Hud for a vehicle with an accurate and low-loss reflective screen in the projector-based imager
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-08
- Publication Date
- 2026-04-08
Smart Images
Figure DE2024100419_05122024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] HUP for a vehicle with an exact and low-loss reflecting screen in the projector-based imager
[0003] The invention relates to a projection unit for head-up display devices that can be used in motor vehicles or other land, air, or water vehicles and are also known as head-up displays (HUDs). They serve to generate a virtual image projected into a user's field of vision via reflection from a reflective screen, such as a windshield, rear window, or side window of the vehicle or a specially provided combiner screen. The invention also relates to a related manufacturing method and to the head-up display device, as well as to a vehicle equipped therewith.
[0004] With a head-up display in a motor vehicle, speed information and other useful navigation, warning, and vehicle operating information, or even entertainment content, are superimposed in the form of a virtual image onto the real image of the surroundings in front of the vehicle as observed by the driver and / or another passenger. To create a panoramic virtual display, a simplified HUD design is known, in which an image sensor is positioned directly opposite the windshield at the base of the windshield without any additional projection optics such as mirrors, etc. The real image generated by the image sensor is thus reflected directly off the windshield and thus reaches the viewer, such as a driver and / or passenger.The most obvious solution for generating a virtual image projected into the driver's field of vision with such a "mirrorless HUD" is to place a strong backlit LCD (liquid crystal display) below the windshield. However, such an LCD-based mirrorless HUD has the disadvantage that a significant portion of the light from the light source is dissipated within the system before it is reflected off the windshield: Conventional LCDs transmit only 3 to 10% of the light from the light source when displaying full white light. For particularly bright displays, such as those typically required in a HUD, this leads to correspondingly high energy consumption and, at times, challenging thermal conditions.The control lever for focusing the HUD light onto the relevant viewing area (eyebox) of a driver or passenger is often difficult, especially when space is limited in the vehicle.
[0005] Alternatively, it is possible to use a projection screen (also called a canvas or screen) instead of an LCD, onto which a projector projects a real image with high brightness. The most technically advanced projection solutions currently on the market are used in so-called "laser TVs". Here, an efficient laser diode in the projector forms the light source. The projection screen is designed so that as much of the light coming from the projector as possible is reflected towards all viewers sitting in front of the TV, while at the same time maintaining the contrast as much as possible in strong ambient light. Compared to an LCD, a projector-based system offers the potential for significantly higher efficiency and greater thermal robustness. However, such screens, which are known from the field of "laser TVs", do not yet meet the efficiency and contrast requirements for application in a HUD.The potential of a smaller, predefined viewing area in the vehicle compared to a TV application, as well as contrast maintenance measures through a special installation situation, are not being fully exploited. Screens based on volume holograms currently offer the greatest potential in this area. However, these have the disadvantage that they only achieve their full efficiency in a very narrow wavelength range. For the best possible efficiency, the light from a projector must be tuned as precisely as possible. This is particularly difficult with temperature fluctuations, which often occur in vehicles.
[0006] Furthermore, EP 2 594 987 A2 proposes a HUD system for a motor vehicle with a facet-type screen. The system comprises a standard vehicle window (i.e., without special coatings), an optical image projector, and an instrument panel equipped with a reflective facet surface. The projector is configured to project an image onto the reflective facet surface. This is configured to project the projector image onto a surface of the standard vehicle window that is oriented to reflect the image from the reflective facet surface toward an occupant. The reflective facet surface can be arranged within a plurality of troughs separated from one another by a plurality of diffusely reflecting partition walls. The plurality of troughs can be configured to shield the occupant from external reflections.To prevent the accumulation of dust and other debris within the plurality of troughs over the vehicle's lifetime, they may be enclosed by a cover glass made of a transparent material such as acrylic. The reflective facet surface may comprise a plurality of electrically addressable facets configured as an array of electrowetting cells.
[0007] The object of the present invention is to provide an alternative and / or improved projection unit for a field-of-view display device, which can be used in particular in a vehicle and is particularly suitable for large-area and / or panoramic virtual image display via reflection on a windshield. This projection unit and field-of-view display device can enable improvements over known approaches, for example, with regard to energy efficiency, manufacturing effort, cost, contrast, user visibility, image quality, and / or other aspects.
[0008] This object is achieved by a projection unit according to claim 1, as well as by an associated manufacturing method, a visual field display device containing this projection unit, 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 manufacturing method, the visual field display device, and the vehicle, and vice versa.
