PROJECTION ARRANGEMENT FOR A HEAD-UP DISPLAY (HUD) WITH P-POLARISED RADIATION

Abstract

A projection arrangement for a head-up display (HUD), includes a composite pane, which includes an outer pane and an inner pane joined to one another via a thermoplastic intermediate layer and has an HUD region; an electrically conductive coating on the surface of the outer pane or the inner pane facing the intermediate layer or within the intermediate layer; and an HUD projector, which is directed at the HUD region; wherein the radiation of the projector is p-polarised, wherein the electrically conductive coating includes a first dielectric layer or layer sequence, a first electrically conductive layer, a second dielectric layer or layer sequence, a second electrically conductive layer, a third dielectric layer or layer sequence, a third electrically conductive layer, a fourth dielectric layer or layer sequence, a fourth electrically conductive layer, and a fifth dielectric layer or layer sequence.

Claims

1. A projection arrangement for a head-up display (HUD), comprising: a composite pane, which comprises an outer pane and an inner pane joined to one another via a thermoplastic intermediate layer and has an HUD region; an electrically conductive coating on a surface of the outer pane or the inner pane facing the intermediate layer or within the intermediate layer; and an HUD projector, which is directed at the HUD region; wherein a radiation of the projector is p-polarised, wherein the electrically conductive coating comprises a first dielectric layer or layer sequence, a first electrically conductive layer with a thickness from 11 nm to 14 nm, a second dielectric layer or layer sequence, a second electrically conductive layer with a thickness from 10 nm to 13 nm, a third dielectric layer or layer sequence, a third electrically conductive layer with a thickness from 10 nm to 13 nm, a fourth dielectric layer or layer sequence, a fourth electrically conductive layer with a thickness from 7 nm to 11 nm, and a fifth dielectric layer or layer sequence, which are arranged in the order specified starting from the substrate.

2. The projection arrangement according to claim 1, wherein the thickness of the first electrically conductive layer is greater than the thickness of the fourth electrically conductive layer.

3. The projection arrangement according to claim 1, wherein the thickness of the first electrically conductive layer is from 11.5 nm to 13.5 nm, the thickness of the second electrically conductive layer is from 10 nm to 12.5 nm, the thickness of the third electrically conductive layer is from 11 nm to 12.5 nm, and the thickness of the fourth electrically conductive layer is from 7.5 nm to 10 nm.

4. The projection arrangement according to claim 1, wherein an optical thickness of the first dielectric layer or layer sequence is from 50 nm to 150 nm, an optical thickness of the fifth dielectric layer or layer sequence is from 50 nm to 150 nm.

5. The projection arrangement according to claim 1, wherein all dielectric layers or layer sequences of the electrically conductive coating are formed from dielectric layers with a refractive index greater than 1.8.

6. The projection arrangement according to claim 1, wherein the second dielectric layer sequence contains a dielectric optically low-refractive-index layer with a refractive index less than 1.8 and at least one dielectric layer with a refractive index greater than 1.8 and wherein the remaining dielectric layers or layer sequences of the electrically conductive coating are formed from dielectric layers with a refractive index greater than 1.8.

7. The projection arrangement according to claim 6, wherein an optical thickness of the optically low-refractive-index layer is from 20 nm to 40 nm.

8. The projection arrangement according to claim 5, wherein a sum of optical thicknesses of all layers with a refractive index greater than 1.8 of each of the second dielectric layer or layer sequence, of the third dielectric layer or layer sequence, and of the fourth dielectric layer or layer sequence is in each case from 100 nm to 200 nm.

9. The projection arrangement according to claim 1, wherein the composite pane with the electrically conductive coating has, in a spectral range from 450 nm to 650 nm, an averaged reflectance relative to p-polarised radiation of at least 5%.

10. The projection arrangement according to claim 1, wherein a difference between a maximally occurring reflectance and a mean of a reflectance as well as a difference between a minimally occurring reflectance and a mean of the reflectance relative to p-polarised radiation in a spectral range from 450 nm to 650 nm is at most 5%.

11. The projection arrangement according to claim 1, wherein the electrically conductive layers are based on silver.

12. The projection arrangement according to claim 1, wherein the radiation of the projector is essentially purely p-polarised.

13. The projection arrangement according to claim 1, wherein a surface of the outer pane and of the inner pane facing away from the intermediate layer are arranged essentially parallel to one another.

14. The projection arrangement according to claim 1, wherein the electrically conductive coating is provided with two bus bars that are connected to a voltage source of 12 V to 14 V such that an electric current can be conducted through the coating to heat the composite pane.

15. A method comprising providing a projection arrangement according to claim 1 as an HUD in a vehicle on land, on water, or in the air.

