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 an outer pane and an inner pane that are joined to one another via a thermoplastic intermediate layer, having a HUD region; and a projector that is directed at the HUD region and that emits p-polarized radiation; wherein a reflection coating is arranged on the surface of the outer pane or of the inner pane facing the intermediate layer or within the intermediate layer, which reflection coating is suitable for reflecting p-polarized radiation and which has exactly one electrically conductive layer based on silver; and an emissivity-reducing coating is arranged on the surface of the inner pane facing away from the intermediate layer, which coating has an electrically conductive layer based on a transparent conductive oxide.

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, having a HUD region; and a projector that is directed at the HUD region and that is adapted to emit p-polarized radiation; wherein a reflection coating is arranged on a surface of the outer pane or of the inner pane facing the thermoplastic intermediate layer or within the thermoplastic intermediate layer, which reflection coating is suitable for reflecting p-polarized radiation and which has exactly one electrically conductive layer based on silver; an emissivity-reducing coating is arranged on a surface of the inner pane facing away from the thermoplastic intermediate layer, which emissivity-reducing coating has an electrically conductive layer based on a transparent conductive oxide.

2. The projection assembly according to claim 1, wherein the reflection coating is implemented such that below the electrically conductive layer, a lower dielectric layer or lower dielectric layer sequence is arranged, whose refractive index is at least 1.9, and above the electrically conductive layer, an upper dielectric layer or upper dielectric layer sequence is arranged, whose refractive index at least 1.9, wherein a ratio of an optical thickness of the upper dielectric layer or upper dielectric layer sequence to the an optical thickness of the lower dielectric layer or lower dielectric layer sequence is at least 1.7.

3. The projection assembly according to claim 2, wherein the optical thickness of the upper dielectric layer or upper dielectric layer sequence is from 100 nm to 200 nm and the optical thickness of the lower dielectric layer or lower dielectric layer sequence is from 50 nm to 120 nm.

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

5. The projection assembly according to claim 1, wherein below the electrically conductive layer of the reflection coating, a first lower dielectric layer, a second lower dielectric layer, and a third lower dielectric layer, with a refractive index of at least 1.9 are arranged, and/or above the electrically conductive layer of the reflection coating, a first upper dielectric layer, a second upper dielectric layer, and a third upper dielectric layer, with a refractive index of at least 1.9 are arranged.

6. The projection assembly according to claim 5, wherein the reflection coating comprises the following layers: an antireflection layer based on silicon nitride with a thickness from 20 nm to 30 nm, above the antireflection layer, a refractive-index-enhancing layer based on mixed silicon-zirconium nitride or mixed silicon-hafnium nitride with a thickness from 8 nm to 12 nm, above the refractive-index-enhancing layer, a matching layer based on zinc oxide with a thickness from 8 nm to 12 nm, above the matching layer, the electrically conductive layer with a thickness from 11 nm to 13 nm, above the electrically conductive layer, a blocking layer based on Ti or NiCr with a thickness from 0.1 nm to 0.5 nm, above the blocking layer, an upper matching layer based on zinc oxide with a thickness from 8 nm to 12 nm, above the upper matching layer, an upper refractive-index-enhancing layer based on mixed silicon-zirconium nitride or mixed silicon-hafnium nitride with a thickness from 8 nm to 12 nm, and above the upper refractive-index-enhancing layer, an upper antireflection layer based on silicon nitride with a thickness from 60 nm to 70 nm.

7. The projection assembly according to claim 1, wherein the reflection coating includes at least one metallic blocking layer that is arranged directly above and/or below the electrically conductive layer and has a geometric thickness of less than 1 nm.

8. The projection assembly according to claim 1, wherein the electrically conductive layer of the emissivity-reducing coating is based on indium tin oxide and has a thickness from 50 nm to 130 nm.

9. The projection assembly according to claim 1, wherein the emissivity-reducing coating comprises a blocking layer against alkali diffusion with a refractive index of at least 1.9, above the blocking layer, a dielectric lower antireflection layer with a refractive index from 1.3 to 1.8, above the dielectric lower antireflection layer, the electrically conductive layer, above the electrically conductive layer, a dielectric barrier layer for regulating oxygen diffusion with a refractive index of at least 1.9, and above the dielectric barrier layer, a dielectric upper antireflection layer with a refractive index from 1.3 to 1.8.

