Compact head-up display with direction-dependent diffuser to suppress parasitic images

Abstract

The invention relates to a compact projection unit for a field-of-view display device for a vehicle, comprising: an imaging unit for generating a light beam with display content; -a commutation element, by means of which the light beam exits the projection unit in a predetermined exit direction in order to be subsequently reflected by a reflective sheet arranged in the field of view of the user to the eye box of the user and thereby present the display content for the user in the form of a virtual image behind the reflective sheet; and a cover sheet in the beam path of the outgoing light beam, which covers the projection unit towards the outside and has direction-dependent transmission and scattering properties, such that the cover sheet is transparent to the outgoing light beam, and the interference path direction directly guided from the imaging unit or other optical elements except the reversing element to the covering sheet is diffused and scattered.

Description

Field of the Invention

[0001] The present invention relates to a projection unit for a field-of-view display device, which is also known under the name head-up display (HUD) and can be used in particular in motor vehicles or other land, air or waterborne vehicles. Such a field-of-view display device is configured to generate a virtual image inserted into the user's field of view by reflection on a vehicle sheet (in particular the front windshield) or on a combined sheet provided specifically therefor, which combined sheet is arranged in the user's field of view. The invention also relates to such a field-of-view display device and a vehicle equipped with the field-of-view display device. Background Art

[0002] Especially for motor vehicles, it is known to superimpose display content, such as information about speed limits or other useful navigation and vehicle operation tips, in the form of a virtual image on the real environment image in front of the vehicle observed by the driver by means of a head-up display, so that the driver does not have to shift his line of sight from the road in order to read the display. In a classical configuration, in order to generate the display content, the head-up display includes a projection unit (see FIG. 1a) mounted inside the instrument panel below the front windshield. The projection unit typically includes a display for generating a light beam with the desired display content, as well as suitable imaging and projection optics for shaping the generated light beam and guiding it to the front windshield or the combined sheet, so that the light beam is reflected from the front windshield or the combined sheet to the driver's eyes, and thus enables the driver to see the virtual image behind the front windshield or the combined sheet in the appropriate size and at the appropriate distance. In a classical head-up display configuration, the projection optics includes a concave mirror, which is especially used for magnifying the image, and the size of the concave mirror is in linear proportion to the size of the virtual display area, and thus a relatively large installation space is required in the vehicle's instrument panel. In addition, the concave mirror is usually implemented as rotatable to adapt to different user body types or positions, which requires even more installation space in the height direction of the vehicle.

[0003] However, this is very limited in a vehicle. In particular, this results in limitations in the geometric design of the transparent cover sheet arranged above the concave mirror, which covers the projection unit or its housing outwardly towards the front windshield and thus protects it from interfering influences, such as dust and moisture. Usually, in addition, in order to protect the driver from the influence of glare from sunlight reflection, it is also desirable that the cover sheet has a concave geometric shape on its outer side that occupies space in the height direction of the vehicle, and this concave geometric shape is called "geometric anti-reflection".

[0004] Here, a predetermined vertical minimum distance must be maintained between the concave mirror and the cover sheet. The technical problem behind this is that in a more compact design, stray light paths are generated, which reach the emitted light beam outside the regular optical path through mirror reflections of the display light at the lower surface of the cover sheet and subsequent mirror reflections at the concave mirror, and thus can lead to the generation of parasitic images (see FIG. 1a). SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide an alternative projection unit or a projection unit for a field-of-view display device that is improved in terms of the required installation space, achievable sunlight protection, presentation quality, and / or other aspects. Here, the field-of-view display device should be particularly suitable for use in a vehicle.

[0006] This object is solved by the projection unit according to claim 1 and by the field-of-view display device comprising the projection unit and the vehicle equipped with the field-of-view display device according to the dependent claims. Further design options are given in the dependent claims. All further features and effects mentioned for the projection unit in the claims and the following description also apply to the field-of-view display device and the vehicle, respectively, and vice versa.

[0007] According to a first aspect, a compact projection unit for a field-of-view display device is provided, which is configured to generate a virtual image in the user's field of view and is particularly suitable for use in a vehicle. The field-of-view display device can, for example, be configured as a head-up display (HUD).

[0008] The projection unit has an imaging unit (also referred to as an image generation unit, PGU) for generating a light beam with the desired display content. In principle, any image generation technology that is particularly suitable for use in a vehicle can be used for this imaging unit. In particular, it can relate to a display, such as a flat screen or a waveguide display, but it can also relate to a projection system, such as a DLP projector or a diffuser sheet illuminated or scanned with light, and many other things.

