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

Abstract

A projection assembly for a head-up display (HUD), includes a windshield, including outer and inner panes that are joined to one another via a thermoplastic intermediate layer and having an HUD region; and a projector aimed at the HUD region. The radiation of the projector is predominantly p-polarised, and the windshield is provided with a reflection coating that is suitable for reflecting p-polarised radiation. The reflection coating has exactly one electrically conductive layer based on silver, a lower dielectric layer or layer sequence whose refractive index is at least 1.9 is arranged beneath the electrically conductive layer, an upper dielectric layer or layer sequence whose refractive index is at least 1.9 is arranged above the electrically conductive layer, the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.7.

Claims

1. 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 and having an HUD region; and a projector that is aimed at the HUD region; wherein the a radiation of the projector is predominantly p-polarised, and the windshield is provided with a reflection coating that is suitable for reflecting p-polarised radiation; and wherein the reflection coating has exactly one electrically conductive layer based on silver, a lower dielectric layer or layer sequence whose refractive index is at least 1.9 is arranged beneath the electrically conductive layer, an upper dielectric layer or layer sequence whose refractive index is at least 1.9 is arranged above the electrically conductive layer, and a ratio of an optical thickness of the upper dielectric layer or layer sequence to an optical thickness of the lower dielectric layer or layer sequence is at least 1.7.

2. The projection assembly according to claim 1, wherein the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.8.

3. The projection assembly according to claim 1, wherein the optical thickness of the upper dielectric layer or layer sequence is from 100 nm to 200 nm.

4. The projection assembly according to claim 1, wherein the optical thickness of the lower dielectric layer or layer sequence is from 50 nm to 100 nm.

5. The projection assembly according to claim 1, wherein the reflection coating does not include any dielectric layers whose refractive index is less than 1.9.

6. The projection assembly according to claim 1, wherein exactly one lower dielectric layer with a refractive index of at least 1.9 is arranged beneath the electrically conductive layer, and/or exactly one upper dielectric layer with a refractive index of at least 1.9 is arranged above the electrically conductive layer.

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

8. The projection assembly according to claim 1, wherein 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 beneath the electrically conductive layer, and/or 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 above the electrically conductive layer.

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

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

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

12. The projection assembly according to claim 1, wherein the radiation of the projector strikes the windshield with an angle of incidence of 60° to 70°.

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

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

15. The projection assembly according to claim 1, wherein the reflection coating is arranged on a surface of the outer pane or the inner pane facing the intermediate layer or within the intermediate layer.

16. The projection assembly according to claim 2, wherein the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.9.

17. The projection assembly according to claim 3, wherein the optical thickness of the upper dielectric layer or layer sequence is from 130 nm to 170 nm.

18. The projection assembly according to claim 4, wherein the optical thickness of the lower dielectric layer or layer sequence is from 60 nm to 90 nm.

19. The projection assembly according to claim 6, wherein the lower dielectric layer with a refractive index of at least 1.9 arranged beneath the electrically conductive layer is based on silicon nitride, and/or the upper dielectric layer with a refractive index of at least 1.9 arranged above the electrically conductive layer is based on silicon nitride.

20. The projection assembly according to claim 7, wherein the first lower dielectric layer is based on silicon nitride, and the second lower dielectric layer is based on zinc oxide, and/or the first upper dielectric layer is based on silicon nitride, and the second upper dielectric layer is based on zinc oxide.

Description

[0080] 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.

[0081] They depict:

[0082] FIG. 1 a plan view of a composite pane of a generic projection assembly,

[0083] FIG. 2 a cross-section through a generic projection assembly,

[0084] FIG. 3 a cross-section through a composite pane of a projection assembly according to the invention,

[0085] FIG. 4 a cross-section through an embodiment of the reflection coating according to the invention on an inner pane,

[0086] FIG. 5 reflection spectra of composite panes relative to p-polarised radiation in accordance with Examples 1 and 2 and Comparative Example 1,

[0087] FIG. 6 reflection spectra of composite panes relative to p-polarised radiation in accordance with Example 3 and Comparative Example 2, and

[0088] FIG. 7 reflection spectra of composite panes relative to p-polarised radiation in accordance with Examples 4 and 5 and Comparative Examples 3 and 4.

[0089] 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, usually 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 eye box E.

[0090] 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 outside environment; the inner pane 2, the vehicle interior.

[0091] 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 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. 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 art—it is not implemented as a so-called “wedge film”.

