Projection display device having a cover plate for suppressing reflections

Abstract

The invention relates to projection display device for a motor vehicle, comprising: - a projection device, which is designed to emit image-carrying projection light for projecting a projection image into an eye region of a vehicle occupant; - a transparent cover plate for protecting the projection device; - an optical system, which is designed to focus the image-carrying projection light into the eye region in such a way that the projection image is perceptible in the eye region of the vehicle occupant; - wherein the transparent cover plate comprises microstructuring on an outwardly directed top face, which microstructuring has mutually adjacent optical microstructure elements as a surface profile for reflecting incident ambient light in a diffusely scattered manner or predominantly into a region outside the eye region, - wherein the microstructure elements of the microstructuring have, in each case, at least in a surface direction, a randomly varying surface shape and / or surface size.

Description

[0001] Description

[0002] Projection display device with a cover plate for reflection suppression

[0003] The invention relates to projection display devices, in particular head-up display devices, for motor vehicles. In particular, the present invention relates to measures for suppressing interfering reflections of incident ambient light on a cover panel of the projection display device.

[0004] Projection display devices, such as head-up displays, for visually displaying information in the field of vision of a motor vehicle driver 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 device via which an image to be displayed is projected through a cover plate onto a windshield of a motor vehicle acting as a combining device. Unlike other display devices in motor vehicles, such projection display devices 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.

[0005] A projection display device typically has a cover plate that protects the projection device from dirt or mechanical damage. The cover plate is transparent and can reflect ambient light depending on the angle of incidence. At certain angles of incidence, ambient light, especially direct sunlight, can be reflected into the eye area of ​​a vehicle occupant, thereby dazzling them.

[0006] In known projection display devices, appropriate measures are provided to prevent ambient light falling on a cover plate of a projection device of the projection display device from falling directly or reflected via the windscreen into the eye area of ​​a vehicle occupant of the motor vehicle, thereby dazzling them and / or impairing the representation and / or perception of the information to be displayed. Therefore, the projection device generally contains a reflective and curved cover plate that reflects incident ambient light towards a light-absorbing surface, also called a mirror bank. The reflected ambient light is reflected only to a small extent and exclusively diffusely by the light-absorbing surface, so that disruptive reflections of ambient light or illumination in a display area on the windscreen can be essentially avoided.

[0007] Projection display devices are typically installed on the top surface of an instrument panel, above the steering column, where installation space is generally limited. However, the assembly consisting of the light-absorbing surface and the reflective, curved cover plate typically has a height of between 5 and 10 cm, which significantly increases the overall height of the projection display device. Reducing the height of this assembly is only partially achievable, since a flatter, i.e., less curved cover plate requires a greater height of the light-absorbing surface.

[0008] From the document DE 10 2014 214 510 A1 an arrangement for reducing reflection for a projection display device for a motor vehicle is known, which comprises a transparent cover plate for protecting a projection device and a shielding grid with one or more flat grid elements of a grid structure arranged perpendicularly or inclined to a surface of the cover plate.

[0009] It is therefore an object of the present invention to provide a projection display device with a low overall height in which disturbing reflections caused by incident ambient light are reduced.

[0010] This object is achieved by a projection display device for a motor vehicle with a cover plate for reflection suppression according to claim 1.

[0011] Further embodiments are specified in the dependent claims.

[0012] According to a first aspect, a projection display device for a motor vehicle is provided, comprising:

[0013] - a projection device configured to emit image-bearing projection light for projecting a projection image into an eye area of ​​a vehicle occupant,

[0014] - a transparent cover to protect the projection device;

[0015] - an optical system designed to focus the image-bearing projection light into the eye area so that the projection image is perceptible in the eye area of ​​the vehicle occupant, wherein the transparent cover plate has a microstructure with adjacent optical microstructure elements as a surface profile on an outwardly directed upper side in order to reflect incident ambient light diffusely or predominantly into an area outside the eye area, wherein the microstructure elements of the microstructure each have a randomly varying surface shape and / or surface size at least along one surface direction.Furthermore, a bottom side opposite the top side can have a microstructure which is designed to be complementary to the microstructure of the top side such that the projection light is transmitted and a fixed assignment of an angle of incidence of the projection light on the bottom side to a specific angle of reflection on the top side is achieved.