16. The projection arrangement according to claim 2, wherein the thicknesses of the second electrically conductive layer and of the third electrically conductive layer are greater than the thickness of the fourth electrically conductive layer.

17. The projection arrangement according to claim 4, wherein the optical thickness of the first dielectric layer or layer sequence is from 90 nm to 110 nm, the optical thickness of the fifth dielectric layer or layer sequence is from 75 nm to 95 nm.

18. The projection arrangement according to claim 7, wherein the optical thickness of the optically low-refractive-index layer is from 25 nm to 35 nm.

19. The projection arrangement according to claim 8, wherein the sum of the optical thicknesses of all layers with a refractive index greater than 1.8 of each of the second dielectric layer or layer sequence, of the third dielectric layer or layer sequence, and of the fourth dielectric layer or layer sequence is in each case from 150 nm to 170 nm.

20. The projection arrangement according to claim 9, wherein the composite pane with the electrically conductive coating has, in the spectral range from 450 nm to 650 nm, an averaged reflectance relative to p-polarised radiation of at least 7%.

Description

[0136] 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.

[0137] They depict:

[0138] FIG. 1 a plan view of a composite pane of a generic projection arrangement,

[0139] FIG. 2 a cross-section through a generic projection arrangement,

[0140] FIG. 3 a cross-section through a composite pane of a projection arrangement according to the invention,

[0141] FIG. 4 a cross-section through an electrically conductive coating according to the invention, and

[0142] FIG. 5 reflection spectrum relative to p-polarised radiation of composite panes according to the invention and of comparative examples.

[0143] FIG. 1 and FIG. 2 depict in each case a detail of a generic projection arrangement for an HUD. The projection arrangement comprises a composite pane 10, in particular the windshield of a passenger car. The projection arrangement also comprises an HUD projector 4 that is directed at a region B of the composite pane 10. In the region B, usually referred to as an HUD region, 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 when his eyes are situated within the so-called eyebox E.

[0144] The composite pane 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 outside surroundings; the inner pane 2, the vehicle interior.

[0145] FIG. 3 depicts an embodiment of a composite pane 10 implemented according to the invention. The outer pane 1 has an exterior-side surface I that faces the outside surroundings in the installed position and an interior-side surface II that faces the interior in the installed position. Likewise, the inner pane 2 has an exterior-side surface III that faces the outside surroundings in the installed position and an interior-side surface IV that faces the interior in the installed position. 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. 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 art.

[0146] The exterior-side surface III of the inner pane 2 is provided with an electrically conductive coating 20 according to the invention, which is provided as a reflection surface for the projector radiation and, additionally, for example, as an IR reflection coating or as a heatable coating.

[0147] According to the invention, the radiation of the projector 4 is p-polarised, in particular essentially purely p-polarised. Since the projector 4 irradiates the composite pane 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 electrically conductive coating 20 according to the invention is optimised for reflection of p-polarised radiation. It serves as a reflection surface for the radiation of the projector 4 to generate the HUD projection.

[0148] FIG. 4 depicts the layer sequence of an embodiment according to the invention of the electrically conductive coating 20 on the inner pane 2. The coating 20 comprises five dielectric layer sequences M1, M2, M3, M4, M5 and four electrically conductive layers 21 (21.1, 21.2, 21.3, 21.4), which are arranged alternatingly. A thin blocking layer 26 (26.1, 26.2, 26.3, 26.4) is arranged in each case between each electrically conductive layer 21 and the dielectric layer sequence positioned above it.

[0149] The first dielectric layer sequence M1 is composed of an anti-reflection layer 22.1, a smoothing layer 23.1, and a first matching layer 24.1.

[0150] The second dielectric layer sequence M2 is composed of a second matching layer 25.1, an anti-reflection layer 22.2, an optically low-refractive-index layer 27 with a refractive index less than 1.8, a smoothing layer 23.2, and a first matching layer 24.2.

[0151] The third dielectric layer sequence M3 is composed of a second matching layer 25.3, an anti-reflection layer 22.3, a smoothing layer 23.3, and a first matching layer 24.3. The anti-reflection layer 22.3 is subdivided into a dielectric layer 22a.3 with a refractive index less than 2.1 and an optically high-refractive-index layer 22b.3 with a refractive index greater than 2.1.

[0152] The fourth dielectric layer sequence M4 is composed of a second matching layer 25.4, an anti-reflection layer 22.4, a smoothing layer 23.4, and a first matching layer 24.4. Here, again, the anti-reflection layer 22.4 is subdivided into a dielectric layer 22a.4 and an optically high-refractive-index layer 22b.4.

