DE102021203529A1 - display device - Google Patents

Abstract

The present invention relates to a display device (1) with an imaging unit (10) with a display element (11) for displaying an image and an optical unit (14) for projecting the image onto a projection surface. The imaging unit (10) and the optics unit (14) are separated from the environment by a housing (15). A transparent heat-buffering element (12) is arranged on the display element (11).

Description

The present invention relates to a display device with an imaging unit with a display element for displaying an image and an optical unit for projecting the image onto a projection surface.

Such display devices can be used, for example, for a head-up display for a means of transportation. A head-up display, also referred to as a HUD, is understood to mean a display system in which the viewer can maintain his line of sight, since the content to be displayed is displayed in his field of vision. While such systems were originally used mainly in the aviation sector due to their complexity and costs, they are now also being installed in large series in the automotive sector.

Head-up displays generally include an imaging unit or PGU (Picture Generating Unit), an optics unit, and a mirror unit. The imaging unit generates the image and uses at least one display element for this purpose. The optics unit directs the image to the mirror unit. The mirror unit is a partially reflective, translucent disc. The viewer thus sees the content displayed by the imaging unit as a virtual image and at the same time the real world behind the pane. In the automotive sector, the windshield is often used as a mirror unit, and its curved shape must be taken into account in the display. Due to the interaction of the optics unit and the mirror unit, the virtual image is an enlarged representation of the image generated by the imaging unit. The imaging unit and the optics unit are generally separated from the environment by a housing with a transparent cover.

A liquid crystal display (LCD: Liquid Crystal Display) with backlighting for the imaging unit is currently usually used for head-up displays. However, liquid crystal displays only have a low thermal load capacity, so that externally introduced or intrinsic heat has to be dissipated or limited. Heat dissipation or cooling of the imaging unit can be achieved, for example, by using a fan.

Against this background describes U.S. 2019/0182994 A1 a head-up display for a vehicle. The head-up display includes a display module for emitting light with an imaging unit, a heat sink attached to the display module to remove heat from the display module by conduction and dissipate it by convection, and an air conditioning duct having an outlet through which airflow from the air conditioning duct to the heat sink.

The use of a fan requires the supply of cool air from the environment for efficient cooling. In a closed housing, as used in head-up displays, cooling with a fan is not particularly efficient. There is also a risk that the fan will carry dust into the optical path. In addition, the noise produced by the fan can be annoying.

A risk with prior art head-up displays is that sunlight can enter the housing through the transparent cover and be focused onto the display element by the optical components of the optics unit, e.g., curved mirrors. The critical entry of sunlight usually occurs only sporadically and for a short time, i.e. for a few minutes. Depending on the curvature of the mirror, i.e. also on the magnification and the length of the optical path, this can lead to thermal hotspots arising from highly concentrated sunlight, which can damage the display element locally if a critical temperature of approx 120°C is exceeded. The use of display elements in head-up displays is therefore restricted by solar radiation and possible thermal stress.

Similar thermal stresses can also occur in display devices that are used in projectors in offices or in the home.

To protect against thermal stress from sunlight, a thermally conductive substrate can be installed in the display element, which dissipates the heat introduced to a heat sink. However, this approach requires the use of special display elements tailored for use in head-up displays, which is associated with increased manufacturing costs.

For example describes DE 10 2014 221 538 A1 a head-up display with an image generating device. The imaging device has an LCD with two transparent substrates between which a liquid crystal is arranged. The substrate on the side of the LCD that faces the beam path is made of a transparent ceramic material. The substrate is thermally coupled to a heat sink to remove heat input from sunlight.

JP 2005-313733 A describes a head-up display for a vehicle. The head-up display has an image generating device with an LCD. For heat dissipation, a crystal heat dissipation plate is disposed on an emission side of the LCD, which transmits light, and on which a polarizing layer of the LCD is coated. The heat dissipation plate is attached to a heat sink.

It is an object of the present invention to provide a display device which provides protection against thermal stress from incident sunlight in a cost-effective manner.

This object is achieved by a display device having the features of claim 1. Preferred developments of the invention are the subject matter of the dependent claims.

• - eine bildgebende Einheit mit einem Anzeigeelement zum Anzeigen eines Bildes;
• - ein auf dem Anzeigeelement angeordnetes transparentes wärmepufferndes Element;
• - eine Optikeinheit zum Projizieren des Bildes auf eine Projektionsfläche; und
• - ein Gehäuse für die bildgebende Einheit und die Optikeinheit.