[0092] 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 reflection coating).

[0093] 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 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 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.

[0094] FIG. 4 depicts the layer sequence of an embodiment of the reflection coating 20 according to the invention. The reflection coating 20 is a stack of thin layers. The reflection coating 20 comprises 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, consisting, from bottom to top, of an upper matching layer 23b, an upper refractive index increasing layer 23c, and an upper antireflection layer 23a, is arranged. Beneath the electrically conductive layer 21, a lower dielectric layer sequence consisting, from top to bottom, of a lower matching layer 22b, a lower refractive index increasing layer 22c, and a lower antireflection layer 22a, is arranged.

[0095] The layer structure depicted is intended merely as an example. Thus, the dielectric layer sequences can also include more or fewer layers, provided at least one dielectric layer is present above and beneath the conductive layer 21. The dielectric layer sequences also need not be symmetrical. Exemplary materials and layer thicknesses can be found in the following examples.

[0096] The layer sequences of a windshield 10 with the reflection coating 20 on the exterior-side surface III of the inner pane 2 according to Examples 1 through 5 are presented in Table 1, 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 aluminium.

TABLE-US-00001 TABLE 1 Layer Thickness Reference Example Example Example Example Example Material Characters 1 2 3 4 5 Soda lime 1 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass PVB 3 0.76 mm 0.76 mm 0.76 mm 0.76 mm 0.76 mm SiN 20 23a 70 nm 70 nm 60 nm 60 nm 60 nm SiZrN 23c — — — 10 nm 10 nm ZnO 23b — — 10 nm 10 nm 10 nm NiCr 24  0.3 nm 0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag 21  11 nm 12 nm 12 nm 11 nm 13 nm ZnO 22b — — 10 nm 10 nm 10 nm SiZrN 22c — — — 10 nm 10 nm SiN 22a 30 nm 35 nm 25 nm 20 nm 20 nm Soda lime 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass

[0097] For the comparison, Comparative Examples 1 to 4, which do not comply with the features according to the invention, were investigated. Their layer sequences are shown in Table 2.

TABLE-US-00002 TABLE 2 Layer Thickness Reference Comparative Comparative Comparative Comparative Material Characters Example 1 Example 2 Example 3 Example 4 Soda lime 1 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass PVB 3 0.76 mm 0.76 mm 0.76 mm 0.76 mm SiN 20 23a 50 nm 35 nm 30 nm 40 nm SiZrN 23c — — 10 nm 10 nm ZnO 23b — 10 nm 10 nm 10 nm NiCr 24  0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag 21  12 nm 13 nm 13 nm 13 nm ZnO 22b — 10 nm 10 nm 10 nm SiZrN 22c — — 10 nm 10 nm SiN 22a 50 nm 35 nm 50 nm 40 nm Soda lime 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass

[0098] The Examples and the Comparative Examples differ primarily in the ratio of the optical thickness of the upper dielectric layer sequence to the optical thickness of the lower dielectric layer sequence. The optical thickness is 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). The optical thicknesses and their ratio are summarised in Table 3. The ratio ϕ describes the ratio of the optical thickness of the upper dielectric layer 23a or layer sequence 23a, 23b, and, optionally, 23c to the optical thickness of the lower dielectric layer 22a or layer sequence 22a, 22b, and, optionally, 22c.

TABLE-US-00003 TABLE 3 Optical Thickness of Optical Thickness of the Upper Dielectric the Lower Dielectric Layer Sequence Layer Sequence Ratio ϕ Example 1 140 60 2.33 Example 2 140 70 2.00 Example 3 140 70 2.00 Example 4 162 82 1.98 Example 5 162 82 1.98 Comp. Example 1 100 100 1.00 Comp. Example 2 90 90 1.00 Comp. Example 3 102 142 0.72 Comp. Example 4 122 122 1.00

[0099] FIG. 5, FIG. 6, and FIG. 7 depict reflection spectra of composite pane 10, as in FIG. 3, in each case with a layer structure according to the Examples 1 through 5 of the invention according to Table 1 and according to the Comparative Examples 1 through 4 according to Table 2. The reflection spectra were recorded with a light source that emits p-polarised 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. For the sake of better clarity, in each case the Examples and the Comparative Examples that have a similar layer structure are summarised. FIG. 5 shows Examples 1 and 2 and Comparative Example 1, each of which has only dielectric antireflection layers 22a, 23a FIG. 6 shows Example 3 and Comparative Example 2, each of which has dielectric antireflection layers 22a, 23a and matching layers 22b, 23b. FIG. 7 shows Examples 4 and 5 and Comparative Examples 3 and 4, each of which has dielectric antireflection layers 22a, 23a, matching layers 22b, 23b, and refractive index increasing layers 22c, 23c.