[0153] The fifth dielectric layer sequence M5 is composed of a second matching layer 25.5 and an anti-reflection layer 22.5, with the latter again being subdivided into an optically high-refractive-index layer 22b.5 and a dielectric layer 22a.5. The optically high-refractive-index layer 22b.5 and the dielectric layer 22a.5 are arranged in reverse order compared to the dielectric layer sequences M3 and M4.

[0154] All dielectric layers except the low-refractive-index layer 27 have a refractive index greater than 1.8. The layer sequence can be seen schematically in the figure. The structure shown corresponds to Example 5 described below. The layer sequence of a composite pane 10 with the coating 20 on the exterior-side surface III of the inner pane 2 is presented, together with the materials and layer thicknesses of the individual layers, in Table 1 (Example 5). Table 1 also shows four further Examples according to the invention (Example 1 through 4).

[0155] Table 2 shows the layer sequences of an electrically conductive coating not according to the invention (Comparative Example 1) and another embodiment of the coating according to the invention (Example 6). The Comparative Example 1 differs from the Examples according to the invention in particular by the thickness of the electrically conductive layers 21, with, in particular, the second electrically conductive layer 21.2, the third electrically conductive layer 21.3, and the fourth electrically conductive layer 21.4 being significantly thicker. In addition, the optical thicknesses of the first dielectric layer sequence M1 (69.46 nm) and of the fifth dielectric layer sequence M5 (77.2 nm) are significantly lower than in the Examples according to the invention (85.52 nm for M1 and 102.4 nm for M5). The Example 6 is essentially the same as Example 5, with the low-refractive-index layer 27 provided in the third dielectric layer sequence M3 instead of in the second dielectric layer sequence M2.

[0156] The optical thickness of a layer is obtained as the product of the refractive index and the geometric layer thickness. The refractive index of silicon nitride (SiN), tin oxide (ZnO), and mixed tin-zinc oxide (ZnSnO) is 2.0 in each case; the refractive index of silicon-zirconium nitride (SiZrN) is 2.2; and the refractive index of silicon oxide (SiO) is 1.5.

[0157] The materials of the layers can have dopants that are not specified in the Table. For example, layers based on SnZnO can be doped with antimony and layers based on ZnO, SiN, or SiZrN with aluminium.

TABLE-US-00001 TABLE 1 Layer Thickness Reference Material Characters Example 1 Example 2 Example 3 Example 4 Example 5 Glass    1 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm PVB    3 0.76 mm 0.76 mm 0.76 mm 0.76 mm 0.76 mm SiN 20 22b.5 22.5 25.0 nm 25.0 nm 25.0 nm 25.0 nm 25.0 nm SiZrN 22a.5 12.0 nm 12.0 nm 12.0 nm 12.0 nm 12.0 nm ZnO 25.5 13.0 nm 13.0 nm 13.0 nm 13.0 nm 13.0 nm NiCr 26.4 0.2 nm 0.2 nm 0.2 nm 0.2 nm 0.2 nm Ag 21.4 7.5 nm 8.0 nm 8.0 nm 9.1 nm 8.1 nm ZnO 24.4 12.0 nm 12.0 nm 12.0 nm 12.0 nm 12.0 nm SnZnO 23.4 10.0 nm 10.0 nm 10.0 nm 10.0 nm 10.0 nm SiZrN 22b.4 22.4 20.5 nm 20.5 nm 20.5 nm 20.5 nm 20.5 nm SiN 22a.4 20.9 nm 20.9 nm 20.9 nm 20.9 nm 20.9 nm ZnO 25.4 16.0 nm 16.0 nm 16.0 nm 16.0 nm 16.0 nm NiCr 26.3 0.1 nm 0.1 nm 0.1 nm 0.1 nm 0.1 nm Ag 21.3 11.0 nm 12.0 nm 12.0 nm 12.5 nm 12.3 nm ZnO 24.3 14.0 nm 14.0 nm 14.0 nm 14.0 nm 14.0 nm SnZnO 23.3 11.0 nm 11.0 nm 11.0 nm 11.0 nm 11.0 nm SiZrN 22b.3 22.3 18.0 nm 18.0 nm 18.0 nm 18.0 nm 18.0 nm SiN 22a.3 17.1 nm 17.1 nm 17.1 nm 17.1 nm 17.1 nm ZnO 25.3 15.0 nm 15.0 nm 15.0 nm 15.0 nm 15.0 nm NiCr 26.2 0.3 nm 0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag 21.2 11.5 nm 11.9 nm 10.6 nm 10.9 nm 10.3 nm ZnO 24.2 16.0 nm 16.0 nm 16.0 nm 16.0 nm 16.0 nm SnZnO 23.2 10.0 nm 10.0 nm 10.0 nm 10.0 nm 10.0 nm SiO   27 — — — — 20.0 nm SiZrN 22.2 32.1 nm 32.1 nm 32.1 nm 32.1 nm 32.1 nm ZnO 25.2 16.0 nm 16.0 nm 16.0 nm 16.0 nm 16.0 nm NiCr 26.1 0.2 nm 0.2 nm 0.2 nm 0.2 nm 0.2 nm Ag 21.1 13.0 nm 13.0 nm 12.0 nm 12.2 nm 12.5 nm ZnO 24.1 11.0 nm 11.0 nm 11.0 nm 11.0 nm 11.0 nm ZnSnO 23.1 8.0 nm 8.0 nm 8.0 nm 8.0 nm 8.0 nm SiZrN 22.1 21.6 nm 21.6 nm 21.6 nm 21.6 nm 21.6 nm Glass    2 1.6 mm 1.6 nm 1.6 mm 1.6 nm 1.6 nm