According to one aspect of the invention, a display device comprises:

• - an imaging unit with a display element for displaying an image;
• - a transparent heat-buffering element arranged on the display element;
• - An optical unit for projecting the image onto a projection surface; and
• - a housing for the imaging unit and the optics unit.

In the solution according to the invention, a transparent heat-buffering element is arranged directly on the display element in order to reduce the temperature rise resulting from an energy input. In other words, an ordinary display is provided with an additional element to protect against excessive heat input, which distributes the heat in the material. This reduces the thermal load on the display element and the resulting mechanical stresses, so that the function of the imaging unit is guaranteed over a larger temperature range and even with increased solar radiation. No highly thermally conductive material is required for the protective effect, for example simple glass also works. Here, the local temperature difference ΔT to the environment is reduced by a factor of 1/C according to ΔT=ΔQ/C, where C is the specific heat capacity of the additional element and ΔQ is the heat supplied.

According to one aspect of the invention, the transparent thermal buffering element is thermally coupled to the display element. Such a thermal coupling can improve the dissipation of the heat generated by the display into the transparent heat-buffering element.

According to one aspect of the invention, the display element is a liquid crystal display. Liquid-crystal displays are the common technology, in particular due to the relatively low costs, which is used in currently customary head-up displays for motor vehicles, so that the solution according to the invention can be widely used.

According to one aspect of the invention, the display element has backlighting. Backlighting or backlighting is used in particular in liquid crystal displays in order to create the impression of a self-illuminating image. Backlighting, for its part, produces heat that has to be dissipated. This is supported by the transparent heat-buffering element.

According to one aspect of the invention, the transparent heat-buffering element is designed as a cover glass for the display element. This enables easy manufacture of the transparent heat-buffering element and easy mounting on the display element. At the same time, a relatively large amount of material is available for thermal buffering.

According to one aspect of the invention, a specific heat capacity of the transparent heat-buffering element has a value of at least 0.5 kJ/(kg K). In this way it is achieved that a relatively large amount of heat can be buffered locally. Suitable materials for the realization of the transparent heat-buffering element are, for example, crown glass, flint glass or quartz glass.

According to one aspect of the invention, the transparent thermal buffering element is air-cooled. With the solution according to the invention, no heat dissipation by a heat sink is required; simple air cooling is sufficient. Of course, the transparent heat-buffering element can also be connected to a heat sink.

According to one aspect of the invention, the transparent thermal buffering element is anti-reflective and/or optically coated. Contrary to what one skilled in the art would expect, no particularly reflective surface is provided here that would reflect thermal radiation. However, the inventors of the present invention have found that when using a transparent heat-buffering element according to the invention, a mirror coating and/or an optical coating can be applied to it without this being accompanied by an unacceptable increase in temperature of the display element goes. A mirror coating or optical coating is easier to attach to the transparent, heat-buffering element than to the display element itself, and thus simplifies and makes its production cheaper.

According to one aspect of the invention, the transparent thermal buffering element has a microstructured surface. This is preferably arranged on the side of the transparent heat-buffering element facing away from the display element. The microstructured surface has the advantage of increasing the surface area of the transparent heat-buffering element, which increases heat dissipation to the environment.

A display device according to the invention is preferably used in a head-up display for a means of transportation, e.g. a head-up display for a motor vehicle. A display device according to the invention can also be used in a projector.

Further features of the present invention will become apparent from the following description and the appended claims in conjunction with the figures.

character list

• 1 shows schematically a head-up display according to the prior art for a motor vehicle;
• 2 shows schematically a head-up display with a display device according to the invention;
• 3 shows an enlarged view of an imaging unit of a display device according to the invention;
• 4 shows schematically a means of locomotion with a head-up display that uses a display device according to the invention.
• 5 shows an enlarged view of an imaging unit of a display device according to the invention;
• 6 shows an arrangement according to the invention; and
• 7 shows a further arrangement according to the invention.

character description

For a better understanding of the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. The same reference symbols are used in the figures for the same or equivalent elements and are not necessarily described again for each figure. It goes without saying that the invention is not limited to the illustrated embodiments and that the features described can also be combined or modified without going beyond the protective scope of the invention as defined in the appended claims.

1 shows a basic sketch of a head-up display according to the prior art for a motor vehicle. The head-up display has a display device 1 with an imaging unit 10 and an optical unit 14 . A beam of rays SB1 emanates from a display element 11 and is reflected by a folding mirror 21 onto a curved mirror 22 which reflects it in the direction of a mirror unit 2 . The mirror unit 2 is shown here as a windshield 20 of the motor vehicle. From there, the bundle of rays SB2 arrives in the direction of an eye of an observer 3.

