PROJECTION ASSEMBLY FOR A HEAD-UP DISPLAY (HUD) WITH P-POLARIZED RADIATION

Abstract

A projection assembly for a head-up display (HUD) includes a windshield, including outer and inner panes joined to one another via a thermoplastic intermediate layer, with an HUD region; and a projector directed at the HUD region having a radiation predominantly p-polarized; and a reflection coating for reflecting p-polarized radiation. The reflection coating contains exactly one electrically conductive layer based on silver. The reflection coating below the electrically conductive layer includes a lower dielectric layer structure with a refractive index of at least 1.9. The reflection coating above the electrically conductive layer includes an upper dielectric layer structure with a refractive index of at least 1.9. A functional coating for reflecting IR radiation and the reflection coating are arranged between the inner and outer panes. The reflection coating is arranged between the inner pane and the functional coating.

Claims

1. A projection assembly for a head-up display (HUD), comprising a windshield, comprising an outer pane and an inner pane that are joined to one another via a thermoplastic intermediate layer, with an HUD region; and a projector, which is directed at the HUD region, wherein a radiation of the projector is predominantly p-polarized; and a reflection coating that is adapted to reflect p-polarized radiation, wherein the reflection coating contains exactly one electrically conductive layer based on silver, the reflection coating below the electrically conductive layer comprises a lower dielectric layer structure with a refractive index of at least 1.9, the reflection coating above the electrically conductive layer comprises an upper dielectric layer structure with a refractive index of at least 1.9; and a functional coating that is suitable for reflecting IR radiation, wherein the functional coating and the reflection coating are arranged between the inner pane and the outer pane, wherein the reflection coating is arranged between the inner pane and the functional coating.

2. The projection assembly according to claim 1, wherein in the reflection coating, a ratio of an optical thickness of the upper dielectric layer structure to an optical thickness of the lower dielectric layer structure is at least 1.6.

3. The projection assembly according to claim 1, wherein the functional coating contains at least one electrically conductive layer based on silver, with a geometric thickness smaller than a geometric thickness of the electrically conductive layer based on silver in the reflection coating, the functional coating below the electrically conductive layer based on silver includes a lowest dielectric layer module with a refractive index of at least 1.9, and the functional coating above the electrically conductive layer based on silver includes an uppermost dielectric layer module with a refractive index of at least 1.9.

4. The projection assembly according to claim 1, wherein in the functional coating, a ratio of an optical thickness of the uppermost dielectric layer module to an optical thickness of the lowest dielectric layer module is between 0.8 and 1.5.

5. The projection assembly according to claim 1, wherein the functional coating contains two electrically conductive layers based on silver and a middle dielectric layer module therebetween, wherein a geometric thickness of all electrically conductive layers based on silver in the functional coating is smaller than a geometric thickness of the electrically conductive layer based on silver in the reflection coating.

6. The projection assembly according to claim 5, wherein in the functional coating, a ratio of an optical thickness of the middle dielectric layer module to the optical thickness of the lowest dielectric layer module and to an optical thickness of the uppermost dielectric layer module is greater than 1.9.

7. The projection assembly according to claim 1, wherein the reflection coating is arranged on an outer face of the inner pane facing the thermoplastic intermediate layer.

8. The projection assembly according to claim 1, wherein the functional coating is arranged on an inner face of the outer pane facing the thermoplastic intermediate layer.

9. The projection assembly according to claim 1, wherein the functional coating or the reflection coating is arranged on a polymeric carrier film, which is embedded in the thermoplastic intermediate layer.

10. The projection assembly according to claim 1, wherein the functional coating and the reflection coating are arranged on a single polymeric carrier film, wherein the polymeric carrier film is embedded in the thermoplastic intermediate layer.

11. The projection assembly according to claim 1, wherein in the reflection coating the lower layer structure comprises a first lower dielectric layer and a second lower dielectric layer, and/or the upper layer structure comprises a first upper dielectric layer and a second upper dielectric layer with a refractive index of at least 1.9.

12. The projection assembly according to claim 1, wherein the reflection coating and the functional coating include in each case at least one metallic blocking layer, which is arranged above and/or below at least one electrically conductive layer and has a geometric thickness of less than 1 nm.

13. The projection assembly according to claim 1, wherein all dielectric layers of the reflection coating have a refractive index of at least 1.9.