[0009] According to a first aspect, a projection unit for a field-of-view display device is provided, which can be designed in particular for use in a vehicle. The vehicle can be a motor vehicle, but also any other land, air, or water vehicle. The field-of-view display device can be designed, for example, as a head-up display (HUD).
[0010] During operation of the field-of-view display device, the projection unit is designed to emit a bundle of light rays, which is then reflected by a reflection disc arranged in the field of view of a respective user to their eyes or a predetermined eyebox, thereby displaying a virtual image floating beyond the reflection disc. 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 virtual image is fully visible to the user in question.
[0011] The respective eyebox can, for example, have a two-dimensional extent of approximately 180 mm wide (horizontally) and 120 mm high (vertically). The present field of view display device can have a single eyebox, but optionally also two or more eyeboxes at a predetermined distance from one another for two or more different users (such as for a driver and one or more front passengers, or for several passengers of the vehicle). The reflection plate can in particular be designed as a partial section of a windshield or another vehicle window, or it can be a combiner plate provided specifically for this purpose. During operation of the field of view display device, it is arranged outside the projection unit, so that the projection unit can also be manufactured and sold separately from the reflection plate.
[0012] The projection unit comprises a projector-based image generator with a projector configured to generate a beam of light with the desired display content, and a projection screen (also called a screen) illuminated by reflection thereof. The projector is configured to generate a real image on the projection screen, and the projection screen is designed to reflect the resulting beam of light in a predetermined shape and direction toward the reflection disc in order to generate a virtual image with the desired display properties for the user.
[0013] For this purpose, the projection screen comprises, on its side facing the projector, a plate- or film-like, transparent substrate, on the rear side of which (i.e., the side facing away from the projector), a mirror surface is formed, which is composed of a plurality of facets to form a facet grid with a sawtooth profile. Each facet has a first mirror segment, which is designed to direct the light beam, for example, into the center of an eyebox predetermined for the eyes of a first user. Through such directed eyebox illumination, the energy efficiency of the field of view display device with the projector-based imager can be significantly increased. The respective mirror segment can, in particular, be designed to be planar.Alternatively, a curved design of the respective mirror segment, for example convex in the direction of the incident projector light, can be useful for particularly homogeneous illumination of the respective eyebox.
[0014] The sawtooth profile can arise, among other things, because the mirror segments of the facets can have different angles depending on their position on the facet grid or mirror array. They therefore do not always connect continuously to one another, so that height offsets between adjacent facets are compensated for by transition surfaces oriented almost perpendicular to their mirror segments, for example, creating a sawtooth profile. The surfaces of the individual facets can, in particular, be below a size resolvable by the human eye, so that the facet grid is not recognizable to the user in the virtual image. Their linear dimensions can, in particular, be larger than the longest wavelength of the projector light used and, for example, be in the micrometer range, in order to avoid disruptive diffraction effects such as color fringing or interference, etc.For the same purpose, the surfaces of the individual facets / mirror segments can also have varying sizes and / or shapes (see Fig. 8b).
[0015] One idea behind the present projection unit with a projector-based imager thus consists of a projection screen with a refractive Fresnel lens in the form of a transparent substrate, on the back of which a mirror grid (referred to herein as a facet grid) is formed for directed guidance of the light beam into the user eyebox(es). This film- or plate-like, optically clear substrate made of a dielectric material ensures that even projector light incident on the substrate at a very shallow angle initially penetrates the substrate medium and thus strikes the facets at a steeper angle through the substrate. This makes it possible to keep the height of the facet relief lower and the efficiency of the system higher due to reduced light losses. At the same time, the substrate protects the sensitive mirror surface relief from scratches and other environmental influences such as moisture and dirt.According to one embodiment, each facet additionally has a second mirror segment designed to direct the light beam, for example, into the center of an eyebox predetermined for the eyes of a second user. For this purpose, the second mirror segment is oriented at a corresponding angle to the first mirror segment, forming an obtuse-angled bend in the substrate backside. Similarly, each facet can also contain additional mirror segments, each angled to all other mirror segments of the same facet, for one or more additional user eyeboxes.
[0016] Particularly in combination with this embodiment, the dimensions of the individual facets in the mirror surface can be selected such that each pixel of the real image generated in the mirror surface extends over several, ideally at least four, facets. This can ensure, among other things, that as equal as possible parts of an incident projector light beam that generates a pixel are directed into individual eyeboxes.
