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, including an outer and an inner pane connected to one another via a thermoplastic intermediate layer, with an HUD region; an electrically conductive coating on the surface of the outer or inner pane facing the intermediate layer or within the intermediate layer; and a projector that is directed toward the HUD region. The radiation of the projector is p-polarised. The composite pane with the electrically conductive coating has reflectance of at least 10% relative to p-polarised radiation in the spectral range from 450 nm to 650 nm. The electrically conductive coating includes at least three electrically conductive layers, which are each arranged between two dielectric layers or layer sequences. The sum of the thicknesses of all electrically conductive layers is at most 30 nm and the electrically conductive layers have a thickness of 5 nm to 10 nm.

Claims

1. Projection arrangement for a head-up display (HUD), comprising: a composite pane, comprising an outer pane and an inner pane, which are connected to one another via a thermoplastic intermediate layer, with an HUD region; an electrically conductive coating on a surface of the outer pane or of the inner pane facing the intermediate layer or within the intermediate layer; and a projector that is directed toward the HUD region; wherein a radiation of the projector is p-polarised, wherein the composite pane with the electrically conductive coating has reflectance of at least 10% relative to p-polarised radiation in the entire spectral range from 450 nm to 650 nm, and wherein the electrically conductive coating includes three electrically conductive layers, which are each arranged between two dielectric layers or layer sequences, wherein a sum of thicknesses of all three electrically conductive layers is at most 30 nm and wherein the three electrically conductive layers have a thickness of 5 nm to 10 nm.

2. The projection arrangement according to claim 1, wherein the composite pane with the electrically conductive coating has reflectance of at least 12% relative to p-polarised radiation in the entire spectral range from 450 nm to 650 nm.

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

4. The projection arrangement according to claim 1, wherein the sum of the thicknesses of all three electrically conductive layers is from 15 nm to 30 nm.

5. The projection arrangement according to claim 1, wherein the electrically conductive layers have a thickness of 7 nm to 8 nm.

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

7. The projection arrangement according to claim 1, wherein each dielectric layer sequence includes an anti-reflective layer, and wherein the anti-reflective layer below a first conductive layer of the three electrically conductive layers has a thickness of 15 nm to 25 nm, the anti-reflective layer between the first conductive layer and a second conductive layer of the three electrically conductive layers has a thickness of 25 nm to 40 nm, the anti-reflective layer between the second conductive layer and a third conductive layer of the three electrically conductive layers has a thickness of 70 nm to 90 nm, the anti-reflective layer above the third conductive layer has a thickness of nm to 45 nm.

8. The projection arrangement according to claim 7, wherein the anti-reflective layers are based on a mixed silicon-metal nitride such as silicon-zirconium nitride or silicon-hafnium nitride.

9. The projection arrangement according to claim 1, wherein a dielectric layer sequence is arranged in each case between two electrically conductive layers, which dielectric layer sequence comprises an anti-reflective layer based on silicon nitride, mixed silicon-metal nitride, aluminium nitride, or tin oxide, a smoothing layer based on an oxide of one or more of the elements tin, silicon, titanium, zirconium, hafnium, zinc, gallium, and indium, a first and a second matching layer based on zinc oxide, and optionally, a blocking layer based on niobium, titanium, nickel, chromium, and/or alloys thereof.

10. The projection arrangement according to claim 1, wherein the electrically conductive coating has sheet resistance of 1Ω/□ to 2 Ω/□.

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

12. The projection arrangement according to claim 1, wherein the external surfaces of the composite pane are arranged substantially parallel to one another.

13. The projection arrangement according to claim 1, wherein the radiation of the projector strikes the composite pane with an angle of incidence of 60° to 70°.

14. The projection arrangement according to claim 1, wherein the electrically conductive coating is connected to a voltage source of 40 V to 50 V in order to heat the composite pane.

15. A method comprising utilizing a projection arrangement according to claim 1 as an HUD in a motor vehicle.

16. The projection arrangement according to claim 3, wherein the difference between the maximally occurring reflectance and the mean of the reflectance as well as the difference between the minimally occurring reflectance and the mean of the reflectance relative to p-polarised radiation is at most 1% in the entire spectral range from 450 nm to 650 nm.