[0016] Furthermore, the microstructure elements of the top side and the bottom side can each have a concave or convex surface, in particular a spherically concave or convex or triangular surface.

[0017] The surface of the upper side of the cover plate can be substantially flat over its extent, regardless of the microstructuring, or curved along a surface direction, in particular concavely curved.

[0018] One idea behind the above projection display device is to provide a transparent cover panel for a projection device that has a microstructure. The microstructure has adjacent optical microstructure elements that have an outward-facing upper side (facing the windscreen) with, for example, a concave or convex design. The microstructure serves to achieve diffuse reflection of ambient light or predominantly reflection of ambient light into an area outside the eye area, e.g., a proportion of more than 80% or more than 90% of the ambient light. With diffuse reflection, incident ambient light or directly incident sunlight is diffusely scattered so that only a small proportion reaches the eye area of ​​a vehicle occupant.

[0019] Furthermore, the microstructure can be designed to reflect incident ambient light into an area or absorption surface, so that the proportion of ambient light falling into the eye area of ​​a vehicle occupant can be significantly reduced, in particular by more than 80%, more than 90%, or more than 99%. Furthermore, in contrast to prior art solutions, the cover plate can be planar or flat, so that the overall height of the projection display device is reduced and the cover plate can be easily integrated on the top of the instrument panel in a motor vehicle.

[0020] The cover plate is preferably designed such that the angle of incidence of a light beam of the projection light incident from an underside of the cover plate is maintained during transmission through the cover plate, so that the cover plate does not influence the direction and focus of the image-bearing projection light emitted by the projection device and an undistorted image in the eye of the vehicle occupant or driver is possible.

[0021] The outward-facing surfaces (top surfaces) of the microstructure elements exhibit a microstructure characterized by concave or convex structures. To ensure the optical property of unaffected transmission of projection light (with respect to the angle of incidence), the correspondingly opposite surface of the cover plate (bottom surface, the surface facing the projection device) exhibits concave or convex structures, thus achieving a planar arrangement of microstructures. The use of achromatic lenses is also possible.

[0022] In order to be able to perceive a projection image that is as undistorted and artifact-free as possible, the microstructure elements can be provided in a size of, for example, 0.05 mm to 0.5 mm, or even up to 1 mm, which excludes the perception of the interfaces between the microstructure elements due to the limited resolution of the vehicle occupant's eyes.

[0023] However, such cover plates can lead to rainbow-like artifacts due to diffraction effects when the microstructure elements are arranged periodically in a regular field arrangement. In this respect, the cover plate described above for the

[0024] The projection device proposes to resolve the periodicity of the arrangement of the microstructure elements of the cover plate in at least one of the surface directions at least within a predetermined surface area of ​​a predetermined minimum size and to form adjacent optical microstructure elements with randomly different surface shapes and sizes. Within the surface area, this is intended to eliminate periodicity that could lead to the display of artifacts and diffraction patterns due to the amplification of light diffraction.

[0025] In such an arrangement of irregularly shaped microstructure elements, it is preferable to maintain the microstructure elements adjacent to one another. The base surfaces of the microstructure elements can be triangular, square, pentagonal, or hexagonal.

[0026] It can be provided that in the surface area, the microstructure elements of the microstructuring each have a random surface shape and / or surface size, wherein the entire surface of the cover plate is formed by, in particular, identical, adjacent surface areas, wherein, in particular, the surface area has a size of 20 mm 2 up to 150 mm 2 has.

[0027] In particular, the microstructuring of the cover plate can be designed such that, within a given surface area of ​​at least 3 mm, at least 4 mm, or at least 5 mm edge length, the arrangement of the individual microstructure elements does not repeat in size and shape. These surface areas can then be arranged as tiles to form the entire cover plate.