[0017] In particular, a diffuser can be arranged inside the substrate or on its front side facing the projector in the beam path of the light beam incident on and reflected from the mirror surface. This diffuser is designed to expand the incoming and outgoing light beams in such a way that they largely fill the entire respective eyebox evenly and, ideally, are also essentially confined to its area. For a typical optical path length from the projection screen to an eyebox of approximately 1200 mm, a diffuser with a full width at half maximum (FWHW) of approximately 5° to 10° is suitable for this purpose. A diffuser with a so-called flat-top scattering characteristic would be particularly suitable in order to achieve the aforementioned optimal illumination of the respective eyebox.According to one embodiment, the projection screen further comprises a cover layer on its rear side facing away from the projector, which covers the entire back of the substrate with the mirror surface formed thereon. The cover layer can be made of a transparent material with the same refractive index as the substrate or of a light-absorbing material. This prevents unwanted reflection of light at the transition surfaces, which extend between the adjacent facets transversely or perpendicularly to the facet surfaces, and additionally mechanically protects the mirror surface on the back.
[0018] Furthermore, a front side of the substrate facing the projector can have an anti-reflective coating designed to minimize or even prevent reflection of incident ambient light and / or the light beam from the projector on this substrate front side. This can also increase both the efficiency and the contrast of the field-of-view display device.
[0019] In the above embodiment with two or more user eyeboxes, the projection screen can be designed to be flexible or bendable, allowing it to be bent to adapt the mirror surface to different positions of the individual user eyeboxes, in particular to different distances between them. If the adjustment must be made once, for example, when installing the projection unit in the vehicle to adapt to the model-specific windshield shape and position and specific front seat distances, the projection screen can be designed not only to be elastic but also to be plastically deformable for this purpose.
[0020] According to a further aspect, a method for producing a projection screen for the projection unit presented herein is provided, comprising the following steps, which can be supplemented by further (intermediate) steps: First, the above-mentioned plate- or film-like transparent substrate is provided or produced, the rear side of which faces away from the projector or is to be turned away from the projector having the above-mentioned sawtooth profile, which is composed of a plurality of facet-shaped surfaces whose shape corresponds to the future reflective facets of the mirror surface, and transition surfaces connecting them. As also mentioned above, the transition surfaces each extend transversely or transversely to the facet-shaped surfaces.
[0021] This is followed by a directional coating of the back of the substrate with a thin layer of metal or another light-reflecting material to create reflective facets on the faceted surfaces. The coating direction is chosen so that the transition surfaces are concealed by the faceted surfaces, in other words, they are in their shadow, and thus not coated. This orientation of the material jet therefore ensures that only the faceted surfaces are coated with the light-reflecting material, such as metal, in a way that saves material and is also optimal for optical functionality.
[0022] The transition surfaces that are not intended to contribute to the reflection remain uncoated, thus largely suppressing unwanted light reflections. To further enhance this effect and completely suppress light reflection at the transition surfaces, they can be coated in an optional additional step, for example, with a light-absorbing material such as black lacquer, or, conversely, with another dielectric layer with the same refractive index as that of the substrate.
[0023] In particular, this can result in a cover layer that covers the entire back of the substrate, including the mirror surface formed thereon in the above coating step, thus additionally protecting it from chemical and mechanical influences. Alternatively or additionally, the above-mentioned anti-reflective coating can be applied in a further step to a front side of the substrate facing the projector.
[0024] According to a further aspect, a field of view display device is provided which can be designed in particular for use (i.e. installation) in a vehicle. In addition to the projection unit presented here, the field of view display device also comprises a user-side reflecting reflection plate which is arranged in the beam path of the light beam emitted by the projection unit as a whole and which can be designed, for example, as a partial section of a vehicle window or as a specially provided combiner plate. The reflection plate is arranged and designed in the field of view of at least one user in such a way that it reflects the said light beam to at least one eyebox predetermined for the eyes of the respective user, whereby the display content can be presented to the user in the form of a virtual image beyond the reflection plate and is also presented during operation of the field of view display device.
