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

Abstract

The invention relates to a compact projection unit for a vehicle. This comprises an imager, imaging and / or projection optics, and an achromatic cover plate that is transparent to the resulting light beam and protects the projection unit from the outside. Refractive array structures with additional optical functionality are formed on the entrance and / or exit surfaces of the cover plate. Such that the light beam leaves the projection unit in a predetermined shape and direction, is subsequently reflected by a partially transparent reflection plate arranged in the user's field of vision to their eyebox, thereby presenting the display content to the user as a real or virtual image floating in the air in a predetermined shape, size, and distance.The achromatic cover plate design comprises at least two material layers which are consecutive in the beam propagation direction and are connected to one another over their entire surface, having refractive indices which differ from one another in a suitable manner and each having refractive array structures formed on one or both sides, wherein the outer material layer has one of these array structures on the outside which is elastically deformable.

Description

[0001] The invention relates to a head-up display device for a motor vehicle or other land, air, or water vehicle, also known as a head-up display (HUD). Such devices generally serve to project a virtual image directly into a user's field of vision by reflecting a light beam off a partially transparent reflective screen, such as a vehicle window or a specially provided combiner screen arranged in the user's field of vision. The invention also relates to a projection unit configured to output a suitable light beam with the desired display content, as well as to a vehicle equipped therewith.

[0002] Field-of-view display devices, such as head-up displays, for visually displaying information in the field of vision of a motor vehicle driver or pilot are known from the prior art. For example, the document DE 10 2010 032 998 A1 describes a head-up display for a motor vehicle with a projection unit, via which an image to be displayed is projected through a cover plate onto a windshield of a motor 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 look away from the traffic situation to view important information, such as the current vehicle speed or visual instructions from a navigation system.

[0003] Typically, an imaging and / or projection lens (typically a mirror lens) housed in the projection unit ensures that the virtual image is displayed at the desired distance, size, and quality, and can be viewed from a spatial area (eyebox) in the vehicle specifically designed for the user's eyes. This widely used HUD design is also known as a mirror HUD.

[0004] 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 projection light emerging from the projection unit. This is necessary to prevent glare for a user of the field of view display device caused by any sunlight reflected from the cover plate to the reflection plate, and from there to the user's eyes. Typically, a cover plate with an elliptical curve on the outside (so-called "geometric anti-reflection coating") is used for this purpose. This reflects sunlight incident on the projection unit from the outside of the HUD beam path toward a light trap, also called a mirror bank.

[0005] However, during HUD development, the problem of integrating head-up displays, which are intended to cover the largest possible field of view (for a corresponding image or eyebox size), into the available installation space continually arises. External requirements and constraints arising from the area of ​​application of the head-up display often hinder the achievement of the target parameters regarding image quality, size, and position. Particularly when used in a vehicle, limitations of the available installation space often prevent the optical elements from being ideally arranged. For example, a desired increase in image size and projection distance—while maintaining the same quality of the virtual image—generally requires an increase in the HUD size, which contradicts the requirement for a small installation space.

[0006] The above geometric anti-reflective coating of the cover plate takes up a particularly large amount of installation space. Therefore, DE 10 2019 131 729 A1 proposes, in a windscreen display device, such as a head-up display, to significantly reduce the overall height of a cover plate, which is designed to suppress interfering reflections in the display image, by arranging a shielding grid with one or more flat grid elements arranged perpendicularly or inclined to a surface of the cover plate directly above or near the cover plate. Ambient light falling on the cover plate can be reflected at its surface and then strike the side surfaces of the grid elements, which absorb the ambient light thus reflected. Thus, the side surfaces of the grid elements each serve as a mirror bank for a corresponding reflective section of the cover plate. Because the individual grid elements are flat, i.e.Lamellar, designed and aligned in the projection direction of the display device, they only minimally impair the display quality and brightness of the projected image and, through their shading effect, also reduce the proportion of ambient light that can hit 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 means that the grid structure is not damaged when touched and, thanks to its flexibility, poses no risk of injury. The material of the grid elements can in particular comprise rubber, elastomer, polyurethane and / or polyethylene or consist entirely of these.

[0007] It is an object of the present invention 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 can be particularly suitable for use in a vehicle.

[0008] This object is achieved by a compact projection unit according to claim 1, as well as by a visual field display device containing the same, and a vehicle equipped therewith according to the independent 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 visual field display device and the vehicle, and vice versa.