[0028] The arrangement of the microstructure elements inevitably leads to diffraction patterns generated by each interface between neighboring microstructure elements. While such diffraction patterns are amplified and thus perceptible in a periodic / regular arrangement of microstructure elements, the irregular arrangement of the microstructure elements ensures that only the zeroth orders of the transmitted useful light overlap, whereas the diffraction patterns of all other diffraction orders are distributed over an angular range whose width depends on the distribution of the surface sizes of the individual microstructure elements. This significantly reduces the perceptibility of overlapping diffractions of non-zero diffraction orders.

[0029] The microstructure elements can each have a spherical, aspherical or free-form convex or concave structure in order to enable the best possible scattering of the incident ambient light when it is reflected on the surface of the cover plate.

[0030] To maximize the quality of the projection light transmission, the microstructures of the top and bottom sides can be offset from each other in the plane of the cover plate. The translation vector is then selected to ensure that a projection light beam (projection light) coupled centrally into one of the microstructure elements of the bottom side microstructure is also coupled centrally out of the corresponding microstructure element of the top side microstructure of the cover plate.

[0031] Furthermore, the profiled configuration of the microstructure elements on the upper side can have a particularly flat transmission surface and an absorption surface that are inclined relative to each other. The transmission surface is designed to transmit projection light and, depending on the angle of incidence of ambient light, reflects this light onto the absorption surface. Thus, the surfaces of the microstructure elements can have a series of triangular contours in cross-section, forming a serrated surface.Furthermore, the surfaces of the microstructure elements can also have a triangular contour in cross-section with transmission surfaces curved on the upper side in the cross-sectional plane, wherein each of the microstructure elements has a curved transmission surface that can be inclined with respect to the incident ambient light such that the reflection of incident light beams falls onto an adjacent absorption surface within an ambient light angular range. The transmission surface and the absorption surface are inclined with respect to one another and form a triangular or quasi-triangular (since curved profiles with respect to the cross-sectional area) groove or a sawtooth-like profile in cross-section. The transmission surface can be curved on the upper side of the cover plate in the opposite direction to the absorption surface, i.e., concave.On the underside, the corresponding surface can be convexly curved to maintain the angular conformity of the transmitted projection light.

[0032] The transmission surface is used to transmit the projection light and is aligned with respect to the ambient light angular range in such a way that any reflections cannot under any circumstances reach the driver's eye area, i.e. they are either absorbed on the absorption surface or - possibly after reflection on the windscreen - are guided past the eye area.

[0033] The absorption surface serves as a so-called glaretrap, so that incident ambient light that falls on the transmission surface and is reflected there is preferentially reflected toward the absorption surface / glaretrap and absorbed there. For this purpose, the absorption surface can be non-reflective, using a black lacquer or similar material, or a diffusely scattering surface structure.

[0034] The microstructure with a triangular cross-section or a quasi-triangular cross-section with a curved transmission surface can be repeated along a surface direction of the cover plate (transverse to the extension of the transmission surfaces and absorption surfaces) with random structure widths in the arrangement direction. The cover plate can be (macroscopically) flat or curved with respect to the arrangement direction. To avoid diffraction effects, the structure width of the microstructure elements can be varied along the arrangement direction, analogous to the lens structures described above.

[0035] In order to achieve undistorted transmission of the useful light, the structure of the upper side of the microstructure elements on the underside of the cover plate is designed accordingly, so that the transmission surface is opposite a correspondingly surface-parallel surface on the underside.

[0036] In all embodiments, the transmission surfaces on the underside of the cover plate can be designed at an angle to the transmission surfaces on the upper side of the cover plate in order to achieve beam deflection or - in the case of angles of incidence of the projection light varying along the arrangement direction - beam bundling, which is compensated in the further optics.

[0037] Furthermore, an intransparent aperture device with aperture openings can be arranged in the cover plate, so that each of the microstructure elements provided with a convex, in particular spherical, surface is assigned an aperture opening in order to enable angle-selective transmission through the cover plate.

[0038] The cover element may preferably have a color that corresponds to the surroundings of the cover plate, in order to enable a visually appealing embedding of the cover plate on the surface of the instrument panel.