[0025] According to one embodiment, the reflection disk is arranged directly opposite the projection screen, with the exception of any covers of the projection unit (for example, in the form of a cover disk that transmits the light beam), which have no beam-shaping, beam-deflecting, or imaging optical effect on the light beam. In other words, in this specific embodiment, the field-of-view display device does not comprise any further optical elements such as deflecting or concave mirrors or lenses, etc., in the beam path of the light beam between the projection screen and the reflection disk. However, any coatings of the projection screen or the reflection disk with optical functionality are still possible.This embodiment allows the implementation of a projection unit that is particularly compact in the vertical direction, making it particularly well-suited for large-scale virtual displays such as panoramic views. According to a further aspect, the aforementioned vehicle is provided. The spatial orientation terms used herein, such as "above," "below," "side," "horizontal," "vertical," etc., refer in this case to the usual vehicle-fixed Cartesian coordinate system with mutually perpendicular longitudinal, transverse, and vertical axes of the vehicle. For example, the vehicle has at least one vehicle window, such as a windshield with an instrument panel extending beneath it, and a passenger compartment partially delimited thereby.It is equipped with the above-mentioned field of view display device, the projection unit of which can, for example, be installed directly in or below the upper surface of the instrument panel, so that the light beam from the projection unit is projected onto the windshield or a combiner disc arranged directly in the field of view of the driver and / or another passenger, which serves as the aforementioned reflection disc of the field of view display device. However, the field of view display device can also be integrated into any other suitable installation location in the vehicle, whereby other vehicle windows or combiner discs arranged at other locations in the passenger compartment can also serve as reflection discs.
[0026] The above aspects of the invention and their embodiments and specific configurations are explained in more detail below with reference to examples shown in the accompanying drawings. The drawings are to be understood as schematic illustrations of the basic optical design principle, i.e., not to scale. They show:
[0027] Figure 1 shows a section of a vehicle with a field of view display device according to an embodiment of the invention in a perspective view;
[0028] Figure 2 is a perspective view of a portion of a projection screen of Figure 1, showing its basic structure; Figure 3 is a further enlarged portion of the projection screen of Figures 1 and 2 from a different perspective;
[0029] Figures 4a-4d show a sequence of three manufacturing stages of the projection screen of Figure 1 according to an embodiment of the method;
[0030] Figure 5 is an enlarged perspective detail view of a further development of the projection screen;
[0031] Figure 6 is a further perspective view of a section of the vehicle as in Figure 1, in which the field of view display device is equipped with the projection screen of Figure 5 according to a further embodiment of the invention;
[0032] Figures 7a-7b each show a plan view of a field of view display device according to a specific embodiment of the invention, in which the projection screen can be elastically bent to adapt to different eyebox distances; and
[0033] Figures 8a-8b each show a plan view of a projection screen of a field of view display device according to an embodiment of the invention with a regular (Fig. 8a) and an irregular (Fig. 8b) facet grid.
[0034] All of the various embodiments, alternatives, and specific design features of the projection unit, the associated manufacturing method, the field of view display device, and the vehicle according to the above aspects of the invention mentioned above in the description and in the subsequent claims can be implemented in the examples shown in Figures 1 to 8b, in particular also alternatively or in addition to the features shown therein. Therefore, they will not all be repeated below. The same applies accordingly to the definitions and effects already given above with regard to individual features shown in Figures 1-8b.
[0035] Fig. 1 shows, in a highly simplified perspective view obliquely from above, a section of a vehicle 1 with a field of view display device 2 according to an exemplary embodiment of the invention. The spatial orientation terms used below, such as “horizontal,” “vertical,” “above,” “below,” “beneath,” etc., 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, with the longitudinal axis X pointing in the direction of travel as usual. In this example, the vehicle 1 is a motor vehicle, which is only indicated in Fig. 1 by its windshield 3, which serves as the aforementioned reflection disk of the field of view display device 2. Below this, in an instrument panel 4 (not shown in detail), a projection unit 5 of the field of view display device 2 is arranged.
[0036] The field of view display device 2 is designed to generate a virtual image (not shown) in the field of view of two users in this example, a driver and a front passenger, who are each indicated in Fig. 1 only by their eyes and a two-dimensional spatial region (eyebox) E1 or E2 in the passenger compartment of the vehicle 1, which is predetermined for this purpose and transverse to the respective beam propagation direction. The field of view display device 2 can be designed, in particular, for a panoramic virtual display in that the windshield 3, with a large part of its extension in the vehicle transverse direction Y, serves as a reflection plate of the field of view display device 2. This is purely an example of a head-up display (HUD).