[0009] According to a first aspect, a compact (i.e., one that can be optimized or is optimized with regard to the required installation space) projection unit is provided for a field of view display device, which can be designed in particular for use in a vehicle. The field of view display device can be configured, for example, 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 imager (also called a picture generating unit, PGU) designed to generate a light beam with the desired display content. In principle, any imaging technology is suitable for the imager, such as a light-transmitting or light-emitting flat panel display, a projector-based imager, or a waveguide-based display.

[0011] In the beam path of the light beam generated by the imager, imaging and / or projection optics are provided, which may include, for example (but not limited to), 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 optics are designed for a predetermined optical functionality, such as image magnification and / or imaging effect and / or beam shaping and / or correction of other imaging errors and / or beam deflection.

[0012] In the further beam path, a cover plate (also called a cover glass) is provided, designed to allow the resulting light beam to pass through. This cover plate protects the projection unit from external influences such as dust, moisture, aggressive substances, and mechanical forces. For this purpose, it can, for example, close an 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 rather has predetermined refractive array structures, such as prism or lens array structures, with additional optical functionality (i.e., supplementing the above imaging and / or projection optics).For the same purpose, additional refractive array structures can be formed in an optical interface extending within the cover plate and / or in a second surface of the cover plate facing the interior of the projection unit, which serves as an entrance surface for the light beam. At the same time, the cover plate is designed to correct associated chromatic aberrations through a suitable achromatic (i.e., virtually dispersion-free) design.

[0013] For this purpose, the cover plate comprises at least two material layers arranged consecutively in the beam propagation direction, bonded to one another over their entire surface (for example, but not necessarily by optical bonding), with different refractive indices or dispersion properties, and with refractive array structures formed on one or both sides in such a way that the resulting material composite has the aforementioned additional optical functionality while being 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 herein as composite surfaces) of the respective successive material layers can, in particular, form a common transition surface. Alternatively, however, an adhesive layer, etc., with the same refractive index as one of the two material layers can also be used to connect them.

[0014] The geometry of the entrance, exit, and composite surfaces is determined to achieve the aforementioned additional optical functionality of the cover plate to minimize installation space and / or for another purpose. As already mentioned, this can be achieved through a corresponding design of the refractive array structures. At the same time, the relative orientation of the entrance, exit, and composite surfaces is selected to correct chromatic aberrations by compensating for the dispersion-induced fanning out of light rays of individual wavelengths in one of these material layers by the dispersion effect of the other material layer(s).

[0015] The mutual arrangement and design of the image generator, the imaging and / or projection optics, and the cover plate in the projection unit are selected such that the light beam leaves the projection unit in a predetermined shape and direction, is then reflected back to the user's eyebox by a typically (but not necessarily) partially transparent reflection plate located in the user's field of vision, thereby presenting the display content to the user in the form of a real or virtual image, which floats in the air in front of or behind this reflection plate in their direct field of vision, in a predetermined shape, size, and distance. A virtual image can be generated at essentially any distance beyond the reflection plate, which is determined by appropriately designed projection optics.Here, for example, the image distance can be selected so that as little accommodation as possible is required while simultaneously observing the route ahead through the partially transparent reflective disc. In contrast to a virtual image, a floating real image is actually generated by suitable imaging optics at the position in the beam path (between the reflective disc and the eyebox) where it is seen. It can therefore be recorded at that point in space, for example, using light-sensitive material or made visible to everyone using a light-diffusing surface. A significantly shorter image distance compared to virtual image generation can, for example, be more suitable for reading.A real image floating in the air can also have a number of advantages over a conventional light-diffusing projection surface, such as visibility only from a limited spatial area (eyebox) or a constructively freely selectable image distance and image orientation in the air, which would not be possible with hard screens or diffusing surfaces in a vehicle due to the required freedom of movement for the occupants.

[0016] The reflection disc can, for example, be formed by a section of a vehicle window, but otherwise also by a combiner disc provided specifically for this purpose. The reflection disc is therefore a component of the overall field of view display device, but not necessarily also a component of the projection unit, which can generally be manufactured and sold without it. A combiner disc can, however, also be integrated into the projection unit in a conventional manner (e.g., retractable and extendable). The eyebox of the field of view display device is, as usual, understood to be a two- or three-dimensional spatial area from which the displayed image is visible in the intended quality.

