Head-up display comprising a dispersion-free structured cover glass having elastic refractive array structures

Abstract

The invention relates to a compact projection unit for a vehicle. Said projection unit comprises an image generator, an imaging and / or projection lens and an achromatic cover plate which is transparent to the resulting light beam and protects the projection unit from the outside, refractive array structures that have an additional optical functionality being formed on the entry and / or exit surface of said cover plate in such a way that the light beam leaves the projection unit in a predetermined shape and direction in order to subsequently be reflected by a partially transparent reflection plate, which is arranged in the field of vision of a user, to the eyebox of said cover plate and to thus show the user the display content as a real or virtual image in a predetermined shape, size and distance that floats in the air. The achromatic cover plate design comprises at least two material layers which follow one another in the beam propagation direction, are interconnected over the entire surface and have refractive indices which differ from one another in a suitable manner, and refractive array structures which are formed in each case on one or both sides, wherein the outer material layer has, on the outside, one of these array structures, which is elastically deformable.

Description

[0001] Description

[0002] Head-up display with a dispersion-free textured cover glass with elastic refractive array structures

[0003] The invention relates to a field-of-view display device for a motor vehicle or other land, air, or water vehicle, also known as a head-up display (HUD). Such devices typically serve to project a virtual image directly into a user's field of vision by reflecting a beam of light onto a semi-transparent reflective surface, such as a vehicle windshield or a specially provided combiner lens, which is positioned within the user's field of vision. The invention also relates to a projection unit designed to emit a suitable beam of light with the desired display content, and to a vehicle equipped with such a unit.

[0004] Head-up displays, such as those used to visually display information within the field of vision of a driver or pilot, are known from the prior art. For example, German patent application DE 10 2010 032 998 A1 describes a head-up display for a motor vehicle with a projection unit that projects an image through a cover plate onto the windshield of the vehicle, which acts as a combining device. Unlike other display devices in motor vehicles, head-up displays have the advantage that the driver does not have to take their eyes off the road to perceive important information, such as the current vehicle speed or visual instructions from a navigation system.In most cases, an imaging and / or projection optic (typically a mirror optic) housed within the projection unit ensures that the virtual image is displayed at the desired distance, size, and quality, and is visible from a specific area within the vehicle designated for the user's eyes (eyebox). This widely used HUD design is also known as a mirror HUD.

[0005] To protect the optical and mechanical components from contamination, a projection unit typically has a cover plate (also called a cover glass) that is transparent to the projected light exiting the unit. It is essential to prevent glare for the user of the view-viewing device caused by any sunlight reflections from the cover plate to the reflector plate, and from there to the user's eyes. This is usually achieved using an outer-cut, elliptically curved cover plate (so-called "geometric anti-reflective coating") that reflects sunlight entering the projection unit from the HUD beam path towards a light trap, also known as a mirror bank.

[0006] However, during HUD development, the ongoing challenge of integrating head-up displays that cover the largest possible viewing area (for a corresponding image or eyebox size) into the available installation space constantly arises. External requirements and constraints arising from the application of the head-up display often hinder the achievement of target parameters regarding image quality, size, and position. Particularly in vehicle applications, limitations of the available installation space often prevent the ideal arrangement of the optical elements. For example, increasing the desired image size and projection distance—while maintaining the same virtual image quality—generally requires a larger HUD, which contradicts the requirement for a compact design. The geometric anti-reflective coating of the cover lens, as described above, occupies a particularly large amount of installation space.Therefore, DE 10 2019 131 729 A1 proposes a significant reduction in the overall height of a cover plate in a windshield display device, such as a head-up display. This cover plate is designed to suppress interfering reflections in the displayed image. This reduction is achieved by placing a shielding grid with one or more planar grid elements arranged perpendicular or inclined to a surface of the cover plate directly above or near the cover plate. Ambient light incident on the cover plate can be reflected from its surface and then strike the side surfaces of the grid elements, which absorb the reflected ambient light. Thus, the side surfaces of the grid elements each act as a mirror bank for a corresponding reflective section of the cover plate. Because the individual grid elements are planar, i.e.,Designed in a lamellar form and aligned with the projection direction of the display device, these grid elements minimally affect the image quality and brightness of the projected image. Furthermore, their shading effect reduces the amount of ambient light reaching the cover plate. The grid elements are made of a flexible or elastic material that deforms reversibly when force is applied and returns to its original shape once the force is removed. This prevents damage to the grid structure upon contact and, due to its flexibility, poses no risk of injury. The grid elements can be made of rubber, elastomer, polyurethane, and / or polyethylene, or consist entirely of these materials.

[0007] The object of the present invention is to provide an alternative and / or improved projection unit for a field-of-view display device with regard to installation space, image quality and / or other aspects, which may be particularly suitable for use in a vehicle.

