Head-up display device for a motor vehicle, motor vehicle and method for operating a head-up display device

Abstract

Head-up display device (3) for a motor vehicle (1), the head-up display device (3) comprising: - an imaging unit (4) having a plurality of segments (7) arranged in a matrix (6), which, depending on an image content of an image (8) to be displayed by means of the head-up display device (3), can be switched independently of one another at least into a first state (Z1), which represents an at least largely transparent state, or into a second state (Z2), which represents an at least largely opaque state, - a backlighting device (5) which is designed to provide a backlight which can be radiated onto a first side (4b) of the imaging unit (4) for backlighting the imaging unit (4), wherein the backlighting device (5) has a laser light source (10), characterized in that - the backlighting device (5) comprises a phosphor element (11) which is designed to convert a laser light beam (13) provided by the laser light source (10) into illumination light (14) with a specific spectral distribution, - wherein the backlighting device (5) is arranged such that the laser light beam (13) provided by the laser light source (10) can be irradiated sequentially in time onto different regions (11a) of the phosphor element (11), and - wherein a respective region (11a) of the phosphor element (11) is assigned to a respective segment (7) of the imaging unit (4) such that the laser light beam (13) irradiated into a specific region (11a) of the regions (11a) of the phosphor element (11) is converted into illumination light (14) which is irradiated at least onto the segment (7) of the imaging unit (4) assigned to the specific region (11a).

Description

[0001] The invention relates to a head-up display device for a motor vehicle, wherein the head-up display device has an imaging unit having a plurality of segments arranged in a matrix, which, depending on the image content of an image to be displayed by means of the head-up display device, can be switched independently of one another to at least a first state, which represents an at least largely transparent state, or to a second state, which represents an at least largely opaque state. Furthermore, the head-up display device has a backlighting device designed to provide a backlighting that can be irradiated onto a first side of the imaging unit for backlighting the imaging unit, wherein the backlighting device has a laser light source.The invention also relates to a motor vehicle with a head-up display device and a method for operating a head-up display device.

[0002] The present interest is directed at display devices for motor vehicles that are designed as head-up displays. Such a display device typically comprises an image generating device or an imaging unit with which light can be emitted to provide a display or an image. Such a head-up display device can typically also have an optical device, such as reflectors or mirrors, with which the light emitted by the imaging unit can be projected onto a projection surface. In so-called windshield head-up displays, this projection surface is provided by a region of the windshield of the motor vehicle. Furthermore, head-up display devices are also known that have a separate projection surface designed as a semi-transparent mirror surface.Such head-up displays are also commonly referred to as combiner head-up displays. The present invention is located in the field of both windshield head-up displays and combiner head-up displays.

[0003] Liquid crystal displays, for example, can be used as imaging units. The individual pixels of such a liquid crystal display can be switched to be transparent or opaque depending on the image content to be displayed.

[0004] Accordingly, ideally, light provided by a corresponding backlight of such a liquid crystal display only passes through the transparent pixels. In reality, however, a small portion of the backlight light also penetrates the opaque pixels of such a liquid crystal display, which in the case of an upside-down display device leads to the so-called postcard effect. This means that through the windshield or the separately provided mirror surface, not only is a symbol or graphic currently being displayed visible to the user, but also the remaining areas of the liquid crystal display not used to display the graphic.

[0005] In liquid crystal displays from other application areas, such as in the consumer sector, for example for LED-based TVs, measures for increasing contrast are known, such as so-called "local dimming". Here, the LED backlight is reduced locally depending on the image content in order to improve the contrast. US 2007 / 0290966 A1 also describes an LCD display that is scanned with a laser beam to increase contrast, with a scanning speed controlled depending on the brightness of the image to be displayed. The laser beam can provide a wavelength in the visible range or in the infrared spectral range. In the latter case, the infrared laser light is converted into visible light by a nonlinear optical method using a fluorescent material.

[0006] Furthermore, the following documents are known from the state of the art: US 2017 / 0138548 A1: Describes a light-emitting device that converts ultraviolet (UV) or near-UV light into white light. The core of the invention is the arrangement of a UV light source, a conversion layer (e.g., quantum dots), and a dichroic filter. The filter reflects the UV light back to the conversion layer, while the generated white light is transmitted. Repeated reflection increases the efficiency of white light generation and minimizes the escape of unwanted UV light.

[0007] US 2007 / 0290966 A1: Discloses a liquid crystal display that uses a laser as a backlight. The brightness of the displayed image is controlled by the speed at which a scanner unit moves the laser beam across the liquid crystal display. The scanning speed is reduced for bright image areas and increased for dark areas. Optionally, the laser intensity and a projection system can also be used to control brightness.