[0017] The refractive array structures formed in the cover plate (i.e. in one or both of its surfaces and optionally 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; an expansion of a beam cross-section for eyebox magnification; an error correction of other optical elements of the field of view display device (for example a vehicle window); and / or a sun reflection suppression, for example similar to the geometric anti-reflection coating of the exit surface of the cover plate mentioned above.Each of these additional functions can contribute to a significant reduction in the installation space for the projection unit while maintaining or improving the optical functionality of the field-of-view display device. Conventional components of the imaging and / or projection optics or the cover plate with this functionality can be eliminated or designed or arranged in a significantly more compact manner. To minimize the thickness (i.e., the 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 here (similar to the Fresnel lens principle).

[0018] The material layer which is located on the outside with respect to the projection unit (i.e. directly facing the reflection disc during operation), in whose light exit surface one of the refractive array structures is formed, consists entirely or at least partially of such an elastic material that it is reversibly deformed when subjected to mechanical forces which can occur in an upper side area of ​​an instrument panel of a vehicle or are customary in use, and completely returns to its original geometric shape after the force has been removed.The elastic deformation range of the outer material layer of the cover panel 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.

[0019] One idea of ​​the projection unit presented here is, on the one hand, a reduction in installation space through the targeted implementation of additional optical functions in its cover plate using refractive array structures, for example, lens- or prism-like array structures, while simultaneously correcting chromatic aberrations, which are associated with refractive array structures due to the dispersive properties of the cover plate material, using 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 structure described here (unlike a simple display, where a lens system with microlenses, etc.) would require a smaller number of layers.structured cover plate can lie 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 conventional LED light sources in the imager lead to a clearly visible color shift of the virtual (or real) image between the wavelengths in the visible spectral range. In order to enable superposition of the displayed images of the individual wavelengths, the use of sufficiently narrowband light sources in the imager, 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-speckle the laser light source.The achromatic design of the cover plate proposed here, however, 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 imager.

[0020] By using a suitable combination of materials for the upper and lower array structures, a virtually dispersion-free cover glass can be achieved. 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 temperature range for a vehicle). However, the edges of the refractive array structures on the upper side of the cover glass are in a very exposed position due to their location on the vehicle's instrument panel. Careless handling (e.g., an object being thrown onto the cover glass) can easily damage the edges of prisms or other refractive structures, which then leads to rounded edges and thus to increased light scattering at the rounded edges. This can significantly impair the image quality of the HUD.

[0021] By constructing the outer (or upper) refractive structures from an elastic material, a durability of the cover glass can be ensured that would not be possible with hard, brittle materials for the upper prisms and other structures. Optical silicone is a suitable example of this, as explained in more detail below. Since not only the optical transparency and mechanical elasticity, but also the refractive index and the Abbe number must have suitable and stably reproducible values ​​across the entire application range of the display device for the dispersion-free and additional optical functionality described here, not every transparent and elastic material, such as many different types of synthetic resin, is automatically suitable.The elastic properties make the cover glass significantly less susceptible to misuse than in the version with inelastic prisms and other refractive structures on the top, since the individual prisms and other refractive elements can react to the external influence by reversibly deforming and do not immediately break off parts of them.

[0022] In one specific embodiment, the elastically deformable material of the outer material layer of the cover plate is optical silicone. Optical silicone is also known as "highly transparent silicone" or "liquid silicone rubber (LSR)." This material is characterized by its particularly long service life and robustness, as well as well-defined and reliably reproducible optical and mechanical properties: among other things, its high optical transparency, its refractive index and associated Abbe number suitable for the functionality presented here, as well as its high mechanical elasticity with reliable temperature resistance of all of these properties across the entire temperature range relevant to a vehicle. In addition, it has excellent manufacturing properties such as injection molding or molding capabilities, which are ideally suited for the cost-effective production of the refractive array structures required in this case.