[0008] This problem is solved by a compact projection unit according to claim 1, as well as by a field-of-view display device containing this unit and a vehicle equipped therewith according to the dependent claims. Further embodiments are specified in the dependent claims. All further features and effects mentioned in the claims and the following description for the projection unit also apply to the field-of-view display device and the vehicle, and vice versa.

[0009] According to a first aspect, a compact (i.e., optimizable or optimized with regard to the required installation space) projection unit for a field-of-view display device is provided, which can be designed specifically for use in a vehicle. The field-of-view display device can, for example, be designed as a head-up display (HUD). The vehicle can be a motor vehicle, but also any other land, air, or water vehicle.

[0010] The projection unit has an image generator (also called a picture generating unit, or PGU) designed to produce a beam of light with the desired display content. In principle, any imaging technology is suitable for the image generator, such as a light-transmitting or light-emitting flat panel display, a projector-based image generator, or a waveguide-based display.

[0011] In the beam path of the light beam generated by the image sensor, an imaging and / or projection optic is provided, which may, for example (but is not limited to), include a concave mirror designed as a freeform mirror and / or other optical elements (such as lenses, prisms, concave mirrors, convex mirrors, or plane mirrors, etc.). Depending on the requirements of a specific application, the imaging and / or projection optic is designed for a predetermined optical function, such as image magnification and / or imaging effect and / or beam shaping and / or correction of other aberrations and / or beam deflection.Further along the beam path, a cover plate (also called a cover glass) is provided, designed to allow the resulting light beam to pass through. This protects the projection unit from external influences such as dust, moisture, aggressive substances, and mechanical stress, and can, for example, seal the otherwise light-tight outer housing of the projection unit. An outer surface of the cover plate, which serves as the exit surface for the light beam, is not planar but features predetermined refractive array structures, such as prism or lens array structures, with additional optical functionality (i.e., complementing the imaging and / or projection optics mentioned above).Further refractive array structures can be formed for the same purpose in an optical interface running within the cover plate and / or in a second surface of the cover plate facing the interior of the projection unit, which serves as the entry surface for the light beam. Simultaneously, the cover plate is designed to correct any associated chromatic aberrations by means of a suitable achromatic (i.e., nearly dispersion-free) design.

[0012] For this purpose, the cover plate comprises at least two successive material layers in the direction of beam propagation, bonded together across their entire surface (for example, but not necessarily by optical bonding), with such different refractive indices or dispersion properties and each layer featuring refractive array structures on one or both sides, such that the resulting composite material exhibits the aforementioned additional optical functionality and is virtually dispersion-free. In other words, the chromatic aberrations associated with refractive optical array structures are specifically minimized by a suitable material combination (i.e., by suitable differences in the refractive indices or dispersion properties of the individual material layers).The interconnected interfaces (referred to here as bonding surfaces) of the respective successive material layers can, in particular, form a common transition surface. Alternatively, an adhesive layer, etc., with the same refractive index as one of the two material layers can be used to bond them.

[0013] The geometry of the inlet, outlet, and bonding surfaces is determined, firstly, to achieve the aforementioned additional optical functionality of the cover plate, thus minimizing the installation space and / or serving another purpose. As already mentioned, this can be achieved through a corresponding design of the refractive array structures. Simultaneously, the relative orientation of the inlet, outlet, and bonding surfaces is chosen to correct chromatic aberrations by compensating for the dispersion-induced scattering of light rays of individual wavelengths in one of these material layers through the dispersion effect of the other material layer(s).

[0014] The arrangement and design of the image source, the imaging and / or projection optics, and the cover plate within the projection unit are such that the light beam leaves the projection unit in a predetermined shape and direction. It is then reflected by a typically (but not necessarily) semi-transparent reflective plate positioned within the user's field of vision, towards their eyebox. This reflection presents the user with the display content as a real or virtual image, suspended in the air in their direct field of vision, either in front of or behind this reflective plate, in a predetermined shape, size, and distance. A virtual image can be generated at virtually any distance beyond the reflective plate, determined by a suitably designed projection optic.Here, the image distance can be chosen, for example, to minimize the need for accommodation while simultaneously observing the road ahead through the semi-transparent reflecting disc. Unlike a virtual image, a floating, real image is actually generated by suitable imaging optics at the exact position in the beam path (between the reflecting disc and the eyebox) where it is seen. At this point in space, it can therefore be captured, for example, by light-sensitive material or made visible to everyone by a light-diffusing surface. A significantly shorter image distance compared to virtual image generation can be more suitable for reading, for instance.A real image suspended in the air can also have a number of advantages over a conventional light-scattering projection surface, such as visibility only from a limited area (eyebox) or a freely selectable image distance and orientation in the air, which would not be possible with hard screens or scattering surfaces in a vehicle due to the required freedom of movement for the occupants.