10. The projection assembly according to claim 9, wherein the lower antireflection layer and the upper antireflection layer are based on an oxide, the lower antireflection layer has a thickness from 5 nm to 50 nm, and the upper antireflection layer has a thickness from 10 nm to 100 nm.

11. The projection assembly according to claim 9, wherein the barrier layer is based on a nitride or a carbide, and has a thickness from 5 nm to 20 nm.

12. The projection assembly according to claim 9, wherein the blocking layer is based on a nitride, and has a thickness from 10 nm to 50 nm.

13. The projection assembly according to claim 9, wherein the windshield has a region, in which the thermoplastic intermediate layer is tinted or colored.

14. The projection assembly according to claim 1, wherein the outer pane is tinted or colored and has light transmittance of at least 80%.

15. The projection assembly according to claim 1, wherein external surfaces of the windshield are arranged substantially parallel to one another.

16. The projection assembly according to claim 5, wherein the first lower dielectric layer is based on silicon nitride, the second lower dielectric layer is based on zinc oxide, and the third lower dielectric layer is based on a mixed silicon-metal nitride, and/or the first upper dielectric layer is based on silicon nitride, the second upper dielectric layer is based on zinc oxide, and the third upper dielectric layer is based on a mixed silicon-metal nitride.

17. The projection assembly according to claim 16, wherein the third lower dielectric layer is a mixed silicon-zirconium nitride layer or a mixed silicon-hafnium nitride layer and/or the third upper dielectric layer is a mixed silicon-zirconium nitride layer or mixed silicon-hafnium nitride layer.

18. The projection assembly according to claim 8, wherein the thickness is from 60 nm to 100 nm.

19. The projection assembly according to claim 10, wherein the lower antireflection layer and the upper antireflection layer are based on a silicon oxide

20. The projection assembly according to claim 11, wherein the nitride is silicon nitride and the carbide is silicon carbide.

Description

[0093] They Depict:

[0094] FIG. 1 a plan view of a composite pane of a generic projection assembly,

[0095] FIG. 2 a cross-section through a generic projection assembly,

[0096] FIG. 3 a cross-section through a composite pane of a projection assembly according to the invention,

[0097] FIG. 4 a cross-section through an embodiment of the reflection coating and emissivity-reducing coating according to the invention on an inner pane,

[0098] FIG. 5 reflection spectra of composite panes for p-polarized radiation of the Example and the Comparative Examples 1 and 2.

[0099] 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.

[0100] 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.

[0101] FIG. 3 depicts an embodiment of a windshield 10 implemented according to the invention. The outer pane 1 has an exterior-side surface I that, in the installed position, faces the external surroundings, and an interior-side surface II that, in the installed position, faces the interior. Likewise, the inner pane 2 has an exterior-side surface III that, in the installed position, faces the external surroundings, and an interior-side surface 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 and have a thickness of 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.

[0102] The exterior-side surface III of the inner pane 2 is provided with a reflection coating 20 according to the invention, which is provided as a reflection surface for the projector radiation (and, possibly, additionally, as an IR-reflecting coating).

[0103] The radiation of the projector 4 is p-polarized according to the invention, 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.

[0104] The interior-side surface IV of the inner pane 2 is provided with an emissivity-reducing coating according to the invention. Such emissivity-reducing coatings 30 increases the thermal comfort in the interior of the vehicle by reflecting thermal radiation. Surprisingly, the presence of the emissivity-reducing coating 30 also results in an improvement of the reflection properties for the p-polarized radiation of the projector 4 such that an improved display of the HUD image is achieved.