[0023] However, one difficulty with the use of optical silicone is the limited (or almost nonexistent) choice / diversity with regard to its optical properties, such as the refractive index and the Abbe number. For example, if you already have an application-specific optical function that needs to be implemented in the cover glass and try to implement it with optical silicone for the upper material layer, you would, for example, Fig. 3, with simple triangular prism structures in the entrance and exit surfaces of the cover glass and only two material layers, it is rare to find a suitable material for the lower material layer that would allow for a cover glass with good dispersion properties. One possible solution to this problem is to place at least one additional material layer and / or refractively structured surface in the beam path of the cover glass, which 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 same problem can be solved by exploiting total internal reflection at one of the flanks of the refractive array structures to optimize light deflection.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 PC, for example. Polycarbonate is just one example material for the lower material layer. A different material could also be chosen, which would then lead to new angles on the optically relevant flanks. A possible embodiment that uses all of these additional approaches simultaneously, purely as an example, is shown in . Fig. 5 and Fig. 6. However, this is by no means limiting, i.e. each of these approaches can also lead to the goal presented here, individually or in a different combination: According to one embodiment, the achromatic cover plate comprises a total of three or more material layers that follow one another in the beam propagation direction and are connected to one another over their entire surface, each with different refractive indices. In this case, each of these material layers can, but does not necessarily have to, be formed with refractive array structures on one or both sides. For example, one of the layers can also have planar or curved sides without refractive array structures and merely contribute to mechanical stabilization and / or beam deflection and / or cancellation of the dispersion effect of the cover plate.

[0024] A material layer located between two other material layers in the beam propagation direction (i.e., the inner material layer in the aforementioned material composite) can consist entirely or partially of a material that imparts 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, significantly less hard / solid materials can then be used for other material layers, which increases the material selection with regard to suitable dispersion properties and their processability for producing the required refractive array structures.

[0025] According to one embodiment, at least one of the refractive array structures is designed to deflect the light beam by total internal reflection at some of its partial surfaces bordering on air. In order to achieve suitable coupling and total 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 light incidence plane (see purely exemplary embodiments). Fig. 5-6). This allows, for example, the beam path and / or its beam cross-section within the projection unit to be made even more compact. Furthermore, such a beam guidance offers additional design freedom for the refractive array structures and the resulting light beam bundle.

[0026] The at least two material layers can be geometrically complementary to each other at their interconnected surfaces, although this is not mandatory if they do not form a common (i.e., single) transition surface. Depending on the specific material selection and the geometry of the interconnected surfaces, both can have advantages and disadvantages.

[0027] One or two composite surfaces, or a common transition surface formed thereby, can in particular be planar, which can be simpler and thus more cost-effective, for example, for the production of the cover plate and for optical bonding. Alternatively, however, at least one or two composite surfaces, or a common transition surface formed thereby, can themselves be designed in the form of refractive array structures, which contribute to the aforementioned additional optical functionality of the cover plate and / or to the correction of chromatic aberrations and can thus create 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 in terms of tolerances and alignment: In contrast to separately formed optical elements and the associated alignment effort, the individual structured material layers in the cover plate are firmly connected to one another, which "preserves" their mutual alignment. Forming a common transition surface can further simplify alignment.

[0028] Sun reflection suppression can also be achieved in the projection unit presented here, for example, by a partially light-absorbing entrance and / or exit surface of the cover plate. For example, refractive array structures formed in the entrance and / or exit surface of the cover plate can be light-absorbing on that part of their surface that faces the sun and is therefore not usable for transmitting the light beam (cf. Fig. 3 simulation shown) to minimize solar reflections on the cover plate.

[0029] According to a further aspect, the above field of view display device is provided. As already mentioned, in addition to the projection unit presented herein, the field of view display device also comprises a reflection plate arranged in the beam path of the light beam emitted by the projection unit. This reflection plate can be configured, in particular, as a partial surface section of a windshield of the vehicle or a specially provided combiner plate and can be, for example, at least partially transparent.The reflection disc is arranged and designed in the field of vision of a user in such a way that it reflects the light beam to an eyebox predetermined for his eyes, whereby the display content can be presented to him in the form of a virtual image beyond the reflection disc (or, in an alternative optical design, in the form of a real image floating in the air between the reflection disc and the eyebox) and is also presented during operation of the field of vision display device.

[0030] According to a further aspect, the above vehicle is provided. The vehicle comprises a passenger compartment and a vehicle window that at least partially defines it, in particular a windshield. Furthermore, the above field of vision display device is provided in the vehicle, the projection unit of which is arranged in the passenger compartment, in particular inside an instrument panel arranged below the windshield, and the reflection disc of which is designed as a section of said vehicle window or as a combiner disc arranged in the passenger compartment. When used in the vehicle and unless otherwise stated, spatial orientation terms such as "vertical", "horizontal", "below", "above", etc. always refer to the usual vehicle-fixed Cartesian coordinate system with mutually perpendicular longitudinal, transverse, and vertical directions of the vehicle.