[0015] The reflective disc can be formed, for example, by a section of a vehicle windshield, or alternatively by a dedicated combiner disc. The reflective disc is thus a component of the overall field-of-view display device, but not necessarily a component of the projection unit, which can generally be manufactured and sold without it. A combiner disc can also be integrated into the projection unit in a known manner (e.g., retractable). As is customary, the eyebox of the field-of-view display device is understood to be a two- or three-dimensional area in space from which the displayed image is visible in the intended quality.

[0016] The refractive array structures formed in the cover plate (i.e., in one or both of its surfaces and, if applicable, also within the cover plate) can be designed for one or more of the following additional optical functions: an optical imaging effect; an image magnification; a widening of a beam cross-section for eyebox enlargement; an error correction of other optical elements of the field-of-view display device (for example, a vehicle windshield); and / or a sun glare suppression, such as the geometric anti-reflection coating of the exit surface of the cover plate mentioned at the beginning.Each of these additional functions can contribute to a significant reduction in the installation space required for the projection unit while maintaining or improving the optical functionality of the field-of-view display device. This is achieved by eliminating or significantly reducing the size of conventional components of the imaging and / or projection optics or the cover plate that incorporate this functionality. To minimize the thickness (i.e., extent in the beam propagation direction) of the cover plate with this optical functionality, a one- or two-dimensional planar arrangement of lenses, prisms, or other refractive optical elements with this functionality in regular or irregular array structures is used (similar to the Fresnel lens principle).

[0017] The material layer located on the outside of the projection unit (i.e., directly facing the reflection disc during operation), in whose light-emitting surface one of the refractive array structures is formed, consists entirely or at least partially of such an elastic material that it deforms reversibly under mechanical forces that may occur or are common in the upper surface of a vehicle's instrument panel and returns completely to its original geometric shape after the force is removed.The aforementioned elastic deformation range of the outer material layer of the cover plate can therefore apply, among other things, to forces such as mechanical pressure or impact, which can occur, for example, from dusting or placing or throwing a notepad, document folder, key ring, or similar personal items onto the instrument panel. Furthermore, this also includes, for example, unintentional contact with a hand or other everyday objects that may be placed on the instrument panel of a vehicle during operation.

[0018] One idea behind the projection unit presented here is, firstly, to reduce the installation space by specifically implementing additional optical functions in its cover plate using refractive, for example, lens-like prism-like array structures, while simultaneously correcting chromatic aberrations that accompany refractive array structures due to the dispersive properties of the cover plate material. This correction is achieved through a suitable achromatic cover plate design based on two or more layers, each made of a different material and with a suitable geometry. Without an achromatic design, the projection unit described here (unlike a simple display, where a microlens, etc., is used) would not be able to achieve the same results.While a structured cover plate can rest directly on the display surface without causing aberrations, chromatic aberrations caused by a refractively structured cover plate with commonly used cover plate materials (such as PMMA or polycarbonate) and ordinary LED light sources in the image sensor can lead to a clearly visible color shift of the virtual (or even real) image between wavelengths in the visible spectral range. To enable superposition of the displayed images of the individual wavelengths, the use of sufficiently narrowband light sources in the image sensor, such as lasers, would therefore be necessary. However, this would in turn be associated with disadvantages such as significantly higher costs and design effort, e.g., for de-specking the laser light source.In contrast, the achromatic design of the cover plate proposed here makes it possible to utilize the additional optical functionality of the refractive array structures while simultaneously using broadband light sources, such as conventional light-emitting diodes (LEDs), in the image generator.

[0019] A suitable material combination for the upper and lower array structures allows for the creation of a virtually dispersion-free cover glass. However, the materials that would be particularly well-suited for this purpose from an optical perspective (such as cycloolefin polymer, COP, or polycarbonate, PC) are generally hard and sometimes even brittle (within the typical operating temperature range for a vehicle). The edges of the refractive array structures on the upper surface of the cover glass are, due to their location on the vehicle's instrument panel, in a very exposed position. Careless handling (e.g., an object being thrown onto the cover glass) can easily damage the edges of prisms or other refractive structures, leading to edge rounding and thus increased light scattering at the rounded edges. This can significantly impair the image quality of the infrared display.

[0020] By using an elastic material for the outer (or upper) refractive structures, a durability of the cover glass can be ensured that would not be achievable with hard, brittle materials for the upper prisms and other structures. Optical silicone is a suitable example, as explained in more detail below. Since not only the optical transparency and mechanical elasticity, but also the refractive index and Abbe number must exhibit suitable and stably reproducible values ​​across the entire operating range of the display device to achieve the dispersion-free properties and additional optical functionality described herein, not every transparent and elastic material, such as many different types of synthetic resin, is readily suitable.The elastic properties make the cover glass significantly less sensitive to misuse than the version with inelastic prisms and other refractive structures on the top side, since the individual prisms and other refractive elements can react to external influences through reversible deformation and do not immediately break off parts of them.