[0037] The projection unit 5 contains a projector-based image generator. This comprises a projector 6, which is designed to generate a light beam L (also referred to herein as projector light) with the desired display content, and a projection screen 7 (also referred to as a screen) illuminated by the projector. The light beam L is indicated in Fig. 1 by its central beam, which leads from the center of the projector 6 to the center of the respective eyebox E1 or E2. The projector 6 is designed to generate a real image on the projection screen 7 in reflection and therefore illuminates it obliquely from above.
[0038] Fig. 2 shows a perspective view of the basic structure of the projection screen 7 of Fig. 1 using an enlarged section of the projection screen 7. The base of the projection screen 7 is formed by a mirror surface 8 in the form of a facet or mirror grid and a refractive Fresnel optic in the form of a transparent substrate 9, on the rear side 10 of which, facing away from the projector 6, the facet grid is formed. The task of the mirror surface 8 is to redirect the light beam L incident from the projector 6 towards the windscreen 3 and, via reflection therefrom, into the center of the respective eyebox E1 / E2 of the two users. The mirror surface 8 is designed to split the light beam L and to direct one part (first partial beam L1) into the driver's eyebox E1 and one part (second partial beam L2) into the passenger's eyebox E2.
[0039] In this example, the projection screen 7 is designed to direct the light beam L generated by the projector 6 as precisely and with as little loss as possible across the windscreen 3 into the eyeboxes E1 and E2 of the two users, in order to enable the most efficient HUD system possible. In this example, the respective eyebox E1, E2 is each a field for the driver and the front passenger with an area of approximately 180 mm wide (measured horizontally) and 120 mm high (measured vertically). In the eyeboxes E1 and E2 defined in this way, the amount of light should be distributed as evenly as possible so that the eyes of the respective user can perceive the virtual image with the same brightness within the entire field. Further or optional features of the projection screen 7, which can contribute to achieving this and other effects mentioned herein, are described below with reference to Figures 3 to 8b.
[0040] For illustrative purposes, only an enlarged section of the projection screen 7 is shown in Fig. 2 and in the following figures 3-5 and 8a-b. The entire mirror surface 8, i.e., the entire mirror or facet grid, in this example has approximately the same dimensions as the desired real image projected onto it by the projector 6, and consists of a plurality of facets 11. One of these facets 11 is highlighted in Fig. 2 by a drawn frame.
[0041] In this example, each facet 11 again consists of two mirror segments 12 and 14. The first mirror segment 12 serves to reflect incident projector light L into the driver's eyebox E1, the second mirror segment 12 serves to reflect it into the passenger's eyebox E2. These purely exemplary planar segments 12 and 14 therefore form an angle to one another, as can be seen in Fig. 2. This is a predetermined obtuse angle < 180° when looking at the back of the respective facet 11, which is determined, among other things, by the distance between the two eyeboxes E1 and E2 and the position of the respective facet 11 relative thereto.
[0042] To ensure that as equal a portion as possible of an incident projector beam used to generate a single pixel is directed into each eyebox, a facet 11 should be smaller than a corresponding projector beam cross-section, or smaller than a pixel, so that, ideally, four or more facets are always struck simultaneously by such a beam. In the advantageous embodiment presented here, the facet grid is incorporated on the back 10 of the film- or plate-like, optically clear substrate 9 (dielectric). This has the advantage that even projector light L incident very flatly on the substrate 9 first penetrates the dielectric medium and then strikes the facets 11 more steeply, as illustrated in Fig. 2. This helps, for example, to keep the height of the facet relief lower and the efficiency of the HUD system higher (or lower light losses).At the same time, the sensitive relief of the mirror surface 8 is protected from scratches by the substrate 9 arranged on the front.
[0043] To maximize the reflectivity of the facets 11, their backs can be coated with a thin metallic layer, for example, made of aluminum. Since the mirror segments 12, 14 of the facets 11 can have different angles or orientations depending on their position on the mirror array, the adjacent facets 11 do not always adjoin one another continuously. Height offsets of adjacent facets 11 must be compensated for by transition surfaces 15, which are oriented, for example, almost perpendicular to the mirror segments 12, 14, in order to be hit as little as possible by the projector light L.
[0044] This is illustrated in Fig. 3, which shows a section of the projection screen 7 of Fig. 2 in a likewise enlarged view from a different perspective than in Fig. 2 and allows a better view of the aforementioned transition surfaces 15 between the individual facets 11 of the mirror surface 8. As can be seen in both Figures 1 and 2, this results in an overall approximately sawtooth-shaped profile of the facet grid.