The viewer 3 sees a virtual image VB, which is located outside the motor vehicle above the hood or even in front of the motor vehicle. The virtual image VB is an enlarged representation of the image displayed by the display element 11 due to the interaction of the optics unit 14 and the mirror unit 2 . A speed limit, the current vehicle speed and navigation instructions are shown here symbolically. As long as the eye of the viewer 3 is within an eye box 4 indicated by a rectangle, all elements of the virtual image VB are visible to the viewer 3 . If the eye of the viewer 3 is outside of the eyebox 4, then the virtual image VB is only partially visible to the viewer 3 or not at all. The larger the Eyebox 4 is, the less restricted the viewer is when choosing his seating position.

The curvature of the curved mirror 22 matches the curvature of the windshield 20 and ensures that the image distortion is stable across the entire eyebox 4. The curved mirror 22 is rotatably supported by a bearing 221 . The rotation of the curved mirror 22 made possible by this enables the eyebox 4 to be moved and thus the position of the eyebox 4 to be adjusted to the position of the viewer 3. The folding mirror 21 serves to ensure that the path covered by the beam of rays SB1 between the display element 11 and the curved mirror 22 is long, and at the same time the optics unit 14 is still compact. The imaging unit 10 and the optics unit 14 are separated from the environment by a housing 15 with a transparent cover 23 . The optical elements Elements of the optics unit 14 are thus protected, for example, against dust located in the interior of the vehicle. An optical film or polarizer 24 is also located on the cover 23. The display element 11 is typically polarized and the mirror unit 2 acts like an analyzer. The purpose of the polarizer 24 is therefore to influence the polarization in order to achieve uniform visibility of the useful light. A glare shield 25 serves to surely absorb the light reflected through the boundary surface of the cover 23 so as not to cause glare to the viewer. In addition to the sunlight SL, the light from another interfering light source 5 can also reach the display element 11 . In combination with a polarization filter, the polarizer 24 can also be used to reduce incident sunlight SL.

2 shows schematically a head-up display with a display device 1 according to the invention. The head-up display largely corresponds to the head-up display 1 , however, a transparent heat-buffering member 12 is disposed on the display member 11 of the imaging unit 10 . In this example, the transparent heat-buffering element 12 is designed as a cover glass for the display element 11 and is thermally coupled to the display element 11 .

3 shows an enlarged view of an imaging unit 10 of a display device according to the invention. The imaging unit 10 has a display element 11 . In this example, the display element 11 is a liquid crystal display. The liquid crystal display has a liquid crystal layer 110 which is arranged between two polarizers 113,114. A backlight 13 for the liquid crystal display is arranged below the lower polarizer 113 . The liquid crystal layer 110 has a multiplicity of cells 111 which can be individually controlled by associated electrodes 112 . In this way, the polarization of the light from the backlight 13, which passes through the liquid crystal layer 110, can be influenced individually for each cell 111, so that it can pass through the upper polarizer 114 or is blocked. A transparent heat-buffering element 12 is arranged on the display element 11 of the imaging unit 10 , which is designed as a cover glass for the display element 11 and is thermally coupled to the display element 11 . The transparent heat-buffering element 12 is preferably air-cooled, heat dissipation by a heat sink is not required. Nevertheless, the transparent heat-buffering element 12 can also be connected to a heat sink.

4 shows schematically a means of transportation 40, in which a solution according to the invention is implemented. In this example, the means of transportation 40 is a motor vehicle. The motor vehicle has a display device 1 according to the invention, which in this case is part of a head-up display. A sensor system 41 can be used, for example, to record data relating to the vehicle environment. The sensor system 41 can in particular include sensors for detecting the surroundings, for example ultrasonic sensors, laser scanners, radar sensors, lidar sensors or cameras. The information recorded by the sensors 41 can be used to generate content to be displayed for the head-up display. In this example, further components of the motor vehicle are a navigation system 42, through which position information can be provided, and a data transmission unit 43. The data transmission unit 43 can be used, for example, to establish a connection to a backend, for example to obtain updated software for components of the motor vehicle. A memory 44 is provided for storing data. The exchange of data between the various components of the motor vehicle takes place via a network 45.

5 12 shows an enlarged view of an imaging unit 10 similar to a display device according to the invention 3 . The transparent heat-buffering element 12 additionally has a microstructured surface 125 here, which is indicated here in part of the surface in an exaggerated manner for the sake of clarity.