[0021] In a specific configuration, the elastically deformable material of the outer layer of the cover plate is optical silicone. Optical silicone is also known as "high-transparency silicone" or "liquid silicone rubber (LSR)." This material is characterized by exceptional durability and robustness in use, as well as well-defined and reliably reproducible optical and mechanical properties: among others, its high optical transparency, its refractive index and associated Abbe number suitable for the functionality presented here, and its high mechanical elasticity with reliable temperature resistance across the entire temperature range relevant to a vehicle. Furthermore, it offers excellent manufacturing properties such as injection molding or compression molding, making it ideally suited for the cost-effective production of the refractive array structures required.

[0022] One difficulty in using optical silicone, however, is the limited (or almost non-existent) selection / diversity regarding its optical properties, such as the refractive index and the Abbe number. For example, if one already has an application-specific optical function that must be implemented in the coverslip, and attempts to achieve this with optical silicone for the upper layer, then, for a solution approach sketched in Fig. 3 with simple triangular prism structures in the entrance and exit surfaces of the coverslip and only two layers, one would rarely find a suitable material for the lower layer that would allow for a coverslip with good dispersion properties.One possible solution to this problem is to introduce at least one additional material layer and / or refractively structured surface into the beam path of the cover plate. This corresponds to at least one optical interface with an additional independent angle of incidence and therefore at least one additional degree of freedom for wavelength-dependent beam deflection. Alternatively or additionally, the total internal reflection at one of the flanks of the refractive array structures can be used to optimize light deflection and solve the same problem. Again, alternatively or additionally, to improve mechanical stability, a glass plate can be placed between the upper, elastic material layer and the lower material layer, which could be made of polycarbonate (PC), for example. Polycarbonate is just one example material for the lower layer.A different material can also be chosen, which would then lead to new angles at the optically relevant edges. One possible embodiment, which uses all these additional solutions simultaneously, is shown in Figures 5 and 6. However, this is by no means limiting; that is, each of these solutions can also be used individually or in different combinations to achieve the goal presented here: According to one embodiment, the achromatic cover plate comprises a total of three or more material layers, arranged successively in the direction of beam propagation and bonded together across their entire surface, each with different refractive indices. In this case, each of these material layers can, but does not necessarily have to, be designed with refractive array structures on one or both sides.For example, one of the layers may also have planar or curved sides without refractive array structures and contribute only to mechanical stabilization and / or beam deflection and / or cancellation of the dispersion effect of the cover plate.

[0023] In this process, a material layer located between two other material layers in the direction of beam propagation (i.e., the inner material layer in the aforementioned material composite) can consist entirely or partially of a material that provides mechanical stability to the entire cover plate, such as glass or a solid or hard plastic. In this way, for example, the overall thickness of the cover plate can be significantly reduced while maintaining the same mechanical stability. Furthermore, considerably less hard / solid materials can then be used for other material layers, thus expanding the material selection options with regard to suitable dispersion properties and their processability for the fabrication of the required refractive array structures.

[0024] According to one embodiment, at least one of the refractive array structures is designed to deflect the light beam by internal total internal reflection at some of its surfaces bordering air. To achieve suitable coupling and total internal reflection angles for these refractive array structures, their refractive optical elements can, for example, have a trapezoidal or other cross-section with more than three corners in the plane of incidence (see, for example, Figures 5-6). This allows, for instance, the beam path and / or its beam cross-section within the projection unit to be made even more compact. Furthermore, such a beam path offers additional design freedom for the refractive array structures and the resulting light beam.

[0025] The at least two material layers can be geometrically complementary to each other at their interconnected interfaces, although this is not strictly necessary if they do not form a common (i.e., single) transition surface. Depending on the specific material choice and the geometry of the interfaces, both approaches can have advantages and disadvantages.

[0026] One or two bonding surfaces, or the resulting common transition surface, can be planar, which can be simpler and therefore more cost-effective for manufacturing the cover plate and optical bonding. Alternatively, at least one or two bonding surfaces, or the resulting common transition surface, can themselves be designed as refractive array structures. These contribute to the aforementioned additional optical functionality of the cover plate and / or to the correction of chromatic aberrations, thus creating additional degrees of freedom for optimizing the optical performance and spatial compactness of the projection unit.In particular, this allows for the replacement of additional refractive elements within the projection unit (i.e., in its imaging and / or projection optics), the use of which would otherwise lead to additional complexity regarding tolerances and alignment: Unlike separately manufactured optical elements and the associated alignment effort, the individual structured material layers in the cover plate are firmly bonded together, thus preserving their mutual alignment. The formation of a common transition surface can further simplify the alignment. For example, in the projection unit presented here, solar reflection suppression can also be achieved by a section of the cover plate's entrance and / or exit surface that is designed to be light-absorbing.For example, refractive array structures formed in the entrance and / or exit surface of the cover plate can be designed to absorb light on the part of their surface that faces the sun and is not usable for the transmission of the light beam anyway (see a simulation shown in Fig. 3) in order to minimize solar reflections on the cover plate.