[0008] DE 11 2006 003 107 T5: Concerns an LCD display with laser diode backlighting. One or more laser diodes spaced from the LCD illuminate part or all of the display. The laser diodes generate polarized light, which is directed onto the LCD pixels by reflectors, beam spreaders, and / or scanners. The use of RGB laser diodes enables narrowband color filters and thus high color purity.

[0009] DE 10 2014 214 767 A1: Describes a display device for motor vehicles, in particular head-up displays. The invention uses an illumination matrix with multiple lighting elements that are controlled differently depending on the image to be displayed. Stored illumination patterns enable selective control, thus reducing power consumption and heat generation. The illumination patterns are assigned to classes of images that are similar in their dark areas.

[0010] Unfortunately, contrast-enhancing measures, such as those used for liquid crystal displays in other applications, are generally only of limited or even non-existent use for imaging units in head-up displays. This is due to the significant size difference between the displays used in head-up displays, and especially their pixels, and conventional liquid crystal displays and their pixels.Since the imaging units used in head-up displays are typically significantly smaller, and especially their pixels, the LED density of this backlight cannot be precisely limited to pixel areas, taking the example of a backlight provided by LEDs. As a result, a single backlight LED would not only illuminate a single pixel of the imaging unit of a head-up display, but also a relatively large pixel area. Similarly, if a single backlight LED were dimmed or switched off in an imaging unit in a head-up display, not only would a corresponding pixel of the imaging unit be unlit, but also a relatively large pixel area.Such measures known for conventional liquid crystal displays, such as “local dimming” to increase the contrast, cannot therefore be used for small imaging units for head-up display devices.

[0011] A generic head-up display device is known from DE 10 2012 222 421 A1, in which a laser light source is used to provide backlighting for a liquid crystal display. This laser light source emits laser light that is irradiated onto a holographic diffuser, so that light passing through the holographic diffuser illuminates the liquid crystal display over as large an area as possible or completely. This allows for a higher-contrast image to be provided, since the laser light provides already polarized light, the polarity of which is no longer changed at the holographic diffuser. This avoids scattering effects that would result from a backlight, for example, based on an LED, with a polarizing filter placed in front of the liquid crystal display.

[0012] Although the increased contrast would subjectively reduce the postcard effect described above, this measure cannot reduce the backlight interference penetrating dark or opaque pixel areas. Another problem associated with the use of laser light is the need to ensure that the coherence properties of the laser light are sufficiently destroyed, otherwise undesirable speckle effects will occur in the image display.

[0013] The object of the present invention is therefore to provide a head-up display device, a motor vehicle and a method for operating a head-up display device which enable the postcard effect to be reduced as efficiently as possible.

[0014] This object is achieved by a head-up display device, by a motor vehicle, and by a method for operating a head-up display device having the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent patent claims, the description, and the figures.

[0015] A head-up display device according to the invention for a motor vehicle comprises an imaging unit having a plurality of segments arranged in a matrix, which, depending on the image content of an image to be displayed by means of the head-up display device, can each be switched independently of one another to at least a first state, which represents an at least largely transparent state, or to a second state, which represents an at least largely opaque state. Furthermore, the head-up display device comprises a backlighting device configured to provide a backlighting irradiable onto a first side of the imaging unit for backlighting the imaging unit, wherein the backlighting device comprises a laser light source.Furthermore, the backlighting device comprises a phosphor element configured to convert a laser light beam provided by the laser light source into illumination light with a specific spectral distribution. The backlighting device is further configured such that the laser light beam provided by the laser light source can be irradiated sequentially onto different regions of the phosphor element, wherein a respective region of the phosphor element is assigned to a respective segment of the imaging unit such that the laser light beam irradiated into a specific region of the regions of the phosphor element is converted into illumination light, which is irradiated at least onto the segment of the imaging unit assigned to the specific region.