[0009] In the optical path of the light beam, the deflection element is configured and arranged such that the deflected light beam leaves the projection unit in a predetermined exit direction, in order to subsequently be reflected by a reflector sheet arranged in the user's field of view to the user's eye box and thus present the display content to the user in the form of a virtual image behind the reflector sheet. For example, it can relate to any suitable type of reflective or refractive deflection element, which can be equipped with other optical functions in addition to light deflection if necessary.

[0010] Here, the eyebox of the field-of-view display device is understood as a two-dimensional or three-dimensional spatial region from which the virtual image is unrestrictedly visible to the user. The reflective sheet can be formed, for example, by a section of a vehicle sheet or by an additionally provided combined sheet. Thus, the reflective sheet is a component of the field-of-view display device given below, but not necessarily also a component of the projection unit. For example, in the case of using a vehicle sheet, the projection unit can also be manufactured and sold without the reflective sheet. In the case of an additionally provided combined sheet, the combined sheet can also be integrated into the projection unit in a known manner (e.g., closable / openable).

[0011] In the optical path of the light beam exiting from the projection unit, a cover sheet (also referred to as cover glass) extends transversely to its exit direction, which outwardly encloses the projection unit or, if possible, its housing, thereby protecting the optical and electronic components inside the projection unit from external interfering influences such as dust and moisture. Here, the cover sheet is configured to have predetermined direction-dependent transmission and scattering characteristics such that the cover sheet is substantially transparent to the entire exiting light beam that should contribute to generating the virtual image, while not being specularly reflective and ideally also not transmissive but diffusely scattering in the direction of the interference path directly guided from the imaging unit or other optical elements other than the commutation element to the cover sheet. In other words, the cover sheet is configured as a direction-dependent diffuser that transmits with little loss only within a predetermined range of incident angles for the exiting light beam, while diffusely scattering for incident angles from other directions.

[0012] One concept in this projection unit is to suppress the interference path that hits the cover sheet from other directions inside the projection unit different from the predetermined exit direction of the light beam by using a direction-dependent diffuser in the cover sheet. Thereby, the cover sheet can be arranged closer to other components of the projection unit (such as the commutation mirror or the imaging unit, etc.) than in the prior art, without parasitic images being generated by specular reflection on the inner surface of the cover sheet via the interference path. The installation space thus obtained can be used for other purposes, for example, so that the cover sheet and / or other components of the projection unit can be made larger and / or more movable, and thereby better optical characteristics and / or a larger image size and / or better sunlight protection and many other effects can be achieved.

[0013] Accordingly, in particular, it is not necessary to follow the vertical minimum distance between the cover sheet and the deflection element (such as a concave mirror) that is required in a head-up display in a conventional vehicle. Instead, the minimum distance between the cover sheet and the deflection element and / or between the cover sheet and the marginal rays of the light beam contributing to the generation of the virtual image can be minimized only taking into account the mechanical boundary conditions. Thereby, the installation space required for the projection unit (compactness) can be optimized. In particular, more degrees of freedom are also obtained in the design of the cover sheet geometry, which, in addition to the installation space optimization, can also be used for sunlight protection optimization. The minimum distance mentioned can in particular be the vertical minimum distance in the height direction of the vehicle. The spatial direction terms used here, such as "above", "below", "front", "rear", "horizontal", "vertical", etc., always refer to the common Cartesian coordinate system fixed to the vehicle when applied in the vehicle, which has the longitudinal direction, transverse direction and height direction of the vehicle perpendicular to each other.

[0014] For example, the cover sheet can be substantially transparent within a predetermined range of incident angles (e.g., up to 5° or up to 10° around its transmission axis selected and fixed during manufacture), and for incident angles increasing beyond this range of incident angles, it becomes increasingly diffusely scattering for the light generated in the projection unit. The transmission axis is ideally oriented along the exit direction of the light beam. For incident directions outside this range of incident angles, the cover sheet can have, for example, a continuously decreasing transmission coefficient and a correspondingly increasing scattering characteristic as the angular deviation from the transmission axis increases, according to a relationship specifically selected and determined during the manufacture of the cover sheet. In particular, for incident angles deviating from the exit direction of the light beam by about 10° to about 70°, in particular about 20° to about 60° or about 30° to about 50°, the cover sheet can be substantially diffusely scattering and thus in particular not specularly reflective.