14. The projection assembly according to claim 1, wherein in the reflection coating, the electrically conductive layer has a geometric thickness of 10 nm to 14 nm.

15. The projection assembly according to claim 1, wherein the functional coating is connected to a voltage source via electrical bus bars and can be heated is heatable by applying a voltage.

16. The projection assembly according to claim 1, wherein the functional coating is implemented in the form of a multilayer polymeric film without electrically conductive layers.

17. The projection assembly according to claim 1, wherein the radiation of the projector is substantially purely p-polarized and strikes the windshield at an angle of incidence of 60? to 70?.

18. The projection assembly according to claim 2, wherein in the reflection coating, the ratio of the optical thickness of the upper dielectric layer structure to the optical thickness of the lower dielectric layer structure is at least 1.8.

19. The projection assembly according to claim 4, wherein in the functional coating, the ratio of the optical thickness of the uppermost dielectric layer module to the optical thickness of the lowest dielectric layer module is between 0.9 and 1.2.

20. The projection assembly according to claim 6, wherein in the functional coating, the ratio of the optical thickness of the middle dielectric layer module to the optical thickness of the lowest dielectric layer module and to the optical thickness of the uppermost dielectric layer module is greater than 2.1.

Description

[0163] In the following, the invention is explained in detail with reference to drawings and exemplary embodiments. The drawings are schematic representations and are not true to scale. The drawings in no way restrict the invention.

[0164] They depict:

[0165] FIG. 1 a plan view of a composite pane of a generic projection assembly,

[0166] FIG. 2 a cross-section through a generic projection assembly,

[0167] FIG. 3 a cross-section through a composite pane of a projection assembly according to the invention,

[0168] FIG. 4 a cross-section through an embodiment of a windshield for a projection assembly according to the invention,

[0169] FIG. 5a,b in each case, a cross-section through an embodiment of a windshield for a projection assembly according to the invention,

[0170] FIG. 6 transmittance spectra of Examples 1, 3, and 4.

[0171] FIG. 1 and FIG. 2 depict in each case a detail of a generic projection assembly for an HUD. The projection assembly comprises a windshield 10, in particular the windshield of a passenger car. The projection assembly also comprises a projector 4 that is directed at a region of the composite pane 10. In this region, commonly referred to as HUD region B, the projector 4 can generate images that are perceived by a viewer 5 (vehicle driver) as virtual images on the side of the composite pane 10 facing away from him if his eyes are situated within the so-called eyebox E.

[0172] The windshield 10 is constructed from an outer pane 1 and an inner pane 2 that are joined to one another via a thermoplastic intermediate layer 3. Its lower edge U is arranged downward in the direction of the engine of the passenger car; its upper edge O, upward in the direction of the roof. In the installed position, the outer pane 1 faces the external surroundings; the inner pane 2, the vehicle interior.

[0173] FIG. 3 depicts an embodiment of a windshield 10 implemented according to the invention. The outer pane 1 has an outer face I that, in the installed position, faces the external surroundings, and an inner face II that, in the installed position, faces the interior. Likewise, the inner pane 2 has an outer face III that, in the installed position, faces the external surroundings, and an inner face IV that, in the installed position, faces the interior. The outer pane 1 and the inner pane 2 are made, for example, of soda lime glass. The outer pane 1 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 made, for example, of a PVB film with a thickness of 0.76 mm. The PVB film has an essentially constant thickness, apart from any surface roughness common in the artit is not implemented as a so-called wedge film.

[0174] The exterior-side surface III of the inner pane 2 is provided with a reflection coating 20, which is provided as a reflection surface for the projector radiation (and, possibly, additionally, as an IR-reflecting coating).

[0175] The radiation of the projector 4 is p-polarized, in particular essentially purely p-polarized. Since the projector 4 irradiates the windshield 10 at an angle of incidence of about 65?, which is close to Brewster's angle, the radiation of the projector is only insignificantly reflected at the external surfaces I, IV of the composite pane 10. In contrast, the reflection coating 20 according to the invention is optimized for reflection of p-polarized radiation. It serves as a reflection surface for the radiation of the projector 4 to generate the HUD projection.

[0176] A functional coating 40 according to the invention is arranged on the inner face II of the outer pane 1. The functional coating 40 is optimized for reflection of infrared (IR) radiation and serves to improve the thermal protection function of the windshield. The arrangement on the inner face II of the outer pane 1 ensures that most of the p-polarized radiation of the projector 4 is already reflected by the reflection coating 20 on the inner pane and can be used to generate the HUD projection. Thus, distracting double images are largely avoided due to the functional coating 40.