[0016] The invention is based on the finding that the use of a laser light source that can radiate laser light sequentially over time onto different areas of a phosphor element makes it possible, even for a very small imaging unit with very small segments that can provide respective pixels, for example with an edge length of 85 µm, to nevertheless provide a background illumination specifically for such respective small segments of the imaging unit that are switched to the first state to display the image, while illumination of segments in the second state of the imaging unit can be largely avoided.By using a laser light source, it is particularly possible to irradiate extremely small areas of the phosphor element, so that the various areas of the phosphor element that emit correspondingly converted light towards the imaging unit when excited by the provided laser light beam can also be extremely small, thus enabling almost pixel-precise backlighting of the imaging unit. This allows the imaging unit to provide extremely high-resolution image content, while at the same time, backlighting of segments of the imaging unit that are to be switched to black to provide the image, i.e., that are to allow as little light through or transmit as possible, can be almost completely avoided. This advantageously reduces the postcard effect described above to a minimum.In addition, the conversion of the laser light by the phosphor element completely destroys the coherence of the laser light, thus completely avoiding speckle effects. Furthermore, the fact that only those segments intended to transmit light can be backlit enables particularly energy-efficient operation of the head-up display device. Thus, the invention makes it possible for the head-up display device to provide high-resolution images with very high contrast, in very good image quality, and with the postcard effect largely avoided, despite the small dimensions of the individual segments caused by the use of the imaging unit in the head-up display device.

[0017] The second state, which represents the at least largely opaque state, should be understood as the state of a segment in which, ideally, no light at all can be transmitted through this segment. In practice, however, at least slight light transmission through such a segment is always possible in such a state. For reasons of simplicity, the at least largely opaque state will also be referred to below as the opaque state, although even in this state, slight light transmission through the relevant segment of the imaging unit in this state is still possible in the case of backlighting. The same applies analogously to the first state.

[0018] In general, it can also be provided that the individual segments of the imaging unit can be switched not only into the translucent and opaque states, but also into at least one or more intermediate states, in which the light transmission is reduced compared to the translucent state and increased compared to the opaque state. In the case of a black-and-white image to be displayed, these intermediate states correspond to the corresponding grayscale to be displayed. In the case of color images, individual color brightnesses can be adjusted in the different segments.In the event that the individual segments of the imaging unit can also be switched into one or more intermediate states, it is preferred that the control device controls the background lighting device as a function of the image content of the image to be displayed by means of the head-up display device in such a way that the laser light beam is also irradiated onto regions of the phosphor element that are assigned to segments that are in such an intermediate state for providing the image or image content to be displayed.

[0019] Alternatively, it is also conceivable for a respective segment of the imaging unit to be switchable exclusively into the two aforementioned states, namely the translucent state and the opaque state. In order to then provide corresponding shades of gray or brightness gradations of specific colors, the light output of the laser beam can be varied accordingly, for example. If a corresponding segment of the imaging unit is to provide reduced brightness, a laser beam with reduced light output can be used to illuminate the associated area of ​​the phosphor. This has the significant advantage that it allows shades of gray or brightness gradations to be provided in a more energy-efficient manner.

[0020] In an advantageous embodiment of the invention, the head-up display device has a control device which is designed to control the background lighting device as a function of an image content of the image to be displayed by means of the head-up display device, in particular in such a way that the laser light beam is only irradiated onto regions of the phosphor element which are assigned to segments which are not in the second state for providing the image content to be displayed, but for example in the first state and / or in one of the intermediate states described above.

[0021] This advantageously allows the image content to be correlated with the control of the backlighting device, allowing targeted backlighting to be provided only for those segments of the image content that are also intended to transmit light to display the image. This advantageously allows for segments through which no light is to be transmitted to provide the image to be either not backlit at all or only very slightly backlit.

[0022] In an advantageous further embodiment of the invention, the imaging unit is designed as a TFT (thin film transistor) screen, in particular as a TFT liquid crystal display. A TFT screen, in particular a TFT liquid crystal display, advantageously allows for a particularly high resolution, particularly in contrast to passive matrix liquid crystal displays, since TFT displays allow significantly smaller pixels and thus a higher pixel density, which in turn is particularly advantageous for imaging units used in head-up display devices due to their small size.

[0023] The TFT screen can, for example, be designed as a monochromatic screen, in which case it has one thin-film transistor per pixel. However, the TFT screen is preferably designed as a color display, in which case it preferably has three thin-film transistors per pixel. In particular, in this case, each pixel can be divided into three subpixels for providing the colors red, yellow, and green by correspondingly assigned color filters, and each subpixel is then assigned a thin-film transistor.

[0024] A so-called RGBW TFT can also be used, with an additional subpixel integrated with the color white.

[0025] In a further advantageous embodiment of the invention, the backlighting device comprises a deflection device. The backlighting device is configured such that the laser light beam provided by the laser light source during operation of the head-up display device is irradiated onto the deflection device. The deflection device is designed to deflect the irradiated laser light beam in different predetermined directions associated with the respective regions of the phosphor element. This makes it possible, in a particularly simple and advantageous manner, to irradiate the laser light beam sequentially over time onto different regions of the phosphor element.