[0027] According to another aspect, the above-mentioned field-of-view display device is provided. As already mentioned, the field-of-view display device comprises, in addition to the projection unit presented herein, a reflective disc arranged in the beam path of the light beam emitted by the projection unit, which is designed in particular as a partial surface section of a windshield of the vehicle or as a specially provided combiner disc and may, for example, be at least partially transparent.The reflective disc is positioned and designed in the user's field of vision in such a way that it reflects the beam of light rays to an eyebox predetermined for his eyes, thereby making the display content visible to him in the form of a virtual image beyond the reflective disc (or, in an alternative optical setup, in the form of a real image suspended in the air between the reflective disc and the eyebox) and actually displaying it during operation of the field-of-vision display device.

[0028] According to another aspect, the vehicle described above is designed. The vehicle comprises a passenger compartment and a vehicle window that at least partially delimits it, in particular a windshield. Furthermore, the vehicle includes the aforementioned field-of-view display device, the projection unit of which is located in the passenger compartment, in particular inside an instrument panel positioned below the windshield, and the reflector of which is designed as a section of the aforementioned vehicle window or as a combiner lens located in the passenger compartment. When used in the vehicle, and unless otherwise specified, spatial orientation terms such as "vertical," "horizontal," "below," "above," etc., always refer to the standard vehicle-mounted Cartesian coordinate system with mutually perpendicular longitudinal, transverse, and vertical directions of the vehicle.

[0029] The above aspects of the invention and its embodiments and specific configurations are explained in more detail below with reference to the examples shown in the accompanying drawings. For the sake of clarity, in the various examples, not only identical but also differently configured elements of the same type are designated with the same reference numerals. The drawings are to be understood as purely schematic illustrations of the basic optical principle, i.e., in particular, not to scale. They show, each in a vertical longitudinal section:

[0030] Figure 1 shows a vehicle with a field-of-view display device according to an embodiment of the invention;

[0031] Figure 2 shows an enlarged section of Fig. 1, which shows the achromatic structure of a cover plate with two optically bonded material layers with different dispersions and with prism array structures on their entry, exit and transition surfaces;

[0032] Figure 3 shows a simulation result for an alternative embodiment of an achromatic cover plate to Fig. 2, in which the two material layers are optically bonded along a planar transition surface and prism array structures are formed only on the entry and exit surfaces;

[0033] Figure 4 shows an alternative embodiment to Fig. 2 of an achromatic cover plate, which is composed of two optically bonded material layers with different dispersions and has lens array structures on its entry, exit and transition surfaces;

[0034] Figure 5 shows a further embodiment of an achromatic cover plate, which has a mechanically stabilizing glass layer between two structured plastic layers, wherein the array structures of the lower material layer serve to deflect the projection light by internal total internal reflection; and

[0035] Figure 6 shows an enlarged section of Fig. 5, which shows the beam guidance in the lower material layer.

[0036] All the various embodiments, variants and specific design features of the projection unit mentioned above in the description and the following claims, the

[0037] The field-of-view display device and the vehicle according to the above aspects of the invention can be implemented in the examples shown in Figures 1 to 6, in particular also alternatively or additionally to the features shown therein. Therefore, they are not all repeated below. The same applies accordingly to the definitions of terms and effects already given above with regard to individual features shown in Figures 1-6.

[0038] Fig. 1 shows in a highly simplified schematic longitudinal section an embodiment of a vehicle 1 with a view-field display device 2 presented herein, which is designed to generate a virtual image V floating outside the vehicle 1 at some distance from its windscreen 3 in the view-field of a user B, who may for example be a driver or passenger of the vehicle 1.

[0039] In this example, vehicle 1 is a motor vehicle, indicated in Fig. 1 only by its windshield 3, which serves as the aforementioned reflective lens for the field-of-view display device 2. Below this, a projection unit 5 of the field-of-view display device 2 is arranged in an instrument panel 4 (not shown in detail). This is, again purely by way of example, a head-up display (HUD). As already mentioned, unless otherwise stated, spatial orientation terms such as "horizontal," "vertical," "upper," "lower," "below," etc., refer to the usual vehicle-fixed Cartesian coordinate system K with mutually perpendicular longitudinal, transverse, and vertical directions X, Y, and Z of vehicle 1.

[0040] The projection unit 5 includes an image sensor 6, which is designed to generate a beam of light rays L (hereinafter also referred to as "projection light") with a desired display content and can, for example, be configured as an LCD (liquid crystal display). The beam of light rays L is greatly simplified in Fig. 1 and indicated solely by its marginal rays. In the path of the beam of light rays L generated by the image sensor 6, the projection unit 5 further comprises imaging and / or projection optics, in this example in the form of a concave mirror 7. The projection unit 5 can, for example, be surrounded by a mechanically protective housing (not shown), which is closed towards the front glass 3 by a cover glass 8 (hereinafter also referred to as a cover plate).The cover plate 8 is largely transparent to the light beam L and can, for example, be arranged flush or recessed in a top surface of the instrument panel 4 (not shown in detail).