[0031] The above aspects of the invention and their embodiments and specific configurations are explained in more detail below with reference to examples illustrated in the accompanying drawings. For the sake of clarity, not only identical but also differently configured elements of the same type are designated by the same reference numerals in the various examples. The drawings are to be understood as purely schematic illustrations of the basic optical principle, i.e., in particular, they are not to scale. They show, in each case in a vertical longitudinal section: Fig. 1 shows a vehicle with a field of view display device according to an embodiment of the invention; Fig. 2 an enlarged section of the Fig. 1, which shows the achromatic structure of a cover plate with two optically bonded material layers with different dispersion and with prism array structures on its entrance, exit and transition surfaces; Fig. 3 a simulation result for a Fig. 2 alternative embodiment of an achromatic cover plate in which the two material layers are optically bonded along a planar transition surface and prism array structures are formed only on the entrance and exit surfaces; Fig. 4 one to Fig. 2 alternative embodiment of an achromatic cover plate composed of two optically bonded material layers with different dispersion and having lens array structures on its entrance, exit and transition surfaces; Fig. 5 shows a further embodiment of an achromatic cover plate having 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 total internal reflection; and Fig. 6 an enlarged section of the Fig. 5, which shows the beam guidance in the lower material layer.

[0032] All of the various embodiments, variants and specific design features of the projection unit, the field of view display device and the vehicle according to the above aspects of the invention mentioned above in the description and the following claims can be implemented in the Fig. 1 to 6, in particular alternatively or in addition to the features shown therein. Therefore, they will not be repeated again below. The same applies accordingly to the definitions and effects already given above with regard to individual features that are described in Fig. 1-6 are shown.

[0033] Fig. 1 shows, in a highly simplified schematic longitudinal sectional view, an embodiment of a vehicle 1 with a field of view 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 field of view of a user B, who may be, for example, a driver or passenger of the vehicle 1.

[0034] Vehicle 1 in this example is a motor vehicle that is Fig. 1 is only indicated by its windshield 3, which serves as the aforementioned reflection disc of the field of vision display device 2. Below it, in an instrument panel 4 (not shown in detail), a projection unit 5 of the field of vision display device 2 is arranged. This is, again purely by way of example, a head-up display (HUD). As already mentioned, the spatial orientation terms such as "horizontal," "vertical," "upper," "lower," "below," etc., unless otherwise stated, refer to the usual vehicle-fixed Cartesian coordinate system K with mutually perpendicular longitudinal, transverse, and vertical directions X, Y, and Z of the vehicle 1.

[0035] The projection unit 5 contains an image generator 6, which is designed to generate a light beam L (also referred to herein as “projection light”) with a desired display content and can be designed, for example, as an LCD (liquid crystal display). The light beam L is in Fig. 1 is greatly simplified and indicated only by its edge rays. In the beam path of the light beam L generated by the imager 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 off from the windscreen 3 by a cover plate 8 (also referred to herein as cover glass). The cover plate 8 is largely transparent to the light beam L and can, for example, be arranged flush or recessed in a top side of the instrument panel 4 (not shown in detail).

[0036] To reduce the installation space required for the projection unit 5, prism array structures 9, 10 and 11 (cf. enlarged view in Fig. 2) with predetermined optical functionality. The cover plate 8 is therefore not only designed to prevent soiling of the projection unit 5 and to prevent solar reflections S. In the Fig. 1 schematically sketched example, the spatial expansion of the entrance-side beam volume for a given eyebox size can be minimized by a suitable choice of the prism angles of the array structures 9-11 (such expansion of the beam cross-section through the cover glass 8 is, for example, in the simulation of the Fig. 3). Consequently, by a suitable choice of 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. On the sides of the prisms formed in the entrance side 17 and / or exit side 18 that are facing the sun and are not required for the exiting light beam L, absorptive materials 12 can also be applied, for example, in order to minimize solar reflections S (cf. Fig. 1 and Fig. 2).

[0037] In order to correct chromatic aberrations of individual prism array structures, Fig. 1, the cover plate 8 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 shown in Fig. 2 using the example of a single polychromatic projection light beam P, while maintaining the desired optical function and reflection suppression. In Fig. Figure 1 shows, purely by way of example, a variation of the respective array structure 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 the vehicle 1) is also possible. The array structures can be regular or irregular.