[0026] It is particularly advantageous if the deflection device is designed as a MEMS (microelectromechanical system) mirror, i.e. as a microsystem mirror. This allows the deflection device to be particularly small and compact, which is particularly advantageous when used in a head-up display, since there is limited installation space available. A MEMS mirror as a deflection device also offers numerous other advantages. The use of conventional rotating mirrors requires additional discrete components, such as holders in which the mirror axis is mounted. The friction generated by the rotation leads to wear and the resulting slippage. Compared to monolithic assemblies, as is the case with the MEMS mirror, assemblies made of discrete components are generally more complex to manufacture and therefore more expensive.Above all, they are less easy to miniaturize and are generally significantly heavier. MEMS mirrors, on the other hand, operate completely wear-free.

[0027] Furthermore, it is advantageous if the MEMS mirror is designed to be rotatable about two mutually perpendicular axes of rotation. This allows the laser light beam provided by the laser light source to be easily radiated sequentially onto each segment of the imaging unit segments arranged in the matrix, in particular in several rows and columns, in particular into the respective area of ​​the phosphor element assigned to this segment, which is to be backlit to provide current image content. Another major advantage of the MEMS mirror is that it can achieve a particularly high operating frequency. The scanning frequency with which the MEMS mirror can scan the rows and columns of the matrix-arranged areas of the phosphor element can thus easily be selected so high that it corresponds to the frame rate of the images to be displayed using the head-up display device.The frame rate can be, for example, 30 frames per second, but is preferably higher, such as 60 Hertz or more. Accordingly, the MEMS mirror can also be designed to completely scan the rows of matrix-arranged segments or the corresponding regions of the phosphor element once in no more than one-thirtieth of a second, or at a frame rate of 60 Hertz, in one-sixtieth of a second.

[0028] To ensure that during this scanning only those areas of the phosphor element are illuminated which are also intended to provide backlighting for the corresponding segments of the imaging unit to produce a current image, the laser light source can also be specifically switched on and off, or the supply of the laser light beam can be specifically interrupted. For example, the laser light beam can be provided in the form of a pulsed or modulated light beam. If the MEMS mirror covers an angular range in which the laser light beam would be deflected into areas of the phosphor element that are not intended to be illuminated, the laser light source can interrupt the supply of the laser light beam. Accordingly, the activation and deactivation of the laser light can advantageously be correlated with the image content to be displayed.In other words, the control device can also control the laser light source depending on the image content of the image currently being displayed.

[0029] Furthermore, MEMS mirrors are typically limited in their deflection, for example, to approximately + / - 10 degrees. However, this is not a disadvantage, especially for scanning an area with a size corresponding to the imaging unit of a head-up display device. In other words, since the imaging unit for the head-up display device has very small dimensions, an extremely compact arrangement can be provided despite the limited deflection angle of the MEMS mirror, as the MEMS mirror can still be positioned very close to the imaging unit.

[0030] In a further advantageous embodiment of the invention, the control device is designed to control an intensity of the laser light beam and / or a deflection of the laser light beam by means of the deflection device depending on the image content to be displayed. As already mentioned at the beginning, it is particularly advantageous to provide brightness gradations by deliberately varying the laser light power and thus the intensity of the laser light beam. Alternatively or additionally, this can also be achieved via a correspondingly designed deflection of the laser light beam by means of the deflection device, in particular the MEMS mirror. For example, the laser light beam can be directed by means of the deflection device for a targeted longer period of time onto regions of the phosphor element that correspond to segments of the imaging unit in which a higher brightness is to be provided than in others.However, it is advantageous if the brightness control of individual pixels or individual segments of the imaging unit is carried out exclusively by correspondingly controlling the laser light power or the intensity of the laser light beam, as this significantly simplifies the control of the MEMS mirror. In particular, this allows the movement of the MEMS mirror to be completely independent of the image content to be displayed.

[0031] In a further advantageous embodiment of the invention, the phosphor element is designed as a phosphor film. Thus, the phosphor element can be designed particularly cost-effectively and simply, and moreover, the design as a phosphor film is particularly flexible in its use. The phosphor film can be designed, for example, as an elastomer in which phosphor particles are embedded. For example, a phosphor element designed as a phosphor film can be applied to the imaging unit particularly easily. In principle, it would also be conceivable for the phosphor element to be arranged at a distance from the imaging unit, in particular from its first side, and to be aligned parallel to it, for example.However, since fluorescent light generated by excitation by the laser light beam is diffusely emitted by the phosphor element, it is particularly advantageous to arrange the phosphor element as close as possible to the imaging unit, and thus, in particular, to position the individual regions of the phosphor element particularly close to the corresponding segments of the imaging unit. Stray light that strikes neighboring segments of the imaging unit that are not intended to be illuminated can be minimized by reducing the distance between the phosphor element and the imaging unit.