[0041] To reduce the installation space required for the projection unit 5, prism array structures 9, 10, and 11 (see enlarged view in Fig. 2) with predetermined optical functionality are formed in the cover plate 8, which is generally flat (and therefore has a small overall dimension in the vertical direction Z of the vehicle 1). The cover plate 8 is thus not only designed to prevent soiling of the projection unit 5 and to prevent solar reflections S. In the example schematically sketched in Fig. 1, the spatial extent of the entrance beam volume can be minimized for a given eyebox size by a suitable selection of the prism angles of the array structures 9-11 (such an expansion of the beam cross-section by the cover plate 8 is clearly visible, for example, in the simulation in Fig. 3).Consequently, by appropriately selecting the prism angles, the effective mirror surface of the concave mirror 7 and thus the necessary size of the projection unit 5 can be minimized. Furthermore, absorptive materials 12 can be applied to the sun-facing sides of the prisms formed in the entrance side 17 and / or exit side 18 that are not required for the emerging light beam L, in order to minimize solar reflections S (see Figs. 1 and 2).

[0042] To correct chromatic aberrations of individual prism array structures, the cover plate 8 in Fig. 1 is composed of two material layers 14 and 15 with different refractive indices, which are optically bonded at a transition surface 16. In this example, a first prism array structure 9 is formed in an entrance surface 17, a second prism array structure 10 in an exit surface 18, and an optional third prism array structure 11 in the transition surface 16 of the cover plate 8. By a suitable combination of these three array structures and materials, the chromatic aberration can be specifically minimized, as illustrated in Fig. 2 using the example of a single polychromatic projection light beam P, while simultaneously maintaining the desired optical function and reflection suppression. Fig. 1 shows, purely by way of example, a variation of the respective array structures 9-11 in the x-direction (longitudinal direction of the vehicle 1).A variation of the individual array structures in the y-direction (transverse direction of vehicle 1) is also possible. The array structures can be regular or irregular.

[0043] The image transmitter 6, the concave mirror 7 and the cover plate 8 are designed and arranged relative to each other in such a way that the light beam L leaves the projection unit 5 in a suitable shape and direction, in order to be reflected by the reflection plate (here windscreen 3) to an eyebox E predetermined for the eyes of the user B in the passenger compartment of the vehicle 1 and thereby present the display content to the user B as a virtual image V with desired properties.

[0044] In this example, the entire outer material layer 14, and thus also the upper prism array structures 10, is made of an elastic material. Optical silicone is a suitable example. The elastic properties make the cover glass 8 significantly less susceptible to damage than in the version with inelastic prisms on the top of the projection unit 5, since the individual prisms can react to external forces through reversible deformation and do not immediately break off pieces if, for example, a hard object (such as a key or a notepad) is thrown onto the instrument panel 4. The lower material layer 15 can, for example, be made of polycarbonate.

[0045] Using an elastic material for the exposed upper prism array structures 10 allows for a significantly higher durability of the cover glass 8. This significantly reduces warranty costs compared to a brittle material variant.

[0046] Fig. 2 shows an enlarged section of Fig. 1, which depicts only the achromatic cover glass 8 (greatly simplified and schematic), designed in this embodiment as a prismatic cover glass made of two materials. In other words, the cover glass 8 represents a combination of two prismatic cover glasses bonded along the transition surface 16 with adapted prism angles and suitable materials. The prism angles of the entrance, transition, and exit surfaces 17 / 16 / 18 of the cover glass 8 are selected in each specific application to achieve a desired additional optical function, to enable the suppression of solar reflections by means of absorptive structures or materials 12, and to achieve compensation of chromatic aberrations. In this example, the image sensor 6 (see Fig. 1) generates the light beam L with polychromatic, for example, white, light.As illustrated by the example of a single polychromatic light ray P (greatly simplified and magnified), the dispersion-induced fanning of the light rays G (green) and R (red) of individual wavelengths within the cover plate 8 is compensated for by the dispersion effect of the second material layer 14. This occurs because the light rays G and R emerging from the cover plate 8 are oriented (here almost parallel) to each other in such a way that they overlap at a single point in the virtual image V, as perceived by the user B. For the sake of clarity, only two different spectral colors (green and red) are shown.