[0015] According to one embodiment, the cover sheet is configured to be substantially diffusely scattering and thus not specularly reflective for the following stray light path, which is directly guided from the imaging unit to the cover sheet and would reach the optical path of the exiting light beam via subsequent deflection at the deflection element in the case of specular reflection on the cover sheet.

[0016] The deflection element mentioned can in particular be a concave mirror, which is configured to magnify the image and / or correct the image such that the virtual image is presented to the user with, for example, a predetermined size, distance, and / or presentation quality.

[0017] The exit direction mentioned can in particular correspond to the central ray direction of the light beam exiting from the projection unit. The central ray direction of the field of view display device is understood as usual to be the direction of the ray that emanates from the center of the imaging surface or display surface and points to the center of the eyebox.

[0018] In particular, the outer surface of the cover sheet facing away from the inside of the projection unit may have a predetermined concave-curved geometry, which is designed to deflect interfering ambient light reflections from the light beam path emitted by the projection unit and is also referred to as geometric anti-specular reflection. Due to the installation space obtained as described above, there is more design freedom for optimizing this geometry compared to the prior art.

[0019] In a specific design, the cover sheet may be constructed as a plastic sheet, and its static, non-holographic material structure has the mentioned direction-dependent transmission and scattering characteristics. This material structure can be, for example, a persistent polymer structure that can be generated during the manufacture of the cover sheet (i.e., a direction-dependent diffuser). Here, the cover sheet can be given, for example, a predetermined transmission axis (along which the cover sheet is transparent) and a predetermined angular dependence for increasing diffuse scattering as the deviation from this direction increases. In other words, it involves a plastic structured in a suitable manner.

[0020] Alternatively, the cover sheet may comprise a plastic layer or plastic film provided with similar characteristics, which is applied to or embedded in a transparent carrier sheet (e.g., made of glass or plastic).

[0021] According to another aspect, there is provided a field-of-view display device, especially for use in a vehicle. The field-of-view display device includes, in addition to the projection unit described herein, the above-mentioned reflective sheet, which can be at least partially transparent. Here, the reflective sheet is arranged / arrangeable and configured in the field of view of the user (e.g., the driver or other occupants of the vehicle) such that the reflective sheet reflects the light beam to the user's eye box, so that the display content can be presented to the user in the form of a virtual image behind the reflective sheet and is also presented when the field-of-view display device is in operation.

[0022] According to another aspect, there is provided a vehicle, especially a motor vehicle or any other land, air, or water vehicle. The vehicle has a vehicle sheet that at least partially defines the passenger compartment, especially the windshield, and is equipped with the above-mentioned field-of-view display device, whose projection unit is arranged inside the passenger compartment and whose reflective sheet is constructed as a section of the vehicle sheet or as a combined sheet arranged inside the passenger compartment. For example, the projection unit can be directly mounted below the upper side of the vehicle's instrument panel, so that the light beam is projected from the projection unit onto the windshield or onto a combined sheet positioned in front of the driver or other occupants in the field of view, and is reflected from the windshield or the combined sheet into the eyes of the driver or other occupants. Description of the Drawings

[0023] The above aspects of the invention, their embodiments and specific design solutions are explained in detail below by way of examples shown in the drawings. The drawings are schematic illustrations. They can be understood, but do not have to be, in accordance with the scale and / or the angles. Among them:

[0024] Figure 1a shows a partial vertical longitudinal sectional view of a motor vehicle having a head-up display according to the prior art;

[0025] Figure 1b Figure 1b shows a partial vertical longitudinal sectional view of a motor vehicle having a field-of-view display device according to an embodiment of the present invention. Detailed Embodiment

[0026] All different embodiments, variants and specific design features of the projection unit, the field-of-view display device and the means of transport according to the above aspects of the present invention mentioned above in the description and in the subsequent claims can be implemented in the Figure 1b examples shown, in particular can be implemented by replacing or supplementing the features shown therein. Therefore, all these are not repeated again below. The same applies mutatis mutandis to the Figure 1b terminology definitions and effects of the individual features shown above.

[0027] Figure 1a shows, for pre-explaining the problem, a partial view of a means of transport 1 with a conventional head-up display (HUD) 200 having the classical structural form as mentioned at the beginning, in a vertical longitudinal sectional view. The head-up display 200 is configured to generate a virtual image (not shown) in the field of view of a user (e.g., the driver of the means of transport 1), who is represented in Figure 1a only by the eye box E determined for his eyes within the passenger compartment of the means of transport 1. The means of transport 1 is here purely by way of example a motor vehicle. In Figure 1a, the means of transport is represented by its front windshield 3 and the instrument panel 4 extending below it, which is not shown in detail.