[0177] FIG. 5a and FIG. 5b depict in each case a cross-section through a windshield with a polymeric carrier film. FIG. 5a depicts a windshield with a reflection coating 20 according to the invention on the outer face of the inner pane 2. The reflection coating 20 is applied directly on the inner pane 2 by a PVD method, in this case, by magnetron sputtering. The functional coating 40 is arranged on a polymeric carrier film 50 made of PET and embedded in the thermoplastic intermediate layer 3 consisting of two plies of PVB. Since the reflection coating 20 is arranged directly on the inner pane 2, no carrier film or thermoplastic intermediate layer interferes with the generation of the HUD image.

[0178] In the embodiment depicted in FIG. 5b, the functional coating 40 and the reflection coating 20 are arranged on a single carrier film 50. Thus, at the time of lamination, only one additional carrier film has to be inserted, which is advantageous from a process engineering standpoint.

[0179] The distance between the reflection coating 20 and the functional coating 40 is defined here only by the carrier film 50. Thus, the generation of distracting ghost images due to the functional coating 40 is particularly efficiently avoided, because any reflections at the functional coating are superimposed with those at the reflection coating and become one image. Thus, any reflections at the functional coating are not perceived as a distracting double image when an HUD image is generated.

[0180] FIG. 4 depicts the layer sequence of an embodiment of a windshield 10 according to the invention. According to the invention, the reflection coating 20 is arranged on the outer face of the inner pane 2 in the form of a stack of thin layers. The reflection coating 20 includes one electrically conductive layer 21 based on silver. A metallic blocking layer 24 is arranged directly above the electrically conductive layer 21. An upper dielectric layer structure 23 is arranged above that. A lower dielectric layer structure 22 is arranged below the electrically conductive layer 21.

[0181] According to the invention, a functional coating 40 is arranged on the inner face of the outer pane 1 in the form of a stack of thin layers. The functional coating 40 includes one electrically conductive layer 41 based on silver. A metallic blocking layer 44 is arranged directly above the electrically conductive layer 41. An uppermost dielectric layer module 43 is arranged above that. A lowest dielectric layer module 42 is arranged below the electrically conductive layer 41.

[0182] The inner pane 2 and the outer pane 1 are joined via a thermoplastic intermediate layer 3.

[0183] The layer thicknesses shown are not to scale. For example, the thickness of the panes 1 and 2 and the thickness of the thermoplastic intermediate layer 3 are much too small compared to the thin layers shown. In addition, the structure shown is provided merely by way of example.

[0184] The blocking layers can be present or not and can be arranged above and/or below the electrically conductive layers. The dielectric layer structures and layer modules can in each case include a single dielectric layer or also multiple layers, provided at least one dielectric layer is present above and below the conductive layers 21 and 41. Exemplary materials and layer thicknesses can be found in the following examples.

[0185] Tables 1 and 2 present the layer sequences of a windshield 10 with a reflection coating 20 on the outer face of the inner pane and a functional coating 40 on the inner face of the outer pane according to Examples 1 through 6 according to the invention, together with the materials and geometric layer thicknesses of the individual layers. Independently of one another, the dielectric layers can be doped, for example, with boron or aluminum.

TABLE-US-00001 TABLE 1 Layer Thickness Material Example 4 Example 3 Example 2 Example 1 Soda lime glass 2.1 mm 2.1 mm 2.1 mm 2.1 mm SIN Lowest 25 nm 25 nm 25 nm 20 nm SiZrN dielectric layer 10 nm 10 nm 10 nm 10 nm ZnO module 10 nm 10 nm 10 nm 10 nm Ag 1st silver layer 8 nm 8 nm 11 nm 10 nm NiCr Blocking layer 0.3 nm 0.3 nm 0.3 nm 0.3 nm ZnO Middle 10 nm 10 nm SIN dielectric layer 70 nm 70 nm ZnO module 10 nm 10 nm Ag 2nd silver layer 9 nm 8 nm NiCr Blocking layer 0.3 nm 0.3 nm ZnO Middle 10 nm SIN dielectric layer 70 nm ZnO module 10 nm Ag 3rd silver layer 8 nm NiCr Blocking layer 0.3 nm ZnO Uppermost 10 nm 10 nm 10 nm 10 nm SiZrN dielectric layer 10 nm 10 nm 10 nm 10 nm SIN module 25 nm 20 nm 25 nm 25 nm PVB 0.76 mm 0.76 mm 0.76 mm 0.76 mm SIN Upper 30 nm 30 nm 30 nm 40 nm SiZrN dielectric layer 10 nm 10 nm 10 nm 10 nm ZnO structure 10 nm 10 nm 10 nm 10 nm NiCr Blocking layer 0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag Silver 11.0 nm 12 nm 12 nm 12 nm ZnO Lower 10.0 nm 10 nm 10 nm 10 nm dielectric layer SIN structure 20 nm 20 nm 20 nm 27 nm Soda lime glass 2.1 mm 2.1 mm 2.1 mm 2.1 mm