[0047] Fig. 3 shows a longitudinal section view similar to Fig. 2, simulating an achromatic prism cover plate 8 according to a further embodiment. To avoid repetition, only the differences and additional details compared to Figs. 1 and 2 are explained. In this simulation example, the cover plate 8 also consists of two suitably chosen materials with different refractive indices. The bonding or transition surface 16 is planar in this example, which can simplify optical bonding in particular. Accordingly, in this example, prism array structures 9 and 10 are formed only on the entrance surface 17 and the exit surface 18 of the cover plate 8. As can be clearly seen in the simulation result (see the respective beam diameters Q2 > Q1 of the light beam L before and after passing through the cover plate 8), their prism angles ensure a spatial minimization of the beam volume on the beam entrance side (in Fig.3 (bottom) opposite the beam exit side (top in Fig. 3), thereby minimizing the footprint on the concave mirror 7 (see Fig. 1) and thus significantly reducing the installation space required for the projection unit 5. Similar to Fig. 2, this combination simultaneously corrects chromatic aberration, enabling the use of broadband light sources in the PGU (image generator 6, see Fig. 1). However, depending on the selected prism angles of the entry and exit surfaces 17 and 18, the bonding or transition surface 16 can also be more general.

[0048] adopt array surface structures, i.e., not simply be planar as in Fig. 3.

[0049] Furthermore, in this example, solar reflections can also be prevented by absorptive surfaces 12 on those prism surfaces of the exit surface 18 and the entrance surface 17 that are not used for the transmission of the light beam L. As can be seen from the simulation, only some prism surfaces 19 are used for the transmission of the light beam L. As can also be seen from the simulation, at each of the optical interfaces formed by these prism surfaces 19 of the entrance and exit surfaces 17 / 18 as well as by the transition surface 16, a large proportion of the projected light L is transmitted (the respective marginal rays are marked by solid lines) and a negligible small proportion is reflected (the respective marginal rays are marked by dashed lines).

[0050] As greatly simplified in Fig. 4, a longitudinal section view similar to Fig. 2, the principle from the preceding implementation possibilities can be extended by designing the cover glass 8 such that the entrance, exit, and bonding surfaces 17, 18, and 16 can assume any function, in this example, such as optical lens arrays. The resulting lens surfaces are designed to implement a desired optical function (such as minimizing installation space, correcting aberrations, imaging effect, etc.) and, again, to achieve reflection suppression through light-absorbing surfaces 12. The surfaces of the respective arrays 9, 10, and 11 can be arranged regularly or irregularly and vary along the x and y directions. Furthermore, similar principles apply here as in Figs. 2 and 3, to whose description reference is made to avoid repetition.

[0051] As greatly simplified in Fig. 5, a longitudinal section similar to Fig. 2, illustrates the principle from the preceding implementation possibilities by additionally including a third, internal material layer 20 of a third material with suitable mechanical and optical properties in the cover glass 8. As mentioned above, in the previous examples, using optical silicone for the upper material layer 14 can be problematic due to the limited selection / diversity available with regard to its optical properties (refractive index and Abbe number). Therefore, if one has a fixed optical function and attempts to implement it using optical silicone for the upper material layer 14, it can be difficult to find a suitable material for the lower material layer 15 that would result in a cover glass 8 with good dispersion properties.One possible solution to this problem is to introduce a third material layer 20 into the beam path, the angle of inclination of which for the incoming and outgoing projection light L corresponds to a further degree of freedom for optical optimization.

[0052] One possible embodiment is shown in Fig. 5. To improve mechanical stability, a third material layer 20, such as a glass plate, can be placed between a silicone layer (upper material layer 14) and a polycarbonate layer (lower material layer 15). Furthermore, the total internal reflection at one of the air-facing flanks 22 of the lower prism structure 9 is utilized to optimize light deflection. The individual prisms, shown here as an example, have a trapezoidal cross-section, so that their lower sides 21 serve to couple in the projected light L. However, polycarbonate is only one example material for the lower prisms. Other materials can be chosen, which would then lead to new angles at the optically relevant flanks.

[0053] Fig. 6 shows an enlarged section 23 of Fig. 5, which further magnifies the beam path in the lower material layer 15. Reference numeral list

[0054] 1 vehicle

[0055] 2. Viewing field indicator device

[0056] 3 Windscreen

[0057] 4 Instrument panel

[0058] 5 projection units

[0059] 6 image sensors

[0060] 7 Concave mirrors

[0061] 8 achromatic cover plate / cover glass

[0062] 9, 10, 11 Prism or lens or other refractive array structures

[0063] 12 absorptive structures or materials

[0064] 14, 15, 20 material layers, each with different refractive indices

[0065] 16. Connecting or transition area

[0066] 17 Entrance surface of the cover plate

[0067] 18 Exit surface of the cover plate

[0068] 19 prism or lens surfaces involved in the transmission of the projected light

[0069] 20 third, inner material layer in the material composite

[0070] 21 light coupling sides of trapezoidal prism structures

[0071] 22 flanks of the trapezoidal prism structures used for internal total reflection