TABLE-US-00002 TABLE 2 Reference Layer Thickness Material Characters Comparative Example 1 Example 6 Glass 1  2.1 mm  2.1 mm PVB 3 0.76 mm 0.76 mm SiN 20 22b.5 22.5 12.4 nm 25.0 nm SiZrN 22a.5 12.0 nm 12.0 nm ZnO 25.5 13.0 nm 13.0 nm NiCr 26.4  0.2 nm  0.2 nm Ag 21.4 13.2 nm  8.1 nm ZnO 24.4 12.0 nm 12.0 nm SnZnO 23.4 10.0 nm 10.0 nm SiZrN 22b.4 22.4 20.4 nm 20.5 nm SiN 22a.4 21.2 nm 20.9 nm ZnO 25.4 16.0 nm 16.0 nm NiCr 26.3  0.1 nm  0.1 nm Ag 21.3 14.3 nm 12.3 nm ZnO 24.3 14.0 nm 14.0 nm SnZnO 23.3 11.0 nm 11.0 nm SiO 27 —   20 nm SiZrN 22b.3 22.3 18.3 nm 18.0 nm SiN 22a.3 17.3 nm 17.1 nm ZnO 25.3 15.0 nm 15.0 nm NiCr 26.2  0.3 nm  0.3 nm Ag 21.2 14.8 nm 10.3 nm ZnO 24.2 16.0 nm 16.0 nm SnZnO 23.2 10.0 nm 10.0 nm SiZrN 22.2 33.0 nm 32.1 nm ZnO 25.2 16.0 nm 16.0 nm NiCr 26.1  0.2 nm  0.2 nm Ag 21.1 11.7 nm 12.5 nm ZnO 24.1 11.0 nm 11.0 nm ZnSnO 23.1  8.0 nm  8.0 nm SiZrN 22.1 14.3 nm 21.6 nm Glass 2  1.6 mm  1.6 nm

[0158] FIG. 5 depicts the reflection spectrum of a composite pane 10 in accordance with the Examples 1 to 6 according to the invention and the Comparative Example 1 relative to p-polarised radiation. The spectra were measured on the interior side at an angle of incidence of 65°, thus replicating the reflection behaviour for the HUD projector. The upper spectrum shows the spectral range from 350 nm to 800 nm; the lower spectrum enlarges the spectral range from 400 nm to 700 nm. The two representations of the figure differ only in the scaling of the ordinate.

[0159] The comparison of the Examples 1 through 4 with the Comparative Example 1 makes it clear that the layer thicknesses according to the invention, in particular of the electrically conductive layers 21, result in a higher average reflectance and a smoother spectrum in the spectral range from 450 nm to 650 nm relevant for the HUD display. Thus, a more intense and colour-neutral display of the HUD projection is obtained. The low-refractive-index layer 27 (Examples 5 and 6) can further increase the average reflectance. Here, it is advantageous for the low-refractive-index layer 27 to be arranged in the layer sequence M2 (Example 5)—if it is contained in the layer sequence M3 (Example 6), a high average reflectance also occurs; however, the spectrum is somewhat red-heavy. The relevant observations are summarised in Table 3.