TABLE-US-00002 TABLE 2 Layer Thickness Material Example 5 Example 6 Comp. Ex. Soda lime 2.1 mm 2.1 mm 2.1 mm glass SiN Lowest 40 nm 20 nm SiZrN dielectric 10 nm 10 nm ZnO layer module 10 nm 10 nm Ag 1st silver layer 10 nm 10 nm NiCr Blocking layer 0.3 nm 0.3 nm ZnO Uppermost 10 nm 10 nm SiZrN dielectric 10 nm 10 nm SiN layer module 30 nm 45 nm PVB 0.76 mm 0.76 mm 0.76 mm SiN Upper 30 nm 30 nm 40 nm SiZrN dielectric 10 nm 10 nm 10 nm ZnO layer structure 10 nm 10 nm 10 nm NiCr Blocking layer 0.3 nm 0.3 nm 0.3 nm Ag Silver 12 nm 12 nm 12 nm ZnO Lower 10.0 nm 10 nm 10 nm SiN dielectric 20 nm 20 nm 27 nm Soda lime layer structure 2.1 mm 2.1 mm 2.1 mm glass

[0186] The optical thicknesses of the upper and lower layer structures and their ratio are summarized in Table 3. The ratio ? describes the ratio of the optical thickness of the upper dielectric layer structure 23 to the optical thickness of the lower dielectric layer structure 22.

[0187] The optical thickness is in each case the product of the geometric thickness shown in Tables 1 and 2 and the refractive index (SiN: 2.0; SiZrN: 2.2, ZnO: 2.0).

TABLE-US-00003 TABLE 3 Optical Thickness of Optical Thickness of the Upper Dielectric the Lower Dielectric Layer Structure Layer Structure Ratio ? Example 1 122 74 1.65 Example 2 102 60 1.70 Example 3 102 60 1.70 Example 4 102 60 1.70 Example 5 102 60 1.70 Example 6 102 60 1.70 Comparative 122 74 1.65 Example

[0188] The optical thicknesses of the uppermost and lowest layer modules and their ratio are summarized in Table 4. The ratio ? describes the ratio of the optical thickness of the uppermost dielectric layer module 43 to the optical thickness of the lowest dielectric layer module 42.

TABLE-US-00004 TABLE 4 Optical Thickness of Optical Thickness of the Uppermost Dielectric the Lowest Dielectric Layer Module Layer Module Ratio ? Example 1 92 82 1.12 Example 2 92 92 1.00 Example 3 82 92 0.89 Example 4 92 92 1.00 Example 5 122 102 0.84 Example 6 82 132 1.61 Comparative 0 0 0 Example

[0189] The optical thicknesses of the uppermost, middle, and lowest layer modules and their ratio are summarized in Table 5. The ratio ?1 describes the ratio of the optical thickness of the middle dielectric layer module to the optical thickness of the uppermost dielectric layer module. The ratio ?2 describes the ratio of the optical thickness of the middle dielectric layer module to the optical thickness of the lowest dielectric layer module 42.

TABLE-US-00005 TABLE 5 Optical Optical Optical Thickness of Thickness of Thickness of the Uppermost the Lowest the Middle Dielectric Dielectric Dielectric Layer Module Layer Module Layer Module Ratio ?1 Ratio ?2 Example 3 82 92 180 1.96 1.96 Example 4 92 92 180 2.20 1.96 lowest module

[0190] Table 6 indicates the values for transmittance in accordance with illuminant A. In addition, the values for thermal comfort in the form of the TTS value. This indicates the total solar energy transmitted and is measured according to ISO 13837.