[0045] These transition surfaces 15, as well as the corners 16 and edges 17 they form, could, if their surfaces are poorly designed, generate unwanted back reflections of ambient light (such as sunlight), thereby reducing contrast in the virtual image or even blinding the user. Therefore, it is particularly useful to design these transition surfaces 15 and their edges 17 with as little reflection as possible. This is achieved in the manufacturing process presented here by coating the mirror segments 12 and 14 directionally, as shown in Fig. 4a.
[0046] Figures 4a-d show an exemplary embodiment of the method presented here for producing the projection screen 7 based on a sequence of three manufacturing stages, each of which shows an enlarged cross-sectional view of the projection screen 7. The arrows drawn between the individual Figures 4a to 4c merely illustrate the sequence of the process steps.
[0047] Fig. 4a shows an example of the coating step in which the substrate 9, with a relief formed on its rear side 10, which geometrically corresponds to the sawtooth profile of the future facet grid, is coated directionally in a direction R shown with a light-reflecting material 18 (in this example, metal). If the coating direction R is selected such that the transition surfaces 15 and their edges 17 are undercut relative to the coating direction R (for example, as in Fig. 4a), they are not coated and the reflectance of their surface is not increased. With the coating direction R selected in this way, the transition surfaces 15 and their edges 17 remain concealed by the sawtooth-shaped protruding surfaces of the future facets 11. In other words, the transition surfaces 15 form an acute solid angle a to the coating direction R, as can be seen in Fig. 4a, into which the material 18 does not reach.
[0048] Fig. 4b shows the projection screen 7 after the completed coating step, so that the projection screen 7, as in Figs. 2 and 3, has a mirror surface 8 formed on the back 10 of the substrate 9. This surface is composed of a plurality of facets 11 to form a facet grid with a sawtooth profile, in which uncoated transition surfaces 15 extend between the mirror-coated facets 11.
[0049] As shown in Fig. 4c, a covering layer 22 (for example, as a coating or encapsulation) made of a light-absorbing material 23 can then be applied to the entire rear surface of the projection screen 7. This further reduces the absorption coefficient of only the transition surfaces 15 and their edges 17, while the previously applied mirror surface 8 faces the substrate 9 and is thus protected from any further influence. Only its rear side is coated with the light-absorbing material 23 in the step shown in Fig. 4c, thereby providing additional sealing or mechanical protection.
[0050] As shown in Fig. 4d, as an alternative to Fig. 4c, the entire rear surface of the projection screen 7 of Fig. 4b can also be coated with an optically clear or transparent material 24 in the form of a cover layer 22, which has the same refractive index as the substrate 9. This also prevents unwanted reflection at the transition surfaces 15 and provides additional mechanical protection for the relief shown in Fig. 4b.
[0051] Fig. 5 shows a further development of the projection screen 7 in an enlarged perspective detail. In addition to the elements of the projection screen 7 which have already been described with reference to Fig. 2-4d, a light diffuser 19 is arranged above the facet grid in or on the substrate 9, which diffuser expands the incoming and outgoing projector beams L and L1 / L2 in total so that they hit the entire eyebox E1 / E2 of the respective user as equally as possible instead of just the center point, as illustrated for example in Fig. 6.
[0052] For a distance from the projection screen 7 across the windscreen 3 to the respective eyebox E1 or E2, which is typical for motor vehicles and is approximately 1200 mm, a diffuser 19 with a full width at half maximum (FWHW) of 5° - 10° is well suited for this purpose. These values can be selected differently for other geometric conditions. It would be particularly useful to equip the diffuser 19 with a so-called flat-top scattering characteristic for the aforementioned angular range and thus achieve optimal illumination of the eyebox E1, E2. The diffuser 19 can be implemented either intermediately in the substrate 9 or directly by means of a corresponding surface finish on the upper side of the substrate (i.e. its front side 20, which faces the projector 6).
[0053] In an advantageous embodiment, this substrate top surface is additionally provided with an anti-reflective coating 21 to minimize reflections from ambient light and further increase the efficiency of the HUD system. The anti-reflective coating 21 should, if possible, also be effective for flat angles of incidence, such as those encountered with the incoming projector beams L (see Fig. 2).