[0039] According to a further aspect, a motor vehicle is provided, comprising: - an instrument panel between a windscreen of the motor vehicle and a steering column;

[0040] - the above projection display device arranged substantially flush with the top of the instrument panel.

[0041] Embodiments are explained in more detail below with reference to the attached drawings. They show:

[0042] Figure 1 is a schematic cross-sectional view of a projection display device for a motor vehicle;

[0043] Figure 2 shows a cross-sectional view through a cover plate with a non-periodic microstructure;

[0044] Figure 3 is a plan view of the cover plate with an exemplary microstructuring of Figure 2;

[0045] Figure 4 shows a cross-sectional view through a cover plate according to a further embodiment with a diaphragm device; and

[0046] Figure 5 is a cross-sectional view through a cover plate with a microstructure with microstructure elements with a triangular cross-section, and

[0047] Figure 6 shows a cross-sectional view through a cover plate with a microstructure with microstructure elements with a quasi-triangular cross-section and transmission surfaces with concave upper sides and convex lower sides.

[0048] Figure 1 schematically shows a cross-sectional view of a projection display device 1, such as a head-up display. The projection display device 1 comprises an optical projection device 2 and a cover with a cover plate 3. The projection display device 1 is essentially inserted into an opening 9 in an upper side 8 of an instrument panel 7 between a steering wheel and a windshield 5 such that it is essentially flush with or adjacent to the upper side 8.

[0049] The projection device 2 suitably outputs a projection beam L, which is directed in a projection direction P onto a display area 4 (e.g. combiner) of a windshield 5 of a motor vehicle. The projection device 2 comprises, in a known manner, a system of one or more mirrors 21, optionally lenses (not shown), and a projector 22. A projection image output by the projector 22 is aligned as a projection beam L by the one or more mirrors 21 in the projection direction P and projected onto the display area 4. The projection light projected onto the display area 4 is reflected by the display area 4 and directed onto an eye area B of a vehicle occupant, so that a projection image is created in the eye of the vehicle occupant, whereby information can be displayed.

[0050] While a curved cover plate 3 is typically provided between the projection device 2 and the display area 4 to direct incident ambient light onto a light-absorbing surface located at the edge, a cover plate 3 is now provided directly on the projection device 2 to protect the projection device 2 from contamination, for example, by dust particles. The cover plate 3 can be essentially flat. However, any curved shape of the cover plate 3 is also conceivable.

[0051] As shown by way of example in the cross-sectional view of Figure 2, the cover plate 3 is provided with a microstructure on an outward-facing (i.e., in the direction of the incident ambient light) upper side 32, which has adjacent optical microstructure elements 31. The microstructure elements 31 are designed such that they transmit the projection light P in an angle-preserving, in particular undistorted, manner. However, they have a profiled surface, which, in particular, as shown in Figure 2, can have a convex shape in order to diffusely reflect and scatter ambient light incident from outside over a larger angular range.

[0052] The planar arrangement of such microstructure elements 31 allows incident ambient light to be diffusely scattered, thus reducing the proportion of reflected ambient light incident on the upper side 32 in the eye area of ​​a vehicle occupant. The design of the optical microstructure elements 32, such that transmitted useful light is transmitted in an angle-preserving manner and thus has the same angle of incidence as the angle of reflection, enables an undistorted representation of an image of the projection image by the projection display device 1.

[0053] The cross-sectional view of Figure 2 through the cover plate 3 shows an arrangement of microstructure elements 31 with a convex shape of the outwardly directed upper side 32 of the cover plate 3. To ensure the undistorted transmission of the projection light P, concave structures corresponding to the convex structures can be located opposite a lower side 33 of the microstructure elements 3 opposite the upper side.

[0054] The convex structures on the top side can also be opposite corresponding convex structures on the bottom side, so that each of the microstructure elements 3 serves as a converging lens, thereby maintaining the angle. This can be achieved with a convex-convex arrangement if the thickness of the convex microstructure elements is selected such that the distance between the top and bottom sides corresponds to twice the focal length.