TABLE-US-00006 TABLE 6 Transmittance TL A/% TTS/% Example 1 71 54.0 Example 2 71 52.3 Example 3 72 51.5 Example 4 71 49.1 Example 5 70 53.0 Example 6 69 52.8 Comparative 76 61.3 Example

[0191] The Comparative Example listed in Table 2 differs from the Examples in that the windshield has no functional coating. The windshield does have, thanks to the reflection coating on the inner pane, good reflection properties for HUD image generation. However, the pane of the Comparative Example has poor thermal insulation properties, as the high TTS value shows. Examples 1 and 3 show, in comparison to the Comparative Example, a significantly lowered TTS value and thus have an improved thermal protection effect. Thanks to the reflection coating according to the invention for reflecting p-polarized radiation, the windshields according to the invention are ideally suited for use in an HUD projection assembly.

[0192] Examples 1 to 6 are all suitable as projection surfaces for HUD image generation with p-polarized radiation. Thanks to the configuration according to the invention with thinner silver layers in the functional coating than in the reflection coating, no distracting double images develop due to reflection at the electrically conductive layers of the functional coating.

[0193] All Examples 1 to 6 have a ratio o of at least 1.6. This ensures a color-neutral display of the HUD projection.

[0194] Examples 5 and 6 differ from Examples 1 and 2 primarily in the ratio ? of the optical thicknesses of the uppermost dielectric layer module to the optical thickness of the lowest dielectric layer module. While the value for Examples 1 and 2 is between 0.9 and 1.1, that for Examples 5 and 6 is below and above, respectively. Surprisingly, this leads to improved transmittance values of 71 for Examples 1 and 2.

[0195] FIG. 6 depicts three transmittance spectra for Examples 1, 3, and 4, whose structure is listed in Table 1. The spectra were recorded under identical conditions such that a direct comparison is possible. It can be seen that all Examples 1, 3, and 4 have very similar transmittance in the visible (VIS) spectral range (400 nm to 800 nm). As listed in Table 6, all Examples 1, 3, and 4 have a TL value for illuminant A of at least 70%. These are thus well suited as a windshield or as a front side window in the automotive sector.

[0196] The glazing according to Example 4 exhibits the best thermal protection effect, as indicated by the low TTS value (Table 6) and the low transmittance in the infrared (IR) range (800 nm-2500 nm).

[0197] As a comparison of the spectra in FIG. 6 shows, the TL value decreases with the increasing number of silver layers in the functional coating. Thanks to the structure according to the invention, high transmittance in the visible spectral range can nevertheless be achieved, such that use as a windshield is possible. Table 5 shows the values for the ratios ?1 and ?2, which indicate the ratio of the optical thickness of the middle dielectric layer module to the optical thickness of the uppermost and lowest dielectric layer module, respectively. The middle dielectric layer modules have a substantially greater optical thickness than the lowest or the uppermost layer modules, respectively. Surprisingly, it has been shown that this ratio results in comparatively high TL values, even though the layer stack of the functional coating includes multiple silver layers.

LIST OF REFERENCE CHARACTERS

[0198] 1 outer pane [0199] 2 inner pane [0200] 3 thermoplastic intermediate layer [0201] 4 projector [0202] 5 viewer/vehicle driver [0203] 10 windshield [0204] 20 reflection coating [0205] 21 electrically conductive layer based on silver in the reflection coating [0206] 22 lower dielectric layer structure in the reflection coating [0207] 23 upper dielectric layer structure in the reflection coating [0208] 24 blocking layer [0209] 40 functional coating [0210] 41 electrically conductive layer based on silver in the functional coating [0211] 42 lowest dielectric layer module [0212] 43 uppermost dielectric layer module [0213] 44 metallic blocking layer [0214] 50 polymeric carrier film [0215] O upper edge of the windshield 10 [0216] U lower edge of the windshield 10 [0217] B HUD region of the windshield 10 [0218] E eyebox [0219] I exterior-side surface of the outer pane 1, facing away from the intermediate layer 3, outer face of the outer pane 1 [0220] II interior-side surface of the outer pane 1, facing the intermediate layer 3, inner face of the outer pane 1 [0221] III exterior-side surface of the inner pane 2, facing the intermediate layer 3, outer face of the inner pane 2 [0222] IV interior-side surface of the inner pane 2, facing away from the intermediate layer 3, inner face of the inner pane 2