[0072] 23 Excerpt

[0073] B Users

[0074] L Light beam

[0075] E Eyebox

[0076] V virtual image

[0077] P single polychromatic projection light beam

[0078] G, R Light rays of individual wavelengths

[0079] Q1 Beam diameter of the light beam before passing through the cover plate Q2 Beam diameter of the light beam after passing through the cover plate

[0080] K vehicle-fixed Cartesian coordinate system

[0081] X, Y, Z Longitudinal, transverse and vertical directions of the vehicle

[0082] Sun reflections or sunlight

Claims

Claims 1. Compact projection unit (5) for a vehicle (1), comprising: an image generator (6) designed to generate a light beam (L) with the desired display content; an imaging and / or projection optic arranged in the beam path of the generated light beam (L); and an achromatic cover plate (8) that is essentially transparent to the resulting light beam (L) and protects the projection unit (5) from the outside, comprising at least two successive material layers (14, 15, 20) bonded together over their entire surface in the direction of beam propagation, each with such different refractive indices and each with refractive array structures (9, 10, 11) formed on one or both sides, such that the resulting material composite has a predetermined additional optical functionality and is essentially dispersion-free;such that the light beam (L) leaves the projection unit (5) in a predetermined shape and direction, in order to be subsequently reflected by a reflective disk arranged in the field of vision of a user (B) to his eyebox (E) and thereby to present the display content to the user (B) as a real or virtual image (V) floating in the air in a predetermined shape, size and distance; wherein the outer material layer (14), in whose exit surface (18) one of the refractive array structures (10) is formed, is made entirely or at least partially of such an elastic material that it deviates under mechanical forces acting on an upper surface area of ​​an instrument panel (4) of a; vehicle (1) are in use, are reversibly deformed and fully return to their original shape after the force is removed.

2. Projection unit (5) according to claim 1, wherein the elastically deformable material of the outer material layer (14) of the cover plate (8) is optical silicone.

3. Projection unit (5) according to claim 1 or 2, wherein the achromatic cover plate (8) comprises a total of three or more material layers (14, 15, 20) successive in the direction of beam propagation and connected to each other over their entire surface, each with different refractive indices, wherein at least two of these material layers (14, 15) each have refractive array structures (9, 10, 11) formed on one or both sides.

4. Projection unit (5) according to claim 3, wherein a material layer (20) lying in the direction of beam propagation between two other material layers (14, 15) consists entirely or partially of a solid or hard material that provides mechanical stability to the entire cover plate (8).

5. Projection unit (5) according to one of the preceding claims, wherein at least one of the refractive array structures (9, 10, 11 ) is configured to deflect the light beam (L) by total internal reflection at some of its air-bound partial surfaces.

6. Projection unit (5) according to one of the preceding claims, wherein at least two of these material layers (14, 15, 20) are geometrically complementary to each other at their interconnected bonding surfaces; and / or at least one or two interconnected bonding surfaces of these material layers (14, 15, 20) or a common transition surface (16) formed therein is / are planar; and / or at least one or two interconnected bonding surfaces of these material layers (14, 15, 20) or a common transition surface (16) formed therein has / have refractive array structures (11) contributing to the said additional optical functionality.

7. Projection unit (5) according to one of the preceding claims, wherein the refractive array structures (9, 10, 11) formed in the cover plate (8) are designed for the following optical functionality: an imaging effect; and / or an image magnification; and / or a widening of a beam cross-section (Q1); and / or a correction of aberrations of other optical elements; and / or a suppression of sunlight reflections (S) on the cover plate (8) or their deflection from the beam path of the light beam (L).

8. Projection unit (5) according to one of the preceding claims, in which refractive array structures (9, 10) formed in the inlet surface (17) and / or in the outlet surface (18) of the cover plate (8) are arranged on that part of its surface which is not the They serve to transmit the light beam (L), and are designed to absorb light.

9. Viewing display device (2) for use in a vehicle (1), comprising: a projection unit (5) according to one of the preceding claims; and a reflection disc, in particular at least partially transparent, arranged in the beam path of the light beam (L) emitted by the projection unit (5); wherein the reflection disc is arranged and designed in the field of vision of a user (B) such that it reflects the light beam (L) to an eyebox (E) predetermined for the eyes of the user (B), whereby the display content can be presented to him in the form of a virtual image (V) floating beyond the reflection disc or a real image floating between the reflection disc and the eyebox (E).

10. Vehicle (1), in particular a motor vehicle, with mutually perpendicular longitudinal, transverse and vertical directions (X, Y, Z) of a vehicle-fixed Cartesian coordinate system (K), comprising: an occupant compartment with a vehicle window that at least partially delimits the occupant compartment, in particular a windshield (3); and a view indicator device (2) according to claim 9, the projection unit (5) of which is arranged in the occupant compartment, in particular inside an instrument panel (4) arranged below the windshield (3), and the reflection disc of which is designed as a section of the said vehicle window or as a combiner disc arranged in the occupant compartment.

Images