[0055] Figure 3 shows a plan view of the cover plate 3, one possible arrangement of the microstructure elements 31. Since a periodic arrangement of microstructure elements 31 leads to pronounced diffraction patterns that can be perceived by color patterns due to increasing diffraction effects, the cover plate 3 in this embodiment of Figures 2 and 3 is provided with an arrangement of the microstructure elements 31 with different surface sizes and surface shapes in a hexagonal pattern. The hexagonal pattern is composed of individual microstructure elements 31 of different shapes and sizes. Alternatively, the basic structure of the microstructure elements can be square, hexagonal and / or have another polygonal basic shape, which enables a gap-free arrangement in a matrix or field arrangement, i.e. which enables the joining of microstructure elements 31 of randomly different shapes and sizes.

[0056] In particular, the microstructuring of the cover plate 3 is provided such that the arrangement of the microstructure elements 31 is not periodic or of random shapes and sizes, i.e., does not have a regular arrangement pattern. This non-periodicity is either maintained over the entire surface area of ​​the cover plate 3 or at least adhered to in a predetermined surface area of, for example, between 5 mm and 10 mm edge length, in order to reliably prevent additive superposition of diffraction effects of higher diffraction orders generated by individual microstructure elements 31. The non-periodic arrangement of the microstructure elements 31 thus results in an irregular superposition of diffraction effects of higher diffraction orders, so that no amplification of the diffraction effects occurs and the perceptibility of the resulting diffraction patterns is significantly reduced.

[0057] The microstructuring of the surface of the cover plate features microstructure elements of a size that results in a resolution smaller than the resolving power of the vehicle occupants' eyes. However, the size of the microstructure elements 31 should be several times larger than the wavelength of visible light to avoid additional diffraction effects caused by the interfaces where the microstructure elements 31 adjoin one another.

[0058] Figure 4 shows a further embodiment of a cover plate 3 with an integrated aperture device 34. For this purpose, the microstructure elements 31 are designed as individual converging lenses with a convex spherical shape on the top and bottom, in each of which an aperture opening 35 of the aperture device 34 is arranged. The aperture openings 35 are positioned such that only light incident on the relevant microstructure element 31 from a specific angular range is transmitted, and other angular ranges, such as preferably the angular range of the direct view of vehicle occupants onto the top side of the cover plate 3, are directed onto the aperture device 34 and are thereby prevented from being transmitted.

[0059] Figure 5 shows a cross-section through a cover plate 3 according to a further embodiment, wherein the microstructure elements 31 on the top and bottom of the cover plate 3 each have a triangular cross-section along an arrangement direction. The microstructure elements 31 are characterized by a transmission region 36 through which the projection light can be transmitted without distorting the display image. An absorption surface 37 facing the transmission region 36 has an angle of approximately 10° to 50° with respect to the surface normal of the cover plate 3 and can preferably be designed as a glare trap, i.e. have a coating or surface structure that absorbs light as much as possible or scatters it diffusely and prevents reflection or coupling of light into the cover plate 3.

[0060] In the arrangement direction, the transmission region 36 and the absorption region 37 are arranged alternately with their width directions. The widths of the transmission region 36 and the adjacent absorption region 37 are selected to be so small that any perception of the microstructuring thus formed in the eye region is excluded, e.g., between 0.1 and 1 mm. In a surface direction transverse to the arrangement direction, the transmission regions 36 and absorption regions 37 can extend across the entire width of the cover plate 3. Thus, ambient light from a specific angular range that is reflected on a surface of the transmission region 36 of a microstructure element 31 can preferably be reflected in the direction of the absorption surface 37 and there either absorbed or diffusely reflected to avoid further reflections of the reflected ambient light.

[0061] As shown in Figure 6, instead of the triangular cross-section, the transmission regions 36 of the microstructure elements 31 of the upper side can also be concavely curved with respect to the arrangement direction in order to increase the angular range from which incident ambient light is directed onto the absorption region 37. Accordingly, the transmission regions on the underside of the cover plate 3 can be convexly curved in the arrangement direction.