[0032] Therefore, it represents a particularly advantageous embodiment of the invention if the phosphor element is arranged directly on the first side of the imaging unit. For example, the phosphor element can also be provided as a phosphor coating on the first side of the imaging unit. However, it is particularly advantageous if the phosphor element is designed as a phosphor film, in particular as described above, and is arranged on the first side of the imaging unit. Such a phosphor film can be easily placed on the first side, i.e., the back of the imaging unit, and fixed thereto. This is significantly less complex to manufacture and thus significantly more cost-effective.

[0033] Conventional TFT screens have two polarizers or polarizing filters rotated by 90 degrees to each other. If a respective liquid crystal pixel is controlled accordingly, the polarization of light passing through the liquid crystal layer in this pixel is rotated by 90 degrees and can pass through the second polarizing filter. With a different control, this is not the case and the light is blocked by the second polarizing filter. These polarizers or polarizing filters, or at least polarizing filters arranged on the rear, often form the outer side of such a TFT screen. Therefore, a further particularly advantageous embodiment of the invention provides for at least part of the first side of the imaging unit, on which the phosphor element is arranged, to be provided by a polarizing element, in particular a polarizing filter, of the imaging unit.For example, the phosphor element, designed as a phosphor film, can be applied directly to the polarization element, i.e., the polarizer or polarizing filter. This advantageously minimizes stray light, as described above, while simultaneously providing an extremely compact arrangement.

[0034] Furthermore, it is advantageous if the laser light source is designed to provide the laser light beam with a predetermined wavelength that lies in the blue and / or ultraviolet spectral range. Accordingly, the excitation spectrum of the phosphor element is then also in the blue and / or ultraviolet spectral range. In this spectral range, particularly efficient excitation of the phosphor element or its individual regions can be achieved.

[0035] For example, the excitation wavelength of the laser light beam can be in a range between 450 nanometers and 460 nanometers, particularly preferably between 445 nanometers and 455 nanometers. To provide the laser light beam, the laser light source can comprise a laser or one or more laser diodes.

[0036] In a further advantageous embodiment of the invention, the phosphor element is designed to convert light with the predetermined wavelength into white illumination light. White phosphors are sufficiently known from the prior art and are also used, for example, in laser spotlights. White illumination light is particularly well suited for backlighting the relevant segments of the imaging unit in order to be able to provide a bright and high-contrast color image, for example using appropriate color filters of the imaging unit. If the imaging unit is to be designed as a monochromatic imaging unit, i.e., to provide images exclusively with brightness gradations of a single color, a phosphor element can also be used to provide white converted illumination light.In this case, however, it is also conceivable that the phosphor element provides the incident laser light beam in light with a different dominant wavelength, for example in the yellow spectral range, the red spectral range or the green spectral range.

[0037] Furthermore, it is preferred that the respective segments be formed as pixels. In general, the segments could also correspond to pixel groups consisting of multiple pixels. However, to enable the most pixel-precise backlighting of the respective pixels of the imaging unit, it is advantageous if the respective segments of the imaging unit simultaneously also represent the pixels of the imaging unit. Accordingly, the individually illuminable regions of the phosphor element correspond to the respective pixels of the imaging unit.

[0038] Furthermore, it is preferred that the matrix in which the individual segments of the imaging unit are arranged has between 200 and 600 rows, with between 200 and 600 pixels being arranged in each row, and with each pixel having a length and a width of between 70 µm and 100 µm. It is also advantageous if the matrix is ​​not square, but has a larger dimension in a first direction than in a second direction perpendicular thereto. The first direction corresponds to a horizontal line of the virtual image provided by the head-up display device when the device is in its intended installation position in a motor vehicle.It is advantageous, for example, if the imaging unit or the matrix in which the individual pixels of the imaging unit are arranged has a diagonal of 1.8 inches, which can be achieved, for example, by 480 pixels in width and 240 pixels in height if the individual pixels are, for example, square with a side length of 85 µm. However, the matrix can also have other dimensions, for example a height of 336 pixels, with the pixels again preferably being between 70 µm and 100 µm, in particular 85 µm. This advantageously makes it possible to provide a particularly small, compact and high-resolution display, which is therefore particularly suitable for use in the head-up display device according to the invention.