[0105] FIG. 4 depicts the layer sequence of embodiments of the reflection coating 20 according to the invention and the emissivity-reducing coating 30 according to the invention. The reflection coating 20 and the emissivity-reducing coating 30 are stacks of thin layers. The reflection coating 20 includes an electrically conductive layer 21 based on silver. A metallic blocking layer 24 is arranged directly above the electrically conductive layer 21. Above that, an upper dielectric layer sequence is arranged, consisting, from bottom to top, of an upper matching layer 23b, an upper refractive-index-enhancing layer 23c, and an upper antireflection layer 23a. Arranged below the electrically conductive layer 21 is a lower dielectric layer sequence, consisting, from top to bottom, of a lower matching layer 22b, a lower refractive-index-enhancing layer 22c, and a lower antireflection layer 22a.

[0106] The layer structure shown is to be construed only by way of example. The dielectric layer sequences can also include more or fewer layers. The dielectric layer sequences also do not have to be symmetrical. Exemplary materials and layer thicknesses can be found in the following Example.

[0107] The emissivity-reducing coating 30 includes an electrically conductive layer 31 based on indium tin oxide (ITO). Arranged below the electrically conductive layer 31 is, first, a blocking layer 32 against alkali diffusion; and, above that, a lower antireflection layer 33. Arranged above the electrically conductive layer 31 is, first, a barrier layer 34 for regulating oxygen diffusion and an upper antireflection layer 35. The layer structure shown is, again, to be construed only by way of example. Exemplary materials and layer thicknesses can be found in the following Example.

[0108] The layer sequences of a windshield 10 with the reflection coating 20 on the exterior-side surface III of the inner pane 2 and the emissivity-reducing coating 30 on the interior-side surface IV of the inner pane 2 in accordance with an Example according to the invention, together with the materials and geometric layer thicknesses of the individual layers are presented in Table 1. Independent of one another, the dielectric layers can be doped, for example, with boron or aluminum. The materials also need not be deposited stoichiometrically, but can deviate from the stoichiometrics of the empirical formulas indicated. For comparison, two Comparative Examples are presented in Table 1. In Comparative Example 1, the windshield 10 has only the reflection coating 20; in Comparative Example 2, only the emissivity-reducing coating 30.

TABLE-US-00001 TABLE 1 Layer Thickness Reference Comp. Comp. Material Character Example Example 1 Example 2 Soda lime 1 2.1 mm 2.1 mm 2.1 mm glass PVB 3 0.76 mm 0.76 mm 0.76 mm Si.sub.3N.sub.4 20 23a 65 nm 65 nm SiZrN 23c 10 nm 10 nm ZnO 23b 10 nm 10 nm NiCr 24 0.3 nm 0.3 nm Ag 21 11 nm 11 nm ZnO 22b 10 nm 10 nm SiZrN 22c 10 nm 10 nm Si.sub.3N.sub.4 22a 25 nm 25 nm Soda lime 2 2.1 mm 2.1 mm 2.1 mm glass Si.sub.3N.sub.4 30 32 30 nm 30 nm SiO.sub.2 33 20 nm 20 nm ITO 31 70 nm 70 nm Si.sub.3N.sub.4 34 9 nm 9 nm SiO.sub.2 35 50 nm 50 nm

[0109] The optical thicknesses of the dielectric layer sequences can be calculated as the product of the indicated geometric thicknesses and the refractive index (Si.sub.3N.sub.4: 2.0; SiZrN: 2.2, ZnO: 2.0; SiO.sub.2: 1.5).

[0110] FIG. 5 depicts reflection spectra of windshields 10 as in FIG. 3, with, in each case, a layer structure in accordance with the Example according to the invention as well as the Comparative Examples 1 and 2 of Table 1. The reflection spectra were recorded with a light source that emits p-polarized radiation of uniform intensity in the spectral range observed, when irradiated via the inner pane 2 (the so-called interior-side reflection) at an angle of incidence of 65 relative to the interior-side surface normal. The reflection measurement is thus approximated to the situation in the projection assembly.

[0111] From the graphic representation of the spectra, it is already apparent that the Example according to the invention has a reflection spectrum that is improved compared to the Comparative Examples. In the Comparative Example 1, similar reflectance is achieved, but the reflection spectrum is less constant (flat) such that the HUD display is less color-neutral, because, in particular, the blue components are reflected with more intensity. Also, the optical appearance of the windshield 10 can have a color cast. The Comparative Example 2 does not result in sufficiently high reflectance for the high-intensity display of an HUD projection.