[0028] The head-up display 200 includes a conventional projection unit 500, which is arranged inside the instrument panel 4 below the front windshield 3 in this example. The projection unit 500 contains an imaging unit 6 for generating a light beam L with the desired display content, which is a display in this example. The light beam L is schematically represented in Figure 1a by its marginal rays, which roughly delimit the light cross-section required for generating the virtual image. In the optical path of the generated light beam L, a concave mirror 8 is arranged in this example, the front side of which with the concave curvature for magnifying the image is configured to project the light beam L onto the front windshield 3 in a suitable form and direction, and then the light beam is reflected from the front windshield to the eye box E. Therefore, the front windshield 3 serves as the reflecting surface of the head-up display 200 mentioned here.

[0029] The projection unit 500 is protected against possible interfering influences, such as dust and moisture, etc., by a cover sheet 700 that is transparent to the emitted light beam L and faces the windshield 3. This conventional cover sheet 700 is typically made of glass or transparent plastic and also has a concave-curved outer surface in this example for the geometric anti-mirror reflection of the sunlight rays incident from the outside as mentioned above.

[0030] Here, the conventional vertical minimum distance 900 between the cover sheet 700 and the upper-edge ray of the light beam L drawn in FIG. 1a must be adhered to, so that the stray light path SP that directly falls on the lower surface of the cover sheet 700 in FIG. 1a from the imaging unit 6 and is specularly reflected from this lower surface in the direction of the concave mirror 8 cannot, as shown for illustration in FIG. 1a, hit the concave mirror 8 and be coupled into the optical path of the light beam L from this concave mirror. Because this would result in interfering parasitic image components in the virtual image. Therefore, in practice, the vertical minimum distance 900 must even be greater than that measured in FIG. 1a, which greatly limits the available installation space and thus also the degrees of freedom in the geometric design of the cover sheet 700 and the concave mirror 8. The solution to this problem is described below with respect to Figure 1b is described.

[0031] Figure 1b A partial view of a vehicle 1 with a field-of-view display device 2 according to an embodiment of the present invention is shown in a vertical longitudinal cross-section. The field-of-view display device is here purely exemplarily configured as a head-up display (HUD). Therefore, to avoid repetition, only the differences from the conventional head-up display 200 in FIG. 1a are described below. Here, the vehicle 1 is also purely exemplarily a motor vehicle, which is represented by its windshield 3 and an instrument panel 4 extending below it (not shown in detail) similar to FIG. 1a. Additionally, a common Cartesian coordinate system K fixed to the vehicle is drawn, which has the longitudinal direction, lateral direction, and height direction X, Y, and Z of the vehicle 1 that are perpendicular to each other. Spatial direction terms such as "above", "below", "front", "rear", "horizontal", "vertical", etc. refer to this coordinate system.

[0032] The field-of-view display device 2 differs from the conventional head-up display 200 in FIG. 1a in the design and arrangement of the cover sheet 7 in its projection unit 5. Different from the conventional cover sheet 700 in FIG. 1a, which is Figure 1bThe position in (is indicated by a dashed line) is opposite, and the covering sheet 7 is configured as a direction-dependent diffuser, which is almost completely transparent to the light beam L to be emitted, while being diffusely scattered for the stray light path from an incident direction significantly deviating from the preset emission direction. Thus, in particular, the stray light path SP directly from the imaging unit 6 can be almost completely suppressed in such a way that this stray light path is converted into diffusely scattered light 10 at the covering sheet 7 instead of being specularly reflected to the concave mirror 8. Therefore, compared with Fig. 1a, the vertical minimum distance 9 between the covering sheet 7 and Figure 1b the upper edge ray of the light beam L drawn in can be significantly reduced, i.e., determined only according to mechanical boundary conditions (such as the desired mobility of the concave mirror 8, etc.). In other words, as Figure 1b shown, in this example, the covering sheet 7 can be lowered by a height amount ΔZ of about 5 to 6 cm in the installation space relative to the conventional covering sheet 700. Thus, this installation space can be used for other purposes, for example, for additionally optimizing other components of the projection unit 5 to achieve better imaging characteristics, image size, and / or anti-mirror reflection than achievable in Fig. 1a.