[0039] In particular, such a backlight would prove useful for larger displays (e.g. 2.6" or 3.1" or larger, pixel count e.g. 800x400) since the disadvantages of classic LED backlighting are particularly noticeable here (temperature load, required total amount of light, etc.).

[0040] Furthermore, the head-up display device according to the invention or one of its embodiments can be designed as a windshield head-up display or as a combiner head-up display. In the case of a windshield head-up display, the image provided by the imaging unit is projected onto the windshield via an optional optical system, which may, for example, have one or more reflectors, and reflected into the field of vision of a driver, who perceives the projected image as a virtual image behind the windshield.If the head-up display device is designed as a combiner head-up display, the image ultimately provided by the imaging unit is again projected via an optional optical system in an analogous manner onto a separately provided semi-transparent mirror surface, which is different from the windshield and can be designed, for example, as a separate glass pane, and is partially reflected by this into the field of vision of the driver, who in turn perceives the reflected image as a virtual image behind this separately provided mirror surface and in particular also behind the windshield as a virtual image.

[0041] Furthermore, the invention also relates to a motor vehicle with a head-up display device according to the invention or one of its embodiments. The advantages mentioned for the head-up display device according to the invention and its embodiments thus apply equally to the motor vehicle according to the invention.

[0042] Furthermore, the invention also relates to a method for operating a head-up display device for a motor vehicle, wherein the head-up display device has an imaging unit which has a plurality of segments arranged in a matrix, which, depending on an image content of an image to be displayed by means of the head-up display device, are each switched independently of one another at least into a first state which represents an at least largely transparent state, or into a second state which represents an at least largely opaque state, and wherein a background illumination radiated onto a first side of the imaging unit is provided by means of a laser light source for backlighting the imaging unit.In this case, the laser light beam provided by the laser light source is irradiated sequentially in time, in particular depending on the image content of the image to be displayed by means of the head-up display device, onto different areas of a phosphor element, which converts the irradiated laser light beam into illumination light with a specific spectral distribution and irradiates it onto a respective segment assigned to the different areas of the phosphor element.

[0043] Here, too, the advantages mentioned for the head-up display device according to the invention and its embodiments apply equally to the method according to the invention. Furthermore, the specific features mentioned in connection with the head-up display device according to the invention and its embodiments enable the method according to the invention to be further developed through additional method steps.

[0044] Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. Thus, embodiments are to be regarded as encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate combinations of features from the explained embodiments. Embodiments and combinations of features are also to be regarded as disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0045] Showing: Fig. 1 is a schematic representation of a motor vehicle with a head-up display device according to an embodiment of the invention; Fig. 2 a schematic representation of an imaging unit in a plan view, with an image provided by the imaging unit; and Fig. 3 a schematic representation of a head-up display device in a side view according to an embodiment of the invention.

[0046] Fig. 1 shows a schematic representation of a motor vehicle 1, of which only a windshield 2 is shown as an example and for reasons of clarity, with a head-up display device 3 according to an exemplary embodiment of the invention. The head-up display device 3 has an imaging unit 4 and a background lighting device 5 for backlighting the imaging unit 4. The imaging unit 4 is preferably designed as a TFT screen, in particular as a TFT liquid crystal screen.

[0047] An exemplary top view of such an imaging unit 4 is shown in Fig. 2 is shown schematically. The imaging unit 4 comprises a plurality of pixels 7 arranged in a matrix 6, of which only one is provided with a reference symbol for reasons of clarity. Also, for reasons of clarity, only a few pixels 7 are shown schematically here. The matrix 6 preferably comprises between 200 and 600 pixels per row and can also comprise between 200 and 600 such rows, wherein a respective pixel 7 has, for example, an edge length between 70 µm and 100 µm. A respective pixel 7 can be switched into different states by a corresponding control, whereby the light transmittance of the respective pixels 7 is controlled. When backlit by the backlight device 5, a corresponding image 8 is then displayed on the imaging unit 4. In this case in Fig. 2, the pixels 7 in a central area of ​​the imaging unit 4 are in a transparent state Z1, and all other pixels 7 are in a non-transparent state Z2. The light transmitted through the pixels 7 in the transparent state Z1 and provided by the backlight device 5 is then correspondingly directed via an optical system which is arranged in Fig. 1 has, for example, two reflectors 9, projected onto the windshield 2 and reflected by it into a driver's field of vision.

[0048] Ideally, the pixels 7 in the non-transparent state Z2 should be completely opaque. In reality, however, the pixels 7 in the opaque state Z2 still transmit some light, at least if they are also illuminated by a backlight, as is the case with conventional liquid crystal displays. Consequently, in conventional upside-down display devices, areas of a displayed image are visible that should not be visible, resulting in the so-called postcard effect. The invention advantageously makes it possible to reduce this postcard effect to a minimum, which can now be demonstrated using Fig. 3 is explained in more detail.