17. The projection arrangement according to claim 4, wherein the sum of the thicknesses of all three electrically conductive layers is from 20 nm to 25 nm.

18. The projection arrangement according to claim 7, wherein the anti-reflective layer below the first conductive layer of the three electrically conductive layers has a thickness of 20 nm to 24 nm, the anti-reflective layer between the first conductive layer and the second conductive layer of the three electrically conductive layers has a thickness of 30 nm to 35 nm, the anti-reflective layer between the second conductive layer and the third conductive layer of the three electrically conductive layers has a thickness of 75 nm to 80 nm, the anti-reflective layer above the third conductive layer has a thickness of 37 nm to 42 nm.

19. The projection arrangement according to claim 9, wherein the mixed silicon-metal nitride is silicon-zirconium nitride.

20. The method according to claim 15, wherein the motor vehicle is a car or a truck.

Description

[0096] They depict:

[0097] FIG. 1 a plan view of a composite pane of a generic projection arrangement,

[0098] FIG. 2 a cross-section through a generic projection arrangement,

[0099] FIG. 3 a cross-section through a composite pane of a projection arrangement according to the invention,

[0100] FIG. 4 a cross-section through an electrically conductive coating according to the invention, and

[0101] FIG. 5 reflection spectrum relative to p-polarised radiation of a composite pane with an electrically conductive coating according to the invention and two Comparative Examples.

[0102] FIG. 1 and FIG. 2 each depict 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 a 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 if his eyes are situated within the so-called eye box E.

[0103] 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 environment; the inner pane 2, the vehicle interior.

[0104] FIG. 3 depicts an embodiment of a composite pane 10 implemented according to the invention.

[0105] The outer pane 1 has an exterior-side surface I that faces the outside environment 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 environment 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.

[0106] 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.

[0107] 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-reflective coating or as a heatable coating.

[0108] 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.

[0109] FIG. 4 depicts the layer sequence of an electrically conductive coating 20 according to the invention. The coating 20 contains three electrically conductive layers 21 (21.1, 21.2, 21.3). Each electrically conductive layer 21 is in each case arranged between two of a total of four anti-reflective layers 22 (22.1, 22.2, 22.3, 22.4). The coating 20 also contains two smoothing layers 23 (23.2, 23.3), three first matching layers 24 (24.1, 24.2, 24.3), three second matching layers 25 (25.2, 25.3, 25.4), and three blocking layers 26 (26.1, 26.2, 26.3).

[0110] The order of the layers can be seen schematically in the figure. The layer sequence of a composite pane 10 with the coating 20 on the exterior-side surface III of the inner pane 2 is also presented, together with the materials and layer thicknesses of the individual layers, in Table 1 (Example). Table 1 also depicts the layer sequence of two Comparative Examples with, in each case, four electrically conductive layers 21. Comparative Example 2 is an electrically conductive coating, as is currently already in use; and Comparative Example 1 is a coating with, in contrast, significantly lower layer thicknesses of the conductive layers 21. The materials of the layers can have dopants that are not indicated in the Table. For example, layers based on SnZnO can be doped with antimony; and layers based on ZnO, SiN, or SiZrN, with aluminium.

[0111] The comparison of the Example with the Comparative Example 2 makes it clear that the coating 20 according to the invention is characterised in particular by substantially thinner electrically conductive layers 21. As a result, the coating 20 according to the invention is more economical to deposit. The conductivity is nevertheless sufficiently high to use the coating 20 according to the invention as a heatable coating, in particular in connection with supply voltages of 40 V to 50 V. The desired reflection properties, the desired sheet resistance, and other optical properties are adjusted by suitable design of the dielectric layers.

[0112] The Comparative Example 1 has a similar total thickness of all electrically conductive layers 21 to that of the Example. However, this is distributed over more conductive layers such that the thickness of the individual layers is lower than in the Example. As has been surprisingly shown, layer thicknesses that are too low result in an increase in light absorption. This can be avoided with the layer structure according to the invention.