6 shows an arrangement according to the invention in which light SL incident from outside is attenuated by reflection on the transparent heat-buffering element 12 . Part is reflected as reflected stray light SLR, and only a small part reaches liquid crystal layer 110 as transmitted stray light SLT. For the sake of simplicity, no folding mirror 21 is shown here; curved mirror 22 is indicated in a position that is not necessarily realistic. It can be seen that light rays SB1 i belonging to the bundle of rays SB1 coming from the liquid crystal layer 110 pass through the transparent heat-buffering element 12 .

7 shows an inventive arrangement similar 6 , in which light SL incident from the outside is attenuated by reflection at the transparent heat-buffering element 12'. The transparent heat-buffering element 12' here has a roof-like shape, with only a particularly small part reaching the liquid-crystal layer 110 as transmitted stray light SLT, particularly in the left-hand part of the illustration.

The present invention enables mechanical stabilization: the imaging unit 11 can be hung without tension. Thermal expansion gradients between the imaging unit 11 and a housing of the display device 1 or a heat sink are avoided.

In one of the JP 2017-83699 A known solution, the mechanical stress of an imaging unit is reduced by a "mounting glass", to which a display is glued, is connected to a housing or an external holder and not directly to the display itself Materials exist, although the stress can still exist with different thermal expansion coefficients. Since the display itself consists of different materials (glass and plastic), a high temperature change (particularly due to solar radiation) leads to severe stress on the display. By contrast, the thermal and structural stabilization of the display element 11 provided according to the invention by the attached transparent heat-buffering element 12 significantly reduces the stress on the display or display element 11 .

Anti-reflective coating: Glass can be simply anti-reflective or optically coated, which means that there are no special requirements for anti-reflective coating on the top side of the display, the top side of the display element 11. According to an advantageous variant of the invention, the surface of the transparent heat-buffering element 12 is microstructured, which also means that its surface is enlarged. This also increases the cooling effect. The microstructuring serves, for example, for antireflection coating and/or for optical compensation. This is for 5 shown.

How to 6 and 7 described, a display device 1 according to the invention has the advantage, even without a coating of the transparent heat-buffering element 12,12', due to the large angular distance between the outgoing beams SB1 i and the focused sunbeams SL in a head-up display, that the sunlight SL is more strongly attached to the Surface of the transparent heat-buffering element 12,12' reflects and thus less light SLT reaches the display element 11. With a suitable shape/tilt angle of the surface of the transparent heat-buffering element 12', the effect is further intensified, see FIG 7 . This increases transmission / efficiency of the display and the backlight.

Cooling: The glass from which the transparent thermal buffering element 12 is preferably made acts as a heat store with high thermal mass. An external thermal connection, e.g. to the housing or heat sink is not necessary. The cooling effect of the transparent heat-buffering element 12 according to the invention lies in a combination of the “filter effect” of the critical, focused sunbeams SL, without negatively affecting the transmission of the backlighting, as stated above, and the dissipation of the thermal energy from the display element 11.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2019/0182994 A1 [0005]
• DE 102014221538 A1 [0010]
• JP2005313733A [0011]
• JP 2017083699 A [0037]

Claims (10)

Display device (1), with: - An imaging unit (10) with a display element (11) for displaying an image; - a transparent heat-buffering element (12) arranged on the display element (11); - An optical unit (14) for projecting the image onto a projection surface; and - A housing (15) for the imaging unit (10) and the optics unit (14). Display device (1) according to claim 1 wherein the transparent heat-buffering element (12) is thermally coupled to the display element (11). Display device (1) according to claim 1 or 2 , wherein the display element (11) is a liquid crystal display. Display device (1) according to claim 3 , wherein the display element (11) has a backlight (13). Display device (1) according to one of the preceding claims, wherein the transparent heat-buffering element (12) is designed as a cover glass for the display element (11). A display device (1) according to any one of the preceding claims, wherein a specific heat capacity of the transparent heat-buffering element (12) has a value of at least 0.5 kJ/(kg·K). A display device (1) according to any one of the preceding claims, wherein the transparent heat-buffering element (12) is air-cooled. Display device (1) according to one of the preceding claims, wherein the transparent heat-buffering element (12) is anti-reflective and/or optically coated. A display device (1) according to any one of the preceding claims, wherein the transparent thermal buffering element (12) has a microstructured surface (125). Display device (1) according to one of the preceding claims, wherein the display device (1) is part of a head-up display for a means of transport (40) or a projector.

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