[0054] Fig. 6 shows, in a perspective view similar to Fig. 1, a section of a vehicle 1 with a field of view display device 2 according to a further exemplary embodiment of the invention, in which the projection screen 7 is equipped with a diffuser 19 according to Fig. 5. The respective partial light beam bundles L1 and L2 are indicated in Fig. 6 by their edge rays, which limit their beam cross-section required for virtual image generation. By appropriately selecting the diffuser 19, as described above, a largely uniform illumination of the respective eyebox E1 / E2 is achieved, which is also essentially limited to its area.
[0055] Since the functionality of the projection screen 7 presented here is similar at different wavelengths, it is suitable for combination with a variety of projector types (such as laser beam scanners, DMDs, etc.). Furthermore, the projection screen 7 does not change the polarization of the projector light L if the transparent dielectric of its substrate 9 and the anti-reflective coating 21, if present, do not exhibit birefringence. This is advantageous if the virtual image is to be viewed even with polarized sunglasses.
[0056] In different vehicles 1, the extent of the driver and front passenger eyebox E1 / E2 varies only slightly. However, the lateral deflection of the projector beams L1, L2 by the projection screen 7 may have to be implemented differently for different types and models of vehicles 1. This may be due, on the one hand, to different seating positions of the occupants in the vehicle 1 and, on the other hand, to different transverse curvatures of the windshield 3. In this regard, Figs. 7a and 7b each show a plan view of a field of view display device 2 according to a specific exemplary embodiment of the invention, in which the projection screen 7 presented here is of flexible design. Fig. 7a can in particular be the field of view display device 2 according to Fig. 1 or 6. In Fig. 7a, the surface of the projection screen 7 is aligned straight, as is also the case, for example, in Figs. 2-5.The above-mentioned lateral light guidance of the projector beams L1, L2 through the projection screen 7 (cf. Fig. 1) can be adjusted for vehicles with differently arranged eyeboxes E1 and E2 by appropriately bending / curving the projection screen 7, in particular its elastic deformation, as shown in Fig. 7b. Here, the two eyeboxes E1 for the driver and E2 for the front passenger are significantly closer to each other than in Fig. 7a, which can be compensated for by appropriately curving the projection screen 7. In this way, a projection screen 7 with specific optics can be used for different types of vehicles 1.
[0057] Figs. 8a and 8b each show a schematic plan view of a section of the projection screen 7 of the field-of-view display device presented herein. This can, for example, be the field-of-view display device 2 of Figs. 1 or 6. In Fig. 8a, the individual facets 11 of its mirror surface 8 are arranged approximately regularly. As schematically indicated in Fig. 8b, they can alternatively be arranged in an irregular facet grid to reliably prevent disruptive diffraction effects (such as double images, color fringes, etc. due to constructive interference) or moiré effects.
[0058] List of reference symbols
[0059] 1 vehicle
[0060] 2 Field of view display device
[0061] 3 Windscreen
[0062] 4 Instrument panel
[0063] 5 Projection unit
[0064] 6 projector
[0065] 7 Projection screen
[0066] 8 mirror surface
[0067] 9 transparent substrate
[0068] 10 Back of the substrate
[0069] 11 facets
[0070] 12, 14 first, second mirror segment
[0071] 15 Transition surface
[0072] 16, 17 corner, edge
[0073] 18 light-reflecting coating material, e.g., metal
[0074] 19 Diffuser
[0075] 20 Front of the substrate
[0076] 21 Anti-reflective coating
[0077] 22 Top layer
[0078] 23 light-absorbing material
[0079] 24 transparent material with the refractive index of the substrate
[0080] L Light beam, also called projector light
[0081] L1 , L2 first, second partial beam
[0082] E1 Eyebox of a first user or driver eyebox
[0083] E2 Eyebox of a second user or passenger eyebox
[0084] R coating direction
[0085] K vehicle-fixed Cartesian coordinate system
[0086] X, Y, Z longitudinal, transverse and height directions of the vehicle
Claims
Claims 1. Projection unit (5) for a field-of-view display device (2) designed to display a virtual image via reflection on a reflective disc arranged in the field of view of a user, in particular a vehicle window (3), wherein the projection unit (5) comprises a projector-based image generator with a projector (6) for generating a light beam (L) with the desired display content and a projection screen (7) illuminated by the projector; the projector (6) is designed to generate a real image on the projection screen (7), and the projection screen (7) is designed to reflect the resulting light beam toward the reflective disc;the projection screen (7) for this purpose has a plate-like or film-like transparent substrate (9) facing the projector (6) and a mirror surface (8) formed on the rear side (10) of the substrate, which mirror surface is composed of a plurality of facets (11) to form a facet grid with a sawtooth profile; and each facet (11) has a first mirror segment (12) designed to direct the light beam (L) into an eyebox (E1) predetermined for the eyes of a first user, in particular to direct it into the center thereof; 2. Projection unit (5) according to claim 1, wherein each facet (11) additionally has a second mirror segment (14) which is designed for directed guidance of the light beam (L) into an eyebox (E2) predetermined for the eyes of a second user, in particular for guidance in the center thereof, and which is angled to the first mirror segment (12) to form an obtuse-angled bend in the substrate rear side (10).