[0049] Fig. Figure 3 shows a schematic representation of the head-up display device 3 with the imaging unit 4 and the background lighting device 5 in detail. The imaging unit 4 is shown in a side view. The front side 4a corresponds to the side of the imaging unit 4, which is also shown in Fig. 2. The backlighting device 5 advantageously comprises a laser light source 10 and a phosphor film 11, which is arranged on the rear side 4b, which is arranged opposite the front side 4a. Furthermore, the backlighting device 5 comprises a deflection device in the form of a MEMS mirror 12. This MEMS mirror is rotatable about two mutually perpendicular axes of rotation. A first axis of rotation A runs parallel to the X-axis of the Fig. 3 and a second rotation axis B lies in the YZ plane of the coordinate system shown here. This advantageously allows a laser light beam 13 provided by the laser light source 10 to be deflected sequentially in different directions. Two directions R1 and R2 are shown here as examples. This advantageously allows the laser light beam 13 to be directed specifically onto regions 11a of the phosphor film 11. A respective region 11a of the phosphor film 11 corresponds to a respective pixel 7 of the imaging unit 4, in particular such that the laser light beam 13 irradiated into a specific region 11a of the phosphor film 11 is converted into illumination light 14, in particular white illumination light 14, which is irradiated at least onto the pixel 7 of the imaging unit 4 assigned to the specific region 11a.Thus, those pixels 7 which are intended to transmit light for displaying the image 8, i.e. which are in the transparent state Z1 or in an at least partially transparent intermediate state, can be specifically backlit, while those pixels 7 which are in the non-transparent state Z2 and are not intended to transmit any light, are not backlit or are backlit to an extremely small extent by scattered light.

[0050] In this one in Fig.In the example shown in Figure 3, to provide a specific image 8, the topmost and bottommost pixels 7 of the imaging unit 4 are in the transparent state Z1. Consequently, the laser light beam 13 provided by the laser light source 10 is irradiated sequentially in time by rotating the MEMS mirror 12 onto the topmost region 11a of the phosphor film 11, which corresponds to the topmost pixel 7, and onto the bottommost region 11a of the phosphor film 11, which corresponds to the bottommost pixel 7. The scan rate or sampling rate at which the individual pixels 7 of the imaging unit 4 to be backlit are illuminated preferably corresponds to the frame rate at which respective images 8 are displayed by the imaging unit 4.

[0051] The laser light source 10 can in particular be operated such that, depending on the image content to be displayed, it only emits laser light 13 when the MEMS mirror 12 is in a position in which it reflects the emitted laser light beam 13 onto a pixel 7 to be illuminated. If, on the other hand, the MEMS mirror 12 covers angular ranges into which no laser light 13 is to be emitted for backlighting pixels 7, the emission of the laser light 13 by the laser light source 10 can be prevented for this period of time. For example, a corresponding control device 15 can be provided to control the laser light source 10. This control device 15 can, in particular, control the light intensity or radiation intensity of the laser light beam 13 emitted by the laser light source 10 depending on the image content to be displayed.In this way, brightness gradations for an image 8 to be displayed can advantageously be provided in a particularly efficient manner. The control device 15 can also control the control of the imaging unit 4 for displaying corresponding image content.

[0052] The light conversion by means of the phosphor film 11 advantageously also destroys the coherence properties of the laser light, thereby effectively preventing speckle effects. By specifically illuminating or backlighting only specific pixels 7, through which light is to be transmitted to create an image 8, the postcard effect can advantageously be avoided or at least reduced to a minimum. Furthermore, since the phosphor film 11 is arranged directly on the back 4b of the imaging unit 4, the stray light components that scatter toward neighboring pixels 7 can also be reduced to a minimum. Furthermore, since the corresponding pixels 7 of the imaging unit 4 are only selectively backlit depending on the image content to be displayed, enormous energy savings can be achieved.