[0113] In the Example according to the invention, the anti-reflective layers 22 are individual layers based on silicon-zirconium nitride. In the Comparative Examples, the anti-reflective layers are sometimes divided into two individual layers: one layer based on silicon nitride and one layer based on silicon-zirconium nitride. Such a division of the anti-reflective layers can contribute to a reduction in sheet resistance and can, in principle, also be used within the scope of the invention. In the present Example, however, it is not necessary in order to achieve the required specifications of the composite pane.

TABLE-US-00001 TABLE 1 Materials and Layer Thicknesses Reference Comp. Comp. Characters Example Example 1 Example 2  1 Glass  2.1 mm Glass  2.1 mm Glass  2.1 mm  3 PVB 0.76 mm PVB 0.76 mm PVB 0.76 mm 22.5 — — SiZrN 36.8 nm SiZrN 52.2 nm 25.5 — — ZnO 10.0 nm ZnO 10.0 nm 26.4 — — NiCr  0.1 nm NiCr  0.2 nm 21.4 — — Ag  6.6 nm Ag 14.1 nm 24.4 — — ZnO 10.0 nm ZnO 10.0 nm 23.4 — — SnZnO  7.0 nm SnZnO  7.0 nm 22.4 SiZrN 39.0 nm SiZrN 23.5 nm SiZrN 22.9 nm SiN 29.8 nm SiN 29.8 nm 25.4 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.3 NiCr  0.1 nm NiCr  0.1 nm NiCr  0.2 nm 21.3 Ag  7.5 nm Ag  2.0 nm Ag 14.2 nm 24.3 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 23.3 SnZnO  7.0 nm SnZnO  7.0 nm SnZnO  7.0 nm 20 22.3 SiZrN 77.6 nm SiZrN 12.9 nm SiZrN 20.1 nm SiN 29.6 nm 25.3 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.2 NiCr  0.1 nm NiCr  0.1 nm NiCr  0.2 nm 21.2 Ag  8.0 nm Ag  8.5 nm Ag 17.1 nm 24.2 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 23.2 SnZnO  7.0 nm SnZnO  7.0 nm SnZnO  7.0 nm 22.2 SiZrN 33.0 nm SiZrN 20.4 nm SiZrN 19.4 nm SiN 34.1 nm 25.2 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.1 NiCr  0.1 nm NiCr  0.1 nm NiCr  0.2 nm 21.1 Ag  7.5 nm Ag  6.0 nm Ag 11.7 nm 24.1 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 22.1 SiZrN 21.8 nm SiN 20.6 nm SiN 28.8 nm  2 Glass  1.6 mm Glass  1.6 mm Glass  1.6 nm

[0114] FIG. 5 depicts the reflection spectrum relative to p-polarised radiation of a composite pane 10 with a prior art conductive coating 20 per the Comparative Examples and a conductive coating according to the invention per the Example (cf. Table 1). The spectra were measured on the interior-side at an angle of incidence of 65°, thus simulating the reflection behaviour for the HUD projector. The two representations of the figure differ only in the scaling of the ordinate.

[0115] Compared to the Comparative Example 2, the Example according to the invention has, on the one hand, a higher average reflection in the relevant spectral range and is, on the other hand, considerably smoother than the Comparative Example. This results in a higher-intensity and more colour-neutral display of the HUD projection.

[0116] The Comparative Example 1 has similar reflectance in the relevant spectral range and similar smoothness to those of the Example. The Comparative Example 1 is, consequently, also suitable for generating an HUD projection with p-polarised light. However, the thin silver layers per of the Comparative Example 1 surprisingly reduce the light transmittance through the composite pane, which can be critical in the case of windshields.

[0117] The reflectance for the Example is at least 13% in the entire spectral range from 450 nm to 650 nm and at least 15% for the Comparative Example 1, whereas values of only 3% occur for the Comparative Example 2. For the Example, the difference between the maximally occurring reflectance and the mean of the reflectance is 0%, and the difference between the minimally occurring reflectance and the mean of the reflectance is 1% in the spectral range from 450 nm to 650 nm. For the Comparative Example 1, the corresponding values are 1% and 0%, respectively; and for the Comparative Example 2, 7% and 6%, respectively.