[0100] From the graphic representation of the spectra, it is already apparent that the Examples according to the invention having the ratio according to the invention of optical thicknesses of upper and lower dielectric layer or layer sequence result in a substantially smoother spectrum in the spectral range of interest from 400 nm to 680 nm. This ensures a more colour-neutral display of the HUD projection. In addition, the general colour impression of the pane is improved.

[0101] The averaged reflectance relative to p-polarised radiation as well as the differences of the maximum and minimum values relative to the reflectance of Examples 1 through 5 are summarised in Table 4; the corresponding values for the Comparative Example 1 through 4, in Table 5. Also, the standard deviation of the reflection spectra is indicated in each case. The analyses refer in each case to the spectral range from 400 nm to 680 nm.

TABLE-US-00004 TABLE 4 Example 1 Example 2 Example 3 Example 4 Example 5 Averaged reflectance 17.6% 19.9% 20.2% 16.6% 22.3% relative to p-polarised radiation, 400 nm-680 nm Difference between 1.8% 1.7% 2.0% 1.1% 1.6% the maximally occurring reflectance and the mean Difference between the 1.1% 0.7% 1.5% 0.9% 1.3% minimally occurring reflectance and the mean Standard deviation, 0.55% 0.48% 0.60% 0.27% 0.62% 400 nm-680 nm

TABLE-US-00005 TABLE 5 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Averaged reflectance 17.6% 19.8% 23.1% 22.0% relative to p-polarised radiation, 400 nm-680 nm Difference between the 4.2% 3.6% 5.1% 5.8% maximally occurring reflectance and the mean Difference between the 1.4% 1.6% 2.2% 2.3% minimally occurring reflectance and the mean Standard deviation, 1.49% 1.11% 2.52% 2.70% 400 nm-680 nm

[0102] In the case of the comparative examples, although relatively high averaged reflection values can also be achieved, the spectra in the relevant spectral range from 400 nm to 680 nm are subject to strong fluctuations, which can lead to undesirable colour shifts in the HUD image as well as to a poorer colour impression of the pane for the viewer. In contrast, the ratio of the optical thicknesses of the lower and upper dielectric layer/layer sequence of the Examples according to the invention causes a significant smoothing of the reflection spectrum, resulting in a more colour-neutral reproduction of the projector image and a more colour-neutral overall impression.

[0103] All of the panes had light transmittance greater than 70% such that they can be used as windshields.

[0104] Tests were also carried out with a windshield having green-coloured outer glass. The reflection coating was substantially the same as Example 1, wherein only the upper antireflection layer 23a was somewhat thinner (60 nm instead of 70 nm). The external reflection was significantly reduced (by 3-4% at observation angles of 8° and 60°, integral reflection).

LIST OF REFERENCE CHARACTERS

[0105] (10) windshield

[0106] (1) outer pane

[0107] (2) inner pane

[0108] (3) thermoplastic intermediate layer

[0109] (4) projector

[0110] (5) viewer/vehicle driver

[0111] (20) reflection coating

[0112] (21) electrically conductive layer

[0113] (22a) first lower dielectric layer/antireflection layer

[0114] (22b) second lower dielectric layer/matching layer

[0115] (22c) third lower dielectric layer/refractive index increasing layer

[0116] (23a) first upper dielectric layer/antireflection layer

[0117] (23b) second upper dielectric layer/matching layer

[0118] (23c) third upper dielectric layer/refractive index increasing layer

[0119] (24) metallic blocking layer

[0120] (O) upper edge of the windshield 10

[0121] (U) lower edge of the windshield 10

[0122] (B) HUD region of the windshield 10

[0123] (E) eye box

[0124] (I) exterior-side surface of the outer pane 1, facing away from the intermediate layer 3

[0125] (II) interior-side surface of the outer pane 1, facing the intermediate layer 3

[0126] (III) exterior-side surface of the inner pane 2, facing the intermediate layer 3

[0127] (IV) interior-side surface of the inner pane 2, facing away from the intermediate layer 3