[0033] List of reference numerals

[0034] 1 Vehicle

[0035] 200 Conventional head-up display

[0036] 2 Field-of-view display device

[0037] 3 Windshield

[0038] 4 Instrument panel

[0039] 500 Conventional projection unit

[0040] 5 Projection unit

[0041] 6 Imaging unit

[0042] 700 Conventional covering sheet

[0043] 7 Covering sheet

[0044] 8 Concave mirror

[0045] 900 Conventional minimum distance

[0046] 9 Minimum distance

[0047] 10 Scattered light

[0048] L Light beam

[0049] E Eyebox

[0050] ΔZ Height amount

[0051] Cartesian coordinate system fixed to the vehicle

[0052] X, Y, Z Longitudinal direction, lateral direction and height direction of the vehicle

Claims

1. A compact projection unit (5) for a field-of-view display device (2), in particular for use in a vehicle (1), the projection unit comprising: - an imaging unit (6) configured to generate a light beam (L) with desired display content; - a deflection element arranged and configured in the optical path of the light beam (L) such that the light beam (L) leaves the projection unit (5) in a predetermined exit direction, for subsequent reflection by a reflective sheet arranged in the user's field of view to the user's eye box (E) and thereby presenting the display content to the user in the form of a virtual image behind the reflective sheet; and - a cover sheet (7) extending transversely to its exit direction in the optical path of the exiting light beam (L) and closing and protecting the projection unit (5) outwardly therewith; wherein the cover sheet (7) has predetermined direction-dependent transmission and scattering properties such that the cover sheet is substantially transparent to the exiting light beam (L), while being substantially diffusely scattering in the direction of interfering paths directly guided from the imaging unit (6) or other optical elements other than the deflection element to the cover sheet (7).

2. The projection unit (5) according to claim 1, wherein - the minimum distance between the cover sheet (7) and the deflection element and / or between the cover sheet (7) and the marginal rays of the light beam (L) contributing to the generation of the virtual image is minimized only taking into account mechanical boundary conditions.

3. The projection unit (5) according to claim 1 or 2, wherein - the cover sheet (7) is substantially diffusely scattering and thus not specularly reflecting for stray light paths that are directly guided from the imaging unit (6) to the cover sheet (7) and would reach the optical path of the exiting light beam (L) via subsequent deflection at the deflection element in the case of specular reflection on the cover sheet.

4. The projection unit (5) according to any one of the preceding claims, wherein - the mentioned deflection element is configured as a concave mirror (8) for magnifying the image and / or correcting errors.

5. The projection unit (5) according to any one of the preceding claims, wherein - the outer surface of the cover sheet (7) facing away from the interior of the projection unit (5) has a predetermined concave-curved geometry configured to deflect ambient light reflections from the optical path of the light beam (L) emitted by the projection unit (5).

6. The projection unit (5) according to any one of the preceding claims, wherein - the cover sheet (7) is configured as a plastic sheet, and the static, non-holographic material structure of the plastic sheet has the mentioned direction-dependent transmission and scattering properties.

7. The projection unit (5) according to any one of claims 1 to 5, wherein - the cover sheet (7) comprises a transparent carrier sheet with a plastic layer or plastic film applied to or embedded in the carrier sheet; and - the plastic layer or plastic film has a static, non-holographic material structure having the mentioned direction-dependent transmission and scattering properties.

8. A field-of-view display device (2), in particular for use in a means of transport (1), the field-of-view display device comprising: - a projection unit (5) according to any one of the preceding claims; - a reflective sheet, in particular at least partially transparent, arranged in the optical path of the light beam (L) emitted by the projection unit (5); - wherein the reflective sheet is arranged and configured in the user's field of view such that the reflective sheet reflects the light beam (L) to a predefined eyebox (E) for the user, so that the display content can be presented to the user in the form of a virtual image behind the reflective sheet.

9. A means of transport (1), in particular a motor vehicle, having mutually perpendicular longitudinal, transverse and height directions (X, Y, Z) of a Cartesian coordinate system (K) fixed to the means of transport, the means of transport comprising: - a means-of-transport sheet, in particular a front windscreen (3), at least partially delimiting the passenger compartment; and - a field-of-view display device (2) according to claim 8, the projection unit (5) of the field-of-view display device being arranged inside the passenger compartment, in particular inside an instrument panel (4) arranged below the front windscreen (3), and the reflective sheet of the field-of-view display device being configured as a section of a means-of-transport sheet or as a combined sheet arranged inside the passenger compartment.

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