[0118] Table 2 indicates some optical values of the composite pane according to the invention (Example per Table 1) and a Comparative Example (Comparative Example 1 per table 1) that are familiar to the person skilled in the art and are customarily used to characterise vehicle windows. Here, RL stands for the integrated light reflection and TL for the integrated light transmittance (per ISO 9050). The notation after RL and TL indicates the light source used, with A representing the light source A and HUD representing an HUD projector with radiation wavelengths of 473 nm, 550 nm, and 630 nm (RGB). The angle notation after the light type indicates the angle of incidence of the radiation relative to the exterior-side surface normal. Angles of incidence less than 90° thus indicate exterior-side irradiation and angles of incidence greater than 90° indicate 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°) and simulates the irradiation with the projector according to the invention. In each case, 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 (light source D65 and HUD projector) and the indication of the observation angle (angle at which the light beam in the eye strikes the retina).

[0119] TTS ISO 13837 represents the total irradiated solar energy, measured per ISO 13837, and is a measure of thermal comfort.

[0120] The integral reflection values and colour values are similar for both panes. The interior-side reflection with regard to the p-polarised HUD projector radiation is sufficiently high to ensure a high-intensity HUD projection. At the same time, the exterior-side reflection colour is relatively neutral such that the composite pane has no unpleasant colour cast. The Example according to the invention has, however, due to the thicker silver layers, significantly higher light transmittance, which is advantageous for use as a windshield.

[0121] The sheet resistance of the coating 20 was 1.5Ω/□ such that with a supply voltage of, for example, 42 V and a typical windshield height (distance between the bus bars), a heating power of about 2300 W/m.sup.2 can be achieved.

TABLE-US-00002 TABLE 2 . Comparative Example Example 1 RL A 8° /% 16.8 16.9  a* (D65 / 10°) −1.9 −2.0  b* (D65 / 10°) −9.5 −5.0 RL A 60° /% 21.8 22.3  a* (D65 / 10°) 0.7 1.1  b* (D65 / 10°) −5.1 −2.6 RL HUD p-pol. 115° /% 14.2 15.2  a* (HUD / 10°) −0.8 −1.0  b* (HUD / 10°) −0.2 0.2 TL A 0° /% 73.0 71.6 TTS ISO 13837 /% 56.0 53.4

LIST OF REFERENCE CHARACTERS

[0122] (10) composite pane [0123] (1) outer pane [0124] (2) inner pane [0125] (3) thermoplastic intermediate layer [0126] (4) projector [0127] (5) viewer/vehicle driver [0128] (20) electrically conductive coating [0129] (21) electrically conductive layer [0130] (21.1), (21.2), (21.3), (21.4) 1st, 2nd, 3rd, 4th electrically conductive layer [0131] (22) anti-reflective layer [0132] (22.1), (22.2), (22.3), (22.4), (22.5) 1st, 2nd, 3rd, 4th, 5th anti-reflective layer [0133] (23) smoothing layer [0134] (23.2), (23.3), (23.4) 1st, 2nd, 3rd smoothing layer [0135] (24) first matching layer [0136] (24.1), (24.2), (24.3), (24.4) 1st, 2nd, 3rd, 4th first matching layer [0137] (25) second matching layer [0138] (25.2), (25.3), (25.4), (25.5) 1st, 2nd, 3rd, 4th second matching layer [0139] (26) blocking layer [0140] (26.1), (26.2), (26.3), (26.4) 1st, 2nd, 3rd, 4th blocking layer [0141] (O) upper edge of the composite pane 10 [0142] (U) lower edge of the composite pane 10 [0143] (B) HUD region of the der composite pane 10 [0144] (E) eye box [0145] (I) exterior-side surface of the outer pane 1, facing away from the intermediate layer 3 [0146] (II) interior-side surface of the outer pane 1, facing the intermediate layer 3 [0147] (III) exterior-side surface of the inner pane 2, facing the intermediate layer 3 [0148] (IV) interior-side surface of the inner pane 2, facing away from the intermediate layer 3