiation.

the U.S. 6,744,478 B1 discloses a HUD system in which a liquid crystal display generates beams of light directed at 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 reflection layer is arranged on an inside of an inner pane of the windshield.

the U.S. 2009/195875 A1 discloses a HUD system having a windshield with a birefringent layer disposed in or on the windshield.

The object of the present invention is to provide a HUD projection arrangement that has good reflectivity for S-polarized radiation in the visible spectral range and 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 embodiments emerge from the dependent claims.

The projection arrangement according to the invention for a head-up display has a windshield that has an outer pane and an inner pane. The outer pane and the inner pane are connected to each other via a thermoplastic intermediate layer. The windshield is intended to separate the interior from the outside environment in a window opening of a vehicle. In the context of the invention, inner pane refers to the pane of the windshield facing the vehicle interior. The outer pane refers to the pane facing the outside environment. The windshield is preferably the windshield of a motor vehicle, in particular a car or truck.

As is usual with HUDs, a projector illuminates an area of the windshield where the beam Development is reflected in the direction of the viewer (driver), whereby a virtual image is generated, which the viewer sees 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 (eg mirrors), in particular 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 that is positioned 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 sandwiched between two sheets of thermoplastic polymer, with the intermediate thermoplastic layer having a constant thickness within the HUD region.

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, as a result of which the reflectivity of the radiation is significantly improved.

Because the typical HUD projection angle of about 65° is relatively close to Brewster's angle for an air-to-glass transition (57.2°, soda-lime-glass), S-polarized radiation is reflected from pane surfaces. The reflection of the radiation takes place mainly on the surface of the inner pane facing away from the intermediate layer on the interior side. 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 that 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 brings about a high level of 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 achieves 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, for example, calcite (CaCO3), sapphire, lithium niobate (LiNbO3), ruby (AI203), rutile (TiO2) and zircon (ZrSiO4). 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 to P-polarized. The P-polarized radiation is hardly reflected at the outer pane. This avoids reflection on the outer pane, resulting in a high-intensity HUD image.

In a further refinement, the windshield has a plurality of half-wave plates. Particularly good results are achieved in this way.

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 illuminates it to create the HUD projection. According to the invention, the radiation of the projector is predominantly S-polarized, ie has an S-polarized radiation component of more than 50%. The higher the proportion of S-polarized radiation in the total radiation of the projector, the higher 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 from it only insignificantly. The specification of the direction of polarization refers to the plane of incidence of the radiation on the windshield. P-polarized radiation is radiation whose electric field oscillates in the plane of incidence. S-polarized radiation is 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 preferably strikes the windshield 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 reflected only insignificantly at the surfaces of the windshield, so that no ghost image is produced. The angle of incidence is the angle between the incidence vector of the projector radiation and the interior surface normal (i.e. the surface normal to the interior 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 common for window panes, is 57.2°. Ideally, the angle of incidence should be as close as possible to this Brewster angle. However, angles of incidence of 65° can also be used, for example, which are customary for HUD projection arrangements, can be implemented without problems in vehicles and deviate only slightly from the Brewster angle, so that the reflection of the P-polarized radiation increases only insignificantly.

Since the reflection of the projector radiation essentially takes place on the interior surface of the inner pane facing away from the intermediate layer and not on the internal pane surfaces, it is not necessary to arrange the internal pane surfaces at an angle to one another in order to avoid ghost images. The external surfaces of the windscreen are therefore preferably arranged substantially parallel to one another. For this purpose, the thermoplastic intermediate layer is preferably not designed in the manner of a wedge, but 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 of 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, are preferably used, for example those with the standard thicknesses of 1.6 mm or 2.1 mm.

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 total transmission refers to the procedure specified by ECE-R 43, Appendix 3, Section 9.1 for testing the light transmittance of motor vehicle windows. The outer pane and the inner panes can be unprestressed, partially prestressed or prestressed independently of one another. If at least one of the panes is to have a prestress, this can be a thermal or chemical prestress.

In an advantageous embodiment, the outer pane is tinted or colored. As a result, the outside reflectivity of the windshield can be reduced, making the impression of the windshield more pleasant for an outside observer. However, in order to ensure 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 at least 85%. The inner pane and the intermediate layer are preferably clear, ie 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 spatial directions, as is conventional for motor vehicle windows, with typical radii of curvature ranging from about 10 cm to about 40 m. However, the windshield can also be flat, for example if it is intended as a pane 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 material. An intermediate layer according to the invention comprises, for example, at least one first PVB layer and a second PVB layer. The half-wave plate is sandwiched between the first and second PVB layers. Alternatively or additionally, the PVB layers can contain 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 methods, vacuum bag methods, vacuum ring methods, calendering methods, vacuum laminators or combinations thereof. The outer pane and inner pane are usually connected 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 drawn to scale. The figures do not limit the invention in any way.

• 1 eine Draufsicht auf eine Verbundscheibe einer gattungsgemäßen Projektionsanordnung,
• 2 einen Querschnitt durch eine gattungsgemäße Projektionsanordnung,
• 3 ein schematisches Diagramm der Lichtstrahlen von S-polarisierten Licht, und
• 4 einen Querschnitt durch eine erfindungsgemäße Windschutzscheibe.