[0112] For the evaluation of the HUD display, the spectral range from 450 nm to 650 nm is of particular interest, since conventional HUD projectors 4 use radiation in this range (RGB: 473 nm, 550 nm, 630 nm). The averaged reflectance for p-polarized radiation as well as the differences of the maximum and minimum values relative to the averaged reflectance in the spectral range are summarized in Table 2. Also, the standard deviation of the reflection spectrum is indicated in each case.

TABLE-US-00002 TABLE 2 Example Comp. Example 1 Comp. Example 2 Averaged reflectance 17.0% 17.8% 3.2% for p-polarized radiation, 450 nm-650 nm Difference between the 0.1% 1.2% 0.6% maximally occurring reflectance and the mean Difference between the 0.2% 0.5% 1.6% minimally occurring reflectance and the mean Standard deviation, 0.09% 0.55% 0.68% 450 nm-650 nm

[0113] As could already be seen from the graphic representation of the reflection spectra in FIG. 5, the Comparative Example 1 results in an averaged reflectance similar to that of the Example according to the invention but in a greater variance in reflectance. The HUD display is thus similarly intense, but less color-neutral. The Comparative Example 2 has an averaged reflectance that is much too low.

[0114] For the evaluation of the overall optical impression of the windshield 10, the entire visible spectral range from 380 nm to 780 nm is of interest. The averaged reflectance for p-polarized radiation as well as the differences of the maximum and minimum values relative to the reflectance in this spectral range are summarized in Table 3. Also, the standard deviation of the reflection spectrum is indicated in each case.

TABLE-US-00003 TABLE 3 Example Comp. Example 1 Comp. Example 2 Averaged reflectance 16.8% 18.0% 2.9% for p-polarized radiation, 380 nm-780 nm Difference between the 0.3% 1.3% 0.9% maximally occurring reflectance and the mean Difference between the 1.4% 1.3% 1.9% minimally occurring reflectance and the mean Standard deviation, 0.33% 0.66% 0.86% 380 nm-780 nm

[0115] As could already be seen from the graphic representation of the reflection spectra in FIG. 5, the example according to the invention resulted in a lower variance of reflectance. The overall optical impression is, consequently, color-neutral; a disturbing color cast can be avoided. All panes have light transmittance greater than 70% such that they can be used as a windshield.

LIST OF REFERENCE CHARACTERS

[0116] (10) windshield [0117] (1) outer pane [0118] (2) inner pane [0119] (3) thermoplastic intermediate layer [0120] (4) projector [0121] (5) viewer/vehicle driver [0122] (20) reflection coating [0123] (21) electrically conductive layer based on silver (silver layer) [0124] (22a) first lower dielectric layer/antireflection layer [0125] (22b) second lower dielectric layer/matching layer [0126] (22c) third lower dielectric layer/refractive-index-enhancing layer [0127] (23a) first upper dielectric layer/antireflection layer [0128] (23b) second upper dielectric layer/matching layer [0129] (23c) third upper dielectric layer/refractive-index-enhancing layer [0130] (24) metallic blocking layer [0131] (30) emissivity-reducing coating [0132] (31) electrically conductive layer based on a TCO (TCO layer) [0133] (32) blocking layer against alkali diffusion [0134] (33) lower antireflection layer [0135] (34) barrier layer for regulating oxygen diffusion [0136] (35) upper antireflection layer [0137] (O) upper edge of the windshield 10 [0138] (U) lower edge of the windshield 10 [0139] (B) HUD region of the windshield 10 [0140] (E) eyebox [0141] (I) exterior-side surface of the outer pane 1, facing away from the intermediate layer 3 [0142] (II) interior-side surface of the outer pane 1, facing the intermediate layer 3 [0143] (III) exterior-side surface of the inner pane 2, facing the intermediate layer 3 [0144] (IV) interior-side surface of the inner pane 2, facing away from the intermediate layer 3