Claims

[1] Head-up display device (3) for a motor vehicle (1), the head-up display device (3) comprising: - an imaging unit (4) having a plurality of segments (7) arranged in a matrix (6), which, depending on an image content of an image (8) to be displayed by means of the head-up display device (3), can be switched independently of one another at least into a first state (Z1), which represents an at least largely transparent state, or into a second state (Z2), which represents an at least largely opaque state, - a backlighting device (5) which is designed to provide a backlight which can be radiated onto a first side (4b) of the imaging unit (4) for backlighting the imaging unit (4), wherein the backlighting device (5) has a laser light source (10), characterized by , that - the backlighting device (5) comprises a phosphor element (11) which is designed to convert a laser light beam (13) provided by the laser light source (10) into illumination light (14) with a specific spectral distribution, - wherein the backlighting device (5) is arranged such that the laser light beam (13) provided by the laser light source (10) can be irradiated sequentially in time onto different regions (11a) of the phosphor element (11), and - wherein a respective region (11a) of the phosphor element (11) is assigned to a respective segment (7) of the imaging unit (4) such that the laser light beam (13) irradiated into a specific region (11a) of the regions (11a) of the phosphor element (11) is converted into illumination light (14) which is irradiated at least onto the segment (7) of the imaging unit (4) assigned to the specific region (11a). [2] Head-up display device (3) according to claim 1, characterized by that the head-up display device (3) has a control device (15) which is designed to control the background lighting device (5) depending on an image content of the image (8) to be displayed by means of the head-up display device (3), in particular in such a way that the laser light beam (13) is only irradiated onto regions (11a) of the phosphor element (11) which are assigned to segments (7) which are in the transparent state (Z1) for providing the image content to be displayed. [3] Head-up display device (3) according to one of the preceding claims, characterized by that the imaging unit (4) is designed as a TFT screen, in particular as a liquid crystal screen. [4] Head-up display device (3) according to one of the preceding claims, characterized byin that the backlighting device (5) has a deflection device (12), wherein the backlighting device (5) is set up such that the laser light beam (13) provided by the laser light source (10) during operation of the head-up display device (3) is irradiated onto the deflection device (12), wherein the deflection device (12) is designed to deflect the irradiated laser light beam (13) in different predetermined directions (R1, R2) which are assigned to the respective regions (11a) of the phosphor element (11). [5] Head-up display device (3) according to claim 4, characterized by that the deflection device (12) is designed as a MEMS mirror (12). [6] Head-up display device (3) according to claim 5, characterized by that the MEMS mirror (12) is designed to be rotatable and / or deflectable or tiltable about two mutually perpendicular axes of rotation (A, B). [7] Head-up display device (3) according to one of claims 2 to 6, characterized by that the control device (15) is designed to control an intensity of the laser light beam (13) and / or a deflection of the laser light beam (13) by means of the deflection device (12) depending on the image content to be displayed. [8] Head-up display device (3) according to one of the preceding claims, characterized by that the phosphor element (11) is designed as a phosphor film [9] Head-up display device (3) according to one of the preceding claims, characterized by that the phosphor element (11) is arranged directly on the first side (4a) of the imaging unit (4). [10] Head-up display device (3) according to claim 9, characterized by that at least a part of the first side (4a) on which the phosphor element (11) is arranged is provided by a polarization element of the imaging unit (4). [11] Head-up display device (3) according to one of the preceding claims, characterized by that the laser light source (10) is designed to provide the laser light beam (13) with a predetermined wavelength which lies in the blue and / or ultraviolet spectral range. [12] Head-up display device (3) according to one of the preceding claims, characterized by that the phosphor element (11) is designed to convert light with the predetermined wavelength into white illumination light (14). [13] Head-up display device (3) according to one of the preceding claims, characterized by that the respective segments (7) are designed as pixels (7), wherein the matrix (6) has between 200 and 600 rows, wherein between 200 and 600 pixels (7) are arranged in a respective row, wherein a respective pixel (7) has a length and a width which are each between 70 µm and 100 µm. [14] Motor vehicle (1) with a head-up display device (3) according to one of the preceding claims. [15] A method for operating a head-up display device (3) for a motor vehicle (1), wherein the head-up display device (3) has an imaging unit (4) having a plurality of segments (7) arranged in a matrix (6), which, depending on an image content of an image (8) to be displayed by means of the head-up display device (3), are each switched independently of one another at least into a first state (Z1), which represents an at least largely transparent state, or into a second state (Z2), which represents an at least largely opaque state, and wherein a background illumination (14) radiated onto a first side of the imaging unit (4) is provided for backlighting the imaging unit (4) by means of a laser light source (10), characterized byin that the laser light beam (13) provided by the laser light source (10) is radiated sequentially in time depending on the image content of the image (8) to be displayed by means of the head-up display device (3) onto different areas (11a) of a phosphor element (11), which converts the radiated laser light beam (13) into illumination light (14) with a specific spectral distribution, and radiates it onto a respective segment (7) assigned to the different areas (11a) of the phosphor element (11).

Images