[0038] The image generator 6, the concave mirror 7 and the cover plate 8 are designed and arranged relative to one another in such a way that the light beam L leaves the projection unit 5 in a suitable shape and direction in order to be subsequently 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 thus to present the display content to the user B as a virtual image V with desired properties.

[0039] 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 misuse than in the version with inelastic prisms on the top of the projection unit 5, since the individual prisms can react to the external influence with reversible deformation and do not immediately break off parts of them if, for example, a hard object (such as a key or a writing pad) is thrown onto the instrument panel 4. The lower material layer 15 can be made of polycarbonate, for example.

[0040] Using an elastic material for the exposed upper prism array structures 10, a significantly higher durability of the cover glass 8 can be achieved. Thus, warranty costs can be significantly reduced compared to a brittle material variant.

[0041] Fig. 2 shows an enlarged section of the Fig. 1, which shows only the achromatic cover plate 8 (highly simplified and schematic), which in this embodiment is designed as a prism cover glass made of two materials. In other words, the cover plate 8 represents a combination of two prism 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 plate 8 are selected for each specific application such that a desired additional optical function is achieved, solar reflection suppression is enabled by absorptive structures or materials 12, and chromatic aberration compensation is achieved.

[0042] The image generator 6 (cf. Fig. 1) in this example generates the light beam L with polychromatic, for example white, light. As illustrated in a greatly simplified and enlarged manner using the example of a single polychromatic light beam P, the dispersion-induced fanning out of the light beams G (green) and R (red) of individual wavelengths in the first material layer 15 within the cover plate 8 is compensated for by the dispersion effect of the second material layer 14, in that the light beams G and R emerging from the cover plate 8 run to one another (here almost parallel) in such a way that they overlap at a point in the virtual image V as perceived by the user B. For reasons of clarity, only two different spectral colors (green and red) are shown.

[0043] Fig. 3 shows in a Fig. 2 similar longitudinal section view, a simulation of an achromatic prism cover plate 8 according to a further embodiment, wherein, to avoid repetition, only the differences or additional details compared to Fig. 1 and Fig. 2. In this simulation example, the cover plate 8 also consists of two suitably selected 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. Their prism angles ensure, as clearly visible in the simulation result (cf. the respective beam diameters Q2 > Q1 of the light beam L before and after passing the cover plate 8), a spatial minimization of the beam volume on the beam entrance side (in Fig. 3 below) opposite the beam exit side (in Fig. 3 above), which minimizes the footprint on the concave mirror 7 (cf. Fig. 1) and thus a considerable reduction in installation space for the projection unit 5 is achieved. The combination simultaneously achieves similar to Fig. 2 a correction of chromatic aberration, which allows the use of broadband light sources in the PGU (imager 6, cf. Fig. 1). However, depending on the selected prism angles of the entrance and exit surfaces 17 and 18, the composite or transition surface 16 can also assume more general array surface structures, ie not as in Fig. 3 simply be planar.

[0044] 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 to transmit the light beam L. As can be seen from the simulation, only some prism surfaces 19 are used to transmit 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 portion of the projection light L is transmitted (the respective edge rays are marked by solid lines) and a negligible portion is reflected (the respective edge rays are marked by dashed lines).

[0045] As in Fig. 4 in one to Fig. 2, the principle from the previous implementation options can be expanded by designing the cover glass 8 in such a way that the entrance, exit and compound surfaces 17, 18 and 16 can assume any desired functions, in this example such as optical lens arrays. The resulting lens surfaces are designed in such a way that, on the one hand, they implement a desired optical function (such as space minimization, correction of aberrations, imaging effect, etc.), and, on the other hand, reflection suppression can be achieved here by light-absorbing surfaces 12. The surfaces of the respective arrays 9, 10, 11 can be arranged regularly or irregularly and can vary along the x- and y-directions. Furthermore, something similar to that in Fig. 2 and Fig. 3 apply, to whose description reference is therefore made to avoid repetition.