Show it:

• 1 a plan view of a composite pane of a generic projection arrangement,
• 2 a cross section through a generic projection arrangement,
• 3 a schematic diagram of the light rays of S-polarized light, and
• 4 a cross section through a windshield according to the invention.

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

1 and 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 an area of the laminated pane 10 . This area is commonly referred to as HUD Area B. Images generated by the projector 4 can be projected in this area, which are perceived by a viewer 5 (eg vehicle driver) as virtual images on the side of the laminated pane 10 facing away from him when his eyes are inside the so-called eyebox E.

The windshield 10 is made up 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 towards the engine of the passenger car, its upper edge O upwards towards the roof. In the installed position, the outer pane 1 faces the outside environment, and the inner pane 2 faces the vehicle interior.

3 Fig. 12 shows a schematic diagram of the light rays of S-polarized light. The outer pane 1 of the windshield 10 has an outside surface 11 (I) which faces the outside environment in the installed position and an inside surface 12 (II) which faces the interior in the installed position. Likewise, the inner pane 2 has an outside surface 13 (III), which faces the outside environment in the installed position, and an interior-side surface 14 (IV), which faces the interior in the installed position. The outer pane 1 and the inner pane 2 consist, for example, of soda-lime glass. The outer pane has a thickness of 2.1 mm, for example, and the inner pane 2 has 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.

If such a windshield 10 is irradiated with S-polarized light radiation and the light radiation hits the windshield 10 with an angle of incidence α of about 65° (which is close to the so-called Brewster angle), the radiation is mainly reflected on the surfaces 14 and 11 .

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

In contrast to 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 a substantially constant thickness of about 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 µm (microns). The Half wave plate 6 covers the entire HUD area. Alternatively, the half-wave plate 6 can contain rutile. In this case, 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 radiation, in particular essentially purely S-polarized radiation. Since the projector 4 irradiates the windshield 10 at an angle of incidence 65°, which is close to Brewster's angle, the radiation is largely reflected on the surface 14 of the windshield 10 . The S-polarized radiation is partly reflected at the surface 14 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 on the surface 11 of the outer pane 1.

No additional reflection is generated by the transmission on the surface 11 of the outer pane 1 . As a result, 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 those skilled in the art.

Reference List

1

outer pane

2

inner pane

3

thermoplastic intermediate layer

3.1

first PVB layer

3.2

second PVB layer

4

projector

5

viewer / vehicle driver

6

half-wave plate

10

windshield

O

Top edge of windshield 10

u

Lower edge of the windscreen 10

B

Windshield HUD area 10

E

eyebox

11

outside surface of the outer pane 1 facing away from the intermediate layer 3

12

Interior surface of the outer pane 1 facing the intermediate layer 3

13

outside surface of the inner pane 2 facing the intermediate layer 3

14

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

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2009/071135 A1 [0005]
• EP 1800855 B1 [0005]
• EP 1880243 A2 [0005]
• US6744478B1 [0007]
• US2009195875A1 [0008]

Claims (14)

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) aimed at the HUD area, the radiation of 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 within the HUD area is provided, the half-wave plate (6) is arranged within the intermediate layer (3) between two sheets of thermoplastic polymer, and wherein the thermoplastic intermediate layer (3) has a constant thickness within the HUD area. projection arrangement claim 1 , characterized in that the half-wave plate (6) has an optically anisotropic material, in particular quartz. projection arrangement claim 1 or 2 , characterized in that the half-wave plate (6) comprises mica. Projection arrangement according to one of Claims 1 until 3 , characterized in that the thermoplastic intermediate layer (3) has a constant thickness. Projection arrangement according to one of Claims 1 until 4 , characterized in that the windscreen (10) has a plurality of half-wave plates (6). Projection arrangement according to one of Claims 1 until 5 , characterized in that the half-wave plate (6) is provided for rotating the S-polarization into P-polarization. Projection arrangement according to one of Claims 1 until 6 , characterized in that the outer pane (1) has a light transmission of at least 80%. Projection arrangement according to one of Claims 1 until 7 , characterized in that the radiation of the projector (4) is essentially purely S-polarized. Projection arrangement according to one of Claims 1 until 8th , characterized in that the radiation of the projector (4) strikes the windshield (10) at an angle of incidence of 60° to 75°. Projection arrangement according to one of Claims 1 until 9 , characterized in that the half-wave plate (6) is plate-shaped, contains quartz and has a thickness of about 28 µm. Projection arrangement according to one of Claims 1 until 9 , characterized in that the half-wave plate (6) contains rutile, the thickness of the half-wave plate (6) being approximately 870 nm. Projection arrangement according to one of Claims 1 until 11 , characterized in that the PVB layers (3.1, 3.2) have a constant thickness of approximately 0.38 mm to 76 mm each. Projection arrangement according to one of Claims 1 until 12 , characterized in that the half-wave plate (6) comprises calcite, sapphire, lithium niobate, ruby, rutile and/or zircon. Projection delegation according to one of Claims 1 until 13 , characterized in that the half-wave plate (6) is arranged between two PVB layers (3.1, 3.2).

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