3. Projection unit (5) according to claim 1 or 2, wherein the dimensions of the individual facets (11) in the mirror surface (8) are selected such that each pixel of the real image generated in the mirror surface (8) extends over several, preferably at least four, facets (11).
4. Projection unit (5) according to one of the preceding claims, wherein a diffuser (19) is arranged in the interior of the substrate (9) or on its front side (20) facing the projector (6) in the beam path of the light beam (L, L1, L2) incident on and reflected from the mirror surface (8), said diffuser being designed to expand the incoming and outgoing light beam (L, L1, L2) in total such that said diffuser substantially uniformly fills the entire respective eyebox (E1, E2) and is preferably also substantially limited to the area thereof.
5. Projection unit (5) according to one of the preceding claims, wherein the projection screen (7) has on its rear side facing away from the projector (6) a cover layer (22) which covers the entire substrate rear side (10) including the mirror surface (8) formed thereon and is made of a light-absorbing material (23) or of a transparent material (24) with the same refractive index as the substrate (9).
6. Projection unit (5) according to one of the preceding claims, wherein a front side (20) of the substrate (9) facing the projector (6) has an anti-reflective coating (21) which is designed to minimize or prevent reflection of incident ambient light and / or the light beam (L) incident from the projector (6) on this substrate front side (20).
7. Projection unit (5) according to one of the preceding claims in conjunction with claim 2, wherein the projection screen (7) is designed to be flexible such that it can be bent to adapt the mirror surface (8) to different positions of the individual user eyeboxes (E1, E2), in particular to their different distances from one another.
8. A method for producing a projection screen (7) for a projection unit (5) according to one of the preceding claims, comprising the steps: Providing a plate- or film-like transparent substrate (9), the rear side (10) of which is facing away from the projector (6) has a sawtooth profile which is composed of a plurality of facet-shaped surfaces and transition surfaces (15) connecting these, which transition surfaces (15) each extend transversely thereto; directional coating of the substrate rear side (10) with metal or another light-reflecting material (18) in such a coating direction (R) for which the transition surfaces (15) are in the shadow of the facet-shaped surfaces and are therefore not coated, to form reflective facets (11) on the facet-shaped surfaces; and then preferably applying a cover layer (22) made of a light-absorbing material (23) or a transparent material (24) with the same refractive index as the substrate (9) to the entire substrate rear side (10) together with the mirror surface (8) formed thereon by the coating step and / or applying an anti-reflective coating (21) to a front side (20) of the substrate (9) facing the projector (6).
9. Field of view display device (2), in particular for use in a vehicle (1), comprising: a projection unit (5) according to one of claims 1 to 7; and a user-side reflecting reflection plate, in particular a vehicle window (3) or a specially provided combiner plate, arranged in the beam path of the entire light beam emitted by the projection unit (5) or its partial beams (L1, L2); wherein the reflection plate is arranged and designed in the field of view of at least one user such that it reflects the light beam to at least one eyebox (E1, E2) predetermined for the eyes of the respective user, whereby the display content can be presented to him in the form of a virtual image beyond the reflection plate; and wherein the reflection plate is preferably arranged directly opposite the projection screen (7), with the exception of any covers of the projection unit (5) which do not have a beam-shaping, beam-deflecting or imaging optical effect on the light beam.
10. A vehicle (1), in particular a motor vehicle, comprising: a vehicle window, in particular a windshield (3), and a passenger compartment partially defined by the windshield; and a field of vision display device (2) according to claim 9, the reflection pane of which is designed as part of the vehicle window or as a combiner pane arranged in the passenger compartment in the field of vision of the respective user.