[0062] List of reference symbols

[0063] 1 projection display device

[0064] Projection device 1 Projection mirror 2 Projector

[0065] 3 Cover plate

[0066] 31 Microstructure element

[0067] 32 Top

[0068] 33 Bottom

[0069] 34 Aperture device

[0070] 35 aperture

[0071] 36 T ransm ission surface

[0072] 37 Absorption surface

[0073] 4 Display area

[0074] 5 Windscreen

[0075] 7 Instrument panel

[0076] 8 Top

[0077] 9 Opening

[0078] L projection beam

[0079] P Projection direction

Claims

Claims Projection display device (1) for a motor vehicle, comprising: - a projection device (2) which is designed to output image-bearing projection light for projecting a projection image into an eye area of ​​a vehicle occupant, - a transparent cover plate (3) for protecting the projection device (2); - an optical system designed to focus the image-bearing projection light into the eye region such that the projection image is perceptible in the eye region of the vehicle occupant; wherein the transparent cover plate (3) has, on an outwardly directed upper side (32), a microstructure with adjacent optical microstructure elements (31) as a surface profile in order to reflect incident ambient light in a diffusely scattering manner or predominantly into an area outside the eye region, wherein the microstructure elements (31) of the microstructure each have a randomly varying surface shape and / or surface size at least along one surface direction.Projection display device (1) according to claim 1, wherein a bottom side (33) opposite the top side (32) has a microstructure which is designed to be complementary to the microstructure of the top side (32) of the cover plate (3) such that the projection light is transmitted for each microstructure element and a fixed assignment of an angle of incidence of the projection light onto the bottom side (33) to a specific angle of reflection on the top side (32) is achieved. Projection display device according to one of claims 1 to 2, wherein the microstructure elements (31) are arranged on the top side (32) and the bottom side thereof. (33) each have a concave or convex surface, in particular a spherical, aspherical, or free-form convex or concave or triangular surface. Projection display device (1) according to one of claims 1 to 3, wherein the surface of the upper side (32) of the cover plate (3) is flat or curved along a surface direction, in particular concavely curved. Projection display device (1) according to one of claims 1 to 4, wherein, in a surface region, the microstructure elements (31) of the microstructure each have a random surface shape and / or surface size along at least one surface direction, wherein the entire surface of the cover plate (3) is formed by adjacent surface regions, wherein, in particular, the surface regions each have a size of 20 mm. 2 up to 150 mm 2Projection display device (1) according to one of claims 1 to 5, wherein the base surfaces of the microstructure elements (31) of the microstructure are each triangular, quadrangular, pentagonal or hexagonal. Projection display device (1) according to one of claims 1 to 6, wherein the amount of the angle of incidence corresponds to the amount of the angle of reflection or wherein the assignment of the angle of incidence of the projection light on the underside to the angle of reflection on the upper side (32) effects the optical property of a prism, a converging lens or a diverging lens. Projection display device (1) according to one of claims 1 to 7, wherein the configuration of the microstructure elements (31) on the upper side (32) of the cover plate (3) has a particularly planar or concavely curved transmission surface (36) and an absorption surface (37) angled away from the cover plate (3), wherein the transmission surface (36) is designed to transmit the projection light and, depending on an angle of incidence of ambient light, reflects said light onto the absorption surface (37). Projection display device (1) according to claim 8, wherein the underside of the cover plate (3) has surface sections that are opposite the transmission surfaces (36) with respect to a surface normal or a direction inclined thereto such that a beam of projection light, which enters through the center of a microstructure element (31) on the underside of the cover plate (3), exits through the center of the corresponding microstructure element (31) on the upper side (32) of the cover plate (3).Projection display device (1) according to one of claims 1 to 8, wherein an opaque aperture device (34) with aperture openings (35) is arranged in the cover plate (3), so that each of the microstructure elements (31) provided with a convex surface is assigned an aperture opening (35) to enable angle-selective transmission through the cover plate (3). Motor vehicle comprising:. - an instrument panel (7) between a windscreen (5) of the motor vehicle and a steering column; - the projection display device (1) according to one of claims 1 to 10, wherein the projection display device (1) is arranged substantially flush with the upper side of the instrument panel (7).

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