[0046] As in Fig. 5 in one to Fig. 2, the principle from the previous implementation options can be expanded by the cover glass 8 additionally comprising a third material layer 20 located inside the material composite and made of a third material with suitable mechanical and optical properties. As mentioned above, in the previous examples, when using optical silicone for the upper material layer 14, it can be difficult because there is not a great deal of choice / diversity available with regard to its optical properties (refractive index and Abbe number). If one has a fixed optical function and attempts to implement this with optical silicone for the upper material layer 14, it can therefore 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 incidence of which for the incoming and outgoing projection light L corresponds to a further degree of freedom for the optical optimization.

[0047] A possible embodiment of this is in Fig. 5. At the same time, to improve mechanical stability, a glass plate, for example, can be placed between a silicone layer (upper material layer 14) and a polycarbonate layer (lower material layer 15) as a third material layer 20. Here, total internal reflection at one of the flanks 22 of the lower prism structure 9 bordering the air is also utilized to optimize light deflection. The individual prisms have, purely as an example, a trapezoidal cross-section, so that their lower sides 21 serve to couple in the projection light L. However, polycarbonate is only one example material for the lower prisms. A different material can also be chosen, which would then lead to new angles at the optically relevant flanks.

[0048] Fig. 6 shows an enlarged section 23 of the Fig.5, which shows the beam guidance in the lower material layer 15 again enlarged. List of reference symbols 1 vehicle 2 Field of view display device 3 Windscreen 4 Instrument panel 5 Projection unit 6 imagers 7 concave mirrors 8 achromatic cover plate / cover glass 9, 10, 11 Prism or lens or other refractive array structures 12 absorptive structures or materials 14, 15, 20 material layers, each with different refractive indices 16 Composite or transition surface 17 Entrance surface of the cover plate 18 Exit surface of the cover plate 19 prism or lens surfaces involved in the transmission of the projection light 20 third material layer inside the composite material 21 light coupling sides of trapezoidal prism structures 22 flanks of the trapezoidal prism structures used for total internal reflection 23 Excerpt B User L bundle of light rays E Eyebox V virtual image P single polychromatic projection light beam G, R Light rays of individual wavelengths Q1 Beam diameter of the light beam before passing the cover plate Q2 Beam diameter of the light beam after passing the cover plate K vehicle-fixed Cartesian coordinate system X, Y, Z longitudinal, transverse and height directions of the vehicle S Sun reflections or sunlight

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 optics arranged in the beam path of the generated light beam (L); and - an achromatic cover plate (8) which is essentially transparent to the resulting light beam (L) and protects the projection unit (5) from the outside, said cover plate comprising at least two material layers (14, 15, 20) which are successive in the direction of beam propagation and are connected to one another over their entire surface, each having such different refractive indices and each having refractive array structures (9, 10, 11) formed on one or both sides in such a way 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, to be subsequently reflected by a reflection disc 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 is reversibly deformed upon application of mechanical forces which are customary in an upper side region of an instrument panel (4) of a vehicle (1) and completely returns to its original shape after the application of the force has ceased. [2] Projection unit (5) according to claim 1, wherein - said 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) which are successive in the direction of beam propagation and are connected to one another over their entire surface and each have 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 between two other material layers (14, 15) in the direction of beam propagation consists entirely or partially of a solid or hard material which imparts 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 designed to deflect the light beam (L) by total internal reflection at some of its partial surfaces bordering on air. [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 one another at their interconnected surfaces; and / or - at least one or two interconnected composite surfaces of these material layers (14, 15, 20) or a common transition surface (16) formed thereby is / are planar; and / or - at least one or two interconnected composite surfaces of these material layers (14, 15, 20) or a common transition surface (16) formed thereby has / have refractive array structures (11) contributing to 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 enlargement; and / or - an expansion of a beam cross-section (Q1); and / or - correction of aberrations of other optical elements; and / or - 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 entrance surface (17) and / or in the exit surface (18) of the cover plate (8) are designed to be light-absorbing on that part of their surface which does not serve to transmit the light beam (L). [9] A field of view 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) in such a way 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 the user 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 height directions (X, Y, Z) of a vehicle-fixed Cartesian coordinate system (K), comprising: - a passenger compartment with a vehicle window which at least partially delimits the passenger compartment, in particular a windscreen (3); and - a field of view display device (2) according to claim 9, the projection unit (5) of which is arranged in the passenger compartment, in particular in the interior of an instrument panel (4) arranged under the windscreen (3), and the reflection disc of which is designed as a section of said vehicle window or as a combiner disc arranged in the passenger compartment.

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