TABLE-US-00003 TABLE 3 Averaged Difference between Difference between reflectance the maximally the minimally relative occurring occurring to p-polarised reflectance reflectance radiation, and the mean, and the mean, 450 nm-650 nm 450 nm-650 nm 450 nm-650 nm Example 1  8.2% 2.5% 1.9% Example 2  7.8% 2.7% 2.0% Example 3  7.8% 2.3% 4.1% Example 4  8.2% 3.7% 4.2% Example 5  9.9% 1.8% 4.2% Example 6 13.7% 5.9% 9.9% Comparative  6.5% 6.4% 4.3% Example 1

[0160] Table 4 and Table 5 indicate some physical parameters of the composite panes according to the invention (Examples) and the Comparative Example according to Tables 1 and 2 that are familiar to the person skilled in the art and are usually used to characterise vehicle windows. RL stands for the integrated light reflection; and TL, for the integrated light transmittance (per ISO 9050). The specification after RL or TL respectively indicates the light source used, where A is the light source A and HUD is an HUD projector with radiation wavelengths of 473 nm, 550 nm, and 630 nm (RGB). The angle specification after the light type indicates the angle of incidence of the radiation relative to the exterior-side surface normals. Angles of incidence less than 90° thus indicate exterior-side irradiation; and angles of incidence greater than 90°, interior-side irradiation. The specified angle of incidence of 115° corresponds to an angle of incidence relative to the interior-side surface normal of 65° (=180°-115°) simulates irradiation with the projector according to the invention. Below the reflection values are the associated colour values a* and b* in the L*a*b* colour space, followed by the indication of the light source used (HUD projector) and the indication of the viewing angle (angle at which the light beam enters the eye and strikes the retina).

[0161] The composite pane has sufficient total transmittance to be used as a windshield. The interior-side reflection with respect to the p-polarised HUD projector radiation is sufficiently high to ensure high intensity HUD projection. At the same time, the reflection colour is relatively neutral such that the HUD projection is reproduced in a colour-neutral manner.

TABLE-US-00004 TABLE 4 Example Example Example Example Example 1 2 3 4 5 TL A 0°/% 71.6 71.3 71.2 71.3 71.2 RL HUD 8.3 7.8 7.9 8.1 9.9 p-pol. 115°/% a* (HUD/10°) 5.5 1.6 -2.3 2.2 2.2 b* (HUD/10°) -4.0 -3.7 -0.8 -4.0 -3.3 Sheet 0.9 0.9 0.9 0.9 0.9 Resistance/ Ω/square

TABLE-US-00005 TABLE 5 Comparative Example 1 Example 6 TL A 0°/% 71.7 64.3 RL HUD p-pol. 115°/% 5.7 16.3 a* (HUD/10°) 8.2 2.4 b* (HUD/10°) -12.6 27.5 Sheet Resistance/ 0.7 0.9 Ω/square

LIST OF REFERENCE CHARACTERS

[0162] (10) composite pane [0163] (1) outer pane [0164] (2) inner pane [0165] (3) thermoplastic intermediate layer [0166] (4) HUD projector [0167] (5) viewer/vehicle driver [0168] (20) electrically conductive coating [0169] (M1), (M2), (M3), (M4), (M5) 1st, 2nd, 3rd, 4th, 5th dielectric layer sequence [0170] (21) electrically conductive layer [0171] (21.1), (21.2), (21.3), (21.4) 1st, 2nd, 3rd, 4th electrically conductive layer [0172] (22) anti-reflection layer [0173] (22.1), (22.2), (22.3), (22.4), (22.5) 1st, 2nd, 3rd, 4th, 5th anti-reflection layer [0174] (22a) dielectric layer of the anti-reflection layer 4 [0175] (22a.3), (22a.4), (22a.5) 1st, 2nd, 3rd dielectric layer [0176] (22b) optically high-refractive-index layer of the anti-reflection layer 4 [0177] (22b.3), (22b.4), (22b.5) 1st, 2nd, 3rd optically high-refractive-index layer [0178] (23) smoothing layer [0179] (23.1), (23.2), (23.3), (23.4) 1st, 2nd, 3rd, 4th smoothing layer [0180] (24) first matching layer [0181] (24.1), (24.2), (24.3), (24.4) 1st, 2nd, 3rd, 4th first matching layer [0182] (25) second matching layer [0183] (25.2), (25.3), (25.4), (25.5) 1st, 2nd, 3rd, 4th second matching layer [0184] (26) blocking layer [0185] (26.1), (26.2), (26.3), (26.4) 1st, 2nd, 3rd, 4th blocking layer [0186] (27) optically low-refractive-index layer [0187] (O) upper edge of the composite pane 10 [0188] (U) lower edge of the composite pane 10 [0189] (B) HUD region of the composite pane 10 [0190] (E) eyebox [0191] (I) exterior-side surface of the outer pane 1 [0192] (II) interior-side surface of the outer pane 1 [0193] (III) exterior-side surface of the inner pane 2 [0194] (IV) interior-side surface of the inner pane 2